Co-reporter:Yang Liu;Zhiyong Zhang;Huilong Xu;Lihuan Zhang;Zhenxing Wang;Wenliang Li;Li Ding;Youfan Hu;Min Gao;Quan Li
The Journal of Physical Chemistry C September 24, 2009 Volume 113(Issue 38) pp:16796-16801
Publication Date(Web):2017-2-22
DOI:10.1021/jp9046038
A significant visible light response of unintentionally doped ZnO nanowire (NW) field effect transistors (FETs) has been observed in a reversible manner (for illumination source on and off). In particular, under white light illumination (wavelength longer than 400 nm), the threshold voltage (VT) of the ZnO NW FET shifts greatly to the negative direction, suggesting a remarkable increase in carrier concentration. A photon-assisted oxygen molecule desorption mechanism is proposed to explain the observed sub-bandgap photoresponse on the basis of the behavior of the experimental devices in different gas atmospheres (air, vacuum, pure N2, and pure O2) and with/without nanowire surface modifications (coated with PMMA).
Co-reporter:Shuang Liang, Nan Wei, Ze Ma, Fanglin Wang, Huaping Liu, Sheng Wang, and Lian-Mao Peng
ACS Photonics March 15, 2017 Volume 4(Issue 3) pp:435-435
Publication Date(Web):February 16, 2017
DOI:10.1021/acsphotonics.6b00856
Applied as on-chip infrared light sources for future nanophotonic circuits and information optoelectronics, light emitters should show a narrow spectral width, strong emission, low onset voltage, and better tunability of light output to an external drive. Here, by utilizing small-diameter (d < 1 nm) chirality-sorted (8,3) and (8,4) carbon nanotube (CNT) films and their charged exciton (trions) electroluminescence (EL), we achieve performance improvements via channel length (Lch) scaling. With a short Lch, the devices can show better emission, and the external EL efficiency (ηEL) in free space can reach ∼6 × 10–4 (that is obtained at a current of ∼5–8 mA and a voltage of ∼4–6 V from the 0.5-μm-channel device, and the corresponding current density is ∼1700–3000 A cm–2). The strong emission at smaller bias gives CNT-based emitters a wider optoelectronic compatibility with other nanomaterial systems. Furthermore, by an integration of the emitter with a λ/2 optical cavity, cavity-controlled well-defined light output can be achieved, with narrow spectral widths at selectable emission windows (e.g., ∼28 meV at a wavelength of 1180 nm). The results show possible applications of chirality-sorted CNT film light emitters for further on-chip nanophotonic systems.Keywords: carbon nanotube film; channel scaling; electroluminescence; impact excitation; on-chip light source; optical cavity;
Co-reporter:Sheng Wang;Lihuan Zhang;Xuelei Liang;Qingsheng Zeng;Zhiyong Zhang;ZhenXing Wang;Li Ding;Min Gao;Qing Chen;Jun Shen;Yan Li;Huilong Xu;RongLi Cui
The Journal of Physical Chemistry C April 30, 2009 Volume 113(Issue 17) pp:6891-6893
Publication Date(Web):Publication Date (Web): April 3, 2009
DOI:10.1021/jp901282h
Photovoltaic effects are studied for asymmetrically contacted single-walled carbon nanotube (SWCNT) barrier-free bipolar diode (BFBD) under infrared laser illumination. The BFBD is based on a SWCNT with a diameter d ∼ 1.5 nm and length L ∼ 800 nm, and the device shows a good open-circuit voltage of VOC = 0.23V and large photocurrent ISC of more than 15 nA.
Co-reporter:Huixin Huang, Fanglin Wang, Yang Liu, Sheng Wang, and Lian-Mao Peng
ACS Applied Materials & Interfaces April 12, 2017 Volume 9(Issue 14) pp:12743-12743
Publication Date(Web):March 21, 2017
DOI:10.1021/acsami.7b01301
The carbon nanotube (CNT) has been proved to be a promising material in infrared detection, due to its many advantages of high mobility, strong infrared light absorption, and carrier collection efficiency. However, the absorption restriction from the single layer limits its effective utilization of incident light. In this paper, we introduce a plasmonic electrode structure in a CNT thin-film photodetector based on random deposited high-purity semiconducting CNTs, which can collect photoinduced carriers effectively and enhance light absorption at the same time. The largest enhancement of photocurrents can be achieved at 1650 nm wavelength with suitable plasmonic structure size. Especially, we further discuss the influence of plasmonic structures on the performance of devices. We demonstrate that the best performance improvement of the carbon nanotube detector with plasmonic structure can be enhanced by 13.7 times for photocurrent mode and 5.62 times for photovoltage mode compared to those devices without structure at 1650 nm resonant wavelength. At last, the plasmonic structures are applied on tandem photodetectors with nine virtual contacts, and both the photocurrent and photovoltage are increased. The application of plasmonic electrodes can improve detector performance and retain compact device structures, which shows great potential for optimizing infrared detectors based on nanomaterials.Keywords: carbon nanotubes; detectivity; infrared detectors; plasmonic; responsivity;
Co-reporter:Yuanhui Zheng;Le Huang;Zhiyong Zhang;Jianzhuang Jiang;Kaiyou Wang;Gui Yu
RSC Advances (2011-Present) 2017 vol. 7(Issue 4) pp:1776-1781
Publication Date(Web):2017/01/04
DOI:10.1039/C6RA27673C
Single-molecule magnets (SMMs) possess many unique magnetic properties and thus attract a wide range of attention. However, the applications of SMMs always need a strict atmosphere, i.e. low temperature, high vacuum and strong magnetic field. In this work, we report the preparation and characterization of sensitivity enhanced graphene Hall elements (GHEs) decorated with Tb-core SMMs. By comparing the magnetic sensing and electronic tests of the GHEs before and after the SMMs modifications, the sensitivity of the GHEs increases by 44.9% in voltage mode and 59.0% in current mode compared with pristine GHEs. The increase of sensitivity may result from the magnetic center introduction of SMMs at room temperature. Moreover, the magnetic molecules may affect the graphene field environment leading to a Hall signal change. In addition, the SMMs modified GHEs present excellent linearity, offset voltage, repeatability and stability in magnetic sensing. This study paves the way to apply SMMs into practical use at room temperature and atmospheric pressure without strong magnetic field excitations.
Co-reporter:Chenguang Qiu;Donglai Zhong;Zhiyong Zhang;Mengmeng Xiao;Yingjun Yang
Science 2017 Volume 355(Issue 6322) pp:
Publication Date(Web):
DOI:10.1126/science.aaj1628
Moving transistors downscale
One option for extending the performance of complementary metal-oxide semiconductor (CMOS) devices based on silicon technology is to use semiconducting carbon nanotubes as the gates. Qiu et al. fabricated top-gated carbon nanotube field-effect transistors with a gate length of 5 nm. Thin graphene contacts helped maintain electrostatic control. A scaling trend study revealed that, compared with silicon CMOS devices, the nanotube-based devices operated much faster and at much lower supply voltage, and they approached the limit of one electron per switching operation.
Science, this issue p. 271
Co-reporter:Shuang Liang, Feifan Wang, Ze Ma, Nan Wei, Gongtao Wu, Gang Li, Huaping Liu, Xiaoyong Hu, Sheng WangLian-Mao Peng
ACS Nano 2017 Volume 11(Issue 1) pp:
Publication Date(Web):December 13, 2016
DOI:10.1021/acsnano.6b06598
A photodetector is a key device to extend the cognition fields of mankind and to enrich information transfer. With the advent of emerging nanomaterials and nanophotonic techniques, new explorations and designs for photodetection have been constantly put forward. Here, we report the asymmetric-light-excitation photoelectric detectors with symmetric electrical contacts working at zero external bias. Unlike conventional photodetectors with symmetric contacts which are usually used as photoconductors or phototransistors showing no photocurrent at zero bias, in this device, the asymmetric-light-excitation structure is designed to ensure that only one Schottky junction between two metallic electrodes and semiconductors is illuminated. In this condition, a device can contribute to a photocurrent without bias. Furthermore, incident light with global illumination will be redistributed by the top Au patterns on devices. The achievement of detectors benefits from the designed redistribution of optical field on specific Schottky barriers within optically active regions and effective carrier collection, producing unidirectional photocurrent for large-scale detection applications. The response mechanisms, including excitations under different polarizations, wavebands, and tilted incidences, were systematically elaborated. Device performances including photocurrent, dynamic response, and detectivity were also carefully measured, demonstrating the possibility for applications in high-speed imaging sensors or integrated optoelectronic systems. The concept of asymmetric-light-excitation photodetectors shows wider availability to other nanomaterials for modern optoelectronics.Keywords: asymmetric excitation; carbon nanotube; photocurrent; photodetector; Schottky barrier;
Co-reporter:Bingyan Chen, Panpan Zhang, Li Ding, Jie Han, Song Qiu, Qingwen Li, Zhiyong Zhang, and Lian-Mao Peng
Nano Letters 2016 Volume 16(Issue 8) pp:5120-5128
Publication Date(Web):July 26, 2016
DOI:10.1021/acs.nanolett.6b02046
Top-gated p-type field-effect transistors (FETs) have been fabricated in batch based on carbon nanotube (CNT) network thin films prepared from CNT solution and present high yield and highly uniform performance with small threshold voltage distribution with standard deviation of 34 mV. According to the property of FETs, various logical and arithmetical gates, shifters, and d-latch circuits were designed and demonstrated with rail-to-rail output. In particular, a 4-bit adder consisting of 140 p-type CNT FETs was demonstrated with higher packing density and lower supply voltage than other published integrated circuits based on CNT films, which indicates that CNT based integrated circuits can reach to medium scale. In addition, a 2-bit multiplier has been realized for the first time. Benefitted from the high uniformity and suitable threshold voltage of CNT FETs, all of the fabricated circuits based on CNT FETs can be driven by a single voltage as small as 2 V.Keywords: Carbon nanotube; field-effect transistor; medium scale integrated circuit; threshold voltage variation;
Co-reporter:Shuang Liang, Ze Ma, Nan Wei, Huaping Liu, Sheng Wang and Lian-Mao Peng
Nanoscale 2016 vol. 8(Issue 12) pp:6761-6769
Publication Date(Web):23 Feb 2016
DOI:10.1039/C5NR07468A
Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ∼5 × 10−4 photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields.
Co-reporter:Jiye Xia, Guodong Dong, Boyuan Tian, Qiuping Yan, Han Zhang, Xuelei Liang and Lianmao Peng
Nanoscale 2016 vol. 8(Issue 19) pp:9988-9996
Publication Date(Web):15 Apr 2016
DOI:10.1039/C6NR00876C
Metal–tube contact is known to play an important role in carbon nanotube field-effect transistors (CNT-FETs) which are fabricated on individual CNTs. Less attention has been paid to the contact effect in network type carbon nanotube thin film transistors (CNT-TFTs). In this study, we demonstrate that contact plays an even more important role in CNT-TFTs than in CNT-FETs. Although the Schottky barrier height at the metal–tube contact can be tuned by the work function of the metal, similar to the case in CNT-FETs, the contact resistance (Rc) forms a much higher proportion of the total resistance in CNT-TFTs. Interestingly, the contact resistivity was found to increase with channel length, which is a consequence of the percolating nature of the transport in CNT films, and this behavior does not exist in CNT-FETs and normal 2D Ohmic conductors. Electrical transport in CNT-TFTs has been predicted to scale with channel length by stick percolation theory. However, the scaling behavior is also impacted, or even covered up by the effect of Rc. Once the contact effect is excluded, the covered scaling behavior can be revealed correctly. A possible way of reducing Rc in CNT-TFTs was proposed. We believe the findings in this paper will strengthen our understanding of CNT-TFTs, and even accelerate the commercialization of CNT-TFT technology.
Co-reporter:Heng Zhang, Youfan Hu, Zongpeng Wang, Zheyu Fang, and Lian-Mao Peng
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 1) pp:381
Publication Date(Web):December 14, 2015
DOI:10.1021/acsami.5b09093
Flexible ZnO thin film UV sensors with 3 orders of magnitude improvement in sensitivity and 2 orders of magnitude acceleration in speed are realized via light absorption efficiency enhancement and surface encapsulation. Devices are constructed on polyethylene substrate incorporating morphology controlled ZnO nanorod arrays (NRAs) as absorbing antireflection layers. By adjusting the morphology of ZnO NRAs, the light absorptance exceeds 99% through effectively trapping incident photons. As a result, the sensitivity of the UV sensor reaches 109 000. Moreover, a mechanism of competitive chemisorption between O2 and H2O at oxygen vacancy sites is proposed to explain the phenomenon of the speed acceleration in moist environment. A new approach of humectant encapsulation is used to make H2O participant rapid processes dominant for speed acceleration. Two orders of magnitude speed enhancement in reset time is achieved by polyethylene glycol encapsulation. After a total 3000 cycles bending test, the decay in the responsivity of UV sensor is within 20%, indicating good mechanical stability. All these results not only demonstrate a simple, effective and scalable approach to fabricate high sensitive and fast response flexible ZnO UV sensors, but also provide meaningful references for performance boosting of photoelectronic devices based on other oxide semiconductors.Keywords: absorbing antireflection; humectant encapsulation; nanorod; nanowire; UV sensor; ZnO
Co-reporter:Yang Liu;Nan Wei;Qingsheng Zeng;Jie Han;Huixin Huang;Donglai Zhong;Fanglin Wang;Li Ding;Jiye Xia;Haitao Xu;Ze Ma;Song Qiu;Qingwen Li;Xuelei Liang;Zhiyong Zhang;Sheng Wang
Advanced Optical Materials 2016 Volume 4( Issue 2) pp:238-245
Publication Date(Web):
DOI:10.1002/adom.201500529
Co-reporter:Shuang Liang, Ze Ma, Gongtao Wu, Nan Wei, Le Huang, Huixin Huang, Huaping Liu, Sheng Wang, and Lian-Mao Peng
ACS Nano 2016 Volume 10(Issue 7) pp:6963
Publication Date(Web):July 5, 2016
DOI:10.1021/acsnano.6b02898
Carbon nanotubes (CNTs) are considered to be highly promising nanomaterials for multiwavelength, room-temperature infrared detection applications. Here, we demonstrate a single-tube diode photodetector monolithically integrated with a Fabry–Pérot microcavity. A ∼6-fold enhanced optical absorption can be achieved, because of the confined effect of the designed optical mode. Furthermore, taking advantage of Van-Hove-singularity band structures in CNTs, we open the possibility of developing chirality-specific (n,m) CNT-film-based signal detectors. Utilizing a concept of the “resonance and off-resonance” cavity, we achieved cavity-integrated chirality-sorted CNT-film detectors working at zero bias and resonance-allowed mode, for specific target signal detection. The detectors exhibited a higher suppression ratio until a power density of 0.07 W cm–2 and photocurrent of 5 pA, and the spectral full width at half-maximum is ∼33 nm at a signal wavelength of 1200 nm. Further, with multiple array detectors aiming at different target signals integrated on a chip, a multiwavelength signal detector system can be expected to have applications in the fields of monitoring, biosensing, color imaging, signal capture, and on-chip or space information transfers. The approach can also bring other nanomaterials into on-chip or information optoelectronics, regardless of the available doping polarity.Keywords: carbon nanotube; microcavity; photocurrent; photodetector; Schottky barrier
Co-reporter:Jia Si, Lijun Liu, Fanglin Wang, Zhiyong Zhang, and Lian-Mao Peng
ACS Nano 2016 Volume 10(Issue 7) pp:6737
Publication Date(Web):June 20, 2016
DOI:10.1021/acsnano.6b02126
A nano self-gating diode (SGD) based on nanoscale semiconducting material is proposed, simulated, and realized on semiconducting carbon nanotubes (CNTs) through a doping-free fabrication process. The relationships between the performance and material/structural parameters of the SGD are explored through numerical simulation and verified by experiment results. Based on these results, performance optimization strategy is outlined, and high performance CNT SGDs are fabricated and demonstrated to surpass other published CNT diodes. In particular the CNT SGD exhibits high rectifier factor of up to 1.4 × 106 while retains large on-state current. Benefiting from high yield and stability, CNT SGDs are used for constructing logic and analog integrated circuits. Two kinds of basic digital gates (AND and OR) have been realized on chip through using CNT SGDs and on-chip Ti wire resistances, and a full wave rectifier circuit has been demonstrated through using two CNT SGDs. Although demonstrated here using CNT SGDs, this device structure may in principle be implemented using other semiconducting nanomaterials, to provide ideas and building blocks for electronic applications based on nanoscale materials.Keywords: carbon nanotube; diode; full-wave rectification; self-gating effect
Co-reporter:Fanglin Wang, Sheng Wang, Fengrui Yao, Haitao Xu, Nan Wei, Kaihui Liu, and Lian-Mao Peng
ACS Nano 2016 Volume 10(Issue 10) pp:9595
Publication Date(Web):September 15, 2016
DOI:10.1021/acsnano.6b05047
Conversion efficiency (CE) is the most important figure of merit for photodetectors. For carbon nanotubes (CNT) based photodetectors, the CE is mainly determined by excitons dissociation and transport of free carriers toward contacts. While phonon-assisted exciton dissociation mechanism is effective in split-gate CNT p–n diodes, the CE is typically low in these devices, approximately 1–5%. Here, we evaluate the performance of a barrier-free bipolar diode (BFBD), which is basically a semiconducting CNT asymmetrically contacted by perfect n-type ohmic contact (Sc) and p-type ohmic contact (Pd) at the two ends of the diode. We show that the CE in short channel BFBD devices (e.g., 60 nm) is over 60%, and it reduces rapidly with increasing channel length. We find that the electric-field-assisted mechanism dominates the dissociation rate of excitons in BFBD devices at zero bias and thus the photocurrent generation process. By performing a time-resolved and spatial-resolved Monte Carlo simulation, we find that there exists an effective electron (hole)-rich region near the n-type (p-type) electrode in the asymmetrically contacted BFBD device, where the electric-field strength is larger than 17 V/μm and exciton dissociation is extremely fast (<0.1 ps), leading to very high CE in the BFBD devices.Keywords: BFBD; carbon nanotube; CNT diode; exciton dissociation; IR detector
Co-reporter:Hua-Rong Xia, Wen-Tao Sun and Lian-Mao Peng
Chemical Communications 2015 vol. 51(Issue 72) pp:13787-13790
Publication Date(Web):22 Jul 2015
DOI:10.1039/C5CC05053G
A facile hydrothermal method was developed to prepare CH3NH3PbBr3 and CH3NH3PbI3. The as-prepared products were utilized in lithium batteries as anode materials with good performance. Considering the structural diversity, more hybrid perovskites can be targets for further optimization, indicating their promising potential in Li-ion battery applications.
Co-reporter:Le Huang, Zhiyong Zhang, Zishen Li, Bingyan Chen, Xiaomeng Ma, Lijun Dong, and Lian-Mao Peng
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 18) pp:9581
Publication Date(Web):April 22, 2015
DOI:10.1021/acsami.5b01070
Multifunctional graphene magnetic/hydrogen sensors are constructed for the first time through a simple microfabrication process. The as-fabricated graphene sensor may act as excellent Hall magnetic detector, demonstrating small linearity error within 2% and high magnetic resolution up to 7 mG/Hz0.5. Meanwhile the same graphene sensor is also demonstrated as high-performance hydrogen sensor with high gas response, excellent linearity, and great repeatability and selectivity. In particular, the graphene sensor exhibits high hydrogen response up to 32.5% when exposed to 1000 ppm hydrogen, outperforming most graphene-based hydrogen sensors. In addition the hydrogen-sensing mechanism of Pd-decorated graphene is systematically explored through investigating its transfer characteristics during gas detection. Our work demonstrates that graphene is a terrific material for multifunctional sensing, which may in principle reduce the complexity of manufacturing process, lower the number of sensors required in the sensing systems, and potentially derive new and more powerful functions.Keywords: graphene; Hall sensors; hydrogen detection; magnetic detection; multifunctional sensors;
Co-reporter:Chenguang Qiu, Zhiyong Zhang, Donglai Zhong, Jia Si, Yingjun Yang, and Lian-Mao Peng
ACS Nano 2015 Volume 9(Issue 1) pp:969
Publication Date(Web):December 29, 2014
DOI:10.1021/nn506806b
Field-effect transistors (FETs) based on moderate or large diameter carbon nanotubes (CNTs) usually suffer from ambipolar behavior, large off-state current and small current on/off ratio, which are highly undesirable for digital electronics. To overcome these problems, a feedback-gate (FBG) FET structure is designed and tested. This FBG FET differs from normal top-gate FET by an extra feedback-gate, which is connected directly to the drain electrode of the FET. It is demonstrated that a FBG FET based on a semiconducting CNT with a diameter of 1.5 nm may exhibit low off-state current of about 1 × 10–13 A, high current on/off ratio of larger than 1 × 108, negligible drain-induced off-state leakage current, and good subthreshold swing of 75 mV/DEC even at large source-drain bias and room temperature. The FBG structure is promising for CNT FETs to meet the standard for low-static-power logic electronics applications, and could also be utilized for building FETs using other small band gap semiconductors to suppress leakage current.Keywords: carbon nanotube; field-effect transistor; gate engineering; low static power;
Co-reporter:Longwei Li;Nai Wen;Huarong Xia;Jia Li;Wentao Sun
Science China Chemistry 2015 Volume 58( Issue 9) pp:1501-1507
Publication Date(Web):2015/09/01
DOI:10.1007/s11426-015-5356-3
TiO2 nanowire (NW) is one of the potential scattering layer materials in dye-sensitized solar cells (DSSCs) owing to its fast electron conductivity and excellent light scattering property resulting from its one-dimensional (1D) morphology. However, TiO2 NWs used as scattering layers in previous works were either aggregated or shortened into shuttles that cannot use their unique 1D properties. In this paper, we present the preparation of a well-dispersed long NW paste (exceeding 1 mm) by a mild method and used as a scattering layer in DSSC. The paste achieved a photoconversion efficiency of 5.73% and an efficiency enhancement of 12% compared with commercial scattering layer (P200 paste). Compared with the DSSC without a scattering layer, an efficiency enhancement of 54.9% was achieved. Also, the largest efficiency of 6.89% was obtained after optimization of photoanode thickness. The photoanodes were investigated through dye desorbed experiments and transmission spectra, which suggested that P25 nanoparticles with the as-prepared NW scattering layer loaded more dye than those with P200 paste. These results indicate that well-dispersed long NW paste has a potential application in scattering layers.
Co-reporter:Zhenxing Wang;Shibo Liang;Zhiyong Zhang;Honggang Liu;Hua Zhong;Lin-Hui Ye;Sheng Wang;Weiwei Zhou;Jie Liu;Yabin Chen;Jin Zhang
Advanced Materials 2014 Volume 26( Issue 4) pp:645-652
Publication Date(Web):
DOI:10.1002/adma.201302793
Co-reporter:Lian-Mao Peng, Zhiyong Zhang, Sheng Wang
Materials Today 2014 Volume 17(Issue 9) pp:433-442
Publication Date(Web):November 2014
DOI:10.1016/j.mattod.2014.07.008
Carbon nanotubes (CNTs) are quasi-one-dimensional materials with unique properties and are ideal materials for applications in electronic devices. Significant progress has been made on CNT electronics, and a doping-free approach has emerged from this research. This approach utilizes the contact control on the properties of field-effect transistors (FETs), preserving the perfect lattice of the CNT making it possible for CNT FETs to outperform state-of-the-art Si devices. Both n-type and p-type CNT FETs with near ballistic performance limits have been fabricated, symmetric CMOS devices have been demonstrated, and pass-transistor-logic, a circuit configuration that is more efficient than CMOS is being explored.
Co-reporter:Tian Pei, Panpan Zhang, Zhiyong Zhang, Chenguang Qiu, Shibo Liang, Yingjun Yang, Sheng Wang, and Lian-Mao Peng
Nano Letters 2014 Volume 14(Issue 6) pp:3102-3109
Publication Date(Web):May 5, 2014
DOI:10.1021/nl5001604
While constructing general integrated circuits (ICs) with field-effect transistors (FETs) built on individual CNTs is among few viable ways to build ICs with small dimension and high performance that can be compared with that of state-of-the-art Si based ICs, this has not been demonstrated owing to the absence of valid and well-tolerant fabrication method. Here we demonstrate a modularized method for constructing general ICs on individual CNTs with different electric properties. A pass-transistor-logic style 8-transistor (8-T) unit is built, demonstrated as a multifunctional function generator with good tolerance to inhomogeneity in the CNTs used and used as a building block for constructing general ICs. As an example, an 8-bits BUS system that is widely used to transfer data between different systems in a computer is constructed. This is the most complicated IC fabricated on individual CNTs to date, containing 46 FETs built on six individual semiconducting CNTs. The 8-T unit provides a good basis for constructing complex ICs to explore the potential and limits of CNT ICs given the current imperfection in available CNT materials and may also be developed into a universal and efficient way for constructing general ICs on ideal CNT materials in the future.
Co-reporter:Haitao Xu, Sheng Wang, Zhiyong Zhang, and Lian-Mao Peng
Nano Letters 2014 Volume 14(Issue 9) pp:5382-5389
Publication Date(Web):August 12, 2014
DOI:10.1021/nl502534j
Carbon nanotubes (CNTs) are promising candidates for future optoelectronics and logic circuits.1−3 Sub-10 nm channel length CNT transistors have been demonstrated with superb performance.4 Yet, the scaling of CNT p–n diodes or photodiodes, basic elements for most optoelectronic devices, is held back on a scale of micrometers.5−8 Here, we demonstrate that CNT diodes fabricated via a dopant-free technique show good rectifying characteristics and photovoltaic response even when the channel length is scaled to sub-50 nm. By making a trade-off between performance and size, a diode with both channel length and contact width around 100 nm, fabricated on a CNT with a small diameter (d ∼ 1.2 nm), shows a photovoltage of 0.24 V and a fill factor of up to 60%. Study on the dependence of turn-on voltage on scaled channel length reveals transferred charges induced potential barrier at the contact in long channel diodes and the effect of self-adjusting charge distribution. This effect could be utilized for realizing stable and high performance sub-100 nm pitch CNT diodes. As elementary building blocks, such tiny electric and photodiodes could be used in nanoscale rectifiers, photodetectors, light sources, and high-efficiency photovoltaic devices.
Co-reporter:Bingyan Chen, Huixin Huang, Xiaomeng Ma, Le Huang, Zhiyong Zhang and Lian-Mao Peng
Nanoscale 2014 vol. 6(Issue 24) pp:15255-15261
Publication Date(Web):30 Oct 2014
DOI:10.1039/C4NR05664G
Chemical vapor deposition (CVD) is considered the most promising method for pushing graphene into commercial products. However, CVD grown graphene is usually of low quality. In this work we explore how good can CVD-derived monolayer graphene be. Through the combinational optimization of the main processes of growth, transfer, device fabrication and measurements, we show that the optimized CVD graphene can present performance comparable to mechanical exfoliated ones: in particular, high carrier mobility at room temperature on the Si/SiO2 substrate, perfect electron–hole symmetry and excellent uniformity (the mobility ranged from 5000 to 12000 cm2 V−1 s−1 with an average mobility of ∼8800 cm2 V−1 s−1 and 50% were higher than 10000 cm2 V−1 s−1). In addition we found that the adsorbed oxygen and water molecules on graphene lead to p-type doping in graphene, and transferred charges bring charged impurity scattering to the transporting carriers in the graphene channel. It is therefore necessary to carry out electrical measurements under vacuum to obtain high intrinsic carrier mobility CVD grown graphene.
Co-reporter:Li Ding, Zhiyong Zhang, Jun Su, Qunqing Li and Lian-Mao Peng
Nanoscale 2014 vol. 6(Issue 19) pp:11316-11321
Publication Date(Web):05 Aug 2014
DOI:10.1039/C4NR03475A
Thin yttria films were investigated for use as gate dielectrics in carbon nanotube field-effect transistors (CNTFETs) with the gate length scaled down to sub-50 nm size. The yttria film provided an omega-shaped gate dielectric with a low interface trap density, a low average sub-threshold swing of 74 mV per decade for both long and short CNTFETs, and a small drain-induced barrier lowering. It was also shown that the performance of CNTFETs increases with decreasing temperature, with an excellent sub-threshold swing of 22 mV per decade at liquid nitrogen temperatures. A method was developed to retrieve the interface trap density in CNTFETs and a low interface trap density of 5.2 × 106 cm−1 was achieved, indicating the high electric quality of the yttria films.
Co-reporter:Hua-Rong Xia, Jia Li, Wen-Tao Sun and Lian-Mao Peng
Chemical Communications 2014 vol. 50(Issue 89) pp:13695-13697
Publication Date(Web):16 Sep 2014
DOI:10.1039/C4CC05960C
CH3NH3PbI3 based photodetectors were fabricated by a facile low-cost process with much enhanced performance. The rise time changed from 2.7 s to 0.02 s, the decay time from 0.5 s to 0.02 s, and the ON/OFF ratio tripled with improved stability. The results indicate that perovskites are promising light-harvesting materials for photodetectors.
Co-reporter:Hua-Rong Xia, Jia Li, Chen Peng, Wen-Tao Sun, Long-Wei Li, and Lian-Mao Peng
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 20) pp:17376
Publication Date(Web):September 22, 2014
DOI:10.1021/am504924w
The floating growth process of large-scale freestanding TiO2 nanorod films at the gas–liquid interface was investigated. On the basis of the experiments, a self-templated growth scenario was developed to account for the self-assembly process. In the scenario, titanium complexes function not only as the Ti source for the growth of TiO2 but also as a soft template provider for the floating growth. According to the scenario, several new recipes of preparing freestanding TiO2 nanorod films at the gas–liquid interface were developed. The freestanding film was applied to a lithium ion battery as a binder-free and conducting agent-free anode, and good cyclability was obtained. This work may pave a new way to floating and freestanding TiO2 and other semiconductor materials, which has great potential not only in basic science but also in the applications such as materials engineering, Li-ion battery, photocatalyst, dye-sensitized solar cell, and flexible electronics.Keywords: self-templated; binder-free; floating; freestanding; gas−liquid interface; Li-ion battery
Co-reporter:Zhenxing Wang;Zhiyong Zhang;Hua Zhong;Tian Pei;Shibo Liang;Leijing Yang;Sheng Wang
Advanced Functional Materials 2013 Volume 23( Issue 4) pp:446-450
Publication Date(Web):
DOI:10.1002/adfm.201202185
Abstract
Field-effect transistors (FETs) fabricated on large diameter carbon nanotubes (CNTs) present typical ambipolar transfer characteristics owing to the small band-gap of CNTs. Depending on the DC biasing condition, the ambipolar FET can work in three different regions, and then can be used as the core to realize multifunctional AC circuits. The CNT FET based circuits can work as a high-efficiency ambipolar frequency doubler in the ambipolar transfer region, and also can function as in-phase amplifier and inverted amplifier in the linear transfer region. Due to current saturation of the CNT FET, an AC amplifier with a voltage gain of 2 is realized when the device works in the linear transfer region. Achieving an actual amplification and frequency doubling functions indicates that complicated radio frequency circuits or systems can be constructed based on just one kind of device: ambipolar CNT FETs.
Co-reporter:Hua-Rong Xia, Jia Li, Chen Peng, Long-Wei Li, Wen-Tao Sun, and Lian-Mao Peng
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 18) pp:8850
Publication Date(Web):August 30, 2013
DOI:10.1021/am4026938
This paper describes a facile one-step synthesis of large-scale floating TiO2 nanorod arrays via a hydrothermal reaction without using any surfactants, which opens a new way to prepare floating photocatalysts for photodecomposition of floating organics and free-standing nanorod arrays for flexible dye-sensitized solar cells. A general model is developed to analyze the driving force for the floating TiO2 film, which may be also useful for other two-dimensional materials to determine the obtainable size of an arbitrary shaped film floated by surface tension and buoyancy.Keywords: buoyancy; floating; flowerlike; free-standing; nanorod arrays; surface tension;
Co-reporter:Hua-Rong Xia, Chen Peng, Jia Li, Wen-Tao Sun, Guo Ai and Lian-Mao Peng
RSC Advances 2013 vol. 3(Issue 39) pp:17668-17671
Publication Date(Web):31 Jul 2013
DOI:10.1039/C3RA42974A
Large-scale floated single-crystal flower-like films were synthesized without any surfactants in a one-step hydrothermal reaction. Enhanced light-harvesting performance was obtained compared to vertical nanorod arrays, and significant improvements of photoelectric conversion efficiency have been achieved in the dye-sensitized solar cells using the films as photoanodes or scattering layers.
Co-reporter:Shibo Liang;Zhiyong Zhang;Tian Pei;Ruoming Li;Yan Li;Lianmao Peng
Nano Research 2013 Volume 6( Issue 7) pp:535-545
Publication Date(Web):2013 July
DOI:10.1007/s12274-013-0330-x
Co-reporter:Leijing Yang, Sheng Wang, Qingsheng Zeng, Zhiyong Zhang, Yan Li, Weiwei Zhou, Jie Liu, and Lian-Mao Peng
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 3) pp:1154
Publication Date(Web):February 10, 2012
DOI:10.1021/am201778x
Carbon nanotube (CNT) diodes with different channel length between L = 0.6μm to 3.5 μm are fabricated on the same tube, and the electric and photovoltaic characteristics are investigated. It is found that although the open voltage of the diode increases rapidly for channel length L less than 1.0 μm, it saturates for longer channel devices. On the other hand, the short circuit current of the diode exhibites a clear peak at intermediate channel length of about 1.5 μm, a large leakage current via tunneling for short channel device and significantly decreased current for long channel device due to the increased recombination and channel resistance. The optimal channel length for a CNT diode in photovoltaic application is thus determined to be about 1.5 μm.Keywords: carbon nanotube; channel length; diode; doping-free; photovoltaic;
Co-reporter:Li Ding, Zhiyong Zhang, Tian Pei, Shibo Liang, Sheng Wang, Weiwei Zhou, Jie Liu, and Lian-Mao Peng
ACS Nano 2012 Volume 6(Issue 5) pp:4013
Publication Date(Web):April 6, 2012
DOI:10.1021/nn300320j
The use of carbon nanotube (CNT)-based field-effect transistors (FETs) as pass transistors is investigated. Logic gates are designed and constructed with these CNT FETs in the pass-transistor logic (PTL) style. Because two of the three terminals of every CNT FET are used as inputs, the efficiency per transistor in PTL circuits is significantly improved. With the PTL style, a single pair of FETS, one n-type and one p-type, is sufficient to construct high-performance AND or OR gates in which the measured output voltages are consistent with those quantitatively derived using the characteristics of the pair of the constituent n- and p-FETs. A one-bit full subtractor, which requires a total of 28 FETs to construct in the usual CMOS circuit, is realized on individual CNTs for the first time using the PTL style with only three pairs of n- and p-FETs.Keywords: carbon nanotube; integrated circuits; logic gates; pass-transistor logic; subtractor
Co-reporter:Sheng Wang;ZhiYong Zhang;LianMao Peng
Science Bulletin 2012 Volume 57( Issue 2-3) pp:149-156
Publication Date(Web):2012 January
DOI:10.1007/s11434-011-4806-3
Semiconducting carbon nanotubes (CNTs) possess outstanding electrical and optical properties because of their special one-dimensional (1D) structure. CNTs are direct bandgap materials, which makes them ideal for use in optoelectronic devices, e.g. light emitters and light detectors. Excitons determine their light absorption and light emission processes due to the strong Coulomb interactions between electrons and holes in CNTs. In this paper, we review recent progress in CNT photodetectors, photovoltaic devices and light emitters. In particular, we focus on the doping-free CNT optoelectronic devices developed by our group in recent years.
Co-reporter:ZhenXing Wang;ZhiYong Zhang;LianMao Peng
Science Bulletin 2012 Volume 57( Issue 23) pp:2956-2970
Publication Date(Web):2012 August
DOI:10.1007/s11434-012-5143-x
Graphene is considered as a promising material to construct field-effect transistors (FETs) for high frequency electronic applications due to its unique structure and properties, mainly including extremely high carrier mobility and saturation velocity, the ultimate thinnest body and stability. Through continuously scaling down the gate length and optimizing the structure, the cut-off frequency of graphene FET (GFET) was rapidly increased and up to about 300 GHz, and further improvements are also expected. Because of the lack of an intrinsic band gap, the GFETs present typical ambipolar transfer characteristic without off state, which means GFETs are suitable for analog electronics rather than digital applications. Taking advantage of the ambipolar characteristic, GFET is demonstrated as an excellent building block for ambipolar electronic circuits, and has been used in applications such as highperformance frequency doublers, radio frequency mixers, digital modulators, and phase detectors.
Co-reporter:Qingsheng Zeng;Sheng Wang;Leijing Yang;Zhenxing Wang;Zhiyong Zhang
Nano Research 2012 Volume 5( Issue 1) pp:33-42
Publication Date(Web):2012 January
DOI:10.1007/s12274-011-0182-1
Random networks of single-walled carbon nanotubes (SWCNTs) were have been grown by chemical vapor deposition on silicon wafers and used for fabricating field-effect transistors (FETs) using symmetric Pd contacts and diodes using asymmetrical Pd and Sc contacts. For a short channel FET or diode with a channel length of about 1 μm or less, the device works in the direct transport regime, while for a longer channel device the transport mechanism changes to percolation. Detailed electronic and photovoltaic (PV) characterizations of these carbon nanotube (CNT) thin-film devices was carried out. While as-fabricated FETs exhibited typical p-type transfer characteristics, with a large current ON/OFF ratio of more than 104 when metallic CNTs were removed via a controlled breakdown, it was found that the threshold voltage for the devices was typically very large, of the order of about 10 V. This situation was greatly improved when the device was coated with a passivation layer of 12 nm HfO2, which effectively moved the threshold voltages of both FET and diode back to center around zero or turned these device to their OFF states when no bias was applied on the gate. PV measurements were then made on the short channel diodes under infrared laser illumination. It was shown that under an illumination power density of 1.5 kW/cm2, the device resulted in an open circuit voltage VOC = 0.21 V and a short circuit current ISC = 3.74 nA. Furthermore, we compared PV characteristics of CNT film diodes with different channel lengths, and found that the power transform efficiency decreased significantly when the device changed from the direct transport to the percolation regime.
Co-reporter:Sheng Wang, Qingsheng Zeng, Leijing Yang, Zhiyong Zhang, Zhenxing Wang, Tian Pei, Li Ding, Xuelei Liang, Min Gao, Yan Li, and Lian-Mao Peng
Nano Letters 2011 Volume 11(Issue 1) pp:23-29
Publication Date(Web):November 30, 2010
DOI:10.1021/nl101513z
Electroluminescence (EL) measurements are carried out on a two-terminal carbon nanotube (CNT) based light-emitting diode (LED). This two-terminal device is composed of an asymmetrically contacted semiconducting single-walled carbon nanotube (SWCNT). On the one end the SWCNT is contacted with Sc and on the other end with Pd. At large forward bias, with the Sc contact being grounded, electrons can be injected barrier-free into the conduction band of the SWCNT from the Sc contact and holes be injected into the valence band from the Pd electrode. The injected electrons and holes recombine radiatively in the SWCNT channel yielding a narrowly peaked emission peak with a full width at half-maximum of about 30 meV. Detailed EL spectroscopy measurements show that the emission is excitons dominated process, showing little overlap with that associated with the continuum states. The performance of the LED is compared with that based on a three-terminal field-effect transistor (FET) that is fabricated on the same SWCNT. The conversion efficiency of the two-terminal diode is shown to be more than three times higher than that of the FET based device, and the emission peak of the LED is much narrower and operation voltage is lower.
Co-reporter:Tian Pei;Zhiyong Zhang;Zhenxing Wang;Li Ding;Sheng Wang
Advanced Functional Materials 2011 Volume 21( Issue 10) pp:1843-1849
Publication Date(Web):
DOI:10.1002/adfm.201002563
Abstract
High-performance top-gate carbon nanotube (CNT) field-effect transistors (FETs) have been fabricated via a doping-free fabrication process in which the polarity of the CNT FET is controlled by the injection of carriers from the electrodes, instead of using dopants. The performance of the doping-free CNT FETs is systemically investigated over a wide temperature range, from very low temperatures of down to 4.3 K up to 573 K, and analyzed using several temperature-dependent key device parameters including the ON/OFF state current and ratio, carrier mobility, and subthreshold swing. It is demonstrated that for ballistic and quasi-ballistic CNT FETs, the operation of the CNT FETs is largely independent of the presence of dopant, thus avoiding detrimental effects due to dopant freeze-out at low temperature and dopant diffusion at high temperature, and making it possible to use doping-free CNT FETs in both low- and high-temperature electronics. A new method is also proposed for extracting the band-gap and diameter of a semiconducting CNT from the temperature dependent OFF-state current and shown to yield results that are consistent with AFM measurements.
Co-reporter:Yang Liu;Zhiyong Zhang;Xianlong Wei;Quan Li
Advanced Functional Materials 2011 Volume 21( Issue 20) pp:3900-3906
Publication Date(Web):
DOI:10.1002/adfm.201100701
Abstract
The thermoelectric parameters, in particular the thermal conductivity and dimensionless figure of merit ZT, of ZnO nanowires, are estimated via two terminal current–voltage measurements. The measurements are carried out in situ in a transmission electron microscope and negative differential conductance is observed on individually suspended ZnO nanowires. From the low bias region of the current–voltage curve, the electrical parameters, including carrier concentration and mobility, are obtained by fitting the experimental data using a metal–semiconductor–metal model. The thermal conductivity is extracted from the high bias region of the same current–voltage curve using a self-consistent method, which combines the self-heating thermal conduction and electrical transport properties of ZnO nanowires. It is shown that the thermal conductivity of ZnO nanowires is suppressed significantly in comparison with that of bulk ZnO, which is attributed to the strong surface scattering of phonons. The thermal conductivity is also found to decrease more steeply than the expected trend, but does obey a relation; this is shown to result from four-phonon processes at high temperatures. The dimensionless figure of merit ZT is determined to be about 0.1 at 970 K. Finally, the thermoelectric properties of individual ZnO nanowires are also discussed, indicating that ZnO nanowires are promising high temperature thermoelectric materials.
Co-reporter:Guo Ai, Wentao Sun, Xianfeng Gao, Yiling Zhang and Lian-Mao Peng
Journal of Materials Chemistry A 2011 vol. 21(Issue 24) pp:8749-8755
Publication Date(Web):12 May 2011
DOI:10.1039/C0JM03867A
Well-aligned TiO2 nanowire arrays are fabricated through a simple hydrothermal method and sensitized with electrodeposited CdSe nanoparticles. Annealing treatments at various temperatures (350 °C, 380 °C, 400 °C and 450 °C) are used to improve the performance of the as-deposited photoelectrode and the effects of various annealing atmospheres (air, O2, N2, Ar and vacuum) are further investigated. Although the film is only 2μm thick, a significant photocurrent density of 8.83 mA cm−2 is observed under 100 mW cm−2 illumination (AM 1.5 G) for the sample annealed at 400 °C in air, which is 5.69 times higher than that of the as-deposited sample and much better compared with that of the samples annealed in other environments. Careful investigation on the annealing effect is performed with a range of analytical techniques, such as SEM, TEM, HRTEM, EDX, UV-vis absorption spectra, and XRD. In particular, HRTEM observation affords a further insight into the exact change in CdSe crystalline structure annealed at different temperature. The results indicate that the crystal structure of CdSe nanoparticles and the interface between TiO2 and CdSe are improved with appropriate annealing below 400 °C, leading to an enhancement of performance. On the other hand, over-annealing at 450 °C results in severe migration and oxidation of CdSe, and leads to a poor photoelectric performance. A better understanding of the influence of the annealing environment is obtained through the adoption of different annealing atmospheres at 400 °C. It is found that both O2 and N2 have a more positive effect on the annealing process compared with Ar and vacuum, while air is found to be the favorite environment for annealing treatment.
Co-reporter:Guo Ai, Wen-Tao Sun, Yi-Ling Zhang and Lian-Mao Peng
Chemical Communications 2011 vol. 47(Issue 23) pp:6608-6610
Publication Date(Web):16 May 2011
DOI:10.1039/C1CC11092F
A novel nanoparticle–nanorod composite TiO2 photoelectrode is fabricated. A 3.20% efficiency is achieved by using a 2.1 μm-thick as-prepared photoelectrode, which is about 3 times of that obtained by a nanorod array electrode (1.05%). The results demonstrate that the composite nanostructure can take advantage of both fast electron transport (nanorod) and high surface area (nanoparticle).
Co-reporter:Huilong Xu, Zhiyong Zhang, Zhenxing Wang, Sheng Wang, Xuelei Liang, and Lian-Mao Peng
ACS Nano 2011 Volume 5(Issue 3) pp:2340
Publication Date(Web):February 16, 2011
DOI:10.1021/nn200026e
A high-quality Y2O3 dielectric layer has been grown directly on graphene and used to fabricated top-gate graphene field-effect transistors (FETs), and the thickness of the dielectric layer has been reduced continuously down to 3.9 nm with an equivalent oxide thickness (EOT) of 1.5 nm and excellent insulativity. By measuring CV characteristics of two graphene FETs with different gate oxide thicknesses, the oxide capacitance and quantum capacitance are retrieved directly from the experimental CV data without introducing any additional fitting process and parameters, yielding a relative dielectric constant of κ = 10 for Y2O3 on graphene and an oxide capacitance of about 2.28 μF/cm2. It is found that for a rather large gate voltage range, this oxide capacitance is comparable and sometimes even larger than the quantum capacitance of graphene. Since the total gate capacitance is determined by the smaller of the oxide and quantum capacitance, our results show that not much further improvement can be gained via further vertical scaling down of the gate oxide, suggesting that Y2O3 may be the ultimate dielectric material for graphene. It is also shown that the Y2O3 gate dielectric layer with EOT of 1.5 nm may also satisfy the ultimate lateral scaling requirement on the gate length of graphene FET and be used effectively to control a graphene FET with a gate length as small as 1 nm.Keywords: gate dielectric; graphene field-effect transistor; quantum capacitance; vertical scaling; yttrium oxide
Co-reporter:Li Ding, Zhenxing Wang, Tian Pei, Zhiyong Zhang, Sheng Wang, Huilong Xu, Fei Peng, Yan Li, and Lian-Mao Peng
ACS Nano 2011 Volume 5(Issue 4) pp:2512
Publication Date(Web):March 3, 2011
DOI:10.1021/nn102091h
A novel self-aligned U-gate structure for carbon nanotube (CNT) field-effect transistors (FETs) is introduced and shown to yield excellent dc properties and high reproducibility that are comparable with that of the best CNT FETs based on the previously developed self-aligned device structures. In particular the subthreshold swing of the U-gate FET is 75 mV/dec and the drain-induced barrier lowering is effectively zero, indicating that the electrostatic potential of the whole CNT channel is most efficiently controlled by the U-gate and that the CNT device is a well-behaved FET. Moreover the high-frequency response of the U-gate FET is investigated, and the parasitic capacitance of the device is measured and shown to be one magnitude smaller than that of the previously developed self-aligned device structures. Direct frequency domain measurements show that the U-gate CNT FETs can operate up to 800 MHz, which is also higher than previously reported values. The large improvement in the device high-frequency behavior is largely due to the replacement of the high-κ dielectric material between the source/drain and the gate by a vacant space with κ ≈ 1, and the significant reduction in the device parasitic capacitance renders the U-gate CNT FETs promising for rf applications.Keywords: carbon nanotube; field-effect transistor; high-speed circuit; parasitic capacitance; self-aligned;
Co-reporter:Huilong Xu, Zhiyong Zhang, Haitao Xu, Zhenxing Wang, Sheng Wang, and Lian-Mao Peng
ACS Nano 2011 Volume 5(Issue 6) pp:5031
Publication Date(Web):April 29, 2011
DOI:10.1021/nn201115p
High-performance graphene field-effect transistors (G-FETs) are fabricated with carrier mobility of up to 5400 cm2/V·s and top-gate efficiency of up to 120 (relative to that of back gate with 285 nm SiO2) simultaneously through growing high-quality Y2O3 gate oxide at high oxidizing temperature. The transconductance normalized by dimension and drain voltage is found to reach 7900 μF/V·s, which is among the largest of the published graphene FETs. In an as-fabricated graphene FET with a gate length of 310 nm, a peak transconductance of 0.69 mS/μm is realized, but further improvement is seriously hindered by large series resistance. Benefiting from highly efficient gate control over the graphene channel, the Dirac point voltage of the graphene FETs is shown to be designable via simply selecting a gate metal with an appropriate work function. It is demonstrated that the Dirac point voltage of the graphene FETs can be adjusted from negative to positive, respectively, via changing the gate material from Ti to Pd.Keywords: Dirac point voltage; field-effect transistor; graphene; transconductance
Co-reporter:Zhenxing Wang, Li Ding, Tian Pei, Zhiyong Zhang, Sheng Wang, Tao Yu, Xiaofei Ye, Fei Peng, Yan Li and Lian-Mao Peng
Nano Letters 2010 Volume 10(Issue 9) pp:3648-3655
Publication Date(Web):August 2, 2010
DOI:10.1021/nl102111j
A small band-gap carbon nanotube (SBG CNT) with a large diameter of 4 nm has been used to fabricate ambipolar field-effect transistors (FETs) with ultrahigh carrier mobility of more than 18 300 and 8300 cm2/V·s for holes and electrons, respectively. Using a top-gate device geometry with 12 nm HfO2 being the gate oxide, the SBG CNT-based FET exhibits an almost perfect symmetric ambipolar transfer characteristic without any noticeable hysteresis, and a highly efficient frequency doubler is constructed based on this near perfect ambipolar FET. The SBG CNT-based frequency doubler is shown to be able to operate in a large signal mode where the input AC signal, being applied to the top-gate electrode, drives the FET operating alternatively in a p- or n-region yielding an output signal at the drain electrode with doubled frequency and high conversion efficiency. For an input AC signal of 1 kHz, detailed frequency power spectrum analysis shows that more than 95% of the output signal is concentrated at the doubled frequency at 2 kHz, with a gain of more than 0.15, and this represents the highest gain so far achieved in carbon-based devices, including graphene-based devices.
Co-reporter:Zhenxing Wang, Huilong Xu, Zhiyong Zhang, Sheng Wang, Li Ding, Qingsheng Zeng, Leijing Yang, Tian Pei, Xuelei Liang, Min Gao and Lian-Mao Peng
Nano Letters 2010 Volume 10(Issue 6) pp:2024-2030
Publication Date(Web):May 10, 2010
DOI:10.1021/nl100022u
High-quality yttrium oxide (Y2O3) is investigated as an ideal high-κ gate dielectric for carbon-based electronics through a simple and cheap process. Utilizing the excellent wetting behavior of yttrium on sp2 carbon framework, ultrathin (about few nm) and uniform Y2O3 layers have been directly grown on the surfaces of carbon nanotube (CNT) and graphene without using noncovalent functionalization layers or introducing large structural distortion and damage. A top-gate CNT field-effect transistor (FET) adopting 5 nm Y2O3 layer as its top-gate dielectric shows excellent device characteristics, including an ideal subthreshold swing of 60 mV/decade (up to the theoretical limit of an ideal FET at room temperature). The high electrical quality Y2O3 dielectric layer has also been integrated into a graphene FET as its top-gate dielectric with a capacitance of up to 1200 nF/cm2, showing an improvement on the gate efficiency and on state transconductance of over 100 times when compared with that of its back-gate counterpart.
Co-reporter:Shengyong Xu;Yong Yang;Dongfei Pei;Xin Zhao;Yanxin Wang;Weiqiang Sun;Bo Ma;Yan Li;Sishen Xie
Advanced Functional Materials 2010 Volume 20( Issue 14) pp:2263-2268
Publication Date(Web):
DOI:10.1002/adfm.201000263
Abstract
The delay time of nanosecond electromagnetic pulses is measured in multiwalled carbon nanotube (MWCNT) bundles and copper wires, with a length of up to 3 cm, as compared with that in standard coaxial cables of the same lengths. Under certain configurations, when the Cu core of a coaxial cable is replaced with a MWCNT bundle of the same length, the measured delay time of a pulsed signal is shortened. The difference between the delay time measured for a device with a Cu core and that of a device with a MWCNT bundle of the same length increases with the length of the samples. The results imply that, compared with Cu wires, MWCNT bundles may be more efficient in guiding the transmission of high-frequency signals along their longitudinal axis, showing a waveguide-like effect.
Co-reporter:Yong Yang;Shengyong Xu;Sishen Xie
Nano-Micro Letters 2010 Volume 2( Issue 3) pp:184-189
Publication Date(Web):2010 September
DOI:10.1007/BF03353639
The progress on novel interconnects for carbon nanotube (CNT)-based electronic circuit is by far behind the remarkable development of CNT-field effect transistors. The Cu interconnect material used in current integrated circuits seems not applicable for the novel interconnects, as it requires electrochemical deposition followed by chemical-mechanical polishing. We report our experimental results on the failure current density, resistivity, electromigration effect and failure mechanism of patterned stripes of Pd, Sc and Y thin-films, regarding them as the potential novel interconnects. The Pd stripes have a failure current density of (8∼10)×106 A/cm2 (MA/cm2), and they are stable when the working current density is as much as 90% of the failure current density. However, they show a resistivity around 210 μΩ·cm, which is 20 times of the bulk value and leaving room for improvement. Compared to Pd, the Sc stripes have a similar resistivity but smaller failure current density of 4∼5 MA/cm2. Y stripes seem not suitable for interconnects by showing even lower failure current density than that of Sc and evidence of oxidation. For comparison, Au stripes of the same dimensions show a failure current density of 30 MA/cm2 and a resistivity around 4 μΩ·cm, making them also a good material as novel interconnects.
Co-reporter:Zhudong Hu, Qing Chen, Zhen Li, Yuan Yu and Lian-Mao Peng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 2) pp:881-889
Publication Date(Web):December 17, 2009
DOI:10.1021/jp9094744
In this study, we report a facile and rapid synthesis strategy for preparing ultralong ZnO nanowire (NW) arrays by anodizing zinc foil at room temperature in a slightly basic solution, followed by annealing treatment. Detailed structure and composition characterizations are presented, including scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, and X-ray diffraction. We also explore the effects of temperature, applied voltage, and pretreatment on the anodization process. On the optimized conditions, dense NW film can be achieved, resulting in the enhanced optical absorption. More importantly, the as-prepared ZnO NWs have exhibited reasonable electronic properties. The zinc anodization technique, which does not involve complex chemicals and steps, is a low-cost and high-efficiency approach to large-scale synthesis of ultralong ZnO NW film, suggesting the great potential in dye-sensitized solar cells and gas sensors.
Co-reporter:Li Ding, Sheng Wang, Zhiyong Zhang, Qingsheng Zeng, Zhenxing Wang, Tian Pei, Leijing Yang, Xuelei Liang, Jun Shen, Qing Chen, Rongli Cui, Yan Li and Lian-Mao Peng
Nano Letters 2009 Volume 9(Issue 12) pp:4209-4214
Publication Date(Web):November 13, 2009
DOI:10.1021/nl9024243
While it has been shown that scandium (Sc) can be used for making high-quality Ohmic contact to the conduction band of a carbon nanotube (CNT) and thus for fabricating high-performance n-type CNT field effect transistors (FETs), the cost for metal Sc is currently five times more expensive than that for gold and one thousand times more expensive than for yttrium (Y) which in many ways resembles Sc. In this Letter we show that near perfect contacts can be fabricated on single-walled CNTs (SWCNTs) using Y, and the Y-contacted CNT FETs outperform the Sc-contacted CNT FETs in many important aspects. Low-temperature measurements on Y-contacted devices reveal that linear output characteristics persist down to 4.3 K, suggesting that Y makes a perfect Ohmic contact with the conduction band of the CNT. Self-aligned top-gate devices have been fabricated, showing high performance approaching the theoretical limit of CNT-based devices. In particular a room temperature conductance of about 0.55G0 (with G0 = 4e2/h being the quantum conductance limit of the SWCNT), threshold swing of 73 mV/decade, electron mobility of 5100 cm2/V·s, and mean free length of up to 0.639 μm have been achieved. Gate length scaling behavior of the Y-contacted CNT FETs is also investigated, revealing a more favorable energy consumption and faster intrinsic speed scaling than that of the Si-based devices.
Co-reporter:Youfan Hu;Yang Liu;Wenliang Li;Min Gao;Xuelei Liang;Quan Li
Advanced Functional Materials 2009 Volume 19( Issue 15) pp:2380-2387
Publication Date(Web):
DOI:10.1002/adfm.200900179
Abstract
Direct experimental evidence for the existence of a 2D electron gas in devices based on ZnO nanowires (NWs) is presented. A two-channel core/shell model is proposed for the interpretation of the temperature-dependent current–voltage (I–V) characteristics of the ZnO NW, where a mixed metallic–semiconducting behavior is observed. The experimental results are quantitatively analyzed using a weak-localization theory, and suggest that the NW is composed of a “bulk” semiconducting core with a metallic surface accumulation layer, which is basically a 2D electron gas in which the electron–phonon inelastic scattering is much weaker than the electron–electron inelastic scattering. A series of I–V measurements on a single NW device are carried out by alternating the atmosphere (vacuum, H2, vacuum, O2), and a reversible change in the conductance from metallic to semiconducting is achieved, indicating the surface accumulation layer is likely hydroxide-induced. Such results strongly support the two-channel model and demonstrate the controllable tuning of the ZnO NW electrical behavior via surface band-bending.
Co-reporter:Xian-Feng Gao, Hong-Bo Li, Wen-Tao Sun, Qing Chen, Fang-Qiong Tang and Lian-Mao Peng
The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7531-7535
Publication Date(Web):April 8, 2009
DOI:10.1021/jp810727n
TiO2 nanotube array films, formed by anodic oxidation, have been shown to yield high efficiency of charge generation and collection in photoelectrochemical (PEC) devices. However, the wide band gap (3.2 eV) of TiO2 limits the efficiency of these devices in the visible region. In this work, four types of presynthesized CdTe quantum dots (QDs) of different sizes were deposited into the TiO2 nanotubes to serve as the sensitizers, and the performance of the CdTe QD-sensitized TiO2 nanotube arrays was measured in a PEC solar cell. It is found that, with decreasing particle size, the driving force for electron injection increases while the visible light response decreases. Maximum photocurrent was obtained for the QDs that have an absorption peak at 536 nm. Under AM 1.5 G illuminations, a 6 mA/cm2 short circuit current density is achieved, which presents a 35 times improvement compared to that based on using a plain TiO2 nanotube film.
Co-reporter:Xian-Feng Gao, Wen-Tao Sun, Zhu-Dong Hu, Guo Ai, Yi-Ling Zhang, Shi Feng, Fei Li and Lian-Mao Peng
The Journal of Physical Chemistry C 2009 Volume 113(Issue 47) pp:20481-20485
Publication Date(Web):November 2, 2009
DOI:10.1021/jp904320d
A heterojunction CdS/TiO2 photoelectrode is prepared by filling CdS nanoparticles into one-dimensional TiO2 nanotube (NT) array films. The self-assembled TiO2 NTs are fabricated by an anodization method and sensitized with CdS nanoparticles by the close space sublimation technique. The photoactivity of the as-prepared photoelectrodes was measured in a photoelectrochemical solar cell. Under AM 1.5G illumination, a 5.6 mA/cm2 short-circuit current density is achieved using the CdS modified photoelectrode, which represents an enhancement by a factor of 36 in photoactivity compared with that of the plain TiO2 NT array film.
Co-reporter:Zhiyong Zhang, Sheng Wang, Zhenxing Wang, Li Ding, Tian Pei, Zhudong Hu, Xuelei Liang, Qing Chen, Yan Li and Lian-Mao Peng
ACS Nano 2009 Volume 3(Issue 11) pp:3781
Publication Date(Web):October 21, 2009
DOI:10.1021/nn901079p
Symmetric n- and p-type field-effect transistors (FETs) have been fabricated on the same undoped single-walled carbon nanotube (SWCNT). The polarity of the FET is defined by controlled injection of electrons (n-type, via Sc electrodes) or holes (p-type, via Pd electrodes) into the SWCNT, instead of via chemically doping the SWCNT. The SWCNT-based FETs with different channel lengths show a clear trend of performance improvement for channel length scaling. Taking full advantage of the perfect symmetric band structure of the semiconductor SWCNT, a perfect SWCNT-based CMOS inverter is demonstrated, which gives a voltage gain of over 160, and for the two adjacent n- and p-type FETs fabricated on the same SWCNT, high field mobility is realized simultaneously for electrons (3000 cm2/V·s) and holes (3300 cm2/V·s).Keywords: carbon nanotube; CMOS; inverter; mobility; scaling
Co-reporter:M. S. Wang;Q. Chen ;L.-M. Peng
Advanced Materials 2008 Volume 20( Issue 4) pp:724-728
Publication Date(Web):
DOI:10.1002/adma.200702411
Co-reporter:Ting Zhang;Qing Chen
Advanced Functional Materials 2008 Volume 18( Issue 19) pp:3018-3025
Publication Date(Web):
DOI:10.1002/adfm.200800360
Abstract
Calculations and detailed first principle and thermodynamic analyses have been performed to understand the formation mechanism of K2Ti6O13 nanowires (NWs) by a hydrothermal reaction between bulk Na2Ti3O7 crystals and a KOH solution. It is found that direct ion exchange between K+ and Na+ plus H+ interactions with [TiO6] octahedra in Na2Ti3O7 promote the formation of an intermediate H2K2Ti6O14 phase. The large lattice mismatch between this intermediate phase and the bulk Na2Ti3O7 structure, and the large energy reduction associated with the formation of this intermediate phase, drive the splitting of the bulk crystal into H2K2Ti6O14 NWs. However, these NWs are not stable because of large [TiO6] octahedra distortion and are subject to a dehydration process, which results in uniform K2Ti6O13 NWs with narrowly distributed diameters of around 10 nm.
Co-reporter:Ting Zhang;Qing Chen
Advanced Functional Materials 2008 Volume 18( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/adfm.200890077
Co-reporter:Youfan Hu ; Yang Liu ; Huilong Xu ; Xuelei Liang ; Lian-Mao Peng ; Ngaisze Lam ; Kawai Wong ;Quan Li
The Journal of Physical Chemistry C 2008 Volume 112(Issue 37) pp:14225-14228
Publication Date(Web):August 22, 2008
DOI:10.1021/jp805936n
Treatment of ZnO nanowires (NWs) using hydrogen peroxide with increasing concentration results in a continuous increase in the amount of −OH group at the surfaces of the NWs, which demonstrates different characteristics in the transport behaviors of the NWs. Combined with results from theoretical simulation and microphotoluminescence, the variation in the nanowire transport property is explained by the change of carrier density and mobility as induced by the surface treatment.
Co-reporter:Z. Zhang;K. Yao;Y. Liu;C. Jin;X. Liang;Q. Chen;L.-M. Peng
Advanced Functional Materials 2007 Volume 17(Issue 14) pp:
Publication Date(Web):2 AUG 2007
DOI:10.1002/adfm.200600475
A metal-semiconductor-metal (M-S-M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi2S3 nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M-S-M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi2S3 nanowires and compared with the field-effect based method.
Co-reporter:R.H. Wang, Q. Chen, F.R. Chen, J.J. Kai, L.-M. Peng
Micron 2007 Volume 38(Issue 4) pp:362-370
Publication Date(Web):June 2007
DOI:10.1016/j.micron.2006.06.005
Some quantitative structural analyses on defects and domain boundaries observed in SBA-16 films were performed using the lattice concept and geometric phase method. These analyses show that there exist low angle, high angle and translational anti-phase domain boundaries in SBA-16 films. While some of the domain boundaries bear analogue to those found in normal solid crystals, others are similar to that found in the liquid crystals. In particular near Σ11 and Σ13b high angle boundaries were observed. On the one hand the Σ11 boundaries were found to exist with or without steps (ledge) associated with them depending on whether or not the boundary plane is parallel to the densely packed lattice plane. On the other hand segments of the boundary plane in the Σ13b boundary were found being always associated with densely packed lattice plane, with the {0 1 1} type of lattice plane in one domain being parallel to the {1 1 2} type of plane in the other domain. The translational domain boundary was observed to have a translation vector having a projected component of (1/2) 〈1 1 0〉 on the (1 1 1) plane. The bending deformation similar to that found in the nematics liquid crystal was also observed and quantitatively analyzed using the geometric phase method, and rotational field associated with the deformation was identified.
Co-reporter:M. S. Wang;L.-M. Peng;J. Y. Wang;Q. Chen
Advanced Functional Materials 2006 Volume 16(Issue 11) pp:
Publication Date(Web):14 JUN 2006
DOI:10.1002/adfm.200500706
A method is developed and shown to be able to shape a carbon nanotube (CNT) into a desired morphology while maintaining its excellent electrical and mechanical properties. Single, freestanding nanotubes are bent by a scanning tunneling microscopy probe, and their morphology is fixed by electron-beam-induced deposition (inside a transmission electron microscope) of amorphous carbon on the bent area. It is shown that the mechanical strength of the bent CNT may be greatly enhanced by increasing the amount of carbon glue or the deposition area, and the electrical conduction of the nanotube shows hardly any dependence on the bending deformation or on the deposition of amorphous carbon. Our findings suggest that CNTs might be manipulated and processed as interconnections between electronic devices without much degradation in their electrical conductance, and be used in areas requiring complex morphology, such as nanometer-scale transport carriers and nanoelectromechanical systems.
Co-reporter:M. S. Wang;J. Y. Wang;Q. Chen;L.-M. Peng
Advanced Functional Materials 2005 Volume 15(Issue 11) pp:
Publication Date(Web):27 OCT 2005
DOI:10.1002/adfm.200590038
The fabrication of carbon nanotube (CNT) structures, including simple tube–tube connections, crossed junctions, T-junctions, zigzag structures, and even nanotube networks, has been achieved by cutting and soldering CNTs using electron-beam-induced deposition of amorphous carbon (a-C), as detailed in the work of Peng and co-workers on p. 1825. These CNT structures have been constructed with a high degree of control, and it is found that the electric conductance and mechanical strength of the junctions can be improved by the deposition of a-C and by increasing the contact area of the junctions.
Individual carbon nanotubes (CNTs) have been cut, manipulated, and soldered via electron-beam-induced deposition of amorphous carbon (a-C) and using a scanning tunneling microscope inside a transmission electron microscope. All CNT structures, including simple tube–tube connections, crossed junctions, T-junctions, zigzag structures, and even nanotube networks, have been successfully constructed with a high degree of control, and their electrical and mechanical properties have been measured in situ inside the transmission electron microscope. It is found that multiple CNTs may be readily soldered together with moderate junction resistance and excellent mechanical resilience and strength, and the junction resistance may be further reduced by current-induced graphitization of the deposited a-C on the junction.
Co-reporter:M. S. Wang;J. Y. Wang;Q. Chen;L.-M. Peng
Advanced Functional Materials 2005 Volume 15(Issue 11) pp:
Publication Date(Web):20 SEP 2005
DOI:10.1002/adfm.200500215
Individual carbon nanotubes (CNTs) have been cut, manipulated, and soldered via electron-beam-induced deposition of amorphous carbon (a-C) and using a scanning tunneling microscope inside a transmission electron microscope. All CNT structures, including simple tube–tube connections, crossed junctions, T-junctions, zigzag structures, and even nanotube networks, have been successfully constructed with a high degree of control, and their electrical and mechanical properties have been measured in situ inside the transmission electron microscope. It is found that multiple CNTs may be readily soldered together with moderate junction resistance and excellent mechanical resilience and strength, and the junction resistance may be further reduced by current-induced graphitization of the deposited a-C on the junction.
Co-reporter:Chuanhong Jin, Jingyun Wang, Mingshen Wang, Jun Su, Lian-Mao Peng
Carbon 2005 Volume 43(Issue 5) pp:1026-1031
Publication Date(Web):2005
DOI:10.1016/j.carbon.2004.11.038
Electron field emission characteristics of individual multi-walled carbon nanotubes (MWCNTs) were investigated in situ inside the transmission electron microscope (TEM). For a single MWCNT it was found that while field-emission can hardly occur from the side of the nanotube, a curved nanotube may result in finite side emission and the best emission geometry is the top emission geometry. Current–voltage (I–V) measurements made at different vacuum conditions and voltage sweeps emphasize the importance of the adsorbates on the electron field emission of MWCNTs. For a contaminated MWCNT, although the field emission current was reduced, the stability of its emission was improved. A current of up to several tens of μA was observed for a single MWCNT, but it was found that long time emission usually results in drastic structure damage that may lead to sudden emission failure.
Co-reporter:Gaohui Du, Qing Chen, Yuan Yu, Shuang Zhang, Wuzong Zhou and Lian-Mao Peng
Journal of Materials Chemistry A 2004 vol. 14(Issue 9) pp:1437-1442
Publication Date(Web):24 Mar 2004
DOI:10.1039/B317095K
Potassium hexaniobate nanotubes have been fabricated from polycrystalline K4Nb6O17 at room temperature using the intercalating and exfoliating methods. These tubular materials were mainly characterized by using electron microscopy. Their structures were found to be multilayer crystalline nanotubes with interlayer spacings from 0.83 to 3.6 nm, depending on the intercalating molecules such as tetra(n-butyl)ammonium hydroxide (TBA+OH−) and alkylamines (CnH2n+1NH2) with different lengths of the alkyl chains. The number of layers in the wall is in the range of 3 to 8. The outer diameters of the nanotubes are distributed around 20 nm to 90 nm for different products obtained with different alkylamines and the lengths of the nanotubes range from a few hundred nanometers to several micrometers. Comprehensive structural characterization revealed that the majority hexaniobate nanotubes were formed by rolling the monolayer (–Nb6O17–)n sheets around the [100] zone axis of K4Nb6O17. Nanotubes with helical angles of larger than 10 degrees were also observed.
Co-reporter:Zhiyong Zhang ; Sheng Wang ; Li Ding ; Xuelei Liang ; Tian Pei ; Jun Shen ; Huilong Xu ; Qing Chen ; Rongli Cui ; Yan Li
Nano Letter () pp:
Publication Date(Web):October 23, 2008
DOI:10.1021/nl8018802
Near ballistic n-type single-walled carbon nanotube field-effect transistors (SWCNT FETs) have been fabricated with a novel self-aligned gate structure and a channel length of about 120 nm on a SWCNT with a diameter of 1.5 nm. The device shows excellent on- and off-state performance, including high transconductance of up to 25 μS, small subthreshold swing of 100 mV/dec, and gate delay time of 0.86 ps, suggesting that the device can potentially work at THz regime. Quantitative analysis on the electrical characteristics of a long channel device fabricated on the same SWCNT reveals that the SWCNT has a mean-free-path of 191 nm, and the electron mobility of the device reaches 4650 cm2/Vs. When benchmarked by the metric CV/I vs Ion/Ioff, the n-type SWCNT FETs show significantly better off-state leakage than that of the Si-based n-type FETs with similar channel length. An important advantage of this self-aligned gate structure is that any suitable gate materials can be used, and in particular it is shown that the threshold voltage of the self-aligned n-type FETs can be adjusted by selecting gate metals with different work functions.
Co-reporter:Hua-Rong Xia, Jia Li, Wen-Tao Sun and Lian-Mao Peng
Chemical Communications 2014 - vol. 50(Issue 89) pp:NaN13697-13697
Publication Date(Web):2014/09/16
DOI:10.1039/C4CC05960C
CH3NH3PbI3 based photodetectors were fabricated by a facile low-cost process with much enhanced performance. The rise time changed from 2.7 s to 0.02 s, the decay time from 0.5 s to 0.02 s, and the ON/OFF ratio tripled with improved stability. The results indicate that perovskites are promising light-harvesting materials for photodetectors.
Co-reporter:Guo Ai, Wen-Tao Sun, Yi-Ling Zhang and Lian-Mao Peng
Chemical Communications 2011 - vol. 47(Issue 23) pp:NaN6610-6610
Publication Date(Web):2011/05/16
DOI:10.1039/C1CC11092F
A novel nanoparticle–nanorod composite TiO2 photoelectrode is fabricated. A 3.20% efficiency is achieved by using a 2.1 μm-thick as-prepared photoelectrode, which is about 3 times of that obtained by a nanorod array electrode (1.05%). The results demonstrate that the composite nanostructure can take advantage of both fast electron transport (nanorod) and high surface area (nanoparticle).
Co-reporter:Guo Ai, Wentao Sun, Xianfeng Gao, Yiling Zhang and Lian-Mao Peng
Journal of Materials Chemistry A 2011 - vol. 21(Issue 24) pp:NaN8755-8755
Publication Date(Web):2011/05/12
DOI:10.1039/C0JM03867A
Well-aligned TiO2 nanowire arrays are fabricated through a simple hydrothermal method and sensitized with electrodeposited CdSe nanoparticles. Annealing treatments at various temperatures (350 °C, 380 °C, 400 °C and 450 °C) are used to improve the performance of the as-deposited photoelectrode and the effects of various annealing atmospheres (air, O2, N2, Ar and vacuum) are further investigated. Although the film is only 2μm thick, a significant photocurrent density of 8.83 mA cm−2 is observed under 100 mW cm−2 illumination (AM 1.5 G) for the sample annealed at 400 °C in air, which is 5.69 times higher than that of the as-deposited sample and much better compared with that of the samples annealed in other environments. Careful investigation on the annealing effect is performed with a range of analytical techniques, such as SEM, TEM, HRTEM, EDX, UV-vis absorption spectra, and XRD. In particular, HRTEM observation affords a further insight into the exact change in CdSe crystalline structure annealed at different temperature. The results indicate that the crystal structure of CdSe nanoparticles and the interface between TiO2 and CdSe are improved with appropriate annealing below 400 °C, leading to an enhancement of performance. On the other hand, over-annealing at 450 °C results in severe migration and oxidation of CdSe, and leads to a poor photoelectric performance. A better understanding of the influence of the annealing environment is obtained through the adoption of different annealing atmospheres at 400 °C. It is found that both O2 and N2 have a more positive effect on the annealing process compared with Ar and vacuum, while air is found to be the favorite environment for annealing treatment.
Co-reporter:Hua-Rong Xia, Wen-Tao Sun and Lian-Mao Peng
Chemical Communications 2015 - vol. 51(Issue 72) pp:NaN13790-13790
Publication Date(Web):2015/07/22
DOI:10.1039/C5CC05053G
A facile hydrothermal method was developed to prepare CH3NH3PbBr3 and CH3NH3PbI3. The as-prepared products were utilized in lithium batteries as anode materials with good performance. Considering the structural diversity, more hybrid perovskites can be targets for further optimization, indicating their promising potential in Li-ion battery applications.
