应力诱导碳纳米管电阻的变化

利用三点弯曲法研究了掺杂和末掺杂碳纳米管薄膜应力诱导电阻的变化。该研究中所用的碳纳米管是用热灯丝化学汽相沉积法合成的。实验结果表明 ,碳纳米管有显著的应力诱导电阻变化的效应。当应力从 0 .2GPa增加到 1GPa时 ,膜的电阻相对变化从 7%增加到 11% ,而非掺杂的薄膜电阻变化小于掺杂膜的情况。电阻随应力变化的原因也许是带隙变化 (掺杂 )和管之间接触电阻变化 (非掺杂 )所致     

退火温度对ZnO掺杂ITO薄膜性能的影响

利用电子束蒸镀方法,在K8玻璃衬底上沉积ZnO掺杂ITO(ZnO-ITO)与ITO薄膜。研究不同退火温度对ZnO-ITO薄膜的微观结构的影响;对比分析了在不同退火温度条件下,ZnO-ITO和无掺杂ITO薄膜的光电性能。结果发现,ZnO-ITO薄膜具有较大的晶粒尺寸,随着退火温度的上升,晶体结构得到改善,表面粗糙度减小,薄膜的光电性能显著提高。ZnO-ITO薄膜经过500℃退火后得到最佳的综合性能,其表面均方根粗糙度(RMS)为32.52nm,电阻率为1.43×10-4Ω.cm;对442nm波长的光,透射率可达98.37%;与ITO薄膜相比,ZnO-ITO薄膜具有显著的抗PEDOT:PSS溶液腐蚀的能力。     

化学处理增强碳纳米管的湿敏效应

研究了多壁碳纳米管的湿敏效应。研究中所用碳纳米管是用热灯丝化学汽相沉积法生长的。实验结果表明 ,经由化学修饰后碳纳米管的湿敏效应有了极大的增强。化学修饰后碳纳米管在水蒸汽中电阻相对变化达到了 30 0 % ,而未修饰只有 3.2 5 %。本文对其结果进行了分析和讨论     

非晶碳和碳纳米管混合薄膜的场发射性能

利用微波等离子体化学气相沉积法在不锈钢衬底上直接合成非晶碳和碳纳米管混合薄膜.采用氢气和甲烷作为反应气体,流量分别为100和16sccm.沉积室内的压强为5.0kPa.利用场发射扫描电镜(SEM)和喇曼谱(Raman)对制备的薄膜的结构和形貌进行了分析.场发射实验在5×10-5Pa的真空下进行.实验结果表明:制备的非晶碳和碳纳米管混合薄膜开启电场较低,仅有0.9V/μm;在电场为3.7V/p.m时电流密度达到4.0mA/cm2,发射点密集,分布均匀.表明此种材料是一种优良的场发射冷阴极材料.     

The effect of introducing Al ions in cationic deposition bath on as-prepared PbS thin film through SILAR deposition method

Undoped and Al doped lead sulfide (PbS) thin films were grown on soda lime glass substrates by Successive Ionic Layer Adsorption and Reaction (SILAR) deposition method. Al content in aqueous cationic solution was varied by adding 0.5–2% of aluminum nitrate in step of 0.5. The characterization of the film was carried out using X-ray diffraction, scanning electron microscopy, and optical and electrical measurement techniques. X-ray diffraction analysis revealed that both the undoped and doped films were polycrystalline and exhibited galena type cubic structure with average crystallite size in the range of 15.5–30.9 nm. The compositional analysis results indicated that Pb, S and Al were present in the samples. Optical studies revealed prominent blue-shift in the absorption edge of as-deposited samples upon doping as compared to that of bulk PbS and this shift was due to a quantum confinement effect. The room temperature conductivity of the PbS thin films was in the range of 1.343×10⁻⁷–1.009×10⁻⁶ (Ω cm)⁻¹for doped samples and 5.172×10⁻⁸ for undoped PbS thin film sample. The optical band gap energy has inverse relation with grain size and electrical conductivity is closely related to structural parameters like grain size, crystallinity and microstrain. The estimated lattice parameter, grain size, optical band gaps and electrical properties were correlated with Al concentration in the cationic solution.     

钇掺杂锆钛酸铅铁电薄膜的电性能研究

对采用Sol-Gel法制备的钇掺杂锆钛酸铅铁电薄膜的电性能进行了研究。实验结果表明，由于钇离子（Y^3 ）的引入造成晶格畸变，使掺钇后的PZT铁电薄膜比未掺钇时具有更大的剩余极化强度、更小的矫顽场和漏电流。此外，钇掺杂锆钛酸铅铁电薄膜具有良好的介电性能，在室温和10kHz频率下，其介电常数和介电损耗分别为437和0．043。     

Dependence of electron mobility on spacer thickness and electron density in modulation-doped Ga0.47In0.53As/Al0.48In0.52As heterojunctions

Modulation-doped Ga0.47In0.53As/Al0.48In0.52As heterojunctions were grown by molecular beam epitaxy. Electron mobilities were measured at room temperature and 77 K as a function of undoped Al0.48In0.52As spacer layer thickness and sheet carrier concentration. Enhanced mobilities were as high as 10 900 cm2V?1s?1 at room temperature and 55 500 cm2V?1s?1 at 77 K in these samples with sheet carrier concentrations at 1 33 × 1012 cm?2 (room temperature) and 1.26 × 1012 cm?12 (77 K).     

Properties of nanostructured Al doped ZnO thin films grown by spray pyrolysis technique

Aluminium doped zinc oxide thin films were deposited on glass substrate by using spray pyrolysis technique. The X-ray diffraction study of the films revealed that the both the undoped and Al doped ZnO thin films exhibits hexagonal wurtzite structure. The preferred orientation is (002) for undoped and up to 3 at % Al doping, further increase in the doping concentration to 5 at % changes the preferred orientation to (101) direction. The surface morphology of the films studied by scanning electron microscope, reveal marked changes on doping. Optical study indicates that both undoped and Al doped films are transparent in the visible region. The band gap of the films increased from 3.24 to 3.36 eV with increasing Al dopant concentration from 0 to 5 at % respectively. The Al doped films showed an increase in the conductivity by three orders of magnitude with increase in doping concentration. The maximum value of conductivity 106.3 S/cm is achieved for 3 at % Al doped films.     

Effect of Electron Drag on Performances of Carbon Nanotubes as Flow Sensors

Experimentally, the electron drag effect on carbon nanotube surface in flowing liquids was investigated. It was found that electric current could be generated in metallic carbon nanotubes immersed in the liquids. Carbon nanotubes were synthesized on Si substrate by hot filament chemical vapor deposition. The experimental results showed that the flow--induced current on the surface of carbon nanotube films was closely depended on the flow rate, concentration, properties and temperature of liquids. The flow--induced current was increased with the increasing of flow rate, concentration and temperature of liquids. The obtained results were discussed in detail.     

Template free titiania photoanodes modified with carbon black or multi-wall carbon nanotubes: Thermal treatment at low and high temperature for the fabrication of quasi-solid state dye sensitized solar cells

A simple procedure was developed to prepare modified titiania (TiO₂) photoanodes for dye sensitized solar cells at low and high temperature in order to improve overall cell efficiency. Modification of TiO₂ films achieved by the incorporation of either carbon black powder (CBP) or multi-wall carbon nanotubes (MWCNTs). A small quantity of titanium alkoxide was added in a dispersion of titiania (TiO₂) powder consisting of nanoparticles at room temperature, which after alkoxide׳s hydrolysis helps to the connection between titiania (TiO₂) particles and to the formation of mechanically stable relatively thick films on conductive glass substrates. The absence of surfactant allowed us to prepare films at relatively low temperature (~100 °C), while the effect of sintering at a higher temperature (500 °C) was also studied. The structural properties of the films were examined with porosimetry method and microscopy analysis. Better electrical results were obtained for the MWCNT (0.1 wt%) modified TiO₂ films, with 3.14% and 4.68% conversion efficiencies under 1 sun illumination after treatment at 100 °C and 500 °C, respectively. The enhancement in photocurrent for MWCNT-TiO₂ films compared to pure TiO₂ films is attributed to the improved interconnectivity between TiO₂ nanoparticles, which further improved the electron transport through the film. For carbon doped CBP-TiO₂ cells, lower efficiencies were observed compared to pure TiO₂.     

Solid‐State Approach for Fabrication of Photostable,Oxygen‐Doped Carbon Nanotubes

A novel procedure for effective fabrication of photostable oxygen‐doped single‐walled carbon nanotubes (SWCNTs) in solid‐state matrices has been developed. SWCNTs drop‐cast on various types of substrates are coated with oxide dielectric thin films by electron‐beam evaporation. Single tube photoluminescence spectroscopy studies performed at room and cryogenic temperatures reveal that such thin film‐coated tubes exhibit characteristic spectral features of oxygen‐doped SWCNTs, indicating the oxide thin film coating process leads to oxygen doping of the tubes. It is also found that the doping efficiency can be effectively controlled by the thin film deposition time and by the types of surfactants wrapping the SWCNTs. Moreover, aside from being the doping agent, the oxide thin film also serves as a passivation layer protecting the SWCNTs from the external environment. Comparing the thin film coated SWCNTs with oxygen‐doped tubes prepared via ozonolysis, the former exhibit significantly higher photostability and photoluminescence on‐time. Therefore, this one‐step deposition/oxygen‐doping procedure provides a possible route toward scalable, versatile incorporation of highly photostable oxygen‐doped SWCNTs in novel optical and optoelectronic devices.     

室温下ZnPc/MWCNTs敏感膜检测NO2

提出了一种以酞菁锌(ZnPc)掺杂多壁碳纳米管(MWCNTs)作为声表面波(SAW)传感器的敏感材料用于室温下检测二氧化氮(NO2).通过超声振荡等方法将研磨的MWCNTs和ZnPc分散于N,N-二甲基中,然后运用微量移液器滴涂到SAW器件的敏感区.我们对ZnPc/MWCNTs薄膜用扫描式电子显微镜(SEM)进行了表面形态表征.实验结果表明,基于MWCNTs的ZnPc SAW器件能在常温下检测最低浓度为10-6的NO2.在3个月内对器件的灵敏度、稳定性、选择性也进行了评估.     

High mobility GaAs-AlxGa1?xAs single period modulation-doped heterojunctions

Single period modulation-doped structures composed of an AlxGa1?xAs layer, part of which is doped with Si, on top of an undoped GaAs layer have been grown by molecular beam epitaxy. The films were characterised using Hall effect measurements carried out at temperatures between 10 and 300 K. With 50?75 ? thick undoped (Al, Ga)As layers near the interface, mobilities in excess of 115000 cm2/Vs at 10 K and 7450 cm2/Vs at 300 K have been achieved for an average doping concentration of ?5×1016 cm?3. These are some of the highest mobilities as yet obtained from modulation-doped structures, and represent an increase in mobility over equivalently doped GaAs by about a factor of 20 at 10 K and by a factor of 2 at 300 K.     

Multiband Mobility in Semiconducting Carbon Nanotubes

We present new data and a compact mobility model for semiconducting single-wall carbon nanotubes, with only two adjustable parameters, the elastic and inelastic collision mean free paths at 300 K. The mobility increases with diameter, decreases with temperature, and has a more complex dependence on charge density. The model and data suggest that the room temperature mobility does not exceed 10 000 cm²/Vmiddots at high carrier density (n > 0.5 nm^-1) for typical single-wall nanotube diameters, due to the strong scattering effect of the second subband.     

On the temperature dependent electrical resistivity of CNT layers in view of Variable Range Hopping models

Thin films of randomly dispersed carbon nanotubes make highly promising material for transparent electrode applications. Knowing and understanding the nature of the films conductivity is crucial for improvement of their electrical properties. In the paper we present our investigation of electrical conductivity of single wall and multiwalled carbon nanotube (SWCNT and MWCNT) thin films deposited on a polymeric substrate by Langmuir-Schaefer technique. The conductivity of the films is consistent with the Variable Range Hopping (VRH) model. Moreover, remarkable differences in SWCNT and MWCNT films conductivity are observed. A significant impact of the thin film annealing and its temperature history on the conductivity properties is shown. The study of the carbon nanotubes layers transferred on polymeric substrate was undertaken in view of the films possible applications in flexible transparent electrodes. The VRH conductivity in carbon nanotube Langmuir-Schaefer layer is reported for the first time.     

InP单晶的磁光和热电效应

对同一原生非掺杂InP单晶进行了一系列物理测试分析,研究了材料的光电导率与温度的依从关系,在295~318 K内,温度系数为-3×10-4eV/K,测得的室温禁带宽度为1.339 2 eV。禁带宽度Eg的磁性系数为8.6×10-4eV/T,材料的磁光特性测量结果为1.8 T。由此数据可得,约化电子有效质量mr*为0.067m0。由热电功率测量结果可得室温塞贝克系数为565μV/K。由此值以及霍尔测量值,可计算出状态密度有效质量md*为0.075 7m0。由该值和上面提到的约化电子有效质量可得到InP样品的价带电子有效质量mv*为0.591m0。     

Effect of doping on the temperature coefficient of resistance of polysilicon films

For doped polysilicon films, an experimental investigation is presented into the variation of temperature coefficient of resistance (TCR) with formation conditions, the dopants being rare-earth elements (Eu, Gd, and Yb), oxygen, germanium, and implanted boron or phosphorus. The sign and magnitude of the TCR are shown to be governed by the dopant concentrations and the conditions of postimplantation annealing. Common and specific features are identified in the behavior of TCR for undoped films and for doped ones differing in dopant and doping technique. A negative TCR is observed in undoped films and in ones doped with a rare-earth element or germanium. B or P ion implantation into films predoped with Ge is shown to give a positive TCR if the implant concentration exceeds 10¹⁸ atoms/cm³. With any of the dopants employed, raising the dopant concentration makes possible the transition from a negative to a positive TCR.     

Carbon nanotube applications in microelectronics

The extraordinary characteristics of carbon nanotubes make them a promising candidate for applications in microelectronics. Catalyst-mediated chemical vapor deposition growth is very well suited for selective in-situ growth of nanotubes compatible with the requirements of microelectronics technology. This deposition method can be exploited for carbon nanotube vias. Semiconducting single-walled tubes can be successfully operated as carbon nanotube field effect transistors (CNTFET). A simulation of an ideal CNTFET is presented and compared with the requirements of the ITRS roadmap. Finally, we compare an upgraded CNTFET with the most advanced silicon metal oxide semiconductor field effect transistors and discuss integration issues.     

Spray deposited carbon nanotubes for organic vapor sensors

In this article a study of chemiresistor sensors based on Single and Multi Wall Carbon Nanotube films deposited at low temperature by means of a spray technique is presented. A dispersion of nanotube powder in a non-polar 1,2-Dichloroethane solvent was used as starting solution. Electron Microscopy in Scanning and Transmission mode were used in order to verify the morphological properties of the deposited films. The conductivity of carbon nanotubes (CNTs) was measured in two organic solvent vapors environments: 2-propanol and carbon-tetrachloride. The solvents used are characterized by different polarities. The results show that the electrical resistance of the sensors increases when exposed to solvent vapors. Finally the effect of Teflon-like and Melanin coatings on the sensitivity yield is presented and discussed.     

The minority carrier lifetime in doped and undoped p-type Hg0.78Cd0.22Te liquid phase epitaxy films

This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg_1-xCd_xTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τ_A7 ⁱ/τ_A1 ⁱ ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped with the carrier concentration ranging from 2 x 10¹⁵ to 1.5 x 10¹⁷ cm^-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x 10¹⁵ and 8 x 10¹⁶ cm^-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τ_A7 ⁱ/τ_A1 ⁱ, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed, a donor-like SRH recombination center located at midgap (E_v+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting lifetime vs temperature curves of undoped films.