硅纳米晶体薄膜热膨胀性质的分子动力学研究

基于Stillinger-Weber势对硅纳米晶体薄膜的热膨胀性质进行了分子动力学模拟.研究表明,硅纳米晶体薄膜表面层原子的二聚现象引起薄膜收缩,而原子之间的非和谐势能引起薄膜膨胀;在约400K以下的低温段,由于硅纳米晶体薄膜表面层原子发生二聚的原子数目随温度的升高而明显增多,而原子间非和谐势能很小,故此时二聚主导热膨胀性质,热膨胀系数为负;在高温段(约400K以上),由于发生二聚的原子数目随温度升高不再显著地增加并渐趋于稳定,而原子间非和谐势能逐渐显著并主导热膨胀性质,故热膨胀系数为正.

氩纳米晶体薄膜热膨胀性质的分子动力学研究

运用分子动力学方法,计算了不同温度下各种厚度的氩纳米晶体薄膜和块体氩晶体的晶格常数,据此计算它们的热膨胀系数,并对它们的晶格常数和热膨胀系数进行比较。计算与分析的结果表明:氩晶体纳米薄膜的晶格常数小于块体氩晶体的晶格常数,且随薄膜厚度减小而减小;氩晶体纳米薄膜的热膨胀系数大于块体氩晶体的热膨胀系数,且随薄膜厚度减小而增加。

碳纳米管薄膜场效应晶体管低温电学特性

基于网络状碳纳米管(carbon nanotube,CNT)薄膜制备了网络状碳纳米管薄膜场效应晶体管(carbon nanotube thin film field effect transistor,CNT-TFT),研究了温度为100~300 K时,CNT-TFT的电学特性,并对关键电学参数,如开态电流I_(on)、跨导G_(m)、阈值电压V_(th)和亚阈值摆幅S_(S)等,进行了深入分析。研究结果表明,随着温度的降低,G_(m)出现了下降,V_(th)向左漂移;在G_(m)和V_(th)共同作用下,I_(on)显著下降。通过对电学参数随温度演化机制的深入分析,发现器件G_(m)的降低不仅与CNT内的散射及CNT-金属接触电阻相关,而且与交叠的碳纳米管间的结电阻密切相关。同时,研究还表明,低温下,界面俘获中心对电子俘获概率的减小是引起器件V_(th)和S_(S)变化的主要因素。

影响染料敏化二氧化钛纳米晶太阳能电池的因素

介绍了染料敏化二氧化钛纳米晶太阳能电池的结构及工作原理,对影响染料敏化太阳能电池性能的因素,如纳米二氧化钛膜的制备、表面修饰、耦合及掺杂或复合,敏化染料与电极表面的吸附、吸收光谱与太阳光谱的匹配、染料的设计合成,以及电解质的研究进展进行了综述。指出染料和电解质的性能是今后发展中的主要制约因素,纳米多孔膜的制备、染料的光电化学反应机理和染料的设计合成、双敏化、固态空穴传输材料替代液体电解质以及纳晶多孔电极与染料间能量传递及电子转移的微观本质等领域是今后的主要研究方向。

掺杂金属离子纳米TiO2/高岭石复合光催化材料制备与表征

本研究以高岭石为载体,用Sol-gel法并掺杂金属离子制备钛溶胶,并以薄膜形式固定在高岭石表面上,经洗涤、过滤、干燥、煅烧得到纳米TiO2/高岭石复合光催化材料.利用XRD、IR、SEM、TEM、Raman等检测手段,分析研究TiO2薄膜和矿物表面的结合形态、界面的某些特性及反应的可能机理,为研究负载固定化技术,提高纳米TiO3/矿物复合材料光催化活性的途径提供理论依据.研究表明,高岭石表面TiO2是以锐钛矿形态存在.搀杂8%Zn2+的样品中发现部分Zn2+和Ti4+化合生成ZnTiO3,应当控制Zn2+含量小于8%.SEM、TEM形貌分析表明在高岭石表面均匀覆盖着1～10nm的TiO2晶体薄膜.

强激光辐照下纳米晶体铜薄膜层裂破坏的实验研究

采用强激光辐照加载技术和激光速度干涉(VISAR)测试技术,对纳米晶体铜薄膜的层裂特性进行实验测量和分析.基于VISAR实测的自由面速度波形,计算得到纳米晶体铜薄膜在超高拉伸应变率下的层裂强度高达3GPa,明显高于多晶铜的层裂强度,其原因归咎于纳米晶体材料中存在大量晶界阻碍了位错运动.

Photoluminescence origin of nanocrystalline SiC films

The nanocrystalline SiC films were prepared on Si then annealed at 800℃ and 1 000℃ for 30 minutes （111） substrates by rf magnetron sputtering and in a vacuum annealing system. The crystal structure and crystallization of as-annealed SiC films were determined by the Fourier transform infrared （FIR） absorption spectra and the X-ray diffraction （XRD） analysis. Measurement of photoluminescence （PL） of the nanocrystalline SiC （nc-SiC） films shows that the blue light with 473 nm and 477 nm wavelengths emitted at room temperature and that the PL peak shifts to shorter wavelength side and the PL intensity becomes stronger as the annealing temperature decreases. The time-resolved spectrum of the PL at 477 nm exhibits a bi-exponential decay process with lifetimes of 600 ps and 5 ns and a characteristic of the direct band gap. The strong blue light emission with short PL lifetimes suggests that the quantum confinement effect of the SiC nanocrystals resulted in the radiative recombination of the direct optical transitions.

360-nm Photoluminescence from Silicon Oxide Films Embedded with Silicon Nanocrystals

Si-rich silicon oxide films were deposited by RF magnetron sputtering onto composite Si/SiO2 targets. After annealed at different temperature, the silicon oxide films embedded with silicon nanocrystals were obtained. The photoluminescenee（PL） from the silicon oxide films embedded with silicon nanocrystals was observed at room temperature. The strong peak is at 360 nm, its position is independent of the annealing temperature. The origin of the 360-nm PL in the silicon oxide films embedded with silicon nanoerystals was discussed.

Length-Sorted Semiconducting Carbon Nanotubes for High-Mobility Thin Film Transistors

We have developed a process for chemical purification of carbon nanotubes for solution-processable thin-film transistors （TFTs） having high mobility. Films of the purified carbon nanotubes fabricated by simple drop coating showed carrier mobilities as high as 164 cm2V-1s -1 normalized transconductances of 0.78 Sm-1 and on/off current ratios of 10^6. Such high performance requires the preparation of a suspension of micrometer-long and highly purified semiconducting single-walled carbon nanotubes （SWCNTs）. Our purification process includes length and electronic-type selective trapping of SWCNTs using recycling gel filtration with a mixture of surfactants. The results provide an important milestone toward printed high-speed and large-area electronics with roll-to-roll and ink-jet device fabrication.

Highly uniform carbon nanotube nanomesh network transistors

A new type of single-walled carbon nanotube （SWNT） thin-film transistor （TFT） structure with a nanomesh network channel has been fabricated from a pre- separated semiconducting nanotube solution and simultaneously achieved both high uniformity and a high on/off ratio for application in large-scale integrated circuits. The nanomesh structure is prepared on a high-density SWNT network channel and enables a high on/off ratio while maintaining the excellent uniformity of the electrical properties of the SWNT TFTs. These effects are attributed to the effective elimination of metallic paths across the source/drain electrodes by forming the nanomesh structure in the high-density SWNT network channel. Therefore, our approach can serve as a critical foundation for future nanotube-based thin- film display electronics.

120 mm Single-crystalline perovskite and wafers： towards viable applications

As the large single-crystalline silicon wafers have revolutionized many industries including electronics and solar cells, it is envisioned that the availability of large single-crystalline perovskite crystals and wafers will revolutionize its broad applications in photovoltaics, optoelectronics, lasers, photodetectors, light emitting diodes(LEDs), etc. Here we report a method to grow large single-crystalline perovskites including single-halide crystals: CH3NH3PbX3(X=I, Br, Cl), and dual-halide ones:CH3NH3Pb(ClxBr1.x)3 and CH3NH3Pb(BrxI1.x)3, with the largest crystal being 120 mm in length. Meanwhile, we have advanced a process to slice the large perovskite crystals into thin wafers. It is found that the wafers exhibit remarkable features:(1)its trap-state density is a million times smaller than that in the microcrystalline perovskite thin films(MPTF);(2) its carrier mobility is 410 times higher than its most popular organic counterpart P3HT;(3) its optical absorption is expanded to as high as910 nm comparing to 797 nm for the MPTF;(4) while MPTF decomposes at 150 °C, the wafer is stable at high temperature up to270 °C;(5) when exposed to high humidity(75% RH), MPTF decomposes in 5 h while the wafer shows no change for overnight;(6) its photocurrent response is 250 times higher than its MPTF counterpart. A few electronic devices have been fabricated using the crystalline wafers. Among them, the Hall test gives low carrier concentration with high mobility. The trap-state density is measured much lower than common semiconductors. Moreover, the large SC-wafer is found particularly useful for mass production of integrated circuits. By adjusting the halide composition, both the optical absorption and the light emission can be fine-tuned across the entire visible spectrum from 400 nm to 800 nm. It is envisioned that a range of visible lasers and LEDs may be developed using the dual-halide perovskites. With fewer trap states, high mobility, broader absorption, and humidity resistance, it is expected that solar cells with high stable efficiency maybe attainable using the crystalline wafers.

Short channel carbon nanotube thin film transistors with high on/off ratio fabricated by two-step fringing field dielectrophoresis

A two-step fringing field dielectrophoretic assembly method for carbon nanotube thin film transistors （CNT-TFTs） fabrication was demonstrated. Densely aligned CNT arrays were assembled at the source and drain electrodes sequentially which form a cascade structure of the aligned CNT arrays. The cascade structure reduces the possibility of percolating metallic pathways in the channel, which is beneficial to device performance. In this way, both high on/off current ratio Ion/loft （up to 107） and high out-put current density （8.5μA/μm） were obtained in short channel length （1-2.5μm） CNT-TFTs. The reported CNT assem- bling strategy is site selective and highly efficient, which can be scaled up to large size substrates and leads to high throughput of CNT-TFTs fabrication.

Impact of nanocrystallinity segregation on the growth and morphology of nanocrystal superlattices

A colloidal solution of 5 nm Au tetradecanethiol-coated nanoparticles is syn-thesized. After fast evaporation of one drop, ordered monolayers both composed of single domain and polycrystalline nanocrystals are obtained. On increasing the amount of materials and the evaporation time, nanocrystal films with irregular outlines are produced together with close-packed 3D superlattices exhibiting a truncated-tetrahedral shape. Using low-frequency micro-Raman scattering spectroscopy and electron microscopy the building block nanocrystallinity is characterized. Spontaneous nanocrystallinity segregation is revealed： the truncated-tetrahedral supracrystals are shown to mainly contain single domain building blocks while the supracrystalline films are composed of a mixture of single domain and polycrystalline nanocrystals. This observation points out the correlation between the nanocrystallinity segregation involved in the growth of the nanocrystal superlattices and their morphology.

High yield fabrication of semiconducting thin-film field-effect transistors based on chemically functionalized single-walled carbon nanotubes

Here we report a simple and scalable method to fabricate high performance thin-film field-effect transistors(FETs) with high yield based on chemically functionalized single-walled carbon nanotubes(SWNTs) by organic radical initiators.The UV-Vis-NIR spectra,Raman spectra and electrical characterization demonstrated that metallic species in CoMoCat 65 and HiPco SWNTs could be effectively eliminated after reaction with some organic radical initiators.The effects of the substrate properties on the electrical properties of FET devices were investigated,and the results showed that the electrical properties of FET devices fabricated on high hydrophobic substrates were better than those on low hydrophobic substrates.Furthermore,it was found that FET devices based on 1,1'-azobis(cyanocyclohexane)(ACN)-modified CoMoCat 65 SWNTs exhibited more excellent electrical performance with effective mobility of ～11.8 cm2/Vs and on/off ratio of ～2×105 as compared with benzoyl peroxide(BPO)-modified CoMoCat 65 SWNTs and lauoryl peroxideand(LPO)-modified HiPco SWNTs,likely due to the introduction of the electron-withdrawing groups(CN group) on the SWNT surface.This method does not require nontrivial reaction conditions or complicated purification after reaction,therefore promising low-cost production of high-performance devices for macroelectronics.