应变影响下单晶Ge薄膜热导率分析

利用非平衡态分子动力学模拟方法研究了应变对Ge薄膜热导率的影响。结果表明系统应变对单晶Ge薄膜热导率产生明显影响,热导率随着拉伸应变的增大而减小,随着压缩应变的增大而增大,得出声子速率降低以及薄膜表面重构是产生该模拟结果的内在原因。同时,采用修正的Callaway模型对NEMD结果进行理论验证,两种方法得到的结果吻合得较好。理论结果表明应变弛豫时间对Ge单晶薄膜的热导率产生了重要影响。     

Grain growth in thin metallic films

Grain growth in thin films deposited on a substrate was studied theoretically. The thrust of the model proposed is the effect of vacancy generation accompanying grain growth on the rate of the process. In addition, the magnitude of a tensile stress developing in the film was considered. It was shown that due to the contribution of vacancies to the free energy of the system, discernible grain growth is preceded by an “incubation” period, during which the grain structure can be considered as stable, as the rate of growth is relatively small over this incubation time. During this time, the vacancy concentration remains nearly constant, staying at a level much higher than the thermal equilibrium concentration. Based on numerical analysis, a simple expression for the incubation time in terms of the vacancy sink spacing, temperature and grain boundary characteristics was derived. With this formula, the stability of the grain structure of a thin film can be assessed for given conditions.     

单晶锗薄膜热导率的分子动力学模拟

采用非平衡分子动力学(NEMD)方法研究平均温度为400 K,厚度d=2.8288～11.315 nm的单晶锗薄膜法向的热导率.模拟结果表明,单晶锗薄膜热导率随薄膜厚度的增加以接近线性的规律增加,其数值明显低于同等温度下体态锗的试验值.当薄膜厚度一定时,单晶锗薄膜的热导率随温度增加变化幅度很小,与同体态锗热导率随温度的变化规律相比表现出明显的尺寸效应.     

单晶Ge纳米薄膜面向热导率的分子动力学模拟

利用非平衡分子动力学模拟方法研究了单晶Ge薄膜的厚度以及温度对其面向热导率的影响规律。针对单晶Ge薄膜的结构特点和导热机制,采用Stillinger-Weber势能模型描述Ge粒子间的相互作用,并且建立面向稳态热传导模型。模拟结果显示,单晶Ge薄膜面向热导率具有明显尺寸效应,随薄膜厚度的增加而增大,随温度的升高而减小。与法向热导率的模拟结果进行比较,证明单晶Ge薄膜热导率具有各向异性的特点。     

A study on the thermal conductivity measurements of Cu thin films utilizing temperature distribution

Thin film type materials are widely used in high-tech industries including electronics, photonics and even machine tools. Often, knowledge of the thermal properties of thin films is needed to assess reliability through thermal stress analysis when the thin film type materials are applied to functional electronic parts. Only a few methods have been developed for thermal conductivity measurement of a thin film on a substrate. In this study Cu thin films were processed on the borosilicate glass substrate of prismatic bar shape using sputtering. Two Cu coated surfaces of specimens were brought into contact to maintain the insulated boundary conditions. The temperature distributions were measured from the back surface of the substrate using radiation thermometry. The thermal conductivities of the Cu thin films were measured and found to be much lower than those of bulk materials. The measured thermal conductivities were found to be closely related to the microstructures of the Cu thin films.     

Semigrand Canonical and Kinetic Monte Carlo simulations of binary B2-ordered nano-films with triple defects

Equilibrium atomic configurations and the kinetics of “order–order” and surface segregation processes in B2-ordering stoichiometric A-50 at.%B binary thin films are investigated by means of Semigrand Canonical Monte Carlo (SGCMC) and Kinetic Monte Carlo (KMC) simulations. The (100)-oriented films are modeled with an Ising-type Hamiltonian with previously evaluated pair-interaction energy parameters yielding the effect of “triple-defect disordering”. The SGCMC simulations provide equilibrium vacancy concentration and atomic configuration in the films with B-atom termination of both free surfaces achieved at high temperatures by the generation of an antiphase boundary. Despite strong vacancy surface segregation, the thermodynamic activation energy for their formation inside the films is the same as in the bulk material. KMC simulations implemented with the SGCMC-determined equilibrium vacancy concentration reveal very slow relaxation of the films towards equilibrium configuration. The B-termination of the (100) free surfaces is produced by A-atom diffusion inwards into the films mediated by vacancies segregating on surfaces.     

Concentration-dependent behavior of hydrogen in Al-doped ZnO thin films

The Al-doped ZnO thin films were synthesized by aerosol-assisted chemical vapor deposition. The concentration-dependent behavior of hydrogen in the films was discussed, finding that as hydrogen is introduced at a relatively low level, it tends to take the oxygen vacancy site and form a hydrogen-oxygen vacancy complex which behaves as a shallow donor, on the other hand it reduces the solubility of the substitutional Al; then higher hydrogen concentration results in the formation of H₂ neutral molecular complex.     

The influence of size effect of conductivity on the microwave absorption properties of thin Al films

采用中频磁控溅射法制备不同厚度的Al膜。利用直线型四探针法测量不同厚度Al膜的电导率,研究薄膜直流电导率随厚度的变化关系（尺寸效应）;并利用网络矢量分析仪测量Al膜与FR4-epoxy环氧树脂玻璃板复合结构微波吸收率,研究电导率尺寸效应对Al膜微波吸收性能的影响。实验结果表明：薄膜厚度对金属Al膜的电导率产生主要影响;在Al膜和FR4-epoxy环氧树脂玻璃板复合结构中,Al膜电导率变化对复合结构的最大吸收峰值以及吸收峰值对应的Al膜厚度会产生显著影响。实验结果利用传输矩阵方法计算得到了验证。     

Growth and transport properties of oriented bismuth telluride films

Oriented n-type bismuth telluride thin films with various layered nanostructures have been fabricated by radio-frequency (RF) magnetron sputtering. The crystal structures and microstructures of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The transport properties including carrier concentration, mobility, Seebeck coefficient and in-plane electrical conductivity were measured, which showed strong microstructure-dependent behaviors. The relationship between morphologies and transport properties of the films was explored. The optimal morphology and transport properties of films were obtained at the substrate temperature of 350 °C under the pressure of 1.0 Pa with oriented layered structure. Based on these results, a formation mechanism of these nanostructures is proposed and discussed. The interfaces and grain boundaries formed in these layered structures are beneficial to the reduction in thermal conductivity, which could result in potential TE films with high ZT value.     

Effect of metallic interfacial layers on the properties of diamond-like carbon thin films

Diamond like carbon (DLC) thin films with metallic interfacial layers of aluminum and nickel-chromium (Al and Ni-Cr) were grown using a low cost hybrid technique involving a resistive heating thermal evaporator and radio frequency plasma enhanced chemical vapor deposition techniques. Stress, hardness, elastic modulus, bonding, phase, and electrical conductivity of these films were investigated. Introduction of interfacial Al and Ni-Cr layers in DLC led to drastic improvement of its conductivity along with a significant reduction in residual stress but with some reduction of hardness and the elastic modulus. The structural and surface properties of thin films were studied using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques.     

Elemental Ratio Controlled Semiconductor Type of Bismuth Telluride Alloy Thin Films

通过磁控共溅射的方法制备了Bi2Te3合金薄膜,并通过423~623 K,1 h热处理提高薄膜的结晶程度。随着热处理温度的升高,Te/Bi原子含量比例逐渐减小,这说明在热处理过程中Te元素有一定的挥发,其挥发量随着温度的升高而增加,这使得薄膜的半导体类型由N型转变为P型,同时赛贝克系数也由负值变为正值。另外,热处理导致了晶粒长大,降低了缺陷密度,使得薄膜的电导率和赛贝克系数等热电性能得到提高     

钨钒共溅热致变色薄膜的制备及其红外光学性能

为解决VO2薄膜相变温度过高,热滞回线温宽过大以及掺杂后红外透过率变低等问题,开展了低成本钨钒共溅热致变色薄膜制备工艺的探索。先在室温条件下采用磁控共溅射的方法于玻璃基片上制备得到含钨量为1.4%的金属薄膜,再在空气中采用后退火工艺使金属薄膜充分氧化为热致变色薄膜。对薄膜样品的物理结构和光学性能进行了分析,发现钨钒共溅没有改变VO2薄膜在玻璃表面择优取向生长,但显著改变了VO2薄膜的表面形貌特征。观察到钨钒共溅热致变色薄膜的相变温度较普通VO2薄膜从68℃降低至40℃,热滞回线温宽由6℃缩小为3℃,低温半导体相的红外透过率分别为62%和57%。结果表明,钨钒共溅可达到相变温度降低,热滞回线温宽变窄,掺杂前后红外透过率变化不大之目的。     

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K-cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.     

Influence of Nitrogen Vacancy Concentration on Mechanical and Electrical Properties of Rocksalt Zirconium Nitride Films

To study the influence of the nitrogen vacancy(V_N)on mechanical and electrical properties of zirconium nitride deeply,Zr N_x films with different V_N concentrations were synthesized on the Si(111)substrates by enhanced magnetic filtering arc ion plating.The morphologies,microstructures,residual stresses,compositions,chemical states,mechanical and electrical properties of the as-deposited films were characterized by field-emission scanning electron microscopy,X-ray diffraction,X-ray photoelectron spectrometry,Nanoindenter and Hall effect measurements.The results showed that Zr N_x films exhibited rocksalt single-phase structure within a V_N concentration ranging from 26 to 5%.The preferred orientation,thickness,grain size and residual stress of the Zr N_x films kept constant at different V_N concentrations.Both the nanohardness and elastic modulus first increased and then decreased with the decrease in V_N concentration,reaching the peaks around 16%.And the electric conductivity of the Zr N_x films showed a similar tendency with nanohardness.The underlying atomic-scale mechanisms of V_N concentration-dependent hardness and electric conductivity enhancements were discussed and attributed to the different electronic band structures,rather than conventional meso-scale factors,such as preferred orientation,grain size and residual stress.     

氮气流量对磁控溅射法沉积NGZO薄膜性能的影响

目的通过磁控溅射镀膜工艺,在玻璃上制备高质量的氮镓共掺杂氧化锌(NGZO)薄膜。方法采用射频磁控溅射法,同时通入氩气和氮气,在流量比分别为25/10、25/20、25/25、25/30((m L/min)/(m L/min))条件下制备NGZO薄膜。通过XRD和SEM对薄膜的物相结构和表面形貌进行分析,通过紫外/可见分光光度计和霍尔效应测试仪对薄膜透过率和载流子浓度、迁移率及薄膜电阻率进行研究。结果与未掺入N的Ga掺杂氧化锌(GZO)薄膜相比,在可见光区,尤其是600~800 nm范围内,NGZO薄膜平均透过率在80%以上,符合透明导电薄膜透过率的要求。GZO薄膜载流子浓度较高,电阻率较低,而掺入N后薄膜的载流子浓度和迁移率有所下降,电阻率有所增加。结论在N-Ga共掺杂薄膜中,N的掺杂主要占据O空位,并吸引空位周围的电子,这减小了薄膜晶格畸变,并产生电子空穴,最终使得薄膜中电子载流子浓度降低,空穴载流子浓度增加,电阻率有所增加。随着氮气流量的变化,发现在25 m L/min时,薄膜具有最佳的综合性能。这种薄膜可用于紫外光探测器等需较大电阻率的应用中,并有望实现n-p型转化。     

Silver Dopant-Induced Effect on Structural and Optoelectronic Properties of CdSe Thin Films

Thin films of CdSe and silver(Ag)-doped CdSe have been prepared on glass substrates by thermal evaporation in argon gas atmosphere. X-ray diffraction pattern indicates the presence of hexagonal structure with preferred orientation along (100) plane. Elemental composition of the thin films has been analyzed using energy dispersive X-ray analysis. Scanning electron microscopy has been used to investigate the morphology of the thin films. Transmission electron microscope reveals spherical nature of nanoparticles. A decrease in the band gap due to the formation of band tails in the band gap with increase in Ag doping in CdSe lattice has been observed. Photoluminescence spectra indicate redshift in band edge emission peak with increase in Ag doping in CdSe. Electrical conductivity measurements are also studied, and two types of conduction mechanisms taking part in the transport phenomena are observed. Hall measurements indicate n-type behavior of undoped and Ag-doped CdSe thin films.     

Thermal undoping in poly(3-alkylthiophenes)

Thin solid films of doped poly(3-hexylthiophene) and poly(3-decylthiophene) undergo rapid conductivity degradation at elevated temperatures (110 °C). We have followed the changes in the electronic structure during thermal treatment by optical spectroscopy. We have also studied thin films of the materials, before and after heat treatment, by means of infrared and X-ray photoelectron spectroscopy. The results show that the materials are undoped by thermal treatment. Comparative studies on poly(3-methylthiophene) show that this polymer also undergoes thermal undoping, but at a much slower rate.     

锗相的存在对Sr_8Ga_(16)Ge_(30)clathrates结构热电材料性能的影响

无机clathrate结构化合物是非常有前景的热电材料.在镓取代的锗基clathrate结构热电材料的合成中,普遍存在锗的第二相.本研究合成了多晶Sr_8Ga_(16)Ge_(30) clathrates 结构热电材料.用X射线衍射结合样品抛光表面的背散射电子像对样品中锗相的含量进行表征.测试可知,材料表现为n型半导体,随着Ge相含量的增大,Seebeck系数绝对值增大,电导和热导率减小.功率因子最大为12.8 μW·K~(-2)cm~(-1).Sr_8Ga_(16)Ge_(30)样品在650 K的最大ZT值达到0.65.     

Effects of the FeCl<Subscript>3</Subscript> concentration on the polymerization of conductive poly(3,4-ethylenedioxythiophene) thin films on (3-aminopropyl) trimethoxysilane monolayer-coated SiO<Subscript>2</Subscript> surfaces

This study examined the effects of the FeCl₃ (oxidant) concentration on the vapor phase polymerization (VPP) of conducting poly (3,4-ethylenedioxythiophene) (PEDOT) thin films on (3-aminopropyl)trimethoxysilane (APS)-coated SiO₂ surfaces, in which the interaction between Fe(III) and the -NH₂ groups of APS enabled a uniform distribution of FeCl₃ on the surface. The FeCl₃ concentration has a strong impact on the thickness, surface morphology, and conductivity of the PEDOT films deposited by VPP on an APS monolayer. The thickness of the PEDOT thin films increased linearly as the FeCl₃ concentration increased, as predicted by a model of spun films from a FeCl₃ solution. However, the rate of the increase in PEDOT thin film thickness per unit of FeCl₃ in wt.% was lower than the predicted value. This suggests that the consumption of FeCl₃ not participating in polymerization to produce Fe₂O₃ or FeCl₃ aggregates increased as the FeCl₃ concentration increased. In addition, the surface morphology improved as the FeCl₃ concentration increased from 1 wt.% to 3 wt.% and the conductivity increased to approximately 400 S/cm. However, further increases in the FeCl₃ concentration to 5 wt.% and 7 wt.% significantly degraded the morphology by creating holes in the PEDOT film, which reduced the conductivity.     

MICROSTRUCTURES AND OPTICAL PROPERTIES OF Te_（81）Ge_（15）Sb_4 THIN FILMS USED FOR PHASE CHANGE RECORDING MATERIALS

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