The effects of porous silicon on the crystalline properties of ZnO thin films

In the present work, ZnO was deposited on porous silicon substrates by sol-gel spin coating and rf magnetron sputtering. The porous silicon (PS) substrates were formed by electrochemical anodization on p-type (1 0 0) silicon wafer, and the starting material for ZnO was Zinc acetate dehydrate. Raman spectroscopy revealed the good quality of the porous silicon substrate. XRD analysis showed that highly (0 0 2) oriented ZnO thin films were formed. SEM, AFM and optical microscope have been used to understand the effects of the substrate on crystalline properties of the samples. The results indicated that the porous silicon substrate is beneficial to improve the crystalline quality in lattice mismatch heteroepitaxy due to its sponge-like structure.     

Porous Silicon as an Intermediate Buffer Layer for Zinc Oxide Nanorods

Zinc thin films were deposited onto porous silicon (PSi) substrates by dc sputtering using a Zn target. These films were then annealed under flowing (6 l/min) oxygen gas environment in the furnace at 600°C for 2 h. Porous silicon is used as an intermediate layer between silicon and ZnO films and it provides a large area composed of an array of voids. The PSi samples were prepared using photoelectrochemical method on n-type silicon wafer with (111) and (100) orientation. To prepare porous structures, the samples were dipped into a mixture of HF:ethanol (1:1) for 5 min with current densities of 50 mA/cm², and subjected to external illumination with a 500 W UV lamp. The surface morphology and the nanorod structure of the ZnO films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). We synthesized the ZnO nanorods with diameter of 80–100 nm without any catalysts or templates. The XRD pattern confirmed that the ZnO nanorods were of polycrystalline structure. The surface-related optical properties have been investigated by photoluminescence (PL) and Raman measurements at room temperature. Micro-Raman results showed that A₁(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at 522 cm^–1 and 530 cm^–1, respectively. PL spectra peaks are clearly visible at 366 cm^–1 and 368 cm^–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The PL spectral peak position in ZnO nanorods on porous silicon is blue-shifted with respect to that in unstrained ZnO (381 nm).     

Stable blue-green and ul traviolet photoluminescence from silicon carbide on porous silicon

β-Silicon carbide layers have been prepared by high temperature pyrolysis of polyimide Langmuir-Blodgett films on porous silicon substrate in vacuum. The formation of silicon carbide is confirmed by the IR and XRD spectra. It is found that photoluminescence still exists and appears in the blue-green and ultraviolet regions after thermal treatment at 900°C. These results indicate that the silicon carbide layers, which are formed, are responsible for the blue-green luminescence.     

In situ micro-Raman analysis and X-ray diffraction of nickel silicide thin films on silicon

This article reports on the in situ analysis of nickel silicide (NiSi) thin films formed by thermal processing of nickel thin films deposited on silicon substrates. The in situ techniques employed for this study include micro-Raman spectroscopy (microRS) and X-ray diffraction (XRD); in both cases the variations for temperatures up to 350 degrees C has been studied. Nickel silicide thin films formed by vacuum annealing of nickel on silicon were used as a reference for these measurements. In situ analysis was carried out on nickel thin films on silicon, while the samples were heated from room temperature to 350 degrees C. Data was gathered at regular temperature intervals and other specific points of interest (such as 250 degrees C, where the reaction between nickel and silicon to form Ni(2)Si is expected). The transformations from the metallic state, through the intermediate reaction states, until the desired metal-silicon reaction product is attained, are discussed. The evolution of nickel silicide from the nickel film can be observed from both the microRS and XRD in situ studies. Variations in the evolution of silicide from metal for different silicon substrates are discussed, and these include (100) n-type, (100) p-type, and (110) p-type silicon substrates.     

Optical Analysis of Nanocrystalline ZnO Films Coated on Porous Silicon by Radio Frequency (RF) Magnetron Sputtering

Zinc oxide thin films have been deposited onto porous silicon (PSi) substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The advantages of the porous Si template are economical and it provides a rigid structural material. Porous silicon is applied as an intermediate layer between silicon and ZnO films and it contributed a large area composed of an array of voids. The nanoporous silicon samples were adapted by photo electrochemical (PEC) etching technique on n-type silicon wafer with (111) and (100) orientation. Micro-Raman and photoluminescence (PL) spectroscopy are powerful and non-destructive optical tools to study vibrational and optical properties of ZnO nanostructures. Both the Raman and PL measurements were also operated at room temperature. Micro-Raman results showed that the A₁(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at around 522 and 530 cm^–1, re- spectively. PL spectra peaks are distinctly apparent at 366 and 368 cm^–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The peak luminescence energy in nanocrystalline ZnO on porous silicon is blue-shifted with regard to that in bulk ZnO (381 nm). The Raman and PL spectra pointed to oxygen vacancies or Zn interstitials which are responsible for the green emission in the nanocrystalline ZnO.     

具有高阻抗本征SnO2过渡层的CdS/CdTe多晶薄膜太阳电池

采用超声喷雾热解法制备了具有高阻抗的本征SnO₂透明导电膜，将其运用在CdS层减薄了的CdS/CdTe多晶薄膜太阳电池中，对减薄后的CdS薄膜进行了XRD,AFM图谱分析，并对电池进行了光、暗I-V，光谱响应和C-V测试.结果表明，在高阻膜上沉积的减薄CdS薄膜(111)取向更明显，但易形成微孔.引入高阻层后，能消除CdS微孔形成的微小漏电通道，有效保护p-n结，改善了电池的并联电阻、填充因子和短波响应，使载流子浓度增加，暗饱和电流密度减小，从而电池性能得到改善，电池转换效率增加了14.4%. 关键词： CdTe电池 过渡层 效率     

Nanocrystalline ZnO Film Grown on Porous SnO2/Si(111) Substrate

Porous tin oxide was prepared on silicon(111) substrate by the sol–gel route. Then, the samples were dried in air at 600°C for 30 min in an electric furnace. Scanning electron microscope (SEM) images indicated the high density of the pores. Circular microvoids formed by the rigid shaped microarray network of 200–300 nm sizes are clearly seen in the plan view SEM image. The high homogeneity and uniformity of the porous region could also be visualized by this easy method. Nanocrystalline zinc oxide (ZnO) thin films have been deposited onto porous SnO₂substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The surface morphology of the nanocrystalline ZnO films was characterized by scanning electron microscope (SEM). Photoluminescence (PL) spectroscopy is a powerful, contactless and excellent nondestructive optical tool to study the acceptor binding energy of ZnO nanostructures. The PL measurements were also operated at room temperature. The peak luminescence energy in nanocrystalline ZnO on porous SnO₂ is blue-shifted with regard to that in bulk ZnO (381 nm). PL spectra peaks are distinctly apparent at 375 nm for ZnO film grown on porous SnO₂/Si(111) substrates.     

Electrochemical formation and properties of thin polyaniline films on Au(111) and p-Si(111)

The specific aspects of phase formation phenomena involved in electrodeposition of conducting polymer layers are critically discussed. The mechanism of formation and the properties of electrodeposited thin polyaniline (PANI) films on Au(111) and p-Si(111) are investigated by means of transient measurements, cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy (AFM). Experimental results show that the initial stages of PANI electrodeposition on Au(111) can be described by a model including progressive appearance and preferential 2D growth of polymer islands. The electropolymerization process on p-Si(111) substrates is preceded by anodic formation of an inhomogeneous thin SiO₂ layer giving rise to a progressive appearance and growth of 3D PANI islands. The electrochemical redox properties of electrodeposited PANI films on p-Si(111) are influenced strongly by the electronic band structure of silicon. PACS 81.10.Aj; 82.45.Wx; 82.45.Vp     

SrTiO3(110) thin films grown directly on different oriented silicon substrates

We have grown (110)-oriented SrTiO₃ (STO) thin films on silicon without any buffer layer, by means of pulsed laser deposition technique. The crystal structures of the grown films were examined by X-ray diffraction analysis including θ–2θ scan and rocking curve as well as Laue diffraction methods. STO films with single (110) out-of-plane orientation were formed on all (100), (110) and (111)-oriented Si substrates. The in-plane alignments for the epitaxial STO films grown directly on Si (100) were found as STO[001]//Si[001] and STO[11̄0]//Si[010]. The results should be of interest for better understanding of the growth of perovskite oxide thin films on silicon wafers. PACS 77.55.+f; 68.55.JK; 81.15Fg     

Surface morphology of ZnO buffer layer and its effects on the growth of GaN films on Si substrates by magnetron sputtering

ZnO thin films were first prepared on Si(111) substrates using a radio frequency magnetron sputtering system. Then the as-grown ZnO films were annealed in oxygen ambient at temperatures of 700, 800, 900, and 1000°C , respectively. The morphologies of ZnO films were studied by an atom force microscope (AFM). Subsequently, GaN epilayers about 500 nm thick were deposited on the ZnO buffer layers. The GaN/ZnO films were annealed in NH₃ ambient at 900°C. The microstructure, morphology and optical properties of GaN films were studied by x-ray diffraction (XRD), AFM, scanning electron microscopy (SEM) and photoluminescence (PL). The results are shown, their properties having been investigated particularly as a function of the ZnO layers. For better growth of the GaN films, the optimal annealing temperature of the ZnO buffer layers was 900°C.     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Hydroxyapatite coating on porous silicon substrate obtained by precipitation process

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area.     

Cu/SiO2/Si(111)体系中Cu和Si的扩散及界面反应

室温下利用磁控溅射在p型Si(111)衬底上沉积了Cu薄膜. 利用X射线衍射和卢瑟福背散射分别对未退火以及在不同温度点退火后样品的结构进行了表征. 在此基础上，研究了Cu/SiO₂/Si(111)体系的扩散和界面反应. 实验结果表明：当退火温度高于450℃时出现明显的扩散现象，并且随着温度的升高，体系扩散现象会更加显著. 当退火温度低于450℃时没有铜硅化合物生成，当温度达到500℃时才有铜硅化合物生成. 关键词： 薄膜 扩散 界面反应 硅化物     

Composition of nanocomposites of thin tin layers on porous silicon,formed by magnetron sputtering

Physics of the Solid State - Morphology and surface composition of the nanocomposite of thin tin layers on porous silicon, formed by magnetron sputtering, are investigated by scanning electron...     

Study of the microporosity in nanoporous carbon films by small-angle X-ray scattering

The structural difference in the microporous structures of nanoporous carbon films is revealed by small-angle X-ray scattering; it consists in a higher porosity of the layers formed from the titanium carbide. The pore shape is shown to be equiaxed. Pores 20 Å in diameter mainly contribute to the porosity of the nanoporous carbon films. The characteristics of the porous structure of the nanoporous carbon layers synthesized from the titanium or silicon carbide are found using small-angle X-ray scattering. The porous structure is shown to consist of two size fractions of equiaxed pores 10 and 40 Å in radius. The porosity of the films is mainly contributed by the pores of the small size fraction; their fraction is 46 or 10% for the layers synthesized from the titanium or silicon carbide, respectively.     

Study on structural properties of epitaxial silicon films on annealed double layer porous silicon

In this paper, epitaxial silicon films were grown on annealed double layer porous silicon by LPCVD. The evolvement of the double layer porous silicon before and after thermal annealing was investigated by scanning electron microscope. X-ray diffraction and Raman spectroscopy were used to investigate the structural properties of the epitaxial silicon thin films grown at different temperature and different pressure. The results show that the surface of the low-porosity layer becomes smooth and there are just few silicon-bridges connecting the porous layer and the substrate wafer. The qualities of the epitaxial silicon thin films become better along with increasing deposition temperature. All of the Raman peaks of silicon films with different deposition pressure are situated at 521 cm⁻¹ under the deposition temperature of 1100 °C, and the Raman intensity of the silicon film deposited at 100 Pa is much closer to that of the monocrystalline silicon wafer. The epitaxial silicon films are all (4 0 0)-oriented and (4 0 0) peak of silicon film deposited at 100 Pa is more symmetric.     

Structural and optical properties study of nanocrystalline Si (nc-Si) thin films deposited on porous aluminum by plasma enhanced chemical vapor deposition

In this paper we report detail investigation and correlation between micro-structural and optical properties of nanocrystalline silicon (nc-Si) deposited by plasma enhancement chemical vapor deposition (PECVD) on porous aluminum structure. The influence of the microstructure of the nc-Si thin films on their optical properties was investigated through an extensive characterization. The effect of anodisation currents on the microstructure of aluminum surface layer and nc-Si films was systematically studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). The optical constants (n and k as a function of wavelength) of the films were obtained using variable angle spectroscopic ellipsometry (SE) in the UV-vis-NIR regions. The silicon layer (SL) was modeled as a mixture of void, crystalline silicon and aluminum using the Bruggeman approximation. Based on this full characterization, it is demonstrated that the optical characteristics of the films are directly correlated to their micro-structural properties. A very bright photoluminescence (PL) was obtained and find to depend on anodisation current.     

基片温度对磁控溅射HfO2薄膜结构和性能影响分析

在纯氧条件下,采用直流磁控溅射技术在单晶硅基片上沉积氧化铪（HfO2）薄膜,并研究了沉积过程中基片温度对薄膜结构和性能的影响规律。利用X射线衍射仪（XRD）和X射线能谱（XPS）表征了薄膜的晶体结构和组分,利用原子力显微镜（AFM）观察薄膜表面形貌,利用纳米力学测试系统表征了薄膜的纳米硬度和弹性模量。结果表明:磁控溅射制备的HfO2薄膜样品呈(111)择优生长,其晶粒尺寸随着基片温度的升高而增大,但其晶型并不发生转变。随着基片温度的增加,基片中的硅元素向薄膜内扩散,影响了薄膜的化学计量比。沉积薄膜的表面形貌和力学性能亦受到其结构和组分变化的影响。在200 ℃条件下制备的HfO2薄膜纯度高,O、Hf元素化学计量达到了1.99,其表面质量和力学性能均达到了最佳值,随着基片温度升高至300 ℃以上,薄膜纯度下降,表面质量和力学性能均产生劣化。     

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 °C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 °C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 °C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).     

HFCVD法制备纳米晶体碳化硅薄膜中氢流量对晶粒尺寸的影响

以甲烷、硅烷和氢气为反应气体,采用热丝化学气相沉积(HFCVD)法在单晶硅衬底上沉积纳米晶体碳化硅(SiC)薄膜.通过X射线衍射(XRD)和扫描电子显微镜(SEM)分别对SiC薄膜的晶体结构和表面形貌进行分析.实验发现氢气流量对碳化硅薄膜晶粒尺寸有很大影响,当氢气流量从10SCCM变化到300SCCM时,薄膜晶粒的平均尺寸将由较大的400 nm左右减小到40 nm左右.