常压化学气相沉积方法制备非晶硅薄膜及其光致发光性能研究

使用改进的常压化学气相沉积(APCVD)系统制备了非晶硅薄膜,测量了样品的光致发光特性,使用Raman光谱和X射线光电子能谱(XPS)谱测量了薄膜的微结构特征.样品在523 nm出现发光峰,Raman光谱和XPS谱表明制备的薄膜结构中存在富氧相和富硅相的分相现象,分析认为相界面的存在是产生发光的原因.Raman光谱分峰结果表明薄膜中存在纳米晶粒.     

The structure and photoluminescence properties of ZnO/SiC multilayer film on Si substrate

ZnO/SiC multilayer film has been fabricated on a Si (111) substrate with a silicon carbide (SiC) buffer layer using the RF (radio frequency)-magnetron technique with targets of a ceramic polycrystalline zinc oxide (ZnO) and a composite target of pure C plate with attached Si chips on the surface. The as-deposited films were annealed at a temperature range of 600–1000°C under nitrogen atmosphere. The structure and photoluminescence (PL) properties of the samples were measured using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and PL spectrophotometry. By increasing the annealing temperature to 800°C, it is found that all the ZnO peaks have the strongest intensities, and the crystallinity of ZnO is more consistent on the SiC buffer layer. Further increase of the annealing temperature allows the ZnO and SiC layers to penetrate one another, which makes the interface between ZnO and SiC layer become more and more complicated, thus reduces the crystallinities of ZnO and SiC. The PL properties of a ZnO/SiC multilayer are investigated in detail. It is discovered that the PL intensities of these bands reach their maximum after being annealed at 800°C. The PL peaks shift with an increase in the annealing temperature, which is due to the ZnO and SiC layers penetrating reciprocally. This makes the interface more impacted and complicated, which induces band structure deformation resulting from lattice deformation.     

Effects of thermal annealing on the structural and optical properties of carbon-implanted SiO2

Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.     

溅射制备非晶氮化镓薄膜的光学性能

利用直流磁控溅射方法制备了GaN薄膜. X射线衍射及Raman光谱结果表明薄膜样品为非晶结构; 傅立叶红外光谱表明薄膜样品的主要吸收峰为Ga--N键的伸缩振动; 光致发光测试得到了360nm处的紫外发光谱; 测量薄膜样品的紫外-可 见谱, 并利用Tauc公式计算得到样品的光学带隙为3.74eV, 这与光致发光谱得到的结果是一致的.     

Electrodeposited carbon nanotube thin films

A successful attempt to grow carbon nanotubes (CNTs) by electrodeposition technique for the first time is reported here. Carbon nanotubes were grown on Si (001) substrate using acetonitrile (1% v/v) and water as electrolyte at an applied d.c. potential ∼20 V. The films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman, optical absorbance, Fourier Transform Infra Red spectroscopy (FTIR) and Electron Spin Resonance (ESR) measurements. The effect of magnetic field on the growth of nanotubes was studied critically. It was found that the presence of magnetic field during electro-deposition played a crucial role on the growth of carbon nanotubes and hence the electronic properties. Photoluminescence (PL) studies indicated band edge luminescence ∼0.72-0.83 eV. Field emission studies indicated lower turn-on voltage and higher current density for films deposited with magnetic field.     

Understanding spectroscopic phonon-assisted defect features in CVD grown 3C-SiC/Si(1 0 0) by modeling and simulation

New phonon-assisted defect features are observed using photoluminescence (PL) and Raman scattering spectroscopy on 3C-SiC/Si(1 0 0) films grown by chemical vapor deposition (CVD) technique. The ultraviolet excitation room-temperature (RT) PL-Raman spectra show a luminescence band near 2.3 eV due to RT recombination over the 3C-SiC indirect band gap. In addition to the strong Raman lines characteristic of Si substrate and 3C-SiC we also observed weaker impurity modes near 620, 743 and 833 cm⁻¹. These frequencies are compared with the results of Green's function simulations of impurity modes with plausible defect structures to best support the observed Raman features as well as modes of some prototypical defect center.     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Preparation and characterization of Ba2TiSi2O8 ferroelectric films produced by sol–gel method

Fresnoite (Ba₂TiSi₂O₈, BTS) thin films were grown on polished Si(100) substrates by sol–gel method. The films were characterized using Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy, X-ray diffraction (XRD) and atom force microscopy (AFM). The results reveal that the crystallinity of fresnoite thin films increases and their structures become more compact as post-annealing temperature increases. Combined with XRD data, the strong FTIR peaks and Raman bands assigned to Ti–O and Si–O vibration indicate the formation of fresnoite phase in the films at a temperature of 750 °C. Besides, the AFM observation showed the films have a smooth surface, fine grains and dense structure.     

Study of dielectric and piezoelectric properties of Pb(Ni,Nb)O3–Pb(Zr,Ti)O3 ceramics using mechanically activated powder

In this paper, we report a new method to prepare the polymer/inorganic nanoparticle composites using electron irradiation-induced polymerization. The mixture of nanoparticles and MMA solution were co-irradiated by 1.6 MeV electron beam to a dose of 10, 20 and 30 kGy at a dose-rate of 60 kGy/h in air at room temperature. The products after irradiation were extracted using a soxhlet extractor with boiling xylene and investigated by X-ray diffraction (XRD), Fourier transmission infrared (FTIR), X-ray photoelectron spectroscopy (XPS), optical absorption spectra (OAP) and photoluminescence (PL). The FTIR and XPS results show that there exist some unextractable PMMA in the nanocomposites after extraction, indicating a strong interaction between the PMMA and nanoparticles. PL results show that new luminescence peaks appear at 415 and 420 nm for the nanocomposites of anatase and γ-Al₂O₃.     

Si和C共掺杂的SiO2薄膜的光致发光

采用双离子束溅射技术制备了Si和C共掺杂的SiO2薄膜,在N2气氛下进行了不同温度的退火处理。分析了样品在室温下的光致发光(PL)特性,在该样品中观察到分别位于410nm和470nm的两个发光峰。这两个发光峰的强度随着退火温度的变化呈现不同的变化趋势,表明两个发光峰的来源并不相同。用XRD和FTIR测试手段分析了样品的结构,认为470nm的发光来源于中性氧空位缺陷(O3≡Si～Si≡O3),而410nm的发光来源于Si1-xCx纳米晶粒与SiO2基质之间的界面缺陷。     

射频磁控溅射制备掺Al的纳米Si-SiO2复合薄膜及其光致发光特性

采用射频磁控技术和退火处理制备掺Al的纳米Si-SiO2复合薄膜.通过X射线衍射(XRD)、X射线光电子能谱(XPS)和傅里叶变换红外光谱(FTIR)表征了薄膜的结构,组分和成键情况.掺Al在SiO2中造成氧空位,使薄膜光致发光强度增强,并出现新的发光峰.退火温度对掺Al薄膜的光致发光的峰位和峰强有较大影响.     

Effects of reaction temperature on size and optical properties of CdSe nanocrystals

We report experimental results on the reaction temperature dependence of luminescence properties in size-controlled CdSe nanocrystals. Such reaction temperature dependent property is also sizedependent. The diameter of the CdSe nanocrystals is tuned from 4–11.0 nm by varying the reaction temperatures. The growth process and characterization of CdSe nanocrystals are determined by photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectrometry (XPS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The influence of reaction conditions on the growth of CdSe nanocrystals demonstrates that low reaction temperature is favourable for the formation of high quality CdSe nanocrystals.     

Preparation and characterization of polymer/inorganic nanoparticle composites through electron irradiation

In this paper, we report a new method to prepare the polymer/inorganic nanoparticle composites using electron irradiation-induced polymerization. The mixture of nanoparticles and MMA solution were co-irradiated by 1.6 MeV electron beam to a dose of 10, 20 and 30 kGy at a dose-rate of 60 kGy/h in air at room temperature. The products after irradiation were extracted using a soxhlet extractor with boiling xylene and investigated by X-ray diffraction (XRD), Fourier transmission infrared (FTIR), X-ray photoelectron spectroscopy (XPS), optical absorption spectra (OAP) and photoluminescence (PL). The FTIR and XPS results show that there exist some unextractable PMMA in the nanocomposites after extraction, indicating a strong interaction between the PMMA and nanoparticles. PL results show that new luminescence peaks appear at 415 and 420 nm for the nanocomposites of anatase and γ-Al₂O₃.     

不同衬底温度下预沉积Ge对SiC薄膜生长的影响

分别在未沉积Ge和不同衬底温度(300、 500、700℃)沉积Ge条件下,利用固源分子束外延(SSMBE)技术在Si衬底上外延SiC薄膜.通过反射式高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)和傅里叶变换红外光谱(FTIR)等仪器对样品进行测试.测试结果表明,预沉积Ge的样品质量明显好于未沉积Ge的样品,而且随着预沉积温度的升高,薄膜的质量在逐渐地变好.     

Optical and structural properties of SiC nanocrystals

This paper presents the results of porous SiC characterizations using photoluminescence, scanning electronic microscopy and X-ray diffraction techniques. It is shown that the intensity of defect-related PL bands (2.13 and 2.54 eV) increases monotonically with PSiC thickness rise from 2.0 up to 12.0 μm. These luminescence centers are assigned to surface defects which appear at the PSiC etching process. Intensity enhancement for exciton-related PL bands (2.84, 3.04 and 3.24 eV ) is attributed to the exciton recombination rate increasing as result of electron-hole confinement realization in big size SiC NCs (6H-PSiC with inclusions of 15R- and 4H-PSiC) and/or quantum confinement exciton recombination in small-size 4H-PSiC NCs.     

Influence of filament-to-substrate distance on the spectroscopic,structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp ² bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.     

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

SiH4／C2H4体系激光合成SiC超细粉

本文报道了ＳｉＨ４／Ｃ２Ｈ４体系激光合成ＳｉＣ超细粉研究及对合成的ＳｉＣ超细粉进行的ＴＥＭ（ＴＥＤ）、ＸＲＤ、ＦＴＩＲ、ＸＰＳ及Ｒａｍａｎ散射等测试分析。在部分样品中发现了ＳｉＣ空心颗粒，讨论了ＳｉＣ超细粉的成核成长规律，得出了一些有价值的新结果：ＳｉＣ超细粉的合成由Ｓｉ成核生长和碳化组成；反应温度较高时，为获得接近化学计量化的ＳｉＣ超细粉，要求有较高的源气Ｃ／Ｓｉ比，并且高的Ｃ／Ｓｉ比有利于降低     

Ti/n型6H-SiC(0001)接触界面的研究

用同步辐射光电子能谱(SRPES)和X射线光电子能谱(XPS)的方法研究了Ti/n型6H-SiC(0001)的接触界面。Ti/n型6H-SiC(0001)样品采用磁控溅射的方法获得,然后将表面的Ti用氩离子刻蚀的方法慢慢刻蚀掉,Ti2p3/2用XPS测得,结合能从刻蚀时间为245 min的457.86 eV逐渐移动到刻蚀时间为255 min时的457.57 eV,移动约为0.3 eV。Si2p用同步辐射光测得,结合能从刻蚀245 min时的101.12 eV移动到干净的100.67 eV,峰形状未发生变化,表明Ti与衬底之间没有发生化学反应,SiC的价带发生弯曲,形成的势垒高度为0.89 eV。向SiC上蒸Si 2.5 min,退火30 min,观察LEED花样,发现当发射电流为30mA,能量37 eV时,SiC表面有√3*√3重构,发射电流为40 mA时,有6√3*6√3的重构。     

Self-assembled flower-like nanostructures of InN and GaN grown by plasma-assisted molecular beam epitaxy

Nanosized hexagonal InN flower-like structures were fabricated by droplet epitaxy on GaN/Si(111) and GaN flower-like nanostructure fabricated directly on Si(111) substrate using radio frequency plasma-assisted molecular beam epitaxy. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano-flowers was derived to be ∼28.5 meV from the temperature dependent PL studies. The formation process of nano-flowers is investigated and a qualitative mechanism is proposed.