Oxygen diffusion through thin Pt films on Si(100)

We have investigated the diffusion of oxygen through evaporated platinum films on Si(100) upon exposure to air using substrates covered with Pt films of spatially and continuously varying thickness (0–500 Å). Film compositions and morphologies before and after silicidation were characterized by modified crater edge profiling using scanning Auger microscopy, energy-dispersive X-ray microanalysis, scanning tunneling microscopy, and transmission electron microscopy. We find that oxygen diffuses through a Pt layer of up to 170 Å forming an oxide at the interface. In this thickness range, silicide formation during annealing is inhibited and is eventually stopped by the development of a continuous oxide layer. Since the platinum film consists of a continuous layer of nanometer-size crystallites, grain boundary diffusion of oxygen is the most probable way for oxygen incorporation. The diffusion constant is of the order of 10^–19 cm²/s with the precise value depending on the film morphology.     

X-ray photoelectron study of annealed Co thin film on Si surface

The X-ray photoelectron spectroscopy (XPS) study on as deposited as well as 500 °C annealed Co (400 Å)/Si thin film synthesized by electron beam evaporation technique under UHV conditions is reported here. The XPS measurements carried out on as deposited sample rule out the possibility of any phase formation at room temperature. Whereas in 500 °C annealed sample the Co-2p_3/2 peak is observed at ∼778.6 eV binding energy position, where the peak expected due to CoSi₂ resides. The Auger parameters were also calculated at each step of experiment because Auger parameter is always very sensitive to changes in the chemical state of the material. The recorded spectrum on annealed sample shows Auger parameter value of ∼1551.4 eV, which is different from that observed in the as deposited sample (∼1552.1 eV). The obtained results are analyzed and interpreted in terms of CoSi₂ phase formation at the interface with annealing.     

A leed-aes study of thin Pd films on Si(111) and (100) substrates

A system Pd (deposit)-Si (substrate) has been studied by LEED and AES. Pd₂Si formed on Si(111) became epitaxial after a short time of annealing at a temperature between 300 and 700°C, while the Pd₂Si formed on Si(100) did not, in both cases the surfaces of the Pd₂Si being covered with a very thin Si layer. A sequence of superstructures (3√3 × 3√3), (1 × 1), and (2√3 × 2√3) was observed successively in Pd/Si(111) as the annealing temperature was increased. A (√3 × √3) structure was obtained by sputtering the 3√3 surface slightly. It was found that the √3 structure corresponds to Pd²Si(0001)-(1 × 1) grown epitaxially on Si(111), and that the 3√3 structure comes from the thin Si layer accumulated over the silicide surface, while the 2√3 and 1 structures arise from a submonolayer of Pd adsorbed on Si(111). Superstructures observed on a Pd/Si(100) system are also studied.     

Ion-beam-induced ferromagnetism in Ca-doped LaMnO3 thin films grown on Si (100)

The ion-bean-induced room temperature ferromagnetic ordering in pulsed laser deposited Ca-doped LaMnO₃ thin films grown on Si (100) are presented in the present study. In addition to this, changes bought by the ion beam in structural, morphological and electrical properties are presented. Dense electronic excitation produced by high energy 120?MeV Ag⁹⁺ ion irradiation causes change in surface roughness, crystallinity and strain. It is also evident that these excitations induce the magnetic ordering in this system. The observed modifications are due to the large electronic energy deposited by swift heavy ion irradiation. The appearance of ferromagnetism at 300?K in these samples after irradiation may be attributed to the canting of the antiferromagnetically ordered spins due to the structural distortion. It is observed that the irradiated films show higher resistance than unirradiated films for all the compositions.     

Photoacoustic spectroscopy of thin SiO2 films grown on (100) crystalline Si substrates

Photoacoustic Spectroscopy (PAS) has been used to measure the thickness of thin SiO₂ films grown on (100) Si wafers. The data are in reasonable agreement with a simple theoretical model. It suggests that photoacoustic Spectroscopy is complementary to optical interferometry, in that it is capable of giving quantitative estimates of thin transparent films on opaque substrates of low reflectivity via the transmitted fraction of the optical energy incident on the sample. Both theoretical and experimental results indicate that PAS can be very useful in the measurement of thin films on substrates of low reflectivity.     

White-light emission from annealed ZnO:Si nanocomposite thin films

As grown ZnO:Si nanocomposites of different compositional ratios were fabricated by thermal evaporation techniques. These films were subjected to post-deposition annealing under high vacuum at a temperature of 250 °C for 90 min. The photoluminescence (PL) spectra of annealed samples have shown marked improvements both in terms of intensity and broadening. Structural and Raman analyses show formation of a Zn–Si–O shell around ZnO nanoclusters wherein on heating Zn₂SiO₄ compound forms resulting in huge UV, orange and red peaks at 310, 570 and 640 nm in PL. The new emissions due to Zn₂SiO₄ completes white light spectrum. The study not only suggests that 1:2 ratio is the best suited for material manipulation but also shows process at the interface of ZnO nanoclusters and silicon matrix leads to new PL emissions.     

Formation of amorphous layers by solid-state reaction. from thin Ir films on Si(100)

Received: 18 November 1997 / Accepted: 16 October 1998 / Published online: 24 February 1999     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Growth of partially strain-relaxed Si1-yCy epilayers on (100)Si

1-y C_y epilayers were grown by MBE on (100) Si single-crystal substrates either directly on a dislocation-free or on a highly dislocated Si buffer layer. The orientation of the epilayers and their strain status were measured by double-crystal X-ray diffraction. Cross sections were prepared for TEM investigations. Epitaxial layers of about 130 nm thickness and carbon contents up to [%at.]1.38 grown on top of dislocation-free 1-μm-thick Si buffer layers were fully strained. In TEM bright field images, no dislocations were found. In order to introduce a high dislocation density in the Si buffer layer, the native oxide on the substrate was only partially removed prior to growing the Si buffer. A Si_1-yC_y film grown on top of that highly dislocated buffer layer showed a partial stress relaxation (a_∥=5.429 Å<a_si=5.431 Å). The large FWHM of transverse rocking scans through the Bragg reflection corresponding to the epilayer indicates a high defect density. TEM cross-section micrographs showed an extension of threading dislocations from the Si buffer layer into the Si_1-yC_y layer. Received: 22 April 1998/Accepted: 22 April 1998     

Strain-driven morphology of Si1-xGex islands grown on Si(100)

A study has been carried out on the morphology and structure of three-dimensional (3D) SiGe islands grown by molecular beam epitaxy (MBE) on Si(100) substrates. Samples of Si1-xGex alloys have been prepared to investigate the effects either of the alloy composition or of the growth temperature. Atomic force microscopy (AFM) evidenced the growth of 3D islands and transmission electron microscopy (TEM) demonstrated wetting layer growth on Si(100), independently on the deposition conditions. Energy dispersive spectroscopy (EDS) micro-analyses carried out on cross-sections of large Si1-xGex islands with defects allowed a measurement of the Ge distribution in the islands. To the best of our knowledge, these have been the first experimental evidences of a composition change inside SiGe islands. The interpretation of the experimental results has been done in terms of strain-enhanced diffusion mechanisms both of the growing species (Si and Ge) and of small islands.     

Ti缓冲层及退火处理对Si(111)基片上生长的ZnO薄膜结构和发光特性的影响

采用反应磁控溅射法在Si（111）基片上制备了带有Ti缓冲层的高c轴取向ZnO薄膜.通过X射线衍射分析和光致荧光光谱测量,研究了Ti缓冲层厚度和退火处理对ZnO薄膜结晶质量和光致荧光特性的影响.研究结果表明,Ti缓冲层的引入可以有效改善Si基片上ZnO薄膜的发光性能,但缓冲层存在一个最佳的厚度.薄膜应力是影响ZnO薄膜紫外荧光发射性能的重要因素,较小的残余应力对ZnO薄膜的紫外荧光发射是有利的,残余应力的存在可以改变ZnO薄膜紫外荧光发射能量.随着退火温度的增加,薄膜中的张应力增大,导致带隙宽度减小以及激子复合跃迁峰逐渐向低能方向移动. 关键词： ZnO薄膜 缓冲层 退火处理 应力分析     

Transformation behavior of Ni-Mn-Ga/Si(100) thin film composites with different film thicknesses

A series of Ni_51.4Mn_28.3Ga_20.3/Si(100) thin film composites with different film thicknesses varying from 0.1 to 5 μm have been prepared by magnetron sputtering and subsequently annealed. X-ray powder diffraction patterns of the films show the features associated with the lattice-modulated martensitic phase and/or cubic austenite at room temperature. 220-fiber texture was confirmed by the X-rays measurements made at 150 °C. While the Curie temperature is almost film thickness independent, the martensitic transformation temperature shows a strong descended dependence in the submicron range. The substrate curvature measurements demonstrate that the forward and reverse martensitic transformation in the films is accompanied by the reversible relaxation and accumulation of residual stress, originally created by the thermal treatment due to the difference in thermal expansion of the film and substrate. The values of residual stresses measured by both substrate curvature and X-rays diffraction methods at constant temperatures are found to be dependent on the film thickness. This behavior appears in correlation with the thickness dependence of the transformation temperature.