In-situ X-ray Diffraction study of Metal Induced Crystallization of amorphous silicon

By covering amorphous silicon (a-Si) with a thin metal film, it is possible to lower the crystallization temperature of the a-Si (typically around 800 °C when using ramp anneals) to levels which can be used in a manufacturing process. This phenomenon of Metal Induced Crystallization (MIC) has been reported previously for Ni, Au and Al. In this work, in-situ X-ray Diffraction was used to study the MIC process for 20 different metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al). The 7 metals which lower the crystallization temperature the most are Ni, Pt, Pd, Cu, Au, Al and Ag. The crystallization kinetics were studied in detail for these 7 materials. In order to explain the MIC process, two models where used depending on the interaction of the metal with Si (eutectic or compound forming).     

铂、钯材料ICP分析方法的研究

由于铂、钯材料被广泛应用于多种精密行业,其材料含量也越来越受到重视,目前采用的方法不是操作复杂就是范围太窄而不符合日常检测要求,因此急需建立一种简捷快速的、适用于铂、钯材料含量为95．0％-99．99％的化学分析方法。该文用电感耦合等离子发射光谱分析,测定铂、钯材料中铂（钯）、铑、铱、钌、金、银、铜、铁、镍、铝、铅、锰、铬、镁、锡、硅、锌及铋等杂质元素的方法,达到了检出限低、重复性好、回收率在88．3％-100％的检测目标。     

Application of surface-enhanced infrared absorption spectroscopy to investigate pyridine adsorption on platinum-group electrodes

In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) was applied to investigate adsorption configurations of pyridine (Py) on platinum, palladium, ruthenium, and rhodium nanoparticle film electrodes. The results reveal that alpha-pyridyl species predominantly form on Pt electrodes by assuming an edge-on configuration with its ring N and alpha-C atoms bonding to the Pt surface, while on Ru and Rh electrodes pyridine molecules essentially remain intact by adopting a slightly edge-tilted configuration through bonding with its N lone pair electrons. Py adsorption on a Pd electrode may lie in between the above two cases; both alpha-pyridyl species and edge-tilted intact pyridine could be significantly present. Further comparison of the typical adsorption configurations on the above four electrodes with those on Ag, Au, Cu, Cd, and Ni film electrodes suggests that valence electrons and the periodic row of metals may play an important role in determining the adsorption configuration.     

Growth Mechanism of Metal Clusters on a Graphene/Ru(0001) Template

Using first‐principles calculations combined with scanning tunneling microscopy experiments, we investigated the adsorption configurations, electronic structures and the corresponding growth mechanism of several transition metal (TM) atoms (Pt, Ru, Ir, Ti, Pd, Au, Ag, and Cu) on a graphene/Ru(0001) moiré template (G/Ru(0001)) at low coverage. We find that Pt, Ru, Ir, and Ti selectively adsorb on the fcc region of G/Ru(0001) and form ordered dispersed metal nanoclusters. This behavior is due to the unoccupied d orbital of the TM atoms and the strong sp³ hybridization of carbon atoms in the fcc region of G/Ru(0001). Pd, Au, Ag, and Cu form nonselective structures because of the fully occupied d orbital. This mechanism can be extended to metals on a graphene/Rh(111) template. By using Pt as an example, we provide a layer by layer growth path for Pt nanoclusters in the fcc region of the G/Ru(0001). The simulations of growth mechanism agree well with the experimental observations. Moreover, they also provide guidance for the selection of suitable metal atoms to form ordered dispersed metal nanoclusters on similar templates.     

Effect of annealing on the characteristics of Au layers grown on the high-temperature deposited Ni50Fe50 layers

80 nm-thick Ni₅₀Fe₅₀ layers were sputter-deposited on glass substrates at 400 °C and then Au layers were sputter-deposited on the Ni₅₀Fe₅₀ layers. The Au/Ni₅₀Fe₅₀ bilayer films were annealed in a vacuum of 5×10⁻⁴ Pa from 250 to 450 °C for 30 min or 90 min. The characteristics of the Au layers were studied by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and a four-point probe technique. When the annealing temperature reaches 450 °C, Fe and Ni atoms diffuse markedly into the Au layer and the Fe content is more than the Ni content. When the annealing temperature is lower than 450 °C, the grain size of the Au layers does not change markedly with annealing temperature. However, as the annealing temperature reaches 450 °C, the annealing promotes the grain growth of the Au layer. As the annealing temperature exceeds 300 °C, the resistivity of the bilayer films increases with increasing annealing temperature. The diffusion of Fe and Ni atoms into the Au layer results in an increase in the resistivity of the annealed bilayer film. Large numbers of Fe and Ni atoms diffusing into the Au layer of the annealed Au/Ni₅₀Fe₅₀ bilayer film lead to a significant decrease in the lattice constant of the Au layer.     

Composition-modulated films: New materials for studying stability and critical phenomena in solid solutions

The technique of producing binary alloy films containing composition modulations with wavelengths between 0.8 and 8.0 nm is discussed. A new method of measuring interatomic potentials up to the sixth neighbor is developed by utilizing modulated films of [111] and [100] textures. The theoretical treatment, which is based on the microscopic theory of diffusion, allows for the estimation of the interatomic potentials from the wavelength dependence of the effective diffusion coefficients D?_B on the two crystallographic orientations. The D?_B values are measured from the decay rate of the X-ray diffraction satellite intensities produced by the modulation. Results for D?_B are presented for a number of systems, such as CuNi, CuPd, AuNi, AgPd and AgAu. The stability of concentration waves at various temperatures is also discussed and an example of the determination of the spinodal temperature for the CuNi modulated films is given. The effect of loss of coherency on the long-wavelength modulations and the appearance of screening singularities in the D?_B values are also considered.     

Ni/Au、Pd/Au与p-AlGaN材料的接触特性

在AlGaNpin型日盲紫外探测器结构中的p-AlGaN层上生长了Ni/Au和Pd/Au,并在600～850℃温度下进行快速热退火,测量其退火前后传输线模型中各金属接触间的电学性质。实验发现,Ni/Au与Pd/Au在p-AlGaN上表现出了不同的接触性能。为了更好的说明金属与p-AlGaN材料接触之间在退火后电流的变化,还测量了p-AlGaN材料裸片两点之间I-V曲线在退火前后的变化。实验表明,比起Ni/Au来,Pd/Au在p-AlGaN材料上制备欧姆接触具有一定的优势,并在文中进行了分析。     

Determination of 18 siderophile elements including all platinum group elements in chondritic metals and iron meteorites by instrumental neutron activation

An instrumental neutron activation method is developed to analyze chondritic metals and iron meteorites. By changing irradiation and decay times, and selecting suitable γ-ray and X-ray photopeaks, not only all platinum group elements (Ru, Rh, Pd, Os, Ir, Pt) but also other siderophilic elements (Fe, Co, Ni, Cu, Ga, Ge, As, Mo, Sb, W, Re, Au) can be nondestructively determined in the meteoritic metal samples. To obtain analytical data as accurate as possible, interfering reactions and neutron flux gradients during irradiation are considered. Siderophile elemental abundances measured for the Odessa iron meteorite are highly consistent with the literature values. Rh abundances for bulk H, L, LL, EH, and EL chondrites, which had been scarcely reported in the literature, are derived from Rh/Ni abundance ratios in the metal separates of the corresponding chondritic groups.     

Material and sensing properties of Pd-deposited WO3 thin films

The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.     

Investigation of quantum systems with surface plasmons and surface state electrons

We report on investigations of thin films of the quantum systems hydrogen and helium both in thermodynamic equilibrium and in metastable states. Information about the film thickness and surface roughness is obtained from the excitation of surface plasmons and mobility measurements of surface state electrons. The equilibrium studies show triple-point wetting for H ₂ on Au substrates, in agreement with earlier results for similar systems. Unexpectedly a distinct hysteretic behavior of the saturated film thickness is found near the triple-point. Superfluid ⁴ He films on as prepared Ag display complete wetting. Investigations of H ₂ films in metastable states prepared by quench-condensation at 1.5K reveal pronounced changes in the film structure upon annealing. These changes set in far below the desorption temperature and are ascribed to surface diffusion.     

Characterization of sputter deposited Au/Ni/Al multilayers on Si substrates

Multilayered Au/Ni/Al thin film metallization deposited by DC sputtering on n⁺Si substrates has been investigated. AES depth profiling was performed to reveal the concentration depth profiles of the Au/Ni/Al multilayers before and after annealing at different temperatures in the range 623-723 K. It was found that Ni aluminide layers begin to form during heat treatments at temperatures above 623 K. In addition to this process, Ni was found to diffuse significantly through the Au layer and segregates at the surface, proportionally to the increased annealing temperature. Consequently, the Ni oxidation process was found to take place thus causing the degradation of electrical contact. On the other hand Ni diffuses faster as well toward the Si/Al interface. No contamination traces at interfaces were observed. Electrical measurements of the metallized diode forward characteristics showed minor influence of the metallization heat treatment on the series resistance. Degradations were observed only in the reverse characteristics if the annealing was performed above 723 K.     

Nanostructured organic-inorganic photodiodes with high rectification ratio

High quality organic-inorganic heterojunction photodiodes based on nanostructured copper (II) phthalocyanine (CuPc) and intrinsic zinc oxide (i-ZnO) have been fabricated. The i-ZnO thin films/layers were grown by RF magnetron sputtering on clean indium tin oxide (ITO) coated glass substrates. These films have been characterized by optical absorption and field emission scanning electron microscopy (FESEM). CuPc thin films deposited at room temperature on i-ZnO have exhibited a change in their surface morphology with the post-deposition annealing temperature under normal atmosphere. The electrical dark conductivity and the photoconductivity of ITO/i-ZnO/CuPc/Au sandwich structures have been measured under various photoexcitation intensities using a xenon light source. The devices have shown excellent reproducibility of their electrical characteristics and high rectification ratios. The highest rectification ratio is nearly 831 calculated above the threshold voltage at room temperature for the sample annealed at 250?°C (i.e.?Pc 250). The effects of the annealing temperature of CuPc on the surface morphology, rectification ratio, and optical properties have been discussed.     

等离子体增强原子层沉积技术制备过渡金属薄膜的研究进展

原子级的处理对应用于计算和数据存储的最先进的电子设备,以及与物联网、人工智能和量子计算相关的新兴技术正变得越来越重要。等离子体增强原子层沉积(PEALD)是一种原子级表面沉积技术,由于其较高的反应活性以及较低的沉积温度日益受到研究者的关注。本文介绍了PEALD技术的基本原理以及相对于其他薄膜沉积技术的优势,之后从前驱体和基底材料的影响等方面介绍了利用PEALD制备Ti、Co、Ni、Cu、Ru、Pd、Ag、Ta、Ir和Pt等过渡金属薄膜以及它们在微电子领域的应用现状,最后进行了总结和展望。     

Metal contacts to n-type AlGaAs grown by molecular beam epitaxy

We report for the first time the barrier heights of Cu, Ni, Ag, Ti on etched n-type Al_0.33Ga_0.67As and their dependence on annealing temperature with I–V and C–V techniques. The barrier heights of Al and Au, measured for comparison, are 0.96 and 1.06 eV, respectively, in excellent agreement with the results reported previously. The barrier heights of the Cu, Ni, Ag and Ti/n---Al_0.33Ga_0.67As diodes are found to be 1.08, 0.90, 0.87 and 0.87 eV, respectively. It is observed that the barrier heights for Al, Au, Cu and Ti contacts monotonically decrease with annealing temperature. For the Ag and Ni contacts, however, they become higher after being annealed at 473 K for 10 min and become lower thereafter, accompanied by a change of their ideality factors in opposite direction. The barrier heights extrapolated from C–V measurements for all metals studied are higher than that deduced from I–V data, and become higher after annealing at high temperatures, indicating the existence of a thin oxide layer at interface and broadening of the oxide after annealing. Our results can be qualitatively explained by the quality of contact and defects created at the semiconductor surface due to interdiffusion.     

Internal stresses and interdiffusion of Ti-Pd-Au films studied by X-ray diffraction techniques

The electrical and structural properties of three layer Ti-Pd-Au films which are widely used for interconnections and terminations in thin film circuits change upon heat treatment at elevated temperatures. The annealing can cause stress relaxation, interdiffusion between the different layers and diffusion-induced structural changes. The objective of this investigation was to study the effect of aging at temperatures between 284° and 425°C on the mechanical and structural properties of these conductor films. It was found that the stresses in the Au film on Pd-Ti were independent of the substrate material and were lower than those of the Au films deposited directly on the Ti bonding layer. During aging, substantial interdiffusion between Au and Pd took place and it was found that the diffusion rate of Pd was higher than that of Au.     

Mass transport in layered polycrystalline thin films

Thin film specimens having the layered structure Pb/Ag/Au and Pb/Ag/Pd were prepared for a study of the reactions between Pb and Au, and Pb and Pd, respectively. These reactions require mass transport through the intermediate layer of Ag. In the case of the reaction between Pb and Au, it is found that after annealing at 200°C for more than 24 h the compound Pb₂Au can be detected in those specimens where the 3000 Å thick Ag layer is polycrystalline but not in specimens where the Ag layer is a single crystal. This result indicates that grain boundaries in the polycrystalline Ag layer act as paths for rapid transport of Au and Pb atoms. In the case of the reaction between Pb and Pd, we prepared only polycrystalline Ag as the intermediate layer and detected the compound Pb₂Pd after a few hours of annealing in the temperature range 160°–200°C. The lattice parameter of the polycrystalline Ag layer before and after annealing has been measured by X-ray diffraction and found to be unchanged, indicating that leakage into the Ag grains by lattice diffusion is negligible and that boundary transport is dominant. Separate study of grain boundary diffusion kinetics is now possible using this technique.     

Magnetic properties of sputtered Co-Ni-Fe-Pd films for thin-filmheads

Magnetic properties of Co-Ni-Fe-M (M=Rh, Ir, Pd, Pt) films prepared by sputtering are investigated. It is found that addition of Pd decreases the magnetostriction constant of the films from 1×10^-5 to around zero. On the other hand, addition of other elements, such as Rh, Ir, and Pt, increases it. However, coercive forces of Co-Ni-Fe-Pd films become more than 10 Oe when the magnetostriction is less than 2×10^-6. Multilayered films are investigated to obtain films with low coercive force. 43Co-27Ni-15Fe-15Pd films of 0.17 μm and Al₂O₃ films of 0.01 μm in thickness are layered time-sequentially. This multilayered film has saturation induction of 1.4 T, ≈0 magnetostriction, and a low coercive force of 1.5 Oe. Furthermore, Co-Ni-Fe-Pd films are ascertained to be as resistant to corrosion as Permalloy films. Recording heads with multilayered Co-Ni-Fe-Pd films with Al₂O₃ interlayers as magnetic cores have been fabricated. Recording characteristics were evaluated. These laminated Co-Ni-Fe-Pd/Al₂O₃ heads exhibit about 6 dB better overwrite than Permalloy heads     

Epitaxially grown model catalyst particles of platinum, rhodium, iridium, palladium and rhenium studied by electron microscopy

In order to obtain oriented thin film model catalysts, small particles of Pt, Rh, Ir, Pd and Re (2–20 nm in size) were grown by high vacuum evaporation on NaCl cleavage faces or on in situ deposited NaCl films at 523–673 K. The particles were covered with a supporting film of Al₂O₃ or carbon and removed from the substrate. High resolution electron microscopy, selected area electron diffraction and weak-beam dark-field imaging were applied to determine the particular morphology, microstructure and orientation of the observed particles. Special attention was paid to Rh particles which appear in a variety of shapes. Pt, Ir and Pd model catalysts consist mainly of (001) oriented half octahedra which may exhibit truncations at the corners or on the top. This was also the dominant shape of Rh particles but in addition half tetrahedra in (011) epitaxy and multiply-twinned particles like decahedra in (001), (011) and (111) orientation were evident. These habits provide a definite “initial state” for study of the changes in structure and morphology of the particles during activating heat treatments necessary to induce catalytic activity of the Al₂O₃ supported metal films. Although Re films consisted of irregularly shaped particles, electron diffraction revealed a partial epitaxial alignment of both c.p.h. and f.c.c. Re.     

A comparative study of catalytic partial oxidation of methane over CeO2 supported metallic catalysts

In the present study, the catalytic partial oxidation of methane (CPOM) over various active metals supported on CeO2 (M/CeO2, M = Ir, Ni, Pd, Pt, Rh and Ru) has been investigated. The catalysts were characterized by X-ray diffraction (XRD), BET surface area, H2-temperature programmed reduction (H2-TPR), CO chemisorption and transmission electron microscope (TEM) analysis. Ir/CeO2 catalysts showed higher BET surface area, higher metal dispersion, small active metal nano-particles (approximately 3 nm) than compared to other M/CeO2 catalysts. The catalytic tests were carried out in a fixed R(mix) ratio of 2 (CH4/O2) in a fixed-bed reactor, operating isothermally at atmospheric pressure. From time-on-stream analysis at 700 degrees C for 12 h, a high and stable catalytic activity has been observed for Ir/CeO2 catalysts. TEM analysis of the spent catalysts showed that the decrease in the catalytic activity of Ni/CeO2 and Pd/CeO2 catalysts is due to carbon formation whereas no carbon formation has been observed for Ir/CeO2 catalysts.     

All-optical hydrogen-sensing materials based on tailored palladium alloy thin films

Optical reflectance measurements were performed to determine the hydrogen response characteristics of 20-nm-thick Pd-Au (Ag) films. The response characteristics displayed a strong dependence on alpha, mixed alpha/beta, and beta Pd-hydride phases formed in the films. The response time peaks in the alpha --> beta phase transition region (1625 s at 0.4% H(2) for Pd(0.94)Ag(0.06) and 405 s at 1% H(2) for Pd(0.94)Au(0.06)), consistent with critical slowing down phenomena. The alpha --> beta phase transition region was shifted and inhibited by changing the alloy element to Au and increasing its corresponding content to 40 atom %, respectively. Initial hydrogen uptake rate measurements determined that, due to the adsorption of ambient background gases, the rate-limiting step for alpha or beta phase PdH formation is dissociative chemisorption of hydrogen for each palladium alloy film. By tuning the alloy content and composition of the palladium films, the surface properties of the film become more receptive toward the rapid detection of hydrogen and a novel hydrogen-sensing material using Pd alloyed with 40 atom % Au is presented.