Characterization of ultra smooth interfaces in Mo/Si-multilayers

The interface structure of Mo/Si-multilayers prepared by Pulsed Laser Deposition (PLD) on Si substrates at room temperature has been investigated. Already the in-situ ellipsometer data acquired during film growth indicate a particular behaviour of this material system that is caused by reaction/diffusion processes of the condensing atoms. MoSi_x interlayers are formed both at the Mo on Si- and at the Si on Mo-interfaces. The results of multilayer characterization carried out by SNMS and RBS show similar concentration profiles for both types of the interlayers. More detailed information about interface structure and morphology can be provided by HREM investigations. In the TEM micrographs of various multilayers prepared for different laser light wavelengths an improvement of layer stack quality, i.e. formation of abrupt interfaces, with increasing photon energy is observed. Layer stacks having almost ideally smooth interfaces were synthesized by UV-photon ablation. HREM micrographs of these multilayers show a pronounced separation of spacer and absorber layers. The roughness _R of the interfaces between the amorphous Si- and MoSi_x-layers was determined by image analysis. On the average a level _R 0.1 nm is found. There is no indication for roughness replication or amplification from interface to interface as it is known from the appropriate products of conventional thin film technologies.     

Neutron reflectometry study of CrAlN/TiAlN nanostructured multilayers

Alternate CrAlN/TiAlN multilayers with different repeated bilayer thickness ranging from 10 to 20 nm were prepared by sputtering Ti, Al and Cr targets with N₂ and Ar gases. The interface structures of multilayers such as the average individual thicknesses, the scattering length densities and interface roughness were characterized using nonpolarized specular neutron reflectometry. The experimental reflectivity can be well described by a multilayer model for all samples. The individual thickness in the repeated bilayers is close to the nominal thickness. The interface roughness diminishes as the thickness of the bilayer in mutilayers decreases. The asymmetric interface roughness on CrAlN‐TiAlN‐Si interfaces causes the larger interface roughness of CrAlN on TiAlN interface. The scattering length density profiles of multilayers suggest that the chemical composition is approximate to Cr_0.86Al_0.14N/Ti_0.5Al_0.5N and which is more accurate for thinner films. Copyright © 2016 John Wiley & Sons, Ltd.     

原位反应合成Mo-Si化合物系复合材料

采用反应烧结法原位合成了Mo Si系化合物复合材料，利用X射线衍射仪、扫描电镜和电子探针等考察了材料的显微结构和相组成.结果表明，随原料粉中Mo含量的增加， Mo Si系反应生成物依次向MoSi2→Mo5Si3→Mo3Si变化；各相分布较为均匀，组织致密，晶粒细小.     

Structure and chemistry of interfaces

It is most desirable to understand the structure and chemistry of the internal interfaces for all classes of materials since the materials' properties often depend on the properties of the interfaces which, in turn, are controlled by their structure and chemistry. In contrast to surface science, there exist only a few techniques for studying the structure and chemistry of internal interfaces. One of the most powerful techniques seems to be transmission electron microscopy (TEM) by which short segments of interfaces can be analyzed. In high-resolution electron microscopy (HREM) a direct image is formed of the projection of the interfaces. A simple analysis of HREM micrographs is not possible owing to the complex image forming processes within HREM. In addition to experimental investigations, calculations of the structures must be performed using material specific interatomic potentials. From the calculated structure, HREM images must be simulated for the specific imaging conditions. The experimental micrographs must be compared to simulated images. An agreement between experimental micrographs and the simulated images results in the best possible atomistic configuration. A quantitative measure for this agreement is the difference image, D, between the experimental micrograph and the simulated image. Best agreement is reached if only the noise is visible in the difference image D. Analytical electron microscopy with high-spatial resolution (typical probe size <0.05 nm) allows the identification of impurities segregated at the interface. However the limit of detectability depends sensitively on the combination between the different elements. Recently developed techniques on spatially resolved electron energy loss spectra give information on bonding and coordination. As an example, the different TEM techniques have been applied to the investigation of grain boundaries in -Al₂O₃. It should be emphasized, however, that the TEM techniques could also be applied to internal interfaces in different boundaries.     

电结晶制Co/Pt多层膜的结构及磁性研究

以单晶Si(111)为基底, 在以P盐[主要成分Pt(NO₂)₂(NH₃)₂]和CoSO₄为主盐的硼酸体系中电结晶Co/Pt多层膜. SEM观察多层膜的断面形貌, 证实多层膜具有周期结构. 经XRD测试, 首次证实了Co-Pt界面上有CoPt₃化合物的存在. 用PPMS测试了多层膜的磁滞回线, 平行于外磁场时膜的矫顽力约为165 Oe, 垂直于外磁场时的矫顽力随Co含量的增加而增加, 最大达到396 Oe. 首次用电结晶方法制得了易磁化轴垂直于膜面的Co/Pt多层膜.     

Mo2C膜表面高度和高差分布规律研究

介绍了金属有机气相沉积（MOCVD）制备Mo2C功能膜的过程和对膜表面粗糙度的测量结果;在测量基础上进行统计,找出Mo2C膜表面高度和高差分布规律;将DT2模型推广,进行2+1维计算机模拟,作出Mo2C膜表面3维模拟图·结果表明：实验测得的高度和高差统计分布与计算机模拟的结果一致。     

Geometries, stabilities, and growth patterns of the bimetal Mo2-doped Sin (n=9-16) clusters: a density functional investigation

The behaviors of the bimetal Mo-Mo doped cagelike silicon clusters Mo2Sin at the size of n=9-16 have been investigated systematically with the density functional approach. The growth-pattern behaviors, relative stabilities, and charge-transfer of these clusters are presented and discussed. The optimized geometries reveal that the dominant growth patterns of the bimetal Mo-Mo doped on opened cagelike silicon clusters (n=9-13) are based on pentagon prism MoSi10 and hexagonal prism MoSi12 clusters, while the Mo2 encapsulated Sin(n=14-16) frames are dominant growth behaviors for the large-sized clusters. The doped Mo2 dimer in the Sin frames is dissociated under the interactions of the Mo2 and Sin frames which are examined in term of the calculated Mo-Mo distance. The calculated fragmentation energies manifest that the remarkable local maximums of stable clusters are Mo2-doped Sin with n=10 and 12; the obtained relative stabilities exhibit that the Mo2-doped Si10 cluster is the most stable species in all different sized clusters. Natural population analysis shows that the charge-transfer phenomena appearing in the Mo2-doped Sin clusters are analogous to the single transition metal Re or W doped silicon clusters. In addition, the properties of frontier orbitals of Mo2-doped Sin (n=10 and 12) clusters show that the Mo2Si10 and Mo2Si12 isomers have enhanced chemical stabilities because of their larger HOMO-LUMO gaps. Interestingly, the geometry of the most stable Mo2Si9 cluster has the framework which is analogous to that of Ni2Ge9 cluster confirmed by recent experimental observation (Goicoechea, J. M.; Sevov, S. C. J. Am Chem. Soc. 2006, 128, 4155).     

FTIR spectroscopy of buried interfaces in molecular junctions

We demonstrate that ATR-FTIR spectroscopy can be used to record high-quality vibrational spectra of molecules at buried interfaces in metal-molecule-silicon and metal-molecule-metal junctions. This provides quantitative information on the structure and conformation of molecules at buried interfaces, an issue of critical importance to molecular electronics. In the model systems of Au on octadecyltrichlorosilane self-assembled monolayer on Si or mecaptohexadecanoic acid multilayers on Au-covered Si, ATR-FTIR suggests that metal deposition leads to not only conformational disorder within the film but also the direct interaction of metal atoms/clusters with alkyl backbones.     

Investigation of the thermal stability of Ni/C multilayers by X-ray methods

Microstructural properties of Ni/C multilayers prepared by PLD (pulsed laser deposition) have been investigated after heat treatment in vacuum at temperatures in the range of 50 degrees C to 500 degrees C. X-ray diffractometry, X-ray reflectometry, fluorescence EXAFS (extended X-ray absorption fine structure) and HREM (high resolution transmission electron microscopy) have been applied to characterize samples in the initial state and after annealing. The multilayer reflectivity remained unchanged or increased at temperatures below 400 degrees C due to sharpening of the interfaces caused by the formation of alpha-nickel and nickel carbide. The reflectivity decreased at temperatures above 400 degrees C because of the fragmentation of the nickel layers. It can be shown, that both chemical and mechanical driving forces are responsible for the observed modifications of the initial specimen state.     

Characterization of the interfacial structure and perpendicular magnetic anisotropy in CoFeB‐MgO structures with different buffer layers

In this study, we describe the deposition of Hf and Mo metal layers individually on Ta to compose new buffer layers, ie, Ta/Hf and Ta/Mo, where CoFeB/MgO stacks are deposited using magnetron sputtering. The synthesised Ta/Hf buffer has higher surface roughness, while the Ta/Mo buffer has lower surface roughness as compared with the Ta buffer. The surface roughness of the buffer appears to influence the interface of the subsequently deposited layers, resulting in rougher or smoother CoFeB/MgO interfaces. Additionally, we present a report on the magnetic properties of Ta, Ta/Hf, and Ta/Mo buffer samples. As the annealing temperature is below 200 °C, the saturation magnetisation (Ms) values for all buffer layers increase at similar rates, whereas the effective magnetic anisotropy energy (K_eff) values increase at varying rates. After annealing at 350 °C, K_eff reaches its maximum value for Ta/Hf and Ta/Mo buffer layers, whereas the CoFeB/MgO interface width decreases to a minimum value. The width increases as the annealing temperature is increased over 350 °C, and K_eff gradually decreases with increase in the annealing temperature. The CoFeB/MgO interface width is primarily dependent on the buffer/CoFeB interface width, which is a critical parameter to obtain high perpendicular magnetic anisotropy (PMA) and high‐quality films. This work provides perspectives for understanding and controlling PMA from the viewpoint of interfacial structure.     

Swift heavy ion induced effects at Mo/Si interface and silicide formation

Swift heavy ion (SHI) induced modification at metal/Si interfaces has emerged as an interesting field of research due to its large applications. In this study, we investigate SHI‐induced mixed molybdenum silicide film with ion fluences. The molybdenum thin films were deposited on silicon substrates using e‐beam evaporation at 10^?8 torr vacuum. Thin films were irradiated with Au ions of energy 120 MeV to form molybdenum silicide. The samples were characterized by grazing incidence X‐ray diffraction (GIXRD) technique for the identification of phase formation at the interface. Rutherford backscattering spectrometry (RBS) was used to investigate the elemental distribution in the films. The mixing rate calculations were made and the diffusivity values obtained lead to a transient melt phase formation at the interface according to thermal spike model. Irradiation‐induced effects at surface have been observed and roughness variations at the surface were calculated using atomic force microscopy (AFM) technique. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of multilayer-interfaces by X-ray diffraction, TEM, SNMS and AES

Summary Prototypes of Ni-C multilayers (up to 40 periods of typically 5 nm thickness) have been prepared by laser pulse vapour deposition (LPVD) and analyzed by a variety of methods. The work showed near normal X-ray reflectivities of typically 5%; an interface roughness ranging from <1 (determined by image processing of TEM micrographs) to 5 (determined by simulation of X-ray diffraction); a compensation for the roughness component that is caused by the substrate surface and impurity concentrations <1 at.–% in layers and in interfacial regions. X-ray diffraction, transmission electron microscopy and image processing have been successfully used for the investigation of the interfacial regions, whereas depth profiling methods that involve sputtering (SNMS and AES) can not provide resolution below 10 .     

Fabrication of photosensitive multilayer films based on polyoxometalate and diazoresin

A novel photosensitive organic-inorganic composite film incorporating polyoxometalate, K7[SiW11O39Co(H3P2O7)] (SiW11CoPP), and diazoresin (DR) has been prepared via layer-by-layer (LBL) self-assembly. Under UV irradiation, followed the decomposition of diazonium in DR, the ionic bonds between the adjacent interfaces of the multilayer film convert to covalent bonds. The LBL multilayers were characterized by UV-vis spectroscopy, X-ray photoelectron spectra (XPS), atomic force microscopy (AFM), FTIR spectrum, cyclic voltammograms (CV), and electron spin resonance (ESR) measurements. UV spectroscopy shows that the deposition process is regular and highly reproducible from layer to layer. XPS spectra confirm the incorporation of DR and SiW(11)CoPP into the films. Atomic force microscopy image indicates that the film surface is uniform and smooth. Solvent etching experiment proves that the film has significant stability towards polar solvent. Electrochemical behavior of the multilayers is investigated.     

Molecular dynamics simulations of carbon nanotube/silicon interfacial thermal conductance

Using molecular dynamics simulations with Tersoff reactive many-body potential for Si-Si, Si-C, and C-C interactions, we have calculated the thermal conductance at the interfaces between carbon nanotube (CNT) and silicon at different applied pressures. The interfaces are formed by axially compressing and indenting capped or uncapped CNTs against 2 x 1 reconstructed Si surfaces. The results show an increase in the interfacial thermal conductance with applied pressure for interfaces with both capped and uncapped CNTs. At low applied pressure, the thermal conductance at interface with uncapped CNTs is found to be much higher than that at interface with capped CNTs. Our results demonstrate that the contact area or the number of bonds formed between the CNT and Si substrate is key to the interfacial thermal conductance, which can be increased by either applying pressure or by opening the CNT caps that usually form in the synthesis process. The temperature and size dependences of interfacial thermal conductance are also simulated. These findings have important technological implications for the application of vertically aligned CNTs as thermal interface materials.     

Investigation of the thermal stability of Ni/C multilayers by X-ray methods

Microstructural properties of Ni/C multilayers prepared by PLD (pulsed laser deposition) have been investigated after heat treatment in vacuum at temperatures in the range of 50°C to 500°C. X-ray diffractometry, X-ray reflectometry, fluorescence EXAFS (extended X-ray absorption fine structure) and HREM (high resolution transmission electron microscopy) have been applied to characterize samples in the initial state and after annealing. The multilayer reflectivity remained unchanged or increased at temperatures below 400°C due to sharpening of the interfaces caused by the formation of -nickel and nickel carbide. The reflectivity decreased at temperatures above 400°C because of the fragmentation of the nickel layers. It can be shown, that both chemical and mechanical driving forces are responsible for the observed modifications of the initial specimen state.     

Modulating the pattern quality of micropatterned multilayer films prepared by layer-by-layer self-assembly

Patterned multilayer films composed of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were prepared using dip and spin self-assembly (SA) methods. A silicon substrate was patterned with a photoresist thin film using conventional photolithography, and PAH/PSS multilayers were then deposited onto the substrate surface using dip or spin SA. For spin SA, the photoresist on the substrate was retained, despite the high centrifugal forces involved in depositing the polyelectrolytes (PEs). The patterned multilayer films were formed by immersing the PE-coated substrates in acetone for 10 min. The effect of ionic strength on the pattern quality in dip and spin multilayer patterns (line-edge definition and surface roughness of the patterned region) was investigated by increasing the salt concentration in the PE solution (range 0-1 M). In dip multilayer patterns, the presence of salt increased the film surface roughness and pattern thickness without any deformation of pattern shape. The spin multilayer patterns formed without salt induced a height profile of about 130 nm at the pattern edge, whereas the patterns formed with high salt content (1 M) were extensively washed off the substrates. Well-defined pattern shapes of spin SA multilayers were obtained at an ionic strength of 0.4 M NaCl. Multilayer patterns prepared using spin SA and lift-off methods at the same ionic strength had a surface roughness of about 2 nm, and those prepared using the dip SA and lift-off method had a surface roughness of about 5 nm. The same process was used to prepare well-defined patterns of organic/metallic multilayer films consisting of PE and gold nanoparticles. The spin SA process yielded patterned multilayer films with various lengths and shapes.     

Effects of combined substitution of Dy and Mo or Si on the crystal structures and magnetic properties of Nd_(1-y)Dy_yFe_(11-x)TiM_x(M=Mo,Si) compounds

A series of Nd1-yDyyFe11-xTiMx(M=Mo,Si) alloys have been prepared by arc melting and studied by X-ray diffraction and neutron diffraction.All samples are found to crystallize in the ThMn12-type structure.The lattice parameters a and c and unit cell volume V of Nd0.5Dy0.5Fe11-xTiMox alloys increase linearly with increasing content of Mo(x),while the lattice parameters a and c and unit cell volume V of Nd0.5Dy0.5Fe11-xTiSix alloys decrease linearly with increasing content of Si(x).In NdyDy1-yFe11-xTiMx(M=Mo,S...     

Detection of carrier information in heterojunctions of nanocrystalline/crystalline Si

Hall effect measurements on heterojunctions of nanocrystalline Si:H (nc-Si:H) film with crystalline Si wafer fabricated by plasma enhanced chemical vapor deposition technique were made as a function of temperature (20–300 K) and magnetic field (0–15 T). Magnetic field-dependent resistivity and Hall data were interpreted with the quantitative mobility spectrum analysis (QMSA) method, which successfully separated the two-dimensional electron gases (2DEGs) at the nc-Si:H/c-Si interface from 3D carriers appearing in the films and substrates. Mobilities and densities of 2DEGs for the specimens were measured. Detail analyses about influences of interface and epitaxial layer quality including doping, film thickness and mean size of nanocrystals on the mobilities and densities of 2DEGs at interfaces were carried out. The important role of the amorphous buffer layer within the junction was identified. Origin of high mobility observed in the prepared films was revealed. Forward and reverse current mechanisms as well as the dependence of breakdown voltages on temperature in the operated nc-Si:H/c-Si heterostructure were elucidated.     

纳米金属多层膜与多层纳米线的电化学制备及其表征

分别采用单槽法和双槽法电沉积Cu/Co多层膜.研究了两种电沉积方法制备多层膜的工艺条件,利用电化学方法、XRD和SEM对多层膜进行表征,并对Cu/Co多层膜的巨磁阻性能进行了测试. 采用电沉积多层膜的方法，以多孔铝阳极氧化膜（AAO）为模板,在纳米孔内沉积Cu/Co多层线,采用TEM对多层纳米线进行了表征.     

Properties of electrodeposited ni/cu multilayer structures

The interface structure and magnetic properties of electrodeposited Ni/Cu multilayers have been investigated. The layer thickness of both Cu and Ni range from 200 to 6000Å. The Ni and the Cu layers are polycrystalline with a dominant (111) fibre texture. The magnetization and M-H loops of the samples were determined using a vibrating sample magnetometer (VSM). Ferromagnetic resonance (FMR) was observed at 9.8 GHz. The linewidth of the granular multilayer is attributed either to some roughness or to small fluctuations of magnetization and is about 1.5 kOe when the applied magnetic field is in the plane of the film.