Analysis of thin films and molecular orientation using cluster SIMS

A study of phenylalanine films of different thicknesses from submonolayer to 55 nm on Si wafers has been made using Bi_n⁺ and C₆₀⁺ cluster primary ions in static SIMS. This shows that the effect of film thickness on ion yield is very similar for all primary ions, with an enhanced molecular yield at approximately 1 monolayer attributed to substrate backscattering. The static SIMS ion yields of phenylalanine at different thicknesses are, in principle, the equivalent of a static SIMS depth profile, without the complication of ion beam damage and roughness resulting from sputtering to the relevant thickness. Analyzing thin films of phenylalanine of different thicknesses allows an interpretation of molecular bonding to, and orientation on, the silicon substrate that is confirmed by XPS. The large crater size for cluster ions has interesting effects on the secondary ion intensities of both the overlayer and the substrate for monolayer and submonolayer quantities. This study expands the capability of SIMS for identification of the chemical structure of molecules at surfaces. © Crown copyright 2010.     

Photo-Induced Hydrophilicity of TiO<Subscript>2</Subscript> Films Deposited on Stainless Steel via Sol-Gel Technique

The photo-induced hydrophilicity of TiO₂ films deposited on stainless steel substrates and silicon wafers using two different sol-gel routes has been investigated. The results indicate that crystalline titanium oxide films with excellent hydrophilic properties can be obtained on silicon wafer with both routes. XPS and XRD data reveal that films deposited on stainless steel exhibit crystallization features similar to those of films deposited on silicon wafers, and only differ by their oxidation degree owing to a TiO₂ reduction process associated to a diffusion of iron ions during deposition of the acidic sol and/or high temperature post-treatment. Consequently, hydrophilic properties of films deposited on stainless steel are inhibited. The deposition of a SiO_x barrier layer at the film/substrate interface allows preventing such a detrimental substrate influence. A low temperature deposition route of the TiO₂ film associated to the presence of a barrier layer yields best results in preventing iron contamination of the films.     

Fabrication of solid thin film electrolyte and LiCoO2 by aerosol flame pyrolysis deposition

Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO₂ cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO₂ and Li₂O–B₂O₃–P₂O₅ electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO₂ was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li₂O–P₂O₅–B₂O₃ glass film completely densified by the sintering at 700 °C for 1 h. After solid state sintering process the thicknesses were reduced to approximately 4 μm and 6 μm, respectively. The cathode and electrolyte layers were deposited by continuous deposition process and integrated into a layer by co-sintering. It was demonstrated that Aerosol flame deposition is one of the good candidates for the fabrication of thin film battery.     

Studies on Mo doped vanadium oxide film by pulsed RF magnetron sputtering

Molybdenum doped vanadium oxide film on quartz and silicon substrates are grown by pulsed RF magnetron sputtering method. Surface morphology, phase analysis and oxide states are investigated by field emission scanning electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy techniques, respectively. Crystalline nature of the film deposited on both quartz and silicon are depicted. The transmittance and reflectance spectra recorded for the entire solar region. Further, optical constants viz. optical band gap and refractive index of the deposited films are estimated. Wavelength dependent low reflectance characteristic is observed for the deposited film on silicon. IR emittance (ε_IR) and sheet resistance (R_s) of the film are also evaluated. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Multilayered Cu–Ti deposition on silicon substrates for chemiresistor applications

Abstract

On the perspective to develop CuO–TiO₂ MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO₂ in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication.     

Fluorescence biosensing micropatterned surfaces based on immobilized human acetylcholinesterase

Human acetylcholinesterase (AChE) is a widely studied target enzyme in drug discovery for Alzheimer’s disease (AD). In this paper we report evaluation of the optimum structure and chemistry of the supporting material for a new AChE-based fluorescence sensing surface. To achieve this objective, multilayered silicon wafers with spatially controlled geometry and chemical diversity were fabricated. Specifically, silicon wafers with silicon oxide patterns (SiO₂/Si wafers), platinum-coated silicon wafers with SiO₂ patterns (SiO₂/Pt/Ti/Si wafers), and Pt-coated wafers coated with different thicknesses of TiO₂ and SiO₂ (SiO₂/TiO₂/Pt/Ti/Si wafers) were labelled with the fluorescent conjugation agent HiLyte Fluor 555. Selection of a suitable material and the optimum pattern thickness required to maximize the fluorescence signal and maintain chemical stability was performed by confocal laser-scanning microscopy (CLSM). Results showed that the highest signal-to-background ratio was always obtained on wafers with 100 nm thick SiO₂ features. Hence, these wafers were selected for covalent binding of human AChE. Batch-wise kinetic studies revealed that enzyme activity was retained after immobilization. Combined use of atomic-force microscopy and CLSM revealed that AChE was homogeneously and selectively distributed on the SiO₂ microstructures at a suitable distance from the reflective surface. In the optimum design, efficient fluorescence emission was obtained from the AChE-based biosensing surface after labelling with propidium, a selective fluorescent probe of the peripheral binding site of AChE.

Structure and dielectric properties of HfO<Subscript>2</Subscript> films prepared by a sol–gel route

Mono- and multilayer HfO₂ sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO₂ grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO₂ layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.     

Nitridation of niobium films by rapid thermal processing: different behaviour of films on oxydized silicon and monocrystalline sapphire substrates

By electron beam evaporation and RF magnetron sputtering 500 nm thick niobium films were deposited on thermally oxidized Si-(100)-wafers and by RF magnetron sputtering on monocrystalline sapphire-(1-102)-wafers. Investigations by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the substrate used: films deposited on SiO₂ exhibited an even surface with small crystallites, films on sapphire showed parallel surface structures with relatively large and well-shaped crystallites pointing at regular crystal growth influenced by the substrate. These differences in film morphology were also reflected in different reflection intensities of the films in XRD patterns, indicating that the films deposited on sapphire were strongly textured. In a first set of experiments nitridation in molecular nitrogen and ammonia was investigated. In a second set of experiments, it was tried to form oxynitrides of niobium by annealing the nitrided films in molecular oxygen. Particularly by X-ray-diffraction the formation of different nitride and oxide phases in dependence of the reaction temperature was examined. Further, elemental depth profiles were recorded by secondary ion mass spectrometry (SIMS) to track the position of the phases formed in the film. The different substrates led to disparate film reactivities, resulting in different nitridation grades of the films at similar reaction temperatures. In general, larger crystallite sizes resulted in less chemical reactivity of the films: even after nitridation at 1000 °C metallic niobium was still present in films deposited on sapphire. However, no evidence was obtained for the formation of oxynitrides by the process sequence observed.     

Investigation of the surface topography for the characterization of microstructures of amorphous SiNx-coatings

SiN_x-coatings have been deposited by reactive magnetron sputtering. Gas pressure and film thickness have been varied. Scanning electron microsopic views of the cross sections show a columnar structure as well as polycrystalline films varying with deposition parameters. For quantitative comparisons of the film morphology an average column diameter has been used as a characteristic value obtained from TEM images. Similar results have been obtained by scanning tunneling microscope avoiding a large expenditure of preparation. Scanning tunneling microscopy is suitable for investigations of the fractal nature of top surface of thin films and to determine the height function of thin SiN_x-coatings on silicon wafers directly. Computer simulations of sputter processes allow to discuss the evolution of microstructures qualitatively.     

Influence of substrate nature on the growth of copper oxide thin films

Cu thin films were deposited on Si(111), glass, and quartz substrates by magnetron sputtering. X‐ray diffraction, SEM, and photoemission electron microscope studies were carried out to characterize the films. An influence of the nature of substrate on the Cu₂O and CuO phases formed was observed. Copper silicide formation in case of silicon substrates aided in formation of Cu₂O rather than CuO unlike glass and quartz substrates. Formation of nanocrystallites was observed by SEM and X‐ray diffraction. Copyright © 2016 John Wiley & Sons, Ltd.     

The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth (RE) doped Ba(Zr,Ti)O₃ (BZT) thin films were prepared by rf-magnetron sputtering from a Ba_0.90Ln_0.067Zr_0.09Ti_0.91O₃ (Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO₃, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0-3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO₃-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO₆-octahedra distortion (M=Ti, Zr) and, thereby, modifying the Ti-O binding length. Polarization-electric field hysteresis loops on Ag/RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.     

Effects of current densities on the formation of LiCoO<Subscript>2</Subscript>/graphite lithium ion battery

The activation characteristics and the effects of current densities on the formation of a separate LiCoO₂ and graphite electrode were investigated and the behavior also was compared with that of the full LiCoO₂/graphite batteries using various electrochemical techniques. The results showed that the formation current densities obviously influenced the electrochemical impedance spectrum of Li/graphite, LiCoO₂/Li, and LiCoO₂/graphite cells. The electrolyte was reduced on the surface of graphite anode between 2.5 and 3.6 V to form a preliminary solid electrolyte interphase (SEI) film of anode during the formation of the LiCoO₂/graphite batteries. The electrolyte was oxidized from 3.95 V vs Li⁺/Li on the surface of LiCoO₂ to form a SEI film of cathode. A highly conducting SEI film could be formed gradually on the surface of graphite anode, whereas the SEI film of LiCoO₂ cathode had high resistance. The LiCoO₂ cathode could be activated completely at the first cycle, while the activation of the graphite anode needed several cycles. The columbic efficiency of the first cycle increased, but that of the second decreased with the increase in the formation current of LiCoO₂/graphite batteries. The formation current influenced the cycling performance of batteries, especially the high-temperature cycling performance. Therefore, the batteries should be activated with proper current densities to ensure an excellent formation of SEI film on the anode surface.     

LiNbO3 and LiTaO3 thin films deposited by chemical and/or physical processes

Lithium niobate LiNbO₃ thin films were deposited onto silicon (111) Si and sapphire (001) AI₂O₃ single crystal substrates by the pyrosol and/or r.f. sputtering processes. A matrix of experiments was designed to determine the effects of several experimental parameters on the resulting film quality (stoichiometry, crystallization state) and properties. Under optimized conditions, requiring the combination of the two above-mentioned deposition techniques, <001 > oriented polycrystalline LiNbO₃ films were grown which exhibit homogeneous and columnar grain structures with the <c > -polar axis normal to the substrate surface.     

Substrate dependent structure and in-plane dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

The structure, microstructure and in-plane dielectric properties of Barium tin titanate Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single crystal substrates through sol–gel process were investigated. The films deposited on (100) LAO substrate exhibited a strong (100) preferred orientation while the film deposited on (100) MgO substrate showed polycrystalline structure. The in-plane ɛ–T measurements reveal that the films grown on (100) LAO substrate exhibited an obvious room-temperature ferroelectric state, while the film grown on MgO substrate showed paraelectric state in the temperature range of 10–130 °C. A high tunability of 52.11% was observed for the BTS films deposited on (100) LAO substrate at the frequency of 1 MHz with an applied electric field of 80 kV/cm, which is about two times larger than that of the BTS films deposited on (100) MgO substrate. The obvious differences in the dielectric properties could be attributed to the stress in the films, which come from lattice mismatch and difference in the thermal expansion coefficients between the film and substrates. This work clearly reveals the highly promising potential of BTS films for application in tunable devices.     

Effects of plasma treatments on correlation between chemical structures of DLC films and liquid crystal alignment

In an effort to obtain an improved liquid crystal (LC) alignment layer for liquid crystal display device applications, amorphous diamond‐like carbon thin films were deposited on ITO‐coated glass substrates by an rf magnetron sputtering technique at room temperature and then treated with plasma in various atmospheres. The polarized images and pretilt angles of the LC cells showed that LC alignment was enhanced by post‐plasma treatments of the films. In Raman and X‐ray photoelectron spectroscopy spectra of the films, an increase in the fraction of sp²‐bonding was observed after post‐plasma treatments of the films. In particular, H₂ plasma‐treated film had the largest fraction of sp²‐bonding at the film surface and showed much improved alignment capabilities. These results suggest that π‐bondings of the sp²‐structure at the surface rather than the bulk play an important role in LC alignment.     

Nitridation of Niobium Pentoxide Films in Ammonia by Rapid Thermal Processing

The feasibility of niobium oxynitride formation through nitridation of niobium pentoxide films in ammonia by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited by sputtering on Si(100) wafers covered by a 100 nm thick thermally grown SiO₂ layer. These as‐deposited films exhibited distinct texture effects. They were processed in three steps using an RTP system. The as‐deposited niobium films were first nitridated in an ammonia atmosphere at 1000 °C for 1 min and then oxidised in molecular oxygen at temperatures ranging from 400 to 600 °C. Those samples in which a single Nb₂O₅ phase was determined after oxidation were additionally nitridated in ammonia at 1000 °C for 1 min. Investigations show that surface roughness of the samples after oxidation of niobium films first nitridated in ammonia is lower than after direct oxidation of as‐deposited films in oxygen, although the niobium pentoxide phase formed after annealing was the same in both cases. We explain this result as being due to the large expansion of the niobium lattice during the direct oxidation of the niobium film in molecular oxygen and also to the high oxidation rate of the as‐deposited niobium film in oxygen. By incorporation of oxygen in the crystal lattice of niobium and rapid formation of niobium pentoxide, substantial intrinsic stress was built up in the film, frequently resulting in delamination of the film from the substrate. Nitrogen hinders the diffusion of oxygen in nitridated films, which leads to a decrease of the oxidation rate and thus slower formation of Nb₂O₅. Nitridation of the completely oxidised niobium films in ammonia leads to the formation of niobium oxynitride and niobium nitride phases.     

Preparation of cuprite (Cu2O), paramelaconite (Cu32+Cu21+O4) and tenorite (CuO) with magnetron sputtering ion plating: characterization by EPMA, XRD, HEED and SEM

Cu-O layers were deposited on Si-<100> wafers at 90°?C by means of reactive magnetron sputtering ion plating (R-MSIP). A Cu-target was sputtered in rf-mode by an oxygen/argon plasma, and the influence of the oxygen partial pressure on composition, structure, texture and morphology of the Cu-O layers was investigated. The analysis with EPMA, XRD, HEED and SEM yielded the following results: with an appropriate setting of the oxygen partial pressure, the oxygen content of the films could be controlled between 0 and 50 at-%. XRD bulk structure analysis shows changes in the crystal structure of the films with increasing oxygen content from the fcc structure of Cu, followed by the sc structure of Cu₂O (cuprite), the tetragonal structure of Cu₃ ²⁺Cu₂ ¹⁺O₄ (paramelaconite) to the monoclinic structure of CuO (tenorite). As revealed by HEED, the structure of the near-surface region of the latter two is the same as that of the bulk, whereas in the case of the films with fcc bulk structure, due to oxidation by air, the surface has the sc structure of Cu₂O, and in the case of the film with the sc structure, a monoclinic surface structure of CuO is observed. SEM analyses detected a disordered columnar growth of all Cu-O films.     

Investigation of the electron beam induced transformation of Cu3 N-films

Homogeneous films of metastable Cu₃N were deposited on Si-<100> wafers at 90°?C by means of reactive magnetron sputtering ion plating. Under electron bombardment with a focused beam at high current (> 700 nA, 15 keV) these films transform into metallic Cu and N₂. The depletion of N was measured quantitatively by EPMA. Structures with a lateral size of 2 μm consisting of metallic copper were written into the Cu₃N films. AFM surface scans revealed a vertical growth of the columnar grains of the Cu₃N film due to the electron bombardment.     

磁控溅射制备择优取向氮化铝薄膜

AlN薄膜;磁控反应溅射;磁控溅射制备择优取向氮化铝薄膜;晶面取向;X射线衍射