Growth of c‐axis‐oriented aluminum nitride thin films onto different substrates and buffer layers

The growth of aluminum nitride thin films onto various substrates (glass, flexible polyimide, or silicon) and onto different buffer layers (Au, Nb, Cu, Ag, Co, Fe, NiFe, or IrMn) is reported. Samples grown on IrMn, Co, NiFe, Nb, or Au show smooth surfaces. This same smooth quality is observed in samples grown at a lower 200 °C temperature directly on glass, Si, or flexible polyimide. In applications where thin and smooth piezoelectric films are necessary, c‐axis‐oriented AlN can be grown onto a wide range of different surfaces: conducting, insulating, ferromagnetic, antiferromagnetic, or flexible. Copyright © 2014 John Wiley & Sons, Ltd.     

V含量对ZnO薄膜结构及光学特性的影响

0引言氧化锌是一种六角纤锌矿结构的直接宽带隙半导体,其室温下禁带宽度为3.37eV。它具有多种优良的物理性能,在声表面波[1,2]、透明电极[3,4]、光电材料[5]、蓝光器件[6]等方面都有较大的应用潜力。氧化锌价格低廉,不仅能制成良好的半导体和压电薄膜,亦能够制成良好的透明导电薄膜。理论计算表明[7],氧化锌掺杂V、Cr、Fe、Co、N i元素能够产生自旋极化,形成高于室温的稀磁性透明半导体,是下一代微电子和光电子领域自旋电子学器件有重要价值的材料之一。根据理论计算,V掺杂的ZnO膜具有最高的居里温度。V yatkin实验小组[8]用钒离子注入…     

Magnetoelectric Bi3.25Nd0.75Ti3O12–La0.6Ca0.4MnO3 composite thin films derived by SOL–GEL method

Magnetoelectric (ME) Bi_3.25Nd_0.75Ti₃O₁₂–La_0.6Ca_0.4MnO₃ (BNT–LCMO) composite thin films were deposited on Pt/Ti/SiO₂/Si(100) substrates by a simple SOL–GEL method and spin-coating process with two different deposition sequences: BNT/LCMO/Pt/Ti/SiO₂/Si(BLP) and LCMO/BNT/Pt/Ti/SiO₂/Si(LBP). Our results show the composite thin films exhibit both good ferroelectric and magnetic properties, as well as a ME effect. BLP thin films have larger maximum ME voltage coefficient values than LBP structured thin films. The deposition sequence has a notable effect on the ferroelectric and magnetic properties and ME coupling behavior of the bi-layer thin films.     

Dielectric and optical properties of BaTiO<Subscript>3</Subscript> thin films prepared by low-temperature process

Barium titanate (BaTiO₃) thin films have been prepared by low temperature processing on Pt/Ti/SiO₂/Si substrates using sol-gel-hydrothermal (SGHT) technique, which combined the conventional sol-gel process and hydrothermal method. X-ray diffraction analysis showed that the barium titanate thin films are polycrystalline. As-reacted barium titanate films grown on Pt(111)/Ti/SiO₂/Si(100) substrates had a dielectric constant (ε) and loss tangent (tanδ) of 80 and 0.05 at 1 MHz, respectively. The optical constants including refractive index n, extinction coefficient k, and absorption coefficient α of the barium titanate thin films in the wavelength range of 2.5–12.6 μm were obtained by infrared spectroscopic ellipsometry.     

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

Large area single and bilayer graphene are grown on Pt/Ti/SiO₂ substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO₂ substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO₂ substrate at a low filament temperature. The approach paves a novel pathway towards the layer-controlled growth of graphene on Pt/Ti/SiO₂ substrates by HFCVD for frontier applications.     

Chemical solution processing and characterization of Ba(Zr,Ti)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> layered thin films

Ba(Zr,Ti)O₃/LaNiO₃ layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O₃ thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO _x /SiO₂/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O₃. Chemically derived LaNiO₃ thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O₃/LaNiO₃ layered thin films of single phase perovskite were fabricated on SiO₂/Si and fused silica substrates. The dielectric constant of a Ba(Zr_0.2Ti_0.8)O₃ thin film prepared at 700°C on a LaNiO₃/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr_0.2Ti_0.8)O₃ thin film on the LaNiO₃/fused silica substrate showed a smaller dielectric constant than the Ba(Zr_0.2Ti_0.8)O₃ thin film on Pt/TiO _x /SiO₂/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O₃/LaNiO₃ films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.     

Recent advances in characterization of CaCu3Ti4O12 thin films by spectroscopic ellipsometric metrology

CaCu3Ti4O12 (CCTO) thin films were successfully grown on LaAlO3(100) and Pt/TiO2/SiO2/Si(100) substrates by a novel MOCVD approach. Epitaxial CCTO(001) thin films have been obtained on LaAlO3(100) substrates, while polycrystalline CCTO films have been grown on Pt/TiO2/SiO2/Si(100) substrates. Surface morphology and grain size of the different nanostructured deposited films were examined by AFM, and spectroscopic ellipsometry has been used to investigate the electronic part of the dielectric constant (epsilon2). Looking at the epsilon2 curves, it can be seen that by increasing the film structural order, a greater dielectric response has been obtained. The measured dielectric properties accounted for the ratio between grain volumes and grain boundary areas, which is very different in the different structured films.     

Enhanced dielectric properties of LSCO-buffered Ba(Sn<Subscript>0.05</Subscript>Ti<Subscript>0.95</Subscript>)O<Subscript>3</Subscript> thin film prepared by sol–gel processing

Ferroelectric Ba(Sn_0.05Ti_0.95)O₃ (BTS) thin films were deposited onto Pt/Ti/SiO₂/Si substrates by sol–gel technique with a 100 nm thick LSCO buffer layer. The influence of buffer layer on the phase and microstructure of the thin films was examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current (DC) electric field. The results show that the LSCO buffer layer had a marked effect on the dielectric properties of the BTS films. The BTS thin films with LSCO buffer layer had enhanced dielectric properties.     

Crystallization of textured PbTiO3 films deposited from gels

Sol-gel processed PbTiO₃ thin films have been deposited by spin coating onto different subtrates; Si[111], Si/Al, Si/SiO₂/Cr/Pt, MgO[100], SrTiO₃[100] and sapphire. Interactions between the substrate and PbTiO₃ films after heat treatment have been studied by X-ray diffraction and Rutherford Back Scattering. When deposited onto sapphire and Si[111], PbTiO₃ films exhibit a preferred orientation with (101) perpendicular to the substrate. These films become oriented along (100) onto MgO and (001) onto SrTiO₃[100] substrates. A strong channelling effect is observed by the RBS technique when the film is oriented along the c axis on SrTiO₃[100] suggesting that these films are epitaxially grown. The diffusion of metal atoms during the thermal treatment gives rise to the formation of lead silicate on Si[111] substrates. As a result a pyrochlore phase is formed. Lead titanate films on Si/SiO₂/Cr/Pt and Si/Al substrates are polycrystalline and do not exhibit any texture.     

Optical and Electrical Properties of Ferroelectric SBN Thin Films Prepared by Sol-Gel Process

Strontium barium niobate thin films were prepared by sol-gel method on various substrates using an improved process, two-step heating process. The two-step heating process applies an additive heat-treatment before crystallization for enhancement of the densification and the nucleation of films. Also, highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. Their optical and electrical properties such as optical propagation loss, refractive index, P-E hysteresis, and dielectric constant, were characterized as a function of the film composition.     

Effect of adhesive and cohesive strength on the tribological behaviour of non‐reactively sputtered TiC thin films

Titanium carbide (TiC) thin films were deposited on D9 steel substrates at room temperature (RT), 200 °C and 400 °C. A compound TiC target was sputtered to deposit films in a non‐reactive argon atmosphere. As‐deposited films were characterised for structural, chemical and mechanical properties. Nanoindentation and scratch tests were performed to evaluate the cohesive and adhesive strength of the films, respectively. Tribological properties of the films were investigated using a tribometer. An increase in nano‐hardness from 7.2 to 10.5 GPa was observed as deposition temperature was increased. The films deposited at RT and 200 °C showed poor adhesion leading to the inferior tribological performance. In contrast, films deposited at 400 °C showed better adhesion which improved the wear resistance. Tribological behaviour of TiC thin films was correlated with contact deformation modes of coatings. These modes revealed significant role of adhesive and cohesive strength associated with the coatings. Copyright © 2009 John Wiley & Sons, Ltd.     

From Au to Pt via surface limited redox replacement of Pb UPD in one-cell configuration

This work is aimed at developing a protocol based on surface limited redox replacement (SLRR) of underpotentially deposited (UPD) Pb layers for the growth of epitaxial and continuous Pt thin films on polycrystalline and single crystalline Au surfaces. Different from previously reported papers using SLRR in multiple immersion or flow cell setups, this work explores the one-cell configuration setup as an alternative to improve the efficiency and quality of the growth. Open circuit chronopotentiometry and quartz-crystal microbalance experiments demonstrate steady displacement kinetics and a yield that is higher than the stoichiometric Pt(II)-Pb exchange ratio (1:1). This high yield is attributed to oxidative adsorption of OH(ad) taking place on Pt along with the displacement process. Also, ex situ scanning tunneling microscopy surface characterization reveals after the first replacement event the formation of a dense Pt cluster network that homogenously covers the Au surface. The Pt films grow homogenously with no significant changes in the cluster distribution and surface roughness observed up to 10 successive replacement events. X-ray diffraction analysis shows distinct (111) crystallographic orientation of thicker Pt films deposited on (111) textured Au thin films. Coarse energy dispersive spectroscopy measurements and finer X-ray photoelectron spectroscopy suggest at least 4 atom % Pb incorporating into the Pt layer compared to 13 atom % alloyed Cu when the growth is carried out by SLRR of Cu UPD.     

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     

Influence of Substrate Steps on the Catalytic Properties of Pt Layers: The Ethanol Electrooxidation Reaction

The ethanol oxidation reaction (EOR) is investigated on Pt/Au(hkl) electrodes. The Au(hkl) single crystals used belong to the [n(111)x(110)] family of planes. Pt is deposited following the galvanic exchange of a previously deposited Cu monolayer using a Pt²⁺ solution. Deposition is not epitaxial and the defects on the underlying Au(hkl) substrates are partially transferred to the Pt films. Moreover, an additional (100)‐step‐like defect is formed, probably as a result of the strain resulting from the Pt and Au lattice mismatch. Regarding the EOR, both vicinal Pt/Au(hkl) surfaces exhibit a behavior that differs from that expected for stepped Pt; for instance, the smaller the step density on the underlying Au substrate, the greater the ability to break the C?C bond in the ethanol molecule, as determined by in situ Fourier transform infrared spectroscopy measurements. Also, we found that the acetic acid production is favored as the terrace width decreases, thus reflecting the inefficiency of the surface array to cleave the ethanol molecule.     

Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

The fabrication of MFI zeolite films with particular b‐axis orientation is especially fascinating. Unlike the conventional alkaline or hydrofluoric acid (HF) assisted neutral synthesis route, here we develop a novel neutral synthesis solution system of TPABr/fumed silica/H₂O without the use of HF and successfully synthesize highly b‐oriented MFI zeolite films on glass‐plate substrates by secondary growth. The localized weak alkaline environment created by the dissolved Na₂O species from the substrate is identified as the key factor for the depolymerization of fumed silica and subsequently the in‐plane growth of zeolite seed layers. Continuous b‐oriented MFI films can also be synthesized on other substrates in the presence of a glass plate or a trace amount of NaOH, which making our neutral synthesis route promising for the direct synthesis of MFI zeolite films and membranes on various substrates.     

Microstructure and ferroelectric properties of r.f. magnetron sputtering derived PZT thin films deposited on interlayer (PbO/TiO2)

Lead zirconate titanate (PZT) thin films were deposited on Pt/Ti/SiO₂/Si and interlayer/Pt/Ti/SiO₂/Si substrate by radio frequency (r.f.) magnetron sputtering with a Pb_1.1Zr_0.53Ti_0.47O₃ target. The crystallization of the PZT thin films was formed only by substrate temperature. When interlayer (PbO/TiO₂) was inserted between the PZT thin film and the Pt electrode, the grain growth and processing temperature of the PZT thin films were considerably improved. Compared to PZT/Pt structure, the dielectric constant and polarization properties of the PZT/interlayer/Pt structure were fairly improved. In particular, PZT/interlayer/Pt at the substrate temperature of 400 °C showed prevalent ferroelectric properties (_r=475.97, tanδ=0.0591, P_r=23 μC/cm²). As a result of an X-ray photoelectron spectroscopy (XPS) depth-profile analysis, it was found that PZT/interlayer/Pt deposited only by substrate temperature without the post-annealing process via r.f. magnetron sputtering method remained independent of each other regardless of substrate temperatures.     

Preparation of Ba(Ti,Sn)O<Subscript>3</Subscript> thin films by PVP-assisted sol–gel method and their dielectric properties

Ba(Ti_1−x Sn _x )O₃ (x = 0.10 or 0.15) thin films were deposited on Si(100) and Pt(111)/TiO _x /SiO₂/Si(100) substrates via sol–gel spin-coating. Crack-free thin films could be obtained by single-step deposition, where the thickness was about 0.46 and 0.29 μm at 1000 and 2000 rpm, respectively. Circular delaminated parts 100 μm in diameter, however, tended to appear in thicker films deposited at 1000 rpm. On both kinds of substrates, the films were crystallized between 500 and 600 °C, where the perovskite phase emerged as the primary phase, and the formation of single-phase perovskite was basically achieved between 700–800 °C. The films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates, however, tended to have small SnO₂ and BaCO₃ diffraction peaks, which decreased with increasing spinning rate. The dielectric properties were evaluated on the films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates at 2000 rpm. The films prepared by single-step depositions had dielectric constants of 350 and 230, and dielectric loss of 0.30 and 0.10 at x = 0.1 and 0.15, respectively. The films prepared by two time deposition had dielectric constants of 450 and 250, and dielectric loss of 0.21 and 0.19 at x = 0.10 and 0.15, respectively.     

(110)‐Oriented ZIF‐8 Thin Films on ITO with Controllable Thickness

(110)‐oriented zeolitic imidazolate framework (ZIF)‐8 thin films with controllable thickness are successfully deposited on indium tin oxide (ITO) electrodes at room temperature. The method applied uses 3‐aminopropyltriethoxysilane (APTES) in the form of self‐assembled monolayers (SAMs), followed by a subsequent adoption of the layer‐by‐layer (LBL) method. The crystallographic preferential orientation (CPO) index shows that the ZIF‐8 thin films are (110)‐oriented. A possible mechanism for the growth of the (110)‐oriented ZIF‐8 thin films on 3‐aminopropyltriethoxysilane modified ITO is proposed. The observed cross‐sectional scanning electron microscopy (SEM) images and photoluminescent (PL) spectra of the ZIF‐8 thin films indicate that the thickness of the ZIF‐8 layers is proportional to the number of growth cycles. The extension of such a SAM method for the fabrication of ZIF‐8 thin films as described herein should be applicable in other ZIF materials, and the as‐prepared ZIF‐8 thin films on ITO may be explored for photoelectrochemical applications.     

Structure evolution of hydrogenated carbon films from amorphous carbon to fullerene‐like nanostructure

A–C:H (hydrogenated amorphous carbon) films were deposited by pulsed direct‐current (d.c.) plasma enhanced chemical vapor deposition on silicon substrates. This study investigated the structural and mechanical evolution of the as‐deposited films with fullerene‐like nanostructure. The results showed that pulsed d.c. negative bias (?500 ~ ?1000 V) signally influenced the growth rate, hardness, surface roughness, sp³ content, and friction behavior of the films. As the pulsed d.c. negative bias voltage increased, the sp³ content, surface roughness, hydrogen content and the friction coefficient of the films decreased; however, the growth rate and the hardness increased. The films deposited at ?1000 V with fullerene‐like microstructure display a nanohardness of about 19.7 GPa and the smallest friction coefficient (~0.06). The evolution on mechanical and structural properties of the films are explained by the a–C:H growth mechanism based on the interaction on plasma‐surface interface and the subsurface reactions in the film. Copyright © 2014 John Wiley & Sons, Ltd.