Adsorption ability comparison of plasma proteins on amorphous carbon surface

To understand why amorphous carbon (a-C:H) film shows antithrombogenicity, an adsorption ability of plasma proteins on a-C:H surface was investigated. Protein adsorption is the initial process of clot formation. The protein adsorption ability on a-C:H film surface was compared by the detection using the surface plasmon resonance (SPR) phenomenon to estimate the protein adsorption. The protein adsorption abilities of a fibrinogen (Fib) and a human γ-globulin (HGG) were estimated by the SPR method using a multilayer structure of a-C:H/Au/Cr/glass. Although the adsorption of HGG for a-C:H was saturated at 32 μM in HGG concentration, the adsorption of Fib was not saturated under the detection limit of this method. These results indicated that the adsorption ability to the a-C:H film surface of Fib was higher than HGG.     

Effect of surface on phase modulation of light in a nematic layer

The nanorelief of orienting surfaces in a nematic layer is studied experimentally. The initial inclination angle of the director and the phase retardation of light in the crystal are determined, and the director reorientation dynamics in the crystal under SB deformation in an electric field is analyzed. It is shown that a thin layer of amorphous hydrogenated carbon (a-C: H) deposited on a GeO monoxide layer with an anisotropic nanorelief produced by the inclined deposition method smoothens the surface topography without changing the surface structure. Modification of the structure and physicochemical properties of the GeO surface alters the conditions of the anisotropic-elastic interaction at the interface with the liquid crystal, as evidenced by an increase in the S-effect threshold and a decrease in the initial inclination of the director from 22° (on the GeO surface) to 0–6°. Strong influence of the surface nanostructure on the dynamics of the director reorientation in the electric field and on the phase modulation of light is experimentally demonstrated. It is shown that the phase retardation of light in the GeO layer covered by an a-C: H film is twice as large as in the layer of the same thickness with a virgin surface.     

Investigation of TiC-C coatings by X-ray photoelectron spectroscopy

Titanium carbide-based coatings deposited by arc-technology in C₂H₂/Ar atmosphere were studied by X-ray photoelectron spectroscopy. It was found that, in addition to the cubic phase of TiC _x O _y oxycarbide, the films contain carbon in the amorphous, presumably graphite-like state. In carbon C1s spectra, bands at 282.0, 284.4, and 286.0 eV correspond to the TiC _x state, amorphous carbon, and C-C bonds, respectively. The maximum at 283.0 eV was interpreted as the C state in titanium carbide nanoforms, i.e., Ti₁₄C₁₃ clusters or Ti₈C₁₄ carbohedra. The phase ratio was varied by coating deposition conditions, i.e., TiC/a-C deposition by Ti cathode sputtering in C₂H₂/Ar, and composite Ti/C target sputtering in Ar and C₂H₂/Ar. When using the Ti cathode and C₂H₂/Ar gas mixture, the ratio of carbide and amorphous a-C phases was estimated as 1: 1; the surface layer ～15 nm thick was enriched with amorphous carbon. It was assumed that TiC/a-C composite coatings with an additional a-C film on the surface would have an increased stability in reaction media and good biocompatibility.     

Structural and magnetic properties of RF sputtered FePt/Fe multilayers

Series of [FePt(4min)/Fe(t_Fe)]₁₀ multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]_n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]_n multilayers decrease with Fe layer deposition time, and the energy product (BH)_max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase.     

Preparation and structural properties of YBCO films grown on GaN/c-sapphire hexagonal substrate

Epitaxial YBCO thin films have been grown on hexagonal GaN/c-sapphire substrates using DC magnetron sputtering and pulsed laser deposition. An MgO buffer layer has been inserted between the substrate and the YBCO film as a diffusion barrier. X-ray diffraction analysis indicates a c-axis oriented growth of the YBCO films. Φ-scan shows surprisingly twelve maxima. Transmission electron microscopy analyses confirm an epitaxial growth of the YBCO blocks with a superposition of three a-b YBCO planes rotated by 120° to each other. Auger electron spectroscopy and X-ray photoelectron spectroscopy reveal no surface contamination with Ga even if a maximum substrate temperature of 700 °C is applied.     

a-Si: H/a-C: H amorphous semiconductor superlattices

A new type of amorphous semiconductor superlattices consisting of alternating layers of a-Si: H and a-C: H has been synthesized by r.f. plasma deposition in a single-chamber plasma reactor. The existence of well-defined layers are demonstrated by TEM studies and the in-depth profiles of the compositions obtained by Auger electron spectroscopy. In some cases, growth imperfections can be observed in the thinner layers. The changes in optical absorption gap of a-Si: H as a function of its layer thickness in the superlattices are interpreted as quantum size effects.     

Annealing effects on the bonding structures, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films

The effects of thermal annealing in vacuum on the bonding structures, optical and mechanical properties for germanium carbide (Ge_1−xC_x) thin films, deposited by radio frequency (RF) reactive sputtering of pure Ge(1 1 1) target in a CH₄/Ar mixture discharge, are investigated. We find that there are no significant changes in the bonding structure of the films annealed below 300 °C. The fraction of Ge-H bonds for the film annealed at temperatures (T_a) above 300 °C decreases, whereas that of C-H bonds show a decrease only when T_a exceeds 400 °C. The out-diffusion of hydrogen promotes the formation of Ge-C bonds at T_a above 400 °C and thus leads to a substantial increase in the compressive stress and hardness for the film. The refractive indices and optical gaps for Ge_1−xC_x films are almost constant against T_a, which can be ascribed to the unchanged ratios of Ge/C and sp²-C/sp³-C concentrations. Furthermore, we also find that the excellent optical transmission for an antireflection Ge_1−xC_x double-layer film on ZnS substrate is still maintained after annealing at 700 °C.     

Influence of substrate crystallography on the room temperature synthesis of AlN thin films by reactive sputtering

A pulsed DC reactive ion beam sputtering system has been used to synthesize aluminium nitride (AlN) thin films at room temperature by reactive sputtering. After systematic study of the processing variables, high-quality polycrystalline films with preferred c-axis orientation have been grown successfully on silicon and Au/Si substrates with an Al target under a N₂/(N₂ + Ar) gas flow ratio of 55%, 2 mTorr processing pressure and keeping the temperature of the substrate holder at room temperature. The crystalline quality of the AlN layer as well as the influence of the substrate crystallography on the AlN orientation has been characterized by high-resolution X-ray diffraction (HR-XRD). Best ω-FWHM (Full Width at Half Maximum) values of the (0 0 0 2) reflection rocking curve in the 1 μm thick AlN layers are 1.3°. Atomic Force Microscopy (AFM) measurements have been used to study the surface morphology of the AlN layer and Transmission Electron Microscopy (TEM) measurements to investigate the AlN/substrate interaction. AlN grew off-axis from the Si substrate but on-axis to the surface normal. When the AlN thin film is deposited on top of an Au layer, it grows along the [0 0 0 1] direction but showing a two-domain structure with two in-plane orientations rotated 30° between them.     

Very high coercivities of top-layer diffusion Au/FePt thin films

The Au/FePt samples were prepared by depositing a gold cap layer at room temperature onto a fully ordered FePt layer, followed by an annealing at 800 °C for the purpose of interlayer diffusion. After the deposition of the gold layer and the high-temperature annealing, the gold atoms do not dissolve into the FePt Ll₀ lattice. Compared with the continuous FePt film, the TEM photos of the bilayer Au(60 nm)/FePt(60 nm) show a granular structure with FePt particles embedded in Au matrix. The coercivity of Au(60 nm)/FePt(60 nm) sample is 23.5 kOe, which is 85% larger than that of the FePt film without Au top layer. The enhancement in coercivity can be attributed to the formation of isolated structure of FePt ordered phase.     

Influence of the active layer thickness on the electrical properties of ZnO thin film transistors fabricated by radio frequency magnetron sputtering

We report on the electrical properties of bottom-gate ZnO thin film transistors (TFTs) with different active layer thicknesses. The ZnO active layer films with thickness varied from 20 to 100 nm were deposited by radio frequency (rf) magnetron sputtering on SiO₂/p-Si substrate and annealed at a high temperature of 950 °C. The transistor with 40 nm thick ZnO exhibited the best performance, with a field effect mobility of 27.5 cm²/V s, a threshold voltage of −2.4 V and an on/off ratio of 7×10³.     

Performances of different metals in optical fibre-based surface plasmon resonance sensor

The capability of various metals used in optical fibre-based surface plasmon resonance (SPR) sensing is studied theoretically. Four metals, gold (Au), silver (Ag), copper (Cu) and aluminium (Al) are considered for the present study. The performance of the optical fibre-based SPR sensor with four different metals is obtained numerically and compared in detail. The performance of optical fibre-based SPR sensor has been analysed in terms of sensitivity, signal-to-noise (SNR) ratio and quality parameter. It is found that the performance of optical fibre-based SPR sensor with Au metal is better than that of the other three metals. The sensitivity of the optical fibre-based SPR sensor with 50 nm thick and 10 mm long Au metal film of exposed sensing region is 2.373 μm/RIU with good linearity, SNR is 0.724 and quality parameter is 48.281 RIU^− 1. The thickness of the metal film and the length of the exposed sensing region of the optical fibre-based SPR sensor for each metal are also optimized.     

Soft X-ray photoelectron spectroscopic investigation of Au-deposited amorphous In–Ga–Zn–O thin-film surface

Thin Au layers (0.04 nm, 0.06 nm, 0.08 nm, 0.21 nm) were deposited on an amorphous In–Ga–Zn–O (a-IGZO) thin-film surface by thermal evaporation in an ultrahigh vacuum. The chemical-state changes of the Au layer and the a-IGZO surface were investigated by measuring the Au 4f, O 1s, In 3d, Ga 3d and Zn 3d peaks as well as the valence bands by soft X-ray photoelectron spectroscopy. Upon initial deposition, an oxidized Au component formed, whereas a metallic Au component was dominant. At the later deposition stages, the metallic Au component dominated the spectral features. When the Au thickness was thicker than 0.08 nm, a split Au 5d feature was apparent. And as the Au thickness continued to increase, In 3d showed a strong lower-binding-energy (lower-BE) component; the Ga 3d and Zn 3d also showed lower-BE components, but of much reduced intensities relative to In 3d. These results seem to imply that compared with other elements, Au atoms prefer to occupy oxygen vacancies and strongly interact with In atoms.     

The effect of alloying on the structure and peculiarities of tribological behavior of vacuum-deposited diamond-like coatings

In this work, we report the results of a study of the atomic and crystalline structures, phase and chemical compositions and tribological properties of DLC coatings deposited by plasma-assisted (PA) CVD (a-C:H:Si and a-C:H:Si:Mo) and magnetron reactive sputtering (a-C:H:Cr). The a-C:H:Si:Mo coatings revealed the formation of ultra-dispersed inclusions of either molybdenum carbides or silicides, whereas no such inclusions were found in the a-C:H:Si compound. The a-C:H:Cr coatings that were deposited in an acetylene–nitrogen gas mixture exhibited a nanocomposite structure composed of chromium, its carbide and nitride phases. The tribological tests showed that the DLC coatings with silicon and silicon–molybdenum have a high friction coefficient and a low working performance, while the chromium-containing coatings have high levels of their mechanical and tribological characteristics, making them promising materials for operation under high contact pressures.     

Low temperature deposition of transparent conducting ITO/Au/ITO films by reactive magnetron sputtering

Transparent conducting indium tin oxide/Au/indium tin oxide (ITO) multilayered films were deposited on unheated polycarbonate substrates by magnetron sputtering. The thickness of the Au intermediated film varied from 5 to 20 nm. Changes in the microstructure, surface roughness and optoelectrical properties of the ITO/Au/ITO films were investigated with respect to the thickness of the Au intermediated layer. X-ray diffraction measurements of ITO single layer films did not show characteristic diffraction peaks, while ITO/Au/ITO films showed an In₂O₃ (2 2 2) characteristic diffraction peak. The optoelectrical properties of the films were also dependent on the presence and thickness of the Au thin film. The ITO 50 nm/Au 10 nm/ITO 40 nm films had a sheet resistance of 5.6 Ω/□ and an average optical transmittance of 72% in the visible wavelength range of 400-700 nm. Consequently, the crystallinity, which affects the optoelectrical properties of ITO films, can be enhanced with Au intermediated films.     

The effect of incident angle on the C60 bombardment of molecular solids

The effect of incident angle on the quality of SIMS molecular depth profiling using C₆₀⁺ was investigated. Cholesterol films of ∼300 nm thickness on Si were employed as a model and were eroded using 40 keV C₆₀⁺ at an incident angle of 40° and 73° with respect to the surface normal. The erosion process was characterized by determining at each angle the relative amount of chemical damage, the total sputtering yield of cholesterol molecules, and the interface width between the film and the Si substrate. The results show that there is less molecule damage at an angle of incidence of 73° and that the total sputtering yield is largest at an angle of incidence of 40°. The measurements suggest reduced damage is not necessarily dependent upon enhanced yields and that depositing the incident energy nearer the surface by using glancing angles is most important. The interface width parameter supports this idea by indicating that at the 73° incident angle, C₆₀⁺ produces a smaller altered layer depth. Overall, the results show that 73° incidence is the better angle for molecular depth profiling using 40 keV C₆₀⁺.     

Structure and magnetic properties of magnetron-sputtered [(Fe/Pt/Fe)/Au]n multilayer films

Using dc magnetron sputtering, Fe/Pt/Au multilayer films were prepared, and the effects of Au layer thickness and annealing temperature on structure and magnetic properties of the Fe/Pt/Au multilayer films were investigated. The as-deposited Fe/Pt/Au multilayer films have good periodic structure with composition modulation along the growth direction. The stress stored in the as-deposited films promoted the ordering of the films annealed at 400 °C. When the films were annealed at 500 °C, the thicker Au layer could restrain the order-disorder transformation region volume and lead to the decrease of the ordered volume fraction with Au layer thickness increasing.     

Nanoroughness control of Al-Doped ZnO for high efficiency Si thin-film solar cells

The Al-doped ZnO (ZnO:Al) front transparent conducting oxide (TCO) for high efficiency Si thin-film solar cell has been developed using RF magnetron sputtering deposition and chemical wet etching. Microscopic surface roughness of the as-deposited ZnO:Al film estimated by spectroscopic ellipsometry is closely related to the compactness of the TCO film, and shown to be a straightforward and powerful tool to optimize the deposition conditions for the proper post-etched surface morphology. Wet-etching time is adjusted to form the U-shaped craters on the surface of the ZnO:Al film without sharp etch pits that can cause the crack-like defects in the overgrown microcrystalline Si-absorbing layers, and deteriorate the V_oc and FF of the Si thin-film solar cells. That is to say, the nanoroughness control of the as-deposited TCO film with proper chemical etching is the key optimization factor for the efficiency of the solar cell. The a-Si:H/a-SiGe:H/μc-Si:H triple junction Si thin-film solar cells grown on the optimized ZnO:Al front TCO with anti-reflection coatings show higher than 14% conversion efficiency.     

Effects of post-thermal annealing temperature on the optical and structural properties of gold particles on silicon suboxide films

In this work, silicon suboxide (SiO_x) thin films were deposited using a RF magnetron sputtering system. A thin layer of gold (Au) with a thickness of about 10 nm was sputtered onto the surface of the deposited SiO_x films prior to the thermal annealing process at 400 °C, 600 °C, 800 °C and 1000 °C. The optical and structural properties of the samples were studied using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and optical transmission and reflection spectroscopy. SEM analyses demonstrated that the samples annealed at different temperatures produced different Au particle sizes and shapes. SiO_x nanowires were found in the sample annealed at 1000 °C. Au particles induce the crystallinity of SiO_x thin films in the post-thermal annealing process at different temperatures. These annealed samples produced silicon nanocrystallites with sizes of less than 4 nm, and the Au nanocrystallite sizes were in the range of 7-23 nm. With increased annealing temperature, the bond angle of the Si-O bond increased and the optical energy gap of the thin films decreased. The appearance of broad surface plasmon resonance absorption peaks in the region of 590-740 nm was observed due to the inclusion of Au particles in the samples. The results show that the position and intensity of the surface plasmon resonance peaks can be greatly influenced by the size, shape and distribution of Au particles.     

Effects of interface on the dielectric properties of Ba0.6Sr0.4TiO3 thin film capacitors

Ba_0.6Sr_0.4TiO₃ thin films were deposited on Pt/SiO₂/Si substrate by radio frequency magnetron sputtering. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is about 7-8 nm thickness. It is found that the transition layer was diminished to about 2-3 nm thickness by reducing the initial RF sputtering power. X-ray photoelectron spectroscopy (XPS) depth profiles show that high Ti atomic concentration results in a thick interfacial transition layer. Moreover, the symmetry ν of ?_r-V curve of BST thin film is enhanced from 52.37 to 95.98%. Meanwhile, the tunability, difference of negative and positive remanent polarization (P_r), and that of coercive field (E_C) are remarkably improved.     

Enhancement of L10 ordered FePt by Pt buffer layer

L₁₀-ordered FePt thin films prepared by molecular-beam epitaxy on MgO (0 0 1) substrate at 320 °C with different thickness of Pt buffer layer have been investigated. The out-of-plane coercivity increases with increasing thickness of Pt buffer. The maximum values of the long-range order parameter and uniaxial magnetic anisotropy energy are 0.72 and 1.78×10⁷ erg/cm³, respectively, for films with 12 nm thick Pt buffer layer, where the c/a ratio (0.976) shows the minimum value. The reason for the enhancement in ordering is due to the proper lattice strains Pt buffer bestows on FePt layer, these strains are equal to the contraction in lattice parameter c and the expansion in a. Studies of angular-dependent coercivity revealed that the magnetization reversal behaviour shifts from a domain-wall motion dominated case towards a near rotational mode with increasing thickness of Pt buffer layer.