Effects Of Substrate Treatment Research Articles

The Effect of Substrate Treatment on the Properties of TiAlSiYN/CrN Nanocomposite Coatings

Nanocomposite multilayer coatings are of large interest to the engineering industry because of their functional properties. Titanium nitride-based multilayer structures are very effective as protective layers for mechanical instrumentation. In this paper, selected mechanical and tribological properties for cutting machinery of TiASiYN/CrN system were considered. The columnar (111) coherent growth of the TiAlSiYN on the CrN without layers mixing has been identified via TEM and XRD. But crystal orientation, crystallite size and residual strain were varied depending on Cr interlayer and pre-treatment. Analysis of the experimental data manifests a decomposed Ti0.25Al0.75N phase stabilized by CrN that was suggested as one of the main factors responsible for superhard phase formation. Wear and scratch experiments highlighted improved wear, crack resistance and adhesion to the substrate (Lc5 = 150.1 N) in the sample prepared in Cr plasma without Cr interlayer. Cutting analysis proved the exceptional durability of inserts after coating deposition. Fracture mechanisms were found out to carry an adhesive character over the cohesive.

Influence of electrochemical deposition parameters on morphological properties of ZnO on Si (100)

In this study, ZnO layer was deposited on Si (100) by electrochemical deposition (ECD) technique. Mixture of zinc chloride (ZnCl2) and potassium chloride (KCl) at different volume ratio was used as the electrolyte. The current density was fixed at 10 mA cm−2 with deposition time of 50 and 30 min. The effect of substrate treatment has also been observed to improve the adhesion of the deposited layer. The morphology of the ZnO layer was analyzed using field emission scanning electron microscopy (FESEM), and variable pressure scanning electron microscopy (VPSEM) equipped with energy dispersive x-ray (EDX) module. Four types of ZnO structure had been obtained; needle, flake, coral and pillar-like structures at different deposition conditions. These structures were obtained by changing several parameters such as substrate doping and chloride medium of electrolyte. It was found that the flake-size become smaller as the amount of Chloride ion (Cl−) in electrolyte increased. In addition, substrate type also found to affect the deposition process. As indicated by the EDX spectra, the ZnO is managed to fully cover the target area of deposition for the n-type Si substrate but a bit poor on p-type Si substrate. The targeted EDX ratio of Zn:O is 1:1, which indicates balance stoichiometry of ZnO. However, the best EDX ratio of Zn:O found in this study was only 1.4:1 which was achieved from deposition on p-type Si substrate with no post-annealing applied. The thickness of deposited ZnO was found to decrease with decreasing deposition time. The average thickness was more than 150 μm for 50 min deposition while 30 min deposition yielded thickness less than 100 μm. It is clearly shown that parameters such as time, electrolyte volume ratio and substrate doping have influence on the morphology and thickness of the deposited ZnO on Si (100) by ECD process.

Growth of Ni and Ni-Cr alloy thin films on MgO(001): Effect of alloy composition on surface morphology

The effects of substrate treatment, growth temperature, and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy and atomic force microscopy. We demonstrate that a combination of acid-etched substrates and high temperature deposition (400 °C) will result in smooth films with well-defined terraces (up to 30 nm wide) that are suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on the phosphoric acid-treated substrates present reduced nucleation density during the initial stages of film growth which results in long and wide terraces. Due to the ≈16% lattice mismatch in the Ni(001)/MgO(001) system, film growth at 400 °C yields discontinuous films and a two-step growth process is necessary to obtain a continuous layer. Ni films are deposited at 100 °C and subjected to a post-growth annealing at 300 °C for 2 h to obtain a smoother surface. The addition of just 5 wt. % Cr drastically changes the film growth processes and yields continuous films at 400 °C without de-wetting in contrast to pure Ni films. With increasing Cr content, the films become progressively smoother with wider terraces. Ni5Cr alloy thin films have an rms surface roughness of 3.63 ± 0.75 nm, while Ni33Cr thin film is smoother with an rms roughness of only 0.29 ± 0.13 nm. The changes in film growth initiated by alloying with Cr are due to changes in the interfacial chemistry which favorably alters the initial adsorption of the metal atoms on MgO surface and suggests a reduction of the Ehrlich-Schwoebel barrier. The growth of smooth Ni-Cr thin films with a well-defined surface structure opens up a new pathway for a wide range of surface science studies related to alloy performance.

Hydrogen-free synthesis of few-layer graphene film on different substrates by plasma enhanced chemical vapor deposition

Few layer graphene were synthesized on different substrates by radio frequency plasma enhanced chemical vapor deposition in the absence of any catalyst under 300 °C. Raman spectral characterization verified the bonding form of the films to be mostly sp2. The principal chemical mechanisms relevant to the growth of graphene from gaseous hydrogen and hydrocarbon species are presented. The kinetic processes during the activation and transport of the gaseous species are described. Furthermore, the effects of substrate treatment in the course of growth are analyzed. We demonstrated that the differences in growth conditions reveal different mechanisms of growth of graphene by chemical vapor deposition. Nevertheless, the overall thermodynamic and dynamics principles are identical. It is reasonable to obtain few layer graphene films by using methane alone without H2 as source gas. Moreover, graphene films of various feature and structures for different purposes can be achieved controllably by modulating the kinetic factors. Also, these graphene films can be used in many photoelectric devices such as solar cells and photodetectors.

三点曲げ試験における TiN コーティング膜の破壊挙動への基材処理の影響

三点曲げ試験における TiN コーティング膜の破壊挙動への基材処理の影響

Electrochemical design of ZnO hierarchical structures for dye-sensitized solar cells

ZnO single-crystalline nanowires (NWs) are highly relevant 1D-nanostructures for efficient charge collection in dye sensitized solar cells (DSSCs). In a first part of the paper, ZnO-NWs have been grown by electrochemistry on various fluorine-doped transparent oxide (FTO) coated glass substrates. The effects of substrate treatments and of the presence of an underlayer of TiO2 or ZnO on the cell performance are reported. In particular, we show that the presence of a TiO2 underlayer gives rise to a dense array of ZnO-NWs with a high aspect ratio (>30) and to the cells with the best performances. However, the roughness of the NW arrayed films were not sufficient for the efficient harvesting of sunlight and low fill factors were found. In a second step, hierarchical structures have been designed by growing electrochemically a secondary nanoporous epitaxial ZnO phase on the wire surface. We have found that the cell performances were significantly improved in that case due to a much larger specific surface area and to a much better fill factor. We also show that the cell efficiencies of hierarchical structures did not follow the performances of the starting ZnO-NWs. The volume occupied by the second phase, its thickness and its connection to the wires are important parameters for cell optimizing.

Semiconductor nanorod layers aligned through mechanical rubbing

AbstractLarge‐scale lateral alignment of nanorods (NRs) is of interest for manifestation of their anistropic properties including polarized emission and directional electrical transport. This study investigates the utility of mechanical rubbing for macroscopic scale alignment of colloidal semiconductor NRs. CdSe/CdS seeded‐rods, exhibiting linearly polarized emission, are aligned by mechanical rubbing of a spin‐coated glass substrate. The dragging force exerted by the rubbing fibers results in deflection and reorientation of the NRs along the rubbing direction. The rubbed samples were characterized by various methods including absorption, polarized emission, optical fluorescence microscopy, atomic force microscopy, and ultra‐high resolution scanning electron microscopy. The emission polarization contrast ratio (CR), defined as the ratio between emission intensities parallel and perpendicular to the rubbing direction, was used to characterize the rods alignment. The effects of substrate treatments on the CR were studied, showing that partially hydrophobic surface provides optimal conditions for alignment. Excess organic ligands added to the deposited NR solution strongly affect the extent of alignment. This was studied for a series of NR samples of different dimensions and an optimal additive ratio of ∼3 ligand molecules per 1 nm2 NR surface area was found to yield the highest CR. Average CR values of 3.5 were detected over the entire 6 cm2 substrate area, with local values exceeding 4.5. While samples of rubbed spherical quantum dots and spin‐coated films of NRs show no emission polarization, the emission intensity from rubbed NR samples is polarized obeying Malus' law (wherein, the intensity is proportional to cos2(θ)). Mechanical rubbing, well known for its use in LC devices, may be considered as a method for large‐scale alignment of NRs on substrates.

Effects of substrate treatment on the initial growth mode of indium-tin-oxide films

The initial growth mode of indium tin oxide (ITO) on polycarbonate (PC) substrates was investigated. Some of the PC substrates were bombarded by 1-keV Ar ions in an oxygen environment to modify the substrate surface before ITO sputter deposition. The initial part of the film growth was transformed from a three-dimensional island growth to a two-dimensional like growth as a result of the surface treatment. The change of the growth mode was attributed to oxygen-bound functional groups newly formed on the PC surface. Models based on thermodynamic theory and on atomic kinetic approach are presented to explain the transition, respectively.

Bonding polycarbonate brackets to ceramic: Effects of substrate treatment on bond strength

This study evaluated the effects of 5 different surface conditioning methods on the bond strength of polycarbonate brackets bonded to ceramic surfaces with resin based cement. Six disc-shaped ceramic specimens (feldspathic porcelain) with glazed surfaces were used for each group. The specimens were randomly assigned to 1 of the following treatment conditions of the ceramic surface: (1) orthophosphoric acid + primer + bonding agent, (2) hydrofluoric acid gel + primer + bonding agent, (3) tribochemical silica coating (silicon dioxide, 30μm) + silane, (4) airborne particle abrasion (aluminum trioxide, 30μm) + silane, and (5) airborne particle abrasion (aluminum trioxide, 30μm) + silane + bonding agent. Brackets were bonded to the conditioned ceramic specimens with a light-polymerized resin composite. All specimens were stored in water for 1 week at 37°C and then thermocycled (1000 cycles, 5°C to 55°C, 30 seconds). The shear bond strength values were measured on a universal testing machine at a crosshead speed of 1 mm/min. Brackets treated with silica coating with silanization had significantly greater bond strength values (13.6 MPa, P = .01) than brackets treated with orthophosphoric acid (8.5 MPa). There was no significant difference ( P = .97) between the bond strengths obtained after airborne abrasion with aluminium trioxide particles followed by silanization (12 MPa) and hydrofluoric acid application (11.2 MPa) (ANOVA and Tukey test). Although brackets conditioned with orthophosphoric acid exhibited only adhesive failures of the luting cement from the ceramic surface, other conditioning methods showed mixed types of failures. Airborne particle abrasion with aluminium trioxide or silica coating followed by silanization gave the most favorable bond strengths. The types of failures observed after debonding indicated that the critical parameter was the strength of the adhesive joint of the luting cement to both the bracket and the ceramic.

Effects of substrate treatment and growth conditions on structure, morphology, and luminescence of homoepitaxial ZnTe deposited by metalorganic vapor phase epitaxy

The structure, morphology, and luminescence of homoepitaxial ZnTe layers grown by metalorganic vapor phase epitaxy on (100)ZnTe:P wafers are reported as function of substrate surface treatment and growth conditions. Epilayers grown on substrates in situ H2 treated at temperatures above 240 °C exhibit long range crystalline perfection comparable to the substrate, but their structure rapidly degrades at lower temperatures, an effect ascribed to the incomplete removal of native oxides from the wafer surface. Instead, the material microscopic structure improves monotonically by annealing the wafer up to 350 °C. A nearly featureless surface morphology is obtained for epilayers grown within a narrow temperature interval around 350 °C, corresponding to the transition between surface kinetics and mass transport limited growth. Surface ridging along a 〈110〉 in-plane direction is observed at lower temperatures, while large pyramidlike hillocks occur randomly on the surface of samples grown above 350 °C. Besides the epilayer band-edge (BE) emission, 4.2 K photoluminescence (PL) of samples show recombination bands characteristic of the ZnTe:P wafer, their excitation being due to diffusion into the substrate of excitons photogenerated in the epilayer. Within the BE emission, both 1s- and 2s- state free exciton (at 2.3809 eV and 2.3904 eV), as well as a neutral donor (at 2.3776 eV) and acceptor bound (at 2.3748 eV, 2.3739 eV, and 2.3706 eV) exciton lines occur. Intense and narrow (1.7 meV) free-exciton emission is observed for samples grown at 350 °C and Te:Zn precursors molar flow ratio around 1, while bound-exciton lines dominate the PL spectra below 350 °C. A weak donor-acceptor pair (DAP) band, ascribed to a transition involving a donor substitutional on Zn site (DZn) and a CTe-DZn acceptor-type complex, appears between 2.16 and 2.27 eV in the PL spectra of epilayers grown below 350 °C or at low Zn precursor supply rates. The DAP band intensity well correlates with that of the 2.3776 eV donor and the 2.3706 eV acceptor bound exciton lines. At higher growth temperatures the epilayer crystallinity and radiative efficiency decrease.

Effects of substrate treatment on the electroluminescence performance of flexible OLEDs

Electroluminescence (EL) performance of flexible organic light-emitting device (FOLED) has been found to be highly dependent upon the morphology of the surface of the indium thin oxide (ITO)/plastic substrate as well as the patterning and processing conditions of the substrate. We will present evidence showing that luminance efficiency of FOLED can be greatly improved by pretreatment. Surface analysis of the ITO/PET by means of atomic force microscope (AFM) and optical microscope will be compared with that of the ITO/glass and the influence of flexible OLEDs substrate treatment by various methods on EL performance will also be discussed.

Adhesion studies of magnetron-sputtered copper films on Inconel substrates: Effects of substrate surface pretreatments

The adhesion strength of sputtered copper films to Inconel substrates has been studied using the scratch adhesion test. The effects of substrate treatments before deposition such as chemical or ion bombardment etchings were investigated by means of a mean critical load derived from a Weibull-like statistical analysis. It was found that the mean critical load was very weak unless the amorphous layer produced by mechanical polishing on the substrate surface was eliminated. Chemical etching in a nitric-hydrochloric acid bath was shown to have practically no effect on the enhancement of the adhesion. In contrast, the addition in this bath of nickel and cooper sulphates allowed removal of the amorphous layer and an increase in the values of the mean critical load. However, it was observed that excessive chemical etching could cancel out the mean critical load enhancement. The results obtained in the case of ion bombardment etching pretreatments could be far higher than those obtained with chemical etching. Moreover, for a sufficiently long period of ion bombardment etching, the adhesion strength was so high that it was impossible to observe evidence of an adhesion failure. The roughness of the etched surface was measured with a profilometer and observations were made by scanning electron microscopy. In addition, the interfacial chemistry was studied by Auger electron spectroscopy. In the case of chemical etching, it was observed that, as a general rule, the mean critical load increases with increasing roughness of the surface. Similar findings had been obtained from earlier studies carried out on aluminium and nickel substrates. The very high values of the mean critical load obtained in the case of ion bombardment etching cannot be accounted for only by a roughness effect. The analyses performed by Auger electron spectroscopy suggest that, in that case, the elimination of the surface contamination could explain the significant adhesion improvement. However, the mechanism might be complex because of the possibility that the ion beam creates vacancies and microcavities on the substrate surface.

Studies of the UV/Ozone oxidation of GaAs using angle‐resolved x‐ray photoelectron spectroscopy

AbstractAngle‐resolved x‐ray photoelectron spectroscopy (ARXPS) has been used to study the composition of oxides grown on 〈110〉 and 〈100〉 GaAs during exposure to UV/ozone. The effects of substrate treatments on oxide growth were compared on 〈100〉 surfaces exposed to an HF treatment and thermal desorption of the oxide and 〈110〉 surfaces prepared by in situ cleaving. Short‐term (10 min) oxidation of 〈110〉 cleaved surfaces resulted in a mixture of Ga and As stoichiometric oxides, with arsenic depletion of the underlying GaAs substrate. Less arsenic depletion of the substrate occurs for acid‐etched 〈100〉 GaAs oxidized under the same conditions. Extended UV/ozone oxidation (60 min) of these substrates yields oxide films that are less stoichiometric, with an arsenic oxide phase segregating nearer to the surface. Cleaved 〈110〉 substrates are again depleted in arsenic just below the interface. UV/ozone oxidation of 〈100〉 GaAs surfaces prepared by thermal desorption produced oxide films of uneven thickness, which yielded poor ARXPS profile results. The Laplace Transform model of Bussing and Holloway was modified to allow the use of different electron inelastic mean free path (λ) values for surface oxide and substrate. The range of values used to test the modified equation did not cause significant changes of the depth profile.