β-NMR experiments with hyperpolarized ^8Li adsorbed on semiconductor and metal surfaces are described (adsorption on Si(111)-(7×7), Si(111)-H, Si(111)-(1×1):H, Ru(001)). They yield detailed information on the electronic properties of these adsorbate-surface systems. Briefly a scenario using hyperpolarized Xe isotopes is sketched, which will extend the potential of the use of hyperpolarized species in NMR experiments on surfaces.
Al-Ti intermetallic compounds were coated by electro-spark deposition. Commercially pure titanium (Cp-Ti) (grade 2) and aluminum rods were used as substrate and electrode materials, respectively. During the electro-spark deposition experiments the following pulse parameters in a group were used: pulse current amplitude, pulse duration and pause between the pulses of a pulse group with 100-300-500 A, 50-100 μs, and 100 μs, respectively. Al-Ti coatings having a thickness range of 15-30 μm were formed on the surface of titanium substrate using electro-spark deposition process. The coating properties such as the roughness and the thickness increased with increasing pulse duration and pulse current amplitude. The mass transfer coefficient decreased with increasing pulse current amplitude and pulse duration. The quality of the adhesion characters of the coatings, determined by Rockwell-C adhesion test, becomes worse from HF-2 to HF-4, due to increase of pulse current amplitude. Depending on the electro-spark deposition process parameters, the coating formed as AlTi or as layered structure consisting of AlTi+AlTi_3 when pulse current amplitude increases. The Al-Ti coatings include some micro cracks lying throughout the coating from surface to interface which is nature of this process. The maximum cross-sectional hardness of the coatings were in the range of 800-1150 HV.
In this study, a method for manufacturing polymer/metal hybrid structure is presented in which traditional plastic injection machine was converted to plastic injection forming (PIF). In this method, deforming of the metal and adhering the metal to the polymer is done in one step. In the experimental study, a special mold within rectangular cavity was used during PIF process. Aluminum plates of different thicknesses were used as the metal parts of the structure. The injected polymers were pure polystyrene and elastomer-added polystyrene. The deformability of the Al plates was examined under different injection pressures. In order to provide adhesion between metal and polymer, an adhesive of elastomeric nature was applied on the metal plate prior to injection molding. Bending test was applied to determine the flexural strength and maximum deflection of the polymer/metal hybrid structures. The obtained results were satisfactorily acceptable in improving the method for designing and manufacturing polymer/metal hybrid structures in one step.
Growth of thin metal films on semiconductors has been always an important subject for extensive experimental and theoretical studies. As the applicability of well-ordered nanostructures in electronic applications depends strongly on their size and distribution, it is necessary to understand the processes that govern the growth of such structures. In this paper we present the results of investigation of the room temperature growth of thin Bi film on Si(111). In our study we clarified that rotationally disordered, pseudo-cubic Bi(012) islands with uniform height of ≈13Å are formed in the initial stage of Bi film growth. With increase in the amount of bismuth on the surface, islands interconnect maintaining however their uniform height. This process is further accompanied by the unique and unexpected structural phase transition of the Bi(012) film into a hexagonal Bi(001) film.
In this work, a diffusion model was applied to estimate the boron diffusion coefficients in the Fe_{2}B layers on the ASTM A-536 ductile iron in the temperature range 1173-1273 K by the powder-pack boriding. The mass balance equation at the (Fe_{2}B/substrate) interface was formulated considering the effect of boride incubation times. As a result, the value of activation energy for boron diffusion in the ductile iron was estimated and compared with the literature. To verify the validity of the present model, the experimental Fe_{2}B layer thickness obtained at 1173 K for 10 h was compared to the predicted value. A good concordance was observed between the predicted value of Fe_{2}B layer thickness and the experimental data.
Composition-depth profiling using different emission angles of X-ray photoelectron spectroscopy showed surface enhancement of platinum concentration of the CoPt(30at%) alloy extensively annealed to 1000~K in ultrahigh vacuum. The results are compared with theoretical predictions basing on models with no crystal face dependence.
This work deals with the simulation of the growth kinetics of the (FeB/Fe_2B) bilayer and the diffusion zone on a substrate of AISI 316 stainless steel exposed to the powder-pack boriding process, in the temperature range of 1123-1273 K and a time duration ranging from 2 to 10 h. The developed diffusion model employs a set of mass balance equations at the three growth fronts: [(FeB/Fe_2B), (FeB/diffusion zone) and (diffusion zone/substrate)] under certain assumptions, including the effect of the incubation times during the formation of iron borides and the diffusion zone. For this purpose, a computer code written in Matlab (version 6.5) was created to simulate the boriding kinetics. A good concordance was obtained when comparing the experimental parabolic growth constants taken from the literature and the simulated values of the parabolic growth constants: (k_{FeB}, k_1 and k_2). Moreover, the present model was also used to predict the thicknesses of the FeB and Fe_2B layers and the diffusion zone thickness at various treatment times and boriding temperatures. The simulated values were in good agreement with the experimental borided layers thicknesses.
In the present work, a diffusion model was applied to estimate the boron diffusion coefficients in the FeB and Fe₂B layers during the pack-boriding of AISI D2 steel in the temperature range of 1223-1323 K during a variable exposure time between 1 and 8 h. The mass balance equations were formulated at each growing interface by considering the effect of boride incubation times. The estimated values of boron activation energies in the FeB and Fe₂B layers were compared with the literature data. Validation of the present model was made by comparing the experimental thickness of each boride layer, taken from the literature data, with the predicted values. In addition, a simple equation was suggested to estimate the required time to obtain a single Fe₂B layer by diffusion annealing.
The magnetic phase diagram of bulk Cr_{100-x}Al_{x} shows interesting behaviour close to the triple point concentration of x ≈2. Since the magnetic properties of Cr are influenced by dimensionality, stress and strain, this study focussed on the investigation of Cr₉₉Al₁ thin films prepared on fused silica substrates with thicknesses t varying from 29 to 452 nm using sputtering techniques. Resistance measurements covering the temperature range 2 to 400 K did not show any clear anomalies that could be indicative of changes in the magnetic ordering. X-ray diffraction (XRD) and atomic force microscopy (AFM) studies indicate the films are polycrystalline textured and that the 80 nm sample has the smallest grain size. In-plane stresses in these thin films were studied using the specialised XRD ın²ψ-method. The results show that the stress varies with film thickness. The 29 nm sample has stress in the order of 833 MPa and with increasing film thickness the stress reaches 1471 MPa for the 80 nm layer, where after it systematically reduces for the thicker coatings to 925 MPa for the 452 nm film. The highest stress for the Cr₉₉Al₁ thickness sample series is seen in the film with the smallest grain size.
The atomic structure and morphology of ultrathin Pb layers deposited on the Ni(001) face in ultrahigh vacuum at the substrate temperature, ranging from 145 K to 900 K, were investigated with the use of the Auger electron spectroscopy and low-energy electron diffraction. The analysis of the Auger electron spectroscopy measurements indicates that the Volmer-Weber growth of the Pb takes place for substrate temperature T < 300 K. Between 300 and 600 K, the Stranski-Krastanov growth mode is observed. For 600 K ≤ T ≤ 700 K, only first two-dimensional Pb layer formation is found. Above 700 K desorption of lead atoms from the first layer is observed. The ordered low-energy electron diffraction patterns corresponding to p(1×1) and c(2×2) structures are observed.
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