Ehab AlShamaileh

A re-interpretation of the Cu{100}/Sn surface phase diagram

The coverage dependent structural phase transitions of Sn on Cu{100} have been re-examined by low energy electron diffraction (LEED). Double scattering LEED pattern simulations have been applied both to a range of possible new models and to previously suggested structures with the aim of identifying the most likely surface geometries throughout the sub-monolayer coverage regime. A model consistent with both the Sn surface coverage and the complex split beam LEED pattern observed has been suggested for the low coverage (θ Sn = 0.21 ML) ordered phase based on a p(2 x 2) structure with light antiphase domain walls. We also demonstrate that higher coverage p(2 x 6) (θ Sn = 0.37 ML) and p(3√2 x √2)R45° (θ Sn = 0.50 ML) structures based on c(2 x 2) local periodicity yield a consistent explanation of the LEED data. While the simulations identify likely structures, the limitations of this approach mitigate against definitive structural assignments. However simulations for models based on c(2 x 2) structures incorporating defects in the form of periodic density modulations combined with substrate reconstruction lead to an enhanced agreement with observed LEED data compared to overlayer models previously suggested.

LEED investigation of the alloying/de-alloying transition in the Cu{100}/Bi system

The surface structures formed by deposition of 0.25 ML and 0.50 ML Bi on Cu{100} at room temperature have been determined quantitatively using the symmetrised automated tensor low energy electron diffraction (SATLEED). At θBi = 0.25 ML, Bi forms a semi-ordered p(2 × 2) surface alloy with the Bi atoms located at a height of 0.56 ± 0.06 A with respect to centre of gravity of the buckled outermost Cu layer (buckling amplitude = 0.11 A). The interlayer spacings in the first three substrate layers are found to be: d12 = 1.71 ± 0.06 A, d23 = 1.82 ± 0.06 A, d34 = 1.81 ± 0.06 A (dbulk = 1.807 A). The first and the third Cu layers are found to be buckled by 0.11 ± 0.06 A and 0.05 ± 0.06 A, respectively. At higher Bi coverage, de-alloying occurs culminating in formation of a well ordered c(2 × 2) overlayer at θBi = 0.50 ML. Bi atoms occupy the four-fold hollow sites with a vertical Bi–Cu interlayer separation of dBi–Cu = 2.17 ± 0.06 A above a slightly perturbed substrate. The interlayer spacing in the first four substrate layers are found to be: d12 = 1.82 ± 0.03 A, d23 = 1.80 ± 0.03 A and d34 = 1.84 ± 0.03 A. A small buckling of 0.02 ± 0.02 A is detected in the second Cu layer in which Cu atoms below Bi atoms are rippled outwards. The structures obtained by LEED are compared to those evaluated recently for the same system by surface X-ray diffraction.

A SATLEED study of the geometric structure of Cu{100}-Pd monolayer surface alloys

Abstract The structure of a Cu {1 0 0} -p(2×2) surface alloy formed by deposition of 1 ML of Pd on Cu {1 0 0} at room temperature has been studied by symmetrised automated tensor low energy electron diffraction. The favoured model from the wide range tested consists of a double layer ordered c(2×2) CuPd alloy with p(2×2)-p2gg symmetry introduced into the outermost layer via clock rotation of the CuPd monolayer with the corners of the p(2×2) unit cell centred over second layer Pd atoms ( R p =0.21). Lateral shifts of the top layer Cu and Pd atoms are determined to be 0.25±0.12 A. Substitution of 0.5 ML of Pd in both layers 1 and 2 leads to a significant expansion of the outermost two interlayer spacing to 1.93±0.02 A (+6.6±1.1%) and 1.90±0.03 A (+5.3±1.7%) and a rippling of Pd and Cu atoms in the outermost layer of 0.06±0.03 A with top layer Pd atoms rippled outwards. This model is in agreement with previous ion scattering studies of a Cu:Pd stoichiometry of 1:1 in the outermost two layers. A second mode of film growth consisting of adsorption of 0.5 ML of Pd on a copper capped Cu {1 0 0} -c(2×2)-Pd underlayer alloy leads to a structure which retains a simpler c(2×2) periodicity, suggesting that the growth of the p(2×2)-glide line phase requires a c(2×2) CuPd outermost template.

Influence of roller burnishing on surface properties and corrosion resistance in steel

Purpose – Roller burnishing (RB) is a finishing treatment method that is used to impart certain physical and mechanical properties, such as surface roughness, improved visual appearance, or increased corrosion, friction, wear, and fatigue resistance. The purpose of this paper is to study, the influence of RB on corrosion resistance in A53 steel in HCl solution.Design/methodology/approach – Microhardness (MH), microstructure, weight loss, and potentiostatic polarization are investigated at pressing forces of 40, 60, 80, 100 and 120 N.Findings – MH increases with increasing the applied force and the percentage improvements are found to be 12, 24, 28, 35 and 65 percent for 40, 60, 80, 100 and 120 N RB pressing forces, respectively. Weight losses, in general, showed an optimum value at about 80 N. Corrosion potential and corrosion current decrease with increasing pressing force and reached a minimum at about 80 N, then begin to increase with increasing RB force.Originality/value – The results present in this ...

Cu-capped surface alloys of Pt/Cu{100}

The room-temperature deposition of 0.5 monolayer (ML) Pt on Cu{100} followed by annealing to 525 K results in a sharp c(2 × 2) low-energy electron diffraction (LEED) pattern. The structure of this surface alloy is investigated by means of symmetrized automated tensor low-energy electron diffraction (SATLEED) analysis and ab initio plane wave density functional calculations. The results are then compared with those for the similar system 0.5 ML Pd/Cu{100}. SATLEED results for the Pt/Cu{100} show that it consists of an ordered c(2 × 2) Cu–Pt second layer alloy capped with a pure Cu first layer. The first and second interlayer spacings are found to be expanded by +5.1 ± 1.7 and +3.5 ± 1.7% respectively (relative to the bulk Cu interlayer spacing of 1.807 A) due to the insertion of the 8% larger Pt atoms into the second layer. The ordered mixed layer is found to be rippled by 0.08 ± 0.06 A with Pt atoms rippled outwards towards the solid–vacuum interface. A smaller rippling of 0.03 ± 0.11 A in the fourth pure Cu layer was also detected with Cu atoms directly underneath Pt atoms rippled towards the second layer Pt resulting in a Pt–Cu bond length of 2.52 A which compares with the sum of metallic radii of 2.67 A. A recent quantitative SATLEED analysis for 0.5 ML Pd/Cu{100} was performed in an earlier study (Barnes et al 2001 Surf. Sci. 492 55). A similar structure to the Pt/Cu{100} has been retrieved with slight differences in the interlayer spacings. The ab initio density functional results are fully consistent with the experimentally determined structures. However, they reveal an interesting difference between the stability of the Pd and Pt systems and highlight the fact that the Pd/Cu structure is best thought of as a metastable structure occurring as an intermediate step in the diffusion of the transitional metal ion into the bulk of the Cu substrate.

Modification of Gold Surface with Gold Nanoparticles and Cyclohexyl Dithiocarbamate as a Selective Sensor for Cysteine

The self-assembly of cyclohexylamine dithiocarbamate (C6DTC) on gold (Au) and gold nanoparticles (AuNPs) was studied electrochemically using cyclic voltammetry (CV). Cyclic voltammetry was used to study the system at the electrode surface of (C6DTC/Au) and (C6DTC/AuNPs). The application of the resulting chemically modified surface as a selective sensor for cysteine, among other amino acids, was investigated. Linear oxidative desorption technique was used to characterize the modified electrode that consists of the self-assembled monolayer of cyclohexylamine dithiocarbamate on gold nanoparticles deposited on Au electrode (C6DTC/AuNPs/Au). The results showed an enhancement in the oxidation peak of cysteine on the modified electrode and hence a greater sensitivity.

Early stages of surface alloy formation: a diffuse LEED I(V) study

The technique of diffuse low energy electron diffraction (LEED) I(V) analysis is shown to be a useful quantitative probe of the structure of surface alloys in the early stages of growth before long-range order develops. The Cu(100)/Pd system has been studied in the Pd coverage range 0.10-0.55 ML. We demonstrate the Pd adsorbs at all coverages primarily by substitutional replacement of top layer copper atoms forming a two-dimensional Cu x Pd 1-x surface alloy. At low coverages a quasi-random substitutionally disordered two-dimensional alloy is formed with local order detected by LEED developing at Pd coverages above 0.25 ML.The surface geometry is not strongly coverage dependent with top layer Cu and Pd atoms almost coplanar and the first interlayer spacing slightly expanded (3%) with respect to the bulk value.

Mechanochemical Synthesis of Slow-Release Fertilizers: A Review

Explanation: The effect of mineral fertilizers on the environment and on living species will be discussed. Moreover, various aspects related to fertilizers production and applications are illustrated. It is found that solid-solid mechanical interaction initiates chemical reactions by lowering their energy of activation when compared to other thermochemical processes. Since milling is an important industrial operation, its contribution to materials processing is discussed.

Initial Growth of Co on Cu{001} Studied with LEED I(V)

The initial growth of Co deposited at room temperature on Cu{001} was studied with low energy electron diffraction (LEED) and temperature-programmed desorption (TPD). Measured I(V) spectra were compared with calculated spectra from several model structures, including substitutionally disordered alloys. The averaged T-matrix approximation (ATA) was used to model the random alloy layers. According to the I(V) analysis, alloying occurs in the first stages of the growth. TPD of CO indicates that both large areas of Co and areas of a surface alloy are already present at the lowest coverage. Both methods show that a transition to layer-by-layer growth occurs as the coverage increases.

Current status of nanotechnology in Jordan

Purpose – The current status of nanotechnology research and development in Jordan is analyzed. In recent years, Jordanian institutions demonstrated considerable interest in the development and production of nanotechnology. Here the purpose of this paper is to provide detailed information about the status of nanotechnology in Jordan in terms of several factors that influence selectivity in nanotechnology and the number of published peer-reviewed research articles. Design/methodology/approach – Several factors that influence selectivity in nanotechnology and the number of published peer-reviewed research articles were analyzed. A detailed analysis of the collected data reveals that the number of publications, citations, and patents is highly dependent on the amount of research fund. Findings – The development in nanotechnology is associated with presence and accessibility of sensitive laboratory equipment. The nanotechnology research output in Jordan is still lower than it should be due to the lack of neces...