Elastic behaviour of an edge dislocation near a sharp crack emanating from a semi-elliptical blunt crack

The interaction between an edge dislocation and a crack emanating from a semi-elliptic hole is dealt with. Utilizing the complex variable method, closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the edge dislocation are also calculated. The influence of the morphology of the blunt crack and the position of the edge dislocation on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases acutely when the dislocation approaches the tip of the crack. The effect of the morphology of the blunt crack on the stress intensity factor of the crack and the image force is very significant.     

Chemisorption of Au on Si（001） surface

The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B_1 site(bridge site), resulting in a Au－Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.     

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.     

Chemisorption of Fe on Au-passivated Si（001） surface

The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au－Fe mixed layer at the Fe/Au－Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au－Si(001) interface effectively, which is in agreement with the experimental results.     

Amorphous/Crystalline （n-n） Si Heterojunction Photodetector Made by Q-Switched 0.532-mm Laser Pulses with Novel Technique

Amorphous/crystalline n-n-isotype Si heterojunetions are made by a pulsed Q-switched second harmonic generation Nd：YAG laser. The process includes melting and subsequently fast resolidification of a thin front layer of monocrystalline Si by laser pulses to create an amorphous layer （phase transition）. Different laser energy densities are used to form the amorphous layer on a monocrystalline Si substrate, the results of the electrical characteristics of the heterojunctions are dependent strongly on the laser energy density. Optoelectronic properties such as current-voltage, capacitance voltage, and spectral sensitivity are measured in a-Si/c-Si hereto junctions （in the absence of anti-reflecting coating and frontal grid contact） prepared by different laser energy densities. The built-in-potential values extracted from current-voltage measurements are close to the published results of （n-p） amorphous/crystalline hereto junction made by glow discharge and plasma enhanced chemical vapour deposition. Furthermore, examination of the formation of amorphous pattern on Si surface is carried out with the help of optical microscopy. Best photovoltaic performance is recognized to be at ,5.6 J/cm^2. The photodetector shows a wide spectral response, and the peak response is at 780nm. On the other hand, this peak is independent of laser energy.     

MBE Growth of Highly Relaxed Si0.45 Ge0.55 Films with Very Low Misfit Dislocation Density on Si （001） Substrates

We investigate the molecular-beam-epitaxy growth of highly relaxed Si0.45 Ge0.55 films with very low dislocation densities. By using the Si3N4 film as the mask material, the Si0.45Ge0.55 film can be grown on a compositionally stepwise graded SiGe buffer layer in 3 μm× 3 μm windows on a Si （001） substrate. Raman scattering spectroscopy measurement shows that more than 90% strain of the Si0.45Ge0.55 film is relaxed, and almost neither misfit dislocation lines nor etch pits of thread dislocations could be observed when the sample is etched by the modified Schimmel etchant. We suggest that the results can be explained by influence of the edge-induced strain relaxation of the epitaxial film and the edge-induced stress of the mask material.     

Shielding effect of a nano-circular inclusion acting on semi-infinite wedge cracks

The model of a screw dislocation near a semi-infinite wedge crack tip inside a nano-circular inclusion is proposed to investigate the shielding effect of nano inclusions acting on cracks. Utilizing the complex function method, the closed-form solutions of the stress fields in the matrix and the inclusion region are derived. The stress intensity factor, the image force, as well as the critical loads for dislocation emission are discussed in detail. The results show that the nano inclusion not only enhances the shielding effect exerted by the dislocation, but also provides a shielding effect itself. Moreover, dislocations may be trapped in the nano inclusion even if the matrix is softer than the inclusion. This helps the dislocation shield crack, and reduces the dislocation density within the matrix.     

Surface-field-induced effects on morphologies of lamella-forming diblock copolymers in nanorod arrays

The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory.In the simulation study,a rich variety of novel morphologies are observed by variations in the strength of the surface field for the diblock copolymers.Different surface-field-induced effects are examined for the diblock copolymers in the arrays with distinct preferential surfaces.It is observed that the majority-block preferential surfaces have more obvious induced effects than those of minority-block preferential surfaces.The strong surface fields exhibit different behaviours from those observed in the weak surface fields,by which the morphologies possess cylindrical symmetries.Results from this research deepen the knowledge of surface-induced effects in a confinement system,which may aid the fabrication of polymer-based nanomaterials.     

Elastic behavior of disclination dipole near nanotube with surface/interface effect

In this paper, we present an analytical solution of the interaction of the nanotube （NT） with a wedge disclination dipole in nanotube-based composites. The corresponding boundary value problem is solved exactly by using complex potential functions. The explicit expression of the force exerted on disclination dipole is given by using the generalized Peach- Koehler formula. As a numerical illustration, both the equilibrium position and the stability of the disclination dipole are evaluated for different material combinations, relative thickness of an NT, surface/interface effects, and the features of the disclination dipole. The results show that as the thickness of the NT layer increases, the NT has a relatively major role in the force acting on the disclination dipole in the NT-based composite. The cooperative effect of surface/interface stresses and the NT becomes considerable as the increase of NT layer thickness. The equilibrium position may occur, even more than one, due to the influences of the surface/interface stress and the NT thickening. The influences of the surface/interface stresses and the thickness of the NT layer on the force are greatly dependent on the disclination angle.     

Wettability of Si and Al–12Si alloy on Pd-implanted 6H–SiC

Si C monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences,and the effects of Pd ion implantation on wettability of Si/Si C and Al–12 Si/Si C systems are investigated by the sessile drop technique.The decreases of contact angles of the two systems are disclosed after the ion implantation,which can be attributed to the increase of surface energy(σ_(SV)) of Si C substrate derived from high concentration of defects induced by the ionimplantation and to the decrease of solid–liquid surface energy(σ_(SL)) resulting from the increasing interfacial interactions.This study can provide guidance in improving the wettability of metals on Si C and the electronic packaging process of Si C substrate.     

Experimental Study on Liquid Free Surface in Buoyant-Thermocapillary Convection

We investigate the surface deformations of buoyant-thermocapillary convection in a rectangular cavity due to gravity and temperature gradient between the two sidewalls. The cavity is 52mm×42 mm in horizontal cross section, the thickness of liquid layer h is changed from 2.5 mm to 6.5 mm. Surface deformations of h = 3.5 mm and 6.0mm are discussed and compared. Temperature difference is increased gradually, and the flow in the liquid layer will change from stable convection to unstable convection. Two kinds of optical diagnostic system with image processor are developed for study of the kinetics of buoyant-thermocapillary convection, they give out the information of liquid free surface. The quantitative results are calculated by Fourier transform and correlation analysis, respectively. With the increasing temperature gradient, surface deformations calculated are more declining. It is interesting phenomenon that the inclining directions of the convections in thin and thick liquid layers are different. For a thin layer, the convection is mainly controlled by thermocapillary effect. However, for a thick layer, the convection is mainly controlled by buoyancy effect. The surface deformation theoretically analysed is consistent with our experimental results. The present experiment proves that surface deformation is related to temperature gradient and thickness of the liquid layer. In other words, surface deformation lies on capillary convection and buoyancy convection.     

Study on the delamination of tungsten thin films on Sb2Te3

To investigate the reliability of electrode materials for chalcogenide random access memory （C-RAM） applications, the geometry and time evolution of the worm-like delamination patterns on a tungsten/Sb2Te3 bilayer system surface are observed by field emission scanning electronic microscope （FESEM） and optical microscopy. The tungsten film stress and interface toughness are estimated using a straight-side model. After confirming the instability of this system being due to large compressive stress stored in the tungsten film and relative poor interface adhesion, a preliminary solution as the inset of a TiN adhesion layer is presented to improve the system performances.     

Initial Processes of Sulfur Adsorption on Si（100） Surface

The adsorption of one monolayer S atoms on ideal Si（100） surface is studied by using the self-consistent tight binding linear muffon-tin orbital method. Energies of adsorption systems ors atoms on different sites are calculated. It is found that the adsorbed S atoms are more favorable on B1 site （bridge site） with a distance 0.131 nm above the Si surface. The .S, Si mixed layer might exist at S/Si（100） interface. The layer projected density of states are calculated and compared with that of the clean surface. The charge transfers are also investigated.     

Elastic behaviour of a wedge disclination dipole near a sharp crack emanating from a semi-elliptical blunt crack

The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the disclination dipole center are also calculated. The influence of the morphology of the blunt crack and the position of the disclination dipole on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases when the wedge disclination dipole approaches the tip of the crack. The effects of the morphology of the blunt crack on the stress intensity factor of the crack and the image force are very significant.     

Thermal stress reduction of GaAs epitaxial growth on V-groove patterned Si substrates

We investigate the thermal stresses for GaAs layers grown on V-groove patterned Si substrates by the finite-element method. The results show that the thermal stress distribution near the interface in a patterned substrate is nonuniform,which is far different from that in a planar substrate. Comparing with the planar substrate, the thermal stress is significantly reduced for the Ga As layer on the patterned substrate. The effects of the width of the V-groove, the thickness, and the width of the SiO₂ mask on the thermal stress are studied. It is found that the SiO₂ mask and V-groove play a crucial role in the stress of the Ga As layer on Si substrate. The results indicate that when the width of V-groove is 50 nm, the width and the thickness of the SiO₂ mask are both 100 nm, the Ga As layer is subjected to the minimum stress. Furthermore,Comparing with the planar substrate, the average stress of the Ga As epitaxial layer in the growth window region of the patterned substrate is reduced by 90%. These findings are useful in the optimal designing of growing high-quality Ga As films on patterned Si substrates.     

Structural Features of Boron-Doped Si（113） Surfaces Simulated by ab initio Calculations

Based on ab initio calculations, boron-doped Si（113） surfaces have been simulated and atomic structures of the surfaces have been proposed. It has been determined that surface features of empty and filled states that are separately localized at pentamers and adatoms indicates a low surface density of B atoms, while it is attributed to heavy doping of B atoms at the second layer that pentamers and adatoms are both present in an image of scanning tunnelling microscopy. B doping at the second layer should be balanced by adsorbed B or Si atoms beside the adatoms and inserted B interstitials below the adatoms.     

Initial Processes of Hydrogen Adsorption on Si（100） Surface

The adsorption of one monolayer H atoms on an ideal Si(100) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of H atoms on different sites are calculated.It is found that the adsorbed H atoms are more favorable on B1 site (bridge site) with a distance 0.056 nm above the Si surface. There does not exist reaction barrier at the Si surface. The layer projected density states are calculated and compared with those of the clean surface. The charge transfers are also investigated.     

Residual Stress on Surface and Cross-section of Porous Silicon Studied by Micro-Raman Spectroscopy

Surface and cross-sectional residual stresses of electrochemical etching porous silicon are investigated quantitatively by micro-Raman spectroscopy. The results reveal that a larger tensile residual stress exists on the surface and increase linearly with the porosity. On the other hand, across the depth direction perpendicular to the surface, the tensile residual stress decreases gradually from the surface to regions near the interface between the porous silicon layer and the Si substrate. However, a compressive stress appears at the interface near to the Si substrate for balancing with the tensile stress in the porous silicon layer. The cross-sectional residual stress profile is due to the porosity and lattice mismatch gradients existing in the cross-section and influencing each other.Furthermore, the presented residual stresses of the porous silicon have a close relation with its microstructure.     

Elastic behaviour of a wedge sharp crack emanating from a disclination dipole near a semi-elliptical blunt crack

The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the disclination dipole center are also calculated. The influence of the morphology of the blunt crack and the position of the disclination dipole on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases when the wedge disclination dipole approaches the tip of the crack. The effects of the morphology of the blunt crack on the stress intensity factor of the crack and the image force are very significant.     

Interaction between many parallel screw dislocations and a semi-infinite crack in a magnetoelectroelastic solid

Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach–Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state.