RESUMO
We report on transmission electron microscopy studies of Au/Pt/Ti/Pt(10-30 nm) contact structures for high power GaAs/InGaAs semiconductor lasers. The studies showed that annealing at 450 degrees C of contact structures causes the reaction of whole Pt with substrate components (Ga and As) and the formation of Pt-GaAs interlayers with smooth interfaces as required for such structures. Annealing of the structures at 470 and 490 degrees C unfavourably affects the contact structure. At this condition, the strong downward diffusion of Au and Pt from the top layers causes a formation of Au-Pt pits, which break the Ti barrier. Transmission electron microscopy observation revealed that Au/Pt/Ti/Pt(10-30 nm) system annealed at 450 degrees C is appropriate for practical applications. The EDS technique used to identify the phase composition in the Pt(30 nm)/GaAs structure (specially produced for the EDS analysis) annealed at 450 degrees C showed that two layers were formed as a result of the reaction of the whole Pt layer with GaAs, and they consist of Ga, Pt and As. The top layer has the highest concentration of Ga. However, the bottom layer, which is close to the substrate, has the highest concentration of As.
RESUMO
In this paper, we present results of transmission electron microscopy studies on erbium silicide structures fabricated under various thermal conditions. A titanium cap has been used as a protective layer against oxidation during rapid thermal annealing of an erbium layer in a temperature range of 300-700 degrees C. Both layers (200 nm Ti and 25 nm Er) were deposited by electron-beam sputtering. The investigations have shown that the transformation of the 25-nm-thick erbium into erbium silicide is completed after annealing at 500 degrees C. At higher temperatures, the formation of a titanium silicide layer above erbium silicide is observed. The lowest Schottky barrier has been measured in the sample annealed at 700 degrees C.
RESUMO
Aiming to determine the contrast mismatch factor i.e. the Stobbs factor between the experimental and simulated high-resolution transmission electron micrographs, we have systematically compared the experimental images and simulations of a cleaved silicon sample for a series of focal settings and specimen thicknesses. For zero-loss energy filtered images, a mismatch factor of about 1.5-2.3 is measured for the image contrast, where the mismatch factor is focal dependent and higher mismatch appears around the focus value of 10nm. Attention is also given to the effects of the sample vibration and drift to the image contrast and pattern of the high-resolution micrographs.
RESUMO
Lattice-distortion analysis from high-resolution transmission electron micrographs offers a convenient and fast tool for direct measurement of strains in materials over a large area. In the present work, we have evaluated the accuracy of the strain measurement when the effects of the realistic experimental variables are explicitly taken into account by the use of image simulation techniques. These variables are focal setting and variation, local thickness and orientation of the sample, as well as misalignments of the sample and the incident beam. The evaluation reveals that consistency of image features and contrast within the micrographs is desired for the analysis to eliminate effects of the variations of local focus value and specimen thickness. After proper orientation of a crystalline specimen, the mis-orientation of the object will not notably influence the strain measurement even though a local bending may exist within the sample. However, the incident beam of the microscope needs to be aligned carefully as the beam misalignment may introduce a notable artefact around the interface region.
RESUMO
Uniform and step-shaped Bi nanowire (NW) arrays have been synthesized by electrochemical deposition inside the uniform and step-shaped nanochannels of an anodic aluminium oxide template. These Bi NWs are highly oriented and single crystalline. The current-voltage characteristics of the parallel uniform Bi nanowires show that the contacts between Bi NWs and gold film do not make significant contributions to the I-V characteristics of the step-shaped Bi NWs. The diameters of the thick segment and the thin segment of the step-shaped Bi NWs are about 70 and 40 nm, respectively. Their current-voltage characteristics show conventional metal-semiconductor junction behaviour. The approach can be exploited to produce one-dimensional metal-semiconductor junctions using step-shaped NWs consisting of other semi-metals without any external doping, which may find various applications in nanotechnology.
RESUMO
The growth and defect structures in free-standing self-assembled In0.6Ga0.4As quantum dots (QDs) grown on (001) GaAs by solid source molecular beam epitaxy has been investigated. The QDs are elongated along [1; 1 0]. At a nominal thickness of eight monolayers defect complexes, associated with intrinsic stacking faults, have been generally observed on both sides of a QD in (1; 1 0) cross-section. The total defect vector of such defect complexes is a/3 <111>. Local strain components on {111} slip planes in the QDs without defects have been measured directly from digitized high-resolution electron microscopy images. The distortion on the two sets of {111} planes of a (1; 1 0) cross-section is different owing to elastic relaxation. The results of strain measurements suggest that a 60 degrees dislocation nucleates first on the set of {111} planes of higher contractive shear strain, i.e. (111) planes on the right side of the QDs, and (1; 1; 1) planes on the left side. A 30 degrees partial dislocation forms subsequently on the other set of {111} planes, i.e. (1; 1; 1) planes on the right side of the QDs and (111) planes on the left side, when the 60 degrees dislocation glides down towards the In0.6Ga0.4As/GaAs interface, as a result of the additional strain field of the 60 degrees dislocation. The efficiency of the defect complexes in strain relaxation of the QDs has been shown by strain measurements in QDs with the presence of defects.
