Existence Of Transition Layer Research Articles

The influences of reactive nanoparticles alloying on grain boundary and melting properties about Sn3.0Ag0.5Cu solder

Herein, we prove that alloying of reactive nanoparticles can improve nanoparticles/β-Sn interfacial bonding and influence the solder alloy's melting point. Furthermore, the alloying effect can enhance the creep resistance of solder alloy. 0-0.5 wt% Ag nanoparticles (NPs) were added to Sn3.0Ag0.5Cu (SAC305) solder paste by mechanical stirring for the preparation of composite solder alloys, which were then extracted from the composite solder pastes. The joints were observed by scanning electron microscope and transmission electron microscope. The elementary composition of the prepared alloys was analyzed by electron dispersive spectrometer. The melting properties of alloys were tested by differential scanning calorimeter. The influences of Ag NPs as reactive nanophase on solder microstructure and melting properties were studied. The results indicated the existence of transition layer at the interface between Ag NPs and β-Sn. Additionally, the interfacial bonding improved after Ag NPs converted to Ag3Sn NPs. Due to Ag NPs alloying and solder alloy microstructure refinement being affected, melting points of alloys increased with 0-0.2 wt% addition of Ag NPs and decreased with 0.2–0.5 wt% addition.

FEM thermal and stress analysis of bonded GaN-on-diamond substrate

A three-dimensional thermal and stress analysis of bonded GaN on diamond substrate is investigated using finite element method. The transition layer thickness, thermal conductivity of transition layer, diamond substrate thickness and the area ratio of diamond and GaN are considered and treated appropriately in the numerical simulation. The maximum channel temperature of GaN is set as a constant value and its corresponding heat power densities under different conditions are calculated to evaluate the influences that the diamond substrate and transition layer have on GaN. The results indicate the existence of transition layer will result in a decrease in the heat power density and the thickness and area of diamond substrate have certain impact on the magnitude of channel temperature and stress distribution. Channel temperature reduces with increasing diamond thickness but with a decreasing trend. The stress is reduced by increasing diamond thickness and the area ratio of diamond and GaN. The study of mechanical and thermal properties of bonded GaN on diamond substrate is useful for optimal designs of efficient heat spreader for GaN HEMT.

Technology and Investigation of Ohmic Contacts to Thermoelectric Materials

Technology is developed, materials and regimes of the fabrication of ohmic contacts to the effective thermoelectric materials Bi2Te2.8Se0.2 (n-type) and Bi0.5Sb1.5Te3 (p-type) are determined. Ohmic contacts were obtained by the vacuum deposition of nickel. Factors determining adhesion strength and resistivity of fabricated contacts are determined. Process of surface preparation of the thermoelectric materials before the ohmic contact deposition is optimized during the technology development. The use of electrochemical polishing, ultrasound treatment, finish cleaning in toluene and isopropyl alcohol vapor, and annealing in vacuum allowed achieving stable results in the formation of contacts. It was shown that contacts fabricated using of electron-beam evaporation of nickel possess maximum adhesion strength of 18–19 N/mm. It was found that high adhesion is caused by the existence of transition layer in the metal-thermoelectric material contact range, formed due to the interaction of metal with the components of thermoelectric material. Proposed technology allows obtaining ohmic contacts with the resistance of the unit area not exceeding 10−10 Ohmm.

Integrated characterization of multilayer periodic systems with nanosized layers as applied to Mo/Si structures

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.

Integrated diagnostics of heterostructures with QW layers

Potential of the integrated diagnostics of III-V complex quantum-well (QW) structures used for fabrication of power lasers is demonstrated for the example of GaInP/GaAs/AlGaAs QW structures grown by the metal-organic chemical vapor deposition method. An analysis of cathodoluminescence spectra enabled estimation of the composition of barrier layers, confirmed the existence of a QW, and detected anomalies in its emission associated with compositional changes. An examination of the structures with a transmission electron microscope determined the thickness of barrier layers and the width and composition of the QW, and discovered transition layers near interfaces. The composition of the barrier layers was precisely determined by electron probe microanalysis. The resulting values of the parameters were used in interpretation of X-ray diffraction data, which confirmed the existence of transition regions and revealed composition gradients and partial relaxation in the main part of barrier layers. The integrated study yielded consistent and substantiated data on the layer thickness and composition and data on the quality of interfaces, partial relaxation of the layers, and existence of transition layers and composition gradients.

Translucent Aluminum Oxide-to-Niobium Metal Seals by a Modified Solder Glass Technique Using an Adhesive in the System CaO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>-MgO

Translucent aluminum oxide-to-Nb metal seals were formed by a modified solder glass technique and the interfaces between the materials were examined by an optical microscope and an electron microanalyzer. The solder glass was formed from 3CaO⋅Al2O3⋅6H2O (Hydrogrossularite) and so on, and belonged to the system CaO-Al2O3-SiO2-MgO. The solder glass was melted at 1500°C during sealing operation and crystallized into a glass-ceramic composite on cooling.The results were as follows:1. Vacuum tight seals were formed by this technique.2. The solder glass which turned into a glass-ceramic composite contained 3CaO⋅Al2O3⋅3SiO2 (Grossularite) as a main constituent phase with small amount of 5CaO⋅3Al2O3 (Calcium Aluminate) and 3CaO⋅2SiO2 (Calcium Silicate).3. Transition layers with concentration gradients of Al and Nb were formed in solder glass at the ceramic-solder glass and metal-solder glass interfaces, respectively.4. Si concentrated anomalously at metal-solder glass interface, suggesting that surface energy at the interface was lowered by the presence and concentration of Si or SiO2.Both the existence of transition layers and the anomalous distribution of Si were expected to strengthen the ceramic-solder glass and metal-solder glass interfaces and relieved the stress concentration caused by thermal expansion difference between the materials.