Modelling imaging based on core-loss spectroscopy in scanning transmission electron microscopy

Recent experimental realizations of atomic column resolution core-loss spectroscopy in the scanning transmission electron microscope have increased the importance of routinely modelling core-loss images. We discuss different approaches to wave function simulation and how they may be used in conjunction with the mixed dynamic form factor model to simulate images resulting from such inelastic scattering events. It is shown that, as resolution improves and in situations where the degree of thermal scattering is high, detailed quantitative comparisons will require the thermal scattering of electrons to be adequately modelled. Indeed, for sufficiently strong thermal scattering even qualitative interpretation may be affected: we give an example where this leads to a contrast reversal. We describe two methods suited to this purpose, the frozen lattice model and the scattering factor model, and explain how they may be combined with the mixed dynamic form factor approach.     

Substitution possibilities and determinants of energy intensity for China

This paper measures technological change, factor demand and inter-factor and inter-fuel substitutability measures for China. We use individual fuel price data and a two-stage approach to estimate total factor cost functions and fuel share equations. Both inter-factor and inter-fuel substitution elasticities are calculated and the change in energy intensity is decomposed into its driving forces. The results suggest that energy is substitutable for capital regionally and for labor nationally. Capital substitutes for energy more easily than labor does. Energy intensity changes vary by region but the major drivers seem to be “budget effect” and the adoption of energy-intensive technologies, which might be embodied in high-level energy-using exports and sectors, capital investment and even old technique and equipment imports. Whether the trend in rising energy intensity continues will be significant for China and the rest of the world.     

Industrial agglomeration,geographic innovation and total factor productivity: The case of Taiwan

The paper analyses the impact of geographic innovation on total factor productivity (TFP) in Taiwan in 2001 using 242 four-digit standard industrial classification (SIC) industries. We compute TFP by estimating Translog production functions with K, L, E and M inputs, and measure the geographic innovative activity using both Krugman's Gini coefficients and the location Herfindahl index. We also consider the geographic innovation variable as an endogenous variable and use two stage least squares (2SLS) to obtain a consistent, albeit inefficient, estimator. The empirical results show a significantly positive effect of geographic innovation, as well as R&D expenditure, on TFP. These results are robust for the Gini coefficients and location Herfindahl index, when industrial characteristics and heteroskedasticity are controlled. Moreover the Hausman test shows that the geographic innovation variable should be treated as endogenous which supports the modern theory of industrial clustering regarding innovation spillovers within clusters.     

Modelling machining processes with a view to their optimization and to the adaptive control of metal cutting machine tools

This paper describes an orthogonal machining theory which can be used to determine the stresses, temperatures etc. involved in chip formation from a knowledge of the work material flow stress and thermal properties and cutting conditions. It is shown how these can be used to predict machinability factors such as power consumption, built-up edge range, tool wear rates (tool life) and those cutting conditions which cause plastic deformation of the cutting edge. An oblique machining theory which is more representative of practical machining processes than the orthogonal theory is then described, taking into account machining on more than one cutting edge as in bar turning. Throughout the paper comparisons are made between predicted and experimental results.     

Q-band (26?40 GHz) GaAs FET single-stage amplifier

The high-frequency S-parameters of a 0.3 ?m-gate-length GaAs FET have been measured and compared with the device equivalent circuit model. From the data a Q-band single-stage low noise (3.1 dB) amplifier was designed.     

Effect of transparency within a semiconductor on emissivity mapping for thermal profile measurements of a semiconductor device

The paper reports on infra-red (IR) measurements made on silicon and gallium arsenide substrates which are transparent to IR radiation. The work showed that the measured emissivity is dependent on the wafer back-face technology, for example, a gold heat-sink or epoxy attachment. The work also indicated that the measured emissivity for the thermal mapping of a device is a function of the emitted radiation from the front, back face and layer interfaces, as well as internally reflected radiation and will be dependent on the thickness of the semiconductor wafer. Experimental work has shown that the two-temperature emissivity correction method will give a very accurate value of the total surface emissivity received from the sample     

Infrared radiance and temperature measurements on the mesa side of Gunn diodes

Radiance and temperature profiles for the first time have been measured along the mesa side of Gunn diode samples, using an infrared microscope with a spatial resolution of 2.5 mum. Bulk heat generation occurs in the transit region, but measurements have shown a small amount of additional ohmic heating in the substrate layer, which will influence the maximum temperature of the device. The presented thermal measurements have been used to improve the existing thermal finite-element model of the diode. The measurements also represent an alternative method to obtain a more accurate temperature of the diode top contact without coating the sample with a high emissivity layer.     

An Improved Small-Signal Parameter-Extraction Algorithm for GaN HEMT Devices

A highly efficient and accurate extraction algorithm for the small-signal equivalent-circuit parameters of a GaN high electron-mobility transistor device is presented. Elements of the extrinsic equivalent-circuit topology are evaluated using a modified “cold field-effect transistor” approach whereby the undesirable need to forward bias the device's gate terminal is avoided. Intrinsic elements are determined based on a circuit topology, which identifies, for the first time, a time delay in the output conductance of GaN-based devices. The validity of the proposed algorithm has been thoroughly verified with excellent correlation between the measured and modeled $S$-parameters up to 50 GHz.