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Spray forming is an advanced casting process that produces refined and homogenous microstructure directly from the liquid metal regardless of the alloy system. However, the microstructure evolution during spray forming is complex because the process comprises two sequential steps with very different cooling rates, i.e., atomization and deposition. It is well known that the microstructure of cast irons is highly dependent on the chemical composition and the cooling rate imposed to the liquid. In order to better understand the microstructural evolution during solidification by spray forming, this study investigated the solidification of two cast irons with different stable–metastable eutectic temperature interval (ΔTES−M), 30 K and 17 K. The microstructures of both overspray powders presented a dendritic array of austenite with cementite in the inter-dendritic spacing. Despite the high cooling rates imposed to the alloys during the atomization step, the final microstructure was defined by the cooling conditions prevailing during the final step of deposit solidification and stable eutectic was formed. This was ascribed to the dynamic process involving heating and remelting of the low melting temperature phases present in the droplets that arrives completely or partially solid in the deposition zone.

We developed a method to calculate the dark current of quantum-well infrared photodetectors without the need to fit any experimental data or to perform extra transport measurements on other samples. The temperature range of the calculations was extended below 30 K by combining a thermionic model valid at high temperature and a miniband-transport model valid at low temperature whenever any superlattice characteristics were relevant in the device.

Capacitance versus voltage, C–V, measurements are used to identify the origin of the difference between current versus voltage, I–V, characteristics of quantum well infrared photodetector, QWIP, devices fabricated simultaneously on the same wafer, i.e., same epitaxial layers. The devices have similar I–V curves at low bias but differ significantly at higher voltages. It is shown that the charge buildup inside the multiple quantum well structure is responsible for changing the conduction mechanism at voltages lower than that would be expected if the entire structure was subjected to a uniform electric field. This charge buildup varies from device to device, indicating local characteristics dependence. Although a non-uniform electric field is established, as identified by C–V measurements, none of the known fingerprints related to the formation and propagation of electric field domains are present in the I–V curves, i.e., no plateau or negative differential conductivity were observed.

It is shown that the inclusion of dopant segregation, negative differential mobility and thermal assisted tunnelling to the calculation of dark current activation energy provides a much better fitting to the experimental results than geometrical or Poole–Frenkel models and handles well its voltage asymmetry and nonlinearity. Besides, the transport model obtained is able to fit the current–voltage curves for both bias polarities with almost the same transport parameters. A practical method to estimate the segregation length is discussed. A consequence of this method is a more accurate set of values for the transport parameters of the structure, considering direct and reverse bias.

We propose a model that realistically describes the experimental noise curves of GaAs/AlGaAs quantum-well intersubband photodetectors and that, additionally, allows the determination of some important transport parameters of these devices. The analysis was based on the quantum mechanical calculation of the capture lifetime in a quantum well and on the assumption that the capture probability can be explicitly expressed as a function of the electronic thermal velocity at zero bias and of the saturation velocity at large bias. Our experimental and theoretical results point out that the plateau observed in the noise measurements at low temperature and low electric field is due to an extra conduction path through the miniband of the superlattice formed by the ground states of all the wells.

The authors describe a novel approach to the measurement of nanofriction, and demonstrate the application of the method by measurement of the coefficient of friction for diamondlike carbon (DLC) on DLC, Si on DLC, and Si on Si surfaces. The technique employs an atomic force microscope in a mode in which the tip moves only in the z (vertical) direction and the sample surface is sloped. As the tip moves vertically on the sloped surface, lateral tip slipping occurs, allowing the cantilever vertical deflection and the frictional (lateral) force to be monitored as a function of tip vertical deflection. The advantage of the approach is that cantilever calibration to obtain its spring constants is not necessary. Using this method, the authors have measured friction coefficients, for load range 0