I. Delgadillo-Holtfort

Time-domain and lock-in rate-window photocarrier radiometric measurements of recombination processes in silicon

Time-domain and lock-in rate-window photocarrier radiometry (PCR) configurations are introduced both experimentally and theoretically to investigate the responses of p- and n-type Si wafers under a repetition-period-scanned square-wave-modulated super-band-gap laser beam which produces free excess photocarriers. The complete asymmetric time-domain carrier diffusion and recombination boundary-value problem with different front- and back-surface recombination velocities was solved in terms of the full spectrum of spatial eigenmodes and used to fit the time-domain data. The accurate measurement of the photocarrier transport properties (bulk lifetime, surface recombination velocities, and ambipolar diffusivity) was found to require the linear superposition of all the effective decay lifetimes associated with the eigenmode spectrum. The effects of the infinite prior pulse train to the current photocarrier radiometric response wave form were quantified and were found to be very important for certain ranges of t...

Photothermal characterization of protective layers and surface modifications

Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications related to friction wear, and the effects of mechanical and thermal cycling of SMA samples have been analysed with respect to the depth profile of the thermal properties by using IR detection of thermal waves. The advantage of IR detection of thermal waves is that this method is most appropriate for remote sensing under industrial conditions, working absolutely contactless with remote detection and without any sample preparation.

Surface modifications and surface-protective coatings analyzed by means of thermal waves (invited) (abstract)

The depth profiles of the thermophysical properties of alloy systems, for example, shape memory alloys (NiTi), steel, and tool steel, can vary considerably due to rolling, surface machining, heat treatment, mechanical wear, and erosion. The same is true for coated tool steel samples, which show variations of the effective thermal depth profiles due to the effects of substrate preparation and deposition of the coatings, for example, plasma-etching, arc erosion, nitriding, chemical vapor deposition (CVD), physical vapor deposition (PVD), sputter deposition, and plasma spraying. In this work we present a large variety of measured effective thermal depth profiles. In a first step, we identify the effects of coating deposition and substrate preparation on the measured depth profiles. In a second step, we identify and try to quantify the effects of mechanical wear and erosion of both coated and uncoated surface. To this finality, the signals, which have been measured with the help of IR radiometry as a function...

Photothermal depth profiles of mechanically and electrolytically polished NiTi shape memory alloys (abstract)

Machining of NiTi shape memory alloys (SMA) is difficult due to the required special tools, techniques, and the wear of cutting tools. Thus metal injection molding (MIM) of NiTi powders followed by polishing processes may be an alternative fabrication process for SMA components. Transient heat input across the surface and heat transport inside SMA components are important aspects for their functional efficiency. In this work the influence of polishing processes on the thermal depth profiles of SMA materials and the thermal bulk properties of MIM samples are analyzed with the help of photothermal IR radiometry. The effects of polishing have been studied both for polycrystalline nearly equiatomic NiTi alloy and MIM samples. Bulk samples, cut from a polycrystalline ingot of nearly equiatomic NiTi, had first been heat treated and flash cooled to reduce the concentration of nonequiatomic precipitations. In the second step, sample 1 was polished mechanically with a plane grinder, sample 2 was polished electroch...