T. A. El-Brolossy

Determination of thermophysical parameters of porous silicon using a photothermal technique

The effective thermophysical properties, diffusivity (α), effusivity (e), and thermal conductivity (k) have been measured by photoacoustic (PA) and photothermal interferometry (PTI) for silicon samples of varying porosities. The experimental results show a reduction in the thermal conductivity with increasing the porosity, by two orders of magnitude. The results obtained by PTI are compared to those obtained by the PA technique.

Photomodulation of the coupled plasmon-LO phonon of GaAs surfaces

Photomodulation of the coupled plasmon–LO phonon modes has been employed to determine the change in both the surface charge density and the depletion electric field as a function of photomodulation beam (PMB) intensity. The samples are two pieces of highly doped (001) n-type GaAs. The total surface charge density has been obtained as a function of the photomodulating intensity using the dependence of the unscreened LO phonon on the depletion width. We are able to separate the impact of the PMB on the surface electric field from the impact on the depletion width. This allows a separate determination of the change in depletion electric field, which reaches ~73% of its original value at the highest intensity used for PMB.

Photomodulation Raman Scattering Spectroscopy of Metal — GaAs Interfaces

Photomodulation Raman spectroscopy (PM‐RS) has been employed to investigate the effect of the interfacial minority carrier traps in metal: n‐type GaAs interfaces; using the forbidden LO phonon scattering as a prob. Photomodulating‐pumping beam (PMB) will decrease the interfacial field and consequently the intensity of forbidden LO scattering. Two molecular beam epitaxy junctions of 80 A° Au on n‐type GaAs (001) substrate with two different doping densities were used. The change in the band bending has been obtained as a function of the photomodulating intensity for the low doping case. The minority carrier’s lifetime was also determined through dynamical measurements for the PM‐RS intensity.

Thermal diffusivity measurements of transparent liquid and powder materials using PAS

Thermal diffusivity of organic dye CV in powder form has been measured using PA effect. It is shown that this method permits to estimate the thermal diffusivity for transparent solvents using the dye at low concentration as a precursor.