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A reflection second harmonic microscope has been developed, equipped with a 2D photodetector. It is shown that the microscope is particularly sensitive to slab structures.

We have investigated the optical transitions in individual self-assembled InAs/Al[sub 0.6]Ga[sub 0.4]As quantum dots (QDs) by means of scanning-tunneling-microscope (STM) light-emission spectroscopy. Localized bright features were observed in the spectrally resolved light intensity images measured by injecting electrons from the STM tip. The light emission spectra measured over the bright features showed single emission peaks having different peak energies with linewidths of 30–45 meV. By comparing these results with atomic-force-microscope images and photoluminescence (PL) spectra, we have identified the bright features with the ground-state interband transition from individual InAs QDs. The emission peak energies were compared with the transition energies calculated for pyramidal-shaped QD structures, based on a single-band and constant-confining-potential model. A reasonable agreement was obtained between the experimental and calculated results. The emission linewidth of individual dots is much narrower than the linewidth (∼200 meV) measured by PL from an ensemble of dots. This fact demonstrates the importance of measuring the linewidth for individual dots rather than for an ensemble of dots with size distribution. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electromagnetic enhancement effect in scanning tunneling microscope (STM) light emission from GaAs has been investigated by the finite difference time domain method. We have calculated the intensity of light emitted by the recombination of minority carriers injected from the tip and majority carriers in the sample. The results depend not only on the material and the shape of the tip but also on light polarization. When the tip is tungsten whose dielectric function has a positive real part at 1.5 eV, the p-polarized light intensity depends strongly on the size of the tip and the location of recombination. However, the s-polarized light emission depends only weakly on these parameters. If the tip is a perfect metal, the p-polarized light intensity becomes a few times stronger than that for the W tip of the same shape. On the other hand, the s-polarized light intensity becomes weaker than that for the W tip due to the electromagnetic screening effect of a perfect metal. We conclude that the combination of the W tip and s-polarized light detection is suitable for precise measurement of the tip-position dependence of STM light emission properties. A tip with a negative value of the real part of dielectric function is preferable to the W tip, if one does not analyze the tip-position dependence of STM light emission, because STM light emission is enhanced relative to the case of the W tip. [ABSTRACT FROM AUTHOR]

We have investigated the formation mechanism of misfit dislocations of GaAs/InGaAs multiquantum well structures by means of photoluminescence (PL) microscopy using the scanning near-field optical microscope. In the PL images, dark lines appeared along both [110] and [&1macr;10] directions. From comparison with the surface topographic images, we found that these dark lines correspond to misfit dislocations, which give rise to nonradiative recombination centers in the InGaAs well. The density of dark lines in the 〈110〉 directions as a function of the total layer thickness shows the existence of two critical layer thicknesses for the formation of misfit dislocations. The two distinct critical thicknesses are explained in terms of the modified J. W. Matthews and A. E. Blakeslee, [J. Cryst. Growth 27, 118 (1974)] model in which a lattice frictional force proportional to the In mole fraction is taken into account. [ABSTRACT FROM AUTHOR]

Research is done on the optical transitions in individual self-assembled InAs/Al0.6Ga0.4As quantum dots (QDs) by means of scanning-tunneling-microscope (STM) light-emission spectroscopy. In conclusion, the importance is demonstrated of measuring the linewidth for individual dots rather than for an ensemble of dots with size distribution.

We have carried out a normal mode analysis of the molecular vibrations of pyridine adsorbed on silver surfaces or coordinated to various molecules and ions. There are two types of bonding that result in distinct shift patterns of the normal mode frequencies upon adsorption or coordination. ‘‘Metal ion-type bonding’’ is characterized by a strong pyridine–substrate bond which results in large frequency shifts, while ‘‘halogen-type bonding’’ causes comparatively smaller shifts due to weaker bonding. Adsorption on silver surfaces corresponds to weak halogen-type bonding, and the major cause of the observed frequency shift is the electron transfer (back donation) into the aromatic ring upon adsorption. [ABSTRACT FROM AUTHOR]