In this work, we developed a photocontrollable substrate which was prepared using an azobenzenecontaining self-assembled monolayer (SAM) on the silicon surface via the chemisorption of 3glycidoxypropyltrimethoxysilane (GPTS) and 4-(4 0 -aminophenylazo) benzoic acid (APABA). The prepared surfaces were chemically characterized by X-ray photoelectron spectroscopy (XPS). The reversible photoswitching performance of APABA molecules were investigated by UV spectroscopy in dimethylsulfoxide (DMSO) solution. To understand and control this reversible photoswitchable mechanism and wettability properties, contact angle measurements were performed by using a variety of liquids after UV and visible light irradiation. These contact angle results are used to approximate the components of the APABA-modified surface energy under UV and visible light using the Lifshitz-van der Waals/acid-base approach. The total surface energy (g s ) after visible light irradiation (for trans formation) was calculated to be 37.28 mJ m À2 , whereas the value after UV light exposure (for cis formation) was also calculated to be 36.95 mJ m À2 . All the results demonstrate the great potential to control molecular events within and on the surfaces of molecular constructs using light.

We present a comparison between accurate ab initio calculations and a high-quality experimental data set (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002) of electric-field gradients of Cd at different sites on Ni, Cu, Pd, and Ag surfaces. Experiments found a systematic rule to assign surface sites on (100) and (111) surfaces based on the main component of the electric-field gradient, a rule that does not work for (110) surfaces. Our calculations show that this particular rule is a manifestation of a more general underlying systematic behavior. When looked upon from this point of view, (100), (111) and (110) surfaces behave in precisely the same way. The physical mechanism behind the systematics of the EFG for other 5sp impurities ͑Cd-Ba͒ at different fcc surfaces sites is revealed, showing in a natural way why the first half of the 5p elements shows a coordination dependence that is opposite with respect to the second half.

We investigated the behavior of the forward bias current-voltage-temperature ͑I-V-T͒ characteristics of inhomogeneous ͑Ni/ Au͒-Al 0.3 Ga 0.7 N / AlN / GaN heterostructures in the temperature range of 295-415 K. The experimental results show that all forward bias semilogarithmic I-V curves for the different temperatures have a nearly common cross point at a certain bias voltage, even with finite series resistance. At this cross point, the sample current is temperature independent. We also found that the values of series resistance ͑R s ͒ that were obtained from Cheung's method are strongly dependent on temperature and the values abnormally increased with increasing temperature. Moreover, the ideality factor ͑n͒, zero-bias barrier height ͑⌽ B0 ͒ obtained from I-V curves, and R s were found to be strongly temperature dependent and while ⌽ B0 increases, n decreases with increasing temperature. Such behavior of ⌽ B0 and n is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution ͑GD͒ of the barrier heights ͑BHs͒ at the metal/semiconductor interface. We attempted to draw a ⌽ B0 versus q /2kT plot in order to obtain evidence of the GD of BHs, and the values of ⌽ B0 = 1.63 eV and 0 = 0.217 V for the mean barrier height and standard deviation at a zero bias, respectively, were obtained from this plot. Therefore, a modified ln͑I 0 / T 2 ͒ − q 2 0 2 /2͑kT͒ 2 versus q / kT plot gives ⌽ B0 and Richardson constant A * as 1.64 eV and 34.25 A / cm 2 K 2 , respectively, without using the temperature coefficient of the barrier height. The Richardson constant value of 34.25 A / cm 2 K 2 is very close to the theoretical value of 33.74 A / cm 2 K 2 for undoped Al 0,3 Ga 0,7 N. Therefore, it has been concluded that the temperature dependence of the forward I-V characteristics of the ͑Ni/ Au͒-Al 0.3 Ga 0.7 / AlN / GaN heterostructures can be successfully explained based on the thermionic emission mechanism with the GD of BHs.

The chemical contrast between Si and Ge obtained by scanning tunneling microscopy on Bi-covered Si(111) surfaces is used as a tool to identify two vertical Ge/Si intermixing processes. During annealing of an initially pure Ge monolayer on Si, the intermixing is confined to the first two layers approaching a 50% Ge concentration in each layer. During epitaxial growth, a growth front induced intermixing process acting at step edges is observed. Because of the open atomic structure at the step edges, relative to the terraces, a lower activation barrier for intermixing at the step edge, compared to the terrace, is observed.