Henry A. Kurtz

Calculation of vibrational dynamic hyperpolarizabilities for H2O, CO2, and NH3

Dynamic vibrational first and second hyperpolarizabilities, applicable to a number of nonlinear optical processes, have been calculated for H2O, CO2, and NH3 at a typical laser frequency. As a percentage of their electronic counterparts, they range from being very small to being on the order of 20–30 %. The static values have also been calculated and are much larger. The calculations were based on perturbation theory and required knowledge of (a) first and second derivatives of the electrical properties (dipole moment, polarizability, and first hyperpolarizability functions) with respect to the normal coordinates, and (b) the harmonic and first anharmonic force constants. These were found at both the SCF and MP2 levels of approximation. In most cases electron correlation has a marked effect on the vibrational hyperpolarizabilities. Anharmonicity contributions are relatively small except for the static case and for the dc‐Kerr effect.

An augmented effective core potential basis set for the calculation of molecular polarizabilities

Calculations of molecular polarizabilities require basis sets capable of accurately describing the responses of the electrons to an external perturbation. Unfortunately, basis sets that yield suitable quantitative results have traditionally been all‐electron sets with large numbers of primitives, making their use computationally intractable even for moderately sized systems. We present a systematic augmentation of the effective core potential basis set of Stevens et al. [J Chem Phys 81, 12 (1984), Can J Chem 70, 612 (1992)] for 39 main group elements based on the procedure used to construct diffuse and polarization functions in the well‐known Sadlej basis sets [Collec Czech Chem Comm 53, 1995 (1988)]. Representative calculations have been performed and we have shown that results to within 1% of all‐electron calculations using the Sadlej basis set can be obtained for <1–35% of the computational cost using this new basis set.

The use of semiempirical energy partitioning terms in the study of through space (homoaromatic) interactions

Abstract MNDO and AMI calculations, including configuration interactions, were performed on cycloheptatriene (2), 1,6-methano[10]annulene (3), and the tautomeric elassovalenes (4), (5), and (6). The goal of this study is to examine these systems and assess indicators of the importance of through space (homoaromatic) interactions. It is established that the two-center energy partitioning terms are capable of detecting favorable (negative two-center term) through space interactions. In cases of cyclic conjugation (homoconjugation), it is also shown that the inclusion of CI is necessary.

POINT DEFECTS IN Si-SiO2 SYSTEMS: CURRENT UNDERSTANDING

Perhaps no other technology developed in the 20th century plays such an important role on the daily life of today’s civilized society as microelectronics. The rapid growth experienced by complementary-metal-oxide-semiconductor (CMOS) technology since the first metal-oxide semiconductor field effect transistor (MOSFET) was realized by Kahng [1] some 40 years ago, accompanied by the advances in integrated circuit (IC) fabrication, has been revolutionizing the field of electronics. The past thirty years have also witnessed tremendous progress toward the miniaturization of CMOS devices, a trend that continues toward further downscaling of the device feature size. While miniaturization of CMOS devices has resulted in higher packing density (more devices per unit area), higher circuit speed (faster computers), and lower power dissipation, it has also created new problems and issues that need resolution for the reliability of the contemporary and future generation technology. In order to appreciate the problems and reliability issues associated with the steady downscaling of CMOS devices, a schematic design of a MOSFET is shown in Fig. 1. The top metal, generally a polycrystalline-silicon (poly-Si) acts as a gate. A thin amorphous SiO1 dielectric layer underneath the gate electrode, normally referred to as the “gate oxide”, lies above the channel regions which separates the “source” (carrier donor) and the “drain” (carrier acceptor) layers. The distance between the source and the drain under the gate dielectric is called the “channel length”. Upon biasing the gate electrode, an image charge builds up under the gate initially forming a “depletion region” and eventually at a certain voltage (called the threshold voltage, Vth) inverts the silicon surface and current starts flowing in the channel between the source and the drain. “Decreasing the feature size” of MOSFET generally means reducing the channel length. The shorter the channel length, the faster the carrier flow and the higher the drive current resulting in higher speed. Also, continued reduction in the supply voltage has lowered power consumption. Of course with the miniaturization of the device components, the primary benefit is that much larger numbers of transistors can be integrated per unit area on the wafer, thus increasing the device density in very large integrated circuits (VLSI). Such desirable features have been the driving force toward miniaturization of the MOSFET.

Proton mobility in a-SiO/sub 2/

A model for proton mobility in a-SiO/sub 2/ is developed. Theoretical first-principles calculations are performed to test this model by obtaining pathways and activation energies for proton motion.

The effect of near-interface network strain on proton trapping in SiO/sub 2/

The buildup of positive charge during annealing in forming gas at 600/spl deg/C was compared for various types of Si/SiO/sub 2/ interfaces. Our data suggest a correlation between the presence of stressed bonds in the SiO/sub 2/ network near the Si/SiO/sub 2/ interface, and the ratio of fixed vs. mobile positive charge (protons) detected near the interface after performing a forming-gas annealing. We further propose that the presence of these stressed bonds near the interface is correlated with the oxygen deficiency at the interface and with the confinement of the oxide due to the presence of a Si cover layer. A model based on first-principles quantum mechanical calculations shows a significant decrease in the overall proton binding energy with increasing network strain near the interface. These calculations support our model of mobile proton generation at Si/SiO/sub 2/ interfaces with large densities of stressed bonds.

Role of bond coordination and molecular volume on the dielectric constant of mixed-oxide compounds

First-principles calculations have been employed to study clusters of Zr embedded in SiO2. Stable complexes are found with four, six, and seven oxygens coordinated to the Zr atom. Consistent with experiment, the higher coordinated complexes are the most stable. These also have a higher density, and hence, smaller molar volume. This smaller molar volume provides an explanation of the increased dielectric constant of ZrxSi1−xO2 mixed-oxide systems for small amounts of Zr (x<0.3). An unusual sevenfold coordinated structure is described.

New fundamental defects in a-SiO/sub 2/

The atomic structure and spin properties of two previously undescribed amorphous silicon dioxide fundamental point defects have been characterized for the first time by ab initio quantum mechanical calculations. Both defects are electrically neutral trivalent silicon centers in the oxide. One of the defects, the X-center, is determined to have an O/sub 2/Si/spl equiv/Si/sup /spl dagger// atomic structure. The other defect, called the Y-center, is found to have an OSi/sub 2//spl equiv/Si/sup /spl dagger// structure. Calculated electronic and electrical properties of the new defect centers are consistent with the published characteristics of the oxide switching trap or border trap precursors.

Modeling intermolecular effects on nonlinear optical properties of transition-metal complexes. An effective core potential study.

An initial effort to study the nonlinear optical (NLO) properties of interacting transition-metal-oxo complexes is presented and studied by effective core potential approaches. Osmium tetroxide is used for this study. Favorable intermolecular interaction effects, even within this weak interaction regime, that yield enhancements in NLO properties have been found. Interaction effects increase alpha (polarizability) up to 6% and gamma (second hyperpolarizability) up to 100% relative to the isolated monomer result for OsO4. The magnitude of the interaction (hyper)polarizabilities, and indeed even the sign, is found to be quite sensitive to the relative orientation of the osmium tetroxide monomers.

NLO properties of interacting polyene chains

Abstract The effects of interchain interactions on the nonlinear optical properties for polyacetylene oligomers of various chain lengths are examined at the semiempirical level using a supermolecule model approach. Results have been obtained for energy, polarizability, and second hyperpolarizability. This study shows that interchain interactions tend to attenuate the polarizability and second hyperpolarizability for polyacetylene oligomers. These results point to the necessity of considering intermolecular interactions in theoretical studies of nonlinear optical properties in condensed phases.