The thermal decomposition and isomerization processes of C3−C4 alkyl radicals, 1-C5H11, and 1-C6H13 have been investigated by using a shock-tube apparatus coupled with atomic resonance absorption spectrometry (ARAS). Isomeric alkyl radicals were generated by the thermal decomposition of respective alkyl iodides. Branching fractions for the competitive pathways (C−C bond cleavage, C−H bond cleavage, and isomerization) have been determined by following the hydrogen-atom concentration by ARAS. In the investigated temperature range (900−1400 K), for all alkyl radicals, the energetically favored C−C bond cleavage was found to dominate over the C−H bond cleavage. The 1,2 or 1,3 isomerization reaction was found to be minor in C3 and C4 alkyl radicals. On the other hand, the results for 1-C5H11 and 1-C6H13 radicals clearly show the occurrence of 1,4 and 1,5 isomerization reactions. From an RRKM analysis of the present result and the previous lower temperature data, with consideration of the tunneling effect, the threshold energies for 1,4 and 1,5 primary-to-secondary isomerization reactions were evaluated to be 21.5 ± 1.2 and 14.6 ± 1.2 kcal mol-1, respectively. The high-pressure limit rate constants for the isomerization processes were evaluated as k ∞(1-C5H11 → 2-C5H11) = 4.88 × 108 T 0.846 exp(−19.53 [kcal mol-1]/RT) s-1 and k ∞(1-C6H13 → 2-C6H13) = 6.65 × 107 T 0.823 exp(−12.45 [kcal mol-1]/RT) s-1 for the temperature range 350−1300 K. Even under relatively high-pressure conditions (∼1 atm), the falloff effect was shown to be important for multichannel dissociation systems. The nonequilibrium effect in the thermal decomposition of energized alkyl radicals formed in the high-temperature reaction system, which has been first suggested by Tsang et al. [J. Phys. Chem. 1996, 100, 4011] was discussed. The possible effect of the tunneling in the isomerization reactions was discussed in comparison with previous lower temperature data.

The competition between the C-I bond fission and the four-center HI elimination in the thermal unimolecular decomposition of C 3 -C 4 alkyl iodides has been investigated at temperatures of 950-1400 K and pressures around 1 atm by a shock tube technique. The concentration of iodine atoms was followed by atomic resonance absorption spectrometry. For primary iodides, the absolute rate constants were measured at temperatures of 950-1100 K. The branching fractions for C-I bond fission channels were determined for all isomers of C 3 and C 4 alkyl iodides at temperatures of 950-1400 K. A drastic change in the branching fraction for the C-I bond fission channel was observed from primary iodides (0.6-0.9) to secondary iodides (0.2-0.4), and further to tertiary iodide (<0.05), which was mainly ascribed to the lowering of the threshold energy for the HI elimination channel from primary to secondary (by ∼14 kJ mol -1 ) and from secondary to tertiary (by ∼20 kJ mol -1 ) iodides. The R-CH 3 substituent effect to the activation energy was in good accordance with previous investigations. The observed temperature dependence of the branching fraction could not be explained by the simple high-pressure limit treatment, and an RRKM analysis showed that the proper treatment of the mutual effect of two dissociation channels is essentially important to reproduce the observed branching fractions and their temperature dependence. A simple interpretation for the R-CH 3 substituent effect is presented in terms of the avoided intersection between ionic dissociation (RI f R + + I -) surface and the repulsive surface of HI approach to the double bond.

A channel layer substitution of a wider bandgap AlGaN for conventional GaN in high electron mobility transistors (HEMTs) is one possible method of enhancing the breakdown voltage for higher power operation. Wider bandgap AlGaN, however, should also increase the ohmic contact resistance. We utilized a Si ion implantation doping technique to achieve sufficiently low resistive source/drain contacts, and realized the first HEMT operation with an AlGaN channel layer. This result is very promising for the further higher power operation of high-frequency HEMTs.

A scattering-type scanning near-field optical microscope in long-wavelength infrared (LWIR) region is developed by using an extremely sensitive detector, called the charge-sensitive infrared phototransistor. A tungsten probe attached to a quartz tuning fork is controlled in shear-force mode. Evanescent wave at a sample surface is periodically scattered by slowly (2 Hz) modulating the probe in the direction normal to the sample surface. Near-field microscopy of thermal LWIR radiation from room-temperature Au/GaAs gratings is demonstrated without using any external illumination or excitation. Achieved spatial resolution is better than 300 nm.

An experimental method to determine the temperature dependence of residual stress in threedimensional (3D) structures was developed using polarized Raman spectroscopy. Stresses of a copper-filled silicon via at three temperatures, 223, 298, and 413 K were derived by measuring the frequency shift of the optical phonons through the backscattering geometry from the cross-section of the structure and assuming non-isotropic biaxial (horizontal and depth) stresses on the crosssection. Both stress components changed from tensile to compressive in almost all areas as the temperature changed from 213 to 413 K. The absolute stress values increased at both low and high temperatures and were smallest at 298 K, which was nearest to the process temperature of copper filling by plating. The main cause of stress is considered to be the difference in the coefficient of thermal expansion between copper and silicon. These results indicate that the temperature dependence of stress of copper-filled vias is affected mainly by their fabrication temperature. Process temperature is one of the key factors for the reduction of thermal stress in 3D structures such as integrated circuits connected by through-silicon vias. V C 2013 AIP Publishing LLC.