The vibrational dynamics of polyatomic solutes in polyatomic liquid and glassy solvents are examined using picosecond infrared photon echo experiments and pump-probe experiments from room temperature to 10 K. The photon echo experiments measure T2, the homogeneous dephasing time (homogeneous line shape), while the pump-probe experiments measure the vibrational lifetime, TI, and the orientational relaxation dynamics.By combining these measurements, a complete analysis of vibrational dynamics is obtained in the liquid, in the supercooled liquid, through the glass transition, and in the glass. Experiments were conducted on the asymmetric CO stretching mode of tungsten hexacarbonyl (-1980 cm-I) in 2-methylpentane (2-MP), 2-methyltetrahydrofuran, dibutyl phthalate (DBP), carbon tetrachloride, and chloroform. The experiments were conducted using the picosecond IR pulses from a superconducting-accelerator-pumped free electron laser. The absorption line widths for all glasses are massively inhomogeneously broadened at low temperature. In the room temperature liquids, while the vibrational line in 2-MP is homogeneously broadened, the line in DBP is still extensively inhomogeneously broadened. The temperature dependences of the homogeneous line widths in the three glasses are a Tz power law. The contributions of vibrational pure dephasing, orientational relaxation, and population lifetime to the homogeneous line shape are examined in detail in the 2-MP solvent. The complete temperature dependence of each of the contributions is determined. In addition, the temperature dependence of TI is observed to be "inverted" in most of the solvents; Le., the lifetime becomes longer as the temperature is increased. of the anharmonic coupling matrix elements.

Metal oxides with high dielectric constants have the potential to extend scaling of transistor gate capacitance beyond that of ultrathin silicon dioxide. However, during deposition of most metal oxides on silicon, an interfacial region of SiOx can form that limits the specific capacitance of the gate structure. We have examined the composition of this layer using high-resolution depth profiling of medium ion energy scattering combined with infrared spectroscopy and transmission electron microscopy. We find that the interfacial region is not pure SiO2, but is a complex depth-dependent ternary oxide of Si–Tax–Oy with a dielectric constant at least twice that of pure SiO2 as inferred from electrical measurements. High-temperature annealing crystallizes the Ta2O5 film and converts the composite oxide to a more pure SiO2 layer with a lower capacitance density. Using low postanneal temperatures, a stable composite oxide structure can be obtained with good electrical properties and an effective SiO2 thickness of less than 2 nm with ∼10 nm of composite oxide.

Articles you may be interested inVibrational spectroscopy and relaxation of an anharmonic oscillator coupled to harmonic bath Picosecond infrared pump-probe experiments are used to measure the vibrational lifetime of the asymmetric (T 1u ) CO stretching mode of W͑CO͒ 6 in supercritical CO 2 , C 2 H 6 , and CHF 3 as a function of solvent density and temperature. As the density is increased at constant temperature from low, gaslike densities, the lifetimes become shorter. However, in all three solvents, it is found that within a few degrees of the critical temperature (T r ϵT/T c Ϸ1.01), the lifetimes are essentially constant over a wide range of densities around the critical value ( c ). When the density is increased well past c , the lifetimes shorten further. At higher temperature (T r ϭ1.06) this region of constant vibrational lifetime is absent. Infrared absorption spectra of W͑CO͒ 6 and Rh͑CO͒ 2 acac in supercritical CO 2 , C 2 H 6 , and CHF 3 acquired for the same isotherms show that the vibrational spectral peak shifts follow similar trends with density. The peak positions shift to lower energy as the density is increased. Near the critical point, the peak positions are density independent, and then redshift further at densities well above c . It is shown that critical fluctuations play a dominant role in the observed effects. Theoretical calculations ascribe the density independence of the observables to the cancellation of various rapidly changing quantities near the critical point. The theory's calculation of density independence implicitly involves averages over all local densities and does not involve any form of solute-solvent clustering.

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The temperature-dependent vibrational population dynamics and spectral diffusion of the CO stretching mode of tungsten hexacarbonyl in 2-methylpentane are observed from the room temperature liquid to the low temperature glass using picosecond infrared transient grating and pump–probe experiments. These experiments were performed between 10 and 300 K on the triply degenerate T1u asymmetric CO stretching mode at 1984 cm−1 using pulses with bandwidths narrower and wider than the absorption bandwidth of the transition. The rate of vibrational population relaxation (100≤T1<150 ps) is observed to decrease with increasing temperature. The orientational dynamics for this transition are observed on a faster time scale than the population relaxation. Although the liquid viscosity changes over 14 orders of magnitude, the orientational relaxation rate slows by less than one order of magnitude over the full temperature range. By comparing polarization-dependent experiments performed with both narrow and broad bandwidth transform-limited pulses, it is possible to measure temperature-dependent spectral diffusion in both the liquid and the glass. The spectral diffusion and the orientational relaxation are shown to be intimately related. It is proposed that both arise from the time evolution of the superposition of the three degenerate states created by the excitation pulse.