Thermodynamic Properties of Krypton. Vibrational and Other Properties of Solid Argon and Solid Krypton

Phonon wave-packet simulations using the quantized definition of energy and a temperature-dependent phonon dispersion relation and phonon density of states

Wave-packet simulations, regarded as phonon dynamics in the literature, have been used to explore interface conductance problems and to study the frequency-based dynamics of systems of particles. In this work we introduce an extension of the method to improve the postsimulation analysis and to add an energy aspect to the definition of a wave packet. In a wave-packet simulation the most populated frequency activated with the wave packet is known through knowledge of the wave number implemented in the atom displacement equation. The one-to-one correspondence of wave number and frequency is known through the phonon dispersion relation (PDR). We add the temperature dependence of this one-to-one correspondence to the analysis of wave packets through consideration of a temperature-dependent PDR and showed the importance of the temperature-dependent PDR in the wave-packet definition by presenting results considering and neglecting the phenomenon. In addition, the temperature-dependent PDR and the density of states provide us the chance to change the nature of the atomic displacement amplitude as an arbitrary parameter to a tuning knob for the amount of energy it carries and utilize the chance to provide a quantitative measure for the validity of molecular-dynamics simulations considering their classical nature in comparison with the quantum particle picture of phonons.

Crystal growth rates in supercooled atomic liquid mixtures

Crystallization is a fundamental process in materials science, providing the primary route for the realization of a wide range of new materials. Crystallization rates are also considered to be useful probes of glass-forming ability^1-3. At the microscopic level, crystallization is described by the classical crystal nucleation and growth theories^4,5, yet in general solid formation is a far more complex process. In particular, the observation of apparently different crystal growth regimes in many binary liquid mixtures greatly challenges our understanding of crystallization^1,6-12. Here, we study by experiments, theory and computer simulations the crystallization of supercooled mixtures of argon and krypton, showing that crystal growth rates in these systems can be reconciled with existing crystal growth models only by explicitly accounting for the non-ideality of the mixtures. Our results highlight the importance of thermodynamic aspects in describing the crystal growth kinetics, providing a substantial step towards a more sophisticated theory of crystal growth.

Measurements of Enthalpy of Sublimation of Ne, N2, O2, Ar, CO2, Kr, Xe, and H2O using a Double Paddle Oscillator

We report precise experimental values of the enthalpy of sublimation (ΔHs ) of quenched condensed films of neon (Ne), nitrogen (N2), oxygen (O2), argon (Ar), carbon dioxide (CO2), krypton (Kr), xenon (Xe), and water (H2O) vapor using a single consistent measurement platform. The experiments are performed well below the triple point temperature of each gas and fall in the temperature range where existing experimental data is very limited. A 6 cm2 and 400 µm thick double paddle oscillator (DPO) with high quality factor (Q ≈ 4 × 105 at 298K) and high frequency stability (33 parts per billion) is utilized for the measurements. The enthalpies of sublimation are derived by measuring the rate of mass loss during temperature programmed desorption. The mass change is detected due to change in the resonance frequency of the self-tracking oscillator. Our measurements typically remain within 10% of the available literature, theory, and National Institute of Standards and Technology (NIST) Web Thermo Tables (WTT) values, but are performed using an internally consistent method across different gases.

Ellipsometry with polarisation analysis at cryogenic temperatures inside a vacuum chamber

In this paper we describe a new variant of null ellipsometry to determine thicknesses and optical properties of thin films on a substrate at cryogenic temperatures. In the PCSA arrangement of ellipsometry the polarizer and the compensator are placed before the substrate and the analyzer after it. Usually, in the null ellipsometry the polarizer and the analyzer are rotated to find the searched minimum in intensity. In our variant we rotate the polarizer and the compensator instead, both being placed in the incoming beam before the substrate. Therefore the polarisation analysis of the reflected beam can be realized by an analyzer at fixed orientation. We developed this method for investigations of thin cryogenic films inside a vacuum chamber where the analyzer and detector had to be placed inside the cold shield at a temperature of T ≈ 90 K close to the substrate. All other optical components were installed at the incoming beam line outside the vacuum chamber, including all components which need to be rotated during the measurements. Our null ellipsometry variant has been tested with condensed krypton films on a highly oriented pyrolytic graphite substrate (HOPG) at a temperature of T ≈ 25 K. We show that it is possible to determine the indices of refraction of condensed krypton and of the HOPG substrate as well as thickness of krypton films with reasonable accuracy.

The Thermodynamic properties of solid and fluid helium-3 and helium-4 above 3 °K at high densities

Measurements have been made of the specific heat at constant volume of solid 3He from 3 K up to the melting point at a number of different densities corresponding to pressures up to 2000 atm. The measurements have been extended through the melting region at constant volume up to 29 °K in the fluid phase. For comparison similar measurements have been made on 4He at four different densities. By combining these data with the p- V- T data of Mills & Grilly (1955) and Grilly & Mills (1959) the complete thermodynamic properties of the solids have been derived in the relevant pressureand temperature range. The results can be understood semi-quantitatively in terms of the zeropointenergy of the solids and a quasi-harmonic model of the lattice vibrations. A brief discussion of the specific heat of the fluid phase is also given.