Search

The crystallization kinetics of nanoscale amorphous solid water (ASW) films are investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). TPD measurements are used to probe surface crystallization and RAIRS measurements are used to probe bulk crystallization. Isothermal TPD results show that surface crystallization is independent of the film thickness (from 100 to 1000 ML). Conversely, the RAIRS measurements show that the bulk crystallization time increases linearly with increasing film thickness. These results suggest that nucleation and crystallization begin at the ASW/vacuum interface and then the crystallization growth front propagates linearly into the bulk. This mechanism was confirmed by selective placement of an isotopic layer (5% D 2 O in H 2 O) at various positions in an ASW (H 2 O) film. In this case, the closer the isotopic layer was to the vacuum interface, the earlier the isotopic layer crystallized. These experiments provide direct evidence to confirm that ASW crystallization in vacuum proceeds by a “top-down” crystallization mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Condensed water particles are known to exist in the high latitude upper mesosphere during the summer months. However, the mechanism or mechanisms through which they nucleate remains uncertain. It is postulated here that particles of amorphous solid water (ASW, condensed water with a non-crystalline structure) may nucleate homogeneously in the summer mesosphere. Using classical nucleation theory and a one-dimensional model, it is shown that more than 105 cm−3 amorphous solid water particles can nucleate homogeneously under mesopause conditions. Furthermore, it is shown that homogeneous nucleation competes with heterogeneous nucleation on meteoric smoke particles when the cooling rate is >0.5K/h. The homogeneous nucleation of amorphous solid water could provide an explanation for the high density of ice particles (many thousands per cm3) thought to be required for electron depletions in the upper mesosphere. A parameterisation for homogeneous nucleation is presented which can be used in other mesospheric cloud models. [Copyright &y& Elsevier]

• Amorphous solid water acts as a unique positive-tone electron resist. • Ice thickness removed by electron irradiation has a strong linear dependence on applied electron doses. • Ice formed on hydrophilic surfaces resists more irradiation than on the hydrophobic. • Ice nanodots and "micro-snowflakes" are attained after e-beam patterning. • Ice can be used to regulate lithographic properties of conventional electron resists. Amorphous solid water (ASW) formed by vapor deposition at cryogenic temperatures acts as an emerging competitive electron resist with virtues like direct patterning and easy removal. In this work, we systematically study the properties of the ASW resist and assess its performance for lithographic applications. Dose curves show that ASW has a low contrast of ~1.6 and it is barely affected by the incident electron energy. Ice elimination is almost linear to applied electron doses. The calculated rate is around 30 μm3/μC at 10 kV, implying approximately seven electrons remove one water molecule in this case. The minimum linewidth of 12 nm is obtained on a 120-nm-thick ASW film and refined nanostructures such as ice nanodots and "micro-snowflakes" are also presented. Finally, we perform e-beam exposure on a bilayer configuration of ASW/PMMA resist and provide an alternative way to regulate lithographic properties of conventional electron resists. [ABSTRACT FROM AUTHOR]