We describe a new approach to producing a sample of supercooled molecular para-hydrogen (pH2) at temperatures down to 1.3 K, well below the predicted superfluid transition temperature for pH2. Unique features of the present scheme are 1) the suppression of both homogeneous and heterogeneous nucleation processes and 2) the possibility to control the liquid temperature in a wide range across the transition. As a first step we demonstrate the stable production in vacuum of continuous hydrogen filaments of macroscopic dimensions. This technique coupled to light scattering experiments will enable microscopic investigations of superfluidity in liquid para-hydrogen.

The temperature dependence of germanium surface segregation during growth by solid source SiGe molecular beam epitaxy (MBE) was studied by x-ray photoelectron spectroscopy and kinetic Monte Carlo (KMC) modeling. Germanium segregation persisted at temperatures 60 °C below that predicted by a two-state exchange model. KMC simulations, where film growth, surface diffusion, and surface segregation are modeled consistently, successfully describe the low temperature segregation of germanium. Realistic descriptions of MBE must follow the physical rates of the growth, surface diffusion, and surface segregation processes.

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