Sputtering yield measurements at glancing incidence using a quartz crystal microbalance

Low energy sputtering yields at grazing incidence have been investigated experimentally using a quartz crystal microbalance (QCM) technique. This method involved precoating the QCM with a thin film of the desired target material and relating the resonance frequency shift directly to mass loss during ion bombardment. A highly focused, low divergence ion beam provided a well defined incidence angle. Focusing most of the ion current on the center of the target allowed for higher sensitivity by taking into account the radial mass sensitivity of the QCM. Measurements of Mo, Cu, and W sputtering yields were taken for low energy (80–1000 eV) Xe+ and Ar+ to validate this experimental method. The target films ranged from 3.5 to 8.0 µm in thickness and were deposited so that their crystal structure and density would match those of the bulk material as closely as possible. These properties were characterized using a combination of scanning electron microscope imagery, profilometry, and x-ray diffraction. At normal incidence, the sputtering yields demonstrated satisfactory agreement with previously published work. At angles of incidence up to 40° off normal, the data agreed well with predictions from existing theoretical models. Sputtering yields were found to increase by a factor of 1.6 over this range. The optimum angle for sputtering occurred at 55°, after which the yields rapidly decreased. Measurements were taken up to 80° from the surface normal

Beam investigations of D2 adsorption on Si(100): On the importance of lattice excitations in the reaction dynamics

The adsorption of D2 on Si(100) has been investigated by means of supersonic molecular beam techniques. We have succeeded in measuring the dependence of the molecular D2 sticking coefficient S on surface temperature Ts and nozzle temperature Tn. The sticking coefficient increases gradually in the range 300≤Tn≤1040 K. The influence of increased v=1 population has not been deconvoluted from the effects of translational energy alone. The dependence on Ts is more interesting. With an incident translational energy of 65 meV, S rises from a value insignificantly different from the background level to a maximum value of (1.5±0.1)×10−5 at Ts=630 K. The decrease in the effective sticking coefficient beyond this Ts is the result of desorption during the experiment. Having established that S increases with both increasing molecular energy and increasing sample temperature, we have demonstrated directly for the first time that the adsorption of molecular hydrogen on Si is activated and that lattice vibrational excitations play an important role in the adsorption process

Hydrogen adsorption on and desorption from Si: Considerations on the applicability of detailed balance

The translational energy of D2 desorbed from Si(100) and Si(111) surfaces was measured and found roughly equal to the thermal expectation at the surface temperature Ts. Combining these results with previously measured internal state distributions, the total energy of the desorbed molecules is approximately equal to the equilibrium expectation at Ts. Thus adsorption experiments, which suggest a large energetic barrier, are at variance with desorption experiments, which exhibit a trivial adsorption barrier, and the applicability of detailed balance for this system needs to be reexamined

Working group written presentation: Trapped radiation effects

The results of the Trapped Radiation Effects Panel for the Space Environmental Effects on Materials Workshop are presented. The needs of the space community for new data regarding effects of the space environment on materials, including electronics are listed. A series of questions asked of each of the panels at the workshop are addressed. Areas of research which should be pursued to satisfy the requirements for better knowledge of the environment and better understanding of the effects of the energetic charged particle environment on new materials and advanced electronics technology are suggested

Study of levitating nanoparticles using ultracold neutrons

Physical adsorption of atoms, molecules and clusters on surface is known. It is linked to many phenomena in physics, chemistry, and biology. Usually the studies of adsorption are limited to the particle sizes of up to ~10^2-10^3 atoms. Following a general formalism, we apply it to even larger objects and discover qualitatively new phenomena. A large particle is bound to surface in a deep and broad potential well formed by van der Waals/ Casimir-Polder forces. The well depth is significantly larger than the characteristic thermal energy. Nanoparticles in high-excited bound states form two-dimensional gas of objects quasi-freely traveling along surface. A particularly interesting prediction is small-energy-transfer scattering of UCN on solid/ liquid surfaces covered by such levitating nanoparticles/ nano-droplets. The change in UCN energy is due to the Doppler shift induced by UCN collisions with nanoparticles; the energy change is about as small as the UCN initial energy. We compare theoretical estimations of our model to all relevant existing data and state that they agree quite well. As our theoretical formalism provides robust predictions and the experimental data are rather precise, we conclude that the recently discovered intriguing phenomenon of small heating of UCN in traps is due to their collisions with such levitating nanoparticles. Moreover, this new phenomenon might be relevant to the striking contradiction between results of the neutron lifetime measurements with smallest reported uncertainties as it might cause major false effects in these experiments; thus it affects fundamental conclusions concerning precision checks of unitarity of the Cabibbo-Kobayashi-Maskawa matrix, cosmology, astrophysics. Dedicated measurements of UCN up-scattering on specially prepared surfaces and nanoparticles levitating above them might provide a unique method to study surface potentials.Comment: 20 pages, 12 figure