Gravity wave analogs of black holes

It is demonstrated that gravity waves of a flowing fluid in a shallow basin can be used to simulate phenomena around black holes in the laboratory. Since the speed of the gravity waves as well as their high-wavenumber dispersion (subluminal vs. superluminal) can be adjusted easily by varying the height of the fluid (and its surface tension) this scenario has certain advantages over the sonic and dielectric black hole analogs, for example, although its use in testing quantum effects is dubious. It can be used to investigate the various classical instabilities associated with black (and white) holes experimentally, including positive and negative norm mode mixing at horizons. PACS: 04.70.-s, 47.90.+a, 92.60.Dj, 04.80.-y.Comment: 14 pages RevTeX, 5 figures, section VI modifie

Passivation of Si surfaces investigated by in situ photoluminescence techniques

We investigated Si surfaces modified by wet chemical and electrochemical treatments using pulsed photoluminescence PL and infrared spectroscopic ellipsometry during and after processing, both also in surface mapping techniques. Etching of oxidized Si surfaces by HF containing solutions lead to an enhancement in PL due to hydrogenation of the surface what improves the surface passivation and reduces the recombination loss of charge carriers via surface interface states. PL measurements show that the H terminated surface is attacked soon by HF or H2O species what increases again the recombination loss, so that a narrow time window for this type of processing exist. Nitrogen purging or exchanging the etching solution by a non etching solution under negative bias decelerated the defect formation in HF solutions. Grafting of organic molecules exchanging the H Si by a C Si bond induces only small amounts of defects at the interface but stabilizes PL on a high level i.e. surface recombination is low for much longer times than for H terminated Si surface

A Surface Scientist's view on Spectroscopic Ellipsometry

none1noneMaurizio CanepaCanepa, Maurizi