Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 75: Oxides and Insulators: Epitaxy and Growth

O 75.1: Talk

Thursday, February 28, 2008, 15:15–15:30, MA 042

Preparation of High-Quality Ultrathin Free-Standing Bismuth Films — •Thomas Payer, Manuel Ligges, Ivan Rajković, Ping Zhou, Dietrich von der Linde, Michael Horn-von Hoegen, and Frank Meyer zu Heringdorf — Universität Duisburg-Essen, FB Physik, Duisburg, Germany

High-quality ultrathin free-standing metal films are used in many applications like X-ray filters or TEM/TED sample preparation. Deposition on top of sodium chloride templates is a well-known method to grow such films. Typically the crystals are either cleaved in UHV and material is deposited immediately afterwards yielding textured films. Alternatively crystals are cleaved in air making the preparation easier but yielding only lower-quality films. Due to step bunches from the cleaving only small area films can be grown. Our new preparation technique yields high-quality films on a millimeter scale.

We start from large (25mm and above) commercially sold sodium chloride single crystals. As sold, the sodium chloride disks are polished for optical applications in the infrared. The surface exhibits a large roughness and 100nm particle contaminations. Using a water rinse on a spin coater, the contaminations are completely removed. After an additional propanol rinse, AFM shows the presence of atomically flat terraces and regularly spaced atomic steps on the surface. Transfer into UHV yields the clean NaCl LEED pattern. Bismuth films of 20nm thickness are deposited in UHV at room temperature. Ex-situ AFM showed a roughness of only 1.5nm and crystallite sizes of 200nm. Additionally the crystallinity was studied with TED and TEM