The origin of faceting of ultrafat gold films epitaxially grown on Mica

A two-step deposition process for the formation of atomically flat gold films on mica is developed. The process starts with a high deposition rate followed by a 1:100 reduced rate. Using this combination a completely wetting of mica by gold resulting in a two-dimensional growth mode and finally extremely flat gold films with large terraces are achieved. Additionally hexagonal facefing of the gold films on mica is observed at moderate temperatures which can be related to the relaxation of stress caused by different thermal coefficients of expansion of mica and gold. The stress release leads to the generation of misfit dislocations that glide along the (100) planes producing facets on the surface. Annealing experiments in a UHV-STM and thermogravimetry point to the inset of intensified hexagonal faceting due to the starting decomposition of mica at elevated temperatures. (c) 2004 Elsevier B.V. All rights reserved

Self-assembled nanostructures on VSe2 surfaces induced by Cu deposition

Analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been applied for the characterization of evolution, lateral arrangements, orientations, and the microscopic nature of nanostructures formed during the early stages of ultrahigh vacuum electron beam evaporation of Cu onto surfaces of VSe2 layered crystals. Linear nanostructure of relatively large lateral dimension (100-500 nm) and networks of smaller nanostructures (lateral dimension: 15-30 nm; mesh sizes: 500-2000 nm) are subsequently formed on the substrate surfaces. Both types of nanostructures are not Cu nanowires but are composed of two strands of crystalline substrate material elevating above the substrate surface. For the large nanostructures a symmetric roof structure with an inclination angle of approximately 30 degrees with respect to the substrate surface could be deduced from detailed diffraction contrast experiments. In addition to the nanostructure networks a thin layer of a Cu-VSe2 intercalation phase of 3R polytype is observed at the substrate surface. A dense network of interface dislocations indicates that the phase formation is accompanied by in-plane strain. We present a model that explains the formation of large and small nanostructures as consequences of compressive layer strains that are relaxed by the formation of rooflike nanostructures, finally evolving into the observed networks with increasing deposition time. The dominating contributions to the compressive layer strains are considered to be an electronic charge transfer from the Cu adsorbate to the substrate and the formation of a Cu-VSe2 intercalation compound in a thin surface layer

Photoemission study of SrTiO3 surface layers instability upon metal deposition

In this work we study the Pt/SrTiO3 (STO) interface system using X-ray photoelectron spectroscopy (XPS). The polycrystalline Pt layers with a thickness of about 2-3 nm are deposited by sputtering and thermal evaporation methods on STO(100) single crystals with two different type of terminations. We propose and show local conductivity (LC) measurements as a good method to check whether such very thin metal layers are continuous. The XPS data show that both methods of Pt deposition lead to changes of the chemical composition of the crystal surface layers, and such chemical instability should be taken into consideration when studying the physical properties of a metal-insulator interface

Method to distinguish ferroelectric from nonferroelectric origin in case of resistive switching in ferroelectric capacitors

We present investigations on the resistive switching effect in SrRuO3/PbZr0.2Ti0.8O3/Pt ferroelectric capacitors. Using a conductive atomic force microscope, the out-of-plane piezoelectric response and the capacitive and resistive current were simultaneously measured as a function of applied bias voltage. We observed two independent switching phenomena, one attributed to the ferroelectric switching process and the other to resistive switching. We show that I-V curves alone are not sufficient in ferroelectric materials to clarify the underlying switching mechanism and must be used with sufficient caution. (C) 2008 American Institute of Physics