Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

Abstract

The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use as epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. In addition, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.

Internal stress induced natural self-chemisorption of ZnO nanostructured films

“… 35 36 and Tolstova et al . 37 , the higher ion bombardment of plasma energy can lead to relaxation of internal stress and grain boundaries efficiently, indicating an obvious variation in total Gibbs free energy. At the same time, the different microstructure induced by internal stress can be observed as depicted in the inset of Fig.…”

Wet-cleaning of MgO(001): Modification of surface chemistry and effects on thin film growth investigated by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy

“…claimed improvement of thin film deposition and epitaxy using pre-cleaning or backsputtering using RF substrate bias prior to deposition 23 .The carbon contaminants were eliminated and the chemical environment of the oxygen modified; nevertheless, the magnesium bonding was not investigated by XPS.…”

Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

“…The crystallographic orientation of a metal thin film affects its surface energy and structure. Surface chemical reactions and interface engineering, which are important in applications including optoelectronic devices and catalysis, as well as understanding crystalline growth, are therefore of paramount importance [1][2][3][4][5]. In this respect, iridium layers that are crystallographically oriented, exhibit low stress, yet high density and low surface roughness, find widespread use in various high-end technological applications, such as diffusion barrier material in ferroelectric random access memories, gate electrode in field effect transistors, template layer for diamond hetero-epitaxy, active layers in gas sensors, hydrogen separation membranes or materials for electro-catalyst [6][7][8][9], and even in ultrahigh quality grazing incidence configuration mirror elements of the Advanced X-ray Astrophysics Facility -Imaging (AXAF-I), a space-based X-ray observatory of NASA [10,11].…”

“…Figure 3b, the following epitaxial relations are obtained: i) out-of-plane: (111) Ir || (111) MgO , ii) in-plane variant 1:[1][2][3][4][5][6][7][8][9][10] Ir ||[1][2][3][4][5][6][7][8][9][10] MgO (180 and ± 60°) and variant 2:[1][2][3][4][5][6][7][8][9][10] Ir || MgO (0 and ± 120°). The existence of two epitaxial variants comes from the fact that there are two possibilities (related by a 180° rotation) to position the iridium unit-cell on the MgO unit-cell: the iridium triangle points either "upwards", or "downwards", as one may conclude from the schematic inFigure 1b.…”