N. Farkas

Local oxidation of metal and metal nitride films

Oxide growth on sputter-deposited thin films is studied on the local scale by atomic force microscope (AFM)-assisted lithography. We investigate the group IV reactive metals Zr, Hf, Ti, and their nitrides. The nitrogen content of the deposition plasma affects the film crystal structure and electrical resistivity, which in turn alter the local oxidation rates. Mass transport plays an important role, producing features with heights ranging from a few nanometers up to hundreds of nanometers. The heights of the largest features are one to two orders of magnitude greater than observed in other material systems, and the growth is well controlled. We use various techniques to investigate the solid-state reaction and transport mechanisms involved in this oxidation driven by a highly localized electric field. Our results demonstrate the potential of AFM lithographic techniques for characterizing oxidation processes across a wide range of time and length scales.Oxide growth on sputter-deposited thin films is studied on the local scale by atomic force microscope (AFM)-assisted lithography. We investigate the group IV reactive metals Zr, Hf, Ti, and their nitrides. The nitrogen content of the deposition plasma affects the film crystal structure and electrical resistivity, which in turn alter the local oxidation rates. Mass transport plays an important role, producing features with heights ranging from a few nanometers up to hundreds of nanometers. The heights of the largest features are one to two orders of magnitude greater than observed in other material systems, and the growth is well controlled. We use various techniques to investigate the solid-state reaction and transport mechanisms involved in this oxidation driven by a highly localized electric field. Our results demonstrate the potential of AFM lithographic techniques for characterizing oxidation processes across a wide range of time and length scales.

Nanoscale Oxidation of Zirconium Surfaces: Kinetics and Mechanisms

We show that atomic force microscope-induced oxide features can be formed reproducibly on both Zr and ZrN surfaces, and that the growth rate decreases rapidly with increasing time. There is an increase in oxide-feature height with humidity for both systems, and an approximately linear dependence of the height of the structures on the applied voltage for all films for short exposure times. As the anodization time increases, only the thinnest (6 nm) films show a large enhancement in oxide-feature height, demonstrating the role of the film/substrate interface. Under the same conditions, the height of features grown on ZrN films is greater than for those grown on Zr films, indicating that nitrogen plays a role in the oxidation process.

Parallel writing on zirconium nitride thin films by local oxidation nanolithography

Parallel pattern transfer of submicrometer-scale oxide features onto zirconium nitride thin films is reported. The oxidation reaction was verified by Auger microprobe analysis and secondary ion mass spectrometry. Oxide features of ∼70nm in height can be formed and selectively etched in a dilute aqueous hydrogen fluoride solution. This provides an interesting route to potential new applications for high-melting point, biocompatible surfaces that possess small feature sizes with controlled geometries.

Measurement of coefficient of restitution made easy

We present a simple activity that permits students to determine the coefficient of restitution of bouncing balls using only a stopwatch, a metre stick and graphical analysis. The experiment emphasizes that simple models, in combination with careful attention to how students make measurements, can lead to good results in a straightforward way.

Non-destructive characterization of films grown on Zircaloy-2 by annealing in air

Zircaloy-2 is often used in engineering applications because of its corrosion resistance; a property attributable to a protective oxide film that grows on its surface. Variable angle infrared (IR) reflection spectroscopy and atomic force microscopy are used to determine the thickness and roughness of such films grown thermally on Zircaloy-2 surfaces in air. We find cubic growth kinetics in the temperature range 500–600uC with an apparent activation energy of 227 kJ mol −1 . We also demonstrate how an increase in microscopic surface roughness at higher temperatures correlates with a loss of oxide homogeneity as sampled by the IR method.

The Role of Subsurface Oxygen in the Local Oxidation of Zirconium and Zirconium Nitride Thin Films

This paper discusses the growth kinetics of nanometer scale oxide structures grown by atomic force microscope (AFM) assisted lithography. The addition of nitrogen into the sputtering gas during zirconium deposition results in a crystalline ZrN material with oxygen held in solid solution. The diffusion rate of oxygen is high through the crystalline material, allowing it to participate in local anodization and resulting in tall oxide features at low relative humidity. These nanostructures are, in some cases, an order of magnitude higher than previously seen in other material systems. Higher nitrogen content in the plasma results in a crystalline to amorphous transition in the films, and the height enhancement of the AFM-grown features disappears. We propose that mass transport of subsurface oxygen has an influence on surface oxidation kinetics in this material system.

Characterization of zirconium nitride films sputter deposited with an extensive range of nitrogen flow rates

ZrNx films are deposited by rf magnetron sputtering using a wide range of nitrogen flow rates to control film properties. Scanned probe microscope (SPM) oxidation is presented as a complimentary characterization tool to x-ray diffraction, colorimetric, and four point probe analyses. The SPM oxidation behavior of the ZrNx films is related to their structural, optical, and electrical properties. Whereas stoichiometric ZrN films have applications as protective and/or decorative coatings, ZrNx films sputtered with higher nitrogen flow rates have potential applications in devices where arrays of high aspect ratio nanostructures would be useful.ZrNx films are deposited by rf magnetron sputtering using a wide range of nitrogen flow rates to control film properties. Scanned probe microscope (SPM) oxidation is presented as a complimentary characterization tool to x-ray diffraction, colorimetric, and four point probe analyses. The SPM oxidation behavior of the ZrNx films is related to their structural, optical, and electrical properties. Whereas stoichiometric ZrN films have applications as protective and/or decorative coatings, ZrNx films sputtered with higher nitrogen flow rates have potential applications in devices where arrays of high aspect ratio nanostructures would be useful.

Index of refraction without geometry

This article presents several activities that permit students to determine the index of refraction of transparent solids and liquids using simple equipment without the need for geometrical relationships, special lighting or optical instruments. Graphical analysis of the measured data is shown to be a useful method for determining the index of refraction.

Optical and structural studies of films grown thermally on zirconium surfaces

Variable angle IR reflection spectroscopy and atomic force microscopy are used to determine the thickness and morphology of films grown thermally on Zr surfaces in air. The density and homogeneity of these films increases with temperature in the range studied (773–873 K) and growth at the highest temperature follows cubic rate law kinetics. We demonstrate a structure-property relationship for these thermally grown films and suggest the application of IR reflectivity as an inspection method during the growth of environmentally passive films on industrial Zr components.

SPM oxidation and parallel writing on zirconium nitride thin films

Systematic investigation of the SPM oxidation process of sputter-deposited ZrN thin films is reported. During the intrinsic part of the oxidation, the density of the oxide increases until the total oxide thickness is approximately twice the feature height. Further oxide growth is sustainable as the system undergoes plastic flow followed by delamination from the ZrN–silicon interface keeping the oxide density constant. ZrN exhibits superdiffusive oxidation kinetics in these single tip SPM studies. We extend this work to the fabrication of parallel oxide patterns 70 nm in height covering areas in the square centimeter range. This simple, quick, and well-controlled parallel nanolithographic technique has great potential for biomedical template fabrication.