University of Oulu

Structural, mechanical, and electronic properties of pulsed laser deposited carbon thin films and C-Si-heterojunctions

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Author: Koivusaari, Jarmo1
Organizations: 1University of Oulu, Faculty of Technology, Department of Electrical Engineering
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 9.2 MB)
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Language: English
Published: 2000
Publish Date: 2000-09-06
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Raahensali (Auditorium L 10), Linnanmaa, on September 22nd, 2000, at 12 noon.
Reviewer: Professor Rolf Hernberg
Doctor Michael Lorenz


Thin carbon films with properties close to those of diamond were deposited using two different experimental set-ups. Diamond-like carbon thin films were produced using an XeCl excimer laser having a wavelength of 308 nm and pulse duration of 20 ns. Amorphic diamond films were deposited using an Nd:YAG laser at a wavelength of 1064 nm. The laser intensities were in the range of 108–1012 W/cm². The deposition conditions of diamond-like carbon thin films were optimised for high quality film deposition by studying the relations between laser intensity, velocity of carbon ions, and bonding in the films using time-of-flight and x-ray absorption near edge spectroscopy.

Adhesion of the amorphic diamond thin films to steel and carbide substrates was studied using a commercial scratch tester. A method was introduced to analyse scratch test measurements. It was demonstrated that substrate penetration and damage by the scratch indenter was considerably reduced by application of amorphic diamond coatings on steel and carbide substrates. Therefore, with amorphic diamond coating the lifetime of the drilling and cutting tools could be remarkably increased.

Current-voltage characteristics of silicon / amorphic diamond heterojunctions were studied both in the dark and under white light conditions. It was shown that, regardless of the doping type of the substrate the rectification of the heterojunction is in the same direction. The reverse breakdown strength of the amorphic diamond on p-type silicon was measured to be 3 × 109 V/m. It was shown that under reverse bias condition, the current increase by two orders of magnitude when the device was exposed to white light. The maximum photoresponse was in the range 600–900 nm. The feasibility using amorphic diamond to enhance the lifetime of the photoconductive switch operation was demonstrated.

Tetrahedral amorphous carbon models with varying and representative deposited thin film structures were modelled using the density functional theory with a local density approximation. Mechanical and electronic properties of both bulk and surfaces were modelled. Model calculations were shown to reproduce well the experimental results. Measured scanning tunnelling spectra, representing surface density of states of the carbon thin films, were in good agreement with the calculated electronic density of states of tetrahedral amorphous models. In addition, the present study provides an understanding of the origins of the relationships between the structural and electronic properties of the tetrahedral amorphous carbon with varying density.

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Series: Acta Universitatis Ouluensis. C, Technica
ISSN-E: 1796-2226
ISBN: 951-42-5749-9
ISBN Print: 951-42-5748-0
Issue: 148
Copyright information: © University of Oulu, 2000. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.