T. Christidis

Enhancement of the molecular nitrogen dissociation levels by argon dilution in surface-wave-sustained plasmas

In this work, the nitrogen molecular dissociation level in Ar/N2 surface-wave plasma is evaluated as a function of plasma parameters such as Ar percentage in the gas mixture, power absorbed in the plasma, and total pressure in order to design an efficient N-atom source that can be used for various applications such as thin-film deposition and materials surface modification. This plasma is operated at 40.68 MHz and the nitrogen dissociation rate is determined, in the remote plasma, by analyzing the optical emission of the first positive molecular nitrogen band. For all operating conditions, the dissociation rate ([N]/[N2]) of N2 molecules was enhanced, as the percentage of Ar in the mixture increased from 0 to ∼95%, and dissociation rates higher than 2.5% were measured. This gain in the dissociation rate became more pronounced when the plasma power and total pressure increased from 40 to 120 W and from 4 to 7.5 Torr, respectively. These results are discussed in terms of the kinetics of the electrons, nitro...

Microstructural characterization of chromium oxide thin films grown by remote plasma assisted pulsed laser deposition

In this work, we investigate the use of Remote Plasma Assisted PLD for the growth of chromium oxide thin films. In an attempt to enhance oxygen incorporation in the growing layers, laser ablation takes place in an activated oxygen background that contains atomic oxygen as well as excited oxygen molecules, thereby creating growth conditions that are inaccessible by reactive PLD. All films were grown on Si (100) substrates by ablating a pure Cr2O3 target using a KrF excimer laser. The micro-structural analysis of the grown layers was achieved using Infra- Red Spectroscopy, X-Ray Diffraction, Atomic Force Microscopy and Rutherford Back- Scattering. It is found that films deposited under remote plasma conditions show a predominance of the higher oxidation states of chromium while the antiferromagnetic Cr2O3 phase is mostly present in films grown in an O2 ambient. The effect of substrate temperature on the microstructure of the films was also studied. At low substrate temperatures (<350°C), the films have an amorphous microstructure with elongated rod-like features that could indicate the formation of the CrO2 phase. With increasing temperature up to 450oC, the structure of the films reverts to a crystalline Cr2O3 phase as inferred from the appearance of the corresponding peaks in the XRD spectra and from the narrowing of the infra-red absorption bands.

Excimer Laser Processing of Novel Materials for Optoelectronic and Spintronic Applications

The interaction of the highly energetic pulsed excimer laser beam with a target material induces non-equilibrium physico-chemical processes which could be harnessed to synthesize a variety of novel and technologically attractive materials that are difficult to grow using more conventional thin film deposition techniques. In this paper, recent advances on two excimer laser based techniques that we have used in the processing of thin films and surfaces will be presented. First, we demonstrate the synthesis, by Pulsed Laser Melting (PLM), of silicon supersaturated with sulfur at concentrations several orders of magnitude greater than the solubility limit of silicon alloys, with strong sub-bandgap optical absorption. This material has potential applications in the fabrication of Si-based opto-electronic devices. Second, the capability of Remote Plasma Pulsed Laser Deposition (RP-PLD) in synthesizing the meta-stable half-metallic CrO2 compound that is of great interest in the field of spintronics was assessed. Infra-Red spectroscopy and Magnetic Force Microscopy indicate that the use of the remote plasma is beneficial to the formation of the CrO2 phase, at a deposition pressure of 30 mTorr and for deposition temperature below 350 °C. Atomic Force Microscopy and Magnetic Force Microscopy studies respectively show that films containing the CrO2 phase have significantly different surface topography and magnetic characteristics from those in which the Cr2O3 phase is dominant.

Synthesis of nano-grained MnO2 thin films by laser ablation

Manganese dioxide (MnO2) is considered as one of the most attractive compound among the manganese oxide phases due to its fundamental chemical and physical properties, its use in energy-storage devices, electrochemical applications, and biosensors. There have been limited attempts to grow high quality MnO2 thin films where high pressure and low substrate temperature are targeted to promote the formation of this phase. In this work, we have exploited the flexibility of Pulsed Laser Deposition (PLD) in order to synthesize thin films of MnO2 on Si substrates by laser ablation of a MnO target in oxygen gas ambient. Substrate temperature was varied from 25 to 800 °C aiming to grow films of good crystalline quality while investigating the temperature range where MnO2 phase is expected to be stable. We have also investigated the effect of oxygen pressure which was varied from 10 to 500 mTorr. X-ray diffraction and Fourier Transform Infra-Red analyses have confirmed the formation of the MnO2 phase for pressures above 250 mTorr, and an optimal deposition temperature of 500 °C, while Mn2O3 is obtained in the range between 550 and 650 °C. Further increase in deposition temperature led to pure Mn3O4 films. Atomic Force Microscopy imaging confirms the nanograined surface structure of the MnO2 films, with a typical grain size of 30 nm.

Synthesis of nano-grained MnO 2 thin films by laser ablation

Manganese dioxide (MnO2) is considered as one of the most attractive compound among the manganese oxide phases due to its fundamental chemical and physical properties, its use in energy-storage devices, electrochemical applications, and biosensors. There have been limited attempts to grow high quality MnO2 thin films where high pressure and low substrate temperature are targeted to promote the formation of this phase. In this work, we have exploited the flexibility of Pulsed Laser Deposition (PLD) in order to synthesize thin films of MnO2 on Si substrates by laser ablation of a MnO target in oxygen gas ambient. Substrate temperature was varied from 25 to 800 °C aiming to grow films of good crystalline quality while investigating the temperature range where MnO2 phase is expected to be stable. We have also investigated the effect of oxygen pressure which was varied from 10 to 500 mTorr. X-ray diffraction and Fourier Transform Infra-Red analyses have confirmed the formation of the MnO2 phase for pressures above 250 mTorr, and an optimal deposition temperature of 500 °C, while Mn2O3 is obtained in the range between 550 and 650 °C. Further increase in deposition temperature led to pure Mn3O4 films. Atomic Force Microscopy imaging confirms the nanograined surface structure of the MnO2 films, with a typical grain size of 30 nm.