P.R. Willmott

Pulsed laser deposition of electrochemically active perovskite films

Abstract La 0.6 Ca 0.4 CoO 3 (LCCO) thin films were deposited on MgO(0xa00xa01) and stainless steel substrates by pulsed reactive crossed-beam laser ablation. High resolution X-ray diffraction (XRD) spectra of the films showed that their quality depends on the oxygen background during cooling. Rutherford backscattering spectrometry measurements reveal that under optimal conditions the films have the same stoichiometry as the original target. X-ray photoelectron spectroscopy (XPS) was applied to characterize the surface of the films, which revealed two oxygen and calcium species: the one at lower binding energy, corresponds to oxygen from the perovskite structure and the one at higher binding energy correspond to Ca–O surface species and adsorbed oxygen. The electrochemical activity of the LCCO films is influenced by the crystallinity of the perovskite electrodes. The structural and electrochemical properties depend on the preparation conditions and substrate.

RHEED analysis of interface growth modes of TiN films on Si(001) produced by crossed beam laser ablation

Abstract Epitaxial growth of TiN thin films on Si(001) using reactive crossed beam laser ablation has been investigated for substrate temperatures between 250 and 800°C. In situ RHEED analysis of the growing film has revealed two distinct interface growth regimes. Under about 550±50°C, TiN(001) grows epitaxially on Si(001) in a Volmer–Weber type 4-on-3 cube-on-cube mode and produces compressive biaxial stress in-plane, whereas at higher temperatures, the growth mode changes to a Stranski–Krastinov 5-on-4 cube-on-cube type with dilation of the strained interface layer.

Materials by design—exploiting the unique properties of pulsed laser deposition for the synthesis of novel hard materials and structures

Novel multilayer thin film structures with an (A-B-C-B) four-sublayer periodicity were synthesized using pulsed reactive crossed-beam laser ablation. The layers were based on transition metal carbonitrides in which one sublayer (A = TiC x N 1-x )was optimized for its high hardness, another (C = ZrC x N 1-x ) for its low frictional properties, and a third (B = VC x N 1-x ) which acted as a barrier to dislocation propagation. Control of growth and stoichiometry was facilitated by using thermally stable gases as sources for the carbon and nitrogen which were activated by collisions with the ablation plasma. It was discovered that the ablation yields of Ti, V, and Zr were almost identical, so that the sublayer thickness was directly proportional to the number of ablated shots per sublayer metal. The four-sublayer structures were harder (H = 35 GPa) than corresponding bilayer structures (H = 30 GPa) in which the VC x N 1-x sublayers were missing. Further improvements are expected by optimizing the sublayer ratios and the absolute period thickness.

Laser-induced integrated processing for heteroepitaxial SixGe(1−x) alloys

Abstract An integrated laser assisted process has been applied to prepare heteroepitaxial Si x Ge (1− x ) alloys on Si(100) using the combination of laser induced chemical vapour deposition (LCVD) and pulsed laser induced epitaxy (PLIE). Both processes have been carried out with 193 nm radiation of an ArF excimer laser leading first to high quality amorphous hydrogenated germanium (a-Ge:H) thin films by LCVD and then to unstrained epitaxial Si x Ge (1− x ) alloys by PLIE. The optimization for depositing homogeneous, low impurity a-Ge:H films has been followed by profilometry, Raman spectroscopy and X-ray diffraction (XRD). Subsequent melting and recrystallization by PLIE was studied by X-ray photoelectron spectroscopy (XPS) for analysing the distribution tail of the graded Si x Ge (1− x ) alloys and conventional XRD analysis to determine the epitaxy of the relaxed, Ge-rich, Si x Ge (1− x ) phase. The analyses evidenced the formation of thin unstrained epitaxial Si x Ge (1− x ) layers, which can be used as buffer layers for the growth of symmetrically strained superlattices.

Gas-phase mechanisms in the growth of ZrCyN1−y thin films by pulsed reactive crossed-beam laser ablation

Superhard zirconium carbonitride films have been grown via pulsed reactive crossed-beam laser ablation (PRCLA) using zirconium metal and a nitrogen- and carbon-containing gas pulse mixture. The control of stoichiometry was much simplified by using the thermally stable gas-phase species N2 and CH4. The gas-phase processes are investigated using quadrupole mass spectroscopy and optical emission spectroscopy. The excitation of the ablation plume depends intimately on the collision partner of the gas pulse, in particular on its density of states and the probability of energy transfer to internal degrees of freedom.