Samuel Guerin

Electrochemical behaviour of electrodeposited nanostructured palladium+platinum films in 2 M H2SO4

Nanostructured palladium + platinum films were electrodeposited from all aqueous binary mixture that contained a non-ionic surfactant to produce a liquid crystalline phase. This phase acts as a template for the formation of mesoporous nanostructured films. The films produced were characterised by X-ray diffraction and transmission electron microscopy in order to assess the existence of a regular nanostructure. Furthermore, cyclic voltammetry in 2 M H2SO4 was used to obtain information about the electrochemical properties of the films. Here we report the existence of two unexpected very sharp peaks in the hydrogen region that were observed by cyclic voltammetry.

Combinatorial arrays and parallel screening for positive electrode discovery

Combinatorial techniques have been applied to the preparation and screening of positive electrode candidates for lithium batteries. This work describes the automated parallel synthesis of 64-electrode arrays using a Packard Multiprobe II liquid handling system. A cell was constructed with a single lithium reference–counter electrode and 64, three-millimeter-diameter working electrodes containing LixMn2O4 active material, PVdF–HFP binder and carbon black as a conducting additive. Eight duplicate electrodes, each of eight respective compositions, were deposited on the array and the mass fraction of carbon was varied in steps from 1 to 25%. The results showed a rapid increase in capacity at the percolation limit of 3% for most cells. Some groups of nominally identical cells showed random variations in capacity, especially at low carbon loadings. The overall result is a demonstration of advantages of the combinatorial concept, which were time-saving and an improved statistical significance of the results compared with on–off experiments.

Reduction in crystallization time of Sb:Te films through addition of Bi

The electrical, optical, and phase change properties of bismuth doped Sb8Te2 films have been characterized. Thin films of the material, with up to 15at.% percent Bi, have been synthesized; amorphous films were stable at room temperature with a Bi concentration of up to 13at.%. The effect of Bi on the phase change properties of the film is shown to reduce the crystallization time by an order of magnitude while the crystallization activation energy reduction is minimal; 0.2eV. Bismuth doped Sb8Te2 materials show potential as the active material in phase change data storage media.

Synthesis of the ferroelectric solid solution, Pb(Zr1−xTix)O3 on a single substrate using a modified molecular beam epitaxy technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1−xTix)O3 (PZT) on single Pt∕Ti∕SiO2∕Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral to tetragonal symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary at Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis. Results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery.

High throughput physical vapour deposition and dielectric and ferroelectric screening of (Bi,Na)TiO3 thin-film libraries

Polycrystalline thin-film libraries of Bi2O3-TiO2-Na2O system have been synthesised over a wide composition region using elemental molecular beam epitaxy sources combined with an oxygen plasma source. Structural characterisation and the screening of both dielectric and ferroelectric properties of fabricated compounds have been carried out. The bismuth sodium titanate perovskite-type phases exhibited a high relative permittivity (up to 375), a loss tangent lower than 0.02 and ferroelectric properties superior to thin films synthesised using other deposition methods: a remnant polarization, Pr, approximately 22 μC/cm2 was observed in the optimal composition range. The high throughput approach allowed us to establish clearly the compositional boundaries of the ferroelectric perovskite phase in the system.

Optimization of synthesis of the solid solution, Pb(Zr1–xTix)O3 on a single substrate using a high-throughput modified molecular-beam epitaxy technique

Synthesis of Pb(Zr1–xTix)O3 (PZT) on a single substrate using a high-throughput molecular-beam epitaxy technique was demonstrated. In situ synthesis of crystalline PZT at elevated substrate temperatures could not be achieved, as reevaporation of Pb (PbO) occurred and the partial pressure of O2 was insufficient to prevent formation of a PbPtx phase during deposition. Instead, ex situ postdeposition annealing was performed on PZT deposited at room temperature. Dense single phase PZT was prepared with a compositional range of 0.1 > x > 0.9, for film thicknesses up to 800 nm. Transmission electron microscopy revealed the grain size increased from 50 nm to ~0.5 µm with increasing Zr-concentration and became more columnar. Raman, x-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy results revealed a morphotropic phase boundary between rhombohedral and tetragonal phases occurred at x ~0.4 rather than at x = 0.47 in bulk ceramics. This was attributed to clamping arising from mismatch in thermal expansion between the film and substrate.

Synthesis and screening of phase change chalcogenide thin film materials for data storage

A combinatorial synthetic methodology based on evaporation sources under an ultrahigh vacuum has been used to directly synthesize compositional gradient thin film libraries of the amorphous phases of GeSbTe alloys at room temperature over a wide compositional range. An optical screen is described that allows rapid parallel mapping of the amorphous-to-crystalline phase transition temperature and optical contrast associated with the phase change on such libraries. The results are shown to be consistent with the literature for compositions where published data are available along the Sb2Te3-GeTe tie line. The results reveal a minimum in the crystallization temperature along the Sb2Te3-Ge2Te3 tie line, and the method is able to resolve subsequent cubic-to-hexagonal phase transitions in the GST crystalline phase. HT-XRD has been used to map the phases at sequentially higher temperatures, and the results are reconciled with the literature and trends in crystallization temperatures. The results clearly delineate compositions that crystallize to pure GST phases and those that cocrystallize Te. High-throughput measurement of the resistivity of the amorphous and crystalline phases has allowed the compositional and structural correlation of the resistivity contrast associated with the amorphous-to-crystalline transition, which range from 5-to-8 orders of magnitude for the compositions investigated. The results are discussed in terms of the compromises in the selection of these materials for phase change memory applications and the potential for further exploration through more detailed secondary screening of doped GST or similar classes of phase change materials designed for the demands of future memory devices.

Synthesis of the Ferroelectric Solid Solution, Pb(Zr 1−x Ti x )O 3 on a Single Substrate Using a Modified Molecular Beam Epitaxy Technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Z:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.

Synthesis of the Ferroelectric Solid Solution, Pb(Zr 1-x Ti x )O 3 on a Single Substrate Using a Modified Molecular Beam Epitaxy (MBE) Technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Z:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.

Material Optimisation for Optical Data Storage

High throughput synthesis and screening methodologies of optical data storage materials have allowed an in depth study of more than 4000 compositions. We report on the optical and electrical compositional dependence of these materials.