Ole F. Göbel

Patterning Lead Zirconate Titanate Nanostructures at Sub-200-nm Resolution by Soft Confocal Imprint Lithography and Nanotransfer Molding

Patterned sol-gel-derived lead zirconate titanate (PZT) thin films with lateral resolutions down to 100 nm on silicon are reported. Both an imprint and a transfer-molding method were employed. The formed patterns after annealing were characterized with scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Despite the small dimensions and flexibility of the poly(dimethylsiloxane) (PDMS) stamps used for patterning, the quality of replication was found to be good. The influence of the surface energies of the substrate, PDMS mold, and precursor solution on the quality of pattern replication is discussed. The colloidal structure of the PZT sol-gels from which the patterns were made was studied with small-angle X-ray scattering. The sols were found to be chemically homogeneous down to a length scale of approximately 2 nm and higher, which is sufficient for pattern replication on approximately 100 nm scale.

Thin Films of Conductive ZnO Patterned by Micromolding Resulting in Nearly Isolated Features

Patterned and continuous thin films of conductive Al-doped zinc oxide (ZnO:Al) were prepared on different substrates from a polymeric precursor solution. Their electric conductivity and light transmittance (for visible and UV light) was measured at room temperature. By means of a simple device, conductive ZnO:Al films with high fidelity patterns with features of 2-20 microm width could be obtained by simply micromolding the liquid precursor film prior to heat treatment. The individual features were interconnected by a very thin residual ZnO layer.

Structure, twinning, and ferroelasticity of bis(tetramethylammonium) hexafluorotitanate(IV), (TMA)2[TiF6]

Abstract The structure of (TMA)2[TiF6] was determined to be rhombohedral (pseudo-cubic) at room temperature and has been refined to wR = 7.6%. It is isostructural with (TMA)2[OsF6]. Crystals grown from aqueous solution have pseudo-octahedron and pseudo-cube faces and exhibit twinning along pseudo-cubic {110} and {100} planes. Ferroelastic switching of the lattice orientation of a single crystal has been achieved by application of shear stress.

Temperature dependent lattice distortion and high temperature phase transition of pseudo-cubic bis(tetramethylammonium) hexafluorotitanate (IV), (TMA)2[TiF6]

Abstract The crystal structure of (TMA)2[TiF6] between –173 °C and 180 °C was refined on the basis of single crystal diffraction data. A phase transition from rhombohedral to cubic at approx. 142 °C was found by measuring the birefringence as a function of temperature, and confirmed by the refined crystal structures.

Thin films of two functional oxides patterned laterally by soft lithography.

Thin films of two laterally patterned functional oxides of uniform thickness were obtained in a two-step soft-lithographic micromolding process. CoFe(2)O(4)/ZnO and CoFe(2)O(4)/BaTiO(3) dual-phase patterns were fabricated. The films showed good replication of the pattern that was defined in the first patterning step. X-ray diffraction showed that the films consisted of two distinct phases, and magnetic force microscopy showed that the compounds were laterally separated, the separation pattern being the same as that of the initial soft-lithographic process. The films exhibited slight height variations near the edges of the phases, which were introduced in the first deposition step and were not fully compensated in the second deposition step. The films are sufficiently smooth to allow fabrication of multilayer structures.

Stacks of functional oxide thin films patterned by micromolding.

Stacks of up to five relief patterned functional oxide thin films were obtained by a low-cost and low-tech soft-lithographic patterning technique. Micromolding was used to pattern a film of a metal-organic precursor solution for Y-stabilized ZrO(2) (YSZO). Subsequent drying and pyrolysis yielded a line-patterned YSZO film. The process was repeated up to four times with a precursor solution for BaTiO(3) on top of the YSZO film, resulting in stacks of YSZO and BaTiO(3) lines with well-defined edges. This approach presents a step forward on the way to a versatile additive micropatterning technique with which simple multi-material device structures can be fabricated in a reliable, fast, and cost-effective manner.

Optical anomaly in artificial cubic hieratite, K2[SiF6]

Crystals of K2[SiF6] were grown in agar gel, silica gel and jelly. Crystals grown in agar gel or jelly exhibit birefringence and consist of six double refracting growth sectors, each having the shape of a tetragonal pyramid. Nevertheless, the structure of the crystals from agar gel could be refined as cubic (space group Fm3m) with a weighted R factor of 0.043. The amount of birefringence was estimated by the Senarmont compensation method and the rotating polarizer method.

A new room temperature phase of diammonium hexafluorogermanate(IV), (NH4)2[GeF6]

Abstract Single crystals of diammonium hexafluorogermanate(IV), (NH4)2[GeF6], grown at room temperature, have hexagonal symmetry with space group P63mc. So far, only a trigonal room temperature phase and a cubic phase grown at 50 °C were known. We refined the crystal structure, excluding the hydrogen atoms, and measured refractive indices and birefringence.