atomically-defined-templates-for-epitaxial-growth-complex-oxide-thin

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

University of Twente

Typical surface areas of 5 × 5 mm(2) were patterned with high-aspect-ratio micrometer- and submicrometer-sized structures of yttria-stabilized zirconia using a combination of micromolding in capillaries and sol-gel chemistry. The influence of precursor solution concentration and mold geometry on the final shape and dimensions of the patterned structures was investigated. At a precursor concentration of [Zr] = 0.724 mol/dm(3), isolated objects-due to the controlled cracking of patterned films-such as crosses (height 1.4 μm, width 6.0 μm) and "dog bones" (height 800-900 nm, width 900 nm) or patterned films (height 450 nm) were obtained, depending on the mold geometry. Lower precursor concentrations led to differently sized and shaped structures, with changes in dimensions of more than an order of magnitude. Employing a precursor concentration of [Zr] = 0.036 mol/dm(3) yielded isolated rings (height 100-150 nm, line width 20 nm) and squares (height 40 nm, line width 40 nm). A better understanding of the relationship between the precursor concentration, mold geometry, and observed coherent crack patterns in as-dried sol-gel structures may lead to new techniques in patterning isolated features.

Concentration dependence on the shape and size of sol-gel-derived yttria-stabilized zirconia ceramic features by soft lithographic patterning.

Large area low-cost patterning is a challenging problem in graphene research. A resist-free, single-step, large area and cost effective soft lithographic patterning strategy is presented for graphene. The technique is applicable on any arbitrary substrate that needs to be covered with a graphene film and provides a viable route to large-area patterning of graphene for device applications.

Large area resist-free soft lithographic patterning of graphene.

Nanosheets of Ti0.87O2 and Ca2Nb3O10 were synthesized and transferred onto Si substrates by Langmuir-Blodgett deposition. Using pulsed laser deposition, SrRuO3 films were formed on top of these samples. The underlying nanosheets determined both the morphology and crystallographic orientation of the films. SrRuO3 grew preferentially in the [110]pc direction on Ti0.87O2 nanosheets, while growth proceeded in the [001]pc direction on Ca2Nb3O10 nanosheets (pc refers to the pseudocubic unit cell of SrRuO3). Besides macroscopic control over the out-of-plane crystal direction, single crystal orientations were measured by electron backscatter diffraction on the level of individual nanosheets, indicating that epitaxial growth was achieved on the nanosheets as imposed by their well-defined crystal lattices. The nanosheets also had a clear effect on the magnetic properties of the films, which showed anisotropic behavior only when a seed layer was used. A monolayer consisting of a mixture of both types of nanosheets was made to locally control the nucleation of SrRuO3. In this context, SrRuO3 was used as model material, as it was used to illustrate that nanosheets can be a unique tool to control the orientation of films on a (sub-)micrometer length scale. This concept may pave the way to the deposition of various other functional materials and the fabrication of devices where the properties are controlled locally by the different crystallographic orientations.

Local control over nucleation of epitaxial thin films by seed layers of inorganic nanosheets.

The exfoliation and deposition of large (10-100 μm) Ti0.87O2 and small (0.1-1 μm) Ti0.91O2 nanosheets from lepidocrocite-type protonated titanates was investigated for getting high quality films. Exfoliation was carried out with different tetra-alkyl ammonium ions (TAA(+)) and varying TAA(+)/H(+) ratios, and the colloidal solutions were characterized by small-angle X-ray scattering (SAXS) and ultraviolet-visible (UV-vis) spectroscopy. Using Langmuir-Blodgett deposition the titanate nanosheets were directly transferred onto a Si substrate. The resulting films were characterized by atomic force microscopy (AFM).The results indicate that the H1.07Ti1.73O4 titanate exfoliated at very low ratios of TAA(+)/H(+); no lower threshold for exfoliation was observed for the TAA(+) concentration. Nanosheets exfoliated at very low ratios of TAA(+)/H(+) typically showed a small size and porous surface. Subsequent exfoliation of the remaining layered titanate particles yielded much higher quality nanosheets. The optimized deposition parameters for Langmuir-Blodgett films suggest that the surface pressure is a key parameter to control the coverage of the film. The bulk concentration of nanosheets was found to be a less important deposition parameter in the LB deposition process. It only influenced whether the desired surface pressure could be reached at a given maximum degree of compression.

Article	Year
Concentration dependence on the shape and size of sol-gel-derived yttria-stabilized zirconia ceramic features by soft lithographic patterning. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 23030350	2012
Large area resist-free soft lithographic patterning of graphene. Small (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 23161747	2013
Local control over nucleation of epitaxial thin films by seed layers of inorganic nanosheets. ACS applied materials & interfaces\| PubMed ID: 24467475	2014
Improved Langmuir-Blodgett titanate films via in situ exfoliation study and optimization of deposition parameters. ACS applied materials & interfaces\| PubMed ID: 24819117	2014

Maarten Nijland

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