| Čoahkkáigeassu: | <p>This thesis focuses on the synthesis and characterisation of two materials, monolayer molybdenum disulphide (MoS<sub>2</sub>) crystals and gold nanocrystals/monolayers, supported on single crystal strontium titanate (SrTiO<sub>3</sub>) substrates. </p>
<p>On three terminations of SrTiO3 substrates, (111), (110), and (001), monolayer MoS<sub>2</sub> crystals are found to preferentially align their <2¯1¯1 0>-type directions (i.e., the sulphur-terminated edge directions) with the <1 ¯1 0>-type directions on SrTiO<sub>3</sub>. These arrangements allow near-perfect coincidence epitaxy between seven MoS<sub>2</sub> unit cells and four SrTiO<sub>3</sub> unit cells. This maximises the interfacial van der Waals bonding between MoS<sub>2</sub> monolayers and SrTiO<sub>3</sub>. </p>
<p>When SrTiO<sub>3</sub>-supported MoS<sub>2</sub> monolayers are annealed in ultrahigh vacuum, the sulphur loss begins at 700 °C. The sulphur vacancies can be filled by annealing the crystals in a hot sulphur atmosphere, and the optical properties of monolayer MoS<sub>2</sub> can nearly be fully recovered. The sulphur annealing no longer takes effect when all the Mo has been oxidised into MoO<sub>2</sub> and MoO<sub>3</sub> at 800–900 °C. The MoS<sub>2</sub> crystal shapes are stable upon annealing until the residual MoO<sub>3</sub> particles evaporate at above 1000 °C.</p>
<p>Gold nucleates as monolayers on SrTiO<sub>3</sub>(001)-(2 × 1) and as multiply twinned particles on SrTiO<sub>3</sub>(001)-c(4 × 2) and SrTiO<sub>3</sub>(111)-(4 × 4)+(6 × 6). In scanning tunnelling microscopy, a square pattern of bright spots with a periodicity of 1.54 ± 0.06 nm is frequently observed. The monolayers are thought to adopt mixed hexagonal and square packing of atoms because of their observed internal angles of 60°/120° and 90°/135°.</p>
<p>The shapes of gold nanocrystals deviate from the equilibrium Wulff shape due to the influence of the SrTiO<sub>3</sub> single crystal substrates. On any SrTiO<sub>3</sub> substrate, the height-to-width ratio of gold crystals is not a constant but rather increases the crystal height. The ratio between the {111} and {001} surface areas of the gold crystals is found to differ on three different SrTiO<sub>3</sub> substrates. The reentrant facets of the Wulff shapes are not observed. </p>
<p>These findings extend our understanding of epitaxial crystals and nanomaterials grown on SrTiO<sub>3</sub>. This yields a platform for the growth of tailored nanomaterials for electronic and catalytic applications.</p>
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