grasp of the underlying science. This situation has changed greatly with our growing understanding of nanoscience, particularly with regard to the role of size effects. Indeed, owing to quantum confinement and surface effects, material properties begin to differ from the bulk at a length scale below ≈100 nm. [2] These effects can impact the electronic, thermal, chemical, and optical properties of a material at the nanoscale. The study of nanocrystals is the driving force behind innovations in electronic, [1,3] optoelectronic, [4,5] and nanophoto nic [6] devices. In addition, nanocrystals are used for catalysis [7,8] and medical applications. [9,10] Nanostructures and nanocrystals are usually fabricated by well-known top-down or bottom-up approaches. [2,[11][12][13] In this contribution, we focus on a distinct third method to create nanocrystalline structures, which combines aspects of those two approaches. Our method utilizes the self-assembly of nanocrystalline structures through thinfilm agglomeration. [14,15] Applying recent developments in epitaxial growth and liftoff of thin films to form membranes, it presents a general framework for achieving self-assembly. The agglomeration achieved by an architectured dewetting process will be described in the following discussion.In the process of annealing a thin film deposited on a substrate, a variety of mass transport phenomena such as surface diffusion, intermixing, evaporation, and condensation may take place (Figure 1). Mass transport occurring on the edge of a film can retract the film to minimize the total surface energy. This process reduces the coverage of the substrate by the film and eventually forms islands of material resting on the substrate. [14,[16][17][18] This inherent ability of thin films to dewet on surfaces and to agglomerate into islands is leveraged to form crystalline nanoparticles to fabricate catalysis [19][20][21][22] as well as electronic [23,24] and nanophotonic devices. [25][26][27][28] This process provides a way to achieve high-throughput nanofabrication [25] of highly oriented and faceted nanostructures that are not obtainable with traditional lithography and etching methods. [29][30][31][32][33][34][35] Dewetting has been studied extensively, both theoretically and experimentally, in single-crystal configurations of elements [31,32,[36][37][38] such as palladium, [39] nickel, [38,40] and silicon, [18,30] which has yielded a detailed understanding of The exploration of crystalline nanostructures enhances the understanding of quantum phenomena occurring in spatially confined quantum matter and may lead to functional materials with unforeseen applications. A novel route to fabricating nanocrystalline oxide structures of exceptional quality is presented. This is achieved by utilizing a self-assembly process of ultrathin membranes composed of the desired oxide. The thermally induced self-assembly of nanocrystalline structures is driven by dewetting the oxide membranes once they are lifted off and transferred onto sapphire surfaces. In thr...
Thermal laser epitaxy (TLE) is a novel film growth technique capable of fabricating ultrapure films of many material systems. For growing oxide films with TLE, the impact of source oxidation on the evaporation rate is a central issue, which, however, has not yet been explored systematically. Here, we report a systematic, experimental study of the role of source oxidation on source evaporation at various oxygen pressures and source temperatures in TLE. The volatility of the oxidized metal sources affects the source evaporation rate. When the oxidized metal source is more volatile than the metal, the source evaporation rate increases with the oxygen supply. In a strongly oxidizing environment, stable oxides with lower volatility tend to form and decrease the evaporation rate of the source. Increasing the laser power—and thereby the source temperature—tends to prevent the formation of stable oxides. At even higher source temperatures, the metal vapor pressure can dominate the oxide vapor pressure even in a high oxygen pressure atmosphere. A power-law relation between deposition rate and oxidizing gas pressure is found in case the formation and evaporation of volatile oxides of the elemental source material dominates the total evaporation process. The exponent of this law is a measure of the relevance of source oxidation for the evaporation of the source.
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