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Register a new userAu-Assisted Substrate-Faceting for Inclined Nanowire Growth
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We study the role of gold droplets in the initial stage of nanowire growth via the vapor liquid solid method. Apart from serving as a collections center for growth species, the gold droplets carry an additional crucial role that necessarily precedes the nanowire emergence, that is, they assist the nucleation of nanocraters with strongly faceted 111B side walls. Only once these facets become sufficiently large and regular, the gold droplets start nucleating and guiding the growth of nanowires. We show that this dual role of the gold droplets can be detected and monitored by high energy electron diffraction during growth. Moreover, gold induced formation of craters and the onset of nanowires growth on the 111B facets inside the craters are confirmed by the results of Monte Carlo simulations. The detailed insight into the growth mechanism of inclined nanowires will help to engineer new and complex nanowire based device architectures.
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The epitaxial growth of {111} oriented Au on MoS$_2$ is well documented despite the large lattice mismatch (~8% biaxial strain), and the fact that a Au {001} orientation results in much less elastic strain. An analysis based on density functional and linear elasticity theories reveals that the {111} orientation is stabilized by a combination of favorable surface and interfacial contributions to the energy, and the compliance of the first layer of the MoS$_2$.
This article presents the use of flexible metal foam substrates for the growth of III-nitride nanowire light emitters to tackle the inherent limitations of thin-film light emitting diodes as well as fabrication and application issues of traditional substrates. A dense packing of gallium nitride nanowires were grown on a nickel foam substrate. The nanowires grew predominantly along the a-plane direction, normal to the local surface of the nickel foam. Strong luminescence was observed from undoped GaN and InGaN quantum well light emitting diode nanowires.
Irradiation of a sharp tungsten tip by a femtosecond laser and exposed to a strong DC electric field led to gradual and reproducible surface modifications. By a combination of field emission microscopy and scanning electron microscopy, we observed asymmetric surface faceting with sub-ten nanometer high steps. The presence of well pronounced faceted features mainly on the laser-exposed side implies that the surface modification was driven by a laser-induced transient temperature rise -- on a scale of a couple of picoseconds -- in the tungsten tip apex. Moreover, we identified the formation of a nano-tip a few nanometers high located at one of the corners of a faceted plateau. The results of simulations emulating the experimental conditions, are consistent with the experimental observations. The presented conditions can be used as a new method to fabricate nano-tips of few nm height, which can be used in coherent electron pulses generation. Besides the direct practical application, the results also provide insight into the microscopic mechanisms of light-matter interaction. The apparent growth mechanism of the features may also help to explain the origin of enhanced electron field emission, which leads to vacuum arcs, in high electric-field devices such as radio-frequency particle accelerators.
Metal halide perovskites have recently emerged as promising materials for the next generation of optoelectronic devices owing to their remarkable intrinsic properties. In the growth of perovskite crystals, the substrates are essential and play a vital role. Herein, substrate engineering in the growth of perovskite crystals have been reviewed. Particularly, various modified strategies and corresponding mechanism based on the substrate engineering applied to the optimization of thickness, nucleation and growth rate are highlighted. Then the alterable adhesion to substrates will also be discussed. Furthermore, applying the structural coherence of epitaxial crystals with substrate, scalable perovskite single-crystalline thin films have been obtained and can be transferred onto arbitrary substrates. Substrate engineering also can stabilize the desired perovskite phases by modulating the strain between crystals and substrates. Finally, several key challenges and related solutions in the growth of perovskite crystals based on substrate engineering are proposed. This review aims to guide the future of substrate engineering in perovskite crystals for various optoelectronic applications.
Contributing to the need of new graphene nanoribbon (GNR) structures that can be synthesized with atomic precision, we have designed a reactant that renders chiral (3,1) - GNRs after a multi-step reaction including Ullmann coupling and cyclodehydrogenation. The nanoribbon synthesis has been successfully proved on different coinage metals, and the formation process, together with the fingerprints associated to each reaction step, has been studied combining scanning tunnelling microscopy, core-level spectroscopy and density functional calculations. In addition to the GNR chiral edge structure, the substantial GNR lengths achieved and the low processing temperature required to complete the reaction grant this reactant extremely interesting properties for potential applications.
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