Containerless metal single-crystal growth via electromagnetic levitation.

The growth of elemental metal single-crystals is usually achieved through classic growth techniques such as the Czochralski or floating zone methods. Drawbacks of these techniques are the susceptibility to contamination from the crucible and thermal stress-induced defects due to contact with the ambient, which can be mitigated by growing in a containerless environment. We discuss the development of a novel crystal growth apparatus that employs electromagnetic levitation in a vacuum to grow metal single-crystals of superior quality and purity. This apparatus enables two growth modes: containerless undercooled crystallization and levitation-based Czochralski growth. We describe the experimental setup in terms of coil design, sample insertion and collection, seed insertion, and sample position and temperature tracking. As a proof of concept, we show the successful growth of copper single-crystals.

Erratum: Structural and Electronic Properties of Germanene on MoS_{2} [Phys. Rev. Lett. 116, 256804 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.256804.

Structural and Electronic Properties of Germanene on MoS_{2}.

To date germanene has only been synthesized on metallic substrates. A metallic substrate is usually detrimental for the two-dimensional Dirac nature of germanene because the important electronic states near the Fermi level of germanene can hybridize with the electronic states of the metallic substrate. Here we report the successful synthesis of germanene on molybdenum disulfide (MoS_{2}), a band gap material. Preexisting defects in the MoS_{2} surface act as preferential nucleation sites for the germanene islands. The lattice constant of the germanene layer (3.8±0.2 Å) is about 20% larger than the lattice constant of the MoS_{2} substrate (3.16 Å). Scanning tunneling spectroscopy measurements and density functional theory calculations reveal that there are, besides the linearly dispersing bands at the K points, two parabolic bands that cross the Fermi level at the Γ point.

Germanene: the germanium analogue of graphene.

Recently, several research groups have reported the growth of germanene, a new member of the graphene family. Germanene is in many aspects very similar to graphene, but in contrast to the planar graphene lattice, the germanene honeycomb lattice is buckled and composed of two vertically displaced sub-lattices. Density functional theory calculations have revealed that free-standing germanene is a 2D Dirac fermion system, i.e. the electrons behave as massless relativistic particles that are described by the Dirac equation, which is the relativistic variant of the Schrödinger equation. Germanene is a very appealing 2D material. The spin-orbit gap in germanene (~24 meV) is much larger than in graphene (<0.05 meV), which makes germanene the ideal candidate to exhibit the quantum spin Hall effect at experimentally accessible temperatures. Additionally, the germanene lattice offers the possibility to open a band gap via for instance an externally applied electrical field, adsorption of foreign atoms or coupling with a substrate. This opening of the band gap paves the way to the realization of germanene based field-effect devices. In this topical review we will (1) address the various methods to synthesize germanene (2) provide a brief overview of the key results that have been obtained by density functional theory calculations and (3) discuss the potential of germanene for future applications as well for fundamentally oriented studies.

Interfering Bloch waves in a 1D electron system.

Using low-temperature scanning tunnelling spectroscopy we have studied the spatial variation of confined electronic states between neighbouring atomic chains on a Ge(001)/Pt surface. The quasi-one-dimensional electronic states reside in the troughs between the atomic chains and exhibit a profound Bloch character along the chain direction. In the proximity of defects an enhancement of the oscillatory standing wave pattern in the density of states is found. The spatial variation of the standing wave pattern can be explained by an interference of incoming and reflected Bloch waves.