The isolation of graphene in 2004 from graphite was a defining moment for the “birth” of a field: two-dimensional (2D) materials In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement Here, we review significant recent advances and important new developments in 2D materials “beyond graphene” We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (ie, silicene, phosphorene, etc) and transition metal carbide- and carbon nitride-based MXenes We then discuss the doping and functionalization of 2

Recent Advances in Two-Dimensional Materials beyond Graphene

Solid-state electronics

Since its discovery1, early in 1928, the scattering of light with altered frequency has been investigated in many crystals, and much valuable information has been accumulated. The significance of the results and their relation to theories of solid state are clearly matters of great interest.

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Scattering of light in crystals

The "textbook" phonon mean free path of heat carrying phonons in silicon at room temperature is ∼40  nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range ∼1-10  μm. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.

Direct Measurement of Room-Temperature Nondiffusive Thermal Transport Over Micron Distances in a Silicon Membrane

https://pure.mpg.de/pubman/item/item_3314332_3/component/file_3324953/1-s2.0-S0370157320300363-main.pdf

A perspective on conventional high-temperature superconductors at high pressure: Methods and materials

We have developed the epitaxial growth technology of Ge 1−x Sn x and related group-IV materials. The crystalline properties and energy band structure have been investigated for integrating group-IV semiconductors into Si ULSI platform.

Growth and applications of GeSn-related group-IV semiconductor materials

Au-Induced Low-Temperature (∼250°C) Crystallization of Si on Insulator Through Layer-Exchange Process

We comprehensively investigate Al-induced crystallization (AIC) of Si to achieve (0 0 1) and (1 1 1)-oriented Si films on quartz substrates. These phenomena are systematically explained by ‘preferential interfacial-nucleation model’ considering the nucleation sites and the phase transition of the interfacial Al oxide layers. Moreover, we demonstrate the lateral liquid phase epitaxy of Ge by using the orientation-controlled AIC-Si films as crystal seed. This technique enables high quality hetero-epitaxy of SiGe and Ge on transparent insulating substrates.

Al-Induced oriented-crystallization of Si films on quartz and its application to epitaxial template for Ge growth

Effects of surface oxide layers on liquid-Sn-driven GeSn crystallization on insulators at various temperatures (<475 °C) are investigated. An amorphous Ge in neighborhood of patterned-Sn (<3.5 μm) becomes to polycrystalline Ge1−xSnx (x ≈ 0.025 − 0.14) after annealing at 150–475 °C, which is independent of the surface oxide thickness. Interestingly, a 50-μm-length lateral growth of polycrystalline Ge0.99Sn0.01 layers achieved by combination of thickening of the surface-oxide treated by NH4OH and annealing above melting temperature of Sn (231.9 °C). The growth length is 15 times longer than without the treatment. The advanced process promises to achieve group-IV-based optic and electronic devices on flexible substrates and Si platforms.

Liquid-Sn-driven lateral growth of poly-GeSn on insulator assisted by surface oxide layer

Hybrid-integration of (111), (110), and (100) Ge-on-insulator (GOI) on an Si chip is essential to merge III-V semiconductor optical-devices as well as high-speed Ge transistors onto Si-large-scale integrated-circuits. We clarify important-parameters to control Ni-metal-induced lateral crystallization and Al-induced layer-exchange crystallization. This achieves artificial (110) and (111) Si micro-seed on insulating-film. Together with Si substrate as (100) Si seed, multi-crystal-seeds with different orientations are aligned on a Si chip. Then, SiGe-mixing triggered rapid-melting-growth of amorphous-Ge is examined from these multi-crystal-seeds. This enables simultaneous Ge lateral-crystallization with (111), (110), and (100) orientations. High-quality, hybrid-orientation GOIs without defects are demonstrated on Si platform.

Masashi Kurosawa

Papers

Growth and applications of GeSn-related group-IV semiconductor materials

Au-Induced Low-Temperature (∼250°C) Crystallization of Si on Insulator Through Layer-Exchange Process

Al-Induced oriented-crystallization of Si films on quartz and its application to epitaxial template for Ge growth

Liquid-Sn-driven lateral growth of poly-GeSn on insulator assisted by surface oxide layer

Hybrid-orientation Ge-on-insulator structures on (100) Si platform by Si micro-seed formation combined with rapid-melting growth