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

https://www.tandfonline.com/doi/pdf/10.1088/1468-6996/16/4/043502

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

The Al-induced crystallization (AIC) yields a large-grained (111)-oriented Ge thin film on an insulator at temperatures as low as 180 °C. We accelerated the AIC of an amorphous Ge layer (50-nm thickness) by initially doping Ge in Al and by facilitating Ge diffusion into Al. The electron backscatter diffraction measurement demonstrated the simultaneous achievement of large grains over 10 μm and a high (111) orientation fraction of 90% in the polycrystalline Ge layer formed at 180 °C. This result opens up the possibility for developing Ge-based electronic and optical devices fabricated on inexpensive flexible substrates.

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Low-temperature (180 °C) formation of large-grained Ge (111) thin film on insulator using accelerated metal-induced crystallization

High-carrier-mobility semiconductors on flexible-plastic are essential to realize flexible electronics For this purpose, electrical properties of orientation-controlled large-grain Ge crystals on flexible-plastic directly formed by nucleation-controlled gold-induced-crystallization (GIC) are examined, and compared with those obtained by aluminum-induced-crystallization (AIC) The Ge crystals show p-type conductions Here, hole concentrations are 22 × 1017 and 58 × 1020 cm−3 for GIC-Ge and AIC-Ge, respectively, which are explained on the basis of the solubility of Au and Al in Ge Thanks to the low hole concentration, GIC-Ge shows high hole mobility (160 cm2 V−1 s−1) compared with AIC-Ge (37 cm2 V−1 s−1) These demonstrate significant advantage of GIC to realize high-performance flexible-electronics

High carrier mobility in orientation-controlled large-grain (≥50 μm) Ge directly formed on flexible plastic by nucleation-controlled gold-induced-crystallization

We investigated the effects of incorporation of 0%–2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1−xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1−xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20–30 nm. The Hall hole mobility of a poly-Ge1−xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

High hole mobility tin-doped polycrystalline germanium layers formed on insulating substrates by low-temperature solid-phase crystallization

Selective formation of Ge(100) and (111) on amorphous-insulator at low-temperatures (∼250 °C) is realized through gold-induced-crystallization using a-Ge/Au/SiO2 stacked-structures by combining interface-energy-modulation of substrates. Introduction of thin-Al2O3 layers (∼7 nm thickness) at a-Ge/Au interfaces enables large-grain (≥20 μm) Ge(111) formation, which is speculated to be due to suppression of random bulk-nucleation and domination of (111)-oriented interface-nucleation on SiO2. To examine this speculation, Al2O3-covered substrates are employed. This results in formation of Ge(100), due to energetically favorable (100)-oriented interface-nucleation on Al2O3. Consequently, large-grain (≥20 μm) Ge(100) and (111) are achieved on amorphous-insulators at 250 °C. This technique is very useful to realize flexible-electronics.

Tsuneharu Suzuki

Papers

Nucleation-controlled gold-induced-crystallization for selective formation of Ge(100) and (111) on insulator at low-temperature (∼250 °C)

Sn-induced low-temperature (∼ 150 °c) crystallization of Ge on insulator