Morphological and Surface-State Challenges in Ge Nanoparticle Applications

Abstract

The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12−14 and 14−16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

Self‐Limiting Synthesis of Ultrathin Ge(110) Single Crystal via Liquid Metal

“…Furthermore, this photon energy reveals a prominent blue shift compared with the bandgap of bulk structure (0.67 eV). [ 5 ] It also overcomes the limitation of the gapless 2D Ge(111) for further optoelectronic device applications. [ 38 ] We also investigate the thickness‐dependent PL spectra in Figures S7 and S8a (Supporting Information), which demonstrate that the process of blue shift is caused by the decrease of thickness.…”

“…Therefore, germanium-based materials are widely used in semiconductors, solid-state electronics, biomedicine, and photoelectronics. [1][2][3][4][5][6][7] Meanwhile, the quantum confinement effect can be observed obviously because of its large Bohr exciton radius ultrathin Ge(110) single crystals exhibit anisotropic honeycomb structure, uniformly incremental lattice, wide tunable bandgap, unique phonon modes, improved quantum efficiency, excellent second harmonic generation (SHG), and high carrier mobilities.…”

“…Therefore, germanium‐based materials are widely used in semiconductors, solid‐state electronics, biomedicine, and photoelectronics. [ 1–7 ] Meanwhile, the quantum confinement effect can be observed obviously because of its large Bohr exciton radius (24.3 nm). [ 4 ] Given these novel physical properties of germanium, uncovering the nanostructure and characteristics of the 2D Ge systems are timely.…”

P‐Type 2D Semiconductors for Future Electronics

“…[ 20a ] Notably, according to the theoretical calculation, the hole mobility of five‐layer b‐As can reach as high as ≈4000 cm 2 V −1 s −1 . [ 20b ] For Ge, its nanocrystals were discovered 40 years ago, in 1982 by Hayashi et al, [ 50 ] and it possesses a narrow bandgap of 0.67 eV for the bulk structure at 300 K. [ 51 ] The angle‐dependent Raman investigation of Ge reveals a twofold anisotropic characteristic accorded with strong in‐plane anisotropy between the armchair and zigzag directions. The hole carrier mobility of as‐synthesized Ge single crystal is 724 cm 2 V −1 s −1 .…”

Synthesis of Ge1−xSnx nanoparticles under non-inert conditions

“…The high tunability of the bandgap of Ge 1−x Sn x particles through composition and size is evident from previous reports where bandgaps already span from about 0.4 eV to above 1.8 eV in Ge 1−x Sn x nanoparticles, with sizes down to 1.5 nm and Sn concentrations up to 42%. [14][15][16][17][18][19] The bandgap of pure Ge particles has been reported to be far above 2 eV, although many of these do not seem to be tunable by quantum confinement 20 but still indicating that the limits of the Ge 1−x Sn x bandgap are few.…”