Germanium

About: Germanium is a research topic. Over the lifetime, 22212 publications have been published within this topic receiving 382980 citations. The topic is also known as: Ge & element 32.

Tin-Nanoparticles Encapsulated in Elastic Hollow Carbon Spheres for High-Performance Anode Material in Lithium-Ion Batteries†

Abstract: Lithium batteries, as a main power source or back-up power source for mobile communication devices, portable electronic devices and the like, have attracted much attention in the scientific and industrial fields due to their high electromotive force andhigh energy density. Tomeet the demand for batteries having higher energy density and improved cycle characteristics, in recent years, a great deal of attempt has been made to develop new electrode materials or design new structures of electrode materials. For anode materials, among them, some elementary substances such as silicon (Si), germanium (Ge), or tin (Sn) provide promising alternative to conventional carbonaceous anode active materials, because they are capable of alloying with more lithium and thus leading to the extreme high initial capacity density. For example, metallic tin has recently been widely concerned as one of the promising anode materials for lithium batteries due to the following reasons. Firstly, its theoretical specific capacity (Li4.4Sn, 992mAhg ) ismuchhigher than that of conventional graphite (LiC6, 372 mA h g ). Secondly, the tin anode has higher operating voltage than graphite, so it is less reactive and the safety of batteries during rapid charge/discharge cycle could be improved. Furthermore, a significant advantage of metallic tin over graphite is that it does not encounter solvent intercalationwhich causes irreversible charge losses at all. Unfortunately, the biggest challenge for employing metallic tin as applicable active anode materials is that it is suffering from huge volume variation during Liþ insertion/extraction cycle, which leads to pulverization of the electrode and very rapid capacity decay. Without appropriate structure design, the tin electrode typically fails after only a few discharge/charge cycles. It is therefore very desirable to design a new tinbased materials mainly composed of metallic tin with high specific capacity as well as good cycle performance. Some metal/oxides and carbon nanocomposites have been reported with high capacity and capacity retention when used as anodematerials, because the carbon shell has itself good electronic conductivity and prevents the aggregation of active materials, and especially thin carbon shell has good elasticity to effectively accommodate the strain of volume change during Liþ insertion/extraction. Very recently, tin-encapsulated spherical hollow carbon was synthesized by the pyrolysis of tin-containing organic precursors have exhibited higher capacity and better cycle performance than unencapsulated mixture materials, in which the content of tin active substance was only 24 wt%. Nanostructured tin dispersed in a carbonmatrix and carbon-encapsulated hollow tin nanopartides were also reported as superior anode materials. These studies showed that both coating tin nanomaterials with carbon layer and dispersing tin nanoparticles in carbon matrix are effective to improve their electrochemical properties in lithium ion batteries. It is obvious that thehigher content of and smaller size of tin, as well as the thinner carbon coating will greatly contribute to the further enhancement of material performance since the lithium storage density in tin ismuch higher than that in carbon. Meanwhile, this tin-based anode material has to be designed to own enough void volume to compensate the volume expansion during Liþ insertion, which is important to improve its cycle performance. In the presentwork,we therefore designed anewapproach to synthesize tin nanoparticles encapsulated elastic hollow carbon spheres (TNHCs) with uniform size, in which multiple tin nanoparticles with a diameter of less than 100 nm were encapsulated inone thin hollow carbon spherewith a thickness of only about 20 nm, thus leading to both the content of Sn up to over 70% by weight and the void volume in carbon shell as high as about 70–80%by volume. This void volume and the elasticity of thin carbon spherical shell efficiently accommodate the volume change of tin nanoparticles due to theLi-Sn alloying-dealloying reactions, and thus prevent the pulverization of electrode. As a result, this type of tin-based nanocomposites have very high specific capacity of >800 mA h g 1 in the initial 10 cycles, and >550mAh g 1 after the 100th cycle, as well as excellent cycling [*] Prof. L.-J. Wan, W.-M. Zhang, Dr. J.-S. Hu, Prof. Y.-G. Guo, S.-F. Zheng, L.-S. Zhong, Prof. W.-G. Song Beijing National Laboratory for Molecular Sciences Institute of Chemistry Chinese Academy of Sciences (CAS) Beijing 100080 (P.R. China) E-mail: wanlijun@iccas.ac.cn

Enhanced thermoelectric figure-of-merit in nanostructured p-type silicon germanium bulk alloys.

Abstract: A dimensionless thermoelectric figure-of-merit (ZT) of 0.95 in p-type nanostructured bulk silicon germanium (SiGe) alloys is achieved, which is about 90% higher than what is currently used in space flight missions, and 50% higher than the reported record in p-type SiGe alloys. These nanostructured bulk materials were made by using a direct current-induced hot press of mechanically alloyed nanopowders that were initially synthesized by ball milling of commercial grade Si and Ge chunks with boron powder. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased phonon scattering at the grain boundaries of the nanostructures combined with an increased power factor at high temperatures.

Experiments on Ge-GaAs heterojunctions

Abstract: The electrical characteristics of Ge-GaAs heterojunctions, made by depositing Ge epitaxially on GaAs substrates, are described. I–V and electro-optical characteristics are consistent with a model in which the conduction- and valence-band edges at the interface are discontinuous. The forbidden band in heavily doped (n-type) germanium appears to shift to lower energy values.

Semiconductor surfaces and interfaces

Abstract: 1 Introduction- 2 Surface Space-Charge Region in Thermal Equilibrium- 3 Surface States- 4 Occupation of Surface States and Surface Band-Bending in Thermal Equilibrium- 5 Surface S pace-Charge Region in Non-Equilibrium- 6 Interface States- 7 Cleaved {110} Surfaces of III-V and II-VI Compound Semiconductors- 8 {100} Surfaces of III-V, II-VI, and I-VII Compound Semiconductors with Zincblende Structure- 9 {100} Surfaces of Diamond, Silicon, Germanium, and Cubic Silicon Carbide- 10 Diamond, Silicon, and Germanium {111}-2 x 1 Surfaces- 11 Si(111)-7 x 7 and Ge(111)-c(2 x 8) Surfaces- 12 Phase Transitions on Silicon and Germanium {111} Surfaces- 13 {111} Surfaces of Compounds with Zincblende Structure- 14 Monovalent Adatoms- 15 Group-III Adatoms on Silicon Surfaces- 16 Group-V Adatoms- 17 Oxidation of Silicon and III-V Compound Semiconductors- 18 Surface Passivation by Adsorbates and Surfactants- 19 Semiconductor Interfaces- References- Index of Reconstructions and Adsorbates

Unusually low surface-recombination velocity on silicon and germanium surfaces.

Abstract: We have found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive. With preparation in this manner, the surface-recombination velocity on Si111g is only 0.25 cm/sec, which is the lowest value ever reported for any semiconductor. Multiple-internal-reflection infrared spectroscopy shows that the surface appears to be covered by covalent Si-H bonds, leaving virtually no surface dangling bonds to act as recombinatiuon centers. These results have implications for the ultimate efficiency of silicon solar cells.