Optical properties of tensilely strained Ge nanomembranes

Group-IV semiconductors, which provide the leading materials platform of micro- electronics, are generally unsuitable for light emitting device applications because of their indirect- bandgap nature. This property currently limits the large-scale integration of electronic and photonic functionalities on Si chips. The introduction of tensile strain in Ge, which has the effect of lowering the direct conduction-band minimum relative to the indirect valleys, is a promising approach to address this challenge. Here we review recent work focused on the basic science and technology of mechanically stressed Ge nanomembranes, i.e., single-crystal sheets with thicknesses of a few tens of nanometers, which can sustain particularly large strain levels before the onset of plastic deformation. These nanomaterials have been employed to demonstrate large strain-enhanced photoluminescence, population inversion under optical pumping, and the formation of direct-bandgap Ge. Furthermore, Si-based photonic-crystal cavities have been developed that can be combined with these Ge nanomembranes without limiting their mechanical flexibility. These results highlight the potential of strained Ge as a CMOS-compatible laser material, and more in general the promise of nanomembrane strain engineering for novel device technologies.The Ge nanomembrane fabrication and characterization efforts were supported initially by DOE under Grant DE-FG02-03ER46028, and subsequently by AFOSR under Grant FA9550-14-1-0361. The development of the photonic-crystal cavities was supported by NSF under Grant ECCS-1308534. The initial photoluminescence studies were funded by NSF under Grant DMR-0907296. The contribution from several students and research scientists involved in this research at Boston University and the University of Wisconsin-Madison (including Cicek Boztug, Francesca Cavallo, Feng Chen, Xiaorui Cui, RB Jacobson, Debbie Paskiewicz, Jose Sanchez-Perez, Pornsatit Sookchoo, Faisal Sudradjat, Xiaowei Wang, and Jian Yin) is also gratefully acknowledged. (DE-FG02-03ER46028 - DOE; FA9550-14-1-0361 - AFOSR; ECCS-1308534 - NSF; DMR-0907296 - NSF)Published versio

The Frictionless Flow in the Region Around Two Circles

This investigation attempts to surpass the boundaries of pure mathematical interest in that it possesses as an example, a flow investigation in a multiply-connected region. Then the results appear to be carried out by means of an appropriate conformal representation of the region around two chosen closed curves. Thus we have the basis of an exact plane theory of the biplane. Certainly, the known difficulties of the accomplishment of this representation depend upon the region around the given curves. It is easier to choose the transformation function so that we obtain the transformal curves which, as contours of the wings of a biplane are at least useful to a certain extent, and correspond to the Joukowski monoplane wing

Opportunities to leverage cell culture technology to create sustainable food systems: The development of Clean Meat

Clean meat — meat produced through cell culture, rather than animal slaughter — can dramatically reduce the environmental footprint of meat while alleviating the severe public health threats and animal welfare concerns posed by factory farming. Recent developments in regenerative medicine, tissue engineering, and large-scale cell culture for cellular therapies have spawned a multitude of technologies that are immediately applicable to clean meat production. Many of these biomedical technologies and tools can already address areas of need within clean meat research and development, but large-scale cell culture for clean meat production presents a number of unique requirements that are not currently met with existing technologies developed for the biomedical, biopharma, and R&D industries. Most notably, cost constraints and scale requirements for the clean meat industry are significantly different than for cellular therapeutics or regenerative medicine, and innovation is needed to develop products that are optimized for the cell types and structures that are relevant for clean meat. Developing these tools for clean meat will simultaneously advance the technology and reduce costs for the biomedical and therapeutic applications. Please click Additional Files below to see the full abstract

Opportunities for applying biomedical production and manufacturing methods to the development of the clean meat industry

Clean meat (meat grown using cell culture methods, rather than obtained from animal slaughter) is an emergent biotechnology industry that will ameliorate the serious environmental, sustainability, global public health, and animal welfare concerns of conventional animal agriculture. Critical Technology Elements (CTEs) for clean meat include immortalized cell lines for meat animals (e.g. chicken, pig, cattle, and turkey), xeno-free media optimized for proliferation and maturation of these cell lines, edible or biodegradable scaffolding for tissue engineering, and efficient bioreactors for cell proliferation and differentiation. While many biomedical products and tools can already be applied to the CTEs of clean meat, the opportunities to expand biomedical product lines are considerable. Large-scale cell culture for clean meat production presents a number of unique requirements that are not currently met with existing products for the biomedical industry. Namely, cost constraints and scale requirements for the clean meat industry are notably different than for cellular therapeutics or regenerative medicine, and innovation is needed to develop products that are optimized for the cell types and structures that are relevant for clean meat. Further, developing these tools for clean meat would simultaneously advance the technology and reduce costs for the biomedical and therapeutic applications. We will discuss new applications for current biomedical products and manufacturing methods for clean meat and discuss potential for symbiotic and synergistic product development through partnerships between researchers, biomedical product manufacturers, and the emergent clean meat industry

Integrated Freestanding Single-Crystal Silicon Nanowires: Conductivity and Surface Treatment

Integrated freestanding single-crystal silicon nanowires with typical dimension of 100 nm × 100 nm × 5 µm are fabricated by conventional 1:1 optical lithography and wet chemical silicon etching. The fabrication procedure can lead to wafer-scale integration of silicon nanowires in arrays. The measured electrical transport characteristics of the silicon nanowires covered with/without SiO2 support a model of Fermi level pinning near the conduction band. The I–V curves of the nanowires reveal a current carrier polarity reversal depending on Si–SiO2 and Si–H bonds on the nanowire surface

Three-Omega Thermal-Conductivity Measurements with Curved Heater Geometries

The three-omega method, a powerful technique to measure the thermal conductivity of nanometer-thick films and the interfaces between them, has historically employed straight conductive wires to act as both heaters and thermometers. When investigating stochastically prepared samples such as two-dimensional materials and nanomembranes, residue and excess material can make it difficult to fit the required millimeter-long straight wire on the sample surface. There are currently no available criteria for how diverting three-omega heater wires around obstacles affects the validity of the thermal measurement. In this Letter, we quantify the effect of wire curvature by performing three-omega experiments with a wide range of frequencies using both curved and straight heater geometries on SiO$_2$/Si samples. When the heating wire is curved, we find that the measured Si substrate thermal conductivity changes by only 0.2%. Similarly, we find that wire curvature has no significant effect on the determination of the thermal resistance of a $\sim$65 nm SiO$_2$ layer, even for the sharpest corners considered here, for which the largest measured ratio of the thermal penetration depth of the applied thermal wave to radius of curvature of the heating wire is 4.3. This result provides useful design criteria for three-omega experiments by setting a lower bound for the maximum ratio of thermal penetration depth to wire radius of curvature.Comment: 4 pages, 3 figure

Interplay of stress, structure, and stoichiometry in Ge-covered Si(001)

Journal ArticleBy calculating the evolution of surface energies and surface stress tensors of Ge-covered Si(001) with increasing Ge coverage, we derive the most probable Ge stoichiometry in the subsurface regions beyond 1 monolayer coverage. We compare the calculated surface reconstruction and surface stress at the thermodynamic and kinetic limits to experiment to provide a quantitative understanding of the recently observed Ge-induced reversal of surface stress anisotropy

Reaction Kinetics in a Tight Spot

The standard analysis of reaction networks based on deterministic rate equations fails in confined geometries, commonly encountered in fields such as astrochemistry, thin film growth and cell biology. In these systems the small reactant population implies anomalous behavior of reaction rates, which can be accounted for only by following the full distribution of reactant numbers

ArabTeX : a system for typesetting Arabic; user manual version 3.00

ArabTeX is a package extending the capabilities of TeX/LaTeX to generate the Arabic writing from an ASCII transliteration for texts in several languages using the Arabic script. It consists of a TeX macro package and an Arabic font in several sizes, presently only available in the Naskhi style. ArabTeX will run with Plain TeX and also with LaTeX. It is compatible with NFSS, NFSS2 and the EDMAC package; other additions to TeX have not been tried. ArabTeX is primarily intended for generating the Arabic writing, but the standard scientific transliteration can also be easily produced. For languages other than Arabic that are customarily written in the Arabic script some limited support is available. ArabTeX defines its own input notation which is both machine, and human, readable, and suited for electronic transmission and Email communication. However, texts in some of the Arabic standard encodings can also be processed. ArabTeX is copyrighted, but free use for scientific, experimental and other strictly private, noncommercial purposes is granted. Offprints of publications using ArabTeX are welcome. Using ArabTeX otherwise requires a license agreement. There is no warranty of any kind, either expressed or implied. The entire risk as to the quality and performance rests with the user

XPASCAL - eine Erweiterung der Sprache Pascal mit exakter Arithmetik

XPASCAL ist ein experimentelles Programmsystem zur Unterstützung exakter Berechnungen in arithmetischen Zahlkörpern, das derzeit in der Abteilung Betriebssoftware am Institut für Informatik der Universität Stuttgart entwickelt wird. Bisher haben daran neben dem Verfasser die Studenten G. Neusetzer, U. Schoppe, G. Wahl, Th. Schöbel und S. Robitschko mitgearbeitet. Der vorliegende Bericht soll die derzeitigen Zielvorstellungen und den Stand der Realisierung aufzeigen und zu Kommentaren, Änderungswünschen und Verbesserungsvorschlägen einladen