Physica Status Solidi (B): Basic Research
1521-3951
0370-1972
Đức
Cơ quản chủ quản: Wiley-VCH Verlag , WILEY-V C H VERLAG GMBH
Lĩnh vực:
Condensed Matter PhysicsElectronic, Optical and Magnetic Materials
Các bài báo tiêu biểu
Optical Properties and Electronic Structure of Amorphous Germanium Abstract The optical constants of amorphous Ge are determined for the photon energies from 0.08 to 1.6 eV. From 0.08 to 0.5 eV, the absorption is due to k ‐conserving transitions of holes between the valence bands as in p‐type crystals; the spin‐orbit splitting is found to be 0.20 and 0.21 eV in non‐annealed, and annealed samples respectively. The effective masses of the holes in the three bands are 0.49 m (respectively 0.43 m ); 0.04 m , and 0.08 m . An absorption band is observed below the main absorption edge (at 300 °K the maximum of this band is at 0.86 eV); the absorption in this band increases with increasing temperature. This band is considered to be due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties and which are considered to be associated with vacancies. The absorption edge has the form: ω2 ϵ2 ∼(hω−E g )2 (E g = 0.88 eV at 300 °K). This suggests that the optical transitions conserve energy but not k vector, and that the densities of states near the band extrema have the same energy‐dependence as in crystalline Ge. A simple theory describing this situation is proposed, and comparison of it with the experimental results leads to an estimate of the localization of the conduction‐band wavefunctions.
Tập 15 Số 2 - Trang 627-637 - 1966
A Statistical Theory of Solid Solution Hardening Abstract The critical shear stress τc to move a dislocation through a random array of obstacles in the glide plane is calculated using a statistical theory. The result is an expression for τc in terms of the obstacle concentration, the line tension of the dislocation, and of the interaction force between the dislocation and a single obstacle. Fleischer's solution of the same problem is not reproduced by the statistical theory. Quantitatively the two results are not very different, but our new result is supported by some recent experimental evidence. Furthermore the theory provides a definite prescription how to combine the concentrations and interaction forces of obstacles of different kinds in the expression for τc .
Tập 41 Số 2 - Trang 659-669 - 1970
Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system
Tập 252 Số 8 - Trang 1700-1710 - 2015
P‐type doping and devices based on ZnO Abstract Both n‐type and p‐type ZnO will be required for development of homojunction light‐emitting diodes (LEDs) and laser diodes (LDs). It is easy to obtain strong n‐type ZnO, but very difficult to create consistent, reliable, high‐conductivity p‐type material. The most natural choice of an acceptor dopant is N, substituting for O, and indeed several groups have been able to obtain p‐type material by such doping. Surprisingly, however, other groups have also been successful with P and As, elements with much larger ionic radii than that of O. Although ZnO substrates are now available, most of the epitaxial p‐type layers so far have been grown on sapphire, or other poorly‐matched materials. The lowest p‐type resistivity obtained up to now is about 0.5 Ω‐cm, which should be sufficient for LED fabrication. In spite of the present availability of p‐type ZnO, very few homojunction LEDs have been reported so far, to our knowledge; however, several good heterojunction LEDs have been demonstrated, fabricated with p‐type layers composed of other materials. One such structure, with fairly strong 389‐nm emission at 300 K, involves n‐type ZnO and p‐type AlGaN, grown on an SiC substrate. Also, an N+ ‐ion implanted ZnO layer, deposited by chemical vapor deposition on Al2 O3 , exhibits 388‐nm emission at 300 K and could be economical to produce. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tập 241 Số 3 - Trang 624-630 - 2004
Solitary excitons in one‐dimensional molecular chains Abstract The change in time of the state of intramolecular excitation in an one‐dimensional molecular chain is investigated, where its deformability is taken into account. It is shown that the excitation which is accompanied by a local deformation of the chain, can move uniformly along the chain, the size of the region under excitation remaining constant. These excitations in one‐dimensional molecular chains can be called particle‐like excitons or solitary excitons .
Tập 59 Số 2 - Trang 465-470 - 1973
Theory of Nucleation Fields in Inhomogeneous Ferromagnets Abstract The effect of the microstructure on the coercive field of sintermagnets is investigated on the basis of the theory of micromagnetism. From the linearized micromagnetic equations nucleation fields are determinded for magnetic inhomogeneities with quasi‐harmonic spatial variations of the magnetocrystalline anisotropy energy. For one‐ and two‐dimensional nucleation modes the eigenvalues of the nucleation fields are derived as a function of the width and the strength of planar magnetic inhomogeneities.
Tập 144 Số 1 - Trang 385-396 - 1987
65 years of ZnO research – old and very recent results Abstract The research on ZnO has a long history but experiences an extremely vivid revival during the last 10 years. We critically discuss in this didactical review old and new results concentrating on optical properties but presenting shortly also a few aspects of other fields like transport or magnetic properties. We start generally with the properties of bulk samples, proceed then to epitaxial layers and nanorods, which have in many respects properties identical to bulk samples and end in several cases with data on quantum wells or nano crystallites. Since it is a didactical review, we present explicitly misconceptions found frequently in submitted or published papers, with the aim to help young scientists entering this field to improve the quality of their submitted manuscripts. We finish with an appendix on quasi two‐ and one‐dimensional exciton cavity polaritons.
Tập 247 Số 6 - Trang 1424-1447 - 2010
Plural and multiple scattering of low‐energy heavy particles in solids Abstract Small‐angle multiple scattering of low‐energy heavy particles (Born parameter α > 1) in solid layers is calculated, using a scattering cross section derived from classical mechanics. The angular distribution of the scattered particles is given as a sum of two functions, which are tabulated. The calculated distributions coincide with those of the well‐known theory of Molière for large thicknesses of material. For small thicknesses there are profound deviations.
Tập 44 Số 1 - Trang 253-268 - 1971
Auxetic behaviour from rotating rigid units Abstract Auxetic materials exhibit the unexpected feature of becoming fatter when stretched and narrower when compressed, in other words, they exhibit a negative Poisson's ratio. This counter‐intuitive behaviour imparts many beneficial effects on the material's macroscopic properties that make auxetics superior to conventional materials in many commercial applications. Recent research suggests that auxetic be‐haviour generally results from a cooperative effect between the material's internal structure (geometry setup) and the deformation mechanism it undergoes when submitted to a stress. Auxetic behaviour is also known to be scale‐independent, and thus, the same geometry/deformation mechanism may operate at the macro‐, micro‐ and nano‐ (molecular) level. A considerable amount of research has been focused on the ‘re‐entrant honeycomb structure’ which exhibits auxetic behaviour if deformed through hinging at the joints or flexure of the ribs, and it was proposed that this ‘re‐entrant’ geometry plays an impor‐ tant role in generating auxetic behaviour in various forms of materials ranging from nanostructured polymers to foams. This paper discusses an alternative mode of deformation involving ‘rotating rigid units’ which also results in negative Poisson's ratios. In its most ideal form, this mechanism may be construc‐ ted in two dimensions using ‘rigid polygons’ connected together through hinges at their vertices. On application of uniaxial loads, these ‘rigid polygons’ rotate with respect to each other to form a more open structure hence giving rise to a negative Poisson's ratio. This paper also discusses the role that ‘rotating rigid units’ are thought to have in various classes of materials to give rise to negative Poisson's ratios. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tập 242 Số 3 - Trang 561-575 - 2005
Negative compressibility, negative Poisson's ratio, and stability Abstract The role of negative compressibility is considered in detail. Experimental observations of negative bulk modulus in pre‐strained foam are presented and interpreted. A constrained microscopic model which exhibits negative compressibility is proposed. Some other negative and counterintuitive properties of matter, like negative Poisson's ratio, negative thermal expansion, negative specific heat, and negative pressure are also discussed. A simple thermodynamic model with negative thermal expansion is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tập 245 Số 3 - Trang 545-551 - 2008