Photoluminescence of Anisotropically etched silicon

Visible room-temperature luminescence of Anisotropically Chemically Etched (ACE) silicon under spontaneous chemical surface modification in HNO₃:HF solution is reported. The material is investigated by SEM, AES, IR transmission and Raman scattering methods.     

Über eine Mikro-Torsionswaage höherer Belastbarkeit

Zusammenfassung Es wird eine Torsionswaage beschrieben, die durch Anwendung eines mechanischen übersetzungsgetriebes die Anwendung stärkerer und damit hochbelastbarer und bruchsicherer Drähte als Mittelachse erlaubt. Ein Modell mit einer Belastbarkeit bis zu 2 g und einer Wägegenauigkeit von ±10g wird beschrieben. Durch optische Projektion auf eine Mattscheibe kann die Einstellung der Nullage kontrolliert und das Gewicht gleichzeitig abgelesen werden. Unter Verwendung einer weitgehend belastungsunempfindlichen Balkenform, eines temperaturunempfindlichen Balken- und Torsionsdrahtmaterials ist die neue Waage anspruchslos hinsichtlich ihrer Aufstellung und Behandlung.

---

Summary A torsion balance is described, which through the use of a mechanical gearing permits the use of stronger and thus more highly loadable and sturdier wires as central axis. A model with a permissible load up to 2 g and an accuracy of ±10g is described. The adjustment of the zero point can be checked by optical projection on a ground glass plate and the weight read off at the same time. Since the beam used is quite insensitive to the load, and the beam and torsion wires are constructed of temperature-insensitive materials, the balance is not demanding with respect to its installation and handling.

---

Résumé On décrit une balance de torsion qui, par un dispositif de surcharge mécanique, permet l'emploi comme suspension centrale de fils plus forts et, par suite de charges plus grandes. On décrit un modèle avec une charge de 2 g et une précision de ±10g. Par projection optique sur un verre dépoli, on peut contrÔler la position du zéro et lire simultanément le poids. Par emploi d'une forme de fléau indépendante de la charge dans un large domaine, de matériaux pour la construction des fils de torsion et du fléau, insensibles à l'effet de la température, la nouvelle balance est très simple du point de vue de son installation et de son maniement.

---

---

Herrn Universitätsprofessor Dr.L. Ebert zum 60. Geburtstag gewidmet !     

Beiträge zur qualitativen „Test Tube“-Papierchromatographie

Zusammenfassung Bei der Trennung und Bestimmung verschiedener reiner Aminosäuren wurde die in vieler Hinsicht einfachere und raschere Test Tube-Methodik näher studiert. Zum Lösen der Aminosäuren erwies sich Ameisensäure als besonders günstig. Bezüglich des Trennungseffektes haben sich als Eintauchmittel besonders eine Mischung von n-Propanol-Wasser und bestimmte ternäre Gemische von tert. Butanol-Methyläthylketon-Wasser und tert. Butanol-Methanol-Wasser bewährt. Außerdem wurde festgestellt, daß die Test Tube-Papierchromatographie besonders auch bei höheren Temperaturen verwendbar ist und hier bessere und raschere Trennungseffekte erzielt werden können. Die Fehlerquellen bei der Bestimmung derR _f Werte wurden eingehend geprüft und dieR _f Werte von 19 Aminosäuren bei verschiedenen Bedingungen in Tabellen angegeben.

---

Summary A closer study of the Test Tube Method, which is simpler and faster, was made in the separation and determination of various amino acids. Formic acid was found to be especially good for dissolving the amino acids. With respect to the separation effect, it was found that a mixture of n-propanolwater and certain ternary mixtures of tertiary butanol -methylethylketone-water and tertiary butanol-methanol-water are good as immersion agents. It was also shown that the Test Tube paper chromatography is also applicable at higher temperatures and gives better and more rapid separation effects. The sources of error in the determination of theR _f values were investigated closely and a table is included showing theR _f values of 19 amino acids under various conditions.

---

Résumé On a approfondi l'étude de la «technique du tube à essais» dont l'emploi pour la séparation et le dosage de différents amino-acides purs est des plus simples et des plus rapides à de multiples points de vue. Il est apparu que l'acide formique était un solvant particulièrement approprié pour les aminoacides. En ce qui concerne l'effet de séparation, on a obtenu d'excellents résultats par immersion dans un mélange de propanol normal et d'eau ou dans des mélanges ternaires définis de butanol tertiaire, de méthyléthylcétone et d'eau ou de butanol tertiaire, de méthanol et d'eau. On a, en outre, établi que la chromatographie sur papier par la méthode du «tube à essais» est également utilisable lorsqu'on élève la température et qu'elle permet alors d'obtenir des effets de séparation meilleurs et plus rapides. Les sources d'erreurs de la détermination des valeurs deR _f ont été étudiées en détail; un tableau fournit les valeurs deR _f relatives à 19 aminoacides dans des conditions diverses.

     

Transformation of optical vortices by polarization dynamic holograms

Results of theoretical and experimental studies of regularities in the transformation of the topological and polarization structures of optical vortices by polarization dynamic holograms formed by pulse Gaussian and singular light beams in dye solutions are presented.     

Gap and out-gap breathers in a binary modulated discrete nonlinear Schrödinger model

We consider a modulated discrete nonlinear Schrödinger (DNLS) model with alternating on-site potential, having a linear spectrum with two branches separated by a forbidden gap. Nonlinear localized time-periodic solutions with frequencies in the gap and near the gap -- discrete gap and out-gap breathers (DGBs and DOGBs) -- are investigated. Their linear stability is studied varying the system parameters from the continuous to the anti-continuous limit, and different types of oscillatory and real instabilities are revealed. It is shown, that generally DGBs in infinite modulated DNLS chains with hard (soft) nonlinearity do not possess any oscillatory instabilities for breather frequencies in the lower (upper) half of the gap. Regimes of exchange of stability between symmetric and antisymmetric DGBs are observed, where an increased breather mobility is expected. The transformation from DGBs to DOGBs when the breather frequency enters the linear spectrum is studied, and the general bifurcation picture for DOGBs with tails of different wave numbers is described. Close to the anti-continuous limit, the localized linear eigenmodes and their corresponding eigenfrequencies are calculated analytically for several gap/out-gap breather configurations, yielding explicit proof of their linear stability or instability close to this limit.Received: 31 October 2003, Published online: 17 February 2004PACS: 63.20.Pw Localized modes - 63.20.Ry Anharmonic lattice modes - 42.65.Wi Nonlinear waveguides     

Spectroscopy of electroreflection, the electron band structure, and the mechanism of visible photoluminescence of anisotropically etched silicon

We present the results of studies of electroreflection in the 1.1–4.4 eV spectral range, of electron Auger spectroscopy, and of electron diffraction involving the photoluminescent Si-SiO₂ system prepared via anisotropic chemical etching of the Si(100) surface. These results are explained on the basis of a four-layer model of the band structure and energy transition diagram for a system with a quantum well at the silicon surface, surface electron states at the boundary, and a gradient of the band potential in the transition layer. We find that light-emitting silicon remains an indirect-gap semiconductor and that the visible photoluminescence is due to direct recombinations of the light-excited electrons and holes in the quantum well at the center of the Brillouin zone with the participation of the band of deep localized states, which is due to the presence of oxygen at the silicon surface. Zh. éksp. Teor. Fiz. 116, 1750–1761 (November 1999)     

Migration of an acetyl group in glucosamine and glucose derivatives by the action of butyllithium. The synthesis of an N-acetylglucosamine 4-phosphate derivative

Conclusions The migration of the acetyl group from C⁴ to C⁶ occurs in partially acetylated derivatives of D-glucose and D-glucosamine upon reaction with butyllithium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2106-2109, September, 1987.     

Untersuchung von Honig

Ohne Zusammenfassung