Depletion layers and domain walls in semiconducting ferroelectric thin films

Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 degrees domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 degrees domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed.     

Some new butylthiobenzoatotin(IV) compounds: spectral studies and analysis of ligand's bonding

Five new monorganotin(IV) compounds with thiobenzoate ligand, [BuSn(SOCPh)2]2O (1), [BuSn(O)(SOCPh)]2 (2), BuSn(Cl)(SOCPh)2 (3), BuSn(Cl)2(SOCPh) (4) and [BuSn(OH)(Cl)(SOCPh)]2 (5) were synthesized and characterized by elemental analyses, IR, 1H and 13C NMR spectroscopy. 119Sn NMR spectroscopy was used to determine the coordination geometry around Sn(IV) in the cases of 2 and 4. 1, 2 and 5 are dimeric while 3 and 4 are monomeric. In all these molecules the thiobenzoate ion is coordinated only through its sulfur atom. Molecular structures of the compounds have been optimized by MM2 calculations. Semi-empirical quantum mechanical calculations (PM3 method) were performed to explain the monodentate-bonding pattern of thiobenzoate ligand.     

Homogeneity of Lanthanide Doped Ceria Nanocrystal Dispersions Using High-resolution Transmission Electron Microscopy

Aqueous sols of crystalline solid solutions of the general formula Ce_1-xLn_xO_2-x/2x/2 [Ln = entire lanthanide range, x = 0–0.50 and square = anion vacancy] were synthesised using inorganic materials. The nanocrystals were dispersed on an amorphous silica support and individual crystals examined for composition and structure by high-resolution transmission electron microscopy (HREM) and energy dispersive analysis of X-rays (EDX). High-resolution pictures showed the nanocrystals to be mainly between 5 and 10 nm in size, rarely elongated and with atomically clean faceted surfaces.Diffractograms were used to measure the lattice parameters of the face-centre-cubic (fcc) fluorite structures giving values, depending on dopant species and concentration of dopant, in the range 5.5–5.8 Å. EDX analysis of individual crystals with the same nominal composition compared closely to each other and to that of an average over a large area indicating good homogeneity from the preparation method.     

Growth of nanostructures of Zn/ZnO by thermal evaporation and their application for room-temperature sensing of H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>S gas

ZnO micro- and nanostructures were prepared by thermal evaporation of Zn and a mixture of ZnO with graphite. On heating Zn powder in a quartz tube at temperatures between 600 °C to 800 °C, radial growth of nanowires was observed on the source. On increasing the temperature to 900 °C, various interesting micro- and nanostructures of Zn and ZnO were observed to have deposited all over the quartz tube. On the other hand, when ZnO was heated in the presence of graphite, predominant growth of ZnO nanotetrapods was observed. Nanowires and tetrapods of ZnO were characterized by photoluminescence measurements and were found to show significantly improved response for detection of H₂S gas at room temperature when compared with earlier studies. The response was seen to improve with increase in oxygen vacancies in the material. PACS 78.55.Et; 07.07.Df     

Instabilities and disorder-driven first-order transition of the vortex lattice

Transport studies in a Corbino disk suggest that the Bragg glass phase undergoes a first-order transition into a disordered solid. This transition shows sharp reentrant behavior at low fields. In contrast, in the conventional strip configuration, the phase transition is obscured by the injection of the disordered vortices through the sample edges, which results in the commonly observed vortex instabilities and smearing of the peak effect in NbSe2 crystals. These features are found to be absent in the Corbino geometry in which the circulating vortices do not cross the sample edges.     

Quantum well and quantum dot lasers: From strained-layer and self-organized epitaxy to high-performance devices

Strained heterostructures are now widely used to realize high-performance lasers. Highly mismatched epitaxy also produces defect-free quantum dots via an island growth mode. The characteristics of high-speed strained quantum well and quantum dot lasers are described. It is seen that substantial improvements in small-signal modulation bandwidth are obtained in both 1 m (48 GHz) and 1.55 m (26 GHz) by tunneling electrons directly into the lasing sub-band. In quantum dots the small-signal modulation bandwidth is limited by electron-hole scattering to 7 GHz at room temperature and 23 GHz at 80 K. The properties of these devices are described.     

Viscosity changes during the slow coagulation of ferric hydroxide sol and the verification of the new equation,connecting the electrolyte concentration and time of coagulation

Summary The viscosity changes with time during the slow coagulation of ferric hydroxide sol was studied in presence of potassium chloride, potassium nitrate, sodium acetate, potassium oxalate and potassium phosphate as electrolytes. The points of inflection in the autocatalytic viscosity-time curves were taken to denote the same kinetic stage of coagulation (d ² x/dt ²=0) brought about by adding different concentrations of the electrolyte. The reciprocal of the times corresponding to the inflection points were plotted against the respective concentrations of the electrolyte used. Straight lines were obtained in all cases showing the validity of the equation,C=a+m/n · 1/t, which is a particular case of the new Equation,C=a+m·1/t/n+1/t.

---

Zusammenfassung Die zeitliche ?nderung der Viskosit?t w?hrend der langsamen Koagulation von Eisenhydroxydsol wurde bei Anwesenheit von Kaliumchlorid, Kaliumnitrat, Natriumazetat, Kaliumoxalat und Kaliumphosphat, welche als Elektrolyte dienten, untersucht. Die Influxionspunkte in den autokatalytischen Viskosit?ts-Zeitkurven wurden verwendet, um denselben kinetischen Koagulationszustandd ² x/dt ²=0) zu kennzeichnen, welcher durch Hinzufügen verschiedener Elektrolytkonzentrationen hervorgerufen wurde. Die reziproken Zeitwerte dieser Knickpunkte wurden gegen die entsprechende Konzentration des verwendeten Elektrolyts aufgetragen. Es wurden in allen F?llen Gerade erhalten welche die Gültigkeit der GleichungC=a+m/n·1/t beweisen. Die Gleichung ist ein Spezialfall der GleichungC=a+(m/n+1/t)· 1/t.

     

Electrical transport of spin-polarized carriers in disordered ultrathin films

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.