Quantum size effects and band structure in InSb

Quantum Size Effects (Q.S.E.) in InSb films have been detected by different experimental procedures.The work function dependence on thickness obtained from photoelectric emission threshold measurements is compared with prior results obtained with the retarding potential method. With both methods, the measured work function values are comparable. They are less than the corresponding bulk values, conforming to current theoretical predictions.The interband energy gap has been determined from photoelectric absorption band edge data: its value differs with respect to the bulk one, by the location of the first allowed energy subband in the conduction band due to the presence of Q.S.E.Some evidence is given for absence of a band structure dependence on Q.S.E.     

Order of phase transition between the Meissner state and the mixed state

The critical value of the Ginzburg-Landau parameter which separates type-II/1 from type-II/2 superconductors is computed by means of the boson formulation of superconductivity. By taking into account the tail effect of the function c(k), which describes the electrodynamics of the superconducting state, it is shown that the attractive part of the interaction energy between two flux lines indeed vanishes for a critical value of κ. The dependence on Λ = VN(O) is also discussed.     

Quantum size effects and negative resistance in MOS structure with polycrystalline InSb (n-type)

Summary The tunnel characteristics (J vs. V) of Al−Al₂O₃−InSb (n type) structures with thin (100÷400)? semiconducting electrode are presented. They are analysed by utilizing the model proposed by Chang, Esaki and Styles. The data obtained by a nonlinear best fit on experimental points describe the MOS structure and the negative-resistance region exibited by the characteristics. Furthermore, the semiconductor gap shows a dependence on the thickness and this variation is explainable with the quantum effects presence in the thinnest films.

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Riassunto Le caratteristiche tunnel (J vs. V) di strutture Al−Al₂O₃−InSb (n type) con eletrodo semiconduttore sottile (100÷400) ? sono presentate. Esse sono analizzate utilizzando il modello proposto da Chang, Esaki e Styles; i dati ottenuti da un adattamento ottimale non lineare sui punti sperimentali descrivono la struttura MOS e la regione a resistenza negativa esibita dalle caratteristiche. Inoltre si osserva che il gap del semiconduttore varia con lo spessore; tale variazione è interpretata mediante la presenza di effetti quantistici di dimensione nei films più sottili.

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Резюме Приводятся туннельные характеристики (J в зависимости отV) для Al−Al₂O₃−InSb (n-типа) структур с тонким (100÷400) ? сверхпроводящим злектродом. Эти нарактеристики анализируются с помощью модели, предложенной Ченгом, Есаки и Стайлсом. Данные, полученные путем нелинейной подгонки, описывают MOS структуры и область отрицательного сопротивления, обнаруженного в характеристиках. Кроме того, щель в свернпроводнике обнаруживает зависимость от толщины. Изменение щели объясняется наличием квантовых эффектов, связанных с размерами образцов, в тончайших пленках.

     

Metal‐assisted regioselectivity in nucleophilic substitutions: a study by Raman spectroscopy and density functional theory calculations

A series of complexes (Fe^II, Cu^II and Ni^II) of the N,O bidentate ligand 6,7‐dichloroquinoline‐5,8‐dione in water was investigated by using Raman spectroscopy, and the experimental peaks were assigned with the help of computed spectra by density functional theory (DFT) calculations. A strong shift to lower wavenumbers was observed for the vibration of the CO group involved in chelation, depending on the type of metal ion. When each complex was used in the substitution reaction by the nucleophilic reagent piperidine, two products having the same molecular composition but showing the substituent in different regions of the molecule were obtained, and moreover their regioselective formation was in agreement with the size of the Raman shifts previously observed for the complexes. This example confirms the potential of the approach involving Raman spectroscopy combined with DFT calculations in the characterization of metal complexes as key intermediates in organic reactions, with the possibility of predicting the metal system capable to achieve the highest selectivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Essential Spectra, Matrix Operator and Applications

This paper gives a survey on some recent results on the spectral theory of block operator matrices. We study the closeness in the product space and we give some conditions to characterize the essential spectra in the Browder resolvent set case. Furthermore, we apply the obtained results to several models such as delay equations, Sturm–Liouville problem and transport equations.     

Classical spin dynamics of anisotropic Heisenberg dimmers

In the present work we study the deterministic spin dynamics of two interacting anisotropic magnetic particles in the presence of an external magnetic field using the Landau-Lifshitz equation. The interaction between particles is through the exchange energy. We study both conservative and dissipative cases. In the first one, we characterize the dynamical behavior of the system by monitoring the Lyapunov exponents and bifurcation diagrams. In particular, we explore the dependence of the largest Lyapunov exponent respect to the magnitude of applied magnetic field and exchange constant. We find that the system presents multiple transitions between regular and chaotic behaviors. We show that the dynamical phases display a very complicated topology of intricately intermingled chaotic and regular regions. In the dissipative case, we calculate the final saturation states as a function of the magnitude of the applied magnetic field, exchange constant as well as the anisotropy constants.     

Cymantrene conjugation modulates the intracellular distribution and induces high cytotoxicity of a cell-penetrating peptide

The conjugation of cymantrene CpMn(CO)(3) to cell-penetrating peptide hCT(18-32)-k7 alters the intracellular distribution in MCF-7 cells compared to the unmodified peptide, as visualized by fluorescence microscopy, and leads to an increased nuclear accumulation; the peptide and cymantrene compound themselves are not toxic, but the bioconjugate shows a significant cytotoxicity with an IC(50) value of 36 micromol l(-1).     

Elaboration and electrochemical characterization of LaZr2Cr4Ni5-based metal hydride alloys

The elaboration of LaZr₂Cr₄Ni₅-based intermetallic compound was performed by mechanical alloying from LaNi₅ and ZrCr₂ precursors and characterized as active materials of negative electrodes in nickel-metal hydride (Ni-MH) batteries. The effect of the milling duration on the phase composition was investigated. The structural properties of the formed phases were determined by X-ray diffraction and quantified from the Rietveld refinement data. The increase of the milling time up to 40 h leads to the highest abundance of the LaZr₂Cr₄Ni₅ phase, estimated at a weight content of 60.6 %, and a complete elimination of the LaNi₅ intermetallic precursor. The chronopotentiometry, cyclic voltammetry, and chronoamperometry techniques were applied to characterize the electrochemical behavior of prepared LaZr₂Cr₄Ni₅-based compounds. The maximum discharge capacity was 152 mAh g⁻¹, and a high electrochemical stability was obtained in the alkaline solution. The value of the hydrogen diffusion coefficient is equal to 2.1 × 10⁻⁸ cm² s⁻¹, reflecting an appropriate electrochemical hydrogenation kinetic in the LaZr₂Cr₄Ni₅-based compounds.

     

Exploring the chemistry of free CI3+: reactions with the weak Lewis bases PX3 (X = Cl-I), AsI3 and Et2O

What is the preferred coordination site of CI3+? Recent computational work suggested the iodine atoms of the Lewis acid CI3+ to be more electrophilic than the classically expected carbon atom, e.g. the complex with water is of type I2C-I...OH2+ and not the classically expected I3C-OH2+. If this structure is correct, one may also anticipate reactions of CI3+ as an I+ donor. Thus, we were interested in investigating the chemistry of CI3+ in the room-temperature stable salt [CI3]+[pftb](-) ([pftb](-) = [Al(OC(CF3)3)4]-) with weak nucleophiles that i) mimic water (OEt2) or ii) are electronically deactivated weak nucleophiles (PX3, X = Cl-I; AsI3). One question was: is it possible to obtain iodine-coordinated Lewis acid-base adducts of the CI3+ cation? With Et2O as a base, the cation behaves as a strong Lewis acid and cleaves the ether to give I3C-OEt, C2H4 and [H(Et2O)2]+. By contrast PX3 and AsI3 coordinate to the CI3+ cations and the adducts have classical, carbon-bound ethane-like structures, as proven by X-ray single-crystal diffraction, IR, UV-Vis and NMR spectroscopy. From variable temperature 13C NMR studies, it followed for the I3C-AsI3+ salt that the equilibrium between CI3+ and AsI3 is reversible and temperature dependent in solution. The I3C-PI3+ salt decomposes at room temperature giving PI4+ and C2I4, likely through an iodine coordinated I2C-I[dot dot dot]PI3+ intermediate. Thus CI3+ may also act as an I+ donor. All reactions are in agreement with ab initio quantum chemical calculations at the MP2/TZVPP level and assignments of experimental spectra were aided by quantum chemistry.