CuCl Crystals Research Articles

Formation process of CuCl nano-particles in silica glass by ion implantation

The formation process of CuCl crystals has been studied in (3 MeV 6 × 10 16 Cl 2+ ions/cm 2 + 3 MeV 6 × 10 16 Cu 2+ ions/cm 2)-implanted silica glass by X-ray absorption spectroscopy and secondary ion mass spectroscopy. It was found from X-ray absorption spectroscopy that Cu atoms were mainly coordinated by oxygen atoms in as-implanted glass. Heat-treatment at 600°C caused the formation of Cu–Cl bonds and heat-treatment at 1000°C caused the formation of CuCl crystals in silica. It was deduced that the migration of Cl atoms is a rate-determining step for the formation of CuCl crystal, on the basis of the conventional precipitation model.

Nucleation and Ordering of an Electrodeposited Two-Dimensional Crystal: Real-Time X-Ray Scattering and Electronic Measurements

We have studied in situ the ordering of a two-dimensional Cu-Cl crystal electrodeposited on a Pt(111) surface. We simultaneously measured x-ray scattering and chronoamperometric transients during Cu desorption and subsequent ordering of the Cu-Cl crystal. In all cases, the current transient occurs on a shorter time scale than the development of crystalline order. The ordering time diverges with applied potential, consistent with the nucleation and growth of two-dimensional islands. We see a time-dependent narrowing of the x-ray peak, corresponding to the growing islands.

On the validity of Haynes rule for the binding of excitonic complexes in low dimensions

Using a two-dimensional geometrical model and fractional dimension approach, it is found analytically that the ratio of the binding energy of a biexciton to that of an exciton is 0.228 in quantum wells and it is independent of the quantum-well width. This agrees very well with the results in GaAs and ZnSe quantum wells, and CuCl crystals and large quantum dots. It is suggested that, while Haynes rule may be valid for bulk, much higher ratios may be expected in lower dimensions.

Temperature Evolution of the Optical Absorption Edge in the A2BX4 Type Compounds with Organic Cation

The temperature evolution of the optical absorption spectra of A2BX4 type compounds with an organic cation have been analyzed. It was shown that the fundamental absorption edge in these materials possesses an exponential shape following the empirical Urbach rule due to the occurrence of the electron–(exciton–)phonon interaction. As an example, the parameters of the EPI have been determined for (NH2(CH3)2)2CuCl4 crystals. Comparison of the obtained results with corresponding data for isomorphous compounds allowed to ascertain some total regularities characteristic of the EPI. Nonfulfilment of the Urbach rule in the incommensurate phase, particularly, was related to the considerable temperature dependence of the period and phase of the modulation. This conclusion is confirmed by data of Raman spectroscopy.

Early Stages of Copper Electrocrystallization: Electrochemical and in Situ X-ray Absorption Fine Structure Studies of Coadsorption of Copper and Chloride at the Au(111) Electrode Surface

Cu K-edge X-ray absorption spectra (XAS) recorded in situ using glancing incidence and fluorescence detection have been employed to study the codeposition of copper and chloride ions on a Au(111) surface under an electrolyte solution. Chronocoulometric measurements provided information about the composition of the overlayer and about the number of electrons flowing to the interface per adsorbed copper ion. The XAS displays a remarkable dichroism consistent with a bilayer in which the Cu adatoms are covered by chloride ions. Previous scanning tunneling microscopy (STM) measurements suggested either a (5 × 5) long-range structure similar to that of the (111) plane of a CuCl crystal or to (4 × 4)-based structures. FEFF 6.01 multiple scattering calculations of the XAS were performed on five different model structures derived from the STM proposals. A unique solution could not be obtained. The results indicate that there is a large degree of static disorder. They rule out high-symmetry structures in which ther...

Spherical cavity-mode laser with self-organized CuCl microspheres

We report lasing of exciton-polaritons in semiconductor microspheres with spherical cavity modes under subpicosecond ultraviolet laser excitation at low temperature. Small bulk crystals of CuCl are melted and formed into fused microspheres with diameters ranging from a few to several tens of micrometers. The threshold for lasing is 1nJ/pulse, which corresponds to 10(9) photons/pulse. We found that the biexciton-to-longitudinal-exciton transition is responsible for the lasing.

Reconsideration of relaxation processes of excitons in CuCl nanocrystals

We report temporal changes of luminescence and induced absorption of excitons in nanometer-size semiconductor crystals (nanocrystals) of CuCl embedded in NaCl or in glass, and discuss relaxation mechanisms of the excitons. In CuCl nanocrystals in NaCl, luminescence-decay or -rise is observed at “free”- or “localized”-state luminescence, respectively. This indicates nonradiative relaxation from the “free” exciton to the “localized” state. In CuCl nanocrystals in glass, the temporal changes of the induced absorption have a longer decay component, in addition to a fast decay component which agrees with the luminescence decay. This result suggests exciton decomposition and existence of an electron remainder in the nanocrystals.

Observation of biexcitonic effect in single ZnCdSe quantum well under very low excitation density

Under an excitation density of 0.4 W/cm2, a strong biexcitonic peak was observed in the photoluminescence (PL) spectrum of a single quantum well which was grown in submonolayer deposition mode. Its intensity was found to increase superlinearly with excitation density. The shape of the biexcitonic peak was found to be similar to that of biexcitons in CuCl and CdS crystal and a binding energy of 9.8 meV was obtained. When the temperature increased from 10 to 31 K, the biexcitonic peak decreased considerably whereas the excitonic peak increased slightly.

Biexciton-biexciton interaction in semiconductors

For a semiconductor with single isotropic conduction and valence bands, the effective biexciton-biexciton interaction is derived starting from the second-quantization representation for the Hamiltonian of the system of interacting excitons and for the biexciton wave function within the framework of the adiabatic approximation. The interaction is found to be an average of the sum of effective interactions between excitons forming interacting biexcitons over the envelope functions of these biexcitons. Depending on the momentum transfer and on the difference between the momenta of interacting biexcitons, the interaction admits an analytical study when the first vanishes. In this case, the interaction has in the r space the form of a function of the interbiexciton distance consisting of a strong repulsive and a weak attractive part. At low temperatures the function describes main features in the behavior of the interaction among biexcitons, in which repulsion predominates over attraction. It is shown that while biexcitons remain stable quasiparticles they weakly attract each other for any value of the distance. A quantitative analysis of obtained results for the CuCl crystal shows that the biexciton system in this model substance is a weakly nonideal Bose gas with positive scattering length ${\mathrm{a}}_{\mathrm{s}}$\ensuremath{\simeq}${3\mathrm{a}}_{\mathrm{x}}$, which closely approaches the ideal one at excitation densities n\ensuremath{\leqslant}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.

Exciton localization and decomposition dynamics in cuprous halide nanocrystals.

We report temporal changes of luminescence and absorption (differential transmission) of excitons in nanometer-size semiconductor crystals (nanocrystals) of CuCl embedded in NaCl or in glass, and CuBr nano- crystals embedded in glass. In CuCl nanocrystals in NaCl, an exciton relaxes nonradiatively to some localized state. In CuCl and CuBr nanocrystals in glass, the temporal changes of the differential transmission have a longer decay component in addition to the fast decay component which agrees with the luminescence decay. This result suggests exciton decomposition and the existence of an electron or a hole remainder in the nano- crystals. The decay time of the longer decay component increases by the accumulation of photoexcitation. This phenomenon indicates persistent trapping of carriers in the glass matrix, which is concerned with persistent spectral hole burning in nanocrystals. \textcopyright{} 1996 The American Physical Society.

Light-induced transition between states in a bistable regime at nonlinear magnetic resonance in (CH3NH3)2CuCl4

It is found that in (CH3NH3)2CuCl4 crystals under nonlinear magnetic resonance conditions in the magnetic-field range in which hysteresis is observed, pulsed laser irradiation induces a transition between different branches of the resonance curve. The effect exhibits a threshold with respect to the optical radiation power.

Polyvinylalcohol film doped with CuCl nanoclusters

Polyvinylalcohol film doped with CuCl nanoclusters was made using a chemical method. The optical absorbance curves of linearly polarized light from the film were determined at room temperature. The room temperature band gap of 3.65 eV determined from the absorbance curve is larger than the value of 3.50 eV found for bulk CuCl crystals.

Growth of CuCl single crystals composed of pure isotopes

Single crystals of CuCl with various pure isotopic compositions, namely63Cu35Cl, 65Cu35Cl, Cu35Cl, 63CuCl and 65CuCl, were grown either by sublimation of small amounts of CuCl source material or by reaction of Cu with HCl. In the case of the 35Cl isotope source material was obtained by conversion of Na35Cl to Cu35Cl. Studies of Raman spectra revealed the changes of LO and TO phonon frequencies with isotopic substitutions of Cu as well as Cl.

Effect of phase separation on precipitation characteristics of CuCl quantum dots in the borosilicate glass system

Abstract Effects of phase separation on the precipitation of CuCl particles in the sodium-borosilicate glass system have been investigated using acid elution measurement, UV/VIS absorption spectroscopy, and scanning and transmission electron microscopy. Compositions of 7.5Na2O40B2O352.5SiO2 and 22.5Na2O340B2O337.5SiO2 (wt%) were chosen as matrix glasses based on their phase separability and the relationship between the phase separation of the glass matrix and the precipitation of CuCl particles was studied. The CuCl precipitation occurred only in the phase-separable glass matrix and the radius of the CuCl nanocrystals increased with heat treatment time. The CuCl crystals were precipitated both in the boron-rich phase and in the silica-rich phase. Larger CuCl particles, with an average size of ∼ 3.3 nm, than those in the silica-rich phase, which averaged ∼ 1.7 nm, were observed to precipitate in the boron-rich phase. The observed CuCl particle size difference and the non-uniform distribution of the particles are attributed to the fast growth of the CuCl particles due to the lower viscosity of the boron-rich phase compared to that in the silica-rich phase.

Polariton solitons in semiconductors: Quantitative study

The reduced semiconductor Maxwell-Bloch equations are used to describe analytically dynamics of polariton solitons in semiconductor excitonic medium. Quantitative estimations of the conditions for the polariton soliton formation in CuCl and CdS crystals are performed.

Finding of the radiative decay channel of a biexciton leaving a Z 1,2-1s exciton behind in CuCl

Luminescence spectra of CuCl crystals are examined under strong photo-excitations of the giant two-photon absorption (GTA) band of biexcitons and the Z 3-exciton band at 2 K. Nonlinear emissions that can be attributed to the radiative decay of a biexciton leaving a Z 1,2-1s exciton behind are newly observed. The contribution of the Z 1,2-exciton state to the biexciton state is confirmed experimentally.

Application of the dead-layer model and A.B.C. conditions to the Z 12 and Z 3 exciton lines in CuCl

We have measured the normal reflection spectrum of (110) cleaved faces of single crystals of CuCl in the spectral range of the Z 3 and Z 12 exciton lines at the temperature of 95 K. We have fitted the experimental data by computing a non local dielectric function and taking into account various additional boundary conditions (ABC) and the dead layer model in a semi-infinite crystal. A quantitative agreement is obtained assuming the following values of the effective masses of the excitons: M(Z 3) = 2.4 m 0 , M(Z 12) = 0.65 m 0 . These results do not depend on the choice of a particular auxiliary boundary condition.

Preparation of CuCl nanocrystals in NaCl

It is demonstrated that the growth of CuCl crystals in a single crystal of NaCl can be observed by monitoring the optical absorption specturm. This technique enables the determination of thermodynamic and kinetic properties of the system. Based on these data the conditions for preparing nanocrystals are found. In comparison with other techniques the growth temperature is rather low which facilitates the modeling of crystal size.

On the ordering in [(C2H5)4N]2CuCl4 crystal: an X-ray study and theoretical considerations

On the ordering in [(C2H5)4N]2CuCl4 crystal: an X-ray study and theoretical considerations

On the ordering in [(C2H5)4N]2CuCl4 crystal: an X-ray study and theoretical considerations

The crystal structure [(C2H5)4N]2CuCl4 has been determined by X-ray diffraction at 243K. The room temperature phase (phase I) belongs to the space group P42/nm [1] whereas the low temperature phase (phase II) is orthorhombic and belongs to the space group Pnna. The phase transition at Tc=258K is of improper ferroelastic type and it is associated with the ordering of the CuCl42− and a partial ordering of the [(C2H5)4N]+ ions which are disordered in the high temperature tetragonal phase. At lower temperature, there occurs another instability which could correspond to a complete ordering in the crystal.