CuCl Nanocrystals Research Articles

Investigation of spectral properties of potassium-aluminum-borate glass with CuCl - CuBr nanocrystals

Heat treatment conditions effect on the characteristics of exciton absorption and luminescence of CuCl and CuBr nanocrystals in potassium-aluminaborate glass is studied. The size effect of the band edge absorption and luminescence energy is confirmed. The simultaneous presence of copper halide nanocrystals and free monovalent copper ions in the glass matrix is shown. Possible conditions for the formation of mixed CuCl-CuBr crystals are considered.

UV pulsed irradiation effect on the exciton luminescence of CuCl nanocrystals in borate glass

Heat treatment conditions effect on the characteristics of the Z3-exciton resonant luminescence of CuCl nanocrystals in potassium-aluminaborate glass is studied. The observed patterns of luminescence buildup are explained by the participation of thermal effects in recombination processes. The size effect in the resonance emission of Z3-excitons at 80 K is confirmed. The inverse dependence of the defectiveness of CuCl crystals in glass on the luminescence buildup rate of Z3-excitons is established.

Insights on the stability of cuprous chloride under high pressure: An equilibrium ab initio atomistic thermodynamics study

Density functional theory, in conjunction with ab initio atomistic thermodynamics, were used to investigate the stability of the low index cuprous chloride surfaces, and predict the morphology of CuCl nanocrystals under high pressures of chlorine. The rocksalt orientation of the lattice was adopted to resemble a CuCl crystal under high pressure. Under Cl-lean conditions, the defective CuCl(100)+Cl structure was found to be the most stable configuration among all surfaces investigated. Under Cl-rich conditions, a flawless, CuCl(111) surface with Cl-termination becomes the most stable configuration. It was shown that in a diluted chlorine environment, the CuCl in zinc blende structures are more stable than the CuCl in rocksalt configurations, while under a chlorine rich environment, the CuCl in rocksalt structures are more stable than the CuCl in zinc blende configurations. At low pressure of chlorine, it was found that the (100) facets are the most dominant to the Wulff construction, giving the crystal a coffin shape. As the pressure of chlorine increases, however, the involvement of the (111) facet increases giving the crystal a semi dodeca-hedron shape. At high pressure of chlorine, the major contributors to the Wulff construction were found to be the (111) facets, resulting in the formation of dodeca-hedron nanocrystals.

Nonisothermal nucleation in a solid solution of CuCl in glass: Concentration effect upon heating of the solid solution

The influence of the heating rate of a solid solution of CuCl in glass on the size distribution of the produced CuCl nanoparticles is studied. The distribution curves of CuCl nanocrystals are determined by the method of exciton-thermal analysis. It is established that the concentration of CuCl nanoparticles increases by ten times upon slowing the sample heating process from 2 to 60 min, while the mean radius of particles decreases almost twice. The concentration of CuCl nanoparticles passes through a maximum in the process of heating the sample. The numerical simulation of the nucleation upon slow heating of a solid solution showed that the formation of the concentration maximum of the new phase clusters is determined by a rapid increase in the critical radius owing to an increase in temperature and decrease in the solution supersaturation. As a result, the formation of new phase nuclei ceases at a certain temperature, and a part of the previously formed clusters dissolves.

Features of copper chloride nanocrystals formation in potassium aluminoborate glass

An unexpected sequence of forming different crystal lattices for the CuCl nanophases in potassium aluminoborate glass depending on the preceding heat treatment temperature is revealed. The hexagonal wurtzite-like nanocrystals are shown to crystallize from the liquid CuCl nanosize droplets separated at the lower heat treatment temperatures (380°C to no more than 400°C) than in the case for the cubic sphalerite-like CuCl nanocrystals (higher than 400°C). This sequence is inverse with respect to the standard temperature sequence of crystallizing the bulk hexagonal and cubic phases from a melt that is known for both CuCl and its structural prototype, ZnS. A tentative explanation for the effects revealed is proposed, the explanation assuming the principal role of internal pressure in the CuCl nanodroplets in setting the location of a phase point at the phase diagram.

Epitaxial Templating of Two-Dimensional Metal Chloride Nanocrystals on Monolayer Molybdenum Disulfide.

We demonstrate the formation of ionic metal chloride (CuCl) two-dimensional (2D) nanocrystals epitaxially templated on the surface of monolayer molybdenum disulfide (MoS2). These 2D CuCl nanocrystals are single atomic planes from a nonlayered bulk CuCl structure. They are stabilized as a 2D monolayer on the surface of the MoS2 through interactions with the uniform periodic surface of the MoS2. The heterostructure 2D system is studied at the atomic level using aberration-corrected transmission electron microscopy at 80 kV. Dynamics of discrete rotations of the CuCl nanocrystals are observed, maintaining two types of preferential alignments to the MoS2 lattice, confirming that the strong interlayer interactions drive the stable CuCl structure. Strain maps are produced from displacement maps and used to track real-time variations of local atomic bonding and defect production. Density functional theory calculations interpret the formation of two types of energetically advantageous commensurate superlattices via strong chemical bonds at interfaces and predict their corresponding electronic structures. These results show how vertical heterostructured 2D nanoscale systems can be formed beyond the simple assembly of preformed layered materials and provide indications about how different 2D components and their interfacial coupling mode could influence the overall property of the heterostructures.

Exciton-thermal analysis of nonisothermal nucleation in solid solution of CuCl in glass

The work presents results of investigation of nucleation of CuCl nanocrystals in glass by method of exiton-thermal analysis (ETA) which is based on measuring the optical absorbance of CuCl phase in sample under heating up to the melting temperature of CuCl nanocrystals. The melting temperature of nanoparticle depends on its radius. Therefore analysis of curve of melting CuCl phase allows to determine distribution curve of nanoparticles on their radii. By the method of ETA the features of variation of CuCl nanoparticles distributions in glass when changing regime of sample annealing (nonisothermal nucleation) were studied. For example, by reducing the heating rate of the sample the concentration of particles of CuCl phase increases considerably while reducing average radius.

Fluorophosphate glass of the xBa(PO3)2 · (90–x)NaPO3 · 10AlF3 system containing CuCl nanocrystals

Fluorophosphate glass containing 1.7 mol % of CuCl was synthesized in the xBa(PO3)2 · (90–x)NaPO3 · 10AlF3 system (mol %). The excess chlorine due to the addition of two different amounts of HCl results in a decrease in glass density indicating the introduction of chlorine in the structure and reduction of the degree of connectivity of the glass network. In glass with a high concentration of chlorine, CuCl nanocrystals with dimensions of about 4–4.6 nm are formed during the heat treatment near the glass transition temperature (Tg); this is registered by the appearance and increase of exciton bands corresponding to the Z1,2 and Z3 transitions.

Specific features of the optical properties of potassium–aluminum borate glasses with copper chloride nanocrystals at high temperatures

It is shown that heating of potassium–aluminum borate glasses with CuCl nanocrystals above 80°C leads to the disappearance of exciton absorption peaks, whereas cooling below 50°C gives rise to these peaks. These effects are related, respectively, to the melting of nanocrystals and crystallization of nanophase.

Spectral properties of copper halide nanocrystals in glasses of fluorine-phosphate matrix

The absorption spectra of glasses of fluorine-phosphate matrix in the near-UV spectral region have been investigated in the temperature range from 20 to 420°C. It is shown that the absorption bands in this spectral region are exciton absorption bands of copper chloride(I) nanocrystals. Results of X-ray diffraction analysis of the glasses are presented. It is shown that the temperature dependences of the exciton absorption bands of CuCl nanocrystals, obtained upon heating and cooling samples, have a a form of hysteresis.

A Green Method for Preparing CuCl Nanocrystal in Deep Eutectic Solvent

Cuprous chloride (CuCl) is extensively used as a catalyst in organic synthesis, and as a desulfurising, decolourising and deodorising agent in the petroleum industry. The traditional synthesis of CuCl nanocrystal powders, which has already caused a big problem in the environment, was via reducing copper(II) by using different additives and a quantity of concentrated acid. In this paper, we report an ecologically and environmental friendly route to prepare nanocrystalline CuCl powders, simply by using the CuCl2 and copper powders in a deep eutectic solvent (DES) at room temperature. The obtained CuCl nanocrystals were characterised by XRD, SEM and XPS techniques, and a possible formation mechanism was also proposed.

Formation of two distributions of nanoparticles of a new phase in a solid solution

Processes of the formation of the double distribution of CuCl nanoparticles in glass in two-stage annealing have been analyzed. The distribution of CuCl nanoparticles with the average radius R 1 = 14 and 18 nm appears in 20 and 40 min at temperature T 1 = 700°C in samples 1 and 2, respectively. By this time, the formation of new clusters ends, and only the growth of previously formed clusters occurs (the second stage of nucleation). Then, the formation of the CuCl phase continues at T 2 = 500°C. A decrease in the temperature is accompanied by a decrease in the critical radius of particles of a new phase. For this reason, the formation and growth of new CuCl nuclei begin again and the second distribution with a mean radius of 1 nm or larger is formed. As a result, double distributions of CuCl nanoparticles with significantly different mean radii are formed in samples 1 and 2. The concentration and mean radius of CuCl particles in distributions have been determined from the optical absorption spectra of CuCl nanocrystals at 80 K in the wavelength range of 300–500 nm.

Production and decay of subcritical nuclei in a solid solution

The decay of “subcritical” nuclei in a solid solution has been revealed in the investigation of the CuCl phase nucleation kinetics in glass. As soon as “supercritical” nuclei with an average radius R = 1.1 nm are created at 500°C, a sharp temperature increase up to 650°C transforms most nuclei created in the first annealing stage into “subcritical” ones, and this results in the decay of 80% of the nuclei in 5 min, while the remaining 20% of the nuclei grow in size to 2.4 nm. Their growth provides a sixfold increase in the CuCl phase growth rate against that in conventional annealing at 650°C. The kinetic dependences of the nucleation parameters—the amount of the phase and the average radius and concentration of the particles—were determined by the intrinsic absorption spectra of the CuCl nanocrystals. The critical radius of the CuCl nanomelt at 650°C has been estimated as 1.3 nm and the evaporation heat of the CuCl phase molecules in glass, as 13 kJ/mol. It is shown that multistage annealing makes it possible not only to control the parameters of the particles of the new phase, but also to determine the critical parameters of the initial nucleation stage.

Effect of preliminary low-temperature annealing on the kinetics of nucleation

The changes observed in the kinetics of CuCl nucleation in glass due to preliminary low-temperature annealing have been investigated using optical spectroscopy. The influence of the number of nuclei formed at a temperature of 500°C on the growth rate of the CuCl phase at 650°C has been examined. The amount of the CuCl phase in the sample is determined from the optical absorption coefficient in the range of band-to-band transitions in the CuCl nanocrystals. The average radius of CuCl particles is calculated from the position of the maximum of the exciton band. It has been demonstrated that the preliminary formation of CuCl nuclei at 500°C for 3 h makes it possible to increase the growth rate of the CuCl phase by a factor of 6. In the sample with preliminarily formed nuclei, there occur two opposite processes: thermal decomposition of part of the small nuclei, which have become subcritical at 650°C; and the growth of larger nuclei, which have become supercritical at 650°C due to the diffusive inflow of the components of the new phase. When the equilibrium concentration is reached, the new phase contains particles with a smaller radius but at a higher concentration as compared to those in the case of the conventional nucleation at 650°C.

Synthesis and Characterization of Copper (I) Chloride (CuCl) Nanocrystals in Conductive Polymer for UV Light Emitters

AbstractIntrinsic γ-Copper (I) Chloride is an ionic I-VII compound semiconductor material with relatively low conductivity. To fabricate an efficient electroluminescent device based on CuCl nanocrystals (NC) the conductivity of the CuCl NC film should be relatively high. In order to improve the conductivity of CuCl films, nanocrystals were embedded in a highly conductive polymer (Polyaniline) and deposited on glass substrates via the spin-coating method. The deposited films were heated at 140°C for durations between 1 and 12 hours in vacuo. The room temperature UV-Vis absorption spectra for all CuCl films showed both Z1,2 and Z3 excitonic absorption features and the absorption intensity increased as the anneal time increased. Room temperature photoluminescence (PL) measurements of the hybrid films reveal very intense Z3 excitonic emission. Room temperature X-ray diffraction (XRD) confirmed the preferential growth of CuCl nanocrystals whose average size is ≈40 nm in the <111> orientation. Resistivity measurements were carried out using a four-point probe system, which confirmed that the resistivity of the composite film was ≈500 Ω/cm. This is an improvement when compared to the vacuum evaporated CuCl thin films.

Hybrid organic–inorganic spin-on-glass CuCl films for optoelectronic applications

Cuprous halides are among the most studied inorganic materials for excitonic related linear/non-linear optical processes due to their large excitonic binding energies (∼190 and 108 meV for CuCl and CuBr, respectively). In recent years, we have studied CuCl thin films deposited by vacuum evaporation and sputtering techniques on a variety of substrates. We now report on the extension of this research to the deposition of CuCl nanocrystals on flexible substrates via a spin-on technology. In this study, we present the synthesis, deposition and characterization of CuCl nanocrystals embedded in organic polysilsesquioxane (PSSQ) films on a variety of substrates via the spin coating method. The nanocrystals were synthesized by a complexation–reduction–precipitation mechanism reaction of CuCl2 · 2H2O, alpha D-glucose and de-ionized (DI) water with a PSSQ based solution as the host matrix material. The deposited films were heated at 120 °C for durations between 1 and 24 h in vacuo. The room temperature UV–Vis absorption spectra for all hybrid films, except the as-deposited film, showed both Z1,2 and Z3 excitonic absorption features. Room temperature photoluminescence measurements of all heated films reveal very intense Z3 excitonic emission at 3.221 eV. Room temperature x-ray diffraction (XRD) of the as-deposited films gave no evidence of the crystallization of CuCl. However, after heating the films, XRD confirmed the preferential growth of CuCl nanocrystals whose average size is ≈25–45 nm in the ⟨1 1 1⟩ orientation. The CuCl hybrid films showed bright electroluminescent emission at 384 nm when subjected to an ac voltage of about 100 V peak to peak.

Size distribution of CuCl nanoparticles in glass in various stages of nucleation

Variations in the size distribution of CuCl particles in the glass formed at different temperatures are studied via the temperature-dependent exciton spectra (the exciton-thermal analysis). The kinetics of melting of CuCl nanocrystals is measured via changes in the strength of exciton absorption during linear heating of the sample. Then, using the known dependence of the melting temperature of CuCl nanoparticles on their size, the size distribution of the CuCl nanocrystals is found. During the first, second, and early third stages of nucleation, the width δ of the size distribution grows with an increase in the mean radius of the nanoparticles Rm. During the first nucleation stage, when Rm = 1.2 nm, which is just above the critical radius, the ratio δ/Rm is about 0.2. While the mean radius of the distribution increases to 8 nm, the ratio δ/Rm varies only slightly in the range 0.20−0.35. A further increase in the mean radius of the distribution to 16 nm is accompanied by a twofold increase in the δ/Rm ratio. The shape of the distribution is close to Gaussian both at the initial and later stages of the growth of CuCl particles in glass.

Optical fabrication of wide‐gap semiconductor nanoparticles in superfluid helium

AbstractThe nanoparticles have been fabricated from CuCl powder by laser ablation in superfluid helium. We found that most of nanoparticles are CuCl nanocrystals with single‐crystal quality by means of electron diffraction and high‐resolution transmission electron microscope. Moreover, we performed cathodoluminescence spectroscopy of single nanoparticle prepared by laser ablation with use of a scanning electron microscope. I1 bound exciton luminescence which is characteristic in the bulk CuCl was clearly observed in the nanoparticle at 15 K. In addition, we found that the cathodoluminescence spectrum changes by the electron beam irradiation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure of copper halide nanocrystals in photochromic glasses

The crystal structure of CuCl nanocrystals with effective radii ranging from 2.4 to 18.5 nm in photochromic glasses heat treated under different conditions is investigated using exciton spectroscopy, x-ray powder diffraction, and small-angle x-ray scattering. It is revealed that the size dependence of the energy of the Z3 exciton exhibits an anomalous behavior. The results obtained suggest that small-sized CuCl nanocrystals can crystallize in a modification different from the stable cubic modification.

Geometrical Recognition: A General Route to Shape-Controlled Syntheses of Transitional Metal Chalcogenides, Silicides, and Copper(I) Chloride Nanocrystals

In our former publications (J. Phys. Chem. B 2005, 109, 11585; and J. Phys. Chem. B 2006, 110, 14107), we have proposed the geometrically kinetic competition (GKC) mechanism to be responsible for the silica-vapor-pressure-dependent growth of silica-sheathed Fe7S8 and digenite Cu2S nanocrystals. Here, we demonstrate that geometrical recognition (GR), the basis of GKC, can be a general route to shape-controlled syntheses of a host of materials' nanocrystals. According to the types of the metal (or silicon for CoSi and MnSi) atom sublattices, the experimental results are presented, and the mechanisms for the growth of various shapes of products are discussed in detail. SiO4 clusters have been proposed as the competing opponents to SiO3 clusters for shape-controlled syntheses of MnS, CuCl, Cu2S, CdS, ZnSe, and ZnS nanocrystals.