Epitaxial growth of semiconductor thin films on metals in the halogenation process. Atomic structure of copper iodide on the Cu(110) surface

The atomic structure of thin (7–20 Å) copper iodide layers formed on the Cu(110) surface during a chemical reaction with molecular iodine in ultrahigh vacuum has been studied with scanning tunneling microscopy. A double stripe superstructure with an average period of 90–100 Å was found on the surface of CuI. The structural model is proposed for the copper iodide surface taking into account the contraction of the CuI lattice and the formation of striped domain walls.     

Ionic plasma oscillations in superionic conductors

Some superionic conductors behave as if their charge was carried by nearly free charged particles. If this is the case, these free particles should undergo plasma oscillations. The plasma oscillations may already have been observed in superionic AgI and CuI. Similar oscillations might also be observable in ionic liquids such as melted AgI.     

High temperature XRD studies of nanoscale AgI-CuI solid solutions

A preliminary high-temperature X-ray diffraction (HT-XRD) study of the nanometer-sized solid solution phases in the AgI-CuI system is reported through an extended range of temperatures (300-723K) covering phase transitions in both AgI and CuI. A major feature of this work is the observation of the coexistence of the zincblende and base-centred cubic phases of AgI over an extended range of temperatures the temperature width being a function of Cu content in the binary. The lattice parameters derived from HT-XRD data reflect systematics of phase transitions with progressive Cu substitution of AgI. The present results are discussed together with our earlier ionic conductivity, dilatometry and DSC data which have helped deduce phase diagrams for both the Ag-rich and Cu-rich regions of the binary.     

火焰原子吸收光谱法间接测定碘

在弱酸性介质中 ,I- 与Cu+生成沉淀 ,经硫代硫酸钠溶解后 ,以火焰原子吸收法测定铜 ,从而间接求得碘的含量。本方法的线性范围为 0～ 80 0 μg·mL- 1 ,回收率为 99 9%～ 1 0 0 3 %,相对标准偏差为 0 7%。将方法应用于碘盐、华素片、紫菜中碘的测定 ,结果满意。     

Deposition of copper iodide thin films by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods

In this paper, we report structural, morphological, electrical studies of copper iodide (CuI) thin films deposited onto glass substrates by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods. CuI thin films were characterized for their structural, morphological and wettability studies by means of X-ray diffraction (XRD), FT-Raman spectroscopy, scanning electron microscopy (SEM), optical absorption, and contact angle measurement methods. Thickness of thin films was 1 ± 0.1 μm measured by gravimetric weight difference method. The CuI thin films were nanocrystalline, with average crystal size of ～60 nm. The FT-IR study confirmed the formation of CuI on the substrate surface. SEM images revealed the compact and cube like structure for CuI thin films deposited by CBD and SILAR methods, respectively. Optical absorption study revealed optical energy gaps as 2.3 and 3.0 eV for CBD and SILAR methods, respectively. Wettability study indicated that CuI thin films deposited by SILAR method are more hydrophobic as compared to CBD method.     

Elastic properties of silver iodide at high pressure and temperatures: Thermally activated velocity anomaly in the B1 phase

Sound velocities have been measured in polycrystalline silver iodide at pressures !up to 1 $\text{GN}\text{m}{}^2$ and temperatures up to 425 K. The measurements covered the P-Tranges of three polymorphs of AgI but the main phase of interest was the B1 phase stable at high pressures. The B1 phase exhibits a large positive pressure derivative and a large negative temperature derivative of longitudinal velocity, both derivatives decreasing considerably at high pressures and low temperatures. The anomalous velocity behavior can be described by considering it due to a thermal activation process with ΔH¹ ≈ 0.4 eV and ΔV¹ ≈11 $\text{cm}{}^3\text{mole}$. The known importance of Frenkel defects in B4 AgI, and cation disorder and anomalously low sound velocities in B23 AgI suggest that Frenkel defects may be important in producing the velocity anomaly. The elastic properties of the different phases of silver iodide show rather complex relationships between lattice defects, cation disorder and sound velocities.     

Room temperature luminescence in CuI/AgI quantum dots

Room temperature luminescence in a CuI/AgI glass system is investigated by irradiating the system at 410 nm (3.02 eV). The spectrum peaks at 635 nm (1.95 eV) and 700 nm (1.77 eV), while the intensity is significantly enhanced (centered at 635 nm) by increasing the amount of AgI. We propose a model based on an increase in the AgI:Cu⁺ species at higher AgI concentration at which the red emission is attributed to the radiative recombination from carriers trapped at the donor sites (e.g., interstitial silver ions) and the acceptor sites (e.g., a vacancy-compensated divalent cation). The PL efficiency is also estimated by comparison with a standard rhodamine B solution.     

Etching of mercuric iodide in cation iodide solutions

The surface properties of mercuric iodide after etching in various cation iodide solutions have been investigated in terms of dissolution rate, morphology, electrical properties and reaction with water vapour. No significant differences have been observed in the etching rates. However, dissolution of HgI₂ in NH₄I, NaI, KI or RbI leaves the surface more or less covered with a residual iodo mercurate compound whose electrical properties and stability with regard to humidity may noticeably influence the behaviour of mercuric iodide devices. The smallest effect has been observed for etching in NaI.     

Optical properties of nanocrystalline silver halides

A review of quantum confinement effects in nanocrystals of silver bromide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect gap semiconductor while AgI has a direct band-to-band lowest energy transition. An examination of the low-temperature optical properties of quantum confined AgBr grown using a variety of synthetic techniques will be made. The dynamics of some of the involved excitonic processes will be measured and discussed in reference to a possible breakdown in the momentum selection rules as the nanocrystals are made smaller. Other explanations for this behavior such as impurity exclusion and surface effects will also be considered, as will the dynamics associated with the trapping of excitons at intrinsic iodide impurities in AgBr. Absorption measurements on AgI nanocrystals will be discussed and compared with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombination of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the conclusion that in the latter material nonradiative decay channels are opening up as the size decreases.     

CuI晶体及其缺陷态电子结构的模拟

利用相对论密度泛函理论和嵌入分子团簇方法,模拟计算了具有闪锌矿结构的γ态CuI晶体及其缺陷态的电子结构。结果显示晶体的本征能级结构:价带顶主要由I5p和Cu3d轨道杂化组成,导带底由Cu4s轨道组成,禁带宽度为3.1eV,该结果与实验相符。在不同缺陷态的计算中,四面体间隙铜缺陷相对其他间隙缺陷更易于在晶体中形成,其中Cu3d→4s跃迁能量为3.2eV,推测与CuI晶体发光密切相关。     

The structure of AgI-Ag2O-V2O5 glasses

Structures of 10AgI-3Ag₂O-2V₂O₅, 3AgI-3Ag₂O---2V₂O₅ and 2AgI---2Ag₂O-V₂O₅ glasses have been investigated by neutron diffraction experiments. The characteristic features of observed structure factors S(Q) in 10AgI-3Ag₂O-2V₂O₅ glass is similar to those of other superionic conducting glasses and molten AgI. From the standpoint of the pair distribution functions, it is clarified that the Ag-I and I-I correlation strength and Ag---Ag correlation length increase with increasing AgI concentration. Observed results suggest that the local AgI structure accompanied by the re-arrangement of silver ions is formed with highly doped iodide ions.     

基于碘化银固定相的薄层色谱-红外光谱联用研究

在分析复杂混合物方面原位薄层色谱-红外光谱联用有巨大潜力,二者联用能够相互取长补短,极大地提高对复杂混合物的解析能力。但因固定相自身的红外吸收能够对样品的检测造成干扰,使该方法进展缓慢。实验应用对中红外光透明的碘化银纳米微粒作为固定相制备薄层层析板,并对碘化银薄层板的层析效果及原位红外光谱检测的可行性进行了初步的研究。通过正交设计实验法优化反应条件,制备出粒径为100 nm左右的碘化银颗粒;应用沉降-挥发法制备薄层层析板,实验表明该薄层板具备分离混合物的能力,且原位红外光谱检测结果表明碘化银作为固定相不干扰样品检测。     

Mixed cation effect and iodide ion conductivity in electrolytes for dye sensitized solar cells

Dye-sensitized solar cells (DSSCs) offer an alternative to conventional silicon solar cell because of low cost and easy fabrication. However, one major drawback in DSSCs is their low efficiency. This paper reports the effect of using a binary iodide salt mixture with different size cations on the efficiency enhancement in dye sensitized solar cells based on polymer gel electrolytes. Several different polymers, such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), poly (vinylidenefluoride (PVdF)), and polyethylene oxide (PEO) have been used as host polymers. A binary iodide mixture consisting of an alkaline iodide salt (small cation) and a quaternary ammonium iodide salt such as tetrapropyl ammonium iodide (Pr₄NI) (large cation) has been used as the iodide ion source. In some of these systems, efficiency enhancement of more than 25% has been reached due to the “mixed cation effect”. From these studies, it was established that the variation of the power conversion efficiency with the concentration ratio of the two iodide salts follows the same trend as the short circuit current density (J _sc) and goes through a maximum at a particular salt concentration ratio. The maximum efficiency was found to be higher than the efficiencies of the DSSCs with only a single iodide salt in the electrolyte. The J _sc in these DSSCs appears to be governed by the iodide ion conductivity of the gel electrolyte. The observed efficiency enhancement has been explained on the basis of the electrode effects as well as electrolyte effects where the cations play a dominant role.

     

Crystal growth and luminescence properties of CuI single crystals

Recently, much attention has been attached to the material of cuprous iodide (CuI) single crystals. In this paper, a detailed study of the variation in the nucleation density and the growth of CuI crystals in silica gel as a function of the concentration of feed solution, pH of gel, gel aging time, growth temperature and volume of the feed solution is presented. The optimum conditions for growth of large size CuI single crystals in gel are: pH 5, concentration of complex 0.244 M, gel aging 72 h, temperature 45 °C. A simple procedure for increasing the size of the crystals is adopted and the CuI single crystal with the size of 4 mm³ is obtained. Also, the photoluminescence (PL) spectrum of as-grown CuI crystals in silica gel is evaluated by comparing its PL spectra with that of CuI crystals grown by solvent evaporation method. The results could provide a useful clue to further improve the properties of CuI single crystals.     

The thermal conductivity of silver iodide

We have measured the thermal conductivity of pressed pellets of 99.999% AgI from 120 K to 500 K using a transient hot wire method. The temperature dependence changes from T^?1.3±0.1 at the lowest temperatures to T^?1.8±0.1 below the phase transition at 420 K. Above this phase transition where AgI is a superionic conductor we see a weak temperature dependence T^+0.5±0.1. These results indicate shortening of the phonon mean free path at high temperatures due to the mobile Ag⁺ ions.     

Band gap determination in lead iodide polytypes

The band gaps of the polytypic crystals of lead iodide have been determined by studying the temperature variation of conductivity. Results obtained on several polytypic crystals show that the band gaps of the higher polytypes are lower than that of the parent 2H structure (2.56 eV). As for example the band gaps for 12H, 14H, 18H and 20H (disordered) were found to be 1.65, 1.44, 1.07 and 1.01 eV. The significance of the band gap determination in regard to the recent anomalous results on the physical properties of lead iodide crystals, has been indicated.     

Molecular structural analysis of 55mol% CuI-45mol% Ag2MoO4 solid electrolyte using XPS and laser raman techniques

The solid electrolyte 55 mol% CuI - 45 mol% Ag₂MoO₄ has been analyzed structurally by employing X-ray photoelectron spectroscopic (XPS) and laser Raman studies. The core level Ag 3d, Cu 2p, Mo 3d, I 3d and O1s XPS spectra of the constituent elements were recorded. The presence of both bridging (BO) and non-bridging (NBO) oxygen atoms in the oxyanion framework has been identified through the deconvolution of the O 1s spectrum. Laser Raman spectroscopic studies tend to reveal that the oxyanion framework is constructed with [MoO ₄ ²⁻ ]-tetrahedral and [MoO₆]-octahedral units as in the case of CuI - Cu₂MoO₄ and AgI - Ag₂O - MoO₃ glasses.     

Light scattering from correlated ion fluctuations in ionic conductors

Inelastic light scattering spectra of CuI and AgI in the α and melt phases are reported and shown to involve two depolarized Lorentzian components centered at zero frequency. The narrow component is interpreted in terms of ionic motions and we propose that the observed depolarized scattering is caused by correlated configurations of the mobile ions.     

Performance of lead iodide nuclear radiation detectors with the introduction of rare earth elements

Lead iodide has been recognized as a promising material for room temperature radiation detectors. It has a wide band-gap (∼ 2.3 eV), high atomic numbers (82, 53) and it is environmentally very stable compared to mercuric iodide. Electrical and optical properties of lead iodide grown crystals purified under the influence of selected rare earth elements have been investigated. Photo-luminescence and capacitance-voltage measurements have been performed using different rare earth elements.     

Effect of tin-doping on polytypism of melt-grown crystals of cadmium iodide

The effect of doping of metallic tin in cadmium iodide crystals has been systematically studied. The method of zone melting has been employed both for purification and for the growth of single crystals of cadmium iodide. The doping has been carried out by zone levelling technique. The as-grown crystals have been characterized by X-ray diffraction and physical methods. All the crystals have been found to consist of the most common polytype 4H. Unlike the case of pure undoped crystals of cadmium iodide grown from melt, all the X-ray photographs showed the presence of arcing. None of the photographs showed the presence of streaking. Besides, the doped crystal were found to be harder than the crystals of undoped cadmium iodide. Unlike the undoped crystals, cleavage in the doped crystals was found to be difficult and highly localized. The results have been discussed.