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The crystal structure of the partially ordered vacancy compound Cu2In14/3□4/3Se8, belonging to the system I3-III7-□2-VI12, was analyzed using X-ray powder diffraction data. Several structural models were derived from the structure of the selenium-rich phaseβ-Cu0.39In1.2Se2by permuting the cations in the available Wyckoff positions. The refinement of the best model by the Rietveld method in the tetragonal space groupP$\overline 4 $2c(No 112), with unit-cell parametersa= 5.7487(3) Å,c= 11.5106(6) Å,V= 380.40(3) Å3, led toRp= 9.0%,Rwp= 9.9%,Rexp= 7.2%,S= 1.4 for 134 independent reflections. This model has the following Wyckoff site atomic distribution: Cu in 2e(0,0,0); In in 2b(½,0,¼), 2d(0,½,¼), and 2f(½,½,0);□ in 2f(½,½,0); Se in 8n(x,y,z).

We report on Raman scattering of GaSe for thicknesses varying from bulk down to bilayer. The Raman spectra using 532 nm excitation show a strong dependence on layer thickness. The two out-of-plane modes of GaSe shift in opposite directions as the thickness increases. However, from pentalayer the Raman spectra of GaSe do not show any further change thus reaching bulk nature in terms of optical properties. We also perform ab initio density functional theory calculations for the geometry, the electronic band structure, and the Raman frequencies for bulk down to one monolayer. Good agreement with the experimental results is found, and we reproduce the trend, driven by the number of layers, in the Raman shifts. Our results present the first systematic approach to a layer dependent Raman study of GaSe and answer contradictions reported in the literature.

In this work we utilize an alternative optical method based on thermal lens spectroscopy for characterizing the thermal diffusion in binary liquid mixtures. In this method, the thermal lens and the Soret signals are separated by a time interval to determine the Soret coefficients. As a demonstrative experiment, the Soret coefficients of isopropanol/water and acetone/water mixtures have been measured using that variant. Our results were compared with the recently published experimental and theoretical calculations and very good agreement was achieved.

Mn 3d electronic states in the dilute magnetic semiconductor Zn(1-x)Mn(x)S (x = 0.1-0.3) are studied using soft x-ray emission (XES) measurements and density functional theory (DFT). Mn L(2,3) emission spectra of Zn(1-x)Mn(x)S (x = 0.1-0.3) suggest that the Mn impurities do not form clusters in the host ZnS lattice, in agreement with previous models. A shift in the position of a Mn L(3) XES feature suggests a change in the nature of the hybridization between the Mn 3d(3/2) and S 3p states as a function of x. Our DFT calculations reproduce the weak interatomic exchange interaction, as well as the strong intra-atomic exchange splitting that is expected from observations of Zeeman splitting in such materials.

The aim of the present work was to determine the structure of the quaternary alloy Zn0.6Mn0.4In2S4and to locate the Mn2+. This was accomplished by means of powder synchrotron X-ray diffraction, high-resolution microscopy and convergent-beam electron diffraction (CBED). The powder X-ray diffraction pattern was indexed in a rhombohedral cell, with cell constantsa= 3.875 (2),c= 37.208 (4) Å, and possible space groupsR\bar{3}morR3m. Rietveld refinements using different cationic arrangements in these space groups were performed. A model in space groupR3m, in which the tetrahedral and octahedral sites were occupied by different proportions of Zn, Mn and In atoms, gave the best result. The Rietveld refinement of this model led to figures of meritRwp= 9.8%,Rp= 9.1% and χ2= 11.1. Selected-area electron diffraction patterns and high-resolution transmission electron micrographs along [001] reveal the rhombohedral configuration. CBED patterns perpendicular to [001], showing the distinctive 3msymmetry, confirmed space groupR3mand the breaking of the centrosymmetry of the parent compound, ZnIn2S4.

Fluoroindate glasses containing 1, 2 and 3, ErF3+YbF3 mol% were prepared in a dry box under argon atmosphere. The optical absorption and photoluminescence spectra have been measured as a function of the temperature in the range from 15 to 300 K . The absolute intensities of the transitions observed in the optical spectra have been interpreted in terms of transitions within 4fN configurations. The energy matrices resulting from the combination of free-ion terms with the crystal field were diagonalized. Excellent correlations were obtained between experimental transition energies and computed level structures. Phenomenological Ω λ intensity parameters for Er+3and Yb+3 ions in fluoroindate glass were also calculated using the standard theory of Judd–Ofelt. Good agreement was obtained between the experimental oscillator strengths determined from the area under the absorption band and the calculated ones. The splitting of the Er+3 ground state was determined from the analysis of photoluminescence spectra.

Local distortions of the sphalerite crystal structure of Zn1-xCox S, Zn1-xCox Se (x =0.01) semiconductor crystals were studied for the first time using thermal neutron diffraction at 300 and 78 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It was detected for both crystals that the intensity of the neutron diffuse scattering essentially decreases with cooling. Some arguments are given to explain the revealed properties of the diffuse scattering for these crystals in terms of a formation of the vibronic effect leading to the emergence of local nanosized distorted regions. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two-dimensional (2D) van derWaals semiconductors have been the subject of intense research due to their low dimensionality and tunable optoelectronic properties. However, the stability of these materials in air is one of the important issues that needs to be clarified, especially for technological applications. Here the time evolution of GaSe oxidation from monolayer to bulk is investigated by Raman spectroscopy, photoluminescence emission, and x-ray photoelectron spectroscopy. The Raman spectroscopy study reveals that GaSe monolayers become oxidized almost immediately after exposure to air. However, the oxidation is a self-limiting process taking roughly 5 h to penetrate up to 3 layers of GaSe. After oxidation, GaSe single-layers decompose into amorphous Se which has a strong Raman cross section under red excitation. The present study provides a clear picture of the stability of GaSe in air and will guide future research of GaSe from single- to few-layers for the appropriate development of novel technological applications for this promising 2D material.

The crystal structure of the ternary semiconductor IIIa-ZnIn2S4 was investigated using convergent-beam electron diffraction (CBED) and single-crystal x-ray diffraction to elucidate whether the structure is fully ordered, as described by the acentric R3m space group, or has some degree of disorder as described by the centric Rm space group. The CBED technique, based upon dynamical diffraction, permitted the unique identification of the true structural symmetry, while x-ray diffraction could not discriminate between the two space groups. CBED patterns perpendicular to the [001] crystal direction showed the 6mm symmetry characteristic of the Rm space group. This result agrees with early Raman and photoluminescence spectroscopy measurements. The structure is best described by the Rm space group, with cell parameters a = 3.8728(6) A and c = 37.0664(1) A and unit-cell volume V = 481.4(1) A3. The length of the c axis can be described by the expression c = N(3.086±0.003) A, where N is the number of sulfur layers in the unit cell and Z = N/4 the number of formula units; for our structure N = 12 and Z = 3. The crystal structure consists of a close-packed arrangement of S atoms, with Zn and half of the In atoms distributed in a disorderly fashion in tetrahedral sites, and the other half of the In atoms located in octahedral sites. The atomic positions and an isotropic temperature factor are reported.

The 4T1(G)→6A1(S) internal Mn2+ transition in the Zn1−xMnxSe single-crystal system is studied in the temperature range between 26 and 300 K, for six samples prepared by chemical transport with Mn concentrations between 0.0008⩽x⩽0.038. The energy position of this band has an anomalous behavior for temperatures below 150 K which can be understood in terms of antiferromagnetic d–d interactions of the Mn2+ ion. This behavior is observed for the first time for samples with concentrations below x=0.5. The observed broadening of this band as a function of temperature indicates the existence of strong electron–phonon coupling.

The diluted magnetic semiconductor system MnxZn1−xS was studied using scanning electron energy-dispersive X-ray spectrometry and X-ray diffraction. The samples were grown using the chemical transport technique with nominal Mn concentration (x) of 0.01, 0.03, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5. Samples with Mn concentration greater than 0.4 presented two different phases while samples with concentration of 0.15 and 0.20 showed chemical inhomogeneities.

The Faraday rotation and infrared studies of (Y/sub 3-y/Ce/sub y/)(Fe,Ga)/sub 5/O/sub 12/ (Ce=0 to 20% relative metal content) garnet films deposited on quartz and Gd/sub 3/Ga/sub 5/O/sub 12/ (GGG) are reported. The value of /spl theta//sub f/ reaches a maximum with Ce between 5 and 15%, depending on the heat pulse annealing temperature. The film crystallinity deposited on quartz, analyzed by X-ray diffraction and by sharpening of bands near 500 cm/sup -1/ in FTIR, reaches a maximum with Ce=5% and then decreases. Values of the Faraday rotation are related to the crystallinity of the deposited films.

We present the Raman scattering of single-crystal ZnIn2S4 as a function or temperature in the range between 12 K and room temperature and an analysis of the relative intensity changes for all the bands. Based on a group theoretical analysis using the different possible space groups for this structure, the vibrational modes for the Raman spectra were obtained and compared with the experimental data. A new space group is proposed for the crystal structure for this semiconductor.

Photodynamic therapy (PDT) is an antitumor method that uses a nontoxic photosensitizer and visible light to produce cytotoxic reactive oxygen species (ROS) that destroy malignant cells. It has been increasingly used in the treatment of nonmelanoma skin cancers, particularly basal cell carcinoma (BCC), providing a high degree of tumor regression and excellent aesthetic results. We report the case of a patient with histopathologically proven superficial BCC in which regression of untreated contiguous tumor was noted after PDT.

Soft x-ray emission and absorption spectra of the Mn ${L}_{2,3}$-edge were obtained from the diluted magnetic semiconductor ${\mathrm{Zn}}_{0.90}{\mathrm{Mn}}_{0.10}\mathrm{S}$, and interpreted with the aid of first-principles computations of the densities of states. The calculations reveal that the Mn $d$ states near the Fermi energy show interesting spin polarization, and are strongly hybridized with the neighboring S atoms, indicative of the $sp\text{\penalty1000-\hskip0pt}d$ hybridization typical of dilute magnetic semiconductors. Resonant inelastic x-ray measurements reveal a 3-eV inelastic energy loss, which is interpreted as a transition from the Mn valence-band $d$ states to a spin-flip multiplet of the $3{d}^{5}$ ground-state configuration, while a 6-eV loss is attributed to observed charge-transfer effects caused by hybridization between the S $p$ states and the occupied Mn $d$ states located a few eV below the Fermi energy.

A new family of semiconducting compounds of the formula with is introduced. A middle infrared study of (x = 0.0, 0.3 and 0.4) suggests that the Mn ion is replacing Zn on tetrahedral sites in cation layers near the S...S interlayer.

Experimental studies of x-ray photoelectron and Co Lalpha x-ray emission spectra of the ZnS:Co semiconductor were carried out. It was established that Co ions are present in isovalent Co2+ configuration and that the Co 3d impurity states are localized above the top of the valence band by 1.0 +/- 0.2 eV.

Two-dimensional materials awakened a strong interest in the scientific and technological communities due to their exceptional properties that can be tuned by the material thickness and chemistry. In order to correlate optical properties with crystallographic structure and morphology, in this work, the authors aim at studying GaSe nanoflakes deposited on highly ordered pyrolytic graphite by means of atomic force microscopy, Raman, and photoluminescence (PL) spectroscopies. The authors found that the basal plane of the flakes can be attributed to the e-phase expected for bulk samples grown by the Bridgman method. However, a strong difference in the Raman spectra was systematically found at the edge of our GaSe flakes. Forbidden Raman modes located around 250 cm−1 were selectively observed at specific locations. These modes could not be directly attributed to the e-phase observed in the basal plane or in the bulk. The atomic force microscopy investigations show that high topographical features characterize the regions with the highest photoluminescence and the forbidden Raman modes. This change in crystal orientation at selective locations of the flake could activate the E′(LO) Raman mode at 255 cm−1. The enhancement of the PL emission around 620 nm is also linked to the change in crystal orientation due to an increase in the probability of electronic transitions. These results show the rich physics of GaSe flakes in contrast to what is known from its bulk counterpart with possible applications in photovoltaics and photodetectors for nanoflakes with engineered geometries.

In this work an analysis of the phenomenological Ωλ intensity parameters for the Tm3+ ion in fluoroindate glass is made using the standard Judd-Ofelt theory, and a modified oscillator strength taking into account odd-order contributions is utilized. Different sets of phenomenological intensity parameters Ωλ(λ=1,2,3,4,5,6) are discussed. The set of better quality is used to analyze the influence of third-order effects through odd intensity parameters in the new approximation. Fluoroindate glasses of compositions (40-x)InF3-20ZnF2-20SrF2-16BaF2-2GdF3-2NaF-xTmF with x=1, 2 and 3 mol% were prepared, and the absorption spectra at room temperature in the spectral range from 300 to 2500 nm were obtained. The experimental oscillator strengths determined from the area under the absorption band are compared to the calculated ones.

The variation of the lattice parameters, from the room temperature to the melting point of the compound, has been studied for the chalcopyrite semiconductor CuGaSn□Se4 by using a high-temperature X-ray camera. The compound shows an increase in the tetragonal of thermal expansionαc. The results are interpreted in terms of expansion of the bonds. The DTA measurement, that has shown a peak at 590°C, has been associated with the decomposition of the quaternary into two phases. At the temperature of 590°C extra lines appeared in the X-ray measurements of θ values of 15.3133o, 18.8235o, 21.0230o, 24.5633o, 26.3712o and 34.7926o. These new extra lines (second phase)_are probably from SnSe2.

Polycrystalline samples have been prepared of 12 defect chalcopyrite quaternary compounds of the form I III IV Se4, where I is Cu or Ag, III Al, Ga or In, and IV Ge or Sn. In all cases room temperature optical absorption measurements have been made to determine values of the fundamental energy gap (Eg) and all gaps shown to be direct. For the cases of AgGaSnSe4 and AgGaGeSe4, values of Eg have been determined as a function of temperature from helium to room and the data fitted to a Manoogian–Leclerc equation. The energy gap values of the quaternary compounds (EgT) have been compared with those of the corresponding ternary chalcopyrite compounds (EgT) and a relation between the values of EgQ−EgT and EgT shown.

Measurements of reflectance as a function of temperature from 4 to 300 K have been made on a single crystal sample of CuGaSnSe4 using light polarised (a) perpendicular and (b) parallel to the c axis of the crystal. Values of the energy gaps EA, EB, and EC between the three valence bands and the conduction band have thus been determined as a function of temperature. The variation of these energy gaps with temperature has been fitted to the equation proposed by Manoogian and Leclerc, i.e., E0 − E = UTs + Vθ(coth (θ/2T) − 1). Values of spin–orbit splitting Δso and crystal field splitting Δcf have been determined and the temperature variation of these explained in terms of contributions from d orbitals to the valence band. Values of the various spin–orbit splittings and deformation potentials are discussed.

The preparation of a range of polycrystalline Selenides and Tellurides of the form I III IV VI 4 was undertaken. Twelve Selenides with quaternary composition were prepared but the eight Tellurides attempted did not grow as quaternaries. Single crystal samples of CuGaSnSe 4 were grown by vapour transport. X-Ray powder photography confirmed that the quaternary Selenides have tetragonal Chalcopyrite structure with a c/a ratio of approximately 2. A systematic variation of unit cell volume and of c/a was found over the entire range of compounds grown.

The crystallographic and optical properties determined for twelve compounds of the form I III IV □Se4 are reviewed, the compounds being those formed by combinations of the elements I Cu, Ag: III Al, Ga, In: IV Ge, Sn. It is found that all of the compounds have the chalcopyrite structure and lattice parameter values have been determined for each. These values are compared with those of the corresponding ternary chalcopyrite I III Se2 compounds and a systematic variation between the parameters for ternary and quaternary compounds is shown. Energy gap values have been determined for the twelve compounds by optical absorption measurements. These also have been compared with the values for the corresponding ternary compounds and again a systematic variation shown. Finally, reflectance spectra have been determined as a function of temperature for a single crystal sample of CuGaSn □Se4 and hence the temperature variation of the three valence band-conduction band gaps investigated.