Enhanced grain growth and improved optical properties of the Sn doped thin films of Sb2S3 orthorhombic phase

The applications of newer Sb₂S₃ material as a suitable absorber material for the solar cells have been effected by the toxicity of Sb. The present study is an effort to synthesize lower Sb contents Sn doped Sb₂S₃ materials by retaining or improving the morphological and optical properties. SnCl₂ and SbCl₃ are used respectively as Sn and Sb sources, while Na₂S₂O₃ has been used as a source of S in chemical bath deposition method. Bath temperature was maintained at 10 °C and the deposition time was 4 h and the annealing of the films in vacuum was done for 2 h at 250 °C. X-ray diffraction, Rutherford backscattering spectroscopy, scanning electron microscopy and ultraviolet/visible light spectroscopy have been used for the study of structural, morphological and the optical properties. The chemical composition determined from RBS is Sn_0.11Sb₂S₃. Phase analysis confirms the orthorhombic Sb₂S₃ phase with b and c axis as the preferred ones for the impurity Sn atoms. Grain growth at lower deposition temperature is enhanced on the account of doping. Nanosized spherical particles are seen in the optical micrographs. Annealing lowers the band gap, the values being 1.50 and 1.31 eV for the unannealed and the annealed samples respectively.     

X-ray Photoelectron Spectroscopy of Sb2S3 Crystals

The paper presents the X-ray photoelectron spectra (XPS) of the valence band and core levels of semiconductor ferroelectric Sb₂S₃ single crystals, which show weak phase transitions and anomalies of various physical properties. The XPS were measured with monochromatized Al K _α radiation in the energy range 0-1450 eV and the temperature range 160-450 K. The valence band is located 0.8-7.5 eV below the Fermi level. Experimental results of the valence band and core levels are compared with the results of theoretical ab initio calculations of the molecular model of Sb₂S₃ crystal. The chemical shifts in Sb₂S₃ crystal for the Sb and S states are obtained. Results revealed that the small structural rearrangements at the phase transition T _c1 = 300 K shift the Fermi level and all electronic spectrum. Also, temperature dependence of a spontaneous polarisation shifts the electronic spectra of the valence band and core levels. Specific temperature-dependent excitations in Sb 3d core levels are also revealed.     

Electronic structure of HgGa2S4

The electronic structure and chemical bonding in HgGa₂S₄ crystals grown by vapor transport method are investigated with X-ray photoemission spectroscopy. The valence band of HgGa₂S₄ is found to be formed by splitted S 3p and Hg 6s states at binding energies BE=3-7 eV and the components at BE=7-11 eV generated by the hybridization of S 3s and Ga 4s states with a strong contribution from the Hg 5d states. At higher binding energies the emission lines related to the Hg 4f, Ga 3p, S 2p, S 2s, Hg 4d, Ga LMM, Ga 3p and S LMM states are analyzed in the photoemission spectrum. The measured core level binding energies are compared with those of HgS, GaS, AgGaS₂ and SrGa₂S₄ compounds. The valence band spectrum proves to be independent on the technological conditions of crystal growth. In contrast to the valence band spectrum, the distribution of electron states in the bandgap of HgGa₂S₄ crystals is found to be strongly dependent upon the technological conditions of crystal growth as demonstrated by the photoluminescence analysis.     

In situ X-ray photoelectron spectroscopy characterization of Al2O3/GaSb interface evolution

GaSb(0 0 1) was treated with (NH₄)₂S_x and the evolution of the interfacial chemistry was investigated, in situ, with monochromatic X-ray photoelectron spectroscopy (XPS), following heat treatment and exposure to trimethylaluminum (TMA) and deionized water (DIW) in an atomic layer deposition reactor. Elemental Sb (Sb-Sb bonding) as well as Sb³⁺ and Sb⁵⁺ chemical states were initially observed at the native oxide/GaSb interface, yet these diminished below the XPS detection limit after heating to 300 °C. No evidence of Ga-Ga bonding was observed whereas the Ga¹⁺/Ga-S chemical state was robust and persisted after heat treatment and exposure to TMA/DIW at 300 °C.     

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg_0.8,Fe_0.2)₂Si₂O₆) and diopside (Ca(Mg_0.8Fe_0.2)Si₂O₆) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO₂ and olivines ((Mg,Fe)₂SiO₄); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M-O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO_2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites.The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t_2g and e_g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si-O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.     

On the structure, morphology, and optical properties of chemical bath deposited Sb2S3 thin films

In the present paper, we have reported the room temperature growth of antimony sulphide (Sb₂S₃) thin films by chemical bath deposition and detailed characterization of these films. The films were deposited from a chemical bath containing SbCl₃ and Na₂S₂O₃ at 27 °C. We have analysed the structure, morphology, composition and optical properties of as deposited Sb₂S₃ films as well as those subjected to annealing in nitrogen atmosphere or in air. As-deposited films are amorphous to X-ray diffraction (XRD). However, the diffused rings in the electron diffraction pattern revealed the existence of nanocrystalline grains in these films. XRD analysis showed that upon annealing in nitrogen atmosphere these films transformed into polycrystalline with orthorhombic structure. Also, we have observed that during heating in air, Sb₂S₃ first converts into orthorhombic form and then further heating results in the formation of Sb₂O₃ crystallites. Optical bandgap energy of as deposited and annealed films was evaluated from UV-vis absorption spectra. The values obtained were 2.57 and 1.73 eV for the as-deposited and the annealed films respectively.     

Scalable synthesis of Sb(III)Sb(V)O4 nanorods from Sb2O5 powder via solvothermal processing

Scalable Sb(III)Sb(V)O₄ nanorods from Sb₂O₅ powder were prepared using solvothermal route. XRD and HRTEM demonstrate that the nanorods are single-crystal orthorhombic-Sb₂O₄ phase with several micrometers long and 200-300 nm diameter size. XPS result further shows that the antimony cations in the nanorods are composed of three valence and five valence antimony ions. The emission of the nanorods appears around 450 nm wavelength. The formation mechanism of the Sb(III)Sb(V)O₄ nanorods was discussed in detail.     

Air-broadening parameters in the ν3 band of NO2 using a multispectrum fitting technique

Air-broadened linewidths, pressure-induced shift coefficients and their temperature dependences were retrieved for over 1000 transitions in the ν₃ band of ¹⁴N¹⁶O₂ at 6 μm. In addition, precise line center positions and relative intensities were also determined. The results were obtained by fitting simultaneously 27 spectra recorded at high resolution (0.002-0.006 cm⁻¹) with two Fourier transform spectrometers and gas sample temperatures ranging from 206 to 298 K. It was necessary to modify the multispectrum fitting software to accommodate constraints on the retrieved parameters of closely spaced spin-split doublets in order to successfully determine their broadening and shift parameters. The variations of the widths, shifts and their temperature dependences with the quantum numbers were investigated. Subsets of the observed linewidths were reproduced to within 3% using an empirical smoothing function.     

XPS study of SnTe(1 0 0) oxidation by molecular oxygen

The interaction between the (1 0 0) surface of SnTe single crystal and molecular oxygen was studied by means of X-ray photoelectron spectroscopy (XPS). Analysis of the obtained spectra shows that the mechanism of surface oxidation does not change in the range of oxygen exposure 10⁸-10¹³ L. During the oxidation an additional component shifted 1.1 eV towards higher binding energies appears in the Sn 3d spectra. The Te 3d_5/2 spectra fitting reveals two additional components with binding energies close to Te⁰ and Te⁺⁴. The dependence of the additional components fraction in both Sn 3d and Te 3d_5/2 spectra on the oxygen exposure is semi-logarithmic. On the base of the experimental data two possible mechanisms are proposed.     

Hydrothermal synthesis of Sb2O3 nanorod-bundles via self-assembly assisted oriented attachment

Sb₂O₃ nanorod-bundles with length of about 4 μm were fabricated in the presence of polyvinyl alcohol (PVA) by a simple hydrothermal method. The composition, morphology, microstructure and optical property of the as-prepared bundles were characterized by XRD, XPS, SEM, TEM and Raman spectrum. The results showed that the nanorod-bundles were composed of massive orthorhombic phase Sb₂O₃ nanorods grown along [0 0 1] direction. It was speculated that the nanorod-bundles developed through self-assembly of initially scattered nuclei into microdisks and subsequent oriented attachment process. PVA played a crucial role in the formation of Sb₂O₃ nanorod-bundles.     

Evolution of the d∥ band across the metal-insulator transition in VO2

We studied the evolution of the electronic structure of VO₂ across the metal-insulator transition. The electronic structure was calculated using the standard TB-LMTO-ASA method. The calculated DOS was compared to previous photoemission and X-ray absorption spectra. The electronic structure is discussed in terms of the usual molecular-orbital scheme. In the metallic phase, the d_∥ band appears at the bottom of the V 3d bands and crosses the Fermi level. In the insulating phase, the d_∥ band is split around 2 eV opening a pseudo band gap at the Fermi level. The largest effect of the splitting appears in the unoccupied part of the d_∥ band. The calculated value of the splitting accounts for 77% of the experimental value, 2.6 eV. The results suggest that electron-lattice interaction seems to be the dominant factor in the splitting of the d_∥ band.     

Electronic structure and chemical bonding of phosphorus-contained sulfides InPS4, TI3PS4, and Sn2P2S6

The electronic structure of phosphorus-contained sulfides InPS₄, Tl₃PS₄, and Sn₂P₂S₆ was investigated experimentally with X-ray spectroscopy and theoretically by quantum mechanical calculations. The partial densities of electron states calculated with the ab initio multiple scattering FEFF8 code correspond well to their experimental analogues—the X-ray K- and L_2,3-spectra of sulfur and phosphorus. The good agreement between theory and experiment was also achieved for K-absorption spectra of S and P in the investigated sulfides. In spite of the difference in the crystallographic structure of InPS₄, TI₃PS₄, and Sn₂P₂S₆ that influence the form of K-absorption spectra, the electronic structure of their valence bands are rather similar. This is due to the strong interaction of the P and S atoms, which are the nearest neighbors in the compounds studied. The electron densities of p- and s-states of phosphorus are shifted by about 3 eV to lower energies in comparison to the analogous electron states of sulfur. This is connected with the greater electro-negativity of sulfur, and is confirmed by the calculated electron charge transfer from P to S.     

Characterization of Pd-CeOx interaction on α-Al2O3 support

The Pd-Ce interaction was studied over CeO₂ (0.3-2.5 wt.%)-Pd (1 wt.%)/α-Al₂O₃ catalysts used in the reforming reaction of CH₄ with CO₂. The samples were characterized by using high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The activity and selectivity behavior was in good agreement with that of other supported metal catalysts (Ni and Pd) modified with different promoters. The preliminary results of HRTEM would indicate that the CeO_x forms small crystallites around the Pd particle. The XPS analysis for the regions of Ce 3d and Pd 3d, gives an account of Ce being present mostly as Ce³⁺ and a high binding energy for Pd 3d_5/2 (335.3 eV), an evidence of Pd-Ce chemical interaction. The Pd/Al XPS intensity ratios vs. the Pd average particle size, determined by TEM, show an excellent correlation for fresh and used catalyst. These results indicate that the diminution of the Pd/Al ratios was due to Pd sintering. Consequently, the small amounts of CeO_x species do not cover the Pd particle, in agreement with the HRTEM results. The overall results stand for the promoter action mechanism of the CeO_x for the reforming reaction with CO₂.     

First-principle study of electronic structure and stability of Sn0.5Sb0.5O2

A theoretical study on Sb-doped SnO₂ has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA) level. Stability and conductivity analyses were performed based on the formation energy and electronic structures. The results show that Sn_0.5Sb_0.5O₂ solid solution is stable because the formation energy of Sn_0.5Sb_0.5O₂ is −0.06 eV. The calculated energy band structure and density of states showed that the band gap of SnO₂ narrowed due to the presence of the Sb impurity energy levels in the bottom of the conduction band, namely there is Sb 5s distribution of electronic states from the Fermi level to the bottom of conduction band after the doping of antimony. The studies provide a theoretical basis to the development and application of Sn_1−xSb_xO₂ solid solution electrode.     

Electronic structure of Cr1−δS (δ=0, 0.17) with NiAs-type crystal structure

Valence-band and conduction-band the electronic structure of the CrS (δ=0) and Cr₅S₆ (δ=0.17) has been investigated by means of photoemission and inverse-photoemission spectroscopies. The bandwidth of the valence bands of Cr₅S₆ (8.5 eV) is wider than that of CrS (8.1 eV), though the Cr 3d partial density of states evaluated from the Cr 3p-3d resonant photoemission spectroscopy is almost unchanged between the two compounds concerning shapes as well as binding energies. The Cr 3d (t_2g) exchange splitting energies of CrS and Cr₅S₆ are determined to be 3.9 and 3.3 eV, respectively.     

A photoelectron spectroscopic study of the carburization of MoO3

MoO₃ and Mo samples containing copper were treated with different hydrocarbon/hydrogen gas mixtures. The formation of Mo₂C was followed by X-ray photoelectron spectroscopy (XPS). Spectra taken in the Mo 3d, C 1s, O 1s, Cu 2p and Cu KLL regions demonstrated that the treatment with the hydrocarbon/hydrogen gas mixtures led to the formation of Mo₂C. From the comparison of the effects of various hydrocarbons on the XP spectra of Mo 3d we can state that the reduction of MoO₃ starts at the lowest temperature for C₂H₆/H₂ (600 K) followed by CH₄/H₂ (700 K) and C₄H₁₀/H₂ (723 K). Binding energies of Mo 3d_5/2 characteristic for Mo₂C are measured in the range of 227.7-228.0 eV. These values were attained at 900 K for CH₄/H₂, at 800 K for C₂H₆/H₂ and at 873 K for C₄H₁₀/H₂. Addition of copper to MoO₃ catalyzed its reduction and promoted the carburization process.     

Magnetic and transport properties of Mn-doped Bi2Se3 and Sb2Se3

We report on the single crystal growth and thermoelectric and magnetic properties of Mn-doped Bi₂Se₃ and Sb₂Se₃ single crystals prepared by the temperature gradient solidification method. The composition and crystal structure were determined using electron probe microanalysis and θ–2θ powder X-ray diffraction studies, respectively. The lattice constants of several percent Mn-doped Bi₂Se₃ and Sb₂Se₃ were slightly smaller than those of the undoped sample due to the smaller Mn atomic radius (1.40 Å) than those of Bi (1.60 Å) and Sb (1.45 Å). Mn-doped Bi₂Se₃ and Sb₂Se₃ showed spin-glass and paramagnetic properties, respectively.     

Effective method for preparation of oxide-free Ge2Sb2Te5 surface: An X-ray photoelectron spectroscopy study

Cleaning the surfaces of the as-deposited Ge₂Sb₂Te₅ was studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The mixed native oxides on the as-deposited Ge₂Sb₂Te₅ surface can be easily removed by dipping Ge₂Sb₂Te₅ in de-ionized water for 1 min, while the surface morphology remains unchanged after cleaning. Native oxides only re-grow after exposure to air for more than 4 min. Although dipping in water leads to a surface layer deficient in Ge and Sb, the surface composition of Ge₂Sb₂Te₅ can recover to its stoichiometric value after annealing at 200 °C in vacuum. The phase remains amorphous at room temperature after dipping in water, and changes to fcc and hcp after annealing at 100 and 220 °C, respectively.     

The 4d-4f dipole resonance of the Pr atom in an endohedral metallofullerene, Pr@C82

The photoion yield spectra of an endohedral metallofullerene Pr@C₈₂ were measured in the photon energy range of 100-150 eV by using time-of-flight mass spectrometry. Parent ions Pr@C₈₂⁺, Pr@C₈₂²⁺ and Pr@C₈₂³⁺ were observed in the mass spectra. The photoion yield spectra of Pr@C₈₂²⁺ showed a broad peak at 120-140 eV that was assigned to the 4d-4f giant dipole resonance of the encapsulated Pr atoms. Absolute photoabsorption cross sections of Pr@C₈₂ were evaluated from the photoion yield spectra to be 37±12 Mb at 110 eV (off-resonance) and 52±13 Mb at 130 eV (on-resonance). These cross sections of Pr@C₈₂ were compared with the results of Ce@C₈₂, the only metallofullerene whose photoionization properties have ever been studied near the 4d edge of the encapsulated metal atom. The enhancement of photoabsorption due to the giant resonance was found to be similar in Pr@C₈₂ and Ce@C₈₂, but there are marked differences in the peak shapes, which can be explained as due to interference effects between the fullerene cage and the encapsulated metal atoms.     

Luminescence from the Pr 4f5d and S0 states in LiLaP4O12

The photoluminescence and excitation spectra of Pr³⁺ activated LiLaP₄O₁₂ has been investigated in the 10-300 K temperature region. At all temperatures, the luminescence consists of optical transitions emanating from both the Pr³⁺ 4f¹5d¹ and the ¹S₀ states. However, at low temperatures the emission spectrum is dominated by the intraconfiguration emission transitions emanating from the Pr³⁺¹S₀ state. With increasing temperature, there is an exchange of intensity between the two emitting states; emission transitions from the ¹S₀ state exhibit strong intensity quenching while the 4f¹5d¹→4f² emission transitions reveal intensity gain. These results are explained on the basis of thermal population of the 4f¹5d¹ state by the ¹S₀ state. The energy barrier of 0.05 eV (403 cm⁻¹) for the nonradiative process is determined from the temperature dependence of the ¹S₀ lifetime.