The sub-millimeter and Fourier transform microwave spectrum of HZnCl (X Σ)

The pure rotational spectrum of HZnCl (X ¹Σ⁺) has been recorded using sub-millimeter direct-absorption methods in the range of 439-540 GHz and Fourier transform microwave (FTMW) techniques from 9 to 39 GHz. This species was produced by the reaction of zinc vapor and chlorine gas with H₂ or D₂ in a d.c. glow discharge for the sub-millimeter studies. In the FTMW measurements, HZnCl was created in a discharge nozzle from Cl₂ and (CH₃)₂Zn. Between 5 and 10 rotational transitions were measured in the sub-millimeter regime for four zinc and two chlorine isotopologues; four transitions were recorded with the FTMW machine for the main isotopologue, each consisting of several chlorine hyperfine components. The data are consistent with a linear molecule and a ¹Σ⁺ ground electronic state. Rotational and chlorine quadrupole constants were established from the spectra, as well as an r_m⁽²⁾ structure. The Zn-Cl and Zn-H bond lengths were determined to be 2.0829 and 1.5050 Å, respectively; in contrast, the Zn-Cl bond distance in ZnCl is 2.1300 Å, longer by ∼0.050 Å. The zinc-chlorine bond distance therefore shortens with the addition of the H atom. The ³⁵Cl electric quadrupole coupling constant of eQq = −27.429 MHz found for HZnCl suggests that this molecule is primarily an ionic species with some covalent character for the Zn-Cl bond.     

The pure rotational spectrum of ZnS (XΣ)

The pure rotational spectrum of ZnS (X¹Σ⁺) has been measured using direct-absorption millimeter/sub-millimeter techniques in the frequency range 372–471 GHz. This study is the first spectroscopic investigation of this molecule. Spectra originating in four zinc isotopologues (⁶⁴ZnS, ⁶⁶ZnS, ⁶⁸ZnS, and ⁶⁷ZnS) were recorded in natural abundance in the ground vibrational state, and data from the v = 1 state were also measured for the two most abundant zinc species. Spectroscopic constants have been subsequently determined, and equilibrium parameters have been estimated. The equilibrium bond length was calculated to be r_e  2.0464 Å, which agrees well with theoretical predictions. In contrast, the dissociation energy of D_E  3.12 eV calculated for ZnS, assuming a Morse potential, was significantly higher than past experimental and theoretical estimates, suggesting diabatic interaction with other potentials that lower the effective dissociation energy. Although ZnS is isovalent with ZnO, there appear to be subtle differences in bonding between the two species, as suggested by their respective force constants and bond length trends in the 3d series.     

Structure and reaction pathways of methyl lactate on Pd(1 1 1)

The adsorption and reaction of methyl lactate (CH₃CH(OH)COOCH₃) is studied in ultrahigh vacuum on a Pd(1 1 1) surface using temperature-programmed desorption (TPD) and reflection–absorption infrared spectroscopy (RAIRS). Methyl lactate reacts at relatively low temperatures (220 K) by O–H bond scission. This intermediate can either react with hydrogen to reform methyl lactate at 280–300 K or undergo β-hydride elimination to form flat-lying methyl pyruvate. This decomposes to form acetyl and methoxy carbonyl species as found previously following methyl pyruvate adsorption on Pd(1 1 1). These species predominantly react to form carbon monoxide, methane and hydrogen.     

Nitridation of organo-silicate glass: A self-limiting process for PVD Ta1+xN/Ta barrier formation

Interfacial reactions of sputter-deposited Ta with a low dielectric constant Si–O–C–H material (SiCOH), and with surface-nitrided SiCOH (N-SiCOH) were investigated using X-ray photoelectron spectroscopy (XPS). The studies were carried out in a system containing a processing chamber attached to an XPS analysis chamber so that sample transport between deposition and analysis environments occurred under ultrahigh vacuum (UHV) conditions. Ta sputter deposition on unmodified SiCOH yielded an interfacial phase 3 nm thick composed of Ta oxide/carbide (Ta–O–C), which is known to interact only weakly with Cu. Bombardment of the vicinal SiCOH surface by 500 eV Ar⁺ in the presence of NH₃ resulted in carbon depletion and the self-limiting nitridation of the surface, with N attachment primarily at Si sites. Subsequent Ta sputter deposition yielded reduced Ta oxide and carbide formation, and formation of a Ta-rich nitride layer of 10 Å average thickness. Subsequent deposition resulted in metallic Ta formation.     

Neutron polarization analysis on the multiferroic TbMn2O5

Polycrystalline TbMn₂O₅ was prepared by the standard solid-state reaction method and characterized by powder X-ray diffraction and magnetization to assure it is of single phase. Heat capacity measurements on the compound reveal an antiferromagnetic phase transition at 45 K. A broad peak below 6 K in the heat capacity measurements corresponds to the crossover transition of Tb³⁺ ordering. To confirm these magnetic orderings, neutron powder diffractions on TbMn₂O₅ with XYZ neutron polarization analysis were performed at the diffuse neutron scattering (DNS) spectrometer, FRJ-II, by using neutron wavelength of 4.8 Å in the temperature range of 1.8–250 K. Magnetic scattering was separated from nuclear coherent and spin incoherent scattering contributions. Long-range ordered magnetic peaks were observed below 39 K which is consistent with the heat capacity results. The drastic increasing intensities below 6 K indicate the ferromagnetic transition in Tb³⁺ orderings.     

Spectroscopic investigation of arsenate and selenate incorporation into hydroxylapatite

The mechanism(s) of arsenate and selenate incorporation into hydroxylapatite (HAP) using extended X-ray absorption fine structure (EXAFS) spectroscopy was investigated for As- and Se-doped HAP samples with concentrations between 200 and 2500 ppm. EXAFS data on As and Se K-edges have shown similar local coordination environments and are similar to that of P in HAP, suggesting the substitution of arsenate or selenate tetrahedra on the phosphate sites. EXAFS best-fitting for As-doped samples shows that the first shell is fitted with approximately 4 O atoms at 1.68 Å, showing As(V) in tetrahedral coordination, and Se K-edge EXAFS data are characterized by the backscattering contributions an oxygen shell at 1.2 Å in the Fourier transform, which can be fit with 4 O atoms at 1.65 ± 0.01 Å. This is characteristic of Se–O distances in SeO₄ tetrahedron. These findings suggest that arsenate and selenate substitute for phosphate groups with local distortions during the incorporation of these metals into the structure of HAP.     

Structure and properties of the one-dimensional cobalt oxide CaCo2O4

We have studied crystal structure and transport properties of the quasi one-dimensional cobalt oxide CaCo₂O₄. The CaCo₂O₄ phase crystallizes in calcium-ferrite type structure, which consists of a corner- and edge-shared CoO₆ octahedron network including one-dimensional double chains. Large thermoelectric power (S  150 μV/K at 390 K) with metallic temperature dependence of S, moderate resistivity (ρ  2.9 × 10⁻¹ Ω cm at 390 K) with carrier localization at low temperature, and normal thermal conductivity (κ  6.3 W/Km at 390 K) were observed. The phonon mean-free path was calculated from the observed data, as a function of temperature. The long phonon mean-free path (l  24 Å at 300 K) implies that the thermal conductivity could be suppressed by impurity scattering of phonons with partial element substitution.     

Gas-phase vibrational spectroscopy and ab initio calculations of Rb(H2O)n and Rb(H2O)nAr cluster ions

The competition between ion–water electrostatic interactions and water–water hydrogen bonding in cluster ions depends on several factors, including charge density of the ion and temperature of the system. Infrared photodissociation spectra of Rb⁺(H₂O)_n=2–5 and Rb⁺(H₂O)_n=1–5Ar are presented here and compared to previous experiments involving potassium and cesium. The temperature, or internal energy, of hydrated rubidium cluster ions is controlled by varying the evaporative path available for cluster formation. Warmer clusters (with effective temperatures of 250–500 K) are formed by the evaporation of water, while colder clusters (40–120 K) can be formed by argon evaporation. Colder cluster ions tend to favor conformers with more hydrogen bonds compared to those cluster ions at warmer temperatures. Previous work from this laboratory has shown significant and dramatic differences between the spectra of hydrated potassium and cesium ions. With a charge density intermediate between that of K⁺ and Cs⁺, Rb⁺ plays an important role in bridging the gap in our previous studies.     

Transmission grating spectrograph with on-line recording of XUV soft X-ray spectra from laser produced plasmas

The setting up and on-line operation of a transmission grating spectrograph in the XUV soft X-ray region is described. The detector was a microchannel plate–image intensifier combination, and the output of the image intensifier was coupled to a CCD camera–frame grabber system through an imaging lens. The spectrograph could be operated in the 5–20 Å range with 0.6 Å spectral resolution and in the 5–50 Å range with 1 Å resolution, respectively. The high sensitivity of the detector enables single shot operation, which is useful for several laser plasma interaction studies.     

High-performance pyroelectric single crystals for uncooled infrared detection applications

Uncooled pyroelectric infrared detectors based on ferroelectric single crystals 0.74Pb(Mg_1/3Nb_2/3)O₃–0.26PbTiO₃ (PMN–0.26PT) were fabricated. The performances of pyroelectric detectors dependence on detector fabrication temperature, absorption layer, and element thickness were compared. The room-temperature voltage responsivity (R_v) of 200 V/W and specific detectivity (D^*) of 10⁸ cm Hz^1/2/W at 12.5 Hz have been achieved. The results reveal that the better pyroelectric response can be expected by controlling temperature below 70 °C during the fabrication of the pyroelectric detectors, selecting absorption layer with high absorption coefficient, and decreasing the thickness of the elements.     

Effect of the synthesis route on the structural properties and shape of the indium oxide (In2O3) nano-particles

Nano-crystalline indium oxide (In₂O₃) particles have been synthesized by sol–gel and hydro-thermal techniques. A simple hydro-alcoholic solution consisting indium nitrate hydrate and citric acid (in sol–gel method) and 1, 4-butandiol (in hydro-thermal method) have been utilized. The structural properties of indium oxide nano-powders annealed at 450 °C (for both methods) have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and specific surface area (SSA) analysis. Structural analysis of the samples shows cubic phase in sol–gel and cubic-hexagonal phase mixture in hydro-thermally prepared particles. The nano-particles prepared by sol–gel method have nearly spherical shape, whereas hydro-thermally-made ones display wire- and needle-like shape in addition to the spherical shape. The obtained In₂O₃ nano-particles surface areas were 23.2 and 55.3 in sol–gel and hydro-thermal methods, respectively. The optical direct band gap of In₂O₃ nano-particles were determined to be 4.32 and 4.24 eV for sol–gel and hydro-thermal methods, respectively. These values exhibit 0.5 eV blue shift from that the bulk In₂O₃ (3.75 eV), which is related to the particle size reduction and approaching the quantum confinement limit of nano-particles.     

Infrared spectra of two isomers of OCS–C2H2 and OCS–C2D2 in the region of OCS ν1 fundamental

Infrared spectra of OCS–C₂H₂ and OCS–C₂D₂ complexes in the region of the C–O stretching fundamental of OCS (2060 cm⁻¹) are studied in a pulsed supersonic slit-jet expansion using a tunable diode laser. For each complex, two bands are observed and assigned to distinct near-parallel and the T-shaped isomers. Ground state parameters were previously determined from microwave studies, so analysis of the infrared spectra gives information on the vibrational shifts upon complex formation as well as rotational and centrifugal distortion parameters for the excited states. All four bands show a red shift with respect to the monomer band origin, with the T-shaped isomer having a much larger shift than the near-parallel isomer. Disappearance of the T-shaped isomer when argon is used as a carrier gas supports the notion that the near-parallel isomer is the lowest energy form of the complex.     

Nanoscale anglesite growth on the celestite (0 0 1) face

In situ atomic force microscopy (AFM) was used to study the growth behaviour of anglesite (PbSO₄) monolayers on the celestite (0 0 1) face. Growth was promoted by exposing the celestite cleavage surfaces to aqueous solutions that were supersaturated with respect to anglesite. The solution supersaturation, β_ang, was varied from 1.05 to 3.09 (where β_ang = a(Pb²⁺) · a(SO₄²⁻)/K_sp,ang). In this range of supersaturation, two single anglesite monolayers (3.5 Å in height each) from pre-existent celestite steps were grown. However, for solution supersaturation β_ang < 1.89 ± 0.06, subsequent multilayer growth is strongly inhibited. AFM observations indicate that the inhibition of a continuous layer-by-layer growth of anglesite on the celestite (0 0 1) face is due to the in-plane strain generated by the slight difference between the anglesite and celestite lattice parameters (i.e. the linear misfits are lower than 1.1%). The minimum supersaturation required to overcome the energy barrier for multilayer growth gave an estimate of the in-plane strain energy: 11.4 ± 0.6 mJ/m²_. Once this energy barrier is overcome, a multilayer Frank–Van Der Merwe epitaxial growth was observed.     

Microwave dielectric properties of (1 − x)(Mg0.95Co0.05)TiO3–x(Na0.5La0.5)TiO3 ceramic system

The microstructures and the microwave dielectric properties of the (1 − x)(Mg_0.95Co_0.05)TiO₃–x(Na_0.5La_0.5)TiO₃ ceramic system were investigated. Two-phase system was confirmed by the XRD patterns and the EDX analysis. A co-existed second phase (Mg_0.95Co_0.05)Ti₂O₅ was also detected. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. A new microwave dielectric material 0.88(Mg_0.95Co_0.05)TiO₃–0.12(Na_0.5La_0.5)TiO₃, possessing an excellent combination of dielectric properties: ε_r  22.36, Q × f  110,000 GHz (at 9 GHz), τ_f  2.9 ppm/°C), is proposed as a candidate dielectric for GPS patch antennas.     

Influence of oxygen growth pressure on laser ablated Cr-doped In2O3 thin films

We present a systematic investigation of the effects of oxygen growth pressure on the structural, optical, and electrical properties of In₂O₃:Cr thin films grown by pulsed laser deposition. X-ray diffraction analysis showed increases in lattice constant from 10.103 Å to 10.337 Å, and in particle size from 13.9 nm to 35.5 nm as the oxygen growth pressure increased from 7.5 × 10⁻⁶ Torr to 7.5 × 10⁻³ Torr, respectively. The observed shift in the X-ray diffraction peaks to lower angles was assumed to be caused by the reduction in the lattice defect density, precisely oxygen vacancies. The optical transparency increased with partial oxygen pressure (P_O2), and an average transmittance of 85% was obtained at 7.5 × 10⁻³ Torr. The films are highly conducting with resistivity as low as 2 × 10⁻⁴ Ω cm and mobility as high as 133 cm/V s. Temperature dependent resistivity measurements in the 45 < T < 300 K temperature range reveal that films grown at 7.5×10⁻⁶≤P_O2≤7.5×10⁻⁴ Torr exhibit negative temperature coefficient of resistivity (TCR) below approximately T = 60 K, T = 120 K, T = 160 K; then positive TCR in the temperature intervals 60 < T < 300 K, 120 < T < 300 K, and 160 < T < 300 K, respectively. This suggests that two disparate mechanisms govern electrical dc transport in the two temperature regions. Film grown at P_O2 of 7.5 × 10⁻³ Torr displayed typical semiconducting behavior with negative TCR in the whole temperature region.     

Electronic stopping power of polymers for heavy ions in the ion energy domain of LSS theory

LSS based computed electronic stopping power values have been compared with the corresponding measured values in polymers for heavy ions with Z = 5–29, in the reduced ion velocity region, v_red ≤ 1. Except for limited v_red  0.6–0.85, the formulation generally shows significantly large deviations with the measured values. The ζ factor, which was approximated to be Z₁^1/6, involved in LSS theory has been suitably modified in the light of the available experimental stopping power data. The calculated stopping power values after incorporating modified ζ in LSS formula have been found to be in close agreement with measured values in various polymers in the reduced ion velocity range 0.35 ≤ v_red ≤ 1.0.     

Chlorine nuclear quadrupole coupling in chlorodifluoroacetyl chloride: Theory and experiment

A potential energy scan of chlorodifluoroacetyl chloride, CF₂ClC(O)Cl, at the MP2/6-311+G(d) level of theory predicts stable gauche and trans conformers, with E_gauche<E_trans. Ab initio calculations were made of approximate equilibrium structures of these and, on these structures, calculations were made of ³⁵Cl and ³⁷Cl nuclear quadrupole coupling constant tensors. Coupling constants here predicted, as well as rotational constants and molecular dipole moments, are applied to aid analyses of experimental microwave spectra. Chirped pulse Fourier transform microwave spectroscopy has been used to rapidly record the rotational spectra of four isotopologues of the title molecule, CClF₂C(O)Cl, namely ³⁵Cl³⁵Cl, ³⁵Cl³⁷Cl, ³⁷Cl³⁵Cl, and ³⁷Cl³⁷Cl. Only the gauche conformer was observed under the experimental conditions. For the four isotopologues a total of 464, 219, 197, and 77 transitions have been recorded, respectively. With the exception of the ³⁷Cl³⁷Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made.     

Luminescence of Strontianite (SrCO3) from Strontian (Scotland, UK)

An historic Strontianite-type specimen from Strontian, Scotland, UK, was characterized to broaden our knowledge on luminescence properties of common carbonates. These fibrous aggregates are Strontianite (Sr_xCa_1−xCO₃) with circa 6% of CaO, interfacial water, hydrosilicate anions and substitutional divalent cations, e.g., Ca²⁺, Mn²⁺, Fe²⁺ in structural Sr²⁺ positions. The specimen was analyzed by X-ray Fluorescence Spectrometry (XRF), Environmental Scanning Electron Microscopy coupled with an Energy Dispersive X-ray Spectroscopy (ESEM-EDS) probe, Spatially-resolved Cathodoluminescence under the Scanning Electron Microscope (SEM-CL), Differential-Thermal Analyses (DTA), Thermogravimetry (TG), Thermoluminescence (TL), Radioluminescence (RL) and High Resolution Spectra Thermoluminescence (3DTL), to gain an overview of the spectral emissions, the defect linkages were modified by heating from room temperature (RT) up to 500 °C. Substitutional transition elements are probably responsible for the spectral emission bands from 500 nm to 800 nm and hydrous molecules from 300 nm to 400 nm. DTA–TG analyses performed on little chips, to preserve the fiber interfaces coherence, exhibit minor endothermic peaks attributed to outflow of water groups in fiber interfaces. Both, CL and RL curves show common spectral positions but UV–blue and red emission intensities are counterbalanced since electron irradiation reduces the UV–blue emissions while X-irradiation increases them. The TL curves show a top thermal limit at 300 °C for the 300–400 nm TL emissions which become irreversibly destroyed, whereas the longer wavelength region emits at higher temperature. The non-reversible changes observed in the 320 nm and 360 nm bands during the spectra 3DTL emission could be linked with non-bridging oxygen defects, protons and hydroxyl groups and the red emissions to the ⁴G (⁴T_1g)–⁶S Mn²⁺ ion transition. Following assignations and similar spectral CL patterns of Russian Strontianite samples, the emission-defect assignments: Dy³⁺ 480 nm; Tb³⁺ 540 nm; Dy³⁺ 580 nm and Sm³⁺ 640 nm cannot be disregarded.     

Analysis of the nuclear quadrupole interaction of Disulfur Dichloride, S2Cl2

Pure rotational spectra of S₂³⁵Cl₂ and S₂³⁵Cl³⁷Cl have been observed using a Fourier-transform microwave spectrometer. An analysis of the hyperfine structure made by considering the nuclear spin statistics showed that S₂Cl₂ has C₂symmetry, where the hyperfine splittings due to the two Cl nuclei were analyzed precisely. The nuclear quadrupole coupling constants including the off-diagonal (χ_ab, χ_ac, χ_bc) components and the nuclear spin–rotation interaction constants associated with the two Cl nuclei have been determined for the first time. We have shown that the nuclear quadrupole interaction plays an important role in the ortho–para mixing.     

The Fe3O4 origin of the “Biphase” reconstruction on α-Fe2O3(0 0 0 1)

The so-called Biphase termination on α-Fe₂O₃ has been widely accepted to be a structure with a 40 Å unit supercell composed of coexisting islands of Fe_1−xO and α-Fe₂O₃. Based on thermodynamic arguments and experimental evidence, including transmission electron diffraction, imaging, magnetic and spectroscopic information, it is found that the previously proposed structure model is inaccurate. The actual Biphase structure is instead a layered structure related to the reduction of α-Fe₂O₃ to Fe₃O₄. A model for the Biphase termination is proposed which does not contain islands of Fe_1−xO but instead consists of bulk α-Fe₂O₃ and a Fe₃O₄-derived overlayer. The proposed model is consistent with all current and previously reported experimental findings.