CVT Method Research Articles

Synthesis of monolayer SiP via chemical vapor transport toward superior optoelectronic and catalytic performance

Single-layer SiP crystals with excellent photoelectric detection and hydrogen evolution reaction properties were synthesized by the one-step CVT method.

Growth of Germanium Crystals by Time-Varying Temperature Profile, Cvt Methods

Growth of Germanium Crystals by Time-Varying Temperature Profile, Cvt Methods

Large Scale Production of High-Quality Sns2 Single-Crystal Grown by Cvt Method

Large Scale Production of High-Quality Sns2 Single-Crystal Grown by Cvt Method

Sheet doping for improved sensitivity of HCl on MoTe2

MoTe2 sheets have shown high sensitivity towards important gas molecules, such as NO2 and NH3. This, in combination with the improved surface recovery via gate bias and UV light, makes MoTe2 a promising platform for high-performance gas detection. However, similar to MoS2, the sensitivity of MoTe2 to other compounds is low making the number of compatible analytes limited. Recent reports have demonstrated that CVT and CVD methods can produce large-size highly-doped sheets of MoTe2, which opens a new avenue of sheet engineering for enhanced molecular sensing. This work investigates, employing DFT calculations, doping of MoTe2 with Ga, Ge, As, Se, and Br for enhanced HCl detection. The results show that the effects on adsorption are correlated with the partial charge accumulated on the doped element. As and Se are predicted to increase the hole transfer into the sheet by 65 and 20%, respectively, with a limited impact on the adsorption energy of the molecule. The latter is shown, via ab-initio molecular dynamics, to have effectively no impact on the HCl diffusion at room temperature. Hence, As and Se doping is predicted to enhance the response of the sheet to changes in concentration of HCl without impeding its surface recovery.

Theoretical study on the reaction of nitric oxide with 2-hydroxyethyl radical

The reaction kinetics of nitric oxide (NO) with 2-hydroxyethyl radical (CH2CH2OH) radical was investigated over a wide temperature range of 200–1300 K and a pressure range of 1.0 × 10−4 –1.0 × 102 bar. Eight reactions channels were explored at G4 and CCSD(T)/cc-pVTZ // B3LYP/6–311++G(d, p) levels of theory, which consist of the same first step involving the formation of a adduct IM1 (ONCH2CH2OH) barrierlessly in the entrance channel. The channel producing P1 (CH2O and CH2NOH) were confirmed to be the most favourable over the calculated temperature range. RRKM – CVT method with Eckart tunnelling correction was employed to calculate the temperature-, pressure-dependent rate coefficients and yield of the most favourable reaction channels. The computed total rate coefficients agreed well with the available literature results. The individual and total rate coefficients showed negative temperature dependences. The reaction forming IM1 was dominated at low temperature and high-pressure conditions with a yield above 0.9 at the temperature less than 350 K and the pressure greater than 3 bar; while the channel producing P1 was dominated at high temperature and low pressure with a yield above 0.9 at the temperature higher than 1100 K and the pressure lower than 10−2 bar.

Chemical vapor transport growth of bulk black phosphorus single crystals

Recent progress in growth of bulk black phosphorus single crystal by CVT method has been briefly reviewed with the emphasis on reaction system, nucleation and growth mechanism as well as advancement in growth of doped BP bulk single crystal.

Synthesis, characterization, and photocatalytic properties of CuO-TiS2 nanocomposite

This research paper reports the photocatalytic degradation of methylene blue dye using CuO-TiS2 nanocomposites. CuO-TiS2 nanocomposite of different weight ratios were synthesized using CVT method, which is simple and low cost with the possibility of mass production. The synthesized materials were characterized using XRD, FESEM, HRTEM, UV-visible and PL spectroscopic techniques. XRD pattern of CuO-TiS2 nanocomposite shows polycrystalline nature, which is confirmed by HRTEM results. The optical band gap of these nanocomposite decreases with increasing wt% of CuO nanorods. The PL of these nanocomposite shows a quenching behavior on addition of CuO nanorods. The use of CuO-TiS2 nanocomposites degrades the MB dye by 83.18% in 180 min as compared to Pure TiS2 which degrades MB dye 80.25% in 210 min. These nanocomposites show faster degradation.

A theoretical study on the dynamics of gas-phase reaction of methyl cation with atomic oxygen

The dynamics and kinetics of the reaction of CH3+ cation with atomic oxygen in its lowest triplet and singlet states in the presence of N2 molecules as the bath gas is theoretically investigated. The potential energies over both surfaces at the CCSD(T)/aug-cc-pVTZ level of theory are explored. Both singlet and triplet surfaces characterize by barrierless initiation step. The entrance channel to form the energized adducts are governed by the capture probability once the centrifugal barrier is surmounted. Multiwell-multichannel mechanisms are found for both singlet and triplet potential energy surfaces. One-dimensional chemical master equation is solved to explore the dynamics and kinetics of the title reaction. The fractional populations of the stationary points as function of time are analyzed to determine the role of the energized intermediates on the dynamics of the title reaction. No significant temperature or pressure dependence for the title reaction was observed over a wide range of temperature (300–3000 K) and pressure (0.1–4.5 atm). The results indicate cis and trans-HCOH+, CH2O+, and H atom are the major products for both surfaces. CVT method was used to explore the importance of tunneling in hydrogen transfer isomerization reactions of CH2O+ to trans-HCOH+ and HOC+ to HCO+ using small-curvature approximation.

Growth of bulk ZnO crystals by self-selecting CVT method

Bulk ZnO crystals were grown by self-selecting CVT method using carbon as the transport agent. The crystal growth process took place on the top of the polycrystalline source material, and deep-red colored ZnO crystals of several millimeters were obtained. The as-grown crystals were characterized by X-ray diffraction (XRD), Energy Dispersive Spectrometer (EDS), Raman scattering (RS) spectroscopy, visible–near infrared (VIS–NIR) spectrophotometer and room temperature photoluminescence (PL) spectroscopy. XRD results indicate good crystallinity of the ZnO crystal. The EDS analysis shows that the crystal has a stoichiometry ratio Zn: O = 52: 48. The results suggest the existence of native defects of oxygen vacancies (OV) in the as-grown ZnO samples, which is caused by the stoichiometry shift to Zn-rich.

Photooxidation of cyclohexanone in simulated atmosphere: A potential source of atmospheric formic acid

Gas phase photooxidation of cyclohexanone (CH) has been studied in the laboratory in a simulated atmospheric environment (synthetic air, 1 bar pressure) under the exposure of 311 nm UV light. Formic acid along with formaldehyde and ethylene are identified as the major photooxidation products. Quantum yield for the production of these species is measured and the values are compared with previous studies on the photo dissociation of CH. For 6 h of light irradiation with initial CH concentration of 9.19 ± 0.1 × 1016 molecules cm−3, the measured quantum yield values of ethylene and formaldehyde, the two primary photooxidation products, are 0.0395 ± 0.001 and 0.0028 ± 0.002, respectively. These values are comparable with CH dissociation quantum yield, 0.24 ± 0.02, and also the quantum yield of CO production, 0.0940 ± 0.001. The energetic parameters of different steps of the proposed reaction mechanism are calculated by electronic structure theory method at DFT/B3LYP/6–311++G** level. A reaction modeling has been performed, and similarity in simulated quantum yield values with that of the experimentally measured ones validates the suggested reaction mechanism. Experimentally measured values of rate constants of most of the elementary reaction steps incorporated in the modeling are not known, and the calculated values, obtained by use of CVT and RRKM theoretical methods are used. The total yield of formic acid, which has been assigned as a secondary oxidation product, is 3.46 ± 0.25 × 1015 molecules cm−3 as obtained from experiment and this data matches well with the value of 2.67 × 1015 molecules cm−3 obtained from reaction modeling for 6 h of UV irradiation. The yield of formic acid is comparable with the yield of primary photo products. The results imply that photooxidation of CH and analogous compounds might have significant contributions to production of formic acid in the earth's troposphere. According to the prediction of the modeling results presented here, the contribution of cyclohexanone photooxidation to the atmospheric concentration of formic acid is ∼1 pptv.

Photoresponsive field-effect transistors based on multilayer SnS2 nanosheets

2D SnS nanosheets are exfoliated by micromechanical exfoliation technique from SnS single crystals which are synthesized by CVT methods. Monolayer SnS nanosheet has been obtained and the Raman spectrum shows that A mode of monolayer SnS shows a slight softening compared with bulk SnS single crystal. The field effect transistors (FETs) based on multilayer SnS nanosheets have been fabricated, of which the electrical and photoelectrical properties have been measured. Under dark condition, with of 1 V, our SnS FET shows n-type behavior. The carrier mobility of the FETs reach 3.51 and the ‘ON/OFF’ ratio is about . The SnS FET is also illuminated under 532 nm laser with the power of 500 mW/cm. The light absorption causes an increment of carrier mobility (from 3.51 under dark condition to 3.85 under 532 nm laser illumination with the power of 500 mW/cm) of SnS. The responsivity (R) and detectivity of our multilayer device under 500 mW/cm 532 nm is 2.08 A/W and J, respectively. All the above properties indicate the potential of SnS nanosheets to be used as FETs and phototransistors.

Analysis of DC Photovoltaic System Voltage Controller Based on Subregional Variable Duty Cycle

A modified MPPT control method which introduces the rapidity of the CVT method and the precision of the IncCond method, and combines the subregional variable duty cycle to optimize the photovoltaic array. To verify and analyze on basis of the setting up of the variable duty cycle ∆D and the time parameter of the power/hour Ta, and verify the method proposed in this paper on the experimental platform, In different areas of photovoltaic power generation using different duty cycle control method, Optimization of the target area using constant voltage method, Reached quickly determine the maximum power point (MPP) when light mutations.

Porous layered and open-framework mixed-valence copper tellurites

|Cu+Cl3|[Cu2+2(TeO3)] (1), |Сu+1.7Cl3.8|[Cu2+4O(TeO3)2] (2) and Tl+2[Cu2+2Te6+Te4+6O18] (3) were obtained by CVT and hydrothermal methods in CuCl-CuCl2-TeO2 and Tl2CO3-CuO-TeO2 systems. 1 demonstrates layered topology with pores (1×0.65nm), whereas 2 has open-framework structural architecture with two-dimensional system of channels (1.16×0.74nm). Channels in open-framework of 3 are occupied by Tl+ cations. ‘Host-guest’ structural organization of 1 and 2 with host Cu2+-tellurite units of different dimensionality formed by oxocentered OCu4 tetrahedra and OCu2Te triangles and guest Cu+-chloride species is the result of formation from gases in CVT reactions. Oxocentered units determine basic topologies of the structures of 1 and 2 and influence their stability and properties. [Te6+Te4+6O18]6− polytellurite-tellurate framework in 3 can be represented as consisting of Kagome-like layers.

Dimers of oxocentred [OCu4]6+ tetrahedra in two novel copper selenite chlorides, K[Cu3O](SeO3)2Cl and Na2[Cu7O2] (SeO3)4Cl4, and related minerals and inorganic compounds

AbstractTwo novel copper selenite chlorides, K[Cu3O](SeO3)2Cl (I) and Na2[Cu7O2](SeO3)4Cl4 (II), have been synthesized by the CVT method. Their crystal structures have been solved by direct methods and refined by least-squares techniques. I is triclinic, space group P1̄, a = 7.6821(5), b = 8.1179(5), c = 8.7836(6) Å, α = 113.193(3), β = 108.735(4), γ = 98.245(4)°, V = 453.32(5) Å3, R1 = 0.0481 for 1210 unique reflections with F≥4σ(F); II is triclinic, space group P1̄,a = 7.4362(6), b = 8.3361(7), c = 9.1343(11) Å,α = 110.277(6), β = 106.212(6), γ = 105.158(4)°, V = 467.94(8) Å3, R1 = 0.0265 for 2498 unique reflections with F≥4σ(F). The structures of I and II can be described in terms of dimers of copper oxocentred tetrahedra. In I, two (OCu4)6+ tetrahedra share a common Cu···Cu edge to form the [O2Cu6]8+ dimer, whereas the structure of II is based upon two (OCu4)6+ tetrahedra linked together by one common Cu atom resulting in the formation of the [O2Cu7]10+ dimer. A comparison with related minerals and inorganic compounds is given.

Efficient topology preserving triangular remeshing algorithm with adaptive vertices insertion

Remeshing is a fundamental problem in 3D modeling and computer aided design. Aiming at the shortcomings of the Euclidean distance measure in CVT method, we present a new topology preserving triangular remeshing algorithm. Two mesh quality measuring criterions are used in the algorithm for determining a new site insertion step: (1) a new mesh error metric; (2) the topology condition of restricted Voronoi cell of each site. While new sites are inserted, a flooding-based remeshing algorithm is called to optimize the location of all sites and achieve the remeshing results iteratively. Experimental results show that the new algorithm can preserve the topology of input mesh efficiently and get remeshing results with good quality than CVT method with Euclidean distance measure.

Hydrogen abstraction mechanisms and reaction rates of toluene+NO3.

The hydrogen abstraction reaction mechanisms of toluene molecule by NO3 radical were investigated theoretically with quantum chemistry and reaction kinetics. All the molecular structures, vibrational properties, and the intrinsic reaction coordinates were determined with B3LYP/6-311G(d,p). The non-dynamic electronic correlations were examined with the CASSCF dominant configurations. The energies and the potential energy profiles were refined with accurate model chemistry G3(MP2). Rate constants were determined using the CVT method over the temperature range 200-2000 K. It was found that in addition to the side chain H-abstraction, the ring H-abstraction reactions are also possible. The side chain H-abstraction rate constant is in very good agreement with the available experiments and has a non-Arrhenius characteristic. Nevertheless, all the ring H-abstractions follow the Arrhenius behavior well. The over-all reaction was found to have a complex reaction mechanism in which the side chain H-abstraction is dominant below 700 K while the ring H-abstractions are competitive above 800 K. The approximate apparent activation energies E app are 15.5 and 66.4 kJ mol(-1) at 300-700 K and 800-2000 K, respectively. Graphical Abstract The calculation of the reaction rate indicates that the over-all reaction has a complex mechanism. The reaction proceeds mainly by the side chain H-abstraction at temperatures lower than 700 K and is nearly irreversible, while the competition of the ring H-abstractions becomes observable at higher temperatures and is reversible.

Optimisation of quantitative lung SPECT applied to mild COPD: a software phantom simulation study.

BackgroundThe amount of inhomogeneities in a 99mTc Technegas single-photon emission computed tomography (SPECT) lung image, caused by reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), is correlated to disease advancement. A quantitative analysis method, the CVT method, measuring these inhomogeneities was proposed in earlier work. To detect mild COPD, which is a difficult task, optimised parameter values are needed.MethodsIn this work, the CVT method was optimised with respect to the parameter values of acquisition, reconstruction and analysis. The ordered subset expectation maximisation (OSEM) algorithm was used for reconstructing the lung SPECT images. As a first step towards clinical application of the CVT method in detecting mild COPD, this study was based on simulated SPECT images of an advanced anthropomorphic lung software phantom including respiratory and cardiac motion, where the mild COPD lung had an overall ventilation reduction of 5%.ResultsThe best separation between healthy and mild COPD lung images as determined using the CVT measure of ventilation inhomogeneity and 125 MBq 99mTc was obtained using a low-energy high-resolution collimator (LEHR) and a power 6 Butterworth post-filter with a cutoff frequency of 0.6 to 0.7 cm−1. Sixty-four reconstruction updates and a small kernel size should be used when the whole lung is analysed, and for the reduced lung a greater number of updates and a larger kernel size are needed.ConclusionsA LEHR collimator and 125 99mTc MBq together with an optimal combination of cutoff frequency, number of updates and kernel size, gave the best result. Suboptimal selections of either cutoff frequency, number of updates and kernel size will reduce the imaging system’s ability to detect mild COPD in the lung phantom.

Chemischer Transport fester Lösungen. 24 [1] Bildung von Mischphasen und chemischer Transport im System MnO/MnS

Chemical Vapor Transport of Solid Solutions. 24. [1] Formation and Chemical Vapor Transport of MnO/MnS mixed Crystals In the System MnO/MnS mixed crystals MnS1−xOx (x = 0 …0,04) are formend. By means of CVT methods using bromine as transport agent (1000 → 900 °C) MnO, MnS and MnS:O-mixed phases could be obtained. The role of traces of water is discussed.

Chemischer Transport fester Lösungen. 18 [1] Der Chemische Transport von ZnIn2S4, ZnIn2Se4 und ZnIn2S4−xSex‐Mischphasen

Chemical Vapor Transport of Solid Solutions. 18. [1] Chemical Vapor Transport of ZnIn2S4, ZnIn2Se4 and ZnIn2S4−xSex‐mixed CrystalsBy means of CVT methods using iodine as transport agent (725 → 675 °C) ZnIn2S4, ZnIn2Se4 und ZnIn2S4−xSex‐mixed phases could be obtained. Mass spectrometric investigations show the formation of ZnI2(g) and InI3(g) are due to the transport reaction. The transport process leads to a significant enrichment of sulphur.

Chemischer Transport fester Lösungen. 20 [1] Der Chemische Transport von Mischphasen in den Systemen CdS/CdTe und CdSe/CdTe

Chemical Vapor Transport of Solid Solutions. 20, Chemical Vapor Transport of Mixed Phases in the Systems CdS/CdTe and CdSe/CdTeBy means of CVT methods using iodine as transport agent (900 → 800 °C) in the systems CdS/CdTe and CdSe/CdTe mixed crystals could be prepared. The system CdS/CdTe shows a broad miscibility gap. Sulfur rich mixed crystals as well as tellurium rich ones could be prepared. The system CdSe/CdTe shows complete miscibility for all Se/Te ratios. In both systems congruent transport has been observed.