Bromine In Methanol Research Articles

Surface and interface chemistry of bromine–methanol‐etched Cd0.9Zn0.1Te crystals

Chemical polishing or chemo‐mechanical polishing is crucial as a last step of surface preparation to remove the damaged layer and contaminants from the surface of CdZnTe crystals. The bromine–methanol solution is widely used for this purpose. However, bromine–methanol solution enriches the surface with Te and results in poor performance of CdZnTe crystals. In this study, the effect of the chemical polishing with 5% bromine–methanol solution on the surface and at the interface is investigated and it is demonstrated that etching duration strongly influences surface stoichiometry and interface contaminants. The evolution of the surface topography with etching and chemical changes are presented. It is shown that after 90 s etching/polishing, subsurface damage is removed and Te enrichment is minimum. Moreover, interface layer thickness is the smallest for 90 s etching duration. It is presented that further increase in the etching duration disturbs the surface stoichiometry and interface depth. It also calculated that 90 s of etching shows low interface barrier and symmetrical current–voltage curve.

Study on the density of trap states between CdZnTe and passivation layer based on MIS structure

CdZnTe room temperature nuclear radiation detectors are widely used in the fields of homeland security, medical imaging and astrophysics. In the Cd1-xZnxTe radiation detector, the purpose of passivation is to reduce dark current and improve stability. In this study, CdZnTe etched by bromine-methanol (BM) was treated with standard H2O2 and NH4F passivation process. With the help of TEM and EDS measurement results, the thickness of the passivation layer ranges from 126 nm to 183 nm, and X-ray photoelectron spectroscopy (XPS) measurement results show that the TeO2 fraction can be increased on the passivated surface. The dispersion phenomenon on the capacitance-voltage and conductance-voltage curves indicates the existence of carrier trap states in the area near the interface. In order to determine the size of the trap state under this passivation method, an equivalent circuit model was constructed using the calculation method of electrical conductivity. Based on this model, when the voltage increases from 0 V to 1.4 V, the value of the trap state density obtained changes in between 1.07 × 1010 eV−1cm−2 and 5.85 × 1010 eV−1cm−2.

The influence of posttreatment processes on the structures and the optical and electrical properties of CuInS2 and its heterojunction with various sulfides (CdS, CdZnS, and CdCuS)

As the first essential step toward understanding how to obtain an efficient CuInS2-based solar cell, this paper studied the photoelectric properties of CuInS2 and sulfide P–N heterojunction. For this purpose, the single-source evaporation method and the chemical bath deposition had been applied to prepare CuInS2 films and sulfide films (CdS, CdZnS, and CdCuS), respectively. The powder source was obtained from CuInS2 polycrystalline ingot, which consists of CuInS2 chalcopyrite phase. The segregated CuxS secondary phase on the surfaces of CuInS2 films could be removed by etching of bromine–methanol (BM) solution. The structures of ternary sulfide films (CdZnS and CdCuS) were similar to that of CdS film. The transient photocurrent of CdZnS thin film was highest, which might be related to the high reaction activity and the good crystal quality. Furthermore, the I–V response of CuInS2 and CdZnS heterojunction was studied, which was close to the ideal diode type behavior. The low reverse saturation current density, the optimal diode ideality factor, and the high barrier height were obtained from the I–V curve of CuInS2 and CdZnS heterojunction, which might mean that the CdZnS film could be suitable to use in photovoltaic application.

Characterization of CdZnTeSe Nuclear Detector Chemically Etched in Bromine Methanol

Semiconductor nuclear radiation detectors made from tertiary and quaternary compounds of cadmium telluride (CdTe) can operate at room temperature without cryogenic cooling. One of such materials that have become of great interest is cadmium zinc telluride selenide (CdZnTeSe). Compared to other CdTe-based materials, such as cadmium zinc telluride (CdZnTe), CdZnTeSe can be grown with much less Te inclusions and sub-grain boundary networks. Chemical etching is often used to smoothen wafer surfaces during detector fabrication. This paper presents the characterization of CdZnTeSe that is chemically etched using bromine methanol solution. Infrared imaging shows that the wafer has no sub-grain boundary networks that often limit detector performance. The current-voltage (I-V) characterization experiment gave a resistivity of 4.6 × 1010 Ω-cm for the sample. The I-V curve was linear in the ±10 to ±50 volts range. An energy resolution of 7.2% was recorded at 100 V for the 59.6-keV gamma line of 241Am.

Halogenation and μH Tautomerism of 7-Benzyl-7,8-dicarba-nido-undecaborate(−1) Anion

Deboration of 1-PhCH2-1,2-C2B10H11 by heating in ethanolic potassium hydroxide afforded Me4N+ [7-PhCH2-7,8-C2B9H11]− which was treated with excess halosuccinimide (NCS, NBS) in acetonitrile or with elemental iodine or bromine in methanol to obtain Me4N+ [7-PhCH2-9,11-X2-7,8-C2B9H9]− (X = Cl, Br, I). The reaction of 1-PhCH2-1,2-C2B10H11 with an equimolar amount of iodine gave a mixture of Me4N+·[7-PhCH2-11-I-7,8-C2B9H10]- and Me4N+[7-C6H5CH2-9-I-7,8-C2B9H10]− at a ratio 1:1.8 due to steric effect of the benzyl substituent. The 11B chemical shifts of each μ-H tautomer of Me4N+ [7-PhCH2-9,11-X2-7,8-C2B9H9]− (X = H, F, Cl, Br, I) were calculated at the DFT level of theory, and their contributions to the average 11B NMR spectrum and the corresponding tautomeric equilibrium constants were determined.

The effect chemical treatment of the substrate cadmium telluride on the quality of epitaxial structures

The etching of wafers of cadmium telluride in aqueous and nonaqueous solutions before the epitaxial process of building structures CdxHg1-xTe and its influence on the surface quality of epitaxial layers. As the etchants investigated 2—20 % solution of bromine in isobutyl alcohol, 5 % solution of bromine in methanol, dimethylsulfoxide, ethylene glycol, solutions of bromine in hydrobromic acid and mixed with glycerin, a saturated solution of potassium dichromate in sulfuric acid. The speed of etching was varied from 0.2 to 9 µm/min. Polishing Set nature of the etching substrate of cadmium telluride in 5 % solution of bromine in i-butanol, the dissolution process is diffusion in nature and is limited by the mass transfer of the reactants in the temperature range of 10—60 °C, depending on the concentration of bromine and the viscosity of the solution. Studied the morphology and surface finish of epitaxial layers of CdxHg1-xTe, depending on the method of etching the original substrate. Found the optimal compositions of etchants for precipitaciones processing of obtaining structures with a height of asperities of the surface at 0.1 atm.

The effect of iron content on the reduction of nickel laterite by direct reduction method

Reduction and the compounds formed when the reduced laterite nickel has been investigated. Nickel laterite with average grain size below 0.149 mm mixed with 13% (weight percent) of coal as reductant then reduced in muffle furnace with temperature from 700 °C to 1000 °C. Type of laterite is used which has high iron (saprolite) and low iron content (limonite). Reaction time varied 30, 60 and 90 minutes. The reduction of nickel during reduction is determined by an analysis of metallization values. Metallization analysis used bromine methanol method, while the compound analysis was formed using x-ray Diffractometer. Based on the metallization test, it is known that the laterite nickel ore containing high iron will produce a higher nickel reduction than the laterite nickel ore containing low iron. This corresponds to the oxide phases formed. The higher iron contain on the ore tend to produce the fayalite mixture and slightly forsterite, while at low iron content will form a forsterite. Forsterite tends to inhibit reduction of nickel.

Maximizing Property Tuning of Phosphorus Corrole Photocatalysts through a Trifluoromethylation Approach.

An eight-member series of CF3-substituted difluorophosphorus corroles was prepared for establishing a structure-activity profile of these high-potential photosensitizers. It consisted of preparing all four possible isomers of the monosubstituted corrole and complexes with 2-, 3-, 4-, and 5-CF3 groups on the macrocycle's periphery. The synthetic pathway to these CF3-substituted derivatives, beginning with (tpfc)PF2, involves two different initial routes: (i) direct electrophilic CF3 incorporation using FSO2CF2CO2Me and copper iodide, or (ii) bromination to achieve the 2,3,8,17,18-pentabrominated compound using excess bromine in methanol. Crystallographic investigations revealed that distortion of the original planar macrocycle is evident even in the monosubstituted case and that it becomes truly severe for the penta-CF3-substituted derivative 5. There is a shift in redox potentials of about 193 mV per -CF3 group, which decreases to only 120 mV for the fifth one in 5. Differences in the electronic spectra suggest that the Gouterman four orbital model decreases in relevance upon gradual -CF3 substitution, a conclusion that was corroborated by DFT calculations. The very significant energy lowering of the frontier orbitals suggested that photoexcitation should lead to a highly oxidizing photocatalyst. This hypothesis was proven true by finding that the most synthetically accessible CF3-substituted derivative is an excellent catalyst for the photoinduced conversion of bromide to bromine (phenol, toluene, and benzene assay).

Impact of surface treatments on I–V characteristics in Cd1−xZnxTe and Cd1−xMnxTe crystals

In this work, we focused on studying the impact of different surface treatments for Cd1−xZnxTe (CZT) and Cd1−xMnxTe (CMT) samples with indium evaporated contacts, specifically: mechanical polishing (MP), mechano-chemical polishing (MCP) and mechanical polishing followed by the chemical etching (MP+Et). We examined 3 samples in each group of Cd0.85Zn0.15Te and 3 samples in each group of Cd0.93Mn0.07Te. Devices were consecutively characterized by current–voltage dependence (I–V). The measured characteristics revealed that for CMT both surface treatments, including chemical exposure to bromine ethylene glycol in MCP or bromine methanol in etching, resulted in linear I–V characteristic consistent with the bulk resistance. At the same time, chemical treatments of CZT samples dramatically increased their current densities (up to several μA/cm2).

Bromination of 6-Methyl-5-nitrouracil

At bromination of 6-methyl-5-nitrouracil with bromine in methanol a mixture formed of the initial compound with 5-bromo-6-methyl-6-methoxy-5-nitrodihydropyrimidine-2,4(1H,3H)-dione.

Low energy ion scattering as a depth profiling tool for thin layers - Case of bromine methanol etched CdTe

We have investigated the properties of the Te-rich surface layer formed after a bromine-methanol etch of CdTe single crystal by two methods: Angle Resolved X-Ray Photoelectron Spectroscopy (ARXPS) and Low Energy Ion Scattering (LEIS) in the Dynamic mode. We compare the acquisition time of each method. The results showed similar, exponential decay of the Te/Cd ratio to a depth of 6 nm. At the depths higher than 6 nm, the substrate becomes stoichiometric. Dynamic LEIS provided more detailed information about composition at depths lower than the probing depth of ARXPS. The Dynamic LEIS measurements suggest that the composition of the outermost layer of CdTe after bromine-methanol etching consists of CdTe4.

An Improved Procedure for the Determination of Ferrous Iron Mass Fraction in Silicate Rocks Using a Schlenk Line‐Based Digestion Apparatus to Exclude Oxygen

Precise and accurate determination of ferrous iron mass fraction in silicate rocks and geological reference materials is still a significant challenge due to the labile nature of the analyte. Here, we report a modified and improved procedure for the determination of ferrous iron mass fraction, capable of yielding moderately accurate and highly precise results in a relatively shorter time than before. This modified technique requires a more convenient operational procedure than the classical method. A sample digestion apparatus was designed that included a Schlenk line to expel air in order to prevent oxidation. The advantages of this procedure over the classical procedure are shorter process flow, higher efficiency and absence of an additional redox indicator. The composition of the acid matrix used to dissolve the samples as well as the incubation temperature and time was investigated. Comparative data for twenty‐one reference materials are reported, with five of them reported for the first time by the Schlenk line procedure. A series of experiments were carried out to identify and minimise the main source of error. In addition, the possibility of eliminating the reducing substances before digestion, by pretreatment of the sample by cold 10% methanolic bromine, was also studied.

Improving the Performances of CdTe Gamma Ray Detectors by H2/Ar ECR Plasma Processing

H2/Ar electron cyclotron resonance plasma processing of the high-resistivity (111) CdTe crystals was studied to find its effect on the leakage current and the gamma ray detection properties of the detectors. All the crystals were chemically etched in a bromine–methanol (BM) solution prior to the plasma processing to obtain a smooth surface. A remarkable reduction in both the surface and the bulk leakage current was observed in the plasma processed detectors when compared with the unprocessed one. The gamma detection property of the detectors, both the spectral resolution and the peak shape, was also significantly improved. X-ray photoelectron spectroscopy confirmed that an excess Te-rich surface layer was present on the BM etched crystal, however, such layer was removed, and the surface atomic ratio was modified after the plasma processing. The improvement in the detector performance could be related to the change in the surface chemical states of the crystals. Hence, this could be a promising process for improving the detectors performance and their stabilities.

A novel approach of chemical mechanical polishing for cadmium zinc telluride wafers.

A novel approach of chemical mechanical polishing (CMP) is developed for cadmium zinc telluride (CdZnTe or CZT) wafers. The approach uses environment-friendly slurry that consists of mainly silica, hydrogen peroxide, and citric acid. This is different from the previously reported slurries that are usually composed of strong acid, alkali, and bromine methanol, and are detrimental to the environment and operators. Surface roughness 0.5 nm and 4.7 nm are achieved for Ra and peak-to-valley (PV) values respectively in a measurement area of 70 × 50 μm2, using the developed novel approach. Fundamental polishing mechanisms are also investigated in terms of X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. Hydrogen peroxide dominates the passivating process during the CMP of CZT wafers, indicating by the lowest passivation current density among silica, citric acid and hydrogen peroxide solution. Chemical reaction equations are proposed during CMP according to the XPS and electrochemical measurements.

The influence of post treatment on physical properties of polycrystalline CuInS2 thin films

In this paper, CuInS2 (CIS) films were prepared by vacuum evaporation method and the soda-lime glass was used as substrate. Crushed CIS powder from polycrystalline CIS ingot was used as starting materials. Then, as prepared CIS films were heat treated in S atmosphere at 400°C for 30min. After annealed, some CIS films were etched by argon plasma or bromine methanol (BM) mixed solution. The results of XRD patterns showed that the argon plasma treatment could remove the CuxS phases on the surface of CIS films perfectly. After argon plasma treatment, the conduction type of the CIS films showed no change, which indicated that argon plasma treatment had no specific selectivity for the elimination of surface atoms. Moreover, as the results of EDX measurement of CIS films, the Cu/In atomic ratio showed a monotonic decreasing tendency with the increasing time of BM solution etching, which might be related to the preferential corrosion of BM solution. Furthermore, the results of Hall measurement also showed that after the etching of BM solution, the conduction type of CIS films was changed from p type to n type due to the preferential corrosion of BM solution, which was consistent with the results of previous published paper.

Effects of Chemomechanical Polishing on CdZnTe X-ray and Gamma-Ray Detectors

Mechanically polishing cadmium zinc telluride (CdZnTe) wafers for x-ray and gamma-ray detectors often is inadequate in removing surface defects caused by cutting them from the ingots. Fabrication-induced defects, such as surface roughness, dangling bonds, and nonstoichiometric surfaces, often are reduced through polishing and etching the surface. In our earlier studies of mechanical polishing with alumina powder, etching with hydrogen bromide in hydrogen peroxide solution, and chemomechanical polishing with bromine–methanol–ethylene glycol solution, we found that the chemomechanical polishing process produced the least surface leakage current. In this research, we focused on using two chemicals to chemomechanically polish CdZnTe wafers after mechanical polishing, viz. bromine–methanol–ethylene glycol (BME) solution, and hydrogen bromide (HBr) in a hydrogen peroxide and ethylene–glycol solution. We used x-ray photoelectron spectroscopy (XPS), current–voltage (I–V) measurements, and Am-241 spectral response measurements to characterize and compare the effects of each solution. The results show that the HBr-based solution produced lower leakage current than the BME solution. Results from using the same chemomechanical polishing solution on two samples confirmed that the surface treatment affects the measured bulk current (a combination of bulk and surface currents). XPS results indicate that the tellurium oxide to tellurium peak ratios for the mechanical polishing process were reduced significantly by chemomechanical polishing using the BME solution (78.9% for Te 3d 5/2O2 and 76.7% for Te 3d 3/2O2) compared with the HBr-based solution (27.6% for Te 3d 5/2O2 and 35.8% for Te 3d 3/2O2). Spectral response measurements showed that the 59.5-keV peak of Am-241 remained under the same channel number for all three CdZnTe samples. While the BME-based solution gave a better performance of 7.15% full-width at half-maximum (FWHM) compared with 7.59% FWHM for the HBr-based solution, the latter showed a smaller variation in performance of 0.39% FWHM over 7 days compared with 0.69% for the BME-based solution.

Effects of different CdCl2 annealing methods on the performance of CdS/CdTe polycrystalline thin film solar cells

In this paper, the effects of different CdCl2 annealing methods, including vapor annealing and dip-coating annealing, on the performance of CdS/CdTe polycrystalline thin-film solar cells are studied. After annealing, the samples are lightly etched with 1% bromine in methanol to remove surface oxides. Both annealing methods give CdTe polycrystalline thin films with good crystallinity and complete structure. For solar cells containing the annealed CdTe films, cell efficiency first increases and then decreases as the concentration of CdCl2 solution used for dip-coating annealing increases, and the optimized CdCl2 concentration is 12%. The uniformity of the performance of all cells is analyzed by calculating the relative standard deviation for each parameter. The uniformity of cell performance can be improved dramatically by dip-coating annealing instead of vapor annealing. Most notably, an appropriate concentration of CdCl2 (12%) acts as a protective layer that is conducive to realizing uniform high-performance CdS/CdTe solar cells. According to the location of depletion regions, the CdTe films treated by dip-coating annealing show a relatively low doping concentration, except for the sample treated with a CdCl2 concentration of 6%, which is consistent with the changes of short-circuit current density of the cells. It is believed that these results can be applied to the large-scale production of CdTe polycrystalline thin-film solar cells.

Large-scale micro- and nanopatterns of Cu(In,Ga)Se2 thin film solar cells by mold-assisted chemical-etching process.

A reactive mold-assisted chemical etching (MACE) process through an easy-to-make agarose stamp soaked in bromine methanol etchant to rapidly imprint larger area micro- and nanoarrays on CIGS substrates was demonstrated. Interestingly, by using the agarose stamp during the MACE process with and without additive containing oil and triton, CIGS microdome and microhole arrays can be formed on the CIGS substrate. Detailed formation mechanisms of microstructures and the chemical composition variation after the etching process were investigated. In addition, various microand nanostructures were also demonstrated by this universal approach. The microstructure arrays integrated into standard CIGS solar cells with thinner thickness can still achieve an efficiency of 11.22%, yielding an enhanced efficiency of ∼18% compared with that of their planar counterpart due to an excellent absorption behavior confirmed by the simulation results, which opens up a promising way for the realization of high-efficiency micro- or nanostructured thin-film solar cells. Finally, the complete dissolution of agarose stamp into hot water demonstrates an environmentally friendly method by the mold-assisted chemical etching process through an easy-to-make agarose stamp.

Alternative Etching for Improved Cu-rich CuInSe2 Solar Cells

ABSTRACTTwo alternative chemical etchings (aqueous solution of bromine and bromine methanol solution) have been here tested to replace the KCN etching step in Cu-rich CuInSe2 based solar cells fabrication process. This new oxidative etch aims also at smoothing and thinning the as-grown films. This directly affects the interface between the absorber and the CdS buffer, interface which causes problems for Cu-rich solar cells. We present here the effect of these two alternative etchings on both the absorber surface and the solar cells parameters: whereas the bromine methanol etching destroys the solar cell, the aqueous solution of bromine leads to an improvement of the device through reduced interface and tunneling enhanced recombination.

X-ray photoelectron spectroscopic study of silicon surface passivation in alcoholic iodine and bromine solutions

We report an X-ray photoelectron spectroscopic (XPS) study of silicon surfaces passivation using alcoholic solutions of iodine and bromine where different behavior with two systems is observed. The minority carrier lifetime determined by microwave photoconductive decay method showed better surface passivation for iodine-alcoholic system with HF preconditioning step. The iodine–ethanol (I–E) passivated samples show strong Si–I bonding (two times) in Si core level spectra for the samples without oxide (25.5%) compared with oxide (10.2%) counterpart. However, bromine–ethanol (B–E) passivated samples show higher Si–Br bonding strength in the samples with oxide (24.7%) compared to without oxide specimens (12.0%). This may be the reason of difference in passivation behavior of I–E and B–E systems. Higher O–Br bonding in O core level spectra of B–E passivated samples with oxide (35.8%), compared to without oxide (20.7%), results in comparable lifetime values in both with and without preconditioning. To understand the effect of solvent on the passivation, experiments are performed using iodine–methanol (I–M) and bromine–methanol (B–M) solutions and XPS analysis shows similar Si–I, Si–Br, and O–Br bonding trends.