Residual Boron Research Articles

Tuning the framework polarity in MFI membranes by deboronation: Effect on mass transport

The polarity of a zeolite is an important parameter determining the transport and separation properties in zeolite packed beds and membranes. This study focuses on the systematic variation of the zeolite polarity for membrane applications by varying the amount of silanol groups within the framework of the MFI zeolite by deboronation and consecutive heat treatment from 9 to 4 silanol groups per unit cell. The decrease in the number of silanol groups after heat treatment is confirmed by diffuse reflection infrared Fourier transform (DRIFT) and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The permeation of pure water through the modified silicalite membranes is insensitive to the number of silanol groups, attributed to a decreased adsorption compensated by an increased diffusivity. The ethanol selectivity in water/ethanol mixtures shows an increase with decreasing amount of silanol groups. Residual boron in the zeolite may react with ethanol and decrease its adsorption capacity. A reduction in flux through the debronated MFI membranes was not observed after ethanol/water permeation.

One-pot synthesis of high silica MCM-22 zeolites and their performances in catalytic cracking of 1-butene to propene

MCM-22 zeolites with high SiO 2/Al 2O 3 (Si/Al 2) ratios were synthesized by a one-pot procedure with the assisting of boron. Based on this boron-containing method, the Si/Al 2 ratios of the MCM-22 zeolites could be greatly extended from 30 to 600 in control by tuning the Si/Al 2 ratios of the starting gels. ICP-AES and 11B MAS NMR results demonstrated that a small part of the boron still existed in the framework of the MCM-22 after calcination and ammonium exchange. However, the residual boron species had little influence on the physicochemical properties of the MCM-22 samples evidenced by XRD, BET, TG–DTA, NH 3–TPD, and Py-IR determinations. The reaction of catalytic cracking of 1-butene to propene was carried out to study the performances of the high silica MCM-22 catalysts. Increasing of the Si/Al 2 ratios in the MCM-22 zeolites suppressed the formation of byproducts such as propane and aromatics effectively, and the optimal selectivity towards propene was obtained on the sample with a Si/Al 2 ratio of 158.

Solid-state NMR characterization of a controlled-pore glass and of the effects of electron irradiation

Controlled-pore glasses (CPGs) are silica-based materials which provide an adequate model system for a better understanding of the radiation chemistry of glasses, especially under nanoscopic confinement. This paper presents a characterization of a nanoporous CPG before and after electron irradiation using multinuclear solid-state magnetic resonance (NMR). 1H MAS NMR has been used for studying the surface proton sites and it is observed that the irradiation leads to a dehydration of the material. Accordingly, concerning the silicon sites near the surface, the observed variation of the Q 4, Q 3 and Q 2 species from 1H– 29Si CPMAS spectra shows an increase of the surface polymerization under irradiation, implying in majority a Q 2 to Q 3/Q 4 conversion mechanism. Similarly, 1H– 17O CPMAS measurements exhibit an increase of Si–O–Si groups at the expenses of Si–OH groups. In addition, modifications of the environment of the residual boron atoms are also put in evidence from 11B MAS and MQMAS NMR These data show that MAS NMR methods provide sensitive tools for the characterization of these porous glasses and of the tiny modifications occurring under electron irradiation.

Deep Levels and Compensation in High Purity Semi-Insulating 4H-SiC

AbstractA study of temperature dependent Hall effect (TDH), electron paramagnetic resonance (EPR), photoluminescence (PL) and secondary ion mass spectrometry (SIMS) measurements has been made on high purity semi-insulating (HPSI) 4H-SiC crystals grown by the physical vapor transport technique. Thermal activation energies from TDH varied from a low of 0.55 eV to a high of 1.5 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Carrier concentration measurements indicated the deep levels had to be present in concentrations in the low 1015 cm-3 range. Several defects were detected by EPR including the carbon vacancy and the carbon-silicon divacancy. PL measurements in the near IR showed the presence of the UD-1, UD-2 and UD-3 emission lines that have been found in HPSI material. No correlation between the relative intensities of the PL lines and the TDH activation energies was seen. SIMS measurements on nitrogen, boron and other common impurities indicate nitrogen and boron concentrations higher than those of individual deep levels as determined by TDH or of intrinsic defects as determined by EPR such as the carbon vacancy or the divacancy. It is determined that several different defects with concentrations greater than or equal to 1x1015 cm-3 are required to compensate the residual nitrogen and boron.

Correlation between Residual Stress and Boron Concentration in Boron-Doped Silicon Films

This paper represents the correlation between the residual stress and the boron concentration in boron-doped silicon films. Residual stress measurement structures of different thicknesses are simultaneously fabricated for the quantitative determination of residual stress profiles. All structures are diffused by various boron diffusion processes and consecutively etched by an improved etch process on the same silicon wafer. The obtained residual stress profiles illustrate that as the drive-in process temperature or the time increases, the average residual stress and the maximum residual stress decrease. For cases of several drive-in process conditions, correlation coefficients between the boron concentration and the residual stress are calculated and the lattice contraction of a boron-doped silicon wafer is measured by high-resolution X-ray diffractometry(HRXRD). The calculated correlation coefficients illustrate that the residual stress profile is closely correlated with the boron concentration after drive-in.

Removal of boron from wastewater by precipitation of a sparingly soluble salt

AbstractThe removal of boron from wastewater has to be considered on a case‐by‐case basis because no boron compound is known to be precipitated quantitatively. Based on an industrial case, many methods were tested for the treatment of wastewater containing 50 g L−1 of sulfuric acid and 0.7 g L−1 of boron, and a well‐adapted precipitation process consisting of the neutralization of boric and sulfuric acids by powdered calcium hydroxide is proposed. Experimental results show that under optimal conditions (50 g L−1 of powdered calcium hydroxide, a temperature of 90° C, and process time of 2 h), the residual boron concentration in solution was reduced from 700 to less than 50 mg L−1, a value never reached before by a precipitation process. © 2004 American Institute of Chemical Engineers Environ Prog, 2004

6H and 4H-SiC Bulk Growth by PVT and Advanced PVT (APVT)

AbstractII-VI, Inc. is a commercial supplier of high-quality SiC substrates (including 2-inch and 3-inch diameter) for RF and power applications to the US market. Semi-insulating 6H-SiC single crystals, doped with vanadium and undoped (vanadium-free), as well as ntype 4H crystals have been grown using the PVT and Advanced PVT (APVT) growth techniques. The APVT process incorporates insitu synthesis and growth of of SiC crystal from Si and C precursors.Grown 6H-SiC and 4H-SiC crystals have been extensively characterized with respect to their purity, crystal quality and electrical properties. COREMA resistivity maps demonstrate that V-compensated boules exhibited axially and radially uniform resistivity around 1011 ω.cm at room temperature. Undoped (V-free) wafers contained residual boron and nitrogen at levels below 1016 atoms/cm3, and demonstrated semi-insulating properties (resistivity between 106 and 1011 ω.cm) as a result of compensation by native point defects with deep levels in the bandgap. The undoped semi-insulating crystals grown by APVT contained boron and nitrogen at 1.9ω1015 cm−3 and 3.8.1015 cm−3, respectively.High-quality 2-inch SiC wafers exhibited micropipe densities on the order of 10 cm−2 and dislocation density on the order of 104 cm−2.

Effect of Ambient on 4H-SiC Bulk Crystals Grown by Sublimation

Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grow ...

Fourier transform photocurrent spectroscopy of dopants and defects in CVD diamond

Fourier-transform photocurrent spectroscopy (FTPS) was used as a very sensitive spectroscopic method to detect shallow and deep impurities (dopants) in CVD diamond layers. Detailed study of experimental conditions (temperature, frequency, electric field, bias light, surface conditions) was performed. Residual boron contamination was detected in many samples, phosphorus spectra were measured in P doped epitaxial layers. Anomalous (opposite) temperature dependence of the defect level with a threshold approximately 0.9 eV was detected and possible explanation of this effect was discussed.

Fourier-Transform Photocurrent Spectroscopy of Defects in CVD Diamond Layers

Fourier-transform photocurrent spectroscopy has been used for the first time to study defects in nominally undoped CVD diamond layers. The hydrogenated surface of diamond (“as grown” or post-hydrogenated) has been annealed in air and changes in surface conductivity and photoconductivity have been monitored as a function of temperature and time. The reduction of surface conductivity with annealing led to an enhancement of photosensitivity and enabled us to study the spectral distribution of the photoionization cross section of shallow and deep defects in the gap over several orders of magnitude in the temperature range of 77–400 K. The photo-Hall effect was used for the determination of the sign of photogenerated carriers. An anomalous temperature dependence of the acceptor defect level was detected. A residual boron contamination was observed in one layer.

Electrical Activity of Residual Boron in Silicon Carbide

Defects in high quality 4H silicon carbide epilayers have been studied using Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Both intrinsic defect related centers HS1, Z(1/2). EH6/EH7 and shallow and deep boron centers were found. Electrical properties of the boron related traps are analyzed. Comparison with the optical decay measurements shows that boron is related to the observed lateral variations of the minority carrier lifetime in low doped 4H-SiC epilayers.

Investigation of Boron Distribution in Martensitic 9% Cr Creep Resistant Steel

Chemical compositions of ferrite matrix and various other phases in a Fe - 0.17 wt.% C - 9.3 wt. % Cr - 1.55 wt.% Mo - 0.27 wt.% V - 0.015 wt.% N - 0.01 wt.% B creep resistant steel in as-received and crept conditions were analyzed with atom probe field ion microscopy. The results show the presence of some residual boron within the ferrite matrix. Analyses showed that boron was uniformly distributed within M23C6, M6C, MX, and Laves phases. Phosphor segregated to the M23C6 - ferrite matrix interface. The results are analyzed with thermodynamic calculations.

Atom probe field ion microscopy investigation of boron containing martensitic 9 Pct chromium steel

The chemical compositions of the ferrite matrix and various other phases in an Fe-0.17 C-9 Cr-1.55 Mo-0.27 V-0.015 N-0.01B (mass pct) steel in as-received and crept conditions were measured with atom probe field ion microscopy (APFIM). The results showed the presence of some residual boron within the ferrite matrix. Analyses showed that boron was distributed within M23C6, M6C, MX, and Laves phases. Phosphor atoms were detected at the M23C6-ferrite interface in the crept condition. The results are compared to predictions from thermodynamic calculations.

Diffusion of light elements in 4H– and 6H–SiC

Deuterium and lithium were introduced in p-type SiC by implantation of 20 keV 2H +or 30 keV 7Li +ions in order to form a diffusion source. The samples were subsequently annealed in vacuum in the temperature range 400–700°C for 0.25 to 16 h. Secondary ion mass spectrometry (SIMS) was used to measure the deuterium and the lithium distribution after heat treatments. Both deuterium and lithium readily decorate the bombardment-induced defects in the vicinity of the ion implantation profile and they are also trapped, most likely by residual boron impurities, during diffusion into the bulk. An effective diffusion coefficient, reflecting the dissociation of trapped lithium, with an activation energy of 2.1 eV is extracted for lithium diffusion in p-type 6H SiC. Furthermore, a capture radius for trapping (most likely by boron) of deuterium is estimated as 10 Å.

Frações de boro e índices de disponibilidade em solos do estado do Ceará

Em 29 amostras superficiais (0-20 cm) de solos do estado do Ceará, foram determinadas diferentes frações de boro e estabelecidas relações com algumas propriedades do solo e com o boro solúvel, usado como índice de disponibilidade para as plantas. As frações de boro foram analisadas, seguindo-se um esquema de fracionamento seqüencial. Determinaram-se o boro solúvel em água (B-Sol), o boro não especificamente adsorvido (B-NEsAd), o boro especificamente adsorvido (B-EsAd), o boro associado a óxidos de Mn (B-OxMn), o boro associado a óxidos de Fe e Al amorfo (B-OxFeA) e a óxidos de Fe e Al cristalino (B-OxFeC), e o boro residual (B-Res). Também foram determinados o boro total (B-Total) e o solúvel em três extratores: água quente, HCl 0,05 mol L-1 e manitol 0,05 mol L-1 + CaCl2 0,01 mol L-1. O teor de boro total nos solos variou de 10,5 a 24,0 mg kg-1 (média de 14,4 mg kg-1). As frações B-Sol, B-NEsAd e B-EsAd apresentaram teores entre 0,05 e 0,79 mg kg-1, representando entre 0,3 a 4,4% do B-Total. Dentre os óxidos, houve predominância do B-OxFeC (média de 4,4 mg kg-1) com teores entre 1 a 2 vezes superiores aos de B-OxFeA (média de 2,72 mg kg-1). Na maioria dos solos, a fração predominante foi o B-Res (média de 6,22 mg kg-1), ocluso em minerais silicatados, com teores que variaram de 19,6 a 70,7% do B-Total. Os valores de B disponível, nos três extratores, correlacionaram-se de forma altamente significativa entre si e com as frações B-Sol, B-NEsAd e B-EsAd. A matéria orgânica e a argila foram as propriedades que se correlacionaram melhor com o B-Sol, B-NEsAd e B-EsAd.

High field/high temperature performance of semi-insulating silicon carbide

Abstract The influence of ambient temperature (295–730 K) and pulsed electric fields (0.5–80 kV/cm) on the electrical properties of high resistivity single-crystal 6H-SiC is reported. It is shown that the resistivity of the undoped 6H-SiC varies strongly, with the ambient temperature following a temperature/field function dominated by an exponential factor containing the activation (ionization) energy of residual boron of 0.35 eV. The dominant activation energy of semi-insulating Vanadium-compensated material (6H-SiC:V) varies with the ambient temperature, increasing from approx. 0 eV at 295–320 K to approx. 0.8 eV at T>600 K. This result can explain the viability of insulating 6H-SiC as a substrate for next-generation high temperature power microwave integrated circuits based on large bandgap semiconductors.

Electrical properties of high resistivity 6H–SiC under high temperature/high field stress

The influence of ambient temperature and applied electric field on the electrical properties of high resistivity (1–30 kΩ cm), semi-insulating (>100 kΩ cm), and insulating (1011–1012 Ω cm) single-crystal 6H–SiC is reported. Current–voltage (I–V) characteristics of lateral metal-semiconductor-metal test structures were measured in vacuum in a temperature range of 295–730 K and under moderate pulsed electric fields (0.5–80 kV/cm). It is shown that the resistivity of the undoped 6H–SiC varies strongly with the ambient temperature after a temperature/field function dominated by a factor containing the activation (ionization) energy of residual boron of 0.35 eV. The dominant activation energy of semi-insulating Vanadium-compensated material (6H–SiC:V) varies with the ambient temperature, increasing from ∼0 eV at 295–320 K to ∼0.8 eV at T⩾600 K. This result can explain the relatively low decrease of the resistivity of insulating 6H–SiC at very high ambient temperatures and its viability as a substrate for next-generation high temperature microwave integrated circuits based on large band gap semiconductors.

Formation of Shallow Junctions during Rapid Thermal Processing from Electron‐Beam Deposited Boron Sources

Diffusion via rapid thermal processing (RTP) has been investigated for fabrication of shallow p‐type layers doped with boron. We used dopant sources deposited by electron beam evaporation in the form of thin boron layers with or without in situ deposited silicon capping films. The deposition process is compatible with the resist mask due to low temperatures and poor step coverage, which facilitate dopant removal via a lift‐off process. Sheet resistance measurements together with secondary ion mass spectroscopy and spreading resistance profiling analyses indicate that doping efficiency is high for both types of sources in the temperature range of 900 to 1050°C for 10 to 30 s. Full dopant activation in the silicon substrate, except for the surface region, has been recorded for all process conditions. High surface concentrations observed in the processed samples were attributed to a residual boron layer. Oxidation during doping via RTP results in diffusion enhancement and in consumption of the boron source. Results of cross‐sectional transmission electron microscopy (TEM) analyses confirm fast oxide growth rates during the diffusion processes in an oxygen ambient. No defects within the doped layers have been found for the process conditions used in the experiments.

Lateral inhomogeneous boron segregation during silicon thin film growth with molecular beam epitaxy

Boron segregation from submonolayer (less than 0.1 monolayer) interfacial boron deposition during thin film silicon growth with molecular beam epitaxy (MBE) in the temperature range 450 to 800°C has been investigated by secondary ion mass spectrometry (SIMS) with high depth resolution abd lateral resolution of a few micrometer. Beginning at 600°C, segregation-induced “kinks” occur in the boron profiles developing into shoulders for higher growth temperatures and/or lower deposition rates. At temperatures above 700°C at the shoulder a concentration of (1–2) × 10 19 cm -3 was found. Interfacial carbon showing significantly less segregation has been used as a marker. Laterally resolved SIMS measurements indicate inhomogeneous boron distribution, mainly due to residual substrate contamination. These inhomogeneities strongly influence the segregation behaviour, as shown by SIMS cross-section analysis, and can result in local boron penetration through multilayer structures, demonstrating the importance of appropriate cleaning procedures for residual boron substrate contamination.

Oscillopolarographic Determination of Trace Amount of Boron in Soil, Water and Plant Samples

Abstract Since boron is a necessary trace nutrient element in the physiological development of growing plants, it is important to be able to determine accurately the total amount of boron, soluble boron, and residual boron in soil samples, the boron in environmental water, and the boron in plant samples. Boron with Beryllon III can produce a stable ionic complex in buffer solution (pH 4–4.5).1 The complex yields a well-defined high-sensitivity polarographic peak at a potential of about -0.46 V (vs SCE). Under optimum conditions, the wave height is proportional to the concentration of boron in the range from 0.004 to 0.4 μg/ml. The method has been used to determine trace amounts of boron in environmental water samples, total boron, soluble boron and residual boron in soil samples, and trace amounts of boron in plant samples.