Function Of Boron Concentration Research Articles

Deactivation kinetics of supersaturated boron:silicon alloys

The effect of laser annealing on the electrical activity of boron-doped silicon wafers has been investigated as a function of boron concentration, annealing time, and annealing temperature (from 600 °C to 1050 °C). Metastable supersaturated alloys were produced by the laser annealing of ion-implanted Si 〈100〉 wafers using an excimer laser with a pulse duration of 30 ns. The extent of dopant activation, deactivation, and tendency towards precipitation were subsequently studied following rapid thermal annealing in an argon ambient using a four-point probe of the sample resistance. Sheet resistances as low as 15 Ω/□ were achieved in 200 nm layers. Following laser anneals, boron atoms remained active at concentrations of 7.5×1020/cm3 up to 800 °C for 210 s. A two-mode relaxation model including defect association and precipitation was proposed to describe the annealing behavior. These results show that laser processing can produce metastable B-doping levels, stable to moderate thermal processing, at concentrations adequate for all anticipated device structures.

Magnetic and structural properties of FeCoB thin films

The magnetic and structural properties of FeCoB thin films as a function of boron content have been investigated for applications requiring soft, high moment materials. The films were either co-sputtered from separate FeCo-35 and B targets or from a (Fe/sub 65/Co/sub 35/)/sub 90/B/sub 10/ alloy target. A peak in the coercivity was observed for small amounts of boron. Measurements of coercivity with fields applied along the radial and circumferential directions of the Si wafer showed isotropic magnetic behavior. The coercivity and saturation induction decreased with increasing amounts of boron above 2 at.%. High angle X-ray diffraction showed a broadening of the [110] peak with increasing boron, indicative of either increased microstrains or smaller average grain size perpendicular to the film. The [110] peak, however, did not shift with added boron, suggesting that on average the boron does not expand the FeCo lattice. The drop in coercivity around 10 at.% B was identified with a transition to a primarily amorphous state. Since these alloys have a high positive magnetostriction, their magnetic properties are particularly sensitive to film stress/strain. Using sputtering gas pressure as a variable, differences in coercivity were also correlated with changes in film strain.

Mid-gap states measurements of low-level boron-doped a-Si:H films

Previous measurements of the effects of low-level boron-doping on a-Si:H thin films indicated that the conductivity decreased as a function of boron concentration. This effect was reinvestigated in this work by measuring the leakage current of stacked p–i–n diodes as a function of boron concentration. The supporting measurements employed films deposited onto insulating substrates. The diodes were also examined by a charge recovery measurement to measure the dangling-bond density of states (DOS) near between 0.7 and 1.0 eV from the conduction band edge. The spectrum shows a broad band with a peak at 0.88 eV, which increases as a function of the boron concentration, but does not shift with respect to energy. The dangling-bond density increase is proportional to the B 2H 6/SiH 4 gas flow ratio, but not linear with respect to boron concentration in the film.

Evolution of {311} type defects in boron-doped structures: Experimental evidence of boron–interstitial cluster formation

Boron-doped well structures formed in Czochralski silicon are subjected to a self-implant and various anneals to form a population of type {311} defects. Quantitative transmission electron microscopy is then used to measure the residual interstitials trapped in the {311} defects as a function of boron concentration and anneal temperature. We have found a strong tendency for increased dissolution rates of {311} type defects at boron concentrations above 1018 cm−3, providing direct evidence for the formation of boron–interstitial clusters. By profiling the samples with secondary ion mass steptroscopy and comparing the results to spreading resistance measurements the degree of deactivation can be determined.

Boron concentration dependence of Raman spectra on {100} and {111} facets of B-doped CVD diamond

Abstract We have investigated Raman spectra of {100} and {111} facets of B-doped diamond crystals grown by microwave plasma assisted chemical vapor deposition as a function of boron concentration. We have used individual crystals rather than films to avoid stresses which can cause shifts and broadening of the Raman line. A small amount of diborane improves the crystal quality of deposited diamond with changing the Raman spectral features. The asymmetry and broadening of the one-phonon are due to Fano interference, and broad bands centered ca 500 and 1230 cm−1 appear.

Microstructure of Rolled Ti-46.5Al-4(CrNb,Ta,B)

ABSTRACTAn industrial Ti-46.5A1–4(CrNb,Ta) alloy, with and without boron additions, has been successfully rolled to sheet 1.5mm thick. The microstructure of the sheet material has been characterised as a function of boron content and subsequent heat treatments. It is observed that rod-like (Ti-Ta)B precipitates are effective in refining the grain structure in both as-rolled and subsequently heat treated material. As-rolled microstructures rapidly cooled from the α + γ phase field contain unstable α2, which transforms to B2 phase on annealing below the α + γ tranus. Annealing in the α-phase field can result in a designed fully lamellar microstructure.

Interactions of ion-implantation-induced interstitials with boron at high concentrations in silicon

Ion implantation of Si (60 keV, 1×1014/cm2) has been used to introduce excess interstitials into silicon predoped with high background concentrations of B, which were varied between 1×1018 and 1×1019/cm3. Following post-implantation annealing at 740 °C for 15 min to allow agglomeration of the available interstitials into elongated {311} defects, the density of the agglomerated interstitials was determined by plan-view transmission electron microscopy observation of the defects. We report a significant reduction in the fraction of excess interstitials trapped in {311} defects as a function of boron concentration, up to nearly complete disappearance of the {311} defects at boron concentrations of 1×1019/cm3. The reduction of the excess interstitial concentration is interpreted in terms of boron-interstitial clustering, and implications for transient-enhanced diffusion of B at high concentrations are discussed.

Internal stress and strain in heavily boron-doped diamond films grown by microwave plasma and hot filament chemical vapor deposition

The internal stress and strain in boron-doped diamond films grown by microwave plasma chemical vapor deposition (MWCVD) and hot filament CVD (HFCVD) were studied as a function of boron concentration. The total stress (thermal+intrinsic) was tensile, and the stress and strain increased with boron concentration. The stress and the strain measured in HFCVD samples were greater than those of MWCVD samples at the same boron concentration. The intrinsic tensile stress, 0.84 GPa, calculated by the grain boundary relaxation model, was in good agreement with the experimental value when the boron concentration in the films was below 0.3 at.%. At boron concentrations above 0.3 at.%, the tensile stress was mainly caused by high defect density, and induced by a node-blocked sliding effect at the grain boundary.

High-temperature metallurgy of advanced borated stainless steels

The high-temperature metallurgy of advanced borated stainless steels has been evaluated through differential thermal analysis, aging studies, quantitative metallography, and impact toughness measurements. Differential thermal analysis (DTA) was conducted on alloys containing a range of boron concentrations and was used to determine the temperatures associated with melting/ solidification reactions. Aging studies, conducted at temperatures near the solidus, were used to determine the effects of elevated temperature exposures on impact properties and micro-structure. Differential thermal analysis quantified the solidus and liquidus temperatures as a function of boron concentration. Impact testing of samples aged at temperatures near the solidus indicated only moderate reductions in toughness. Particle shape measurements indicated that the boride particles were initially nearly spherical and remained so during elevated temperature exposure, although some faceting and agglomeration of the borides did occur. Measurements of boride particle size distributions were used to define the time, temperature, and composition dependence of the boride coarsening. Coarsening data were analyzed in terms of current coars-ening models. These analyses indicated that the boride particle coarsening followed the theo-retically predictedt1/3 time dependence and that the coarsening rate increased with increasing volume fraction of the boride phase. Analysis of the particle size data for aging at various temperatures indicated that the boride coarsening was consistent with the activation energy for Cr diffusion in austenite. Scanning electron microscopy of the impact fracture surfaces showed that the failure mode in isothermally heat-treated samples was ductile and essentially identical to the failure mode for as-received material.

Magnetoresistance of the magnetically ordered icosahedral quasicrystals Al-Pd-Mn-B

The transverse magnetoresistance has been measured for the newly discovered magnetically ordered icosahedral quasicrystals Al70−xPd15Mn15Bx (x=0,2,4,6,8,10). Experiments were conducted at 4.2 K in magnetic fields up to 5.5 T. The results showed a systematic change as a function of boron concentration. The magnetoresistance for x=0,2,4,6 showed a negative field dependence which became weak with increasing x. The samples with x=8,10 showed a negative magnetoresistance at low fields, which became positive for higher applied fields. The minimum in the magnetoresistance shifted to lower field value with increasing boron content (to about 0.5 T for 10 at. %B). The analysis of the results has been based on the theory of three-dimensional weak localization, with a strong influence of spin-orbit scattering. The magnetoresistance is negative for low boron concentration due to weak spin-orbit scattering, and is positive for high boron concentration due to strong spin-orbit scattering.

Inorganic factors in the synthesis of large-pore borosilicates from tricyclo [5.2.1.0 2,6] decane organo-cations

The synthesis of borosilicate zeolites was carried out using two stereoisomers of the N,N,N-trimethyl-8-tricyclo [5.2.1.0 2,6]decane ammonium cation. Each isomer produces two different zeolites as a function of boron concentration in the synthesis. All four zeolites produced are large pore (twelve-ring), consistent with the tendencies of this family of organo-cations to stabilize pores greater than 6 Å. Higher boron substitution favored multi-dimensional zeolites. Whether this is a result of substructure features needed to incorporate trivalent elements or a consequence of the potential amount of charge balancing needed for a pore-filling organo-cation is discussed. The syntheses were adversely affected by using sodium borate to increase boron concentration, with the phyllosilicate, Kenyaite, being produced instead. Keeping the sodium concentration sufficiently low and varying boron with boric acid allowed for successful crystallization of Beta or SSZ-33 zeolites, depending upon the organo-cation isomer. Beta zeolite was more efficient in incorporating boron into the structure.

The Effects of Process‐Induced Defects on the Chemical Selectivity of Highly Doped Boron Etch Stops in Silicon

Chemical etch selectivity using and water was determined for solid‐source diffused, ion implanted, and in situ, epitaxially‐grown boron‐doped etch stops formed in single‐crystal, polycrystalline, and low‐percentage germanium‐alloyed silicon. Defects in the etch stops were investigated using defect etching and Nomarski optical interference microscopy, scanning electron microscopy with energy dispersive x‐ray, and transmission electron microscopy. Defect density and type were found for all samples. Experimental results show that etch selectivity is not only a function of boron concentration but is also a function of the defect density, and to a lesser degree, defect type. Etch selectivity degrades approximately proportional to a one‐fourth power relationship with defect density.

Self-propagating high-temperature synthesis of titanium borides

The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated. Using the plane wave propagation mode, the synthesis of titanium borides in the cold-pressed cylindrical specimens of the component powder mixtures was effected and was studied as a function of boron content in the initial mix and the specimen size. SHS reaction in compacts having diam. of 6 mm or less and high bulk density could not be initiated and/or sustained and was considered to be a result of rapid heat dissipation.

Microwave permeability and structural properties of CoFeSiB alloys prepared by ion beam sputtering (abstract)

Structural properties and microwave permeability of CoFeSiB (Co content ≊87 at. %) films prepared by an ion beam deposition technique were investigated as a function of boron content and growth temperature. A microcrystalline phase is obtained for low boron content and substrate temperatures above 80 °C. X-ray rocking curve indicate that the material is textured with 〈111〉 direction perpendicular to the film plane. The dispersion of the 〈111〉 axis is below 6°. Kerr measurements show that the magnetization is oriented in the film plane and has a uniform direction over the sample. Moreover, coercive force Hc is no higher than 0.5 Oe. The gyromagnetic resonance frequency is 2.2 GHz while the initial permeability is 700 along the hard axis and zero along the easy axis. In contrast, when substrate temperature is decreased below 50 °C, the films are amorphous. Lorentz microscopy domain observations and Kerr effect reveal a local dispersion of magnetization. This is related to the higher coercive force observed in the amorphous samples. As a consequence, microwave permeability shows several resonances and is isotropic in the film plane. It cannot be described by the Bloch–Bloembergen model.

Two-element track autoradiography of boron and nitrogen in various materials

Abstract A non-destructive method of quantitative autoradiographic analysis of boron and nitrogen in a single object is described. Plastic track detectors (PTDs) were used to record tracks of particles from 10B(n, α)7Li and 14N(n, p)14C reactions. The potentialities of the method in determining the nitrogen content as a function of boron content in an object using a CR-39 detector are estimated. The application of the method to microanalysis of individual precipitates in the structure of iron-chromium alloys is demonstrated.

Effects of boron and heat treatment on structure of dual-phase Ti-TiC

Anin situ method was developed to fabricate a two-phase mixture of titanium carbide in a titanium matrix by solidification from a titanium-carbon melt. The solidified morphology consisted of three-dimensional TiC dendrites in a titanium matrix. The secondary dendrite arm spacing was found to be influenced by the presence of boron. The structure and microhardness of the components as a function of boron content and heat-treatment procedure were determined. Heat treatment plays a major role in the structure while the effect of boron is minimal. Results from X-ray diffraction analysis indicate that the solidified carbide is very rich in vacancies in the carbon sublattice. Annealing leads to a redistribution of the titanium atoms to occupy some of the vacant carbon sites. This thermal redistribution effect results in a dramatic decrease in the hardness of the carbides. The lattice parameter measurement supports the above structure evolution.

Characterization of boron-doped silicon epitaxial layers by x-ray diffraction

Heavily boron-doped (Na≳1×1019 cm−3)Si epilayers grown on (100)Si by molecular beam epitaxy are investigated using double-crystal x-ray diffractometry. The variation of the Si lattice constant as a function of boron concentration is obtained from a combination of (400) rocking curve analysis and secondary-ion mass spectrometry measurements on uniformly doped epilayers. This result is then used to determine the concentration profile in nonuniformly doped structures via dynamical simulations of experimental x-ray rocking curves. The structures investigated include a pipi doping superlattice and the results are found to be in excellent agreement with secondary-ion mass spectrometry depth profiles.

Mossbauer and soft X-ray appearance potential spectroscopy of iron-nickel-boron metallic glasses

Mossbauer spectra and soft X-ray appearance potential spectra from (Fe0.5Ni0.5)1-xBx metallic glasses for 0.16<or=x<or=0.26 are reported. Mossbauer and magnetic data are determined by the occupation difference between majority and minority subbands. Appearance potential spectra, on the other hand, reveal the total density of unoccupied states. From a combination of the two sets of data for iron the authors derive the change of subband occupation as a function of boron concentration. As a result they find charge transfer not only from boron to empty minority iron states but also from majority to minority states. Unoccupied d states of nickel do not show any change as a function of boron content.

Effects of boron addition on a melt-spun Ni-base superalloy

Melt spinning of a nickel-base superalloy containing various amounts of boron up to 3.0 wt% has been carried out to explore the potential of extended boride alloyability through rapid solidification. More specifically, the melt-spinning castability, ribbon-solidification microstructure and heat-treatment precipitation were studied as a function of boron concentration by using analytical electron microscopy and a number of other techniques. Special attention was given to the boride structure, chemistry and thermal stability. The microstructural observations were then correlated to the ribbon bend ductility tested in as-cast and annealed conditions. On the basis of the present results, future investigation of superalloys using the rapid solidification process and the boride alloying concept is discussed.

Studies on the valence state of Ce and Eu in some new boron and silicon containing rare earth intermetallic compounds

Compounds of the formula RPd3B x (R=rare earth with 0⩽x⩽1) and RPd3Si x (R=La, Ce, Eu with 0⩽x⩽0.3) can be prepared by alloying boron or silicon with parent RPd3 compounds. Addition of boron (silicon) does not change the structure but results in lattice expansion. The valence state of Ce in CePd3 and that of Eu in EuPd3 is strongly influenced by boron and silicon. Ce is known to be in a valence fluctuating state in CePd3 while Eu is trivalent (J=0) in EuPd3. The increase in the lattice parameter as a function of boron concentration is observed to be larger in CePd3B x and EuPd3B x compared to that in other RPd3B x alloys giving the first indication of the change in the valence state of Ce and Eu. This is confirmed from susceptibility measurements. With the addition of boron, susceptibility increases and the effective paramagnetic moments approach the values corresponding to Ce3+ (J=5/2, μeff=2.54 μ B ) and Eu2+ (J=7/2, μeff=7.94 μ B ) in the two alloy systems CePd3B x and EuPd3B x respectively. In the case of europium alloys,151Eu Mossbauer studies point out the importance of near-neighbour environment effects. Further, in EuPd3B, where all the europium ions are crystallographically equivalent, a single Mossbauer line, with an isomer shift characteristic of europium ions in valence-fluctuating state, is observed at 300 K. However, at 88 K the Mossbauer absorption splits into two lines corresponding to europium ions in two valence states,e.g. divalent- and trivalent-like. Such a behaviour indicates thermally-induced charge ordering of europium ions. Addition of silicon to CePd3, like boron, results in unusual lattice expansion and changes the valency of cerium towards 3+. the valence change is further corroborated by susceptibility measurements. In EuPd3Si x alloys, susceptibility and Mossbauer studies indicate that in the limiting single phase alloy EuPd3Si0.25 the europium ions are on the verge of valence instability. Susceptibility results on CeRh3B x alloys are also presented.