Boron Surface Research Articles

Surface proximity and boron concentration effects on end-of-range defect formation during nonmelt laser annealing

The effects of surface proximity and B concentration on end-of-range defect formation during nonmelt laser annealing in preamorphized silicon have been studied. These effects were analyzed by observing the activation and diffusion of an ultrashallow B implant, using Hall effect and secondary ion mass spectrometry measurements. By adjusting the preamorphizing implant and laser annealing conditions, B deactivation and diffusion were minimized, resulting in a sheet resistance of ∼600Ω∕sq with a 16nm junction depth. This is attributed to a combination of enhanced dissolution of end-of-range defects and preferential formation of B-interstitial clusters due to the surface proximity and high B concentration, respectively.

Surface characterization of silver and palladium modified glassy carbon

In this work, the influence of silver and palladium on the surface of undoped, boron doped and phosphorus doped glassy carbon has been studied. The silver and palladium concentrations in solution, after metal deposition, were measured by atomic absorption spectrophotometer. The morphology of metal coatings was characterized by scanning electron microscopy. In order to investigate the nature and thermal stability of surface oxygen groups, temperature-programmed desorption method combined with mass spectrometric analyses, was performed. The results obtained have shown that silver and palladium spontaneously deposit from their salt solutions at the surface of glassy carbon samples. Silver deposits have dendrite structure, whilst palladium forms separate clusters. The highest amount of both silver and palladium deposits at the surface of sample containing the highest quantity of surface oxide complexes. It has been concluded that carboxyl groups and structure defects are responsible for metal reduction. Calculated desorption energies have shown that the surface modification by metal deposition leads to the formation of more stable surface of undoped and doped glassy carbon samples.

High Surface and High Nanoporosity Boron Nitride Adapted to Hydrogen Sequestration

High surface area nanoporous powders of hexagonal boron nitride (h-BN) have been prepared from molecular precursors to be used for hydrogen sequestration. The more promising samples were obtained using a precursor derived from trichloroborazine (TCB). The precursor was first reacted with ammonia at room temperature leading to the molecular complex Cl3B3N3H3, 6 NH3 which was heated up to 650 °C under ammonia and then up to 1000 °C under nitrogen, giving rise to a high reactive h-BN powder. This crude powder was stabilised by an annealing up to 1800 °C under nitrogen atmosphere leading to a very stable compound exhibiting a specific area of more than 300 m2·g-1 and presenting a very specific nanometric spherical texture. Some samples were doped with platinum (about 1 wt.%) to enhance the activity of pure h-BN using an original one step synthesis route starting from a mixture of BN and Pt precursors. Attempts to sequester hydrogen into these powders were made successfully at -196 °C under 10 MPa, but the stored amount was only about 0.3 wt.% and the platinum added BN powders did not lead to an enhancement of the storage capacity.

Can we predict the location of impurities in diamond nanoparticles?

Although most commercial nanodiamonds contain impurities, it is still largely unknown whether a given species will be located within the core or at the surface of the nanocrystals. This question is significant, since in the former case a suitable atom may act as a dopant, but in the latter case it will merely be an adsorbate. Presented here are density functional tight-binding simulations examining the potential energy surface of substitutional nitrogen and boron in diamond nanocrystals, directly comparing results for a number of crystallographically inequivalent sites. The results predict that both nitrogen and boron are metastable within the core of bucky-diamond and nanodiamond, and are therefore unlikely to be stable as dopants within these nanoparticles.

Growth kinetics of borided layers: Artificial neural network and least square approaches

The present study evaluates the growth kinetics of the boride layer Fe 2B in AISI 1045 steel, by means of neural networks and the least square techniques. The Fe 2B phase was formed at the material surface using the paste boriding process. The surface boron potential was modified considering different boron paste thicknesses, with exposure times of 2, 4 and 6 h, and treatment temperatures of 1193, 1223 and 1273 K. The neural network and the least square models were set by the layer thickness of Fe 2B phase, and assuming that the growth of the boride layer follows a parabolic law. The reliability of the techniques used is compared with a set of experiments at a temperature of 1223 K with 5 h of treatment time and boron potentials of 2, 3, 4 and 5 mm. The results of the Fe 2B layer thicknesses show a mean error of 5.31% for the neural network and 3.42% for the least square method.

CVD Delta-Doped Boron Surface Layers for Ultra-Shallow Junction Formation

A new doping technique is presented that uses a pure boron atmospheric/low-pressure chemical vapor deposition (AP/LPCVD) in a commercially available epitaxial reactor to form less than 2-nm-thick δ-doped boron-silicide (BxSi) layers on the silicon surface. For long exposure B segregates at the surface to form a very slow growing amorphous layer of pure B (α-B). The electrical properties of the as-deposited α- B/BxSi stack have been studied by fabricating and measuring diodes where the B depositions are formed directly in the diode contact windows for different exposure times. It is demonstrated that the presented doping technique can be used to form high-quality δ-doped p+n junctions. Moreover, the formed α-B/BxSi layer is an attractive source of high-concentration B dopants for thermal annealing processes that does not induce any transient-enhanced diffusion (TED) effects.

Photo‐ and electrochemical bonding of DNA to single crystalline CVD diamond

AbstractAlkene and nitrophenyl molecules have been covalently bonded to single crystal diamond using photochemical and electrochemical techniques. The surface density of electrochemically grafted nitrophenyl groups is about 5% of a monolayer (8 × 1013 molecules/cm2) on initially H‐terminated diamond. Covalently‐bonded nitrophenyl groups on single‐crystalline diamond are characterized to have two successive reversible one‐electron transfer reactions due to a regularly‐oriented arrangement. On oxidized surface of boron doped electrodes, a slightly (10%) smaller density is detected. Photochemical attachment of alkene molecules results also in a well arranged films as detected by angle resolved X‐ray photoelectron spectroscopy (XPS). The density of 10‐amino‐dec‐1‐ene molecules protected with trifluoroacetic acid (“TFAAD”) is calculated to be in the range 2 × 1014 molecules/cm2. The bonding mechanism of Alkene molecules to high quality hydrogen terminated single crystalline CVD diamond has been characterized using a variety of experiments which show that photo‐excited electrons of 5 eV energy trigger the photochemical attachment. The minimum time required to achieve a monolayer attachment of TFAAD molecules on (100)(2 × 1):H diamond is discussed and compared with experimental data from XPS. The benzene and alkene linker molecules are then reacted with the heterobifunctional cross linker sulphosuccinimidyl‐4‐(N‐maleimidomethyl)cyclohexane‐1‐carboxylate and finally with thiol‐modified ss‐DNA to produce a DNA‐modified diamond surface. The interaction with complementary and partially mismatched DNA is characterized by fluorescence microscopy. Microscopic properties of DNA layers on diamond have been characterized by contact‐ and oscillatory‐mode atomic force microscopy (AFM). A comparison of bonding forces, detected by contact mode AFM, reveals significant bonding strength differences. For both, electro‐ and photochemically bonded DNA, tilted molecule arrangements are detected, with angles in the range 30 ° to 46° with respect to the diamond surface. The DNA films are dense with a surface roughness of about 5 Å. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CVD Delta-Doped Boron Surface Layers for Ultra-Shallow Junction Formation

not Available.

11B NMR investigation of boron interaction with mineral surfaces: Results for boehmite, silica gel and illite

Boron is an important micronutrient for plants but is toxic at high pore solution concentrations. Its mobility and migration in many geochemical environments is often controlled by reactions with mineral surfaces, and thus its speciation on mineral surfaces has been extensively investigated. Most previous studies have used IR spectroscopy to characterize the surface B-environments. We present here the first 11B MAS NMR study of surface sorbed boron on minerals. The results demonstrate the capability of this method to effectively probe the local structure of the sorption sites at total B-concentrations in the samples as small as 0.03 wt% and to provide insight into the mechanisms of sorption. Signal is readily resolved for both trigonal (B(3)) and tetrahedral (B(4)) boron exchanged onto boehmite, silica gel and illite, and the resonances are readily assigned on the basis of chemical shift and quadrupole coupling constant. Boron surface densities on illite are approximately order of magnitude greater than on silica gel or boehmite. For boehmite, both B(3) and B(4) occur dominantly as inner-sphere complexes formed by ligand exchange reaction with surface aluminol sites. The B(3)/[B(3) + B(4)] ratio of approximately 0.87 does not vary significantly with pH from 3 to 11, with solution B-concentration, or with washing. The occurrence of B(3) and B(4) as inner-sphere complexes is in agreement with previous suggestions from IR studies of B-sorption on iron hydroxide, allophone, kaolinite, and hydrous ferric oxide. For silica gel, B(3) and B(4) occur principally as outer-sphere complexes or as residual precipitate from un-removed solution. The B(3)/B(4) ratio decreases with increasing pH paralleling the speciation in solution, but the relative abundance of B(4) is greater than in solution. A small fraction of the B(4) occurs as inner-sphere complexes with B(4)–O–Si linkages formed by ligand exchange reaction with silanol sites. For illite, surface boron occurs as outer-sphere B(3) and B(4), as for silica gel, and as inner-sphere B(3) and B(4), as for boehmite. Outer-sphere B(3) and B(4) are dominant at pH 3 and 5, whereas inner-sphere B(3) and B(4) are dominant at pH 9 and 11. The inner-sphere complexes probably form dominantly by ligand exchange reactions involving sites on the broken edges of illite layers.

Boron as an anti-surfactant in sublimation growth of AlN single crystals

We study the influence of B evaporating from BN crucible walls on the nucleation and growth of AlN by a physical vapor transport. An experimental analysis by means of electron microscopy and optical spectroscopy shows that B incorporation and surface segregation depends on the orientation of the respective surface facet. Surface segregation is found to be predominant on {11-20} facets. This leads to the formation of wurtzite BN nuclei on these facets which extend over the whole surface and may form closed layers. Both boron surface segregation and growth of BN nuclei influence Al and N adsorption and surface diffusion, and in consequence reduce the growth rate. The differences in surface segregation of B on different facets can be understood in terms of incorporation kinetics of boron adatoms into the AlN crystal. B thus acts as a facet selective antisurfactant.

Computer simulation of monolayer growth kinetics of Fe2B phase during the paste-boriding process: Influence of the paste thickness

This paper deals with the effect of boron paste thickness on the study of the monolayer growth kinetics of Fe2B phase forming on AISI 1045 steel by the paste-boriding process. A mathematical diffusion model based on the Fick's phenomenological equations was applied in order to estimate the growth rate constant at (Fe2B/γ-Fe) interface, the layer thickness of iron boride as well as the associated mass gain depending on the boriding parameters such as time, temperature and surface boron concentration related to the boron paste thickness. The simulation results are found to be in a fairly good agreement with the experimental data derived from the literature.

Study of boron and molybdenum plasmas on multipulse interaction of femtosecond radiation with a target

Laser plasmas generated by femtosecond radiation on the surface of boron and molybdenum targets are investigated by the shadowgraph method. The modes of single-pulse and multipulse interaction of laser radiation with a target are compared. The occurrence of plasma bullets is discussed, which were observed on both single-pulse and multipulse interaction with the same area of a target. The wavefront velocities of expanding boron and molybdenum plasmas were measured to be 5 × 104 and 6 × 103 m s−1, respectively. The electron density measured by interferometry using a time delay of 800 ps in a boron plasma excited by 795-nm radiation with an intensity of 1016 W cm−2 amounted to 8 × 1019 cm−3. The correlation between some specific features of the plasma and the generation of the 3/2 harmonic, observed on multipulse interaction of femtosecond radiation with a boron target, is discussed.

Amperometric detection of ultra trace amounts of Hg(I) at the surface boron doped diamond electrode modified with iridium oxide

Iridium oxide (IrOx) films formed electrochemically on the surface boron doped diamond electrode by potential cycling in the range −0.2 to 1.2 V from a saturated solution of alkaline iridium(III) solution. A strongly adherent deposit of iridium oxide is formed after 5–10 potential scans. The properties, stability and electrochemical behavior of iridium oxide layers were investigated by atomic force microscopy and cyclic voltammetry. The boron doped diamond (BDD) electrode modified with electrodeposition of a thin film, exhibited an excellent catalytic activity for oxidation of Hg(I) over a wide pH range. The modified electrode shows excellent analytical performance for Hg(I) amperometric detection. The detection limit, sensitivity, response time and dynamic concentration ranges are 3.2 nM, 77 nA μM −1, 100 ms and 5 nM–5 μM. These analytical parameters compare favorably with those obtained with modern analytical techniques and recently published electrochemical methods.

Boron isotopic fractionation related to boron sorption on humic acid and the structure of surface complexes formed

Boron isotopic fractionation during adsorption onto Ca-flocculated Aldrich humic acid (HA) has been investigated experimentally as a function of solution pH at 25°C and I = 0.15 M. Boron aqueous concentration and isotopic composition were determined by Cs 2BO 2 + Positive Thermal Ionization Mass Spectrometry analysis, while the structure of B surface complexes on HA was characterized using 11B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). Significant B sorption on HA was observed at 6 < pH < 12 with a maximum value of Kd, the partition coefficient between adsorbed and aqueous boron, equal to 40 at pH = 9.5–10. Combined 11B MAS NMR analysis and FITEQL modeling of B sorption on HA showed that this element forms tetrahedrally coordinated five- or six-membered ring chelates, most likely 1,2-diol and 1,3-diol complexes at alkaline pH (8 < pH < 11) and dicarboxylic complexes at near neutral conditions (6 < pH < 9). Results of this study demonstrate for the first time that boron sorption on HA induces a strong pH-dependent isotope fractionation—with 11B depleted at the surface of HA—that reaches a maximum at 5 < pH < 9 (α = 0.975, Δ = −25‰) and decreases sharply at pH >9. The measured isotope fractionation cannot be modeled assuming that the isotopic composition of the sorbed borate species is identical to that of B(OH) 4 - species in the parent solution. It is shown that the extent of isotopic fractionation depends not only on B aqueous speciation but also on the distribution and structure of the borate surface complexes formed. In agreement with energetic constrains, calculation of the isotope fractionation factors between aqueous boric acid and boron surface complexes suggests that the formation of the strained six-membered ring 1,3-diol complex yields a much higher fractionation (α BL P1 −III = 0.954–0.960, Δ = −41/-47‰) than that of the very stable five-membered ring 1,2-diol (α BL P2 −III = 0.983, Δ = −18‰). The results of this study open new perspectives to understand and model boron biogeochemical cycle. It is predicted that boron sorption onto organic matter can have important consequences for the boron isotopic composition of surface water reservoirs (seawater, groundwater, soil waters) in which either abundant organic surfaces or significant boron concentrations are available. In addition, the large isotope fractionation between aqueous boric acid and surface boron-organic complexes found in the present work makes boron a promising tracer of biologic activity.

A diffusion model for describing the bilayer growth (FeB/Fe 2B) during the iron powder-pack boriding

In this paper, a diffusion model is proposed for studying the bilayer growth kinetics (FeB/Fe 2B) on pure iron substrate during the powder-pack boriding in the temperature range of 1023–1273 K. This model based on Fick's laws was solved, under certain assumptions, considering a parabolic growth of iron borides. For this purpose, a computer simulation program was created for predicting the boride layer thickness as a function of process parameters (temperature, time and surface boron content). A fairly good agreement was observed between the simulation calculations and experimental data derived from the literature.

On the lifetime of wall conditioning layers

Motivated by the large-scale application of tungsten as first wall material in the tokamak ASDEX Upgrade, we performed a numerical study about the erosion behaviour of boron films from carbon and tungsten substrates using the Monte-Carlo code TRIDYN. We compared the erosion caused by monoenergetic ions as well as the case of a plasma with a temperature of 10eV containing boron as an impurity. In both cases we obtained, that on tungsten substrates a pure tungsten surface film is formed with some boron inventory buried underneath. For a carbon substrate, however, the boron inventory depletes slowly due to ion beam mixing effects in the case of monoenergetic ion bombardment. In the case of a thermal plasma containing boron as an impurity, an equilibrium boron surface concentration is established at high fluences. This boron concentration is strongly enhanced as compared to the boron impurity concentration in the plasma.

Surface modification of boron fibres for improved strength in composite materials

When boron fibres are combined with an organic matrix, such as an epoxy resin, a high-performance composite structure is created. This study investigates the surface chemistry of plasma- and organosilane-treated boron fibres with the key aim to improving the adhesion properties between the boron fibre and the epoxy matrix. Optimisation of this interfacial region plays a critical role in influencing the mechanical behaviour of composite materials and has considerable industrial applications in the aerospace and manufacturing industries. The surface chemistry of a model boron surface and boron fibres was monitored using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Initial investigation of the as-received fibres showed the presence of silicone contamination on the fibre surface, which would affect adhesion. Removal of this contaminant through solvent cleaning and plasma oxidation provided an ideal surface for attachment of the organosilane adhesion promoter. A model for the interaction of the organosilane with a boron surface is proposed. The pull-out strength of boron fibres, with different surface treatments, embedded in the epoxy resin was measured using a custom designed adhesiometer. Compared with as-received boron fibres, a 6-fold improvement in the apparent interfacial shear strength was achieved for the organosilane treated fibres. Optical microscopy was used to determine the failure mechanisms between the fibre and epoxy resin. Typically, as the surface treatment improved adhesion, the locus of failure changed from the boron–epoxy interface to failure within the epoxy and ultimately fibre breakage.

SC1 Cleaning Effect on Electrical Characteristics of 256 Mbit Mobile DRAM with Dual Gate Oxide

The electrical effects of RCA standard clean 1 (SC1) prior to the second gate oxidation for dual gate oxide formation was investigated by splitting the SC1 cleaning time for a 256 Mbit mobile dynamic random access memory (DRAM) operating at 1.8 V. The etch rate with respect to the oxide by SC1 cleaning was approximately 1.6 Å/min. The threshold voltage of the n-type metal-oxide-semiconductor field-effect transistor (nMOSFET) in the thin oxide region was shown to be a similar value with varying the SC1 time, while the absolute threshold voltage of the pMOSFET increased by 4%. In the thick oxide MOSFETs, decreased by 15%, while on the contrary, increased by 7%. was found to be mainly dependent on the decreased gate oxide thickness due to the deep boron peak depth. However, appeared to be more dependent on the decrease of surface boron concentration due to a shallow boron peak and also to the influence by the enhanced pocket implantation effect. Consequently, it is proposed that the SC1 cleaning time should be less than 300 s in order to retain the reliable electrical properties for both thin and thick gate oxide MOSFETs due to the drastic decrease of and breakdown voltage © 2004 The Electrochemical Society. All rights reserved.

BORON PARTICLE IGNITION AND THE MARANGONI EFFECT

The use of boron as a high-energy fuel additive is generally compromised by the appearance of a strongly protective liquid oxide layer that covers the boron surface. The paper predicts that for ambient temperatures well below 1820 K this surface layer can be destabilized by the Marangoni effect, due to the peculiarity of boron oxide for which the Marangoni numbers are positive. To show the destabilization, a thin-film model is employed that allows the oxide flow field to be derived in the creeping-flow approximation. Ignition, assisted by a heat flow toward the particle, may then be caused by the Marangoni effect, which is shown to entail the spreading of punctures and ruptures in the oxide layer, leading to layer thinning or even complete layer removal. Since previous models of boron particles ignition insisted on conservation of symmetry, they were forced to expressly exclude the treatment of punctures and ruptures in the layer because their appearance constitutes an act of symmetry breaking.

Analysis of historical salinity and boron surface water monitoring data from the San Joaquin River watershed: 1985-2002.

The objectives of this study were to use both parametric and probabilistic approaches to analyze water column concentrations of both salinity (24,845 measurements) and boron (13,028 measurements) from numerous investigations conducted in the San Joaquin River watershed from 1985 to 2002 to assess spatial and temporal trends and determine the probability of exceeding regulatory targets during both the irrigation and non-irrigation season. Salinity and boron concentrations from 26 mainstem and tributary sites were highly correlated based on this 17 yr data set. Generally, salinity and boron concentrations were higher in winter/spring and lower in summer/fall; higher concentrations of both constituents were reported in tributary sites when compared with the mainstem San Joaquin River. Approximately half the sites showed showed a negative correlation between flow and both constituents. Concentrations of both salinity and boron were somewhat variable with flow conditions for the other sites. Both linear and curvilinear trends were inconsistent over time. The salinity 90th centiles for the 26 sites ranged from 143 to 7,559 micros cm(-1) with the highest 90th centiles in tributary sites. Probabilistic analysis of salinity 90th centiles by year for five sites with extensive data showed a significant decrease over time at two sites and no significant trend for the other three sites. The probability of exceeding the salinity targets during either the irrigation (700 microm cm(-1)) or non-irrigation (1,000 micros cm(-1)) season was greater than 19% for all but three sites. The boron 90th centiles for the 26 sites ranged from 0.41 to 13.6 mg L(-1) with the highest 90th centiles from tributary sites. Probabilistic analysis of the boron 90th centile values by year for the five sites with the most extensive data showed a significant decrease over time at two sites and no significant trend for the other three sites. The probability of exceeding the boron target during the irrigation season (0.80 mg L(-1)) and non-irrigation (1.0 mg L(-1)) season was greater that 18% for all but three sites. Results from this analysis have important regulatory implications as targets for both salinity and boron are frequently exceeded at various sites in the San Joaquin River watershed.