Boron Films Research Articles

Formation of borohydride-reduced nickel–boron coatings on various steel substrates

Electroless nickel–boron coatings are widely used in industrial on various substrates: ferrous and non-ferrous alloys mainly but also in some cases non-metallic materials. However, their growth process is still not fully understood and the influence of the nature of the substrate on this process is completely unknown.The formation of electroless nickel–boron was observed on five ferrous alloys: a mild steel, a high carbon unalloyed steel, a cryogenic steel (that contains 9wt.% nickel), an austenitic stainless steel and an austeno-ferritic (duplex) stainless steel.Nickel–boron films were prepared by electroless deposition, using sodium borohydride as a reducing agent. Samples were immersed in a plating bath for times ranging from 5s to 60min. The influence of the nature of the substrate on the initial deposition of the coatings was investigated in detail: the initiation mechanism was identified for all substrates and it was found to be related to catalytic oxidation of the reducing agent rather than to a displacement process.The delay before initiation was influenced by the nickel content of the coating and by a high number of grain boundaries.In all cases, the plating rate varied with plating time, with a slower period during the first 10min that corresponds to morphological modification of the coating.

Synthesis of Atomically Thin Boron Films on Copper Foils.

Two-dimensional boron materials have recently attracted extensive theoretical interest because of their exceptional structural complexity and remarkable physical and chemical properties. However, such 2D boron monolayers have still not been synthesized. In this report, the synthesis of atomically thin 2D γ-boron films on copper foils is achieved by chemical vapor deposition using a mixture of pure boron and boron oxide powders as the boron source and hydrogen gas as the carrier gas. Strikingly, the optical band gap of the boron film was measured to be around 2.25 eV, which is close to the value (2.07 eV) determined by first-principles calculations, suggesting that the γ-B28 monolayer is a fascinating direct band gap semiconductor. Furthermore, a strong photoluminescence emission band was observed at approximately 626 nm, which is again due to the direct band gap. This study could pave the way for applications of two-dimensional boron materials in electronic and photonic devices.

Synthesis of Atomically Thin Boron Films on Copper Foils

AbstractTwo‐dimensional boron materials have recently attracted extensive theoretical interest because of their exceptional structural complexity and remarkable physical and chemical properties. However, such 2D boron monolayers have still not been synthesized. In this report, the synthesis of atomically thin 2D γ‐boron films on copper foils is achieved by chemical vapor deposition using a mixture of pure boron and boron oxide powders as the boron source and hydrogen gas as the carrier gas. Strikingly, the optical band gap of the boron film was measured to be around 2.25 eV, which is close to the value (2.07 eV) determined by first‐principles calculations, suggesting that the γ‐B28 monolayer is a fascinating direct band gap semiconductor. Furthermore, a strong photoluminescence emission band was observed at approximately 626 nm, which is again due to the direct band gap. This study could pave the way for applications of two‐dimensional boron materials in electronic and photonic devices.

Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO2 by capacitance voltage measurement on inverted metal oxide semiconductor structure

We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO2. The ncSi thin films with high resistivity (200–400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO2/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 1018–1019 cm−3 despite their high resistivity. The saturation of doping at about 1.4 × 1019 cm−3 and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10−3 cm2/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

Fabrication of sandwich-type MgB2/Boron/MgB2 Josephson junctions with rapid annealing method

Sandwich-type MgB2/Boron/MgB2 Josephson junctions were fabricated using magnetron sputtering system. The rapid-anneal process was adopted to replace traditional way of annealing, trying to solve the problem of interdiffusion and oxidation with multilayer films. The boron film was used as barrier layer to avoid the introduction of impurities and improve reproducibility of the junctions. The bottom MgB2 thin films deposited on c-plane sapphire substrate exhibits a critical temperature TC of 37.5 K and critical current density JC at 5 K of 8.7 × 106 A cm−2. From the XRD pattern, the bottom MgB2 thin film shows c-axis orientation, whereas the top MgB2 became polycrystalline as Boron barrier layer grown thicker. Therefore, all junction samples show lower TC than single MgB2 thin film. The junctions exhibit excellent quasiparticle characteristics with ideal dependence on temperature and Boron barrier thickness. Subharmonic gap structure was appeared in conductance characteristics, which was attributed to the multiple Andreev reflections (MAR). The result demonstrates great promise of this new fabrication technology for MgB2 Josephson junction fabrication.

In‐situ observation of chemical vapor deposition using SiHCl3 and BCl3 gases

AbstractThe lowest temperature for initiating the film deposition was evaluated by in situ monitoring using a highly sensitive langasite crystal microbalance (LCM) in order to produce a thin boron doped silicon film using trichlorosilane gas and boron trichloride gas at low temperatures. The thin films of silicon, boron and boron‐doped silicon were individually formed from the trichlorosilane gas, boron trichloride gas and their gas mixture, respectively, on the LCM. The silicon film deposition occurred between 570 and 600 °C, while the boron film deposition occurred between 470 and 530 °C. The film deposition from both gases occurred at temperatures higher than 530 °C. Based on secondary ion mass spectrometry measurements, the boron‐doped silicon film was determined to be formed on the silicon substrate at 570 °C. Thus, the LCM could be useful for developing a thin film formation process including that for doping. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Free-standing boron and oxygen co-doped carbon nanofiber films for large volumetric capacitance and high rate capability supercapacitors

Carbon-based materials are the most common and important supercapacitor electrode materials, and have been attracting much attention for researchers. Although much work has focused on increasing the gravimetric capacitance of carbon materials, it is highly needed to obtain high volumetric capacitance for real compact device application. Therefore, a finely tuned carbon material structure with both optimal gravimetric and volumetric capacitances has been becoming a considerable challenge. In this work, we synthesized free-standing boron and oxygen co-doped carbon nanofiber (BO-CNF) films for the first time. Both high gravimetric and volumetric capacitances (192.8Fg−1 and 179.3Fcm−3 at 1Ag−1) can be obtained by an optimized design with regulating the heteroatom content and packing density. Meanwhile, the BO-CNF film with a relatively high packing density exhibits an excellent rate capability (78.5% capacitance retention from 1 to 100Ag−1), which is due to the formation of continuous electrolyte ion diffusion network as well as good electrical conductivity. Such BO-CNF film provides an excellent platform for depositing polyaniline active materials and the boron dopant can be recycled to reduce the cost for the possibly scalable application.

XPS, SIMS and FTIR-ATR characterization of boronized graphite from the thermonuclear plasma device RFX-mod

In this paper the characterization of a thin (tens of nanometers) boron layer on fine grain polycrystalline graphite substrate is presented. The boron film is used as conditioning technique for the full graphite wall of the Reversed Field eXperiment–modified (RFX-mod) experiment, a device for the magnetic confinement of plasmas of thermonuclear interest. Aim of the present analysis is to enlighten the chemical structure of the film, the trapping mechanism that makes it a getter for oxygen and hydrogen and the reason of its loss of effectiveness after exposure to about 100s of hydrogen plasma. X-ray Photoelectron Spectroscopy (XPS), Secondary Ions Mass Spectrometry (SIMS) and Fourier Transform Infra Red spectroscopy in combination with the Attenuated Total Reflectance (FTIR-ATR) were used to obtain the structure and the chemical composition of graphitic samples as coated or coated and subsequently exposed to hydrogen plasma after boron deposition.The boron layers on the only coated samples were found to be amorphous hydrogenated boron carbide plus a variety of bonds like B-B, B-H, B-O, B-OH, C-C, C-H, C-O, C-OH. Both the thickness and the homogeneity of the layers were found to depend on the distance of the sample from the anode during the deposition. The samples contained oxygen along the layer thickness, at level of 5%, bound to boron. The gettering action of the boron is therefore already active during the deposition itself. The exposure to plasma caused erosion of the boron film and higher content of H and O bound to boron throughout the whole thickness. The interaction of the B layer with plasma is therefore a bulk phenomenon.

Superconducting MgB2 film prepared by chemical vapor deposition at atmospheric pressure of N2

A simple and effective chemical vapor deposition equipment was developed for deposition of superconducting MgB2 thin films. The pure precursor Boron films were prepared in base pressure of low vacuum and deposited in atmospheric pressure. After the precursor film annealed in Mg vapor, the superconducting MgB2 film was fabricated. During the precursor Boron films preparation, N2 and Ar were used as carrier gas. Compared to Ar gas, the films show better crystallization, surface morphology and superconducting performance when N2 is adopted as carrier gas. With flow rate of 200 sccm of N2 gas, the fabricated MgB2 films exhibit the highest superconducting transition temperature of 39.5K, which is among the best results of MgB2 thin films. This method provides a suitable method to realize high quality MgB2 Josephson junctions and industrial manufacture of MgB2 superconducting thin films on a large scale.

XPS investigation of impurities containing boron films affected by energetic deuterium implantation and thermal desorption

Effect of impurities on existing states of boron, carbon and oxygen in boron films were investigated by XPS technique. Carbon mainly exists as BCB bond and BC bond in 70% B boron films, and BC bond and CC bond in 50% B boron films. The existing state of oxygen depends on impurities composition in 70% B and 50% B boron films. D+ implantation and thermal desorption result in the reconstruction of boron films, which mainly includes the elimination of B2O3, increasing of BO bond and decreasing of BB bond. Implanted D+ into boron films can be trapped by carbon and oxygen, and remits as D2O and CDx in TDS process. Comparing to carbon, oxygen can be trapped easily by BB bond and difficult to remit from boron films.

Influences of Working Power on Properties for Boron Films Deposited by R. F. Magnetron Sputtering

Boron and boron-rich boride has attracted considerable attention in the past few years for their wide varieties of structures and property associated with their unusual three-center electron-deficient bonds. Boron film also exhibits many unique and fascinating properties, such as high melting point (~ 2500K) with low density, high harness close to diamond, and excellent thermoelectric property. In this paper, boron (10B) films were prepared on (100) silicon substrate by radio frequency (r. f.) magnetron sputtering method under the different working pressure and power with a target of boron and boron oxide (B:B2O3 40wt%). After 3 hours sputtering deposition, the substrate was covered with boron films tightly. The morphology of deposited films under different temperature was characterized by high resolution scanning electron microscopy (HRSEM), FTIR spectrum (FTIR), Raman spectrum (Raman). The results show that the film contains boron and little oxygen. At last, the growth mechanism of B film was analyzed.

Fuel retention measurements in Alcator C-Mod using accelerator-based in situ materials surveillance

This paper presents the first in situ time- and space-resolved measurements of deuterium (D) fuel retention in plasma-facing component (PFC) surfaces using Accelerator-based In-situ Materials Surveillance (AIMS) on the Alcator C-Mod tokamak. AIMS is a novel in situ materials diagnostic technique based on the spectroscopic analysis of nuclear reaction products induced in PFC surfaces using an ∼MeV beam of deuterons from a compact linear accelerator in between plasma shots. AIMS measurements of D retention on inner wall PFCs were acquired during diverted and limited plasma operations and during wall conditioning experiments. Intershot measurements demonstrate the local erosion and codeposition of boron films on PFC surfaces with a constant D/B ratio. This is consistent with previous results suggesting that D codeposition with boron is insufficient to account for the net retention observed in Alcator C-Mod. Changes in deuterium concentration during boronization, electron cyclotron and glow cleanings were also measured.

Optical characteristic analysis of the boronization process by using carborane

Boronization with carborane (C2B10H12) was archieved in a vacuum vessel coupled to a filament discharge system. Optical emission spectroscopy was employed to characterize the boronization process. The Balmer lines of hydrogen and deuterium were measured, and the boronization process was analyzed by using the intensity ratio of the Hα to the Dα line (IH/ID). The relation between the pressure and the intensity ratio was investigated, and the thickness of the deposited boron film was predicted. Also, the dilution ratio H/(H + D) of the boron film was analyzed and compared with the one predicted from an optical analysis of the emission spectrum.

Noble gas excimer scintillation following neutron capture in boron thin films

Far-ultraviolet scintillation signals have been measured in heavy noble gases (argon, krypton, xenon) following boron-neutron capture (10B(n,α)7Li) in 10B thin films. The observed scintillation yields are comparable to the yields from some liquid and solid neutron scintillators. At noble gas pressures of 107 kPa, the number of photons produced per neutron absorbed following irradiation of a 1200 nm thick 10B film was 14 000 for xenon, 11 000 for krypton, and 6000 for argon. The absolute scintillation yields from the experimental configuration were calculated using data from (1) experimental irradiations, (2) thin-film characterizations, (3) photomultiplier tube calibrations, and (4) photon collection modeling. Both the boron films and the photomultiplier tube were characterized at the National Institute of Standards and Technology. Monte Carlo modeling of the reaction cell provided estimates of the photon collection efficiency and the transport behavior of 10B(n,α)7Li reaction products escaping the thin films. Scintillation yields increased with gas pressure due to increased ionization and excitation densities of the gases from the 10B(n,α)7Li reaction products, increased frequency of three-body, excimer-forming collisions, and reduced photon emission volumes (i.e., larger solid angle) at higher pressures. Yields decreased for thicker 10B thin films due to higher average energy loss of the 10B(n,α)7Li reaction products escaping the films. The relative standard uncertainties in the measurements were determined to lie between 14% and 16%. The observed scintillation signal demonstrates that noble gas excimer scintillation is promising for use in practical neutron detectors.

Study on the Microstructure and Electrical Properties of Boron and Sulfur Codoped Diamond Films Deposited Using Chemical Vapor Deposition

The atomic‐scale microstructure and electron emission properties of boron and sulfur (denoted as B‐S) codoped diamond films grown on high‐temperature and high‐pressure (HTHP) diamond and Si substrates were investigated using atom force microscopy (AFM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), and current imaging tunneling spectroscopy (CITS) measurement techniques. The films grown on Si consisted of large grains with secondary nucleation, whereas those on HTHP diamond are composed of well‐developed polycrystalline facets with an average size of 10–50 nm. SIMS analyses confirmed that sulfur was successfully introduced into diamond films, and a small amount of boron facilitated sulfur incorporation into diamond. Large tunneling currents were observed at some grain boundaries, and the emission character was better at the grain boundaries than that at the center of the crystal. The films grown on HTHP diamond substrates were much more perfect with higher quality than the films deposited on Si substrates. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate n‐type conduction.

A 10B-based neutron detector with stacked MultiWire Proportional Counters and macrostructured cathodes

We present the results of the measurements of the detection efficiency for a 4.7 \\r{A} neutron beam incident upon a detector incorporating a stack of up to five MultiWire Proportional Counters (MWPC) with Boron-coated cathodes. The cathodes were made of Aluminum and had a surface exhibiting millimeter-deep V-shaped grooves of 45°, upon which the thin Boron film was deposited by DC magnetron sputtering. The incident neutrons interacting with the converter layer deposited on the sidewalls of the grooves have a higher capture probability, owing to the larger effective absorption film thickness. This leads to a higher overall detection efficiency for the grooved cathode when compared to a cathode with a flat surface. Both the experimental results and the predictions of the GEANT4 model suggests that a 5-counter detector stack with coated grooved cathodes has the same efficiency as a 7-counter stack with flat cathodes. The reduction in the number of counters in the stack without altering the detection efficiency will prove highly beneficial for large-area position-sensitive detectors for neutron scattering applications, for which the cost-effective manufacturing of the detector and associated readout electronics is an important objective. The proposed detector concept could be a technological option for one of the new chopper spectrometers and other instruments planned to be built at the future European Spallation Source in Sweden. These results with macrostructured cathodes generally apply not just to MWPCs but to other gaseous detectors as well.

An experimental and first-principles study of the effect of B/N doping in TiO2 thin films for visible light photo-catalysis

Abstract Thin films of TiO2 and boron–nitrogen (B/N) co-doped TiO2 on glass substrates have been prepared by a simple sol–gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV–vis spectroscopy. The TiO2 thin films with co-doping of different B/N atomic ratios (0.27–20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV–vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results.

Study and optimization of boronization in Alcator C-Mod using the Surface Science Station (S3)

A Surface Science Station (S3) on the Alcator C-Mod tokamak is used to study and optimize the location and rate of boron film deposition in situ during electron cyclotron (EC) discharge plasmas using 2.45GHz radio-frequency (RF) heating and a mixture of helium and diborane (B2D6) gasses. The radial profile of boron deposition is measured with a pair of quartz microbalances (QMB) on S3, the faces of which can be rotated 360° including orientations parallel and perpendicular to the toroidal magnetic field BT ∼0.1T. The plasma electron density is measured with a Langmuir probe, also on S3 in the vicinity of the QMBs, and typical values are ∼1×1016m−3. A maximum boron deposition rate of 0.82μg/cm2/min is obtained, which corresponds to 3.5nm/min if the film density is that of solid boron. These deposition rates are sufficient for boron film applications between tokamak discharges. However the deposition does not peak at the EC resonance as previously assumed. Rather, deposition peaks near the upper hybrid (UH) resonance, ∼5cm outboard of the EC resonance. This has implications for RF absorption, with the RF waves being no longer damped on the electrons at the EC resonance. The previously inferred radial locations of critical erosion zones in Alcator C-Mod also need to be re-evaluated. The boron deposition profile versus major radius follows the ion flux/density profile, implying that the boron deposition is primarily ionic. The application of a vertical magnetic field (BV ∼0.01T) was found to narrow the plasma density and boron deposition profiles near the UH resonance, thus better localizing the deposition. A Monte Carlo simulation is developed to model the boron deposition on the different QMB/tokamak surfaces. The model requires a relatively high boron ion gyroradius of ∼5mm, indicating a B+1 ion temperature of ∼2eV, to match the deposition on QMB surfaces with different orientation to BT. Additionally, the boron ion trajectories become de-magnetized at high neutral gas throughput (∼0.5Pam3s−1) and pressure (∼2Pa) when the largest absolute deposition rates are measured, resulting in deposition patterns, which are independent of surface orientation to BT in optimized conditions.

Study on the retention behavior of hydrogen isotopes and the change of chemical states of boron film exposed to hydrogen plasma in LHD

The behavior of hydrogen retention and the change of chemical states of boron film exposed to hydrogen plasma in LHD were investigated. The sample was prepared in LHD, and atomic concentrations for the boron film after hydrogen plasma exposure were changed from 75% for boron, 15% for carbon and 8% for oxygen to 53%, 18% and 22%, respectively. BC bond was a major chemical state of the boron film after hydrogen plasma exposure, although abundance of BB bond was the highest before the plasma exposure. Total hydrogen retention measured by TDS was evaluated to be 1.7×1020Hm−2, and the retentions of hydrogen as BHB, BH and BCH bonds were, respectively, 4.8×1019, 7.2×1019 and 5.2×1019Hm−2. It was concluded that the hydrogen retention could be estimated by taking account not only of chemical states of impurities, but also of hydrogen depth profile.

Removal of Deuterium Retained in B, Ti, and TiO2 by Neon Glow Discharge

The removal of deuterium retained in boron, titanium, and titanium oxide films by neon glow discharge was investigated. The films were exposed to deuterium glow plasma to retain the deuterium and subsequently exposed to neon glow plasma. The temperature of the exposures was room temperature. The residual deuterium was estimated by thermal desorption spectroscopy. The removal ratio of deuterium by neon glow discharge largely depended on the material. Namely, the ratios for boron, titanium, or titanium oxide were 14%, 2%, or 40%, respectively. The ratios for the boron and the titanium oxide roughly agreed with the estimation from SRIM code calculations, while the ratio for the titanium did not agree with the estimation. These results suggest that the reduction of the deuterium retention is owing to the etching and the ion impact desorption of neon ions in the cases of boron and titanium oxide, and the prompt re-trapping of deuterium by titanium atoms might occur in the case of titanium. The comparison between titanium and titanium oxide clearly shows that the removal effect by glow discharge largely depended on the surface conditions, such as oxygen impurity.