Effects of experimental parameters on composition of boron carbon nitride thin films deposited by magnetron sputtering

We have synthesized boron carbon nitride thin films by radio frequency magnetron sputtering. The films structure and composition were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the three elements of B, C, N are chemically bonded with each other and atomic-level hybrids have been formed in the films. The boron carbon nitride films prepared in the present experiment possess a disordered structure. The influence of PN₂/PN₂+Ar, total pressure and substrate bias voltage on the composition of boron carbon nitride films is investigated. The atomic fraction of C atoms increases and the fractions of B, N decrease with the decrease of PN₂/PN₂+Ar from 75% to 0%. There is an optimum total pressure. That is to say, the atomic fractions of B, N reach a maximum and the fraction of C atoms reaches a minimum at the total pressure of 1.3 Pa. The boron carbon nitride films exhibit lower C content and higher B, N contents at lower bias voltages. And the boron carbon nitride films show higher C content and lower B, N contents at higher bias voltages.     

Site-specific electron-induced cross-linking of ortho-carborane to form semiconducting boron carbide

Semiconducting boron carbide (B₁₀C₂H_x) films have been formed by bombardment of condensed ortho-carborane (closo-1,2-dicarbadodecaborane) multilayers on polycrystalline copper substrates by 200 eV electrons under ultra-high vacuum conditions. The film formation process was characterized by X-ray and ultraviolet photoelectron spectroscopies. Electron bombardment results in the cross-linking of the icosahedral units. The cross-linking is accompanied by a shift in the B(1s) binding energy indicating site-specific cross-linking between two boron sites on adjacent carborane icosahedra. An additional shift in valence band binding energies attributed to the surface photovoltage effect is indicative of the formation of a p-type semiconductor. This is the first report of B₁₀C₂H_x formation by electron bombardment of condensed films, and the data indicate that this method is a viable route towards formation of ultra-thin films of tailored composition and cross-linkages for emerging nanoelectronics and sensor applications.     

Possibilities of the formation of carbides and borides by ion implantation

In the system of boron and carbon, the formation of boron carbide was investigated after ion implantation of 25 keV B ions into carbon or of 25 keV C ions into boron and subsequent annealing. TEM and electron diffraction studies showed that the crystallization of boron carbide begins only at temperatures above 1050°C. By implantation of 20 keV C ions into iron (ion dose 10¹⁷ C ions/cm²) only the metastable ε-Fe₂O will be generated, which at above 220°C transforms into the stable cementite Fe₃C. After implantation of 20 keV B ions into iron, no formation of iron boride could be found. These experimental facts can be understood qualitatively with the help of the thermal-spike model. The energy density or the temperature in the thermal spikes is not sufficient for the generation of cementite iron boride or boron carbide.     

The properties of boron carbide/silicon heterojunction diodes fabricated by Plasma-Enhanced Chemical Vapor Deposition

p-n heterojunction diodes have been fabricated from boron carbide (B_1–x C _x ) and n-type Si(111). Boron carbide thin films were deposited on Si(111) using Plasma-Enhanced Chemical Vapor Deposition (PECVD) from nido-pentaborane (B₅H₉) and methane (CH₄). Composition of boron carbide thin films was controlled by changing the relative partial pressure ratio between nido-pentaborane and methane. The properties of the diodes were strongly affected by the composition and thickness of boron carbide layer and operation temperatures. Boron carbide/silicon heterojunction diodes show rectifying properties at temperatures below 300° C. The temperature dependence of reverse current is strongly dependent upon the energy of the band gap of the boron carbide films.     

Boron doping of silicon by excimer laser irradiation in a reactive atmosphere

UV excimer lasers have been used to dope semiconductors by a one-step process in which the laser serves both to melt a controlled thickness of a sample placed in dopant ambient and to photodissociate the dopant molecules themselves. Here we report the boron doping of silicon by means of an ArF (193 nm) excimer laser. Dopant atoms are obtained by photolysis of BCl₃ or pyrolysis of BF₃ molecules. The doping is performed both in gas ambient and using only an adsorbed layer. We have investigated the dependence of doping parameters such as laser pulse repetition and gas pressure on the subsequent boron impurity profiles and the dopant incorporation rate. These results indicate that the laser doping process is dopant-flux limited for BF₃ and externally rate limited for BCl₃.     

First principles modeling of boron-doped carbon nanotube sensors

We investigated the interactions between two different geometrical configurations of single-walled carbon nanotubes and boron atoms using first-principle calculations within the framework of the density functional theory. With the aid of ab initio calculations, we introduced a new type of toxic gas sensor that can detect the presence of CO, NO and H₂ molecules. We proved that the dopant concentration on the surface of the nanotube plays a crucial role in the sensitivity of this device. Furthermore, we showed that small concentrations of dopants can modify the transport and electronic properties of the single-walled carbon nanotube and can lend metallic properties to the nanotube. Band-gap narrowing occurs when the nanotube is doped with boron atoms. The emerged new energy level near the Fermi level upon boron doping clearly indicates the coupling between the p orbital of the boron atom and the large p bond of the carbon nanotube. We also predicted a weak hybridization between the boron atoms and the nanotube for the valence-band edge states; this weak coupling leads to conducting states around the band gap.     

Preparation of boron carbon nitride thin films by radio frequency magnetron sputtering

Boron carbon nitride films were deposited by radio frequency magnetron sputtering using a composite target consisting of h-BN and graphite in an Ar-N₂ gas mixture. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results suggest that the films are atomic-level hybrids composed of B, C and N atoms. The boron carbon nitride films prepared in the present experiment have a disordered structure. The sputtering power varied from 80 W to 130 W. This sputtering power was shown to have regular effect on the composition of boron carbon nitride films. The samples deposited at 80 W and 130 W are close to the stoichiometry of BC₃N. The sample deposited at 110 W is close to the stoichiometry of BCN. The samples deposited at 100 W and 120 W approach to BC₂N. It is very significant for us to synthesize boron carbon nitride compound with controllable composition by changing the sputtering power.     

A Monte Carlo simulation study of boron profiles as-implanted into LPCVD-NiDoS polycrystalline thin films

This work presents a Monte Carlo simulation study of boron profiles obtained from as-implanted ions into thin films nitrogen doped silicon (NiDoS) thin films. These films are performed by LPCVD technique from Si₂H₆ and NH₃ gas sources, four values deliberately chosen, of the ratio NH₃/Si₂H₆ to obtain samples, differently in situ nitrogen-doped. Taking into account the effect of the codoping case, and the structure specificity of these films, an accurate Monte Carlo model based on binary collisions in a multi-atomic target was performed. Nitrogen atoms present in the target is shown to affect the boron profiles and confirms clearly a reduction penetration effect which becomes more significant at high nitrogen concentrations. Whereas, the fine-grained polysilicon structure, and thus the presence of grains (G) and grain boundaries (GB), is known to enhance the opposite phenomenon by assuming an effective role played by GB's in the scattering calculation process of the incident ions. This role is represented by the change in direction of the incident ion after interaction with GB without corresponding loss in its energy.The results obtained show an enhancement of the stopping parameter when nitrogen concentration increases, while the GB interaction remains very important. This behavior is due to a great number of GB's interactions with boron atoms which gave low deflection angles. So that, the average positions described by the sequences of trajectories took place farther than what expected with channeling effect in crystal silicon materials.     

Dopant-dependence of one-step metal-induced dopant activation process in silicon

We investigate dopant-dependence of low temperature dopant activation technique in α-Si featuring one-step metal-induced crystallization (MIC) to decrease resistivity of p⁺ and n⁺ Si films by forming Ni_xSi_y. Ni not only crystallizes p-type α-Si film but also facilitates activation of boron atoms in the α-Si during the crystallization at 500 °C. However, phosphorus atoms are poorly activated because of the suppressed Ni-MIC rate in n-type α-Si. Finally, p⁺/n and n⁺/p junction diodes are demonstrated on single crystalline Si substrates by the low temperature dopant activation technique promising for high performance TFTs as well as transistors with an elevated S/D.     

Tuning the electronic and magnetic properties of boron nitride nanotubes

Density Functional Theory is used to investigate the effect of altering the B/N ratio and carbon doping on the electronic and magnetic structure of zigzag, (7, 0) and armchair (5, 5) boron nitride nanotubes. The calculations indicate that increasing the boron content relative to the nitrogen content significantly reduces the band gap to a value typical of a semiconductor. Calculations of carbon doped semiconducting BN tubes, which have more boron atoms than nitrogen atoms have a net spin and a difference in the density of states at the valence band between the spin up and spin down state.     

Effect of laser fluence on the deposition and hardnessof boron carbide thin films

We deposited amorphous thin films of boron carbide by pulsed laser deposition using a B₄C target at room temperature. As the laser fluence increased from 1 to 3 J/cm², the number of 0.25–5 μm particulates embedded in the films decreased, and the B/C atomic ratio of the films increased from 1.8 to 3.2. The arrival of melt droplets, atoms, and small molecular species depending on laser fluence appeared to be involved in the film formation. In addition, with increasing fluence the nanoindentation hardness of the films increased from 14 to 32 GPa. We believe that the dominant factor in the observed increase in the films’ hardness is the arrival of highly energetic ions and atoms that results in the formation of denser films. Received: 23 March 2001 / Accepted: 1 July 2001 / Published online: 2 October 2001     

First-principles calculations of BC4N nanostructures: stability and electronic structure

In this work, we apply first-principles methods to investigate the stability and electronic structure of BC₄N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 Å, or cut and bent to form nanocones, with 60^° and 120^° disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B–N and C–C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D ² law. The results show that the 60^° disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene.     

Growth of boron nitride nanotube film in situ

A novel method was demonstrated to fabricate boron nitride nanotube films on silicon substrate in a location-controlled fashion. The pre-deposited SiO₂ layer on the substrate controls the growth space of BN nanotubes synthesized by an ammonothermal reaction of boron and its oxide. PACS 71.20.Tx; 81.07.De; 81.10.Dn; 61.46.+w; 81.05.Tp     

Electronic properties of boron and nitrogen doped graphene nanoribbons and its application for graphene electronics

On the basis of density functional theory calculations, we have systematically investigated the electronic properties of armchair-edge graphene nanoribbons (GNRs) doped with boron (B) and nitrogen (N) atoms. B (N) atoms could effectively introduce holes (electrons) to GNRs and the system exhibits p- (n-) type semiconducting behavior after B (N) doping. According to the electronic structure calculations, Z-shape GNR-based field effect transistors (FETs) is constructed by selective doping with B or N atoms. Using first-principles quantum transport calculations, we demonstrate that the B-doped p-type GNR-FETs can exhibit high levels of performance, with high ON/OFF ratios and low subthreshold swing. Furthermore, the performance parameters of GNR-FETs could be controlled by the p-type semiconducting channel length.     

New spectral assignment of n‐propanol in the C―H stretching region

The C―H stretching vibration serves as an important probe for characterizing molecular structures and properties of hydrocarbons. In this work, we present a detailed study on gas‐phase Raman spectrum of n‐propanol in the C―H stretching region using stimulated photoacoustic Raman spectroscopy. A complete assignment was carried out with the aid of quantum chemistry calculations and depolarization ratio measurement as well as isotope substitutions, i.e. CH₃CD₂CD₂OH, CD₃CH₂CD₂OH and CD₃CD₂CH₂OH. It is shown that the spectra of three C―H groups of n‐propanol overlap each other because of Fermi resonance coupling and different molecular conformations, leading to complex features that were not determined previously. In addition, the comparisons between the spectra of three isotopologues reveal that the C―H vibrations at different sites of carbon chain exhibit different sensitivity to conformational change of n‐propanol. The CH₃ stretching vibration at terminated γ‐carbon is not sensitive whereas the CH₂ stretching vibrations at both α‐carbon and β‐carbon atoms are sensitive. Furthermore, Raman spectra of liquid propanol recorded by conventional spontaneous Raman technique are reassigned on the basis of gas‐phase analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

The coadsorption and interaction of molecular icosahedra with mercury

We have investigated the changes in the electronic structure of molecularly adsorbed orthocarborane films, as a function of Hg co-adsorption, using photoemission. The interaction between Hg and molecular orthocarborane is weak and results in the formation of some small aggregates of Hg. This behavior is very different from alkali metals interaction with molecular carborane films and the interaction of Hg with semiconducting boron carbide films. Hg doping of semiconducting boron carbide may decrease the activation barrier for intrinsic carrier mobility, but does not significantly increase the number of carriers. PACS 72.80 Ga; 74.25 Fy; 71.20 Ps     

Ion-Polymer Interactions in SmCl3(H2O)6 Doped Poly(ethylene oxide) Electrolytes

Pure and SmCl₃(H₂O)₆ doped poly(ethylene oxide) (PEO) samples were prepared using a solvent casting method. These samples were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and differential scanning colorimetry (DSC) techniques. The FTIR spectra indicate that, only at low dopant concentrations, the interactions between Sm³⁺ and ether oxygen atoms in PEO are dominant. As the dopant concentration increases, these interactions result in the formation of dopant aggregates or agglomerates leading to a phase separation into a polymer-rich phase and a dopant-rich phase in the films, which have been confirmed by XRD and DSC results.     

Proton transfer reactions of hydrazine‐boranes

Hydrazine‐borane and hydrazine‐diborane contain, respectively, 15.4 and 16.9 wt% of hydrogen and are potential materials for hydrogen storage. In this work we present the gas‐phase complexation energies, acidities, and basicities of hydrazine‐borane and hydrazine‐bisborane calculated at MP2/6‐311 + G(d,p) level. We also report the release of dihydrogen from both protonated complexes (ΔG_{hydrazine‐borane} = ?20.9 kcal/mol and ΔG_{hydrazine‐bisborane} = ?27.2 kcal/mol) which is much more exergonic than from analogues amine‐boranes. The addition of the first BH₃ to the hydrazine releases 17.1 kcal/mol, and the second addition releases 15.8 kcal/mol. The attachment of BH₃ also increases the N―H acidity of hydrazine by 46.3 kcal/mol. It was found that the B―H deprotonation leads to intramolecular rearrangement. The basicity values for hydrazine‐borane and ‐bisborane are 180 and 172.8 kcal/mol, respectively. For both complexes the protonation centres are located at the boron moiety. The protonated structure of hydrazine‐bisborane is cyclic and can be described as H₂ captured between a negatively charged B―H hydrogen and positive boron (B―H??H2??B). Atoms in molecules analysis are used to investigate bond paths in concerning structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrical properties and Raman scattering investigation of Ag doped ZnO thin films

Ag-doped ZnO thin films were deposited on quartz glass substrates by a radio-frequency (RF) magnetron sputtering technique at room temperature (RT). The influence of Ag doping content on the electrical and Raman scattering properties of ZnO films were systematically investigated by Hall measurement system and Raman scattering spectrum. Two additional local vibrational modes (LVMs) at 230.0 and 394.5 cm^?1 induced by Ag dopant in ZnO:Ag films were observed by Raman analyses at RT, corresponding to Ag atoms located at O sites (LV M_Zn?Ag) and Zn sites (LV M_Ag?O) in ZnO lattice. Moreover, we further studied the effect of donor Ag_O and acceptor Ag_Zn defects on the electrical properties of ZnO:Ag films. The results indicate that O-rich condition is preferred to suppress the formation of Ag_O defects and enhance Ag_Zn defects. The p-type ZnO:Ag film was achieved by properly optimizing the annealing conditions under O-rich condition.     

Stoichiometric controlling of pulsed laser deposited boron–carbon thin films

The stoichiometry of B–C thin films was controlled via pulsed laser deposition using a series of ceramic B–C targets (B/C ratio was 3.04–5.92). The effects of B/C ratio in target, laser power and substrate-to-target distance on deposition rate, microstructure, stoichiometry and chemical structure were investigated. The maximum deposition rate was obtained at laser power of 90 mJ and substrate-to-target distance of 50 mm. Boron rich B–C films were obtained and the stoichiometry in B–C thin films was controlled in the range 2.9–4.6. Carbon atoms were bonded with only sp³ hybridization when boron was rich,but with sp² and sp³ hybridizations when carbon was rich.