The influence of processing gas on the mechanical properties of sputtered B-C-N-H films

This work describes the microstructure and mechanical properties of B-C-N-H films synthesized by medium frequency magnetron sputtering from a boron target in a N₂ + CH₄ + Ar gas mixture. The increase in the CH₄ flow rate increases the carbonaceous compound species, causes the increase of the C atomic concentration and promotes the formation of sp³-hybridized carbon. The change of hardness with the CH₄ flow rate had a relationship with the residual stress. The coefficient of friction was reduced approximately from 0.8 to 0.18, and wear resistance was considerably improved by increasing the flow of CH₄ gas component from 0 to 40 sccm. The change of films’ hardness was discussed and attributed primarily to the internal defects and bonding characteristics, while the superior tribological properties of the films could be assigned to the formation of sp³-hybridized carbon and the C-H bonding.     

Study of structural and electronic environments of hydrogenated amorphous silicon carbonitride (a-SiCN:H) films deposited by hot wire chemical vapor deposition

Hydrogenated amorphous silicon carbon nitride (a-SiCN:H) thin films were deposited by hot wire chemical vapor deposition (HWCVD) using SiH₄, CH₄, NH₃ and H₂ as precursors. The effects of the H₂ dilution on structural and chemical bonding of a-SiCN:H has been investigated by Raman and X-ray photoelectron spectroscopy (XPS). Increasing the H₂ flow rate in the precursor gas more carbon is introduced into the a-SiCN:H network resulting in decrease of silicon content in the film from 41 at.% to 28.8 at.% and sp² carbon cluster increases when H₂ flow rate is increased from 0 to 20 sccm.     

Structure and properties of DLC–MoS2 thin films synthesized by BTIBD method

Diamond-like carbon (DLC)–MoS₂ composite thin films were synthesized using a biased target ion beam deposition (BTIBD) technique in which MoS₂ was produced by sputtering a MoS₂ target using Ar ion beams while DLC was deposited by ion beam deposition with CH₄ gas as carbon source. The structure and properties of the synthesized films were characterized by X-ray diffraction, X-ray absorption near edge structure (XANES), Raman spectroscopy, nanoindentation, ball-on-disk testing, and corrosion testing. The effect of MoS₂ target bias voltage, ranging from −200 to −800 V, on the structure and properties of the DLC–MoS₂ films was further investigated. The results showed that the hardness decreases from 9.1 GPa to 7 GPa, the Young?s modulus decreases from 100 GPa to 78 GPa, the coefficient of friction (COF) increases from 0.02 to 0.17, and the specific wear rate coefficient (k) increases from 5×10⁻⁷ to 5×10⁻⁶ mm³ N⁻¹ m⁻¹, with increasing the biasing voltage from 200 V to 800 V. Also, the corrosion resistance of the DLC–MoS₂ films decreased with the raise of biasing voltage. Comparing with the pure DLC and pure MoS₂ films, the DLC–MoS₂ films deposited at low biasing voltages showed better tribological properties including lower COF and k in ambient air environment.     

Mechanical properties and platelet adhesion behavior of diamond-like carbon films synthesized by pulsed vacuum arc plasma deposition

Diamond-like carbon (DLC) is an attractive biomedical material due to its high inertness and excellent mechanical properties. In this study, DLC films were fabricated on Ti6Al4V and Si(1 0 0) substrates at room temperature by pulsed vacuum arc plasma deposition. By changing the argon flow from 0 to 13 sccm during deposition, the effects of argon flow on the characteristics of the DLC films were systematically examined to correlate to the blood compatibility. The microstructure and mechanical properties of the films were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) surface analysis, a nano-indenter and pin-on-disk tribometer. The blood compatibility of the films was evaluated using in vitro platelet adhesion investigation, and the quantity and morphology of the adherent platelets was investigated employing optical microscopy and scanning electron microscopy.The Raman spectroscopy results showed a decreasing sp³ fraction (an increasing trend in I_D/I_G ratio) with increasing argon flow from 0 to 13 sccm. The sp³:sp² ratio of the films was evaluated from the deconvoluted XPS spectra. We found that the sp³ fraction decreased as the argon flow was increased from 0 to 13 sccm, which is consistent with the results of the Raman spectra. The mechanical properties results confirmed the decreasing sp³ content with increasing argon flow. The Raman D-band to G-band intensity ratio increased and the platelet adhesion behavior became better with higher flow. This implies that the blood compatibility of the DLC films is influenced by the sp³:sp² ratio. DLC films deposited on titanium alloys have high wear resistance, low friction and good adhesion.     

Effect of ECR-assisted microwave plasma nitriding treatment on the microstructure characteristics of FCVA deposited ultra-thin ta-C films for high-density magnetic storage applications

There are higher technical requirements for protecting layer of magnetic heads and disks used in future high-density storage fields. In this paper, ultra-thin (2 nm thickness) tetrahedral amorphous carbon (ta-C) films were firstly prepared by filtered cathodic vacuum arc (FCVA) method, then a series of nitriding treatments were performed with nitrogen plasma generated using electron cyclotron resonance (ECR) microwave source. Here it highlighted the influence of nitrogen flow and applied substrate bias voltage on the structural characteristics of ta-C films during the plasma nitriding process. The chemical compositions, element depth distribution profiles, physical structures and bonding configurations of plasma-nitrided ta-C films were investigated by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and UV-vis Raman spectroscopy. The experimental results show that the carbon nitride compounds (CN_x) are formed in nitrogenated ta-C films in which the N content and its depth distribution depends on bias voltage to large extent rather than N₂ flow. The N content of nitrogenated ta-C films can reach 16 at.% for a substrate bias of −300 V and a N₂ flow of 90 sccm. With increasing nitrogen content, there is less G peak dispersion and more ordering of structure. Furthermore, appropriate nitriding treatment (substrate bias: −100 V, N₂ flow: 150 sccm) can greatly increase the fraction of sp³ and sp³C-N bonds, but the values begin to fall when the N content is above 9.8 at.%. All these indicate that suitable ECR-assisted microwave plasma nitriding is a potential modification method to obtain ultra-thin ta-C films with higher sp³ and sp³C-N fractions for high-density magnetic storage applications.     

Thin porous Ni-YSZ films as anodes for a solid oxide fuel cell

Porous Ni-YSZ (YSZ—yttria-stabilized zirconia) films were fabricated by reactive co-sputtering of a Ni and a Zr-Y target, followed by sequentially annealing in air at 900 °C and in vacuum at 800 °C. The Ni-YSZ films comprised small grains and pores that were tens of nanometers in size. The porous Ni-YSZ films were used as an anode on one side of a YSZ electrolyte disc and a La_0.7Sr_0.3MnO₃ thick film was used as a cathode on the other side of the disc to form solid oxide fuel cells (SOFCs). The voltage-current curves of the SOFCs with single- and a triple-layered porous anodes were measured in a single-chamber configuration, in a mixture of CH₄ and air (CH₄:O₂ volume ratio=2:1). The maximum power density of the SOFC using the single-layered porous Ni-YSZ thin films as the anode was 0.38 mW cm⁻², which was lower than that of 0.76 mW cm⁻², obtained using a screen-printed Ni-YSZ thick anode. The maximum power density of the SOFC with a thin anode was increased, but varied between 0.6 and 1.14 mW cm⁻² when a triple-layered porous Ni-YSZ anode was used.     

Influence of boron concentration on growth characteristic and electro-catalytic performance of boron-doped diamond electrodes prepared by direct current plasma chemical vapor deposition

A series of boron-doped diamond (BDD) electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) with different compositions of CH₄/H₂/B(OCH₃)₃ gas mixture. A maximum growth rate of 0.65 mg cm⁻² h⁻¹ was obtained with CH₄/H₂/B(OCH₃)₃ radio of 4/190/10 and this growth condition was also a turning point for discharge plasma stability which arose from the addition of B(OCH₃)₃ that changed electron energy distribution and influenced the plasma reaction. The surface coating structure and electro-catalytic performance of the BDD electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Hall test, and electrochemical measurement and electro-catalytic oxidation in phenol solution. It is suggested that the boron doping level and the thermal stress in the films are the main factors affecting the electro-catalytic characteristics of the electrodes. Low boron doping level with CH₄/H₂/B(OCH₃)₃ ratio of 4/199/1 decreased the films electrical conductivity and its electro-catalytic activity. When the carrier concentration in the films reached around 10²⁰ cm⁻³ with CH₄/H₂/B(OCH₃)₃ ratio over a range of 4/195/5-4/185/15, the thermal stress in the films was the key reason that influenced the electro-catalytic activity of the electrodes for its effect on diamond lattice expansion. Therefore, the BDD electrode with modest CH₄/H₂/B(OCH₃)₃ ratio of 4/190/10 possessed the best phenol removal efficiency.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

Characterization of BCN films synthesized by radiofrequency plasma enhanced chemical vapor deposition

Boron carbonitride (BCN) films have been synthesized on Si(1 0 0) substrate by radio frequency plasma enhanced chemical vapor deposition using tris-(dimethylamino)borane (TDMAB) as a precursor. The deposition was performed at the different RF powers of 400-800 W, at the working pressure of 2×10⁻¹ Torr. The formation of the sp²-bonded BCN phase was confirmed by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy measurements showed that B atoms were bonded to C and N atoms to form the BCN atomic hybrid configurations with the chemical compositions of B₅₂C₁₂N₃₆ (sample 1; prepared at the RF power of 400 W), B₅₂C₁₀N₃₈ (sample 2; at 500 W) and B₄₆C₁₈N₃₆ (sample 3; at 800 W), respectively. Near-edge X-ray absorption fine structure (NEXAFS) measurements indicated that B atoms were bonded not only to N atoms but also to C atoms to form various configurations of sp²-BCN atomic hybrids. The polarization dependence of NEXAFS suggested that the predominant hybrid configuration of sp²-BCN films oriented in the direction perpendicular to the Si substrate.     

Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OⁱPr)₂(tbaoac)₂] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has -CH₃ terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO₂ and ZrO₂ were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300-500 °C and deposition pressure of 1×10⁻³-3×10⁻² Torr. N₂ gas (5 sccm) was used as a carrier gas during film depositions. TiO₂ and ZrO₂ thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO₂ or Si-OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.     

The evolution of magnetic,electrical and structural properties of nanogranular [FeCoBN/SiN]×n thin films

Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si₃N₄]×n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si₃N₄]×n thin films is also reported. The [FeCoBN/Si₃N₄]×n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m²/kg, Hc of 318–1433 A/m and ρ of 82–48×10⁻⁷ Ω m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system.     

Characterization of sp carbon produced by plasma deposition on gamma-TiAl alloys

Surfaces of two gamma-TiAl alloys, Ti-47%Al-2%Nb-2%Cr (MJ12) and Ti-47%Al-2%Nb-2%Mn + 0.8%TiB₂ (MJ47), were modified by acetylene plasma deposition at −3 kV bias voltage for 0.5-4 h. By using GIXRD and SAED, C (n-diamond), TiC, Al, AlTi, AlTi₂, AlTi₃, Al_0.64Ti_0.36 and Al₂Ti were detected on both alloys. Additional TiB₂ was detected on MJ47. XPS and Raman analyses revealed the presence of sp³ and sp² carbon deposited on the alloy surfaces with their binding energies of 283.9-284.8 eV for MJ12 and 283.9-285.0 eV for MJ47. Both sp³ and sp² contents were increased with the increase in the exposure times. The increasing rate of the first was less than that of the second, due to the stress developed in the films. Moiré fringe and crystallographic planes were detected using TEM. Knoop hardness of the deposited alloys, influenced by sp³ carbon, was increased with the increase in the exposure time. Those of MJ12 and MJ47 with 4 h deposition are 1.88 and 1.57 times of the corresponding untreated alloys, respectively.     

Chemical and morphological difference between TiN/DLC and a-C:H/DLC grown by pulsed vacuum arc techniques

In order to improve the adherence of DLC films, interlayers of amorphous hydrogenated carbon (a-C:H) and titanium nitride (TiN) were deposited by means of the pulsed vacuum arc technique. Bilayers were obtained by using a carbon target of 99.98% of purity in mixtures of (Ar + CH₄) and (Ar + H₂) for producing a-C and DLC, respectively and a target of titanium of 99.999% in a mixture of (Ar + N₂) for growing TiN. After the deposition, chemical and morphological differences between TiN/DLC and a-C:H/DLC bilayers grown on silicon and stainless steel 304 were studied using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and scanning probe microscopy (SPM) techniques. XPS analysis showed a difference in sp³/(sp²+sp³) bonds ratio for each bilayer, being 0.67 for TiN/DLC and 0.45 for a-C:H/DLC bilayers. sp³ and sp² bonds were also observed by the FTIR technique. SPM images, in atomic force microscopy (AFM) and lateral force microscopy (LFM) modes were carried out for illustrating the comparison between TiN/DLC and a-C/DLC morphologic characteristics. Roughness and grain size were studied as a function of the H₂ concentration for both bilayers.     

Hierarchically porous nanoflowers from TiO2–B nanosheets with ultrahigh surface area for advanced lithium-ion batteries

In this work, hierarchically porous TiO₂–B nanoflowers have been successfully synthesized via a facile solvothermal method followed by calcination treatment. The TiO₂–B nanoflowers are constructed by thin nanosheets, presenting ultrahigh specific surface area, up to 214.6 m² g⁻¹. As anode materials for Li-ion batteries, the TiO₂–B sample shows high reversible capacity, excellent cycling performance and superior rate capability. The specific capacity of TiO₂–B could remain over 285 mA h g⁻¹ at 1 C and 181 mA h g⁻¹ at 10 C rate after 100 cycles. We believe that the pseudocapacitive mechanism, ultrahigh surface area and scrupulous nanoarchitecture of the TiO₂–B are responsible for the enhancement of electrochemical properties.     

Hydrocarbon film growth by energetic CH3 molecule impact on SiC (0 0 1) surface

Classic molecular dynamics (MD) calculations were performed to investigate the deposition of thin hydrocarbon film. SiC (1 0 0) surfaces were bombarded with energetic CH₃ molecules at impact energies ranging from 50 to 150 eV. The simulated results show that the deposition yield of H atoms decreases with increasing incident energy, which is in good agreement with experiments. During the initial stages, with breaking Si-C bonds in SiC by CH₃ impacting, H atoms preferentially reacts with resulting Si to form Si-H bond. The C/H ratio in the grown films increases with increasing incident energy. In the grown films, CH species are dominant. For 50 eV, H-Csp3 bond is dominant. With increasing energy to 200 eV, the atomic density of H-Csp2 bond increases.     

Structure and elastic recovery of Cr-C:H films deposited by a reactive magnetron sputtering technique

Cr-containing hydrogenated amorphous carbon (Cr-C:H) films were deposited on silicon substrates using a DC reactive magnetron sputtering with Cr target in an Ar and C₂H₂ gas mixture. The composition, bond structure, mechanical hardness and elastic recovery of the films were characterized using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nano-indentation. The film tribological behavior was also studied by a ball-on-disc tribo-tester. The results showed that the films deposited at low C₂H₂ flow rate (<10 sccm) presented a feature of composite Cr-C:H structure, which consisted of hard brittle chromium carbide phases and amorphous hydrocarbon phase, and thus led to the observed low elastic recovery and poor wear resistance of the films. However, the film deposited at high C₂H₂ flow rate (40 sccm) was found to present a typical feature of polymer-like a-C:H structure containing a large amount of sp³ C-H bonds. As a result, the film revealed a high elastic recovery, and thus exhibited an excellent wear resistance.     

Characterization of Zr-Si-N films deposited by cathodic vacuum arc with different N2/SiH4 flow rates

Zr-Si-N films were deposited on silicon and steel substrates by cathodic vacuum arc with different N₂/SiH₄ flow rates. The N₂/SiH₄ flow rates were adjusted at the range from 0 to 12 sccm. The films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), hardness and wear tests. The structure and the mechanical properties of Zr-Si-N films were compared to those of ZrN films. The results of XRD and XPS showed that Zr-Si-N films consisted of ZrN crystallites and SiN_x amorphous phase. With increasing N₂/SiH₄ flow rates, the orientation of Zr-Si-N films became to a mixture of (1 1 1) and (2 0 0). The column width became smaller, and then appeared to vanish with the increase in N₂/SiH₄ flow rates. The hardness and Young's modulus of Zr-Si-N films increased with the N₂/SiH₄ flow rates, reached a maximum value of 36 GPa and 320 GPa at 9 sccm, and then decreased 32 GPa and 305 GPa at 12 sccm, respectively. A low and stable of friction coefficient was obtained for the Zr-Si-N films. Friction coefficient was about 0.1.     

Raman spectroscopy of a-C:H:N films deposited using ECR-CVD with mixed gas

Ultraviolet (UV) and visible Raman spectroscopy were used to study a-C:H:N films deposited using ECR-CVD with a mixed gas of CH₄ and N₂. Small percentage of nitrogen from 0 to 15% is selected. Raman spectra show that CN bonds can be directly observed at 2220 cm⁻¹ from the spectra of visible and UV Raman. UV Raman enhances the sp¹ CN peak than visible Raman. In addition, the UV Raman spectra can reveal the presence of the sp³ sites. For a direct correlation of the Raman parameter with the N content, we introduced the G peak dispersion by combining the visible and UV Raman. The G peak dispersion is directly relative to the disorder of the sp² sites. It shows the a-C:H:N films with higher N content will induce more ordered sp² sites. In addition, upper shift of T position at 244 nm excitation with the high N content shows the increment of sp² fraction of films. That means the films with high N content will become soft and contain less internal stress. Hardness test of films also confirmed that more N content is with less hardness.     

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.     

Synthesis and characterization of sprayed Zn-doped polycrystalline CuInS2 thin films

Copper indium disulphide (CuInS₂) is an efficient absorber material for photovoltaic applications. In this work Zn (0.02 and 0.03 M) doped CuInS₂ thin films are (Cu/In = 1.25) deposited onto glass substrates in the temperature range 300–400 °C. XRD patterns depict, Zn-doping facilitates the growth of CuInS₂ thin films along (1 1 2) preferred plane and other characteristic planes. Optical studies show, 90% of light transmission occurs in the IR regions; hence Zn-doped CuInS₂ can be used as an IR transmitter. The absorption coefficient in the UV–vis region is found to be in the order of 10⁴–10⁵ cm⁻¹. Optical band gap energies increase with increase of temperatures (0.02 M – (1.93–2.05 eV) and 0.03 M – (1.94–2.04 eV)). Well defined, broad Blue and Green band emissions are exhibited. Resistivity study reveals the deposited films exhibit semiconducting nature. Zn species can be used as a donor and acceptor impurity in CuInS₂ films to fabricate efficient solar cells and photovoltaic devices.