Peiling Ke

Amperometric glucose sensor based on boron doped microcrystalline diamond film electrode with different boron doping levels

Boron doped microcrystalline diamond (BDMD) films with different boron concentrations were deposited on Si (100) by microwave plasma chemical vapor deposition in a gas mixture of CH4/H-2/TMB. The influence of boron concentration on the surface morphology, microstructure, and electrochemical properties of BDMD film electrodes was studied. It was found that boron dopants play an important role in the structural quality and electrochemical properties of BDMD film electrodes. The increase of doped boron concentration results in the reduction of diamond grain size and the domination of two peaks located at approximately 500 and 1220 cm(-1) in the Raman spectra. Marked differences are observed for BDMD film electrodes with various boron concentrations in impedance characteristics. The electron transfer reaction on BDMD film electrodes becomes faster and reversibility is improved with the increase of boron concentration. Meanwhile, the electrochemical reactions on the BDMD film electrodes become a diffusion controlled process. The non-enzymatic glucose sensors based on as-prepared BDMD film electrodes were developed. The glucose oxidation peak position and current density are dependent on the B/C ratio for the BDMD film electrodes. The results show that appropriate boron doping concentration can improve the conductivity and electrocatalytic activity of BDMD film electrodes. The BDMD film electrode with B/C ratio of 10 000 ppm exhibits the highest sensitivity of 96.88 mu A mM(-1) cm(-2), lowest detection limit of 0.018 mM and widest linear range of 0.1 to 5 mM. The developed nonenzymatic glucose sensors based on as-prepared BDMD film electrodes demonstrate selective detection of glucose in alkaline solution containing interfering species of ascorbic acid and uric acid.

Microstructure and properties of duplex coatings on magnesium alloy

The duplex Ti cold spray + MAO coatings were deposited on the Mg alloy substrates using combined cold spray and micro arc oxidation (MAO). The microstructure, mechanical property and corrosion resistance of the duplex coatings were investigated compared with the MAO coated Mg alloy substrate. Results indicate that the Ti cold spray coating with 130 µm showed an obvious boundary between the Mg substrate, and the TiO2 phase was formed by MAO on the top coating. The duplex coating showed a little coarse and porous structure, which resulted in low mechanical property and wear resistance compared with the MAO treated Mg substrate. However, it showed an excellent corrosion resistance due to the difference of chemical stability for the coatings. Furthermore, this duplex coating might be very useful for improving the photocatalytic ability of titania due to its markedly increasing specific area.

Ab Initio Investigation on Cu/Cr Codoped Amorphous Carbon Nanocomposite Films with Giant Residual Stress Reduction

Amorphous carbon films (a-C) codoped by two metal elements exhibit the desirable combination of tribological and mechanical properties for widely potential applications, but are also prone to catastrophic failure due to the inevitable residual compressive stress. Thus far, the residual stress reduction mechanism remains unclear due to the insufficient understanding of the structure from the atomic and electronic scale. In this paper, using ab initio calculations, we first designed a novel Cu/Cr codoped a-C film and demonstrated that compared with pure and Cu/Cr monodoped cases, the residual stress in Cu/Cr codoped a-C films could be reduced by 93.6% remarkably. Atomic bond structure analysis revealed that the addition of Cu and Cr impurities in amorphous carbon structure resulted in the critical and significant relaxation of distorted C-C bond lengths. On the other hand, electronic structure calculation indicated a weak bonding interaction between the Cr and C atoms, while the antibonding interaction was observed for the Cu-C bonds, which would play a pivot site for the release of strain energy. Those interactions combined with the structural evolution could account for the drastic residual stress reduction caused by Cu/Cr codoping. Our results provide the theoretical guidance and desirable strategy to design and fabricate a new nanocomposite a-C films with combined properties for renewed applications.

Incorporated W roles on microstructure and properties of W-C:H films by a hybrid linear ion beam systems

W-incorporated diamond-like carbon (W-C:H) films were fabricated by a hybrid beams system consisting of a DC magnetron sputtering and a linear ion source. The W concentration (1.08∼31.74 at.%) in the film was controlled by varying the sputtering current. The cross-sectional topography, composition, and microstructure of the W-C:H filmswere investigated by SEM, XPS, TEM, and Raman spectroscopy. The mechanical and tribological properties of the films as a function of Wconcentration were evaluated by a stress-tester, nanoindentation, and ball-on-disk tribometer, respectively. The results showed that films mainly exhibited the feature of amorphous carbon when W concentration of the films was less than 4.38 at.%, where the incorporated W atoms would be bonded with C atoms and resulted in the formation of WC1-x nanoparticles. The W-C:H film with 4.38 at.% W concentration showed a minimum value of residual compressive stress, a higher hardness, and better tribological properties. Beyond this W concentration range, both the residual stress and mechanical properties were deteriorated due to the growth of tungsten carbide nanoparticles in the carbon matrix.

Friction and Wear Mechanism of MoS2/C Composite Coatings Under Atmospheric Environment

Tribological properties of MoS2/C coatings with different carbon contents (44.7–84.3 at.%) deposited by magnetron sputtering were systematically investigated under atmospheric environment. During tribological tests, the coating with the least MoS2 content exhibited the lowest friction coefficient and wear rate, while coating with the most MoS2 showed the worst performance. To understand friction and wear mechanism, multiple analytical tools such as SEM, EDS, Raman, XPS and TEM were applied to investigate the composition and structure. TEM and SEM characteristics proved that the tribofilm with multilayered structure was formed on the tribopair. The C-rich layer adhered to the tribopair and the top layer was well-ordered MoS2 tribofilm, and the dominated amorphous MoS2 was found between the two layers. It suggested that the shear plane was mainly made of well-ordered MoS2 transfer film, while carbon improved the mechanical properties of the coatings, served as a lubricant and also inhibited the oxidation of MoS2.

Microstructure and tribological behavior of self-lubricating (Si:N)-DLC/MAO coatings on AZ80 magnesium substrate

The combined micro arc oxidation (MAO) and a hybrid beam deposition process was used to deposit duplex (Si:N)-DLC/MAO coatings on AZ80 magnesium alloy. The microstructure and composition of the duplex coatings were analyzed by Raman spectroscopy, X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM) and atomic force microscopy (AFM). Tribological behaviors of the coatings were studied by ball-on-disk friction test. It was found that the ID/IG ratio of the (Si:N)-DLC (diamond-like carbon) top films increases with decreasing C2H2/N2 ratio. The (Si:N)-DLC top film with Si3N4 was formed on the MAO coated sample as the C2H2/N2 ratio was 10sccm:5sccm, which showed an increasing critical load compared with the pure DLC directly deposited on the Mg alloy substrate. As a result, the (Si:N)-DLC/MAO coating exhibited an advanced wear protection for the substrate.

Failure Mechanism of D-Gun Sprayed Thermal Barrier Coatings Subjected to Thermal Shock Cycling

Thermal barrier coatings (TBCs) with the ceramic coats of hollow spherical ZrO2-8%Y2O3 powder (HSP-YSZ) were obtained on Ni-base superalloy by detonation gun (D-gun) spraying. Thermal shock cyclic tests were performed by holding samples at 1100°C for 10 min and then water quenching to room temperature repeatedly. The D-gun sprayed TBCs didn’t fail up to 300 cycles and exhibited excellent resistance to thermal shock. Failure mechanism of D-gun sprayed TBCs subjected to thermal shock cycling was discussed.

Growth properties and resistive switching effects of diamond-like carbon films deposited using a linear ion source

Diamond-like carbon (DLC) films were prepared using an anode-layer linear ion beam source with C2H2 as the precursor and various negative bias voltages. The growth properties, microstructures, mechanical properties, and the resistive switching behaviors of the as-deposited DLC films were investigated as a function of bias voltage. The results showed that adjusting the bias voltage could vary the carbon atomic bonding structure (sp3/sp2 carbon hybridized bonding) of the films. The sp3/sp2 ratio initially increased as bias voltage increased and then decreased once the bias voltage exceeded −100 V. The variations in the film hardness and residual stress at different bias voltages were similar in profile to the sp3 bond fractions, indicating that both the residual stress and the mechanical properties of the DLC films were highly dependent on sp3-C bonding structures. The resistive switching characteristics of the DLC films were studied via a Cu/DLC/Pt cell structure. It was found that the bias voltages had a ...

Stress reduction of Cu-doped diamond-like carbon films from ab initio calculations

Structure and properties of Cu-doped diamond-like carbon films (DLC) were investigated using ab initio calculations. The effect of Cu concentrations (1.56∼7.81 at.%) on atomic bond structure was mainly analyzed to clarify the residual stress reduction mechanism. Results showed that with introducing Cu into DLC films, the residual compressive stress decreased firstly and then increased for each case with the obvious deterioration of mechanical properties, which was in agreement with the experimental results. Structural analysis revealed that the weak Cu-C bond and the relaxation of both the distorted bond angles and bond lengths accounted for the significant reduction of residual compressive stress, while at the higher Cu concentration the increase of residual stress attributed to the existence of distorted Cu-C structures and the increased fraction of distorted C-C bond lengths.

The effect of substrate bias on the characteristics of CrN coatings deposited by DC-superimposed HiPIMS system

Chromium nitride coatings were prepared by reactive DC-superimposed high-power-impulse magnetron sputtering (HiPIMS) system. The influence of substrate bias on the microstructure and mechanical properties of CrN coatings was investigated. XRD and cross-sectional SEM were utilized to characterize the film structures. Mechanical properties were characterized by nanoindentation and Vickers indentation test. The results revealed that the microstructure and mechanical properties of CrN coatings were affected by bias voltage. The CrN coatings exhibited dense and fine columnar grain structure with the hardness of about 18.7 GPa. The fracture toughness of CrN coatings was around 3.16 MPa ⋅ m1/2. However, further increase of the bias voltage from −250 V to −300 V led to the degradation of coating properties.