Signal-to-Noise Enhancement of a Nanospring Redox-Based Sensor by Lock-in Amplification

A significant improvement of the response characteristics of a redox chemical gas sensor (chemiresistor) constructed with a single ZnO coated silica nanospring has been achieved with the technique of lock-in signal amplification. The comparison of DC and analog lock-in amplifier (LIA) AC measurements of the electrical sensor response to toluene vapor, at the ppm level, has been conducted. When operated in the DC detection mode, the sensor exhibits a relatively high sensitivity to the analyte vapor, as well as a low detection limit at the 10 ppm level. However, at 10 ppm the signal-to-noise ratio is 5 dB, which is less than desirable. When operated in the analog LIA mode, the signal-to-noise ratio at 10 ppm increases by 30 dB and extends the detection limit to the ppb range

Silica Particle-Mediated Growth of Single Crystal Graphene Ribbons on Cu(111) Foil

The authors report the growth of micrometer-long single-crystal graphene ribbons (GRs) (tapered when grown above 900 degrees C, but uniform width when grown in the range 850 degrees C to 900 degrees C) using silica particle seeds on single crystal Cu(111) foil. Tapered graphene ribbons grow strictly along the Cu direction on Cu(111) and polycrystalline copper (Cu) foils. Silica particles on both Cu foils form (semi-)molten Cu-Si-O droplets at growth temperatures, then catalyze nucleation and drive the longitudinal growth of graphene ribbons. Longitudinal growth is likely by a vapor-liquid-solid (VLS) mechanism but edge growth (above 900 degrees C) is due to catalytic activation of ethylene (C2H4) and attachment of C atoms or species ("vapor solid" or VS growth) at the edges. It is found, based on the taper angle of the graphene ribbon, that the taper angle is determined by the growth temperature and the growth rates are independent of the particle size. The activation enthalpy (1.73 +/- 0.03 eV) for longitudinal ribbon growth on Cu(111) from ethylene is lower than that for VS growth at the edges of the GRs (2.78 +/- 0.15 eV) and for graphene island growth (2.85 +/- 0.07 eV) that occurs concurrently

Dissolving Diamond: Kinetics of the Dissolution of (100) and (110) Single Crystals in Nickel and Cobalt Films

We report a study of the kinetics of dissolution of (100) and (110) single-crystal diamond plates (???D(100)??? and ???D(110)???) in thin films of nickel (Ni) and cobalt (Co). This dissolution occurs at the metal???D(100) or metal???D(110) interface and was studied in the presence and also in the absence of water vapor at temperatures near 1000 ??C. The single-crystal D(100) dissolves in Ni, and also in Co, in the temperature range 900???1050 ??C. The dissolution is too slow to measure below 900 ??C. In an argon (Ar) atmosphere (under an Ar(g) flow at 1000 sccm and 1 atm pressure, with no water vapor present in the reaction chamber) and at any temperature in the range 900???1050 ??C, the metal film is rapidly saturated with dissolved carbon (C), thin graphite films form on the free metal surface and at the metal???D interface during heating at or above 650 ??C, and the dissolution of the diamond then stops. For addition of water vapor, its partial pressure was controlled by using a water bubbler immersed in a constant temperature bath and Ar(g) was used as the carrier gas. We discovered two different regimes (I and II) for the kinetics of dissolution of D(100) and D(110), in which the rate-determining step was the removal of carbon atoms on the open metal surface (regime I, lower partial pressure of water vapor) or dissolution of diamond at the metal???diamond interface (regime II, higher partial pressure of water vapor) that yielded different Arrhenius parameters. Time-of-flight-secondary ion mass spectrometry depth profiles show the concentration gradient of C from a certain depth into the metal film surface down to the M???D(100) interface, and residual gas analyzer measurements show that the gas products formed in the presence of water vapor on the metal surface are CO and H2. It was found that the rate of dissolution of diamond in Co was higher than that in Ni for both D(100) and D(110) and for both regimes I and II, and possible reasons are suggested. We also found that D(111) could not be dissolved at the Ni/D(111) and Co/D(111) interface in the presence of water vapor (over the same range of sample temperatures). The reaction paths for dissolution of C at the M???D(100) or M???D(110) interface and for removal of C from the free surfaces of Ni and Co were assessed through density functional theory modeling at 1273 K

Controllable electrodeposition of ordered carbon nanowalls on Cu(111) substrates

We report the growth of amorphous carbon nanowalls with molten salt electrolytes and a carbonate carbon source at 600 ??C on home-made Cu(111) foil as the growth substrate (and cathode). The nanometer thick nanowalls grow preferentially along symmetric slip lines on the Cu(111) surface and their ordered arrangement appears to also be dictated by the electrosynthesis parameters. Computational chemistry suggests that nucleation of carbon growth is favored at the slip lines (atomic steps) of the Cu(111) surface. The electrodeposited carbon structures can be varied by tuning the potential on the electrodes and temperature of the molten salt. The macro, micro, and nanoscale structure of the nanowalls was studied and is reported

Chemically induced transformation of chemical vapour deposition grown bilayer graphene into fluorinated single-layer diamond

Notwithstanding the numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film carried out to date, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface triggers the formation of interlayer carbon???carbon bonds, resulting in a fluorinated diamond monolayer (???F-diamane???). Induced by fluorine chemisorption, the phase transition from (AB)-stacked bilayer graphene to single-layer diamond was studied and verified by X-ray photoelectron, UV photoelectron, Raman, UV-Vis and electron energy loss spectroscopies, transmission electron microscopy and density functional theory calculations

Large-area single-crystal AB-bilayer and ABA-trilayer graphene grown on a Cu/Ni(111) foil

High-quality AB-stacked bilayer or multilayer graphene larger than a centimetre has not been reported. Here, we report the fabrication and use of single-crystal Cu/Ni(111) alloy foils with controllable concentrations of Ni for the growth of large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films by chemical vapour deposition. The stacking order, coverage and uniformity of the graphene films were evaluated by Raman spectroscopy and transmission electron microscopy including selected area electron diffraction and atomic resolution imaging. Electrical transport (carrier mobility and band-gap tunability) and thermal conductivity (the bilayer graphene has a thermal conductivity value of about 2,300 W m(-1) K-1) measurements indicated the superior quality of the films. The tensile loading response of centimetre-scale bilayer graphene films supported by a 260-nm thick polycarbonate film was measured and the average values of the Young's modulus (478 GPa) and fracture strength (3.31 GPa) were obtained. Large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films have been achieved, with fine control of Ni content, on single-crystal Cu/Ni(111) alloy foils

Colossal grain growth yields single-crystal metal foils by contact-free annealing

Single-crystal metals have distinctive properties owing to the absence of grain boundaries and strong anisotropy. Commercial single-crystal metals are usually synthesized by bulk crystal growth or by deposition of thin films onto substrates, and they are expensive and small. We prepared extremely large single-crystal metal foils by ???contact-free annealing??? from commercial polycrystalline foils. The colossal grain growth (up to 32 square centimeters) is achieved by minimizing contact stresses, resulting in a preferred in-plane and out-of-plane crystal orientation, and is driven by surface energy minimization during the rotation of the crystal lattice followed by ???consumption??? of neighboring grains. Industrial-scale production of single-crystal metal foils is possible as a result of this discovery