Bonding regimes of nitrogen in amorphous carbon

Nitrogen can have numerous effects on diamond-like carbon: it can dope, it can form the hypothetical superhard compound C3N4, or it can create fullerene-like bonding structures. We studied amorphous carbon nitrogen films deposited by a filtered cathodic vacuum arc as a function of nitrogen content, ion energy and deposition temperature. The incorporation of nitrogen from 10-2 to 10 at% was measured by secondary ion mass spectrometry and elastic recoil detection analysis and was found to vary slightly sublinearly with N2 partial pressure during deposition. In the doping regime from 0 to about 0.4% N, the conductivity changes while the sp3 content and optical gap remain constant. From 0.4 to approximately 10% N, existing sp2 sites condense into clusters and reduce the band gap. Nitrogen contents over 10% change the bonding from mainly sp3 to mainly sp2. Ion energies between 20 and 250 eV do not greatly modify this behaviour. Deposition at higher temperatures causes a sudden loss of sp3 bonding above about 150 °C. Raman spectroscopy and optical gap data show that existing sp2 sites begin to cluster below this temperature, and the clustering continues above this temperature. This transition is found to vary only weakly with nitrogen addition, for N contents below 10%.

Protein functionalized ZnO thin film bulk acoustic resonator as an odorant biosensor

ZnO thin film bulk acoustic resonators (FBARs) with resonant frequency of ∼1.5 GHz have been fabricated to function as an odorant biosensor. Physical adsorption of an odorant binding protein (AaegOBP22 from Aedes aegypti) resulted in frequency down shift. N,N-diethyl-meta-toluamide (DEET) has been selected as a ligand to the odorant binding protein (OBP). Alternate exposure of the bare FBARs to nitrogen flow with and without DEET vapor did not cause any noticeable frequency change. However, frequency drop was detected when exposing the OBP loaded FBAR sensors to the nitrogen flow containing DEET vapor against nitrogen flow alone (control) and the extent of frequency shift was proportional to the amount of the protein immobilized on the FBAR surface, indicating a linear response to DEET binding. These findings demonstrate the potential of binding protein functionalized FBARs as odorant biosensors. © 2012 Elsevier B.V. All rights reserved.

Comparison between granular pillared, organo- and inorgano-organo-bentonites for hydrocarbon and metal ion adsorption

Granular reactive materials have higher permeability and are therefore desirable for in situ groundwater pollution control. Three granular bentonites were prepared: an Al-pillared bentonite (PBg), an organo-bentonite (OBg) using a quaternary ammonium cation (QAC), and an inorgano-organo-bentonite (IOBg), using both the pillaring agent and the QAC. Powdered IOB (IOBp) was also prepared to test the effect of particle size. The modified bentonites were characterised with X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), thermal gravimetric analysis (TGA) and uniaxial compression tests. The d-spacing increased only with QAC intercalation. The Young's modulus of IOBg was twice as high as OBg. Batch adsorption tests were performed with aqueous multimetal solutions of Pb2+, Cu2+, Cd2+, Zn2+ and Ni2+ ions, with liquid dodecane and with aqueous dodecane solutions. Metal adsorption fit the Langmuir isotherm. Adsorption occurred within 30min for PBg, while the granular organo-bentonite needed at least 12h to reach equilibrium. IOBp had the maximum adsorption capacity at higher metal concentration and lower adsorbent content (Cu2+: 2.2, Ni2+: 1.7, Zn2+: 1.4, Cd2+: 0.9 and Pb2+: 0.7 all in mmolg-1). The dual pillaring of the QAC and Al hydroxide increased the adsorption. The adsorption of liquid dodecane was in the order IOBg>OBg>PBg (3.2>2.7>1.7mmolg-1). Therefore IOBg has potential for the removal of toxic compounds found in soil, groundwater, storm water and wastewater. © 2012 Elsevier B.V.

A comprehensive study of lysozyme adsorption using dual polarization interferometry and quartz crystal microbalance with dissipation.

Protein adsorption plays a crucial role in biomaterial surface science as it is directly linked to the biocompatibility of artificial biomaterial devices. Here, elucidation of protein adsorption mechanism is effected using dual polarization interferometry and a quartz crystal microbalance to characterize lysozyme layer properties on a silica surface at different coverage values. Lysozyme is observed to adsorb from sparse monolayer to multilayer coverage. At low coverage an irreversibly adsorbed layer is formed with slight deformation consistent with side-on orientation. At higher coverage values dynamic re-orientation effects are observed which lead to monolayer surface coverages of 2-3 ng/mm² corresponding to edge-on or/and end-on orientations. These monolayer thickness values ranged between 3 and 4.5 nm with a protein density value of 0.60 g/mL and with 50 wt% solvent mass. Further increase of coverage results formation of a multilayer structure. Using the hydration content and other physical layer properties a tentative model lysozyme adsorption is proposed.

A comprehensive study of lysozyme adsorption using dual polarization interferometry and quartz crystal microbalance with dissipation

Protein adsorption plays a crucial role in biomaterial surface science as it is directly linked to the biocompatibility of artificial biomaterial devices. Here, elucidation of protein adsorption mechanism is effected using dual polarization interferometry and a quartz crystal microbalance to characterize lysozyme layer properties on a silica surface at different coverage values. Lysozyme is observed to adsorb from sparse monolayer to multilayer coverage. At low coverage an irreversibly adsorbed layer is formed with slight deformation consistent with side-on orientation. At higher coverage values dynamic re-orientation effects are observed which lead to monolayer surface coverages of 2-3 ng/mm2 corresponding to edge-on or/and end-on orientations. These monolayer thickness values ranged between 3 and 4.5 nm with a protein density value of 0.60 g/mL and with 50 wt% solvent mass. Further increase of coverage results formation of a multilayer structure. Using the hydration content and other physical layer properties a tentative model lysozyme adsorption is proposed. © 2012 Elsevier Ltd.

Extreme sensitivity of graphene photoconductivity to environmental gases.

Graphene is a single layer of covalently bonded carbon atoms, which was discovered only 8 years ago and yet has already attracted intense research and commercial interest. Initial research focused on its remarkable electronic properties, such as the observation of massless Dirac fermions and the half-integer quantum Hall effect. Now graphene is finding application in touch-screen displays, as channels in high-frequency transistors and in graphene-based integrated circuits. The potential for using the unique properties of graphene in terahertz-frequency electronics is particularly exciting; however, initial experiments probing the terahertz-frequency response of graphene are only just emerging. Here we show that the photoconductivity of graphene at terahertz frequencies is dramatically altered by the adsorption of atmospheric gases, such as nitrogen and oxygen. Furthermore, we observe the signature of terahertz stimulated emission from gas-adsorbed graphene. Our findings highlight the importance of environmental conditions on the design and fabrication of high-speed, graphene-based devices.