[Show abstract][Hide abstract] ABSTRACT: A detailed investigation of electron emission from a set of chemical vapour deposited (CVD) diamond films is reported using high-resolution PeakForce-controlled tunnelling atomic force microscopy (PF-TUNA). Electron field emission originates preferentially from the grain boundaries in low-conductivity polycrystalline diamond samples, and not from the top of features or sharp edges. Samples with smaller grains and more grain boundaries, such as nanocrystalline diamond, produce a higher emission current over a more uniform area than diamond samples with larger grain size. Light doping with N, B or P increases the grain conductivity, with the result that the emitting grain-boundary sites become broader as the emission begins to creep up the grain sidewalls. For heavy B doping, where the grains are now more conducting than the grain boundaries, emission comes from both the grain boundaries and the grains almost equally. Lightly P-doped diamond samples show emission from step-edges on the (1 1 1) surfaces. Emission intensity was time dependent, with the measured current dropping to ∼10% of its initial value ∼30 h after removal from the CVD chamber. This decrease is ascribed to the build-up of adsorbates on the surface along with an increase in the surface conductivity due to surface transfer doping.
[Show abstract][Hide abstract] ABSTRACT: In this study some affinity and dielectric properties of molecularly imprinted (MIP) conducting polymer – polypyrrole (Ppy) based thin films were evaluated. Films of polypyrrole molecularly imprinted with theophylline (MIP-Ppy) and non-imprinted polypyrrole (NIP-Ppy) were formed on boron doped silicon (Si) substrates in order to evaluate the efficiency of Ppy to bind theophylline. The substrates were modified with boron-doped oxygen terminated nanocrystalline diamond (B:NCD:O) The dielectric properties of B:NCD:O/Ppy-based multi-layered structures were analyzed using spectroscopic ellipsometry and spectrophotometric techniques. Electrochemical impedance spectroscopy was applied for the investigation of kinetics of theophylline interaction with MIP-Ppy and NIP-Ppy. The sensitivity of molecularly imprinted and non-imprinted polymer films was analyzed by injection of different theophylline concentrations. Assuming that Ppy film electrical capacitance change is a result of Ppy dielectric constant change induced by absorbed theophylline molecules, the electrical capacitance change (ΔC) kinetics at different concentrations of theophylline was analyzed using first pseudo order kinetic equation. The dissociation equilibrium constant KD of MIP-Ppy/theophylline complex at room temperature was calculated as 1.7·10-8 M, and Gibbs free energy change (ΔG) of MIP-Ppy/theophylline complex formation was calculated as-43.5 kJ/mol. It was concluded that molecularly imprinted polypyrrole thin film could be used for the detection of theophylline.
[Show abstract][Hide abstract] ABSTRACT: Photoactive reaction centers (RCs) are protein complexes in bacteria able to convert sunlight into other forms of energy with a high quantum yield. The photo-stimulation of immobilized RCs on inorganic electrodes result in the generation of photocurrent that is of interest for bio-solar cell applications. This paper reports on the use of novel electrodes based on functional conductive nanocrystalline diamond onto which bacterial RCs are immobilized. A 3-dimensional conductive polymer scaffold grafted to the diamond electrodes enables an efficient entrapment of photoreactive proteins. The electron transfer in these functional diamond electrodes is optimized through the use of a ferrocene-based electron mediator, which provides significant advantages such as a rapid electron transfer as well as high generated photocurrent. A detailed discussion of the generated photocurrent as a function of time, bias voltage and mediators in solution unveils the mechanisms limiting the electron transfer in these functional electrodes. This work featuring diamond-based electrodes in bio-photovoltaics, offers general guidelines that can serve to improve the performance of similar devices based on different materials and geometries.
[Show abstract][Hide abstract] ABSTRACT: Lead phthalocyanine (PbPc) thin films of 5 and 50 nm have been deposited on hydrogen and oxygen terminated single crystal diamond (SCD) using organic molecular beam deposition. Atomic force microscopy and X-ray diffraction (XRD) studies showed that PbPc grown on the hydrogen terminated SCD forms layers with a high degree of crystallinity, dominated by the monoclinic (320) orientation parallel to the diamond surface. The oxygen terminated diamond led to a randomly oriented PbPc film. Absorption and photocurrent measurements indicated the presence of both polymorphs of PbPc, however, the ratio differed depending on the termination of the SCD. Finally, polarized Raman spectroscopy was used to determine the orientation of the molecules of the thin film. The results confirmed the random orientation on the O-terminated diamond. On SCD:H, the PbPc molecules are lying down in accordance with the XRD results.
[Show abstract][Hide abstract] ABSTRACT: Nanocrystalline diamond (NCD) is a promising material for electronic and
mechanical micro- and nanodevices. Here we introduce a versatile pick-up and
drop technique that makes it possible to investigate the electrical, optical
and mechanical properties of as-grown NCD films. Using this technique, NCD
nanosheets, as thin as 55 nm, can be picked-up from a growth substrate and
positioned on another substrate. As a proof of concept, electronic devices and
mechanical resonators are fabricated and their properties are characterized. In
addition, the versatility of the method is further explored by transferring NCD
nanosheets onto an optical fibre, which allows measuring its optical
absorption. Finally, we show that NCD nanosheets can also be transferred onto
2D crystals, such as MoS2, to fabricate heterostructures. Pick-up and drop
transfer enables the fabrication of a variety of NCD-based devices without
requiring lithography or wet processing.
[Show abstract][Hide abstract] ABSTRACT: In this study we show an optical biosensor concept, based on elastic light scattering from sapphire microspheres. Transmitted and elastic scattering intensity of the microspheres (radius 500 μm, refractive index 1.77) on an optical fiber half coupler is analyzed at 1510 nm. The 0.43 nm angular mode spacing of the resonances is comparable to the angular mode spacing value estimated using the optical size of the microsphere. The spectral linewidths of the resonances are in the order of 0.01 nm, which corresponds to quality factors of approximately 105. A polydopamine layer is used as a functionalizing agent on sapphire microspherical resonators in view of biosensor implementation. The varying layer thickness on the microsphere is determined as a function of the resonance wavelength shift. It is shown that polymer functionalization has a minor effect on the quality factor. This is a promising step toward the development of an optical biosensor.
Sensors and Actuators A Physical 02/2015; 222. DOI:10.1016/j.sna.2014.11.024 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Boron doped diamond layers have been grown on (110) single crystal diamond substrates with B/C ratios up to 20 ppm in the gas phase. The surface of the diamond layers observed by scanning electron microscopy consists of (100) and (113) micro-facets. Fourier Transform Photocurrent Spectroscopy indicates substitutional boron incorporation. Electrical properties were measured using Hall effect from 150 to 1000 K. Secondary ion mass spectrometry analyses are consistent with the high incorporation of boron determined by electrical measurements. A maximum mobility of 528 cm2.V- 1.s- 1 was measured at room temperature for a charge carrier concentration of 1.1 1013 cm- 3. Finally, properties of boron doped (110) diamond layers are compared with layers on (100) and (111) orientated substrates.
Diamond and Related Materials 01/2015; 53. DOI:10.1016/j.diamond.2015.01.006 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphene has potential for applications in solar cells. We show that the short circuit current density of P3HT (Poly(3-hexylthiophene-2,5-diyl):PCBM((6,6)-Phenyl C61 butyric acid methyl ester) solar cells is enhanced by 10% upon the addition of graphene, with a 15% increase in the photon to electric conversion efficiency. We discuss the performance enhancement by studying the crystallization of P3HT, as well as the electrical transport properties. We show that graphene improves the balance between electron and hole mobilities with respect to a standard P3HT:PCBM solar cell. (C) 2014 AIP Publishing LLC.
[Show abstract][Hide abstract] ABSTRACT: In this study development of impedimetric sensor based on oxygen terminated boron-doped nanocrystalline diamond (B:NCD:O) modified with theophylline imprinted polypyrrole is described. Hydrogen peroxide induced chemical formation of polypyrrole molecularly imprinted by theophylline was applied for the modification of conducting silicon substrate covered by B:NCD:O film. Non-imprinted polypyrrole layer was formed on similar substrate in order to prove efficiency of imprinted polypyrrole. Electrochemical impedance spectroscopy was applied for the evaluation of analyte-induced changes in electrochemical capacitance/resistance. The impact of polymerization duration on the capacitance of impedimetric sensor was estimated. A different impedance behavior was observed at different ratio of polymerized monomer and template molecule in the polymerization media. The influence of ethanol as additive to polymerization media on registered changes in capacitance/resistance was evaluated. Degradation of sensor stored in buffer solution was evaluated.
[Show abstract][Hide abstract] ABSTRACT: Donor-acceptor type light-harvesting molecular wires are covalently attached to a boron-doped diamond surface via a combination of diazonium electrografting and Suzuki cross-coupling. For the Suzuki reaction, various catalytic systems are compared with respect to their imposed surface coverage. Combining 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (SPhos) and Pd(0), the diamond coverage improves considerably (by 98%) as compared to the standard tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4) catalyst. As the energy levels between the molecular chromophores and the diamond film align well, the sophisticated functionalized diamond surfaces present a first step towards the development of fully carbon-based devices for light to electricity conversion.
[Show abstract][Hide abstract] ABSTRACT: Surface conductivity in hydrogen-terminated single crystal diamond is an intriguing phenomenon for fundamental reasons as well as for application driven research. Surface conductivity is also observed in hydrogen-terminated nanocrystalline diamond although the electronic transport mechanisms remain unclear. In this work, the piezoresistive properties of intrinsic surface conductive nanocrystalline diamond are investigated. A gauge factor of 35 is calculated from bulging a diamond membrane of 350 nm thick, with a diameter of 656 μm and a sheet resistance of 1.45 MΩ/sq. The large piezoresistive effect is reasoned to originate directly from strain-induced changes in the resistivity of the grain boundaries. Additionally, we ascribe a small time-dependent fraction of the piezoresistive effect to charge trapping of charge carriers at grain boundaries. In conclusion, time-dependent piezoresistive effect measurements act as a tool for deeper understanding the complex electronic transport mechanisms induced by grain boundaries in a polycrystalline material or nanocomposite.
[Show abstract][Hide abstract] ABSTRACT: In this article, we report on a label-free real-time method based on heat transfer resistivity for thermal monitoring of DNA denaturation and its potential to quantify DNA fragments with a specific sequence of interest. Probe DNA, consisting of a 36-mer fragment was covalently immobilized on a nanocrystalline diamond surface, created by chemical vapor deposition on a silicon substrate. Various concentrations of full matched 29-mer target DNA fragments were hybridized with this probe DNA. We observed that the change in heat transfer resistance upon denaturation depends on the concentration of target DNA used during the hybridization, which allowed to determine the dose response curve. Therefore, these results illustrate the potential of this technique to quantify the concentration of a specific DNA fragment and to quantify the hybridization efficiency to its probe.
Diamond and Related Materials 09/2014; 48. DOI:10.1016/j.diamond.2014.06.008 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphene has potential for applications in solar cells. We show that the short circuit current density of P3HT (Poly(3-hexylthiophene-2,5-diyl):PCBM((6,6)-Phenyl C61 butyric acid methyl ester) solar cells is enhanced by 10% upon the addition of graphene, with a 15% increase in the photon to electric conversion efficiency. We discuss the performance enhancement by studying the crystallization of P3HT, as well as the electrical transport properties. We show that graphene improves the balance between electron and hole mobilities with respect to a standard P3HT:PCBM solar cell.
[Show abstract][Hide abstract] ABSTRACT: The modification of the diamond surface with organic molecules is a crucial aspect to be considered for any bio-application of this material. There is a great interest in broadening the range of linker molecules which can be covalently bound to the diamond surface. In the case of protein immobilization, the hydropathicity of the surface has a major influence on the protein conformation and, thus, on the functionality of proteins immobilized at surfaces. For electrochemical applications, particular attention has to be devoted to avoid that the charge transfer between the electrode and the redox center embedded in the protein is hindered by a thick insulating linker layer. This paper reports on the grafting of 6-phosphonohexanoic acid on OH-terminated diamond surfaces, serving as linkers to tether electro-active proteins onto diamond surfaces. X-ray photoelectron spectroscopy (XPS) confirms the formation of a stable layer on the surface. The charge transfer between electro-active molecules and the substrate is studied by electrochemical characterization of the redox activity of aminomethylferrocene and cytochrome c covalently bound to the substrate through this linker. Our work demonstrates that OH-terminated diamond functionalized with 6-phosphonohexanoic acid is a suitable platform to interface redox-proteins, which are fundamental building blocks for many bioelectronics applications.
[Show abstract][Hide abstract] ABSTRACT: A straightforward protocol for the covalent functionalization of boron-doped diamond electrodes with either ferrocene or single-stranded deoxyribonucleic acid (DNA) is reported. The functionalization method is based on a combination of diazonium salt electrografting and click chemistry. An azide-terminated organic layer is first electrografted onto the diamond surface by electrochemical reduction of 4-azidophenyldiazonium chloride. The azidophenyl-modified surface then reacts rapidly and efficiently with molecules bearing a terminal alkyne moiety by means of CuI-catalyzed alkyne–azide cycloaddition. Covalent attachment of ferrocene moieties was analyzed by X-ray photoelectron spectroscopy and cyclic voltammetry, whereas impedance spectroscopy was applied for the characterization of the immobilized DNA.
[Show abstract][Hide abstract] ABSTRACT: Hydrogen and oxygen surface-terminated nanocrystalline diamond (NCD) films are studied by the contactless time-resolved microwave conductivity (TRMC) technique and X-ray photoelectron spectroscopy (XPS). The opto-electronic properties of undoped NCD films are strongly affected by the type of surface termination. Upon changing the surface termination from oxygen to hydrogen, the TRMC signal rises dramatically. For an estimated quantum yield of 1 for sub-bandgap optical excitation the hole mobility of the hydrogen-terminated undoped NCD was found to be ~0.27 cm2/Vs with a lifetime exceeding 1 µs. Assuming a similar mobility for the oxygen-terminated undoped NCD a lifetime of ~100 ps was derived. Analysis of the valence band spectra obtained by XPS suggests that upon oxidation of undoped NCD the surface Fermi level shifts (towards an increased work function). This shift originates from the size and direction of the electronic dipole moment of the surface atoms, and leads to different types of band bending at the diamond/air interface in the presence of a water film. In the case of boron-doped NCD no shift of the work function is observed, which can be rationalized by pinning of the Fermi level. This is confirmed by TRMC results of boron-doped NCD, which show no dependency on the surface termination. We suggest that photo-excited electrons in boron-doped NCD occupy non-ionized boron dopants, leaving relatively long-lived mobile holes in the valence band.
[Show abstract][Hide abstract] ABSTRACT: N3 dye molecules [cis-bis(isothiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)] are covalently attached onto boron-doped nanocrystalline diamond (B:NCD) thin films through a combination of coupling chemistries, i.e. diazonium, Suzuki and EDC-NHS. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) are used to verify the covalent bonding of the dye on the B:NCD surface (as compared to a hydrogen-terminated reference). The spectroscopic results confirm the presence of a dense N3 chromophore layer and the positions of the frontier orbitals of the dye relative to the band edge of the B:NCD thin film are inferred as well. Proof of concept photoelectrochemical measurements show a strong increase in photocurrent as compared to non-dye-functionalized B:NCD films. This study opens up the possibility to apply N3-sensitized B:NCD thin films as hole conductors in dye-sensitized solar cells.