A high-temperature procedure to hydrogenate diamond films using molecular hydrogen at atmospheric pressure was explored. Undoped and doped chemical vapour deposited (CVD) polycrystalline diamond films were treated according to our annealing method using a H 2 gas flow down to ∼50 ml/min (STP) at ∼850• C. The films were extensively evaluated by surface wettability, electron affinity, elemental composition, photoconductivity, and redox studies. In addition, electrografting experiments were performed. The surface characteristics as well as the optoelectronic and redox properties of the annealed films were found to be very similar to hydrogen plasma-treated films. Moreover, the presented method is compatible with atmospheric pressure and provides a low-cost solution to hydrogenate CVD diamond, which makes it interesting for industrial applications. The plausible mechanism for the hydrogen termination of CVD diamond films is based on the formation of surface carbon dangling bonds and carbon-carbon unsaturated bonds at the applied temperature, which react with molecular hydrogen to produce a hydrogen-terminated surface. © 2013 AIP Publishing LLC. [http://dx
Nanocrystalline diamond (NCD) is a promising material for electronic and mechanical microand 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 MoS 2 , to fabricate heterostructures. Pick-up and drop transfer enables the fabrication of a variety of NCD-based devices without requiring lithography or wet processing.Keywords: nanocrystalline diamond, nanosheets, electronic circuits, mechanical resonator, heterostructures This is the post-peer reviewed version of the following article: V Seshan and JO Island et al. "Pick-up and drop transfer of diamond nanosheets".
A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to $1 nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport measurements. The structural changes produced by the elevated temperature, achieved by Joule heating during current annealing, are characterized using Raman spectroscopy. The formation of hybridized diamond/graphite structure is observed at the point of maximum heat accumulation. V C 2012 American Institute of Physics.[http://dx.doi.org/10.1063/1.4766346] During the last decade, carbon-based materials like diamond, 1 graphene, 2 and carbon nanotubes (CNTs) 3 have been extensively studied due to their outstanding physical properties and potential applications. Consequently, hybrid structures combining the advantages of different allotropes of carbon into one structure have slowly gained interest. For instance, hybrid diamond/graphite structures can be relevant in molecular electronic applications because they benefit from both the robustness of sp 3 bonds and the flexibility of sp 2 hybridization for functionalizing with a large variety of molecules. Hybrid structures such as diamond/graphite nanowires, 4 diamond/graphite nanoflakes, 5 and diamond/CNTs 6 composites have been reported in recent years.So far these hybrid structures have been synthesized using the conventional plasma-based chemical vapor deposition (CVD) technique. This technique, however, does not allow in situ fabrication of hybrid structures in specific domains. The current annealing technique, 7 on the other hand, has proven to be effective to induce structural transformations and even to fabricate nanometer-sized gaps. For example, the transformation of amorphous carbon layers into graphene 8 and restructuring of CNTs 9 have been reported using this technique. Furthermore, high-current annealing has also been used to fabricate nanogaps in few-layer graphene 10 and CNTs. 11 High-current annealing can therefore be a promising technique to fabricate nanogaps and hybrid structures also in diamond-based devices, which has not been explored yet. Nanocrystalline diamond 12 films are unique due to their close resemblance to single crystal diamond for many properties, the flexibility to grow on different substrates, and the control over their electrical properties via boron doping (ranging from wide bandgap insulator to semiconductor to superconductor behavior). Boron-doped nanocrystalline diamond (B:NCD) films have been implemented as an electrochemical electrode, 13 sensor, 14 and even superconducting quantum interference device (SQUID). 15 However, engineering B:NCD for using it as an electrode material for molecular electronics applications has been a big challenge because the strong covalent carbon network of diamond requires an unconventional approach to structure it.In this letter, we introduce a technique ...
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 optoelectronic 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 cm(2)/(V s) 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 (toward 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 photoexcited electrons in boron-doped NCD occupy nonionized boron dopants, leaving relatively long-lived mobile holes in the valence band.
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