High temperature annealing in vacuum, air, hydrogen, chlorine, and ammonia are described as a means to change surface chemistry and phase composition of nanodiamond powders of three different grades, which have different sp2/sp3 carbon ratios. The changes in surface chemistry and phase composition of the powders are analyzed using Raman spectroscopy and Fourier Transform Infra Red (FTIR) spectroscopy. Advantages and limitation of high-temperature treatment techniques as well as potential applications of the gas-treated nanodiamond powders are discussed.

Miniaturized DNA sensitive field-effect transistors (DNA-FET) have been realized using single crystalline diamond grown by plasma-enhanced chemical vapor deposition (CVD). To bond DNA to diamond, amine linker-molecules are covalently attached by photochemical means to H-terminated diamond surfaces. Using hetero-bifunctional cross-linker and thiol-modified single-strand (ss) cancer marker DNA (CK20), the gate of diamond FETs is modified to sense hybridization of DNA, forming double-strand (ds) DNA molecules on the gate. The density of DNA bonded to diamond has been adjusted to about 1012 cm−2 and the experiments have been performed in phosphate buffer with different ionicity to control the Debye length of the Helmholtz layer. By hybridization, a gate-potential shift of 64 mV is detected in case of the 100 Å Debye lengths, while 46 mV is detected for 10 Å. This is discussed with respect to DNA related variations of charge and pH by hybridization. Time resolved experiments reveal exponential hybridization dynamics with a time constant of 600 s. The sensitivity limit of our experiment is about 1 nM.

The effect of ultrasonic method of seeding on the growth of nanocrystalline diamond (NCD) films has been studied by investigating the nucleation densities of two nanodiamond slurries- 1) nanodiamond powder suspended in acetone 2) mixture of titanium nanopowder and nanodiamond powder suspended in acetone. The former has resulted in a lower nucleation density on the order of 108 cm−2 while the later has increased the nucleation density by over two orders (>1010 cm−2) of magnitude. NCD films were grown on Si(100) substrates in a Cyrannus I Iplas microwave plasma enhanced chemical vapor deposition (MPECVD) reactor using 0.5% CH4, 1% H2 and 98.5% Ar gas chemistry at a substrate temperature of ∼ 750°C, pressure of 135 T and a microwave power of 1.8 kW. The double anchored cantilever structures with NCD as structural material have been fabricated by conventional photolithography. It was observed that the films grown after pre-treating the substrates in pure nanodiamond slurry have not provided a complete coverage at the anchor regions of the cantilevers due to the lower nucleation density. Hence during the sacrificial oxide etch, the anchor regions did not adhere well to the substrate and the entire structures got detached from the substrate. But on the other hand, the films grown by seeding the substrates in a suspension of titanium nanopowder and diamond nanopowder showed complete film coverage and consequently very good bonding to the Si substrate at the anchor pads. In this case, the cantilevers have been successfully released without any problems at the anchor pads. Further the mechanical properties of the films were conducted by evaluating the Young's modulus and the hardness by nano-indentation technique.

DNA sensors fabricated on single-crystalline B-doped diamond (SBDD) electrodes were characterized by scanning electrochemical microscopy (SECM). These experiments show that circular arranged DNA sensors of typically 2 mm diameter show some spatial variations in electrochemical response. The variation of the diamond electrode with respect to DNA bonding is electrochemically characterized and discussed in the context of ion attraction/repulsion by the negatively charged backbones of DNA and the negatively charged diamond surface. Our results show that repulsive forces affect the mediator propagation of Fe(CN)64- in the close vicinity of the DNA layer which can be used to investigate DNA density variations on sensor areas.

We report on the realization of a solid-state single-photon source in the near infrared at room temperature. It is based on the photoluminescence of a single NE8 colour center in a CVD grown diamond nanocrystal. Antibunching has been observed in the fluorescence light under both continuous and pulsed excitation. Our source delivers 30 kcts/s single-photon pulses at an excitation repetition rate of 20 MHz.

Nanocrystalline diamond (NCD) has been grown on oxide coated silicon wafers by microwave plasma assisted chemical vapour deposition using a novel seeding technique followed by optimised growth conditions, and leads to a highly-dense form of this material with grain sizes around 100nm for films approximately 1.5 microns thick. The electrical properties of these films have been investigated using Impedance Spectroscopy, which enables the contributions from sources characterised by differing capacitances, such as grain boundaries and grain interiors, to be isolated. After an initial acid clean the electrical properties of the film are not stable, and both grain boundaries and grains themselves contribute to the frequency dependant impedance values recorded. However, following mild oxidation grain boundary conduction is completely removed and the films become highly resistive (>1013 ohm/sq). This is most unusual, as conduction through NCD material is more normally dominated by grain boundary effects. Interestingly, the AC properties of these films are also excellent with a dielectric loss value (tan δ) as low as 0.002 for frequencies up to 10MHz. The dielectric properties of these NCD films are therefore as good as high quality free-standing (large grain) polycrystalline diamond films, and not too dissimilar to single crystal diamond, and are therefore ideally suited to future ‘silicon-on-diamond’ applications.

High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator.

The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

CVD diamond combines attractive properties for the fabrication of detection devices operating in specific environments. One problem that remains critical for device stability is the presence of defect levels that alter the detection performances, and the detection characteristics often appear as they are very depending on time, temperature, and history of the preceding irradiations.

One issue we have proposed is to adapt one technique that is commonly used for time of flight spectroscopy in order to maintain a uniform electric field in the probed device, and based on the synchronisation of the device bias with the period of the excitation source. This can be applied to several types of detection applications, as long as we can rely on periodical triggering in order to synchronise the device polarisation. We apply it here to a LINAC electron accelerator used for photon pulse generation at the frequency of 25Hz. The result is a remarkable improvement of the performance of a polycrystalline diamond detector that exhibits a particularly defective response when used in the steady state excitation, to reach that of a perfectly stable and reproducible device response in the pulsed mode. We claim this method to be applicable to several types of excitations and particularly to present a high interest for monitoring accelerator sources, e.g. for medical dosimetry applications.

Ultrapure, homoeptaxially grown CVD single crystal diamond is a material with great potential for the fabrication of ionizing radiation detectors for high energy, heavy ion physics, and realtime dosimetry for radiotherapy. Only diamond has suitable transmission properties and can offer the required radiation hardness for synchrotron X-ray beam monitoring applications. We report on experiments made using a synchrotron X-ray microbeam probe to investigate the performance of single crystal diamonds operated as position sensitive, solid state ‘ionization chambers’. We show that for a wide range of electric fields >0.3Vµm−1, suitably prepared devices give excellent spatial response uniformity and time stability. With an applied field of 2Vµm−1 complete charge collection times are ∼1nsec for a diamond plate thickness of 100µm. Position sensitivity was obtained for an X-ray beam incident on the isolation gap between adjacent electrodes of a quadrant device: here, a crossover response region that results from charge carrier diffusion extends over ∼20µm. Using GHz bandwidth signal processing electronics, the signal charge collection process was measured with spatial and temporal resolutions of 1µm and <50ps.