Search

A new characterization technique to identify qualitatively diamond surface terminations and to measure quantitatively the density of hydrogen atoms bonded to the diamond surface is introduced using electrochemical grafting of diamond with diazonium salts. The cathodic peak potentials for the grafting of nitrophenyl layers reveal qualitative information about surface terminations ranging from –H, to –OH to –O–. The charges consumed during the conversion of nitro- to aminophenyl are used to calculate quantitatively the density of hydrogen atoms bonded to the diamond surface. As hydrogen is generally very difficult to detect by other methods like X-ray Photon Spectroscopy, this new method will add significantly to the understanding of surface related properties of transducers. Keywords: Diamond electrochemistry, Surface termination, Diazonium salts

In this review, we introduce a novel procedure to fabricate vertically aligned diamond nanowires with controlled geometrical properties like length and distance between wires by use of nanodiamond particles as a hard mask and by use of reactive ion etching. We summarize the characterizations of nanowires by atomic force microscopy and scanning tunneling microscopy as well as electrochemical techniques. In the last section, we show biofunctionalization of nucleic acid molecules on diamond nanowires using electrochemically bond nitrophenyl molecules as linker for deoxyribonucleic acid (DNA) sensing. The tip biofunctionalization and performance of as-prepared DNA sensors are discussed in detail.

Chemical vapour deposition has been utilised for the fabrication of nickel–nitrogen defects in diamond. By introducing nickel, as well as nitrogen into the process gas, this approach offers the advantage, that a direct formation of nickel–nitrogen centres on the growing surface is possible. This could therefore make postannealing steps superfluous. Nanocrystalline diamond films, as well as single crystal layers were grown under addition of nickel and nitrogen using different doping sources, namely: gaseous nickelocene, nickel powder and nickel wire. The amount of nickel present in the gas phase was characterised by optical emission spectroscopy (OES). In order to investigate the presence of nickel or nickel–nitrogen-related defects, photoluminescence (PL) measurements at different temperatures have been applied. A strong fluorescence in the range between 800 and 900 nm, accompanied by a peak at around 817 nm, as well as a narrow peak at 788 nm has been observed at cryogenic temperatures (10 K). The peak at 788 nm indicates the presence of nickel and nickel–nitrogen-related complexes in our samples. PL measurements at higher temperatures reveal, an initially rising intensity of a broad emission band at temperatures up to 200 K, while the emission is quenched at 300 K.

Vertically aligned diamond nanowires are biofunctionalized using aminophenyl linker molecules to bond nucleic acid molecules with a well-defined nanometer-sized spacing to the transducer. This novel DNA biosensor combines the outstanding electrochemical properties of diamond as a transducer with the controlled bonding of DNA molecules to the tips of nanowires by use of an electrochemical attachment scheme. Nucleic acid molecules are bonded in this way and dispersed to the transducer, giving rise to optimized hybridization kinetics of DNA. Negatively charged redox mediator molecules (Fe(CN) 6 3-/4- ) are applied for DNA-hybridization sensing. Voltammetric detection of DNA hybridization by differential pulse voltammetry is performed with respect to its sensitivity and reproducibility. On a sensor area of 0.03 cm 2 , a detection limit of 2.0 pM is achieved. As for the chemical stability of the DNA bonding to the diamond nanowires, no degradation over 30 hybridization/denaturation cycles could be detected. By use of this dilute DNA arrangement, single-base mismatch discrimination is achieved. Under the same conditions, smooth diamond modified with phenyl is not suitable for amperometric DNA sensing.

The bonding and growth mechanism of photochemically attached olefin molecules to (1 0 0)(2 × 1):H diamond is characterized using atomic force (AFM) and scanning tunneling microscopy (STM) experiments in combination with molecular orbital calculations. To identify growth schemas, diamond surfaces after 10, 40 and 90 min of photo-chemically stimulated growth have been characterized. These data show clearly island formation which is discussed taking into account a growth model from silicon. The island growth shows no directional properties which are attributed to arrangement and geometrical properties of hydrogen terminated carbon bonds at the surface of (1 0 0) oriented (2 × 1) reconstructed diamond.

In this study, the field emission properties of P-doped diamond with various surface treatments were measured in order to understand the effects of surface treatments on the barrier height. The emission properties were acquired for diamond with C-reconstructed, oxidized, and H-plasma treated surfaces. The voltage drop across the vacuum was estimated for each surface, using threshold voltage–anode distance (V–d) measurement. The estimated electric fields near the diamond surface were 4.95, 26.6, and 54.1 V/µm for the C-reconstructed, oxidized, and H-plasma treated surfaces, respectively. The barrier height ratio of these surfaces derived from their electric fields was 1:3.1:4.9, which agrees with the result derived from Fowler–Nordheim (F–N) plots. Considering the electron affinities of all surfaces and the obtained results, positive electron affinities dominate the field emission properties of the C-reconstructed and oxidized surfaces. An internal barrier due to upward band bending on the H-plasma treated surface limits the field emission properties, even though it has a negative electron affinity. Our results suggest that the emission properties strongly depend on the barrier height, which is modified by surface treatment.

Vertically aligned diamond nanowires with controlled geometrical properties like length and distance between wires were fabricated by use of nanodiamond particles as a hard mask and by use of reactive ion etching. The surface structure, electronic properties, and electrochemical functionalization of diamond nanowires were characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) as well as electrochemical techniques. AFM and STM experiments show that diamond nanowire etched for 10 s have wire-typed structures with 3-10 nm in length and with typically 11 nm spacing in between. The electrode active area of diamond nanowires is enhanced by a factor of 2. The functionalization of nanowire tips with nitrophenyl molecules is characterized by STM on clean and on nitrophenyl molecule-modified diamond nanowires. Tip-modified diamond nanowires are promising with respect to biosensor applications where controlled biomolecule bonding is required to improve chemical stability and sensing significantly.

The relationship between field emission properties and C 1s core level shifts of heavily phosphorus-doped homoepitaxial (1 1 1) diamond is investigated as a function of annealing temperature in order to optimize surface carbon bonding configurations for device applications. A low field emission threshold voltage is observed from surfaces annealed at 800 °C for hydrogen-plasma treated surface, while a low field emission threshold voltage of wet-chemical oxidized surface is observed after annealing at 900 °C. The C 1s core level by X-ray photoelectron spectroscopy (XPS) showed a shoulder peak at 1 eV below the main peak over 800 and 900 °C annealing temperature for hydrogen-plasma treated and wet-chemical oxidized surfaces, respectively. When the shoulder peak intensity is less than 10% of the main peak intensity, lower threshold voltages are observed. This is due to the carbon-reconstruction which gives rise to a small positive electron affinity. By increasing annealing temperature, the shoulder peak ratios also increase, which indicates that a surface graphitization takes place. This leads to higher threshold voltages.

The initial nucleation and growth characteristics of amine layers photochemically attached from 10-amino-dec-1-ene molecules protected with tri-fluoroacetic acid group to H-terminated undoped single crystal CVD diamond surfaces are characterized by tapping and contact mode atomic force microscopy (AFM) and scanning tunneling microscopy (STM) with nanometer resolution. The diamond is atomically flat which allows attributing variations of tunneling currents in STM to amine grafted surface areas. Island formation and growth of islands with increasing photochemical attachment time is revealed by these experiments. This results support the growth model, where hydrogen cleavage reactions from the diamond surface by amine molecules bonded to diamond is the major growth mechanism. These reactions might be initiated by UV light illumination of pyrolysis of organic peroxides in the presence of the adsorbate, which are proposed to break H–C bonds to create surface dangling bonds. It occurs at the periphery of islands which gives rise to island growth.

Amine layers photochemically attached from TFAAD (10-amino-dec-1-ene molecules protected with trifluoroacetic acid group) on H-terminated undoped single crystal CVD diamond surfaces at different illumination time was investigated using X-ray photoelectron microscopy (XPS), atomic force microscopy (AFM) in a nano-scale view, and conductivity measurements. The experiments reveal a two-dimensional (2D) growth and formation of a mono-molecular layer on diamond for photo-attachment times up to 8–10 h. Longer exposure gives rise to secondary nucleation and cross-polymerization. Conductivity measurement of diamond before and after attachment of TFAAD suggested a partial photochemical reaction of hydrogen atoms on diamond surface with TFAAD.

Vacuum anneal treatments effects on field emission properties of phosphorus doped diamond are discussed. The C1s core level of diamond is characterized by X-ray photoelectron spectroscopy (XPS). With increasing annealing temperature, firstly oxygen desorption takes place from surface, which induce surface reconstruction followed by graphitization of surface. Field emission properties, therefore, strongly depend on vacuum anneal temperature. The threshold voltage of diamond annealed at 900 °C is the lowest. Fowler–Nordheim plots indicate that diamond annealed at 900 °C has the lowest barrier height, which is in good agreement with electron affinities as measured on carbon reconstructed surface. Further increased annealing temperature induces surface graphitization, which causes a threshold voltage increase of field emission.

High-quality homoepitaxial diamond films grown by microwave plasma-assisted chemical vapor deposition from 12C, 13C and naturalC containing methane (CH4) gases have been studied by cathodoluminescence (CL) spectroscopy. Near-band-gap CL spectra at low temperatures were characterized in two isotopically enriched C diamond (12C, 13C) films. We observe an energy shift of the free-exciton recombination radiation with a change of the isotope composition from 12C to 13C. This result is in good agreement with both theoretical prediction as well as experimental results reported in the literature. In addition, strong excitonic emiss ion is detected from the isotopic clean 12C diamond films at 79 K.

Field emission from heavily phosphorus-doped homoepitaxial (111) diamonds after surface modifications are discussed. To develop a model for emission, we applied X-ray photoelectron spectroscopy (XPS) to characterize surface properties of H-plasma treated, oxidized and carbon-reconstructed surfaces. In addition, reflection high energy electron diffraction (RHEED) is used to evaluate atomic arrangements. Atomic force microscopy (AFM) is used to investigate surface morphologies. From AFM, no major difference is observed between H-terminated, oxidized and carbon reconstructed surfaces. Field emission properties of carbon reconstructed surfaces show a lower threshold than hydrogen-terminated or oxidized surfaces.

Double stranded deoxyribonucleic acid (ds-DNA) layers, bonded to hydrogen terminated polycrystalline diamond, are characterized by scanning electron (SEM), fluorescence (FM), and atomic force microscopy (AFM). DNA grafting has been achieved using photochemical bonding of ω-unsaturated 10-amino-dec-1-ene molecules. SEM detects local variations of electron affinities on polycrystalline diamond, revealing distinct grain structures. FM applied on fluorescence labeled ds-DNA show laterally varying intensities of typically 20%, which resembles also grain structure as detected by SEM. Contact and tapping-mode AFM characterization reveal a tilted DNA bonding to diamond and a dense layer formation which gives rise to smoothening of surface properties. The lateral density variation of DNA is attributed to local variations of the photo-electron emission efficiency which affects the photochemical attachment chemistry of amine-linker molecules to diamond.

Immobilization of biomolecules on transducer surfaces depends on detailed characteristics of linker molecular layers. In this paper, we investigate amine layer growth on atomically smooth hydrogen-terminated diamond surfaces, applying a photochemical attachment process using ω-unsaturated 10-amino-dec-1-ene molecules protected with trifluoroacetic acid groups. The layer formation and growth is characterized by atomic force microscopy (AFM) in tapping and contact mode, X-ray photoelectron spectroscopy (XPS), and surface conductivity experiments. A two-dimensional (2D) formation of a mono-molecular amine-layer is revealed that needs about 8−10 h to form a closed layer on the surface of diamond. Application of photochemical attachment for longer times results in three-dimensional (3D) growth, governed by cross-polymerization and generation of layer protrusions. The diamond/amine interface remains basically hydrogen-terminated, which points toward low surface-defect generation by olefin addition. The 2D growt...

Surface electronic properties on oxidized boron (B) doped (111) homoepitaxial diamond films are investigated by Hall effect measurements and Schottky junction characterizations. Surface electronic properties on (111) diamond strongly depend on annealing treatments after wet-chemical oxidation, whereas for those on (001) diamond no change due to annealing can be detected. Hall effect results show that a p-type surface conductive layer (SCL) exists on (111) diamond surface in air after wet-chemical oxidation followed by annealing in Ar atmosphere (WO–AN) above 300 °C, but does not if only wet-chemical oxidation or air-oxidation is applied. This SCL disappears at annealing temperature above 350 °C in air. Schottky junction characteristics suggest that the Fermi level is unpinned at the (111) surface after WO–AN. Surface electronic characteristics on (111) diamond after WO–AN are similar to those generated by hydrogen termination.

Ion-sensitive field-effect transistors (ISFET) are fabricated using intrinsic hydrogen-terminated mono-crystalline diamond films. Transistor properties are realized by a surface conductive channel on hydrogen-terminated diamond. The gating is realized by immersing the diamond surface into electrolyte solution which is contacted by a platinum electrode. Hydrogen termination of diamond surface acts as a gate insulation without any additional oxide layer. The response of gate potential to pH is about − 56 mV/pH. The results are discussed in terms of transfer doping mechanism, Nernst equation, and electrochemical properties of diamond surfaces. They are also compared with ISFETs which employ ion-sensitive gate oxides.

International audience; Vulnerability of drinking water distribution systems which would have major public health, economic and psychosocial consequences, has become a big concern to governmental agencies and water supply authorities. In case of an extremely alerting situation, such as Fukushima, the alpha emitters in water are probed on samples after very long chemical operations and time for the delivery of results extends over several days. The main objective of the ActiFind project is the realization of a high sensitivity alpha particles sensor working into water for the rapid detection and identification of traces of actinides at the 1 Bq/L level, after a short electro precipitation step. A 200 μm thick BDD layer is deposited on a CANBERRA PIPS detector. Under low cathodic current density, nitrate reduction occurs and produces a layer of (OH - ) at the BDD surface and solid actinides hydroxides are accumulated at the entrance window of the PIPS sensor. After deposition, the ActiFind sensor is directly connected to a spectrometry chain. The coupling of the system to an integrated microfluidic F.F.E. platform has been developed in order to render the system compatible with more complex aqueous solutions in real environments containing interfering ions or substances. Further extension of the system will explore the possibility to use it as a decontaminating system on a scale up basis. The ability to perform alpha spectrometry directly in liquid media at trace levels constitutes a real breakthrough. Bq/L range is reachable within 10 minutes, opening the field to the development of a portable system with low energy requirement, and enabling real time monitoring of media at risk. This new technology can be used in the analysis of water used for cleaning surfaces in fuel reprocessing plants, sampling of environmental water around waste storage facilities, analysis of water samples after a nuclear accident or in the Mining sector where water quality should be assessed in the surrounding area.

A combined layer structure of aluminum nitride (AlN) and silicon nitride (Si x N y ) enables the fabrication of multisegment piezo-actuated micro lenses with a precise control of the lens surface. It is demonstrated that these micro lenses offer free aspheric deformation of the lens surface and can operate at high repetition rates along with reproducible and precise tunability. The AlN/Si x N y micro lenses are highly advantageous to be used as wave front filter or for fast focus correction.

Monosized (∼4 nm) diamond nanoparticles arranged on substrate surfaces are exciting candidates for single-photon sources and nucleation sites for ultrathin nanocrystalline diamond film growth. The most commonly used technique to obtain substrate-supported diamond nanoparticles is electrostatic self-assembly seeding using nanodiamond colloidal suspensions. Currently, monodisperse nanodiamond colloids, which have a narrow distribution of particle sizes centering on the core particle size (∼4 nm), are available for the seeding technique on different substrate materials such as Si, SiO2, Cu, and AlN. However, the self-assembled nanoparticles tend to form small (typically a few tens of nanometers or even larger) aggregates on all of those substrate materials. In this study, this major weakness of self-assembled diamond nanoparticles was solved by modifying the salt concentration of nanodiamond colloidal suspensions. Several salt concentrations of colloidal suspensions were prepared using potassium chloride as an inserted electrolyte and were examined with respect to seeding on SiO2 surfaces. The colloidal suspensions and the seeded surfaces were characterized by dynamic light scattering and atomic force microscopy, respectively. Also, the interaction energies between diamond nanoparticles in each of the examined colloidal suspensions were compared on the basis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. From these investigations, it became clear that the appropriate salt concentration suppresses the formation of small aggregates during the seeding process owing to the modified electrostatic repulsive interaction between nanoparticles. Finally, monosized (

We realize diamond electro-optomechanical resonators operated at frequencies above 100 MHz. The nanomechanical motion is read-out via on-chip diamond photonic circuits showing Q-factors above 1300.

Single crystalline diamond nanowires of different sizes and shapes were fabricated with electron beam lithography and inductively coupled plasma etching using oxygen. Titanium and chromium have been used as etching mask, where titanium appeared to be more chemically resistant. We were able to fabricate nanowires from 60 nm diameter to 200 nm with a length of approximately 1 μm. As the nanowire should be used in the future as a waveguide for the NV fluorescence originating from the apex of the structure, simulations were done with Comsol Multiphysics in order to determine the dependency between shape and guidance properties.

Heavily boron-doped diamond electrode has been applied as a robust substrate for Pt based catalyst. However, by simply applying a planar electrode the effective surface area of the catalyst is limited. In this article we for the first time prepared vertically aligned Pt-diamond core-shell nanowires electrode in a convenient and scalable method (up to 6-inch wafer size). The diamond nanowires are first fabricated with reactive ion etching with metal nanoparticles as etching masks. The following Pt deposition was achieved by DC sputtering. Different amounts of Pt were coated on to the nanowires and the morphology of the core-shell wires is characterized by SEM and TEM. The catalytic oxygen/hydrogen adsorption/desorption response are characterized by cyclic voltammetry. The results show that the active Pt surface area is 23 times higher than a planar Pt electrode, and 4.3 times higher than previously reported on Pt nanoparticles on diamond by electro-deposition. Moreover, this highly active surface is stable even after 1000 full surface oxidation and reduction cycles. Keywords: Diamond nanowires, Platinum catalyst, Core-shell structure, High surface area, High stability

Diamond integrated photonic devices are promising candidates for applications in nanophotonics and optomechanics. Here I present active modulation of diamond-based devices by exploiting mechanical degrees of freedom in free-standing electro-optomechanical resonators.

International audience; For a long time sp(2) carbon has been the dominating material for supercapacitor applications. In this paper a new concept of using boron-doped diamond for supercapacitors is proposed. Diamond surface enlargement is realized via bottom-up template-growth. In this method, silicon nanowire electrodes are coated with a thin (similar to 100 nm) layer of nanocrystalline diamond (NCD) by microwave enhanced chemical vapor deposition (MWCVD). The quality of overgrowth is characterized by high resolution scanning electron microscopy which reveals a homogeneous coverage of diamond on Si nanowire surface. To enhance the potential window to 4 V, a room temperature ionic liquid is used as electrolyte. The dilution of the ionic liquid is investigated in terms of conductivity and specific capacitance. The capacitance as measured via cyclic voltammetry reaches 105 mu F/cm(2). An energy density of 84 mu J/cm(2) and a high power density of 0.94 mW/cm(2) are obtained in combination with good stability of over 10,000 charging/discharging cycles. (C) 2014 Elsevier B.V. All rights reserved.

Nanophotonic circuits based on polished diamond thin films are prepared. These circuits cover a wide wavelength range across the entire visible spectrum. Integrated devices are surface functionalized site-specifically and in parallel using dip-pen nanolithography with a minimum linewidth of 100 nm. Multicolor fluorescence is coupled into the underlying photonic network using microring resonators and grating structures., Advanced Optical Materials 2014

Alkene and nitrophenyl molecules have been covalently bonded to single crystal diamond using photochemical and electrochemical techniques. The surface density of electrochemically grafted nitrophenyl groups is about 5% of a monolayer (8 × 1013 molecules/cm2) on initially H-terminated diamond. Covalently-bonded nitrophenyl groups on single-crystalline diamond are characterized to have two successive reversible one-electron transfer reactions due to a regularly-oriented arrangement. On oxidized surface of boron doped electrodes, a slightly (10%) smaller density is detected. Photochemical attachment of alkene molecules results also in a well arranged films as detected by angle resolved X-ray photoelectron spectroscopy (XPS). The density of 10-amino-dec-1-ene molecules protected with trifluoroacetic acid (“TFAAD”) is calculated to be in the range 2 × 1014 molecules/cm2. The bonding mechanism of Alkene molecules to high quality hydrogen terminated single crystalline CVD diamond has been characterized using a variety of experiments which show that photo-excited electrons of 5 eV energy trigger the photochemical attachment. The minimum time required to achieve a monolayer attachment of TFAAD molecules on (100)(2 × 1):H diamond is discussed and compared with experimental data from XPS. The benzene and alkene linker molecules are then reacted with the heterobifunctional cross linker sulphosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate and finally with thiol-modified ss-DNA to produce a DNA-modified diamond surface. The interaction with complementary and partially mismatched DNA is characterized by fluorescence microscopy. Microscopic properties of DNA layers on diamond have been characterized by contact- and oscillatory-mode atomic force microscopy (AFM). A comparison of bonding forces, detected by contact mode AFM, reveals significant bonding strength differences. For both, electro- and photochemically bonded DNA, tilted molecule arrangements are detected, with angles in the range 30 ° to 46° with respect to the diamond surface. The DNA films are dense with a surface roughness of about 5 A. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Charge-transport parameters measured for several single-crystal CVD-diamond films are discussed as well as the consequences for the energy- and the time resolution of charged-particle detectors made of these samples. Applying a transient-current technique, where 241 Am α-particles are used for e-h pair creation, low-field electron mobility values varying in the range 1300

The quality of hydrogen termination of undoped diamond surfaces is investigated on a microscopic level by applying atomic force microscopy, Kelvin force microscopy, and scanning electron microscopy. The results show that high temperature hydrogenation in a microwave plasma can lead to microscopic inhomogeneities at the surface, both in morphology and electron emission properties. These inhomogeneities are due to a very thin (1 nm) layer of non-diamond material on the surface, which appears to be inherently generated by the hydrogen plasma process. By scanning in contact AFM an underlying diamond surface can be exposed, which retains properties typical for hydrogenated diamond and exhibits significantly improved electron emission properties.

From total photoyield spectroscopy (TPYS) experiments we derive information about electron generation and emission properties in diamond. From the spectra, dynamic change between negative and positive electron affinities are detected. Temperature dependent TPYS experiments reveal a decrease of the optical band gap of diamond at high temperature. In addition, we show that a low density of boron can be detected, combining TPYS and cathodoluminescence experiments. We discuss properties of partially hydrogen terminated diamond surfaces, which are realized by in-situ thermal evaporation of hydrogen with TPYS experiments, with respect to a variation of electron affinity affecting sub-band and band gap excited electron emission properties.

Electrochemical surface modification via reduction of 4-nitrobenzene diazonium tetrafluoroborate in acetonitrile solution has been performed on highly boron-doped homoepitaxial single-crystalline CVD diamond films to build up surface functionalization for DNA hybridization. Due to significantly improved voltammetric resolution and regularly oriented arrangements, covalently bonded 4-nitrophenyl groups on single-crystalline diamond are characterized to have two successive reversible one-electron transfer reactions interacting with stable radical anion and dianion species. This is new and has not been detected on other electrode materials. Their surface density is in the range of 7.9 × 1013 molecules/cm2 or 1.3 × 10−10 mol/cm2 as detected by cyclic voltammetric measurements. The aminophenyl-modified diamond surface was further modified by cross linker molecules and thiol-modified DNA oligonucleotides. The resulting DNA immobilization on diamond surface is confirmed by DNA hybridization reaction, using fluorescein-labeled complementary/non-complementary target DNA oligonucleotides. We characterize the DNA film using AFM experiments which reveal a closed and dense film with a height of about 90 Å. Finally, we compare the attachment efficiency on initially H-terminated and oxidized diamond surfaces. Keywords: Electrochemical surface modification with diazonium salt, Single-crystalline CVD diamond, Covalent DNA attachment, Hybridization reaction, AFM characterization

Surface conductive layers (SCL) on oxidized (111) diamonds with smooth surfaces after exposure to air were detected and characterized by Hall effect measurements and Schottky junction characterizations. The reproducibility of the SCL is confirmed by a sequence of wet chemical oxidation treatments. The SCL vanishes by thermal annealing at temperature higher than 460 K in He atmosphere, and recovers in air. Hall effect measurements and Schottky junction properties show that the conductivity is p-type with a sheet hole concentrations around of 1012 cm− 2 and Hall mobilities between 5 and 130 cm2/V s. Furthermore, Schottky junction characteristics indicate that the Fermi level is unpinned at the (111) surface. These characteristics are similar to those generated by hydrogen termination, and are discussed in the frame hood of surface carbon dangling bond passivation most likely by OH molecules.

Total photoyield spectroscopy (TPYS) is applied to characterize the surface electronic properties of hydrogen-terminated and reconstructed diamond. All samples (n-, p-type doped, undoped) show an onset of electron emission at around 4.4 eV. Obviously, direct excitation of valence-band electrons into the vacuum, which is on hydrogen-terminated diamond 1.1 eV below the conduction band minimum, takes place in the close vicinity of the surface. This photoexcitation on hydrogen-terminated diamond with negative electron affinity is discussed applying different annealing treatments in UHV on diamond. Hydrogen evaporation results in a shift of the TPY spectrum. Taking into account the energy dependent properties of TPY spectra, an electron affinity of + 1.17 ± 0.05 eV is calculated for the clean (001) diamond surface. After a re-hydrogenation of the surface the properties recover completely, which results in a comparable spectrum as before hydrogen evaporation. Applying annealing treatments, where only a small fraction of hydrogen evaporates, results in a shift of the sub-band TPY onsets towards high energies. An indication that with decreasing hydrogen-termination of the diamond surface a decrease of negative electron affinity is detected. These data are discussed in detail taking into account a new photoexcitation mechanism.

Ion-sensitive field effect transistors (ISFETs) produced on hydrogen-terminated homoepitaxial intrinsic diamond films exhibit pronounced sensitivity to pH of aqueous electrolyte solutions. Gating of the transistor channels is realized by immersing the ISFET into pH buffer solution which is in contact with the platinum gate electrode. Conductivity through the ISFET channel is studied as a function of bias voltage on the gate electrode for pH 2–12. The conductivity decreases as pH increases. The ISFET response follows a linear trend of − 56 mV/pH. The sensing mechanism is discussed in terms of transfer doping, Nernst equation, and electrochemical properties of diamond surfaces.

The photochemical attachment of 10-amino-dec-1-ene molecules protected with trifluoro acetamide acid group (“TFAAD”) on hydrogen terminated single crystalline CVD diamond, using a high-pressure mercury lamp with a peak emission around 250 nm, is described and characterized by XPS measurements. Angular resolved XPS experiments reveal oriented molecular bonding on diamond with protecting amide groups at the top. The time dependence of photoattachment follows an exponential law, with a time constant of only 1.7 h due to spin-coating of TFAAD. Based on total photoyield spectroscopy (TPYS) and spectrally resolved photoconductivity (SPC) data, measured on high quality single crystalline diamond, we introduce a model where valence-band electrons are optically excited with energies of 4.7 to 5.2 eV into empty states of TFAAD molecules. This transition is stimulated by the negative electron affinity of H-terminated diamond, which shifts the photochemical reaction window of diamond below its optical gap (5.47 eV) into a regime where commercially available UV light sources emit and organic molecules like TFAAD are still transparent.

Intrinsic CVD diamond is well known as insulator, however if the surface is hydrogen terminated, a surface conduction can be detected if exposed to air and covered by an adsorbate layer. In this paper we show that hydrogen terminated intrinsic single crystalline CVD diamond undergoes an insulator metal transition if immersed into redox electrolyte solutions with chemical potentials below the valence-band maximum. We have applied cyclic voltammetry experiments using different redox couples to characterize this phenomenon. The experiments reveal a large chemical window (> 4.6 V) of undoped diamond. We detect the same formal potentials as reported in the literature for H-terminated boron doped polycrystalline diamond. The peaks show comparable symmetries but are shifted towards higher and lower potentials, and are significantly broadened. We attribute this to the rate limited electron transfer at the interface. The results are discussed based on the transfer doping model.

Boron-doped diamond as one of the best electrode materials has been used for the fabrication of diamond ultramicro- and nano-electrode arrays. These arrays amplify the signal of individual micro-/nano-electrodes but do not lose the beneficial characteristics of individual micro-/nano-electrodes. In this chapter we summarize the fabrication, properties, and applications of diamond ultramicro- and nano-electrode arrays. The technologies for the fabrication of these arrays and the characterization methods applied at Fraunhofer IAF are explained in detail as examples.

Total photoyield spectroscopy (TPYS) is applied to characterize the surface electronic properties of n-type chemical-vapour-deposited (CVD) (111) homoepitaxial diamond with hydrogen termination (H-termination). To discuss the negative electron affinity of n-type diamond surfaces in a general way, TPYS is also applied on p-type diamond such as a high-pressure and high-temperature synthetic (HPHT) IIb (001) and a homoepitaxially grown CVD (111) film with H-termination. In case of IIb sample, a temperature dependent experiment was also applied. The onset of electron emission at 4.4 eV on p-, and n-type diamond indicates that Fermi levels do not affect the sub-band spectra. The sub-band spectra in the energy regime 4.5–5.2 eV shows nearly no temperature dependence between RT and 300 °C, than the TPY spectra above 5.2 and below 4.4 eV. Obviously, direct excitation of valence-band electrons into the vacuum takes place in the close vicinity of the surface with temperature independent optical cross sections. It is interesting to note that the expected rise of photoyield due to NEA in the regime hν > 5.47 eV is missing in n-type diamond. We attribute this to a surface space charge region arising from ionized phosphorous atoms.

Cyclic voltammetry experiments have been performed on high quality intrinsic hydrogen terminated single crystalline CVD diamond to characterize the electron transfer at the interface of the diamond/redoxelectrolyte system. In vacuum these diamond films are insulating, but immersed into electrolyte solutions which contain Fe(CN) 3-/4- 6 or Ru(NH 3 ) 2+/3+ 6 generates insulator-metal transition. The two redox systems have chemical potentials below the valence-band maximum E VBM as calculated from the formal potentials. The same experiments applied with methyl viologen (MV) as redox couple results in no detectable electron exchange. MV has two levels, but both are above E VBM . The reversible electron exchange with Fe(CN) 3-/4- 6 or Ru(NH 3 ) 2+/3- 6 is rate limited, as peaks are broadened and shifted to higher and lower potentials. The results are compared with data available in the literature for high quality H-terminated boron doped (metallic) polycrystalline diamond which shows that the formal potentials are basically comparable. Electrochemical oxidation terminates the experiments as the surface conductivity is removed and films become highly resistive. The results are discussed using the transfer-doping and the Marcus-Gerischer models for interpretation.

The results, resolution and accuracy of Kelvin force microscopy (KFM) on highly conductive (hydrogenated) and highly resistive (oxidized) diamond surfaces are discussed in detail. Electronic properties of the interface between hydrogen and oxygen terminated surface regions are investigated using KFM profiles across in-plane gate transistor structures. Measurements under sub-band gap illumination are interpreted in terms of a surface photovoltage effect and are used to deduce information about surface and interface states.

Boron-doped nanocrystalline diamond (NCD:B) elastic layers combined with aluminum nitride (AlN) piezo-actuators are well suitable for ultrathin, highly transparent and mechanically stable micro-optical devices operating at high frequencies. In such unimorph structures NCD:B layers serve as advanced transparent electrodes instead of commonly used indium tin oxide. The carrier transport properties of heavily p-doped NCD thin films are characterized by temperature-dependent voltage-current and Hall measurements. In addition, the piezo-driven aspheric deformation of NCD:B/AlN micro lenses is demonstrated by means of integrated multi-sector actuators.

Tip-coated diamond nanowires with nickel nanoparticles (Ni/Dia NW) were applied as a three-dimensional electrode for electrochemical oxidation of glucose and reduction for hydrogen evolution. For glucose oxidation in alkaline solution on Ni/Dia NW, the oxidation potential is 110 mV lower and the oxidation current is 30 times higher than those on a bare diamond electrode. For hydrogen evolution in an acidic solution, the potential (defined as a current density is higher than −0.3 mA cm−2 at a scan rate of 10 mV s−1) reduces from −0.7 V on a bare diamond electrode to −0.2 V (vs. Ag/AgCl) on Ni/Dia NW. These high currents and low overpotentials are probably due to a large electrode area of Ni/Dia NW, a three-dimensional effect, electrocatalytic ability of Ni nanoparticles, and changed mass transport on this electrode. This three-dimensional electrode thus provides a new platform for electrochemical applications. Keywords: Three-dimensional electrode, Diamond nanowires, Electrocatalysis, Nickel

Atomic force (AFM) and Kelvin force microscopy (KFM) are employed to characterize and modify both morphologic and electronic properties of (100) hydrogenated diamond surfaces with high lateral resolution. Contrasts in AFM and KFM images are discussed and values of the local surface work function and Fermi level are deduced using gold and aluminum pads. A shift of Fermi level is observed by KFM during sample illumination, in agreement with an increase in conductivity. Using negatively biased cantilevers in AFM, surface hydrogen termination of diamond is locally removed with a resolution of 10 nm. Thus insulating nanoscale patterns are scribed into the diamond surface. Conductivity through such patterns is orders of magnitude lower than for H-terminated diamond.

A form of charge-based deep level transient spectroscopy (Q-DLTS) has been used to investigate electrically active defects within three phosphorus (P)-doped, n-type, homoepitaxial diamond films, grown by the chemical vapor deposition technique, in an attempt to obtain a Q-DLTS signal related to the P-donor level itself. Four distinct peaks were observed in the Q-DLTS spectra, two of which could be fully analyzed. One of the other two peaks overlapped other structures in the measured spectra and so could not be fully characterized, while the fourth emerged at temperatures corresponding to the limit of the experimental system used. The two fully characterized peaks arose through the presence of levels with activation energies within the range 0.42–0.6 eV depending on the sample, contact scheme, and charging time used. One of these two peaks was only observed within two of the three samples. It occurred as a shoulder on the left-hand side of a more prominent and sharp Q-DLTS feature. Both of these Q-DLTS pea...

The first aluminum nitride/diamond heterojunction light-emitting diode is realized by plasma-induced molecular beam epitaxy. The pn heterojunction consists of a silicon doped AlN (n-type) epitaxial film on (100) naturally boron-doped (p-type) diamond substrate. The diode shows excellent rectifying properties with intense light emission in the spectral range of approximately 2.7 and 4.8 eV. Heterojunctions manufactured from AlGaN alloys and diamond hold great promise for new applications in optoelectronics as well as in high frequency and high power electronics.

Hydrogen-terminated diamond surfaces are very attractive for devices based on surface electronics. The hole channel that governs the surface conductivity and the simplicity of the surface patterning are key features which allow a large flexibility for device design. In-plane gate field effect transistors have been fabricated with the conductive channel separated from the ohmic gate contacts by insulating thin lines, obtained by using a combination of electron beam lithography with surface oxidation. Depletion regions spreading from the highly resistive oxidized lines which separate the channel and gate regions can be controlled by applying a voltage to both lateral gate contacts. A wire structure has been designed in such a way that the gate voltage effectively modulates the conductance of the channel. The channel modulation is discussed in terms of a quasi two-dimensional surface carrier density. The effect of surface defects on the transistor properties has also been investigated. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thin films of crystalline silicon–germanium (SiGe) alloys could be an interesting material for next generation solar cells. SiGe alloys with a Ge content of approximately 80 at.% have an indirect band gap only slightly smaller than that of Si. However, the first direct optical transition occurs at approximately 1.5 eV, leading to a strongly enhanced optical absorption compared to Si. Thin μc-SiGe films were prepared by crystallization of evaporated amorphous or nanocrystalline alloys with a pulsed Nd:YAG laser, using homogeneous as well as laser interference methods to achieve lateral grain growth. Structural properties were characterized by atomic force microscopy and transmission electron microscopy. Raman measurements were performed to study possible phase separation and to analyze residual strain in the recrystallized films.