Hydrogenated Diamond Surface Research Articles

Low voltage fabrication of sub-nanometer insulating layers on hydrogenated diamond

A new regime of electrochemical anodic oxidation with an atomic force microscope (AFM) is introduced for producing insulating layers on a hydrogenated diamond surface. In this new regime, when a low surface voltage (VS<+2 V) is applied to the sample, an insulating layer is created without any measurable change in the topography. Insulating layers created in this fashion are shown to preserve the high sub-surface conductance of hydrogenated diamond surfaces, contrary to the oxide layers accompanied by a topographic change, which destroy sub-surface conductance.

The influence of hydrogen plasma pre-treatment on the structure of BDND electrode surface applied for phenol detection

The surface properties of boron-doped nanocrystalline diamond films treated with H2 plasma was investigated in regard to their electrochemical response for phenol oxidation. The surface of these films is relatively flat formed by crystallites with sizes of about 40 nm. X-ray photoelectron spectroscopy analyses showed that electrode surface has a high amount of C–H bonds. This behavior is in agreement with Mott-Schottky plot measurements concerning the flat band potential that presented a value as expected for hydrogenated diamond surface. This electrode presented the phenol detection limit of 0.08 mg L−1 for low phenol concentrations from 40 to 250 μmol L−1.

Chemical modification of diamond surface with linoleic acid by using benzoyl peroxide

In this study, the introduction of the C=C bond, which is known to be chemically active, on diamond surface was attempted using a reaction with unsaturated fatty acid. The chemical reactivity of a hydrogenated diamond surface with linoleic acid, which was most effective for introducing of the C=C bond, using benzoyl peroxide was investigated in detail. The diamond surface modified with the C=C bond was used as the substrate for the surface-modified diamond. Different radical source such as NCS, NBS, AIBN, and TEMPO were allowed to react with the diamond surface treated with linoleic acid. After the reaction with NCS, NBS, or AIBN, IR peaks at 3011 cm − 1 , which correspond to the C–H bond on the C=C bond, significantly decreased in size, and XPS spectra showed that the elements that derived from the reacted radical source, that is Cl, Br, or N, existed on the diamond surface. On the other hand, after the reaction with TEMPO no XPS peak of the N atoms appeared although the IR peak at 3011 cm − 1 slightly decreased. These experimental results indicate that the C=C bond introduced on diamond surface can participate in chemical reaction. The method used in this study could become a very useful technique if the coverage factor of the C=C bond is improved by optimization of the reaction condition.

Processing of 50 nm gate-length hydrogen terminated diamond FETs for high frequency and high power applications

To better understand the intrinsic scaling limitations of sub-100nm gate-length hydrogen-terminated diamond Field Effect Transistors (FETs), the fabrication and DC characterisation of 50nm gate length devices have been investigated. Physical processing of the hydrogenated diamond surface presents a challenge for the realisation of short gate length, high performance devices due to the inherent sensitivity of the surface to device processing. Through the development of a finely optimised device fabrication process, we have demonstrated transistor operation at a reduced gate length of 50nm. This is believed to be the shortest gate length operational diamond transistor yet reported. Inspection of device operation at larger voltages indicates the onset of potential short channel effects, attributed to the reduced dimensions of the gate. This is an important result in the investigation of the high frequency and high power potential of hydrogen terminated diamond transistors.

New one step functionalization of polycrystalline diamond films using amine derivatives

Diamond received tremendous interest for analytical sciences due to its intrinsic properties. However, the analytical perception of chemical environment requires surface functionalization that brings selectivity to the detection event. Thereby, many works focused on diamond modification using chemical or biochemical entities. We proposed here, a new and straightforward methodology for diamond (bio)functionalization. This method involves the chemical reaction between (bio)chemical entities presenting a primary amine moiety, used as grafting site, and hydrogenated diamond surface. This reaction allows in one step to modify diamond surface whatever its doping level and its crystalline quality. The effectiveness of this new method is exposed here through the grafting of one redox species, ferrocene, and of one biochemical, biotin. The impacts of both functionalization duration and pH are investigated and the robustness of the formed bond is demonstrated owing to biotin-avidin coupling.

Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond

We report on sub-bandgap optoelectronic phenomena of hydrogen-terminated diamond patterned with a submicron oxidized line. The line acts as an energy barrier for the two-dimensional hole gas located below the hydrogenated diamond surface. A photoconductive gain of the hole conductivity across the barrier is measured for sub-bandgap illumination. The findings are consistent with photogenerated electrons being trapped in defect levels within the barrier. We discuss the spatial and energetic characteristics of the optoelectronic phenomena, as well as possible photocurrent effects.

In-situ oxidation and annealing of hydrogenated diamond (100) surfaces studied by high resolution electron energy loss spectroscopy

Homoepitaxially grown single crystal diamond (100) surface on polished natural type 2a diamond was carefully prepared and examined for morphology and chemical composition. Atomic force microscopy (AFM) analysis showed smooth polishing scratches consisting of broad and shallow patterns also seen by electron microscope examination in the secondary electron emission detection mode. High resolution electron energy loss spectroscopy (HREELS) was used to determinate different chemical bonding configurations present on the as grown surface and their thermal stability induced by vacuum annealing and exposure to activated hydrogen. In-situ hydrogen terminated surfaces were oxidized by exposure to thermally activated oxygen. Gradual annealing leads to the removal of oxygen containing species and to regeneration of the hydrogenated diamond surface. Annealing results in desorption of peroxide and ether groups and recovers the diamond optical phonon overtones in the HREELS. There was no indication of hydroxyl groups after oxygen exposure. Possible chemical processes involving activated hydrogen and oxygen during the exposures and subsequent annealing are suggested. Activated hydrogen and oxygen possess sufficient energy to attack absorbed species in order to form new chemical bonds absorbed onto the diamond surface.

Chemical modification of diamond surface with X–(C 6H 4)–COOH ( X = F, Cl, Br, I) using benzoyl peroxide

The chemical reactivity of a hydrogenated diamond surface with X–(C 6H 4)–COOH ( X = F, Cl, Br, I) when using benzoyl peroxide was investigated in this study. After the reaction processes the shapes of the IR spectra changed. It was confirmed from the XPS measurements that halogen atoms existed on the samples after the reaction process. The position of the IR peak at ca. 700 cm − 1 depended on the kind of halogen in X–(C 6H 4)–COOH. Moreover, the peak position depended on the kind of constitutional isomer, that is, ortho-, meta-, or para-. It was confirmed from the experimental results of this study that halogen-containing organic functional groups can be introduced onto a diamond surface.

Chemical reaction of hydrogenated diamond surface with amino acids by using N-chlorosuccinimide

Various organic compounds can be immobilized on a diamond surface if a chemically active organic functional group, such as an NH 2 group, is introduced on the diamond surface. We therefore attempted to introduce an NH 2 group on a diamond surface by using chemical reaction of a hydrogenated diamond surface with an amino acid and NCS ( N-chlorosuccinimide). From our previous experimental results (Diamond Relat. Mater., 15, 668 (2006)), we expected that a functional group could be introduced on the diamond surface. However, there was no peak assigned to the NH 2 group in the IR spectra for diamond powder treated with amino acids. The diamond powder treated with L-serine, L(−)-threonine, L(−)-phenylalanine, L(+)-arginine, L-histidine, or L-asparagine monohydrate had a specific peak at 2275 cm − 1 in the IR spectra. Moreover, the diamond powder treated with L(−)-threonine had the highest intensity of the peak at 2275 cm − 1 . Therefore, the chemical reaction of a hydrogenated diamond surface with L(−)-threonine was further examined in detail. Unfortunately, the assignment of the peak at 2275 cm − 1 was unclear. However, we speculate from the compounds in the chemical reaction process that the peak is assigned to the CN group, although the peak position is slightly different from that of the normal CN group.

Electronic structures of hydrogenated and oxygenated boron-doped diamond films

The hydrogenated and oxygenated boron-doped diamond films have been prepared by hydrogen-plasma treatment and boiling in the strong acids, respectively. By means of the X-ray photoelectron spectroscopy and contact angle measurements, the two surface-terminated diamond films have been evaluated. The scanning tunneling spectra have been measured by scanning probe microscope. The results indicated that for the hydrogenated diamond surface, the surface energy bands bend downwards and there exists a shallow acceptor above the valence band maximum. However, the surface energy bands for the oxygenated film bends upwards and its band gap is wide and clean. The conduction mechanisms for the two surface-terminated diamond films have been discussed.

Gas Sensing Interactions at Hydrogenated Diamond Surfaces

Hydrogenated diamond (HD) samples exhibit a p-type surface conductivity (SC) which is caused by transfer doping to an adsorbed liquid electrolyte layer. We report on gas sensing experiments showing that such samples selectively respond to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gases at room temperature. Successive substitution of H-terminated surface sites by O-termination ones causes an increase in both the sensor baseline resistance and the gas-induced resistance changes. Thermal desorption of the surface electrolyte layer, on the other hand, causes the sensor baseline resistance to increase and the gas sensing effect to disappear. Readsorption of the surface electrolyte reestablishes both the sensor baseline resistance and the gas sensing effect. Our results indicate that the gas sensing effect is caused by local pH-changes due to acid/base reactions of the adsorbed gas molecules in the surface electrolyte layer. It is argued that this dissociative gas sensing mechanism represents a valuable complement with regard to the established surface combustion mechanism that is operative on heated metal oxide surfaces.

Tip voltage controlled local modification of hydrogenated diamond surface with an atomic force microscope

AbstractThe influence of the voltage applied to the tip of an atomic force microscope (AFM) on the local modification of the surface of CVD‐grown diamond films is studied. By applying a negative voltage to the conductive (highly doped) silicon AFM tip, two kinds of patterns can be created. In the voltage range –6 V to –10 V structures that are elevated with respect to the surface (creation of bumps) are obtained, while at higher voltages (–12 V to –15 V) the patterns are scribed into the diamond surface (creation of pits). The origin of the observed modifications is discussed in terms of an electrochemical process that is enhanced by local heating occurring due to severe current crowding. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Surface photo-voltage effect of hydrogenated diamond subjected to low energy electron irradiation

In this paper we report on the influence of sub-band gap photon illumination on the electron emission of hydrogenated diamond surfaces subjected to continuous low energy electron irradiation. Hydrogenated diamond surface traps charge by resonance electron attachment (REA) and formation of C–H (ads) − anionic transient surface species with a maximum cross section at an incident electron energy of ∼ 9 eV. The steady state population of these anionic surface species results in up-wards surface band bending and consequent decrease of low energy electron emission. It is demonstrated that concurrent low energy electron bombardment and illumination of the diamond surface with sub-band gap photons enhances the secondary electron emission yield of diamond. It is argued that these effects are associated to a surface photo-voltage effect, which results in unpinning of the surface band.

Quantization of 2D Hole Gas in Conductive Hydrogenated Diamond Surfaces Observed by Electron Field Emission

Discrete jumps are observed in the emitted current density (J) versus extraction electric field (E) curves in electron field emission measurements from a conductive, hydrogen-terminated air-exposed diamond surface. These jumps are well reproduced by computations based on the assumption that a 2D nanoscale quantum system with discrete energy levels exists in the diamond near-surface layer. The present results confirm the formation of well-defined quantum states of holes in the 2D surface layer present on hydrogenated air-exposed diamond surfaces.

Surface science of diamond: Familiar and amazing

The crystal structure of diamond is identical with that of its more common semiconductor relatives silicon and germanium. Consequently, a number of surface properties in terms of reconstructions, surface states and surface band diagrams are similar as in the case of Si or Ge. But diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms (donor-like), surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. In this article the surface properties of diamond will be reviewed with special emphasis on this new kind of doping mechanism.

Cycloadditions on Diamond (100) 2 × 1: Observation of Lowered Electron Affinity due to Hydrocarbon Adsorption

The adsorption of allyl alcohol, acrylic acid, and allyl chloride, as well as unsaturated organic molecules such as acetylene and 1,3 butadiene, on reconstructed diamond (100) 2 x 1 have been investigated using high-resolution electron energy loss (HREELS) spectroscopy and synchrotron radiation spectroscopy. The cycloadditions of these organic molecules produce chemically adsorbed adlayers with varying degree of coverages on the clean diamond. The organic adsorbed surface has a lowered electron affinity and shows a secondary electron yield that varies between 12 and 40% of the yield obtained from a fully hydrogenated diamond surface. The diamond surface can be functionalized with hydroxyl, carboxylic, and chlorine functionalities by the adsorption of these allyl organics. The [2 + 2] adduct of acetylene on the diamond (100) 2 x 1 surface can be observed. 1,3-butadiene attains a higher coverage as well as forms a thermally more stable adlayer on the diamond surface compared to the other organic molecules, due to its ability to undergo [4 + 2] cycloaddition.

Introduction of molecules containing a NO 2 group on diamond surface by using radical reaction in liquid phase

Chemical reaction of hydrogenated diamond surface with nitrobenzoic acid (NO 2-C 6H 4-COOH) and the radical species was investigated. The IR peak assigned to the NO 2 group appeared after the reaction process. The peak intensity of the NO 2 group depended on the steric structure of the reacted nitrobenzoic acid. The NO 2 peak intensity of the diamond reacted with p-nitrobenzoic acid is much smaller than that of the diamond reacted with o-, or m-nitrobenzoic acid. In this study, 3,4-dinitorobenzoic acid or 3,5-dinitorobenzoic acid was also used. The IR spectra for the diamond treated with 3,4-dinitorobenzoic acid were unclear. On the other hand, the IR spectra for the diamond treated with 3,5-dinitorobenzoic acid showed the peak assigned to the NO 2 group. From the experimental results, we may assume that the NO 2 group at para-position against the COOH group hindered the reaction of the COOH group with diamond surface. The NO 2 peak intensity for the diamond treated with 3,5-dinitorobenzoic acid was comparable with that for the diamond treated with o- or m-nitrobenzoic acid. These results should means that the amount of the NO 2 group introduced on diamond surface was comparable. The introduction of NO 2 group on diamond surface was realized by the method applied in this study.

Investigation of hydrogenated CVD diamond films by photo-thermal ionization spectroscopy

Different hydrogenated CVD diamond films as well as bulk IIb and IIa diamonds were investigated by means of photo-thermal ionization spectroscopy. All samples show a new photocurrent signal at temperatures lower than 120–20 K depending on the sample with a threshold around 100 meV what suggests a presence of shallow levels on the hydrogenated diamond surface. The photocurrent spectrum due to these shallow levels consists of features similar to the two-phonon absorption in diamond. Influence of annealing in air on the photocurrent behavior was investigated as well.

Diamond surfaces: familiar and amazing

Diamond is the only wide band gap representative of the elemental semiconductors, with a crystal structure identical to its more common relatives silicon and germanium. On first glance one might also expect similar surface properties in terms of reconstructions, surface states, and surface band diagrams. In part, this expectation is indeed fulfilled, but diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms, (donor-like) surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. The understanding of those phenomena requires in fact concepts of surface science, semiconductor physics, and electrochemistry, which makes the diamond surface a true ‘interdisciplinary’ research topic.

Surface transfer doping of diamond by fullerene

Fifteen years after Landstrass and Ravi [1] [I.M. Landstrass, K.V. Ravi, App. Phys. Lett, 55 (1989) 975] reported a hydrogen induced surface conductivity of diamond, it has now been established that the phenomenon is based on a sub-surface hole accumulation layer. A quantitative model for the origin of this layer has been proposed by our group earlier and is based on the charge exchange between the diamond surface and solvated ions in a water layer that forms spontaneously on all surfaces in air. The process relies on the particularly low ionization energy of the hydrogenated diamond surface [2] [F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley, Phys. Rev. Lett. 85 (2000) 3472]. Here, we report on fullerenes (C 60) and fluorinated fullerenes (C 60F 48) as alternative adsorbate systems. They induce surface conductivity on a level comparable (C 60) or even higher (C 60F 48) than that observed under atmospheric conditions. Whereas in the case of C 60 efficient doping requires the formation of the van-der Waals solid on top of the surface of diamond, C 60F 48 acts as surface acceptor even as isolated molecule. In both cases, the doping efficiency can be modeled by considering the electrochemical equilibrium between the diamond and the adsorbate layer.