Single Crystal Diamond Surfaces Research Articles

Fabrication of monolithic diamond photodetector with microlenses.

A monolithic diamond photodetector with microlenses is fabricated by etching microlens arrays (MLAs) on single crystal diamond surface and patterning tungsten electrode strips on the edge of these arrays. Firstly, compact MLAs are etched on half of diamond sample surface by thermal reflow method. Secondly, via magnetron sputtering technique, two sets of interdigitated tungsten electrodes are patterned on the sample surface, one set is on the edge of MLAs, the other set is on the planar area. The optoelectronic performances of photodetectors have been investigated and indicated that the photocurrent of microlens photodetector increases by 74.8 percent at 10 V under 220 nm UV light illumination by comparing with that in planar case. Simulations of photodetectors' electrical and optical properties have been carried out, illustrating an improvement of charge collection ability and light absorption efficiency in microlens case. Furthermore, the present device structure can be extended to other semiconductor photodetectors.

Etching Kinetics of (100) Single Crystal Diamond Surfaces in a Hydrogen Microwave Plasma, Studied with In Situ Low‐Coherence Interferometry

A low‐coherence interferometry (LCI) was used to measure in situ the etch rate (ER) of synthetic single crystal (SC) diamonds in H2 microwave plasma, at substrate temperatures in the broad range of 800–1370 °C. The method allows the collection of the kinetic data on a single sample without switching off the plasma. (100)‐orientated SC plates of CVD and IIa type HPHT diamond were systematically etched in pure hydrogen at pressure p = 130 Torr and microwave power density of ≈300 W cm−3. The activation energies Ea of 42 ± 5 and 32 ± 4 kCal mol−1 have been determined for the CVD and HPHT substrates. An enhanced etching rate of a subsurface defected layer with thickness of ∼1 μm or less, formed upon polishing of the samples, is revealed. Surface morphology, roughness, and the shape of etch pits produced by a selective etching of defects, were characterized with optical profilometry. CH and dimer C2 radicals were detected in the H2 plasma with optical emission spectroscopy, as a result of the diamond etching, and the emission intensity of these species was linked to the substrate etch rate.

Sub-micrometer scale patterning on single-crystal diamond surface using focused ion beam and deep ultraviolet laser irradiations

In this study, a novel method is proposed for patterning the surface of a single-crystal diamond in the sub-micrometer scale using a combination of focused ion beam (FIB) and deep ultraviolet (DUV) laser irradiations. The surface area of the diamond irradiated by the FIB was selectively machined using a low-power DUV laser, whereas the non-FIB-irradiated area was hardly machined. Hence, diamonds can be patterned at the sub-micrometer scale by selectively machining the FIB-irradiated area using lasers. To investigate the machining characteristics in this process, the effects of the FIB and DUV laser-irradiation parameters were investigated. Consequently, the shape of the DUV-irradiated area was improved by applying the gallium removal step; debris was not formed. In addition, a structure with a maximum depth of approximately 80nm was fabricated. The damage density induced by the FIB irradiation was employed to determine the depth induced by the FIB; the depth obtained using this method is more than twice that of the heating technique in air. A concave structure was fabricated based on these results. The results indicate that the proposed method is effective for fabricating sub-micrometer-scale structures on diamond surfaces.

Thermochemical micro imprinting of single-crystal diamond surface using a nickel mold under high-pressure conditions

Single-crystal diamond is an important material for cutting tools, micro electro mechanical systems, optical devices, and semiconductor substrates. However, the techniques for producing microstructures on diamond surface with high efficiency and accuracy have not been established. This paper proposes a thermochemical imprinting method for transferring microstructures from a nickel (Ni) mold onto single-crystal diamond surface. The Ni mold was micro-structured by a nanoindenter and then pressed against the diamond surface under high temperature and pressure in argon atmosphere. Results show that microstructures on the Ni mold were successfully transferred onto the diamond surface, and their depth increased with both pressure and temperature. Laser micro-Raman spectroscopy, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses indicate that a graphite layer was formed over the contact area between diamond and Ni during pressing, and after washing by a mixed acid, the graphite layer could be completely removed. This study demonstrated the feasibility of a cost-efficient fabrication method for large-area microstructures on single-crystal diamond.

Preferential etching by flowing oxygen on the {100} surfaces of HPHT single-crystal diamond

Application of diamond is determined by its oxidation behaviour in some measure. Oxidation process of single-crystal diamond prepared under high pressure and high temperature (HPHT) has been studied by the thermal analysis, scanning electron microscope (SEM) and Raman spectrometer. The result of a simultaneous thermal analysis indicates that single-crystal diamond is oxidized at ~ 818°C at a heating rate of 5°C/min in the flowing oxygen. Based on the data of the thermal analysis at different heating rates, the activation energy is calculated by the Kissinger method. A weight loss rate increases with the rising heat treatment temperature from 600 to 800°C. After the oxidation at 800°C, etch pits emerge on the {100} surfaces of single-crystal diamond, while the {111} surfaces are smooth. Shapes of the etch pits on the {100} surfaces are inverted pyramidal hollows, with edges direction parallel to the direction.

Mechanisms of micro-groove formation on single-crystal diamond by a nanosecond pulsed laser

Micro-grooves were machined onto a single-crystal diamond surface by laser irradiation with a nanosecond pulse, and the resulting damage was investigated. The causes of four different forms of damage have been identified and examined; cracking, ripple formation, groove shape deformation and debris deposition. Cracking is caused by a rapid temperature change; ripples by interference of the laser reflected from the groove walls; groove shape deformation by enhanced absorption of the laser-induced plasma; deposited ablation debris by two different ablation regimes. Cracking and shape deformation is reduced at the center of the groove, which is very smooth and ripple-free for line irradiations using a single pass. These results provide useful information for reducing the laser-induced damage in diamond and creating damage-free micro-grooved diamond cutting tools.

Removal and characterization of focused-ion-beam-induced damaged layer on single crystal diamond surface and application to multiple depth patterning

In this research, we investigated both the etching characteristics of the non-diamond phase induced by focused ion beam (FIB) irradiation and the patterning method of shallow multiple depth structures. FIB irradiation on the diamond surface induces a non-diamond phase, and this area can be selectively etched by heating in air. The dependence of the shape on the FIB and heating conditions was investigated. Process temperatures equal to or lower than 600°C were effective for structure fabrication in terms of the fine shape of the structure. The removal depth can be controlled by varying the ion fluence and ion energy. The process temperature and heating time were important factors for determining the depth range and etch rate. The shape of the structure was affected by the morphology of the FIB-induced non-diamond phase, and the maximum etching depth was dependent on the defect density induced by FIB irradiation. Concave multiple-depth structures with depths of several tens of nanometres were fabricated based on these results, indicating the possible use of this method for shallow multiple depth patterning on diamond surfaces.

Photoelectrical characteristics of ultra thin TiO2/diamond photodetector

Characterization of UV photodetector on ultra thin TiO2/diamond has been carried out. TiO2 film has been deposited on single crystal diamond surface through radio frequency magnetron sputtering method, upon which interdigitated electrodes were patterned to form the photodetector. The photodetector showed an obvious response selectivity between UV and visible regions, and exhibited two response peaks at around 225nm and 290nm which stemmed from the response of diamond and TiO2, respectively, indicating a stretch of detection range of pure diamond or TiO2 photodetector. When TiO2 film became thinner, the transient response performance was improved.

Comparative investigation of surface transfer doping of hydrogen terminated diamond by high electron affinity insulators

We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb2O5, WO3, V2O5, and MoO3. The low electron affinity Al2O3 was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron accepting materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 1013 cm−2, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 1013 cm−2 and 10 kΩ/sq, respectively. On the other hand, hole mobilities were reduced by using high electron affinity insulator dopants. Hole mobility as a function of hole concentration in a hydrogenated diamond layer was also investigated, showing a well-defined monotonically decreasing trend.

Reprint of "Palladium Ohmic contact on hydrogen-terminated single crystal diamond film"

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρc) of 1.8×10−6Ωcm2 evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700°C for 3min at each temperature. As the temperature increased, ρc firstly decreased to 4.93×10−7Ωcm2 at 400°C and then increased. The barrier height was evaluated to be −0.15eV and −0.03eV for as-deposited and 700°C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρc, among which HNO3 vapor treated sample indicates a lower value of 5.32×10−6Ωcm2.

Self-assembling diacetylene molecules on atomically flat insulators.

Single crystal sapphire and diamond surfaces are used as planar, atomically flat insulating surfaces, for the deposition of the diacetylene compound 10,12-nonacosadiynoic acid. The surface assembly is compared with results on hexagonal boron nitride (h-BN), highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces. A perfectly flat-lying monolayer of 10,12-nonacosadiynoic acid self-assembles on h-BN like on HOPG and MoS2. On sapphire and oxidized diamond surfaces, we observed assemblies of standing-up molecular layers. Surface assembly is driven by surface electrostatic dipoles. Surface polarity is partially controlled using a hydrogenated diamond surface or totally screened by the deposition of a graphene layer on the sapphire surface. This results in a perfectly flat and organized SAM on graphene, which is ready for on-surface polymerization of long and isolated molecular wires under ambient conditions.

Palladium Ohmic contact on hydrogen-terminated single crystal diamond film

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρc) of 1.8×10−6Ωcm2 evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700°C for 3min at each temperature. As the temperature increased, ρc firstly decreased to 4.93×10−7Ωcm2 at 400°C and then increased. The barrier height was evaluated to be −0.15eV and −0.03eV for as-deposited and 700°C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρc, among which HNO3 vapor treated sample indicates a lower value of 5.32×10−6Ωcm2.

Nitrogen termination of single crystal (100) diamond surface by radio frequency N2 plasma process: An in-situ x-ray photoemission spectroscopy and secondary electron emission studies

In this letter, we report the electronic and chemical properties of nitrogen terminated (N-terminated) single crystal (100) diamond surface, which is a promising candidate for shallow NV− centers. N-termination is realized by an indirect RF nitrogen plasma process without inducing a large density of surface defects. Thermal stability and electronic property of N-terminated diamond surface are systematically investigated under well-controlled conditions by in-situ x-ray photoelectron spectroscopy and secondary electron emission. An increase in the low energy cut-off of the secondary electron energy distribution curve (EDC), with respect to a bare diamond surface, indicates a positive electron affinity of the N-terminated diamond. Exposure to atomic hydrogen results in reorganization of N-terminated diamond to H-terminated diamond, which exhibited a negative electron affinity surface. The change in intensity and spectral features of the secondary electron EDC of the N-terminated diamond is discussed.

Characterizations of etch pits formed on single crystal diamond surface using oxygen/hydrogen plasma surface treatment

Etch pits formed on (001)-oriented single crystal diamond surfaces by O/H plasma etching have been investigated using optical microscopy. Shapes of the formed pits are basically inverted-pyramidal hollows with the edge directions of the 〈110〉, but central areas of these pits have two types of shapes, point-bottom and flat-bottom ones. Depth profiles of the number densities of these two-type pits showed that at an early stage of the etching, a large number of the flat-bottom pits are observed, but disappear to a depth shallower than ~10μm. Compared with the other etching experiment using ion beam sputtering, such flat-bottom pits most likely correspond to the dislocations or microfractures introduced around the surface during surface polishing of the diamond substrates. On the other hand, point-bottom pits still continue to appear even in a deeper region. These correspond to “intrinsic” dislocations included originally inside the diamond substrate. All the tilt angles of the pit between the slope of the pit and top face of the substrate, characterizing the pit shape, were within the range of 3–7° and independent of their sizes in many pits investigated. It was found that the tilt angle and the activation energy of the etch rate obtained in this study are similar to that of an oxygen-gas related etching process.

Nitrogen and Silicon Defect Incorporation during Homoepitaxial CVD Diamond Growth on (111) Surfaces

ABSTRACTChemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. Altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.

Molecular orientation of lead phthalocyanine on (100) oriented single crystal diamond surfaces.

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.

High conductivity micro-wires in diamond following arbitrary paths

High quality graphitic wires embedded beneath the surface of single crystal diamond are fabricated using a combination of adaptive ultrashort pulsed laser fabrication, high numerical aperture focusing, and an axial multi-fabrication scheme. Wires are created with micrometer and sub-micrometer dimensions that can follow any three dimensional path within the diamond. The measured conductivities are over an order of magnitude greater than previously reported wires fabricated by ultra-short pulsed lasers. The increased level of graphitization control in this scheme appears particularly important for fabrication of wires parallel to the diamond surface.

Silica based polishing of {100} and {111} single crystal diamond

Diamond is one of the hardest and most difficult to polish materials. In this paper, the polishing of {111} and {100} single crystal diamond surfaces by standard chemical mechanical polishing, as used in the silicon industry, is demonstrated. A Logitech Tribo Chemical Mechanical Polishing system with Logitech SF1 Syton and a polyurethane/polyester polishing pad was used. A reduction in roughness from 0.92 to 0.23 nm root mean square and 0.31 to 0.09 nm rms for {100} and {111} samples respectively was observed.

A near edge X-ray absorption fine structure study of oxidized single crystal and polycrystalline diamond surfaces

The influence of oxidizing environments on single crystal diamond and polycrystalline chemical vapor deposited CVD diamond films was studied using the near edge X-ray absorption fine structure (NEXAFS) pre-edge region in both bulk and surface sensitive modes. The NEXAFS of (100) oriented single crystal diamond was measured following (i) exposure to a microwave (MW) hydrogen plasma, (ii) annealing to 1000 °C, (iii) exposure of the as annealed surface to H2O, and (iv) exposure of the as annealed surface to O2. From these measurements particular surface bonding configurations have been assigned to features in the pre-edge structure. The NEXAFS of microcrystalline CVD diamond films was studied following different oxidative treatments using (i) a thermal atomic oxygen (AO) environment, (ii) a hyperthermal (5 eV) AO source, and (iii) an RF oxygen plasma exposure. The nature of the surface layer was found to be different for differently oxidized surfaces. These treatments were carried out as part of a study of CVD diamond durability in the low Earth orbit space environment.

Diamond processing by focused ion beam—surface damage and recovery

The nitrogen vacancy color center (NV−) in diamond is of great interest for photonic applications. Diamond nano-photonic structures are often implemented using focused-ion-beam (FIB) processing, leaving a damaged surface which has a detrimental effect on the color center luminescence. The FIB processing effect on single crystal diamond surfaces and their photonic properties is studied by time of flight secondary ion mass spectrometry and photoluminescence. Exposing the processed surface to hydrogen plasma, followed by chemical etching, drastically decreases implanted Ga concentration, resulting in a recovery of the NV− photo-emission and in a significant increase of the NV−/NV0 ratio.