Refractive index variation in a free-standing diamond thin film induced by irradiation with fully transmitted high-energy protons

Ion irradiation is a widely employed tool to fabricate diamond micro- and nano-structures for applications in integrated photonics and quantum optics. In this context, it is essential to accurately assess the effect of ion-induced damage on the variation of the refractive index of the material, both to control the side effects in the fabrication process and possibly finely tune such variations. Several partially contradictory accounts have been provided on the effect of the ion irradiation on the refractive index of single crystal diamond. These discrepancies may be attributable to the fact that in all cases the ions are implanted in the bulk of the material, thus inducing a series of concurrent effects (volume expansion, stress, doping, etc.). Here we report the systematic characterization of the refractive index variations occurring in a 38 µm thin artificial diamond sample upon irradiation with high-energy (3 MeV and 5 MeV) protons. In this configuration the ions are fully transmitted through the sample, while inducing an almost uniform damage profile with depth. Therefore, our findings conclusively identify and accurately quantify the change in the material polarizability as a function of ion beam damage as the primary cause for the modification of its refractive index.

Single-photon emitting diode in silicon carbide

Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide an ideal material to build such devices. Here, we demonstrate the fabrication of bright single-photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of >300 kHz) and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single-photon source is proposed. These results provide a foundation for the large scale integration of single-photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.

Ultra-high-density 3D DNA arrays within nanoporous biocompatible membranes for single-molecule-level detection and purification of circulating nucleic acids

Extracellular nucleic acids freely circulating in blood and other physiologic fluids are important biomarkers for non-invasive diagnostics and early detection of cancer and other diseases, yet difficult to detect because they exist in very low concentrations and large volumes. Here we demonstrate a new broad-range sensor platform for ultrasensitive and selective detection of circulating DNA down to the single-molecule level. The biosensor is based on a chemically functionalized nanoporous diamond-like carbon (DLC) coated alumina membrane. The few nanometer-thick, yet perfect and continuous DLC-coating confers the chemical stability and biocompatibility of the sensor, allowing its direct application in biological conditions. The selective detection is based on complementary hybridization of a fluorescently-tagged circulating cancer oncomarker (a 21-mer nucleic acid) with covalently immobilized DNA on the surface of the membrane. The captured DNAs are detected in the nanoporous structure of the sensor using confocal scanning laser microscopy. The flow-through membrane sensor demonstrates broad-range sensitivity, spanning from 10(15) molecules per cm(2) down to single molecules, which is several orders of magnitude improvement compared to the flat DNA microarrays. Our study suggests that these flow-through type nanoporous sensors represent a new powerful platform for large volume sampling and ultrasensitive detection of different chemical biomarkers.

Surface charge effects in protein adsorption on nanodiamonds

Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids.

On-chip manipulation of single photons from a diamond defect

Operating reconfigurable quantum circuits with single photon sources is a key goal of photonic quantum information science and technology. We use an integrated waveguide device containing directional couplers and a reconfigurable thermal phase controller to manipulate single photons emitted from a chromium related color center in diamond. Observation of both a wavelike interference pattern and particlelike sub-Poissionian autocorrelation functions demonstrates coherent manipulation of single photons emitted from the chromium related center and verifies wave particle duality.

Direct measurement and modelling of internal strains in ion-implanted diamond

We present a phenomenological model and finite element simulations to describe the depth variation of mass density and strain of ion-implanted single-crystal diamond. Several experiments are employed to validate the approach: firstly, samples implanted with 180 keV B ions at relatively low fluences are characterized using high-resolution x-ray diffraction; secondly, the mass density variation of a sample implanted with 500 keV He ions, well above its amorphization threshold, is characterized with electron energy loss spectroscopy. At high damage densities, the experimental depth profiles of strain and density display a saturation effect with increasing damage and a shift of the damage density peak towards greater depth values with respect to those predicted by TRIM simulations, which are well accounted for in the model presented here. The model is then further validated by comparing transmission electron microscopy-measured and simulated thickness values of a buried amorphous carbon layer formed at different depths by implantation of 500 keV He ions through a variable-thickness mask to simulate the simultaneous implantation of ions at different energies.

A comparative study of carbonate determination in human teeth using Raman spectroscopy

Carbonate determination in dental apatites such as dentine and enamel is important for studying the dynamics of dental caries and developmental defects of these tissues. Traditionally, these determinations have been performed by acidic digestion with the subsequent measurement of released carbon dioxide gas. As an alternative, Raman spectroscopy has been used for the determination of carbonate in synthetic carbonated apatites with at least four analytical methods published thus far. However, these methods have not been applied to biological apatites. The aim of this comparative study was to test the suitability of these four methods for the determination of B-type carbonate in human enamel and dentine. A method for determining the A-type carbonate content of enamel using the Raman technique is also presented. Raman spectra were obtained from 10 human enamel and dentine samples and analysed with each of the four methods using either a single or multiple ν(1)(PO(4)(3-)) band spectral fitting model. Each of the methods resulted in a different determination for the carbonate content when using the same measurement data. The method that used the full-width-at-half-maximum of the ν(1)(PO(4)(3-)) band to determine the B-type carbonate concentration was found to be in best agreement with (i) the results (using the acid digestion method) of teeth collected from the same sample population and (ii) previously reported values for both enamel and dentine. The use of a multiple-band spectral fitting model produced the highest determination precision (particularly in the case of dentine).

Dynamic stabilization of the optical resonances of single nitrogen-vacancy centers in diamond

We report electrical tuning by the Stark effect of the excited-state structure of single nitrogen-vacancy (NV) centers located ≲100  nm from the diamond surface. The zero-phonon line (ZPL) emission frequency is controllably varied over a range of 300 GHz. Using high-resolution emission spectroscopy, we observe electrical tuning of the strengths of both cycling and spin-altering transitions. Under resonant excitation, we apply dynamic feedback to stabilize the ZPL frequency. The transition is locked over several minutes and drifts of the peak position on timescales ≳100  ms are reduced to a fraction of the single-scan linewidth, with standard deviation as low as 16 MHz (obtained for an NV in bulk, ultrapure diamond). These techniques should improve the entanglement success probability in quantum communications protocols.

Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells

Fluorescent particles are routinely used to probe biological processes. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry, but not yet in biological environments. Here, we demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 1° angular precision over acquisition times of 89 ms. The quantum spin levels served as fingerprints, allowing individual centres with identical fluorescence to be identified and tracked simultaneously. Furthermore, monitoring decoherence rates in response to changes in the local environment may provide new information about intracellular processes. The experiments reported here demonstrate the viability of controlled single spin probes for nanomagnetometry in biological systems, opening up a host of new possibilities for quantum-based imaging in the life sciences.

Diamond penetrating electrode array for epi-retinal prosthesis

This paper presents progress in the characterization and application of diamond penetrating electrode arrays for Epi-Retinal Prostheses. Electrical stimulation of degenerate retina has already been shown to restore partial vision for some blind patients, albeit at low spatial resolution. Higher resolution may be achievable by building arrays with electrodes that have greater areal density and closer proximity to target neurons. However, high standards of biocompatibility and hermeticity must be maintained, limiting the range of available materials of manufacture. Here, the design and histology of high density electrode arrays (approximately 100 electrodes/mm(2)) made from polycrystalline diamond and implanted into rat retinae are discussed. Results from initial steps in this process are reported.

An Investigation into the Use of a Diffusion Barrier in the Microwave Plasma Assisted Chemical Vapor Deposition of Diamond on Iron Based Substrates

The growth of CVD diamond onto iron based substrates is complicated by preferential soot formation and carbon diffusion into the substrate, leading to poor quality films and poor adhesion. One strategy to overcome these problems is the use of thin film barrier layers between the Fe substrate and the growing diamond film. The present investigation reports the growth of diamond films on Fe substrates coated with thin films of TiN. The effectiveness of the TiN layers in inhibiting C diffusion into the Fe substrate was investigated by Auger measurements of the C distribution within the TiN layer, through the interface and into the substrate both before and after diamond deposition.

The results show that a layer of TiN only 250Å thick is sufficient to inhibit soot formation and C diffusion into the Fe bulk, as well as providing nucleation sites for CVD diamond growth.

Quantitative Studies of Tetrahedral Bonding in Amorphous Carbon Films Using Ultraviolet Raman Spectroscopy

The bonding in a series of unhydrogenated amorphous carbon films has been analysed quantitatively using Raman spectroscopy with ultraviolet excitation. The Raman spectra exhibit two broad Raman peaks at 1650 cm−1 and 1100 cm−1, due to sp2 and sp3 vibrational modes respectively. The former is a resonance feature associated with a large proportion of paired sp2 sites, while the latter is a weighted vibrational density-of-states for the distorted random network of sp3 sites. The position and relative intensity of the two peaks are shown to be strongly correlated with the percentage of sp3 sites in the films, providing a reliable measure of sp3 bonding which is both quantitative and non-destructive.

Imaging and quantum-efficiency measurement of chromium emitters in diamond

We present direct imaging of the emission pattern of individual chromium-based single photon emitters in diamond and measure their quantum efficiency. By imaging the excited state transition dipole intensity distribution in the back focal plane of high numerical aperture objective, we determined its 3D orientation. Employing ion implantation techniques, the emitters were placed at various distances from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, we measured an average quantum efficiency of 28%.

Superconducting transition in Nb nanowires fabricated using focused ion beam

Making use of focused Ga-ion beam (FIB) fabrication technology, the evolution with device dimension of the low-temperature electrical properties of Nb nanowires has been examined in a regime where crossover from Josephson-like to insulating behaviour is evident. Resistance-temperature data for devices with a physical width of order 100 nm demonstrate suppression of superconductivity, leading to dissipative behaviour that is shown to be consistent with the activation of phase-slip below T(c). This study suggests that by exploiting the Ga-impurity poisoning introduced by the FIB into the periphery of the nanowire, a central superconducting phase-slip nanowire with sub-10 nm dimensions may be engineered within the core of the nanowire.

Nano-manipulation of diamond-based single photon sources

The ability to manipulate nano-particles at the nano-scale is critical for the development of active quantum systems. This paper presents a technique to manipulate diamond nano-crystals at the nano-scale using a scanning electron microscope, nano-manipulator and custom tapered optical fibre probes. The manipulation of a approximately 300 nm diamond crystal, containing a single nitrogen-vacancy centre, onto the endface of an optical fibre is demonstrated. The emission properties of the single photon source post manipulation are in excellent agreement with those observed on the original substrate.

Single nitrogen vacancy centers in chemical vapor deposited diamond nanocrystals

Nanodiamond crystals containing single color centers have been grown by chemical vapor deposition (CVD). The fluorescence from individual crystallites was directly correlated with crystallite size using a combined atomic force and scanning confocal fluorescence microscope. Under the conditions employed, the optimal size for single optically active nitrogen-vacancy (NV) center incorporation was measured to be 60-70 nm. The findings highlight a strong dependence of NV incorporation on crystal size, particularly with crystals less than 50 nm in size.

Stark shift control of single optical centers in diamond

Lifetime-limited optical excitation lines of single nitrogen-vacancy (NV) defect centers in diamond have been observed at liquid helium temperature. They display unprecedented spectral stability over many seconds and excitation cycles. Spectral tuning of the spin-selective optical resonances was performed via the application of an external electric field (i.e., the Stark shift). A rich variety of Stark shifts were observed including linear as well as quadratic components. The ability to tune the excitation lines of single NV centers has potential applications in quantum information processing.

Stable Superhydrophobic Surface via Carbon Nanotubes Coated with a ZnO Thin Film

We report the formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film. The CNT template was synthesized by chemical vapor deposition on an Fe-N catalyst layer. The ZnO film, with a low surface energy, was deposited on the CNT template by the filtered cathodic vacuum arc technique. Contact angle measurement reveals that the surface of the ZnO-coated CNTs is superhydrophobic with water contact angle of 159 degrees . Unlike the uncoated CNTs surface, the ZnO-coated CNTs surface shows no sign of water seepage even after a prolonged period of time. The wettability of the surface can be reversibly changed from superhydrophobicity to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.

Micromorphological investigation of noncarious cervical lesions treated with demineralizing agents

PURPOSE

The purpose of this study was to examine the micromorphology of noncarious cervical lesions (NCCL) and the change occurring after acid conditioning.

MATERIALS AND METHODS

Nine wedge-shaped lesions, 9 saucer-shaped lesions, and 5 third molars with prepared cervical cavities were used. All NCCLs exhibited a hard, smooth surface with no discoloration. The teeth were sectioned and divided into three groups, each containing the three lesion types. Teeth in Group I were not etched, and teeth in Groups II and III were etched with 35% phosphoric acid and 20% polyacrylic acid/3% aluminum chloride, respectively. Field emission SEM and atomic force microscopy were used to examine the lesion surfaces.

RESULTS

The surfaces of the prepared cervical (control) lesions were covered with a smear layer. Treatment with phosphoric acid and polyacrylic acid resulted in removal of the smear layer, although some residual smear layer was found on the surface treated with polyacrylic acid. The images of the untreated surfaces of NCCL showed highly mineralized dentin with complete obliteration of the dentinal tubules. After treatment with phosphoric and polyacrylic acids, the images revealed demineralization of the surface, which was more pronounced on those treated with phosphoric acid.

CONCLUSION

The mineral deposits on the surface of NCCL decreased the effect of acid conditioning. Although there was no apparent difference between the two forms of NCCL used in this study, further work is needed to better understand these lesions.

Infrared emission from selected areas in ion-beam-irradiated diamond

The infrared emission properties of an electrically heated single resistive element produced by ion implantation of diamond is reported. It is found that good contrast can be obtained between the implanted and unimplanted regions of the diamond mainly because of the increased emissivity following implantation. The infrared output is stronger if the diamond is viewed with the implanted surface facing away from the detector. The possible utilization of diamond-based pixels in infrared scene generation is discussed.

A double-blind evaluation of topical capsaicin in pruritic psoriasis

BACKGROUND

Substance P, an undecapeptide neurotransmitter, has been implicated in the pathophysiology of psoriasis and pruritus.

OBJECTIVE

Safety and efficacy of topical capsaicin, a potent substance P depletor, were evaluated in patients with pruritic psoriasis.

METHODS

Patients applied capsaicin 0.025% cream (n = 98) or vehicle (n = 99) four times a day for 6 weeks in this double-blind study. Efficacy was based on a physician's global evaluation and a combined psoriasis severity score including scaling, thickness, erythema, and pruritus.

RESULTS

Capsaicin-treated patients demonstrated significantly greater improvement in global evaluation (p = 0.024 after 4 weeks and p = 0.030 after 6 weeks) and in pruritus relief (p = 0.002 and p = 0.060, respectively), as well as a significantly greater reduction in combined psoriasis severity scores (p = 0.030 and p = 0.036, respectively). The most frequently reported side effect in both treatment groups was a transient burning sensation at application sites.

CONCLUSION

Topically applied capsaicin effectively treats pruritic psoriasis, a finding that supports a role for substance P in this disorder.

Tretinoin emollient cream: a new therapy for photodamaged skin

BACKGROUND

Tretinoin administered topically in 0.1% concentration has been shown to improve the wrinkling and irregular pigmentation of photoaged skin.

OBJECTIVE

The purpose of this study was to assess the safety and efficacy of various concentrations of tretinoin in a new emollient cream base in the treatment of photoaged skin.

METHODS

Three concentrations of tretinoin (0.05%, 0.01%, and 0.001%) in a new emollient cream formulation were compared with vehicle in a 24-week, double-blind, randomized, multicenter study of 296 subjects with photodamaged facial skin.

RESULTS

Tretinoin emollient cream 0.05% gave a significantly better global response to therapy than vehicle (p less than 0.001), with 68% of subjects exhibiting improvement at the end of therapy, compared with 43% of subjects in the vehicle group. An excellent or good response was found in 26% of subjects treated with tretinoin emollient cream 0.05% versus 11% of vehicle-treated subjects. Fine wrinkling, mottled hyperpigmentation, and roughness were more improved in subjects who received tretinoin emollient cream 0.05% than in vehicle-treated subjects (p less than 0.05). No significant difference was found between vehicle and tretinoin emollient cream 0.01% or 0.001%. Histologic examination showed increases in epidermal and granular layer thickness, decreased melanin content and compaction of the stratum corneum after therapy with tretinoin emollient cream 0.05% or 0.01%. Mild to moderate skin reactions, such as erythema, peeling, and burning, were the most common side effects and, although most prevalent in the group using the 0.05% concentration, generally did not limit tretinoin use.

CONCLUSION

Tretinoin emollient cream 0.05% appears to be safe and effective in the treatment of photodamaged skin.

Interferon therapy for condylomata acuminata

Current therapy for condylomata acuminata (genital warts) is not consistently effective. Therefore, we conducted a randomized, double-blind trial to compare interferon alpha-2b with placebo in the treatment of this disorder. Our rationale was that interferon has both antiproliferative and antiviral properties. The placebo or interferon (1 X 10(6) IU) was injected directly into one to three warts three times weekly for three weeks. The injections were well tolerated by both groups of patients. The side effects of fever, chills, myalgia, headache, fatigue, and leukopenia occurred more commonly in the interferon group than in the placebo group, but such effects rarely disrupted daily routines. Only 13 of 296 patients (4 percent) discontinued therapy because of side effects (11 in the interferon group and 2 in the placebo group). Twenty-six other patients were excluded from analysis because of a loss to follow-up or other deviations from protocol, thus leaving 257 patients in the final evaluation. At one week after the completion of therapy, interferon had produced a large and significantly greater reduction in mean wart area (a 62.4 percent decrease), as compared with placebo (a 1.2 percent increase in mean area) (P less than 0.001). At the conclusion of the study (13 weeks after the completion of therapy), the mean wart area was still decreased 39.9 percent below the initial size in the interferon group, whereas it had increased by 46 percent over base-line measurements in the placebo group (P less than 0.001). At the same time, all treated warts had completely cleared in 36 percent of the interferon recipients and in 17 percent of the placebo recipients (P less than 0.001), whereas treated warts progressed in 13 percent of the interferon recipients and in 50 percent of the placebo recipients (P less than 0.001). We conclude that injection of interferon alpha-2b directly into genital warts appears to be an effective and fairly well-tolerated form of therapy.

The Room Temperature Elastic Behaviour of CsH2PO4

The components of the elastic constant matrix of monoclinic caesium dihydrogen phosphate (CDP) have been determined using ultrasonic velocity measurements to be Cl1 = 28� 83 � 0 '43, C22 = 26�67 � O� 37, C33 = 65 �45 � 0'48, C44 = 8 .1O� 0,15, Css = 5 �20� 0,24, C66 = 9�17 � 0,22, C12 = 1l'4�3'6, C13 = 42�87�1�58, CIS = 5'13�0'67, C23 = 14�5�4�4, C 2S = 8'4�4'3, C3S = 7�50�0�81 and C46 = -2�25�0�31 GPa. Calculations of the velocity surfaces, ray directions, Young's modulus surfaces and linear compressibility show marked elastic anisotropy, which has been correlated with the chain and layer-like structure of CDP.

The Room Temperature Elastic Constants of Caesium Thiocyanate

The velocities of propagation of elastic waves in caesium thiocyanate have been measured along the three orthorhombic axes and normal to the (110), (011) and (101) planes using a double-transducer technique at 10 MHz. The velocities are found to be consistent with the orthorhombic crystal symmetry, and in favourable agreement with a recently published rigid-ion model calculation. The calculated elastic stiffness constants have values C11 = 18'9�0'7, C22 = 20�6�1�0, C33 = 28�1�1�6, C44 = 1'96�0'05, Css = 7�30�0�2, C66 = 3�04�0�07, C12 = 7'8�4'3, Cl3 = 14�8�4 and e23 = 6�3�4GPa. The calculated values for the adiabatic bulk modulus and the low temperature limiting value of the Debye temperature are 13�2 � 3�5 GPa and 132 K respectively