High aspect ratio sapphire micromachining by ultraviolet laser-induced plasma-assisted ablation (LIPAA)

The ultraviolet laser-induced plasma-assisted ablation performed in this article can attain deep and high-quality engravings in sapphire without necessitating volatile solutions or expensive equipment such as high-power ultrashort-pulsed lasers. The dominant mechanism of ablation is discovered to be from the direct ablation of excited sapphire surfaces and not from the plasma generated from the target material. Only an initial deposition from the target is needed to initiate the direct ablation. Note that 20-µm wide, 30-µm deep channel and hole features with a surface roughness (Sa) of .65 µm are achieved at an etching rate of .3 µm per pulse without the need for extensive cleaning. Engravings can reach up to 150-µm depths at a maximum tapering angle of 5° until the shrinking absorbent surface vanishes, and 500-µm wide 430-µm deep topside through-cutting is achieved. This study characterizes the morphology of direct laser ablation of transient absorbent sapphire surfaces. This method demonstrates the potential for the low-cost rapid engraving of high aspect ratio features in transparent sapphire substrates.     

Patterning of graphene with tunable size and shape for microelectrode array devices

Large size and high quality graphene grown by chemical vapour deposition (CVD) has been fabricated into an array of discrete graphene sheets with well-defined sizes and shapes. A fabrication process based on nanoimprint lithography has been developed to achieve shape tunability with sizes ranging from micrometer to nanometer. The technique preserves the quality of the CVD grown graphene and offers the versatility of transferring the graphene array onto any rigid or flexible substrate. The process is then expanded to fabricating a graphene based microelectrode array whose performance is demonstrated in the real time sensing of peroxidase excreted by breast cancer cells. The device displayed a linear working range of 0.01–25 mM and a sensitivity of 8.8 mA mol⁻¹.     

Ordered array of diamond ultramicroband electrodes for electrochemical analysis

Boron-doped diamond ultramicroband arrays with different array densities and interelement spacings were fabricated using silicon technology and selective diamond deposition (SAD) technique to yield microvoltammetric electrodes. The electroactive ultramicroband elements were designed with one microscopic critical dimension to impart microelectrode behavior while the other dimension was made larger to yield an increase in signal current. Cyclic voltammetry studies in this work showed that with sufficient interelement separation, the ultramicroband arrays display sigmoidal pseudo-steady-state cyclic voltammograms characteristic of microband electrodes. The ultramicroband arrays yielded higher faradaic current per unit area, than either square ultramicroelectrode array or conventional planar diamond electrode from earlier reported work. This is due to enhanced mass transport to the ultramicroband elements at slow scan rates. Larger current density and higher signal-to-noise (S/N) ratio leads to better limits of detection, making it possible to fabricate a more sensitive electrode for applications such as electroanalysis, electrocatalysis, trace element analysis, mechanistic and fast transfer kinetics studies, electrochemistry in highly resistive media, as well as sensors in flow and biological system.     

Fabrication of a NCD microelectrode array for amperometric detection with micrometer spatial resolution

We report on the fabrication of a boron-doped nanocrystalline diamond (NCD) 3 × 3 high-density microelectrode array (MEA) for amperometric measurements, with a single electrode area of 3 × 5 μm² and a separation in the μm scale. The NCD microelectrodes were grown by hot filament chemical vapor deposition (HFCVD) on a double-side polished sapphire wafer in order to preserve the diamond transparency. Bias enhanced nucleation (BEN) was performed to ensure a covalent adhesion of the films to the substrate. A current background noise of less than 5 pA peak to peak over a 1 kHz bandwidth resulted from an electrochemical investigation of the new device, using 100 mM KCl solutions and ferrocyanide red-ox couples. Cyclic voltammetry measurements in physiological buffer solution and in the presence of oxidizable bio-molecules strengthened its suitability for bio-sensing. When compared to a 2 × 2 NCD microelectrode array prototype, already used for in vitro cell measurements, the signal to noise ratio of the amperometric response of the new 3 × 3 device proved twice as good. In addition, the optical transmittance of the boron-doped thin layers exceeded 40% in the visible wavelength range.The excellent electrochemical properties of NCD electrodes and the transparency in combination with the high spatial resolution make the new 3 × 3 NCD MEA a promising tool for electrochemical sensing in a variety of applications, ranging from medical to industrial, in neutral or harsh environments.     

Electrochemical measurements of serotonin (5-HT) release from the guinea pig mucosa using continuous amperometry with a boron-doped diamond microelectrode

Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) disorder characterized by chronic abdominal discomfort, including pain, bloating and changes in bowel habits. The pathophysiology of IBS is multi-factoral to be sure, but is not fully understood. Recent studies have shown that IBS may be associated with altered serotonin (5-hydroxytryptamine, 5-HT) levels within the GI tract. About 90% of 5-HT in the human body is produced and stored in enterochromaffin (EC) cells that reside in the mucosal layer of the intestine. Measurements of serotonin availability locally in the mucosa can provide insight on the functionality of these cells and potentially the pathophysiology of the disease. In this study, we used continuous amperometry with a diamond microelectrode to record serotonin levels in vitro in the ileum mucosa as an oxidation current. The boron-doped diamond (BDD) microelectrode is quite practical for these measurements because if its low background signal, low sensitivity to solution pH changes, and excellent resistance to fouling by adsorbed serotonin oxidation reaction products. In fact, the measurements are only possible because of the unique properties of diamond. We present electrochemical data that demonstrate the diamond microelectrode's utility for assessing 5-HT handling on the gut. Confirmation that the oxidation current measured was associated with endogenous serotonin release came from pharmacological studies. These types of in vitro electrochemical measurements may lead to a better understanding of the pathophysiology of IBS.     

High spatial resolution photoluminescence and Raman spectroscopic measurements of a natural polycrystalline diamond, carbonado

Photoluminescence and Raman spectra with high spatial resolution (< 1 μm) were observed on a natural polycrystalline diamond, carbonado. The studied sample is from Central African Republic (CAR) and was polished to optical grade. In addition to observation by optical microscopy, Scanning Near-field Optical Microscopy (SNOM) was applied for spectral and topographic analysis at high spatial resolution less than 300 nm. Mapping of the photoluminescence intensity of carbonado using SNOM indicated that the emission intensity was lower at the grain boundaries and the fringe of pores of carbonado revealed weakest intensity. Photoluminescence spectra of carbonado observed using optical microscopy and SNOM comprised three sharp bands at 504, 575 and 638 nm with their side bands and the color of photoluminescence changed according to its location. Raman spectra measured using optical microscopy revealed that the residual stress locally exists underneath the sample surface and the maximum stress value observed in this study was 0.72 GPa. Additionally, pressure dependence of the 575 nm band was measured using a diamond anvil cell up to 3.5 GPa. The 575 nm band shifted linearly to a lower wavelength with increasing pressure with a gradient of − 0.57 GPa/nm. This relationship was applied to estimations of the stress distribution of carbonados using SNOM. No significant changes in peak positions of photoluminescence spectra were detected on the surface of carbonados. This result suggests that carbonado is well sintered and that the residual stress of carbonado exists locally inside the crystal.     

A model for supersaturation and aspect ratio for growth dominated crystallization from solution

A model for predicting supersaturation, crystal growth rate, crystal size distribution, and aspect ratio is presented. The model applies to isothermal anti‐solvent crystallization where crystal growth is the dominant phenomena and for systems where crystal habit can be characterized by two‐dimensional variables. A parameter estimation algorithm was derived to extract solute integration coefficients in the two growth directions from experimental data about temporal evolution of concentration during crystallization, the final aspect ratio, and the aspect ratio at the end of the seed age period. Model's predictions for supersaturation and aspect ratio were in good agreement with experimental data obtained on an investigational drug that crystallizes in the parallelepipedic shape. Finally, model simulations predict that for a given initial seed size, the seed loading is the main factor impacting the final aspect ratio and thus identified the range of seed loading that would result in undesired powder flow. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4456–4469, 2015     

High quality homoepitaxial CVD diamond for electronic devices

Recent achievements in homoepitaxial CVD diamond films for electronic devices have been discussed. We have successfully synthesized high-quality homoepitaxial diamond films with atomically flat surface by the microwave plasma chemical vapor deposition (CVD) using a low CH₄ concentration of CH₄/H₂ gas system less than 0.15% CH₄/H₂ ratio and Ib (001) substrates with low-misorientation angle less than 1.5°. These films are atomically flat over an area as large as 4×4 mm² and have shown a strong excitonic emission of 5.27 eV line, even at room temperature, with no essential emission lines in the visible light region in the cathodoluminescence (CL) spectra. Furthermore, high-quality Schottky junctions between Al and P type high-conductivity layers near the surface of these films have been obtained. Based on this growth method, we have also successfully synthesized B-doped diamond films using trimethylboron [B(CH₃)₃,TMB] gas as a B-doping source, whose Hall mobility is 1840 cm²/Vs at 290 K. Schottky junction fabricated by the B-doped diamond also shows excellent performances, indicating that the homoepitaxial diamond films presented here have a high potentiality for electronic devices.     

Usability of diamond detectors for spectrometric measurements of lost alpha particles

Measurement of energy of the lost alpha particles (‘escaping alpha particles’) from the thermonuclear reaction in the tokamak is important to obtain information on the energetic balance in future thermonuclear reactors which will be used in power plants. A synthetic high purity CVD monocrystalline diamond detector has been tested in aspect of its potential application for spectrometric diagnostic of the lost alphas of which maximum energy from the thermonuclear reaction is equal to 3.5 MeV. Spectrometric properties of the diamond detector (Diamond Detector, Ltd.) of the 50 μm thickness have been performed using alpha particles of defined energies. The energy calibration and the study on the energy resolution have been carried out using a triple alpha particle isotopic source AMR33 (²³⁹Pu + ²⁴¹Am + ²⁴⁴Cm) with the alpha energy peaks at ca. 5.2, 5.5 and 5.8 MeV, the (²¹²Bi + ²¹²Po) isotopic source of energy 6.0 and 8.7 MeV and a van de Graaff accelerator delivering a well defined monoenergetic alpha beam, changed between 0.4 and 2 MeV. A 14 MeV neutron generator has been employed as a source of alpha particles from D–T reaction accompanied by another induced radiation to test the behaviour of the diamond detector under such conditions.     

高深径比通孔电镀铜的添加剂优化

以75 g/L CuSO₄·5H₂O、230 g/L硫酸和0.1 g/L十二烷基苯磺酸钠(SDBS)组成的溶液作为基础镀液,并以Cl^-、聚乙二醇(PEG-10000)、聚二硫二丙烷磺酸钠(SPS)及2,2′-二硫代二吡啶(2-PDS)作为添加剂,在温度(23±2)℃、电流密度1.8 A/dm²和空气搅拌的条件下对印制电路板(PCB)上深径比为10∶1的通孔电镀铜。以深镀能力作为评价指标,通过正交试验对添加剂用量进行优化,得到较优的组合为:SPS 5 mg/L,PEG 250 mg/L,Cl^- 60 mg/L,2-PDS 2 mg/L。采用该组合添加剂电镀通孔时,深镀能力高达112.9%,镀层均匀、细致、平整,抗热冲击性能良好,符合PCB生产对可靠性的要求。     

23.1-26低断面振动压路机轮胎设计及改进

介绍23．1—2614PR振动压路机轮胎的技术性能要求、结构设计和施工设计。据此设计，轮胎成品充气尺寸、各项性能指标完全达到设计要求。采取增大气门嘴底座直径、气门嘴底座打孔、内胎气门嘴胶垫上加贴锦纶帘布等措施后，气门嘴脱落问题大大减少，达到了预期效果。     

Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas-liquid operations

The mass transfer performance of a gas-liquid self-ingesting stirred reactor is reported both for coalescing and non-coalescing systems. The vessel features are a high aspect ratio and a rather narrow multiple-impeller draft tube, through which the gas phase is ingested and led down to the vessel bottom, where it is finely dispersed into the liquid rising in the annular portion of the vessel. Comparison is made between k_La values determined by several variants of the dynamic method, among which pure oxygen absorption in a previously de-gassed liquid phase. Results show that the gas-liquid mass transfer coefficient values obtained with the last approach are remarkably larger than those measured with all other techniques in which nitrogen is initially dissolved in the liquid phase. Possible reasons behind this discrepancy are discussed.The gas-liquid mass transfer performance of the investigated gas inducing contactor is finally compared with literature data on other self-inducing/ingesting devices. Comparison results encourage further development of the investigated apparatus.     

Preparation and characterization of boron doped diamond electrodes on diamond anvil for in situ electrical measurements under high pressure

A layer of boron doped diamond (BDD) film was deposited selectively on a diamond anvil and employed as electrodes for measuring the electrical resistivity of matter under high pressure. Both heavily doped and lightly doped electrodes were characterized by Raman spectroscopy and scanning electron microscopy. Though the BDD film electrodes contain sp² carbon, it is still suitable for in situ high pressure electrical measurements. The dependability of diamond film electrodes was tested at high pressure up to 36 GPa, by measuring the electric resistance of C60 fullerene powder, and no damage of the electrodes was observed.     

New strategy for impedance measurement of surface oxidation characteristic in ceramic fiber by controlling aspect ratio

Silicon carbide fibers (SiC_f) are promising materials for high-temperature applications, because of their excellent thermal and mechanical properties. Due to the inevitable oxidation of SiC_f used at high-temperature, the surface and interfacial properties of SiC_f can be changed. Impedance analysis is necessary to confirm the useful information for various properties. However, since single SiC_f has a long length and a very small cross-section area, its capacitance is so small that impedance analysis is almost impossible. In this study, an in-situ analysis tool that can estimate the impedance of SiC_f to confirm the resistance elements is proposed using bundled fiber specimens. It is confirmed that it is possible to measure the impedance of the SiC_f under high-temperature and oxidation atmospheres by controlling the aspect ratio of the specimen. This tool provides a new pathway that can be applied in various systems by investigating the electrical properties according to the oxidation behavior.     

Laser-induced spark for measurements of the fuel-to-air ratio of a combustible mixture

This work investigates the use of the laser-induced gas breakdown for fuel-to-air ratio measurements. In essence, we examine the late time behavior of the line radiation at the wavelength of the H_α-lines and the O I triplet emitted from the laser-induced spark in CH₄-air mixtures. Sparks were produced using a single-mode, Q-switched Nd-YAG laser. The laser produced a beam of 6 mm in diameter at the wavelength of 1064 nm and a pulse duration of 5.5 ns. For the equivalence ratio from 0.1 to 5.0, the radiation intensity ratio of the H_α-lines to the O I triplet increased linearly with the equivalence ratio. For the laser energy from 10 to 50 mJ it was independent of the laser energy when the laser energy was higher than 20 mJ. The technique, therefore, has a potential for measuring the fuel-to-air ratio of a combustible flow environment.     

Experimental methods for activity measurements in environmental catalysis

The very specific operating conditions of catalytic processes for the abatement of pollutants from mobile or fixed sources, require an unusual experimental set-up to determine the catalyst performance. Selected examples of environmental catalysis applications such as deNO_x with NH₃ or hydrocarbons, deSO_x with either powder or monolith catalysts, low temperature soot oxidation, are discussed with respect to the experimental methods to be employed for catalytic activity measurements.     

Use of high-sensitivity diamond detectors in DC mode for detailed beam-profile measurements in particle accelerators

Because of its high radiation hardness, diamond can be used better than other materials in the intense radiation field characterizing the interior region of a particle beam in an accelerator. In effect, the measurements reported here were carried out by placing diamond detectors under continuous irradiation in the 26-MeV proton beam of the 15-MV TANDEM accelerator of Southern National Laboratory (LNS) of INFN in Catania. The diamond detectors were built in the Rome Tor Vergata Laboratory. Diamond films were deposited by microwave plasma enhanced chemical vapor deposition on silicon substrates. A four-pixel beam monitor prototype was then realized by depositing four titanium gold contacts on the diamond surface. The signal was found to be stable and reproducible. The collected charge in DC mode was more than 20 000 electrons/protons for a diamond thickness of 65 μm, thus exhibiting a gain of approximately 10⁴ with respect to the Faraday cup. For the measured samples, both response and release times of approximately 1 s were observed in the above experimental conditions. An analysis of the relative sensitivity between pixels was also performed. No differences of the detector current and Faraday cup current ratio were observed for different pixels, indicating the homogeneity of the beam monitor response.     

High mobility single crystal diamond detectors for dosimetry: Application to radiotherapy

Diamond exhibits properties of interest for applications in the medical field. It is a very attractive material for detector fabrication due to its intrinsic properties and particularly its soft-tissue equivalence (Z = 6 compared to Z = 7.42 for human tissue), mechanical robustness and radiation hardness. Detectors fabricated from natural diamonds are used in several hospitals as dosimetric tools for the dose measurement received by the patient during radiotherapy and for beam calibration. Natural diamond based devices are expensive and long delivery times are common. The use of synthetic single crystal diamond is a promising issue for point dosimeter. Here we report on the growth of synthetic diamond using the CVD technique to fabricate free standing single crystals. Samples were characterized from their optical and electronic properties (Raman, TOF) and mounted as solid ionisation chambers with blocking contacts, for the evaluation of their dosimetric properties. Clinical tests were conducted in a medical facility at the Institute Gustave Roussy (IGR) in France specialised in the medical treatment of tumours. The results obtained demonstrate that our single crystal diamond detectors comply with the required specifications for radiotherapy applications.