Advances in Science and Technology Vol. 48

Abstract: A number of installations for electric discharge sintering of powder materials is developed. There are installations in which energy is delivered by following currents: 1) superposition of the direct and alternating (with frequency up 7900 Hz) currents, 2) alternating current (50 Hz). The sintering is carried out in conductive (graphite) moulds. The sintering is often done in thermal and electric insulator moulds (for example, ceramic on Si3N4 base, asbestos cement). At sintering of metal-diamond composition in insulator moulds metallic electrodespunches (steel) are used. Such a variant of sintering allows one its duration to short from ~900 s down to ~60–150 s. This ensures complete safety of dimensions and operating characteristics of diamond grains. The technologies of various diamond elements for tools for treatment of glasses and soft stones (stone saws, tools in forms of tablets, rings). The preliminary pressure which is applied to powder sample simultaneously with current was equal to ~10 MPa (~100 kg/cm2). The end pressure was equal to ~100 MPa (~1000 kg/cm2). The current density was equal to ~700– 1200 A/cm2. Tests of diamond tablets (diamond 20/14 mkm, binder 80 % Cu+20 % Sn) at grinding of glass had shown: the abrasivity of tablets with common diamonds is equal to ~50 g/(cm2 min), and abrasivity in case with diamonds annealed in hydrogen is equal to ~70 g/(cm2 min).

Abstract: Highly compressively stressed diamond-like carbon and polymer films were used to fabricate normally closed microgrippers with diameters as small as 30~40μm. The microgrippers consisted of a DLC layer of 30-50nm, a thin Al layer of 40nm as a heater and an SU8 layer of 250~500nm, and were fabricated by a self-aligned two-mask process. Electrical tests and nonelectrical tests on a Peltier device confirmed the devices have an operation temperature of ~100°C for an opening angle of 90°, much lower than the ~400°C needed for previously fabricated Ni/DLC microgrippers. This value is consistent with finite element modelling and analytical calculation. The power needed to open the microgripper was only ~10 mW, less than half of those used for the previous Ni/DLC microgrippers. It has been successfully demonstrated that the microgrippers can be used to capture and confine micro-objects using microbeads for the tests.

Abstract: Conventional loudspeaker membranes made of metal or synthetic material such as fabric, ceramics or plastics suffer from nonlinearities and cone breakup modes at fairly low audio frequencies. Due to their mass, inertia and limited mechanical stability the speaker membranes made of conventional materials cannot follow the high frequency excitation of the actuating voice-coil. Low sound velocity causes phase shift and sound pressure losses due to interference of adjacent parts of the membrane at audible frequencies. Therefore, loudspeaker engineers are searching for lightweight but extremely rigid materials to develop speaker membranes whose cone resonances are well above the audible range. With its extreme hardness, paired with low density and high velocity of sound, diamond is a highly promising candidate for such applications. We report on the realization of dome shaped CVD diamond membranes by deposition on curved silicon substrates. Domes with diameters between 20 and 65 mm and with a thickness ranging from 50 to 120 μm were prepared. After deposition, the substrate is dissolved and the rim of the diamond dome is cut by laser scribing. Free standing diamond membranes are mounted onto dynamic voice coils and integrated into tweeter and/or midrange driver chassis. Extended tests and optimisations led to loudspeaker systems that show a second and third harmonic distortion behaviour in the important frequency range between 3 to 10 kHz that is reduced by 40% in comparison to already excellent established values obtained with sapphire membranes. Cone resonance frequencies of CVD diamond membranes are increased by a factor of two, as predicted by simulations.

Abstract: Bio-chips need active surfaces for sensing, actuation, synthesis and analysis. Thus, they should be realized with materials, widely suppressing corrosion and hydrolysis in combination with conducting, semiconducting and insulating properties, biocompatibility and chemical inertness. An ideal candidate is diamond. Two forms are considered: single crystal and nanocrystalline diamond, the later also containing non-diamond phases and graphic grain boundaries. Their surface properties and functionalization are discussed together with their electrode, ISFET and cell attachment and related neuron activity characteristics. Furthermore an outlook is given for system approaches.

Abstract: Nanoporous-carbon (NPC) is compared directly to commonly-used polymers as a gassorbing coating material on surface acoustic wave (SAW) microsensor devices. The sensing capability of these materials is measured for volatile organic compounds (VOCs), toxic-industrial chemicals (TICs), and a chemical warfare agents (CWA) simulant. All of the coatings reversibly sorb and desorb the volatile VOC and TIC compounds, however, NPC outperforms the polymers over the range of analyte concentrations studied, especially at the lowest levels, by multiple ordersof- magnitude. Conversely, NPC has good retention properties for the semi-volatile CWA simulant tested, which while detrimental for use on a reversible SAW device, infers that NPC may be wellsuited as a preconcentrator coating for such analytes. NPC is a highly-disordered low-density carbon containing both nanopores and increased interplanar spacing between graphene sheet fragments, self-assembles using pulsed laser deposition, has no residual-stress at room temperature, is stable to 600 °C, and is chemically-inert in harsh environments. It has superior chemical and aging properties compared to the conventional polymer films used in microsensor devices.

Abstract: The electrochemical behavior of a boron-doped diamond film electrode prepared by chemical vapor deposition was studied. The surface microstructure of the electrode was studied by means of scanning electron microscopy. The electrochemical behavior of the electrode was investigated by cyclic voltammetry and AC Impedance. The diamond films exhibited a “cauliflower-like” morphology and contained microcrystallites. The results showed the electrode having a very wide potential window and very low background current. The potential windows in acidic, neutral or alkaline medium were respectively 4.4[V], 4.0[V] and 3.0[V]. The background current was as low as -8×10-6～5×10-7[A]. In the electrolyte including Ferri/Ferrocyanide, the electrode surface kept good activity, and the electrochemical reaction occurring on the surface was a diffusion-controlled reaction, with good quasi- reversibility. Compared with Pt and graphite electrodes, diamond electrodes can oxidize compounds like phenol effectively, and the process of oxidization was very simple and complete.