Fabrication of optics by use of plasma chemical vaporization machining with a pipe electrode

We figure optical surfaces by plasma chemical vaporization machining (CVM) with a pipe electrode, in which an rf plasma generated at the electrode tip under approximately atmospheric pressure moves over the surfaces. We propose a shaping method in which the movement of plasma on the surfaces can be determined. Flat and aspheric surfaces are successfully figured with the desired peak-to-valley shape accuracy of 0.1 microm. The root-mean-square roughness of the resultant surfaces is at the subnanometer level. These results confirm that the plasma CVM and the shaping method have the capability to fabricate optics with high accuracy.     

Computer numerically controlled plasma chemical vaporization machining with a pipe electrode for optical fabrication

We have developed a chemical vaporization machining device that has computer numerically controlled plasma, by using a pipe electrode for optical fabrications. In this device, less than approximately 1 atm of pressure, plasma is generated around the tip of a pipe electrode. During the process, a workpiece is scanned against the electrode under computer control to achieve the desired shape to be removed. A workpiece of silica glass plate is shaped by use of this device, and the removal characteristics of the device are examined. The equations to characterize numerically the shape resulting from scanning of a workpiece have been derived. The new device allows the high precision of optics from the micrometer to the nanometer level with high-speed removal. The shaped surface is sufficiently smooth to be suitable for optical use.     

Shape correction of optical surfaces using plasma chemical vaporization machining with a hemispherical tip electrode

We propose a plasma chemical vaporization machining device with a hemispherical tip electrode for optical fabrication. Radio-frequency plasma is generated close to the electrode under atmospheric conditions, and a workpiece is scanned relative to the stationary electrode under three-axis motion control to remove target areas on a workpiece surface. Experimental results demonstrate that surface removal progresses although process gas is not forcibly supplied to the plasma. The correction of shape errors on conventionally polished spheres is performed. As a result, highly accurate smooth surfaces with the desired rms shape accuracy of 3 nm are successfully obtained, which confirms that the device is effective for the fabrication of optics.     

Ion beam machining error control and correction for small scale optics

Ion beam figuring (IBF) technology for small scale optical components is discussed. Since the small removal function can be obtained in IBF, it makes computer-controlled optical surfacing technology possible to machine precision centimeter- or millimeter-scale optical components deterministically. Using a small ion beam to machine small optical components, there are some key problems, such as small ion beam positioning on the optical surface, material removal rate, ion beam scanning pitch control on the optical surface, and so on, that must be seriously considered. The main reasons for the problems are that it is more sensitive to the above problems than a big ion beam because of its small beam diameter and lower material ratio. In this paper, we discuss these problems and their influences in machining small optical components in detail. Based on the identification-compensation principle, an iterative machining compensation method is deduced for correcting the positioning error of an ion beam with the material removal rate estimated by a selected optimal scanning pitch. Experiments on ?10?mm Zerodur planar and spherical samples are made, and the final surface errors are both smaller than λ/100 measured by a Zygo GPI interferometer.     

Ion-beam machining of millimeter scale optics

An ion-beam microcontouring process is developed and implemented for figuring millimeter scale optics. Ion figuring is a noncontact machining technique in which a beam of high-energy ions is directed toward a target substrate to remove material in a predetermined and controlled fashion. Owing to this noncontact mode of material removal, problems associated with tool wear and edge effects, which are common in conventional machining processes, are avoided. Ion-beam figuring is presented as an alternative for the final figuring of small (<1-mm) optical components. The depth of the material removed by an ion beam is a convolution between the ion-beam shape and an ion-beam dwell function, defined over a two-dimensional area of interest. Therefore determination of the beam dwell function from a desired material removal map and a known steady beam shape is a deconvolution process. A wavelet-based algorithm has been developed to model the deconvolution process in which the desired removal contours and ion-beam shapes are synthesized numerically as wavelet expansions. We then mathematically combined these expansions to compute the dwell function or the tool path for controlling the figuring process. Various models have been developed to test the stability of the algorithm and to understand the critical parameters of the figuring process. The figuring system primarily consists of a duo-plasmatron ion source that ionizes argon to generate a focused (~200-mum FWHM) ion beam. This beam is rastered over the removal surface with a perpendicular set of electrostatic plates controlled by a computer guidance system. Experimental confirmation of ion figuring is demonstrated by machining a one-dimensional sinusoidal depth profile in a prepolished silicon substrate. This profile was figured to within a rms error of 25 nm in one iteration.     

Fabrication and characterization of sputtered-carbon microelectrode arrays

This paper describes a robust and reliable process for fabricating a novel sputter-deposited, thin-film carbon microelectrode array using standard integrated circuit technologies and silicon micromachining. Sputter-deposited carbon films were investigated as potential candidates for microelectrode materials. The surface properties and cross section of the microelectrode arrays were studied by atomic force microscopy and scanning electron microscopy, respectively. Electrical site impedance, crosstalk, and lifetime (dielectric integrity) of microelectrodes in the array were characterized. Electrochemical response of the microelectrodes to hexaammineruthenium(III) chloride and dopamine were investigated by fast-scan cyclic voltammetry and high-speed, computer-based chronoamperometry; results show that thin-film carbon microelectrodes are well-behaved electrochemically. The thin carbon films offer extremely good electrical, mechanical, and chemical properties and thus qualify as viable candidates for various electroanalytical applications, particularly acute neurophysiological studies.     

Laser-triggered high-voltage plasma switching with diffractive optics

High-power lasers can be used to induce ionization of gases and thereby enable rapid triggering of electrical discharge devices, potentially faster than any devices based on mechanical or solid-state switching. With diffractive optical elements (DOEs) the laser light can conveniently be directed to positions within the gas so that an electrical discharge between two high-voltage electrodes is triggered reliably and rapidly. Here we report on two different types of DOE used for creating an electrical discharge in pure argon for potential high-voltage applications. One is the diffractive equivalent of a conventional axicon that yields an extended, and continuous, high-intensity focal region between the electrodes. The other is a multiple-focal-distance kinoform-a DOE that is designed to produce a linear array of 20 discrete foci, with high peak intensities, between the electrodes. We show that DOEs enable efficient, rapid switching and may provide increased flexibility in the design of novel electrode configurations.     

Fabrication of nanocrystalline silicon carbide thin film by helicon wave plasma enhanced chemical vapour deposition

Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapour deposition on Si substrates using the mixture of SiH₄, CH₄, and H₂ at a low substrate temperature of 300 °C. The infrared absorption spectroscopy analyses and microstructural characteristics of the samples deposited at various magnetic fields indicate that the high plasma intensity in helicon wave mode is a key factor to the success of growing nanocrystalline silicon carbide thin films at a relative low substrate temperature. Transmission electron microscopy measurements reveal that the films consist of silicon carbide nanoparticles with an average grain size of several nanometers, and the light emission measurements show a strong blue photoluminescence at room temperature, which is considered to be caused by the quantum confine effect of small size silicon carbide nanoparticles.     

Fabrication of micro optics on coreless fiber segments

Fabrication of micro optics for fiber optics applications is a challenge due to their size and the issues associated with alignment of the optics to single-mode fibers. This study summarizes a method for fabricating diffractive optical elements on the ends of coreless fiber segments for passive alignment to single-mode fibers. Results are presented for passively aligned diffractive lens elements used for both collimation and beam shaping.     

Fabrication of superhydrophobic copper by wet chemical reaction

A wet chemical reaction was employed herein to fabricate a stable superhydrophobic surface on a polished copper substrate at ambient temperature. The resulting surface showed superhydrophobic properties as evidenced by a water contact angle (CA) of about 154° and a water sliding angle (SA) of about 4°, which may be attributed to the combination of the roughened surface morphology by means of wet chemical reaction and the formed low surface free energy per chemical modification with poly (dimethysiloxane) vinyl terminated (PDMSVT). Scanning electron microscopy (SEM) images of the resulting surface reveal the resulted copper oxalate microscopic sizes with average diameter of about 0.5 μm and circular submicroscopic structures with diameter of about 100 nm, constructing a hierarchical structure consisted by micro- and nano-scale elements similar to that of lotus leaf in some extent. The elemental and chemical compositions of the resulting surface were also identified by Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. This work provides improved understanding of the effect of surface roughness and surface energy on superhydrophobicity.     

Fabrication and characterization of an all-diamond tubular flow microelectrode for electroanalysis

The development of the first all-diamond hydrodynamic flow device for electroanalytical applications is described. Here alternate layers of intrinsic (insulating), conducting (heavily boron doped), and intrinsic polycrystalline diamond are grown to create a sandwich structure. By laser cutting a hole through the material, it is possible to produce a tubular flow ring electrode of a characteristic length defined by the thickness of the conducting layer (for these studies ～90 μm). The inside of the tube can be polished to 17 ± 10 nm surface roughness using a diamond impregnanted wire resulting in a coplanar, smooth, all-diamond surface. The steady-state limiting current versus volume flow rate characteristics for the one electron oxidation of FcTMA(+) are in agreement with those expected for laminar flow in a tubular electrode geometry. For dopamine detection, it is shown that the combination of the reduced fouling properties of boron doped diamond, coupled with the flow geometry design where the products of electrolysis are washed away downstream of the electrode, completely eradicates fouling during electrolysis. This paves the way for incorporation of this flow design into online electroanalytical detection systems. Finally, the all diamond tubular flow electrode system described here provides a platform for future developments including the development of ultrathin ring electrodes, multiple apertures for increased current response, and multiple, individually addressable ring electrodes incorporated into the same flow tube.     

爆炸辅助气相沉积法制备炭纳米线的研究

根据爆炸辅助气相沉积法生长碳纳米管的机理,设计了两种制备炭纳米线的方案:(1)使用低活性铁-镍二元金属催化剂;(2)对钴催化剂作用下碳纳米管的生长实施冷冻。透射电子显微镜显示这两种方法制备的炭纳米线均为纳米颗粒组装而成,具有非常粗糙的表面。其中,使用铁-镍二元催化剂所制炭纳米线直径分布不均匀,黏结情况严重;而在冷冻钴催化剂作用下炭纳米管生长过程所得的炭纳米线直径分布比较均匀,黏结情况也大为减少。这两种纳米线的差别与金属催化剂的活性有关。光催化降解亚甲基蓝实验表明:冷冻碳纳米管生长所得炭纳米线具有良好的催化辅助功能,可以提高ZnS纳米晶的光催化活性。     

Fabrication of glass-capsuled CdTe microcrystals using laser evaporation and plasma chemical vapour deposition method

CdTe microcrystals encapsulated in a silica glass layer were successfully fabricated. Spherical CdTe microcrystals were prepared by laser evaporation of a CdTe target in an argon gas atmosphere. The ensuing microcrystals plus argon gas passed through a tetramethoxysilane (TMOS)+O₂ plasma in which they were encapsulated in an amorphous layer, 2–2.5 nm thick. Characteristic X-rays from the surface layer were measured using an energy dispersive X-ray spectrometer equipped in a high-resolution transmission electron microscope. Measurements indicated that the glass layer consisted of silicon and oxygen, with no cadmium or tellurium included. The CdTe microcrystals fabricated with our laser evaporation system showed two specific kinds of particle: small particles (below 10 nm) and large ones (over 100 nm). Using precise electron-beam diffraction testing, we concluded that the large microcrystal is a single crystal with a hexagonal structure. The deposition rates and infrared transmission of silica glass prepared by TMOS or tetraethoxysilane plasma-enhanced chemical vapour deposition are also discussed. The highest deposition rate, 30 nm s^–1, of silica glass can be achieved in the centre of the plasma when the input r.f. power is 150 W.     

Fabrication and measurement of low-stress membrane mirrors for adaptive optics

We have fabricated low-stress membranes from single-crystal silicon for use as deformable mirrors in adaptive optics. These membranes have lower stress than membranes made from silicon nitride or other materials and therefore are capable of greater deformation than previously used membrane mirrors. Membranes were assembled into devices by flip chip bonding to electrode chips with either 256 or 1024 electrodes. We have characterized devices with static and dynamic tests and compared their performance with an analytical model. We tracked the evolution of strain in the membrane during the device's fabrication and assembly and identified sources of stress and strain in this process. We identified boron dopant concentration as a critical determinant of intrinsic stress in the membrane.     

Fabrication of ordered arrays of InP microstructures by wet chemical etching with Au masks

Ordered arrays of InP microstructures have been fabricated on InP(001) substrates by wet chemical etching in aqueous HCl with patterned Au masks. The masks were produced by Au deposition through copper grids or a monolayer of polystyrene microspheres. Square InP mesas (20 x 20 microns) and pillars (approximately 100 nm in both diameter and height) were both produced and characterized by scanning electron microscopy and atomic force microscopy.     

Fabrication of bulk Al-La-Ni alloy by spark plasma sintering

The bulk Al₈₅La₁₀Ni₅ alloy is sintered by spark plasma sintering (SPS) method. The microstructure and mechanical properties of the Al₈₅La₁₀Ni₅ samples are investigated. The results show that the bulk Al₈₅La₁₀Ni₅ alloy with less than 1.5% porosity has been obtained at 693 K. The hardness of the alloy sintered at 693 K reaches HRB 98 and the wear resistance of the alloy is twice of the conventional A390 aluminum alloy. The high wear resistance of aluminum alloy is attributed to second-phase strengthening.     

Effect of vaporization and melt ejection on laser machining of silica glass micro-optical components

A new regime for silica glass machining for micro-optical fabrication applications, which uses pulsed CO2 laser radiation in the 2.5-100-micros pulse width region that has been generated by an acousto-optic modulator, is investigated. A filamentary melt ejection process that generates fibers and significant melt displacement limits machining quality below 30-micros pulse width. Ablation and melt ejection thresholds are quantified relative to pulse width, and the region from 30 to 50 micros is identified for low-threshold, smooth machining without melt displacement and ejection effects.     

Fabrication of nano-pillar chips by a plasma etching technique for fast DNA separation

The fabrication of quartz nano-pillars was investigated using dry etching with a Ni mask. The mask diameter increased during etching due to re-sputtering of the Pt/Cr seed layer. However, once the seed layer had been eroded the enlarged mask diameter did not increase any further. Hence, the use of the mask enabled the fabrication of nano-pillars with a high aspect ratio. In situ FTIR-ATR observation of HF quartz plate pressure bonding developed a new bonding technique involving the use of H₂SiF₆. The nano-pillar chips allowed then to size-separate DNA of 10 kbp and 38 kbp within 20 s.