New Technique For Fabrication Research Articles

Fabrication of microchannel and diaphragm for a MEMS acoustic sensor using wet etching technique

This paper reports a new technique for fabrication of diaphragm and microchannel in a single step for the development of a piezoelectric MEMS acoustic sensor. It describes the design of the sensor based on ZnO to be utilized for aero-acoustic measurements. A primary requirement for such devices is a high maximum sound pressure level [(SPL) ~180 dB] and flat frequency response in the audio band (20 Hz - 20 kHz). The Si-diaphragm thickness was optimized for the desired SPL range using Coventorware. The complete frequency response of the structure was determined using analytical formulations based on lumped element modeling (LEM). The fabricated device was tested using Laser Doppler Vibrometer (LDV). The lower cut-off frequency, bandwidth, resonance frequency and flat band sensitivity of the optimized device have been found to be 26.3 Hz, 40.0 kHz, 78.688 kHz and 148 μV/Pa respectively.

Evaluation of advanced methods and materials for construction of scintillation detector light guides

New techniques for fabrication of optically clear structures (3D printing and casting) can be applied to fabrication of light guides, especially complex -shaped ones, for scintillation detectors. In this investigation, we explored the spectral transmissivity of sample light guides created with different fabrication methods and materials. A spectrophotometer was used to measure the transmissivity of the samples to determine their compatibility with a number of commonly used inorganic scintillators (NaI(Tl), BGO, LaBr3, LaCr3, CSI(Tl) and LYSO). These measurements showed that stereolithography with a Stratasys 3D printer using Somos WaterClear Ultra 10122® produced the most compatible light guide with common organic scintillators, especially LYSO (peak emission λ=420 nm) (a scintillator commonly used in positron emission tomography (PET) imaging). Additionally, Polytek Poly-Optic® 1730 clear urethane produced a cast light guide that was the most optically compatible with these scintillators. To demonstrate the ability to create a unique shaped scintillation detector using 3D-printing and casting methods, a small arc-shaped piece of LYSO was coupled to a 4 × 4 array of 4 mm2 silicon photomultipliers (SiPM) using light guides made from these materials. For comparative purposes, a light guide was also fabricated using standard acrylic, a material often used in current light guides. All detectors produced similar event position maps. The energy resolution for 18F (511 keV photopeak) was 13% for the acrylic light-guide-based detector, while it was 18% for the printed light-guide-based detector and 20% for the cast light-guide-based detector. Results from this study demonstrate that advanced fabrication methods have the potential to facilitate creation of light guides for scintillation detectors. Continued advancements in materials and methods will likely result in improved optical performance for 3D-printed structures.

Polyacrylamide-based phantoms of human skin for hyperspectral fluorescence imaging and spectroscopy

Based on the combined use of polymerisable polyacrylamide, collagen and an aqueous solution of Flavin adenine dinucleotide (FAD), we have developed a new technique for fabrication of composite phantoms mimicking fluorescence properties of human skin. A comparative analysis of the absorption and scattering coefficients, refractive indices, as well as fluorescence spectra of phantoms with different concentrations of FAD measured with the combined use of a CCD spectrometer and a hyperspectral camera is presented. To obtain values of scattering coefficients close to those for human skin, zinc oxide (ZnO) nanoparticles are added to the polyacrylamide polymer structure. Variations both in the shape of the spectrum and in the intensity of the fluorescence signal in the phantoms are provided by the changes in the volume fraction of FAD and collagen. It is shown that the model fluorescence spectra are in good agreement with the results of direct human skin measurements in vivo.

Superconducting Integrated Terahertz Spectrometers

A superconducting integrated receiver (SIR) comprises all of the elements needed for heterodyne detection on a single chip. Light weight and low power consumption combined with nearly quantum-limited sensitivity and a wide tuning range of the superconducting local oscillator make the SIR a perfect candidate for many practical applications. For the first time, we demonstrated the capabilities of the SIR technology for remote operation under harsh environmental conditions and for heterodyne spectroscopy at atmospheric limb sounding on board a high-altitude balloon. Recently, the SIR was successfully implemented for the first spectral measurements of THz radiation emitted from intrinsic Josephson junction stacks (BSCCO mesa) at frequencies up to 750 GHz; linewidth below 10 MHz has been recorded in the high bias regime. The phase-locked SIR has been used for the locking of the BSCCO oscillator under the test. To extend the operation range of the SIR well above 1 THz, a new technique for fabrication of high-quality SIS tunnel junctions with gap voltage Vg up to 5.3 mV has been developed. Integration of a superconducting high-harmonic phase detector with a cryogenic oscillator opens a possibility for efficient phase locking of the sources with free-running linewidth up to 30 MHz that is important both for BSCCO mesa and NbN/MgO/NbN oscillators.

PDMS-Based Nanoimprint Lithography for Photonics

Implementation of planar surface photonic crystal (PhC) structures leads to improvement of optical properties of optoelectronic devices. Application of such structures can be attractive for overall and local enhancement of light from patterned areas of the light emitting diode surface and for lightwave-guiding devices. We present techniques useful for PhC patterning and for patterning of different optic structures in surface of new promising material polydimethylsiloxane (PDMS). Paper proposes nanoimprint technology for fabrication of PhC in the surface of thin PDMS membranes for possible application in light emitting diodes. By PDMS patterning and its positioning on the device surface one can achieve original optical properties of optoelectronic devices. We also present new technique for fabrication of surface-relief fiber Bragg grating (SR FBG) based on PDMS waveguide.

Evaluation of using xurography as a new technique for the fabrication of disposable gold electrodes with highly reproducible areas

This communication describes the use of xurography as a new technique for the rapid fabrication of gold disk electrodes with highly reproducible areas. Adhesive vinyl films and a cutting plotter were used to produce masks containing the electrode layouts, and recordable compact disks (CDs) were used as gold source. Electrode area was defined by transferring the vinyl adhesive mask to the gold surface. The electrochemical behavior of the “vinyl-CDtrodes” was studied by cyclic and square wave voltammetry experiments on model systems such as potassium ferrocyanide, sulfuric acid, and dopamine. The electrodes constructed using this technique meets the most important characteristics of a disposable device: low cost, reproducibility between different devices, and possibility of large-scale production.

Development of porous powder printed high density polyethylene for personalized bone implants

In this study, three dimensional printing (3DP) coupled with heat treatment was investigated as a new technique for fabrication of bone implant. An influence of using different content of polyethylene (0.60–0.80 w/w) in the raw material formulation upon the microstructure, density, porosity, shrinkage and tensile properties of porous high density polyethylene structure was investigated. It was found that the relationship between structure and properties was strongly influenced by the interplay between polyethylene content and heat treatment steps. This heat treatment process could increase the properties of porous high density polyethylene significantly over the as-fabricated 3DP sample without destroying porous structure. Porous high density polyethylene bodies having a porosity ranging from 22.3–49.7% and pore diameters of 132.6–136.2 microns with tensile strength up to approximately 4 MPa which was comparable to commercial product could be successfully prepared in this study. Biocompatibility of selected formulation (0.70 w/w) indicated that the prepared structure was not toxic and could support the osteoblast cell proliferation.

Atomic Layer Deposition of Lead Sulfide Quantum Dots on Nanowire Surfaces

Quantum dots provide unique advantages in the design of novel optoelectronic devices owing to the ability to tune their properties as a function of size. Here we demonstrate a new technique for fabrication of quantum dots during the nucleation stage of atomic layer deposition (ALD) of PbS. Islands with sub-10 nm diameters were observed during the initial ALD cycles by transmission electron microscopy, and in situ observations of the coalescence and sublimation behavior of these islands show the possibility of further modifying the size and density of dots by annealing. The ALD process can be used to cover high-aspect-ratio nanostructures, as demonstrated by the uniform coating of a Si nanowire array with a single layer of PbS quantum dots. Photoluminescence measurements on the quantum dot/nanowire composites show a blue shift when the number of ALD cycles is decreased, suggesting a route to fabricate unique three-dimensional nanostructured devices such as solar cells.

Laser desorption ionization mass spectrometry on silicon nanowell arrays.

This paper describes a new technique for fabrication of nanostructured porous silicon (pSi) for laser desorption ionization mass spectrometry. Porous silicon nanowell arrays were prepared by argon plasma etching through an alumina mask. Porous silicon prepared in this way proved to be an excellent substrate for desorption/ionization on silicon (DIOS) mass spectrometry (MS) using adenosine, Pro-Leu-Gly tripeptide, and [Des-Arg(9)]-bradykinin as the model compounds. It also allows the analyses of complex biological samples such as a tryptic digest of bovine serum albumin and a carnitine standard mixture. Nanowell array surfaces were also used for direct quantification of the illicit drug fentanyl in red blood cell extracts. This method also allows full control of the surface features. MS results suggested that the pore depth has a significant effect on the ion signals. Significant improvement in the ionization was observed by increasing the pore depth from 10 to 50 nm. These substrates are useful for laser desorption ionization in both the atmospheric pressure and vacuum regimes.

Fabrication of Large-Area Self-Organizing Gold Nanostructures with Sub-10 nm Gaps on a Porous Al2O3 Template for Application as a SERS-Substrate

A new technique for fabrication of large-area self-organizing variably ordered gold nanostructures with sub-10 nm gaps on templates of hexagonally ordered porous anodic aluminum oxide is demonstrated. The size as well as the interparticle distance of the fabricated gold nanostructures are adjusted by application of various electrolytes used in anodization of the aluminum template and the thickness of gold sputter-coated on the pore layer. The fabricated substrates are characterized by SEM and optical extinction measurements in reflection. The applicability as SERS substrates is investigated by adsorption of rhodamine 6G on the nanostructures. These substrates are found to exhibit high and uniform enhancement of the Raman signal across the entire surface. The nanostructures can be utilized as low-cost SERS-active substrates that within a short time can be fabricated reproducibly in large amounts.

New Technique for Fabrication of Individual Carbon-Nanotube Field Emitters

Currently, field emission experiments on individual carbon nanotubes (CNTs) are carried out by placing the CNTs inside a transmission electron microscope. In this work we report an alternative method of fabricating and measuring individual multiwalled CNT-field emitters fabricated on a silicon substrate by the e-beam lithography technique. A field emission experiment is then performed in a high-vacuum system for CNTs with various radii, lengths, interelectrode separations and tip structures. The geometrical enhancement factors β exhibit three ranges: low (β∼10), medium (β∼100) and high (β>200) depending on whether the CNT tip is closed-tipped, open-tipped with a flat end or open-tipped with an oblique-angle end, respectively. The turn-on voltage Vto also depends on the tip structure and the lowest Vto occurs in open-tipped-with-oblique-angle CNTs. The geometrical enhancement factor depends on the tube geometry via a linear equation β=β0(1+d/kr) with k≈40 and β0 equals 163 and 53 for the high-β and medium-β lines, respectively, where r is the radius and d is the CNT tip-anode spacing. The new method may open a path leading to the integration of nanotube field emitters with other miniature devices using semiconductor integrating technology.

Nano-sized Taper Structure Formed by Wet Process Using Catalysis of Gold Nanoparticle

ABSTRACTThis paper describes a new technique for fabrication of nano-sized taper structure formed by simple wet chemical etching using catalysis of gold (Au) nanoparticle. Single nano-sized Au particle dispersion solution was coated onto Si(111) substrate with polished surface. Then, the samples were soaked in an aqueous etching solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). The surface of 15-min-etched Si substrate appeared black. The reflectivity of the Si substrate was reduced to below 5% throughout the entire spectrum from 300 to 800 nm owing to nano-sized taper structure called subwavelength structure (SWS). The fractional area occupied by Si as a function of the depth across the textured layer showed a smooth increase of density up to a depth. The observed optical effects are explained by the formation of a nanoscale taper structure, representing an effective medium with a smooth transition of the refractive index from that of air to that of Si.

A New Technique for Fabrication of Flat PP/Talc Graded Material

This work deals with a novel processing method that combined extrude with laminate molding for preparing polymeric graded material (PGM). The variations of inhomogeneous property were generated by altering the feeding speed and/or weight ratio of the components as well as changing the order or numbers of the folded layers. Three modes of polypropylene (PP)/ talcum powder (talc) flat PGM (signed with T1, T2, T3) are fabricated successfully by using this new technique. The preparation, structure and property of the resultant PP/talc graded composite were investigated. Results indicate that the composition, morphology and properties show a gradient variation along their thickness direction of the flat PGMs.

A new fabrication process for a flexible skin with temperature sensor array

In the present study, a new technique for fabrication of a flexible skin with 64 sensors inside a 7×7 mm2 area is reported. Each sensor has a dimension of 110 μm×110 μm. A simplified fabrication process using platinum resistors as sensing materials and polyimide layers as flexible substrates is developed. Systematic investigation of the performance of the sensors has been conducted, including sensors on rigid and flexible substrates for comparison. Sensors on rigid substrates have a sensitivity of 74.6 mV/°C with a cut‐off frequency of 90 kHz using a constant‐current circuit. Sensors on the flexible skin have been experimentally proven to have the same sensitivity as those on the rigid substrate. Moreover, the frequency response has been improved due to lower inertia for sensors on the flexible skin. The flexible skin with a temperature sensor array could be easily attached on a highly curved surface to detect temperature distribution inside a small area. The development of the temperature sensor array on the flexible skin could be crucial for temperature measurement in the fields of aerodynamics, space exploration, automaking etc.

Fabrication of microchannel structures in fluorinated ethylene propylene.

A new technique for fabrication of channel structures with diameters down to 13 microm in fluorinated ethylene propylene (also known as poly(tetrafluoroethylene-co-hexafluoropropylene), FEP) is described. The technique is based on the unique property of a dual-layer fluoropolymer tubing consisting of an outer layer of poly(tetrafluoroethylene) (PTFE) and an inner layer of FEP. When heated (>350 degrees C), the outer PTFE layer shrinks while the inner FEP layer melts, resulting in filling of all empty space inside the tubing with FEP. The channel structures are formed using tungsten wires as templates that are pulled out after completion of the shrinking and melting process. While several analytical devices have been reproducibly prepared and shown to function, this report describes a single example. A microreactor coupled to an electrochemical flow cell detects the biuret complex of the natively electroinactive peptide des-Tyr-Leu-enkephalin.

New Techniques for Fabrication of Flexible Plastic LCD's

We report simple techniques to manufacture low-powered, high-resolution, reflective cholesteric displays using flexible plastic substrates. We use wax transfer printing to replace photo-lithography and incorporate polymer walls to increase the mechanical strength and lifetime of the displays. These printing methods can easily be adapted to roll-to-roll production.

Invited review

The studies of superlattices in ferroelectric crystals have made a rapid progress since 1980s. A superlattice is composed of modulated domains on the micron scale, controllable with modern techniques. It reveals a number of novel physical properties of optical and acoustic character. In this paper, we review recent advances in developing new techniques for fabrication and characterization of ferroelectric superlattices, and in exploring new physical effects for applications. The outlook for superlattice applications is briefly described.

Tribological Characteristics of Si3N4-based Self-Lubricating Materials

A new technique for fabrication of self-lubricating ceramic-based composites has been developed. Multi-channel ceramic matrices with a predetermined number, diameter, and distribution of channels are fabricated and then filled with a lubricant such as polytetrafluoroethylene or perfluoropolyether. Friction coefficients of lubricant-filled silicon nitride against 52100 steel were found to be 0.1 to 0.2, in contrast with pure silicon nitride for which values of 0.6 to 0.7 were found. This friction reduction is insensitive to applied load or to sliding speed. The controlled pattern of porosity allows these materials to have lubricant loading of 7.5 to 10 volume percent, instead of 20–25% typical of traditional self-lubricating materials. This configuration permits higher crushing resistance and stiffness in comparison with conventional self-lubricating antifriction materials. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Novel technique for fabrication of one- and two-dimensional systems

A new technique for fabrication of nano- and atomic-scale device elements and quantum systems which cannot be obtained by any other technology is proposed. The technique is based on the experimentally established possibility of creating atomically sharp-edged cracks of desired length and direction in a given layer of a heterostructure. Ultra-narrow (1 nm) and perfectly straight window-slits in the GaAs layer-mask of semiconductor structures and ultra-thin (2 nm) semiconductor membranes have been fabricated for the first time.

Nanoscale engineering using controllable formation of ultra-thin cracks in heterostructures

A new technique for fabrication of nano- and atomic- scale device elements and quantum systems which cannot be obtained by any other technology is proposed. The technique is based an experimentally established possibility to create atomically sharp-edged cracks of a desired length and direction in a given layer of heterostructure. Ultra-narrow (1 nm) and perfectly straight windows-slits in the GaAs layer-mask of semiconductor structures and atomicaly sharp -edged windows of a complicated form have been fabricfted for the fist time. It was shown, that the width of a window-slit can be varied with high precision needed for a self-alignment fabrication technology. New maskless techniques for fabricating nanoscale elements are described.