Microtip Arrays Research Articles

Atomic-scale investigation of Mo distribution and its effect on phase stability of a nanocrystalline CrCoNi-based medium-entropy alloy

“Suzuki segregation” of Mo to planar defects was proposed to contribute to secondary hardening after post-deformation annealing in the MP35N alloy, a CrCoNi-based single-phase superalloy. However, a direct proof of this proposal is challenging and reported observations are controversial. Here, we prepared nanocrystalline MP35N thin films by co-deposition on a microtip array of pre-sharpened Si tips. This enabled a direct investigation of the Mo distribution in a nanoscale structure with many grain boundaries (GBs) after annealing by atom probe tomography. We observed that no Mo but Cr segregates to GBs between 360 and 460 °C. Additionally, we found that MP35N is thermally more stable than a (Mo-free) Cr-Co-Ni medium-entropy alloy under the same conditions. Factors that influence the kinetics of phase decomposition and thermal stability, including grain size, Mo addition, and the loss of Cr due to oxidation at GBs were addressed.

Efficient preparation of microtip arrays for atom probe tomography using fs-laser processing

Microtip arrays, also called microtip coupons, are routinely used in atom probe tomography (APT) as specimen carriers. They are commercially available consumables, usually made of Si with high electrical conductivity, produced via dedicated shaping techniques. Their purpose is to act as a specimen mount after focused ion beam (FIB) based lift-out procedures. Within this work, an alternative approach to prefabricated microtip coupons is presented, by directly creating a microtip array on the sample to be investigated utilizing fs-laser processing. An exemplary array of microtip posts was fs-laser processed from a TiN coating on Si substrate and subjected to final preparation via annular FIB milling. Subsequently, APT specimen of the TiN coating as well as of the Si substrate were successfully measured in laser assisted mode, using a commercial local electrode APT system. To further emphasize the versatility of the proposed approach, additional voltage measurements of highly conductive B doped Si arrays as well as exemplarily fs-laser processed microtip arrays of various other materials are provided as supplementary material to this article. The presented methodology bypasses the lift-out and avoids the necessity of a Pt weld between specimens and coupon posts which is frequently considered to represent a weak spot. It reduces consumables consumption and provides a high number of specimens in short time, while it is applicable for a wide range of materials and has thus the potential to revolutionize APT specimen preparation.

Overview of Adhesive Bonding Technology for Nano- and Microsystem Technics

The review focuses on adhesive bonding technology, which is used both for manufacturing various micro- and nanoelectronic devices, sensors and microsystems, and for assembling or integrating various components. Information on the theory of adhesive bonding mechanisms is presented. The properties and applications of four classes of polymers are reviewed: thermoplastic, ther-mosetting, elastomeric, and hybrid. The classification of different mechanisms used to initialize the curing process of adhesives is presented. Existing methods of applying polymers to the wafer surface are described. The main types of designs and principles of operation of adhesive wafer bonding equipment are presented, as well as its main suppliers. Examples of procedures and suitable process parameters are given for both wafer bonding with a continuous layer of adhesive and wafer bonding with patterned adhesive layers (also called selective or local bonding). The conditions required to improve the quality of the adhesive bond and to reduce the density of defects are specified, including cases of bonding wafers made from different materials. Adhesive wafer bonding is used for the fabrication of three-dimensional integrated circuits, and for the integration of integrated circuits with microsystems such as infrared focal plane arrays, spatial light modulators (micromirror arrays), microtip arrays for data storage systems, and laser systems. Adhesive wafer bonding is also used for the fabrication of microcavities in packaging applications, for manufacturing of liquid crystal on silicon (LcoS) components, for thin-film solar cells, for radiofrequency components, for microfuel cells, for hard disk drive microactuators, for the bioMEMS and micrototal analysis systems.

Fabrication and Measurement of Fiber Optic Surface Plasmon Resonance Sensor Based on Polymer Microtip and Gold Nanoparticles Composite

Fiber optic surface plasmon resonance (FO SPR) sensor offers attractive advantages over the conventional prism-based SPR platforms, such as simplicity, cost-effectiveness, and miniaturization. To improve the performance of the existing FO SPR sensor which has been fabricated by depositing a gold thin film on the flat fiber cross-section or side surface, we propose to fabricate the polymer microtip array on optical fiber using simple cost-effective soft and imprint lithography because SPR instruments mainly depend on the structural aspect of the thin metal plasmonic film deposited on the optical fiber substrate. The fabricated microstructures are also combined with the gold nanoparticles to expand the sensing area. The proposed sensor displayed 175% improved sensitivity with linear response according to refractive index changes, when developed FO SPR sensor and conventional FO SPR sensor without microtip array were applied to refractive index measurement, respectively. Based on the obtained results, the proposed FO SPR sensor can ultimately be used in various applications, ranging from food safety, environmental monitoring, and biomarker analysis.

Graphene encapsulation enabled high-throughput atom probe tomography of liquid specimens

A new method for imaging liquid specimens with atom probe tomography (APT) is proposed by introducing graphene encapsulation. By tuning the encapsulation speed and the number of encapsulations, controllable volumes of liquid can be encapsulated on a pre-sharpened specimen tip, with the end radius less than 75 nm to allow field ionization and evaporation. Encapsulation of liquid has been confirmed by using various characterization techniques, including electron microscopy and stimulated emission depletion microscopy. The graphene-encapsulated liquid specimen was then directly frozen at the cryogenic stage inside the atom probe instrument, followed by APT imaging in laser-pulsed mode. Using water as a test example, water-related ions have been identified in the acquired mass spectrum, which are spatially correlated to a reconstructed three-dimensional volume of water on top of the base specimen tip, as clearly revealed in the chemical maps. In addition, the proposed method has also been shown to produce multiple liquid specimens simultaneously on a pre-sharpened silicon micro-tip array for high-throughput APT imaging of liquid specimens. It is expected that the proposed lift-out-free method for preparing APT specimens in their hydrated state will open a new avenue for obtaining insights into various materials at atomic resolution.

Fabrication of hollow microtip electrode array with variable diameter using self-aligned etching process

In this paper, we propose the fabrication of a hollow microtip electrode array with variable diameter. The intended application of the fabricated electrode is the perfusion or aspiration at the localized area of a biological sample in a microfluidic system. The conductive electrode covered with an insulating layer formed the hollow microtip structure. The lower diameter and height of the fabricated hollow microtip electrode array were measured as approximately 4 and 35 μm, respectively. A fabrication process for controlling the hollow diameter is proposed based on the self-aligned etching process of the sharp silicon microtip array without an additional photolithography mask. The silicon microtip was exposed only at the tip end by using the self-aligned etching process after coating the conductive and insulating layer. The area of the exposed silicon tip could be controlled by varying the self-aligned etching time, which determined the hollow dimeter after removing the silicon structure. The hollow diameter was adjusted from 0.94 to 2.82 μm depending on the self-aligned etching time. Moreover, the proposed hollow microtip electrode array was characterized as the electrode to be used in electrochemical reaction measurements using cyclic voltammetry. Additionally, the perfusion of the fluid was demonstrated through the hollow microtip electrode assembled with a microfluidic channel.

Microfluidic platform for cell analysis using through-polydimethylsiloxane micro-tip electrode array

In this study, we present the fabrication and measurement of a microfluidic system combined with a through-polydimethylsiloxane (PDMS) microtip electrode that can be used to measure the photosynthetic reaction of green algae cells in the microfluidic channel. The conventional single-cell based method has a disadvantage of low efficiency. To solve this problem, we propose a method of electrical feed-through interconnection of a microfluidic channel platform using a microtip electrode array. Silicon microtip arrays were fabricated using a combination of processes using deep reactive ion etching (DRIE) and reactive ion etching (RIE) steps. In the RIE process, the shape of the cylindrical silicon pillar changed from a cylinder to a probe shape according to the local change of the side-wall etching rate of the silicon pillar. The local ultra-micro electrode (UME) structure was fabricated using a self-alignment fabrication method without additional photolithography steps, and its electrochemical properties were confirmed using a cyclic voltammetry (CV) experiment. The photosynthetic algae cells were stacked in the PDMS microfluidic chip and then combined with the microtip electrode array using an acrylic jig. After assembling the microtip electrode array, the microtip was confirmed to penetrate the PDMS thin film through the CV experiment. When irradiated with light, the current induced by the oxygen produced by a photosynthetic reaction in the algae cells (stacked in the PDMS microfluidic chip) was measured using the microtip electrode array. Further, experiments were conducted to measure the force applied by the acrylic jig when combining the microtip electrode array with the PDMS microfluidic chip.

Development of a Novel Modular Compliant Gripper for Manipulation of Micro Objects.

This paper proposes a modular gripping mechanism for the manipulation of multiple objects. The proposed micro gripper combines traditional machining techniques with MEMS technologies to produce a modular mechanism consisting of a sturdy, compliant aluminium base and replaceable end-effectors. This creates an easily-customisable solution for micro manipulation with an array of different micro tips for different applications. We have provided the kinematic analysis for the gripper to predict the output and have also optimised design parameters based on FEA (finite element analysis) simulation and the effects of altering flexure beam lengths. The gripper is operated by a piezo actuator capable of 18 m displacement at 150 V of applied DC voltage. This is then amplified by a factor of 8.1 to a maximum tip displacement of 154 m. This is achieved by incorporating bridge and lever amplifying techniques into the design. An initial experimental analysis of the micro gripper is provided to investigate the performance of the micro gripper and to gauge the accuracy of the theory and simulation through comparison with experimental results.

Dielectric Breakdown-Based Gas Leakage Detector Using Poly-Si Microtips

There has been a growing need for portable gas detection device for gas leakage monitoring. Here, we report the development of dielectric breakdown-assisted ionization (DBAI)-based on-chip gas sensor (GSEN) and temperature sensor (TSEN), which were integrated to serve as leakage gas (L-gas) identification and detection device. The TSEN with single microtip architecture provides high temperature sensitivity but renders itself chemically inert toward different L-gases. The GSEN with an array of microtips imparts high chemical specificity toward different L-gases together with high temperature sensitivity. High chemical and thermal responsiveness of GSEN make it suitable for the chemical identification of different L-gases in air through the temperature-driven DBAI process. The TSEN plays the role of the temperature monitor. The chemical recognizability of the integrated device for different L-gases was demonstrated using Ar, O2, and CO2 as L-gases in air. This chemical recognizability of GSEN for different L-gases was imparted through their characteristic molecular polarizability, resulting in different rates of DBAI and hence the output current. The device finds the application for the detection of a wide variety of ionizable L-gases.

Development and Investigation of a Field Emission Medium for Autocathodes of Mobile Power Microwave Devices

Silicon-diamond heterostructure based field emission media with silicon microtip arrays at the heterointerface were proposed and experimentally studied. The architecture of the heterostructures is optimized for the applications as an active medium for the field emission cathodes of mobile power microwave devices.

Partial reduction of anthracene by cold field emission in liquid in a microreactor with an integrated planar microstructured electrode

We report a novel microreactor with a photolithographically defined integrated electrode containing micro tips that serve as emission points for solvated electrons into liquid n-hexane in a microfluidic channel. The implementation of sharp electrode tips permits to extract electrons from the electrode material at relatively low voltages. The electric field distribution in the gap between a planar patterned platinum microtip array and a planar rectangular counterelectrode is analyzed by a computational model. Cold field emission using these microdevices is experimentally verified, and the partial reduction of anthracene to 9,10-dihydroanthracene, via solvated electrons emitted in solutions with or without ethanol in n-hexane is investigated. It is found that in the current microreactor configuration, the majority of the products are products originating from coupling of ethanol fragments to, and/or oxidation of 9,10-dihydroanthracene at the platinum counterelectrode, leaving no detectable yield of the desired reduction product.

Novel microbial photobioelectrochemical cell using an invasive ultramicroelectrode array and a microfluidic chamber.

To fabricate a novel microbial photobioelectrochemical cell using silicon microfabrication techniques. High-density photosynthetic cells were immobilized in a microfluidic chamber, and ultra-microelectrodes in a microtip array were inserted into the cytosolic space of the cells to directly harvest photosynthetic electrons. In this way, the microbial photobioelectrochemical cell operated without the aid of electron mediators. Both short circuit current and open circuit voltage of the microbial photobioelectrochemical cell responded to light stimuli, and recorded as high as 250pA and 45mV, respectively. A microbial photobioelectrochemical cell was fabricated with potential use in next-generation photosynthesis-based solar cells and sensors.

Fabrication of a micro-tip array mold using a micro-lens mask with proximity printing

In this study, a mold for a micro-tip array is fabricated using a microlens array mask with proximity exposure. The micro-tip array uses a microlens array mask with geometrical optics. Light passing through a microlens is focused at the focal points. There is microlens on the mask and the pattern that results from the light passing through the mask is directly projected onto the photoresist surface. A concave profile is developed using a positive photoresist and the remaining photoresist microstructures are formed after the development process. By changing the distance between the mask and the photoresist and the radius of curvature of the microlens, various tip shapes can be fabricated. The exposure gap is calculated using the microlens array mask and the geometry of the mold of micro-tip array is established using the irradiance absorption maps for the different levels. These methods respectively use the model of the positive photoresist and optical software. When electroforming a metallic micro-tip copy of the patterned photoresist, masters are created. The metal micro-tip array is used membrane probe card.

Developing barbed microtip-based electrode arrays for biopotential measurement.

This study involved fabricating barbed microtip-based electrode arrays by using silicon wet etching. KOH anisotropic wet etching was employed to form a standard pyramidal microtip array and HF/HNO3 isotropic etching was used to fabricate barbs on these microtips. To improve the electrical conductance between the tip array on the front side of the wafer and the electrical contact on the back side, a through-silicon via was created during the wet etching process. The experimental results show that the forces required to detach the barbed microtip arrays from human skin, a polydimethylsiloxane (PDMS) polymer, and a polyvinylchloride (PVC) film were larger compared with those required to detach microtip arrays that lacked barbs. The impedances of the skin-electrode interface were measured and the performance levels of the proposed dry electrode were characterized. Electrode prototypes that employed the proposed tip arrays were implemented. Electroencephalogram (EEG) and electrocardiography (ECG) recordings using these electrode prototypes were also demonstrated.

Superhydrophobic properties of a hierarchical structure using a silicon micro-tip array decorated with ZnO nanowires

In this study, wetting properties of a hierarchical structure using a silicon micro-tip array covered with ZnO nanowire are characterized, and compared with hierarchical structures composed of micro-pillars for micro-scale roughness. The superhydrophobicity of a surface can be efficiently enhanced by using a micro-tip array, compared with a micro-pillar structure, because a micro-tip structure with high aspect ratio and small apex radius can significantly reduce fractions of liquid droplet area in contact, maintaining the droplet in the regime of the Cassie state. The micro-tip array was simply fabricated by combining anisotropic and isotropic silicon etching processes with one-step photolithography and a single etch mask. The measured height and aspect ratio of the fabricated micro-tip was around 40 μm and 8, respectively, when the center-to-center distance between micro-tips was 30 μm. The maximum CA on the hierarchical surface using the micro-tip array was measured to be 165.0 ± 2.3° with a period of 30 μm, while the hierarchical surface using the micro-pillar array showed the maximum CA of 158.6 ± 1.1° with 20 μm-diameter and 70 μm-gap between micro-pillars. The smallest CAH on the hierarchical micro-tip array was measured to be 5.0 ± 0.3° for the center-to-center distance between micro-tips of 30 μm.

A Low-Power/Low-Voltage CMOS Wireless Interface at 5.7 GHz With Dry Electrodes for Cognitive Networks

This paper describes a low-power/low-voltage CMOS wireless interface (CMOS-WiI) at 5.7 GHz with dry electrodes for congnitive networks. The electrodes are 4 X4 microtip arrays and acquire electroencephalogram (EEG) signals in key- points for processing. The CMOS-WiI was fabricated in a UMC 0.18 μm RF CMOS process and its total power consumption is 23 mW with a voltage-supply of only 1.5 V. The carrier frequency is digitally selectable and it can be one of 16 possible values in the range 5.42-5.83 GHz, with 27.12 MHz steps. These multiple carriers allow a better spectrum allocation as well as the acquisition, processing and transmission of high-quality EEG signals from 16 electrode arrays. The microtips array was fabricated through bulk micromachining of a 〈100 〉-type silicon substrate in a potassium hydroxide solution and avoids long subject preparations for EEG data acquisition. The reactive sputtering of iridium dioxide (IrO) on the surface of the array guarantees its biocompatibility. The fabrication process was trimmed in a way that each microtip presents solid angles of 54.7° , a width in the range 150-200 μm, a height of 100-200 μm, and a microtip interspacing of 2 μm. The microtips array coated with IrO together with the CMOS-WiI permit the remote monitoring of EEG signals from freely-moving subjects.

Track technology for creating the arrays of nickel microtips, micronozzles, and microtubes

A method for obtaining surface arrays of nickel objects (microtips, micronozzles, and microtubes) with preset geometric parameters by means of a track technology has been developed using the data of scanning electron microscopy. It is shown that Ni microtips with a radius as small as 10–25 nm can be obtained, which allows these microobject arrays to be used as multiple-tip field emission cathodes capable of providing high emission current densities.

Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Mirco-textured Metal Anode

AbstractMuch attention has been directed towards the enhancement of electron transport in dye-sensitized solar cells (DSSC) using one-dimensional nanoarchitectured semiconductors. However, the improvement resulting from these ordered 1-D nanostructured electrodes is often offset or diminished by the deterioration in other device parameters intrinsically associated with the use of these 1-D nanostrucutres, such as the two-sided effects of the length of the nanowires impacting the series resistance and roughness factor. In this work, we mitigate this problem by allocating part of the roughness factor to the collecting anode instead of imparting all the roughness factors onto the semiconductor layer. A microscopically rough Zn microtip array is used as an anode on which ZnO nanotips are grown to serve as the semiconductor component in a DSSC. For the same surface roughness factor, our Zn microtip/ZnO nanotip DSSC exhibits an enhanced fill factor compared to a corresponding planar anode supported ZnO nanowire DSSC. In addition, the open circuit voltage of the Zn-microtip|ZnO-nanotip DSSC is also enhanced due to a favorable band shift at the Zn-ZnO interface, which raises the quasi Fermi level of the semiconductor and consequently enlarges the energy gap between the quasi Fermi level of ZnO and the redox species. The overall improvement demonstrates a new fundamental approach to enhance the efficiency of dye-sensitized solar cells.

Formation and field emission property of single-crystalline Zn microtip arrays by anodization

A highly ordered array of single-crystalline Zn microtips is obtained after anodizing of Zn foil in NH 4Cl/H 2O 2 solution, and the formation mechanism and field emission property of such Zn microtips have been described. Sixfold single-crystalline Zn microtips are obtained by selective anisotropic etching of crystallographic planes with different dissolution rates. From the results of TEM analysis, the single-crystalline Zn microtips, formed on the Zn foil after anodic dissolution treatment, are enclosed by { 1 1 ¯ 0 0 } and are preferentially oriented along the c-axis. Besides, the improvement of turn-on field from 33.9 to 20.0 V/μm is achieved with thin surface ZnO after annealing treatment.

Folding field emission from GaN onto polymer microtip array by femtosecond pulsed laser deposition

Microtip field-emitter array (FEA) has been formed using femtosecond pulsed laser deposited GaN thin film onto polymer microtip array. X-ray diffraction, scanning electronic microscope, and field emission measurements were carried out to analyze the profile, crystalline structures, and field emission properties of the emission array. The results indicate that the GaN thin film deposited on a like-conical-type polymer microtip array is hexagonal polycrystalline, and the GaN microtip FEA has uniform size, sharp tip, and well-defined profile, which shows a field emission characteristics.