Micropore Arrays Research Articles

Spatial resolution and light output of pixelated CsI(Tl) scintillation screen based on oxidized silicon micropore array template

The effect of pixel size of CsI(Tl) scintillation screen based on oxidized silicon micropore array template on spatial resolution and light output in X-ray imaging was investigated by using Geant4 Monte Carlo simulation code. The quantitative relations between the pixel size and the spatial resolution as well as the light output were obtained. The results reveal that the pixelated structure can largely improve the spatial resolution of the screen. It improves rapidly when the pixel size decreases from 60 μm to 10 μm. Unlike that of a conventional scintillation screen, the spatial resolution of the pixelated CsI(Tl) scintillation screen isn't obviously deteriorated by increasing the thickness of the screen. As far as the relation between the spatial resolution and X-ray energy is concerned, the resolution does not change significantly with X-ray energy when the energy is less than 80 keV . When the X-ray energy exceeds 80 keV, the spatial resolution becomes sensitive to X-ray energy because the effect of Compton scattering cannot be neglected. The light output increases with the increase of the pixel size, but doesn't change significantly with the thickness of the screen when the thickness is three times more than the X-ray attenuation length. In addition, the angular distribution of the emitted scintillation light from the screen was studied. The maximum emission occurs at the angle about 46° relative to the normal direction of the screen.

2.5-Dimensional Parylene C micropore array with a large area and a high porosity for high-throughput particle and cell separation

Large-area micropore arrays with a high porosity are in high demand because of their promising potential in liquid biopsy with a large volume of clinical sample. However, a micropore array with a large area and a high porosity faces a serious mechanical strength challenge. The filtration membrane may undergo large deformation at a high filtration throughput, which will decrease its size separation accuracy. In this work, a keyhole-free Parylene molding process has been developed to prepare a large (>20 mm × 20 mm) filtration membrane containing a 2.5-dimensional (2.5D) micropore array with an ultra-high porosity (up to 91.37% with designed pore diameter/space of 100 μm/4 μm). The notation 2.5D indicates that the large area and the relatively small thickness (approximately 10 μm) of the fabricated membranes represent 2D properties, while the large thickness-to-width ratio (10 μm/ < 4 μm) of the spaces between the adjacent pores corresponds to a local 3D feature. The large area and high porosity of the micropore array achieved filtration with a throughput up to 180 mL/min (PBS solution) simply driven by gravity. Meanwhile, the high mechanical strength, benefiting from the 2.5D structure of the micropore array, ensured a negligible pore size variation during the high-throughput filtration, thereby enabling high size resolution separation, which was proven by single-layer and multi-layer filtrations for particle separation. Furthermore, as a preliminary demonstration, the prepared 2.5-dimensional Parylene C micropore array was implemented as an efficient filter for rare cancer cell separation from a large volume, approximately 10 cells in 10 mL PBS and undiluted urine, with high recovery rates of 87 ± 13% and 56 ± 13%, respectively.

High-quality microhole arrays by water-assisted femtosecond laser perforating for improved particle sorting

For microseparation devices, the quality of the microholes, e.g., smooth surfaces and edges, is of crucial importance for high-performance separating ability. Here, we used water-assisted femtosecond laser perforating technology to fabricate high-quality size-controllable (from several to tens of micrometers) micropore arrays on ultrathin aluminum foil surface, which have smooth edges without fragments and debris. The micropore arrays can effectively filtrate particles with diverse diameters. Compared to the micropores prepared in air under the same laser processing parameters, the water-assisted micropores have greatly improved the surface quality, and the particle separation ratio can be increased by ∼40 % . This method for preparing high-quality micropore arrays can also be applied to other sheet materials, such as titanium, silicon, and even plastic, and so on, which can be widely used in the fields of microfluidic devices for microseparation.

Multifunctional oil-water and immiscible organic liquid separation by micropore arrayed Ti foil

In this work a multifunctional micropore array (size from 5 to 42 μm) was produced by using one-step femtosecond laser microdrilling for oil-water and oil-oil separation. This novel method has many advantages, such as high precision (size error is less than 1 μm), simple operation (one step), extensible function (even complex microstructures) just to name a few. The prepared foil exhibited superhydrophilic and underwater superoleophobic properties, which can be used to separate the light oil (C8H18) and water mixtures. After heating in dark environment 0.5 h, the prepared foil showed superhydrophobic and underwater superoleophilic properties, and can be used to separate the heavy oil (C2H4Cl2) and water mixtures. In addition, the heated sample also showed robust ability to separate the immiscible organic liquid mixtures (formamide and C2H4Cl2), exhibiting multifunctional applications. Interestingly, the heated samples would recover its original superhydrophilicity after UV irradiation in ethanol for 1 h. The samples don’t contain any fluorinated compounds and display environmental stability even after sonic cleaning and scratch. This work will provide a new insight into the design of intelligent devices for oil/water mixtures separation, organic liquid mixtures separation, and water droplet manipulation.

Caffeine-imprinted conducting polymeric films with 2D hierarchical pore arrays prepared via colloidal mask-assisted electrochemical polymerization

We developed novel caffeine-imprinted conducting polymer sensors with 2D hierarchical pore arrays. Colloidal mask-assisted electrochemical polymerization was used to design the molecularly imprinted conducting polymers (MICPs). First, 2D MICP micropore arrays were obtained by electropolymerization on 2D polystyrene (PS) colloidal arrays (d = 1 μm) fabricated via colloidal lithography. As a second step, each of two smaller PS colloids (d = 200 and 500 nm) was aligned onto the MICP pores, and second step electropolymerization was performed to fabricate hierarchical pore arrays. Relative to the single MICP pore array (MICP1) film, the two designed MICP films (MICP1-200 and MICP1-500) showed highly enhanced sensing properties such as sensing capacity, sensitivity, and selectivity. MICP1-200 film with nanoscale porous MICP network formed in each micropore exhibited significantly improved sensing behaviors, superior to MICP1-500 film. This sensing improvement is attributed to well-controlled MICP pore structures increasing the recognition cavities during surface imprinting. Thus, this novel strategy can be extensively used for the development of various MICP-based sensors.

Lamellar Ni3Si Microchannels and Ni3Si Micropore Arrays in Ni─Ni3Si Hypereutectic Alloys

Lamellar Ni3Si microchannels and Ni3Si micropore arrays were fabricated in directionally solidified Ni–Ni3Si hypereutectic alloys by selective dissolution. Regular lamellar and rod-like structures were obtained at growth rates of 1–6 μm/s for the hypereutectic alloys. The dissolution of the lamellar or rod-like Ni phases while passivating the continuous Ni3Si matrix resulted in continuous microchannels or nanopore arrays in the Ni–Ni3Si hypereutectic alloys. During selective dissolution, SiO2 preferentially formed on the Ni3Si phase and retarded its dissolution. The width of the microchannel was 2.85 μm, and the micropore diameter was approximately 7.86 μm. The structural materials with narrow microchannels can be applied in the field of catalyst, microfiltration, and micro/nanostructure fabrication.

Polygonal pits on silicon surfaces that are created by laser-assisted chemical etching

Laser-assisted chemical etching was conducted for creating periodic textures on silicon surfaces. Silicon plates with the (111) surface orientation were immersed in an aqueous solution of potassium hydroxide, and a pulsed laser beam (532 nm wavelength, 5 ns duration, 10 pulse/s) was irradiated on their surface to promote anisotropic etching. The laser beam was patterned by using a glass capillary plate that contained a hexagonal array of micropores (10μm diameter, 12μm period). The focused beam projected the hexagonal image on the silicon surface, creating bright spots of 4μm period. During the laser irradiation process of 3 min, both laser-induced ablation and chemical etching took place at these bright spots. After stop of laser irradiation, the chemical etching progressed further, and consequently, a periodic array of triangular or hexagonal pits emerged on the silicon surface. The direction of the triangular pits changed by rotation of the silicon plate. When a silicon plate with the (100) surface orientation was used, diamond or rectangular pits were created on its surface. The mechanism of this polygonal texturing was explained by using the normal and intersecting vectors of the (100), (110), and (111) planes that exhibited different etching rates.

A single-layer Janus membrane with dual gradient conical micropore arrays for self-driving fog collection

Inspired by natural creatures, the development of a device that collects water from fog represents an important research direction.

Nanostructure directed interfaces created from nanoparticle island sites deposited to microporous arrays and forming sensor platforms

Nanostructure directed interfaces created from nanoparticle island sites deposited to microporous arrays and forming sensor platforms

Peptide-Mediated Platelet Capture at Gold Micropore Arrays.

Ordered spherical cap gold cavity arrays with 5.4, 1.6, and 0.98 μm diameter apertures were explored as capture surfaces for human blood platelets to investigate the impact of surface geometry and chemical modification on platelet capture efficiency and their potential as platforms for surface enhanced Raman spectroscopy of single platelets. The substrates were chemically modified with single-constituent self-assembled monolayers (SAM) or mixed SAMs comprised of thiol-functionalized arginine-glycine-aspartic acid (RGD, a platelet integrin target) with or without 1-octanethiol (adhesion inhibitor). As expected, platelet adhesion was promoted and inhibited at RGD and alkanethiol modified surfaces, respectively. Platelet adhesion was reversible, and binding efficiency at the peptide modified substrates correlated inversely with pore diameter. Captured platelets underwent morphological change on capture, the extent of which depended on the topology of the underlying substrate. Regioselective capture of the platelets enabled study for the first time of the surface enhanced Raman spectroscopy of single blood platelets, yielding high quality Raman spectroscopy of individual platelets at 1.6 μm diameter pore arrays. Given the medical importance of blood platelets across a range of diseases from cancer to psychiatric illness, such approaches to platelet capture may provide a useful route to Raman spectroscopy for platelet related diagnostics.

Fabrication of superhydrophilic or superhydrophobic self-cleaning metal surfaces using picosecond laser pulses and chemical fluorination

ABSTRACTBioinspired superhydrophilic/phobic self-cleaning surfaces have recently drawn a lot of interest in both fundamental and applied research. A hybrid method to produce the self-cleaning property of micro/nanostructured surface using ultra-fast laser pulses followed by chemical fluorination is proposed. The typical micro/nanocomposite structures that form from microporous arrays and microgroove groups have been processed by picosecond laser on titanium alloy surface. The surface hydrophilic/phobic and self-cleaning properties of micro/nanostructures before and after fluorination with fluoroalkyl-silane were investigated using surface contact angle measurements. The results indicate that surface properties change from hydrophilic to hydrophobic after fluorination, and the micro/nanostructured surface with increased roughness contributes to the improvement of surface hydrophobicity. The micro/nanomodification can make the original hydrophilic titanium alloy surface more hydrophilic or superhydrophilic. It also can make an originally hydrophobic fluorinated titanium alloy surface more hydrophobic or superhydrophobic. The produced micro/nanostructured titanium alloy surfaces show excellent self-cleaning properties regardless of the fluorination treatment, although the fluorinated surfaces have slightly better self-cleaning properties. It is found that surface treatment using ultra-fast laser pulses and subsequent chemical fluorination is an effective way to manipulate surface wettability and obtain self-cleaning properties.

An efficient multipaction suppression method in microwave components for space application**Project supported by the National Natural Science Foundation of China (Grant No. U1537211), the National Key Laboratory Key Foundation, China (Grant No. 9140C530101150C53011), and China Postdoctoral Science Foundation (Grant No. 2015M572661XB).

Multipaction, caused by the secondary electron emission phenomenon, has been a challenge in space applications due to the resulting degradation of system performance as well as the reduction in the service life of high power components. In this paper we report a novel approach to realize an effective increase in the multipaction threshold by employing micro-porous surfaces. Two micro-porous structures, i.e., a regular micro-porous array fabricated by photolithography pattern processing and an irregular micro-porous array fabricated by a direct chemical etching technique, are proposed for suppressing the secondary electron yield (SEY) and multipaction in components, and the benefits are validated both theoretically and experimentally. These surface processing technologies are compatible with the metal plating process, and offer substantial flexibility and accuracy in topology design. The suppression effect is quantified for the first time through the proper fitting of the surface morphology and the corresponding secondary emission properties. Insertion losses when using these structures decrease dramatically compared with regular millimeter-scale structures on high power dielectric windows. SEY tests on samples show that the maximum yield of Ag-plated samples is reduced from 2.17 to 1.58 for directly chemical etched samples. Multipaction testing of actual C-band impedance transformers shows that the discharge thresholds of the processed components increase from 2100 W to 5500 W for photolithography pattern processing and 7200 W for direct chemical etching, respectively. Insertion losses increase from 0.13 dB to only 0.15 dB for both surface treatments in the transmission band. The experimental results agree well with the simulation results, which offers great potential in the quantitative anti-multipaction design of high power microwave components for space applications.

New Generation Devices for Gas (Liquid) Sensing

We present a short review and novel approach for the construction of conductometric sensors demonstrating considerably higher sensitivities than traditional metal oxide sensors. Sensor platforms do not require film-based technology, operate at room temperature, and can be obtained without the use of time consuming self-assembly processes. A combined nanopore coated micro-porous array, is deposited with nanostructure directing acidic metal oxide island sites which vary in their Lewis acidity, decorate the micropores, and control an electron transduction process. The interaction of analytes with these island sites varies in a predictable manner and can be modified through in-situ functionalization of their Lewis acidity through formation of the oxynittrides or oxysulfides. Microporesallow rapid Fickian diffusion of the analytes to the active nanostructured island sites whose reversible interaction with the analyte dominates the sensor response. We require only that the island sites be deposited at sufficiently low concentration so as not to interact electronically with each other. Highly accurate repeat placement of the nanostructured island depositions is not required. The nanoporous walls of the microarray act as a phase match for the deposition of a diversity of nanostructures that are selected for deposition from a variety of solution-based sources and the forgiving deposition process requires a minimum of energy consumption and time. Comparisons to a variety of metal oxide systems are considered. Observed sensitivities and the sensor system reversibility can be predicted from the recently developing IHSAB model.

Multifunctional ultrathin aluminum foil: oil/water separation and particle filtration

We present here a kind of novel multifunctional ultrathin aluminum foil which consists of large-area regular micropore arrays covered with nanostructures.

Response Simulation and Extraction of Gas Concentrations for Nanostructure Decorated Nano-/Microporous Silicon Interfaces

Sensor and microreactor technology plays a major role in the detection, monitoring, and transformation of materials at interfaces. We study the dynamics of a matrix of reversible interactions of gas analytes with the majority charge carriers of nanostructure modified extrinsic semiconductor interfaces. Nanostructures are deposited on highly sensitive surface layers, created by forming an array of nanopore-coated micropores on p- or n- type silicon semiconductors. The balance of physisorption and chemisorption of the interacting gas analyte on the porous silicon interface is achieved by following the tenants of the developing inverse hard and soft acid/base (IHSAB) interaction model to select metal oxide nanostructures for deposition. These electronically independent metal oxide catalyst sites are readily modified through in-situ nitridation and sulfidation to create a broad sensing matrix. The resulting relative sensor responses of the modified interfaces to gas analytes are explained by the IHSAB interaction model, rather than simply by a shift in system basicity. This expanded matrix of observed sensitivities can then be used to predict the relative response of the interface to a variety of gas phase analytes, as well as direct the choice of porous silicon interface modification for enhanced reversible chemical sensing and electron transduction, in the absence of significant chemical bond formation. The characterization of multiple gas detection, under the guiding model of the IHSAB concept, describes the synergism of two or more analytes simultaneously interacting with an extrinsic semiconductor interface. We are now extending the application of the porous silicon sensors to the identification of organic solvents by measuring impedance. Through the use of an equivalent circuit model, we can explore the physical changes of the porous silicon sensor after metal oxide nanostructure depositions and exposure to various organic solvents.

Hydrophobic light-trapping structures fabricated on silicon surfaces by picosecond laser texturing and chemical etching

Light-trapping structures are fabricated on crystalline (100) silicon (c-Si) surfaces by picosecond (ps) laser irradiation followed by chemical etching. First, 1064-nm ps laser scanning is used to form micropore arrays on c-Si. The ps laser processing causes little reconsolidation of the silicon surface, which is beneficial to achieve precise etching. Control of the laser scanning interval, number of scans, and etching time gives a micro-nano hierarchical structure. In this hierarchical structure, the average diameter of the micropores is 25 to 30 μm, while the size of the finer nanostructures on the micropore inner walls ranges from dozens to hundreds of nanometers. Unlike traditional laser texturing techniques, the whole laser process is carried out without mask and photolithography. The reflectance of the c-Si surface with a micro-nano hierarchical structure is as low as 6% in the wavelength range from 400 to 1000 nm without coating. Moreover, the samples also show good hydrophobicity. This is a potential method to fabricate economical antireflective structures that are ideal for applications in c-Si solar cells and self-cleaning c-Si microelectronic devices.

PerFlexMEA: a thin microporous microelectrode array for in vitro cardiac electrophysiological studies on hetero-cellular bilayers with controlled gap junction communication.

The new microelectrode array device presented is called PerFlexMEA and it enables controlled coupling between myocytes and nonmyocytes used in cardiovascular conduction studies. The device consists of an 8 μm thin parylene microporous membrane with a 4 × 5 microelectrode array patterned on one side. Myocytes and nonmyocytes can be plated on either side of the parylene membrane to create a tissue bilayer. The 3-3.5 μm diameter pores allow inter-layer dye and electrical coupling without transmembrane cell migration. Cell migration was found to vary with cell-type and micropore diameter. Pore density can be varied based on desired coupling ratio. The flexible parylene membrane is packaged between two rigid thermoplastic layers, such that the microelectrode array region is exposed, while the rest of the device remains insulated. The packaged PerFlexMEA fits in a 60 mm culture dish. Recording experiments are performed by simply plugging it into a commercially available multielectrode amplifier system. Recorded signals were processed and analysed using scripts generated in MATLAB. Our experimental results provide evidence of the reliability of this device, as conduction velocity was observed to decrease after inducing lateral hetero-cellular controlled coupling between myocytes and HeLa cells expressing connexin 43.

Fractional thermolysis by bipolar radiofrequency facilitates cutaneous delivery of peptide and siRNA with minor loss of barrier function.

In this study, we aimed to illustrate the utility of fractional radiofrequency (RF) that generated microchannels in the skin, allowing delivery of peptide and siRNA via the skin. The mechanisms involved in the correlation between macromolecule permeation and skin structure were also elucidated. The morphology of the skin was examined by transmission electron microscopy (TEM), higher harmonic generation microscopy (HGM), and physiological factors. In vivo skin distribution of macromolecules was assessed by fluorescence and confocal microscopies. RF thermolysis selectively created an array of micropores deep into the epidermis without significant removal of the stratum corneum (SC). With energy of 30 mJ, a pore depth of 35 μm was achieved. The bipolar RF resulted in a 3-fold increase of transepidermal water loss (TEWL) compared with intact skin. The respective skin accumulation and flux of the peptide with a molecular weight (MW) of 2335 Da was 3- and 23-fold greater for the RF-treated group than for the non-treatment group. RF enhanced skin accumulation of siRNAs with MW of 10 and 15 kDa by 6.2- and 2.6-fold, respectively. Cutaneous penetration of the macromolecules with an MW of at least 40 kDa could be accomplished by RF. Confocal microscopy imaging revealed that RF could effectively deliver the peptide up to at least a 74-μm depth. The penetration depth of siRNA by RF irradiation was about 50 μm. The novel RF device efficiently delivered macromolecules into the skin while reserving SC layers to support some barrier functions. In this work, for the first time the assistance of fractional RF on peptide and siRNA transport was demonstrated.

External-integrated biomimetic micropump for microfluidic system

An external-integrated biomimetic micropump for a microfluidic system is demonstrated. An “artificial leaf” is constituted, which mimics the stomatal transpiration process in plants and utilizes the negative pressure generated to drive the fluid flow. The biomimetic micropump integrated an SU-8 film with a micropore array, agarose gel, a flow rate control unit, and additional necessary operating auxiliaries. SU-8 film with micropores and agarose gel is used to mimic the stomata and the mesophyll cells in a leaf, respectively. The flow rate control unit can change the flow rate of the micropump by adjusting the number of micropores that participate in transpiration. Additional necessary operating auxiliaries can fix a microchip, provide a continuous fluid supply, and speed up the fluid flow rate. Experiments on a microchip are conducted to evaluate the performance of the micropump platform. Results have shown that the flow rate of the micropump can be increased by accelerating the wind speed or raising the temperature.

Electroless plating of thin gold films directly onto silicon nitride thin films and into micropores.

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses <100 nm were grown at 3 and 10 °C between 0.5 and 3 h, with mean grain sizes between ∼20 and 30 nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200 nm thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces.