Nanochannel devices have been fabricated using standard micromachining techniques such as optical lithography, deposition and etching. 1D nanochannels with thin glass capping and through-wafer inlet/outlet ports were constructed. 2D nanochannels have been made transparent by oxidation of polysilicon channel wall for optical detection and these fragile channels were successfully connected to macro inlet ports. The interfacing from the macro world to the nanochannels was especially designed for optical observation of filling liquid inside nanochannels using an inverted microscope. Toward single-molecule studies, individual quantum dots were visualized in 150 nm height 1D nanochannels. The potential of 2D nanochannels for single-molecule studies was shown from a filling experiment with a fluorescent dye solution.

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Fabrication and interfacing of nanochannel devices for single-molecule studies

Nanoscale core–shell CoMoO4@Co3O4 composite materials are fabricated by a multi-step hydrothermal process on the surface and side wall of an ordered macro-porous electrode plate (OMEP) as the active electrode in a high power density storage device. The morphology, formation mechanism of the CoMoO4@Co3O4 nanostructure, and capacitor performance are systematically studied. The CoMoO4@Co3O4/OMEP electrode has a capacity of 7.13 F cm−2 (1168.0 F g−1) at a constant current density of 0.6 A g−1 and a retention ratio of 81.4% after 5000 cycles. The large specific capacitance and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid–solid interfacial area, prevents agglomeration of nanomaterials, and boosts the utilization efficiency of the active materials. Reconstruction on the surface of the porous structured substrate enhances the power density and cycling performance at large current densities. Using the CoMoO4@Co3O4/OMEP electrode as the positive electrode and active carbon/nickel foam (AC/NF) as the negative electrode, the electrochemical electrode packaged in a CR2025 battery cell as a miniature hybrid device exhibits stable power characteristics (10 000 cycles with 91.7% retention at a current of 0.1 A). The device produces large instantaneous power that charging it for 10 s and using three devices in series can power four parallel LED arrays at a current of 0.152 A.

Hierarchical CoMoO4@Co3O4 nanocomposites on an ordered macro-porous electrode plate as a multi-dimensional electrode in high-performance supercapacitors

Miniaturization of the energy systems and high powered electronic devices necessitates the high capacity compact heat exchangers to dissipate the heat generated. Microchannel heatsinks (MCHS) are modern heat exchangers with the fluid flowing channels of size in microscale. These are very compact heat exchangers with higher ratios of heat transfer area to the volume. Huge research work has been going on to improve the hydraulic and thermal performance of the MCHS. This article provides the information about experimental and numerical studies that has been done on the heat transfer and its enhancement in micro-scale cooling devices. This review mainly concentrate on the heat transfer enhancement techniques in microchannel, numerical methods that has been implemented for the study of micro-channels and the parameters which effects the heat transfer rate. The recent studies on microchannel heat sink to improve its performance by geometry modifications, jet impingement, using Nano fluids, flow boiling and Magneto-hydrodynamics are thoroughly discussed in this article.

Latest Advancements in Heat Transfer Enhancement in the Micro-channel Heat Sinks: A Review

A Ni/silicon microchannel plate (Ni/Si MCP) electrode modified with poly(3,4-ethylenedioxythiophene) (PEDOT) was successfully fabricated. The analytical performance of prepared electrode for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) was investigated by using cyclic voltammetry and differential pulse voltammetry (DPV). The sensitivities for AA, DA and UA obtained by DPV are 5.39 A m−2 mM−1, 0.054 A m−2 μM−1 and 0.022 A m−2 μM−1, respectively. The calculated detection limits were 10 μM (AA), 1.5 μM (DA) and 2.7 μM (UA). The prepared electrode was successfully applied to the detection of AA, DA and UA in urine samples. The experiments illustrate that Ni/Si MCP is a good electrode material which provides a large surface-to-volume ratio and enhances the selectivity and sensitivity.

Poly(3,4-ethylenedioxythiophene)-modified Ni/silicon microchannel plate electrode for the simultaneous determination of ascorbic acid, dopamine and uric acid

Nanoscale cobalt molybdate (CoMoO4) particles are fabricated hydrothermally on the surface and sidewall of three-dimensional nickel-coated silicon microchannel plates (also called macroporous electrically conductive network, MECN) as the active electrode in a miniature energy storage device. The relationships between the reaction time, morphology, formation mechanism of the CoMoO4 nanostructure, and electrochemical performance are studied. After an optimal hydrothermal synthesis time of 2.5 h, the CoMoO4 electrode has a capacity of 32.40 mA h g−1 (492.48 μA h cm−2) at constant current density of 1 A g−1 and retention ratio of 85.98% after 5000 cycles. The large specific capacity and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid–solid interfacial area, and enhances the utilization efficiency of the active materials. Furthermore, the weight and size of the device are reduced. By using the CoMoO4/MECN electrode as the positive electrode and carbon/nickel foam (carbon/NF) as the negative electrode, the faradaic electrode was packaged by a CR2025 battery cell as the miniature hybrid device exhibits stable power characteristics (5000 cycle times with 71.82% retention). After charging each hybrid device for 10 s, three devices in series can power two 5 mm diameter light-emitting diodes (LED) efficiently.

Hierarchical 3-dimensional CoMoO4 nanoflakes on a macroporous electrically conductive network with superior electrochemical performance

A silicon microchannel plate (Si MCP) is of large interest for electron multiplication. Conventional fabrication processes utilize an etching process on the front side and wafer thinning on the backside. In this note, a process based on electrochemical etching, developed to generate a gap between the device layer and the substrate, is presented. A sample containing a microchannel through-hole structure can be directly obtained with a laser cut by scanning the laser beam on the surface without cutting through the wafer. An oxidation step is used to increase the MCP's electrical resistance. After dry oxidation at 900 °C, structure distortion is observed in the free-standing sample. Thus, oxidizing before cutting the microchannel plate from the substrate is recommended.

Obtaining a high area ratio free-standing silicon microchannel plate via a modified electrochemical procedure

The influence of backside illumination and temperature on the fabrication of large and high aspect ratio silicon microchannel plates (MCPs) by photoelectrochemical (PEC) process is described. Backside illumination is provided by three 150-W tungsten halogen lamps with a feedback loop, keeping a constant current density. The etching temperature is maintained by a circulation system. Proper backside illumination and the lower temperature can provide better integrated etching conditions compared to that without illumination and temperature control. Etching under the improved conditions results in smoother undercutting and better surface topography for large (effective diameter of about 80 mm for 4-inch silicon substrates) silicon microchannel plates. Enhancing the backside illumination within the etching temperature range ensures that the aspect ratio is more than 40, boding well for applications of silicon microchannel plates.

Large-size P-type silicon microchannel plates prepared by photoelectrochemical etching

Silicon microchannel structures exhibit numerous possible applications. In this report, the oxidation of high area ratio silicon microchannels used in weak light detection and night vision is studied. High area ratio microchannels are fabricated by electrochemical etching, and the influences of oxidation time and environments on the microstructures are investigated and analyzed combined with computer simulation. Damages and distortion are found after the oxidation process. It is found that after oxidation at high temperature, surface morphology becomes rough and followed polishing step is recommended to smooth the silicon microchannels' surfaces.

Oxidation of high area ratio silicon microchannels fabricated by electrochemical etching

Silicon microchannel plates have been explored intensively for numerous applications especially for weak light detection and night vision. The electrochemical etching in hydrofluoric acid-based solutions is known as a technique for porous silicon formation. This paper presents a new process for the formation of microchannel structure and the separation of the Si MCP from p-type starting substrates by a single-step electrochemical etching in HF-based electrolytes. High aspect ratio microchannels are fabricated by electrochemical etching and the conditions under which the undercut occurs are investigated. The formation of the undercut is found to be primarily determined by both current density and HF concentration, which determine the MCP structure thickness as well.

Investigation of the formation of undercut during the fabrication of silicon microchannels by electrochemical etching

In this report, p-type macroporous silicon has been prepared by anodization. A phosphorus diffusion step is employed for
the formation of three dimensional pn junction structures on this macroporous silicon. I-V and C-V measurement were
employed to characterize the electrical properties. The results were compared with numeric simulation with T-SUPREM4
and MEDICI. It has been demonstrated that three-dimensional structure can increase the effective junction
area and the collective efficiency remarkably, and hence improve the performance of semiconductor radiation detector.

Peisheng Xin

Papers

Obtaining a high area ratio free-standing silicon microchannel plate via a modified electrochemical procedure

Large-size P-type silicon microchannel plates prepared by photoelectrochemical etching

Oxidation of high area ratio silicon microchannels fabricated by electrochemical etching

Investigation of the formation of undercut during the fabrication of silicon microchannels by electrochemical etching

Fabrication and characterization of 3D pn junction structure for radiation detection