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Existing methods for sealing chip-to-chip (or module-to-motherboard) microfluidic interconnects commonly use additional interconnect components (O-rings, gaskets, and tubing), and manual handling expertise for assembly. Novel gasketless superhydrophobic fluidic interconnects (GSFIs) sealed by transparent superhydrophobic surfaces, forming liquid bridges between the fluidic ports for fluidic passages were demonstrated. Two test platforms were designed, fabricated, and evaluated, a multi-port chip system (ten interconnects) and a modules-on-a-motherboard system (four interconnects). System assembly in less than 3 sec was done by embedded magnets and pin-in-V-groove structures. Flow tests with deionized (DI) water, ethanol/water mixture, and plasma confirmed no leakage through the gasketless interconnects up to a maximum flow rate of $100~\mu \text{L}$ /min for the multi-port chip system. The modules-on-a-motherboard system showed no leakage of water at a flow rate of $20~\mu \text{L}$ /min and a pressure drop of 3.71 psi. Characterization of the leakage pressure as a function of the surface tension of the sample liquid in the multi-port chip system revealed that lower surface tension of the liquid led to lower static water contact angles on the superhydrophobic-coated substrate and lower leakage pressures. The high-density, rapidly assembled, gasketless interconnect technology will open up new avenues for chip-to-chip fluid transport in complex microfluidic modular systems. [2020-0168]

An improved, laser-induced fluorescence-based micro-optical biosensor was designed and fabricated, with cyclic olefin copolymer (COC) optical waveguides, a poly(methyl methacrylate) (PMMA) fluidic substrate with an array of microlenses, and a COC coupling prism integrated with the waveguide substrate or cover plate. The double-sided hot embossed fluidic substrate had sampling zone microchannels on the bottom and microlenses on the top. Dissolved COC injected into polydimethylsiloxane (PDMS) lost molds embedded the waveguides in the PMMA cover plate and formed the integrated coupling prism. The embedded COC waveguide was flycut down to $50~\mu \text{m}$ . The cover plate and shallow, 1:20 aspect ratio, microchannels were thermal fusion bonded using a pressure-assisted boiling point control system, without sagging. The large COC prism coupled better to the waveguide. The highest intensity evanescent excitation of the waveguide was obtained near the critical angle. The maximum signal-to-noise ratio (SNR) was 119 and the lowest detection limit was 7.34 $\times 10^{\mathbf {-20}}$ mol at a SNR of 2 for a $100~\mu \text{m}$ wide by $50~\mu \text{m}$ deep waveguide. The microlenses highly focused the fluorescent radiation in the sampling zone. The microfabricated waveguide enables rapid, low-cost detection of fluorescent samples with high SNR, a low detection limit, and high sampling efficiency. [2020-0067]

Chip-to-chip and world-to-chip fluidic interconnections are paramount to enable the passage of liquids between component chips and to/from microfluidic systems. Unfortunately, most interconnect designs add additional physical constraints to chips with each additional interconnect leading to over-constrained microfluidic systems. The competing constraints provided by multiple interconnects induce strain in the chips, creating indeterminate dead volumes and misalignment between chips that comprise the microfluidic system. A novel, gasketless superhydrophobic fluidic interconnect (GSFI) that uses capillary forces to form a liquid bridge suspended between concentric through-holes and acting as a fluid passage was investigated. The GSFI decouples the alignment between component chips from the interconnect function and the attachment of the meniscus of the liquid bridge to the edges of the holes produces negligible dead volume. This passive seal was created by patterning parallel superhydrophobic surfaces (water contact angle ≥ 150°) around concentric microfluidic ports separated by a gap. The relative position of the two polymer chips was determined by passive kinematic constraints, three spherical ball bearings seated in v-grooves. A leakage pressure model derived from the Young–Laplace equation was used to estimate the leakage pressure at failure for the liquid bridge. Injection-molded, Cyclic Olefin Copolymer (COC) chip assemblies with assembly gaps from 3 to 240 µm were used to experimentally validate the model. The maximum leakage pressure measured for the GSFI was 21.4 kPa (3.1 psig), which corresponded to a measured mean assembly gap of 3 µm, and decreased to 0.5 kPa (0.073 psig) at a mean assembly gap of 240 µm. The effect of radial misalignment on the efficacy of the gasketless seals was tested and no significant effect was observed. This may be a function of how the liquid bridges are formed during the priming of the chip, but additional research is required to test that hypothesis.

Hypothesis Compared to vertical micro-pillars, re-entrant micro-structures exhibited superior omniphobicity for suspending liquids to Cassie-Baxter state. However, the existing re-entrant structures rely on complex multi-step deposition and etching procedures. The conventional, rigid-templated imprinting would instead damage the re-entrant structures. This leads to the question: is it possible to preserve the re-entrant curvatures by a flexible-templated imprinting? Experiments We facilely imprinted the re-entrant structures on a plastic substrate using a flexible nylon-mesh template. The effect of imprinting time (15–35 min), temperature (110–120 °C) and pressure (15–50 Bar) was investigated. To further improve the liquid-repellency and abrasion resistance, the silica nanoparticles (30–650 nm) along with epoxy resin binder (10 mg/mL) were pre-coated. Findings A one-step imprinting is sufficient to fabricate the re-entrant structures by utilizing flexible nylon-mesh template, without damaging the imprinted structures after the demolding process. The pre-coated silica nanoparticles and epoxy resin (1) improved liquid repellency by introducing hierarchical surface structures (e.g. contact angle hysteresis of olive oil reduced > 10°), and (2) acted as a protective layer against mechanical abrasion (omniphobicity maintained after 25 cycles, ~1.6 kPa sand paper abrasion). Additionally, the fluorine-free post-treatment was sufficient for the omniphobicity on the obtained plastic structures.

Antimony(V) carboxylate photoresists incorporating polymerizable olefins have demonstrated high photospeeds. The work of Passarelli et al. reported a sensitivity hypothesis, polymerizable olefin loading (POL), in which an increase in photospeed correlates to an increase in the number of olefins per molecular weight of resist.1 Utilizing this sensitivity trend, a photoresist of higher molecular weight, triphenylantimony(V) bis(4-vinylbenzoate) (JP-30), was developed exhibiting moderate photospeed at the cost of improved pattern fidelity. Herein we report three approaches for improving the lithographic performance of polymerizable olefin antimony carboxylate photoresists. Approach 1 increased the number of olefins per molecule through functionalization of the R-group. Tristyreneantimony(V) dicarboxylate photoresists were lithographically evaluated exhibiting high photospeeds and improved resolution capabilities (Figure 1). Approach 2 examined the benefits of blending two antimony carboxylate photoresists with high and low POL values and observing the changes in photospeed. Approach 3 increased the POL relative to JP-30 through reduction in molecular weight of the R-groups by the synthesis and lithographic evaluation of trimethylantimony(V) bis(4-vinylbenzoate).

Hypothesis The superhydrophobic lotus leaf has dual-scale surface structures, that is, nano-bumps on micro-mountains. Large hydrophilic particles, due to its high surface energy and weight, have high affility to substrates and tend to precipitate at the bottom of coating films. Small hydrophobic particles, due to its low surface energy and weight, tends to sit on the top of coating films and form porous structures. To mimic the lotus leaf surface, it may be possible to develop dual-sized particle films, in which small particles are decorated on large particles. Experiments A one-step spin coating of a mixture of dual-sized silica particles (55/200 nm) was used. Epoxy resin was added to improve the adhesion of particle films. The single-sized and dual-sized particle films were compared. The mechanical robustness of particle films was tested by tape peeling and droplet impact. Findings The novel combination of hydrophobic silica (55 nm) and hydrophilic silica (200 nm) is essential in creating the hierarchical structures. By combining the strong adhesion of hydrophilic silica (bottom of coating film) to polymer substrates and porous structures of hydrophobic silica (top of coating film), we first time report a one-step and versatile approach to create uniform, transparent, robust, and superhydrophobic surface.

A method for the design, construction, and assembly of modular, polymer-based, microfluidic devices using simple micro-assembly technology was demonstrated to build an integrated fluidic system consisting of vertically stacked modules for carrying out multi-step molecular assays. As an example of the utility of the modular system, point mutation detection using the ligase detection reaction (LDR) following amplification by the polymerase chain reaction (PCR) was carried out. Fluid interconnects and standoffs ensured that temperatures in the vertically stacked reactors were within ± 0.2 C° at the center of the temperature zones and ± 1.1 C° overall. The vertical spacing between modules was confirmed using finite element models (ANSYS, Inc., Canonsburg, PA) to simulate the steady-state temperature distribution for the assembly. Passive alignment structures, including a hemispherical pin-in-hole, a hemispherical pin-in-slot, and a plate-plate lap joint, were developed using screw theory to enable accurate exactly constrained assembly of the microfluidic reactors, cover sheets, and fluid interconnects to facilitate the modular approach. The mean mismatch between the centers of adjacent through holes was 64 ± 7.7 μm, significantly reducing the dead volume necessary to accommodate manufacturing variation. The microfluidic components were easily assembled by hand and the assembly of several different configurations of microfluidic modules for executing the assay was evaluated. Temperatures were measured in the desired range in each reactor. The biochemical performance was comparable to that obtained with benchtop instruments, but took less than 45 min to execute, half the time.

One of the long-standing problems for nanoparticle-based liquid-repellent coatings is their poor adhesion to substrates. For polymers with low glass transition temperatures, it is highly desirable to have a low temperature coating strategy to fabricate robust superhydrophobic films. Here, we report a facile method for fabricating robust, transparent, superhydrophobic films on polymer substrates. A mixture of silica particles and silica-based oligomers was spin coated on polymer substrates, followed by oxygen plasma treatment and vapor deposition of 1 H,1 H,2 H,2 H-Perfluorodecyltriethoxysilan (FDTS). The resulting superhydrophobic surface has a static contact angle of 160° and contact angle hysteresis less than 5°. This is a practical solution for improving the adhesion of superhydrophobic films on polymer substrates under ambient conditions.

With sizes larger than molecules but smaller than colloidal particles, nanoparticles exhibit unique transport properties in porous media. They can easily pass through typical pore throats in reservoir formations with micron diameters, but may get retained by physicochemical interaction with the pore walls. Based on detailed analysis of nanoparticle retention data from an extensive series of transport experiments, we examine the limitations of classical models of transport and interaction with a stationary phase. Some features of nanoparticle transport and retention are similar to those of adsorbing/desorbing solutes, while others are similar to those of depositing colloids. But neither solute sorption nor colloid filtration alone can explain all nanoparticle retention features, and of particular importance for subsurface applications, neither model can predict the effect of changing flow conditions on nanoparticle retention. The model that accounts for most observations is an independent two-site model which postulates physically independent sites of fixed capacity: one for reversible attachment and the other for irreversible attachment. We validate the model against five distinctly different groups of experimental data from the literature, through a rigorous approach of obtaining the model parameters from one experiment and blind testing against data from other experiments when experimental conditions vary.

This paper describes the photoreactivity of six organometallic complexes of the type PhnMX2 containing bismuth, antimony and tellurium, where n = 3 for bismuth and antimony and n = 2 for tellurium, and where X = acetate (O2CCH3) or pivalate (O2CC(CH3)3). These compounds were exposed to EUV light to monitor photodecomposition via in situ mass spectral analysis of the primary outgassing products of CO2, benzene and phenol. This paper explores the effect of metal center and carboxylate ligand on the EUV reactivity of these EUV photoresists.

The photo-mechanism of EUV exposures in chemically amplified photoresists are much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the PAG molecule to decompose if an electron is trapped. Low-energy electrons unlikely to produce holes and secondary electrons generate acid indicating electron-PAG interactions are capable to induce decomposition. Additionally, a more easily reduced PAG (i.e. higher likelihood of trapping an electron) produces a higher acid yield supporting electron trapping as a process of acid production. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron-PAG interactions are a source of acid production through electron trapping; thus, increasing the number of electron-hole pairs available to induce chemical reactions would improve sensitivity. It is expected that lower band gap materials produce more electron-hole pairs after an absorption event. Subsequently, these measurements show that lower band gap polymers generate higher acid yields.

Scalable syntheses of two-dimensional topological insulators are critical to material exploration. We demonstrate a controlled assembly of a two-dimensional V–VI group compound, Sb2Te3 nanoplates (NPs), through a vapor–solid growth process. The physical thickness of Sb2Te3 NPs can be rationally controlled in a wide range, from hundreds of nm down to sub-10 nm. Single-quintuple-layer Sb2Te3 NPs were obtained, with a high domain density of ∼2.465 × 108 cm−2 over a large surface area (1 cm × 1 cm) of a SiO2/Si substrate, verifying a scalable synthesis method. Extensive material analyses were conducted to explore the basic properties of Sb2Te3 NPs using SEM and AFM, etc. HRTEM analysis confirms that the NP samples exhibit a highly crystalline structure and XPS analysis confirms the chemical composition and material stoichiometry. The growth of 2D topological insulator nanostructures may open up new opportunities in surface-state studies and potential applications in low-dissipative electronic systems.

Pure thin-films of unimolecular organometallic photoresists were lithographically evaluated using extreme ultraviolet light (EUV, λ = 13.5 nm) and developed using solutions containing carboxylic acids. Optimization of development solutions used with a cobalt-oxalate EUV resist (NP1, 2) led to a switch in lithographic tone from negative to positive. Additional optimization led to an improvement in top loss (35 to 7%) with development in cyclohexanone and 2-butanone, respectively. We saw a drastic improvement in photo-speed (Emax = 5 mJ/cm2) and contrast of the negative-tone imaging with development in certain acidic solutions. Additionally, carboxylic acid solutions provide excellent development conditions for resists that we, in the past, have been unable to successfully develop.

the microelectronics industry. Traditional EUV photoresists have been composed of organic compounds which are moderately transparent to EUV. Resist stochastics and sensitivity can be improved by increasing the number of photons absorbed. Molecular organometallic resists are a type of metal containing resist aimed at improving EUV absorption. This work focuses on studying the role of the metal center (Metal = Co, Fe, Cr) in an oxalate complex by comparing the number of absorbed photons and the photoelectron reactivity in each compound. In the study presented here, the EUV absorption coefficients are determined experimentally by measuring the transmission through a resist coated on a silicon nitride membrane using an Energetiq EQ-10M xenon plasma EUV source. Additionally, the photochemistry is evaluated by monitoring outgassing reaction products. This particular resist platform eliminates oxalate ligands when exposed to electrons or EUV photons resulting in a solubility difference between the exposed and unexposed regions. In the process, carbon dioxide is produced and is monitored using mass spectrometry, where quantitative values are obtained using a calibration technique. For the metal oxalate complexes studied, the absorption of EUV changed minimally due to the low concentrations of metal atoms. However, EUV and electron reactivity greatly changed between the three compounds likely due to the reducibility of the metal center. A correlation is shown between Esize and the reducibility of each photoresist.

Extreme ultraviolet (EUV, ~13.5 nm) lithography is the prospective technology for high volume manufacturing by the microelectronics industry. Significant strides towards achieving adequate EUV source power and availability have been made recently, but a limited rate of improvement in photoresist performance still delays the implementation of EUV. Many fundamental questions remain to be answered about the exposure mechanisms of even the relatively well understood chemically amplified EUV photoresists. Moreover, several groups around the world are developing revolutionary metal-based resists whose EUV exposure mechanisms are even less understood. Here, we describe several evaluation techniques to help elucidate mechanistic details of EUV exposure mechanisms of chemically amplified and metal-based resists. EUV absorption coefficients are determined experimentally by measuring the transmission through a resist coated on a silicon nitride membrane. Photochemistry can be evaluated by monitoring small outgassing reaction products to provide insight into photoacid generator or metal-based resist reactivity. Spectroscopic techniques such as thin-film Fourier transform infrared (FTIR) spectroscopy can measure the chemical state of a photoresist system pre- and post-EUV exposure. Additionally, electrolysis can be used to study the interaction between photoresist components and low energy electrons. Collectively, these techniques improve our current understanding of photomechanisms for several EUV photoresist systems, which is needed to develop new, better performing materials needed for high volume manufacturing.

Dual-layer graphene (DLG) interconnects with hexagonal boron nitride ( h -BN) as intercalated insulating layer have been demonstrated. The DLG employs graphene grown by chemical vapor deposition process with h -BN serving as a barrier preventing interlayer scattering, which degrades carrier transport in multilayer graphene. The conductive behavior in dual-layer structures is compared with monolayer graphene and randomly stacked bilayer graphene. Reduced resistance is observed in DLG, which exhibits higher current-carrying capacity and maximum power density. In addition, DLG wire is shown to be robust under constant voltage stressing (10 V) at an elevated temperature (150 °C) with the mean time to failure $\sim 75$ times higher than that of stacked bilayer graphene wires.

Arrays of nanowires and nanotubes of bismuth–tellurium (Bi–Te) were fabricated by electrodeposition techniques. Scanning electron microscopy was employed to characterize the morphology of the fabricated BiTe nanowires and nanotubes. The fabricated BiTe nanowire and nanotube arrays are shown to be polycrystalline with no preferred orientation. Wavelength dispersive spectroscopy analysis shows that either p-type (Bi rich) or n-type (Te rich) nanowires or nanotubes can be obtained by changing the electrodeposition potentials. The lamellar thickness of the nanowires and nanotube crystallites were determined using the Scherrer equation and found to be ∼17–24 nm. The Seebeck coefficient measurements at room temperature obtained for the nanowires and nanotubes deposited at −400 mV were +11.5 and +17 μV K−1, respectively, whereas those obtained at −65 mV were −48 and −63 μV K−1, respectively. The electrical resistance measurements indicated that the resistance of the nanowires and nanotubes decreased with increasing temperature, suggesting that these nanostructures behave like semiconductors.

This study addresses gas–liquid two-phase flows in polymer (PMMA) micro-channels with non-molecularly smooth and poorly wetting walls (typical contact angle of 65°) unlike previous studies conducted on highly wetting molecularly smooth materials (e.g., glass/silicon). Four fundamentally different topological flow regimes (Capillary Bubbly, Segmented, Annular, Dry) were identified along with two transitory ones (Segmented/Annular, Annular/Dry) and regime boundaries were identified from the two different test chips. The regime transition boundaries were influenced by the geometry of the two-phase injection, the aspect ratio of the test micro-channels, and potentially the chip material as evidenced from comparisons with the results of previous studies. Three principal Segmented flow sub-regimes (1, 2, and 3) were identified on the basis of quantified topological characteristics, each closely correlated with two-phase flow pressure drop trends. Irregularity of the Segmented regimes and related influencing factors were addressed and discussed. The average bubble length associated with the Segmented flows scaled approximately with a power law of the liquid volumetric flow ratio, which depends on aspect ratio, liquid superficial velocity, and the injection system. A simplified semi-empirical geometric model of gas bubble and liquid plug volumes provided good estimates of liquid plug length for most of the segmented regime cases and for all test-channel aspect ratios. The two-phase flow pressure drop was measured for the square test channels. Each Segmented flow sub-regime was associated with different trends in the pressure drop scaled by the viscous scale. These trends were explained in terms of the quantified flow topology (measured gas bubble and liquid plug lengths) and the number of bubble/plug pairs. Significant quantitative differences were found between the two-phase pressure drop in the polymer micro-channels of this study and those obtained from previous glass/silicon micro-channel studies, indicating that the effect of wall surface properties is important. Pressure drop trends on the capillary scale along gas bubbles extracted from the measurements in square micro-channels indicated a linear dependence on the Capillary number and did not agree with those predicted by highly idealized theory primarily because explicit and implicit assumptions in the theory were not relevant to practical conditions in this study.

Potential two-dimensional (2D) van der Waals crystals with mechanical flexibility, transparency, and low cost are viable material platforms for future nanodevices. Resistive switching behavior in 2D layered Sb2Te3 nanosheets is demonstrated. Nearly three orders of magnitude switch in sheet resistance were realized for more than 20 cycles. The observed hysteretic behavior is due to the change between crystalline and amorphous phases under a melt-quench-recrystallization mechanism. More importantly, the energy required to amorphize the nanosheets decreases exponentially with layer thickness reduction. It is expected that scaling to the ultimate two-dimensional limit in chalcogenide nanosheet-based phase change devices may meet or even exceed the energy efficiency of neurobiological architectures.

The ability to electrodeposit magnetic (CoNiFeCu) and semiconductor (Bi2Te3) nanotubes was demonstrated from two different electrochemical systems. Electrodeposited multilayered CoNiFeCu/Cu nanotubes were fabricated by pulsing the applied potential. The electrolyte temperature affected the tube formation and the nanotubes giant magnetoresistance (GMR) saturation field. Both p/n-type Bi2Te3 alloy nanotubes were deposited under constant potential from different electrolyte concentrations and component ratios. We report the Seebeck coefficient measurement method for Bi2Te3 alloy nanotubes obtained by electrodeposition.

This work is a part of an on-going research effort to fabricate a device consisting of an array of micro thermoelectric coolers (μTECs) for highly localized control of temperature in biological systems. A preliminary lumped 1-D parameter model was developed and numerical simulations were carried out to identify the critical and optimal design parameters for a μTEC operating under steady state conditions. The lumped parameter analysis revealed the presence of a new limitation on the maximum possible current through the system, which we denoted as the secondary breakdown current (as opposed to the primary breakdown current associated with Joules heating). To further understand the effect of contact resistances (thermal and electrical), radiative effects, and lateral effects (interactions between μTECs) in our device, we developed a 3-D finite element model (FEM) using ANSYS®. The FEM analysis identified the optimal distance between μTECs to generate discrete and distinct temperatures within the cells located in the extracellular matrix and thus, generating the optimal design specifications for our device.

An overview of recent topics at Louisiana State University is reviewed with an emphasis on electrodeposited alloys into deep recessed geometries. Microposts of CoCu/Cu have been fabricated that exhibit magnetoresistance when the current is perpendicular to the layers. Invar-like FeNiCu/Cu microposts having low coefficient of thermal expansion (CTE) are presented and exhibit a negative CTE prior to heat treatment. Microhardness of the Invar-like copper multilayered microposts was comparable to NiW alloys deposited as microposts. The electrodeposition of rare earth-transition metals were found to behave similar to NiW. Nanowire and nanotube deposition of CoGd and CoGd/Cu multilayers were presented.

This paper present a method of rapid replication of polymeric high aspect ratio microstructures (HARMs) and a method of rapid reproduction of metallic micromold inserts for HARMs using polydimethylsiloxane (PDMS) casting and standard LIGA processes. A high aspect ratio (HAR) metallic micromold insert, featuring a variety of test microstructures made of electroplated nickel with 15:1 height-to-width ratio for 300 μm microstructures, was fabricated by the standard LIGA process using deep X-ray lithography (DXRL). A 10:1 mixture of pre-polymer PDMS and a curing agent were cast onto the HAR metallic micromold insert, cured and peeled off to create reverse images of the HAR metallic micromold insert in PDMS. In addition to the replication of polymeric HARMs, replicated PDMS HARMS were coated with a metallic sacrificial layer and electroplated in nickel to reproduce another metallic micromold insert. This method can be used to rapidly and massively reproduce HAR metallic micromold inserts in low cost mass production manner without further using DXRL.

We demonstrate extraordinary photoconductive behavior in two-dimensional (2D) crystalline indium selenide (In2Se3) nanosheets. Photocurrent measurements reveal that semiconducting In2Se3 nanosheets have an extremely high response to visible light, exhibiting a photoresponsivity of 3.95 × 10(2) A·W(-1) at 300 nm with an external quantum efficiency greater than 1.63 × 10(5) % at 5 V bias. The key figures-of-merit exceed that of graphene and other 2D material-based photodetectors reported to date. In addition, the photodetector has a fast response time of 1.8 × 10(-2) s and a specific detectivity of 2.26 × 10(12) Jones. The photoconductive response of α-In2Se3 nanosheets extends into ultraviolet, visible, and near-infrared spectral regions. The high photocurrent response is attributed to the direct band gap (EG = 1.3 eV) of In2Se3 combined with a large surface-area-to-volume ratio and a self-terminated/native-oxide-free surface, which help to reduce carrier recombination while keeping fast response, allowing for real-time detection under very low-light conditions.

High aspect ratio microposts of bismuth telluride alloy with heights of up to 500 μm and a diameter of 150 μm have been fabricated with the LIGA technique. This work is part of an on-going research effort to develop a microprobe based on the Peltier effect for highly localized temperature manipulation on the microscale. Bismuth telluride alloys were electrodeposited galvanostatically into microfeatures on a titanium substrate using an acidic solution containing Bi3+and HTeO- 2 ions in 1 mol/dm3 nitric acid (pH∼0). The Bi–Te alloy microposts were monophasic, had a polycrystalline structure, demonstrated excellent adhesion to the substrate, and good mechanical strength. The chemical composition of the microposts was dependent on the electrolyte composition of the deposition bath and the current density used in electroplating; by controlling these two factors either p- or n-type Bi–Te alloy microposts may be produced. This research demonstrates that the microfabrication of Peltier effect probes is feasible.

A Peltier-effect module suitable for applications that require manipulation of the temperature (cooling or heating) of microsized subjects or at a highly localized spot was developed. The module was constructed from a commercial electronic refrigeration device based on the Peltier effect with an array of microprobes attached to its top surface. The microprobes were fabricated using the LIGA (German acronym for lithographie, galvanoformung, abformung) process—one of the microelectromechanical systems technologies. The 1000-μm-tall microprobes were fabricated on a titanium plate and then bonded onto the top surface of a commercial Peltier device. When an electrical current was supplied to the Peltier device, the top surface (with microprobes) of the device was cooled and the other side was heated. Heat was conducted from a microsample on the tip of microprobe to the top surface of the Peltier device. A dynamic model of the module was developed and numerical simulation studies were conducted. The prototype m...

Copper is widely used as a plating base for soft magnetic alloy electrodeposition in sensors and actuators. PMMA, the X-ray resist used in the LIGA process, typically has poor adhesion with copper. The use of black oxide of copper to enhance PMMA-copper adhesion was investigated. In this work, peel strength as a function of treatment time and the method of bonding was evaluated using an ASTM standard T-peel test. Peel strength increased with increasing treatment time. The feasibility of producing microstructures with predictable 3-D geometry for use in resonating sensors was investigated using the process developed. Nickel-iron structures of 100-1000 micrometers wide and 500 micrometers tall were successfully electrodeposited. Growth of other representative microstructures is being investigated.

Measurement of three-dimensional, skeletal kinematics is important for clinicians and engineers alike. Most in vivo motion data are acquired using skin-mounted markers or marker arrays. Experiments were carried out to quantitatively evaluate the validity of using skin-mounted markers to measure the three-dimensional kinematics of the underlying bone. Kinematic data for marker arrays mounted on skeletal pins screwed directly into the bone were compared with data for markers, and arrays of markers, mounted on the skin. Findings included: (1) Task-dependent soft tissue motion relative to the underlying bone of up to twenty millimeters was measured; (2) The accuracy of segmental rigid body velocity estimates was inadequate for determining instantaneous helical axis (IHA) parameters; (3) Power spectra for skin- and pin-mounted arrays cover similar frequency bands and there was no evidence of a distinct, frequency domain soft tissue artifact; (4) Joint angles calculated from the relative rotation of skin-mounted arrays had significant differences compared to the expected values due to soft tissue effects; and (5) Skin-mounted marker data exhibited a transient response to heel strike in gait, but for low-mass markers the transient was well-damped and could be removed with optimal smoothing.

Large surface areas (tens of square centimeters to square meters) covered with high-aspect-ratio microstructures (HARMs) have potential applications in a wide range of fields including heat transfer, adaptive aerodynamics, acoustics, catalysts, seal and bearing design, and composite materials. HARMs are typically hundreds of micrometers in height, with widths ranging from a few micrometers to tens of micrometers, and they can be manufactured from a variety of materials such as metals, polymers, and ceramics. Three of the barriers to extensive use of large HARM-covered surfaces are cost, nonplanarity of typical surfaces, and adhesion of the microstructures to the surface. A starting point for inexpensive reproduction of large arrays of HARMs is the plastic molding step of the LIGA micromanufacturing process. In order to address the latter two problems, the standard LIGA process was modified/extended. Free-standing polymer sheets, perforated with a pattern of high-aspect-ratio throughholes, were clamped to conductive substrates. The sheets provide a template for electrodeposition of nickel microstructures onto the target surface. This process makes it economically feasible to electroform metal microstructures directly onto large planar and nonplanar metal surfaces (cylinders).

A polymer-based, multiplex single molecule detection module (SMD) was developed with a fluidic substrate and a cover plate. The fluidic substrate was fabricated using a single-step, double-sided hot embossing in poly(methyl methacrylate) (PMMA) with sampling zone microchannels on the bottom side and microlenses on the top. Shallow sampling zone microchannels (5 μm deep and 100 μm wide) were made to improve sampling efficiency and microlenses were adopted to collect the fluorescent radiation from the sampling zone microchannels. A cyclic olefin copolymer (COC) embedded waveguide in PMMA along with an integrated coupling prism was fabricated using polydimethylsiloxane (PDMS) stencils and melted COC (40% w/v in toluene) on the cover plate. The COC waveguide with a COC integrated coupling prism will be used for evanescent excitation of fluorescent samples in the sampling zone microchannels. The fluidic substrate was bonded with the cover plate using thermal fusion bonding based on a pressure-assisted boiling point control system. This approach allowed for sealing of shallow microchannels without observable sagging of the cover plate, which was confirmed by leakage testing with fluorescent dyes. The completed SMD module will be tested for characterization of the optical performances such as signal-to-noise ratio and sampling efficiency and it will provide the capability for rapid screening of stroke at low cost.Copyright © 2013 by ASME

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le ). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.

A modular, microfluidic device was designed to aid in the rapid detection and treatment of stroke. The device modules process whole blood for the detection of genes expressed in response to a stroke event using a series of assay steps including: cell capture using antibodies, thermal lysis, solid-phase reversible immobilization (SPRI) of nucleic acids, reverse transcription (RT), ligase detection reaction (LDR), and single pair fluorescence resonance energy transfer (spFRET) readout. Cell lysis, RT, and LDR require temperatures of 90°C, 37°C, 65°C and 95°C respectively, therefore strict thermal isolation constraints between thermal zones in the device modules were necessary. Thermal isolation was accomplished using 2 mm and 1 mm air gaps between the fluidic modules and heating elements in the polymer device. Finite element mathematical models (ANSYS v. 12.1, Houston, PA) were used to characterize the thermal zones in two 2D simulations. Section 1 simulation results showed ±1.5°C in cell lysis, ±1.6°C in RT, and ±1.6°C in the denaturation section of LDR. Section 2 simulation showed ±2.6°C in denaturation and ±0.4°C in the annealing/extension zone of LDR.Copyright © 2012 by ASME

With a number of advantages hitherto unrecognized, nanoparticle-stabilized emulsions and foams have recently been proposed for enhanced oil recovery (EOR) applications. Long-distance transport of nanoparticles is a prerequisite for any such applications. The transport of the particles is limited by the degree to which the particles are retained by the porous medium. In this work, experiments that quantify the retention and provide insight into the mechanisms for nanoparticle retention in porous media are described. Sedimentary rock samples (Boise sandstone and Texas Cream limestone) were crushed into single grains and sieved into narrow grain size fractions. In some cases, clay (kaolinite or illite) was added to the Boise sandstone samples. These grain samples were packed into long (1 ft–9 ft) slim tubes (ID = 0.93 cm) to create unconsolidated sandpack columns.The columns were injected with aqueous dispersions of silica-core nanoparticles (with and without surface coating) and flushed with brine. The nanoparticle effluent concentration history was measured and the nanoparticle recovery was calculated as a percentage of the injected nanoparticle dispersion. Fifty experiments were performed in this fashion, varying different experimental parameters while maintaining others constant to allow direct comparisons between experiments. The parameters analyzed in this work are: specific surface area of the porous medium, lithology, brine salinity, interstitial velocity, residence time, column length, and temperature.Our results indicate that retention is not severe, with an 8% average of the injected amount, for all our experiments. Of the parameters analyzed, specific surface area was the most influential, with a linear effect on nanoparticle retention independently of lithology. Larger salinity increased nanoparticle retention slightly and delayed nanoparticle arrival. Velocity, residence time and sandpack length are coupled parameters and were studied jointly; they had a minor effect on retention. Temperature had a marginal effect, with two percentage points greater retention at 80°C compared to 21°C. Both surface coated and bare silica nanoparticles were successfully transported, so surface coating is not a prerequisite for transport for the particle and rock systems studied.

A novel, modular, microfluidic interconnect was developed using parallel superhydrophobic interfaces to facilitate the transport of fluids between component chips in modular microfluidic systems. A static analytical model, derived from the Laplace equation [1], approximates the maximum steady-state pressure of the liquid at the liquid bridge which forms across the gap between the chips. Preliminary experiments using parallel superhydrophobic surfaces on PMMA validated the concept. Additional experiments controlled the gap distance, measured contact angles of the superhydrophobic surfaces, gradually increased the pressure of the novel, gasketless, interconnect until rupture to find the maximum pressure across the liquid bridge and verify the model. The measured pressures were on the same order of magnitude (1–10 kPa) as estimated using the model for gap distances of 25 μm and 100 μm.

Arrays of continuous flow thermal reactors were designed, configured, and fabricated in a 96-device (12 × 8) titer-plate format with overall dimensions of 120 mm × 96 mm, with each reactor confined to a 8 mm × 8 mm footprint. To demonstrate the potential, individual 20-cycle (740 nl) and 25-cycle (990 nl) reactors were used to perform the continuous flow polymerase chain reaction (CFPCR) for amplification of DNA fragments of different lengths. Since thermal isolation of the required temperature zones was essential for optimal biochemical reactions, three finite element models, executed with ANSYS (v. 11.0, Canonsburg, PA), were used to characterize the thermal performance and guide system design: (1) a single device to determine the dimensions of the thermal management structures; (2) a single CFPCR device within an 8 mm × 8 mm area to evaluate the integrity of the thermostatic zones; and (3) a single, straight microchannel representing a single loop of the spiral CFPCR device, accounting for all of the heat transfer modes, to determine whether the PCR cocktail was exposed to the proper temperature cycling. In prior work on larger footprint devices, simple grooves between temperature zones provided sufficient thermal resistance between zones. For the small footprint reactor array, 0.4 mm wide and 1.2 mm high fins were necessary within the groove to cool the PCR cocktail efficiently, with a temperature gradient of 15.8 °C/mm, as it flowed from the denaturation zone to the renaturation zone. With temperature tolerance bands of ±2 °C defined about the nominal temperatures, more than 72.5% of the microchannel length was located within the desired temperature bands. The residence time of the PCR cocktail in each temperature zone decreased and the transition times between zones increased at higher PCR cocktail flow velocities, leading to less time for the amplification reactions. Experiments demonstrated the performance of the CFPCR devices as a function of flow velocity, fragment length, and copy number. A 99 bp DNA fragment was successfully amplified at flow velocities from 1 mm/s to 3 mm/s, requiring from 8.16 min for 20 cycles (24.48 s/cycle) to 2.72 min for 20 cycles (8.16 s/cycle), respectively. Yield compared to the same amplification sequence performed using a bench-top thermal cycler decreased nonlinearly from 73% (at 1 mm/s) to 13% (at 3 mm/s) with shorter residence time at the optimal temperatures for the reactions due to increased flow rate primarily responsible. Six different DNA fragments with lengths between 99 bp and 997 bp were successfully amplified at 1 mm/s. Repeatable, successful amplification of a 99 bp fragment was achieved with a minimum of 8000 copies of the DNA template. This is the first demonstration and characterization of continuous flow thermal reactors within the 8 mm × 8 mm footprint of a 96-well micro-titer-plate and is the smallest continuous flow PCR to date.

Numerical simulations were performed to see the effect of geometrical misalignment in pressure driven flows. Geometric misalignment effects on flow characteristics arising in three types of interconnection methods a) end-to-end interconnection, b) channel overlap when chips are stacked on top of each other, and c) the misalignment occurring due to the offset between the external tubing and the reservoir were investigated. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the interconnection through channel overlap, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction) for all the configurations. The effect of misalignment in a Tube-in-Reservoir interconnection was investigated by positioning the tube at an offset of 164μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at reynolds numbers ranging from 0.075 to 75. The results are interpreted in terms of equivalent length (Le) as a function of Re and misalignment area ratio (A1:A2), where A1 is the original cross-sectional area of the channel and A2 is the available flow area at mismatch location. Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the most insignificant when compared to the other two methods of interconnection

Metallic large area mold inserts (LAMIs) are essential for the replication of polymer microfluidic devices. Successful molding of micro- or nanoscale features over large areas is dependent on improving the dimensional control of the mold inserts, particularly those fabricated by electrodeposition using the LIGA or UV-LIGA processes. A systematic approach to controlling the internal stress of the nickel deposits, which was essential for predicting the final flatness of the LAMIs prior to electroplating, was carried out. The internal stress of the nickel deposits from a nickel sulfamate solution was estimated using a bent strip stress measurement method after maintaining electroplating chemicals and conditions and reducing contamination. Over-electroplating of the nickel LAMIs was performed on SU-8 electroplating molds on 150 mm diameter Si wafers. Detailed characterization of the nickel LAMIs to determine the relationship between the overall flatness of the LAMIs and the internal stress identified a suitable process window in terms of the current densities (10–20 mA/cm2) and the internal stress (−8.3 ∼ −3.0 MPa) for the high quality nickel LAMIs with an overall flatness of 100 μm.

Liquid-liquid segmented flows in microchannels fabricated on polymer test chips were investigated experimentally. Polymer test chips were prepared using hot embossing of polycarbonate (PC) sheets with micro-milled brass mold inserts. Three different configurations of microchannels were prepared with injection to test channels expansion ratios of 16, 4 and 2 and a fixed test channel geometry. Deionized water with blue food-coloring dye (1% v/v) was used as a dispersed fluid at flow rates (QD ) between 0.5 and 60 μl/min. The carrier fluid was perfluorocarbon (FC 3283) with nonionic fluorous-soluble surfactant (Perfluorooctanol, 10% v/v) at flow rates (QC ) between 3 and 25 μl/min. The two fluids were injected separately into the chips. Droplet and Plug flows with transient Irregular Segmented flows between two flow regimes were mainly observed in the test channels of the three different chips. Flow pattern maps and transitions between flow regimes were determined in terms of a fixed homogeneous carrier fluid volumetric flow ratio (βC ) to compare the effect of the expansion ratios from the injection to the test channels. The droplet and plug regimes were shifted to higher carrier and lower dispersed fluid superficial velocities and the plug flow regime was broader with the lower expansion ratio channels. The transient irregular segmented flow was favored in the higher expansion channel ratio and the interval of transient irregular segmented flow between droplet and plug flow regimes were shorter for the low expansion channel ratios. This is evidence that flow regime maps in micro-channels are not universal and depend on the configuration part of the micro-injection system. The length of the dispersed segmented flows and the distance between consecutive droplets or plugs as a function of βC were determined by image processing of frames acquired via CCD camera with bright field illumination. The average length of the dispersed fluid was shown to scale approximately with βC to the −1.2 power. Velocities of the dispersed droplet and plug flows were measured using double-pulsed laser illumination and were found to be 1.25 ± 0.049 and 1.46 ± 0.077 times faster than the superficial velocity of the segmented flow respectively. Two-phase pressure drop measurements were also carried out for all flow regimes and associated trends were correlated with changes in flow topology. Comparisons of experimental pressure drop with the predictions for a modified Lockhart-Martinelli correlation were also made.Copyright © 2009 by ASME

A novel method of thermoplastic fusion bonding (TPFB), or thermal bonding, for polymer fluidic devices was demonstrated. A pressure cooker was used in a simple sealing and packaging process with precise control of the critical parameters. Polymer devices were enclosed in a vacuum-sealed polymer container. This produced an even pressure distribution and a precise temperature boundary condition over the whole surface of the device. Deformation indicators were integrated on the devices to provide a rapid means of checking deformation and pressure distribution with the naked eye. Temperature, pressure, and time are the fundamental parameters of TPFB. The temperature and pressure are dominated by the material and contact area of the device. The temperature and pressure can be manipulated by controlling the water vapor pressure. The boiling solution guarantees an accurate, constant temperature boundary condition. Time can be eliminated as a variable by choosing a sufficient time to achieve good bonding, since there was no apparent damage to the microstructures after one hour. This new method of TPFB was demonstrated for sealing and packaging a PMMA (polymethylmethacrylate) microfluidic device. Good results were obtained using the vacuum sealed polymer container in the pressure cooker. This method is also suitable for scaling up for mass production.Copyright © 2009 by ASME

Flipchip assembly is the direct electrical connection of the device die on the substrates or circuit boards using conductive stud bumps. Stud bumps help in the reduction of the number of bond wires and weight, and improve performance. Ueno et al. [1] fabricated copper column bumps with a diameter of 75 μm, a height of 50 μm and a pitch of 200 μm. Ni/Au bumps were also fabricated using electroless plating method with a pitch of 50 μm [2]. Tomita et al. [3] successfully fabricated tip capped copper column bumps with a height of 5 μm that were spaced 100 μm apart. Lead free solder bumps have been fabricated using pure-tin (Sn), tin-bismuth (80wt%Sn:20wt%Bi), tin-copper (99.3wt%Sn:0.7wt%Cu), tin-silver (96.5wt%Sn:3.5wt%Ag), and tin-silver-copper (93.8wt%Sn:3.5wt%Ag:0.7wt%Cu) alloys with a diameter of 200 μm and a pitch of 400 μm [4]. Low cost gold bumps have also been fabricated on polymer substrates with dimensions of 40 μm in diameter, 41 μm in height and a pitch of 100μm [5]. More recently Chu et al. [6] have demonstrated the use of cylindrical indium solder bumps with 80 μm diameter for optical interconnect and microwave applications.

Protein adsorption is a critical issue in microfluidic devices especially for those reactions depending on proteins like the polymerase chain reaction (PCR). Understanding protein absorption phenomena in different geometry microchannels and evaluating the efficiency of dynamic coating, which has been using as a method to prevent protein adsorption, are important tasks. Two different sets of microchannels were designed and fabricated on polymers. Bovine serum albumin (BSA) was used as a model protein for quantification of and monitoring the protein loss in different microchannel geometries. Up to 58% of the BSA was lost after flowing a 2030 mm long microchannel. The BSA adsorption rate changed along the microchannel. Smaller microchannels required a longer time to achieve protein saturation point. Dynamic coating was shown to be a time consuming and inefficient method to prevent protein adsorption in a continuous flow environment.Copyright © 2008 by ASME

Validation of a tolerance analysis for the assembly of modular, polymer microfluidic devices was performed using simulations and experiments. A set of three v-groove and hemisphere-tipped post joints was adopted as a model assembly features. An assembly function with assembly feature dimensions and locations was modeled kinematically. Monte Carlo methods were applied to the assembly function to simulate variation of the assembly. Assembly accuracy was evaluated assuming that the variations of the assembly features were randomly distributed. The estimated mismatches were 118 ± 30 μm and 19 ± 13 μm along the X- and Y-axes, respectively. The estimated vertical gap between the modules at the alignment standards along the X- and Y-axes 312 ± 37 μm and 313 ± 37 μm, compared to the designed value of 287 μm. To validate the tolerance model, two micromilled brass mold inserts containing the assembly features and alignment standards were used to double-sided injection mold polymer parts. The accuracy of the assembly of the modular microdevices was estimated by measuring the mismatch and vertical gaps between alignment standards on each axis. The measured lateral mismatches were 103 ± 6 μm and 16 ± 4 μm along the X- and Y-axes, respectively. The vertical gaps measured for the assemblies were 316 ± 4 μm and 296 ± 9 μm at the X- and Y-axes, compared to the designed distance of 287 μm. Simulation and experimental results were in accordance with each other. The models can be used to predict the assembly tolerance of polymer microfluidic devices and have significant potential for enabling the realization of cost-effective mass production of modular instruments.Copyright © 2008 by ASME

A thermal system used to evaluate a high throughput 96 continuous flow polymerase chain reactor (CFPCR) array was designed, fabricated, and tested. Each polymerase chain reactor (PCR) in the array required three different temperature zones to realize denaturaiton at 90°C–94°C, renaturation at 50°C–70°C, and extension at 72°C; a total of 288 temperature zones were required for the 96 CFPCR array. In an initial configuration, 18 copper strips were used to define the 288 temperature zones. Each copper strip was controlled by a PID feedback control loop. Numerical simulations were used to understand the thermal crosstalk phenomena between the micromilled copper strips, which were tightly packed since the high throughput micro-titer plate format restricted each CFPCR to a square 8 mm on a side. The lowest achievable temperature in each renaturation zone in this complicated thermal environment was also identified. Thermal crosstalk limited the minimum renaturation temperature to 61.1°C. An infrared camera was used to investigate the temperature uniformity over a 0.25 mm thick polycarbonate sheet mounted on the thermal system. The temperature distribution was not uniform due to poor contact between the copper strips and device, warm air accumulated between the packed copper strips, and greater heat transfer around the boundaries of the device. More work is required to overcome these limitations and achieve a more uniform temperature distribution for a multi well CFPCR.Copyright © 2008 by ASME

Continuous flow polymerase chain reactors (CFPCRs) are BioMEMS devices that offer unique capabilities for the ultra-fast amplification of target DNA fragments using repeated thermal cycling, typically over the following temperature ranges: 90 degrees C-95 degrees C for denaturation, 50 degrees C-70 degrees C for renaturation, and 70 degrees C-75 degrees C for extension. In CFPCR, DNA cocktail is pumped through the constant temperature zones and reaches thermal equilibrium with the channel walls quickly due to its low thermal capacitance. In previous work, a polycarbonate CFPCR was designed with microchannels 150 microm deep, 50 microm wide, and 1.78 m long-including preheating and post-heating zones, fabricated with LIGA, and demonstrated. The high thermal resistance of the polycarbonate led to a high temperature gradient in the micro-device at steady-state and was partly responsible for the low amplification yield. Several steps were taken to ensure that there were three discrete, uniform temperature zones on the polycarbonate CFPCR device including: reducing the thickness of the CFPCR substrate to decrease thermal capacitance, using copper plates as heating elements to ensure a uniform temperature input, and making grooves between temperature zones to increase the resistance to lateral heat conduction between zones. Finite element analyses (FEA) were used to evaluate the macro temperature distribution in the CFPCR device and the micro temperature distribution along a single microchannel. At steady-state, the simulated CFPCR device had three discrete temperature zones, each with a uniform temperature distribution with a variation of +/-0.3 degrees C. An infrared (IR) camera was used to measure the steady-state temperature distribution in the prototype CFPCR and validated the simulation results. The temperature distributions along a microchannel at flow velocities from 0 mm/s to 6 mm/s were used to estimate the resulting temperatures of the DNA reagents in a single microchannel. A 500 bp DNA fragment was generated from a bacteriophage lambda-DNA target using 20 cycles of PCR. The amplification efficiencies compared to a commercial thermal cycler were 72.7% (2 mm/s), 44% (3 mm/s), and 29.4% (4 mm/s). The amplification efficiency with the modified CFPCR device increased by 363% at 2 mm/s and 440% at 3 mm/s compared to amplification obtained using a CFPCR device with the same fluidic layout, (Hashimoto et al., Lab Chip 4:638, 2004) strictly due to the improved temperature distribution.