Glass Channel Research Articles

Simulation of erosive smoothing in the abrasive jet micro-machining of glass

Abrasive jet micro-machining (AJM) is a promising technique to machine micro-features in brittle and ductile materials. However, the roughness of micro-channels machined using AJM is generally greater than that from other methods of micro-machining such as wet etching. Previous investigators have suggested that the surface roughness resulting from AJM can be reduced by post-blasting with abrasive particles at a relatively low kinetic energy. This approach was investigated in the present work by measuring the roughness reduction of a reference unmasked channel in borosilicate glass as a function of post-blasting particle size, velocity, dose, and impact angle. Post-blasting the reference channels reduced the roughness by up to 60%. It was observed that post-blasting at shallower angles was more efficient, probably due to the increased amount of edge chipping as opposed to cratering, which contributed to the enhanced removal of profile peaks, leaving a smoother surface. Moreover, post-blasting with smaller particles ultimately resulted in smoother surfaces, but at the penalty of requiring a relatively large particle dose, and consequently a significantly increased channel depth, before reaching the steady-state roughness. Hence, finishing with smaller particles until reaching the steady-state roughness may not be practical when a shallow channel is desired. A previously developed numerical model was modified and used to simulate the post-blasting process leading to the creation of smooth channels as a function of particle size, velocity, dose, impact angle, and target material properties. The model simulated both crater formation (due to growth of lateral cracks) and the chipping of facet edges. Comparisons with centerline roughness measurements for channels in borosilicate glass showed that the model can predict the transient roughness reduction with post-blasting particle dose with a 7% average error.

Efficient generation of ozone in arrays of microchannel plasmas

Ozone is produced efficiently in arrays of low-temperature, linear microplasmas having a trapezoidal or parabolic cross-sectional profile and generated within nanoporous alumina (Al2O3) microchannels. Fabricated from aluminum foil by wet chemical processing, micropowder ablation, and one photolithographic step, arrays of microchannel plasma devices 3 cm in length and 250 µm in width at the aperture of the channel produce spatially uniform glow discharges in O2 feedstock gas at a pressure of 1 atm and flow rates of 0.25–2.5 standard litres per minute. Several device and array structures, incorporating embedded electrodes and Al/Al2O3 or glass channels, have been fabricated and tested extensively. A design based solely on microchannels fabricated in nanoporous alumina, flanked by Al electrodes buried in the channel wall, is found to be superior in performance to other materials and geometries. Altering the electric field profile inside the microchannels (by means of the electrode geometry) is found to have a significant impact on the reactor efficiency. Ozone output is observed to scale linearly with the number of microchannels in the array and the feedstock gas flow rate. Efficiencies and O3 concentrations surpassing 85 g kWh−1 and 17 g m−3, respectively, have been measured, and arrays as large as 120 microchannels have been realized to date. The results presented here suggest a new approach to plasma-chemical reactors, one in which ‘massively parallel’ processing of one or more gases in non-streamer (glow) discharges efficiently produces products of commercial value in thousands of micropores or microchannels fabricated in recyclable and inexpensive materials. Reductions of an order of magnitude in the weight and volume of microplasma-based O3 reactors, relative to conventional dielectric barrier discharge technology, appear to be feasible.

Does Colloid Shape Affect Detachment of Colloids by a Moving Air–Water Interface?

Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

Characteristics of abrasive slurry jet micro-machining: A comparison with abrasive air jet micro-machining

Abrasive slurry jet micro-machining (ASJM) uses a well-defined jet of abrasive slurry to erode features in a solid target. Compared with abrasive water jet machining (AWJM), the present ASJM system operates at pressures that are roughly two orders of magnitude lower and uses a premixed slurry of relatively low concentration. The objective of the present study was to gain a better understanding of the mechanics of erosion in ASJM by comparing its performance in the micro-machining of holes and channels in borosilicate glass with that of abrasive air jet micro-machining (AJM), a process that is simpler and relatively well understood. A new ASJM system was developed and used to machine blind holes and smooth channels of relatively uniform depth that did not suffer from the significant waviness previously reported in the literature. The effect of particle velocity, particle concentration, jet traverse speed and jet impact angle were examined. A direct comparison of ASJM and AJM results was possible since novel measurements of the crushing strength of the aluminum oxide abrasive particles used in both experiments proved to be unaffected by water. Brittle erosion was shown to be the dominant material removal mechanism in both ASJM and AJM in spite of the significant flow-induced decrease in the local impact angles of many of the particles in ASJM. A new model of the rapid particle deceleration near the target surface helped explain the much smaller erosion rates of ASJM compared with those in AJM. The modeling of the erosion process during the micro-machining of channels showed that the effect of the local impact angle at the leading edge of the advancing jet was much more significant in ASJM than in AJM, primarily due to the narrower focus of the jet impact zone in ASJM. The differences in the water and air flow fields and associated particle trajectories were used to explain the steeper side walls and flatter bottoms of the holes and channels machined with unmasked ASJM compared to those with masked AJM. The respective structures of the water and air jets also explained the much sharper definition of the edges of these features using ASJM compared with maskless AJM. The results of the study show that ASJM can be used to accurately micro-machine channels and holes with a width of 350–500μm and an aspect ratio of 0.5–1.3 without the use of masks.

Micromachining of microfluidic channels in glass by microjoule femtosecond laser pulses

This study presents overlapping multiple pulse scanning, an alternative approach for forming the microfluidic channels in glass through the interaction of infrared femtosecond laser (FS-laser) irradiation with microjoule-energy pulses. The study employs a scanning-based laser system at a 1035nm wavelength with a pulse duration of 350fs and a repetition rate of 100kHz. In this work, the FS-laser pulses easily induced the dynamics of the optical breakdown process with the laser energy in glass. In addition, a single pulse generates an ablation crater with the irradiation pulse energy of 5@mJ. The study demonstrates that the beam profile, pulse overlap, accumulated fluence, and the number of pulses have the strongest influence on surface morphology to form microfluidic-channels. Herein the surface roughness can be improved to 287nm, and the pulse overlap is 75%. Furthermore, the study analyzes the incubation effect on the number of pulses and the accumulated fluence to confirm the validity of the process model for FS-laser ablation in glass. The technique is useful for prototyping the integrated microfluidic chips that have great potential applications for a lab-on-a-chip.

Ion-exchanged Tm^3+:glass channel waveguide laser

Continuous wave laser action around 1.9 μm has been demonstrated in a Tm(3+)-doped germanate glass channel waveguide laser fabricated by ion-exchange. Laser action was observed with an absorbed power threshold of only 44 mW and a slope efficiency of up to 6.8% was achieved. Propagation loss at the lasing wavelength was measured to be 0.3 dB/cm. We believe this to be the first ion-exchanged Tm(3+)-doped glass waveguide laser.

A ferrofluid inclinometer with a Time Domain Readout strategy

In this paper a tilt sensor exploiting the effect of the imposed tilt on a mass of ferrofluid free to slide along a glass channel is presented. The proposed inclinometer consists of a 10mm diameter pipe containing a 0.25ml of ferrofluid, an actuation coil to control the ferrofluid mass movement and two sensing coils to monitor its position. The actuation and the sensing coils are wound around the pipe and the length of the actuation/sensing system is 78mm.The novelty of this device, as respect to solutions already presented in the literature, consists in the conversion of the device tilt into the time elapsed between transitions of the ferrofluid mass in two fixed positions inside the channel. This Time Domain Readout strategy allows to implement a device with a frequency output which can be intended as the main advantage of the solution proposed.

Eu3+ and Sm3+ co-activated aluminum germanate glass channel waveguide as irradiation source for photodynamic therapy

A bright and compact orangish-red fluorescence trace is observed in an Eu3+/Sm3+ co-doped K+Na+ ion-exchanged aluminum germanate (NMAG) glass channel waveguide under excitation with a 488nm Ar+ laser. The excitation wavelength range and the emission intensity of Eu3+ in NMAG glass are remarkably improved by the sensitization of Sm3+, and the energy transfer probability and efficiency are calculated to be 151.2s−1 and 25.3%, respectively. Meanwhile, the energy transferred from Sm3+ can be efficiently utilized to generate intense fluorescence of Eu3+ due to the large spontaneous emission probabilities of the Eu3+: 5D0→7FJ (J=1, 2, and 4) transitions that reach up to 68.9, 364.7, and 152.6s−1, respectively. Enhanced fluorescence in the Eu3+/Sm3+-doped NMAG glass channel waveguide, which matches the excitation band of most photosensitizers, holds great promise for photodynamic therapy.

White upconversion luminescence in Tm3+/Ho3+/Yb3+ triply doped K+–Na+ ion-exchanged aluminum germanate glass channel waveguide

Rare-earth ions doped K+–Na+ ion-exchanged aluminum germanate (NMAG) glass channel waveguides have been designed and fabricated. Under 980nm laser pumping, an intense upconversion white light transmission trace was observed in Tm3+/Ho3+/Yb3+ triply doped NMAG glass channel waveguide and a high-brightness light spot was achieved from the output end of the fiber connected to the waveguide channel. The fluorescent colors were diverse and located within or near the white region in CIE chromaticity diagram under various pumping powers. These admirable results indicate that Tm3+/Ho3+/Yb3+ triply doped NMAG channel waveguide is a promising light source for medical and high-precision processing illumination.

Diode-pumped femtosecond solid-state waveguide laser with a 49 GHz pulse repetition rate

We report on the first demonstration of a passively mode-locked, diode-pumped, monolithic Yb:glass channel waveguide laser that incorporates a semiconductor saturable absorber mirror. Stable and self-starting mode-locking is achieved in a Fabry-Perot cavity configuration producing a pulse repetition rate up to 4.9 GHz. The shortest pulse duration of 740 fs is generated with 30 mW of average output power at a center wavelength of 1058 nm. A maximum output power of 81 mW is produced during mode-locking with corresponding pulse duration of 800 fs.

Optical amplification of Pr^3+-doped ZBLA channel waveguides for visible Laser emission

We report on the first observation of optical signal amplification in the visible range into praseodymium doped ZBLA glass channel waveguides obtained by ion exchange. Up to 30% signal amplification was obtained at 639 nm. This result shows the potential of rare earth doped fluoride glasses in the form of channel waveguides for integrated solid state visible laser sources.

Effect of PVP on the electroosmotic mobility of wet‐etched glass microchannels

We present an experimental study on the effect of polymer PVP on EOF mobility of microchannels wet etched into optical white soda lime glass, also known as Crown glass. We performed experiments to evaluate the effect of PVP concentration and pH on EOF mobility. We used on-chip capillary zone electrophoresis and a neutral fluorescent dye as a passive marker to quantify the electroosmotic flow. We performed experiments under controlled conditions by varying pH from 5.2 and 10.3 and concentration of PVP from 0 to 2.0% w/w at constant ionic strength (30 mM). Our experiments show that PVP at concentrations of 1.0% or above very effectively suppress EOF at low pH (6.6). At high pH of 10.3, PVP has a much weaker suppressing effect on EOF and increasing its concentration above about 0.5% showed negligible effect on EOF mobility. Finally, we briefly discuss the effects of pH on using PVP as an adsorbed coating. Our experiments provide useful guidelines on choosing correct pH and concentration of PVP for effective EOF suppression in glass channels.

Determination of the Néel temperature from measurements of the thermal conductivity of the Co3O4 antiferromagnet nanostructured in porous glass channels

The Neel temperature T N(n) of the Co3O4 antiferromagnet nanostructured in channels of porous borosilicate glass with channel cross sections of ∼7 nm has been determined from thermal conductivity measurements. It has been shown that the Neel temperature T N(n) of this nanomaterial is approximately equal to 20 K, which is considerably lower than T N = (30–40) K for the bulk Co3O4 sample.

Attenuated Total Reflection-Infrared Nanofluidic Chip with 71 nL Detection Volume for in Situ Spectroscopic Analysis of Chemical Reaction Intermediates

We present a micromachined silicon attenuated total reflection-infrared (ATR-IR) crystal with integrated nanofluidic glass channels which enables infrared spectroscopic studies with only 71 nL sample volume. Because of the short path length through silicon, the system allows IR spectroscopy down to 1200 cm(-1), which covers the typical fingerprint region of most organic compounds. To demonstrate proof-of-principle, the chip was used to study a Knoevenagel condensation reaction between malononitrile and p-anisaldehyde catalyzed by different concentrations of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in solvent acetonitrile. By in situ measurement, it was demonstrated for the first time that at certain concentrations of DBU, reaction intermediates become stabilized, an effect that slows down or even stops the reaction. This is thought to be caused by increased ionic character of the solvent, in which protonated DBU stabilizes the intermediates. This clearly demonstrates that infrared mechanistic studies of chemical reactions are feasible in volumes as little as 71 nL.

Fabrication of three-dimensional microfluidic channels inside glass using nanosecond laser direct writing

We show that fabrication of three-dimensional microfluidic channels embedded in glass can be achieved by using a Q-switched, frequency-doubled Nd:YAG laser. The processing mainly consists of two steps: (1) formation of hollow microfluidic channels in porous glass immersed in Rhodamine 6G dissolved in water by nanosecond laser ablation; and (2) postannealing of the fabricated porous glass sample at 1120 °C for consolidation of the sample. In particular, a bilayer microfluidic structure is created in glass substrate using this technique for showcasing its capability of three-dimensional structuring.

Surface acoustic wave-induced precise particle manipulation in a trapezoidal glass microfluidic channel

Surface acoustic wave (SAW) excitation of an acoustic field in a trapezoidal glass microfluidic channel for particle manipulation in continuous flow has been demonstrated. A unidirectional interdigital transducer (IDT) on a Y-cut Z-propagation lithium niobate (LiNbO3) substrate was used to excite a surface acoustic wave at approximately 35 MHz. An SU8 layer was used for adhesive bonding of the superstrate glass layer and the substrate piezoelectric layer. This work extends the use of SAWs for acoustic manipulation to also include glass channels in addition to prior work with mainly poly-di-methyl-siloxane channels. Efficient alignment of 1.9 µm polystyrene particles to narrow nodal regions was successfully demonstrated. In addition, particle alignment with only one IDT active was realized. A finite element method simulation was used to visualize the acoustic field generated in the channel and the possibility of 2D alignment into small nodal regions was demonstrated.

Characterisation and comparison of microfluidic chips formed using abrasive jet micromachining and wet etching

The electro-osmotic flow limit of detection and separation efficiency of glass channels machined using abrasive jet micromachining (AJM) were measured and compared with those for channels machined using conventional wet etching with hydrofluoric acid. It was found that the electro-osmotic mobility in AJM channels was similar to that in wet-etched channels, ∼4 × 10−4 cm2 V−1 s−1 for 20 µm channels, despite a two-decade difference in surface roughness. Similarly, limits of detection measured on the two types of chips were roughly comparable to each other and on the order of 1 nM (injected sample concentration). The separation efficiency calculated from TAMRA dye injections in AJM channels, however, was found to be significantly lower, ∼0.2–0.25 times, than that in wet-etched channels. The effect of surface roughness on the separation efficiency and electro-osmotic mobility in micro-channels is discussed in the context of the literature. Furthermore, experimental data concerning the effect of the AJM process conditions on the surface roughness are presented and discussed with the aim of exploring methods to improve surface quality in AJM. Commercially available self-adhesive elastomeric masks were found to be particularly suitable for rapid prototyping as they provided reasonably high resolution and machining flexibility.

Sm^3+-doped germanate glass channel waveguide as light source for minimally invasive photodynamic therapy surgery

In Sm(3+)-doped K(+)-Na(+) ion-exchanged aluminum germanate (NMAG) glass channel waveguide, a clear and compact red amplified spontaneous emission (ASE) trace is observed under the excitation of a 488nm Ar(+) laser. 78% photons of ASE fluorescence in visible region are demonstrated to be located in 600-730nm wavelength range. High-directivity and high-brightness ASE fluorescence of Sm(3+)-doped NMAG glass channel waveguide, which matches the excitation band of most photosensitizers (PS) currently used in photodynamic therapy (PDT) or clinical trials, has promising potential application as an excitation light source for PDT treatment.

A Ferrofluid Inclinometer with a Time Domain Readout Strategy

In this paper a tilt sensor exploiting the effect of the imposed tilt on a ferrofluid drop free to move inside a glass channel is presented. The proposed inclinometer consists of a 10 mm diameter pipe containing a 0.25 ml of ferrofluid, an actuation coil to control the ferrofluid mass movement and two sensing coils to monitor the mass position. The actuation and the sensing coils are wound around the pipe and the length of the actuation/sensing system is 78 mm. The novelty of this device, as respect to solutions already presented in the literature, consists in the conversion of the device tilt into the time elapsed between transitions of the ferrofluid mass in two fixed positions inside the channel. This time domain readout strategy allows to implement a digital form of the device output which can be intended as the main advantage of the solution proposed.

Formation of slab waveguides in eulytine type BGO and CaF2 crystals by implantation of MeV nitrogen ions

Ion implantation, compared with other waveguide fabrication methods, has some unique advantages. It has proved to be a universal technique for producing waveguides in most optical materials. The authors of the present article reported fabrication of channel and slab waveguides in an Erbium-doped tungsten tellurite glass by implantation of MeV energy N+ ions. The present article reports successful adaptation of the same technique to the fabrication of slab waveguides in eulytine type bismuth germanate (BGO) and CaF2 crystals. This is the first report on successful waveguide fabrication in these materials using 3.5MeVN+ ions at implanted fluences between 5×1015 and 4×1016ions/cm2. Spectroscopic ellipsometric measurements revealed the existence of guiding structures in both materials. M-line spectroscopic measurements indicated guiding effect in the as-implanted BGO up to 1550nm and up to 980nm in the as-implanted CaF2. Ion implantation induced the appearance of three peaks in the UV/Vis absorption spectrum of CaF2, that can be attributed to colour centres.