Glass Pillars Research Articles

Study on stochastic nature of plasticity of Cu/Zr metallic glass micropillars

Abstract Micro-sized metallic glass pillars with a diameter ranging 2.5∼7.5 μm were subjected to compression experiments using a nanoindentation tester equipped with a flat punch, to characterize their deformation behaviors. The strain-stress response and scattering mechanical properties were studied in statistics. The intermittent and trigger-aftershock shear avalanches exhibited a stochastic nature of plasticity of metallic glass specimens under microscale. The size distribution of strain bursts versus the stress where they occurred indicated the flow dynamics as a self-organized behavior with collective motion of multiple shear bands, and the maximum burst size increased with applied stress following in a power-law manner independent of burst order and pillar size. According to the experimental observation, universal features were proposed to characterize the current jerky deformation, meanwhile a Monte Carlo simulation method was developed to predict the stochastic plasticity of metallic glass under microscale.

Tunable Three-Dimensional Plasmonic Arrays for Large Near-Infrared Fluorescence Enhancement.

Metal-enhanced fluorescence (MEF), resulting from the near-field interaction of fluorophores with metallic nanostructures, has emerged as a powerful tool for dramatically improving the performance of fluorescence-based biomedical applications. Allowing for lower autofluorescence and minimal photoinduced damage, the development of multifunctional and multiplexed MEF platforms in the near-infrared (NIR) windows is particularly desirable. Here, a low-cost fabrication method based on nanosphere lithography is applied to produce tunable three-dimensional (3D) gold (Au) nanohole-disc arrays (Au-NHDAs). The arrays consist of nanoscale glass pillars atop nanoholes in a Au thin film: the top surfaces of the pillars are Au-covered (effectively nanodiscs), and small Au nanoparticles (nanodots) are located on the sidewalls of the pillars. This 3D hole-disc (and possibly nanodot) construct is critical to the properties of the device. The versatility of our approach is illustrated through the production of uniform and highly reproducible Au-NHDAs with controlled structural properties and tunable optical features in the NIR windows. Au-NHDAs allow for a very large NIR fluorescence enhancement (more than 400 times), which is attributed to the 3D plasmonic structure of the arrays that allows strong surface plasmon polariton and localized surface plasmon resonance coupling through glass nanogaps. By considering arrays with the same resonance peak and the same nanodisc separation distance, we show that the enhancement factor varies with nanodisc diameter. Using computational electromagnetic modeling, the electric field enhancement at 790 nm was calculated to provide insights into excitation enhancement, which occurs due to an increase in the intensity of the electric field. Fluorescence lifetime measurements indicate that the total fluorescence enhancement may depend on controlling excitation enhancement and therefore the array morphology. Our findings provide important insights into the mechanism of MEF from 3D plasmonic arrays and establish a low-cost versatile approach that could pave the way for novel NIR-MEF bioapplications.

Micro-thermoelectric generators based on through glass pillars with high output voltage enabled by large temperature difference

Micro-thermoelectric generators can convert low-grade waste heat to electrical power and have potential applications in wearable electronics, wireless sensors, medical devices and so on. It is challenging to increase the output voltage and power of the cross-plane micro-thermoelectric generators, because their thermoelectric legs are short and a large temperature difference cannot be established on the devices. In this work, we fabricate a micro-thermoelectric generator based on Bi2Te3 and Sb2Te3 through glass pillars with a length of 200 μm. These thermoelectric pillars are electrodeposited in the through holes of glass templates, and the glass templates are used to support the pillars. A temperature difference of 138 K is successfully established for the thermoelectric generator with 4 thermocouples. The maximum output voltage of the device is 40.89 mV under a temperature difference of 138 K; each thermocouple delivers a voltage of 10.22 mV. The maximum output power of the device is 19.72 μW. Both the temperature difference and the output voltage per thermocouple are the largest for the cross-plane micro-thermoelectric generators based on thin-film deposition technologies in the literature. In addition, finite element modeling is carried out to study the effects of the length and coverage rate of the thermoelectric pillars on the performance of the thermoelectric generators. Both the experimental and simulation data show that it is an effective way to enhance the temperature difference and output voltage of cross-plane micro-thermoelectric generators using through glass pillars.

Fabrication and characterization of Au dimer antennas on glass pillars with enhanced plasmonic response

AbstractWe report on the fabrication and dark-field spectroscopy characterization of Au dimer nanoantennas placed on top of SiO2 nanopillars. The reported process enables the fabrication of nanopillar dimers with gaps down to 15 nm and heights up to 1 μm. A clear dependence of the plasmonic resonance position on the dimer gap is observed for smaller pillar heights, showing the high uniformity and reproducibility of the process. It is shown how increasing the height of nanopillars significantly affects the recorded elastic scattering spectra from Au nanoantennas. The results are compared to finite-difference time-domain (FDTD) and finite-element method (FEM) simulations. Additionally, measured spectra are accompanied by dark-field microscopy images of the dimers, showing the pronounced change in color. Placing nanoantennas on nanopillars with a height comparable to the in-plane dimer dimensions results in an enhancement of the scattering response, which can be understood through reduced interaction of the near-fields with the substrate. When increasing the pillar height further, scattering by the pillars themselves manifests itself as a strong tail at lower wavelengths. Additionally, strong directional scattering is expected as a result of the interface between the nanoantennas and nanopillars, which is taken into account in simulations. For pillars of height close to the plasmonic resonance wavelength, the scattering spectra become more complex due to additional scattering peaks as a result of larger geometrical nonuniformities.

Fabrication of High Aspect Ratio SiO2and Tempax Glass Pillar Structures and Its Application for Optical Modulator Device

This paper presents the fabrication of deep SiO2 and Tempax glass pillar structures by using reactive ion etching system, which intends to realize optical modulator mounted on an image sensor. The optical modulator consists of high aspect ratio SiO2 or Tempax glass pillars that can modulate the transmitted light intensity by moving a liquid in and out of the spaces between pillars based on the reversible electrowetting of liquid on top of micro-pillars surfaces. SiO2 pillars having smooth surfaces, vertical shapes, and high aspect ratio of 12 with a depth of 12 $\mu \text{m}$ , diameter of 1 $\mu \text{m}$ , and the pitch of the two pillars of $2~\mu \text{m}$ has been achieved. In addition, Tempax glass pillar structures are also successfully fabricated under investigation of gas mixtures of SF6 and O2. Finally, a 7.2 mm $\times \,\, 9.6$ mm optical window area integrated with an image sensor for an optical modulator has been demonstrated where high transmission modulation together with a large contrast has been observed of approximately 65% and 0.86 for cases with and without matching oil penetration, respectively. [2016-0036]

Enhanced plasticity of bulk metallic glass in different aspect ratios via laser shock peening with multiple impacts

In this study laser shock peening (LSP) with multiple laser impacts was used to improve the mechanical properties especially the plasticity of Zr35Ti30Cu8.25Be26.75 bulk metallic glass (BMG) pillars in two aspect ratios (1:1 and 2:1). It was found that, with increasing laser impacts up to 5, the compression plastic strain of BMG pillar with aspect ratio of 1:1 increased from 0 to 1.48% and the compression strength increased significantly from 1569MPa to 1721MPa. With further laser impacts beyond 5, the changes in the plasticity and the compression strength were observed to be insignificant. Considering the effect of sample geometry at the same laser impacts, it could be concluded that the BMG pillars with smaller aspect ratio of 1:1 had better mechanical properties than that of the lager BMG pillars with aspect ratio of 2:1. Besides, the elastic strain limit of BMG pillars with LSP was not only independent of the laser impacts, but also irrelevant to the aspect ratio. At last, we discussed the reason for the increase of plasticity in view of the creation of excess free volume during LSP.

An Investigation of Processes for Glass Micromachining.

This paper presents processes for glass micromachining, including sandblast, wet etching, reactive ion etching (RIE), and glass reflow techniques. The advantages as well as disadvantages of each method are presented and discussed in light of the experiments. Sandblast and wet etching techniques are simple processes but face difficulties in small and high-aspect-ratio structures. A sandblasted 2 cm × 2 cm Tempax glass wafer with an etching depth of approximately 150 µm is demonstrated. The Tempax glass structure with an etching depth and sides of approximately 20 μm was observed via the wet etching process. The most important aspect of this work was to develop RIE and glass reflow techniques. The current challenges of these methods are addressed here. Deep Tempax glass pillars having a smooth surface, vertical shapes, and a high aspect ratio of 10 with 1-μm-diameter glass pillars, a 2-μm pitch, and a 10-μm etched depth were achieved via the RIE technique. Through-silicon wafer interconnects, embedded inside the Tempax glass, are successfully demonstrated via the glass reflow technique. Glass reflow into large cavities (larger than 100 μm), a micro-trench (0.8-μm wide trench), and a micro-capillary (1-μm diameter) are investigated. An additional optimization of process flow was performed for glass penetration into micro-scale patterns.

Sample size effects on strength and deformation mechanism of Sc75Fe25 nanoglass and metallic glass

The mechanical properties and deformation mechanism of Sc75Fe25 nanoglass and Sc75Fe25 metallic glass pillars with diameter from 2μm to 95nm were investigated by means of ex-situ and in-situ compression tests. The results showed that the yield strength and deformation mechanism in the metallic glass were size-dependent while these in the nanoglass were not. It is suggested that the reduced shear band nucleation sites in metallic glass with decreasing sample size results in the increased yield strength and transition of deformation mode. In contrast, the glass/glass interfaces in nanoglass which have reduced density could serve as shear band nucleation sites and therefore promote multiple shear banding.

Design principles for superamphiphobic surfaces

To predict the properties of superamphiphobic layers we analyzed the wetting of a square and a hexagonal array of vertical pillars composed of spheres (radius R) partially sintered together. Apparent contact angles above 150° are obtained by pinning of a non-polar liquid surface at the underside of the top sphere resulting in a Fakir or Cassie state. Analytical equations are derived for the impalement pressure in the limiting case A0 ≫ R2, where A0 is the area of the regular unit cell containing a single pillar. The case of close pillars is investigated numerically. By balancing forces at the rim of a drop, we calculate the apparent receding contact angle. To describe drag reduction of a flowing liquid we calculate the apparent slip length. When considering pressure-induced flow through cylindrical capillaries of radius rc, significant drag reduction occurs only for thin capillaries. The mechanical stability with respect to normal forces and shear is analyzed. Nanoscopic silica glass pillars would be able to sustain the normal and shear stresses caused by capillary and drag forces. For a high impalement pressure and good mechanical stability A0 should be small and R (respectively the neck diameter) should be large, whereas a large A0 and a small R imply low contact angle hysteresis and high slip length.

Intrinsic size effects in the mechanical response of taper-free nanopillars of metallic glass

Both quantitative stress-strain curves and in situ transmission electron microscope observations demonstrate intrinsically strong sample size effects on the deformation mode of taper-free metallic glass pillars. With the pillar diameter gradually decreasing from 640 to 70 nm, the deformation mode evolves from (i) highly localized and catastrophic shear banding to, (ii) initially nonlocalized deformation developing toward stop-and-go shear banding accompanied by softening, (iii) apparently homogeneous and banding-less deformation but with intermittent shear events, and eventually (iv) fully homogeneous and smooth plastic flow.

A statistical physics consideration about the strength of small size metallic glass pillars

We have fabricated micro-/nano- pillars of a Zr-based metallic glass, Zr50Ti16.5Cu15Ni18.5, with pillar tip diameters ranging from ~750 nm to ~110 nm. These pillars were mechanically tested quantitatively in-situ in a Transmission Electron Microscope (TEM). Due to a slight tapering of ~3°, the deformation accommodated with shear bands is driven downwards from the top. However, the real time monitoring of shear bands evolution in-situ in TEM makes it possible to measure the effective load-bearing diameter, i.e., the diameter ahead of the most forefront shear band, which enables the precise measurement of yield strength of these pillars. Consequently, it turns out that the yield strength is essentially size independent and close to the bulk value. Statistical physics description of strength of small size metallic glasses is discussed, and it is concluded that Weibull Statistics is inappropriate in describing strength of metallic glasses at micro and nano length scales.

Advances in transmission electron microscopy: In situ straining and in situ compression experiments on metallic glasses

In the field of transmission electron microscopy (TEM), fundamental and practical reasons still remain that hamper a straightforward correlation between microscopic structural information and deformation mechanisms in materials. In this article, it is argued that one should focus in particular on in situ rather than on postmortem observations of the microstructure. This viewpoint has been exemplified with in situ straining and in situ compression studies on metallic glasses. In situ TEM straining of amorphous metals permits an evaluation of the thickness of the liquid-like layer (LLL) formed because of heat evolution after shear band development. The experimental evaluation confirms that the thickness of a LLL present at the last moment of fracture substantially exceeds the generally accepted thickness of a shear band. In situ TEM and in situ SEM compression experiments on metallic glass pillars lead to the conclusion that smaller sized pillars deform more homogeneously than larger sized pillars.

In-situ TEM investigation of deformation behavior of metallic glass pillars

AbstractWe show results of in situ TEM (Transmission electron microscope) quantitative investigations on the compression behaviors of amorphous micropillars fabricated by focused ion beam from Cu47Ti33Zr11Ni6Sn2Si1 metallic glass (MG) ribbon. Pillars with well defined gauge sections and tip diameter ranging from 100 nm to 640 nm are studied. Quantitative compression tests were performed by a recently developed Picoindenter TEM holder, with the evolution of individual shear bands monitored in real time in TEM. It is found that the deformation of the MG pillars at the present size domain is still dominated by discrete shear banding as demonstrated by intermittent events in the load-displacement curves. However, the frequency, amplitude and distribution of these shear banding events are clearly size dependent at submicrometer scale, leading to an apparently transition in deformation mode from highly localized inhomogeneous deformation to less localized and more distributed deformation with decreasing pillars diameter. Deformation of a 105 nm diameter pillar having rounded tips is characterized with fully homogeneous bulge at the initial stage of deformation, indicating prompting effect of multi-axial stress state on transition to fully homogeneous deformation.

Plastic flow and failure resistance of metallic glass: Insight fromin situcompression of nanopillars

We report in situ nanocompression tests of Cu-Zr-Al metallic glass (MG) pillars in a transmission electron microscope. This technique is capable of spatially and temporally resolving the plastic flow in MGs. The observations reveal the intrinsic ability of fully glassy MGs to sustain large plastic strains, which would otherwise be preempted by catastrophic instability in macroscopic samples and conventional tests. The high ductility in volume-limited MGs and the sample size effects in suppressing the rapid failure common to MGs are analyzed by modeling the evolution of the collectivity of flow defects toward localization.

Formation of Nanoporous Glass Layer

Porous layers have been formed in Pyrex glass by reactive ion etching (RIE). Chromium is used as an etch mask. Different etch gases (SF6, CF4/Ar) have been used, and depending on flow ratio, etch time and applied power, a dense array of high aspect ratio glass pillars with submicrometer dimensions was obtained instead of a smooth channel bottom. The pillars were about 500nm tall and 50–100nm in cross-section. The formation of porous layers is explained by the effect of mask material re-deposition during the plasma etching. Porous glass layers could have applications in chromatographic separations or microchemicalsample concentrators.

Solid-state storage display panel

A flat solid-state storage display panel has been designed for a variety of applications. Construction, which is of inorganic material, involves multiple feedback cells composed of cadmium sulfide coated glass pillars mounted on a flat electroluminescent panel. The final assembly can be subjected to high temperatures (650°C). Present geometries with resolution of 16 lines to the inch are photo-reproduced by a method suitable for large displays. Triggering of individual cells has been accomplished with light pulses as short as 25 microseconds and with electron beams. In certain ranges of operating parameters an interesting variable-duration storage is observed. Stable operation has been maintained over a period of several months.