Pillar Height Research Articles

Fluidic Force Microscopy and Atomic Force Microscopy Unveil New Insights into the Interactions of Preosteoblasts with 3D‐Printed Submicron Patterns (Small 2/2023)

Interactions of Preosteoblasts Physical patterns are potential surface cues for promoting osteogenic differentiation of stem cells and improving osseointegration of orthopedic implants. Fluidic force microscopy and atomic force microscopy are used to quantitatively investigate the early interaction of preosteoblasts with 3D-printed patterns having different pillar heights and osteogenic properties. The study explains the differential cell adhesion behaviour induced by different pillar heights, enabling advancements in the rational design of osteogenic patterns. More details can be found in article number 2204662 by Livia Angeloni, Murali K. Ghatkesar, Lidy E. Fratila-Apachitei, and co-workers.

Influence of rheology and micropatterns on spreading, retraction and fingering of an impacting drop.

Rheology and surface microstructure affect many drop impact processes, including in emerging printing and patterning applications. This study reports on experiments systematically addressing the influence of these parameters on drop impacts. The experiments involved drop impacts of water, glycerol, and shear-thinning carbopol solutions on ten different microstructured surfaces, captured using high-speed photography. The impact Weber number (We) was varied from 70 to 350, and the microstructures consisted of 20 μm wide pillars with circular and square cross sections arranged in square arrays. The data focus on maximum spreading, retraction rates, threshold conditions for asymmetric (non-circular) spreading, and fingers protruding from the spreading rim. The extent of spreading was reduced by the presence of micropillars, and was well-explained using a hybrid scaling model. The drop retraction rate () showed moderate agreement with the inertial regime scaling  ∝ We-0.50, but did decrease with effective viscosity. Retraction was slower when the contact line was pinned on surfaces that were flat or had relatively tall or closely-spaced pillars, and was disrupted by drop break-up at We ≳ 250 for low-viscosity fluids. Impact velocities at the onset of asymmetric spreading had weak dependence on viscosity. Fingers were more numerous for greater We, lower effective viscosity, lower pillar height, and for pillars with square cross-sections. Fingers were favoured in directions parallel to the rows of the pillar array, especially near the onset of finger formation. Consistent comparisons between Newtonian and non-Newtonian fluids were enabled by calculating an effective Reynolds number.

A novel ferroelectric nanopillar multi-level cell memory

In this work, we present a novel multi-level non-volatile memory (NVM) device where ferroelectric (FE) nanopillars are embedded in a dielectric (DE) medium. Using our in-house 3D phase field simulator developed to treat the FE–DE composite system stably, we demonstrate that n FE nanopillars can generate more than 2n states, enabling high storage capacity. The multistates of the pillar array device are attributed to the depolarization field modulation with the pillar height and the multi-domain topological states of nanoscale FE structures.

Design and Analysis of the Capacitive RF MEMS Switches with Support Pillars.

Conventional parallel capacitive RF MEMS switches have a large impact during the suction phase. In general, RF MEMS switches have to be switched on and off in a considerably fast manner. Increasing the driving voltage enables fast switching but also increases the impact force, which causes the beam membrane to be prone to failure. In the present study, the addition of two support pillars was proposed for slowing down the fall of the beam membrane based on the conventional RF MEMS parallel switch, so as to reduce the impact velocity. As such, a novel RF MEMS switch was designed. Further, simulation software was used to scan and analyze the positioning and height of the support pillars with respect to electromechanical and electromagnetic performance. The simulation results show that the optimal balance of impact velocity and pull-in time was achieved at a height of 0.8 um, a distance of 10 um from the signal line, and an applied voltage of 50 V. The impact velocity was reduced from 1.8 m/s to 1.1 m/s, decreasing by nearly 40%. The turn off time increased from 3.9 us to 4.2 us, representing an increase of only 0.05%. The insertion loss was less than 0.5 dB at 32 GHz, and the isolation was greater than 50 dB at 40 GHz.

Fluidic Force Microscopy and Atomic Force Microscopy Unveil New Insights into the Interactions of Preosteoblasts with 3D-Printed Submicron Patterns.

Physical patterns represent potential surface cues for promoting osteogenic differentiation of stem cells and improving osseointegration of orthopedic implants. Understanding the early cell-surface interactions and their effects on late cellular functions is essential for a rational design of such topographies, yet still elusive. In this work, fluidic force microscopy (FluidFM) and atomic force microscopy (AFM) combined with optical and electron microscopy are used to quantitatively investigate the interaction of preosteoblasts with 3D-printed patterns after 4 and 24h of culture. The patterns consist of pillars with the same diameter (200nm) and interspace (700nm) but distinct heights (500 and 1000nm) and osteogenic properties. FluidFM reveals a higher cell adhesion strength after 24h of culture on the taller pillars (32 ± 7kPa versus 21.5 ± 12.5kPa). This is associated with attachment of cells partly on the sidewalls of these pillars, thus requiring larger normal forces for detachment. Furthermore, the higher resistance to shear forces observed for these cells indicates an enhanced anchorage and can be related to the persistence and stability of lamellipodia. The study explains the differential cell adhesion behavior induced by different pillar heights, enabling advancements in the rational design of osteogenic patterns.

Comparison of laser micro-inscribed pillars on flat versus tilted substrates

When laser micromachining is performed at a non-zero angle of incidence, it is possible to fabricate microstructures with tilted sidewalls that could not be achieved using a perpendicular beam. In this report, we examine the influence of the angle of incidence (0–70°), feature size and spacing (10–150 µm), lens focal length (25 and 100 mm), and spot radius (15–50 µm) on the minimum achievable feature width (\(W_{{{\text{half}}}}\)) of periodic arrays of square micropillars. A new empirical model is developed that is applicable to both flat and tilted substrates, and accurately predicts the pillar height as a function of the feature width. By comparing structures inscribed at different tilt angles, we found that when the angle of incidence is increased \(W_{{{\text{half}}}}\) also rises, such that it becomes more difficult to fabricate thin microstructures on angled substrates. Based on this knowledge, we establish a correlation that predicts \(W_{{{\text{half}}}}\) as a function of the angle of incidence and the beam’s spot radius. Therewith, we can predict the minimum feature width that can be achieved over a wide range of laser processing parameters, with an average error of only 4.5% within the bounds of this investigation. Finally, by testing lenses with different focal lengths, we found that a shorter focal length reduces \(W_{{{\text{half}}}}\) (improves the spatial resolution) when the angle of incidence is zero, but increases \(W_{{{\text{half}}}}\) when the angle of incidence is high. We attribute this discrepancy to the angular spread of the beam cone, which can interact significantly with adjacent pillars, leading to degradation of the intended microstructure and a reduction in pillar height.

Micropillar Compression of Additively Manufactured 316L Stainless Steels after 2 MeV Proton Irradiation: A Comparison Study between Planar and Cross-Sectional Micropillars

A micropillar compression study with two different techniques was performed on proton-irradiated additively manufactured (AM) 316L stainless steels. The sample was irradiated at 360 °C using 2 MeV protons to 1.8 average displacement per atom (dpa) in the near-surface region. A comparison study with mechanical test and microstructure characterization was made between planar and cross-sectional pillars prepared from the irradiated surface. While a 2 MeV proton irradiation creates a relatively flat damage zone up to 12 µm, the dpa gradient by a factor of 2 leads to significant dpa uncertainty along the pillar height direction for the conventional planar technique. Cross-sectional pillars can significantly reduce such dpa uncertainty. From one single sample, three cross-sectional pillars were able to show dpa-dependent hardening. Furthermore, post-compression transmission electron microscopy allows the determination of the deformation mechanism of individual micropillars. Cross-sectional micropillar compression can be used to study radiation-induced mechanical property changes with better resolution and less data fluctuation.

Shape dependence of all-dielectric terahertz metasurface.

All-dielectric metasurfaces have been attracting attention in the terahertz spectral range for low-loss planar optical elements such as lenses, beam splitters, waveplates, vortex plates, and magnetic mirrors. Various shapes of meta-atoms have been used in many studies; however, no systematic comparative study of each shape has been reported. The optical properties of various shapes of metasurfaces are reported in this work using finite difference time domain simulation. The phase of a pillar-type all-dielectric metasurface is mainly determined by the cross-sectional area, rather than its detailed shape. Consequently, in the square lattice geometry, the square shape meta-atom performs best in terms of full phase control at the lowest pillar height with negligible polarization dependence. Furthermore, we compare the transmission, phase, and polarization dependence of the hexagonal and square lattices. Square-shape metasurface successfully realizes subwavelength focusing metalens and vortex plate.

Shortwave infrared single-pixel spectral imaging based on a GSST phase-change metasurface.

Shortwave infrared (SWIR) spectral imaging obtains spectral fingerprints corresponding to overtones of molecular vibrations invisible to conventional silicon-based imagers. However, SWIR imaging is challenged by the excessive cost of detectors. Single-pixel imaging based on compressive sensing can alleviate the problem but meanwhile presents new difficulties in spectral modulations, which are prerequisite in compressive sampling. In this work, we theoretically propose a SWIR single-pixel spectral imaging system with spectral modulations based on a Ge2Sb2Se4Te1 (GSST) phase-change metasurface. The transmittance spectra of the phase-change metasurface are tuned through wavelength shifts of multipole resonances by varying crystallinities of GSST, validated by the multipole decompositions and electromagnetic field distributions. The spectral modulations constituted by the transmittance spectra corresponding to the 11 phases of GSST are sufficient for the compressive sampling on the spectral domain of SWIR hyperspectral images, indicated by the reconstruction in false color and point spectra. Moreover, the feasibility of optimization on phase-change metasurface via coherence minimization is demonstrated through the designing of the GSST pillar height. The concept of spectral modulation with phase-change metasurface overcomes the static limitation in conventional modulators, whose integratable and reconfigurable features may pave the way for high-efficient, low-cost, and miniaturized computational imaging based on nanophotonics.

A Case Study on Deformation Failure Characteristics of Overlying Strata and Critical Mining Upper Limit in Submarine Mining

Unlike land mining, the safety of seabed mining is seriously threatened by an overlying water body. In order to ensure the safety of subsea mining projects, it is of great importance to understand the failure characteristics and influencing factors of overlying strata deformation. Focusing on the Sanshandao Gold Mine, a typical submarine deposit in China, geomechanical model testing and numerical simulations were carried out. The results show that in the mining of a steeply dipping metal ore body, subsidence deformation mainly occurs on the hanging wall; the subsidence center is located on the surface of the hanging wall, and the uplift center is located on the upper surface of the ore body. The critical mining upper limit, which represents the minimum thickness of the reserved isolation pillar between the overlying seawater and the goaf, was determined to be 50 m in the Xinli mine; fault slip would occur if this critical value was exceeded. The dip angle and thickness of the ore body were negatively correlated with the vertical surface deformation. As the dip angle and thickness increased, the critical upper mining limit increased. When the fault was located in the footwall, the critical upper mining limit increased as the distance between the fault and the ore body increased, and the failure mode of the goaf was fault slip. When the fault was located in the hanging wall, the final failure mode of the goaf changed to a combined failure mode of overlying rock collapse as well as fault slip. These research results provide a theoretical basis for the selection of the reserved pillar height in the Xinli mining area, as well as a reference for safe mining practices under similar geological conditions.

Dropwise condensation on single-micro-scale roughness hydrophobic surfaces

Dropwise condensation (DWC) usually occurs on superhydrophobic surfaces with dual-scale (or multi-scale) roughness in discrete droplets to avoid liquid film formation, enhancing overall heat transfer efficiency. In this study, we demonstrate that the dual-scale roughness hydrophobic surface is not a necessary condition for DWC to occur. A series of single-scale roughness surfaces of regular arrays of square micro-pillars are fabricated to investigate the effect of surface roughness on the wetting behavior of condensed droplets and DWC. A sequence of the wetting behavior of condensed water droplets larger than 200 μm in diameter on single-scale roughness hydrophobic surfaces: Wenzel state → Cassie state → partial Cassie (Cassie-Wenzel mixed) state → Wenzel state (with the irregular shape of three-phase-contact-line) is observed along with increasing surface roughness (pillar height). An in-house design inverted microscopy system is applied for further confirmation of the wetting behavior of condensed droplets. A tiny Wenzel droplet nucleated grow in the microstructure can be dewetted by colliding with a Cassie droplet. This coalescence-induced dewetting transition can effectively make Cassie DWC occur on these single-scale roughness substrates, providing the surface structure design of condensers for Cassie DWC much easier to implement than on dual-scale roughness surfaces.

Extendibility Study of Conventional IPA Drying Process From Dynamic Fluid Model for Pattern Collapse

1. IntroductionIPA (iso-Propyl alcohol) has been widely used in semiconductor manufacturing for drying silicon wafer to mitigate water mark and keep the surface clean after wet cleaning process. Then, IPA process has been extended by combining with the other engineering techniques such as surface modification treatment to dry fragile nano-sized Si patterns [1]. As the scaling of advanced semiconductor devices continues, however, the pattern collapse is one of the most challenging issues for IPA drying process today. Capillary force model explains the pattern collapse in the earlier studies, where Laplace pressure originated from meniscus between patterns is a critical factor [2]. And the model has been well referred to and extensively studied in semiconductor industry [3]. Although, the model does not take dynamics of fluid into account, our experimental result suggests that drying rate is also critical, i.e., pattern collapse rate decreases as drying rate increases. This result is not explained by the reported models since the drying rate is not considered as a variable. In this report, a new model is suggested and verified by unique experiments. Our proposed model assumed that osmosis of metastable liquid to nano-size structures occurs from the triple line which is the air-liquid-solid interface, and the region of osmosis is less favorable for pattern collapse. The width of osmosis region would be determined by the drying rate. Also, based on this study, extendibility of IPA drying process to smaller device feature size for advanced node is discussed.2. ExperimentalWafer processing was conducted in spin process chamber on HVM equipment for drying experiment. IPA was dispensed on rotating wafer then dried at 0 or 1500 rpm. Nano-structured wafer used was with 34 nm-diameter of Si pillars, and aspect ratio (AR) of the pillar was 12:1. Pattern collapse was observed by top-view SEM, and collapse rate was calculated by automated image analysis with obtained SEM pictures. For osmosis observation at the triple line, FPM was prepared by mixing 49% HF, 30% H2O2 and H2O at volume ratio of 1:2:100. A droplet of FPM was dropped on the surface of Si pillar pattern wafer and observed by optical microscopy while the drop was drying out. After drying, pattern collapse of the pillar pattern was observed by X-SEM. To study effect of drying rate and to maximize it, IPA was dispensed on 10×12 mm2 coupon, then vaporized at 0 rpm with flash lamp annealing. AR of the pillar was 16:1. Observation of pattern collapse by top-view SEM was also conducted.3. Results and DiscussionIPA drying at 0 and 1500 rpm resulted in collapse rate of 91.1% and 46.9%, respectively, on the pillar AR = 12:1 (Fig. 1). IPA was dried out faster when wafer rotation speed was 1500 rpm. Thus, collapse rate decreases as drying speed increases. On osmosis observation, FPM droplet was sucked into between the pillars, causing osmosis at around droplet, and generated colored interference according to liquid film thickness. X-SEM inspection after the droplet drying indicated the most pattern collapse seemed to occur at the osmosis region where liquid thickness nearly equals to the pillar height. We assumed by increasing drying rate the osmosis region would be minimized and the pattern collapse would be suppressed. To verify this model, the following evaluation was conducted. With extremely high drying rate of IPA by flash lamp annealing, we obtained 0% of collapse rate even in the pillar AR = 16:1 (Fig. 2). This result indicates that there is some more process margin for the pattern collapse on IPA drying process.4. ConclusionIn the IPA drying process, collapse rate decreases as drying rate increases. Our proposed model assumed that osmosis region of metastable liquid to nano-size structures occurs from the triple line, and the pattern collapse happens there. That explains reasoning for lower collapse rate at higher drying speed is that osmosis is minimized when drying rate is maximized. Test result from maximized IPA drying rate by flash lamp annealing indicates that there is some more process margin for the pattern collapse. In our view, by this method IPA drying process might be extended to two more device nodes.

THE DEVELOPMENT OF NEW CONSTRUCTION METHODS ABOUT SHAKE PREVENTION DUCT STRUCTURES

Experimental studies are carried out on the newly devised method of shake-proof ducts with earthquake resistance, and it is verified whether the method will satisfy the allowable values of the construction guidelines in Japan. Based on the results, the aim is to improve the workability of the new method. The jig was installed on two shake prevention duct structures, fixed, and loaded horizontally. The vertical load was approximately 1kN assuming an actual duct, and the horizontal load was 4.9kN according to the construction guidelines. The interlaminar deformation angle and deflection angle was measured to determine if the allowable values are met. The construction methods about shake prevention duct structures was to install two pillars and connect the duct ring to the pillar with a plate. Bolts ware used to connect the duct ring to the plate and the pillar to the plate. Nine different tests conducted with parameters such as pillar height and cross-sectional standard. For a pillar length of 1500 mm, the allowable value in the Japanese construction guidelines was met, but for a pillar length of 2000 mm or more, it was difficult to meet the allowable horizontal displacement. However, it was possible to meet the allowable value by increasing the pillar cross section, increasing the bolts connecting the pillar to the plate, and reinforcing the base of a pillars.

Factors Affecting Pillar Top Morphology and Height Uniformity on High Speed Copper Electroplating

Factors Affecting Pillar Top Morphology and Height Uniformity on High Speed Copper Electroplating

Influence of the Core Pillar Height on the Bandgap Characteristics of Piezoelectric Phononic Crystals with Ring-Shaped Grooves

Dispersion profiles and surface acoustic wave attenuation characteristics of ring-shaped phononic crystals are investigated as a function of the core pillar height. Finite element method simulations are carried out for both band analyses and transmission spectra calculations. The results reveal that increasing core pillar height results in a decrement in the local resonance band frequency and the corresponding transmission peaks. The obtained dispersion profiles show that the phononic crystal bandgap also expands from 6 MHz to 11 MHz while the pillar height increases from 5 um to 7 um. Similar characteristics are also seen in the transmission spectra for the varying core pillar heights of the ring-shaped periodic grooves. In addition, surface acoustic wave attenuation competency depends on the core pillar height. The frequencies where the investigated phononic crystals are functional can be tuned by adjusting the core pillar height.

Nanoscale Melting of 3D Confined Azopolymers through Tunable Thermoplasmonics.

Phase transitions that are thermally induced by using light at the nanoscale play a vital role in material science. Enhanced optical heating sustained by resonant nanostructures can turn out to be insignificant when a higher thermal conductivity of a heatsink, regardless of the pumping intensity. In this Letter, we demonstrate an approach to control an operating temperature range due to excess heating of a structured heatsink. A design rationale has been performed by using a 2D array of TiN:Si voxels, consisting of stacked TiN and Si pillars. All the TiN nanoheaters responsible for enhanced light absorption at plasmon resonance are of equal size, and the height of the Si pillars varies to control heat localization. A height-dependent temperature rise of the Si pillars is found from Raman thermometry. Herein, for the first time, we have determined the melting temperature of azobenzene-functionalized polymers at the nanoscale using the tunable plasmonic metasurface.

THE DEVELOPMENT OF NEW CONSTRUCTION METHODS ABOUT SHAKE PREVENTION DUCT STRUCTURES

Experimental studies are carried out on the newly devised method of shake-proof ducts with earthquake resistance, and it is verified whether the method will satisfy the allowable values of the construction guidelines in Japan. Based on the results, the aim is to improve the workability of the new method. The jig was installed on two shake prevention duct structures, fixed, and loaded horizontally. The vertical load was approximately 1kN assuming an actual duct, and the horizontal load was 4.9kN according to the construction guidelines. The interlaminar deformation angle and deflection angle was measured to determine if the allowable values are met. The construction methods about shake prevention duct structures was to install two pillars and connect the duct ring to the pillar with a plate. Bolts ware used to connect the duct ring to the plate and the pillar to the plate. Nine different tests conducted with parameters such as pillar height and cross-sectional standard. For a pillar length of 1500 mm, the allowable value in the Japanese construction guidelines was met, but for a pillar length of 2000 mm or more, it was difficult to meet the allowable horizontal displacement. However, it was possible to meet the allowable value by increasing the pillar cross section, increasing the bolts connecting the pillar to the plate, and reinforcing the base of a pillars.

Use of Polymer Micropillar Arrays as Templates for Solid-Phase Immunoassays.

We investigate the use of periodic micropillar arrays produced by high-fidelity microfabrication with cyclic olefin polymers for solid-phase immunoassays. These three-dimensional (3D) templates offer higher surface-to-volume ratios than two-dimensional substrates, making it possible to attach more antibodies and so increase the signal obtained by the assay. Micropillar arrays also provide the capacity to induce wicking, which is used to distribute and confine antibodies on the surface with spatial control. Micropillar array substrates are modified by using oxygen plasma treatment, followed by grafting of (3-aminopropyl)triethoxysilane for binding proteins covalently using glutaraldehyde as a cross-linker. The relationship between microstructure and fluorescence signal was investigated through variation of pitch (10–50 μm), pillar diameter (5–40 μm), and pillar height (5–57 μm). Our findings suggest that signal intensity scales proportionally with the 3D surface area available for performing solid-phase immunoassays. A linear relationship between fluorescence intensity and microscale structure can be maintained even when the aspect ratio and pillar density both become very high, opening the possibility of tuning assay response by design such that desired signal intensity is obtained over a wide dynamic range compatible with different assays, analyte concentrations, and readout instruments. We demonstrate the versatility of the approach by performing the most common immunoassay formats—direct, indirect, and sandwich—in a qualitative fashion by using colorimetric and fluorescence-based detection for a number of clinically relevant protein markers, such as tumor necrosis factor alpha, interferon gamma (IFN-γ), and spike protein of severe acute respiratory syndrome coronavirus 2. We also show quantitative detection of IFN-γ in serum using a fluorescence-based sandwich immunoassay and calibrated samples with spike-in concentrations ranging from 50 pg/mL to 5 μg/mL, yielding an estimated limit of detection of ∼1 pg/mL for arrays with high micropillar density (11561 per mm2) and aspect ratio (1:11.35).

Stability of inner dump slope under coal pillar support: case study in an open-pit coal mine

The stability of an inner dump slope was investigated under the effect of coal pillar support considering the development position of dumping. Based on the instability mechanism and load distribution characteristics of the supporting coal pillar, the three-dimensional mechanical effects of the supporting coal pillar are characterized. Using the two-dimensional equivalent principle and the residual thrust method, the stability of the inner dump slope was analyzed under the effect of pillar support at different dump development positions. The quantitative effects of various factors on the inner dump slope stability were revealed, and the coal pillar shape parameters were optimized through numerical simulations. The results indicate that the slope stability coefficient is linearly related to the top width and height of the coal pillar, slope angle, and base inclination angle, and has an exponential relation with the coal pillar strike length and slope height increment. There are quadratic and absolute value relations with the coal pillar outer and the inner bottom angle, respectively. The top width of the coal pillar in the inner dump of Shengli East No.2 open-pit coal mine should be at a level of + 824 m, and the optimal top width and height are 15 and 36.7 m, respectively. The instability mechanism of the supporting and retaining coal pillar obtained by numerical simulations and the stability of the inner dump are in good agreement with the theoretical analysis. Our results provide a theoretical basis for the design, treatment, and safe implementation of similar open-pit mine slope engineering.

Optically Tunable Terahertz Metasurface Absorber

AbstractTunable absorbers are promising for reconfigurable metasurface applications. Here a tunable terahertz (THz) perfect absorber is proposed which consists of high resistance silicon (undoped silicon) and can realize the switch between perfect reflection and perfect absorption (optical pumping, 1064 nm continuous wave). The proposed THz absorber exhibits perfect absorption around 0.74 THz and a 90% absorption bandwidth of 0.5 THz. Additionally, the working frequency range of the device can be easily designed by adjusting the side length and height of the square silicon pillars. Effective medium theory, mode analysis, and impedance matching theory are used to design and explain the proposed THz absorber. The experimental results agree well with the simulations. The proposed scheme allows for more flexible design of THz absorbers, and the device is easier to be fabricated. The proposed tunable THz absorber can find applications in THz sensing, modulator, and optic‐electro switches.