Width Aspect Ratio Research Articles

Internal modification for cutting transparent glass using femtosecond Bessel beams

Taking advantage of the nonlinear laser-material interaction, femtosecond lasers can process transparent materials internally on micro- or nanoscales, whose applications include fabrication of micro-optical waveguides and fluidics, as well as stealth dicing of glass, ceramics, and semiconductor materials. A femtosecond Bessel beam has a long invariant transverse intensity profile up to several millimeters with a width of a few microns. Such characteristics allow the materials processing to be completed without moving the beam focusing points as in the case of the Gaussian beam. An experimental femtosecond Bessel beam microprocessing system is built up to investigate the glass internal modification characteristics, such as the width variation and aspect ratios of modification areas. The residual stresses in the irradiated area of glass after modification are also studied using micro Raman spectrum. Finally, an application to thin glass panel cutting is demonstrated by the process of internal modification and breaking. The glass panel is well cut with the chipping on the breaking edge <1 μm .

Mechanical property effects of Si1 − xGex channel and stressed contact etching stop layer on nano-scaled n-type metal–oxide–semiconductor field effect transistors

This study demonstrated that advanced strained engineering in contact etching stop layer (CESL) combined with silicon germanium (Si1−xGex) stressors can be efficiently utilized to enhance the performance of devices. Lattice mismatch stress was induced to establish an Si1−xGex channel integrated with intrinsic stress of CESL, which consists of multiple stressors, to analyze the stress contour of the concerned channel in n-type metal–oxide–semiconductor field effect transistors (nMOSFETs) by three-dimensional (3D) finite element analysis (FEA). The types of intrinsic CESL stress considered in this study were tensile (1.1GPa) (t-CESL) and compressive (−2.0GPa) (c-CESL). Germanium mole fractions, including 0%, 22.5%, and 25%, utilized in the Si1−xGex channel were selected to carefully analyze their impact on the Si1−xGex channel. The effect of channel geometries, which are composed of aspect ratio of length and width, was considered as well. Results reveal that the stress components of the Si1−xGex channel increases significantly when the amount of Si1−xGex layer increases. A change in the length and width of the channel induces inversion in the Si1−xGex channel regarding stress conventions in the direction of the channel's length and width. Results predicted by the proposed FEA were consistent with experimental data as validated by the nMOSFET with an Si0.775Ge0.225 channel. Comparison of the simulation results of FEA with two-dimensional (2D) and 3D models was performed. The results show that wide gate width in the 3D model can induce a response to the calculated results similar to that obtained in a 2D situation.

Note: Design principles of a linear array multi-channel effusive metal-vapor atom source

Atomic beams can easily be produced by allowing atoms to effuse through a channel. In an earlier investigation [A. Majumder et al., Vacuum 83, 989 (2009)], we had designed, fabricated, and characterized an effusive metal-vapor source using collinear-array of multi-channel. In this note, we describe the theoretical basis of designing the source. Atom density in atomic beam has been estimated using a set of analytical expressions for long-channel operated in transparent mode. Parametric studies on aspect ratio of channel, inter-channel separation, beam width, and vertical distance from the source are carried out. They are useful in providing physical picture and optimizing design parameters.

Simulations of flow instability in three dimensional deep cavities with multi relaxation time lattice Boltzmann method on graphic processing units

The D3Q19 multi relaxation time (MRT) lattice Boltzmann model is adopted to simulate the instability phenomenon within a three-dimensional cavity at various depth–width aspect ratios ranging from 1 to 3. The computations are conducted on a single node multi graphic processing unit (GPU) system, consisting of three nVIDIA M2070 devices using OpenMP. Results show that transition takes place between 1750<Recr<1950, for cubic cavity and 1100<Recr<1450, for deep cavity flows with aspect ratio 2 and 3. This indicates that an increase of the depth–width aspect ratio would induce the transition at lower Reynolds number and is consistent with the previous results for two-dimensional cavities, though the critical Reynolds number is approximately 75% lower for three dimensional cavity.

Excimer Laser Micromachining Using Binary Mask Projection for Large Area Patterning With Single Micrometer Features

Excimer laser micromachining using binary mask projection has been investigated for rapid patterning of single micrometer features over large areas of various substrates. Simple limit for depth of focus that determines the depth to width aspect ratios is given and verified for different materials. Binary mask projection technique is found to conformally reproduce the mask features from the millimetre to the micrometer scale under proper focusing conditions. Large arrays of 1 μm and 15 μm holes on Kapton are made with high resolution and uniform periodicity. Material removal rate (MRR) for the laser machining of these holes are examined and the machining efficiency for these are found to have different dependence on the fluence. A saturation of hole-depth with increasing number of pulses is obtained.

Fault nucleation, restriction, and aspect ratio in layered sections: Quantification of the strength and stiffness roles using numerical modeling

3D numerical modeling has been used to investigate how the variations of mechanical properties in sedimentary layered sections affect the development of normal faults. We calculated the distribution of the Coulomb stress to assess the proximity of the layers to failure through an elastic layered section. The simulation of various combinations of rock properties allowed us to compare the effect of the stiffness and strength contrasts, which promote or inhibit faulting in the stiff layer, respectively. For rock systems showing little variation in strength, nucleation of the fault occurs in the stiff layer (e.g., limestones or sandstones), whereas it occurs in the compliant layer (e.g., clay‐rich rocks) if the stiff layer has a high cohesion. Considering a mean strength profile of the carbonate sequences, nucleation occurs in limestones if the ratio of Young's moduli between the limestone and clay‐rich rock is greater than 2; otherwise, clay‐rich layers fail first. We also showed that nucleation is promoted in sandstones or limestones if these layers are thinner than the clayey layers. In a second set of simulation, using a slip on a fault, we examined the conditions needed to overcome the restriction of the fault propagation. Our results suggest that the lateral propagation of the fault, within a layer, produces increasingly favorable conditions for vertical propagation. A maximum aspect ratio of width to height of 13 is predicted for faults in limestone‐clay sequences, and this maximum aspect ratio is expected to decrease as the contrast in the rock properties decreases.

Demagnetizing factors in patterned CoNiFe films with rectangular elements

CoNiFe patterned films with rectangular elements, all 600-nm wide but of different lengths, were fabricated and investigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with the increase of the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non-uniform demagnetizing field decreased from 0.26 to 0.16 with the increase of the length—width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge-to-edge spacing between neighboring elements was larger than 3 μm in our patterned films.

Mechanism of axis switching in low aspect-ratio rectangular jets

In this work we systematically study one square jet (AR=1) and four rectangular jets with an aspect ratio of width over height AR=1.5,2,2.5, and 3 respectively using the lattice Boltzmann method for direct numerical simulation. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the downstream velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. As the length of the PC (potential core) region maintains about the same, that of the CD (characteristic decay) region strongly depends on the jet aspect-ratio (AR) and Reynolds number (Re). The 45° and 90° axis-switching occur in the CD region, with the former followed by the latter at the early and late stages of the CD region respectively. The half-width streamwise velocity contour reveals that 45° axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when 45° axis-switching occurs. The close examinations of flow pattern and vorticity contour, as well as the correlation between streamwise velocity and vorticity, indicate that 90° axis-switching results from the boundary effect. Specific flow patterns for 45° and 90° axis-switching are identified to reveal the mechanism of the axis-switchings respectively.

The influence of surface slope on the shape of river basins: Comparison between nature and numerical landscape simulations

We investigate the influence of initial conditions of slope and surface roughness on the shape (length to width aspect ratio) of incipient drainage basins in numerical experiments of simple tilted surfaces using the CASCADE code of landscape evolution. Comparison with data on the shape of river basins in nature shows that simple rules of the steepest-descent routing of water are sufficient to account for a natural range of incipient drainage basin shape, independently of the erosion processes at work. To produce numerical basins that respect the main aspect ratio of natural drainage basins, one must use very low initial regional surface slopes of less than 1° at the scale of the entire drainage basins, and a local roughness slope of less than 3° at the scale of local surface irregularities. Numerical studies addressing real study cases may take advantage of the relation between local roughness and regional slope in order to produce catchment aspect ratios similar to the natural studied cases.

Tunable Young's Modulus in Carbon MEMS Using Graphene-Based Stiffeners

Carbon composite micro-electromechanical systems (C-MEMS) incorporating 2 wt.% graphene stiffeners show a 65% increase in Young's modulus and 11% increase in conductivity. An improved reduced graphene oxide (iRGO), is blended into pyrolytic carbon beams prepared for resonant frequency testing. Designed around a 10:1 (length: width) aspect ratio, the linearity of wt.% iRGO in the cantilevers as a function of resonant frequencies is evaluated. The collection of the 1st through 3rd bending modes using laser doppler velocimetery (LDV) of the graphene filled cantilevers shows an increase in frequency response with nanomaterial loading (wt.%). A model was developed using the 3-bending modes and correlated with cross sectional geometry and density to extract a Young's modulus.

Fabrication and characterization of injection molded multi level nano and microfluidic systems

We here present a method for fabrication of multi-level all-polymer chips by means of silicon dry etching, electroplating and injection molding. This method was used for successful fabrication of microfluidic chips for applications in the fields of electrochemistry, cell trapping and DNA elongation. These chips incorporate channel depths in the range between 100nm and [email protected] and depth to width aspect ratios between 1/200 and 2. Optimization of the sealing process of all-polymer COC microfluidic chips by means of thermal bonding is also presented. The latter includes comparing the bonding strength of UV-treated foils and presentation of a simple model for estimating the delamination pressure. With UV surface treatments, foils of [email protected] thickness were found to withstand pressures up to 9atm in O4mm cylindrical inlets when thermally bonded to micropatterned substrates of 2mm thickness.

Flow Investigations in a Wide Meandering Compound Channel

Extreme complexities present in flow behavior of meandering compound channels necessitate the study and analysis of such channels under different geometric and hydraulic condition to further our knowledge in understanding the dependency of flow characteristics e.g. velocity, boundary shear etc. on different sectional parameters like width ratio, aspect ratio and hydraulic parameter such as relative depth. The present paper draws on our investigations on a meandering compound channel,where physical experiments were conducted on a smooth sine generated trapezoidal main channel flanked on both sides by wide flood plainsunder different relative depths. A 2dimensional hydrodynamic model CCHE2D and another quasi1D model Conveyance estimation System (CES) were then applied in turn to the same test cases to numerically investigate the flow in the compound meandering channel. The results of such investigations were then compared for validation purpose with observed experimental values of important flow parameters like depth averaged velocity and boundary shear distribution across the channel cross section. It is seen that CCHE2D is quite capable of producing results in agreement with their physical values and also it partly agrees with results of CES.It is expected that the results shown in this paper would enrich the research data base in the field of compound channels and help the scientists in using the numerical model CCHE2D, as a viable research tool in the field of river engineering.

Theoretical development and critical analysis of burst frequency equations for passive valves on centrifugal microfluidic platforms

This paper presents a theoretical development and critical analysis of the burst frequency equations for capillary valves on a microfluidic compact disc (CD) platform. This analysis includes background on passive capillary valves and the governing models/equations that have been developed to date. The implicit assumptions and limitations of these models are discussed. The fluid meniscus dynamics before bursting is broken up into a multi-stage model and a more accurate version of the burst frequency equation for the capillary valves is proposed. The modified equations are used to evaluate the effects of various CD design parameters such as the hydraulic diameter, the height to width aspect ratio, and the opening wedge angle of the channel on the burst pressure.

Dependence of model-based RSA accuracy on higher and lower implant surface model quality

BackgroundModel-based Roentgen Stereophotogrammetric Analysis (MBRSA) allows the accurate in vivo measurement of the relative motion between an implant and the surrounding bone (migration), using pose-estimation algorithms and three dimensional geometric surface models of the implant. The goal of this study was thus to investigate the effect of surface model resolution on the accuracy of the MBRSA method.MethodsFour different implant geometries (knee femoral and tibial components, and two different hip stems) were investigated, for each of which two reversed engineering (RE) models of differing spatial digitizing resolution were generated. Accuracy of implant migration measurement using MBRSA was assessed in dependence on surface model resolution using an experimental phantom-model set up.ResultsWhen using the lower quality RE models, the worst bias observed ranged from -0.048 to 0.037 mm, and -0.057 to 0.078 deg for translation and rotation respectively. For higher quality reverse engineering models, bias ranged from -0.042 to 0.048 mm, and -0.449 to 0.029 deg. The pair-wise comparisons of digitizing resolution (higher vs. lower quality) within the different implant type revealed significant differences only for the hip stems (p < 0.001).ConclusionThe data suggest that the application of lower resolution RE models for MBRSA is a viable alternative method for the in vivo measurement of implant migration, in particular for implants with non symmetrical geometries (total knee arthroplasty). Implants with larger length to width aspect ratio (total hip arthroplasty) may require high resolution RE models in order to achieve acceptable accuracy. Conversely, for some axis the bias for translation are clearly worse for translation, and are marginally better for rotations using the lower resolution RE models instead of the higher ones. However, performed box plots ranges were well within what has been reported in the literature. The observed lower accuracy and precision of the measurements for hip stem components for rotations about the superior-inferior direction is presumably the result of the nature of the MBRSA method. This well known effect within MBRSA for rotations about the axis of symmetry of axially-symmetric objects do not change the contour of the projected image to as large a degree as motion about a non-symmetric axes. It is not possible to detected this small motion as accurately using pose-estimation methods. This may affect the “higher” accuracy for the applied lower resolution RE models.

Single crystalline Si substrate growth by lateral diffusion epitaxy

A novel crystal growth method named lateral diffusion epitaxy (LDE) as well as the necessary growth apparatus are described in detail. Single crystalline Si strips are grown on (111) Si substrates by LDE. The thickness of the LDE Si strips is around 100μm, and the aspect ratio of width to thickness is around 2 which is an improvement compared with Si strips grown by conventional liquid phase epitaxy (LPE). The LDE Si strip can be peeled off from the substrate for further device processing since the 100μm thickness provides reasonable mechanical strength. Due to the low cost of LDE technology it is potentially a good candidate for PV application if the LDE can achieve continuous growth and therefore grow Si strips in sizes for practical application.

PREPARATION OF CHITIN NANOFIBERS-GOLD METALLIC NANOCOMPOSITE BY PHASE TRANSFER METHOD

Chitin nanofibers (CNFs)- Au(0) nanoparticles ( Au NPs) blends in dispersion, flakes and thin film or sheet forms were first prepared by mixing pre-organized Au NPs prepared in triblock copolymer with diluted CNFs suspension. Water soluble polymer triblock copolymer poly (methyl vinyl ether, PMVE) in the amount 0.6 wt.% was used to prepare NPs and 0.12 wt.% net chitin content was used as CNFs suspension to prepare the blended composite. Au NPs of size 4.4 nm (σ = 1.2) were obtained when Au salt ( HAuCl4⋅3H2O (hydrogen tetrachloroaurate (III) trihydrate) was reduced by 5 equivalents of NaBH4 . PMVE polymer acted as a stabilizing or capping agent for pre-organized NPs. Completion of reaction was fast, all salt reduced to metallic form in just 15 min after the addition of NaBH4 . CNFs (1 wt.% chitin) which was used to prepare CNFs- Au NPs blend composite were prepared from crab shell in never dried acidic condition by established combination of chemical and mechanical processes that gave 25–40 nm width and high aspect ratio CNFs. When polymer capped Au NPs mixed with CNF suspension, all Au NPs and 56% polymer were mass transferred from water phase to entangle with more polar moieties of CNFs-water suspension as no trace of Au NPs were noticed in water–polymer mother liquor after blending with CNFs suspension. Particles size of CNFs- Au NPs composite was measured by employing TEM, SAXS and SEM techniques. CNFs- Au NPs composite were characterized in solution and compressed dried sheet form by recording digital images, UV-vis and XRD spectroscopies. CNFs- Au NPs suspension had antibacterial activity against gram positive bacteria S. aureus.

Welcome to Fibers—A New Open Access Journal for Fibrous Material Science

Fibers are materials in the form of elongated threads. They can possess elastic features that are relevant to the integrity and bonding of cells. These features also give man-made fibers a wide range of applications. The large ratio of length to width (aspect ratio), which defines fibers, strongly influences their physical and chemical properties. This quality gives them a relatively large surface area, which can lead to powerful tensile and absorptive characteristics, which are remarkably different from, and cannot be predicted by study of the non-fibrous parent materials. An example of this is asbestos, where the toxicity of the material is heavily influenced by its structural anatomy. Distinctive chemical processes can take place on fibrous surfaces that may themselves seem to be chemically inert. Certain commonalities result from the distinctive geometry of fibers, and lie behind the apparently great diversity of fiber types and materials. [...]

Growth dynamics of low-dimensional CoSi2 nanostructures revisited: Influence of interface structure and growth temperature

The growth of cobalt silicide nanostructures on clean Si(001) was studied using scanning tunnelling microscopy and transmission electron microscopy. Two types of CoSi2 nanostructures, flat and ridge-type islands, were formed when 0.1ML Co was deposited onto clean Si(001) between 500°C and 800°C. These islands form elongated islands along [110] directions and grow into the Si-substrate within the temperature range. The formation of the two types of islands arises primarily due to the type of CoSi2{111}–Si{111} interface formed between the island and the substrate. Flat islands are bound by CoSi2{111}–Si{111} Type-A interfaces such that CoSi2(001)//Si(001) and CoSi2[001]//Si[001]. Ridge islands, on the other hand, are bound by a “twinned” CoSi2{111}–Si{111} Type-B interface such that CoSi2(221)//Si(001) and CoSi2[11¯0] //Si[11¯0]. This leads to the formation of three less energetically-favourable interfaces: CoSi2(1¯1¯1¯)–Si(115¯), CoSi2(1¯1¯2¯)–Si(112¯), and CoSi2(1¯1¯5¯)–Si(111¯). Analysis of the interfacial energies through dangling bond counting per interfacial area for each interface shows that the formation of the Type-B interface is energetically more favourable compared to the rest of the interfaces. As a result, the island elongates preferentially along the Type B interface leading to the formation of long nanowires with large length–width aspect ratio of 20:1. However, this formation is only achieved at high growth temperatures due to the presence of corner-barriers constraining the growth at low temperatures. Conversely, flat islands are slightly elongated at low growth temperatures with aspect ratio reaching 7:1 at 650°C. As temperature increases towards 760°C, they are brought closer to equilibrium and hence become less elongated with aspect ratio reduced to 1.6:1.

LiDAR derived morphology of the 1993 Lascar pyroclastic flow deposits, and implication for flow dynamics and rheology

Abstract Pumice flows are potentially destructive volcanic events that derive from eruption column collapse and whose dynamics are poorly understood. The challenges in studying these flows include the lack of constraints on the dynamics, kinematics and initial conditions that control their emplacement. We present a morphological study of the distal deposits (lobes) of the pumice flows resulting from the 1993 eruption at Lascar, Chile. The surface geometry of the lobes was measured in detail using a LiDAR device, which allowed for detailed characterisation of their morphology, consisting of central channel and lateral levees, and terminal frontal snout. In particular we find that the ratio of channel/levee height as a function of the ratio of the distance between levees/total width of the lobe has a characteristic curve for these pumice flow lobes. Our analysis of several of the Lascar pumice lobe deposits (south east sector) identified several dimensionless groups of the available parameters which, when compared against published results from both experimental and numerical investigations, allowed us to constrain crucial kinematic and dynamic information on the terminal phase of the pumice flows. Notably, we estimate the velocity of the terminal phase of pumice flows to be 5–10 m/s. Froude numbers of 1.5–2 are comparable with values found for experimental granular flows. Height–width aspect ratios for the levee–channel section of the pumice lobes are similar to those for experimental flows although these same aspect ratios for the snout are much larger for the natural deposits than their small-scale analogues. Finally, we discuss the possible emplacement dynamics of the terminal Lascar 1993 pumice flows. A pseudo-Reynolds number based on the velocity estimation is found to be up to 100 times larger for the pumice flows than experimental-scale flows. This suggests that the flow-retarding frictional forces for large-scale flows are relatively unimportant compared to flows at smaller scales. Mechanical effects such as fluidisation, mobilisation of material lying on the slopes over which they propagate and lubrication due to polydispersivity could provide an explanation for their ability to propagate on shallow slopes (6–11°).

Oxidative stress-mediated cytotoxicity and apoptosis induction by TiO2 nanofibers in HeLa cells

Titanium dioxide nanoparticles are increasingly being used in pharmaceutical and cosmetic products. The high aspect ratio of fibrous nanomaterials, such as carbon nanotubes and TiO2 nanofibers (TiO2NFs), similar to the one used in this study makes them an attractive structural material and has attracted a lot of attention due to their possible negative health effects as suggested by their morphological similarities with asbestos. In the present study, therefore, toxicity of TiO2NFs was evaluated in human cervical adenocarcinoma HeLa cells. The TEM and XRD analyses showed that TiO2NFs used in this study are pure with uniform diameter of around 200nm, and their length to width aspect ratio ranged between 5 and 15. Exposure of HeLa cells to TiO2NFs induced significant cytotoxicity even at doses as low as 2μg/ml. The intracellular uptake of TiO2NFs in cells was shown by Alizarin Red S (ARS) labeled nanofibers. The mechanism of toxicity is mainly due to the induction of cellular oxidative stress, as revealed by elevated ROS levels, reduced antioxidant levels, and increased lipid peroxidation leading to apoptosis. The cell cycle analysis indicated G2/M cell cycle arrest in the cells exposed to TiO2NF. TiO2NFs treatment to HeLa cells resulted in increased expression of proapoptotic proteins Bax with an increase in cytosolic Cytochrome-C and inhibition of anti-apoptotic protein Bcl-2. Our results revealed the potential mechanism of cellular effects of TiO2NFs.