Sidewall Shape Research Articles

Comparative study of the sidewall shape and proximity effect in bilayer electron beam resist systems

The experimental investigation and simulation of electron beam lithography (EBL) for bilayer and trilayer resist systems have been carried out. Important parameters of the EBL process, such as dissolution rate, resolution, absorbed energy, and resist profile in the investigated bilayer resist systems, have been studied and discussed. Various combinations of resist layers with positive electron resist have been proposed to examine the effects of lithographic process parameters on the resist profile. The results of this work are intended for use in multilayer resist systems to produce high-frequency electronics, where the fabrication of a T-shaped gate is one of the most crucial processes.

Axial segregation characteristics and size-induced flow behavior of particles in a novel rotary drum with curved sidewalls

Particle mixing and segregation are common phenomena in rotary drums, which are challenging to be controlled and driven artificially in powder technology. In this work, the discrete element method (DEM) was applied to construct the novel rotary drum composed of different shaped curved sidewalls. By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter (L/D) ratio of drums, the axial mixing and segregation processes of binary size-induced particles were investigated. The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases, making the non-spherical particles to mix better in rotary drums compared to the spherical particles. Besides, in the short drums with size-induced spherical particles, the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls. However, for size-induced non-spherical particles, the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls. Moreover, the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios. In contrast, the non-spherical particles cannot form obvious multi-proportional segregation bands.

Vertical sidewalls in thick epoxy resists – a challenge for laser-based direct write lithography

Straight, almost vertical sidewalls can be achieved in thick negative-tone resist using focused laser beam-based direct write lithography (DWL). This is possible despite beam divergence and Gaussian intensity distribution that cause non-homogeneous illumination over the resist thickness and non-sharp edges between exposed and non-exposed areas. Three write modes with different focal lengths, numerical apertures and resolutions were used in our DWL 66+ pattern generator from Heidelberg Instruments. By variation of dose, vertical adjustment of location of focus, and multipass exposure, up to 88° sidewalls were achieved in 60 μm high and 100 μm wide ridges. The results show the potential of DWL to achieve resist structures with larger height up to 200 μm, higher resolution down to 5 μm, aspect ratio of over 8 and defined sidewall shape.

How macrostructures enhance droplet coalescence jumping: A mechanism study

Macrostructures exhibit excellent performance in coalescence-induced droplet jumping enhancement. Previous velocity prediction models were mainly established for flat plain surface, which usually set up the balance relationship between excess surface energy, kinetic energy and dissipation. But these models are no longer appropriate in macrostructure cases due to great variation of oscillational kinetic energy and gravitational potential energy caused by textures. In this work, coalescence-induced droplet jumping on macrostructures was investigated numerically on flat, sidewall, string, ridge and egg shape substrates. An energy conversion model based on energy efficiency rather than energy balance was established for departure velocity by proposing three sub-efficiencies to evaluate jumping enhancement. In this model, oscillational kinetic energy was distinguished from dissipation, gravitational potential energy induced by macrostructures were considered, and the real droplet morphology were used to calculate surface energy. By dividing the whole droplet jumping process into merge and contact stage, the influence of macrostructures on duration of each stage was closely connected to the macrostructure effects on dissipation and kinetic energy conversion. Pressure and velocity distributions near the macrostructure were also discussed to further explore the mechanism for droplet jumping enhancement. Further, the significant increase of initial surface energy for egg case points out a possible new approach to enhance jumping velocity. This model helps us understand the determinants of jumping enhancement with macrostructures and it also applies to flat plain.

Numerical Analysis of the Influence of Side Wall Shape on the Efficiency of Thermal Energy Storages Based on Granular Phase Change Materials

Numerical Analysis of the Influence of Side Wall Shape on the Efficiency of Thermal Energy Storages Based on Granular Phase Change Materials

The effect of side walls on particles mixing in rotating drums

In this paper, we study the effects of the presence and shape of side walls and of the overall length of rotating cylindrical drums on the mixing of particles with differing sizes by application of the discrete element method (DEM). By varying the semi-axis of the spheroidally shaped side walls and the length of the overall drum, we observe the formation of circulation patterns near the side walls. Although there is a vast amount of literature studying mixing regimes in rotating drums, little is known about the effect of the side walls of the drum on particle mixing. The results of our study demonstrate that introducing curved side walls induces a strong circulation pattern near these side walls, but has, paradoxically, a negative impact on mixing and actually promotes segregation. The cause for this segregation is the difference in velocity of differently sized particles near the curved side walls. Large particles accumulate at the curved side walls, whereas small particles move away from the curved side walls. When the length of the drum is increased, the overall effect of the side walls is decreased, although it does remain observable, even in very large drums.

Comparative study of the sidewall shape and proximity effect of the AR-N 7520 negative electron beam resist

This paper deals with the performance of the AR-N7520 (Allresist) negative electron beam resist (EB resist) which was selected as an etch mask for the fabrication of gratings on GaAs substrates. The developed resist sidewall shape is crucial for this purpose. The required near-to-vertical sidewall shape can be achieved by optimizing the electron beam lithography (EBL) process based on experimental investigations and computer simulations. The sidewall shape dependence on the EBL parameters (exposure dose, resist pattern, etc.) and the proximity effect are studied.

Toward Surfaces with Droplet Impact Robustness and Low Contact Angle Hysteresis

AbstractSuperhydrophobic surfaces show excellent water repellent performance. However, liquid impalement occurs when a droplet impacts on the surface at high velocity. To achieve higher resistance to liquid impalement at the same scale, a dense array of structures or structures with pinning at the structures top are typically used, but they also lead to increased contact angle hysteresis and higher energy dissipation. Changing the structure side wall shape can help to maintain low hysteresis and withstand high impact energy at the same scale. Droplet contact angle, contact angle hysteresis and droplet impact experiments are performed on both conical and cylindrical pillar surfaces. Comparing conical and cylindrical pillar structures with the same pitch and height, it is found that cylindrical pillars exhibit higher critical Weber number but result in larger contact angle hysteresis and larger liquid residue size when above a critical Weber number. A proper design of conical structures can maintain large contact angle, low hysteresis, strong resistance to impalement, higher number of bouncing and smaller liquid residue size. In addition, the critical Weber number for the conical structures in this work is higher than micro‐patterned pillar surfaces at the same pitch range, implying that we improve the anti‐wetting performance further.

Direct comparison of line edge roughness measurements by SEM and a metrological tilting-atomic force microscopy for reference metrology

Background: Conventional scanning electron microscopy (SEM) that is used for 2D top-view metrology, a classical line edge roughness (LER) measurement technique, is incapable of measuring 3D structures of a nanoscale line pattern. For LER measurements, SEM measurement generates a single line-edge profile for the 3D sidewall roughness, although the line-edge profile differs at each height in the 3D sidewall. Aim: To develop an evaluation method of SEM-based LER measurement techniques and to verify how the 3D sidewall shape is reflected in the SEM’s 2D result. Approach: Direct comparison by measuring an identical location of a line pattern by SEM and an atomic force microscopy (AFM) with the tip-tilting technique that is capable of measuring the 3D sidewall. The line pattern has vertical stripes on the sidewall due to its fabrication process. Measured line edge profiles were analyzed using power spectral density, height-height correlation function, and autocorrelation function. Results: Line edge profiles measured by SEM and AFM were well matched except for noise level. Frequency and scaling analyses showed that SEM profile contained high noise and had lost a property of self-affine fractals in contrast to AFM. Conclusions: In the case of the line pattern with vertical stripes on the sidewall, SEM profile is generally consistent with 3D sidewall shape. The AFM-based LER measurement technique is useful as LER reference metrology to evaluate other LER measurement techniques.

Tenacious wall states in thermal convection in rapidly rotating containers

Convection in a container, heated from below, cooled from above and rapidly rotated around a vertical axis, starts from its sidewall. When the imposed vertical temperature gradient is not sufficiently large for bulk modes to set in, thermal convection can start in the form of wall modes, which are observed near the sidewall as pairs of hot ascending and cold descending plumes that drift along the wall. With increasing temperature gradient, different wall and bulk modes occur and interact, leading finally to turbulence. A recent numerical study by Favier & Knobloch (J. Fluid Mech., 895, 2020, R1) reveals an extreme robustness of the wall states. They persist above the onset of bulk modes and turbulence, thereby relating them to the recently discovered boundary zonal flows in highly turbulent rotating thermal convection. More exciting is that the wall modes can be thought of as topologically protected states, as they are robust with respect to the sidewall shape. They stubbornly drift along the wall, following its contour, independent of geometric obstacles.

Mixed Convection in Lid-Driven “T” Shallow Cavity Heated From Bottom and Filled by Two Immiscible Fluids of Air and Al2O3-Water Nanofluid

This work present numerical simulation results of mixed convection in lid-driven “T” shallow cavity, filled by two immiscible fluids layers of air and Al2O3-water nanofluid. Mixed convection condition is created by the upper wall movement and temperature difference between the alveolus bottom and upper wall. Hydrodynamic and thermal characteristics of the flow have been predicted by solving the Navier- Stokes and energy equation using finite volume method. Coupling between two fluids layers are achieved using continuity of temperature and velocity at the interface air-nanofluid. Nano-particle volume fraction effect and geometrical shape of alveolus sidewalls (plane shape, concave shape and convex shape) have been chosen as discussed parameters. Analysis of obtained results shows that the heat transfer rate decreased with increasing volume fraction of solid inside the nanofluid layer. In addition, geometrical shape of alveolus sidewalls has a poor effect on flow structure and isotherms distribution in the physical domain.

INFLUENCE OF STRUT SECTION ON THE FLOW QUALITY OF THE SLOTTED TEST SECTION OF TRANSONIC WIND TUNNELS

The numerical analysis and performance evaluation of the flow field uniformity in a slotted test section of a 0.3 m cryogenic continuous transonic wind tunnel in full and half models were conducted. Factors affecting the flow field uniformity in the slotted test section of the transonic wind tunnel were analyzed. The regular pattern of a stationary region and expansion waves on the solid wall surface of the strut section was studied. On the basis of the distribution of expansion and compression waves on the strut section, the optimal design and performance of sting surface, cross section, and sidewall shapes and the area expansion ratio of the strut section were evaluated. In the slotted test section of the transonic wind tunnel, the root-mean-square deviation of Mach numbers was improved. The area expansion ratio of the strut section decreased from 1.30 to 1.22. The expansion wave caused by the wall expansion structure at the entrance of the strut section is the main factor causing strut section choking, which further explains the mechanism for the failure of the second throat at a high subsonic speed in the slotted test section of traditional transonic wind tunnels.

Investigating the Effects of the Block Geometries and Sidewall Divergences on the Local Scour Downstream of Baffled Chute Spillways

Due to the lack of any specific study about the sidewalls and other blocks’ changes in the case of hydraulic and scour downstream, the present study was conducted to investigate this issue. For this purpose, drainage projects and spillway chutes, as well as many baffle block chutes, were designed and constructed with the parallel sidewalls and trapezoidal shape using the U.S. Bureau of Reclamation (USBR) instructions. Three divergence ratios of ((b1/b2) = 1.45, 1.75, and 2.45), a parallel sidewall of (b1/b2 = 1), and also three geometry blocks including trapezoidal USBR, trihedral, and semicircle blocks were applied and tested in the hydraulic laboratory using a baffle chute with the slope of (2 : 1), (H : V). The material used in this study was sediment sand with a uniform grain size of d50 = 1.2 mm, 15 cm of thickness, and 2 m of length. The experiment was conducted with seven different discharges in lasting condition, and the flow characteristic and scour hole dimensions were measured. The results revealed that in comparison with the USBR blocks, changes in the baffle sidewall and block shape made an approximate 50% reduction in the maximum depth of the scour hole. Thus, increasing the divergence ratio from 1 to 2.45 had a significant effect on reducing the maximum depth and the topographic shape of the scour hole. According to the range mentioned in the literature for the Weber number, the scale effect was negligible for the chute with baffle blocks. Generally, it can be concluded that the sidewall changes also can make a reduction in the number of overbaffle blocks, causing a reduction in the construction cost.

Numerical analysis of the influence of side wall shape on the efficiency of thermal energy storages based on granular phase change materials

This work is devoted to a numerical study of processes in thermal energy storages based on granular phase change materials. The influence of the side walls shape on the efficiency of such heat accumulators is studied when the plane-parallel flows of gas heat transfer fluid take place. The shape of the energy storage affects the heat transfer fluid flow in the object, and this affects the heat transfer, heat accumulation and heat recovery. Using the novel numerical model, the influence of narrowing and expansion of the side walls on the charging and discharging processes of thermal energy storages with rectangular cross sections are studied under two types of boundary conditions: the known mass flow rate of gas at the object inlet and the known gas pressure drop at its open borders for different phase change temperatures of the phase change material .Different efficiency criteria are used to estimate the preferred shape of a heat storage. For the charging process, the preference criteria considered are the maximum instantaneous storage efficiency, the maximum cumulative storage efficiency, and the minimum time to fully charge the device. For the discharge process, the considered preference criteria are the maximum energy recovery efficiency, the maximum total utilization ratio, and the maximum time to maintain the temperature of the heat transfer fluid at the outlet not lower than the desired value. It is shown that the preferred shape of the energy storage depends on the choice of the efficiency criterion and specific process conditions such as boundary conditions, phase transition temperature, etc. Narrowing and expanding thermal energy storages have an advantage in rare cases, and storages with straight walls are often most preferable.

A novel shaped-controlled fabrication of nanopore and its applications in quantum electronics

High-intensity (107–108 A m−2) electron beams can be used to fabricate nanoscale pores. This approach enables real-time observation of nanopore drilling and precise control of the diameter of the nanopore. Nevertheless, it is not suitable for tuning the nanopore’s sidewall shape. In this study, we demonstrate the use of low-intensity electron beams to fabricate nanopores on a silicon nitride (SiNx) membrane. This technique allows the precise adjustment of the nanopore dimension and the shaping of its three-dimensional (3D) nanostructure. The 3D structures of the nanopore were evaluated by electron tomography, and series of oblique images were used in reconstructing the 3D images of nanopores using a weighted back-projection method. The sidewall shape of the nanopore was observed at different electron-beam conditions, and the formation mechanism was elucidated based on these results. The nanopore fabricated with this technique can be used as a template to develop electronics at the nanoscale based on which a quantum-dot device can be prepared with a simple evaporation process. The measured results show that the device can resolve well-defined electronic states that are characteristic for the behaviors of the quantum-dot device.

Effects of BCl3 addition to Cl2 gas on etching characteristics of GaN at high temperature

Gallium nitride films were etched at 400 °C and 20 Pa with a radio-frequency-generated Cl2–BCl3 mixed plasma. While dog-legged profiles were obtained by plasma etching using pure Cl2, straight sidewall shapes were achieved through BCl3 gas addition into the Cl2 plasma by suppressing the plasma-induced damage on the etched surface. Etching by-products containing boron on the etched surface affected the etch rate. Smooth etched profiles were obtained by controlling the redeposition of by-products of boron and chlorine compounds, particularly for substrate temperatures above 230 °C.

On-Chip Tunable Cell Rotation Using Acoustically Oscillating Asymmetrical Microstructures.

The precise rotational manipulation of cells and other micrometer-sized biological samples is critical to many applications in biology, medicine, and agriculture. We describe an acoustic-based, on-chip manipulation method that can achieve tunable cell rotation. In an acoustic field formed by the vibration of a piezoelectric transducer, acoustic streaming was generated using a specially designed, oscillating asymmetrical sidewall shape. We also studied the nature of acoustic streaming generation by numerical simulations, and our simulation results matched well with the experimental results. Trapping and rotation of diatom cells and swine oocytes were coupled using oscillating asymmetrical microstructures with different vibration modes. Finally, we investigated the relationship between the driving voltage and the speed of cell rotation, showing that the rotational rate achieved could be as large as approximately 1800 rpm. Using our device, the rotation rate can be effectively tuned on demand for single-cell studies. Our acoustofluidic cell rotation approach is simple, compact, non-contact, and biocompatible, permitting rotation irrespective of the optical, magnetic, or electrical properties of the specimen under investigation.

Geometrical Parameter Effects on Film-Cooling Effectiveness of Rectangular Diffusion Holes

This paper presents an experimental investigation of the rectangular diffusion hole. The effects of rectangular aspect ratio and lateral diffusion angle on film-cooling effectiveness were studied at a low-speed flat-plate experimental facility. The pressure-sensitive paint (PSP) measurement technique was employed to determine the adiabatic effectiveness. The experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The blowing ratio was varied from M = 0.5 to M = 2.5. Three aspect ratios and three lateral diffusion angles were chosen to match the semicircle and straight-line sidewall shape of the rectangular cross section. A comparative investigation was performed among a typical fan-shaped hole and ten rectangular diffusion holes. The experimental results exhibited diversified film distribution patterns of the rectangular diffusion hole, including single-, bi-, and tripeak patterns. The overall cooling effectiveness increased with the increase of rectangular aspect ratio. The improved magnitude was amplified as blowing ratio increased. The holes with semicircle sidewall were shown to be more suitable for high blowing ratio conditions. The maximum increase of cooling effectiveness was over 70% compared to the fan-shaped hole. The reduction of the lateral diffusion angle affected the film distribution pattern significantly, thereby influencing the cooling effectiveness. To obtain a fixed coverage ratio of film hole row, the rectangular diffusion hole with a larger cross-sectional aspect ratio and a slightly smaller lateral diffusion angle is a preferred scheme.

タイヤへのCAE活用の歴史

A finite element method (FEM) was developed in 1950s as a tool of computational mechanics. In the tire manufacturers, the FEM was started applying to a tire analysis in the beginning of 1970s and this was much earlier than the vehicle industry, electric industry, and others. The main reason was that construction and configurations of a tire were so complicated that analytical approach could not solve many problems related with tire mechanics. Since FEM could make the stress/strain behavior visible in a tire, the application area was mainly tire durability in the early stage. Combining FEM with optimization technique, the tire design procedure has been developed in side wall shape, tire crown shape, tire pattern, and etc. After that the computational mechanics becomes an indispensable tool for tire industry. Furthermore, an insight to improve tire performances is obtained from the optimized solution and the new technologies are created from the insight. The computational mechanics will be applied in multi-disciplinary area and nano-scale area to create a new technology of the environmental subjects such as rolling resistance (RR), noise and wear.

Advancing liquid front shape control in capillary filling of microchannel via arrangement of microposts for microfluidic biomedical Sensors

This paper presents the effect of micropost arrangements on the meniscus shape of the advancing liquid front for capillary filling in a microchannel of biomedical diagnostic sensors. Four different arrangements of cylindrical microposts inside microchannels including hexagonal array with smooth sidewall, hexagonal array with rugged sidewall, rectangular array with smooth sidewall, and rectangular array with rugged sidewall were considered. The meniscus shape of the fluid front were estimated by the volume-of-fluid based computational simulation and compared with experimental results. For hexagonal array, overall meniscus shapes of the advancing liquid front were concave form regardless of sidewall shape. On the other hand, capillary filling through rectangular arrangement of microposts occurred as a step-wise movement with maintaining the flat shape of the advancing liquid fronts. Sidewall microposts affected the capillary filling times rather than the meniscus shape of advancing liquid front. The shape of advancing liquid front and capillary filling time could be passively controlled by arrangement of microposts inside microchannel.