Block Elements in Contact Problems with a Variable Friction Coefficient

Contact problems on the surface interaction of rigid stamps with a deformed layered medium are considered provided that the variable friction coefficients arise in the contact zone as a function of the coordinate under the horizontal motion of stamps. The cause of the variable friction coefficients arising may be surface phenomena induced by a complex rheology of the deformed-medium surface, the chemical reactions proceeding, or a change in the properties of the contact surface of the stamps, for example, as a result of the presence of separate particles of the wear contact surface of the stamp and the base.     

UV-curable nanoimprint resin with enhanced anti-sticking property

This paper reports on a newly developed anti-sticking resin obtained by mixing a fluorine-containing monomer (F-monomer) for UV nanoimprinting lithography (UV-NIL) to reduce the contact adhesion force during the demolding process. The new resin system shows an enhanced reliability and resolution of pattern transfer with no treatment on the surface of the quartz stamp. We fabricated various nanopatterns with F-monomer resins of various concentrations in the low pressure UV-NIL. The number of process steps of a release layer treatment for UV-NIL was reduced by using F-monomer with anti-sticking property.     

Influence of un-cured PDMS chains in stamp using PDMS-based lithography

We present the compatibility of elastomeric stamp, poly(dimethylsiloxane) (PDMS), with inks for non-photolithography. This ink limitation is important in considering the lamination of hydrophilic solution on the patterned ink surface using an elastomeric stamp. We focus on an increase of the hydrophobicity of the patterned surface due to diffusion of low molecular weight (LMW) silicone polymer chains. This hydrophobicity increases inversely with the PDMS–ink interaction parameter (χ), which is correlated with the solubility parameter (δ). This study's results translate into proposed design factors for ink used in the patterned functional layer for PDMS-based lithography. Both the XPS and the contact angle measurement show that the hydrophobicity can be increased by LMW PDMS chains transfer from stamps, and this increase can cause the expansion of the free volume in PDMS pores through a swelling effect.     

Singular solutions of contact problems and block elements

In this work, we consider mixed problems of elasticity theory, in particular, contact problems for cases that are nontraditional. They include mixed problems with discontinuous boundary conditions in which the singularities in the behavior of contact stresses are not studied or the energy of the singularities is unbounded. An example of such mixed problems is contact problems for two rigid stamps approaching each other by rectilinear boundaries up to contact but not merging into one stamp. It has been shown that such problems, which appear in seismology, failure theory, and civil engineering, have singular components with unbounded energy and can be solved by topological methods with pointwise convergence, in particular, by the block element method. Numerical methods that are based on using the energy integral are not applicable to such problems in view of its divergence.     

Micro via and line patterning for PCB using imprint technique

Today’s electronic devices such as mobile phones, PDA, computers, etc. have more functions in a smaller size. Thus conducting lines and via holes of PCB (printed circuit board) which has a role of land for all kinds of electronic components are getting finer. In this study, the conducting lines and via holes are produced using thermal imprint technique rather than the conventional photo-lithography process. Imprint technique is a press process that transfers patterns of stamp to resins. Imprint technique is used to produce micro size trench lines and via holes in epoxy resins.Resins used in this work are silica (SiO₂) reinforced epoxy. Resins were imprinted using 10 * 10 mm size Ni or polymer stamp. Line/space of pattern is 10/10 μm while diameter of via hole is 30 μm. The depths of lines and via holes are 15 and 30 μm, respectively. The anti-sticking treated stamp and epoxy resins were pressed at 100 °C for 30 min in vacuum. The stamp was released after resins were cured for 1 h at 130 °C. All patterns of stamp were successfully transferred with high fidelity and any noticeable defect was not observed within imprinted area. Imprinted resins were de-smeared to remove the residue at the bottom of via holes and to enhance the adhesion of resins with Cu. Electro/less copper plating was followed to fill in the imprinted patterns. Since the excess Cu layer was formed on the resins during Cu plating, the planarization process was introduced to obtain isolated lines and via holes.     

Minimizing silicone transfer during micro-contact printing

Methods to minimize the transfer of silicone from PDMS stamps during micro-contact printing have been investigated. This study focused on amino-silanes stamped onto PTFE substrates. Analysis of the stamped surfaces was through surface sensitive techniques such as XPS and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that curing the PDMS at elevated temperatures minimized the amount of silicone transferred. The amount of silicone transferred also depended on the pretreatment of the stamp and the type of ink used.     

邮票上的光谱学史、化学史和光学史课件的制作

介绍了运用多媒体技术将美国F．A．米勒教授的《邮票上的光谱学史》,《邮票上的化学史》和《邮票上的光学史》三篇杰作制作成电子课件的设计思想,开发过程及关键技术。     

Heterogeneity of surface potential in contact electrification under ambient conditions: A comparison of pre- and post-contact states

We measured the pattern of charging by contact electrification, following contact between a polydimethylsiloxane (PDMS) stamp and a glass substrate with gold electrodes. We used scanning Kelvin probe microscopy to map the surface potential at the same regions before and after contact, allowing a point-by-point comparison. After contact, the mean surface potential of the glass shifted by 360 mV and micron-scale heterogeneity appeared with a magnitude of ∼100 mV. The gold electrodes showed charge transfer but no discernible heterogeneity. These results show that contact electrification causes heterogeneity of surface potential even on non-polymer surfaces such as glass under ambient conditions.     

Molecular dynamics simulations on the direct sputtering of Al2O3 insulating film in a magnetic tunneling junction

The molecular dynamics (MD) simulation is used to study the direct deposition of aluminum-oxide (Al₂O₃) to grow an insulating thin film on cobalt substrate in a magnetic tunneling junction (MTJ). The direct deposition of Al₂O₃ may produce a very thin film with very smooth surface and form an averagely oxidized insulator. A high magnetoresistance ratio is desired in an MTJ device, so that smooth surface and good structural integrity for the insulating thin film is anticipated. The MD simulation is an effective way in determining optimal processing parameters that can be used to fabricate high-quality MTJ devices. The Buckingham and many-body tight-binding potentials are applied in the MD simulations for different interactions between particles. The effects of the cluster size and the incident energy on the thin film’s surface morphology and Al₂O₃ purity are investigated. Some optimal parameters that could be used as the reference for practical processing purposes are derived.     

High-speed residue-free transfer of two-dimensional materials using PDMS stamp and water infiltration

A high-speed residue-free transfer method using PDMS (polydimethylsiloxane) stamp and water infiltration between graphene and a hydrophilic surface is reported. Monolayer graphene was transferred from an enhanced fluorinated Al₂O₃ surface using PDMS. Water infiltration dramatically reduced the time required to separate the graphene from the Al₂O₃ substrate to a few minutes. The graphene was then successfully transferred to a target substrate (SiO₂) using the PDMS stamp. Atomic force microscopy and lateral force microscopy was used to confirm the absence of residue on the transferred graphene surface.     

High-refractive-index measurement with an elastomeric grating coupler

An elastomeric grating coupler fabricated by the replica molding technique is used to measure the modal indices of a silicon-on-insulator (SOI) planar waveguide structure. Because of the van der Waals interaction between the grating mold and the waveguide, the elastomeric stamp makes conformal contact with the waveguide surface, inducing a periodic index perturbation at the contact region. The phase of the incident light is changed to match the guided modes of the waveguide. The modal and bulk indices are obtained by measuring the coupling angles. This technique serves to measure the high refractive index with a precision better than 10(-3) and allows the elastomeric stamp to be removed without damaging the surface of the waveguide.     

Replication of microchannel structures in polymers using laser fabricated glass–ceramic stamp

A new microreplication process with photo-etchable glass–ceramic stamps and polymers is presented. This process has two main advantages: a rapid master fabrication with a laser process and a flexible replication process compared with conventional nano- or microreplication technique on polymers. Photo-etchable glass–ceramics are used for the master stamp. Micropatterns can be rapidly transferred with a laser direct writing process and the removal of the glass–ceramics can be efficiently achieved with a wet etching process. Therefore, microstructures with flat bottom surfaces and straight sidewall structures can be obtained, which is difficult in the laser direct writing process. A microstamping process of applying heat and pressure, also referred to as hot embossing lithography or microstamping, can replicate microstructures on polymer surfaces. In this work, the fabricated glass–ceramic stamps are used for the replication process and various replicated polymer microstructures are presented.     

Effects of wettability and interfacial nanobubbles on flow through structured nanochannels: an investigation of molecular dynamics

Solid–fluid boundary conditions are strongly influenced by a number of factors, including the intrinsic properties of the solid/fluid materials, surface roughness, wettability, and the presence of interfacial nanobubbles (INBs). The interconnected nature of these factors means that they should be considered jointly. This paper employs molecular dynamics (MD) simulation in a series of studies aimed at elucidating the influence of wettability in boundary behaviour and the accumulation of interfacial gas. Specifically, we examined the relationship between effective slip length, the morphology of nanobubbles, and wettability. Two methods were employed for the promotion of hydrophobicity between two structured substrates with similar intrinsic contact angles. We also compared anisotropic and isotropic atomic arrangements in the form of graphite and Si(100), respectively. A physical method was employed to deal with variations in surface roughness, whereas a chemical method was used to adjust the wall–fluid interaction energy (?_wf). We first compared the characteristic properties of wettability, including contact angle and fluid density within the cavity. We then investigated the means by which variations in solid–fluid interfacial wettability affect interfacial gas molecules. Our results reveal that the morphology of INB on a patterned substrate is determined by wettability as well as the methods employed for the promotion of hydrophobicity. The present study also illustrates the means by which the multiple effects of the atomic arrangement of solids, surface roughness, wettability and INB influence effective slip length.     

Fabrication of structures with tunable morphologies and sizes by soft molding

This paper presents a simple and versatile patterning method to fabricate polymer patterns with different morphologies and sizes by utilizing soft molding. When a patterned elastomeric stamp was placed on the polymer solution dropped on the substrate, the polymer solution will fill into the grooves of the stamp under capillary force. Through the modulation of the polymer concentration, it is possible to produce highly regular and reproducible polymer patterns with tunable morphologies and sizes using the same microscopic patterned mold. The gained polymer patterns can be further transferred to produce second-generation stamps.     

Hot embossing of PTFE: Towards superhydrophobic surfaces

Three types of reusable stamps with features in the form of 2D arrays of pits having lateral dimensions in the range of 2-80 μm and heights of 1.5-15 μm were successfully employed for the hot embossing of PTFE at temperatures up to 50 °C above the glass transition temperature of PTFE amorphous phase. Due to the softening of PTFE at the temperatures used in this study, we were able to decrease imprint pressure significantly when comparing with the imprint conditions reported by other authors. Impact of the imprint temperature, pressure and time on the fidelity of pattern transfer as well as on water repellency was tested. The best results of embossing were achieved by applying pressure of 10 kg/cm² for 2 min at 170 °C. In this case, flattening of a natural PTFE roughness and pretty accurate deep replicas of the stamp patterns were observable on the whole imprinted area. Improvement in water repellency was largest for the samples imprinted by Ni stamp patterned with a 2D array of 2 μm square pits spaced by the same dimension and having a depth of 1.5 μm. Cassie-Baxter wetting regime was observed for the deepest imprints with water contact angles up to the superhydrophobic limit.     

低能原子沉积在Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学方法模拟了六种贵金属原子(Ni,Pd,Pt,Cu,Ag,Au)分别在Pt(111)表面低能沉积的动力学过程.结果表明:随着入射能量从0.1eV升高到200eV,基体表面原子是按层迁移的,沉积过程对基体表面的影响和沉积原子在基体表层的作用均存在两个转变能量(ET1≈5eV,ET2≈70eV).当入射能量低于5eV时,基体表面几乎没有吸附原子和空位形成,沉积原子在基体表层几乎没有注入产生;当入射能量在5—70eV范围内时,沉积原子在基体表层有注入产生,其注入深度小于两个原子层,即为亚注入,此时吸附原子主要由基体表层原子形成,基体表面第三层以下没有空位形成;当入射能量高于70eV时,沉积原子的注入深度大于两个原子层,将会导致表面以下第三层形成空位,并且空位产额随入射能量的升高而急剧增加.基于分子动力学模拟的结果,对低能沉积作用下的薄膜生长以及最优沉积参数的选择进行了讨论.     

Superhydrophobic surface structures in thermoplastic polymers by interference lithography and thermal imprinting

We present a method to produce superhydrophobic surfaces in thermoplastic polymer substrates. The method involves the creation of a nickel stamp using a customized laser interference lithography technique and electroplating processes. This stamp is used to emboss sub-micrometer periodic structures into the thermoplastic. The modified surface is coated with a hydrophobic plasma-polymerized hexafluoropropene layer. Surfaces with different periodicity and relief depth were created. On the surface with the highest aspect ratio, advancing water contact angles of 167° were measured with a water contact angle hysteresis of below 5°.     

The fabrication of 3-D nanostructures by a low- voltage EBL

Three-dimensional (3-D) structures are used in many applications, including the fabrication of opto-electronic and bio-MEMS devices. Among the various fabrication techniques available for 3-D structures, nano imprint lithography (NIL) is preferred for producing nanoscale 3-D patterns because of its simplicity, relatively short processing time, and high manufacturing precision. For efficient replication in NIL, a precise 3-D stamp must be used as an imprinting tool. Hence, we attempted the fabrication of original 3-D master molds by low-voltage electron beam lithography (EBL). We then fabricated polydimethylsiloxane (PDMS) stamps from the original 3-D mold via replica molding with ultrasonic vibration.First, we experimentally analyzed the characteristics of low-voltage EBL in terms of various parameters such as resist thickness, acceleration voltage, aperture size, and baking temperature. From these e-beam exposure experiments, we found that the exposure depth and width were almost saturated at 3 kV or lesser, even when the electron dosage was increased. This allowed for the fabrication of various stepped 3-D nanostructures at a low voltage. In addition, by using line-dose EBL, V-groove patterns could be fabricated on a cured electron resist (ER) at a low voltage and low baking temperature. Finally, the depth variation could be controlled to within 10 nm through superposition exposure at 1 kV. From these results, we determined the optimum electron beam exposure conditions for the fabrication of various 3-D structures on ERs by low-voltage EBL. We then fabricated PDMS stamps via the replica molding process.     

Dynamical structure of α-Ag0.99Cu0.01I crystal by Cu NMR chemical shift, spin-lattice relaxation time and molecular dynamics simulation

Solid ⁶³Cu NMR and Molecular Dynamics (MD) methods have been used to investigate the dynamical structure of Ag_0.99Cu_0.01I crystal, through the viewpoint of the chemical shift and the spin-lattice relaxation. In the superionic phase (α-phase), we obtained the temperature variation of the chemical shift as −0.2 ppm/K, and the activation energy of the Cu⁺ ion diffusion as 11 kJ/mol. The temperature dependence of the chemical shift was explained by the calculated chemical shielding surface based on ab initio MO calculation, and by the probability density of Cu⁺ ion estimated by MD simulation. The spin-lattice relaxation was also analyzed by using the MD method in which we assumed two jumping models as the diffusion process of the mobile cations. It is concluded that the temperature dependence of the chemical shift is dominated by the shielding in the vicinity of the 24(h) site, and the observed activation energy is due to the diffusion process of the mobile cations jumping from the 6(b) intrasub-lattice to the nearest-neighbor 6(b) sub-lattice.     

Fabrication of Nanoimprint Stamp Using Interference Lithography

Interference lithography is used to fabricate a nanoimprint stamp, which is a key step for nanoimprint lithography. A layer of chromium in thickness of about 20 nm is deposited on the newly cleaned fused silica substrate by thermal evaporation, and a layer of positive resist in thickness of 150nm is spun on the chromium layer. Some patterns, including lines, holes and pillars, are observed on the photoresist film by exposing the resist to interference patterns and they are then transferred to the chromium layer by wet etching. Fused silica stamps are fabricated by reactive ion etching with CHF3/O2 as etchants using the chromium layer as etch mask. An atomic force microscope is used to analyse the pattern transfer in each step. The results show that regular hole patterns of fused silica, with average full width 143nm at half maximum （FWHM）, average hole depth of 76nm and spacing of 450nm, have been fabricated. The exposure method is fast, inexpensive and applicable for fabrication of nanoimprint stamps with large areas.