Thermomechanical properties of polymer nanolithography using atomic force microscopy

The temperature-dependent mechanical properties of polyethylene terephthalate (PET) polymers are investigated using force-distance curves, adhesion force, and atomic force microscope (AFM) nanolithography combined the heating techniques. The results show that the width of grooves on the polymers at 20-60 °C were in the range of 14-363 nm. The wear depth of the polymers increased with increasing heating temperature. A volume of 251.85-2422.66 μm(3) at a load of 30-50 nN with heating to 30-60 °C was removed, as compared to that of 26.60-70.30 μm(3) obtained at room temperature. The contact forces of PET started increasing at 9 nN, whereas the size of the holes was average at a pressure. The results may be of importance in explaining the heating relationship among adhesion force, volume removal rate, and pressure.     

Physical bounds of metallic nanofingers obtained by mechano-chemical atomic force microscope nanolithography

To obtain metallic nanofingers applicable in surface acoustic wave (SAW) sensors, a mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50 nm in thickness)/piezoelectric substrate covered by a spin-coated polymeric mask layer (50-60 nm in thickness) was implemented. The effective shape of cross-section of the before and after etching grooves have been determined by using the AFM tip deconvolution surface analysis, structure factor, and power spectral density analyses. The wet-etching process improved the shape and aspect ratio (height/width) of the grooves and also smoothed the surface within them. We have shown that the relaxed surface tension of the polymeric mask layer resulted in a down limitation in width and length of the lithographed nanofingers. The surface tension of the mask layer can be changed by altering the initial concentration of the polymer in the deposition process. As the surface tension reduced, the down limitation decreased. In fact, an extrapolation of the analyzed statistical data has indicated that by decreasing the surface tension from 39 to 10 nN/nm, the minimum obtainable width and length of the metallic nanofingers was changed from about 55 nm and 2 μm to 15 nm and 0.44 μm, respectively. Using the extrapolation’s results, we have shown that the future SAW sensors buildable by this nanolithography method possess a practical bound in their synchronous frequency (∼58 GHz), mass sensitivity (∼6125 MHz-mm²/ng), and the limit of mass resolution (∼4.88 × 10⁻¹⁰ ng/mm²).     

Splitting of atomic beams by light for creation of high-resolution spatial structures in optical nanolithography

Diffraction of atomic wave packets from a standing laser wave with a Gaussian profile is studied theoretically and numerically in pursuing the aim of creating high-resolution spatial structures in optical nanolithography. To this end, we propose to use nonadiabatic transitions between two optical potentials which take place when square of the value of detuning off the resonance is approximately equal to the Doppler shift. In this case, atomic wave packets experience splitting at nodes of the standing wave, which allows creating atomic structures on a substrate with a period substantially smaller than the standard nanofabrication limit equal to half the wavelength of light. We propose a scheme of the experiment for the observation of nonadiabatic transitions and splitting of the wave of matter caused by them. A number of computer simulations with parameters corresponding to real atoms have been performed, which exhibit this effect in both momentum and coordinate spaces.     

Equilibrium capillary forces with atomic force microscopy

We present measurements of equilibrium forces resulting from capillary condensation. The results give access to the ultralow interfacial tensions between the capillary bridge and the coexisting bulk phase. We demonstrate this with solutions of associative polymers and an aqueous mixture of gelatin and dextran, with interfacial tensions around 10 microN/m. The equilibrium nature of the capillary forces is attributed to the combination of a low interfacial tension and a microscopic confinement geometry, based on nucleation and growth arguments.     

On the possibility of observing nonadiabatic atomic transitions in a laser field and their application to nanolithography

The scheme of an experiment has been proposed to observe nonadiabatic atomic transitions in the standingwave laser field and splitting of atomic wave packets on the nodes of the standing wave induced by these transitions in a certain range of optical detuning. The effect can be implemented in atomic-optical nanolithography for making spatial atomic structures with a period much smaller than the optical wavelength.     

Cold-atom physics using ultrathin optical fibers: light-induced dipole forces and surface interactions

The strong evanescent field around ultrathin unclad optical fibers bears a high potential for detecting, trapping, and manipulating cold atoms. Introducing such a fiber into a cold-atom cloud, we investigate the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface. Using high resolution spectroscopy, we observe and analyze light-induced dipole forces, van der Waals interaction, and a significant enhancement of the spontaneous emission rate of the atoms. The latter can be assigned to the modification of the vacuum modes by the fiber.     

Material transport in dip-pen nanolithography

Dip-pen na.nolithography （DPN） is a useful method for directly printing materials on surfaces with sub-50nm resolution. Because it, involves the physical transport of materials from a scanning probe tip to a surface and the subsequent chemical interaction of that material with the surface, there are many factors to consider when attempting to understand DPN. In this review, we overview the physical and chemical processes that are known to play a role in DPN, Through a detailed review of the literature, we classify inks into three general categories based on their transport properties, and highlight the myriad ways that. DPN can be used to perform chemistry at the tip of a scanning probe.     

Atomistic simulations of fluid structure and solvation forces in atomic force microscopy

We describe results of atomistic molecular dynamics simulations modelling an atomic force microscope (AFM) tip immersed in a fluid. Both the tip and the surface are modelled by rigid arrays of atoms. The tip is pyramidal and the surface is the (100) face of a fcc crystal. The focus is on the solvation forces acting on the tip and on the surface and their relation to the structural and dynamic properties of the fluid. Fluid particles in the neighborhood of the tip-surface junction are found to be highly ordered compared to the bulk, as shown by localized variations in the average fluid density. The atomistic nature of the model gives rise to several effects related to the discrete sizes of the fluid, tip, and surface particles which are not observed in continuum-based theories. A number of simulated force-distance curves are presented, along with an analysis of the effect of changing fluid particle size, tip (lateral) position, tip shape, and the lyocompatability of the tip and surface materials. The atomic-scale distribution of fluid-surface forces is examined for various positions of the tip, and the extent to which the fluid can act as a “cushion” by increasing the effective area of the tip-surface interaction is studied. The effect of a fluid on AFM imaging is investigated by generating “fluid images”, which are shown to be comparable in magnitude to the direct tip-surface interaction in the noncontact mode. We compare images generated by defective and defect-free surfaces, and analyse the fluid-tip forces acting in a lateral direction. An image formed from fluid forces acting in the direction of the surface normal does not show the presence of a vacancy, but an image formed from lateral fluid forces does.     

Far-field superlens for nanolithography

A far-field optical lithography is developed in this paper. By designing the structure of a far-field optical superlens, lithographical resolution can be improved by using a conventional UV light source. The finite different time domain numerical studies indicate that the lithographic resolution at 50~nm line width is achievable with the structure shown in this paper by using 365~nm wavelength light, and the light can be transferred to a far distance in the photoresist.     

Direct low-energy electron beam nanolithography

We describe here an alternative approach to direct low-energy electron beam nanolithography process with no conventional deposition of any resist or self-assembled monolayer. The method is based on direct formation of ultrathin dielectric layer on electron irradiated surface, without generation of structural defects. High-quality electron-induced patterns with lateral resolutions of about 10 nm are demonstrated on SiO₂ surface.     

Interference nanolithography with a UV laser

The sensitivity and resolution of a photoresist composed of a two-layer (polymer-metallic indium) film are measured. 2D masks used to create nanodimensional metallic and insulating islands on a silicon substrate are prepared by direct laser action. Conditions are found for preparing submicron periodic structures on TiO₂ films that are applied on a glass substrate by the sol-gel technology. Optical properties of these arrays are measured, and it is shown that they can be used for exciting plane electromagnetic waves.     

原子力显微镜探针耦合变形下的微观扫描力研究

原子力显微镜(AFM)的微探针系统是典型的微机械构件，它在接触扫描过程处于耦合变形状态.采用数值模拟方法探究恒力模式下探针耦合变形对微观扫描力信号、微观形貌信号的影响.研究表明，AFM的恒力模式扫描中，法向扫描力并不是恒定大小，与轴向扫描力存在耦合作用，在粗糙峰峰值增加阶段，二力均增加；在粗糙峰峰值减小阶段，二力均减小；该耦合作用随形貌坡度、针尖长度等增加而加强.微观形貌的测试信号和横向扫描侧向力信号受探针耦合变形影响较小，但侧向力与形貌斜率密切相关，且其极值点与形貌极值点存在位置偏差，这些结果均与原子力 关键词： 原子力显微镜 探针悬臂梁 耦合变形 扫描力     

Ordering of Ge nanocrystals using FIB nanolithography

Formation and ordering of Ge nanocrystals (NC) are studied on Si(0 0 1) and SiO₂/Si(0 0 1) substrates patterned by focused ion beam (FIB). In both cases we use a three step process consisting of FIB milling of hole patterns with various periodicities, ex-situ substrate cleaning to remove Ga contamination and Ge NC growth by molecular beam epitaxy (MBE). We show that Ge NC can be ordered between or inside the holes on patterned Si(0 0 1) substrates and inside the holes on patterned SiO₂/Si(0 0 1) substrates.     

Capillary force on a nanoscale tip in dip-pen nanolithography

Monte Carlo simulation has been used to characterize the capillary force due to the condensation of a liquid meniscus between a tip with a nanoscale asperity and a flat surface. To consider both hydrophobic and hydrophilic molecules coating the tip as a model of dip-pen nanolithography, tips with various wettabilities are studied. The capillary force due to the meniscus is calculated for various saturations (humidities). We have implemented a thermodynamic integration technique that can project the force into energetic and entropic contributions. In most cases, the force is mainly energetic in origin. At the snap-off separation where the meniscus disappears, the tip feels a significant entropic force at high saturation. Our calculation shows nonmonotonic behavior of the pull-off force as a function of saturation, which is in qualitative accord with experiments.     

Adsorption effects in light-induced drift

We describe the effect of light-induced drift, while allowing for adsorption of the active atoms on the wall of the cell. Assuming a rapid rate of adsorption and desorption, we express this effect by a modification of the diffusion equation for the volume density in the boundary layer near the wall. Explicit solutions are discussed in opposite special cases, corresponding to a large or a small mean free path of the active atoms.