Ampere A. Tseng

Nanofabrication by scanning probe microscope lithography: A review

In addition to its well-known capabilities in imaging and spectroscopy, scanning probe microscopy (SPM) has recently shown great potentials for patterning of material structures in nanoscales. It has drawn the attention of not only the scientific community, but also the industry. This article examines various applications of SPM in modification, deposition, removal, and manipulation of materials for nanoscale fabrication. The SPM-based nanofabrication involves two basic technologies: scanning tunneling microscopy and atomic force microscopy. Major techniques related to these two technologies are evaluated with emphasis on their abilities, efficiencies, and reliabilities to make nanostructures. The principle and specific approach underlying each technique are presented; the differences and uniqueness among these techniques are subsequently discussed. Finally, concluding remarks are provided where the strength and weakness of the techniques studied are summarized and the scopes for technology improvement and future research are recommended.

Recent developments in micromilling using focused ion beam technology

The application of focused ion beam (FIB) technology in microfabrication has become increasingly popular. Its use in microfabrication has advantages over contemporary photolithography or other micromachining technologies, such as small feature resolution, the ability to process without masks and being accommodating for a variety of materials and geometries. An overview of the recent development in FIB microfabrication technology is given. The emphasis will be on direct milling, or maskless techniques, and this can distinguish the FIB technology from the contemporary photolithography process and provide a vital alternative to it. After an introduction to the technology and its FIB principles, the recent developments in using milling techniques for making various high-quality devices and high-precision components at the micrometer scale are examined and discussed. Finally, conclusions are presented to summarize the reviewed work and to suggest the areas for improving the FIB milling technology and for future research.

Electron beam lithography in nanoscale fabrication: recent development

Miniaturization is the central theme in modern fabrication technology. Many of the components used in modern products are getting smaller and smaller. In this paper, the recent development of the electron beam lithography technique is reviewed with an emphasis on fabricating devices at the nanometer scale. Because of its very short wavelength and reasonable energy density characteristics, e-beam lithography has the ability to fabricate patterns having nanometer feature sizes. As a result, many nanoscale devices have been successfully fabricated by this technique. Following an introduction of this technique, recent developments in processing, tooling, resist, and pattern controlling are separately examined and discussed. Examples of nanodevices made by several different e-beam lithographic schemes are given, to illustrate the versatility and advancement of the e-beam lithography technique. Finally, future trends in this technique are discussed.

Removing Material Using Atomic Force Microscopy with Single‐ and Multiple‐Tip Sources

Atomic force microscopy (AFM) has been an effective material removing tool for fabricating various nanostructures because of its sub-nanometer precision and simplicity in operation. AFM material removing techniques have evolved from a solely mechanical process to one in which the tip can be loaded by additional energy sources, such as thermal, electric, or chemical, to enhance its fabrication abilities. In this paper, these material removing techniques are reviewed with an emphasis on their capabilities and recent progress. The recent hardware and software developments are first presented to provide a general view on the current status of the technology to be assessed. Following an overview of the feasibility and effectiveness of using mechanical scratching for removing various types of soft and hard materials, the processes of a wide range of approaches using multiple tip sources are then assessed with a focus on their principles, versatilities, and potentials for future applications.

Fabrication of high-aspect-ratio microstructures using excimer laser

An excimer laser micromachining system is developed to study the ablation of high-aspect-ratio microstructures. The study examines the ablation efficiency, specifically, the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The study focuses on glass, although results on silicon and aluminum are also included for comparison. In ablating grooved structures, the ablation depth has been observed to be linearly proportional to the operating parameters, such as the pulse number and fluence. The results specifically indicate that ablation at low fluence and high repetition rates tends to form a V-shaped cross-section or profile, while a U-shaped profile can be obtained at high fluence and low repetition rate. The ablation rate or ablated volume has then been quantified based on the ablation depth measured and the ablated profile observed. The threshold fluence has also been obtained by extrapolating experimental data of ablation rate. The extrapolation accuracy has been established by the good agreement between the extrapolated value and the one predicted by Beers law. Moreover, a one-dimensional analytical solution has been adopted to predict the ablated volume so as to compare with the experimental data. The reasonable agreement between the two indicates that a simple analytical solution can be used for guiding or controlling further laser operations in ablating glass structures. Finally, the experimental results have shown that increasing the repetition rate favors the morphology of ablated surfaces, though the effect of repetition rate on ablation depth is insignificant.

Scratching properties of nickel-iron thin film and silicon using atomic force microscopy

Atomic force microscopy (AFM) is well known for its ability for nanopatterning many different materials. The patterning technique using an AFM tip as a scratch tool, known as scratch nanolithography, is used to study the scratch characteristics of 80% Permalloy thin film and silicon, with the emphasis on establishing their scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force, scratch speed, and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary factors that measure the scratchability were then identified and the governing material properties for scratchability were evaluated. To demonstrate its versatility, the scratching technique was applied to fabricate a NiFe-based nanoconstriction, which is used for many ferromagnetic devices. All results indicated that NiFe thin film has much better scratchability than that of Si and the scratched groove geometry can be accurately correlated with and pre...

Scratch properties of nickel thin films using atomic force microscopy

Experiments using atomic force microscopy (AFM) as a machining tool for scratching patterns on nickel thin films have been conducted with an emphasis on establishing the material scratchability or more general, the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and scratch direction, on the size of the scratched geometry were investigated. The primary factors that measure the scratchability were then assessed. The scratchability of Ni as compared to that of Si was specifically evaluated and discussed. A stress-hardness analysis was also performed to further validate the experimental and correlation results. All results indicate that the Ni thin film possesses excellent scratchability and one order of magnitude higher than that of Si. Based on the correlation formula developed, Ni should be able to be precisely scratched by AFM tip with the required dimension and nanoscale accuracy and precision.

Milling of submicron channels on gold layer using double charged arsenic ion beam

The capability of using a focused ion beam (FIB) for milling of submicron channel structures on a gold layer is investigated. A double-charged arsenic (As2+) FIB is adopted to assess the effect of the dwell time on the final profiles of the milled structures. A single-pass milling, which creates relatively shallow microchannels, is conducted in order to estimate the corresponding milling yields. The condition to provide a uniform ion flux in milling is first studied. The procedure on conducting the milling experiment is then presented. The atomic force microscope (AFM) is applied for measuring the profiles of the milled channels. Based on the AFM measurements, the milling yields have been estimated and compared with the sputtering yields predicted by a more sophisticated numerical simulation. The milling yield for the relatively shallow microchannels presently considered has been discovered to be roughly equal to the predicted normal-incidence sputtering yield. Consistence has also been found as the prese...

Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC)-coated Si probe

Atomic force microscope (AFM) equipped with diamond-like carbon (DLC)-coated Si probe has been used for scratch nanolithography on Si surfaces. The effect of scratch direction, applied tip force, scratch speed, and number of scratches on the size of the scratched geometry has been investigated. The size of the groove differs with scratch direction, which increases with the applied tip force and number of scratches but decreases slightly with scratch speed. Complex nanostructures of arrays of parallel lines and square arrays are further fabricated uniformly and precisely on Si substrates at relatively high scratch speed. DLC-coated Si probe has the potential to be an alternative in AFM-based scratch nanofabrication on hard surfaces.

Deformation behavior of steels in mushy state

Abstract Processing metals in a semisolid or mushy state has emerged as a vital commercial process to produce metal and metal-matrix composite components. The understanding of the basic deformation behavior of materials in the mushy state is critical for better control of various semisolid processes. The aim of the present study is to quantify the flow stress of mushy-state steels under uniaxial deformation conditions. A hot compression tester has been developed to provide the high temperature setting required for testing mushy-state steels. An analytical scheme, which only requires measuring the dimensions of the final solidified specimen, has been developed to eliminate the barreling effects occurring in compression tests. The temperature of specimens has been carefully controlled to correlate the solid phase content. It has been found that the flow stress of steels in mushy states was highly dependent on the solid phase percentage. The relaxation of steel and stress reduction at mushy states is also discussed.