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New approaches to nanofabrication: molding, printing, and other techniques.

Advances in top-down and bottom-up surface nanofabrication: techniques, applications & future prospects.

A review of atomic force microscopy imaging systems: application to molecular metrology and biological sciences

The nanoscale control afforded by scanning probe microscopes has prompted the development of a wide variety of scanning-probe-based patterning methods. Some of these methods have demonstrated a high degree of robustness and patterning capabilities that are unmatched by other lithographic techniques. However, the limited throughput of scanning probe lithography has prevented its exploitation in technological applications. Here, we review the fundamentals of scanning probe lithography and its use in materials science and nanotechnology. We focus on robust methods, such as those based on thermal effects, chemical reactions and voltage-induced processes, that demonstrate a potential for applications.

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Advanced scanning probe lithography

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.

Nanofabrication by scanning probe microscope lithography: A review

The chemical modification of hydrogen‐passivated n‐Si (111) surfaces by a scanning tunneling microscope (STM) operating in air is reported. The modified surface regions have been characterized by STM spectroscopy, scanning electron microscopy (SEM), time‐of‐flight secondary‐ion mass spectrometry (TOF SIMS), and chemical etch/Nomarski microscopy. Comparison of STM images with SEM, TOF SIMS, and optical information indicates that the STM contrast mechanism of these features arises entirely from electronic structure effects rather than from topographical differences between the modified and unmodified substrate. No surface modification was observed in a nitrogen ambient. Direct writing of features with 100 nm resolution was demonstrated. The permanence of these features was verified by SEM imaging after three months storage in air. The results suggest that field‐enhanced oxidation/diffusion occurs at the tip‐substrate interface in the presence of oxygen.

Modification of hydrogen-passivated silicon by a scanning tunneling microscope operating in air

Recent results employing scanning tunneling microscope‐based techniques for the generation of nanometer‐scale patterns on passivated semiconductor surfaces are presented. Preparation and characterization of hydrogen‐passivated silicon and sulfur‐passivated gallium arsenide surfaces are described and the determination of the chemical and morphological properties of the patterned regions by scanning electron microscopy and time‐of‐flight secondary ion mass spectrometry are discussed. Our recent demonstration that ultrashallow, oxide features written by scanning tunneling microscope (STM) can serve as an effective mask for selective‐area GaAs heteroepitaxy on silicon is used to illustrate key requirements necessary for the realization of a unique, STM‐based nanotechnology.

Pattern generation on semiconductor surfaces by a scanning tunneling microscope operating in air

We report a novel method of GaAs substrate preparation which imparts significantly improved topographical and chemical uniformity to the surface. The procedure, employing an aqueous P2S5/(NH4)2S solution, leaves the surface in a highly ordered state and resistant to air oxidation for periods of a day or more without the presence of foreign chemical layer such as sulfur. Surface quality was determined by scanning tunneling microscopy (STM), time‐of‐flight secondary ion mass spectrometry, reflection high‐energy electron diffraction, and x‐ray photoelectron spectroscopy. The remarkable stability and smoothness of treated III‐V surfaces is illustrated by STM imaging of an Al0.51Ga0.49As/GaAs superlattice in air. The superlattice consisted of periodic alternating AlGaAs/GaAs layers of various thicknesses from 10 to 1000 nm.

P2S5 Passivation of GaAs Surfaces for Scanning Tunneling Microscopy in Air

The emerging field of nanoelectronics demands innovative methods to fabricate nanometer‐scale structures. Such structures will play a critical role in the quantum‐effect device physics of future highly integrated circuit architectures. An integrated approach to compound semiconductor nanostructure fabrication based on scanning tunneling microscope (STM) nanolithography, molecular‐beam epitaxy, and reactive ion etching techniques is described. The critical elements of this approach, which have been demonstrated recently, are reviewed. Prospects for the coevolutionary development of nanoelectronics and STM‐based fabrication and characterization are considered.

Integration of scanning tunneling microscope nanolithography and electronics device processing

Nanometer‐scale pattern generation on III‐V semiconductor substrates using a scanning tunneling microscope (STM) operating in air is demonstrated. The sample substrates, consisting of arsenic‐capped, epitaxial layers of n‐doped GaAs, AlxGa1−xAs and InyGa1−yAs were prepared by molecular beam epitaxy and characterized by time‐of‐flight secondary‐ion mass spectrometry and x‐ray photoelectron spectroscopy. The direct patterning of features of width ≤50 nm on GaAs and In0.2Ga0.8As surfaces is shown to be the result of the formation of a strongly bonded surface oxide induced under high electric field conditions existing between the scan tip and the substrate. The significance of STM pattern generation of nanometer‐scale oxide masks for use in the fabrication of low‐dimensional heterostructures is discussed.

J. Bennett

Papers

Modification of hydrogen-passivated silicon by a scanning tunneling microscope operating in air

Pattern generation on semiconductor surfaces by a scanning tunneling microscope operating in air

P2S5 Passivation of GaAs Surfaces for Scanning Tunneling Microscopy in Air

Integration of scanning tunneling microscope nanolithography and electronics device processing

Nanolithography on III‐V semiconductor surfaces using a scanning tunneling microscope operating in air