A modification of the nudged elastic band method for finding minimum energy paths is presented. One of the images is made to climb up along the elastic band to converge rigorously on the highest saddle point. Also, variable spring constants are used to increase the density of images near the top of the energy barrier to get an improved estimate of the reaction coordinate near the saddle point. Applications to CH4 dissociative adsorption on Ir~111! and H2 on Si~100! using plane wave based density functional theory are presented. © 2000 American Institute of Physics. @S0021-9606~00!71246-3#

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A climbing image nudged elastic band method for finding saddle points and minimum energy paths

An improved way of estimating the local tangent in the nudged elastic band method for finding minimum energy paths is presented. In systems where the force along the minimum energy path is large compared to the restoring force perpendicular to the path and when many images of the system are included in the elastic band, kinks can develop and prevent the band from converging to the minimum energy path. We show how the kinks arise and present an improved way of estimating the local tangent which solves the problem. The task of finding an accurate energy and configuration for the saddle point is also discussed and examples given where a complementary method, the dimer method, is used to efficiently converge to the saddle point. Both methods only require the first derivative of the energy and can, therefore, easily be applied in plane wave based density-functional theory calculations. Examples are given from studies of the exchange diffusion mechanism in a Si crystal, Al addimer formation on the Al(100) surfa...

Improved tangent estimate in the nudged elastic band method for finding minimum energy paths and saddle points

A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.

https://science.sciencemag.org/content/sci/272/5258/85.full.pdf

Imprint Lithography with 25-Nanometer Resolution

SINCE the invention of the scanning tunnelling microscope1, the value of establishing a physical connection between the macroscopic world and individual nanometre-scale objects has become increasingly evident, both for probing these objects2–4 and for direct manipulation5–7 and fabrication8–10 at the nanometre scale. While good progress has been made in controlling the position of the macroscopic probe of such devices to sub-angstrom accuracy, and in designing sensitive detection schemes, less has been done to improve the probe tip itself4. Ideally the tip should be as precisely defined as the object under investigation, and should maintain its integrity after repeated use not only in high vacuum but also in air and water. The best tips currently used for scanning probe microscopy do sometimes achieve sub-nanometre resolution, but they seldom survive a 'tip crash' with the surface, and it is rarely clear what the atomic configuration of the tip is during imaging. Here we show that carbon nanotubes11,12 might constitute well defined tips for scanning probe microscopy. We have attached individual nanotubes several micrometres in length to the silicon cantilevers of conventional atomic force microscopes. Because of their flexibility, the tips are resistant to damage from tip crashes, while their slenderness permits imaging of sharp recesses in surface topography. We have also been able to exploit the electrical conductivity of nanotubes by using them for scanning tunnelling microscopy.

Nanotubes as nanoprobes in scanning probe microscopy

4.1. Nanomachining with Scanning Probes 1831 4.2. Soft Lithography 1832 4.3. Embossing with Rigid Masters 1835 4.4. Near-Field Phase-Shifting Photolithography 1835 4.5. Topographically Directed Photolithography 1837 4.6. Topographically Directed Etching 1837 4.7. Lithography with Neutral Metastable Atoms 1838 4.8. Approaches to Size Reduction 1839 5. Techniques for Making Regular or Simple Patterns 1839

https://www.engr.colostate.edu/ECE581/fall07/xia%20chem%20rev%2099.pdf

Unconventional Methods for Fabricating and Patterning Nanostructures.

The scanning tunneling microscope has been used to desorb hydrogen from hydrogen-terminated silicon (100) surfaces. As a result of control of the dose of incident electrons, a countable number of desorption sites can be created and the yield and cross section are thereby obtained. Two distinct desorption mechanisms are observed: (i) direct electronic excitation of the Si-H bond by field-emitted electrons and (ii) an atomic resolution mechanism that involves multiple-vibrational excitation by tunneling electrons at low applied voltages. This vibrational heating effect offers significant potential for controlling surface reactions involving adsorbed individual atoms and molecules.

https://science.sciencemag.org/content/sci/268/5217/1590.full.pdf

Atomic scale desorption through electronic and vibrational excitation mechanisms

Nanoscale patterning of the hydrogen terminated Si(100)‐2×1 surface has been achieved with an ultrahigh vacuum scanning tunneling microscope. Patterning occurs when electrons field emitted from the probe locally desorb hydrogen, converting the surface into clean silicon. Linewidths of 1 nm on a 3 nm pitch are achieved by this technique. Local chemistry is also demonstrated by the selective oxidation of the patterned areas. During oxidation, the linewidth is preserved and the surrounding H‐passivated regions remain unaffected, indicating the potential use of this technique in multistep lithography processes.

https://works.bepress.com/t_shen/46/download/

T. C. Shen

Papers

Atomic scale desorption through electronic and vibrational excitation mechanisms

Nanoscale patterning and oxidation of H‐passivated Si(100)‐2×1 surfaces with an ultrahigh vacuum scanning tunneling microscope

Breaking individual chemical bonds via STM-induced excitations

STM-induced H atom desorption from Si(100): isotope effects and site selectivity

Al nucleation on monohydride and bare Si(001) surfaces: atomic scale patterning