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1.
J Nanosci Nanotechnol ; 11(12): 10687-90, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22408974

RESUMO

Two kinds of new nano tips with potential to magnetic application are fabricated. One is a PtCo alloy pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the epitaxy with a proper growth mode. Ultra high vacuum-field ion microscopy with atomic resolution is used to investigate the atomic structures of the tip apex after various sharpen treatments.

2.
Nanotechnology ; 20(33): 335701, 2009 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-19636091

RESUMO

We report a reliable method for preparing a pure Ir single-atom tip by thermal treatment in oxygen. The atomic structure of the tip apex and its ion emission characteristics are investigated with field ion microscopy. We have shown that the Ir single-atom tip can be a good field ion emitter, capable of emitting a variety of gas ion beams, such as He+, H2+, N2+, and O2+, with high brightness and stability. In addition, this tip can easily be maintained and regenerated in vacuum, ensuring it has sufficient lifetime for practical applications.

3.
Phys Rev Lett ; 102(19): 196102, 2009 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-19518977

RESUMO

We use scanning tunneling spectroscopy to explore the quantum well states in the Pb islands grown on a Cu(111) surface. Our observation demonstrates that the empty quantum well states, whose energy levels lie beyond 1.2 eV above the Fermi level, are significantly affected by the image potential. As the quantum number increases, the energy separation between adjacent states is shrinking rather than widening, contrary to the prediction for a square potential well. By simply introducing a phase factor to reckon the effect of the image potential, the shrinking behavior of the energy separation can be reasonably explained with the phase accumulation model. The model also reveals that there exists a quantum regime above the Pb surface in which the image potential is vanished. Moreover, the quasi-image-potential state in the tunneling gap is quenched because of the existence of the quantum well states.

4.
Nanotechnology ; 20(11): 115401, 2009 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-19420438

RESUMO

In quantum mechanics, a wavefunction contains two factors: the amplitude and the phase. Only when the probing beam is fully phase coherent, can complete information be retrieved from a particle beam based experiment. Here we use the electron beam field emitted from a noble-metal covered W(111) single-atom tip to image single-walled carbon nanotubes (SWNTs) in an electron point projection microscope (PPM). The interference fringes of an SWNT bundle exhibit a very high contrast and the fringe pattern extends throughout the entire beam width. This indicates good phase correlation at all points transverse to the propagation direction. Application of these sources can significantly improve the performance and expand the capabilities of current electron beam based techniques. New instrumentation based on the full spatial coherence may allow determination of the three-dimensional atomic structures of nonperiodic nanostructures and make many advanced experiments possible.

5.
Nanotechnology ; 19(32): 325703, 2008 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-21828825

RESUMO

A two-dimensional (2D) dopant profiling technique is demonstrated in this work. We apply a unique cantilever probe in electrostatic force microscopy (EFM) modified by the attachment of a multiwalled carbon nanotube (MWNT). Furthermore, the tip apex of the MWNT was trimmed to the sharpness of a single-walled carbon nanotube (SWNT). This ultra-sharp MWNT tip helps us to resolve dopant features to within 10 nm in air, which approaches the resolution achieved by ultra-high vacuum scanning tunnelling microscopy (UHV STM). In this study, the CNT-probed EFM is used to profile 2D buried dopant distribution under a nano-scale device structure and shows the feasibility of device characterization for sub-45 nm complementary metal-oxide-semiconductor (CMOS) field-effect transistors.

6.
Phys Rev Lett ; 99(21): 216103, 2007 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-18233232

RESUMO

Gundlach oscillation (or the standing-wave state) is a general phenomenon manifesting in the tunneling spectrum acquired from a metal surface using scanning tunneling spectroscopy. Previous studies relate the energy shift between peaks of the lowest-order Gundlach oscillation observed on the thin film and the metal substrate to the difference in their work functions. By observing Gundlach oscillations on Ag/Au(111), Ag/Cu(111), and Co/Cu(111) systems, we demonstrate that the work function difference is not the energy shift of the lowest order but the ones of higher order where a constant energy shift exhibits. Higher order Gundlach oscillations can thus be applied to determine the work function of thin metal films precisely.

7.
Phys Rev Lett ; 97(8): 089601; discussion 089602, 2006 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-17026340
8.
Phys Rev Lett ; 94(13): 136101, 2005 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-15904006

RESUMO

Electronic Moirè patterns found on lead (Pb) quantum islands can serve as a template to grow self-organized cluster (nanopucks) arrays of various materials. These patterns can be divided into fcc- and hcp-stacked areas, which exhibit different binding strengths to the deposited adatoms. For Ag adatoms, the binding energy can differ substantially and the confined nucleation thus occurs in the fcc sites. Both the size distribution and spatial arrangement of the Ag nanopucks are analyzed and found to be commensurate with the characteristics of the template island, which exhibits a bilayer oscillatory behavior.

9.
Phys Rev Lett ; 94(4): 045505, 2005 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-15783571

RESUMO

We have observed interesting H-atom adsorption induced atomic rearrangements of a Pb monolayer on the Si(111) with a scanning tunneling microscope. A hexagonal ringlike pattern is formed around the point defect. The interactions among nearby H-adsorbed defects can even produce interferencelike superstructures. Phase boundaries are found to either enhance or suppress the formation of the interference pattern. These phenomena are produced by an intricate interplay between electronic and atomic interactions as perturbed by the adsorbed hydrogen atoms.

10.
Phys Rev Lett ; 93(10): 106101, 2004 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-15447421

RESUMO

We study a reversible, temperature-driven structural surface phase transition of Pb/Si(111) nanoislands with a variable-temperature scanning tunneling microscope. Our quantitative measurements indicate that the transition temperature decreases with decreasing island and domain size. The boundaries of the nanoislands also influence the transition. Careful examination of the change in the interior structure of nanoislands near the transition temperature allows us to image the effects of the thermal fluctuations.

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