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1.
Nanotechnology ; 28(25): 255301, 2017 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-28548051

RESUMO

Focused ion beam (FIB) systems have become powerful diagnostic and modification tools for nanoscience and nanotechnology. Gas field ion sources (GFISs) built from atomic-size emitters offer the highest brightness among all ion sources and thus can improve the spatial resolution of FIB systems. Here we show that the Ir/W(111) single-atom tip (SAT) can emit high-brightness Xe+ ion beams with a high current stability. The ion emission current versus extraction voltage was analyzed from 150 K up to 309 K. The optimal emitter temperature for maximum Xe+ ion emission was ∼150 K and the reduced brightness at the Xe gas pressure of 1 × 10-4 torr is two to three orders of magnitude higher than that of a Ga liquid metal ion source, and four to five orders of magnitude higher than that of a Xe inductively coupled plasma ion source. Most surprisingly, the SAT emitter remained stable even when operated at 309 K. Even though the ion current decreased with increasing temperature, the current at room temperature (RT) could still reach over 1 pA when the gas pressure was higher than 1 × 10-3 torr, indicating the feasibility of RT-Xe-GFIS for application to FIB systems. The operation temperature of Xe-SAT-GFIS is considerably higher than the cryogenic temperature required for the helium ion microscope (HIM), which offers great technical advantages because only simple or no cooling schemes can be adopted. Thus, Xe-GFIS-FIB would be easy to implement and may become a powerful tool for nanoscale milling and secondary ion mass spectroscopy.

2.
Nanoscale Res Lett ; 8(1): 416, 2013 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-24103192

RESUMO

The formation of nano-islands on both a Ge(111)-c(2 × 8) surface and an Ag/Ge(111)-(√3 × âˆš3) surface evaporated with 0.1 ML Ni was investigated by scanning tunneling microscopy (STM). We have noticed that at temperatures lower than 670 K, the reaction between Ni and the individual substrate surfaces proceeds to form different structures: flat-topped islands with a 2√7 × 2√7 or a 3 × 3 reconstruction on the Ni/Ge(111)-c(2 × 8) surface vs. islands with a 7 × 7 reconstruction on the Ni/Ag/Ge(111)-(√3 × âˆš3) surface. From this we have inferred that within a temperature range between room temperature and 670 K, the intermediate Ag layer retards mixing between Ni and Ge atoms. As a result, the grown islands are composed of pure Ni atoms. Within a temperature range from 670 to 770 K, most islands produced on the Ag/Ge(111)-(√3 × âˆš3) surface are identical with those formed on the Ni/Ge(111)-c(2 × 8) surface, suggesting that above 670 K, Ni atoms are likely to bind with Ge atoms. However, an essential difference between STM images of the surfaces under study exists in the appearance of large elongated islands on the Ni/Ag/Ge(111)-(√3 × âˆš3) surface. The formation of the latter is explained in terms of a difference in energy for Ni diffusion on the Ge(111)-c(2 × 8) and Ag/Ge(111)-(√3 × âˆš3) surfaces.

3.
Nanoscale Res Lett ; 7(1): 189, 2012 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-22424268

RESUMO

We have found that Co-2 × 2 islands grown on an Ag/Ge(111)-√3 × âˆš3 surface have hcp structure with the (11-20) orientation. The island evolution involves transformation of the unit cell shape from parallelogram into rectangular, which is accompanied by the island shape transformation from hexagonal into stripe-like. Identified are two crystallographic directions for the island growth, the pseudo-[0001] and the pseudo-[1-100]. We have observed the occurrence of a lateral shift between the topmost and the underlying bilayers in the case of the island growth along the pseudo-[0001] direction. In contrast, the topmost and the underlying bilayers are unshifted for the growth along the pseudo-[1-100] direction.

4.
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.

5.
J Nanosci Nanotechnol ; 10(7): 4500-4, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21128447

RESUMO

The growth of uniform nanostructures requires simple and reproducible ways to control the size. It is found that Co atoms can form two-dimensional structural islands on √3 x √3-Ag/Ge(111) surfaces. Temperature and Co coverage are two factors to modulate the island size. By using scanning tunneling microscopy, the surface structures and morphology for different annealing temperatures and variable Co coverage have been investigated. For 100 degrees C annealing temperature, Co atoms are difficult to condense into structural islands at 0.35 ML whereas several structural Co islands are found at 1.4 ML. This difference is due to the quantity of Co atoms per unit area for forming structural islands. As the temperature increases, Co atoms get more energy to diffuse. Therefore, the average island size increases with rising temperatures until the coverage of 3.5 ML. Yet, the island size stops growing above the coverage of 3.5 ML because of the limitation for the Co covered area. Therefore the Co islands increase their height rather than their size. In addition, the shape of Co islands can also be controlled. It transforms from random shapes to the hexagonal shape with increasing temperature.

6.
Phys Chem Chem Phys ; 12(45): 14950-9, 2010 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-20949220

RESUMO

Molecular structures of dicarboxylated viologens (1,1'-bis (7-carboxyheptyl)-4,4'-bipyridinium dibromide molecules, V-(C(7)-COOH)(2)) on a Cu(100) surface are studied by means of in situ scanning tunneling microscopy (STM) in combination with cyclic voltammetry (CV). Self-assembled monolayers of adsorbed dicarboxylated viologens form during an ongoing charge transfer reaction. Mainly six structures of the organic molecules are observed, including a dot array, metastable phases, stripe patterns, a closed stacking stripe pattern, chloride desorption, and a dimer phase. The molecular structural models for all the structures have been successfully established. The carboxylated viologen molecules in the dicationic state prefer the face-on configuration on the surface and form the dot array phase. The other phases are shown by the radical state of the viologens. The metastable phases show two forms: cluster-like and stripe pattern-like structures. Main features of the metastable phases are face-to-face configurations of the radical viologens in π-stacking form between neighboring parallel bipyridiniums. Hydrogen bonding is considered to be the major factor in constructing the network of the stripe pattern. At a more negative potential, the bilayers of the stripe pattern transform to be a monolayer of the closed stacking stripe pattern because of the enhanced electrostatic force. The closed stacking stripe pattern is stable on the surface until chloride desorption. As the chloride anions desorb from the Cu(100) surface, the disordered dimers transform to an ordered dimer phase on a Cu(100)-1×1 surface due to the hydrogen bonding between neighboring dimer rows.

7.
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.

8.
J Nanosci Nanotechnol ; 8(2): 608-12, 2008 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-18464378

RESUMO

Structural evolution of Co/Ag/Ge(111) at high temperatures was studied by using scanning tunneling microscopy and low energy electron diffraction. The mean square root of 3 x mean square root of 3-Ag layer between the substrate Ge( 11) and Co adatoms can avoid the formation of Co-Ge compounds below 800 K. The Co atoms nucleate to form islands where mean square root of 13 x mean square root of 13 or 2 x 2 reconstructions were observed after annealing between 373 K and 737 K. The mean square root of 13 x mean square root of 13 structure with mirror symmetry relative to [-211], [11-2], and [1-21] axes was observed for 1-2 layer Co islands. Co islands with over 2 layers appear 2 x 2 structure. All reconstruction structures of the nano-sized Co islands and substrate Ag/Ge(111) mean square root of 3 x mean square root of 3 surface were analyzed using the atomic hard sphere model. The bright protrusions of these reconstructions all sit in the centers of Ag or Ge trimers, which were predicted to have maximum binding energy.

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