M. Shimojo

Electron-beam-induced deposition using a subnanometer-sized probe of high-energy electrons

Electron-beam-induced deposition was performed to fabricate nanostructures using a subnanometer-sized probe of high-energy electrons emitted by a 200 kV transmission electron microscope equipped with a field emission gun. We fabricated nanometer-sized dots with a diameter of less than 5 nm, controlling their position and size by the introduction of a organometallic precursor gas near the substrate surface. The relation between the size of the deposit and the deposition time was studied, and, in addition, the effect of the substrate thickness was examined.

Absorption spectroscopy of gold nanoisland films: optical and structural characterization.

Nanoisland films prepared by annealing thin gold films at high temperatures were imaged using scanning electron microscopy (SEM) and atomic force microscopy, and optically characterized through absorption spectroscopy. Thin gold films of effective thicknesses 2, 5 and 7 nm annealed at 500, 700 and 900 degrees C were fabricated and studied experimentally. The measured absorption characteristics in support of theoretical calculations showed that the shapes of gold islands were partial spheres. The position of the peak absorption wavelength measured with s-polarized light or at normal incidence confirmed that the island shape grew from a near-hemisphere towards a sphere with increasing annealing temperature. The SEM images confirmed that the size of islands increased from 15 nm in diameter to 40 nm in diameter as film thickness increased from 2 to 5 nm. The affect of the index of the substrate material on absorption characteristics were also studied by comparing the absorption spectra of gold island films on quartz and LaSF15 glass substrates. The use of gold nanoisland films for preparing localized surface plasmon resonance substrates was suggested as they held advantages over the gold colloid films.

Fabrication of magnetic nanostructures using electron beam induced chemical vapour deposition

Finely focused electron beam induced chemical vapour deposition with iron carbonyl gas, Fe(CO)5, was carried out at room temperature to fabricate desired-shape nanostructures such as dots, rods and rings. The as-formed structures exhibited an amorphous phase containing iron, carbon and oxygen elements in the whole volume and iron oxide nanocrystals existed near their surfaces. A post-deposition heat treatment at about 600 °C resulted in the transformation into a crystalline alpha-iron phase, while their shapes were maintained. The residual magnetic flux density Br of the as-formed and alpha-iron nanorods was quantitatively measured by electron holography after magnetization, showing that their Br values were similar to those of iron micro-powders, although the alpha-iron nanorod has a smaller Br value than the as-formed nanorod.

Development of a stage-scanning system for high-resolution confocal STEM

A stage-scanning system is composed of a specially designed transmission electron microscopy specimen holder equipped with a piezo-driven specimen stage, power supplier and control software. This system enables the specimen to be scanned three-dimensionally, and therefore confocal scanning transmission electron microscopy (STEM) can be performed with a fixed electron-optics configuration. It is demonstrated that stage-scanning confocal STEM images can be obtained with the lateral atomic resolution and the specimen can be moved three-dimensionally with high precision.

Fabrication and electron holography characterization of FePt alloy nanorods

Well-aligned, ferromagnetic FePt nanorods have been fabricated by electron beam-induced deposition using an ultrahigh-vacuum scanning electron microscope. A mixture gas of iron pentacarbonyl and cyclopentadienylplatinum (IV) trimethyl was used as a precursor and post-annealing at 600 °C for 2 h was performed to accomplish the crystallization process. Each nanorod was composed of a chain of crystalline Fe-Pt alloy nanoparticles encapsulated within a carbon-containing sheath. The nanoparticles were identified to be face centered tetragonal (fct) FePt phase (L10,P4∕mmm) by electron diffraction and high-resolution transmission electron microscopy (HRTEM). The residual magnetic flux density Br of the nanorods was evaluated to be about 1.53 T via off-axis electron holography, showing a strong ferromagnetic character.

Fatigue tests of Ni-P amorphous alloy microcantilever beams

Development of micromachines and MEMS (microelectromechanical system) devices are making steady progress at present. The size of components used in these micromachines and MEMS devices is expected to be of the order of μm, and the mechanical properties of such materials may be different from those of bulk materials. Therefore, the evaluation of mechanical properties such as Youngs modulus, tensile strength and fatigue properties is essential for the design of micromachines and MEMS devices. Youngs modulus, fracture stress and hardness of thin films and small elements of silicon single crystals have been measured. In addition to modulus and strength of such micro-sized materials, the fatigue properties are extremely important to design micromachines and MEMS devices. However, there have been few fatigue data for micro-sized materials, and the fatigue properties of such materials are still unclear. In the present study, fatigue life and fatigue crack propagation tests have been performed on Ni-P amorphous alloy microcantilever beams by using a newly developed fatigue testing machine.

Mechanisms of nano-hole drilling due to nano-probe intense electron beam irradiation on a stainless steel

Holes with diameters of a few nanometers were drilled in a stainless steel foil using intense electron beams of 2.4nm nominal probe size from a field-emission electron gun in a high-resolution transmission electron microscope. Drilling experiments were carried out at regions of different foil thicknesses for different durations using three different condenser lens apertures. A better understanding of the mechanisms of nano-hole drilling by nano-probe electron beams has been achieved in this article. It was observed that the drilling process initiates from the bottom surface of a thin region while it initiates from the top surface for a thick region. It is concluded that material removal during nano-hole drilling is mainly by localized vaporization within the foil and drilling progresses through the formation of a row of interconnected nano-voids along the irradiated volume across the foil thickness.

Formation of crystalline iron oxide nanostructures by electron beam-induced deposition at room temperature

Electron beam-induced deposition (EBID) using organometallic precursors is a promising technique for nanometre-sized fabrication, but the deposits have been mostly limited to carbonaceous materials. In this study, vapours of water and iron pentacarbonyl were mixed with precise control and the mixture used as a precursor for EBID. We have succeeded in achieving direct formation of Fe3O4 nanostructures at room temperature. This will contribute to broadening the range of materials that can be produced by EBID.

Nanostructure characterization of tungsten-containing nanorods deposited by electron-beam-induced chemical vapour decomposition

Electron-beam-induced chemical vapour decomposition was performed in a scanning transmission electron microscope using a precursor of tungsten carbonyl (W(CO)6). The self-supporting nanorods were grown from the edges of a C film with widths that depend on the electron-beam scanning speed used in the fabrication process. The nanostructure of as-deposited nanorods has been characterized in detail using energy-dispersive X-ray spectroscopy, selected-area electron diffraction, microdiffraction and high-resolution transmission electron microscopy. A mixture of nanocrystallites and amorphous phases was observed for all beam scanning speeds used for deposition. High-resolution transmission electron microscopy demonstrated that the size of nanocrystallites in as-deposited nanorods ranges between 1.5 and 2.0 nm. The direct evidence of the presence of pure W nanocrystallites in as-deposited nanorods was revealed by microdiffraction.

Second-harmonic spectroscopy of surface immobilized gold nanospheres above a gold surface supported by self-assembled monolayers.

We have investigated linear and nonlinear optical properties of surface immobilized gold nanospheres (SIGNs) above a gold surface with a gap distance of a few nanometers. The nanogap was supported by amine or merocyanine terminated self-assembled monolayers (SAMs) of alkanethiolates. A large second-harmonic generation (SHG) was observed from the SIGN systems at localized surface plasmon resonance condition. The maximum enhancement factor of SHG intensity was found to be 3 x 10(5) for the SIGN system of nanospheres 100 nm in diameter with a gap distance of 0.8 nm. The corresponding susceptibility was estimated to be chi((2))=750 pmV (1.8 x 10(-6) esu). In the SIGN system supported with the merocyanine terminated SAMs, the SHG response was also resonant to the merocyanine in the nanogap. It was found that the SHG response of the SIGN systems is strongly frequency dependent. This leads us to conclude that the large chi((2)) is caused by enhanced electric fields at the localized surface plasmon resonance condition and is not due to an increase of the surface susceptibility following from the presence of the gold nanospheres. The observed SHG was consistent with the theoretical calculations involving Fresnel correction factors, based on the quasistatic approximation.