Yoh Yamamoto

Blue shift in room temperature photoluminescence from photo-chemical vapor deposited ZnO films

Abstract Highly transparent ZnO films were deposited on (001) α-Al 2 O 3 at substrate temperature in the range of room temperature to 300°C by photo-chemical vapor deposition. This enabled selective deposition of ZnO films on the selected substrate area irradiated by the light source. With the descending substrate temperature as low as 100°C, band gap widening of the films has been observed, which resulted in the shift of room temperature ultraviolet photoluminescence of ZnO from 380 nm to the shorter wavelength of 360 nm. It implies that in situ patterning of ZnO with different wavelength emission characteristics is possible on the same substrate by controlling the deposition temperature.

Fabrication of nanometric zinc pattern with photodissociated gas-phase diethylzinc by optical near field

In situ patterning of zinc on a nanometric scale has been accomplished by photodissociation of gas-phase diethylzinc by optical near field. By using an ultraviolet optical fiber probe with an aperture diameter of 60 nm, dots with full width at half maxima of 60 and 70 nm were deposited, and were separated by 100 nm. The aspect ratio of the dots increased at the rate of 0.03/μJ, as the optical near field energy increased. A T-shape pattern was also fabricated by scanning the probe in an optical near field microscope system.

Fabrication of nanometric single zinc and zinc oxide dots by the selective photodissociation of adsorption-phase diethylzinc using a nonresonant optical near field

We demonstrated a deposition of nanometer-scale Zn dots using the selective photodissociation of adsorption-phase diethylzinc with a nonresonant optical near field, where the photon energy is lower than that of the absorption edge of gas-phase diethylzinc. We achieved nanometric prenucleation by dissociating diethylzinc molecules adsorbed on a substrate. Subsequent deposition was performed by dissociating the adsorbed molecules on the prenucleated Zn. The topographic image of the deposited Zn dot had a full width at half maximum (FWHM) of 25 nm. Furthermore, the photoluminescence intensity distribution from a single ZnO dot fabricated using laser annealing had a FWHM of 85 nm.

Nanometric patterning of zinc by optical near‐field photochemical vapour deposition

A new technique, optical near‐field photochemical vapour deposition (NFO‐PCVD) enables maskless production of nanometric structures with controllable size, chemical composition and morphology. By placing a near‐field optical microscope inside the reaction chamber for photochemical vapour deposition we have deposited nanoscale metal patterns. We demonstrate for the first time, successfully deposited in the near‐field region, lines of metallic zinc with the observed stripe width of 20 nm.

Fabrication of a nanometric Zn dot by nonresonant near-field optical chemical-vapor deposition

We demonstrate a technique for the deposition of nanometric Zn dots by photodissociation of gas-phase diethylzinc using an optical near field under nonresonant conditions. The observed deposited Zn dot was less than 50 nm in size. The photodissociation mechanisms are based on the unique properties of optical near fields, i.e., enhanced two-photon absorption, induced near-field transition, and a direct excitation of the vibration-dissociation mode of diethylzinc.

Observation of size-dependent features in the photoluminescence of zinc oxide nanocrystallites by near-field ultraviolet spectroscopy

The optical properties of single zinc oxide (ZnO) nanocrystallites were investigated at room temperature by extending the optical near-field technique to the UV region. Using a UV fiber probe with a subwavelength aperture, we performed spatially- and spectrally-resolved photoluminescence (PL) imaging of individual ZnO nanocrystallites with a spatial resolution of 55 nm. Furthermore, decreasing the spot size increased the intensities of higher-energy components of the PL spectrum due to the quantum size effect.

Vacuum Shear Force Microscopy Application to High Resolution Work

A new technique–Vacuum Shear Force Microscopy (VSFM)–is introduced as a reliable method for maintaining a constant separation between a probe and sample. Elimination of many of the instabilities observed when applying the shear force mechanism to imaging under ambient conditions, allows for routine nanometer lateral and sub-nanometer normal resolution. In this paper this technique is applied, firstly, to the imaging of microtubules (biology) and, secondly, to the patterning and subsequent imaging of nanoscale metal lines (nanofabrication).

Near-field ultraviolet photoluminescence spectroscopy for evaluating the crystallinity of polycrystalline zinc oxide

By extending the optical near-field technique to the ultraviolet region, a two-dimensional evaluation of the optical properties and crystallinity of polycrystalline zinc oxide (ZnO) was carried out at room temperature. Using an ultraviolet fiber probe with an aperture diameter of 80 nm, we obtained spatially resolved photoluminescence spectra from individual ZnO nanocrystallites; the emission intensity depended on the topography and on crystal orientation.

Fabrication of ZnO nanostructure using near-field optical technology

ZnO nanodots have been successfully fabricated on a (001) Al2O3 substrate by photo-enhanced chemical vapor deposition (PE-MOCVD) combined with near-field optical technology. The optical near-field generated from an optical fiber probe tip allowed ZnO dots to selectively grow on the irradiated substrate surface, with a size smaller than the wavelength of the light source (λ=244 nm). The crystallinity and composition of ZnO were evaluated from planar films using x-ray diffraction analysis, optical transmittance and x-ray photoelectron spectroscopy. The planar films were grown using PE-MOCVD with a direct irradiation by an ultraviolet light source without probe tip. Above a deposition temperature of 150°C, stoichiometric ZnO films (R O:Zn=1), strongly the c-axis oriented and exhibiting a band gap of about 3.3 eV were obtained.

Novel charge neutralization techniques applicable to wide current range of FIB processing in FIB-SEM combined system

FIB-induced charging is one of the most critical issues for achieving successful circuit modifications of LSI. We have developed novel charge neutralization techniques applicable to a wide current range (from pico to nanoampere-order) of FIB processing in a FIB-SEM combined system. The method utilizes a 500 eV focused electron beam instead of an electron shower, and also a combination of microprobing and FIB-assisted deposition to make a current path from FIB processing point to the grounded microprobe. The effects of our techniques on charge neutralization capability were investigated using electrically erasable-programmable read-only memory devices and n-MOS transistors. For the low FIB current condition of less than 500 pA, it is found that the focused electron beam prevents threshold voltage shifts of both irradiated and neighboring transistors, and that the ratio of electron to ion beam currents is a key parameter to achieving effective charge neutralization. We also demonstrated that the combined method of microprobing and FIB-assisted deposition prevents parameter shifts of transistors even for high-current (nanoampere-order) FIB irradiation. Moreover, we evaluated the upper-limit resistance of the current path formed by FIB-assisted carbon deposition to prevent charging induced by a given FIB current.