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A compact high-resolution elastic recoil detection analysis (ERDA) system was developed for precise Li analysis. 200–400 keV He+ ions were used as primary ions and the energy spectra of recoiled Li ions were measured using a magnetic spectrometer. Due to its dispersion the background originating from the scattered primary ions is reduced. The recoiled ions of the substrate other than Li, which may also contribute to the background, were rejected by a thin mylar foil placed in front of a focal plane detector. An electrostatic quadrupole lens was installed at the entrance of the magnetic spectrometer to improve the depth resolution by correcting the effect of the kinematic broadening. The performance of the developed high-resolution ERDA was examined by measuring several samples. A thin Li layer (1.5 × 1015 cm−2) deposited on a graphite surface was clearly observed and the detection limit was estimated to be less than 0.01 ML under typical measurement conditions. The depth resolution was estimated to be 0.5 nm at the surface and was better than 3 nm in the surface region within 5 nm from the surface.

Irradiation of materials with either swift heavy ions or slow highly charged ions leads to ultrafast heating on a timescale of several picosecond in a region of several nanometer. This ultrafast local heating result in formation of nanostructures, which provide a number of potential applications in nanotechnologies. These nanostructures are believed to be formed when the local temperature rises beyond the melting or boiling point of the material. Conventional techniques, however, are not applicable to measure temperature in such a localized region in a short time period. Here, we propose a novel method for tracing temperature in a nanometer region in a picosecond time period by utilizing desorption of gold nanoparticles around the ion impact position. The feasibility is examined by comparing with the temperature evolution predicted by a theoretical model.

In this paper, we demonstrate remarkable photoacoustic emission from self-supported Au nanoparticle/dielectric/Ag mirror structures. They were prepared by depositing thin films on both sides of a 50-nm-thick silicon nitride membrane. The photoacoustic emission generated by the self-supported sample is more than 2 orders of magnitude larger than that of a similar structure supported by a Si wafer at a laser modulation frequency of 1 kHz. In this frequency region, the thermal diffusion length becomes much greater than the thickness of the multilayers, so that the photoacoustic amplitude is determined mainly by the thermal conductivity of the substrate. Therefore, the large enhancement of the photoacoustic emission can be understood in terms of the reduced thermal conductivity of the substrate.

We have investigated, both theoretically and experimentally, highly localized photothermal conversions in Au nanoparticle array/dielectric layer/Ag mirror sandwiches, namely local plasmon resonators. The depth profile of the optical absorption in the local plasmon resonators was calculated using a simple model comprising homogeneous multilayers. The calculation results show highly localized light absorption in the ∼ 10-nm-thick Au nanoparticles layer (more than 99% of total optical absorption). The photoacoustic measurements, which are sensitive to the surface temperature of the sample, were performed on the fabricated local plasmon resonators. The photoacoustic amplitude of the local plasmon resonator possessing a high optical absorption (A = 0.97) was 15 times larger than the absorbance of the bulk Si wafer (A = 0.67) and 8 times larger than the absorbance of graphite (A = 0.85). These results suggest that the photothermal conversion is localized in the thin Au nanoparticles layer, which enables rapid modulation of the temperature of the surrounding fluid.

Surface structures of binary mixtures of imidazolium-based ionic liquids having a common anion (bis(trifluoromethanesulfonyl)imide ([TFSI]), namely [C2MIM]1-x[C10MIM]x[TFSI] (x = 0.5 and 0.1), are studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and time of flight secondary ion mass spectroscopy (TOF-SIMS). Although both measurements show surface segregation of [C10MIM] the degrees of the segregation are different. The surface fraction xsurf of [C10MIM] is estimated to be 0.6 ± 0.05 and 0.18 ± 0.02 by HRBS for x = 0.5 and 0.1, respectively. On the other hand, TOF-SIMS indicates much stronger surface segregation, namely xsurf = 0.83 ± 0.03 and 0.42 ± 0.04 for x = 0.5 and 0.1, respectively. The observed discrepancy can be attributed to the difference in the probing depth between HRBS and TOF-SIMS. The observed surface segregation can be roughly explained in terms of surface tension.

Efficient photoacoustic emission from Au nanoparticles on a porous SiO2 layer was investigated experimentally and theoretically. The Au nanoparticle arrays/porous SiO2/SiO2/Ag mirror sandwiches, namely, local plasmon resonators, were prepared by dynamic oblique deposition (DOD). Photoacoustic measurements were performed on the local plasmon resonators, whose optical absorption was varied from 0.03 (3%) to 0.95 by varying the thickness of the dielectric SiO2 layer. The sample with high absorption (0.95) emitted a sound that was eight times stronger than that emitted by graphite (0.94) and three times stronger than that emitted by the sample without the porous SiO2 layer (0.93). The contribution of the porous SiO2 layer to the efficient photoacoustic emission was analyzed by means of a numerical method based on a one-dimensional heat transfer model. The result suggested that the low thermal conductivity of the underlying porous layer reduces the amount of heat escaping from the substrate and contributes to the efficient photoacoustic emission from Au nanoparticle arrays. Because both the thermal conductivity and the spatial distribution of the heat generation can be controlled by DOD, the local plasmon resonators produced by DOD are suitable for the spatio-temporal modulation of the local temperature.

Surface structures of equimolar mixtures of imidazolium-based ionic liquids (ILs) having a common cation (1-butyl-3-methylimidazolium ([C4MIM]) or 1-hexyl-3-methylimidazolium ([C6MIM])) and different anions (bis(trifluoromethanesulfonyl)imide ([TFSI]), hexafluorophosphate ([PF6]) or chlorine) are studied using high-resolution Rutherford backscattering spectroscopy (HRBS). Both cations and anions have the same preferential orientations at the surface as in the pure ILs. In the mixture, the larger anion is located shallower than the smaller anion. The [TFSI] anion is slightly enriched at the surface relative to [PF6] with coverage of ~ 60% for the equimolar mixtures of [C4(6)MIM] [TFSI] and [C4(6)MIM] [PF6]. No surface segregation is observed for [C6MIM] [TFSI]0.5[Cl]0.5 and [C6MIM] [PF6]0.5[Cl]0.5. These results are different from the recent TOF-SIMS measurement where very strong surface segregation of [TFSI] was concluded for the mixture of [C4MIM] [TFSI] and [C4MIM] [PF6].

Thin films of amorphous Si3N4 (thickness 20 nm) were irradiated with 120–720 keV C60+, 2+ ions and observed using transmission electron microscopy (TEM). The ion track produced in an amorphous material was directly observed by TEM. For quantitative analysis, the ion tracks were also observed using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The observed ion track consists of a low density core (radius ∼2.5 nm) and a high density shell (width ∼2.5 nm), which is very similar to the ion tracks in amorphous SiO2 irradiated with high energy heavy ions observed by small angle X-ray scattering (SAXS). Although the observed ion tracks may be affected by surface effects, the present result indicates that TEM and HAADF-STEM have potential to observe directly the fine structures of ion tracks in amorphous materials.

We have investigated the heat generation from gold nanoparticles resulting from their local plasma resonance. We have demonstrated the self-assembly of Au nanoparticle arrays/dielectric layer/Ag mirror sandwiches, i.e., a local plasmon resonator, using a dynamic oblique deposition technique. The thicknesses of the Au and dielectric layers were changed combinatorially on a single substrate. As a result, local plasmon resonator chips were successfully fabricated. Because of strong interference, their optical absorption can be controlled between 0.0% and 97% in the near-IR region, depending on the thickness of the dielectric layer. We evaluated the heat generation from Au nanoparticles by measuring the temperature of water with which a cell prepared on a chip is filled under laser illumination. The change in the water temperature is proportional to the optical absorption of the local plasmon resonator chips. This suggests that the photothermal conversion efficiency can be controlled by interference. These features make the application of the local plasmon resonator to nanoheaters, which can spatiotemporally control heat generation, suitable.

The sensitivity (limit of detection) of high-resolution Rutherford backscattering spectroscopy (HRBS) is mainly determined by the background noise of the spectrometer. There are two major origins of the background noise in HRBS, one is the stray ions scattered from the inner wall of the vacuum chamber of the spectrometer and the other is the dark noise of the microchannel plate (MCP) detector which is commonly used as a focal plane detector of the spectrometer in HRBS. In order to reject the stray ions, several barriers are installed inside the spectrometer and a thin Mylar foil is mounted in front of the detector. The dark noise of the MCP detector is rejected by the coincidence measurement with the secondary electrons emitted from the Mylar foil upon the ion passage. After these improvements, the background noise is reduced by a factor of 200 at a maximum. The detection limit can be improved down to 10 ppm for As in Si at a measurement time of 1 h under ideal conditions.

Composition depth profiling of HfO2 (2.5 nm)/SiON (1.6 nm)/Si(001) was performed by three diffetent analytical techniques: high-resolution Rutherford backscattering spectroscopy (HRBS), angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and high-resolution elastic recoil detection (HR-ERD). By comparing these results we found the following: (1) HRBS generally provides accurate depth profiles. However, care must be taken in backgroud subtraction for depth profiling of light elements. (2) In the standard AR-XPS analysis, a simple exponential formula is often used to calculate the photoelectron escape probability. This simple formula, however, cannot be used for the precise depth profiling. (2) Although HR-ERD is the most reliable technique for the depth profiling of light elements, it may suffer from multiple scattering, which deteriorates the depth resolution, and also may cause a large background.

The surface structures of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(n)MIM][TFSI], n=2, 4, 6) are studied by high-resolution Rutherford backscattering spectroscopy. The average composition of the surface molecular layer is very close to the stoichiometric composition, showing that neither ion is enriched in the surface layer. A detailed analysis indicates that both cations and anions have preferential molecular orientations at the surface. The alkyl chains of the [C(n)MIM] cations protrude to the vacuum and the CF(3) groups of the [TFSI] anions are also pointing toward the vacuum. While the orientation of the [TFSI] anion becomes weaker with increasing alkyl-chain length, the protrusion of the alkyl chain occurs irrespective of the chain length. It was also found that the N(SO(2))(2) moiety is located nearly at the same depth as the imidazolium ring, suggesting that one of oxygen atoms in [TFSI] is bonded to the hydrogen of the C(2) carbon atom of the imidazolium ring.

Nitrogen depth profiling in a high-k gate stack structure, SiON/HfO2/SiON/Si(0 0 1) was performed by high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The nitrogen depth profile is determined so that both the HRBS spectrum and the angular dependence of the XPS yield are reproduced. The obtained nitrogen profile is compared with the result of high-resolution elastic recoil detection (ERD) which is the most reliable technique for depth profiling of light elements. The agreement between the result of the present combination analysis and that of high-resolution ERD is fairly good, showing that the present combination analysis is a promising method for the analysis of light elements.

Angular and energy distributions of fragment protons dissociated from HeH+ during grazing-angle scattering from a KCl (001) surface are measured. The surface of KCl (001) is heated at 180°C and the beam current is kept lower than 1 fA to prevent macroscopic surface charging. The angular distribution of the fragment protons shows a well-defined peak similarly to the grazing-angle scattering of atomic ions. The observed peak, however, is shifted from the specular angle toward larger scattering angles. The observed angular shift for the trailing proton is larger than that for the leading proton. These results clearly indicate that the motion of the fragment protons is affected by the surface track potential induced by the partner He ion.

In this study, we carry out high temperature glancing angle deposition HT-GLAD of Fe and Al on a heated substrate with trench patterns. When vapor is incident perpendicular to the trench direction, nanowhiskers grow only on the surface exposed to the vapor and not inside the trenches. When vapor is incident at a deposition angle larger than 80° on the sidewall of the trench and not on the substrate surface, nanowhiskers grow only on the sidewall because the condition of deposition at a high temperature and a large deposition angle is satisfied only for the sidewall. Thus, we succeed in the selective growth of nanowhiskers by controlling the geometrical deposition conditions. Further, we also discuss the effect of the local deposition geometry on the growth process. Geometrically selective growth by HT-GLAD is expected to be useful for growing nanowhiskers on nano- and microstructured substrates.

In this study, we carry out high temperature glancing angle deposition (HT-GLAD) of Fe and Al on a heated substrate with trench patterns. When vapor is incident perpendicular to the trench direction, nanowhiskers grow only on the surface exposed to the vapor and not inside the trenches. When vapor is incident at a deposition angle larger than 80° on the sidewall of the trench and not on the substrate surface, nanowhiskers grow only on the sidewall because the condition of deposition at a high temperature and a large deposition angle is satisfied only for the sidewall. Thus, we succeed in the selective growth of nanowhiskers by controlling the geometrical deposition conditions. Further, we also discuss the effect of the local deposition geometry on the growth process. Geometrically selective growth by HT-GLAD is expected to be useful for growing nanowhiskers on nano- and microstructured substrates.

Charge state, angular and energy distributions of reflected projectiles are measured when 3 keV C60+, 2+ ions are scattered from a clean and flat KCl(001) surface under grazing incidence. The dominant charge state is found to be C60+ irrespective of the incident charge state as is expected by the electronic structure of KCl and C60 ions. The observed angular distribution has a well defined peak at a specular angle, indicating that the normal energy is not dissipated during the grazing angle scattering. In spite of no dissipation of the normal energy we observe the fragmentation of the scattered C60+ ions. The energy transferred from the parallel energy to the internal excitations was estimated from the observed fragment distribution. The transferred energy changes from almost 0 eV to ~ 15 eV when the angle of incidence changes from 1 º to 6 º, which is less than 10% of the observed energy loss of the C60+ ions.

Using a dynamic oblique angle deposition technique, we demonstrate the direct formation of Ag nanorods with quasi-parallel major axes on a template layer of oxide having a strongly anisotropic surface morphology. The optical properties of the nanorods are tuned by varying the deposition conditions without any pre- or post-treatment, and the resulting Ag nanorod arrays exhibit high surface-enhanced Raman scattering (SERS) activity. In addition to high macroscopic uniformity over a large area, our nanorod arrays contain a high density of isolated nanorods. Using the optimum Ag nanorod arrays, the SERS imaging of the microdroplets of a rhodamine 6G solution is successfully demonstrated. The space resolution of the imaging is of the order of at least a few µm. These features are suitable for the SERS imaging of biomaterials.

The authors demonstrate the growth of unusual Al whiskers by glancing angle deposition on a high temperature (HT-GLAD) substrate, while the usual columnar structures completely disappear due to accelerated surface diffusion. HT-GLAD is essential for the nucleation of the whiskers and efficient supply of Al atoms on the side surface of the vertically growing whiskers. HT-GLAD will, for the first time, reveal the mechanisms for the vapor growth of metal whiskers. ©2006 American Institute of Physics

We have demonstrated surface-enhanced Raman spectroscopy on arrays of Ag nanorods aligned in line by a dynamic oblique deposition technique. For the light polarized along the major axis of the nanorods, the plasma resonance of the Ag nanorods has been tuned to a wavelength suitable for Raman spectroscopy. The average width and the length-to-width ratio of the resulting nanorods are 56 nm and 3.5, respectively, and the nanorods align in line with small gaps of a few 10 nm. The Raman scattering for the polarized light along the nanorods is enhanced significantly as compared with that perpendicular to the nanorods. This polarization dependent Raman enhancement is attributed to the local field concentration at the ends of the nanorods. Since the preparation process is physical and completely bottom up, it is robust in its selection of the materials and is useful in providing the surface-enhanced Raman scattering sensors at low cost. ©2006 American Institute of Physics