High-resolution Elastic Recoil Detection Analysis Research Articles

High-resolution depth profiling of soda-lime silicate glass using high-resolution RBS and ERDA

Composition depth profiles of soda-lime silicate glasses were measured using high-resolution Rutherford backscattering spectroscopy (HRBS) and high-resolution elastic recoil detection analysis (HERDA). Surface enrichment of modifier cations (Na+ and Ca2+) followed by a depletion in the deeper regions was observed using HRBS. The observed surface enrichment was attributed to the effect of radiation damage caused by the He+ irradiation. It was shown that the precise depth profiling of glass surfaces can be performed using HRBS when the fluence is limited below 3 × 1014 He ions cm−2. HERDA measurements demonstrated that there is a substantial amount of hydrogen (7.3 ± 1.3 × 1021 hydrogen cm−3) in the subsurface region as well as on the surface (1.6 ± 0.2 × 1015 hydrogen cm−2), which is very different from the silica glass surface where no subsurface hydrogen was observed.

Quantification of outermost OH group on silica glass surface by high-resolution elastic recoil detection analysis

High-resolution elastic recoil detection analysis (HERDA) has been conducted to quantify outermost OH group on a silica glass surface. The results of HERDA showed that the surface number density of OH groups (silanol number) can be measured with a good reproducibility by heating the sample in vacuum to remove the surface adsorbates. The measured silanol number depends on the temperature and is in good agreement with the result reported for porous silicas. Furthermore, by investigating the relationship between the contact angle of water and the silanol number, it was confirmed that the contact angle increases with decreasing silanol number.

Development of high-resolution ERDA with double MCP system and determination of detection limit for H and D

Abstract A double MCP (micro channel plate) system is developed for the improvement of detection limit in HERDA (high-resolution elastic recoil detection analysis) for hydrogen (H) and its isotope. One MCP detects the recoils of hydrogen (or deuterium (D)), the other one detects the secondary electrons emitted from stopper foil. While the dark current noise is reduced down to 2%, the detection efficiency still remains as 80%. The improved detection limit for H and D achieved ∼6.3 × 1019 atoms/cm3 (∼0.06 at.%) for 360 s and ∼2.3 × 1020 atoms/cm3 for 114 s, respectively. It is also found that the contributions of recoils of other light elements to the detection limit are crucial from the comparison with the previous study, in which both H and D are included in the samples. The developed system successfully determines the D depth profile in a SiO2 thin film (t = 5 nm) caused by the D2 annealing.

Development of slew-rate-limited time-over-threshold (ToT) ASIC for a multi-channel silicon-based ion detector

High-resolution Elastic Recoil Detection Analysis (HERDA), which consists of a 90̂ sector magnetic spectrometer and a position-sensitive detector (PSD), is a method of quantitative hydrogen analysis. In order to increase sensitivity, a HERDA system using a multi-channel silicon-based ion detector has been developed. Here, as a parallel and fast readout circuit from a multi-channel silicon-based ion detector, a slew-rate-limited time-over-threshold (ToT) application-specific integrated circuit (ASIC) was designed, and a new slew-rate-limited ToT method is proposed. The designed ASIC has 48 channels and each channel consists of a preamplifier, a slew-rate-limited shaping amplifier, which makes ToT response linear, and a comparator. The measured equivalent noise charges (ENCs) of the preamplifier, the shaper, and the ToT on no detector capacitance were 253±21, 343±46, and 560±56 electrons RMS, respectively. The spectra from a 241Am source measured using a slew-rate-limited ToT ASIC are also reported.

Installation of high-resolution ERDA in UTTAC at the University of Tsukuba: Determination of the energy resolution and the detection limit for hydrogen

A newly developed high-resolution elastic recoil detection analysis (HERDA) system installed at the 1MV Tandetron in UTTAC at the University of Tsukuba is introduced. The effective solid angle of detector, energy resolution and detection limit for hydrogen are, for the first time, determined quantitatively by the measurements on an a-C:H (and D) film deposited on a Si substrate. In the case of a 500keV 16O+ as the incident beam, an energy resolution of ∼0.45keV and a detection limit of ∼3.8×1020atoms/cm3 (∼0.18at.%) with a data acquisition time of ∼310s are derived.

Perfect Composition Depth Profiling of Ionic Liquid Surfaces Using High-resolution RBS/ERDA.

In order to reveal the surface structures of large molecular ionic liquids (ILs), the near-surface elemental depth distributions of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnC1Im][Tf2N], n = 2, 6, 10) were studied using high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with high-resolution elastic recoil detection analysis (HR-ERDA). The elemental depth profiles of all constituent elements, including hydrogen, were derived from HR-ERDA/HRBS measurements, so that the profiles would reproduce both HR-ERDA and HRBS spectra simultaneously. The derived elemental depth profiles agree with state-of-the-art molecular dynamics simulations, indicating the feasibility of this method. A controversy concerning the preferential orientation of [C2C1Im] at the surface has been resolved by this new combination analysis; namely, the [C2C1Im] cation has a preferential orientation with the ethyl chain pointing towards the vacuum in the topmost molecular layer.

Electrical and physical characterizations of the effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and

The effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and were investigated using both electrical and physical characterization methods. Hall measurements and split capacitance–voltage (C–V) measurements revealed that the difference in field-effect mobility between wet oxide and dry oxynitride interfaces was mainly attributed to the ratio of the mobile electron density to the total induced electron density. The surface states close to the conduction band edge causing a significant trapping of inversion carriers were also evaluated. High-resolution Rutherford backscattering spectroscopy (HR-RBS) analysis and high-resolution elastic recoil detection analysis (HR-ERDA) were employed to show the nanometer-scale compositional profile of the SiC-MOS interfaces for the first time. These analyses, together with cathode luminescence (CL) spectroscopy and transmission electron microscopy (TEM), suggested that the deviations of stoichiometry and roughness at the interface defined the effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and .

Behavior of Li on graphene surfaces observed using high-resolution ERDA

Behavior of Li atoms deposited on the surfaces of highly oriented pyrolytic graphite (HOPG) and graphene-based thin films were observed at room temperature using high-resolution elastic recoil detection analysis (ERDA). On the HOPG surface, the deposited Li atoms intercalate into the bulk and no Li was observed in the surface region. The Li atoms were found to stay in the surface region (from the surface down to at least 3nm) when the HOPG was irradiated with 200keV He ions to a fluence of 5×1015ions/cm2 before Li deposition. This indicates that stable Li sites are produced by the ion irradiation. It was also found that Li atoms are accumulated on the surface due to the oxidation by the residual gas. This oxidation occurs only on the surface and not inside HOPG. Graphene-based thin films were prepared on Cu by microwave plasma chemical vapor deposition. The Li atoms deposited on the graphene-based thin films are found to distribute through the film almost uniformly and no accumulation either on the surface or at the interface was observed.

A compact high-resolution elastic recoil detection system for lithium depth profiling

A compact high-resolution elastic recoil detection analysis (ERDA) system was developed for precise Li analysis. 200–400keV 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 (1.5×1015cm−2) deposited on a graphite surface was clearly observed and the detection limit was estimated to be less than 0.01ML under typical measurement conditions. The depth resolution was estimated to be 0.5nm at the surface and was better than 3nm in the surface region within 5nm from the surface.

Depth profile analysis of helium in silicon with high-resolution elastic recoil detection analysis

Helium depth profiling in silicon was investigated by high-resolution elastic recoil detection analysis (HERDA) using a high-resolution Rutherford backscattering spectrometry system. A 0.7 μm Mylar film was installed in front of the detector of this system to eliminate the background signals originating from incident nitrogen ions scattered at the sample surface. This film successfully eliminated the background signals without the loss of helium signals or serious degradation of the depth resolution. The HERDA has several attractive features for helium depth profiling in silicon, including high sensitivity (detection limit of 1 at. % or less), excellent depth resolution (less than 1 nm), and good quantitative accuracy, giving it significant advantages over other surface analysis methods such as secondary ion mass spectrometry.

Characterization of carbonaceous films deposited on metal substrates by liquid-phase electrodeposition in methanol

In this study, we report the characterization of carbonaceous films deposited on metal substrates by liquid-phase electrodeposition in methanol. The characterization of carbonaceous films by electrodeposition was examined by means of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), secondary ion mass spectrometry (SIMS), atom probe (AP) and high resolution-elastic recoil detection analysis (HR-ERDA). From these results, it was found that the films deposited on the metal substrates were composed of the sp 2 and sp 3 carbon contents, of which the ratio was about 7:3. Furthermore, the films by electrodeposition contained much hydrogen. The hydrogen contents in the surface were about 60 at.% and those in the subsurface were a few 10 at.%.

The initial oxidation of magnesium: an in situ study with XPS, HERDA and ellipsometry

AbstractThe initial oxidation of magnesium at oxygen partial pressures between 1.3 × 10−8 and 1.3 × 10−5 Pa and at temperatures ranging from 273 to 550 K has been investigated in situ with X‐ray photoelectron spectroscopy (XPS), ellipsometry and high resolution elastic recoil detection analysis (HERDA). Quantitative analysis of the XPS spectra showed a clear oxygen deficiency with respect to MgO for the initial oxide. HERDA measurements confirmed this relatively low oxygen content in the thin oxide layers formed. Ellipsometry measurements showed that the electronic structure of the initially formed oxide differs significantly from that of bulk MgO. The band gap values at room temperature for the oxide layers investigated are clearly smaller than the value for bulk MgO. Copyright © 2006 John Wiley & Sons, Ltd.

Characterization of subsurface hydrogen in diamond films by high-resolution elastic recoil detection analysis

High-resolution elastic recoil detection analysis (HERDA) was carried out to characterize the subsurface structure in highly oriented diamond films that had been treated by hydrogen/deuterium plasma before and after a conventional wet oxidation. The results were compared with those obtained by high-resolution Rutherford backscattering spectrometry (HRBS) and secondary ion mass spectroscopy (SIMS). The results of HERDA revealed that residual deuterium of 3.8×10 14 cm −2 was present after the wet oxidation, while the film surface had been covered with a monolayer deuterium of 1.5×10 15 cm −2 before the treatment. On the other hand, deuterium was not observed in the film annealed at 1000 °C before the oxidation. In accordance with these results, the deuterium content in the subsurface region of the film annealed at 1000 °C before the oxidation (down to 50 nm from the surface) decreased by two orders of magnitude compared to that for the films without annealing, as revealed by SIMS. It is thus concluded that the subsurface hydrogen cannot be removed by the wet oxidation, which could cause the surface Fermi level pinning as commonly observed in oxidized diamond films.

An (un)solvable problem in SIMS: B-interfacial profiling

To get an insight in the diffusion behavior of boron after annealing and in particular its segregation characteristics towards the interface in oxide structures on silicon, it is necessary to probe the boron profile with very high accuracy and depth resolution. Sputter depth profiling as employed in secondary ion mass spectrometry (SIMS) is frequently used as the most suited tool for dopant profiling in view of its sensitivity and depth resolution. However, in order to determine the segregated boron peak, sub-nm depth resolution is required and artifacts such as beam induced broadening effects, potential ionization yield changes at interfaces, transient sputter yields need to be considered in detail. When reducing the primary beam energy the depth resolution can be improved and sub-nm depth sensitivity can be demonstrated. However, comparisons with high-resolution elastic recoil detection analysis demonstrate that even under those conditions no reliable depth profile can be obtained in the first nm near the surface nor even in the oxide part of the profile, where no ionization nor sputter yield transients are expected. Enhanced beam induced migration of boron during the initial phase of the bombardment needs to be invoked to explain the results.