High-resolution Rutherford Backscattering Spectroscopy Research Articles

Low energy ion-solid interactions: a quantitative experimental verification of binary collision approximation simulations

Ultra-low energy ion implantation has become an attractive method for doping of two-dimensional materials and ultra-thin films. The new dynamic Monte Carlo program IMINTDYN based on the binary collision approximation allows a reliable prediction of low energy implantation profiles and target compositional changes, as well as efficient simulation of high energy light ion scattering. To demonstrate the quality of these predictions and simulations, we present a model case experiment where we implanted W ions into tetrahedral amorphous carbon with low (10 keV) and ultra-low (20 eV) ion energies and analyzed the W implantation profiles with high resolution Rutherford backscattering spectrometry (HR-RBS). This experiment is compared with a complete simulation of all aspects of ion-solid-interactions of the experiment using the new IMINTDYN program. A unique novel simulation option, also relevant for implantation into 2D materials, is the inclusion of the vacancy as target species with dynamic vacancy generation and annihilation. Whereas simulations neglecting vacancy formation cannot reproduce the measured implantation profiles, we find excellent agreement between simulated and measured HR-RBS spectra. We also demonstrate the important role of simultaneous weak collisions in the binary collision approximation at low projectile energies.

Enhanced thin film analysis via High Resolution RBS using the NEC CARBS system

Advancements in thin film deposition techniques can now produce films of only a few monolayers in thicknesses, with multiple applications emerging in the nano technology field. This maturing manufacturing technique is driving the need for diagnostics tools able to accurately measure depth profiles. To meet this need, the Compact Automated Rutherford Back-Scattering (CARBS) system is under development at National Electrostatics Corp. (NEC) for nanometer thin film analysis using High-resolution RBS (HRBS) within a 4 x 4meter footprint. We present the recent development of the system and demonstrate a study of HRBS applied to a 30nm CoAl alloy film. We compare the performance of the CARBS system with the conventional NEC HRBS end station and discuss the advantages of HRBS over SIMS method.

Surface analysis of glass and ionic liquids with high-resolution Rutherford backscattering spectroscopy

Surface analysis of glass and ionic liquids with high-resolution Rutherford backscattering spectroscopy

Surface analysis of glass and ionic liquids using high-resolution Rutherford backscattering spectroscopy

Surface analysis of glass and ionic liquids using high-resolution Rutherford backscattering spectroscopy

Intermixing reduction in ultra-thin titanium nitride/hafnium oxide film stacks grown on oxygen-inserted silicon and associated reduction of the interface charge dipole

Oxygen-insertion (OI) layers in Si were found to reduce the intermixing of a 3.0 nm titanium nitride (TiN)/3.5 nm hafnium oxide (HfO2) film stack, as measured by secondary ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), and high-resolution Rutherford backscattering spectroscopy (HR-RBS). In addition, a 5% reduction in HfO2 film density and modification of in-gap state densities of bulk HfO2 film were observed from HR-RBS and absorption spectra from spectroscopic ellipsometry (SE), respectively. Furthermore, the barrier height at HfO2/Si was found to increase by 250 mV from Fowler–Nordheim (F–N) tunneling characteristics, and 172 mV lower flatband voltage (VFB) was observed from capacitance–voltage (C–V) characteristics. These observations suggest that interfacial charge dipole formation of the high-k dielectric/metal gate (HKMG) stack on Si follows the O-vacancy model, in which charge dipole is explained as electrostatic energy stored at the interface from the intermixing process involving electron transition from oxygen vacancy in metal oxide to Si. OI-Si modifies the balance of the oxygen flux due to the supply of partially ionized oxygen in Si and, thus, leads to the reduction of the intermixing phenomena, modification of the resultant film properties, and reduction of the interfacial charge dipole. This discovery opens up a new technique for tuning HKMG electrical characteristics.

Thickness-Dependent Photoelectrochemical Water Splitting Properties of Self-Assembled Nanostructured LaFeO3 Perovskite Thin Films.

Tuning the intrinsic structural and stoichiometric properties by different means is used for increasing the green energy production efficiency of complex oxide materials. Here, we report on the formation of self-assembled nanodomains and their effects on the photoelectrochemical (PEC) properties of LaFeO3 (LFO) epitaxial thin films as a function of layer’s thickness. The variation with the film’s thickness of the structural parameters such as in-plane and out-of-plane crystalline coherence length and the coexistence of different epitaxial orientation—<100>SrTiO3//<001> LFO, <100>SrTiO3//<110> LFO and [110] LFO//[10] STO, as well as the appearance of self-assembled nanodomains for film’s thicknesses higher than 14 nm, is presented. LFO thin films exhibit different epitaxial orientations depending on their thickness, and the appearance of self-assembled nanopyramids-like domains after a thickness threshold value has proven to have a detrimental effect on the PEC functional properties. Using Nb:SrTiO3 as conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, the dependence of the photocurrent density and the onset potential vs. RHE on the structural and stoichiometric features exhibited by the LFO photoelectrodes are unveiled by the X-ray diffraction, high-resolution transmission electron microscopy, ellipsometry, and Rutherford backscattering spectroscopy results. The potentiodynamic PEC analysis has revealed the highest photocurrent density Jphotocurrent values (up to 1.2 mA/cm2) with excellent stability over time, for the thinnest LFO/Nb:SrTiO3 sample, both cathodic and anodic behavior being noticed. Noticeably, the LFO thin film shows unbiased hydrogen evolution from water, as determined by gas chromatography in aqueous 0.5 M NaOH solution under constant illumination.

High-resolution Rutherford backscattering spectrometry with an optimised solid-state detector

Rutherford Backscattering Spectrometry (RBS) is a powerful ion beam analysis technique in frequent use within materials science. The recent emergence of targets incorporating complex features such as ultra-scaled diffusion barriers and isotopically-enriched films has started to push the limits of the technique, necessitating the expanded use of systems with a higher energy resolution. The increased cost and complexity of these systems based on already well-established schemes may present a barrier to their more widespread adoption. Here, we present an RBS detection system specifically designed for simple integration into existing nuclear probe infrastructure, but with a considerably higher energy resolution than a standard passivated planar detector. We employ a modified silicon p–i–n photodiode integrated within an optimised in-vacuum preamplifier to achieve a relative energy resolution of 3 × 10−3 with 2.2 MeV He+ ions. In a glancing angle geometry, this corresponds to a depth resolution of ∼1.5nm and a mass resolution of <1u from light elements up to Cu. We demonstrate the use of this detector to measure the thermal diffusion of near-surface As implants in a Si substrate, important for the formation of ultra-shallow junctions; and the residual 29Si concentration in an isotopically enriched 28Si specimen, a promising platform for quantum computation.

Development of PC based automation of ion beam analysis and ion implantation experiments

This paper presents the details of a personal computer (PC) based automation of ion beam analysis and ion implantation experimental setup that has been developed and implemented in a 1.7 MV Tandetron accelerator. Hardware and software of the PC automated system were designed to automate multiple sample ion implantation, standard Rutherford Backscattering spectrometry (RBS), and High resolution Rutherford Backscattering spectrometry (Hi-RBS) experiments. The system uses in-house developed signal conditioning circuitry, isolation amplifiers, and transistor drivers along with cost-effective and off-the-shelf commercial components like a general purpose, multifunction data acquisition card, etc. A five axis goniometer is used for handling multiple samples and their automatic positioning according to the commands from the PC over RS232 interface. Key tasks carried out in the automation of system include control and mesurement of ion beam fluence, selection of backscattered particles through screening of their energies by controlling a set of +/−25 kV and −3 kV high voltage power supplies, controlled collection of backscattered yield using single and multi channel analysers, controlling the region-of-interest windows in the energy spectra and the cumulative counts in them. Controlling the position of the samples and facilitating the experiments on multiple samples, online display of energy spectra and its auto storage, and vacuum interlocking are also automatically done. This PC based setup has been automated using a windows based LabVIEW software making it easy to port the set up between different computer operating systems apart from achieving many other advantages like quick and easy development of versatile, multi-purpose, and user friendly graphical interface. Extensive tests carried out on the hardware established correct functioning of various modules of the hardware. The 0–10 V control inputs applied to the +/−25 kV and −3 kV high voltage power supplies were tested and seen providing an <0.1% accuracy, <0.05% linearity, very low drift of 50 ppm, 0.01% precision, and <1mv rms output noise. The software modules have been tested to check independent control and monitoring the irradiated dose, energy to voltage conversion, the multi channel analyser control in addition to other tasks such as computing the region-of-interest counts. The fluence computed from the pulse counts from the ion beam current integrator and the actual fluence were found to be matching within 0.1%. The vacuum interlocking scheme was tested covering a range of 10−5 mbar to 10−9 mbar. Hi-RBS was carried out on a 3 nm thick Ag film grown on Si substrate using 0.3 MeV H+ ion beam over a backscattered energy range of 10–300 keV for a fixed ion fluence 2 × 1012 ions/cm2 at each energy. The recorded spectrum showed well separated Si edge and Ag peaks. The energy resolution is calculated to be 1.2 keV and a relative energy resolution (ΔE/E) of ∼0.4% is obtained.

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.

Electrical and structural characterization of neutron irradiated amorphous boron carbide/silicon p-n heterojunctions

Abstract The electrical and structural properties of amorphous hydrogenated semiconducting boron carbide on silicon p-n heterojunction diodes have been examined following irradiation with thermal neutrons to a maximum dose of 1.08 × 109 neutrons/cm2. Improvements in the current-voltage response of the heterojunction diode, along with a decrease in the diode ideality factor, are observed with neutron exposure. Capacitance-voltage data were used to extract the hydrogenated boron carbide carrier density and diode built-in potential, both of which decrease with irradiation. Structural and defect characterization, carried out with high resolution TEM and RBS in channeling mode, show that the hydrogenated boron carbide remains amorphous and no discernible damage occurs in the Si component of the diode. These data suggest that the observed changes in electrical properties result from irradiation induced defect passivation in the amorphous boron carbide. For n-type plasma enhanced chemical vapor deposition hydrogenated semiconducting boron carbide on p-type silicon, the improvements in the heterojunction diode are quite dramatic.

Impact of Tungsten Sputtering Condition on Magnetic and Transport Properties of Double-MgO Magnetic Tunneling Junction With CoFeB/W/CoFeB Free Layer

We investigated an effect of sputtering gas species (Ar, Kr, and Xe) for deposition of a W insertion layer in the CoFeB/W/CoFeB free layer on magnetic properties of the free layer and tunnel magnetoresistance (TMR) ratio of magnetic tunnel junctions (MTJs) stacks using the free layer annealed at 400 °C for 1 h. As the W insertion layer thickness tW increased, we found the degradation of perpendicular anisotropy and larger reduction of saturation magnetic moment per unit area mS in the free layer using Ar compared to those using Kr and Xe. We also found a smaller TMR ratio for the MTJ stack using Ar compared to those using Kr and Xe. Energy-dispersive X-ray spectrometry line analysis revealed more significant interdiffusion between W and CoFeB layers in the free layer using Ar than those using Kr and Xe, that could result in the smaller mS and perpendicular anisotropy in the free layer and smaller TMR ratio for the MTJ stack using Ar than those using Kr and Xe. We also investigated concentration of Ar, Kr, and Xe in W layers deposited using Ar, Kr, and Xe, respectively, by high-resolution Rutherford backscattering spectrometry, revealing that 0.2 at% Ar was detected in the W layer using Ar, while Kr and Xe were not detected in W layers using Kr and Xe. Such a difference in concentration of inert gas atoms in the W layer could be one possible reason for the difference about degree of interdiffusion between W and CoFeB layers.

Degradation by water vapor of hydrogenated amorphous silicon oxynitride films grown at low temperature

We report on the degradation process by water vapor of hydrogenated amorphous silicon oxynitride (SiON:H) films deposited by plasma-enhanced chemical vapor deposition at low temperature. The stability of the films was investigated as a function of the oxygen content and deposition temperature. Degradation by defects such as pinholes was not observed with transmission electron microscopy. However, we observed that SiON:H film degrades by reacting with water vapor through only interstitial paths and nano-defects. To monitor the degradation process, the atomic composition, mass density, and fully oxidized thickness were measured by using high-resolution Rutherford backscattering spectroscopy and X-ray reflectometry. The film rapidly degraded above an oxygen composition of ~27 at%, below a deposition temperature of ~150 °C, and below an mass density of ~2.15 g/cm3. This trend can be explained by the extents of porosity and percolation channel based on the ring model of the network structure. In the case of a high oxygen composition or low temperature, the SiON:H film becomes more porous because the film consists of network channels of rings with a low energy barrier.

Ion induced intermixing and consequent effects on the leakage currents in HfO2/SiO2/Si systems

Atomic layer deposited (ALD) samples with layer stacks of HfO2 (3 nm)/SiO2 (0.7 nm)/ Si were subjected to 120 MeV Au ion irradiation at different fluences to study intermixing effects across the HfO2/SiO2 interface. High-resolution Rutherford backscattering spectrometry (HRBS) and X-ray reflectivity (XRR) measurements confirm an increase in the interlayer thickness as a result of SHI induced intermixing effects. Current–voltage (I–V) measurements reveal an order of magnitude difference in the leakage current density between the pristine and irradiated samples. This can be explained by considering the increased physical thickness of interlayer (HfSiO). Furthermore, the samples were subjected to rapid thermal annealing (RTA) process to analyze annealing kinetics.

Surface structures of binary mixture of ionic liquids

Surfaces of 11 equimolar mixtures of ionic liquids (ILs) consisting of 1-alkyl-3-methylimidazolium cations (from [C2C1Im] to [C12C1Im]) with anions (Cl, [BF4], [TfO], [PF6], [Tf2N]) were observed using high-resolution Rutherford backscattering spectroscopy (HRBS). The elemental depth profiles of these IL mixtures were derived from the observed HRBS spectra through spectrum modeling. By comparing the observed depth profiles with those of pure ILs, the surface mole fractions of constituent ILs were estimated. We found a general tendency that larger IL is enriched at the surface. The observed surface enrichment can be reasonably well reproduced by a simple thermodynamic calculation based on the Sprow-Prausnitz equation. A slight deviation from the calculated result was ascribed to the nonideal behavior of the IL mixtures, which was neglected in the calculation.

Thermal Stability of Annealed Germanium-Tin Alloys Grown by Molecular Beam Epitaxy

The thermal stability of undoped and boron-doped germanium tin (Ge1−xSnx) alloys grown by molecular beam epitaxy with varying composition and layer thickness was investigated. The alloys were annealed in forming gas at various temperatures up to 800°C for 1 min using rapid thermal processing, and were characterized using high-resolution x-ray diffraction and Rutherford backscattering spectrometry. It was found that the Ge1−xSnx alloys were stable to well above the growth temperature, but the stability decreased with increasing thickness, Sn content, and doping. Ge1−xSnx alloys with low Sn composition (x ∼ 0.025) were stable up to 700°C, and for a given Sn composition, the undoped alloys were more thermally stable than the doped alloys. As the thickness of the Ge0.975Sn0.025 alloys increased to about 950 nm, the temperature of thermal stability dropped to 500°C. As the Sn composition of the 90 nm-Ge1−xSnx alloys increased up to x = 0.08, the temperature of thermal stability dropped to 300°C. At higher annealing temperatures, the Ge1−xSnx alloy degraded with lower crystal quality, and a gradient in the Sn composition appeared, which may be due to Sn diffusion or segregation.

高分解能RBSによるイオン液体表面構造解析

高分解能RBSによるイオン液体表面構造解析

Surface segregation in a binary mixture of ionic liquids: Comparison between high-resolution RBS measurements and moleculardynamics simulations.

Surface structure of equimolar mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2C1Im][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2C1Im][BF4]) is studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and molecular dynamics (MD) simulations. Both HRBS and MD simulations show enrichment of [Tf2N] in the first molecular layer although the degree of enrichment observed by HRBS is more pronounced than that predicted by the MD simulation. In the subsurface region, MD simulation shows a small depletion of [Tf2N] while HRBS shows a small enrichment here. This discrepancy is partially attributed to the artifact of the MD simulations. Since the number of each ion is fixed in a finite-size simulation box, surface enrichment of particular ion results in its artificial depletion in the subsurface region.

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.

Far-and mid-infrared properties of carbon layers elaborated by plasma sputtering

The far-and mid-infrared reflectivity spectra of two carbon layers deposited on pure (100) silicon substrates by DC magnetron sputtering were investigated at room temperature in the 10–5000cm−1 wavenumber range. Their structural and textural features were also studied by combining Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HRTEM), X-Ray Reflectivity (XRR) and Rutherford Backscattering Spectroscopy (RBS). The set of results was used to discuss afterwards the influence of the texture on the infrared properties at varying length scale. Thereby, the two layers were found to be heterogeneous as assessed by RBS, XRR and FESEM and their thicknesses had been measured by XRR and FESEM. The information on the structural organization and “crystallite” size was given by Raman spectroscopy. The influence of both the textural and structural parameters on the measured infrared reflectivity spectra was discussed. Finally, a methodology was proposed to recover the intrinsic index of refraction and the intrinsic index of absorption of each layer.

System on chip (SoC) microcontrollers (μC) as digitisers for ion beam analysis (IBA) instruments

Data digitisation of the analogue signals from detectors to digital data is an essential process in ion beam analysis (IBA). The low-cost, easy availability and development environments that have a low learning threshold makes system-on-chip (SoC) microcontrollers (μC) attractive for this task. These μC combine, on one die, analogue and digital inputs and outputs with serial USB interfaces, which opens up simple implementation of tailor-made interfaces for specific IBA measurement systems. We have investigated the design and performance limitations based on development of three different digitisation interfaces for IBA. These were a two-channel nuclear instrumentation module (NIM) ADC event mode interface (EMI) for a high-resolution magnetic RBS spectrometer, a simple headless-multi-channel analyser (MCA) and a combined dual channel headless MCA and EMI. It is shown that SoC μC based interfaces for digitisation of analogue spectroscopy pulses in IBA systems can be implemented for material costs less than 100€. The performance of the SoC devices for many IBA applications is close to what can be achieved with state-of-the-art instruments. The simple pulse spectroscopy interface circuit and software are included in the auxiliary archive.