Rutherford Backscattering Measurements Research Articles

Magnetic properties of Sm-Co thin films grown on MgO(100) deposited from a single alloy target

We have grown epitaxial Sm-Co thin films by sputter deposition from a single alloy target with a nominal SmCo5 composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo5-like to a Sm2Co7-like phase. The composition, crystal structure, morphology, and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction, and magnetization measurements. We find that we can grow films with, at room temperature, coercive fields as high as 3.3 T, but with a remanent magnetization which is lower than can be expected from the texturing. This appears to be due to the Sm content of the films, which is higher than expected from the content of the target, even at the lowest possible sputtering pressures. Moreover, we find relatively large variations of film properties using targets of nominally the same composition. At low temperatures, the coercive fields increase, as expected for these hard magnets, but in the magnetization, we observe a strong background signal from the paramagnetic impurities in the MgO substrates.

Cation non-stoichiometry in pulsed laser deposited Sr2+yFe1+xMo1-xO6 epitaxial films

Sr2FeMoO6 (SFMO) films were grown on SrTiO3 (100)- and (111)-oriented substrates via pulsed laser deposition (PLD). In order to study the fundamental characteristics of deposition, films were grown in two different PLD chambers. In chamber I, the best films were grown with a relatively long substrate-to-target distance (89 mm), high substrate temperature (850 °C), and low pressure (50 mTorr) in a 95% Ar/5% H2 atmosphere. Although X-ray diffraction (XRD) measurements indicate these films are single phase, Rutherford Backscattering (RBS) measurements reveal considerable non-stoichiometry, corresponding to a Sr2Fe1−xMo1+xO6 composition with x ≅ 0.2–0.3. This level of non-stoichiometry results in inferior magnetic properties. In chamber II, the best films were grown with a much shorter substrate-to-target distance (38 mm), lower temperature (680 °C), and higher pressure (225 mTorr). XRD measurements show that the films are single phase, and RBS measurements indicate that they are nearly stoichiometric. The degree of ordering between Fe and Mo was dependent on both the temperature and pressure used during deposition, reaching a maximum order parameter of 85%. The saturation magnetization increases as the Fe/Mo ordering increases, reaching a maximum of 2.4 μB/f.u. Based on prior studies of bulk samples, one would expect a higher saturation magnetization for this degree of Fe/Mo order. The presence of extra strontium oxide layers in the form of Ruddlesden-Popper intergrowths appears to be responsible for the lower than expected saturation magnetization of these films.

Defect structure and electronic properties of SiOC:H films used for back end of line dielectrics

Back end of the line dielectrics (BEOL) with low dielectric constants, so called low-k dielectrics, are needed for current and future integrated circuit technology nodes. However, an understanding of the defects which limit reliability and cause leakage currents for these films is not yet developed. We primarily utilize conventional electron paramagnetic resonance (EPR) and leakage current measurements to investigate amorphous hydrogenated carbon doped oxide (a-SiOC:H) dielectrics, the most important in current BEOL technology. The resonance measurements were complemented by transmission Fourier-transform infra-red spectroscopy, x-ray reflectivity, and Rutherford backscattering measurements. Various compositions of a-SiOC:H films were deposited on 300 mm diameter Si (100) wafers. They exhibit a wide range of dielectric constant, composition, and porosity. Variations in deposition method, process chemistry, and post deposition curing were also investigated. We observe a remarkable range of paramagnetic defect populations within the films. In a large subset of the films with similar defect structure, we observe a strong correlation between carbon dangling bond paramagnetic defect densities and leakage currents, especially at lower electric fields. This correspondence strongly suggests that, in this subset, defects observed by EPR are in a large part responsible for the leakage currents at low electric fields. In addition, the results suggest that the observed defects likely limit the dielectric reliability in problems such as time dependent dielectric breakdown and stress induced leakage current in many of these films. However, the EPR results are complex, and a simple universal correspondence between defect populations and leakage does not seem to be present.

Channeled PIXE and magnetic measurements in Co implanted and thermally annealed ZnO single crystals

Abstract Single crystals of ZnO were implanted with 0.6 × 10 16 cm −2 and 1.2 × 10 16 cm −2 of Co ions produced by MEVVA type implanter. Channeled Rutherford backscattering (cRBS) measurements reveal incomplete amorphisation. Thermal annealing at 800 °C in argon leads to a reduction of point-type defects. The channeled particle-induced X-ray emission (cPIXE) measurements show partial substitutionality of Co ions directly following implantation with further growth of substitutional occupation after annealing. Magnetic measurements reveal the presence of paramagnetic and ferromagnetic phases after implantation. The value of magnetization can be interpreted as due to defects rather than Co content. The ferromagnetic phase disappears after annealing and the paramagnetic phase grows in intensity.

Influence of hydrogen content and network connectivity on the coefficient of thermal expansion and thermal stability for a-SiC:H thin films

Thin films of a-SiC:H are of interest for numerous applications in optoelectronic, nanoelectronic, and nanoelectromechanical devices due to a large optical band gap and excellent chemical inertness. In many cases, a low coefficient of thermal expansion (CTE) and high temperature stability are also desired. In this regard, we report an investigation of the influence of hydrogen content and average bond coordination (〈r〉) on the thermal stability and CTE of a-SiC:H thin films deposited by plasma enhanced chemical vapor deposition. The a-SiC:H hydrogen content determined by combined nuclear reaction analysis and Rutherford backscattering measurements (NRA–RBS) was skewed from 25 to 60% resulting in films with 〈r〉 ranging from 2.0 up to 3.2. We show that increased hydrogen content is accompanied by changes in the thermal stability and CTE for the a-SiC:H films. The most dramatic changes were observed to occur for films with hydrogen content >45% where 〈r〉 is near the critical coordination number (〈r〉c) that delineates over and under constrained materials. For a-SiC:H films above 〈r〉c, relatively little change was observed in CTE with 〈r〉. However for films near or below 〈r〉c, CTE was observed to increase with decreasing 〈r〉 and significant hydrogen loss was observed after the annealing measurements.

Investigation of atomic layer deposited beryllium oxide material properties for high-k dielectric applications

Beryllium oxide (BeO) is a wide band gap alkaline earth oxide material that has recently shown significant promise as a high-k dielectric material in Si and III-V metal–oxide–semiconductor field effect transistor devices. However, many of the basic material properties for BeO thin films utilized in these devices have not been reported or remain in question. In this regard, the authors report an investigation of the chemical, physical, electrical, and mechanical properties of BeO thin films formed via atomic layer deposition (ALD). Combined Rutherford backscattering and nuclear reaction analysis measurements show that ALD BeO thin films exhibit a low hydrogen content (<5%) and are nearly stoichiometric (Be/O ≅ 1.1 ± 0.05). Reflection electron energy loss spectroscopy measurements reveal a wide band gap of 8.0 ± 0.14 eV, and nanoindentation measurements show that ALD BeO has a high Young's modulus and hardness of 330 ± 30 and 33 ± 5 GPa, respectively.

Enhanced ZnTe infiltration in porous silicon by Isothermal Close Space Sublimation

Isothermal Close Space Sublimation (ICSS) technique was used for embedding porous silicon (PS) films with ZnTe. It was studied the influence of the preparation conditions and in particular of a chemical etching step before the ZnTe growth, on the composition profile and final porosity of ZnTe embedded PS. The structure of the embedded material was determined by X-ray diffraction analysis while the thickness of the samples was determined by scanning electron microscopy (SEM). Rutherford backscattering (RBS) and Energy Dispersive (EDS) spectrometries allowed determining the composition profiles. We conclude that the etching of the PS surface before the ZnTe growth has two main effects: increasing the porosity and enhancing the reactivity of the inner surface. It was observed that both effects benefit the filling process of the pores. Since RBS and EDS cannot detect the porosity in the present system, we explore the evolution of porosity by the fitting of the UV–VIS reflectance spectra. The atomic percent determined with this method was in relatively good agreement with that obtained from the RBS and EDS measurements.

Non-isothermal desorption process of hydrogenated nanocrystalline Pd-capped Mg films investigated by Ion Beam Techniques

Nanocrystalline Pd-capped Mg films were prepared by e-beam evaporation and hydrided/deuterated in order to investigate the hydride decomposition mechanism. To that aim, different techniques were used (XRD, FEG, TPD–MS, isotope exchange and “in situ” desorption optical measurements). Obtained results show that hydride films decomposed at T = 165 °C by a process controlled by the Mg/MgH2 interface reaction with an activation energy Ea = 136 ± 5 kJ/mol H2. Interface is located into each MgH2 nanocrystallite according to RBS (Rutherford Backscattering) and ERDA (Elastic Recoil Detection Analysis) measurements performed during hydride decomposition. Moreover, RBS and ERDA spectra also show the formation of a MgxPdy intermixed region. This intermixed region does not modify the type of control mechanism but increases the activation energy of the desorption process and slows down further hydrogenation events.

Complete Elemental Analysis of Low-k a-SiC:H Thin Films by Transmission FTIR Spectroscopy

Fourier transform infrared (FTIR) spectroscopy is a popular technique for qualitatively investigating the chemical bonding of low dielectric constant (low-k) materials utilized in nanoelectronic Cu interconnects. However, quantitative FTIR analysis of low-k materials with widely varying stoichiometry has proven challenging due to numerous optical interference effects, variations in IR absorption strength with optical constants, and a negligible IR activity for homopolar bonds. In this paper, these challenges are overcome to demonstrate full elemental composition analysis by applying multivariate partial least squares (PLS) modeling to the true IR absorbance spectra obtained using previously described methods for eliminating optical interference effects from thin film FTIR spectra. To demonstrate the validity of this approach, transmission FTIR spectra were collected from a series of low-k a-SiC:H thin films with hydrogen content ranging from 25–60%. The elemental concentrations determined from PLS analysis of the corrected low-k a-SiC:H FTIR spectra were found to be in agreement to within ±5% of results obtained from independent nuclear reaction analysis and Rutherford backscattering measurements. These results demonstrate a clear path for establishing transmission FTIR as a quantitative metrology for full compositional analysis (elemental and chemical bond) for a wide range of thin film materials.

Growth of Co2MnAl Thin Films by Pulsed Laser Deposition

The effects of the deposition temperature and laser energy on the characteristics of Co2MnAl films deposited on GaAs substrates were investigated. The grown films were characterized by AFM for film roughness and surface topography. Film thickness and elemental composition were measured using Rutherford Back Scattering (RBS) technique, while crystalline structure and phase composition were investigated by XRD. The RBS measurements showed that the stochiometry of the films was satisfactory and very close to that of the target Co: 0.5, Mn: 0.25, Al: 0.25. The thickness of the films was found to increase as the laser energy was increased from 200 to 400 mJ, in particular for the films deposited at 400 °C. We also found an increase in the films thicknesses as the deposition temperature was increased for the samples grown at 200 and 300 mJ. The best film quality as deduced from XRD, RBS and AFM results for producing these single layers were those deposited at 600 °C with the laser energy at 300 mJ.

Electroless Deposition of Silver Investigated with Rutherford Backscattering and Electron Microscopy

The electroless deposition of silver on Hydrogen terminated Silicon (100) substrates has been investigated with 2.0 MeV He+ ions Rutherford backscattering measurements and electron microscopy observations for 1 mM and 5 mM AgNO3 solutions. The RBS analyzes provide the amount of deposited Ag atoms as a function of the immersion time (1 s-160 s), the particle size and density are given by electron microscopy. A nuclei density in excess of 1011 cm−2 was instantaneously generated. The amount of deposited Ag increases with the square root of the immersion time, following the Cottrell equation, for the 1 s-5 s interval. A diffusion coefficient of about 2 × 10−5 cm2 s−1 for the Ag ions in the solution fits the experimental data. At longer deposition times the Ag ions flux is constant and the diffusion is governed by a static boundary layer few hundred microns thick. With increasing deposition time the particles density decreases of about a factor two. Experiments indicate that clusters dissolution occurs mainly through Ostwald ripening. The cluster radius growth follows a time dependence as tα with α equal to 0.24 for 1 mM and 0.33 for 5 mM solution respectively, i.e. it is mainly planar (1D) diffusion governed although Ostwald ripening, aggregation and coalescence effects should be considered too.

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode (LED) on an 80-μm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxial (HVPE), and laser lift-off (LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Rutherford back-scattering (RBS), photoluminescence, current-voltage and light output-current measurements. The width of (0002) reflection in XRD rocking curve, which reaches 173″ for the thick GaN template LED, is less than that for the conventional one, which reaches 258″. The HRTEM images show that the multiple quantum wells (MQWs) in 80-μm-thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.

Possibilities of the use of ion-beam methods for the diagnostics of planar nanostructures

The possibilities of the nondestructive ion-beam diagnostics of planar nanostructures by the Rutherford backscattering (RBS) of H+ and He+ ion beams with energies of 0.9–1.6 MeV is briefly reviewed. The results of the ion-beam testing of Ba1−x Sr x TiO3 deposited onto Si (100), MgO (100), and NdGaO3 (100) single-crystal substrates are discussed. The degree of element inhomogeneity over the thickness of the coatings under study and the level of the diffuse contamination of the films by substrate atoms are determined by means of RBS measurements.

Role of oxygen in multiferroic behavior of BiFeO3 films grown on 0.2% Nb doped SrTiO3

Effect of oxygen partial pressure on the structural, transport and magnetic properties of BiFeO3 (BFO) films grown on n-type conducting SrNb0.002Ti0.998O3(SNTO) substrates has been investigated. Variation in oxygen partial pressure, during pulsed laser deposition (PLD), results in the modifications in the physical properties of the films. Rutherford Backscattering (RBS) measurement shows that, BFO/SNTO films grown at 100 and 300mT oxygen partial pressures, exhibit better polarization and magnetization. Tuning of electrical and magnetic properties with oxygen partial pressure has been discussed in the light of oxygen vacancies. Various charge transport mechanisms have been discussed to understand the leakage current mechanisms in BFO/SNTO films.

High-Throughput Compositional and Structural Evaluation of a Lia(NixMnyCoz)Or Thin Film Battery Materials Library

A Lia(NixMnyCoz)Or cathode materials library was fabricated by combinatorial magnetron sputtering. The compositional analysis of the library was performed by a new high-throughput approach for Li-content measurement in thin films, which combines automated energy-dispersive X-ray spectroscopy, Deuteron-induced gamma emission, and Rutherford backscattering measurements. Furthermore, combining this approach with thickness measurements allows the mapping of density values of samples from the materials library. By correlating the obtained compositional data with structural data from high-throughput X-ray diffraction measurements, those compositions which show a layered (R3̅m) structure and are therefore most interesting for Li-battery applications (for cathode (positive) electrodes) can be rapidly identified. This structure was identified as being most pronounced in the compositions Li0.6(Ni0.16Mn0.35Co0.48)O2, Li0.7(Ni0.10Mn0.37Co0.51)O2, Li0.6(Ni0.23Mn0.33Co0.43)O2, Li0.3(Ni0.65Mn0.08Co0.26)O2, Li0.3(Ni0.63Mn0.08Co0.29)O2, Li0.4(Ni0.56Mn0.09Co0.34)O2, Li0.5(Ni0.45Mn0.13Co0.42)O2, and Li0.6(Ni0.34Mn0.14Co0.52)O2.

AlGaN/GaN/InGaN/GaN DH-HEMTs with GaN channel layer grown at high temperature

The AlGaN/GaN/InGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) sample has been grown by MOCVD on (0 0 0 1) sapphire substrate. The structure features a 7 nm In 0.046 Ga 0.954 N interlayer determined by Rutherford backscattering (RBS). Since the polarization field in the InGaN interlayer is opposite to it in the AlGaN layer, an additional potential barrier is introduced between the two-dimensional electron gas (2DEG) channel and buffer, leading to enhanced carrier confinement and improved buffer isolation. The GaN layers between the AlGaN layer and InGaN interlayer are divided into two layers consisting of GaN channel layer which provides high mobility 2DEG grown at 1070 °C and GaN spacer layer grown at the same temperature as InGaN interlayer (800 °C) to prevent indium diffusion. RBS measurement confirms that the 3 nm GaN spacer layer isolates the InGaN interlayer well and free from diffusion. Hall measurement has been performed, the mobility as high as 1552 cm 2 /V s at room temperature is obtained and the sheet carrier density is 1.55 × 10 13 cm −2 . The average sheet resistance is 331 Ω/sq, respectively. The mobility obtained in this paper is about 20% higher than similar structures reported.

Annealing induced compositional changes in SmCo5/Fe/SmCo5 exchange spring trilayers and its impact on magnetic properties

SmCo5/Fe/SmCo5 sandwich configurations have gained renewed interest when compared to the conventional SmCo5/Fe bilayers, as they exhibit enormous scope to impart high energy product values with strong magnetization reversal behavior. The compositional changes that occur in the intermediate soft layer upon annealing play a critical role in determining the phase chemistry, as well as magnetic performance of the trilayers and herein we address such a study. SmCo5/Fe/SmCo5 sandwich films with fixed layer thicknesses of SmCo5 (25nm) and Fe (8nm) were grown by sputtering on Cr buffered Si (100) substrates and subsequently, annealed at different temperatures: 673, 773 and 873K. The effect of post-deposition annealing on the structure, composition and magnetic properties of the trilayer architecture was investigated by X-ray diffraction (XRD), Rutherford back-scattering (RBS) and super-conducting quantum interference device (SQUID), respectively. The XRD studies showed significant decrease in the lattice parameter values with increasing annealing temperature, which suggests an increase in the diffused Co-content in the Fe-intermediate layer. The XRD results were further validated by RBS measurements, which confirmed that both composition and thickness of the Fe-intermediate layer were strongly affected by the annealing temperature. The SQUID measurements demonstrated the existence of in-plane anisotropy and strong exchange coupling between the hard and soft layers for all the annealed sandwich films. The trilayer stack annealed at 773K showed the best magnetic performance such as high coercivity (814kA/m), remanence (944kA/m) and energy product (243kJ/m3).

Rutherford backscattering studies of strain-relaxed SiGe films grown on Si substrate with compositionally graded buffer layers

We investigated the structural properties of 2-μm thick Si0.58Ge0.42 thin films grown on a combined set of Si1−xGex stepwise buffer layers and a Si0.51Ge0.49 strain-inverted layer on Si substrates. Raman spectroscopy and Rutherford backscattering measurements showed smaller residual strain and superior crystalline lattice ordering compared to a sample without any buffer layer. Furthermore, a Si0.58Ge0.42 thin film with a low dislocation density of less than 105cm−2 and a smooth surface roughness of 0.903nm can be achieved by using a combined set of Si1−xGex stepwise buffer layers and a Si0.51Ge0.49 strain-inverted layer, because most dislocations can be confined within each Si1−xGex buffer layer.

Investigation of the structural, optical and electrical properties of Nd-doped ZnO thin films deposited by spray pyrolysis

Neodymium-doped zinc oxide (NZO) thin films were deposited on glass substrates by spray pyrolysis technique. X-ray diffraction patterns have shown that both undoped and Nd-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along (0 0 2) direction. The effective doping concentration has been determined by Rutherford backscattering measurements show- ing that the neodymium is not incorporated easily into ZnO host matrix. The surface roughness was shown to increase with Nd doping. NZO films are highly transparent in the visible region. The lowest electrical resistivity value of about 4.0 10 �2 Ω cm was obtained for 1% Nd effective doping.

Real time in situ spectroscopic ellipsometry of the growth and plasmonic properties of au nanoparticles on SiO2

The evolution of the film thickness and plasmonic properties for sputtered deposited Au nanoparticles on SiO2 layers have been monitored in real time using in situ spectroscopic ellipsometry in the photon energy range 0.75–4.1 eV. The spectroscopic ellipsometry data were analyzed with an optical model in which the optical constants for the Au nanoparticles were parameterized by B-splines which simultaneously provide an accurate determination of an effective thickness and an effective dielectric function. The effective thickness is interpreted with support of transmission and scanning electron microscopy and Rutherford backscattering measurements. Further parameterization of the optical constants by physical oscillators in the isolated spherical particle region allows the microstructural parameters such as size and Au fraction to be extracted. Real time in situ monitoring allows the growth of nanoparticles from the nucleation phase to near percolation to be followed, and there is a red-shift of the plasmon resonance absorption peak as the nanoparticles increase in size and their interaction becomes stronger.