Backscattering Channeling Research Articles

Room Temperature Giant Hall Effect in (Ni61Fe39) x (Al2O3)1−x Percolating Nanogranular Films

A series of (Ni61Fe39) x (Al2O3)1−x films were prepared using the magnetron sputtering technique. The maximum of saturated Hall resistivity 4.06 μΩ⋅cm was observed in (Ni61Fe39)60(Al2O3)40 nanogranular film at room temperature, which was about two orders larger than that of pure ferromagnetic metallic films. For the first time, the composition in the atomic fraction at the quantum percolation threshold was accurately characterized by the Rutherford backscattering (RBS) channelling technique in order to substantiate the newly metal-insulator fraction of percolation threshold in the Giant Hall Effect. It also was identified from the TEM image of an as-deposited sample that this large enhancement of the Hall resistivity coefficient was interrelated with the percolation threshold. With a different annealing temperature (T A ) up to 300 °C , the saturated Hall resistivity of (Ni61Fe39)60(Al2O3)40 granular film decreased only a little, which showed its good thermal stability for potential application.

Irradiation damage in Gd2Ti2O7single crystals: Ballistic versus ionization processes

The structural transformations induced in Gd${}_{2}$Ti${}_{2}$O${}_{7}$ single crystals irradiated at high energies (870-MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4-MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling (RBS/C), Raman spectroscopy, and transmission electron microscopy (TEM) experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic-energy deposition, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters lie in the range 6--9 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both direct-impact/defect-stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher at low energy (0.5 ion nm${}^{\ensuremath{-}2}$) than at high energy (0.05 ion nm${}^{\ensuremath{-}2}$), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm).

Superparamagnetic nanoparticles formed in Fe-implanted ZnO

Due to its potential application to diluted magnetic oxides, transition metal doped ZnO has been under intensive investigation. We present a correlation between the structural and the magnetic properties of Fe implanted ZnO bulk crystals. Crystalline damage recovery, structural and magnetic properties are studied by Rutherford backscattering spectrometry and channelling (RBS/C), synchrotron radiation X-ray diffraction (SR-XRD), and superconducting quantum interference device magnetometer (SQUID), respectively. The 623 K Fe ion implantation and the high vacuum annealing at 823 K lead to the formation of secondary phase -Fe and -Fe nanoparticles. The discrepancy between the zero-field cooling and the field cooling curves further indicates that Fe-implanted ZnO is superparamagnetic and the observed ferromagnetism originates from the Fe nanoparticles.

Multipath Fading Measurements at 5.8 GHz for Backscatter Tags With Multiple Antennas

Multipath fading can be heavy for ultra-high frequency (UHF) and microwave backscatter radio systems used in applications such as radio frequency identification (RFID). This paper presents measurements of fading on the modulated signal backscattered from a transponder for backscatter radio systems that use multiple antennas at the interrogator and transponder. Measurements were performed at 5.8 GHz and estimates of the backscatter channel envelope distributions and fade margins were calculated. Results show that multipath fading can be reduced using multiple transponder antennas, bistatic interrogators with widely separated transmitter and receiver antennas, and conventional diversity combining at the interrogator receiver. The measured envelope distribution estimates are compared to previously derived distributions and show good agreement.

Damage recovery and optical activity in europium implanted wide gap oxides

In this study we compare and discuss the defects and optical behaviour of sapphire and magnesium oxide single crystals implanted at room temperature with different fluences (1 × 10 15–1 × 10 16 cm −2) of europium ions. Rutherford backscattering channelling shows that for fluences above 5 × 10 15 cm −2 the surface disorder level in the Al-sublattice reaches the random level. Implantation damage recovers fast for annealing in oxidizing atmosphere but even for the highest fluence we recover almost completely all the damage after annealing at 1300 °C, independently of the annealing environment (reducing or oxidizing). Annealing above 1000 °C promotes the formation of Eu 2O 3 in the samples with higher concentration of Eu. The optical activation of the rare earth ions at room temperature was observed after annealing at 800 °C by photoluminescence and ionoluminescence. In Al 2O 3 lattice the highest intensity line of the Eu 3+ ions corresponds to the forced electric dipole 5D 0 → 7F 2 transition that occurs ∼616 nm. For the MgO samples the Eu 3+ optical activation was also achieved after implantation with different fluences. Here, the lanthanide recombination is dominated by the magnetic dipole 5D 0 → 7F 1 transition near by 590 nm commonly observed for samples were Eu 3+ is placed in a high symmetry local site. The results clearly demonstrate the possibility to get Eu incorporated in optical active regular lattice sites in wide gap oxides.

Fe-implanted SiC as a potential DMS: X-ray diffraction and rutherford backscattering and channelling study

Single crystalline (0 0 0 1)-oriented 6H-SiC samples were implanted at 380 °C with low-energy Fe ions (in the 100 keV range) with the aim of synthesizing so-called diluted magnetic semiconductors. X-ray diffraction and Rutherford backscattering spectrometry and channeling are used to study the microstructural changes in these Fe-implanted SiC crystals submitted to furnace annealing and laser processing, both treatments being performed in order to eliminate the implantation-induced defects.

Structural and magnetic properties of Co+ implanted n-GaN dilute magnetic semiconductors

The n-type GaN epilayer was grown on sapphire prepared by metal organic chemical vapour deposition and subsequently Co+ ions implanted. The properties of Co+ ions implanted GaN epilayer were investigated by structural and magnetic measurements. The results of Rutherford backscattering spectrometry and channeling illustrate that an excellent crystalline quality (χmin=1.3%) of as-grown GaN. After the implantation of 150 keV Co+ ions with dose 3×1016 cm−2 into GaN and subsequently annealed at 700, 800 and 900 °C, no secondary phase or metal related-peaks were detected by typical XRD. In addition high-resolution X-ray diffraction (HRXRD) was performed to study structural related properties. The magnetization curves were obtained by SQUID and AGM measurements, a well-defined hysteresis loop was observed even at 300 K. The temperature dependence of magnetization was taken in FC and ZFC conditions showed the highest Curie temperature (TC) ∼370 K recorded for Co+ implanted GaN.

Multistep damage evolution process in cubic zirconia irradiated with MeV ions

This work reports the study, via the combination of Rutherford backscattering spectrometry and channeling, x-ray diffraction, and transmission electron microscopy experiments, of the damage formation in cubic yttria-stabilized zirconia single crystals irradiated with medium-energy (4 MeV) heavy (Au) ions. The damage buildup, which is accounted for in the framework of the multistep damage accumulation model, occurs in three steps. The first step at low fluences (up to 1015 cm−2), characterized by a regular increase in both the damage yield and the elastic strain, is related to the formation of small defect clusters. The second step in the intermediate fluence range (from 1015 to 5×1015 cm−2) leads to a sharp increase in the damage yield and to a large drop of the strain due to the formation of dislocation loops which collapse into a network of tangled dislocations. The third step at high fluences (above 5×1015 cm−2) exhibits a surprising decrease in the damage yield, which may be attributed to the reorganization of the dislocation network that leads to the formation of weakly damaged regions with a size of the order of 100 nm.

Azimuthal dependence and accurate determination of the half-angle in RBS channeling

Rutherford Backscattering Channeling (RBSC) is often used in the studies of single crystalline materials with regard to issues hinging upon the location of specific atomic species within the crystal lattice. Results are deduced from the characteristics of an angular scan curve representing the yield of close collision events from the constant scattering of the probing projectiles from the crystalline sample in a sequence of directions lying in a plane perpendicular to one particular crystal lattice direction. Such angular scans exhibit dips near major channels, and their angular widths are of concern. On a fundamental level, accurate determination of these angular widths in the case of axial channeling and their interpretation come up against uncertainties arising out of the absence of a preferred choice for the plane of scan. Here, we shall illustrate these uncertainties in a representative case, channeling of 2 MeV He + ions in the 〈1 0 0〉 direction of Si.

Structural and optical characterization of Eu-implanted GaN

GaN was implanted with 300 keV Eu ions over a wide fluence range from 1 × 1013 to 1 × 1016 Eu cm−2 at room temperature (RT) or 500 °C. Detailed structural and optical characterizations of the samples were performed using Rutherford backscattering spectrometry and channelling, transmission and scanning electron microscopy, wavelength dispersive x-ray emission and RT cathodoluminescence (CL) spectroscopy. RT implantation results in a sigmoidal-shaped damage build-up curve with four regimes that were correlated with the formation of specific kinds of defects. After annealing at 1000 °C only samples implanted to fluences below 0.8 × 1015 Eu cm−2 showed near complete recovery of the crystal. Implantation at elevated temperature significantly decreases the implantation damage and increases the fraction of Eu incorporated on substitutional Ga-sites. The improved structural properties of samples implanted at elevated temperature are reflected in a higher intensity of Eu-related red light emission after annealing at 1000 °C. The RT CL intensity is correlated with the number of Eu ions on substitutional Ga-sites after annealing. Furthermore, a detailed study of optical activation shows that the optimum annealing temperature depends on the implantation fluence due to the sensitive balance of defects removed and created during high temperature annealing.

A geometric procedure for improved Rutherford backscattering channeling analysis of materials

Solving geometric and sample alignment issues is a major part of multi-axial Rutherford backscattering channeling (RBS-C) analysis of materials, especially involving complicated samples. However, a geometric standard does not exist for RBS-C, which complicates experimental procedures and makes experimental methods and data presentation inconsistent among different experiments. Our approach to solving RBS-C geometric issues, discussed here, is to introduce a geometric adjustment and sample manipulation procedure which defines the orientation and rotation of the sample with respect to a fixed coordinate system. This method makes rotational, alignment and sample manipulation operations involved in RBS-C more flexible and simpler. As a test case, we present multi-axial RBS-C maps of Si obtained via this methodology. Distortions arising in such RBS-C maps due to geometric effects, how they can affect alignment procedure and data extraction, and how our approach treats these issues are discussed.

Amorphization and dynamic annealing of hexagonal SiC upon heavy-ion irradiation: Effects on swelling and mechanical properties

Structural, mechanical, and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are studied by means of Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation, and surface profilometry measurements. 4H- and 6H-SiC single crystals were irradiated with 4 MeV Au2+ and 4 MeV Xe+ ions at room temperature (RT) or 400 °C. Using a Monte Carlo program to simulate the RBS/C spectra (MCCHASY code), we find that Au ion irradiation at RT induces a total silicon sublattice disorder related to full amorphization at a dose of about 0.4 displacement per atom (dpa). A two-step damage process is found on the basis of the disordered fractions deduced from RBS/C data. Complete amorphization cannot be reached upon both Au and Xe ion irradiations at 400 °C up to about 26 dpa because of the dynamic annealing of defects. When complete amorphization is reached at RT, the Young’s modulus and Berkovich hardness of irradiated 6H-SiC samples are lower by, respectively, 40% and 45% than those of the virgin crystals. The out-of-plane expansion measured by surface profilometry increases versus irradiation dose and the saturation value measured in the completely amorphous layer (normalized to the ion projected range) is close to 25%. We show that the modifications of the macroscopic properties are mainly due to the amorphization of the material. The macroscopic elasticity constants and dimensional properties are predicted for a composite material made of crystalline matrix containing dispersed amorphous inclusions using simple analytical homogenization models. Voigt’s model seems to give the best approximation for disordered fractions larger than 20% in the second step of the damage process.

Complete Link Budgets for Backscatter-Radio and RFID Systems

Backscatter radio - wireless communication by modulating signals scattered from a transponder (RF tag) - is fundamentally different from conventional radio because it involves two distinct links: the power-up link for powering passive RF tags, and the backscatter link for describing backscatter communication. Because of severe power constraints on the RF tag, a thorough knowledge of the backscatter channel is necessary to maximize backscatter-radio and radio-frequency identification (RFID) system performance. This article presents four link budgets that account for the major propagation mechanisms of the backscatter channel, along with a detailed discussion of each. Use of the link budgets is demonstrated by a practical UHF RFID portal example. The benefits of future 5.8 GHz multi-antenna backscatter-radio systems are shown. An intuitive analogy for understanding the antenna polarization of RF tag systems is presented.

Thermal and irradiation induced interdiffusion in magnetite thin films grown on magnesium oxide (0 0 1) substrates

Epitaxial Fe 3O 4(0 0 1) thin films (with a thickness in the range of 10–20 nm) grown on MgO substrates were characterized using low-energy electron diffraction (LEED), conversion electron Mössbauer spectroscopy (CEMS) and investigated using Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). The Mg out-diffusion from the MgO substrate into the film was observed for the directly-deposited Fe 3O 4/MgO(0 0 1) films. For the Fe 3O 4/Fe/MgO(0 0 1) films, the Mg diffusion was prevented by the Fe layer and the surface layer is always a pure Fe 3O 4 layer. Annealing and ion beam mixing induced a very large interface zone having a spinel and/or wustite formula in the Fe 3O 4-on-Fe film system.

Lattice location and annealing studies of Hf implanted CaF2

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the 〈110〉 crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with 181Hf(181Ta) show quadrupole interactions with νQ1=300(3) MHz (η=0.00), νQ2=1285(13) MHz (η=0.43) and νQ3=1035(10) MHz (η=0.00) after annealing up to 1200K.

Thermal and irradiation induced interdiffusion in Fe3O4/MgO(0 0 1) thin film

The interface reactions in an epitaxial 10nm-thick Fe3O4/MgO(001) film were investigated by using Rutherford Backscattering spectrometry (RBS), channeling (RBS-C) and X-ray reflectometry (XRR). The as-grown film had a good crystallinity indicated by the minimum yield and the half-angle value for Fe, respectively, χmin(Fe)=22% and ψ1/2(Fe)=0.62°. Annealing the films under partial argon pressure up to 600°C led to a large enhancement of Mg out-diffusion into the film forming a wustite-type phase, but the total layer thickness did not change much. Ion irradiation of the film by 1MeV Ar ion beam caused a strong Fe ion mixing resulting in a large interfacial zone with a thickness of 23nm.

Defects and magnetic properties in Mn-implanted3C-SiC epilayer on Si(100): Experiments and first-principles calculations

The effect of structural and chemical disorder on magnetism of Mn-implanted 3C-SiC epilayer on Si(100) is investigated experimentally using Rutherford backscattering channeling spectroscopy (RBS/C), x-ray diffraction (XRD), micro-Raman spectroscopy $(\ensuremath{\mu}\text{RS})$, and magnetometry, and theoretically using ab initio calculations. A single 3C-SiC epilayer on Si(001) was implanted at room temperature (RT) with Mn ions at 80 keV and at a dose of $5\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }{\text{cm}}^{\ensuremath{-}2}$. RBS data show the formation of a highly disordered implanted layer of $\ensuremath{\sim}45\text{ }\text{nm}$ with a peak Mn atomic concentration of $\ensuremath{\sim}1.8%$ randomly distributed, in agreement with the stopping and range of ions in matter (SRIM) simulation. The experimental results of magnetic moment per Mn are interpreted by assuming that the implanted layer consists of two respective main regions, C--rich and Si--rich regions, as reflected by the presence of a graphitic phase, in which the local atomic environment of Mn is essentially C. Annealing seems to favor Mn substitution into Si sites, indicated by the substantial expansion of the lattice constant due to larger covalent Mn radius as observed by XRD and due to a high local tensile strain determined from $\ensuremath{\mu}\text{RS}$. This interpretation is also supported by recent calculations, showing that it is energetically favorable for Mn to substitute Si sites. The temperature dependence of magnetization shows an insulatinglike character for the as-implanted film and metalliclike for the annealed-implanted film with Curie temperature above RT. In addition, the magnetic moment per Mn increases strongly with annealing from 0.23 to $0.65{\ensuremath{\mu}}_{\text{B}}$. The experimental behavior is supported by our ab initio calculations, showing that magnetism in Mn-doped 3C-SiC can be enhanced by carefully growing a structure with Mn in Si sites using a C-deficient SiC host, possibly resulting in localized magnetic interactions.

Defect Analysis of Silicon-Silicide-on-Insulator Substrates

The electrical reliability of silicon-silicide-on-insulator (SSOI) substrates is studied by diode analysis method. Diodes are fabricated in epitaxial silicon on silicon-on-insulator (SOI) and SSOI substrates. At low reverse bias the diodes on SSOI substrates show a general increase in leakage current. However, as the reverse bias increases to , the leakage current for diodes on SOI substrates surpasses that on SSOI substrates. The correlation between the electrical behavior of the diodes and the threading dislocations in the epitaxial layer is explored by applying a controllable preferential etching process based on an electrochemical capacitance–voltage system. The crystal quality of the SSOI substrates is also studied by Rutherford backscattering spectrometry and channeling.

High electron mobility of phosphorous-doped homoepitaxial ZnO thin films grown by pulsed-laser deposition

The transport properties of phosphorous-doped ZnO thin films, grown by pulsed-laser deposition on thermally pretreated hydrothermally grown ZnO single-crystal substrates, are reported. The ZnO:P thin films show very good morphological and structural properties as confirmed by atomic force microscopy (AFM), high resolution x-ray diffraction, and Rutherford backscattering (RBS) channeling. Steps of height c/2 are visible in AFM investigations for all samples. For an oxygen partial pressure of 0.1 mbar, two-dimensional growth was found. RBS channeling of a ZnO:P film shows a minimum yield of 0.034 which is comparable to that of an annealed substrate (0.033). Hall effect measurements revealed that all films are n-type for the present growth conditions. Peak mobilities of 800 cm2/Vs have been observed around 70 K, in line with the high structural quality of the samples. Room-temperature mobility in ZnO:P is up to 170 cm2/Vs.

A Software-Defined Radio System for Backscatter Sensor Networks

Backscatter radio is proposed for sensor networks. In that way, the transmitter for each sensor is simplified to a transistor connected to an antenna and therefore, the cost for each sensor's communicator becomes negligible, while energy used for wireless communication per sensor is minimized. A software-defined transceiver is built to transmit a carrier, receive the reflections from various sensors and extract their transmitted messages. This work presents a thorough model of the backscatter radio link, the system architecture and a set of data extraction techniques for each sensor's information, testing in practice a sensor communicating through backscatter at a range of approximately 15 meters indoors, with 5 milliwatt transmission power at 10 bits per second. This work highlights the idiosyncrasies of the backscatter channel and provides a new communication perspective in the fertile area of scalable sensor networks, especially when low bit-rate, ultra-low cost sensors are required.