Ion Channeling Measurements Research Articles

An Artificial Lipid Bilayer Formed on Agarose-coated Glass for Simultaneous Electical and Optical Measurement of Single Ion-Channels

Purpose: Development of an apparatus for simultaneous measurement of electrical and spectroscopic parameters of single ion-channels.

Modification of the Si amorphization process byin situ ultrasonic treatment during ion implantation

We report the first study of the effect of in situultrasound treatment (UST) during ion implantation on amorphizationof crystalline silicon. Rutherford backscattering spectroscopy,ion channelling and cross-section transmission electronmicroscopy measurements show that amorphization of Si during Arion implantation is enhanced by UST,especially at ultrasound frequencies around 2 MHz. Theinfluence on the amorphization process depends mainly on ionflux, ion masses and ultrasound frequency. For implantationconditions without amorphization, for example in the case of implantationwith light atoms such as boron, defect concentrations arelower for wafers implanted with UST comparedto reference wafers implanted without UST. Theinfluence of ultrasound is discussed in terms of itsinteraction with point defects and ultrasound-stimulatedenhanced diffusion of interstitials.

Ti:sapphire formation via the co-implantation of Ti and O ions into sapphire

Sequential implants of Ti and O ions into Al 2O 3 lead to stabilisation of Ti in the optically active 3+ oxidation state when suitable implantation and annealing conditions are used. The presence of Ti 3+ in sapphire gives rise to luminescence over the wavelength range ∼650–1100 nm and is the basis of the broadly tunable Ti:sapphire laser. We present results of Rutherford backscattering spectrometry and ion channeling (RBS-C) measurements which show the structural changes that accompany increases in the Ti 3+ luminescence yield during post-implantation thermal processing of Ti/O implanted sapphire substrates. Complementary information is provided by proton induced X-ray emission and channeling measurements indicating the lattice location of the Ti atoms.

Ion channeling studies of hydrogen in homoepitaxially grown CVD diamond

Abstract Using ion channeling measurements in conjunction with the resonant 1 H( 15 N,αγ) 12 C nuclear reaction or with proton Rutherford backscattering spectrometry we studied the incorporation of hydrogen from the plasma into homoepitaxial (100) and (111) CVD diamond films. The measured hydrogen concentration and the structural defect density of the diamond lattice derived from proton channeling yields were observed to be correlated. Hydrogen lattice location studies for different incident ion channeling directions showed no dominant fraction of H occupying either one of the two theoretically predicted sites. These results suggest that in CVD films with quite high dislocation densities and relative H concentrations above 10 −3 , hydrogen is predominantly incorporated at structural defect sites uncorrelated with the lattice symmetry.

Fast impedance spectroscopy: General aspects and performance study for single ion channel measurements

In the present work, we propose a novel technical approach in time domain impedance spectroscopy enabling both enhanced time and current resolution by an improved data analysis and hardware setup. We introduce nonstationary time-to-frequency conversion methods such as short-time Fourier transform and wavelet transform resulting in an improved time resolution. The combination of a time domain impedance spectrometer with a patch-clamp amplifier enables the resolution of gigaohm impedance at low perturbation signal amplitudes. A fast impedance spectroscopy (FIS) setup is presented which is optimized for biophysical application of single ion channel measurements in supported biomembranes. The applicability and performance of the technique is first evaluated by simulations. It is then verified by measurements on model circuits which exhibit the characteristic key properties of single ion channel measurements. Here, FIS improves the time resolution by about three orders of magnitude down to milliseconds. The general aspects derived in this work are also valid in other fields, where the spectral information of a perturbation applied on a system and its response is analyzed, e.g., mechanical impedance spectroscopy and microrheology.

An Artificial Lipid Bilayer Formed on an Agarose-Coated Glass for Simultaneous Electrical and Optical Measurement of Single Ion Channels

The purpose of this study is to develop an apparatus for simultaneous measurement of electrical and spectroscopic parameters of single ion channels. We have combined the single channel recording apparatus with an artificial lipid bilayer and a fluorescence microscope designed to detect single fluorescent molecules. The artificial membranes were formed on an agarose-coated glass and observed with an objective-type total internal reflection fluorescence microscope (TIRFM). The lateral motion of a single lipid molecule (β-BODIPY 530/550 HPC) was recorded. The lateral diffusion constant of the lipid molecule was calculated from the trajectories of single molecules as D = 8.5 ± 4.9 × 10−8 cm2/s. Ionic channels were incorporated into the membrane and current fluctuations were recorded at the single-channel level. After incorporation of Cy3-labeled alametithin molecules into the membrane, bright spots were observed moving rather slowly (D = 4.0 ± 1.6 × 10−8 cm2/s) in the membrane, simultaneously with the alametithin-channel current. These data show the possibility of the present technique for simultaneous measurement of electrical and spectroscopic parameters of single-channel activities.

Ion-channeling studies of cubic GaN and In xGa 1 − xN on GaAs substrates

Rutherford backscattering (RBS), dechanneling and angular scan measurements with 2 MeV 4He + ions have been performed to investigate molecular-beam epitaxially (MBE)-grown cubic GaN and In x Ga 1 − x N layers on semi-insulating GaAs (0 0 1) substrates. The thickness of the epitaxial layers and the In concentration were determined by RBS, the crystalline quality by ion-channeling measurements. The predominant defect type was determined to be dislocations. Due to the lack of a perfect crystal we used an approximation for the minimum yield given by Lindhard and Barrett to normalize the measured minimum yields. The determined concentration of dislocations varies between 6×10 10 and 2.2×10 11 cm −2. Furthermore, a mosaic spread of crystallites was detected with angular scan measurements. Both the concentration of dislocations and the distribution of crystallite orientations do not show a significant dependence on the In concentration.

Tensile Stress in Nanometre Thick MBE Grown CaF2 on (111) Si

CaF2 epitaxial layers were prepared by MBE and investigated by RBS and ion channeling measurements. Films of about 30 nm thickness were found to be strained by tensile stress causing a rhombohedral symmetry of the layers. These results are interpreted in terms of the different thermal expansion coefficients of substrate and deposit, respectively.

Heteroepitaxy of ZnO on GaN and its implications for fabrication of hybrid optoelectronic devices

ZnO thin films have been grown heteroepitaxially on epi-GaN/sapphire (0001) substrates. Rutherford backscattering spectroscopy, ion channeling, and high resolution transmission electron microscopy studies revealed high-quality epitaxial growth of ZnO on GaN with an atomically sharp interface. The x-ray diffraction and ion channeling measurements indicate near perfect alignment of the ZnO epilayers on GaN as compared to those grown directly on sapphire (0001). Low-temperature cathodoluminescence studies also indicate high optical quality of these films presumably due to the close lattice match and stacking order between ZnO and GaN. Lattice-matched epitaxy and good luminescence properties of ZnO/GaN heterostructures are thus promising for ultraviolet lasers. These heterostructures demonstrate the feasibility of integrating hybrid ZnO/GaN optoelectronic devices.

Transport and magnetic properties of epitaxial and polycrystalline magnetite thin films

The transport and magnetic properties of magnetite (Fe3O4) thin films grown epitaxially on single crystal MgO(100) and SrTiO3(100) substrates, and with multiple grain orientations on polycrystalline SrTiO3 substrates, have been investigated. The films are grown using pulsed laser deposition and their epitaxial quality determined using ion channeling measurements. Transport and magnetic studies of Fe3O4 films as a function of thickness and morphology suggest that epitaxial strain and growth defects affect the width and temperature of the Verwey transition. In addition, these factors also significantly influence the magnetic coercivity of the films. The low-field magnetoresistance (MR) behaviors of epitaxial and polycrystalline films as a function of temperature have been compared and they were found to be quite similar, suggesting very small contribution to the MR from grain boundaries.

Ion channeling studies of GaN layers on c-oriented sapphire

The successful growth of epitaxial GaN films by metal organic vapor phase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE) has opened up new applications in short wavelength photonic devices for displays and optical data storage systems. The large lattice mismatch of 14% between GaN and sapphire, usually used as the substrate, and the different thermal expansion coefficients generally lead to high densities of structural defects. In this paper we investigate the defect structure of MOVPE- and GSMBE-grown GaN layers on sapphire by Rutherford backscattering and ion channeling measurements. In addition to axial c-axis channeling, which reveals χ min values as low as 1.2%, channeling measurements along the (2 1 1 0) and (1 1 0 0) crystal planes were performed in order to improve the sensitivity to dechanneling by crystalline defects. Angular scans around the c-axis indicate clearly the hexagonal symmetry of the GaN lattice. Dechanneling results were compared to observations of defects by transmission electron microscopy (TEM). This comparison suggests that the cross-section of dechanneling by edge dislocations is about a factor of 4 larger than the dechanneling cross-section of screw dislocations.

A Raman Scattering, Ion Channelling and Photoluminescence Study of Argon Ion Radiation Damage in Cu(Ga,In)Se2 - Dose Dependence and Dose Rate Effects

AbstractThe ternary chalcopyrite semiconductor CuInSe2 and related ternary compounds are promising materials for the production of high-efficiency thin film solar cells. In this paper we study the dose dependence of ion radiation damage produced by 30 keV and 80 keV Ar ions in single crystals and polycrystalline films of Cu(In,Ga)Se 2 over a wide dose range from 1012 to 1017 cm-2, using Raman spectroscopy and ion channeling measurements. For the first time, we also report on the dose rate dependence with a variation of the beam current density in the range 0.44 to 44 µcm-2. Even for low damage levels no significant dependence of the defect concentration or damage mechanism on the dose rate could be observed. From phonon correlation length considerations we estimate defect densities. They are in agreement with ion channeling data obtained in the 1015 to 1016 dose range, where the breakdown of the lattice structure occurs. In this dose range, the defect density is close to the concentration of implanted atoms. We conclude, that this high impurity concentration is responsible for the amorphization.

Ion Scattering Studies of Defects In Gan Thin Films on C-Oriented Sapphire

ABSTRACTEpitaxial GaN films grown by metal organic vapour phase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE) have opened up new applications in short wavelength photonic devices as well as high-power and high-temperature devices. The large lattice mismatch of 14% between GaN and sapphire, which is frequently used as the substrate, and the different thermal expansion coefficients generally lead to high densities of structural defects. We investigate the defect structure of MOVPE- and GSMBE-grown GaN layers on sapphire by Rutherford backscattering and ion channeling measurements. Channeling along the c-axis revealed χmin-values as low as 1.2% even in samples with dislocation densities in the order of 109 cm−2. Channeling measurements along different crystal planes were performed in order to improve the sensitivity to dechanneling by crystalline defects. Angular yield scans around the c-axis indicate clearly the hexagonal symmetry of the GaN lattice. Dechanneling results were combined with transmission electron microscopy investigations (TEM). The results suggest that the dechanneling-cross-section of edge dislocations is about 4 times larger than the dechannelingcross-section of screw dislocations. screw dislocations.

Characterization of electrochemically grown Ba 1− xK xBiO 3 single crystals by ion channeling methods

The crystallographic quality of Ba 1− x K x BiO 3 single crystals grown by electrochemical methods has been investigated by using ion channeling methods in detail. Well-shaped cubic crystals are obtained and the size of the crystals is large enough for the ion channeling measurements. It is revealed that the quality of the crystals is strongly affected by extrinsic growth conditions. When the crystal is grown under very tranquil environment, the quality of the crystal is drastically improved. Degradation of crystallinity in the surface region is observed. Chemical etching with Br 2CH 3OH is effective to remove the damaged surface layers.

Effect of substrate miscut on low-temperature homoepitaxial growth on Si(111) mediated by overlayers of Au: Evidence of step flow

Observations of homoepitaxial growth on low-angle miscut (∼0.1°) Si(111) substrates through an overlayer of Au, together with earlier results on highly miscut Si(111) surfaces, indicate that growth in this system occurs by step flow. The growth temperatures were between 375 and 500 °C. In the optimum range of Au coverage (0.6–1.0 ML), ion channeling measurements yield at best χmin=5.0%, and cross-sectional transmission electron microscopy reveals stacking faults on (111) planes. Films produced under similar conditions on bare Si(111) substrates are much more defective. On the other hand, the defect density in the present films is higher than that in films grown on substrates with a higher miscut angle. The improvement in film quality resulting from the Au overlayers is attributed to an increase in the diffusion length of the Si adatoms, caused by Au passivation of the Si terraces. It is suggested that Au is more efficient than other overlayers in promoting step flow because Au passivates the Si(111) terraces without passivating the step edges.

Structural characterization and surface lattice strain determination of ZnS/GaAs heterostructures grown by metalorganic vapour phase epitaxy

We report on the structural characterization of ZnS epilayers grown on (1 0 0)GaAs by metalorganic vapour-phase epitaxy (MOVPE). The crystalline quality at the ZnS epilayer surface and the defect depth distribution was studied by Rutherford Backscattering Spectrometry (RBS)-ion channeling measurements as a function of the epilayer thickness. Transmission electron microscopy (TEM) observations were performed on selected ZnS/GaAs heterostructures. Misfit dislocations (MD) were observed at the ZnS/GaAs interface. In addition, a high density of planar defects such as stacking faults (SF) and microtwins (MT) were identified into the epilayer up to 200–300 nm. The density of these defects decreases by increasing the epilayer thickness, but a quite high and constant density of microtwins still occurs in epilayers thicker than 400 nm. However, absorption measurements point out a high optical quality for all the measured ZnS epitaxial layers. Finally, surface lattice strain was determined in the ZnS/GaAs samples by ion channeling measurements. Our data indicate that the initial lattice misfit is already fully relaxed in epilayers as thick as 400 nm and only a small residual thermal strain is measured in thicker samples.

Tribological properties of carbon- and nitrogen-implanted Si(100)

The knowledge of tribological properties of silicon is important due to its potential application for micromechanical devices. The present work focuses on the friction and wear studies of single crystal silicon (100) implanted with carbon and nitrogen at 60 keV. These tests were performed using a pin-on-disc (POD) apparatus with a 52100 pin, under contact stress of 225 MPa and at 35% relative humidity. Changes in surface roughness before and after the wear tests were studied using atomic force microscopy (AFM). Transmission electron microscopy (TEM) investigations and ion-channeling measurements revealed amorphous phases for all the implanted species at all doses. Although the surface hardness measurements performed by nano-indentation indicated no improvement in surface hardness for samples implanted with carbon, the tribological studies indicated an improvement in wear and frictional properties. We relate this improved wear behavior to the formation of amorphous SiC.

Ion beam analysis of MgAl 2O 4 spinel irradiated with fast neutrons to 50–250 dpa

Non-destructive ion beam analysis techniques have been employed to examine the radiation damage in MgAl 20 4 spinel single crystals irradiated with fast neutrons at 400 and 750°C to high fluences (≥ 5 × 10 22 n/cm 2, E n > 0.1 MeV). Rutherford backscattering and ion channeling measurements using 1–4 MeV He-ion beams revealed that the radiation damage saturated after irradiation at 400°C to 50 displacements per atom. The energy dependence of dechanneling indicated the dominant extended defects present in the highly irradiated spinel are in the form of dislocations. Channeling angular scans of particle induced X-ray emission further suggested that neutron irradiation tends to randomize cation distribution for Mg 2+ and Al 3+ cations on the lattice sites. These results are compared to the microstructure observations of Kinoshita et al. and the neutron scattering results of Sickafus et al.

An X-ray diffraction study of the strain and structure of SiGeC/(100)Si alloys

High resolution X-ray diffraction studies were conducted on samples of Si 1- x- y Ge x C y grown on (100)Si by chemical vapor deposition. The measurements were made with the diffractometer in its triple-axis configuration to produce reciprocal space maps. Films with compositions of approximately Si 0.78Ge 0.21C 0.01 and thicknesses ranging from 120 nm to 750 nm were found to be pseudomorphic with a tetragonal distortion strain, ε T , near 1%. The tetragonal strain was found to be independent of sample thickness. The strain in samples with compositions near Si 0.47Ge 0.50C 0.03 and thicknesses ranging from 61 to 115 nm were found to have tetragonal strain values greater than 2%. These strain measurements correlated well with ion channeling measurements. The experimental perpendicular lattice parameters were used to estimate the relaxed film lattice constants. These values fell midway between predicted values using Vegard's law for complete strain compensation by the carbon and no compensation by the carbon.

Dose-rate effects in GaAs investigated by discrete pulsed implantation using a focused ion beam

The dependence of the retained lattice damage upon dose rate was investigated by focused ion beam (FIB) implantation of 210 keV Si++ into GaAs at room temperature. The as-implanted and postannealed states were characterized by ion channeling and Hall-effect measurements, respectively. Dose-rate effects arise from stabilizing interactions between populations of defects produced by different ions, and these experiments were designed to probe the time constants of those interactions. In the context of dose-rate experiments, direct-write FIB represents a much more controllable means of implantation over conventional broad beams since the exact timing of dose delivery may be precisely defined and varied. In this work, the final implanted dose was achieved by the successive application of individual flux pulses of constant intensity but of varying duration td and repetition period tr. A consistent trend toward a greater concentration of displaced atoms directly after implantation and a higher sheet resistance after annealing was observed for longer td and for shorter tr. This effect did not manifest itself simply in terms of the average current density, Javg∝td/tr. Furthermore, it was observed on all time scales accessible in this experiment, suggesting that the important self-annealing mechanisms have a wide range of time constants, from less than 1 μs to more than 1 s. A heterogeneous model of damage nucleation is discussed whereby the defect track of an individual ion event self-anneals until it is overlapped by a following event.