Localised modifications of anatase TiO2 thin films by a Focused Ion Beam

A Focused Ion Beam (FIB) has been used to implant micrometer-sized areas of polycrystalline anatase TiO₂ thin films with Ga⁺ ions using fluencies from 10¹⁵ to 10¹⁷ ions/cm². The evolution of the surface morphology was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the chemical modifications of the surface were followed by X-ray photoelectron spectroscopy (XPS). The implanted areas show a noticeable change in surface morphology as compared to the as-deposited surface. The surface loses its grainy morphology to gradually become a smooth surface with a RMS roughness of less than 1 nm for the highest ion fluence used. The surface recession or depth of the irradiated area increases with ion fluence, but the rate with which the depth increases changes at around 5 × 10¹⁶ ions/cm². Comparison with implantation of a pre-irradiated surface indicates that the initial surface morphology may have a large effect on the surface recession rate. Detailed analysis of the XPS spectra shows that the oxidation state of Ti and O apparently does not change, whereas the implanted gallium exists in an oxidation state related to Ga₂O₃.     

Introduction of conductivity on non-conducting polyaniline by low-energy proton implantation

The semiconductor characteristics of a non-conducting polyaniline pellet can be modified by implantation of low-energy protons, that is, the resistivity became less than 50 Ω cm by proton doping at the fluence rate and fluence of 4 × 10¹¹ ions/cm²/s and 1 × 10¹⁵ ions/cm², respectively. The resistivity increased with the increasing fluence rate of the protons. FT/IR spectra have shown that a new band resulted from the appearance of N⁺-H due to the proton implantation.     

10 MeV Au ion irradiation effects in an MgO-HfO2 ceramic-ceramic (CERCER) composite

Room temperature ion irradiation damage studies were performed on a ceramic composite intended to emulate a dispersion nuclear fuel. The composite is composed of 90-mole% MgO and 10-mole% HfO₂. The as-synthesized composite was found to consist of Mg₂Hf₅O₁₂ (and some residual HfO₂) particles embedded in an MgO matrix. X-ray diffraction revealed that nearly all of the initial HfO₂ reacted with some MgO to form Mg₂Hf₅O₁₂. Ion irradiations were performed using 10 MeV Au³⁺ ions at room temperature over a fluence range of 5 × 10¹⁶-5 × 10²⁰ Au/m². Irradiated samples were characterized using both grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM), the latter using both selected-area electron diffraction (SAED) and micro-diffraction (μD) on samples prepared in cross-sectional geometry. Both GIXRD and TEM electron diffraction measurements on a specimen irradiated to a fluence of 5 × 10²⁰ Au/cm², revealed that the initial rhombohedral Mg₂Hf₅O₁₂ phase was transformed into a cubic-Mg₂Hf₅O₁₂ phase. Finally, it is important to note that at the highest ion fluence used in this investigation (5 × 10²⁰ Au/m²), both the MgO matrix and the Mg₂Hf₅O₁₂ second phase remained crystalline.     

Studies on the corrosion behavior of cerium-implanted zirconium

In order to study the influence of cerium ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted with cerium ions with a fluence ranging from 1 × 10²⁰ to 1 × 10²¹ ions/m² at about 150 °C, using a MEVVA source at an extracted voltage of 40 kV. The valence and element penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) respectively. The potentiodynamic polarization technique was employed to investigate the aqueous corrosion resistance of zirconium in a 1N H₂SO₄ solution. It was found that there was a remarkable improvement in the aqueous corrosion behavior of zirconium implanted with cerium ions compared with that of the as-received zirconium. The corrosion resistance improvement of the cerium-implanted zirconium is probably due to the addition of cerium oxide dispersoid into the zirconium matrix and oxidization protection.     

Structural and optical properties of 6H-SiC helium-implanted at 600 K

Single crystals of 6H-SiC were implanted at 600 K with 100 keV He ions to three successively fluences and subsequently annealed at different temperatures ranging from 873 to 1473 K in vacuum. The recovery of lattice damage was investigated by different techniques including Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy and Fourier transform infrared spectroscopy. All three techniques showed that the damage induced by helium ion implantation in the lattice is closely related to the fluence. Rutherford backscattering spectrometry/channeling data on high temperature implantations suggest that for a fluence of 3 × 10¹⁶ He⁺/cm², extended defects are created by thermal annealing to 1473 K. Apart from a well-known intensity decrease of scattering peaks in Raman spectroscopy it was found that the absorbance peak in Fourier transform infrared spectroscopy due to the stretching vibration of Si-C bond shifted to smaller wave numbers with increasing fluence, shifting back to larger wave numbers with increasing annealing temperature. These phenomena are attributed to different lattice damage behavior induced by the hot implantation process, in which simultaneous recovery was prevailing.     

Radiation damage in ZnO ion implanted at 15 K

Commercial O-face (0 0 0 1) ZnO single crystals were implanted with 200 keV Ar ions. The ion fluences applied cover a wide range from 5 × 10¹¹ to 7 × 10¹⁶ cm⁻². The implantation and the subsequent damage analysis by Rutherford backscattering spectrometry (RBS) in channelling geometry were performed in a special target chamber at 15 K without changing the target temperature of the sample. To analyse the measured channelling spectra the computer code DICADA was used to calculate the relative concentration of displaced lattice atoms.Four stages of the damage evolution can be identified. At low ion fluences up to about 2 × 10¹³ cm⁻² the defect concentration increases nearly linearly with rising fluence (stage I). There are strong indications that only point defects are produced, the absolute concentration of which is reasonably given by SRIM calculations using displacement energies of E_d(Zn) = 65 eV and E_d(O) = 50 eV. In a second stage the defect concentration remains almost constant at a value of about 0.02, which can be interpreted by a balance between production and recombination of point defects. For ion fluences around 5 × 10¹⁵ cm⁻² a second significant increase of the defect concentration is observed (stage III). Within stage IV at fluences above 10¹⁶ cm⁻² the defect concentration tends again to saturate at a level of about 0.5 which is well below amorphisation. Within stages III and IV the damage formation is strongly governed by the implanted ions and it is appropriate to conclude that the damage consists of a mixture of point defects and dislocation loops.     

Temperature effect study of silicon-on-insulator structures prepared by high dose implantation of nitrogen

The temperature effect on the microstructure of the N⁺-ion implantation-induced Si₃N₄ buried layer was investigated. The underlying silicon nitride layers were formed in a Si (1 1 1) wafer after implantation of 50 keV nitrogen ions (fluence: 1 × 10¹⁷, 2 × 10¹⁷ and 5 × 10¹⁷ ions/cm²). It was observed that a continuous amorphous layer of about 200 nm thickness was formed in all implanted samples due to the irradiation damage. After 30 min annealing at 900 °C, poly-crystalline Si₃N₄ products were found by TEM examination in the specimen implanted with 5 × 10¹⁷ ions/cm² dose. In the case of annealing at 1200 °C a continuous single-crystalline α-Si₃N₄ buried layer was formed indicating that the amorphous layer in the implanted samples could be transformed into three successive layers, which are amorphous SiO₂, single-crystal α-Si₃N₄ and retained defects from surface to inner substrate, respectively.     

Study of surface activation of PET by low energy (keV) Ni and N ion implantation

Polyethyleneterephthalate (PET) has been modified by 100 keV Ni⁺ and N⁺ ions using metal ion from volatile compound (MIVOC) ion source to fluence ranging from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². The increasing application of polymeric material in technological and scientific field has motivated the use of surface treatment to modify the physical and chemical properties of polymer surfaces. When a material is exposed to ionization radiation, it suffers damage leading to surface activation depending on the type. The surface morphology was observed by atomic force microscopy (AFM). That show the roughness increases with fluence in both the cases. The Ni particles as precipitation in PET were observed by cross-section transmission electron microscopy (XTEM). The optical band gap (E_g) deduced from absorption spectra; was calculated by Tau’c relation. Raman spectroscopy shows quantitatively the chemical nature at the damage caused by the Ni⁺ and N⁺ bombardment. The ration of I_D/I_G shows graphite-like structure is formed on the surface. A layer of hydrogenated amorphous carbon is formed on the surface, which has confirmed by XPS results also.     

Irradiation effect of carbon negative-ion implantation on polytetrafluoroethylene for controlling cell-adhesion property

We have investigated the irradiation effect of negative-ion implantation on the changes of physical surface property of polytetrafluoroethylene (PTFE) for controlling the adhesion property of stem cells. Carbon negative ions were implanted into PTFE sheets at fluences of 1 × 10¹⁴-1 × 10¹⁶ ions/cm² and energies of 5-20 keV. Wettability and atomic bonding state including the ion-induced functional groups on the modified surfaces were investigated by water contact angle measurement and XPS analysis, respectively. An initial value of water contact angles on PTFE decreased from 104° to 88° with an increase in ion influence to 1 × 10¹⁶ ions/cm², corresponding to the peak shifting of XPS C1s spectra from 292.5 eV to 285 eV with long tail on the left peak-side. The change of peak position was due to decrease of C-F₂ bonds and increase of C-C bonds with the formation of hydrophilic oxygen functional groups of OH and CO bonds after the ion implantation. After culturing rat mesenchymal stem cells (MSC) for 4 days, the cell-adhesion properties on the C⁻-patterned PTFE were observed by fluorescent microscopy with staining the cell nuclei and their actin filament (F-actin). The clear adhesion patterning of MSCs on the PTFE was obtained at energies of 5-10 keV and a fluence of 1 × 10¹⁵ ions/cm². While the sparse patterns and the uncontrollable patterns were found at a low fluence of 3 × 10¹⁴ ions/cm² and a high fluence of 3 × 10¹⁵ ions/cm², respectively. As a result, we could improve the surface wettability of PTFE to control the cell-adhesion property by carbon negative-ion implantation.     

Structural characterization of buried nitride layers formed by nitrogen ion implantation in silicon

The synthesis of buried silicon nitride insulating layers was carried out by SIMNI (separation by implanted nitrogen) process using implantation of 140 keV nitrogen (¹⁴N⁺) ions at fluence of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² into 〈1 1 1〉 single crystal silicon substrates held at elevated temperature (410 °C). The structures of ion-beam synthesized buried silicon nitride layers were studied by X-ray diffraction (XRD) technique. The XRD studies reveal the formation of hexagonal silicon nitride (Si₃N₄) structure at all fluences. The concentration of the silicon nitride phase was found to be dependent on the ion fluence. The intensity and full width at half maximum (FWHM) of XRD peak were found to increase with increase in ion fluence. The Raman spectra for samples implanted with different ion fluences show crystalline silicon (c-Si) substrate peak at wavenumber 520 cm⁻¹. The intensity of the silicon peak was found to decrease with increase in ion fluence.     

Neutron radiation effects on metal oxide semiconductor (MOS) devices

The main purpose of this study is to provide the knowledge and data on Deuterium-Tritium (D-T) fusion neutron induced damage in MOS devices. Silicon metal oxide semiconductor (MOS) devices are currently the cornerstone of the modern microelectronics industry. However, when a MOS device is exposed to a flux of energetic radiation or particles, the resulting effects from this radiation can cause several degradation of the device performance and of its operating life. The part of MOS structure (metal oxide semiconductor) most sensitive to neutron radiation is the oxide insulating layer (SiO₂). When ionizing radiation passes through the oxide, the energy deposited creates electron-hole pairs. These electron-hole pairs have been seriously hazardous to the performance of these electronic components. The degradation of the current gain of the dual n-channel depletion mode MOS caused by neutron displacement defects, was measured using in situ method during neutron irradiation. The average degradation of the gain of the current is about 35 mA, and the change in channel current gain increased proportionally with neutron fluence. The total fusion neutron displacement damage was found to be 4.8 × 10⁻²¹ dpa per n/cm², while the average fraction of damage in the crystal of silicon was found to be 1.24 × 10⁻¹². All the MOS devices tested were found to be controllable after neutron irradiation and no permanent damage was caused by neutron fluence irradiation below 10¹⁰n/cm². The calculation results shows that (n,α) reaction induced soft-error cross-section about 8.7 × 10⁻¹⁴ cm², and for recoil atoms about 2.9 × 10⁻¹⁵ cm², respectively.     

Lateral straggling and its influence on lateral diffusion in implantation with a focused ion beam

Parallel stripes of nanostructures on an n-type Si substrate have been fabricated by implanting 30 keV Ga⁺ ions from a focused ion beam (FIB) source at three different fluences: 1 × 10¹⁵, 2 × 10¹⁵ and 5 × 10¹⁵ ions/cm². Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) measurements were carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 × 100 nm², appear as bright regions in the PEEM image. Line scans of the intensities from PEEM images were recorded along and across these stripes. Intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ∼10⁻¹⁵ m²/s. No significant dependence of diffusion coefficient on ion fluence was observed in the fluence range investigated here. Radiation enhanced diffusion has been discussed in the light of the associated defect distribution due to lateral straggling of the implanted ions.     

Raman investigation of incident N-, Xe-ions induced effects in ZnO thin films

Highly c-axis orientation ZnO thin films with hundreds nanometers in thickness have been deposited on (1 0 0) Si substrate by RF magnetron sputtering. These films are implanted at room temperature by 80 keV N-ions with fluences from 5.0 × 10¹⁴ to 1.0 × 10¹⁷ ions/cm², implanted by 400 keV Xe-ions with 2.0 × 10¹⁴ to 2.0 × 10¹⁶ ions/cm², irradiated by 3.64 MeV Xe-ions with 1.0 × 10¹² to 1.0 × 10¹⁵ ions/cm², or irradiated by 308 MeV Xe-ions with 1.0 × 10¹² to 5.0 × 10¹⁴ ions/cm², respectively. Then the ZnO films are investigated using a Raman spectroscopy. The obtained Raman spectra show that a new Raman peak located at about 578 cm⁻¹ relating to simple defects or disorder phase appears in all ZnO films after ion implantation/irradiation, a new Raman peak at about 275 cm^-1 owing to N-activated zinc-like vibrations is observed in the N-implanted samples. Moreover, a new Raman peak at about 475 cm⁻¹ is only seen in the samples after 400 keV and 3.64 MeV Xe-ions bombardment. The area intensity of these peaks increases with increasing ion fluence. The effects of ion fluence, element chemical activity, atom displacements induced by nuclear collisions as well as energy deposition on the damage process of ZnO films under ion implantation/irradiation are discussed briefly.     

Effect of 200 MeV Ag ion irradiation on structural and electrical transport properties of Fe3O4 thin films

Thin films of Fe₃O₄ have been deposited on single crystal MgO(1 0 0) and Si(1 0 0) substrates using pulsed laser deposition. Films grown on MgO substrate are epitaxial with c-axis orientation whereas, films on Si substrate are highly 〈1 1 1〉 oriented. Film thicknesses are 150 nm. These films have been irradiated with 200 MeV Ag ions. We study the effect of the irradiation on structural and electrical transport properties of these films. The fluence value of irradiation has been varied in the range of 5 × 10¹⁰ ions/cm² to 1 × 10¹² ions/cm². We compare the irradiation induced modifications on various physical properties between the c-axis oriented epitaxial film and non epitaxial but 〈1 1 1〉 oriented film. The pristine film on Si substrate shows Verwey transition (T_V) close to 125 K, which is higher than generally observed in single crystals (121 K). After the irradiation with the 5 × 10¹⁰ ions/cm² fluence value, T_V shifts to 122 K, closer to the single crystal value. However, with the higher fluence (1 × 10¹² ions/cm²) irradiation, T_V again shifts to 125 K.     

Microstructure damage of titanium films by irradiation with fission fragments

Radiation damage caused by fission fragments to metal surfaces is an important research topic. Thin titanium foils were irradiated with a continuous wave beam of 132 MeV ¹³²Xe⁺²⁹ at the current intensity of 2 pnA. Pre- and post-irradiated surface topologies were investigated using atomic force microscopy and the observed defects were quantified by root mean square roughness, depth profile of the disordered zones, size and areal density of the voids, and discussed as a function of the applied fluencies (1-9) × 10¹³ Xe/cm². The first ellipsoidal dislocation loops appeared at the fluence of 3.0 × 10¹³ Xe/cm² with the areal density of 1.56 × 10⁶/cm² that increased to 2.0 × 10⁷ cm⁻² when the dose rose to 9.0 × 10¹³ Xe/cm². At this point also the first dislocation lines with the density of 1.3 × 10⁷ cm⁻² were seen. Our results suggest that the fission fragments might maximize large voids and dislocations and increase the degradation in depth resolution.     

Atom probe tomography characterization of radiation-sensitive KS-01 weld

The microstructure of a radiation-sensitive KS-01 test weld has been characterized by atom probe tomography. The levels of copper, manganese, nickel and chromium in this weld were amongst the highest of all the steels used in Western reactor pressure vessels. After neutron irradiation to a fluence of 0.8 × 10²³ n m⁻² (E>1 MeV) at a temperature of 288 °C, this weld exhibited a large Charpy T_41J shift of 169 K, a large shift of the fracture toughness transition temperature of 160 K, a decrease in upper shelf energy from 118 to ∼78 J, and an increase in the yield strength from 600 to 826 MPa. However, the mechanical properties data conformed to the master curve. Atom probe tomography revealed a high number density (∼3 × 10²⁴ m⁻³) of Cu-, Mn-, Ni-, Si- and P-enriched precipitates and a lower number density (∼1  × 10²³ m⁻³) of P clusters.     

Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition

A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La_0.7Sr_0.3MnO₃ (LSMO) thin film using atomic force microscope (AFM) is presented. Highly c-axis oriented LSMO thin films were grown on LaAlO₃ (1 0 0) (LAO) substrates by the pulsed laser deposition (PLD) technique. The films were annealed at 800 °C for 12 h in air (pristine films) and subsequently, irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 × 10¹² to 1 × 10¹⁴ ions/cm² and 1 × 10¹¹ to 1 × 10¹² ions/cm² for oxygen and silver ions, respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology such as rms roughness (σ), the surface rms roughness averaged over an infinite large image (σ_∞), fractal dimension (D_F) and the lateral coherence length (ξ) were estimated using the length dependent variance measurements. In case of irradiated films, the surface morphology shows drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine in each case. In case of oxygen ion irradiated films both, σ_∞ and D_F are observed to increase with fluence up to a dose value of 1 × 10¹³ ions/cm². With further increase in dose value both σ_∞ and D_F decreases. In case of silver ion irradiated films, σ_∞ and D_F decrease with increase in fluence value in the range studied.     

Study of silver diffusion in silicon carbide

Diffusion of silver in 6H-SiC and polycrystalline CVD-SiC was investigated using α-particle channeling spectroscopy and electron microscopy. Fluences of 2 × 10¹⁶ cm⁻² of ¹⁰⁹Ag⁺ were implanted with an energy of 360 keV at room temperature, at 350 °C and 600 °C, producing an atomic density of approximately 2% at the projected range of about 110 nm. The broadening of the implantation profile and the loss of silver through the front surface during vacuum annealing at temperatures up to 1600 °C was determined. Fairly strong silver diffusion was observed after an initial 10 h annealing period at 1300 °C in both polycrystalline and single crystalline SiC, which is mainly due to implant induced radiation damage. After further annealing at this temperature no additional diffusion took place in the 6H-SiC samples, while it was considerably reduced in the CVD-SiC. The latter was obviously due to grain boundary diffusion and could be described by the Fick diffusion equation. Isochronal annealing of CVD-SiC up to 1400 °C exhibited an Arrhenius type temperature dependence, from which a frequency factor D_o ∼ 4 × 10⁻¹² m² s⁻¹ and an activation energy E_a ∼ 4 × 10⁻¹⁹ J could be extracted. Annealing of 6H-SiC above 1400 °C shifted the silver profile without any broadening towards the surface, where most of the silver was released at 1600 °C. Electron microscopy revealed that this process was accompanied by significant re-structuring of the surface region. An upper limit of D < 10⁻²¹ m² s⁻¹ was estimated for 6H-SiC at 1300 °C.     

Structural studies of silicon oxynitride layers formed by low energy ion implantation

Silicon oxynitride (Si_xO_yN_z) layers were synthesized by implanting ¹⁶O₂⁺ and ¹⁴N₂⁺ 30 keV ions in 1:1 ratio with fluences ranging from 5 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻² into single crystal silicon at room temperature. Rapid thermal annealing (RTA) of the samples was carried out at different temperatures in nitrogen ambient for 5 min. The FTIR studies show that the structures of ion-beam synthesized oxynitride layers are strongly dependent on total ion-fluence and annealing temperature. It is found that the structures formed at lower ion fluences (∼1 × 10¹⁷ ions cm⁻²) are homogenous oxygen-rich silicon oxynitride. However, at higher fluence levels (∼1 × 10¹⁸ ions cm⁻²) formation of homogenous nitrogen rich silicon oxynitride is observed due to ion-beam induced surface sputtering effects. The Micro-Raman studies on 1173 K annealed samples show formation of partially amorphous oxygen and nitrogen rich silicon oxynitride structures with crystalline silicon beneath it for lower and higher ion fluences, respectively. The Ellipsometry studies on 1173 K annealed samples show an increase in the thickness of silicon oxynitride layer with increasing ion fluence. The refractive index of the ion-beam synthesized layers is found to be in the range 1.54-1.96.     

Radiation-induced phenomena related to electrical properties of hydrogen-doped strontium-cerium-ytterbium oxides under reactor irradiation

The effects of radiation on the electrical properties of hydrogen-doped (H-doped) strontium-cerium-ytterbium oxide (SrCe_0.95Yb_0.05O_3−δ), a perovskite-type ceramic, were investigated by irradiating specimens with thermal and fast neutrons and gamma rays in a fission reactor. The electrical conductivities of the H-doped SrCe_0.95Yb_0.05O_3−δ, which were measured at thermal and fast neutron fluxes of 4.1 × 10¹⁷ and 2.7 × 10¹⁶ n/m²s and an ionizing dose rate of 0.5 kGy/s, were approximately two orders of magnitude higher than the base conductivity in the absence of radiation and slightly higher compared to those of the non-doped SrCe_0.95Yb_0.05O_3−δ. The radiation-induced phenomena on the electrical properties can allow radiation-enhanced diffusion of H as well as electronic excitation, which is caused by ionization effects. It was observed that the radiation-enhanced diffusion of H significantly depended on the irradiation temperatures in the range 384-519 K, whereas it was not affected by radiation-induced defects produced with a fast neutron fluence of approximately 1.3 × 10²³ n/m² under the present experimental conditions.