Ar Ion Irradiation Research Articles

Effect of swift heavy ion irradiation on single- and multiwalled carbon nanotubes

The effect of irradiation with swift heavy ions on the structure and properties of carbon nanotubes was investigated by Raman spectroscopy. It was found that disordering of the system occurred mainly at the surface. No ordering phenomena have been observed over a whole range of both fluences and electronic stopping powers studied. The disorder parameter (i.e., the ratio of the D and G band intensities (ID/IG)) increases non-linearly with the irradiation dose, showing a tendency to saturate at high fluences. The increase in the disorder parameter upon irradiation was proportional to the square root of the ion fluence. The radiation stability of the few-walled nanotubes was ca. 1.6 higher than that of the single-walled ones. The irradiation with both the Xe and Kr ions leads to essentially the same increase in the ID/IG ratio with respect to the deposited electronic energy density. In the case of the Ar ion irradiation, the observed increase in the ID/IG ratio is much lower, suggesting that the electronic stopping power threshold for defects creation in carbon nanotubes is lower than that for graphite.

Modifications in structure and optical property of Cu nanoparticles in SiO2 by post heavy ion irradiation

The implantation-synthesized Cu nanoparticles (NPs) in silica were irradiated with 500keV Xe and Ar ions, respectively. After Xe ion irradiation at a fluence of 2×1016/cm2, the average diameter of Cu NPs was increased from 7.3 to 8.5nm, and especially, Cu NPs with a diameter of 11–14nm were formed beyond the projected range of Cu ions and nearly aligned at the same depth, which presented a higher volume fraction. As a result, the Cu surface plasmon resonance (SPR) absorption peak was enhanced. However, if Xe ion fluence was less than 1×1016/cm2, no clear variation of the Cu SPR absorption peak could be found. Further, it was also revealed that Xe ion irradiation caused the Cu SPR absorption peak to more drastically change than Ar ion irradiation at the same ion fluence. The underlying processes for the above findings were discussed and tentatively proposed.

Air, aqueous and thermal stabilities of Ce3+ ions in cerium oxide nanoparticle layers with substrates.

Abundant oxygen vacancies coexisting with Ce(3+) ions in fluorite cerium oxide nanoparticles (CNPs) have the potential to enhance catalytic ability, but the ratio of unstable Ce(3+) ions in CNPs is typically low. Our recent work, however, demonstrated that the abundant Ce(3+) ions created in cerium oxide nanoparticle layers (CNPLs) by Ar ion irradiation were stable in air at room temperature. Ce valence states in CNPs correlate with the catalytic ability that involves redox reactions between Ce(3+) and Ce(4+) ions in given application environments (e.g. high temperature in carbon monoxide gas conversion and immersion conditions in biomedical applications). To better understand the mechanism by which Ce(3+) ions achieve stability in CNPLs, we examined (i) extra-long air-stability, (ii) thermal stability up to 500 °C, and (iii) aqueous stability of Ce(3+) ions in water, buffer solution and cell culture medium. It is noteworthy that air-stability of Ce(3+) ions in CNPLs persisted for more than 1 year. Thermal stability results showed that oxidation of Ce(3+) to Ce(4+) occurred at 350 °C in air. Highly concentrated Ce(3+) ions in ultra-thin CNPLs slowly oxidized in water within 1 day, but stability was improved in the cell culture medium. Ce(3+) stability of CNPLs immersed in the medium was associated with phosphorus adsorption on the Ce(3+) sites. This study also illuminates the potential interaction mechanisms of stable Ce(3+) ions in CNPLs. These findings could be utilized to understand catalytic mechanisms of CNPs with abundant oxygen vacancies in their application environments.

Forming-Free Resistive Switching in Multiferroic BiFeO3 thin Films with Enhanced Nanoscale Shunts

A controlled shunting of polycrystalline oxide thin films on the nanometer length scale opens the door to significantly modify their transport properties. In this paper, the low energy Ar(+) irradiation induced shunting effect of forming-free, non-volatile resistive switching in polycrystalline BiFeO3 thin film capacitor-like structures with macroscopic bottom and top contacts was investigated. Oxygen atoms at the BiFeO3 surface are preferentially sputtered by Ar(+) ion irradiation and oxygen vacancies and a metallic Bi phase are formed at the surface of the BiFeO3 thin film before deposition of the top contacts. A phenomenological model is that of nanoscale shunt resistors formed in parallel to the actual BiFeO3 thin film capacitor-like structure. This model fits the noticeable increase of the retention stability and current density after irradiation. The formation of stable and conductive shunts is further evidenced by conductive atomic force microscopy measurements.

Modification of Barium Cerate by Heavy Ion Irradiation

The effect of irradiation with heavy ions Ne, Ar, and Kr of various energies on the structure and properties of ceramic barium cerate doped with neodymium and annealed in air at 650°C for 7 hours is studied. It is noted that blistering was observed on cerate surface during its irradiation by low energy Ne ions, whereas it was not observed under low-energy Ar and Kr ions irradiation. Irradiation of the cerate with high energy ions caused partial amorphization of the irradiated surface of the material, while the structure of the non-irradiated surface did not change. In addition, the irradiated surface of the cerate endured solid-phase structural changes. Thus, upon high-energy ions irradiation in the range of Ne, Ar, Kr the cerate surface resembled the stages of spherulite formation - nucleation, growth (view of cauliflower), formation of spherulitic crust, respectively. The increase in water molecules release and reduction of molecular oxygen release from the barium cerate, irradiated by high-energy ions is found during vacuum constant rate heating. It is concluded that cerates undergo changes to the distances significantly exceeding the ion ranges in these materials. Features of high-energy ions influence on thermal desorption of carbon dioxide from cerates show, apparently, the formation of weakly bound carbonate compounds on the cerate surface in the irradiation process.

Irradiation Hardening in Ferritic/Martensitic Steel P92 during Ar-Ions Irradiation at Elevated Temperature

The irradiation hardening behavior in a commercial ferritic/martensitic steel P92 has been investigated through 250KeV Ar-ions irradiations to a dose of 10dpa at 473, 673 and 973K combined with nanoindentation techniques. The results show that irradiation-induced hardening was observed at the all irradiation temperatures. There appear to have no previous reports of the irradiation-induced hardening at the temperature higher than 873K in ferritic/martensitic steels. Irradiation-induced hardening at elevated temperature of 973K has been found, for the first time, in ferritic/martensitic steel. The irradiation-induced hardening at 973K in the ferritic/martensitic steel P92 may be ascribed to the defects in the steel generated by Ar-ions irradiation.

Ion irradiation synthesis of Ag–Au bimetallic nanospheroids in SiO2 glass substrate with tunable surface plasmon resonance frequency

Ag–Au bimetallic nanospheroids with tunable localized surface plasmon resonance (LSPR) were synthesized by 100 keV Ar–ion irradiation of 30 nm Ag–Au bimetallic films deposited on SiO2 glass substrates. A shift of the LSPR peaks toward shorter wavelengths was observed up to an irradiation fluence of 1.0 × 1017 cm−2, and then shifted toward the longer wavelength because of the increase of fragment volume under ion irradiation. Further control of LSPR frequency over a wider range was realized by modifying the chemical components. The resulting LSPR frequencies lie between that of the pure components, and an approximate linear shift of the LSPR toward the longer wavelength with the Au concentration was achieved, which is in good agreement with the theoretical calculations based on Gans theory. In addition, the surface morphology and compositions were examined with a scanning electron microscope equipped with an energy dispersive spectrometer, and microstructural characterizations were performed using a transmission electron microscope. The formation of isolated photosensitive Ag–Au nanospheroids with a FCC structure partially embedded in the SiO2 substrate was confirmed, which has a potential application in solid-state devices.

Cavity swelling of RAFM steel under 792 MeV Ar-ions irradiation at 773 K

China reduced-activation ferritic/martensitic steel is irradiated at 773 K with 792 MeV Ar-ions to fluences of 2.3×1020 and 4.6×1020 ions/m2, respectively. The variation of the microstructures of the Reduced-activation ferritic/martensitic (RAFM) steel samples with the Ar-ion penetration depth is investigated using a transmission electron microscope (TEM). From analyses of the microstructure changes along with the Ar-ions penetrating depth, it is found that high-density cavities form in the peak damage region. The average size and the number density of the cavities depend strongly on the damage level and Ar-atom concentration. Swelling due to the formation of cavities increases significantly with an increased damage level, and the existence of deposited Ar-atoms also enhances the growth of the average size of the cavities. The effect of atom displacements and Ar-atoms on the swelling of the RAFM steel under high energy Ar-ion irradiation is discussed briefly.

Effect of ion irradiation on the thermal conductivity of UO2 and U3O8 epitaxial layers

The effect of 2MeV Ar+-ion irradiation on the thermal conductivity of epitaxial layers of UO2 and U3O8 was studied with time-domain thermoreflectance (TDTR) at temperatures between 323 and 658K. The thermal conductivity of unirradiated UO2 is 10.2Wm−1K−1 at 323K and scales with temperature like 1/T. Upon irradiation with doses >0.7×1015Ar+cm−2, the thermal conductivity decreases to a nearly constant value <4Wm−1K. By comparing the data to an analytic model, we report the point-scattering strength of irradiation induced defects in UO2. Unirradiated U3O8 has a thermal conductivity of 1.6Wm−1K−1 at 333K. Low and medium doses of Ar-ion irradiation decrease the thermal conductivity of U3O8 to <1.0Wm−1K−1. Unexpectedly, it is found that higher doses of Ar+ irradiation increased the conductivity of U3O8 to ∼2.0Wm−1K−1.

Controlled surface damage of amorphous and crystalline carbon nanotubes for enhanced field emission

The effect of argon (Ar) ion treatment on the field-emission (FE) properties of amorphous carbon nanotubes (aCNTs) and crystalline multiwall carbon nanotubes (MWCNTs) is reported in this article. Under optimum Ar-ion irradiation conditions, the FE properties of carbon nanotubes (CNTs) have been found to improve. The turn-on field of MWCNTs downshifted from 2.81 to 0.85 V μm−1 and from 9.17 to 3.27 V μm−1 for aCNTs. Improvement of the FE behavior is associated with the morphological modifications of CNTs, as a result of Ar-ion irradiation. Ar-ion bombardment creates defect sites on the CNT surface as confirmed by various techniques such as field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). We have proposed that the defects caused modifications of the CNT surfaces resulting in an effective increment of the field-enhancement factor β.

Shift of localized surface plasmon resonance by Ar-ion irradiation of Ag–Au bimetallic films deposited on Al2O3 single crystals

Effects of Ar-ion induced surface nanostructuring were studied using 100keV Ar-ion irradiation of 30nm Ag–Au bimetallic films deposited on Al2O3 single crystals, under irradiation fluences ranging from 5.0×1015cm−2 to 6.3×1016cm−2. Scanning electron microscope was used to study the ion-beam-induced surface nanostructuring. As the irradiation fluence increased, dewetting of the bimetallic films on the Al2O3 substrate was observed, and formation of isolated Ag–Au nanostructures sustained on the substrate were obtained. Next, thermal annealing was performed under high vacuum at 1073K for 2h; a layer of photosensitive Ag–Au alloy nanoballs partially embedded in the Al2O3 substrate was obtained when higher fluence irradiation (>3.8×1016cm−2) was used. The microstructures of the nanoballs were investigated using a transmission electron microscope, and the nanoballs were found to be single crystals with a FCC structure. In addition, photoabsorption spectra were measured, and localized surface plasmon resonance peaks were observed. With increase in the irradiation fluence, the size of the Ag–Au nanoballs on the substrate decreased, and a blue-shift of the LSPR peaks was observed. Further control of the LSPR frequency over a wide range was achieved by modifying the chemical components, and a red-shift of the LSPR peaks was observed as the Au concentration increased. In summary, ion irradiation is an effective approach toward surface nanostructuring, and the nanocomposites obtained have potential applications in optical devices.

Preparation of a Functionally Graded Fluoropolymer Thin Film and Its Application to Antireflective Coating

Fluoropolymer thin films were prepared by the ion-assisted vapor deposition polymerization (IAD) of 2-(perfluorohexyl) ethylacrylate (Rf-6) under Ar ion irradiation. The ion acceleration voltage Va largely affected the film characteristics. With increasing Va, the adhesion strength between the film and the substrate improved, while the surface energy and the refractive index increased. To attain a high adhesion strength, a low surface energy, and a low optical reflectivity simultaneously, a functionally graded film was prepared by varying Va from 300 to 0 V continually in the course of film growth. As a consequence, an antireflective coating with good adhesion and low surface energy was obtained. The optical reflectivity of a glass substrate was reduced from 4.9 to 0.55% at a wavelength of 400 nm by depositing a 100-nm-thick single-layer functionally graded fluoropolymer film. The surface energy of this film was 8.5 mJ/m2.

The sink effect of the second-phase particle on the cavity swelling in RAFM steel under Ar-ion irradiation at 773 K

The microstructures of the Chinese RAFM steel irradiated at 773K with 792MeV Ar-ions to fluences of 2.3×1020 and 4.6×1020ions/m2, respectively, were investigated by using a transmission electron microscope with the cross-sectional specimen technique. Preferential nucleation and enhanced growth of the cavities at the interface between the second-phase particles and the matrix were observed in the irradiated specimen. The observation of the cavity-particle complex at lower dose indicated that the dose threshold for a cavity formation at the interface between MC particle and matrix was lower than that in matrix. With increasing irradiation dose, it was found that the second-phase particles changing their shape by attached cavities occurred. Furthermore, the role of the particle–matrix interface on nucleation and growth of the attached cavity with an increase of the dose were discussed in this work.

Ion irradiation induced solid-state amorphous reaction in Ni/Ti multilayers

The effects of Ar ion irradiation on interfacial reactions induced in Ni/Ti multilayers were investigated. Structures consisting of 10 alternate Ni (∼26nm) and Ti (∼20nm) layers of a total thickness ∼230nm were deposited by ion sputtering on Si (100) wafers. Argon irradiations were done at 180keV, to the doses of 1–6×1016ions/cm2, the samples being held at room temperature. The projected implanted ion range is 86±36nm, maximum energy loss is closer to the surface, and maximum displacements per atom (dpa) from 47 to 284 for Ni and 26 to 156 for Ti. Characterizations of samples were performed by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is shown that ion irradiation induced a progressed intermixing in the mostly affected zone already for the lowest dose, the thickness of the mix increasing linearly with the irradiation dose. The mixed phase is fully amorphous, starting with a higher concentration of Ni (which is the diffusing species) from the initial stages, and saturating at Ni:Ti∼66:34. A thick amorphous layer (∼127nm) formed towards the surface region of the structure for the irradiation dose of 4×1016ions/cm2 remains stable with increasing the dose to 6×1016ions/cm2, which introduces up to 6–7at.% of Ar within the mix. The results are discussed in light of the existing models. They can be interesting for introducing a selective and controlled solid-state reaction and towards further studies of ion irradiation stability of amorphous Ni–Ti phase.

Development of the sputtering yields of ArF photoresist after the onset of argon ion bombardment

Modification of an advanced ArF excimer lithographic photoresist by 400 eV Ar ion irradiation was observed in situ in real time using both infrared spectroscopy and a quartz microbalance sensor. The photoresist sputtering yields had a characteristic behavior; the sputtering yields were higher than unity at the beginning, until an ion dose of 2 × 1016 ions cm−2. Thereafter, the yields decreased immediately to almost zero and remained constant with the yield at zero until a dose of approximately 4 × 1016 ions cm−2 was reached. At larger doses, the yields increased again and reached a steady-state value of approximately 0.6. This development of the sputtering yield after the onset of ion bombardment is explained by an ion-induced modification of the photoresist that includes preferential sputtering of individual groups, argon ion implantation and the generation of voids. All these effects must be taken into account to assess line-edge-roughness on a photoresist subjected to highly energetic ion irradiation.

Structural Evolution of Fe Particles in Fe–Al2O3 Granular Films by Ar Ion Irradiations

Fe–Al2O3 granular films were prepared by helicon plasma sputtering. Fe64(Al2O3)36 in volume percent of as-prepared films was irradiated with 400 keV Ar ions in the fluence range of 1×1015–5×1016 ions/cm2. The growth of Fe particles with increasing ion fluence was observed from X-ray diffraction (XRD) patterns, magnetization curves, and conversion electron Mössbauer (CEM) spectra. The magnetization curves and CEM spectra of as-prepared Fe–Al2O3 films indicated the superparamagnetic nature and the ferromagnetic nature with increasing ion fluence. In addition, the reduction of Fe3+ component to the Fe2+ and metallic Fe components by ion irradiation was observed from CEM spectra.

Photoelectrical properties and the electronic structure of Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single crystalline alloys

Photoelectrical properties of Tl1-xIn1-xSnxSe2 single crystalline alloys (x = 0, 0.1, 0.2, 0.25) grown using the Bridgman-Stockbarger method were studied. The temperature dependence of electrical and photoconductivity for the Tl1-xIn1-xSnxSe2 single crystals was explored. It has been established that photosensitivity of the Tl1-xIn1-xSnxSe2 single crystals increases with x. The spectral distribution of photocurrent in the wavelength spectral range 400-1000 nm has been investigated at various temperatures. Photoconductivity increases in all the studied crystals with temperature. Therefore, thermal activation of photoconductivity is caused by re-charging of the photoactive centers as the samples are heated. Based on our investigations, a model of center re-charging is proposed that explains the observed phenomena. X-ray photoelectron valence-band spectra for pristine and Ar(+)-ion irradiated surfaces of the Tl1-xIn1-xSnxSe2 single crystals have been measured. These results reveal that the Tl1-xIn1-xSnxSe2 single-crystal surface is sensitive to the Ar(+) ion irradiation that induced structural modification in the top surface layers. Comparison on a common energy scale of the X-ray emission Se Kβ2 bands representing energy distribution of the Se 4p-like states and the X-ray photoelectron valence-band spectra was done.

High dose ion irradiation effects on immiscible AlN/TiN nano-scaled multilayers

The effects of high dose Ar ion irradiation on immiscible AlN/TiN multilayered structures were studied. The structures with 30 alternate layers of a total thickness of ~260nm were deposited by reactive sputtering on (100) Si wafers. Individual layer thickness was ~8nm AlN and ~9.3nm TiN. Irradiation was done with 180keV Ar+ ions to 1×1016–8×1016ions/cm2, with the projected range around mid-depth of the structures. It was found that the highest applied dose induced a considerable intermixing, where the growing TiN grains consume the adjacent AlN layers, transforming partly to (TiAl)N phase. Intermixing occurs due to a high contribution of collision cascades, which was not compensated in demixing by chemical driving forces. However, a multilayered structure with relatively flat surface and interfaces is still preserved, with measured nano-hardness value above the level for the as-deposited sample. The results are compared to other systems and discussed in the light of the existing ion beam mixing models. They can be interesting towards better understanding of the processes involved and to development of radiation tolerant coatings.

Ar 이온빔 조사에 따른 SnO2박막의 물성 연구

<TEX>$SnO_2$</TEX> thin films were prepared on the Si substrate by radio frequency (RF) magnetron sputtering and then surface of the films were irradiated with intense Ar ion beam to investigate the effect of Ar ion irradiation on the properties and hydrogen gas sensitivity of the films. From atomic force microscope observation, it is supposed that intense Ar bombardments promote rough surface and increase gas sensitivity of <TEX>$SnO_2$</TEX> films for hydrogen gas. The films that Ar ion beam irradiated at 6 keV show the higher sensitivity than the films were irradiated at 3 keV and 9 keV. These results suggest that the <TEX>$SnO_2$</TEX> thin films irradiated with optimized Ar ion beam are promising for practical high-performance hydrogen gas sensors.

Ion irradiation induced formation of CdO microcrystals on CdTe surfaces

Formation of cadmium oxide microcrystals, induced by Ar ion irradiation, on CdTe crystals is reported. The formation of the oxide crystallites is proved by the detection of a low temperature cathodoluminescence emission, centered at 2.2eV. The emission is localized at the microcrystals on the irradiated CdTe surfaces. The compositional changes, after the irradiation, are studied by Energy Dispersive X-Ray spectroscopy and X-Ray Diffraction. The concurrent decrease of the near band edge CdTe luminescence emission and the increase of the 2.2eV band intensity are correlated to the irradiation fluence.