Beam Irradiation Time Research Articles

Electron-beam-induced annealing of natural zircon: a Raman spectroscopic study

The annealing of radiation damage in zircon by low-energy electron irradiation was explored systematically. Natural zircon samples spanning a wide range of self-irradiation damage were irradiated with the focused electron beam of an electron probe microanalyser. The effects of beam current and irradiation time were tested systematically, and the changes in zircon were measured using Raman spectroscopy. Our results confirm the damage-annealing effect of an accelerated electron beam. We demonstrate that non-thermal annealing occurs through electron-enhanced defect reactions and that the extent of the annealing is a function of both the irradiation time and the beam current. The complete annealing of radiation damage in zircon by an accelerated electron beam was not possible under the conditions of our experiments. Our results indicate that Raman band broadening in ion-irradiated zircon can possibly be explained through phonon confinement, as the estimated domain sizes of the crystalline volume amid recoil clusters decrease with increasing α dose. The results underlay the importance of doing Raman spectroscopy before electron-beam and ion-beam analysis. To avoid unwanted beam-induced annealing of damage in zircon during EPMA analysis, the electron energy transferred per volume unit of sample should be minimised, for instance by keeping the integrated charge low and/or by defocusing the electron beam.

Proton beam irradiation induced synthesis of Size- and morphology-controlled Pt nanomaterials in an aqueous solution

We present a facile one-pot preparation route for the production of Pt nanomaterials by using a simple proton beam irradiation process at room temperature. Size- and shape-controlled Pt nanoparticles were prepared in an aqueous solution without the addition of any harsh reducing agents. The morphology of the Pt nanoparticles was easily tuned by varying the average beam current and duration time. The addition of isopropyl alcohol to the reaction mixture was observed to have played a vital role in the synthesis of Pt cubes. We found that the shape of the prepared Pt nanoparticles without the addition of isopropyl alcohol was ~99% spheres while Pt nanoparticles synthesized with the addition of isopropyl alcohol under the same reaction conditions was over 70% cubes. The beam irradiation time was also an important factor for optimizing the morphologycontrolled preparation condition for Pt cubes. As the beam irradiation time was increased from 20 min to 120 min, the percentage of cubes increased from 7% to 70%; however, for extended irradiation time, the percentage of cubes fell off.

Calculated Radioactivity Yields of Cu-64 from Proton-Bombarded Ni-64 Targets Using SRIM Codes

The End-Of-Bombardment (EOB) Yields from 64 Ni(p,n) 64 Cu nuclear reaction have been calculated for optimizing irradiation parameters that correspond to future 64 Cu radionuclide production using the BATAN’s 26.5-MeV cyclotron in Serpong. Enriched Ni target thickness, proton beam current and irradiation time which play significant role in the success of the Positron Emission Tomography (PET) radionuclide were also discussed in this paper. For a 26.5-MeV proton beam, the optimum target thickness for 64 Cu production was nearly 1.5 mm with yields up to 560 mCi/µA.hr at the end of the irradiation. The comparisons with some selected experimental data indicated that the much-lower-than-expected EOB yields were mainly due to incorrect target thickness prepared for the irradiation. Nevertheless, these calculations were in good agreement with the previous predicted data with a maximum difference of less than 10%. The discrepancies were mostly due to different cross-section data employed in the calculations. Received: 23 October 2014; Revised: 24 December 2014; Accepted: 27 December 2014

An effective route for size- and morphology-controlled synthesis of Pt nanomaterials in aqueous solutions via proton beam irradiation

We present a facile one-pot synthetic route for the production of Pt nanomaterials via a simple proton beam irradiation process at room temperature. Size- and shape-controlled Pt nanostructures were prepared in an aqueous phase-based solution without the addition of any harsh reductants. We observed that the sizes and the morphologies of the resulting Pt nanoparticles were easily varied by changing the proton beam current and duration time. We also observed that the addition of isopropyl alcohol to the reaction mixture played a vital role in the morphology-controlled synthesis of Pt nanomaterials. We found that the size of the prepared Pt nanoparticles increased as the beam irradiation time was increased under the same beam current. When the beam irradiation time was set the same, the average particle size decreased as the beam current was increased. We also observed that the average size of the Pt nanocrystals generally increased as the concentration of isopropyl alcohol was increased, and more importantly, a gradual morphology change of the Pt nanocrystals was observed.

Application of ion exchange and extraction chromatography to the separation of actinium from proton-irradiated thorium metal for analytical purposes

Actinium-225 (t1/2=9.92d) is an α-emitting radionuclide with nuclear properties well-suited for use in targeted alpha therapy (TAT), a powerful treatment method for malignant tumors. Actinium-225 can also be utilized as a generator for 213Bi (t1/2 45.6min), which is another valuable candidate for TAT. Actinium-225 can be produced via proton irradiation of thorium metal; however, long-lived 227Ac (t1/2=21.8a, 99% β−, 1% α) is co-produced during this process and will impact the quality of the final product. Thus, accurate assays are needed to determine the 225Ac/227Ac ratio, which is dependent on beam energy, irradiation time and target design. Accurate actinium assays, in turn, require efficient separation of actinium isotopes from both the Th matrix and highly radioactive activation by-products, especially radiolanthanides formed from proton-induced fission. In this study, we introduce a novel, selective chromatographic technique for the recovery and purification of actinium isotopes from irradiated Th matrices. A two-step sequence of cation exchange and extraction chromatography was implemented. Radiolanthanides were quantitatively removed from Ac, and no non-Ac radionuclidic impurities were detected in the final Ac fraction. An 225Ac spike added prior to separation was recovered at ≥98%, and Ac decontamination from Th was found to be ≥106. The purified actinium fraction allowed for highly accurate 227Ac determination at analytical scales, i.e., at 227Ac activities of 1–100kBq (27nCi to 2.7μCi).

Study of the radioactivity induced in air by a 15-MeV proton beam.

Radioactivity induced by a 15-MeV proton beam extracted into air was studied at the beam transport line of the 18-MeV cyclotron at the Bern University Hospital (Inselspital). The produced radioactivity was calculated and measured by means of proportional counters located at the main exhaust of the laboratory. These devices were designed for precise assessment of air contamination for radiation protection purposes. The main produced isotopes were (11)C, (13)N and (14)O. Both measurements and calculations correspond to two different irradiation conditions. In the former, protons were allowed to travel for their full range in air. In the latter, they were stopped at the distance of 1.5 m by a beam dump. Radioactivity was measured continuously in the exhausted air starting from 2 min after the end of irradiation. For this reason, the short-lived (14)O isotope gave a negligible contribution to the measured activity. Good agreement was found between the measurements and the calculations within the estimated uncertainties. Currents in the range of 120-370 nA were extracted in air for 10-30 s producing activities of 9-22 MBq of (11)C and (13)N. The total activities for (11)C and (13)N per beam current and irradiation time for the former and the latter irradiation conditions were measured to be (3.60 ± 0.48) × 10(-3) MBq (nA s)(-1) and (2.89 ± 0.37) × 10(-3) MBq (nA s)(-1), respectively.

Site-controlled fabrication of Ga nanodroplets by focused ion beam

Ga droplets are created by focused ion beam irradiation of GaAs surface. We report that ordered Ga droplets can be formed on the GaAs surface without any implantation damage. The droplets are characterized with bigger sizes than those droplets formed on damaged area. These aligned Ga droplets are formed via the migration of Ga atoms from ion irradiation area to the edge of undamaged GaAs surface and further nucleation into droplets. The morphological evolution and size distribution of these nanodroplets are investigated systematically with different beam irradiation time and incident angles. Based on this method, well positioned Ga nanodroplets, such as chains, are achieved by using focus ion beam patterning. The controllable assembly of droplets on undamaged semiconductor surface can be used to fabricate templates, to fabricate quantum structures and quantum devices by droplet epitaxy technique.

In situ growth of In2O3 nanocrystals by electron irradiation in transmission electron microscope

We performed a detailed in situ TEM observation of the growth of In2O3 nanocrystals under high-energy electron beam irradiation. The In2O3 nanocrystal growth on the In2S3 nanosheets can be induced by the electron irradiation with a beam intensity of 450–635pA/cm2. The individual nanocrystals grow up to 10–15nm after 210s of electron irradiation with an intensity of ~635pA/cm2. The In2O3/In2S3 nanocomposites or pure In2O3 nanocrystals can be obtained by controlling the beam intensity and irradiation time. EELS experiments confirmed the conversion from In2S3 to In2O3. This study demonstrates that electron beam irradiation within the TEM can be employed as an effective and promising tool to fabricate nanostructures.

Enhanced red emission from praseodymium-doped GaN nanowires by defect engineering

GaN nanowires (NWs) were implanted with low fluences of rare-earth ions. Ion channelling measurements revealed the perfect vertical alignment of the NWs and their orientation with respect to the silicon substrate. The channelling properties were not altered by the implantation or annealing treatments, and X-ray diffraction measurements demonstrated the full structural recovery of the NWs after post-implant annealing. Strong Pr-related cathodoluminescence at room temperature was observed after annealing and results indicate the successful incorporation of Pr on substitutional Ga sites inside the NWs. Furthermore, an intriguing behaviour of the cathodoluminescence as a function of the electron beam irradiation time was observed, suggesting that Pr luminescence can be sensitized by the same defect that is responsible for the yellow luminescence band frequently seen in GaN. The formation of this Pr–defect complex can be controlled by defect engineering using a combination of ion implantation, annealing and electron beam irradiation, and leads to an increase of the Pr luminescence by a factor of more than 4.

Formation process and electron-beam incident energy dependence of one-dimensional uneven peanut-shaped C60 polymer studied using in situ high-resolution infrared spectroscopy and density-functional calculations

A 3 kV electron-beam irradiation of a C60 film gives rise to formation of one-dimensional (1D) uneven peanut-shaped C60 polymer with a cross-linked structure close to that of the P08 C120 stable isomer obtained from the general Stone–Wales rearrangement. In this study, we examined the evolution of infrared (IR) spectra of C60 films with respect to electron beam (EB) irradiation time, using in situ high-resolution IR spectroscopy and first-principles density-functional calculations, and found semi-quantitatively that the 1D uneven peanut-shaped C60 polymer is formed via intermediate polymers with a cross-linkage close to that of P04 and P06 C120 isomers obtained from GWS rearrangement. In addition, we examined the dependence of EB-induced C60 polymerization on an incident energy of EB in the range 3–7 kV. IR spectra obtained for 5 and 7 kV EB irradiation of C60films showed the same product as for 3 kV EB irradiation. However, when 5 and 7 kV EBs continued to irradiate C60 films for a long time after the polymer formation, the 1D peanut-shaped polymer did not proceed to become 1D polymers with a more coalesced linkage than that of the P08 one but was destroyed to become amorphous carbons.

Low-temperature formation of epitaxial graphene on 6H-SiC induced by continuous electron beam irradiation

It is observed that epitaxial graphene forms on the surface of a 6H-SiC substrate by irradiating electron beam directly on the sample surface in high vacuum at relatively low temperature (∼670 °C). The symmetric shape and full width at half maximum of 2D peak in the Raman spectra indicate that the formed epitaxial graphene is turbostratic. The gradual change of the Raman spectra with electron beam irradiation time increasing suggests that randomly distributed small grains of epitaxial graphene form first and grow laterally to cover the entire irradiated area. The sheet resistance of epitaxial graphene film is measured to be ∼6.7 kΩ/sq.

Characterization of dose delivery in a hard X-ray irradiation facility

The Radiation Bioengineering Laboratory at Seoul National University (SNU) operates a user-constructed hard X-ray irradiation facility for radiation biology and radiation therapy physics studies. The system package of YXLON model 450-D08 operating at the anode voltage of up to 450 kV is a key part of the facility, which enables in vitro cell irradiation and animal irradiation for in vivo studies. In this article, dose delivery in the hard X-ray irradiation facility was characterized in terms of the dose vs. operational parametric combination of the facility. The operational parameters included beam tube anode voltage, beam tube current, irradiation time, and beam exit-to-sample distance. Bremsstrahlung X-rays at energy below approximately 20 keV were filtered out by a 3 mm-thick aluminum plate fitted over the 5 mm-thick beryllium window. Gafchromic EBT films were used as radiation sensor materials in dose measurement. The characterization was validated via experimental observation of the in vitro biological responses of cells to radiation exposure. The biological responses obtained using the new hard X-ray irradiator were highly comparable with those obtained using a commercial gamma-ray irradiator.

Computer simulation of charging the silicon dioxide surface and subsurface layers by electron bombardment

A physical model and program of calculating the parameters of charging dielectrics by electron bombardment is described. A method of computer simulation is used to investigate the main processes of charging the subsurface silicon dioxide layers. Dependences of the current density, volume charge density, and electric field strength on the material layer depth are calculated for variable electron beam parameters, irradiation time, and grid potential near the sample surface.

Effects of spontaneous polarization on GaInN/GaN quantum well structures

Using electron beam irradiation, cathodoluminescence, and photoluminescence under ultrahigh vacuum conditions, we study the effect of spontaneous polarization on polar (0001) and nonpolar (11−00) GaInN/GaN quantum well structures. We use cathodoluminescence measurements with an electron beam irradiation time of up to several hours. A drastic blueshift of the quantum well emission accompanied by a 100-fold increase of intensity is observed in polar samples. These changes can be described by an activation of the spontaneous polarization field due to the desorption of surface charges, which counteracts the piezoelectric field in the quantum well. Etching or annealing of the surface leads to similar effects. The influence of the sample structure was investigated by varying the cap thickness of the samples. A different time- dependent behavior of changes in the quantum well emission energy and the intensity depending on cap thickness and acceleration voltage was observed. This can be explained by de-screening and screening effects induced by the electron beam which are discussed in detail. For nonpolar (11−00) samples, no change in quantum well emission energy or intensity was observed. This is consistent with a spontaneous-polarization-induced surface field in the c-plane case and verifies the absence of the spontaneous polarization field in the nonpolar (11−00) direction.

유리와 PET 기판에 잉크젯 인쇄된 실버 도선의 레이저 소결

잉크젯으로 인쇄된 실버 도선의 레이저 소결에 관한 연구를 수행하였다. 요구적출(DOD) 방식의 잉크젯 프린터를 이용하여 서로 다른 두께의 유리와 PET 기판에 실버 나노 잉크를 이용한 미세 도선을 인쇄하였으며, 인쇄된 실버 도선에 집광된 레이저 빔을 조사하여 소결하였다. 레이저 강도와 조사시간을 달리하여 소결된 실버 도선의 비저항을 측정하였으며, 오븐을 이용한 소결 처리 결과와 비교하였다. 단순화된 이론식으로부터 레이저 강도, 조사 시간, 표면 반사율 및 기판의 물성에 따른 온도 증가를 추산하였으며, 추산된 온도 증가와 레이저 소결에 의한 전기전도도 향상의 관계에 대하여 논의하였다.

Poster — Thur Eve — 14: Pretreatment IMRT QA Program for Low‐Dose Control Points Based on Dynamic Noise Correction Using a 2D Matrix of Ionization Chambers

We developed a pre‐treatment intensity modulated radiation therapy (IMRT) QA program for verification of low‐dose control points registered by a 2D matrix of ionization chambers (ICs). The program eliminates the dose error caused by the induced reading or noise for every chamber electrically. It was found that the low‐dose deviation was in the rate of 20–40% outside the field (i.e. in the volume of the normal tissue). Moreover, the voxel‐to‐voxel dose was found to have non‐uniform deviation, which increased linearly with time. The rates of the electrically induced chamber readings were 0.3–1.3 cGy per 0.5 minute, when a beam of 100 monitor units using dose rate equal to 300 MU/min with consideration of the time for the leaf motion, was used in the irradiation with time > 20 s. This means that if low dose point (3–5 cGy) is registered by an IC of the highest induced readings (1.3 cGy), the deviation between the planned and delivered doses would be in the rate of 40−25%. Comparison of the fluence maps may be affected by the non‐uniformly induced dose readings. A field function depending on the beam irradiation time to correct the registered dose profile is therefore needed. In this study, a pre‐treatment IMRT QA program fully based on absolute dose measurements has been established. The program includes a comparison between the calculated and measured doses. The electrically induced readings of the 2D matrix were subtracted from the beam dose map to correct the measurements.

Controllable surface modification of nanowires by focused-electron- beam-induced deposition of carbon

Surface-modified nanowires generally own some additional properties,and thus in this paper,the authors particularly studied the surface modification of nanowires via irradiation of focused electron beam in a Tecnai F-30 field emission transmission electron microscope (TEM).It was observed that controllable deposition of all kinds of amorphous carbon nanostructures,such as carbon particles,carbon rods and carbon films with local bulging,could be got on the surface of nanowires after intentional irradiation.In details,the controllable deposition of carbon nanostructures could be easily and precisely controlled by changing of some irradiation parameters such as beam spot diameter,irradiation manner,irradiation time and irradiation position.The possible deposition mechanisms of carbon nanostructures on the wire surface as induced by irradiation of focused electron beam in TEM were further discussed.In addition,some suggestions were also proposed on reducing of specimen pollution caused by undesired deposition of amorphous carbon materials during the irradiation.

Formation of Si Nanocrystallites in Al-Added Amorphous Si Films by Electron Beam Irradiation

Si nanocrystallites were formed in Al-added amorphous Si films (Al/a-Si, a-AlxSi1-x) by the irradiation of a focused electron beam. In-situ heating of the a-Al0.025Si0.975 films was performed at temperatures up to 400 °C. The size, shape, and concentration of the Si crystallites varied significantly with the film temperature and electron beam irradiation time. Si nanocrystallites with a mean size of ∼10 nm were formed when the films were kept at 200 °C, and irradiated using an electron beam with a current density of 15.7 pA/cm2. The total crystallite volume fraction in the films increased from ∼9.2 to ∼94.8% with increasing temperature from 100 to 400 °C. The estimated activation energy for the crystallization in the a-Al0.025Si0.975 film under the electron beam irradiation was 0.78±0.05 eV.

Ion beam induced liquid crystal alignment properties of 4-alkylphenoxymethyl-substituted polystyrenes

The pretilt angles of liquid crystals (LCs) can be controlled over the range 0° to 90° using ion beam treated 4-alkylphenoxymethyl-substituted polystyrene films as alignment layers, where the alkyl group is –(CH2) n H (n = 1, 2 or 4), by changing the ion beam irradiation time, incidence angle and energy. In general, LC cells made using a polymer film with a longer irradiation time, higher irradiation incidence angle with respect to the planar direction and higher irradiation energy exhibited lower pretilt angles relative to the planar direction. Furthermore, the LC cells produced using polymer films containing longer alkyl groups and a higher molar content of 4-alkylphenoxymethyl side groups exhibited greater pretilt angles under similar irradiation conditions. The LC alignment behaviour demonstrated good correlation with the wettability of the polymer films, due to fragmentation of the side groups on the polymer surfaces during ion beam irradiation. The electro-optical characteristics of the LC cells formed using these polymer films were similar to those produced using rubbed polyimide films, which are the LC alignment layers most commonly encountered.

A study of electrical characteristic changes in MOSFET by electron beam irradiation

Mechanisms for electrical characteristic changes in MOSFET caused by electron beam irradiation were studied using a SEM-based nano-probing system. A shift in V th occurs when a hole is trapped in a defect (oxygen vacancy) in the gate dielectric layer. Holes are generated when the plasmon is excited by electron beam irradiation. Further, an electric field is created by the positive charge-up resulting from electron beam irradiation of the ILD, causing an increase in leakage between gate and drain leading to an increase in I off. This study shows that advanced devices can be measured using a SEM-based nano-probing system without inducing electrical characteristic changes by optimizing the measurement conditions such as acceleration voltage, electron beam current, image magnification, ILD thickness, and electron beam irradiation time.