首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Ion implantation induced defects and their consequent electrical impact have been investigated. Unintentionally doped n-type gallium nitride was implanted with 100 keV Si+ and 300 keV Ar+ ions in a fluence range of 1014–1015 ions/cm2. The samples were characterized with Rutherford backscattering/Channeling method for damage buildup. Time of flight elastic recoil detection analysis was implied on the Si implanted samples to see the ion depth distribution. Ar implanted GaN samples were studied electrically with scanning spreading resistance microscopy. Our results show that an Ar fluence of 5 × 1014 cm?2 increases the resistance by five orders of magnitude to a maximum value. For the highest fluence, 6 × 1015 cm?2, the resistivity decreases by two orders of magnitude.  相似文献   

2.
Monocrystals of sapphire have been subjected to ion implantation with 86 keV Si and 80 keV Cr ions to doses in the range of 5 × 1014–5 × 1016 cm−2 prior to thermal stress testing in a pulsed plasma. Above a certain critical dose ion implantation is shown to modify the near-surface structure of samples by introducing damage, which makes crack nucleation easier under the applied stress. The effect of ion dose on the stress resistance is investigated and the critical doses which produce a noticeable change in the stress resistance are determined. The critical dose for Si ions is shown to be much lower than that for Cr ions. However, for doses exceeding 2 × 1016 cm−2 the stress resistance parameter decreases to approximately the same value for both implants. The size of the implantation-induced crack nucleating centers and the density of the implantation-induced defects are considered to be the major factors determining the stress resistance of sapphire crystals irradiated with Si and Cr ions.  相似文献   

3.
Ion implantation induced damage formation and subsequent annealing in 4H–SiC in the temperature range of 100–800 °C has been investigated. Silicon Carbide was implanted at room temperature with 200 keV 40Ar ions with two implantation fluences of 4 × 1014 and 2 × 1015 ions/cm2. The samples were characterized by Rutherford backscattering and nuclear reaction analysis techniques in channeling mode using 2.00 and 4.30 MeV 4He ion beams for damage buildup and recovery in the Si and C sublattices, respectively. At low ion fluence, the restoration of the Si sublattice is evident already at 200 °C and a considerable annealing step occurs between 300 and 400 °C. Similar results have been obtained for the C sublattice using the nuclear resonance reaction for carbon, 12C(α,α)12C at 4.26 MeV. For samples implanted with the higher ion fluence, no significant recovery is observed at these temperatures.  相似文献   

4.
Swift Heavy Ion (SHI) irradiation of the polymeric materials modifies their physico-chemical properties. Lexan polycarbonate films were irradiated with 95 MeV oxygen ions to the fluences of 1010, 1011, 1012, 1013 and 2 × 1013 ions/cm2. Characterization of optical, chemical, electrical and structural modifications were carried out by UV–Vis spectroscopy, FTIR spectroscopy, Dielectric measurements and X-ray Diffraction. A shift in the optical absorption edge towards the red end of the spectrum was observed with the increase in ion fluence. The optical band gap (Eg), calculated from the absorption edge of the UV–Vis spectra of these films in 200–800 nm region varied from 4.12 eV to 2.34 eV for virgin and irradiated samples. The cluster size varied in a range of 69–215 carbon atoms per cluster. In FTIR spectra, appreciable modification in terms of breaking of the cleavaged C–O bond of carbonate and formation of phenolic O–H bond was observed on irradiation. A rapidly decreasing trend in dielectric constant is observed at lower frequencies. The dielectric constant increases with fluence. It is observed that the loss factor increases moderately with fluence and it may be due to scissoring of polymer chains, resulting in an increase in free radicals. A sharp increase in A.C. conductivity in pristine as well as in irradiated samples is observed with frequency and is attributed to scissoring of polymer chains. XRD analyses show significant change in crystallinity with fluence. A decrease of ~9.02% in crystallite size of irradiated sample at the fluence of 2 × 1013 ions/cm2 is observed.  相似文献   

5.
We report the conversion of a 65 nm Si(1 1 1) overlayer of a SIMOX(1 1 1) into 30–45 nm SiC by 40 keV carbon implantation into it. High temperature implantation (600 °C) through a SiO2 cap, 1250 °C post-implantation annealing under Ar ambient (with 1% of O2), and etching are the base for the present synthesis. Sequential C implantations (fluence steps of about 5 × 1016 cm?2), followed by 1250 °C annealing, has allowed to estimate the minimum C fluence to reach the stoichiometric composition as ~2.3 ×  1017 cm?2. Rutherford Backscattering Spectrometry was employed to measure layer composition evolution. A two-sublayers structure is observed in the synthesized SiC, being the superficial one richer in Si. Transmission electron microscopy has shown that a single-step implantation up to the same minimum fluence results in better structural quality. For a much higher C fluence (4 × 1017 cm?2), a whole stoichiometric layer is obtained, with reduction of structural quality.  相似文献   

6.
Ge nanocrystals embedded in SiO2 matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO2 films. In the present study, 400 keV Ge+ ions were implanted into SiO2 films at dose of 3 × 1016 ions/cm2 at room temperature. The as-implanted samples were irradiated with 150 MeV Ag12+ ions with various fluences. Similarly 400 keV Ge+ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au8+ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO2 matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.  相似文献   

7.
Thickness, composition, concentration depth profile and ion irradiation effects on uranium nitride thin films deposited on fused silica have been investigated by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He+ ions. The films were prepared by reactive DC sputtering at the temperatures of ?200 °C, +25 °C and +300 °C. A perfect 1U:1N stoichiometry with a layer thickness of 660 nm was found for the film deposited at ?200 °C. An increase of the deposition temperature led to an enhancement of surface oxidation and an increase of the thickness of the mixed U–N–Si–O layers at the interface. The sample irradiation by 1 MeV Ar+ ion beam with ion fluence of about 1.2–1.7 × 1016 ions/cm2 caused a large change in the layer composition and a large increase of the total film thickness for the films deposited at ?200 °C and at +25 °C, but almost no change in the film thickness was detected for the film deposited at +300 °C. An enhanced mixing effect for this film was obtained after further irradiation with ion fluence of 2.3 × 1016 ions/cm2.  相似文献   

8.
The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H+ ion beam in the fluence range 6.5 × 1011–1.8 × 1013 ions/cm2 are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P1 lines (e, f, g) and the P2 lines (a, b, c, d) that exhibit different trends with the ion fluence. The P1 group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 1012 ions/cm2 and then decreases. The P2 group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 1012 ions/cm2 and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P1 and P2 lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.  相似文献   

9.
Metastable pseudomorphic Ge0.06Si0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF2+ ions with three different doses of 3 × 1013, 1 × 1014, and 2.5 × 1014 cm−2. The implanted samples were subsequently annealed at 800°C and 900°C for 30 min in a vacuum tube furnace. Observed by MeV 4He channeling spectrometry, the sample implanted at a dose of 2.5 × 1014 BF2+ cm−2 is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge0.06Si0.94 samples become pronounced as the dose increases. Only the samples implanted at 3 × 1013 cm−2 do not visibly degrade nor relax during anneal at 800°C . In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 800°C for 30 min after implantation to a dose of 2.5 × 1014 cm−2. It is concluded that such a low dose of 3 × 1013 BF2+ cm−2 can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900°C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.  相似文献   

10.
《Journal of Nuclear Materials》2006,348(1-2):122-132
The release of Wigner energy from the graphite of the inner thermal column of the ASTRA research reactor has been studied by differential scanning calorimetry and simultaneous differential scanning calorimetry/synchrotron powder X-ray diffraction between 25 °C and 725 °C at a heating rate of 10 °C min−1. The graphite, having been subject to a fast-neutron fluence from ∼1017 to ∼1020 n cm−2 over the life time of the reactor at temperatures not exceeding 100 °C, exhibits Wigner energies ranging from 25 to 572 J g−1 and a Wigner energy accumulation rate of ∼7 × 10−17 J g−1/n cm−2. The shape of the rate-of-heat-release curves, e.g., maximum at ca. 200 °C and a fine structure at higher temperatures, varies with sample position within the inner thermal column, i.e., the distance from the reactor core. Crystal structure of samples closest to the reactor core (fast-neutron fluence >1.5−5.0 × 1019 n cm−2) is destroyed while that of samples farther from the reactor core (fast-neutron fluence <1.5−5.0 × 1019 n cm−2) is intact, with marked swelling along the c-axis. The dependence of the c lattice parameter on temperature between 25 °C and 200 °C as determined by Rietveld refinement for the non-amorphous samples leads to the expected microscopic thermal expansion coefficient along the c-axis of ∼ 26 × 10−6 °C−1. However, at 200 °C, coinciding with the maximum in the rate-of-heat-release curves, the rate of thermal expansion abruptly decreases indicating a crystal lattice relaxation. The 14C activity in the inner thermal column graphite ranges from 6 to 467 kBq g−1. The graphite of the inner thermal column of the ASTRA research reactor has been treated by heating to 400 °C for 24 h in a hot-cell facility prior to interim storage.  相似文献   

11.
In this paper, we study the optical and microstructural properties of silver–fullerene C60 nanocomposite and their modifications induced by swift heavy ion irradiation. Silver nanoparticles embedded in fullerene C60 matrix were synthesized by co-deposition of silver and fullerene C60 by thermal evaporation. The nanocomposite thin films were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 1012 to 3 × 1013 ions/cm2. Optical absorption studies revealed that the surface plasmon resonance of Ag nanoparticles showed a blue shift of ~49 nm with increasing ion fluence up to 3 × 1013 ions/cm2. Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction in the nanocomposite film. Growth of Ag nanoparticles was observed with increasing ion fluence. Raman spectroscopy was used to understand the effect of heavy ion irradiation on fullerene matrix. The blue shift in plasmonic wavelength is explained by the transformation of fullerene C60 matrix into amorphous carbon.  相似文献   

12.
The erosion of soft a-C:D films by heat treatment in air and under vacuum is studied by ion-beam analysis. When the films are heated in air above 500 K, the film thickness and the areal densities of C and especially D decrease, and oxygen is incorporated in the films. The initial atomic loss rates of carbon and deuterium from the films are 2.6 × 1017 C atoms cm−2 h−1 and 4.8 × 1017 D atoms cm−2 h−1 at 550 K. However, after D depletion the films show a resistivity against further erosion due to annealing in air. When the films are heated under vacuum erosion starts at about 600 K and all components including D decrease proportionally to the film thickness. Thermal desorption spectroscopy of the films reveals the evolution of CxDy type hydrocarbons. Infrared analysis shows that the incorporated oxygen is chemically bonded to carbon. The thermally-activated decomposition of the soft a-C:D films is compared to that of hard a-C:D films and a reaction scheme is suggested.  相似文献   

13.
A study of the effects of ion irradiation of organically modified silicate thin films on the loss of hydrogen and increase in hardness is presented. NaOH catalyzed SiNawOxCyHz thin films were synthesized by sol–gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H+ or 250 keV N2+ at fluences ranging from 1 × 1014 to 2.5 × 1016 ions/cm2. Elastic Recoil Detection (ERD) was used to investigate resulting hydrogen concentration as a function of ion fluence and irradiating species. Nanoindentation was used to measure the hardness of the irradiated films. FT-IR spectroscopy was also used to examine resulting changes in chemical bonding. The resulting hydrogen loss and increase in hardness are compared to similarly processed acid catalyzed silicate thin films.  相似文献   

14.
The bonding environment of oxygen implanted in GaN is studied using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The implantation of 70 keV O ions in GaN results in the formation of a 200 nm – thick subsurface layer that is highly defective or amorphous depending on the implantation fluence which ranges from 1 × 1015 to 1 × 1017 cm?2. The NEXAFS spectra are simulated using the FEFF8 code assuming models that account for the formation of point defects (various configurations of O interstitial and O substitutional in N and Ga sites) as well as chemical effects such as the formation of various polymorphs of Ga oxides and oxynitrides. The implantation-induced lattice disorder is modeled by displacing atoms from their equilibrium positions by adding to their Cartesian coordinates random numbers that belong to normal distributions. The simulations reveal that when the fluence is 1 × 1015 cm?2, the O implants occupy interstitial sites preferentially in the empty channels aligned parallel to the c-axis in the plane that contains the Ga atoms and/or in the columns that consist of Ga and N atoms along the c-axis. When the fluence is equal to 1 × 1016 cm?2 the O ions substitute for N while at 1 × 1017 cm?2 they participate in the formation of mixed GaOxNy phases.  相似文献   

15.
Polyimide (PI), polyetheretherketone (PEEK) and polyethyleneterephthalate (PET) were implanted with 40 keV Ni+ ions at room temperature at fluences ranging from 1.0 × 1016 to 1.5 × 1017 ions cm?2 and with ion current density varying between 4 and 10 μA cm?2. The depth profiles of the implanted Ni atoms determined by the RBS technique were compared with those predicted by the SRIM and TRIDYN codes. Hydrogen depletion as a function of the ion fluence was determined by the ERDA technique, and the compositional and structural changes of the polymers were characterised by the UV–vis and XPS methods. The implanted profiles differed significantly from those predicted by the SRIM code while the lower fluences were satisfactorily described by the TRIDYN simulation. A significant hydrogen release from the polymer surface layer was observed along with significant changes in the surface layer composition. The UV–vis results indicated an increase in the concentration and conjugation of double bonds.  相似文献   

16.
The change in electric properties of back-field silicon solar cells was investigated under the irradiation of protons with the energies less than 200 keV at 77 K. Experimental results showed that the short circuit current, maximum output power and open circuit voltage decrease to different extent with increasing the fluence and energy of protons. Under the 120 keV proton irradiation for the fluence of 1 × 1016 cm−2, a large amount of radiation-induced defects with the energy level H1 +0.47 eV were formed. In terms of analyzing the time dependence of electric properties, the performance lifetime of the silicon cells under the exposure of <200 keV protons was predicted.  相似文献   

17.
Si nanocrystals, formed by Si ion implantation into SiO2 layers and subsequent annealing at 1150°C, were irradiated at room temperature either with He+ions at energies of 30 or 130 keV, or with 400 keV electrons. Transmission electron microscopy (TEM) and photoluminescence (PL) studies were performed. TEM experiments revealed that the Si nanocrystals were ultimately amorphized (for example at ion doses ∼1016 He cm−2) and could not be recrystallized by annealing up to 775°C. This contrasts with previous results on bulk Si, in which electron- and very light ion-irradiation never led to amorphization. Visible photoluminescence, usually ascribed to quantum-size effects in the Si nanocrystals, was found to decrease and vanish after He+ ion doses as low as 3 × 1012–3 × 1013 He cm−2 (which produce about 1 displacement per nanocrystal). This PL decrease is due to defect-induced non-radiative recombination centers, possibly situated at the Si nanocrystal/SiO2 interface, and the pre-irradiation PL is restored by a 600°C anneal.  相似文献   

18.
Stability of extended defects created by high fluence helium implantation (50 keV, 5 × 1016 cm−2) from room temperature to 800 °C has been studied using transmission electron microscopy. Our results clearly show that the cavities behave as good sinks for interstitial type defects generated during ion implantation, leading in some cases to the cavity dissolution. A three-dimensional “phase diagram” related to the formation and evolution of interstitial-type defects is also proposed. It is plotted in terms of quantity of damage, annealing time and implantation temperature.  相似文献   

19.
Titanium dioxide (TiO2) films have been deposited on Si substrates using reactive magnetron sputtering. The resulting films, having a polycrystalline anatase phase with a dense columnar structure, were analysed by time-of-flight elastic recoil detection analysis (ToF-ERDA) using 40 MeV I9+ ions. A clear decrease in the areal atomic density (atoms/cm2) of Ti and O was observed during measurement, but the stoichiometry remained essentially constant up to a fluence of 4 × 1013 ions/cm2.To investigate this effect in more detail, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were applied in order to characterize the films prior to and after ion irradiation with fluences in the range of 1010–1013 ions/cm2. Distinct morphological and structural changes of the polycrystalline film were observed. XRD revealed that the crystallinity of the film was gradually destroyed, and the film became amorphous at a fluence above 5 × 1012 ions/cm2. SEM and AFM measurements revealed topographical changes in the form of surface recession and smoothing compared to the pristine polycrystalline surface. The observed change in areal atomic density during ERD measurement is believed to be due to the combined effects of electronic sputtering, amorphization and ion hammering.  相似文献   

20.
The behaviour of oxygen and nitrogen sequentially implanted into silicon at an energy of 100 and 175 keV with total doses of 5 × 1016 and 2 × 1017 cm−2 is reported. The implantation sequence and energies were varied. In all cases the wafer temperature during implantation was maintained at 300°C. The samples were pulse annealed in using a halogen lamp to achieve temperatures of 1100°C and 1200°C for 2–60 s. The samples were analysed using FTIR, XRD and SIMS. For a total dose of 5 × 1016 cm−2 no mutual redistribution of oxygen and nitrogen occurs during annealing. The impurity atoms (O and N) are found to bind to radiation defects. Annealing does not lead to any detectable new phase formation but does cause dissociation of oxygen–vacancy complexes and loss of oxygen from the bulk. For a dose of 2 × 1017 cm−2 phase formation occurs during implantation. The mutual redistribution of the impurity atoms during annealing occurs but only if oxygen is implanted deeper than nitrogen. This redistribution is greatest if nitrogen is implanted prior to oxygen.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号