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Effects of accumulation of radiation damage in silicon carbide are important concerns for the use of silicon carbide in advanced nuclear energy systems. In the present work lattice damage in silicon carbide crystal (4H type) implanted with 100 keV He-4(+) ions was investigated with Rutherford backscattering spectrometry in channeling geometry (RBS/c) and positron beam Doppler broadening spectrometry (PBDB). Helium implantation was performed at the specimen temperature of 510 K to avoid amorphization of the SiC crystal. Fluences of helium ions were selected to be in the range from 1 x 10(16) to 3 x 10(16) ions cm(-2), around the dose threshold for the formation of observable helium bubbles under transmission electron microscopes (TEM). The RBS/c measurements show distinctly different annealing behavior of displaced Si atoms at doses below or above the threshold for helium bubble formation. The RBS/c yield in the peak damage region of the specimen implanted to 3 x 10(16) He-ions cm(-2) shows an increase on the subsequently thermal annealing above 873 K, which is readily ascribed to the extra displacement of Si atoms due to helium bubble growth. The RBS/c yield in the specimen implanted to a lower ion fluence of 1.5 x 10(16) He-ions cm(-2) decreases monotonously on annealing from ambient temperatures up to 1273K. The PBDB measurements supply evidence of clustering of vacancies at temperatures from 510 to 1173 K, and dissociation of vacancy clusters above 1273 K. The similarity of annealing behavior in PBDB profiles for helium implantation to 1 x 10(16) and 3 x 10(16) ions cm(-2) is ascribed to the saturation of trapping of positrons in vacancy type defects in the damaged layers in the specimens helium-implanted to the two dose levels. (C) 2014 Elsevier B.V. All rights reserved.

Single crystals of z-cut LiNbO3 were implanted at room temperature using 3.0 MeV oxygen ions at a fluence of 5 × 1014 ions/cm2. The relative intensity of the light (TM polarized) reflected from a prism versus effective index profile for waveguides experiencing different annealing conditions (as-implanted, 200, 300, 400, and 500 °C for 30 min in air) were detected using the prism-coupling method. The refractive index profile in the implanted waveguide region was reconstructed using the SRIM (the stopping and ranges of ions in matter) and RCM (reflectivity calculation method) simulation packages. Damage formation was investigated by the Rutherford backscattering spectrometry/channeling (RBS/C) method. The results of RBS/C indicating that O+ implantation did not cause detectable lattice damage in the near-surface region of the sample. Measured transmission spectra show that the implantation conditions we selected have little influence on the transmission ratio. The propagation losses and near-field profiles of the light in the planar waveguide were measured with an end-face coupling system. The propagation loss of the O+-implanted planar waveguide is reduced to 0.45 dB/cm after annealing at 300 °C for 30 min.

In recent years, tapered glass capillary ion beam focusing is developing rapidly. It is attractive for simple, compact, low cost and easy use. However, the focusing mechanism for MeV ion beams is still indistinct. We present several experimental results of focusing 2 MeV He+ beam. Ion beams were focused by tapered glass capillaries with various outlet inner diameters from several micron to hundred micron. The current densities, angle divergences and energy spectra of the transmitted ion beams are measured. The results proved that 2 MeV He+ ions can focused and guided by our capillaries. The energy spectra show that a great part of transmitted ions experienced obvious energy loss, which is different from results of others research groups. We discussed the reason and charged it to the larger incident angle. Considered the incident ions with larger incident angle, the charge will distribute in a layer of micro meter depth in the capillary’s inner wall, but not the surface. The energy loss and many other spectra characters can be explained in this way.

We report on the optical planar waveguide formation and modal characterization in Nd: GdVO4 crystals by triple oxygen ion implantation at energies of (2.4, 3.0, and 3.6 MeV) and fluences of (1.4, 1.4, and 3.1) × 1014ions/cm2. The prism-coupling method is used to investigate the dark-mode property at wavelength of 632.8 nm. The refractive index profiles of the waveguide are reconstructed by an effective refractive index, neff method. The modal analysis shows that the fields of TE modes are well restricted in the guiding region, which means the formation of nonleaky waveguide in the crystal.

Oxygen ions with energies of 6.0 or 3.0 MeV were implanted into y-cut Yb:YCOB crystals at fluences ranging from 5.0 × 1013 to 2.0 × 1015 ions/cm2 at room temperature, forming optical planar waveguide structures. Dark-mode line spectroscopy was applied at two wavelengths, 633 and 1539 nm, in various excitation configurations, showing strong enhancement of one of the indices (nx) in the implanted near surface. The nx refractive index profile is reconstructed by a reflectivity calculation method and compared to the ion energy losses profiles deduced from SRIM-code simulation. Moreover, the near-field patterns were imaged by an end-fire coupling arrangement.

Single-mode waveguides in LiNbO 3 are demonstrated by use of prism coupling method. The waveguides are fabricated by three different energies and single energy C 2+ implantations at the equal total doses, respectively. Dark modes and propagation loss are measured by use of prism coupling and moving fiber methods, respectively. Damages produced by implantation are measured by RBS/channeling technique. The waveguide structures are investigated in two different implantation cases. The results of analysis indicate that the heavy ion-implanted waveguides are still defined by synergetic characteristics from both the raised-index region and the low-index barrier. The broadened barrier from multienergy implantation is demonstrated to play a significant role in reducing propagation loss.

The selected etching in lithium niobate (LiNbO 3 ) crystals is carried out by two different ion implantation and differential wet etching. The LiNbO 3 samples are cleaned and partially masked with photoresist in lithographic procedure firstly, followed by 1.5 MeV O + or Si + ion implantation at a dose of 1×10 15 ions/cm 2 at room temperature. It is found that the ion implanted region can be etched more easily than that protected by photoresist mask using mixture of hydrofluoric and nitric acids at room temperature. The surface morphology of the etched samples is examined using surface profilometer and SEM. Ridge structures are formed by the ion implantation and the subsequent selective wet etching. The results show that this technique may be suitable for fabrication of high quality ridge waveguides.

The planar waveguides have been fabricated in Nd:YVO 4 crystals by single and multi energy Si ion implantation. Optically polished Nd:YVO 4 samples were implanted at room temperature by 2.6 MeV Si ions and multi energy (3.0 MeV, 2.6 MeV and 2.2 MeV) Si ions, to the dose of 6 x 10 14 ions/cm 2 . The prism-coupling method was carried out to measure the dark modes in the Nd:YVO 4 crystal waveguides by using a model 2010 prism coupler. In both waveguides 3 modes were observed before annealing and after annealing the effective refractive index of all these modes gets smaller. The two waveguides show much similarity in prism-coupling results. Reflectivity Calculation Method was applied to fitting the single energy ion implanted waveguide refractive index profile. TRIM'98 (Transport of Ions in Matter) code was used to simulate the damage profile in Nd:YVO 4 by a single and multi energy ion implantation, respectively. It is found that the electronic energy loss in ion implantation may play an important role in Nd:YVO 4 waveguide formation.

A planar optical waveguide has been formed in a LiB 3 O 5 crystal using 6.0 MeV Cu + -ions with a dose of 1 × 10 15 ions/cm 2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE 0 and TM 0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change.

Si films with an embedded Ta marker layer are irradiated by Al n ( n = 1, 3), Cu n ( n = 1, 2) and Ge n ( n = 1, 2), respectively. The profiles of Ta marker with and without irradiation are measured by using Rutherford backscattering (RBS). The more spreading of the profiles of Ta marker induced by the cluster irradiations is observed. The enhanced atomic mixing at the location of Ta marker layer is probably governed by the collective effect of the cluster constituents during the cluster irradiations.

z-Cut stoichiometric lithium niobate crystals are implanted by 3.6 MeV Si2+ ions at doses of 3–10 × 1013 ions/cm2 at room temperature. Planar waveguides are formed by the ion irradiation induced extraordinary refractive index enhancement in the near surface regions. The waveguide properties are characterized by prism coupling and finite difference method. The effective refractive indices of the TM modes increase when implantation of higher doses is performed. It is found that the lattice damage could be considerably reduced or even almost removed by suitable annealing treatment.

Lithium niobate (LiNbO3) samples were implanted with 500 keV Nd3+ ions at a dose of 1 × 1015 ions/cm2 at room temperature. Annealing at different temperature was carried out in dry oxygen ambient after the implantation. Diffusion behaviors of Nd atoms and lattice defect annealing were determined using the Rutherford backscattering/channeling technique. Low lattice defect was obtained and more than 80% of the implanted Nd atoms remained in the sample after annealing at 1000 °C for an hour. A planar optical waveguide was successfully fabricated on the annealed sample using subsequent 3.0 MeV O+ implantation. Possible propagating modes of the waveguide were measured at wavelength of 633 nm and of 1539 nm, respectively. The present results provide information for the fabrication of waveguide laser in lithium niobate using ion implantation.

Samples of highly oriented pyrolytic graphite (HOPG) were irradiated by Si n ( n = 1, 2, 3, 4, 5) with energy of 300 keV/atom and Ge n ( n = 1, 2, 3) with energy of 500 keV/atom at perpendicular incidence and at a fluence of 5 × 10 12 projectiles/cm 2 , respectively. The observations by scanning tunneling microscopy (STM) clearly show a non-linear effect of the average damage area on the surface induced by clusters of different size. The dependence of the relative radiation damage on the cluster size follows a n 1.47 law for Si n irradiation and a n 1.1 law for Ge n irradiation, respectively.

We report a planar optical waveguide in AgGaS2 crystal that is fabricated by 3.0 MeV Si+ ion implantation at a dose of 1 × 1015 ions/cm2 at room temperature. A classic m-lines arrangement is performed to investigate the waveguide properties by measuring the dark modes. The reconstructed refractive index profiles show, at the near surface region, that the extraordinary index increases while the ordinary index decreases. Two TE modes and one TM mode are considered to be real propagation modes from a waveguide mode analysis. The nuclear energy loss distribution of the Si ions into AgGaS2 shows an inherent relationship between the waveguide formation and the energy deposition of the energetic ions.

Low loss index enhanced planar waveguides in Nd3+-doped silicate glass were fabricated by 3.0 MeV C+ ion implantation. The enhancement of the refractive index confined the light propagating in the waveguide. The prism-coupling method was used to measure dark modes in the waveguide. The effective refractive indices of the waveguide were obtained based on the dark modes. The moving fiber method was applied to measure the waveguide propagation loss. Loss measured in non-annealed samples is about 0.6 dB/cm. And the waveguide mode optical near-field output at 633 nm was presented. (c) 2005 Elsevier B.V. All rights reserved.

We report a bi-layer optical waveguide in a Ce-doped strontium barium niobate (SBN) crystal formed by double boron ion implantation. The energies of the B + and B 3+ ions are 3 and 6 MeV, respectively, while the doses of the two boron implantation are both 2 × 10 14 ions/cm 2 . A classic m -lines arrangement is performed to investigate the waveguide properties of the sample. The reconstructed refractive index profile of the waveguide shows a double-barrier confined shape, which suggests the formation of a bi-layer waveguide structure. The thickness of the two guide layers are 2.6 and 4.6 μm, respectively, which is in a good agreement with the mean projective range of the implanted boron ions of 3 and 6 MeV in the crystal. The nuclear energy loss distribution of the boron ions into SBN has a similar shape to that of the waveguide index, which means an inherent relationship between the waveguide formation and the energy deposition of the energetic ions.

The planar waveguides have been fabricated in z-cut beta barium metaborate crystals by 2.8 MeV Si+ ion implantation with doses of 1 × 1015 and 3 × 1015 ions/cm2 at room temperature. The waveguides were characterized by the prism-coupling method. The refractive index profiles were reconstructed using reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and the negative changes of ordinary refractive indices happen at the end of the track. TRIM’98 (transport of ions in matter) code was used to simulate the damage profile in β-BBO by 2.8 MeV Si+ ion implantation.

As an air and water pollutant and a common metabolite of methanol, formaldehyde and acetone, formic acid has won the interest of toxicologists. Using accelerator mass spectrometry (AMS) associated with liquid scintillation counting (LSC), we investigated the formation and persistence of the formate induced liver/kidney DNA adducts and hemoglobin (Hb) adducts in mice to obtain more toxicological information of formic acid. Both the kidney/liver DNA adducts levels and the Hb adducts levels increase with increasing dose (10.0 μg/kg b.w. to 100.0 mg/kg b.w.) in a good log/log linear correlation. Even at the lowest dose, the number of formate-DNA adducts was so high compared with the published data of other chemicals. Adduction mechanisms are proposed.

Secondary ion emissions from carbon nanotubes under bombardments of MeV Si and Si 2 clusters are measured by using a time of flight (TOF spectrometer). The measurements show that the emission yields of the secondary ions increase with increasing energy of Si and the secondary ion emissions are attributed to the electronic stopping processes. The emission yields of the secondary ions decrease with increasing energy of Si 2 clusters and the vicinage effect of cluster constituents plays more significant role in the enhanced secondary ion emissions at the low energies.

Planar waveguides were fabricated in nonlinear crystal KTiOAsO4 by the implantation of 2.6 MeV He+ ions (at a dose of 2 × 1016 ions/cm2) or 3.0 MeV Si+ ions (at a dose of 2 × 1015 ions/cm2) at room temperature. The prism-coupling method was carried out to measure the dark modes in the waveguides and reflectivity calculation method was applied to fitting the refractive index profiles of the waveguides. TRIM’98 (Transport and Range of Ions in Matter) code was used to simulate the damage profile in KTiOAsO4 by 2.6 MeV He+ or 3.0 MeV Si+ ion implantation, which is helpful to a better understanding of the waveguide formation.

We reported for what is to be believed the first time a double optical waveguide in a Cu-doped potassium sodium strontium barium niobate (KNSBN) crystal formed by double boron ion implantation. The energy and dose of B + and B 3+ ions were (3+6) MeV and (2+2)×10 14 ions/cm 2 , respectively. The refractive index profile of the waveguide showed a double-barrier confined shape, which suggested the formation of a two-layer waveguide structure. The two waveguide layers were with thickness of 2.6 and 2 μm, respectively, which was in a good agreement with the parameters obtained from transport and range of ions in matter 98 (TRIM) code simulation. The nuclear energy loss distribution of the MeV B ions implanted into this crystal had a similar shape to that of the waveguide index profile, which means an inherent relationship between the waveguide formation and the energetic energy deposition.

Optically polished LiNbO 3 was implanted by 3.0 MeV B 3+ ions at room temperature, forming planar optical waveguides at a dose of 4 × 10 14 ions/cm 2 . The prism-coupling method was used to take dark mode measurements. Four waveguide modes were observed for both ordinary and extraordinary light. Contrary to high-dose ion-implanted waveguides, the extraordinary refractive index was found to increase in the guide region for low-dose implantations. The reflectivity calculation method was used to reconstruct the refractive index profile in the waveguide. TRIM’98 was also used to simulate the damage distribution in the LiNbO 3 .

The unintentionally doped epitaxial GaN was grown on (0 0 0 1) sapphire by metal organic chemical vapor deposition (MOCVD). The effects of 2 MeV electron irradiation with the doses of 1 × 10 15 /cm 2 and 5 × 10 15 /cm 2 on the GaN epilayers were investigated by photoluminescence (PL) and Rutherford backscattering spectroscopy (RBS). The blue luminescence (BL) from the GaN epitlayers decreases significantly after the dose of 1 × 10 15 /cm 2 electron irradiation. This is attributed to complex formation of BL-related defects with other point defects. On the contrary, the BL intensity from the GaN epilayers subjected to electron irradiation with the dose of 5 × 10 15 /cm 2 increases beyond the BL intensity from the low-dose irradiated one. It is deduced that the surplus gallium vacancies in 1− charge state ( V Ga 1 - ) could lead to the BL intensity rebounding as electron irradiation damage accumulated.

To meet the requirements of the Xia‐Shang‐Zhou Chronology project, an upgrade of the AMS facility at Peking University has been carried out, commencing in 1996, and a new sample preparation system with high eAciency and low memory has been set up in the Department of Archaeology. A NEC MC-SNICS ion source has been installed and the injection system has been reconstructed. Computer control of the beam line has been implemented using Group 3 ControlNet, and a new data acquisition system has been developed. The alignment and vacuum of the beam line have also been improved. The upgraded system was commissioned in 1998. Subsequent experience has led to eAcient procedures for beam tuning and 14 C/ 13 C measurement. A precision of 0.5% in the 14 C/ 13 C ratio has been achieved. Many samples have now been measured for the Xia‐Shang‐Zhou Chronology project. ” 2000 Elsevier Science B.V. All

Bones are very important samples to determine the hosts of the cemetery of Jin Marquises which were excavated at Tianma-Qucun site in Shanxi Province in China. In order to obtain accurate AMS radiocarbon dates, bones were pretreated by two kinds of methods, the gelatin-extraction method and the amino-acid method. Charcoals collected from the same sites were also used. The measured dates agree with historical record.

The possibility and problems of using radiocarbon dating to historical chronology are discussed. The current situation of ancient Chinese chronology and the project of Xia–Shang–Zhou chronology are introduced. A chronological study requires the AMS radiocarbon dating with high precision, high reliability and high efficiency. The Peking University AMS facility (PKUAMS) has been upgraded and a series of quality control steps were adopted. To reduce the error of calendar age, wiggle matching with serial samples should be used. Some preliminary results of Xia–Shang–Zhou chronology are presented.

Bone sample preparation has been studied in detail to find a suitable method for the processing of smaller sample amounts such as oracle bones. In a recent research project only 1 g of bone material will be available for radiocarbon dating of these valuable bones with the AMS method. The standard methods for the preparation of gelatin were compared with the amino acids treated by XAD-2 resin. Additionally, it was tested if the alkaline step in the procedure may be skipped or not. According to our results we may conclude that for well preserved bones the gelatin production yields reliable results. We could also show that the XAD-2 treatment is an effective method for the removal of humic acids.

The decay kinetics of nicotine–DNA adducts and NNK–DNA adducts in mice liver after single dosing was studied by accelerator mass spectrometry (AMS). The decay is characterized by a two-stage process. The half-lives of nicotine–DNA adducts are 1.3 d (4–24 h) and 7.0 d (1–21 d), while for NNK–DNA adducts are 0.7 d (4–24 h) and 18.0 d (1–21 d). The relatively faster decay of nicotine–DNA adducts suggests that the genotoxicity of nicotine is weaker than that of NNK. The in vitro study shows that the metabolization of nicotine is necessary for the final formation of nicotine–DNA adducts, and nicotine Δ1′(5′) iminium ion is a probable metabolite species that binds to DNA molecule covalently.

The emission yields of the secondary ions are measured by using a conventional time of flight (TOF) technique under bombardments of Mg and C 2 , Ni and Si 2 with different energies, and C n , Si n and Ni n ( n = 1–3) with the different charge states and with energy of 1.5 MeV per atom, respectively. For the bombardments of C n , Si n and Ni n , the enhancements of the secondary ion emissions increase with increasing cluster sizes and charge states. For the bombardments of Mg and C 2 , Ni and Si 2 , although the mass and the nuclear charges of C 2 and Si 2 are the same as or equivalent to Mg or Ni, respectively, the enhancements of the secondary ion emissions induced by the clusters of C 2 and Si 2 in a wide energy range are also clearly indicated. The instantaneous collective interaction of the cluster constituents plays an important role in the secondary ion emissions.