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Electronic stopping powers for 0.05–10 MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley's dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley's model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research.

We perform the calculations on geometric and electronic structures of Si-doped heterofullerene C50Si10 and its derivatives, a C40Si20-C40Si20 dimer and a C40Si20-based nanowire by using density-functional theory. The optimized configuration of the C40Si20-based nanowire exhibits a regular dumbbell-shaped chain nanostructure. The electronic structure calculations indicate that the HOMO-LUMO gaps of the heterofullerene-based materials can be greatly modified by substitutionally doping with Si atoms and show a decreasing trend with increase cluster size. Unlike the band structures of the conventional wide band gap silicon carbide nanomaterials, the C40Si20-based nanowire has a very narrow direct band gap of 0.087eV.

The hydrogen storage capacity of (5, 5) single-walled carbon nanotubes (SWNTs) decorated chemically with benzene moieties is studied by using molecular dynamics simulations (MDSs) and density functional theory (DFT) calculations. It is found that benzene molecules colliding on (5, 5) SWNTs at incident energy of 50 eV form very stable configurations of benzene moiety adsorption on the wall of SWNTs. The MDSs indicate that when the benzene moiety decorated (5, 5) SWNTs and a pristine (5, 5) SWNT are put in a box in which hydrogen molecules are filled to a pressure of ~26 atm, the hydrogen storage capacity of the benzene moiety decorated (5, 5) SWNT is about 4.7 wt.% and that of the pristine (5, 5) SWNT is nearly 3.9 wt.%.

A Monte Carlo approach to simulate the transport and energy deposition of low energy electrons (E0≤10 keV) in liquid water is presented. The elastic scattering of electrons is described by Mott cross section, which is derived from the relativistic wave equation of Dirac. The inelastic scattering model of electrons is based on the dielectric response theory with exchange effect included. A new method of sampling various inelastic scattering events is proposed in the simulation. Using the approach stated, the spatial distribution of inelastic scattering events and energy deposition of electrons in liquid water are computed and the results are compared with other theoretical studies.

The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged single-walled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.

We study the collisions of energetic methane molecules with single-walled carbon nanotubes in the incident energy range from 5 to 100 eV using classical molecular dynamics simulations combined with ab initio calculations. The methane molecules can be decomposed into different hydrocarbon radicals, e.g. CHn (n = 1–3), in the collisions depending on the incident energy. Chemical functionalization of the single-walled carbon nanotubes resulting from the chemical adsorption of these hydrocarbon radicals on the outside wall of single-walled carbon nanotubes can be achieved simultaneously. Some stable adsorption configurations of hydrocarbon-functionalized single-walled carbon nanotubes are also presented based on ab initio calculations.

We perform ab initio calculations on the self-assembled base-functionalized single-walled carbon nanotubes (SWNTs) which exhibit the quasi-1D `ladder' structure. The optimized configuration in the ab initio calculation is very similar to that obtained from molecular dynamics simulation. We also calculate the electronic structures of the self-assembled base-functionalized SWNTs that exhibit distinct difference from the single-branch base-functionalized SWNT with a localized state lying just below the Fermi level, which may result from the coupling interaction between the bases accompanied by the self-assembly behaviour.

The reaction channels and the reaction products in the collisional reactions between two C60 molecules are found to be sensitively dependent on the relative orientation between the colliding partners. The detailed collision processes and the stable structures of the products are studied by using a molecular dynamics simulation method combined with a Langevin molecular dynamics scheme. The defects of the reaction products are also analyzed.

The stopping power of an electron gas for hydrogen ions is calculated based on the full self-consistent nonlinear density-functional frame. Three different configurations of hydrogen ions are considered and a criterion to test the validity of the self-consistent calculation is proposed. Comparison of calculation with available experimental data shows good agreement.

Depth profiles of fluorine in 19F+ implanted Ni0.8Fe0.2 alloy have been accurately measured by using 19F(p, ??)16O resonance nuclear reaction at ER?=?872.1 keV. A proper convolution calculation method was used to extract the true distribution of fluorine from the experimental excitation yield curves. The range parameters, Rp and ?Rp, were thereby obtained and compared with those simulated with TRIM'90 code. It shows that the experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental ?Rp values are systematically larger than the calculation values.

The sputtering of Hg0.8Cd0.2Te target by low energy Ar+ ions has been simulated using Monte Carlo method. The simulation results show that the concentration of Hg in the surface region of the target after ion bombardment is lower than the one before ion bombardment, but in a deeper region an excess concentration of Hg is produced due to recoil implantation. The excess concentration of Hg there may act as a donor dopant diffusion source for over doping the acceptor levels in the adjacent region and turn the p-type Hg0.8Cd0.2Te into an n-type material.

Depth profiles of fluorine in 19F+implanted LiNbO3 have been accurately measured using the 19F(p, αγ)16O resonant nuclear reaction at ER = 872.1 keV, with Γ = 4.2 keV. A proper convolution calculation method was used to extract the true distribution of fluorine from the experimental excitation yield curves. The experimental range distribution parameters, Rp and ΔRp, were compared with those obtained by Monte Carlo simulation using a computer code developed recently in this group and with results obtained using the TRIM90 code. It shows that the experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental ΔRp values are larger than those obtained from the simulations. The simulation with our computer code improves the agreement between the experimental and calculated range straggling, ΔRp.

The quantal harmonic oscillator model and the shell-wise model in conjunction with a modified BK effective charge are used to calculate the electronic energy loss of heavy ions colliding with atoms. The stopping power near the stopping maximum obtained from the model calculations is compared with experimental data. It is shown that the experimentally well-known Z1- and Z2-oscillations of the electronic stopping cross sections are reproduced by the model calculations.

The impact-parameter dependence of the electronic energy loss has been investigated using the quantal harmonic oscillator model and the shell-wise model of atomic stopping for ions with velocity v >v0 and v < v0, respectively. The electronic energy losses obtained by the impact-parameter dependent formalism have been used in a Monte Carlo simulation code to give the angular dependence of the energy loss of protons, helium ions and heavy ions transmitted through thin foils. The model calculations are compared with available experimental data.

A shell-wise calculation method and a quantal harmonic-oscillator model have been used to calculate the electronic stopping cross sections for heavy ions colliding with atoms or penetrating matter. The electronic energy loss is given in an impact parameter formalism. In order to generalize the theoretical models, which pertain to the case of point charge interacting with matter, to the case for heavy ions, an effective stopping charge based on the modified BK theory is used by way of simple scaling in the calculations. The comparisons between the calculated results and the experimental data demonstrate a favourable evidence to justify the theoretical models.

Chemical adsorption and desorption of hydrogen atoms on single-walled carbon nanotubes (SWNTs) are investigated by using molecular dynamics simulations. It is found that the adsorption and desorption energy of hydrogen atoms depend on the hydrogen coverage and the diameter of the SWNTs. Hydrogen-adsorption geometry at the coverage of 1.0 is more energetically stable. The adsorption energy decreases with the increasing diameter of the armchair tubes. The adsorption and desorption energy of hydrogen atoms can be modified reversibly by externally radial deformation. The averaged C-H bond energy on the high curvature sites of the deformed tube increases with increasing radial deformation, while that on the low curvature sites decreases.

Si+ ions of 350 keV have been implanted into AlGaAs/AlGaInAs quantum well samples in the dose range from 5×1013cm-2to 5×1014cm-2. The Raman spectra and high resolution x-ray diffraction (HRXRD) were measured from these implanted samples as well as the non-implanted sample. In the implanted layers the average strain which was evaluated by HRXRD increases with the implantation doses and varies from 0.0011 to 0.0029. The quantum well interface intermixing effect and compositional modification are also observed from HRXRD. At the higher doses, an abnormal annealing procedure takes place and it partly removes damage, but the strain remains almost unchanged in the epilayers.

The impact parameter dependence of electronic energy loss for heavy ions colliding at low velocity with atoms has been studied using the shell-wise local electron-density model. Roothaan-Hartree-Fock wave functions are used to calculate the local electron density of the atoms studied. The Brandt-Kitagawa effective stopping power charge theory is modified to incorporate the effective charge obtained using Fermi-level scattering phase shift calculations based on the density-functional formalism. The theoretical results are compared with available experimental measurements.

Experimental evidence of abnormally deep penetration in some botanical targets by low-energy ion beams is presented. The energy spectra of 818 keV He+ ions penetrating a 70 µm thick seed coat of maize, fruit peel of grape and of tomato all have a common feature. The leading edges of these broad spectra indicate that some of the penetrating ions pass through the thick targets easily and only lose a small fraction of their initial incident energy. Rutherford backscattering spectrometry and electron microprobe measurements are used to determine the argon concentration in multilayer samples of the seed coat of maize implanted by 200 keV Ar+ ions. The results show that about 10% of the Ar+ ions can penetrate deeper than ~100 µm in these samples.

Depth profiles of fluorine in F-doped tin oxide (FTO) films prepared by atmospherical pressure chemical vapour deposition method have been studied by use of 19F(p, αγ) 16O resonance nuclear reactions near 872.1 keV. A proper convolution method was used to get the real depth profiles of fluorine from the measured γ-ray excitation curves. Secondary ion mass spectrometry in conjunction with Rutherford backscattering spectrometry analysis was used to determine the density of the FTO films. It was found that the density of the films is markedly different from an earlier reported value.

A molecular dynamics simulation method is used to study the growth of narrow single-wall carbon nanotubes. It is found that the growth temperature and the species of small carbon clusters in the feedstock are important for the quality of the nanotubes grown. There is a temperature range of 1000-1500 K in which the narrow armchair single-wall carbon nanotubes can grow rapidly via adduction of C2 dimers, even without the existence of catalysts. The narrow zigzag tubes cannot keep open-ended growth. If the feedstock consists of various species of carbon clusters, the tubes cannot keep open-ended growth. At higher temperatures, the narrow nanotubes close rapidly in the noncatalytic environment, and the products grown are fullerene-like capsules. PACS: 61. 46. +w, 36. 40. -c

A Monte Carlo simulation program was developed to calculate ion range distributions in amorphous targets. In order to test to what degree the electronic stopping power can affect the range distribution, the ZBL universal potential, which is used in TRIM89, and an experimentally fitted four-parameter electronic stopping power are adopted to treat energy losses in our simulation. Results obtained by our simulation are in good agreement with both experimental and theoretical results. Some of these give improved agreement with the experiment as compared with TRIM89 simulation.

A Monte Carlo method is utilized to simulate the energy spectra for low-energy electron backscattered from different thin films deposited on different bulk substrates. A method of thickness determination for ultra-thin films is presented, which is obtained from the analysis of the basic characteristics of the energy spectra of backscattered electrons. This method is predicted to be particularly suitable for determining the thickness of ultra-thin films, and to be useful for both cases of light film on heavy substrate and heavy film on light substrate. The thickness resolution is estimated to be as high as subnanometer scale, provided the resolution of the electron energy spectrometer used to be high enough.

Inelastic mean free paths (MFPs) of 0.05–10 MeV protons in a group of 10 organic compounds are systematically calculated. The calculations are based on the method newly derived from the Ashley optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP is given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the considered organic compounds expect for kapton. The proton inelastic MFPs for these 10 organic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of stopping power calculation for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects on these materials.

We theoretically show that H atoms can be chemically adsorbed onto the surface of the Si-C heterofullerene-based nanotubes. The adsorbing energy of the H atom on Si-C heterofullerene-based nanotubes is in the range of 4.28–5.66eV without any barrier for the H atom to approach to the Si-C heterofullerene-based nanotubes. The band-gap of Si-C heterofullerene-based nanotubes can be dramatically modified by introducing dopant states, i.e., there is a transition from semiconductor to conductor of the Si-C heterofullerene-based nanotubes induced by the adsorption of the H atom. These results actually open a way to tune electronic properties of heterofullerene-based nanotubes and thus may propose an efficient pathway for band structure engineering.

Transmitting energy spectra of 500keV—1MeV He+ ions penetrating 50—90μm thick seed coat of maize, fruit peel of grape and of tomato are measured. The results indicate that these thick biological targets, as seen by penetrating ions, are inhomogencous and there are open“channel like” paths along which the incident ions can transmit the targets easily. While most of the incident ions are stopped in the targets, some of the transmitting ions only lose a small fraction of their initial incident energy. The transmitting energy spectra show a pure electronic stopping feature. Transmission electron microscopic taken from these samples with thickness of 30μm indicate that 150keV electron beam can penetrate the thick samples to give very good images with clear contrast. The electronic structures of β-1,4-glucosan molecular chains, which is deemed as the important constituent of the cell walls of seed coats and peels of fruits, are calcuated to show the possible channeling directions existing in biological samples.

A set of four parameter formulae of the electronic stopping cross section is provided for use in the prediction of electronic stopping cross sections of ions in various solids in the low energy range, 0.25 keV/amu E / m 1 , ≤ 200 keV/amu. The parameters, a , b , a and E 0 in the formulae are determined. The formulae can be used not only to describe the experimental Z 1 and Z 2 oscillations of electronic stopping powers but also to satisfactorily describe the dependence of the electronic stopping cross section, S e , on ion energy E .

The stopping power of 100–600 keV F + , Ar + , As + , Br + and Xe + ions in silicon have been obtained from measured range distribution obtained by NRA and RBS techniques. A deconvolution program was used in order to obtain true range distributions from the measured NRA excitation curves or RBS spectra. The total stopping powers were determined through fitting the projected ranges based on LSS transport theory to the experimentally determined projected ranges. After subtracting calculated nuclear stopping cross sections, the electronic stopping cross sections were obtained. These results indicate that the electronic stopping cross sections at low velocities may be described by the four-parameter formulae proposed previously and that deviation from the velocity-proportional electronic stopping is evident.

The 19 F(p,αγ) 16 O resonance nuclear reaction at 872.1 keV, with Γ = 4.2 keV was used to measure the depth profiles of fluorine in 19 F + -implanted Pb 1−x Sn x Te and CdTe samples. A deconvolution procedure was performed to extract the depth profiles from the experimental excitation yield curves. The range parameters. Rp, ΔRp and SK, obtained in this experiment were compared with theoretical calculations.

Ellipsometry combined with Ar + ion sputtering layer-removal and channeling was used to study the radiation damage profiles created by 40 Ar + and 11 B + ion implantation in silicon substrates. For the substrates implanted with 200 keV 40 Ar + ions at the fluence of 10 16 ions cm −2 the ellipsometruc method measured oscillatory apparent extinction coefficients, k, vs depth x , characteristic of amorphous layers. This result agrees with the channeling measurements very well. For the substrates implanted with 100 keV 11 B + ions at the dose of 5 x 10 14 ions cm −2 , both the ellipsometric and channeling measurements give the peaked damage profiles. Ellipsometric measurements combined with Ar + sputtering gives a useful method for characterizing the damage profiles both in damaged crystalline layers by lower dose ion implantation and in amorphous layers made by high dose ion implantation.

Electronic stopping cross sections for 19 F + in Pb 1− x Sn x Te and 19 F + , 40 Ar + , 75 As + , 79 Br + and 132 Xe + in silicon were obtained by range measurements. Depth profiles of F in Pb 1− x Sn x and Si were measured by 19 F(p, αγ) 16 O resonance nuclear reaction and those of Ar, As, Br and Xe were determined by RBS. In order to obtain the true range distribution from the measured NRA excitation curves or RBS spectra, a deconvolution program was developed using a reference function, the Edgeworth distribution function, and parameter optimization process. By forcing a fit between the experimentally determined projected range and that calculated with the range statistics program the total stopping power was obtained. After subtracting the nuclear stopping power the electronic stopping power was derived. The electronic stopping power can be described by a four-parameter formula.

In recent years ion implantation has been used to develop MCT and other infrared photovoltaic detectors, However, the implanted ions usually have a nonuniform depth profile in the implanted layer, with the typical depth less than lμm, within which the concentration of the implanted species may change over 3 to 4 orders. Thus within the layer there is an electric field outside the space-charge region. The electric field can be estimated with its intensity as high as 1x102-1x103v/am at 77k. In the present work the effect of the electric field is studied to show its way to effect the performance of the infrared photovoltaic detectors. Using the formulae obtained in this work, the RoA, product, responsibility, noise and detectivity of n-on-p Hgo.8Cd0.2Te photovoltaic detector operating at 77k are calculated for 300k backgrond and 27πfield of view. The results show that they are all related to the electric field in the implanted layer. It is interesting that when the electric field direct to the surface of n-region, namely negative field, the RoAlv=0 product contributed by n-region can not be neglected and the responsibility R,. and detectivity De, decrease. In the case of positive electric field, responsibility RA and the noise Vn both increase while the De increases slightly. Our calculation suggests that the proper technology process should be taken in manufacturing the MCT n-on-p infrared photovoltaic detector by use of ion implantation to eliminate the negative field in the n-region in order to avoid the harmful effect. The calculation is performed to show how the electric field in the ion implanted layer on Hg0.8Cd0.2Te to effect the performance of Hg0.8Cd0.2,Te photovoltaic detectors. The result shows that a reverse electric field is unfavorable for the performance of the photovoltaic detectors.

An empirical formula of electronic Stopping Cross Section, Se, for low energy ions, such as Li+,Be+,B+,C+,N+,O+,F+ and Ne+, in solid materials is established according to the experimental electronic stopping power data in solid media. The formula can be used not only to describe the experimental Z1 and Z2-oscillation of electronic stopping power, but also to describe very satifactorily the Se varying with ion energy, E. The projected rang distribution moments up to third order for ten light ion species from H+ to Ne+ in different substrates, such as amorphous Al2O3,SiO2, 20/25/Nb stainless steel, LiNbO3 and UO2, are calculated by use of the electronic stopping cross section formula proposed by the present authors and the nuclear scattering function which agrees with the WHB atomic interaction potential. Our theoretical results are compared with the experimental results published recently, and our projected ranges, Rp agree with the experimental measurements more closely in the low energy end of the energy regime which we deal with in the present work.

In this paper, we present a new method for calculation of depth profiles of implanted ions in multilayer materials. It combines the Monte Carlo simulation method with the method of numerical solution of the LSS transport equation. Taking into account the reflection of the ions at the interfaces of the layers the analytical expression of the range distribution in the multilayer materials is obtained. The comparison between the theoretical and the experimental results is made and good agreement is shown.

A model is proposed to describe the diffusion and release behaviour of inect gases implanted into various solids. According to this model, in which the interactions between different defects or radiation damage and the inert gas atoms are taken into account, a set of diffusion equations is derived and the analytical solutions of these equations are obtained.The comparison between the theoretical results and the experimental results shows that this model can be used to describe the release of inert gases from the surfaces of solids very well. By least-squares fitting the theoretical release curve to that of the experiment, a method to determine the activation energies of different trapping centres and the trapped concentration is provided.