Electron reflectivity from clean and oxidized steel surface

This paper aims to elucidate the effect of an air-formed native oxide covering mild steel surface on the contrast in the scanning electron microscopy (SEM) images obtained with the landing energy from 5 keV down to 0 eV. Part of the mild steel surface was in-situ cleaned by Ar⁺ ion sputtering process in order to remove native oxide from the surface. It enabled us to observe the oxide-free and the naturally oxidized area on the mild steel surface simultaneously in the SEM micrographs. Presence of the native oxide starts to play a role in the SEM images acquired at landing energy below roughly 3 keV. Contrast between differently oriented grains situated inside the area covered by the native oxide starts to be negligible with landing energy decreasing below 3 keV, up to some ultra-low values where the contrast increases again. Total reflectivity contrast between the clean and the oxidized area increases exponentially with landing energy decreasing below 3 keV. The reflectivity-versus-energy curves of the cleaned and the naturally oxidized mild steel surface are markedly different. The reflectivity of the electrons is correlated with the density of states (DOS), as is demonstrated at very low landing energies. Sensitivity of the very low-energy electrons to the electronic structure was verified by comparison of the experimental data with the simulations of reflectivities, band structure, and DOS. The theoretical predictions are based on the density-functional theory calculations and they have been performed in energy range corresponding to specular reflectivities of the Fe-BCC (001) orientation. We have also observed that close to the mirror condition, that is, near-zero landing energies, the primary electrons become sensitive to the surface potential differences caused by the work function differences of clean and native oxide-covered steel surfaces.     

Synthesis of Poly[（3-octanoylpyrrole-2,5-diyl）-p-（N, N-dimethylamino）benzylidene] and Its Properties by Nitrogen Ion Implantation

Introduction Nonlinearoptical(NLO)organicpolymers havereceivedincreasingattentionbecauseoftheir excellentbehaviorandthegoodprospectsoftheir applicationsinhigh-techareas,suchasoptical communication,high-densityopticalstorageand all-opticalinformationprocess.Poly(pyrrolylme- thine)isanNLOmaterialwithpromisingapplica- tions[1_3].However,itssolubilityandfilm-forming performancearepoor.Inthispaper,anovelsolu- blepoly(pyrrolylmethine),poly[(3-octanoyl-pyr- role-2,5-diyl)-p-(N,N-dimethylamino)ben…     

Calculations of electron inelastic mean free paths. XIII. Data for 14 organic compounds and water over the 50 eV to 200 keV range with the relativistic full Penn algorithm

We have calculated inelastic mean free paths (IMFPs) for 14 organic compounds (26-n-paraffin, adenine, β-carotene, diphenyl-hexatriene, guanine, Kapton, polyacetylene, poly (butene-1-sulfone), polyethylene, polymethylmethacrylate, polystyrene, poly(2-vinylpyridine), thymine, and uracil) and liquid water for electron energies from 50 eV to 200 keV with the relativistic full Penn algorithm including the correction of the bandgap effect in insulators. These calculations were made with energy-loss functions (ELFs) obtained from measured optical constants and from calculated atomic scattering factors for X-ray energies. Our calculated IMFPs could be fitted to a modified form of the relativistic Bethe equation for inelastic scattering of electrons in matter from 50 eV to 200 keV. The average root-mean-square (RMS) deviation in these fits was 0.17%. The IMFPs were also compared with a relativistic version of our predictive Tanuma–Powell–Penn (TPP-2M) equation. The average RMS deviation in these comparisons was 7.2% for energies between 50 eV and 200 keV. This average RMS deviation is smaller than that found in a similar comparison for our group of 41 elemental solids (11.9%) and for our group of 42 inorganic compounds (10.7%) for the same energy range. We found generally satisfactory agreement between our calculated IMFPs and values from other calculations for energies between 200 eV and 10 keV. We also found reasonable agreement between our IMFPs for organic compounds and measured IMFPs for energies between 50 eV and 200 keV. Substantial progress for IMFP measurements for liquid water has been made in recent years through the invention of liquid water microjet photoelectron spectroscopy and droplet photoelectron imaging. We found that the IMFPs from these experiments and the associated analyses were larger than our IMFPs by factors between two and four for energies between about 30 eV and 1000 eV. The energy dependences of the measured IMFPs are, however, similar to that of our IMFPs in the same energy range. Since IMFPs calculated from the same algorithm for a number of inorganic compounds agree reasonably well with measured IMFPs for energies between 100 eV and 200 keV, the large differences between IMFPs for water from recent experiments and our results are surprising and need to be resolved with additional experiments.     

The electronic structure of parallel β-pleated sheets in proteins: An ab initio computation including electron correlation

The electronic structure of a 2D polyglycine network with a pleated sheet structure has been computed at the Hartree–Fock level and by including electron correlation effects within the second order of many-body perturbation theory (electron polaron model). The influence of the size of the atomic basis set and of the extension of the virtual space has been investigated both for single- and many-particle properties. Comparison with the energy of the corresponding single chains showed that interchain interactions (mainly hydrogen bonding) provide an extra stabilization for the 2D network by 7.4 and 10 kcal/mole per glycine residue at the Hartree–Fock and correlated levels, respectively. The energy dispersions are rather anisotropic for all bands whose widths are about 0.5–1 eV along the polypeptide backbones and 0.1–0.2 eV in the perpendicular direction (hydrogen bonds). The HF value of the fundamental energy gap is reduced by 4 eV to 9.2 eV for electron polarons. The wave functions and interaction integrals obtained can be used to calculate further optical and lattice vibrational properties.     

Differential track structure of electrons in liquid water

The differential spectrum of energy loss events produced in liquid water by electrons has been calculated using a differential cross-section incorporating exchange and binding. The average energy loss in a single event is found to vary from about 28 to about 68 eV for 100 eV for 100 eV to 1 MeV electrons, respectively. All energy loss events above a certain level (set either to 1 or to 5 keV) are assumed to produce branch tracks, which are further degraded using a Monte Carlo technique. The total track averaged energy loss per event for a 1 MeV electron is found to be about 57 eV.     

Conductive and optical properties of PPV modified by N+ ion implantation

In this article, a soluble poly[2‐methoxy‐5‐(3′‐methyl)butoxy]‐p‐phenylene vinylene (MMB‐PPV) was synthesized by dehydrochlorination reaction and the MMB‐PPV film was implanted by nitrogen ions (N⁺) with the ion dose and energy in the range of 3.8 × 10¹⁵ to 9.6 × 10¹⁶ ions/cm² and 15–35 keV, respectively. The surface conductivity, optical absorption, optical band gap (E_g) of modified MMB‐PPV film were studied, and the third‐order nonlinear optical susceptibility (χ⁽³⁾) as well as its environmental stability of modified MMB‐PPV film were also measured by degenerate four‐wave mixing system. The results showed that the surface conductivity of MMB‐PPV film was up to 3.2 × 10^?2 S when ion implantation was performed with the energy of 35 keV at an ion dose of 9.6 × 10¹⁶ ions/cm², which was seven order of magnitude higher than that of the pristine film. UV‐Vis absorption spectra demonstrated that the optical absorption of MMB‐PPV film was enhanced gradually in the visible region followed by a red shift of optical absorption threshold and the E_g value was reduced from 2.12 eV to 1.59 eV with the increase of ion dose and energy. The maximum χ⁽³⁾ value of 2.45 × 10^?8 esu for modified MMB‐PPV film was obtained with the ion energy of 20 keV at an ion dose of 3.8 × 10¹⁶ ions/cm², which was almost 33 times larger than that for pristine film. In comparison to the reduction of 17% in the χ⁽³⁾ value of pristine MMB‐PPV film, the maximum χ⁽³⁾ value of 2.45 × 10^?8 esu for modified MMB‐PPV film decreased by over 5.3% when they had been exposed under the same ambient conditions for 90 days. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2072–2077, 2010     

Ultraviolet photoluminescence of silanol species in mesoporous silica

The optical properties of sol-gel synthesized porous silica excited by synchrotron radiation in the 4-10 eV range of samples with different porosity at 8 K and room temperature are reported. The analysis of the ultraviolet photoluminescence indicate the contributions of two different emitting centers. The spectral and temporal characteristics of the two luminescence bands are reported: emission peaks at about 3.7 and 4.0 eV, excitation channels around 5.4-5.7 and 6.2-6.5 eV, and mean lifetimes of about 17 and 2 ns, respectively. The analysis of the optical properties in samples with different porosity allows us to propose a silanol-related model for the two centers.     

Electrical, optical, thermoelectric power, and dielectrical properties of organic semiconductor poly(1,12-bis(carbazolyl) dodecane) film

Electrical conductivity, optical, thermoelectric, and dielectrical properties of the poly(1,12-bis(carbazolyl) dodecane) film have been investigated. The activation energy for electrical conductivity and room-temperature electrical conductivity (at 25 degrees C) values were found to be 0.25 eV and 2.65 x 10-6 S/cm, respectively. The thermoelectric power results suggest that the conductivity is due to large polarons (i.e., the carriers in polymer move by hopping in the localized states at band gap edges). Electrical conductivity and thermoelectric power results confirm that the polymer is a p-type organic semiconductor. Optical absorption results suggest that the direct allowed transitions are dominant in the fundamental absorption edge in the polymer with optical band gap value of 2.72 eV. The refractive index dispersion of the polymer obeys the single oscillator model with oscillator energy (Eo = 3.06 eV) and dispersion energy (Ed = 17.82 eV) values. Alternating current conductivity results suggest that the hopping conductivity is dominant in the polymer. The dielectrical properties exhibit a non-Debye relaxation.     

Collision energy effects in tanden mass spectrometry as revealed by a proton-bound dimer ion

Mass spectra resulting from collision-induced decomposition of the proton-bound dimer of iso-propylamine and sec-butylamine have been obtained as a function of laboratory collision energy over the range 10-6000 eV. The ratio of the two principal fragment ions from the dimer ion measured as a function of collision energy is compared with the ratio expected as a function of internal energy as calcualted based on the statistical theory of mass spectra. This comparison indicates that the average energy deposited into the dimer ion upon collision reaches a maximum at a collision energy of ～70 eV. The average internal energy of the ions at this collision energy is ～4.3 eV. Other fragment ions which arise from higher energy decompositions are also observed in the spectra at much lower intensities. The relative intensities of these fragments indicate that the probability for large energy transfers are highest at ke V collision energies. These observations are interpreted on the basis of differences in the postcollision internal energy distributions resulting from keV and eV collisions.     

Evaluation of elastic‐scattering cross sections for electrons and positrons over a wide energy range

Quantification of surface‐ and bulk‐analytical methods, e.g. Auger‐electron spectroscopy (AES), X‐ray photoelectron spectroscopy (XPS), electron‐probe microanalysis (EPMA), and analytical electron microscopy (AEM), requires knowledge of reliable elastic‐scattering cross sections for describing electron transport in solids. Cross sections for elastic scattering of electrons and positrons by atoms, ions, and molecules can be calculated with the recently developed code ELSEPA (Elastic Scattering of Electrons and Positrons by Atoms) for kinetic energies of the projectile from 10 eV to 50 eV. These calculations can be made after appropriate selection of the basic input parameters: electron‐density distribution, a model for the nuclear‐charge distribution, and a model for the electron‐exchange potential (the latter option applies only to scattering of electrons). Additionally, the correlation‐polarization potential and an imaginary absorption potential can be considered in the calculations. We report comparisons of calculated differential elastic‐scattering cross sections (DCSs) for silicon and gold at selected energies (500 eV, 5 keV, 30 keV) relevant to AES, XPS, EPMA, and AEM, and at 100 MeV as a limiting case. The DCSs for electrons and positrons differ considerably, particularly for medium‐ and high‐atomic‐number elements and for kinetic energies below about 5 keV. The DCSs for positrons are always monotonically decreasing functions of the scattering angle, while the DCSs for electrons have a diffraction‐like structure with several minima and maxima. A significant influence of the electron‐exchange correction is observed at 500 eV. The correlation‐polarization correction is significant for small scattering angles at 500 eV, while the absorption correction is important at energies below about 10 keV. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamic computer simulations of Cs incorporation in Si during low‐energy (0.2–3 keV) irradiation

The incorporation of Cs atoms in silicon was investigated by dynamic computer simulations using the Monte‐Carlo code T‐DYN that takes into account the gradual change of the target composition due to the Cs irradiation. The implantation of Cs atoms at normal incidence was studied for four energies (0.2, 0.5, 1, and 3 keV) and three different Cs surface‐binding energies U_Cs (0.4, 0.8, and 2.4 eV). The total implantation fluences were 2 × 10¹⁷ Cs cm^?2 for 0.2 keV, 1.5 × 10¹⁷ Cs cm^?2 for 0.5 keV, and 1 × 10¹⁷ Cs cm^?2 for 1 and 3 keV. At these values, a stationary state has been reached. The steady‐state Cs‐surface concentrations exhibit a pronounced dependence both on impact energy and U_Cs, varying between ～1 (at 0.2 keV and U_Cs = 2.4 eV) and ～0.13 (3 keV and U_Cs = 0.4 eV). Under equilibrium, the partial sputtering yield of Si, Y_Si, experiences little influence of U_Cs, but varies with the Cs energy: at U_Cs = 0.8 eV from 0.09 to 1.0 Si atoms/Cs projectile. For all irradiation conditions a strongly preferential sputtering of Cs atoms as compared to Si atoms is found, increasing from 1.8 (at 3 keV and U_Cs = 2.4 eV) to 13.3 (at 0.2 keV and U_Cs = 0.4 eV). Preferential sputtering of Cs increases with decreasing irradiation energy and decreasing U_Cs. Copyright © 2008 John Wiley & Sons, Ltd.     

N+离子注入聚对苯乙炔衍生物的非线性光学性能

以对甲氧基苯酚和溴代异戊烷为原料,用脱氯化氢反应制备可溶性聚[2-甲氧基-5-(3'-甲基)丁氧基]对苯乙炔(MMB-PPV),通过核磁氢谱(1HNMR)和红外光谱(FTIR)对产物分子的结构进行表征.用能量为15keV、剂量为3.8×1015～9.6×1016ions/cm2的氮正离子(N+)对MMB-PPV薄膜进行注入改性.紫外-可见吸收光谱(UV-Vis)显示,注入离子在MMB-PPV薄膜内部引入杂质能级,破坏了分子的共轭结构.随着注入剂量增加,吸收边逐渐向长波方向移动,且分子激发态和基态间的光学带隙由2.12eV减小至1.81eV.用简并四波混频(DFWM)技术研究了离子注入MMB-PPV薄膜的三阶非线性光学性能.结果表明,未注入薄膜的三阶非线性极化率(χ(3))值为7.1×10-10esu,随着注入剂量的增加,χ(3)值逐渐增大,当注入剂量达到3.8×1016ions/cm2时,χ(3)值提高到9.3×10-9esu,继续增加注入剂量,χ(3)值开始下降,当注入剂量为9.6×1016ions/cm2时,χ(3)值降低到1.5×10-10esu.对离子注入MMB-PPV薄膜χ(3)值变化的机理进行了探讨.     

Complex model optical potential for electron scattering from oxygen

We report calculations of the total (elastic plus inelastic) cross-sections for the e-O system over a wide energy range 10–5000 eV. A local complex optical potential is calculated for the system using the atomic wavefunctions at the Hartree-Fock level. The real part of potential is composed of the attractive static, correlation polarisation and exchange potential. The imaginary component of the complex potential is a function of target charge density, incident electron energy and mean excitation energy. The resulting complex potential is treated in variable phase approach to yield complex phase shifts and total cross-sections. The total and elastic cross-sections are compared with the other available results. The agreement is excellent for total cross-sections with other theoretical work at energies greater than 100 eV. We have excellent agreement for elastic cross-sections with the experimental and theoretical results at all the energies. The elastic differential cross-sections are presented at 50 eV and 1000 eV. We fit the absorption cross-section values to Bethe asymptotic formula in high energy range (≥ 5500 eV). Ionisation cross-sections above 1000 eV are also deduced from the theory.     

Time resolved ultraviolet photoluminescence of mesoporous silica

We studied the optical properties of sol-gel synthesized porous silica excited by synchrotron radiation in the 4-10 eV range. The spectral and temporal characteristics of the ultraviolet photoluminescence at about 3.7 eV are reported. The UV emission results from the contribution of two different centers: the first one centered at 3.7 eV with a decay time of 2.0 ns and the second one peaked at 3.9 eV with a decay time of 20 ns. We propose to assign the observed luminescence to different interacting surface silanols.     

Structural,Electronic,Optical and Thermodynamic Properties of Nanolaminated Boride Cr_4AlB_6

Density functional calculations were used to investigate the structural,electronic,optical and thermal properties of Cr_4AlB_6.The optimized lattice constants and atomic positions accord well with the experimental data.The analysis of band structure and density of states confirms the metallic nature of Cr_4AlB_6.The static dielectric constant e1(0) is about 128.0,and the maximum optical conductivity occurs at about 8.12 eV.In the photon energy range from 7.87 to 23.48 e V,Cr_4AlB_6 presents a metal reflective property.The plasma resonance frequency wp of Cr_4AlB_6 is at the photon energy of 23.85 eV,and Cr_4AlB_6 will be transparent and change from metallic to dielectric response if the incident light has frequency greater than the plasma frequency of Cr_4AlB_6.Thermodynamic properties including the primitive cell volume and thermal expansion,the bulk modulus and heat capacity Cv were further investigated with the increasing temperature and pressure by using the quasi-harmonic Debye model.     

Synthesis and properties of a new polydiacetylene: Poly[1,6-di(N-carbazolyl)-2,4-hexadiyne]

The solid-state synthesis and properties are reported for a new polydiacetylene: poly[1,6-di(N-carbazolyl)-2,4-hexadiyne]. The monomer crystals polymerize quantitatively with γ irradiation or thermal annealing. An Autocatalytic effect is observed in both γ-ray polymerization and thermal polymerization and is attributed to an increase in chain propagation length at about 5% conversion. The activation energy for thermal polymerization is about 25 kcal/mole, independent of the degree of conversion to polymer. The exceptional thermal stability of the polymer crystals allowed a thermomechanical analysis over a large temperature range, ?50 to 300°C. With increasing temperature, the polymer contracts in the chain direction linearly with temperature over the entire range, yielding a thermal expansion coefficient of (?2.32 ± 0.02) × 10^?5°C^?1. Photoconductivity action spectra are reported for the polymer crystals. The energies for the photoconductivity onset (ca. 2.3 eV) and for the lowest energy optical transition (1.89 eV) are the lowest reported for the polydiacetylenes. The photoconduction onset is blue-shifted with respect to optical absorption—a result which is consistent with the excitonic assignment for the lowest energy optical transition in the polydiacetylenes.     

Synthesis and properties of methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole

The synthesis and full characterization of new derivatives of indolo[3,2-b]carbazole with differently substituted phenyl groups at nitrogen atoms is reported. Comparative study on their thermal, optical electrochemical, and photoelectrical properties is presented. The synthesized compounds are electrochemically stable. Their highest occupied molecular orbital energy values range from -5.14 to -5.07 eV. The electron photoemission spectra of the films of synthesized materials revealed the ionization potentials of 5.31-5.47 eV. Hole drift mobility of the amorphous film of 5,11-bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole exceed 10(-3) cm(2)/V·s at high electric fields, as it was established by xerographic time-of-flight technique. In contrast to diphenylamino substituted derivatives of carbazole, no effect of the position of methoxy groups on the photoelectrical properties was observed for the synthesized methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole. The indolo[3,2-b]carbazole core has a larger resonance structure that includes 3 phenyl rings, and thus the energy gap of the HOMO and LUMO π orbitals is lower as compared to that of carbazoles. With a larger energy difference between the phenyl substituents and the core moiety, the indolo[3,2-b]carbazole derivatives studied all have a weaker coupling between the phenyl group and a much weaker dependence of the molecular properties on the position of substituents on the phenyl groups as compared to those observed in substituted carbazoles.     

Do solid surface potential barriers retard convoy peak electrons?

Using a coaxial cylindric electron spectrometer and an electrostatic ion energy analyzer in tandem, a direct measurement of the difference of the energy of convoy peak electron and the electron equivalent ion energy of protons emerging from the downstream surface of C, Au and Al foils is performed in the proton energy range from 60 to 250 keV. This measurement is made possible using the accepted evidence that for a gas target these energies are equal. It is found that also for the beam foil convoy peak electrons, within an experimental average uncertainty of about ±0.1 eV, there is no difference between these energies. If one accepts that the origin of convoy electrons is from inside the solid, the conclusion is that no retardation by the solid surface potential barrier, which is of the order of a few eV, is observed. This is attributed to the strong electron-ion Coulomb interaction which almost completely overshadows the force exerted on the electron by the field of the surface barrier.     

Interface for a four-sector mass spectrometer with a dual-purpose collision cell: High transmission at low to intermediate energies

A new interface system that consists of an ion decelerator, a floating collision cell-chemical ionization ion source, and an ion extractor was designed and installed in the third field-free region of a four-sector tandem mass spectrometer. Important features include the use of cylindrical deceleration lenses and an extraction lens assembly. This new design was found to provide enhancement of ion transmission at low to intermediate ion kinetic energies (3 eV to 1 keV) compared with the standard collision cell design. Collision-induced dissociation experiments from 3 eV to 10 keV and ion-molecule reactions of mass-selected ions can be performed conveniently. A second, grounded, collision cell is located after the extraction lenses, which allows MS⁴ experiments to be carried out via the normal linked (B/E) scan function in MS2. Incorporation of chemical ionization capability into the electrically isolated collision cell makes it possible to carry out neutralization chemical-reionization mass spectrometry.     

Influence of organic ions on DNA damage induced by 1 eV to 60 keV electrons

We report the results of a study on the influence of organic salts on the induction of single strand breaks (SSBs) and double strand breaks (DSBs) in DNA by electrons of 1 eV to 60 keV. Plasmid DNA films are prepared with two different concentrations of organic salts, by varying the amount of the TE buffer (Tris-HCl and EDTA) in the films with ratio of 1:1 and 6:1 Tris ions to DNA nucleotide. The films are bombarded with electrons of 1, 10, 100, and 60?000 eV under vacuum. The damage to the 3197 base-pair plasmid is analyzed ex vacuo by agarose gel electrophoresis. The highest yields are reached at 100 eV and the lowest ones at 60 keV. The ratios of SSB to DSB are surprisingly low at 10 eV (～4.3) at both salt concentrations, and comparable to the ratios measured with 100 eV electrons. At all characteristic electron energies, the yields of SSB and DSB are found to be higher for the DNA having the lowest salt concentration. However, the organic salts are more efficient at protecting DNA against the damage induced by 1 and 10 eV electrons. DNA damage and protection by organic ions are discussed in terms of mechanisms operative at each electron energy. It is suggested that these ions create additional electric fields within the groove of DNA, which modify the resonance parameter of 1 and 10 eV electrons, namely, by reducing the electron capture cross-section of basic DNA units and the lifetime of corresponding transient anions. An interstrand electron transfer mechanism is proposed to explain the low ratios for the yields of SSB to those of DSB produced by 10 eV electrons.