Application of time-dependent density-functional theory to electron—ion coupling in ethylene

To examine the applicability of the time-dependent density-functional theory (TDDFT) for treating the electron–nucleus coupling in excited states, we calculate the strength distribution associated with the π–π* transition in ethylene. The observed optical transition strength in the 7–8.5 eV region shows a complex structure arising from coupling to C–C stretch motion, to torsional motion, and to Rydberg excitations. The mean energy of the observed peak is reproduced to about 0.2 eV accuracy by the TDDFT in the local density approximation (LDA). The reflection approximation is used to calculate the peak broadening. Roughly half of the broadening can be attributed to the fluctuation in the C–C coordinate. The asymmetry in the line shape is also qualitatively reproduced by the C–C coordinate fluctuation. We find, in agreement with other theoretical studies, that the torsional motion is responsible for the progression of weak transition strength extending from the peak down to about 6 eV. The LDA reproduces the strength in this region to a factor of about 3. We conclude that the TDDFT is rather promising for calculating the electron–nucleus coupling at short times.     

Diamond growth by carbon ion implantation of diamond

Medium energy (5–25 keV) ¹³C⁺ ion implantation into diamond (100) to a fluence ranging from 10¹⁶ cm⁻² to 10¹⁸ cm⁻² was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 × 10¹⁷ to 2 × 10¹⁸ at. cm⁻² (with a dose rate of 5 × 10¹⁵ at. cm⁻² s⁻¹ at 5 to 25 keV and 800 °C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.     

Gradual modification of the YSZ structures by Au ion implantation and high-energy Si ion irradiation

Gold nanoparticles (Au-NPs) were created in crystalline yttria-stabilized zirconia (YSZ). (100)-, (110)- and (111)-oriented YSZ samples were implanted by 1 MeV Au⁺ ions at room temperature and fluences ranging from 1.5 × 10¹⁶ cm⁻² to 7.5 × 10¹⁶ cm⁻². The prepared Au: YSZ structures were annealed at 1100 °C for 1 h on air to support the Au-NPs coalescence and YSZ structure recovery. Subsequent irradiation with the 10 MeV Si³⁺ ions with a fluence of 5.0 × 10¹⁴ cm⁻² was performed to enable gradual modification of Au-NPs. Au-depth profiles and YSZ structure modification in the produced samples were analysed via Rutherford backscattering spectrometry in channelling mode (RBS-C) and X-ray diffraction (XRD). RBS-C showed the gold distributed in the region of about 50–300 nm below the YSZ surface. The disorder was accumulated in the region with Au-NPs and the concentration of the disorder increases as a function of ion implantation fluence. The Zr-disorder was partially decreased after the annealing, while the subsequent Si-ion irradiation increased Zr-disorder again, however, the disorder does not reach values before the annealing. XRD measurement evidenced elastic deformation of the YSZ host lattice in the Au-implanted samples. Optical absorbance showed the appearance of the new absorption band at 550 nm for the Au-ion fluences above 5.0 × 10¹⁶ cm⁻² ascribed to the Au-NPs formation. After the annealing, the absorption band is shifted to the wavelength of 580 nm which could be connected to the proceeding clustering of Au. The maximum absorption peak intensity increases which is connected to the increasing amount of the Au-NPs. Transmission electron microscopy (TEM) with Energy dispersive spectroscopy (EDS) confirmed the presence of Au-NPs in the implanted layer after the annealing. The subsequent Si-ion irradiation did not change the Au-NP shape which remained spherical with a slight size increase.     

Molecular dynamics simulation of color centers in silicon carbide by helium and dual ion implantation and subsequent annealing

Atomic and close-to-atomic scale fabrication with high yield for the color centers in silicon carbide is critical in developing its applications. Combined with Wigner-Seitz method and identify diamond structure method to consider the structure around the silicon vacancy (V_Si), it is found that He ion implantation is more likely to fabricate a small number of silicon vacancies with complete structure but locating deep, while Si ion implantation is more likely to introduce more silicon vacancies with incomplete structure but a large number and closer to the near surface. Therefore, a method of dual ion implantation is proposed in this paper. By adjusting the ratio of He to Si ion concentration for dual ion implantation, the fabrication yield of color centers with depth below 5 nm can be increased compared with that of He implantation after high temperature annealing. Molecular dynamics (MD) simulation is employed to discover the underlying mechanism of V_Si color center and damage evolution by helium ion and dual ion implantation into four-hexagonal silicon carbide (4H–SiC) with subsequent annealing. Density-functional theory (DFT) calculation proves that magnetic-spin polarization enhances the stability of carbon anti-vacancy pair (C_SiV_C) defect, which indicates C_SiV_C defects are more stable than V_Si defects. The evolution of the V_Si color centers of different defect models are also calculated at various temperatures by MD, and the dynamic process of V_Si defects to C_SiV_C defects is demonstrated. It is revealed that the decrease of the V_Si color center at high temperature annealing is partly due to the transformation of some silicon vacancies to C_SiV_C defects.     

Enhancing the ferromagnetization of graphite by successive C ion implantation steps

¹²C⁺ ion implantation has been shown to be an efficient way to increase the magnetization of highly oriented pyrolytic graphite, and a saturation magnetization of 17.6 emu g⁻¹ at room temperature has been produced. The implantation was performed in four steps with decreasing ion energy for each step. Increasing the magnetization with the number of implantation steps has shown that the magnetization is correlated to the defect density. The temperature dependence of spin susceptibility calculated according to the electron spin resonance spectra indicates that the magnetism in the sample is intrinsic. The evolution of Raman spectra along with the degree of implantation supplied further evidence to the correlation between in-plane defects and the magnetization of the sample, and explained the decreased magnetization resulting from the final implantation step.     

Surface modification of polyethylene and polypropylene by ion implantation

The creation of oxidized structures and double bonds in polyethylene (PE) and polypropylene (PP) samples implanted with P⁺ ions was studied. The surface polarity and the electrical conductivity of the ion-implanted polymers were also examined. As a result of the ion implantation, the polymer macromolecules are broken up and the material is degraded. An oxygen penetration into the radiation-damaged polymers is also observed, with PE being more vulnerable to the oxidation. The ion-implanted PP exhibits higher surface polarity and sheet conductivity compared to that of PE. © 1993 John Wiley & Sons, Inc.     

Characteristics of carbon films prepared by plasma-based ion implantation

A series of carbon films have been prepared by plasma-based ion implantation (PBII) with C on pure Al and Si. Emphasis has been placed on the effect of implanting voltage on the characteristics of these films. The structures of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The morphologies were observed by atomic force microscope (AFM). Surface hardness and electrical resistivity were also measured. The results indicate that the characteristics of these films are strongly dependent on the implanting voltage. An implanting voltage threshold value ranging from 3 to 5 kV starts to form a C-substrate transition layer owing to C⁺ ions implanted into the substrate. The transition layer exhibits a gradual change in composition and structure and effectively connects the carbon film and the substrate. Also, an implanting voltage threshold value ranging from 5 to 10 kV starts to form diamond-like carbon (DLC) films. An increasing voltage causes the resultant DLC films to be smoother and more compact. Moreover, Raman spectrum, chemical state of C1s, surface hardness and electrical resistivity all prove an optimum voltage of approximately 30 kV corresponding to the lowest ratio of sp²/sp³.     

悬浮PVC树脂颗粒形成新理论——凝聚理论

提出了一种悬浮PVC树脂颗粒形成的新理论——凝聚理论:液态氯乙烯在搅拌作用下以约0.7μm的微滴分散在水中发生聚合反应,当聚合转化率达到25%左右时,这些微滴凝聚成粒径约为130μm的树脂颗粒。通过实验研究、文献资料及逻辑推理证明了其正确性。     

Production of amorphous carbon by plasma immersion ion implantation of polymers

The surface of poly ether ether ketone (PEEK) has been treated with plasma immersion ion implantation using hydrogen ions. Nanoindentation and transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) studies of the modified surface show that the modified layer is harder, denser and has a greater elastic recovery than the unmodified material. The electronic structure of the material is characterized by low-loss EELS and UV-Visible spectroscopy, which show that the surface molecular structure is strongly disrupted by the ion implantation. The changes observed are consistent with the modification creating a carbon-rich amorphous material containing a sp² rich network structure.     

Characterization of ultra-high-molecular-weight polyethylene (UHMWPE) modified by ion implantation

Surface modification of ultra high molecular weight polyethylene (UHMWPE) is induced by ion implantation of different ions at 300 keV energy. The aim of this work was the chemical, physical and mechanical characterization of the modified material in order to know deep inside about the effect of the ion beam upon the polymer.The irradiated surfaces are investigated by Raman spectroscopy, infrared absorption and micro-hardness analysis, scanning electron microscopy. Pin on disc measurements valuated the wear of the UHMWPE against a stainless steel probe; wear resistance increases of about 76% after the ion implantation. This result can be attributed to the ion bombardment inducing a micro-hardness increasing in the irradiated layers due to the high carbon surface concentration and cross-linking effects in the polymeric chains. The irradiated UHMWPE surfaces may find special applications to the field of the mobile prosthesis.     

Electrochemical study of the corrosion behaviour of copper surfaces modified by nitrogen ion implantation

Electrochemical impedance spectroscopy (EIS) and d.c polarization resistance measurements (Rp) were used to study the corrosion resistance of surface layers produced by nitrogen ion implantation into copper substrates. Ion implantation was carried out using a Wickham ion beam generator, applying an acceleration voltage of 100keV, a mean current of 0.40 mA and a nitrogen dosage of 4 × 1017 ions cm–2. Surface analyses were made by Auger electron spectroscopy (AES). Electrochemical measurements (EIS and Rp) performed in a 0.6m sodium chloride solution show nitrogen-implanted specimens have greater a.c. and d.c. apparent polarization resistance than nonimplanted specimens. The results obtained with electrochemical measurements indicate that nitrogen ion implantation in copper forms a protective surface layer which improves the corrosion resistance of the pristine material, a feature of great interest for the design of new contact materials for the electricity and electronic industries.     

The enhanced anticoagulation for graphene induced by COOH+ ion implantation

Graphene may have attractive properties for some biomedical applications, but its potential adverse biological effects, in particular, possible modulation when it comes in contact with blood, require further investigation. Little is known about the influence of exposure to COOH⁺-implanted graphene (COOH⁺/graphene) interacting with red blood cells and platelets. In this paper, COOH⁺/graphene was prepared by modified Hummers'' method and implanted by COOH⁺ ions. The structure and surface chemical and physical properties of COOH⁺/graphene were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. Systematic evaluation of anticoagulation, including in vitro platelet adhesion assays and hemolytic assays, proved that COOH⁺/graphene has significant anticoagulation. In addition, at the dose of 5 × 10¹⁷ ions/cm², COOH⁺/graphene responded best on platelet adhesion, aggregation, and platelet activation.     

p-type doping by B ion implantation into diamond at elevated temperatures

We have studied B ion implantation at 400 °C into undoped homoepitaxial chemical vapor deposition diamond films and high-pressure and high-temperature (HPHT) synthetic IIa substrates. The highest Hall mobility at room temperature is 268 cm²/Vs among B implanted homoepitaxial films, while it is 38 cm²/Vs for the B implanted HPHT synthetic IIa substrate. The present result reveals that the quality of a doped layer is strongly dependent upon that of a diamond substrate employed for ion implantation.     

Surface amorphization and deoxygenation of graphene oxide paper by Ti ion implantation

Ti ion implantation with different doses was used to modify the surface and deoxygenate graphene oxide (GO) papers. The morphologies, microstructures and surface chemical states of the modified GO papers were investigated. Based on the results, the surface amorphization of GO papers is realized by Ti ion implantation. In addition, the whole GO paper is reduced or deoxygenated, which can be attributed to the annealing effect. However, at a low implantation dose of 5 × 10¹⁶ cm⁻², the deoxygenation of GO paper is found to be incomplete. With a high implantation dose of 3 × 10¹⁷ cm⁻², a surface composed of whirlpool-like structures is generated, while the layer-by-layer stacking structure of the as-prepared GO paper is retained.     

Magnetic Properties of Ni-doped ZnO Nanocombs by CVD Approach

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role.     

Modification of the structure of diamond with MeV ion implantation

We present experimental results and numerical simulations to investigate the modification of structural–mechanical properties of ion-implanted single-crystal diamond. A phenomenological model is used to derive an analytical expression for the variation of mass density and elastic properties as a function of damage density in the crystal. These relations are applied together with SRIM Monte Carlo simulations to set up finite element simulations for the determination of internal strains and surface deformation of MeV-ion-implanted diamond samples. The results are validated through comparison with high resolution X-ray diffraction and white-light interferometric profilometry experiments. The former are carried out on 180 keV B implanted diamond samples, to determine the induced structural variation, in terms of lattice spacing and disorder, whilst the latter are performed on 1.8 MeV He implanted diamond samples to measure surface swelling. The effect of thermal processing on the evolution of the structural–mechanical properties of damaged diamond is also evaluated by performing the same profilometric measurements after annealing at 1000 °C, and modeling the obtained trends with a suitably modified analytical model. The results allow the development of a coherent model describing the effects of MeV-ion-induced damage on the structural–mechanical properties of single-crystal diamond. In particular, we suggest a more reliable method to determine the so-called diamond “graphitization threshold” for the considered implantation type.     

Adsorption and diffusion of Pb(II) on the kaolinite(001) surface: A density-functional theory study

The adsorption and diffusion of Pb(II) atom on the hydroxylated (001) surface of kaolinite were investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites was the two-fold bridge site followed by the one-fold top site, and the adsorption energy increased with the coverage, thus indicating the higher stability of surface adsorption and a tendency to the formation of Pb(II) islands (clusters) with increasing coverage. Moreover, the energy barrier for diffusion of Pb(II) atom between the one-fold top and the two-fold bridge adsorption sites on kaolinite(001) surface was 0.23 (0.31) eV, implying that the Pb(II) atom is prone to diffusing on kaolinite(001) surface. The other properties of the Pb(II)/kaolinite(001) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.     

Electroluminescence from electron injection junctions created by carbon and phosphorus ion implantation

A p-type (type IIb) natural diamond was implanted with either carbon or phosphorus ions using the cold implantation rapid annealing (CIRA) process. In each case, the energies and doses were chosen such that upon annealing, the implanted layer would act as an n-type electrode. The electroluminescence (EL) emitted from these carbon and phosphorus junctions, when biased in the forward direction, was compared as a function of annealing and diode temperatures. Typical luminescence bands such as those observed in cathodoluminescence (CL), in particular a blue band A (≈2.9 eV) and a green band (≈2.4 eV), were observed. Two bands centred around ≈2.1 and 4 eV were also observed for both the carbon and phosphorus junctions, whereas a band at ≈4.45 eV appeared only in the phosphorus-implanted junction.     

Vertically aligned carbon nanotube growth from Ni nanoparticles prepared by ion implantation

Vertically aligned carbon nanotubes (CNTs) were synthesized from Ni nanoparticles prepared by ion implantation. Ni ions were implanted at 30 keV into thermally grown SiO₂ substrates using a focused-ion-beam. High-density nanoparticle formation was investigated with high doses up to 5.0 × 10¹⁷ ions/cm². Dense Ni nanoparticles in the order of 10¹¹–10¹² cm^{− 2} were obtained on a SiO₂ substrate, and the particle density and diameter were controlled by post-implantation annealing. Particles annealed at 700 °C led to vertically aligned CNTs. Interestingly, catalysts were longer along the vertical axis and the lower half of the Ni particle was buried in SiO₂.     

Isomerisations of the fullerenes

The Stone-Wales (pyracylene) rearrangement is a hypothetical mechanism for interconversion of fullerene isomers, accounting for mobility of the pentagons on the surfaces of these clusters. Two versions of the transformation, involving patches of 4 and 12 rings, respectively, can be defined. Energetic and group-theoretical aspects of the transformation are discussed, symmetry-based selection rules devised and complete isomerisation maps presented for small fullerenes (C₂₀ to C₄₀) and isolated-pentagon isomers (C₇₈ to C₈₈). Fullerenes that self-racemise under this transformation include D₂ C₂₈. Limitations on the usefulness of this mechanism as a means of rationalising experimental isomer distributions are briefly discussed.