Ion Implantation into Fullerene

Abstract

Various elements - H, Li, B, Ar, Kr, Xe, Cs, Pb and Bi - have been implanted at 20 - 200 keV and at room temperature up to different fluences into thin fullerene layers evaporated onto polished Si substrates. Subsequently their depth profiles were determined by NRA, NDP, or RBS analysis. These measurements were compared with ion implantation into amorphous carbon and with theory. In most cases the degree of fullerene destruction was monitored by Raman spectroscopy earlier.

The results show that there exists a general trend insofar as theory appears to underestimate both ranges and range stragglings for heavy projectile ions, whereas for light and medium-heavy ions experimental range results agree with theory within some 30%. In a few cases range stragglings are found to be considerably larger than predicted by theory, which may be attributed to post-implantational radiation enhanced diffusion. There is only little influence of the degree of fullerene destruction onto the implantation profile parameters. Ranges in amorphous carbon appear to be in general a little bit larger than those ones in fullerene.     

Lithium Implantation into Fullerite

The depth profiles of lithium, implanted into fullerene at different fluences and temperatures are reported. They deviate considerably from the simple ballistic predictions. They can be understood in terms of depth dependent Li mobility immediately after the ion implantation. This mobility depends considerably on the temperature and on the degree of fullerene damage. It appears that the fullerene destruction products which act as traps for the mobile lithium are somewhat mobile themselves, essentially at high temperatures, and at low damage levels.     

Lithium Implantation into Fullerite

The depth profiles of lithium, implanted into fullerene at different fluences and temperatures are reported. They deviate considerably from the simple ballistic predictions. They can be understood in terms of depth dependent Li mobility immediately after the ion implantation. This mobility depends considerably on the temperature and on the degree of fullerene damage. It appears that the fullerene destruction products which act as traps for the mobile lithium are somewhat mobile themselves, essentially at high temperatures, and at low damage levels.     

Lithium Implantation into Fullerite

Abstract

The depth profiles of lithium, implanted into fullerene at different fluences and temperatures are reported. They deviate considerably from the simple ballistic predictions. They can be understood in terms of depth dependent Li mobility immediately after the ion implantation. This mobility depends considerably on the temperature and on the degree of fullerene damage. It appears that the fullerene destruction products which act as traps for the mobile lithium are somewhat mobile themselves, essentially at high temperatures, and at low damage levels.     

Lithium Implantation into Fullerite

Abstract

The depth profiles of lithium, implanted into fullerene at different fluences and temperatures are reported. They deviate considerably from the simple ballistic predictions. They can be understood in terms of depth dependent Li mobility immediately after the ion implantation. This mobility depends considerably on the temperature and on the degree of fullerene damage. It appears that the fullerene destruction products which act as traps for the mobile lithium are somewhat mobile themselves, essentially at high temperatures, and at low damage levels.     

Modification of fullerene nanocolumn structure by accelerated C60 ions

Crystalline C60 and amorphous graphite-like films of nanocolumn arrays fabricated by glancing angle deposition of C60 fullerene at substrate temperatures of -425 K were studied by transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Characteristic dimension of columns is 200-400 nm. We used co-deposition of C60 molecules and accelerated C60 ions to modify the structure and properties of nanocolumn arrays. Influence of incidence angle for C60 ions on formation of film morphology was revealed. Raman spectrum analysis showed that amorphous carbon nanocolumns consist of nanographite areas with average size of -1.5 nm. The films have high conductivity (close to graphite) and have no mechanical stresses. The carbon films were applied in all-solid-state rechargeable thin-film battery as an anode layer. The nanocolumn amorphous carbon film as anode electrode showed the discharge capacity of about 50 microAh cm(-2)microm(-1) and good cycling ability over 100 times in full cell system.     

Rutherford backscattering/channeling study of the implanted MeV Au+ in silicon

1.0 MeV Au⁺ ions were implanted into a Si single crystal and an amorphous silicon film at room temperature. For the case of the Si single crystal, ion implantation was performed at angles of 7, 45 and 60°, respectively. The amorphous silicon film was deposited on SiO₂ substrate with a thickness of ∼500 nm. The longitudinal and lateral distributions of implanted Au ions in silicon were measured by Rutherford backscattering spectrometry. The lateral spread was estimated from the tilt angle implantation. The results show that the experimental mean projected range is larger than the calculated value by ∼20%, and the experimental range straggling and lateral spread deviate significantly from the TRIM prediction. The damage in the Si single crystal induced by MeV Au⁺ under different fluences was studied by Rutherford backscattering/channeling. Also, the thermal behaviour of the implanted Au⁺ in silicon was investigated.     

Fullerene nanocage capacity for hydrogen storage

We model fullerene nanocages filled with hydrogen, of the general formula Hn@Ck, and study the capacity of such endohedral fullerenes to store hydrogen. It is shown using density functional theory that for large numbers of encapsulated hydrogen atoms, some of them become chemisorbed on the inner surface of the cage. A maximum of 58 hydrogen atoms inside a C60 cage is found to still remain a metastable structure, and the mechanism of its breaking is studied by ab initio molecular dynamics simulations. Hydrogen pressure inside the fullerene nanocage is estimated for the first time and is shown to reach the values only a few times smaller than the pressure of hydrogen metallization. We provide a general relation between the hydrogen pressure and resulting C-C bond elongation for fullerene nanocages of arbitrary radii. This opens a way to assess possible hydrogen content inside larger carbon nanocages, such as giant fullerenes, where significant capacity can be reached at reasonable conditions.     

Rare-Gas Implantation and Damage of Fullerene at High Fluence

Abstract

100 keV Ar⁺and Kr⁺ ions were implanted into fullerene films up to fluences which exceed the fullerene destruction threshold. The depth profiles of implanted atoms were measured using conventional RBS techniques. The depth profile parameters differ significantly from theoretical estimates and with increasing ion fluence the depth profiles move to the sample surface. This suggests a high degree of fullerene sputtering. In annealing experiments at temperatures up to 375 °C no significant changes of the depth profiles were observed.     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).     

Tem characterization of nanodiamond thin films

The microstructure of thin films grown by microwave plasma-enhanced chemical vapor deposition (MPCVD) from fullerene C₆₀ precursors has been characterized by scanning electron microscopy (SEM), selected-area electron diffraction (SAED), bright-field electron microscopy, high-resolution electron microscopy (HREM), and parallel electron energyloss spectroscopy (PEELS). The films are composed of nanosize crystallites of diamond, and no graphitic or amorphous phases were observed. The diamond crystallite size measured from lattice images shows that most grains range between 3–5 nm, reflecting a gamma distribution. SAED gave no evidence of either sp²-bonded glassy carbon or sp³-bonded diamondlike amorphous carbon. The sp²-bonded configuration found in PEELS was attributed to grain boundary carbon atoms, which constitute 5–10% of the total. Occasionally observed larger diamond grains tend to be highly faulted.     

多能碳离子注入纯铁研究

利用离子注入表面优化技术,在不同温度下,采用多能量叠加方式将碳离子注入纯铁表面;利用XRD和AES等技术分析了表面改性层的相结构以及元素的分布;利用电化学极化法测试了注入样品的抗腐蚀性能.结果表明,573 K时注入的碳离子比373 K时注入的碳离子深;纯铁表面改性层有Fe2C、Fe3C新相生成;离子注入碳提高了纯铁表面抗电化学腐蚀的能力.     

Influence of buffer gas and vibration temperature of carbon clusters on fullerene formation in a carbon plasma

A new model for calculation of fullerene formation rate in carbon containing plasma is proposed. The model takes into account carbon cluster heating and cooling during transformations due to chemical bonds formation and destruction. In addition, the heating and cooling of carbon clusters by buffer gas is considered. The calculations give the qualitatively correct correlation between fullerene yields in helium and argon.     

Microstructure of interface for high-adhesion DLC film on metal substrates by plasma-based ion implantation

The diamond-like carbon (DLC) film was prepared on various metal substrates with a plasma-based ion implantation and deposition using superimposed RF and negative high-voltage pulses. The adhesion strength of DLC film was enhanced above the epoxy resin strength by implantation of carbon ions or mixed ions of carbon and silicon to the substrate surface before DLC deposition. In order to clarify the mechanism for improvement in adhesive strength, the microstructure of an interface between DLC film and substrate was examined in detail by transmission electron microscopy (TEM) observations in combination with EDS analysis. As a result, the enhancement in adhesion strength of DLC film by C ion implantation resulted from the formation of amorphous-like phase in the ion-implanted region of substrate, the production of carbon-component graded interface, the destruction of the oxide layer on the top surface of substrate, and the reduction of residual stress in DLC film by ion implantation during the deposition. The production of stress-free DLC film allowed us to demonstrate a supra-thick DLC film of more than 400 μm in thickness.     

Multiple Charged Nitrogen Ion Beam Irradiation of Fullerene Thin Films

In this work, the results of structural modification of fullerene thin films bombarded by multiple charged nitrogen ions have been reported. The properties of as-deposited and irraditated fullerene thin films have been investigated by Raman and FTIR spectroscopy and AFM analysis. After irradiation by multiple charged nitrogen ions (N²⁺, N⁵⁺) new bondings in fullerene films have been formed and the amorphicity has been enhanced at higher doses. Raman and FTIR spectra showed structural changes of deposited films depending on the energy and implantation dose. AFM analysis showed that the ion beam had destroyed the surface ordering. At lower doses the surface order has been characterized by carbon clusters of 500 nm. At higher doses significantly smaller clusters have been formed (200 nm).     

Self‐Organization of Amorphous Carbon Nanocapsules into Diamond Nanocrystals Driven by Self‐Nanoscopic Excessive Pressure under Moderate Electron Irradiation without External Heating

Phase transformation between carbon allotropes usually requires high pressures and high temperatures. Thus, the development of low‐temperature phase transition approaches between carbon allotropes is highly desired. Herein, novel amorphous carbon nanocapsules are successfully synthesized by pulsed plasma glow discharge. These nanocapsules are comprised of highly strained carbon clusters encapsulated in a fullerene‐like carbon matrix, with the formers serving as nucleation sites. These nucleation sites favored the formation of a diamond unit cell driven by the self‐nanoscopic local excessive pressure, thereby significantly decreasing the temperature required for its transformation into a diamond nanocrystal. Under moderate electron beam irradiation (10–20 A cm^?2) without external heating, self‐organization of the energetic carbon clusters into diamond nanocrystals is achieved, whereas the surrounding fullerene‐like carbon matrix remains nearly unchanged. Molecular dynamics simulations demonstrate that the defective rings as the active sites dominate the phase transition of amorphous carbon to diamond nanocrystal. The findings may open a promising route to realize phase transformation between carbon allotropes at a lower temperature.     

A new technique for fullerene onion formation

We present an original technique for growing large fullerene onions: carbon-ion implantation at high temperature into copper substrates. Used for carbon film growth (diamond or turbostratic carbon), this method is based on the immiscibility of carbon into copper and can produce an important density of giant carbon onions with size up to some micrometres which is the largest size observed up to now. We characterize these giant fullerenes by TEM, HRTEM and for the first time with AFM. On the basis of both experimental and numerical results we propose a mechanism of formation of the carbon onions during the implantation process.     

Morphology of New Fullerene Families with Negative Curvature

We consider the morphology of new fullerene families having negative Gaussian curvature formed by the introduction of 7- or 8-membered rings in a graphite sheet. The objects of our interest include the hypothetical structures of fullerene donuts and graphitic sponges. Their geometries are discussed based on the projection method on a honeycomb sheet which we have developed for normal fullerenes. Special emphasis is put on the new construction method for the structures of graphitic sponges. We demonstrate new carbon forms with three dimensionally periodic network based on polyhedral packing in space. The method can be applied to examine the local structures of amorphous carbon systems.     

N离子注入改性SnO2缓冲层及其CdTe太阳电池应用

使用等离子注入技术对SnO_2薄膜进行N离子注入改性,进行方块电阻、光学透过、表面形貌、Kelvin探针和X射线光电子能谱(XPS)表征,并将其作为缓冲层应用到CdTe太阳电池中。研究结果发现,对于30nm厚的SnO_2缓冲层,经过30s、10min不同时间N离子注入以后,其300~800nm波长范围透过率有所降低,而体电阻率则明显增加,特别是N离子注入10min的SnO_2缓冲层,表面出现很多凹孔,呈蜂窝状结构,且对后续沉积的CdS层表面形貌产生了明显影响。Kelvin探针表征结果显示,随着N离子注入时间的延长,SnO_2缓冲层功函数逐渐增加,最高达到约5.075eV,比本征SnO_2缓冲层的功函数高出0.15eV。XPS测试结果显示,N离子注入10min后,SnO_2缓冲层N1s结合能峰位向低结合能方向发生了明显移动,而O1s结合能峰位则向高结合能方向移动了,且表面区非晶格氧所占比例增大。对比电池结果,有N离子注入改性SnO_2缓冲层的电池与无缓冲层的电池相比,效率从10%左右增加到12%以上,最高达到12.47%,其中开路电压提高最为显著,从约750mV提高到790mV以上,提升了约5%,电池的整体均匀性也明显改善。     

Thermal effects on the microstructure and mechanical properties of ion implanted ceramics

The effects of varying the substrate temperature on the implantation-induced structures and surface mechanical properties of single crystal sapphire and MgO have been investigated for a range of 300 keV implanted ions. As the implantation temperature is lowered, the dose at which amorphization occurs is reduced and thus, for the same doses, more amorphous material is produced at lower temperatures. Quantitative modelling shows that the activation energy for annealing of the amorphous material during implantation is very much lower than might be expected for post-implantation thermal annealing of the same material. Also, as the implantation temperature increases there is a small amount of damage annealing in the damaged-but-crystalline material.Both the microhardness and implantation-induced stresses depend critically on the presence of amorphous material since this is relatively soft and can support only small stresses. However, while the hardness behaviour in the damaged-but-crystalline material is dominated by radiation hardening, the substitutionality, ionic misfit and charge state of the implanted ions have also been found to contribute to the further solid solution component of the hardening produced by ion implantation. These effects are also observed to be temperature dependent. Crazing of the implanted layers has also been reappraised. It has been established that the formation and configuration of crazes is a sensitive function of implantation temperature, and it is now proposed that crazes form in response to the stresses generated as a result of the thermal expansion mismatch between the amorphous layer and the substrate.