Fullerene films deposited by evaporation in vacuum using spot-focused annular electron beam

A rapidly focused annular electron beam can provide for the effective evaporation of a fullerene mixture in a vacuum of ～10^?2 Pa. A 1-kW beam focused into a spot within 0.1–1 s produces explosive evaporation of a fullerene target at an extremely high efficiency of heating. A comparison of the Raman and electronic absorption spectra of the initial fullerene powder and a film deposited upon its evaporation shows that C₆₀ and C₇₀ fullerenes are evaporated without rupture of C-C covalent bonds. The electron beam evaporation in vacuum has been successfully used to obtain fullerene films on substrates with an area of ～0.1 m².     

Fullerene Research in Poland

Abstract

Main results of the investigations of fullerene and its derivatives are briefly reviewed. Such topics as plasma spectroscopy, fullerenes and nanotubes formation, C₆₀ carbyne knots, fullerene reduction and doping, charge transfer states and electroabsorption of C₆₀, electrical conductivity, superconductivity, ESR properties, fullerene clathrates, C₆₀/C₇₀ complexes with organic donors, fullerene adducts, hydrogenated fullerenes, metallofullerenes and carbon nanotubes are discussed.     

Effect of electron beam irradiation on structure and properties of SiCN thin films prepared by plasma assisted radio frequency magnetron sputtering

Silicon carbon nitride thin films were deposited on Si (100) substrate at room temperature by plasma assisted radio frequency magnetron sputtering. The bonding structure and properties of SiCN films irradiated by pulsed electron beams were studied by means of X-ray photoelectron spectroscopy and nano-indentation. The results showed that electron beam irradiation had a great effect on the structure and property of the films. Under sputtering gas pressure of 3.7 Pa, a transition from the (Si,C)N_x bonded structure to the (Si,C)₃N₄ bonded structure was found in the SiCN thin film with electron beam irradiation. At sputtering gas pressure of 6.5 Pa, the enhancement of hardness in the SiCN film after treatment with electron beam irradiation resulted from the promotion of the sp³-hybridization of carbons bonds.     

Effect of electron beam irradiation on structure and properties of SiCN thin films prepared by plasma assisted radio frequency magnetron sputtering

Silicon carbon nitride thin films were deposited on Si (100) substrate at room temperature by plasma assisted radio frequency magnetron sputtering. The bonding structure and properties of SiCN films irradiated by pulsed electron beams were studied by means of X-ray photoelectron spectroscopy and nano-indentation. The results showed that electron beam irradiation had a great effect on the structure and property of the films. Under sputtering gas pressure of 3.7 Pa, a transition from the (Si,C)N_x bonded structure to the (Si,C)₃N₄ bonded structure was found in the SiCN thin film with electron beam irradiation. At sputtering gas pressure of 6.5 Pa, the enhancement of hardness in the SiCN film after treatment with electron beam irradiation resulted from the promotion of the sp³-hybridization of carbons bonds.     

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

In this contribution, for the first time, the polarity of fullerene derivatives is tailored to enhance the miscibility between the host and dopant molecules. A fullerene derivative with a hydrophilic triethylene glycol type side chain (PTEG‐1) is used as the host and (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine n ‐DMBI) as the dopant. Thereby, the doping efficiency can be greatly improved to around 18% (<1% for a nonpolar reference sample) with optimized electrical conductivity of 2.05 S cm^?1, which represents the best result for solution‐processed fullerene derivatives. An in‐depth microstructural study indicates that the PTEG‐1 molecules readily form layered structures parallel to the substrate after solution processing. The fullerene cage plane is alternated by the triethylene glycol side chain plane; the n ‐DMBI dopants are mainly incorporated in the side chain plane without disturbing the π–π packing of PTEG‐1. This new microstructure, which is rarely observed for codeposited thin films from solution, formed by PTEG‐1 and n ‐DMBI molecules explains the increased miscibility of the host/dopant system at a nanoscale level and the high electrical conductivity. Finally, a power factor of 16.7 µW m^?1 K^?2 is achieved at 40% dopant concentration. This work introduces a new strategy for improving the conductivity of solution‐processed n‐type organic thermoelectrics.     

Adjustment of the selenium amount during ion beam sputtering deposition of CIS thin films

CuInSe₂ (CIS) films were prepared by ion beam sputtering depositing Cu, In and Se layers sequentially on BK7 glass substrates and annealing the 3-layer film in the same vacuum chamber. The adjustment of the Se amount in the film was achieved by controlling the sputtering time of the Se target. X-ray diffraction pattern shows CIS films have chalcopyrite structure and preferential (112) orientation when the sputtering of the Se layer is between 60 and 180 min. It also can be seen that the most intense and narrow peak indicates the highest crystallinity for the sample with sputtering Se of 60 min, which is in agreement with the Raman measurement. The content of Cu, In and Se in the film deviates from 1, 1 and 2 with increasing the sputtering time of the Se target. Direct band gap energy between 0.96 and 1.05 eV, depending on the Se amount, and a high absorption coefficient of 10⁵ cm⁻¹ are found. The measured film resistivities vary from 0.01 to 0.05 Ω cm. Thus, the structural, optical and electrical characteristics of the CIS thin films were dependent on the Se amount during the fabrication of films and after fitting the sputtering time of Se, an optimization of the properties and a saving of Se consumption were achieved.     

Influence of additives on the morphological,phase and chemical characteristics of gas sensitive SnO2 sprayed films

The morphology, and also the chemical and phase composition of sprayed SnO₂ films doped with Cu, Zr, Fe and P have been investigated. It was found that in general, the film morphology was characterized by a fine grained basic layer with a few large crystallites located on the surface. All the doping elements decreased the grain size in the basic layer. For Fe, Zr and P the grain size depended on the doping level in the spray solution. It was established that the dopant: Sn ratio in the films was much lower than that in the spray solution. The doping element was preferentially accomodated in the large crystallites with only a small quantity of the dopant being introduced into the basic layer. The gas sensing properties of the films have are discussed on the basis of these results.     

The structure of fullerene C60 films modified by helium glow discharge plasma

The structure of fullerene C₆₀ films modified by helium dc glow discharge plasma was studied using Raman scattering spectroscopy. The vibrational spectra of the C₆₀ films exhibit certain features depending on the plasma treatment duration. The helium ion bombardment leads to the degradation of the fullerene structure and the formation of an amorphous carbon phase. The coefficient of carbon sputtering by helium was estimated.     

Pulsed Laser Processing of Carbon and Silicon Clusters and Thin Films

Abstract

Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C₆₀ powder target produced single phase C₆₀ thin films when the laser energy fluence was in the range between 40 and 50mJ/cm². By atomic force microscopy, the laser-deposited C₆₀ thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MC_n(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)₆₀ and (M_xC_60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C₆₀ and C₇₀ were found to exists in the laser-deposited films, indicating a new applicability of pulsed laser processing for segregative cluster synthesis from solid solution. Preliminiary results on thin film deposition via pulsed ablation of (Ba,Na)_xSi₄₆ clathrate were also presented.     

The optical attenuation of laser radiation in thin fullerene C70-polyimide films. Effect of fullerenes on the transmission of azide films

The phenomenon of optical attenuation of laser radiation in the visible spectral range was studied in a promising photosensitive medium based on fullerene C₇₀-polyimide films. The effect of fullerenes on the transmission of laser radiation in azide-based systems is demonstrated.     

New Molecular Complex of Fullerene C60 with Porphyrin Dimer [FeTPP]2O: Synthesis and Crystal Structure

Abstract

New molecular complex of C₆₀ with covalently linked (Fe^IIITPP)₂O · C₆₀ dimer has been obtained. The complex has isolated packing of fullerenes in which fullerene molecule is embraced in a pocket built by porphyrins. (Fe^IIITPP)₂O preserves its initial geometry in the complex. The Fe···C(C₆₀) contacts are in the 3.239–3.513 Å range indicating the absence of Fe–C₆₀ coordination. This results in the similarity of the EPR spectra of the complex and parent (Fe^IIITPP)₂O.     

Effect of sputtering pressure and post-annealing on hydrophilicity of TiO2 thin films deposited by reactive magnetron sputtering

A series of TiO₂ thin films was deposited onto glass substrates without intentional heating or biasing by magnetron sputtering of a titanium target using Ar/O₂ reactive mixtures over a broad range of total sputtering pressures from 0.12 Pa to 2.24 Pa. Each of the film types was deposited by the threshold poisoned mode at a specific given oxygen flow rate monitored in-situ by optical emission spectroscopy. Both the sputtering pressure and thermal annealing are the key factors for the TiO₂ films to yield fast-response superhydrophilicity with a water contact angle of 5°. The mechanism of superhydrophilicity for the TiO₂ films deposited by high-pressure sputtering will be discussed based on empirical studies of X-ray diffractometry, high-resolution scanning microscopy and atomic force spectroscopy.     

Nucleation and growth of sputtered and evaporated trigonal selenium films

Critical nucleation temperature experiments, scanning electron microscopy and light microscopy were used to study the nucleation and growth of trigonal Se films deposited by evaporation and sputtering on both gold and anodized aluminum substrates. The major nucleation and growth processes were shown to be the condensation of Se₂ molecules followed by their polymerization into Se_n chains, where n can be very large. In sputtering, these chains have a higher surface mobility, due in part to their higher residual kinetic energy, and thus they can form large trigonal Se crystallites. The high incident kinetic energies also allow the Se to break through the surface contamination of the substrate. This is important since the Se chain mobility should also be dependent on the surface free energy and on the nucleation site density of the substrate. Very adherent large-grained trigonal Se films were grown by sputtering on Au substrates. It was shown that nucleation sites for the large trigonal Se crystallites were not created by the incident flux but are inherent on the substrate. The high energy incident flux did, however, increase nucleation probability for the initial Se₂ condensation. For sputtering on anodized aluminum substrates the combination of low surface energy and high nucleation site density decreased chain mobility and thus prevented formation of large crystallites.     

Extraction equilibria in a fullerene-containing C<Subscript>60</Subscript>-C<Subscript>70</Subscript>-<Emphasis Type="Italic">o</Emphasis>-Xylene-<Emphasis Type="Italic">i</Emphasis>-butylamine-water system

Extraction equilibria of the liquid(I)-liquid(II) type have been studied for the first time in a system containing light fullerenes C₆₀ and C₇₀. The experiments were performed with a five-component mixture of fullerene C₆₀, fullerene C₇₀, o-xylene, ibutylamine, and water at 25°C. Isothermal diagrams describing the distribution of fullerene components between separating liquid phases have been obtained. The distribution coefficients of fullerenes (C₆₀ and C₇₀ concentrations in the xylene phase relative to those in the amine phase) are found to be almost constant and approximately equal to ～16.1 for both C₆₀ and C₇₀.     

Estimating the effect of C<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and C<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> radicals and neutral clusters on the fullerene formation

The mass spectrum of the products of arc discharge in helium between graphite electrodes has been studied for various values of the gas flow rate. As the gas flow rate increases, the intensity of C₆₀^±, C₇₀^±, C₈₄^± and C₉₀^± fullerene peaks increases and that of the C₂⁻ and C₃⁺ cluster radicals decreases, but the total decay in radicals amounts to only 21% of the total growth of fullerenes. From this it follows that a contribution to the formation of fullerenes from the neutral clusters (which are taken into account for the first time) significantly exceeds the contribution due to small radical species.     

Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Abstract

Macroscopic quantities of boron-doped fullerenes, such as C_60-nB_n and C_70-nB_n(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS₂, and characterized by field desorption mass spectra. Among them C₅₈B₂ and C₆₈B₂ were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.     

Electrical properties/Doping efficiency of doped microcrystalline silicon layers prepared by hot-wire chemical vapor deposition

Microcrystalline silicon (μc-Si) doped films were prepared by hot-wire chemical vapor deposition (HWCVD) to investigate the doping efficiency. The incorporation probability of different dopant atoms into the solid-phase is always increasing with the doping gas concentrations, but very different for the doping gases used: trimethylboron (TMB), boron trifluoride (BF₃) and phosphine (PH₃). At the same doping gas concentration in the process gas the incorporation of phosphorus atoms into the solid μc-Si phase is much larger than that of boron atoms with respect to the dissociation probability of the doping gases. The electron and hole concentrations, estimated from Hall measurements, are directly related to the solid phase concentration of the doping atoms and independent of the type of dopant and the doping gas used. This results in an equal doping efficiency of about 20 % for the incorporated B and P atoms in doped HWCVD μc-Si films. For the dopant atom concentration regime investigated the doping efficiency of B atoms is in good agreement with corresponding PECVD doping efficiencies however, the doping efficiency of P atoms is considerably lower for our n-doped films.     

Electron structure of thin fullerene films deposited by various methods

The valence-band photoelectron spectra and the photoelectron energy loss spectra behind the C1s peak in the X-ray photoelectron spectra were studied in thin fullerene films deposited by various methods. The fine structure in the density of states near the valence band bottom observed for the fullerene films deposited by the method of pulsed supersonic molecular beam (SMB) with a helium carrier may be indicative of the presence of a long-range order. The spectra of π-plasmon losses in the films obtained by methods of thermal and SMB deposition exhibit a significant difference that can be related to a closer packing of C₆₀ molecules in the latter case.     

Influence of doping concentration on the properties of ZnO:Mn thin films by sol-gel method

Thin films of Mn-doped ZnO with different doping concentration (0.8, 1, 3, 5 at%) were prepared on Pt/Ti/SiO₂/Si substrates by using sol-gel method. The effects of the doping concentration on the structural properties, electrical characteristics and element binding energy in films were investigated. X-ray diffraction (XRD) results showed that the c-axis orientation of ZnO films was affected by Mn²⁺ content. Current-voltage (I-V) measurements indicated that resistivities of ZnO films were observably enhanced by dopant of Mn²⁺ and the resistivities value increased with a doping level up to 5 at% Mn. X-ray photoelectron spectroscopy (XPS) patterns suggested that the binding energies of O1s and ZnL₃M₄₅M₄₅ were affected by the content of Mn²⁺.     

About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)]

The iron carbonyl complexes with C₆₀ and C₇₀ fullerenes were synthesized in high yield by photochemical irradiation of solutions of C₆₀ and C₇₀ in presence of Fe(CO)₅. The resulting complexes were studied by FT-IR, Raman and electronic absorption spectroscopy. All the data are consistent with the structures [Fe(CO)₄(η²C₆₀)] and [Fe(CO)₄(η²C₇₀)]. The thermal stability and decomposition reaction of the two complexes were studied by TGA-FTIR and Differential Scanning Calorimetry (DSC). Both complexes decompose at moderate temperatures releasing CO and Fe(CO)₅ in the vapor phase leaving a residue of metallic iron and free C₆₀ or C₇₀ fullerenes that can be recovered by solvent extraction of the decomposition residue.