M. Konstantinova

Ferromagnetic Nanomaterials Obtained by Thermal Decomposition of Ferrocene

Ferromagnetic micro and nano particles that are chemically resistant have been obtained by thermal decomposition of ferrocenes in a tightly closed chamber at high pressures. The investigation is focused on the influence of decomposition temperature, work atmosphere, temperature-change rate and process duration. According to the conditions, Fe3C, Fe3O4 and pure α-Fe particles have been created. Their composition and structure have been studied by Mössbauer spectroscopy, Scanning and Transmission Electron Microscopy, Electron Probe X-ray Micro Analysis and Energy Dispersive X-ray Spectrometry. In a tightly closed chamber, all components obtained during the decomposition process remain there. This difference to the widely-used Chemical Vapor Deposition method is very important. It inhibits the decomposition process and growth of ordered structures, preventing the end materials to be separated from each other. During the process, iron is liberated from the ferrocene molecule. Experiments have shown that it is highly chemically active to carbon and oxygen. For example, creation of carbide occured in conditions that are not allowed according to the iron-carbon phase diagram valid for bulk iron. Parallel to the reaction of iron with carbon (according to work atmosphere), the surplus of carbon atoms causes emerging of carbon nanoparticles.

Investigation of sorption by an electrode deposit

The electrode deposit obtained at a.c. and d.c. arc discharge on the anode or cathode is mechanically stiff and contains a large diversity of carbon structures of a fullerene nature with different forms and sizes. Gaps of various sizes separate the structures. The large surface area of the carbon structures, their locations with respect to each other and the large porosity of some of the structures, allow us to consider the material as promising in sorption and catalysis. The ability to reduce the amorphous phase carbon found within the deposit is discussed with the aim of seeking to increase the effective surface area and activation ability of the fullerene type carbon structures. The adsorption properties of the electrode deposit were investigated. A complete desorption was observed. Information was gained with regard to the cyclic sorption properties of the fullerene material under investigation. A narrow adsorbate fraction was employed in vapor adsorption studies for 11 organic compounds. The nature of adsorption for different classes of compounds was studied and the application of this material in organic compound gas chromatographic separation is discussed. It was found that when a fullerene type deposit is used as a sorbent, the retention volumes (Vg) for the organic compounds under investigation were significantly smaller than those manifested for carbon black material and hence the efficiency in column use is higher.

Carbon electrodes for solar cells and other semiconductor devices

Nanotube materials substantially improve the properties of carbon contacts. A low contact resistance, a high stability and quality doping control were obtained. Carbon parallel nanotube deposits were shown to be a convenient source of acceptor and donor impurities for activating the subcontact layers in solar cells, photoresistors and other devices.

Fullerene macro structures

Abstract At an arc discharge with CH 4 present in the gas ambient, conditions were created stimulating the simultaneous formation of single layer fullerene structures, which after being covered by many layers, yield multiple layer structures. As a result well formed regions containing numerous spherical, conical and polyhedral macro forms of the order of several micrometers were grown. Also obtained were regions containing large quantities of nanotubes over 10 μm in length. A model is proposed to explain the structure built up. To aid in the pyrolytic growth of cover layers the temperature of the deposit was maintained high by the “inverse method”.

Carbon macrostructures obtained at AC arc discharge

The differences in arc discharge specifics at various locations on the inside of the plasma cord lead to the growth of different carbon structures. Amorphous and low order structures with many defects were observed along the periphery of the deposits. Radially directed layers containing very small size graphite crystals predominate in the regions close to the periphery of the deposit. Conditions favor bucky-tube growth in the deposit center regions, the carbon macrostructures formed represent columns separated well apart, a diverse range of bucky tubes oriented at random have been observed in the spaces between the columns. After etching it was found that graphite crystals directed perpendicular to the axis of the deposit are contained in the column structures. It is shown that due to discharge fluctuations there arise layers that terminate the process of deposit growth. In the periodic process of resublimation, at some locations the layer structure breaks up and multiple-layer spherical perfect formations are synthesized at high temperatures. A wide pore carbon material suitable as a catalyst has been grown.

Growth of plasma pyrolytic carbon

Abstract At arc discharge in a methane ambient, the heat-up of the anodic and cathodic patches can under certain conditions be high enough to initiate gas pyrolysis. Then carbon deposits grow onto the electrodes within the patches. The anodic deposits have a column shape, while the cathodic deposits are radical growths of a hemispherical nature. Because the temperature is relatively low for arc discharge within the patches, the arc ion supply and the electric current limitation by means of the power supply are reasons why we have termed the process abnormal arc discharge. The growth of carbon deposits within the arc patches is observed for the first time and includes three stages, nucleation, growth along the shortest path between the anode and cathode and growth in a direction subtending an angle to the shortest path between the anode and cathode. An analysis of the thermal balance at the anodic and cathodic patches has been conducted, while the parameters of the processes influencing this phenomenon have also been discussed. The growth process observed is presented by a series of consecutive photos. At a work gas pressure of P = 30000Pa, an H 2 CH 4 ratio of 90 10 and a discharge power of 36 W, the growth rate is 15 mm/h. In accordance with the classification for carbon obtained at methane pyrolysis, the growths are considered as “compact silver grey carbon.”

Investigation of a.c. electroluminescent structures with fullerene inclusions

The influence of fullerene and carbon inclusions in the active layer of a.c. electroluminescent structures has been investigated. A considerable increase in brightness for samples with fullerene inclusions has been established. The mechanism of interaction between the fullerene molecules and the luminophor grains is considered.

Fullerene structure synthesis by DC arc discharge in ferrocene vapours

Abstract The DC discharge between carbon electrodes in Ar and ferrocene gas mixture ambient was used to obtain fullerene structures (FS) and FS with incorporated iron atoms. The used method has been developed by the authors and it supplies the electrode deposit growth with carbon from the ferrocene mainly. In contrast to the classical method for iron in fullerenes incorporation when iron or its compounds are inserted into the sublimated electrode and are supplied from there during electrode consummation, in the concerned method iron is provided to a substantial degree from the ferrocene, too. The existence of five already structured carbon atom rings in the ferrocene corresponds to the method when naphthalene is used for fullerene synthesis. This makes fullerene creation easier and increases the fabricated product quantity. The proposed gas mixture peculiarities and advantages are discussed. The differences and the advantages of the produced electrode deposits and the FS are pointed out and clarified.

Specifics at obtaining buckytubes in an arc discharge

Due to a diversity of physical processes taking place during arc discharge burning, the conditions at different locations within the discharge space are not the same. The analyses conducted address above all the temperature differences that arise on the electrode surfaces. The question of how to manage the processes of sublimation and condensation is discussed.

An Arc Discharge by Closely Situated Electrodes for Synthesis of Nanostructures

Geometry of electrodes, distance between them, work atmosphere and ambient temperature are the important factors, which determine quantity and variety of structures synthesized via arc discharge. Usually, electrodes of different cross-section are placed away from each other, allowing a large vapor stream directed into the reactor inside to be obtained. Generally, the anode is thinner than the cathode; it heats up to a high temperature, sublimates and supplies the carbon vapor required for nanoparticle synthesis. In contrast to this commonly used approach, when electrode dimensions are appropriately chosen and electrodes placed closely together, temperature interaction between them becomes considerable, discharge area constrains and hot electrodes can be used as heaters for the evaporation of materials of high melting point.