Depozice uhlíkových nanotrubek metodou depozice z plynné fáze s asistencí plazmatu

Carbon nanotube properties provoked interest in many fields of application but there is still need to develop deposition techniques, which enable precise control of nanotubes positioning, alignment and properties. Chemical vapor deposition (CVD) methods and lately also plasma enhanced CVD (PECVD) are most promising to reach this goal. In the first part of the article we will briefly describe carbon nanotubes structure and properties and review the necessary conditions and possible control mechanisms used in PECVD deposition method. In the second part, examples of two deposition techniques, one working at a low pressure and one at an atmospheric pressure, will be described and reached results analyzed

Nanocrystalline diamond films deposition by PECVD in ASTEX type microwave reactor

Nanocrystalline diamond film was deposited by microwave CVD in the ASTeX type reactor on a mirror polished (111) oriented n-doped silicon substrate. The deposition mixture consisted of 9 pct of methane in hydrogen. The applied microwave power (2.45 GHz)and pressure were 850 W and 7.5 kPa, respectively. The substrate temperature was 1 090 K. The diamond nucleation process was enhanced by rf induced dc selfbias of -125 V. The film exhibited very low roughness (rms of heights 9.1 nm). Its hardness and elastic modules were 70 and 375 GPa, respectively. The optical constants were determined by combination of spectroscopic ellipsometry and reflectometry employing the Rayleigh-Rice theory for the roughness and the dispersion model of optical constants based on the parameterization of densities of states. The deposition rate was 57 nm/min including the 5 min nucleation step

Magnetic Properties of γ−Fe2O3γ-Fe_2O_3 Nanopowder Synthesized by Atmospheric Microwave Torch Discharge

A nanopowder containing $γ-Fe_2O_3$ particles was synthesized by adding a gas mixture of $H_2//Fe(CO)_5$ into a microwave torch discharge at 1 bar. The presence of $γ-Fe_2O_3$ phase was confirmed by powder X-ray diffraction (mean crystallite size $d_{XRD}$=24 nm). The dominating characteristic sextets of $γ-Fe_2O_3$ were identified in the Mössbauer spectrum taken at 5 K. The presence of pure $Fe_3O_4$ in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported

Magnetic Properties of γ-Fe₂O₃ Nanopowder Synthesized by Atmospheric Microwave Torch Dischargie. Acta Physica Polonica A 122, 9 (2012), ERRATUM

A nanopowder containing γ-Fe₂O₃ particles was synthesized by adding a gas mixture of H₂/Fe(CO)₅ into a microwave torch discharge at 1 bar. The presence of γ-Fe₂O₃ phase was confirmed by powder X-ray diffraction (mean crystallite size $d_{XRD}$=24 nm). The dominating characteristic sextets of γ-Fe₂O₃ were identified in the Mössbauer spectrum taken at 5 K. The presence of pure $Fe_3 O_4$ in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported

Magnetic Properties of γ-Fe 2

A nanopowder containing $γ-Fe_2O_3$ particles was synthesized by adding a gas mixture of $H_2//Fe(CO)_5$ into a microwave torch discharge at 1 bar. The presence of $γ-Fe_2O_3$ phase was confirmed by powder X-ray diffraction (mean crystallite size $d_{XRD}$=24 nm). The dominating characteristic sextets of $γ-Fe_2O_3$ were identified in the Mössbauer spectrum taken at 5 K. The presence of pure $Fe_3O_4$ in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported

Nanocrystalline α-Fe Layer Examined by Mössbauer Spectrometry

A few micrometers thick nanocrystalline α-Fe layer with the mean crystallite size $d_{XRD}$=14 nm was deposited in low-pressure microwave plasma, using $Fe(CO)_{5}$ vapour. Its nanocrystalline character was proved on its surface under SEM (surface was formed of deposited nanoparticles) and in its volume using TEM (deposited nanoparticles were stacked up, creating columns). No significant iron oxide phases were observed in the transmission $\text{}^{57}Fe$ Mössbauer spectrum measured at 5 K nor in the surface-sensitive $\text{}^{57}Fe$ conversion electron Mössbauer spectrum measured at 293 K

Atmospheric-pressure microwave torch discharge generated gamma-Fe2O3 nanopowder

Microwave torch discharge ignited in Ar at 1 bar was used for the synthesis of gamma-Fe2O3 nanoparticles. A double-walled nozzle electrode enabled to introduce gases separately: Ar flowed in the central channel, whereas the mixture of H-2/O-2/Fe(CO)(5) was added into the torch discharge through an outer channel. The composition and properties of the synthesized nanopowders were studied by TEM, XRD, Raman and Mossbauer spectroscopies. Basic magnetic measurements at low/high temperatures were performed. The gamma-Fe2O3 phase with the mean crystallite size of 24 nm was identified by XRD in the representative sample. The measured Raman spectrum matched well those reported for gamma-Fe2O3 powders in the literature. In the transmission Mossbauer spectrum measured at 5 K the two sextets characteristic for gamma-Fe2O3 were clearly identified. No change in specific magnetic moment typical of Fe3O4 at its Verwey temperature was observed on the zero field curve, which smoothly increased with temperature. Neither Fe3O4 nor alpha-Fe2O3 were present in the sample. We also report on the high-temperature magnetic properties of the representative sample and describe its structural changes and phase transformations up to 1073 K

Effects of metal underlayer grain size on carbon nanotube growth

In this paper we demonstrate that the nucleation density of single-walled carbon nanotubes (SWNTs), formed by thermal catalytic chemical vapor deposition, strongly depends on the grain size of Al underlayers covered with a native oxide (Al/Al2O3). By varying the Substrate temperature during Al sputter deposition it was possible to investigate the effect of Al grain size on growth without inducing changes in the underlayer thickness, surface chemistry, or any other growth parameter. The resulting SWNT growth structures ranged from low-density 2D nanotube networks that lay across the surface of the substrate to high density 3D nucleation which gave rise to vertical "forest" growth. The height of the SWNT "forest" was observed to increase with increasing Al deposition temperature as follows, 200 > 100 > 60 > 20 degrees C on Si/Al but in the order 100 > 200 > 60 > 20 degrees C on SiO2/Al substrates for fixed growth conditions. The differences in the SWNT growth trends on Si and SiO2 substrates are believed to be due to the existence of an optimal Al/Al2O3 underlayer grain size for the formation of active catalytic nanoparticles, with larger Al/Al2O3 grains forming on SiO2 than Si at a fixed substrate temperature. Numerous surface analysis techniques including AFM, XPS, FESEM, TEM, and Raman spectroscopy have been employed to ascertain that the observed changes in nanotube growth for this system are related primarily to changes in underlayer morphology