Maziar Shakerzadeh

Re-ordering Chaotic Carbon: Origins and Application of Textured Carbon

Formation of nanocrystals with preferred orientation within the amorphous carbon matrix has attracted lots of theoretical and experimental attentions recently. Interesting properties of this films, easy fabrication methods and practical problems associated with the growth of other carbon nanomaterials such as carbon nanotubes (CNTs) and graphene gives this new class of carbon nanostructure a potential to be considered as a replacement for some applications such as thermal management at nanoscale and interconnects. In this short review paper, the fabrication techniques and associated formation mechanisms of these nanostructured films have been discussed. Besides, electrical and thermal properties of these nanostructured films have been compared with CNTs and graphene.

Electronic conductance of ion implanted and plasma modified polymers

The authors used the plasma immersion ion implantation and deposition technique to modify polyethylene terephthalate (PET) and by using conductive atomic force microscope, the spatial distribution of ∼10nm size titanium nanoclusters embedded in PET matrices were observed. The I-V plots showed typical metal-semiconductor junction conductivity between the conductive tip and the surface. In addition, the authors also measured the temperature dependent conductivity and fitted it well to the Mott law, which implied that the conductance arose from electron hopping process. Such technique to create the surface structure of metal/polymer nanocomposites may open an alternative way for plastic nanoelectronics.

Growth of few-wall carbon nanotubes with narrow diameter distribution over Fe-Mo-MgO catalyst by methane/acetylene catalytic decomposition

Few-wall carbon nanotubes were synthesized by methane/acetylene decomposition over bimetallic Fe-Mo catalyst with MgO (1:8:40) support at the temperature of 900°C. No calcinations and reduction pretreatments were applied to the catalytic powder. The transmission electron microscopy investigation showed that the synthesized carbon nanotubes [CNTs] have high purity and narrow diameter distribution. Raman spectrum showed that the ratio of G to D band line intensities of IG/ID is approximately 10, and the peaks in the low frequency range were attributed to the radial breathing mode corresponding to the nanotubes of small diameters. Thermogravimetric analysis data indicated no amorphous carbon phases. Experiments conducted at higher gas pressures showed the increase of CNT yield up to 83%. Mössbauer spectroscopy, magnetization measurements, X-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction were employed to evaluate the nature of catalyst particles.

Thickness dependency of field emission in amorphous and nanostructured carbon thin films

Thickness dependency of the field emission of amorphous and nanostructured carbon thin films has been studied. It is found that in amorphous and carbon films with nanometer-sized sp2 clusters, the emission does not depend on the film thickness. This further proves that the emission happens from the surface sp2 sites due to large enhancement of electric field on these sites. However, in the case of carbon films with nanocrystals of preferred orientation, the emission strongly depends on the film thickness. sp2-bonded nanocrystals have higher aspect ratio in thicker films which in turn results in higher field enhancement and hence easier electron emission.

Structure and wetting properties of metal polymer nanocomposites

Polystyrene thin films of thickness 180-200 nm are modified by plasma immersion ion implantation and deposition (PIII&D) technique together with titanium filtered cathodic vacuum arc. The surface structure of modified films turns into a metal polymer nanocomposite where Ti nanoclusters of spatial size 10 - 20 nm are embedded in polystyrene matrices. Such structural formation is the interplay between ion sputtering and ion diffusion effect. The wetting properties of this nanocomposite, such as contact angle aging effect and hysteresis are investigated. The changes in various properties are believed to be due to structure of polymer nanocomposites as well as the basic principles of ion polymer interaction.

The effect of high deposition energy of carbon overcoats on perpendicular magnetic recording media

High-energy carbon deposition techniques provide thin overcoats with high corrosion and wear protection for magnetic recording media applications. The effect of high-energy (0–300 V substrate bias) deposition on the implantation induced changes in magnetic and structural properties of granular perpendicular magnetic recording media is studied. To observe subtle changes in a thin region of recording media, antiferromagnetically coupled layer structure was used. Clear changes in the magnetic properties, observed as a function of the carbon deposition energy, correlate with other measurements such as X-ray photoelectron spectroscopy, indicating the need to consider such effects when designing media and overcoat.

Nonvolatile Memory Effects of ZnO Nanoparticles Embedded in an Amorphous Carbon Layer

Nonvolatile memory devices utilizing ZnO nanoparticles (NPs) embedded in an amorphous carbon (a-C) dielectric layer were investigated by capacitance–voltage (C–V) measurements. C–V curves for the Al/ZnO NPs embedded in an amorphous carbon layer/SiO2/p-Si capacitor at 298 K showed a clockwise hysteresis with flat band voltage shift due to charge trapping in the ZnO NPs. Capacitance–time measurements showed that the devices exhibited excellent memory retention ability under ambient conditions. Operating mechanism for the memory devices was proposed based on the C–V results.

Laser Heating-Induced Degradation of Ultrathin Media Carbon Overcoat for Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording (HAMR) is a technique for overcoming the superparamagnetic limit and enabling large increases in the storage density of hard disk drives. A tiny area of the magnetic recording media has to be heated up to a high temperature with a laser to lower the coercivity temporarily before information can be written on the area. The possible degradation of the ultrathin media carbon overcoat induced by the laser heating is a concern. In this paper, the laser heating-induced degradation of ultrathin a-C:Nx, a-C:Hx, and a-C overcoats on HAMR media is studied. Surface topography changes induced by the laser heating are evaluated with atomic force microscopy and structure changes with the visible Raman spectrum and X-ray photoelectron spectroscopy (XPS). Laser heating areas are analyzed with time-of-flight secondary ion mass spectrometry and XPS to reveal the underlying mechanism of the degradations. It is found that at a proper HAMR writing temperature and for a total laser heating duration corresponding to a five-year drive life, the surface topography, structure, and composition of the a-C:Nx overcoat are changed by the laser heating. However, the surface topographies of the a-C:Hx and a-C overcoats are not changed. The structure and composition of the a-C:Hx and a-C overcoats are also not changed much. Interlayer diffusion between the carbon overcoat and the underlying magnetic layer is confirmed in the laser heating area for all the three overcoats.

Microstructure and electrical properties of in-situ annealed carbon films

The microstructure and electrical properties of in-situ annealed carbon films is studied in this paper. The structure of the films is studied by transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The microstructure of the films strongly depends on the deposition temperature for the films deposited at high temperatures (higher than 400° C). However, at low temperatures the substrate bias is the other crucial factor which governs the microstructure of the film. Electrical conductivity of the film strongly depends on the formation of preferred orientation in the microstructure of the films.

Structural and wetting properties of metal polymer nanocomposites

Polystyrene thin films of thickness 180-200 nm are modified by plasma immersion ion implantation and deposition (PIII&D) technique together with titanium filtered cathodic vacuum arc. The surface structure of modified films turns into a metal polymer nanocomposite where Ti nanoclusters of spatial size 10 - 20 nm are embedded in polystyrene matrices. Such structural formation is the interplay between ion sputtering and ion diffusion effect. The wetting properties of this nanocomposite, such as contact angle aging effect and hysteresis are investigated. The changes in various properties are believed to be due to structure of polymer nanocomposites as well as the basic principles of ion polymer interaction.