Elena D. Obraztsova

Mode-locked 1.93 μm thulium fiber laser with a carbon nanotube absorber

We report a ring-cavity thulium fiber laser mode locked with a single-wall carbon nanotube absorber used in transmission. A carboxymethyl cellulose polymer film with incorporated carbon nanotubes synthesized by the arc discharge method has an absorption coinciding with in the amplification bandwidth of a Tm-doped fiber. This laser is pumped by an erbium fiber laser at 1.57 μm wavelength and produces a 37 MHz train of mode-locked 1.32 ps pulses at 1.93 μm wavelength with an average output power of 3.4 mW.

Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles

Controlling chirality in growth of single-walled carbon nanotubes (SWNTs) is important for exploiting their practical applications. For long it has been conceptually conceived that the structural control of SWNTs is potentially achievable by fabricating nanoparticle catalysts with proper structures on crystalline substrates via epitaxial growth techniques. Here, we have accomplished epitaxial formation of monometallic Co nanoparticles with well-defined crystal structure, and its use as a catalyst in the selective growth of SWNTs. Dynamics of Co nanoparticles formation and SWNT growth inside an atomic-resolution environmental transmission electron microscope at a low CO pressure was recorded. We achieved highly preferential growth of semiconducting SWNTs (~90%) with an exceptionally large population of (6, 5) tubes (53%) in an ambient CO atmosphere. Particularly, we also demonstrated high enrichment in (7, 6) and (9, 4) at a low growth temperature. These findings open new perspectives both for structural control of SWNTs and for elucidating the growth mechanisms.

Predominant (6,5) Single-Walled Carbon Nanotube Growth on a Copper-Promoted Iron Catalyst

We have developed a magnesia (MgO)-supported iron-copper (FeCu) catalyst to accomplish the growth of single-walled carbon nanotubes (SWNTs) using carbon monoxide (CO) as the carbon source at ambient pressure. The FeCu catalyst system facilitates the growth of small-diameter SWNTs with a narrow diameter distribution. UV-vis-NIR optical absorption spectra and photoluminescence excitation (PLE) mapping were used to evaluate the relative quantities of the different (n,m) species. We have also demonstrated that the addition of Cu to the Fe catalyst can also cause a remarkable increase in the yield of SWNTs. Finally, a growth mechanism for the FeCu-catalyzed synthesis of SWNTs has been proposed.

A novel method for metal oxide nanowire synthesis.

Nanowires (NWs) of metal oxides (Fe(2)O(3), CuO, V(2)O(5) and ZnO) were grown by an efficient non-catalytic economically favorable method based on resistive heating of pure metal wires or foils at ambient conditions. The growth rate of iron oxide NWs exceeds 100 nm s(-1). Produced NWs were typically 1-5 microm long with diameters from 10 to 50 nm. The produced metal oxide NWs were characterized by means of SEM, TEM, EDX, XPS and Raman techniques. The field emission measurements from the as-produced CuO NWs were found to have a threshold field as low as 4 V microm(-1) at 0.01 mA cm(-2). The formation mechanism of the NWs is discussed.

D.c. arc plasma deposition of smooth nanocrystalline diamond films

We report on chemical vapour deposition growth of nanocrystalline (grain size 30–50 nm) diamond films of 100 nm to 2 μm thickness in methane-rich mixtures. A d.c. arc discharge in CH4H2Ar gas mixtures with a methane percentage CH4(CH4 + H2) varied from 10% to 100% was used for diamond deposition on Si substrates seeded with ultrafine (5 nm) diamond particles. The films obtained were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray excited Auger electron spectroscopy. Remarkably well-crystallized diamond films were produced even in hydrogen-free gas mixtures. Raman spectra confirmed the nanocrystalline structure of all the films examined. The film hardness measured with a nanoindenter was in the range 70–85 GPa typical for diamond, the highest values corresponding to 100% methane content. The films were very smooth with surface roughness Ra < 20 nm. The essential improvement in surface smoothness was obtained by means of laser-induced disintegration of coalesced seeding particles.

DNA interaction with single-walled carbon nanotubes: a SEIRA study

Abstract Interaction of nucleic acids with graphite powder and SWCNT was studied by surface enhanced infrared absorption spectroscopy. The analysis of DNA-SWCNT complex vibrational modes shows that the numerous structural changes in DNA are connected to appearance of new sugar and bases conformations, changes in phosphate vibrations, which may be interpreted as A–B conformation transition and stabilisation of structure in some DNA fragments. A slight graphite influence on the DNA structure has been registered. The spectroscopic data could be explained by the model of DNA interaction with SWCNT based on wrapping of nucleic acid molecules around carbon nanotubes proposed by R. Smalley. A similar situation seems to occur in chromosome during DNA assembling by histones.

177fs erbium-doped fiber laser mode locked with a cellulose polymer film containing single-wall carbon nanotubes

A mode-locked soliton erbium-doped fiber laser generating 177fs pulses is demonstrated. The laser pumped by a 85mW, 980nm laser diode emits 7mW at 1.56μm at a pulse repetition rate of 50MHz. Passive mode locking is achieved with a saturable absorber made of a high-optical quality film based on cellulose derivative with dispersed carbon single-wall nanotubes. The film is prepared with the original technique by using carbon nanotubes synthesized by the arc-discharge method.

Aligned carbon nanotube films for cold cathode applications

Thin film material of oriented multiwall carbon nanotubes was obtained by noncatalytical chemical vapor deposition in a glow-discharge plasma. The film phase composition, surface morphology, and structural features were studied by Raman and electron microscopy techniques. Low-voltage electron field emission of thin film nanotube material was obtained and examined in diode configuration. The I–V curves in Fowler–Nordheim coordinates were linear and the corresponding threshold average field was about 1.5 V/μm. The emission current density was up to 50 mA/cm2 at the field of 5 V/μm. The emission site density reached 107 cm−2 at the same value of electric field.

Structural measurements for single-wall carbon nanotubes by Raman scattering technique

The single-wall carbon nanotubes grown by different techniques have been investigated by Roman scattering and high resolution transmission electron microscopy (HRTEM). The tube diameter values and the tube distribution over diameter have been estimated from the position and shape of the low-frequency band in the Raman spectrum containing the ‘breathing” modes. The diameter-dependent enhancement of the Raman signals from the different nanotube fractions occurred not only due to optical resonance with the laser excitation energy, but also due to thermo-induced resonances. The low-field electron emission from the single-wall carbon nanotube material has been measured. The threshold fields were 0.75–2 V/μm, the emission current reached the value 15 mA/cm2 at fields of 10 V/μm.

Broadband Light-Induced Absorbance Change in Multilayer Graphene

We report the ultrafast light-induced absorbance change in CVD-grown multilayer graphene. Using femtosecond pump-probe measurements in 1100-1800 nm spectral range, we revealed broadband absorbance change when the probe photon energy was higher than that of the pump photon. The observed phenomenon is interpreted in terms of the Auger recombination and impact ionization playing a significant role in the dynamics of photoexcited carriers in graphene.