I. I. Bobrinetskiy

Photophysical and photochemical effects in ultrafast laser patterning of CVD graphene

The micro-scale patterns in graphene on Si/SiO2 substrate were fabricated using ultrashort 515 nm laser pulses. For both picosecond and femtosecond laser pulses two competitive processes, based on photo-thermal (ablation) and photochemical (oxidation/etching) effects, were observed. The laser-induced etching of graphene starts just below the threshold energy of graphene ablation: 1.7 nJ per 280 fs pulse and 2.7 µJ per 30 ps pulse. Whilst etching is not sensitive to thermal properties of graphene and provides uniform patterns, the ablation, in contrast, is highly affected by defects in the graphene structure like wrinkles and bilayer islands. The mechanisms of ultrafast laser interaction with graphene are discussed.

Features of flexible transparent conducting films based on polyaniline-carbon nanotube composite

We propose a new concept in the formation of transparent conducting films based on single-walled carbon nanotubes (SWNTs) and polyaniline (PANI) on a flexible polyethylene naphthalate substrate. It is established that the resistance of SWNT-PANI composite films decreases to less than half as compared to pure nanotubes, while the transparency is retained. Mechanisms responsible for a change in the conductivity of composite molecular systems are discussed based on differences in the transport of charge carriers in nanotubes and the polymer with allowance for their interaction.

Photodetectors based on single-walled carbon nanotubes and thiamonomethinecyanine J -aggregates on flexible substrates

The present paper is devoted to observations of the photoresistive effect in multilayer structures with a sensitive layer of J-aggregates of thiamonomethinecyanine polymethine dye and a transparent electrode of a conductive carbon-nanotube network on a flexible polyethylenenaphtalate substrate. The effect of narrow-band emission with a wavelength of 465 nm on a change in the conductivity of the fabricated structures is studied. The prepared samples are studied by atomic-force microscopy, Raman spectroscopy, and spectrophotometry methods. It is shown that these structures are photosensitive to the indicated spectral region, and the dye layer is a film of dye J-aggregates. The change in the sample conductivity upon exposure to light one hundred times exceeds the dark conductivity. In general, the principal possibility of developing a photoresistive detector based on J-aggregates of cyanine dyes on flexible supports on account of the use of transparent and conductive carbon-nanotube layers is shown.

Molecular doping of single-walled carbon nanotube transistors: optoelectronic study

Single-walled carbon nanotubes (SWCNT) are a promising material for future optoelectronic applications, including flexible electrodes and field-effect transistors. Molecular doping of carbon nanotube surface can be an effective way to control the electronic structure and charge dynamics of these material systems. Herein, two organic semiconductors with different energy level alignment in respect to SWCNT are used to dope the channel of the SWCNT-based transistor. The effects of doping on the device performance are studied with a set of optoelectronic measurements. For the studied system, we observed an opposite change in photo-resistance, depending on the type (electron donor vs electron acceptor) of the dopants. We attribute this effect to interplay between two effects: (i) the change in the carrier concentration and (ii) the formation of trapping states at the SWCNT surface. We also observed a modest ~4 pA photocurrent generation in the doped systems, which indicates that the studied system could be used as a platform for multi-pulse optoelectronic experiments with photocurrent detection.

Effect of an Organic Molecular Coating on Control Over the Conductance of Carbon Nanotube Channel

It is shown that the coating of carbon nanotubes with molecules with a constant dipole moment changes the conductance of the tubes due to a variation in the structure of energy levels that participate in charge transport. The I–V characteristics of the investigated structures exhibit significant dependence of the channel conductance on the gate potential. The observed memory effect of conductance level can be explained by the rearrangement of polar groups and molecules as a whole in an electric field. The higher the dipole moment per unit length and the weaker the intermolecular interaction, the faster the rearrangement process is

Photosensitive in-plane junction in graphene field effect transistor modified under femtoseconds laser irradiation

The development of planar functional junction provides continuous, single-atom thick, in-plane integrated circuits. The production of atomic contacts of different materials (hetero/homostructures) is still a challenging task for 2D materials technology. In this paper we describe a new method of formation of a photosensitive junction by femtosecond laser pulses patterning of graphene FET. The laser-induced oxidation of graphene goes under high intensity laser pulses, which provide nonlinear effects in graphene like multiphoton absorption and hot carrier generation. The process of laser induced local oxidation is studied on single-layer graphene FET produced by wet transfer of CVD grown graphene on copper foil onto a Si/SiO2 substrate. The 280 fs laser with 515 nm wavelength with various pulse energies is applied to modify of local electrical and optical properties of graphene. Thus, the developed process provides mask-less laser induced in-plane junction patterning in graphene. The scale of local heterojunction fabrication is about 1 μm. We observe that with an increasing of the laser fluence the number of defects increases according to two different mechanism for low and high fluences, respectively. The change of the charge carrier concentration causes the Dirac point shift in produced structures. We investigate the photoresponse in graphene junctions under fs pulsed laser irradiation with subthreshold energies. The response time is rather high while relaxation time is large because of charge traps at the graphene/SiO2 interface.

Femtosecond laser-induced CNT heterojunction as visible light photodetector

Carbon nanotubes (CNTs) are one of the most promising materials for advanced electronic applications, due to its extraordinary chemical and physical properties. Non-linear interactions between photons and carbon bonds provide the possibility to fabricate unique photonic devices. In this paper we present the new technological route of single walled CNTs (SWCNTs) modification using femtosecond (fs) laser pulses to produce junctions in nanotubes through multiphoton oxidation of the carbon lattice with nanoscale resolution. SWCNTs were deposited onto Si/SiO2 substrate using gas-phase process based on thermal decomposition of ferrocene in the presence of carbon monoxide. Source and drain 100/20 nm Au/Ti electrodes were fabricated by photolithography, the gate electrode was p++ Si substrate. Samples were irradiated via fs laser with different energy fluence. Fs laser pulses at low energies were used to perform photocurrent measurements. Not modified SWCNTs and structures modified upon fs laser demonstrate a huge difference for light induced charge generation. We observed significant changes in optical and electrical properties of SWCNTs after the modification. Varying the parameters of power and laser scanning speed we can change the level of local oxidation of SWCNT and photocurrent in produced photodetectors.

On the high charge-carrier mobility in polyaniline molecular channels in nanogaps between carbon nanotubes

This study is devoted to the fabrication of molecular semiconductor channels based on polymer molecules with nanoscale electrodes made of single-walled carbon nanotubes. A reproducible technology for forming nanoscale gaps in carbon nanotubes using a focused Ga+ ion beam is proposed. Polyaniline molecules are deposited into nanogaps up to 30 nm wide between nanotubes by electrophoresis from N-methyl-2-pyrrolidone solution. As a result, molecular organic transistors are fabricated, in which the field effect is studied and the molecular-channel mobility is determined as 0.1 cm2/(V s) at an on/off current ratio of 5 × 102.

Narrow-Spectrum Photosensitive Structures Based on J-Aggregates of Cyanine Dyes

The fabrication processes for narrow-spectrum photosensitive structures based on J-aggregates of cyanine dyes are studied. Two technological approaches are proposed: the electrokinetic deposition of single J-aggregates in the planar electrode configuration and the fabrication of multilayer structures with a sensitive layer of cyanine dye J-aggregates and a transparent electrode made of a conductive carbon nanotube network on a flexible polyethylene naphthalate substrate.

Ultrafast laser patterning of graphene

This paper describes the recent results in ultrafast (femtoseconds and picoseconds) pulsed laser patterning of graphene films (single layer graphene, graphene oxide (GO)). We investigated such effects of nonlinear optical interaction like selective laser ablation of graphene, laser reduction of graphene oxide and local functionalization (oxidation) of graphene based on multiphoton absorption for microelectrode patterning. The graphene oxide and reduction was demonstrated under femtosecond laser pulses as well as fine ablation for monolayer GO films under ps laser pulses. We demonstrated the patterned laser reduction over the GO film leads to minimum in resistance for laser fluence because of interplay of chemical and thermal effects in carbon lattice and photons. The micro-scale patterns in graphene on SiO2 substrates were fabricated using ultrashort 515 nm laser pulses. For both picosecond and femtosecond laser pulses two competitive processes, based on photo-thermal (ablation) and photochemical (oxidation/etching) effects, were observed. The laser-induced etching of graphene starts just below the threshold energy of graphene ablation. The mechanisms of ultrafast laser interaction with graphene are discussed. Patterned graphene was investigated by AFM, microRaman, SEM and sheet resistance measurements and other techniques. The mechanisms of ultrafast laser interaction with graphene are discussed. The comprehensive models of graphene oxidation/reduction are suggested.