Annotation of the results obtained in 2021
On the third year of the project, modifying functional structures based on graphene and related materials in various environments methods were developed for in different chemical environments. Planar structures of field-effect transistors based on a graphene monolayer with locally changed properties of the band structure due to photochemical doping in an inert atmosphere have been formed. A linear dependence of the Dirac point shift on the power of the modifying laser pulse is found. In this case, a partial compensation of charge carriers occurs in an inert gas atmosphere, which indicates the recrystallization of a polymer monolayer on the graphene surface in an inert atmosphere. A change in the topology of the graphene channel in the vertical direction (reconfiguration with the formation of a 3D structure) to a height of up to 40 nm was found, depending on the laser radiation power. This configuration leads to an increase in the resistance of the field-effect transistor channel by no more than an order of magnitude, which may be associated with a change in local mechanical stresses in the graphene structure. The discovered phenomenon of simultaneous local changes in the chemical profile and topological structure can be promising for creating free-standing and three-dimensional configurations of functional elements using all-optical methods. Methods for the formation of suspended structures based on graphene and graphene oxide in the configuration of field-effect transistors with a free-standing channel have been developed. Techniques for laser ablation and modification of suspended structures during the formation of conducting channels are proposed. Taking into account a significant increase in the rigidity of structures with an increase in the number of layers in the formed film, methods of forming non-sagging channels of transistors are proposed. Suspended structures of conducting channels with laser-induced modifications are formed due to the introduction of local chemical inhomogeneities and mechanical stresses in graphene oxide under laser pulsed action. The effect of controlling the spatial position of laser-modified graphene oxide films using external weak ion irradiation is revealed. A mechanism is proposed for the difference in electron scattering in a laser-modified structure, which causes a gradient in the local heating of the modified and unmodified regions. A frequency-selective photothermoelectric effect is demonstrated in suspended planar reconstructed graphene oxide films during detection of ultrafast laser pulses. A mechanism for decreasing the photoresponse of the structure at high frequencies of the detected radiation due to the high sensitivity to the relaxation of photogenerated carriers on phonons is proposed. The processes of local photochemical reconstruction of two-dimensional structures based on MoS2 monolayers have been investigated. The mechanism of the local substitution reaction of sulfur with oxygen under the action of local optical radiation is proposed. Sensor structures based on a transistor with a modified MoS2 channel were manufactured, which have a sufficiently high mobility and an on / off current ratio of 10-100 in dry air. A high sensitivity of these structures to low NH3 concentrations was found. It was found that the gas sensitivity of MoS2 transistors to ammonia can be increased by modulating the gate potential. Applying a negative potential to the gate results in a 20% increase in sensor sensitivity to ammonia. Methods have been developed for creating optoelectronic sensor systems for converting photoelectronic processes in fluorescent protein molecules. Demonstrated functional elements with switchable transport properties due to the difference in the centers of covalent attachment of the protein to the nanotube, which provide different local molecular environment of the nanotube body. When a protein is attached to a nanotube by a hydrophobic part, a phototransistor with a selective sensitivity to 470 nm radiation with response and recovery times of 30 and 200 seconds, respectively, is realized. An optoelectronic memory element has been implemented by attaching a green fluorescent protein with a hydrophilic polar side to the body of a single nanotube during photochemical covalent bonding. The switching speed reaches 15 seconds with a state of preservation time of at least 10 minutes. Switching the state of the optoelectronic memory is provided by a short pulse on the lower gate of the transistor. In general, the properties of functional devices based on laser-modified and reconstructed carbon nanomaterials (graphene, nanotube) and transition metal halogenates have been investigated. Improvement of the properties of these materials in the composition of biological sensors was demonstrated, and planar single-molecular phototransducers and suspended nanochannels were created using optical methods.

 

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Annotation of the results obtained in 2019
Ultrashort (pico- or femtosecond) laser pulses began to reveal their scientific, technological and industrial potential in a wide field of application more than 20 years ago. Nonlinear effects arising from the strong interaction between photons and the atomic lattice of a material occurring at time scales of less than a few picoseconds have not been systematically considered. Ultrafast lasers can provide a new tool for maskless environmentally friendly processing of graphene and other two-dimensional layered materials in a wide range of subtractive and additive processes, opening up new physical properties and applications. Taking advantage of the synergistic effect of energy states in the atomic layers and ultrafast laser radiation, an unprecedented resolution of up to several nanometers can be achieved. A review of the current state of the art of ultrashort pulsed laser processing of 2D nanostructures is carried out. The main result of the analysis was the identification of the relationship between the rate of thermalization of hot electrons in graphene during femtosecond laser irradiation and structural changes in the material during two-photon modification of graphene. The review is designed as a review article for publication in a refereed journal. The modes of femtosecond functionalization of the graphene plane were tested with control of the parameters of laser exposure and subsequent analysis of the type of functional groups and structural changes in graphene. Based on the earlier theoretical calculations, a model was proposed for the formation of functional groups on graphene in the process of two-photon absorption of radiation. A method was developed for femtosecond laser functionalization of the surface of single single-walled CNTs on solid-state substrates in the channel of a field-effect transistor with a lower gate. Previous theoretical estimates suggest a significant presence of epoxy groups on the surface of the modified CNT region. This model is confirmed by a significant increase in hysteresis in the transient response of a transistor on a modified CNT. A significant (by an order of magnitude) increase in the resistance of nanotubes associated with the scattering of the main charge carriers by defects and an increase in the ratios of the on and off currents, which indicate an increase in the band gap in the modified nanotube, are also confirmed. Methods have been developed for binding organic molecules to a graphene surface. The following types of organic semiconductor molecules were selected: perylene diimide (PDI), polyaniline (PANI), pyrenebutyric acid ester (PBASE), Tris (4-carbazoyl-9-ylphenyl) amine (TCTA) to study the effects of doping with functionalized and non-functionalized graphene. In particular, PDI and PBASE molecules have a planar structure consisting of benzene rings, providing a fairly strong pi-pi bond with graphene. The effect of the precipitation of perylene molecules on the photosensitivity of the developed graphene structures was investigated. It was found that preliminary photoprocessing of graphene significantly changes the adsorption of organic molecules on the surface, which is associated with a change in surface states, including the surface energy of graphene. The dependence of the photocurrent of the graphene / graphene heterostructure modified by organic molecules after UV treatment of the modified CNT films was measured. A robust and scalable technology has been developed for the functionalization of graphene field effect transistors by inkjet printing. Semiconductor organic inks and methods for the deposition of organic molecules on the surface of graphene have been developed. The proposed technology is flexible and can provide modification of an array of MIS transistors based on graphene on the same substrate by various organic molecules, which can fine-tune the created photodetectors to specific wavelengths. Significant modulation of changes in the electrical properties of graphene functionalized by organic molecules is shown. The planar photosensitive transition was developed based on a partial coating of the graphene channel treated with short-wave (UV) radiation. The structure is sensitive to visible light with a photoresponse of up to 0.5 A / W for 532 nm. It is proposed that the photovoltaic effect is responsible for the generation of a photocurrent in the pn junction created by doping part of graphene with organic molecules when exposed to light. Based on the developed methods of photochemical modification of graphene, a sensor technology for mycotoxins (toxins secreted by molds) was implemented using transistors with a channel from graphene, the selectivity of which is provided by covalent sewing of specific aptamers. The transistor itself is created using CMOS compatible technology. It was demonstrated that a significant step in the assembly of the sensor layer is the processing of high-energy radiation, which ensures the formation of functional groups on the surface of graphene. At the next stage, the developed technologies for controlling the band gap in graphene with its modification by a laser will be used to increase the selectivity of sensor structures. In general, a comprehensive model was developed to describe the interaction of the graphene plane with the molecular environment in the presence of intense light exposure (short-wave (UV) or pulsed (fs)), which provides a transition to the development of new methods for creating functional structures based on 2D materials reconstructed by optical radiation.

 

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Annotation of the results obtained in 2020
Sensor structures based on single-walled carbon nanotubes modified with organic monolayers have been developed. A study was carried out of the effect of UV radiation and molecular environment on the optical, electrical and sensory properties of carbon nanotubes. The formation of PTCDA and TAPC crystals on the SWCNT surface was confirmed, while the polymer (PANI) forms a polymer film. To study the sensor properties in various gas atmospheres, a sensor array was created based on a clean layer of SWCNTs, SWCNTs treated with UV radiation, and six layers, where SWCNTs are functionalized with organic molecules. Graphene transistors, graphene structures on interdigital electrodes, and suspended graphene have been developed. The technological route was modified to create the possibility of supplying external electrical influences during laser processing of graphene, by increasing the contact areas, as well as increasing the area of ​​the transistor channel. The process of graphene transfer to finished electrodes in the form of an array of interdigital transducers (IDTs) of various metals (gold or platinum) formed on various types of substrates was investigated: traditional silicon oxide on silicon, glass, polyethylene terephthalate (PET) and polyimide (PI). ... MoS2 channel transistors have been developed. Transistor structures were created using a standard explosive photolithography process over the entire surface of the substrate. Also, transistors based on graphene oxide were investigated to develop methods for two-photon modification of these structures. Crystals were fabricated with transistors differing in the dimensions of the channel formed from graphene oxide: 5x10, 10x20, 20x10, 20x20 μm2. Using the methods of local femtosecond laser oxidation, heterojunctions are formed in a single nanotube for the creation of promising elements of optoelectronics and photovoltaics. It has been demonstrated that, at a high repetition rate of ~ 80 MHz of laser pulses, the oxidation of the carbon surface occurs not only in the region of passage of the laser spot, but also goes beyond it, due to the prevalence of thermal processes at high frequencies of fs pulses. The on-off current ratio after oxidation was> 10 ^ 4. A new design of a sensitive broadband photodetector with a high spatial resolution based on a carbon nanotube has been proposed, which provides not only an increase in the sensitivity of the photodetector by increasing the injection of charge carriers in the region of the formed junction, but also high flexibility in integrating this device. Exposure of graphene to a femtosecond laser pulse is determined by the presence of physical or chemical effects during irradiation. To achieve the predicted effect of changing the morphology of the transistor, it is necessary to calibrate the degree of exposure to femtosecond radiation on the graphene sheet. For this, CVD graphene from various manufacturers was used. The main tool for studying the effect of femtosecond laser radiation was Raman spectroscopy. As a result of the study, the required parameters of processing by femtosecond graphene radiation were obtained, at which the surface morphology changes. It was revealed that the ablation threshold begins to manifest itself, starting from 18 mW and higher at a speed of exposure in the range of 400-500 μm / s. The relationship between the processing parameters of graphene in the channels of transistors and changes in electrical properties was investigated. With a decrease in the slope of the transmission characteristics, the resistance of the structure also decreases with an increase in the dose of exposure to laser radiation, since the number of introduced defects and functional groups in graphene increases. The influence of the direction of polarization of optical radiation on the modification of graphene was also found. The difference in parameters between the samples modified with different directions of polarization along the direction of beam motion is associated with the interaction with the electron density in graphene. A method is proposed for the local femtosecond modification of graphene oxide, including controlled photochemical and photothermal changes in the film structure. The high precision laser processing of the upper layers of the film has been repaired, which can be used to create single-layer graphene transistors with a field effect. A method was developed for the covalent functionalization of transistors based on semiconductor single-walled carbon nanotubes by green fluorescent proteins (GFB). Sewing of ZFB was performed by covalent functionalization of CNTs using the click chemistry technique. The change in the electrical properties of CNTs was investigated when the ZFB is attached to its surface. Due to the azide group, the functionalization of the ZPB is donor in nature. In addition, the ZPB is an electron donor when exposed to light. A selective change in the conductivity of CNTs with attached ZPBs under the action of a certain wavelength was found. In conclusion, technological foundations for controlling the energy structure in carbon nanomaterials (graphene, nanotube) have been proposed, which provide a transition to the creation of new functional structures with improved properties, such as biological sensors, planar single-molecular photodetectors, and field-effect transistors.

 

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