Nanoscale deformations and corrugations occur in graphene-like two-dimensional materials during their incorporation into hybrid structures and real devices, such as sensors based on surface-enhanced ...Raman scattering (SERS-based sensors). The structural features mentioned above are known to affect the electronic properties of graphene, thus highly sensitive and high-resolution techniques are required to reveal and characterize arising local defects, mechanical deformations, and phase transformations. In this study, we demonstrate that gap-mode tip-enhanced Raman Scattering (gm-TERS), which offers the benefits of structural and chemical analytical methods, allows variations in the structure and mechanical state of a two-dimensional material to be probed with nanoscale spatial resolution. In this work, we demonstrate locally enhanced gm-TERS on a monolayer graphene film placed on a plasmonic substrate with specific diameter gold nanodisks. SERS measurements are employed to determine the optimal disk diameter and excitation wavelength for further realization of gm-TERS. A significant local plasmonic enhancement of the main vibrational modes in graphene by a factor of 100 and a high spatial resolution of 10 nm are achieved in the gm-TERS experiment, making gm-TERS chemical mapping possible. By analyzing the gm-TERS spectra of the graphene film in the local area of a nanodisk, the local tensile mechanical strain in graphene was detected, resulting in a split of the G mode into two components, G
+
and G
−
. Using the frequency split in the positions of G
+
and G
−
modes in the TERS spectra, the stress was estimated to be up to 1.5%. The results demonstrate that gap-mode TERS mapping allows rapid and precise characterization of local structural defects in two-dimensional materials on the nanoscale.
Nanoscale deformations and corrugations occur in graphene-like two-dimensional materials during their incorporation into hybrid structures and real devices, such as sensors based on surface-enhanced Raman scattering (SERS-based sensors).
Tip-enhanced Raman scattering (TERS) has recently emerged as a powerful technique for studying the local properties of low dimensional materials. Being a plasmon driven system, a dramatic enhancement ...of the TERS sensitivity can be achieved by an appropriate choice of the plasmonic substrate in the so-called gap-mode configuration. Here, we investigate the phonon properties of CdSe nanocrystals (NCs) utilizing gap-mode TERS. Using the Langmuir-Blodgett technique, we homogeneously deposited submonolayers of colloidal CdSe NCs on two different nanostructured plasmonic substrates. Amplified by resonant gap-mode TERS, the scattering by the optical phonon modes of CdSe NCs is markedly enhanced making it possible to observe up to the third overtone of the LO mode reliably. The home-made plasmonic substrates and TERS tips allow the analysis of the TERS images of CdSe phonon modes with nanometer spatial resolution. The CdSe phonon scattering intensity is strongly correlated with the local electromagnetic field distribution across the plasmonic substrates.
We demonstrated resonant/non-resonant gap-mode TERS on CdSe nanocrystals analyzing of LO (up to 3rd order), SO/TO phonons, as well as Se vibrational modes.
Surface- and tip-enhanced resonant Raman scattering (resonant SERS and TERS) by optical phonons in a monolayer of CdSe quantum dots (QDs) is demonstrated. The SERS enhancement was achieved by ...employing plasmonically active substrates consisting of gold arrays with varying nanocluster diameters prepared by electron-beam lithography. The magnitude of the SERS enhancement depends on the localized surface plasmon resonance (LSPR) energy, which is determined by the structural parameters. The LSPR positions as a function of nanocluster diameter were experimentally determined from spectroscopic micro-ellipsometry, and compared to numerical simulations showing good qualitative agreement. The monolayer of CdSe QDs was deposited by the Langmuir-Blodgett-based technique on the SERS substrates. By tuning the excitation energy close to the band gap of the CdSe QDs and to the LSPR energy, resonant SERS by longitudinal optical (LO) phonons of CdSe QDs was realized. A SERS enhancement factor of 2 × 10
3
was achieved. This allowed the detection of higher order LO modes of CdSe QDs, evidencing the high crystalline quality of QDs. The dependence of LO phonon mode intensity on the size of Au nanoclusters reveals a resonant character, suggesting that the electromagnetic mechanism of the SERS enhancement is dominant. Finally, the resonant TERS spectrum from CdSe QDs was obtained using electrochemically etched gold tips providing an enhancement on the order of 10
4
. This is an important step towards the detection of the phonon spectrum from a single QD.
Electromagnetic enhancement of CdSe quantum dots in surface and tip-enhanced Raman scattering with improved sensitivity.
We report on the study of localized surface plasmon resonances (LSPRs) arising in arrays of metal (Au) nanoclusters, dimers, and nanoantennas under the influence of external electromagnetic ...radiation. Using nanolithography, the plasmonic arrays with different morphologies including cylindrical nanoclusters and dimers, linear and H-type nanoantennas were fabricated. Their LSPR frequencies were determined from the analysis of optical reflection and IR spectra. LSPR frequency depends strongly on morphology of metal nanostructures and is varied from visible to terahertz spectral range with variation of the structures from cylindrical nanoclusters to the nanoantennas with a high aspect ratio. We established the interconnection between the structural parameters of the plasmonic arrays and their LSPR frequencies based on the results of 3D electrodynamic simulations.
This paper presents a combustion model for a solid propellant consisting of a matrix capable of self-sustained combustion and particles of a polydisperse coolant distributed in it. Heat transfer ...between the exothermically decomposing matrix and coolant particles in the condensed phase and the gas-phase products of their gasification. The leading reaction in the region of the matrix and the coolant evaporation surface are assumed to be located at the interface. The heat consumption for coolant evaporation is determined by the depth of coolant gasification during passage through the interface, which depends on the coolant particle size and the propellant burning rate. Parametric identification of the model was carried out using the results of sieve analysis of the coolant particle size distribution and an experimental dependence of the burning rate on pressure. It is shown that the model can be used to predict and provide the required ballistic performance of the propellant during its development and series production.
We report on a study of surface-enhanced infrared absorption (SEIRA) by optical phonons in monolayers (MLs) of CdSe, CdS, and PbS nanocrystals (NCs) deposited on arrays of linear nanoantennas the ...optimized structural parameters of which allow coupling between the localized surface plasmon resonance (LSPR) and diffraction modes in the far-infrared spectral region. The Langmuir–Blodgett technique was used for homogeneous deposition of the NCs. The structural parameters of the arrays and the NC MLs were determined by scanning electron microscopy. According to the three-dimensional electrodynamic simulations of the electromagnetic field distribution around the antennas, the maximal SEIRA enhancement is realized for an array period of about 15 μm when the energy of a diffraction mode coincides with that of the LSPR mode. SEIRA experimental results are in perfect quantitative agreement with the simulation. The maximal SEIRA enhancement is observed for the nanoantenna length and transverse periodicity predicted by the simulations. The frequency positions of the absorption features indicate that only the NC surface optical phonons are activated in the SEIRA spectra.
Condensed combustion products of model propellants based on aluminum boride in the combustion chamber of the gas generator of a ducted rocket engine have been studied. The mass fraction of the ...condensed combustion products, their chemical composition, and their particle size distribution have been determined. It has been demonstrated that the condensed combustion products mainly contain boron compounds with carbon, nitrogen, and oxygen, and it is in this form that boron enters the secondary combustion chamber of the ducted rocket engine. The mass fraction of elemental boron in the condensed combustion products does not exceed 15% and decreases with increasing pressure. It has been found that, regardless of the types and contents of the major components of the model propellants, there are no large (more than 100 μm in size) particle conglomerates at the outlet of the gas-generator nozzle. A comparison of the experimental data with the results of thermodynamic calculations indicates that the calculation methods should be corrected for the nonequilibrium of the combustion products.
The purpose of the work is to carry out the segmentation of modern Russian society by generational groups, based on the theory of modern generational segmentation. Segmentation is the first necessary ...step in the analysis of each generational group in terms of lifestyle and value picture of the world. In accordance with the Russian cultural and historical development the authors identified 6 generations, whose representatives live in modern Russian society: “revolutionary generation”, “military generation”, “thaw generation”, “stagnation generation” (generation X), “fracture generation” (generation Y), “digital generation” (generation Z). The article also reveals the essence of the category “generation” from the point of view of sociology.
We report on the study of surface enhanced infrared absorption (SEIRA) by steroid hormone cortisol molecules with different concentrations deposited on linear Au nanoantenna arrays. Localized surface ...plasmon resonances (LSPRs) arise in the nanoantennas under the influence of external electromagnetic radiation. LSPR frequency depends mainly on the nanoantenna length and can vary from the visible to the terahertz range. We establish the ratio between the structural parameters of nanoantenna arrays and LSPR frequencies based on the results of 3D electrodynamic simulations. Using nanolithography we fabricate nanoantenna arrays having LSPR frequencies close to the frequencies of the most intense absorption modes of steroid hormone cortisol. We deposit cortisol molecules onto the surface of nanoantenna arrays by drop- coating. SEIRA spectra of the nanoantenna arrays make it possible the determination of the presence of cortisol and establishing the sensitivity limit of this method. Thus, we show possibility of SEIRA application for cortisol concentration analysis.
The mechanism of stabilization of the combustion in the duct of the solid fuel grain of a solid fuel ramjet with a flame holder was analyzed for the first time. The flame holder can be either a ...shoulder in the inlet part of the duct, or an autonomous gas generator running on solid fuel capable of self-sustained combustion. A mathematical model for evaluating the stability of the combustion in the solid fuel ramjet grain duct was developed. It was shown that there are several parameters characterizing the solid fuel grain and the solid fuel ramjet as a whole that affect the stability of the operation of the solid fuel ramjet. The main control parameters are the temperature of the combustion products in the flame holder and the flow rate of the combustion products from the flame holder (which can be controlled by varying the sizes and shape of the flame holder), and also the degree of turbulence of the air flow in the solid fuel grain duct. The stability of the combustion in the duct of the solid fuel grain of the solid fuel ramjet was studied, and the possible modes of the operation of the solid fuel ramjet while varying the control parameters were determined.
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