Modern nanophotonics allows one to engineer the optical modes and localize light at the nanoscale. In this work, we visualize the local density of optical states (LDOS) distribution of the single femtosecond-laser-printed gold nanobump with ultrahigh spatial resolution. Scanning tunneling microscope-induced light emission allows us to achieve LDOS mapping with a spatial resolution of around 15 nm for single nanobumps and their agglomerates with gold plasmonic nanoantennas, having a relatively small diameter. Our experimental and theoretical results show that a plasmonic nanoantenna can be integrated into an optical system to enhance its radiation outcoupling efficiency, while leaving its modal structure mainly unaffected. A deep understanding of the optical modes in nanostructures opens up possibilities for creating new types of optoelectronic components based on inelastically tunneling electrons, providing light emission.

Nanowires (NWs) of III-V semiconductors provide a promising platform for the development of electronic and photonic components of integrated circuits. For the development of complex NW-based devices, it is crucial to precisely study structural, electronic, and optical properties at the nanoscale. Scanning tunneling microscopy (STM) is commonly used to achieve such precision. In this work we optimize the tunneling contact parameters in an ultrahigh vacuum STM (at room temperature) for reproducible high-quality topographic imaging of conductive GaP NWs, especially promising for photonic integrated circuits. Two methods were employed for transferring NWs onto auxiliary conducting substrates: ultrasonication in liquid (deionized water or isopropyl alcohol) followed by drop casting and mechanical scratching. Five substrate materials were tested: highly oriented pyrolytic graphite, single crystal silicon wafers, thin films of nickel, indium tin oxide and gold. The experimental results showed that the tunneling contact parameters, substrate material, and transfer method significantly affect the quality of STM images. It was found that bias voltages of 7-10 V, tunneling current up to 400 pA, and image recording rates in the range of 500-1500 nm s-1were optimal, with nickel-coated substrates providing the best stability and image quality. Potentially harmful procedures for NW and substrate surfaces, such as ion treatment and high-temperature annealing, were avoided during the sample preparation. The results expand the understanding of STM studies of NWs and their applications in electronic and photonic devices.

Electrically conductive nanoporous membranes represent a class of stimuli-responsive materials, which selectivity/permeability characteristics can be adjusted by varying the surface potential. In this work, we perform a comprehensive theoretical and experimental study of ionic conductivity of such membranes. The 2D Space charge and 1D Uniform potential models are used to describe the ion transport through a cylindrical nanopore. The calculations show that the imposed electric field polarizes the conductive surface, which results in the continuous variation of electronic surface charge from positive to negative along the nanopore. A higher concentration of cations (anions) is observed at negatively (positively) charged part of the nanopore. The increase of charge carries concentration due to polarization effect results in the enhancement of ionic conductivity with increasing the voltage difference. The corresponding current-voltage curves are non-linear. The enhancement can reach a few orders of magnitude at low salt concentrations, but becomes much smaller at high concentrations. The presence of chemical charge has a screening effect on the interaction of electric field with the electronic charge on the nanopore surface, and reduces the conductivity enhancement. A novel analytical solution is derived for the dependence of ionic current on the Stern layer capacitance, salt concentration, and the applied potential difference. The theoretical predictions are first confirmed by the ionic conductivity measurements in porous anodic alumina membranes with carbon nanotubes inside the pores. The experimental data are approximated by the 1D Uniform potential model curves using chemical charge as a fitting parameter. Strong enhancement of ionic conductivity (more than 6 times) and the corresponding nonlinear dependence of current on the applied voltage is experimentally registered at low KCl concentrations (0.1 - 10 mM) with increasing the voltage difference.

Experimental methods of single-molecule enzymology allow scientists to determine physicochemical properties of distinct single molecules of various enzymes and to perform direct monitoring of functioning of enzymes at different steps of their catalytic cycle. The approach based on the use of solid-state nanopores is a promising tool for studying the functioning of single-enzyme molecules. Herein, this approach is employed for monitoring the functioning of cytochrome P450 BM3, which represents a very convenient model of cytochrome P450-containing monooxygenase systems. A nanopore of ~5 nm in diameter has been formed in a 40 nm-thick silicon nitride chip by electron beam drilling (EBD), and a single molecule of the BM3 enzyme has been entrapped in the pore. The functioning of the enzyme molecule has been monitored by recording the time dependence of the ion current through the nanopore during the reaction of laurate hydroxylation. In our experiments, the enzyme molecule has been found to be active for 1500 s. The results of our research can be further used in the development of highly sensitive detectors for single-molecule studies in enzymology.

Solid-state nanopore devices with plasmonic nanoantennas are powerful tools that allow for working with individual particles and molecules in solution as well as providing light-induced control of ionic current flow through them. However, the ionic current flow manipulation by light still requires high power densities and, thus, results in the optical heating of the nanopore. Here, we solve this problem by using a 5 nm nanopore in the gap of a plasmonic bow-tie nanoantenna on a SiNx membrane irradiated by a broadband spectrum of incident light. In this regime, photons are not only strongly localized around the nanopore but also efficiently excite and trap charge carriers on defect states in the band gap of the material of the nanopore walls. As a result, ionic current flow modulation is achieved with several orders of magnitude lower power densities (around 0.035 W/cm(2)) from a white-light lamp than in previous works employing spectrally narrow laser sources (10(0)-10(5) W/cm(2)). The lamp irradiation causes a 21% increase in conductivity for a nanopore without a nanoantenna and a 35% increase in conductivity for a nanoantenna-decorated nanopore at the same power of irradiation. The revealed low-intensity approach for ionic current control is preferable for the study of biological objects.

The key components of photonic integrated circuits are nanoscale optica emitters and nanowaveguides. III-V semiconductor nanostructures are considered as the most promising material platform for these components due to highly efficient luminescence and high refractive index, but the problem of emission coupling with waveguide is to be solved. In this work, the use of GaP nanowires (NWs) with different types of doping (GaP:Si or GaP:Be) is proposed as optical waveguides with directly integrated electrically-driven light sources, solving the problem of emission-to-waveguide coupling. Single NWs are integrated with electrodes and pump electroluminescence by a tunnel junction allowing to study emission properties with nanoscale spatial resolution. Basing on the experiments on scanning tunnelling microscopy (STM), electron microscopy, time-resolved photoluminescence micro-spectroscopy, X-ray diffraction, and STM-induced electroluminescence, it is proven that GaP NWs exhibit different integrated light-source on doping type of NWs. GaP:Be NWs contain inclusion of the crystalline wurtzite phase with a direct bandgap, and, thus, these NW regions can be considered as electrically-driven nanoscale sources of light monolithically integrated into GaP NW-based waveguides. Meanwhile, GaP:Si NWs work as optical waveguides capable of efficient light generation over the entire length of NW. The developed designs are promising for construction of integrated photonic circuits. GaP nanowires (NWs) with different types of doping (GaP:Si or GaP:Be) are empolyed as optical waveguides with integrated electrically-driven light sources, solving the problem of emission-to-waveguide coupling. GaP:Be NWs contain inclusions of the crystalline wurtzite phase with a direct bandgap, and, thus, these NW regions can be considered as electrically-driven nanoscale light sources monolithically integrated into GaP NW-based waveguides. image

Currently, nanopore-based technology for the determination of the functional activity of single enzyme molecules continues its development. The use of natural nanopores for studying single enzyme molecules is known. At that, the approach utilizing artificial solid-state nanopores is also promising but still understudied. Herein, we demonstrate the use of a nanotechnology-based approach for the investigation of the enzymatic activity of a single molecule of horseradish peroxidase with a solid-state nanopore. The artificial 5 nm solid-state nanopore has been formed in a 40 nm thick silicon nitride structure. A single molecule of HRP has been entrapped into the nanopore. The activity of the horseradish peroxidase (HRP) enzyme molecule inserted in the nanopore has been monitored by recording the time dependence of the ion current through the nanopore in the course of the reaction of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) oxidation reaction. We have found that in the process of ABTS oxidation in the presence of 2.5 mM hydrogen peroxide, individual HRP enzyme molecules are able to retain activity for approximately 700 s before a decrease in the ion current through the nanopore, which can be explained by structural changes of the enzyme.

Nanoscale electrically driven light-emitting sources with tunable wavelength represent a milestone for implementation of integrated optoelectronic chips. Plasmonic nanoantennas exhibiting an enhanced local density of optical states (LDOS) and strong Purcell effect hold promise for fabrication of bright nanoscale light emitters. Here, we justify gold parabola-shaped nanobumps and their ordered arrays produced by direct ablation-free femtosecond laser printing as broadband plasmonic light sources electrically excited by a probe of scanning tunneling microscope (STM). I-V curves of the probe-nanoantenna tunnel junction reveal characteristic bias voltages correlating with visible-range localized (0.55 and 0.85 μm) and near-IR (1.65 and 1.87 μm) collective plasmonic modes of these nanoantennas. These multiband resonances confirmed by optical spectroscopy and full-wave simulations provide enhanced LDOS for efficient electrically driven and bias-tuned light emission. Additionally, our studies confirm remarkable applicability of STM for accurate study of optical modes supported by the plasmonic nanoantennas at nanoscale spatial resolution.

This paper considers the photoelectrochemical characteristics of a composite porous TiO2 thin film with deposited plasmonic gold nanoparticles. The deposition of gold nanoparticles was carried out by the laser-induced chemical liquid-phase deposition (LCLD) method. The structural characteristics of the composite have been studied; it has been shown that the porous TiO2 film has a lattice related to the tetragonal system and is in the anatase phase. Gold nanoparticles form on the surface of a porous TiO2 film. A complex of photoelectrochemical measurements was carried out. It was shown that the deposition of plasmonic gold nanoparticles led to a significant increase in the photocurrent density by ~820%. The proposed concept is aimed at testing the method of forming a uniform layer of plasmonic gold nanoparticles on a porous TiO2 film, studying their photocatalytic properties for further scaling, and obtaining large area Au/TiO2/FTO photoelectrodes, including in the roll-to-roll process.

A micro- or nanosized electrically controlled source of optical radiation is one of the key elements in optoelectronic systems. The phenomenon of light emission via inelastic tunneling (LEIT) of electrons through potential barriers or junctions opens up new possibilities for development of such sources. In this work, we present a simple approach for fabrication of nanoscale electrically driven light sources based on LEIT. We employ STM lithography to locally modify the surface of a Si/Au film stack via heating, which is enabled by a high-density tunnel current. Using the proposed technique, hybrid Si/Au nanoantennas with a minimum diameter of 60 nm were formed. Studying both electronic and optical properties of the obtained nanoantennas, we confirm that the resulting structures can efficiently emit photons in the visible range because of inelastic scattering of electrons. The proposed approach allows for fabrication of nanosized hybrid nanoantennas and studying their properties using STM.

Electrically driven plasmonic nanoantennas can be integrated as a local source of the optical signal of advanced photonic schemes for on-chip data processing. The inelastic electron tunneling provides the photon generation or launch of surface plasmon waves. This process can be enhanced by the local density of optical states of nanoantennas. In this paper, we used scanning tunnel microscopy-induced light emission to probe the local optoelectronic properties of single gold nanodiscs. The electromagnetic field distribution in the vicinity of plasmonic structures was investigated with high spatial resolution. The obtained photon maps reveal the nonuniform distribution of electromagnetic near-fields, which is consistent with nanoantenna optical modes. Also, the analysis of derived I(V) curves showed a direct correlation between the nanoantenna optical states and the appearance of features on current-voltage characteristics.

We developed a technique for fabrication microfluidic silicon-glass chips with a system of nanochannels connecting two microchannel using traditional optical lithography and a focused ion beam. To investigate the transport phenomena in the nanochannels we experimentally studied their ion conductivity and using optical microscopy confirmed the existence of the diffusion flow through them. The developed method allows us to create systems of nanochannels with on-purpose geometry and controlled sizes. Devices with such nanochannels can be applied in the creation of biosensor devices and for genetic studies.

This work is devoted to the study of plasmonic properties of electrically driven gold nanodisks employing scanning tunnel microscopy induced luminescence (STML). Gold disks were fabricated with the use of e-beam lithography. The size of the disks (diameter of 120-180 nm and height of 60 nm) was comparable with the wavelength emitted. To confirm that the observed emission of photons is associated with inelastic tunneling of electrons, but not with the collision of the probe with the nanodisk surface, the nanodisk was STML scanned at different angles of the probe motion (0, 90, 270 degrees). In all cases the obtained images were identical. It was shown that nanodisk provided nonuniform STML map, the edges of the nanodisk emitted light with higher intensity compared to the center. Also, current-voltage I(V) characteristics at different points of a nanodisk were obtained and analyzed, and the acquired features at I(V) curves were correlated to the STML results. The proposed approach based on I(V) curves analyzing is very promising for the indirect study of optical properties of the electrically driven nanoscale photon sources.

Nanocomposite membranes have been actively developed in the last decade. The involvement of nanostructures can improve the permeability, selectivity, and anti-fouling properties of a membrane for improved filtration processes. In this work, we propose a novel type of ion-selective Glass/Au composite membrane based on porous glass (PG), which combines the advantages of porous media and promising selective properties. The latter are achieved by depositing gold nanoparticles into the membrane pores by the laser-induced liquid phase chemical deposition technique. Inside the pores, gold nanoparticles with an average diameter 25 nm were formed, which was confirmed by optical and microscopic studies. To study the transport and selective properties of the PG/Au composite membrane, the potentiometric method was applied. The uniform potential model was used to determine the surface charge from the experimental data. It was found that the formation of gold nanoparticles inside membrane pores leads to an increase in the surface charge from −2.75 mC/m2 to −5.42 mC/m2. The methods proposed in this work allow the creation of a whole family of composite materials based on porous glasses. In this case, conceptually, the synthesis of these materials will differ only in the selection of initial precursors.

Herein, I(V) characteristics of the tunnel junction between the scanning tunneling microscopy (STM) Pt/Ir probe and atomically flat Au film on mica using ultrahigh vacuum STM is investigated. To ensure cleanness and flatness of the Au films, optimization of the substrate annealing and Ar plasma treatment are performed. The obtained technological parameters allow to drastically improve the reproducibility of I(V) measurements. The analysis of I(V), d2I/dV2 (V), and Fowler–Nordheim plots is conducted, and the presence of the features in the bias region near 1.8 V in the form of peak and minimum, peak and anomalous extra minimum, respectively is demonstrated. The direct optical measurements confirm that the features on I(V) curves are associated with the generation of photons from the STM probe‐sample gap, governed by inelastic tunneling processes. The proposed I(V) analysis approach is used for indirect sensing and investigation of the light emission in the tunnel junction offering a powerful tool for the studies of the photonic sources with deeply subwavelength dimensions.

Catalyst-free chemical vapor deposition is used to form thin (1-2 nm) carbon layers on the surface of alumina nanofibers resulting in carbon-alumina nanocomposites. Thermal analysis, X-ray fluorescent microanalysis, Raman spectroscopy, and electrical resistance measurements of these composites show that increasing of synthesis time not only increases the amount of carbon on alumina surface, but also the ordering and density of the carbon layers. Nitrogen adsorption data reveal the decrease of total pore volume with increasing the synthesis time. The obtained composite material could be employed for the preparation of ion-selective membranes with switchable ion transport, electroconductive ceramics, and electrochemical sensors.

In this work, we reported in situ laser-induced synthesis of sensor-active copper‑silver microcomposite. This bimetallic microelectrode exhibits highly developed surface area and good electrical conductivity, and can be successfully used for glucose and alanine sensing demonstrating decent sensitivity (31,000 μА cm−2 mМ−1 for d-glucose and 11,177 μА cm−2 mМ−1 for l-alanine) and low limit of detection (2.8 μM for d-glucose and 0.83 μM for l-alanine). High sensor activity and good electrochemical characteristics of the synthesized material can be associated with the eutectic type of the Cu-Ag system. The implemented technique is quite useful for fabrication of new promising small size sensors for enzymeless determination of different biological analytes.

In this work, a promising approach that provides conditions for in situ laser-induced synthesis of Raney-like copper-based nano-sized catalysts was reported. Their activity with respect to selective catalysis of acetylene homo-coupling versus Pd/Cu-catalyzed Sonogashira cross-coupling reactions was investigated. For that purpose, we studied the reaction of phenyl acetylene with p-iodanisole in the presence of a palladium(II) acyclic diaminocarbene complex and laser-induced copper-based nano-sized catalyst. It was found that the growth of particles generated within the focus of the laser beam can last even if laser irradiation is off and can be controlled by adding phenanthroline as the stabilizing ligand to the reaction mixture or by increasing its temperature and concentration. Thus, it is possible to manage the course of the catalytic reaction towards formation of either homo-coupling or cross-coupling products by changing the size of catalytically active copper-based particles produced during laser-induced synthesis.

We report a new mechanism for the generation of membrane potential in polarizable nanoporous membranes separating electrolytes with different concentrations. The electric field generated by diffusion of ions with different mobilities induces a non–uniform surface charge, which results in charge separation inside the nanopore. The corresponding Donnan potentials appear at the pore entrance and exit leading to a dramatic enhancement of membrane potential in comparison with an uncharged non–polarizable membrane. At high concentration contrast, the interaction between electric field and uncompensated charge at a low concentration side results in the development of electrokinetic vortices. The theoretical predictions are based on the Space–Charge model, which is extended to nanopores with polarizable conductive surface for the first time. This model is validated against full Navier–Stokes, Nernst–Planck, and Poisson equations, which are solved in a high aspect ratio nanopore connecting two reservoirs. The experimental measurements of membrane potential of dielectric and conductive membranes in KCl and NaCl aqueous solutions confirm the theoretical results. The membranes are prepared from Nafen nanofibers with ∼10nm in diameter and modified by depositing a conductive carbon layer. It is shown theoretically that the membrane potential enhancement becomes greater with decreasing the electrolyte concentration and pore radius. A high sensitivity of membrane potential to the ratio of ion diffusion coefficients is demonstrated. The described phenomenon may find applications in precise determination of ion mobilities, electrochemical and bio–sensing, as well as design of nanofluidic and bioelectronic devices.

The authors propose a novel type of ion-selective membranes, which combine the advantages of ceramic nanofibrous media with good electrical conductivity. The membranes are produced from Nafen alumina nanofibers (diameter around 10nm) by filtration of nanofiber suspension through a porous support followed by drying and sintering. Electrical conductivity is achieved by depositing a thin carbon layer on the nanofibers by chemical vapor deposition (CVD). Raman and FTIR spectroscopy, X-ray fluorescence analysis, and TEM are used to confirm the carbon structure formation. The deposition of carbon leads to decreasing porosity (from 75 to 62%) and specific surface area (from 146 to 107m(2) g(-1)) of membranes, while the pore size distribution maximum shifts from 28 to 16nm. Measurements of membrane potential in an electrochemical cell show that the carbon coated membranes acquire high ionic selectivity (transference numbers 0.94 for anion and 0.06 for cation in aqueous KCl). Fitting the membrane potential data by the Teorell-Meyer-Sievers model shows that the fixed membrane charge increases proportionally with increasing electrolyte concentration. The carbon coated membranes are ideally polarizable for applied voltages from -0.5 to +0.8V. The potential applications of produced membranes include nano- and ultrafiltration, separation of charged species, and switchable ion-transport selectivity.