Registration of Functioning of a Single Horseradish Peroxidase Macromolecule with a Solid-State Nanopore.

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.

Photoluminescence imaging of single photon emitters within nanoscale strain profiles in monolayer WSe2.

Local deformation of atomically thin van der Waals materials provides a powerful approach to create site-controlled chip-compatible single-photon emitters (SPEs). However, the microscopic mechanisms underlying the formation of such strain-induced SPEs are still not fully clear, which hinders further efforts in their deterministic integration with nanophotonic structures for developing practical on-chip sources of quantum light. Here we investigate SPEs with single-photon purity up to 98% created in monolayer WSe2 via nanoindentation. Using photoluminescence imaging in combination with atomic force microscopy, we locate single-photon emitting sites on a deep sub-wavelength spatial scale and reconstruct the details of the surrounding local strain potential. The obtained results suggest that the origin of the observed single-photon emission is likely related to strain-induced spectral shift of dark excitonic states and their hybridization with localized states of individual defects.

Femtosecond Laser-Printed Gold Nanoantennas for Electrically Driven and Bias-Tuned Nanoscale Light Sources Operating in Visible and Infrared Spectral Ranges.

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.

Elastic Gallium Phosphide Nanowire Optical Waveguides-Versatile Subwavelength Platform for Integrated Photonics.

Emerging technologies for integrated optical circuits demand novel approaches and materials. This includes a search for nanoscale waveguides that should satisfy criteria of high optical density, small cross-section, technological feasibility and structural perfection. All these criteria are met with self-assembled gallium phosphide (GaP) epitaxial nanowires. In this work, the effects of the nanowire geometry on their waveguiding properties are studied both experimentally and numerically. Cut-off wavelength dependence on the nanowire diameter is analyzed to demonstrate the pathways for fabrication of low-loss and subwavelength cross-section waveguides for visible and near-infrared (IR) ranges. Probing the waveguides with a supercontinuum laser unveils the filtering properties of the nanowires due to their resonant action. The nanowires exhibit perfect elasticity allowing fabrication of curved waveguides. It is demonstrated that for the nanowire diameters exceeding the cut-off value, the bending does not sufficiently reduce the field confinement promoting applicability of the approach for the development of nanoscale waveguides with a preassigned geometry. Optical X-coupler made of two GaP nanowires allowing for spectral separation of the signal is fabricated. The results of this work open new ways for the utilization of GaP nanowires as elements of advanced photonic logic circuits and nanoscale interferometers.

Self-assembled photonic structure: a Ga optical antenna on GaP nanowires.

Semiconductor nanowires are the perfect platform for nanophotonic applications owing to their resonant, waveguiding optical properties and technological capabilities providing control over their crystalline and chemical compositions. The vapor-liquid-solid growth mechanism allows the formation of hybrid metal-dielectric nanostructures promoting sub-wavelength light manipulation. In this work, we explore both experimentally and numerically the plasmonic effects promoted by a gallium (Ga) nanoparticle optical antenna decorating the facet of gallium phosphide (GaP) nanowires. Raman, photoluminescence and near-field mapping techniques are used to study the effects. We demonstrate several phenomena including field enhancement, antenna effect and increase in internal reflection. We show that the observed effects have to be considered when nanowires with a plasmonic particle are used in nanophotonic circuits and discuss the ways for utilization of these effects for efficient coupling of light into nanowire waveguide and field tailoring. The results open up promising pathways for the development of both passive and active nanophotonic elements, light harvesting and sensorics.

Structural Features of Eu3+ and Tb3+-Bipyridinedicarboxamide Complexes.

Photoluminescent lanthanide complexes of Eu3+ and Tb3+ as central atoms and N6,N6'-diisopropyl-[2,2'-bipyridine]-6,6'-dicarboxamide as ligand were synthesized. The structure of these complexes was established by single-crystal X-ray diffraction, mass spectrometry, 1H and 13C nuclear magnetic resonance, ultraviolet-visible, infrared spectroscopy, and thermogravimetry. Bipyridinic ligands provide formation of coordinatively saturated complexes of lanthanide ions and strong photoluminescence (PL). The Eu3+- and Tb3+-complexes exhibit PL emission in the red and green regions observed at a 340 nm excitation. The quantum yield for the complexes was revealed to be 36.5 and 12.6% for Tb3+- and Eu3+-complexes, respectively. These lanthanide compounds could be employed as photoluminescent solid-state compounds and as emitting fillers in polymer (for example, polyethylene glycol) photoluminescent materials.

Silicone Materials for Flexible Optoelectronic Devices.

Polysiloxanes and materials based on them (silicone materials) are of great interest in optoelectronics due to their high flexibility, good film-forming ability, and optical transparency. According to the literature, polysiloxanes are suggested to be very promising in the field of optoelectronics and could be employed in the composition of liquid crystal devices, computer memory drives organic light emitting diodes (OLED), and organic photovoltaic devices, including dye synthesized solar cells (DSSC). Polysiloxanes are also a promising material for novel optoectronic devices, such as LEDs based on arrays of III-V nanowires (NWs). In this review, we analyze the currently existing types of silicone materials and their main properties, which are used in optoelectronic device development.

Nanoscale Electric Field Probing in a Single Nanowire with Raman Spectroscopy and Elastic Strain.

In this work we investigate the Raman response of extremely strained gallium phosphide nanowires. We analyze new strain-induced spectral phenomena such as 2-fold and 3-fold phonon peak splitting which arise due to nontrivial internal electric field distribution coupled with inhomogeneous strain. We show that high bending strain acts as a probe allowing us to define the electric field distribution with deep subwavelength resolution using the corresponding changes of the Raman spectra. We investigate the nature of the localization with respect to nanowire diameter, excitation spot position, and light polarization, supporting the experiment with 3D numerical modeling. Based on our findings we propose a research tool allowing to precisely localize the electric field in a certain subwavelength region of the nanophotonic resonator.

Nanoscale Electrically Driven Light Source Based on Hybrid Semiconductor/Metal Nanoantenna.

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.

Anisotropic Radiation in Heterostructured "Emitter in a Cavity" Nanowire.

Tailorable synthesis of axially heterostructured epitaxial nanowires (NWs) with a proper choice of materials allows for the fabrication of novel photonic devices, such as a nanoemitter in the resonant cavity. An example of the structure is a GaP nanowire with ternary GaPAs insertions in the form of nano-sized discs studied in this work. With the use of the micro-photoluminescence technique and numerical calculations, we experimentally and theoretically study photoluminescence emission in individual heterostructured NWs. Due to the high refractive index and near-zero absorption through the emission band, the photoluminescence signal tends to couple into the nanowire cavity acting as a Fabry-Perot resonator, while weak radiation propagating perpendicular to the nanowire axis is registered in the vicinity of each nano-sized disc. Thus, within the heterostructured nanowire, both amplitude and spectrally anisotropic photoluminescent signals can be achieved. Numerical modeling of the nanowire with insertions emitting in infrared demonstrates a decay in the emission directivity and simultaneous rise of the emitters coupling with an increase in the wavelength. The emergence of modulated and non-modulated radiation is discussed, and possible nanophotonic applications are considered.

Single GaP nanowire nonlinear characterization with the aid of an optical trap.

Semiconductor nanowires exhibit numerous capabilities to advance the development of future optoelectronic devices. Among the III-V material family, gallium phosphide (GaP) is an attractive platform with low optical absorption and high nonlinear susceptibility, making it especially promising for nanophotonic applications. However, investigation of single nanostructures and their waveguiding properties remains challenging owing to typically planar experimental arrangements. Here we study the linear and nonlinear waveguiding optical properties of a single GaP nanowire in a special experimental layout, where an optically trapped structure is aligned along its major axis. We demonstrate efficient second harmonic generation in individual nanowires and unravel phase matching conditions, linking between linear guiding properties of the structure and its nonlinear tensorial susceptibility. The capability to pick up single nanowires, sort them with the aid of optomechanical manipulation and accurately position pre-tested structures opens a new avenue for the generation of optoelectronic origami-type devices.

Flexible Perovskite CsPbBr3 Light Emitting Devices Integrated with GaP Nanowire Arrays in Highly Transparent and Durable Functionalized Silicones.

The architecture of transparent contacts is of utmost importance for creation of efficient flexible light-emitting devices (LEDs) and other deformable electronic devices. We successfully combined the newly synthesized transparent and durable silicone rubbers and the semiconductor materials with original fabrication methods to design LEDs and demonstrate their significant flexibility. We developed electrodes based on a composite GaP nanowire-phenylethyl-functionalized silicone rubber membrane, improved with single-walled carbon nanotube films for a hybrid poly(ethylene oxide)-metal-halide perovskite (CsPbBr3) flexible green LED. The proposed approach provides a novel platform for fabrication of flexible hybrid optoelectronic devices.

Tailoring Morphology and Vertical Yield of Self-Catalyzed GaP Nanowires on Template-Free Si Substrates.

Tailorable synthesis of III-V semiconductor heterostructures in nanowires (NWs) enables new approaches with respect to designing photonic and electronic devices at the nanoscale. We present a comprehensive study of highly controllable self-catalyzed growth of gallium phosphide (GaP) NWs on template-free silicon (111) substrates by molecular beam epitaxy. We report the approach to form the silicon oxide layer, which reproducibly provides a high yield of vertical GaP NWs and control over the NW surface density without a pre-patterned growth mask. Above that, we present the strategy for controlling both GaP NW length and diameter independently in single- or two-staged self-catalyzed growth. The proposed approach can be extended to other III-V NWs.

Stretchable Transparent Light-Emitting Diodes Based on InGaN/GaN Quantum Well Microwires and Carbon Nanotube Films.

We propose and demonstrate both flexible and stretchable blue light-emitting diodes based on core/shell InGaN/GaN quantum well microwires embedded in polydimethylsiloxane membranes with strain-insensitive transparent electrodes involving single-walled carbon nanotubes. InGaN/GaN core-shell microwires were grown by metal-organic vapor phase epitaxy, encapsulated into a polydimethylsiloxane film, and then released from the growth substrate. The fabricated free-standing membrane of light-emitting diodes with contacts of single-walled carbon nanotube films can stand up to 20% stretching while maintaining efficient operation. Membrane-based LEDs show less than 15% degradation of electroluminescence intensity after 20 cycles of stretching thus opening an avenue for highly deformable inorganic devices.

XRD Evaluation of Wurtzite Phase in MBE Grown Self-Catalyzed GaP Nanowires.

Control and analysis of the crystal phase in semiconductor nanowires are of high importance due to the new possibilities for strain and band gap engineering for advanced nanoelectronic and nanophotonic devices. In this letter, we report the growth of the self-catalyzed GaP nanowires with a high concentration of wurtzite phase by molecular beam epitaxy on Si (111) and investigate their crystallinity. Varying the growth temperature and V/III flux ratio, we obtained wurtzite polytype segments with thicknesses in the range from several tens to 500 nm, which demonstrates the high potential of the phase bandgap engineering with highly crystalline self-catalyzed phosphide nanowires. The formation of rotational twins and wurtzite polymorph in vertical nanowires was observed through complex approach based on transmission electron microscopy, powder X-ray diffraction, and reciprocal space mapping. The phase composition, volume fraction of the crystalline phases, and wurtzite GaP lattice parameters were analyzed for the nanowires detached from the substrate. It is shown that the wurtzite phase formation occurs only in the vertically-oriented nanowires during vapor-liquid-solid growth, while the wurtzite phase is absent in GaP islands parasitically grown via the vapor-solid mechanism. The proposed approach can be used for the quantitative evaluation of the mean volume fraction of polytypic phase segments in heterostructured nanowires that are highly desirable for the optimization of growth technologies.

Luminescent Erbium-Doped Silicon Thin Films for Advanced Anti-Counterfeit Labels.

The never-ending struggle against counterfeit demands the constant development of security labels and their fabrication methods. This study demonstrates a novel type of security label based on downconversion photoluminescence from erbium-doped silicon. For fabrication of these labels, a femtosecond laser is applied to selectively irradiate a double-layered Er/Si thin film, which is accomplished by Er incorporation into a silicon matrix and silicon-layer crystallization. The study of laser-induced heating demonstrates that it creates optically active erbium centers in silicon, providing stable and enhanced photoluminescence at 1530 nm. Such a technique is utilized to create two types of anti-counterfeiting labels. The first type is realized by the single-step direct laser writing of luminescent areas and detected by optical microscopy as holes in the film forming the desired image. The second type, with a higher degree of security, is realized by adding other fabrication steps, including the chemical etching of the Er layer and laser writing of additional non-luminescent holes over an initially recorded image. During laser excitation at 525 nm of luminescent holes of the labels, a photoluminescent picture repeating desired data can be seen. The proposed labels are easily scalable and perspective for labeling of goods, securities, and luxury items.

Recrystallization of CsPbBr3 Nanoparticles in Fluoropolymer Nonwoven Mats for Down- and Up-Conversion of Light.

Inorganic halides perovskite CsPbX3 (X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) nanoparticles are efficient light-conversion objects that have attracted significant attention due to their broadband tunability over the entire visible spectral range of 410-700 nm and high quantum yield of up to 95%. Here, we demonstrate a new method of recrystallization of CsPbBr3 nanoparticles inside the electrospun fluoropolymer fibers. We have synthesized nonwoven tetrafluoroethylene mats embedding CsPbBr3 nanoparticles using inexpensive commercial precursors and syringe electrospinning equipment. The fabricated nonwoven mat samples demonstrated both down-conversion of UV light to 506 nm and up-conversion of IR femtosecond laser radiation to 513 nm green photoluminescence characterized by narrow emission line-widths of 35 nm. Nanoparticle formation inside nonwoven fibers was confirmed by TEM imaging and water stability tests controlled by fluorimetry measurements. The combination of enhanced optical properties of CsPbBr3 nanoparticles and mechanical stability and environmental robustness of highly deformable nonwoven fluoropolymer mats is appealing for flexible optoelectronic applications, while the industry-friendly fabrication method is attractive for commercial implementations.

Scanning Tunneling Microscopy-Induced Light Emission and I(V) Study of Optical Near-Field Properties of Single Plasmonic Nanoantennas.

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.

Degradation kinetic study of ZIF-8 microcrystals with and without the presence of lactic acid.

The zeolitic imidazolate framework ZIF-8 (Zn(mim)2, mim = 2-methylimidazolate) has recently been proposed as a drug delivery platform for anticancer therapy based on its capability of decomposing in acidic media. The concept presumes a targeted release of encapsulated drug molecules in the vicinity of tumor tissues that typically produce secretions with elevated acidity. Due to challenges of in vivo and in vitro examination, many studies have addressed the kinetics of ZIF-8 decomposition and subsequent drug release in phosphate buffered saline (PBS) with adjusted acidity. However, the presence of hydrogen phosphate anions [HPO4]2- in PBS may also affect the stability of ZIF-8. As yet, no separate analysis has been performed comparing the dissolving capabilities of PBS and various acidification agents used for regulating pH. Here, we provide a systematic study addressing the effects of phosphate anions with and without lactic acid on the degradation rate of ZIF-8 microcrystals. Lactic acid has been chosen as an experimental acidification agent, since it is particularly secreted by tumor cells. Interestingly, the effect of a lactic acid solution with pH 5.0 on ZIF-8 degradation is shown to be weaker compared to a PBS solution with pH 7.4. However, as an additive, lactic acid is able to enhance the decomposition efficacy of other solutions by 10 to 40 percent at the initial stage, depending on the presence of other ions. Additionally, we report mild toxicity of ZIF-8 and its decomposition products, as examined on HDF and A549 cell lines.

Structural and Optical Properties of Self-Catalyzed Axially Heterostructured GaPN/GaP Nanowires Embedded into a Flexible Silicone Membrane.

Controlled growth of heterostructured nanowires and mechanisms of their formation have been actively studied during the last decades due to perspectives of their implementation. Here, we report on the self-catalyzed growth of axially heterostructured GaPN/GaP nanowires on Si(111) by plasma-assisted molecular beam epitaxy. Nanowire composition and structural properties were examined by means of Raman microspectroscopy and transmission electron microscopy. To study the optical properties of the synthesized nanoheterostructures, the nanowire array was embedded into the silicone rubber membrane and further released from the growth substrate. The reported approach allows us to study the nanowire optical properties avoiding the response from the parasitically grown island layer. Photoluminescence and Raman studies reveal different nitrogen content in nanowires and parasitic island layer. The effect is discussed in terms of the difference in vapor solid and vapor liquid solid growth mechanisms. Photoluminescence studies at low temperature (5K) demonstrate the transition to the quasi-direct gap in the nanowires typical for diluted nitrides with low N-content. The bright room temperature photoluminescent response demonstrates the potential application of nanowire/polymer matrix in flexible optoelectronic devices.