Stacked submonolayer (SML) InAs/GaAs nanostructures, assembled by cyclic, alternating deposition of SML (<1 ML) InAs and few-monolayer GaAs using molecular beam epitaxy, have been attracting interest, owing to their unique optical and electronic properties. Recently, it has been demonstrated that a growth transition during SML deposition can lead to two types of nanostructures: 2D islands and 3D structures. The properties of SML nanostructures also make them strong candidates for spintronic and quantum information applications. However, the spin properties of SML nanostructures have not yet been investigated. In this study, the spin properties of SML nanostructures are investigated using optical spin injection and detection experiments by circularly polarized photoluminescence (CP-PL). Spins are injected into the SML nanostructures using the optical selection rules in GaAs for CP excitation, whereas the spin state in the SML nanostructures is detected by measuring the right (σ+) and left (σ−) CP intensity components of the PL. The degree of CP-PL is estimated by quantity P=[I(σ+)−I(σ−)]/[I(σ+)+I(σ−)], where I(σ±) is the luminescence intensity for the σ± component. The quantity P is a direct measure of the spin state in the SML nanostructures. Using a sample containing both 2D and 3D SML nanostructures, experimental results yield a relatively high P=6% for the 3D SML nanostructures and a relatively low P=2% for the 2D SML nanostructures. The difference may be attributed to the higher carrier confinement for 3D SML resulting in preservation of the spin state. Analytical calculations considering the spin and carrier lifetimes are also carried out to model the experimental results. These results provide insight into the fundamental spin dynamics of 2D and 3D SML nanostructures and pave the way for spintronics and quantum information applications of SML nanostructures.

Surface-enhanced Raman spectroscopy (SERS) performed in microfluidic channels offers multiple benefits to the sensitive and reliable detection of dilute analytes while utilizing the advantages of microfluidics, including small samples, high throughput, and portability. Physical deposition of metallic nanoparticles by techniques, such as electron beam deposition, results in dense populations of nanoparticles and hotspots between nanoparticles for sensitive detection. However, not only do physically deposited SERS-active surfaces necessitate additional steps during device fabrication, but also surface fabrication is itself complicated by the constraints imposed by the microfluidic channel. Our work demonstrates a robust approach to the physical fabrication of an SERS-active substrates inside a poly(dimethylsiloxane) (PDMS) microfluidic channel. Direct growth of zinc oxide nanowires inside the PDMS channel and e-beam deposition of silver to coat the nanowires was performed before bonding PDMS to glass. This process enables label-free SERS sensing of micromolar crystal violet and melamine with minimal spectral interference from the PDMS-based channel.

Plasmonic supercrystals (PSCs) made by colloidal self-assembly metallic nanoparticles can be regarded as a special kind of optical metamaterials with intriguing properties, such as engineered refractive indices and densely distributed near field “hot spots.” Analysis of the Purcell effect of PSCs is crucial for many applications related to light-emission processes, such as surface-enhanced Raman scattering and spontaneous emission enhancement. We present a detailed theoretical and numerical study on the Purcell effect of films and nanocavities made of PSCs. We first demonstrate that the spectral response of the Purcell effect of a monolayer PSC can be basically divided into the surface plasmon polariton regime, the collective plasmon (CP) regime, and the dielectric regime. In particular, we reveal that the resonances in the CP regime have rich fine structures of near fields, resulting in a strong dependence of the Purcell effect on the position and polarization of emitters. We further show that nanocavities consist of PSCs that sustain Mie-like electric and magnetic multipolar resonances that can be utilized to enhance the Purcell effect in the near-infrared band. Our results are helpful for understanding the light–matter interactions at nanoscale and may promote applications of PSCs in light-emission engineering.

We studied spectroscopical properties of tiny TiO2 nanoparticles (TiO2 NPs) with potential applications by the stimulation of multi-modal energy modes. Thus, nanoparticles of 2 to 4 nm sizes were modified with short modified organosilane with a fluorescent laser dye reporter. By this manner, it was covered with silanized spacer lengths of few nm with an additional protective shell. The non-modified TiO2 NPs showed high interactions between them due to their reduced sizes that afforded to homogeneous nano-patterned arrays observed by TEM. Silanized nanoparticles also afforded higher dispersible colloidal dispersion with strong interactions. As it is known, silanol groups could form strong polar and hydrogen bridges between them, but the aggregates could be easily re-dispersed just by sonication. By this manner, generation of a high-ordered nano-pattern was lost in the absence of silica shells. By dynamic light scattering, I recorded within colloidal dispersions sizes of 2 to 3 nm in presence of aqueous solvent and smaller nanoaggregates of 30 nm corresponding to decamer forms. In this context, I highlighted the possibility of managing interactions and nano-patterns controlling nano-surfaces and media. Non-labeled TiO2 NPs showed strong absorptions centered at 298.0 and 560.0 nm. Moreover, modified nanoparticles showed a constant and proportional increase of the 298.0 nm absorption band with the augmentation of the concentration. Moreover, the UV band was accompanied with a redshifted maximal absorption wavelength by the fluorophore incorporated from 553.0 to 557.0 nm. This fact was explained between an interaction between the absorption of the laser dye centered at 537 nm and the longer band by the nanoplatforms. Then, in order to evaluate their interactions in the excited state, I evaluated fluorescence lifetime decays (τ) of the free fluorophore and deposed on nanoplatforms. In addition, I evaluated the detection of the modified TiO2 nanoplatforms within in-flow cytometry (IFC). In this manner, I observed τ shortening accompanied with augmented counting of fluorescence events detected. It should be noted that in these conditions, I did not observe degradation of the fluorescent reporter. However, in absence of the modified organosilanes, I observed potential insights of fast photo-degradation under UV light irradiation. Therefore, I designed and synthesized a stable and improved tiny nano-emitter with potential use for nanophotonics, biophotonics, and nanomedicine applications. Thus, in this perspective, I discuss the development of multimodal nanoplatforms for varied functionalities and applications.

Morphological disorder is commonplace in bioworld structures, as exemplified by the layered helical structures in the exocuticle in many beetle species. Circular-polarization-state selective reflection from disordered chiral structures was theoretically explored, the disorder being that each helical turn may be different from its adjacent helical turns. The boundary-value problem of plane-wave reflection by a disordered chiral structure was solved. Numerical results indicate the remarkable resilience of circular-polarization-state-selective reflection against morphological disorder.

We explore oxide passivation in photoelectrochemical (PEC) electrodes featuring nanostructures. The introduction of nanostructures not only offers the advantage of improved light absorption but also introduces challenges such as surface defects and hydrophobic surface properties. Oxide passivation provides a simple solution to these problems by offering a variety of material options. However, the high bandgap nature of plain oxides requires thickness optimization due to their dual role as passivation and insulating layers. Among various materials, TiO2 was selected for passivation of nanoporous silicon photocathode electrodes due to its relatively narrow bandgap and conduction band position, which closely matches the hydrogen evolution potential. We meticulously analyzed the PEC property changes induced by varying the thickness in steps of 0.5 nm, with the goal of identifying the optimal thickness for improved PEC performance. The results conclusively demonstrate that a 1.5 nm thick direct tunnelable oxide layer provides the best PEC performance. By applying a 1.5 nm thin nanolayer for passivation, a 1.6-fold improvement in photocurrent characteristics compared with black Si was observed at −1.23 V relative to the reversible hydrogen electrode. Deposition of TiO2 not only increased the photocurrent but also enhanced the photovoltage up to 110 mV, resulting in an overall positive shift in the electrode potential that is favorable for hydrogen evolution reaction applications. This study highlights the importance of fine-tuning the oxide layer thickness to optimize the performance of PEC systems and highlights the potential of TiO2 passivation in overcoming limitations posed by the unique properties of nanostructured electrodes.

We experimentally demonstrate the fabrication of optical micro/nanofibers (MNFs) using chemical etching and gas-flame techniques. In the chemical etching technique, a two-step process involves 40% and 24% hydrofluoric acid solutions for the first and second steps, respectively. The measured diameters of MNFs range from 0.34 to 1.4 μm. In the gas-flame technique, we design the pulling parameters in a four-step process to achieve the desired diameter of MNFs. The single-mode fiber is adiabatically tapered using high-precision stages while heating the fiber with hydrogen-oxygen flame. The measured diameters of the pulled MNFs range from 0.48 to 0.53 μm, showing good correspondence with the designed diameters. Due to the strong confinement of the field around the MNF, it has diverse applications in various fields, such as sensing, nanophotonics, quantum optics, quantum photonics, and nonlinear optics.