A Sequential Electrospinning of a Coaxial and Blending Process for Creating Double-Layer Hybrid Films to Sense Glucose.

This study presents a glucose biosensor based on electrospun core-sheath nanofibers. Two types of film were fabricated using different electrospinning procedures. Film F1 was composed solely of core-sheath nanofibers fabricated using a modified coaxial electrospinning process. Film F2 was a double-layer hybrid film fabricated through a sequential electrospinning and blending process. The bottom layer of F2 comprised core-sheath nanofibers fabricated using a modified process, in which pure polymethacrylate type A (Eudragit L100) was used as the core section and water-soluble lignin (WSL) and phenol were loaded as the sheath section. The top layer of F2 contained glucose oxidase (GOx) and gold nanoparticles, which were distributed throughout the polyvinylpyrrolidone K90 (PVP K90) nanofibers through a single-fluid blending electrospinning process. The study investigated the sequential electrospinning process in detail. The experimental results demonstrated that the F2 hybrid film had a higher degradation efficiency of ß-D-glucose than F1, reaching a maximum of over 70% after 12 h within the concentration range of 10-40 mmol/L. The hybrid film F2 is used for colorimetric sensing of ß-D-glucose in the range of 1-15 mmol/L. The solution exhibited a color that deepened gradually with an increase in ß-D-glucose concentration. Electrospinning is flexible in creating structures for bio-cascade reactions, and the double-layer hybrid film can provide a simple template for developing other sensing nanomaterials.

Mid-infrared photoluminescence revealing internal quantum efficiency enhancement of type-I and type-II InAs core/shell nanowires: publisher's note.

This publisher's note contains corrections to Opt. Lett.47, 5208 (2022)10.1364/OL.473154.

Mid-infrared photoluminescence revealing internal quantum efficiency enhancement of type-I and type-II InAs core/shell nanowires.

Internal quantum efficiency (IQE) is an important figure of merit for photoelectric applications. While the InAs core/shell (c/s) nanowire (NW) is a promising solution for efficient quantum emission, the relationship between the IQE and shell coating remains unclear. This Letter reports mid-infrared PL measurements on InAs/InGaAs, InAs/AlSb, and InAs/GaSb c/s NWs, together with bare InAs NWs as a reference. Analyses show that the IQE is depressed by a shell coating at 9 K but gets improved by up to approximately 50% for the InGaAs shell coating at 40 -140 K and up to approximately 20% beyond 110 K for the AlSb shell. The effect is ascribed not only to the crystal quality but more importantly to the radial band alignment. The result indicates the high-temperature IQE improvement of the type-I and type-II c/s NWs and the appropriateness of the mid-infrared PL analyses for narrow-gap NW evaluation.

Hole array enhanced dual-band infrared photodetection.

Photonic structures have been attracting more attention due to their ability to capture, concentrate and propagate optical energy. In this work, we propose a photon-trapping hole-array structure integrated in a nip InAsSb-GaSb heterostructure for the enhancement of the photoresponse in both near- and mid-infrared regions. The proposed symmetrical hole array can increase the photon lifetime inside the absorption layer and reduce reflection without polarization dependence. Significant enhancements in absorption and photoelectric conversion efficiency are demonstrated in dual bands for unpolarized incidence. The enhancement factors of responsivity at room temperature under zero-bias are 1.12 and 1.33 for the near- and mid-infrared, respectively, and they are increased to 1.71 and 1.79 when temperature drops to the thermoelectric cooling temperature of 220 K. Besides, such an integrated hole array also slightly improves working frequency bandwidth and response speed. This work provides a promising way for high-efficiency polarization-independent photoelectric conversion in different electromagnetic wave ranges.

Midinfrared Photoluminescence up to 290 K Reveals Radiative Mechanisms and Substrate Doping-Type Effects of InAs Nanowires.

Photoluminescence (PL) as a conventional yet powerful optical spectroscopy may provide crucial insight into the mechanism of carrier recombination and bandedge structure in semiconductors. In this study, mid-infrared PL measurements on vertically aligned InAs nanowires (NWs) are realized for the first time in a wide temperature range of up to 290 K, by which the radiative recombinations are clarified in the NWs grown on n- and p-type Si substrates, respectively. A dominant PL feature is identified to be from the type-II optical transition across the interfaces between the zinc-blend (ZB) and the wurtzite (WZ) InAs, a lower-energy feature at low temperatures is ascribed to impurity-related transition, and a higher-energy feature at high temperatures originates in the interband transition of the WZ InAs being activated by thermal-induced electron transfer. The optical properties of the ZB-on-WZ and WZ-on-ZB interfaces are asymmetric, and stronger nonradiative recombination and weaker carrier-phonon interaction show up in the NWs on p-type substrate in which built-in electric field forms and leads to carrier assembling around the WZ-on-ZB interface. The results indicate that wide temperature-range infrared PL analysis can serve as efficient vehicle for clarifying optical properties and bandedge processes of the crystal-phase interfaces in vertically aligned InAs NWs.

Infrared photoreflectance investigation of resonant levels and band edge structure in InSb.

Temperature-dependent infrared photoreflectance (PR) is employed on InSb for clarifying resonant levels (RLs) and band edge structure. Abundant PR features are well resolved around the bandgap and are verified to be of electronic inter-level transitions rather than the Franz-Keldysh oscillations. The evolution of the critical energies with temperature reveals the nature of the PR processes, from which one acceptor RL, two donor RLs, and a shallow acceptor level are quantitatively identified, and a detailed band edge structure is derived. The results show that temperature-dependent infrared PR analysis can serve as an efficient vehicle for clarifying both bound and resonant levels in semiconductors.

Hybrid Films Prepared from a Combination of Electrospinning and Casting for Offering a Dual-Phase Drug Release.

One of the most important trends in developments in electrospinning is to combine itself with traditional materials production and transformation methods to take advantage of the unique properties of nanofibers. In this research, the single-fluid blending electrospinning process was combined with the casting film method to fabricate a medicated double-layer hybrid to provide a dual-phase drug controlled release profile, with ibuprofen (IBU) as a common model of a poorly water-soluble drug and ethyl cellulose (EC) and polyvinylpyrrolidone (PVP) K60 as the polymeric excipients. Electrospun medicated IBU-PVP nanofibers (F7), casting IBU-EC films (F8) and the double-layer hybrid films (DHFs, F9) with one layer of electrospun nanofibers containing IBU and PVP and the other layer of casting films containing IBU, EC and PVP, were prepared successfully. The SEM assessments demonstrated that F7 were in linear morphologies without beads or spindles, F8 were solid films, and F9 were composed of one porous fibrous layer and one solid layer. XRD and FTIR results verified that both EC and PVP were compatible with IBU. In vitro dissolution tests indicated that F7 were able to provide a pulsatile IBU release, F8 offered a typical drug sustained release, whereas F9 were able to exhibit a dual-phase controlled release with 40.3 ± 5.1% in the first phase for a pulsatile manner and the residues were released in an extended manner in the second phase. The DHFs from a combination of electrospinning and the casting method pave a new way for developing novel functional materials.

Spatially resolved and two-dimensional mapping modulated infrared photoluminescence spectroscopy with functional wavelength up to 20 µm.

The pixel-scale nonuniformity of the photoelectric response may be due either to the in-plane electronic inhomogeneity of the narrow-gap semiconductor or to the craft fluctuation during the fabrication process, which limits the imaging performance of the infrared focal plane array (FPA) photodetector. Accordingly, a nondestructive technique is most desirable for examining the spatial uniformity of the optoelectronic properties of the narrow-gap semiconductor to identify the origin of the FPA response nonuniformity. This article introduces a spatially resolved and two-dimensional mapping infrared photoluminescence (PL) technique, especially suitable for characterizing FPA narrow-gap semiconductors, based on the modulated PL method with a step-scan Fourier transform infrared spectrometer. The experimental configuration is described, and typical applications are presented as examples to a 960 × 640 µm2 area of an InAsSbP-on-InAs layer in the medium-wave infrared range and a 960 × 960 µm2 area of a HgTe/HgCdTe superlattice (SL) in the long-wave infrared range. The results indicate that, within a measurement duration of about 30 s/spectrum, a sufficiently high signal-to-noise ratio (SNR) of over 50 is achieved with a spectral resolution of 16 cm-1 for the InAsSbP-on-InAs layer and a SNR over 30 is achieved with a spectral resolution of 12 cm-1 for the HgTe/HgCdTe SL, which warrants reliable identification of the subtle differences among the spatially resolved and two-dimensional mapping PL spectra. The imaging of the in-plane distribution of PL energy, intensity, and linewidth is realized quantitatively. The results indicate the feasibility and functionality of the spatially resolved and two-dimensional mapping PL spectroscopy for the narrow-gap semiconductors in a wide infrared range.

Self-Seeded MOCVD Growth and Dramatically Enhanced Photoluminescence of InGaAs/InP Core-Shell Nanowires.

We report on the growth and characterization of InGaAs/InP core-shell nanowires on Si-(111) substrates by metal-organic chemical vapor deposition (MOCVD). The strain at the core-shell interface induced by the large lattice mismatch between the InGaAs core and InP shell materials has strong influence on the growth behavior of the InP shell, leading to the asymmetric growth of InP shell around the InGaAs core and even to the bending of the nanowires. Transmission electron microscopy (TEM) measurements reveal that the InP shell is coherent with the InGaAs core without any misfit dislocations. Furthermore, photoluminescence (PL) measurements at 77 K show that the PL peak intensity from the InGaAs/InP core-shell nanowires displays a ∼ 100 times enhancement compared to the only InGaAs core sample without InP shell due to the passivation of surface states and effective carrier confinement resulting from InP shell layer. The results obtained here further our understanding of the growth behavior of strained core-shell heterostructure nanowires and may open new possibilities for applications in InGaAs/InP heterostructure nanowire-based optoelectronic devices on Si platform.

Nanoscale distribution of Bi atoms in InP1-xBix.

The nanoscale distribution of Bi in InPBi is determined by atom probe tomography and transmission electron microscopy. The distribution of Bi atoms is not uniform both along the growth direction and within the film plane. A statistically high Bi-content region is observed at the bottom of the InPBi layer close to the InPBi/InP interface. Bi-rich V-shaped walls on the (-111) and (1-11) planes close to the InPBi/InP interface and quasi-periodic Bi-rich nanowalls in the (1-10) plane with a periodicity of about 100 nm are observed. A growth model is proposed to explain the formation of these unique Bi-related nanoscale features. These features can significantly affect the deep levels of the InPBi epilayer. The regions in the InPBi layer with or without these Bi-related nanostructures exhibit different optical properties.

Anomalous photoluminescence in InP1-xBix.

Low temperature photoluminescence (PL) from InP1-xBix thin films with Bi concentrations in the 0-2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 µm in optical coherent tomography (OCT).