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Abstract We report longer surface plasmon polariton propagation distance based on crystalline crystal silver at low temperature. Although enhanced plasmonic performance at low temperature has been predicted for a long time, it has not been directly observed on polycrystalline silver films which suffer from significant plasmonic losses due to grain boundaries and rough silver surface. Here we show that longer propagation distance can be achieved with epitaxial silver at low temperature. Importantly, the enhancement at low temperature are consistent across silver films grown with different methods.

Exciton energy transfer in monolayer transition metal dichalcogenides is limited to short distances. Here, Shi et al. fabricate a planar metal-oxide-semiconductor structure and show that exciton energy transfer can be extended to tens of microns, mediated by an exciton-surface-plasmon-polariton–exciton conversion mechanism.

ZnO nanowire-based surface plasmon polariton (SPP) nanolasers with metal–insulator–semiconductor hierarchical nanostructures have emerged as potential candidates for integrated photonic applications. In the present study, we demonstrated an SPP nanolaser consisting of ZnO nanowires coupled with a single-crystalline aluminum (Al) film and a WO3 dielectric interlayer. High-quality ZnO nanowires were prepared using a vapor phase transport and condensation deposition process via catalyzed growth. Subsequently, prepared ZnO nanowires were transferred onto a single-crystalline Al film grown by molecular beam epitaxy (MBE). Meanwhile, a WO3 dielectric interlayer was deposited between the ZnO nanowires and Al film, via e-beam technique, to prevent the optical loss from dominating the metallic region. The metal–oxide–semiconductor (MOS) structured SPP laser, with an optimal WO3 insulating layer thickness of 3.6 nm, demonstrated an ultra-low threshold laser operation (lasing threshold of 0.79 MW cm−2). This threshold value was nearly eight times lower than that previously reported in similar ZnO/Al2O3/Al plasmonic lasers, which were ≈2.4 and ≈3 times suppressed compared to the SPP laser, with WO3 insulating layer thicknesses of 5 nm and 8 nm, respectively. Such suppression of the lasing threshold is attributed to the WO3 insulating layer, which mediated the strong confinement of the optical field in the subwavelength regime.

An indium nitride (InN) gas sensor of 10 nm in thickness has achieved detection limit of 0.4 ppm acetone. The sensor has a size of 1 mm by 2.5 mm, while its sensing area is 0.25 mm by 2 mm. Detection of such a low acetone concentration in exhaled breath could enable early diagnosis of diabetes for portable physiological applications. The ultrathin InN epilayer extensively enhances sensing sensitivity due to its strong electron accumulation on roughly 5–10 nm deep layers from the surface. Platinum as catalyst can increase output current signals by 2.5-fold (94 vs. 37.5 μA) as well as reduce response time by 8.4-fold (150 vs. 1,260 s) in comparison with bare InN. More, the effect of 3% oxygen consumption due to breath inhalation and exhalation on 2.4 ppm acetone gas detection was investigated, indicating that such an acetone concentration can be analyzed in air.

An Ultrathin (~10 nm) InN ion sensitive field effect transistor (ISFET) with gate regions functionalized with phosphotyrosine (p-Tyr) is proposed to detect calcium ions (Ca2+) in aqueous solution. The ISFET was miniaturized to a chip size of 1.1 mm by 1.5 mm and integrated at the tip of a hypodermic injection needle (18 G) for real-time and continuous monitoring. The sensor shows a current variation ratio of 1.11% with per decade change of Ca2+ and a detection limit of 10-6 M. The response time of 5 sec. reveals its great potential for accomplishing fast detection in chemical and physiological sensing applications. The sensor would be applied in medical diagnosis and used to monitor continuous and real-time variations of Ca2+ levels in human blood in the near future.

The article presents a new approach, which can be used for the synthesis of various large-area, three-dimensional colloidal gold and silver nanoparticle supercrystal films. The various plasmonic properties and the application of these films as plasmonic crystals are also discussed.

A combination of Hall effect measurement and scanning Kelvin probe microscopy techniques is employed to explain the various effects of the [([NH.sub.4]).sub.2][S.sub.x] treatment on the indium nitride surfaces. The treatment is shown to lead to a significant increase in the sheet resistance, while reducing the sheet carrier density of the system.

Comprehensively characterization of a generic and efficient chemical patterning method based on local plasma-induced conversion of surface functional groups on self-assembled monolayers (SAMs) is described. Spatially controlled plasma exposure realized by elastomeric poly(dimethylsiloxane) (PDMS) contact masks or channel stamps with feature sizes ranging from nanometer, micrometer, to centimeter is also presented.

Ultrafast carrier thermalization in n-type indium nitride (InN) with an electron concentration is examined by using femtosecond transient transmission measurements at room temperature with different wavelengths. The femtosecond thermalization time is consistent with the prediction based on a Coulomb screening effect, but there is no evidence on the existence of the hot phonon effect.

We present ultrafast time-resolved optical spectroscopy on GaN nanorods at room temperature. The studied GaN nanorods, with diameters of ~50 nm and lengths of ~400 nm, were grown on the silicon substrate. After femtosecond optical pulses excited carriers in the GaN nanorods, the carriers thermalized within a few picoseconds. Subsequently, the electrons are trapped by the surface states on the order of 20 ps. After the surface electric field was reformed in the GaN nanorods, we found the lifetime of the residue carriers in GaN nanorods is longer than 1.7 ns at room temperature, while the lifetime of carriers in GaN thin film is typically a few hundred picoseconds. Our findings indicate that GaN nanorods have higher electrical quality compared with GaN thin film. [ABSTRACT FROM AUTHOR]

The immobilization scheme of monodispersed gold nanoparticles (10-nm diameter) on piezoelectric substrate surfaces using organosilane molecules as cross-linkers has been developed for lithium niobate (LiNbO3) and silicon oxide (Si02)/gold-covered lithium tantalate (LiTaO3) of Rayleigh and guided shear horizontal- (guided SH) surface acoustic wave (SAW) sensors. In this study, comparative measurements of gold nanoparticle adsorption kinetics using high-resolution field-emission scanning electron microscopy and SAW sensors allow the frequency responses of SAW sensors to be quantitatively correlated with surface densities of adsorbed nanoparticles. Using this approach, gold nanoparticles are used as the "nano-sized mass standards" to scale the mass loading in a wide dynamical range. Rayleigh-SAW and guided SH-SAW sensors are employed here to monitor the surface mass changes on the device surfaces in gas and liquid phases, respectively. The mass sensitivity (∼20 Hz·cm²/ng) of Rayleigh-SAW device (fundamental oscillation frequency of 113.3 Mhz in air) is more than 2 orders of magnitude higher than that of conventional 9-MHz quartz crystal microbalance sensors. Furthermore, in situ (aqueous solutions), real-time measurements of adsorption kinetics for both citrate-stabilized gold nanoparticles and DNA-gold nanoparticle conjugates are also demonstrated by guided SH-SAW (fundamental oscillation frequency of 121.3 MHz). By comparing frequency shifts between the adsorption cases of gold nanoparticles and DNA-gold nanoparticle conjugates, the average number of bound oligonucleotides per gold nanoparticle can also be determined. The high mass sensitivity (∼6 Hz·cm²/ng) of guided SH-SAW sensors and successful detection of DNA-gold nanoparticle conjugates paves the way for real-time biosensing in liquids using nanoparticle-enhanced SAW devices. [ABSTRACT FROM AUTHOR]

We report on precise control of film crystal polarity in fully relaxed, thin InN/AlN heterojunctions grown on sapphire by plasma-assisted molecular beam epitaxy. Using these samples, we have measured asymmetric valence band offset values (0.8 ± 0.1 eV for the In/Al- and 1.8 ± 0.1 eV for the N-polar case) at polar InN/AlN heterojuncitons by synchrotron soft x-ray photoelectron spectroscopy. We confirm that the discontinuities of spontaneous polarizations at polar InN/AlN heterointerfaces lead to the large core level shift of the Al 2p peak related to the In 4d peak (1.0 eV). [ABSTRACT FROM AUTHOR]

The screening effect of heavy-hole LO-phonon interaction is observed and studied through the pump-probe transmission measurement in Mg-doped InN. Combining the measured transient hole dynamics with the absorption spectra, the optical based observation is able to prevent the influence of the surface n-type layer and the depression layer in Mg-doped InN. With the observed heavy-hole heating time at different photoexcited carrier densities and the measured absorption edge, we show that it is now possible to estimate the background hole density and band gap energy in Mg-doped InN. [ABSTRACT FROM AUTHOR]

Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaN p-n nanorods can span the entire visible spectrum with a large linear polarization ratio (∼0.85). Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes (LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths. [ABSTRACT FROM AUTHOR]

Conventional InGaN/GaN light-emitting diodes based on planar quantum well structures do not allow for efficient long-wavelength operation beyond the blue region due to a strong quantum confined Stark effect in lattice-mismatched polar InGaN quantum wells. Here we overcome the limitation by using self-assembled GaN nanorod arrays as strain-free growth templates for thick InGaN nanodisks. In combination with enhanced carrier localization and high crystalline quality, this approach allows us to realize full-color InGaN nanodisk emitters. By tailoring the numbers, positions, and thicknesses of polychromatic nanodisk ensembles embedded vertically in the GaN nanorod p-n junction, we are able to demonstrate natural white (color temperature ∼6000 K) electroluminescence from InGaN/GaN nanorod arrays. [ABSTRACT FROM AUTHOR]

We report that the electron cooling time in indium nitride can be as fast as sub-100 femtosecond at low electron concentration (<5×1017/cm3), which is much faster than previous reports. Through investigating the dependence of the measured carrier cooling time on electron density, our study proved the dominant role of the screened Fröhlich interaction in the reduction in carrier cooling rate at an electron density higher than 1.8×1018/cm3. [ABSTRACT FROM AUTHOR]

Ultrathin β-Si3N4(0001) epitaxial films formed by N2-plasma nitridation of Si(111) substrates have been studied by photoelectron spectroscopy using synchrotron radiation. The valence band offset at the β-Si3N4/Si interface was determined by valence-band photoelectron spectra to be 1.8 eV. Furthermore, the Si 2p core-level emissions were analyzed for nitride (Si4+) and subnitride (Si3+ and Si+) components to characterize the interface stoichiometry. In contrast to the interfaces formed by ammonia thermal nitridation and N2-plasma nitridation at room temperature, the interface formed by N2-plasma nitridation at high substrate temperature is very close to subnitride free with an abrupt composition transition. [ABSTRACT FROM AUTHOR]

Low-cost black coating with freestanding well-aligned carbon nanotubes (CNTs), fabricated from CNT-dispersive in water-soluble poly(vinyl alcohol) (PVA) matrix, exhibits a bright white-light emission with narrow-band RGB (red, green, blue) colors having CIE (0.327, 0.349) chromaticity coordinate when subjected to the microwave irradiation. [ABSTRACT FROM AUTHOR]

Femtosecond pulses at wavelengths ranging from 750 to 900 nm (1.38–1.65 eV) were used in the excitation and probing of ultrafast carrier dynamics in InN epitaxial films. Experimental results show that the hot electron relaxation rate increases with increasing electron energy, which is measured as E0.53. This observation agrees with the prediction of electron-electron scattering relaxation mechanism. In addition, the electron-hole recombination rates are independent of the electron energy and have values of ∼7×109 Hz. We attribute this result to the Auger recombination in InN being insensitive to temperature. [ABSTRACT FROM AUTHOR]

The electrical properties of N-polar undoped InN and nonpolar a-InN:Mg ion sensitive field effect transistors (ISFETs) have been investigated by electrolyte-gate-biased current-voltage (IDS-VGS) measurements. IDS-VGS characteristics reveal that the a-InN:Mg ISFETs have a large (∼52%) current variation ratio at a gate bias of 0.3 V with respect to the unbiased one, which is higher than that from the undoped InN ISFETs (∼18% and <0.1% for 10-nm and 1-μm-thick -c-InN epilayers, respectively). The a-InN:Mg ISFETs can also function as a pH sensor with a sensitivity of 56.5 mV/pH and a response time less than 10 s. [ABSTRACT FROM AUTHOR]

Ultrathin (∼10 nm) InN ion selective field effect transistors (ISFETs) have been demonstrated to perform ion sensing in aqueous solutions with a sensitivity of 5 μA/decade and a response time smaller than 10 s. The positively charged surface states on InN surfaces selectively adsorb anions, building Helmholtz voltages in solutions and modulating the drain-source current of the ISFETs. The ISFET performance is greatly enhanced by depleting carriers in the ultrathin InN channel where the film thickness is close to depth of surface electron accumulation. [ABSTRACT FROM AUTHOR]

Scaling down semiconductor lasers in all three dimensions holds the key to the development of compact, low-threshold, and ultrafast coherent light sources, as well as integrated optoelectronic and plasmonic circuits. However, the minimum size of conventional semiconductor lasers utilizing dielectric cavity resonators (photonic cavities) is limited by the diffraction limit. To date, surface plasmon amplification by stimulated emission of radiation (spaser)-based plasmonic nanolaser is the only photon and plasmon-emitting device capable of this remarkable feat. Specifically, it has been experimentally demonstrated that the use of plasmonic cavities based on metal-insulator-semiconductor (MIS) nanostructures can indeed break the diffraction limit in all three dimensions. In this review, we present an updated overview of the current status for plasmonic nanolasers using the MIS configuration and other related metal-cladded semiconductor microlasers. In particular, by using composition-varied indium gallium nitride/gallium nitride core–shell nanorods, it is possible to realize all-color, single-mode nanolasers in the full visible wavelength range with ultralow continuous-wave (CW) lasing thresholds. The lasing action in these subdiffraction plasmonic cavities is achieved via a unique auto-tuning mechanism based on the property of weak size dependence inherent in plasmonic nanolasers. As for the choice of metals in the plasmonic structures, epitaxial silver films and giant colloidal silver crystals have been shown to be the superior constituent materials for plasmonic cavities due to their low plasmonic losses in the visible and near-infrared (NIR) spectral regions. In this review, we also provide some perspectives on the challenges and opportunities in this exciting new research frontier. [ABSTRACT FROM AUTHOR]

We used the spin-coating method combined with ultrasonic atomization as a continuous, one-step process to generate a two-dimensional honeycomb network that was constructed from pure multi-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

Temperature-dependent photoluminescence (PL) and photoreflectance (PR) spectroscopy and room-temperature Raman spectroscopy and X-ray diffraction have been utilized to investigate the optical properties, electron concentration, crystalline quality, and electronic band structures, especially valence-band splittings, of InN films grown by plasma-assisted molecular beam epitaxy (PAMBE) and metal–organic chemical vapor deposition (MOCVD). The smaller thermal activation energies imply the PAMBE-grown InN film exhibits low-density localized states from band tail states. PR signals of the InN film are detectable when the temperature is below about 100 K due to the cooling down of free electrons to trap states. For the MOCVD-grown InN film, no PR signal is observed even at 15 K due to the higher free electron concentration. To analyze the energetic positions of the features in the PR spectra without ambiguity, the moduli of individual PR resonances are considered. Based on the PR results and appropriate Hamiltonian, the values of the crystal-field splitting and the spin–orbit splitting in InN are experimentally determined as 26.8 and 14.5 meV, respectively. Theoretical and experimental reports are compared and discussed to verify this result. [ABSTRACT FROM AUTHOR]

Fabrication of isolated noble metal nanoparticles embedded in transparent substrates is the fasting growing demand for innovative plasmonic technologies. Here we report a simple and effective methodology for the preparation of highly stable plasmonic nanoparticles embedded in a glass surface. Size-controllable (10-70 nm) Au nanoparticles were rapidly prepared when subjected to the home-microwave plasma. Accordingly, the optical extinction maximum of the localized surface plasmon resonance (LSPR) can be systematically tuned in the range 532-586 nm. We find that the plasmonic structures are exceedingly stable toward immersion in ethanol solvents and pass successfully the adhesive tape test, which makes our system highly promising for efficient transmission-LSPR nanosensors. Besides, the attractive features of substrate-bound plasmonic nanostructures include its low cost, versatility, robustness, reusability and a promising ability to make a multi-arrayed LSPR biochip. [ABSTRACT FROM AUTHOR]

Real time chloride ion detection using InN gated AlGaN/GaN high electron mobility transistors (HEMTs) was demonstrated. The InN thin film on the gate area of the HEMT provided fixed surface sites for reversible anion coordination. The drain current of the HEMT sensor exhibited increased a function of chloride ion concentration. The positive ions (Na+, Mg+2, and H+) in the chloride ion solutions showed no effect on the chloride ion concentration detection. The sensor was tested over a range of chloride ion concentrations from 100 nM to 100 μM. The chloride ion HEMT sensors can be integrated with AlGaN/GaN HEMT based pH and glucose sensors for exhaled breath condensate glucose monitoring technology. The HEMT based sensor can also be integrated into a wireless data transmission system for remote sensing applications. [ABSTRACT FROM AUTHOR]

The article provides information on a study that uses spatially and time-resolved photoluminescence (PL) measurements to investigate the influence of the moiré potential on interlayer exciton (IX) diffusion in WSe2/MoSe2 hBLs. Topics discussed include explanation on the strikingly different IX diffusion in chemical vapor deposition (CVD) and mechanical exfoliation and transfer (MET) hBLs, and results of the study.

A nanolaser is a key component for on-chip optical communications and computing systems. Here, we report on the low-threshold, continuous-wave operation of a subdiffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium. The atomic smoothness of the metallic film is crucial for reducing the modal volume and plasmonic losses. Bimodal lasing with similar pumping thresholds was experimentally observed, and polarization properties of the two modes were used to unambiguously identify them with theoretically predicted modes. The all-epitaxial approach opens a scalable platform for low-loss, active nanoplasmonics. [ABSTRACT FROM AUTHOR]

The article reports on the self-assembly of highly ordered 2D superlattices of alkanethiolate-stabilized gold nanoparticles onto quartz substance with varying lattice constants, which can be controlled by the alkyl chain lengths. According to the author, the 2D nanoparticle superlattices show strong CSPR extinction bands which are tunable via near-field coupling of adjacent nanoparticles. He added that the approcah provides a unique and viable means of building bottom-up plasmonic crystals.

The interplays between different quasiparticles in solids lay the foundation for a wide spectrum of intriguing quantum effects, yet how the collective plasmon excitations affect the quantum transport of electrons remains largely unexplored. Here we provide the first demonstration that when the electron-plasmon coupling is introduced, the quantum coherence of electrons in graphene is substantially enhanced with the quantum coherence length almost tripled. We further develop a microscopic model to interpret the striking observations, emphasizing the vital role of the graphene plasmons in suppressing electron-electron dephasing. The novel and transformative concept of plasmon-enhanced quantum coherence sheds new insight into interquasiparticle interactions, and further extends a new dimension to exploit nontrivial quantum phenomena and devices in solid systems. [ABSTRACT FROM AUTHOR]