Light Absorption Cross Section Research Articles

Numerical study of near-field radiative heat transfer between bio-inspired spiny particles

The spine-like structure appears on some smooth organisms and has a high light absorption cross-section. Inspired by the spiny structure in the nature, this study establishes models of solid and hollow spiny particles. The effects of spine cross-section size, uniform and nonuniform spine distribution, hollow size, gap, and spine dislocation on near-field radiative heat transfer of spiny particles are investigated based on the thermal discrete dipole approximations method. The spectral radiative conductance and volumetric net power distribution are obtained. The results indicate that the coupling of localized surface phonons between two particles is affected by spine cross-section size and spine distribution. Near-field radiative heat transfer of spiny particles is enhanced maximumly when the frequencies are slightly lower than the resonance frequency of smooth particles. The peak of the spectral conductance is red-shifted and decreases with the increase of hollow size. The uniformity of volumetric power absorbed distribution increases and the variation of the relative spectral conductance decreases with increasing gap. The influence of two particles’ spine dislocation on near-field radiative heat transfer and volumetric power absorbed distribution is not obvious.

Optical properties and simple forcing efficiency of the organic aerosols and black carbon emitted by residential wood burning in rural central Europe

Abstract. Recent years have seen an increase in the use of wood for energy production of over 30 %, and this trend is expected to continue due to the current energy crisis and geopolitical instability. At present, residential wood burning (RWB) is one of the most important sources of organic aerosols (OAs) and black carbon (BC), posing a significant risk to air quality and health. Simultaneously, as a substantial aerosol source, RWB also holds relevance in the context of aerosol radiative effects and climate. While BC is recognized for its large light absorption cross-section, the role of OAs in light absorption is still under evaluation due to their heterogeneous composition and source-dependent optical properties. Existing studies that characterize wood-burning aerosol emissions in Europe primarily concentrate on urban and background sites and focus on BC properties. Despite the significant RWB emissions in rural areas, these locations have received comparatively less attention. The present scenario underscores the imperative for an improved understanding of RWB pollution, aerosol optical properties, and their subsequent connection to climate impacts, particularly in rural areas. We have characterized atmospheric aerosol particles from a central European rural site during wintertime in the village of Retje in Loški Potok, Slovenia, from 1 December 2017 to 7 March 2018. The village experienced extremely high aerosol concentrations produced by RWB and near-ground temperature inversion. The isolated location of the site and the substantial local emissions made it an ideal laboratory-like place for characterizing RWB aerosols with low influence from non-RWB sources under ambient conditions. The mean mass concentrations of OA and BC were 35 µg m−3 (max⁡=270 µg m−3) and 3.1 µg m−3 (max⁡=24 µg m−3), respectively. The mean total particle number concentration (10–600 nm) was 9.9×103 particles cm−3 (max⁡=59×103 particles cm−3). The mean total light absorption coefficients at 370 and 880 nm measured by an AE33 Aethalometer were 120 and 22 Mm−1 and had maximum values of 1100 and 180 Mm−1, respectively. The aerosol concentrations and absorption coefficients measured during the campaign in Loški Potok were significantly larger than reported values for several urban areas in the region with larger populations and a larger extent of aerosol sources. Here, considerable contributions from brown carbon (BrC) to the total light absorption were identified, reaching up to 60 % and 48 % in the near-UV (370 nm) and blue (470 nm) wavelengths. These contributions are up to 3 times higher than values reported for other sites impacted by wood-burning emissions. The calculated mass absorption cross-section and the absorption Ångström exponent for RWB OA were MACOA,370nm=2.4 m2 g−1, and AAEBrC,370-590nm=3.9, respectively. Simple-forcing-efficiency (SFE) calculations were performed as a sensitivity analysis to evaluate the climate impact of the RWB aerosols produced at the study site by integrating the optical properties measured during the campaign. The SFE results show a considerable forcing capacity from the local RWB aerosols, with a high sensitivity to OA absorption properties and a more substantial impact over bright surfaces like snow, typical during the coldest season with higher OA emissions from RWB. Our study's results are highly significant regarding air pollution, optical properties, and climate impact. The findings suggest that there may be an underestimation of RWB emissions in rural Europe and that further investigation is necessary.

Microscale imaging sheds light on species-specific strategies for photo-regulation and photo-acclimation of microphytobenthic diatoms.

Intertidal microphytobenthic (MPB) biofilms are key sites for coastal primary production, predominantly by pennate diatoms exhibiting photo-regulation via non-photochemical quenching (NPQ) and vertical migration. Movement is the main photo-regulation mechanism of motile (epipelic) diatoms and because they can move from light, they show low-light acclimation features such as low NPQ levels, as compared to non-motile (epipsammic) forms. However, most comparisons of MPB species-specific photo-regulation have used low light acclimated monocultures, not mimicking environmental conditions. Here we used variable chlorophyll fluorescence imaging, fluorescent labelling in sediment cores and scanning electron microscopy to compare the movement and NPQ responses to light of four epipelic diatom species from a natural MPB biofilm. The diatoms exhibited different species-specific photo-regulation features and a large NPQ range, exceeding that reported for epipsammic diatoms. This could allow epipelic species to coexist in compacted light niches of MPB communities. We show that diatom cell orientation within MPB can be modulated by light, where diatoms oriented themselves more perpendicular to the sediment surface under high light vs. more parallel under low light, demonstrating behavioural, photo-regulatory response by varying their light absorption cross-section. This highlights the importance of considering species-specific responses and understanding cell orientation and photo-behaviour in MPB research.

Seasonal Variations and Source Apportionment of Carbonaceous Components in Luoyang: Implication for Brown Carbon Contribution

A total of 98 samples were collected to analyze the seasonal variation and source apportionment of carbonaceous components, especially brown carbon (BrC), of PM2.5in Luoyang during 2018-2019. The concentrations of organic carbon (OC) and elemental carbon (EC) ranged from (7.04±1.82) μg·m-3to(23.81±8.68) μg·m-3and (2.96±1.4) μg·m-3to (13.41±7.91) μg·m-3, respectively, showing the seasonal variation of being high in winter and low in summer; the carbonaceous fraction and secondary organic aerosol percentages were higher by 8.33%-141.03% and by 0.77%-63.14%, respectively, compared with that in 2015. The light absorption cross section (MAC) values showed different seasonal variations with the concentration of carbonaceous fraction, shown in descending order as autumn (7.67 m2·g-1)>winter (5.65 m2·g-1)>spring (5.13 m2·g-1)>summer (3.84 m2·g-1). The MAC values ranged from 3.84 to 7.67 m2·g-1 at 445 nm, which was lower than that in coal ash. Seasonal variation in light absorption and the contribution of BrC to total light absorption (babs,BrC,405 nm, babs,BrC,405 nm/babs,405 nm) in descending order was winter (31.57 Mm-1, 33%), autumn (11.40 Mm-1, 25%), spring (4.88 Mm-1, 23%), and summer (2.12 Mm-1, 21%). The proportion of carbonaceous components decreased as haze episodes evolved, whereas the contribution of light absorption of BrC increased, highlighting the important contribution of BrC to the total light absorption. The results of PMF and correlation coefficients of babs,BrC,405 nm and PM2.5 components indicated that motor vehicles and secondary nitrate contributed 27.7% and 24.0%, respectively. Our findings have significant scientific implications for the deep controlling of carbonaceous aerosol, especially for BrC, in Luoyang in the future.

Secondary Organic Aerosol (SOA) from Photo-Oxidation of Toluene: 1 Influence of Reactive Nitrogen, Acidity and Water Vapours on Optical Properties

Many climate models treat the light-absorbing SOA component called “brown carbon” (BrC) as non-light absorbing because its formation and transformations are poorly understood. We therefore investigated the influence of reactive nitrogen (NOx, NH3)-, acidity (H2SO4)-, and water-mediated chemistry on SOA formed by the photo-oxidation of toluene, the subsequent formation and transformation of BrC, and its optical properties. We discovered that nitrogen-poor (NP) SOA is formed when the molar ratio of NOx to reacted toluene (henceforth, [NOx/ΔHC]) is 0.15 or less, whereas nitrogen-rich (NR) SOA is formed when [NOx/ΔHC] > 0.15. NR and NP SOA have markedly different characteristics. The light absorption coefficient (Babs) and mass absorption cross-section (MAC) of the SOA increased with [NOx/ΔHC] under both the NP and NR regimes. For NP SOA, the MAC increased with [NOx/ΔHC] independently of the relative humidity (RH). However, the MAC of NR SOA was RH-dependent. Under both NP and NR regimes, acidity promoted SOA browning while NH3 increased Babs and MAC at 80% RH. The highest MAC was observed at the lowest RH (20%) for acidic NR SOA, and it was postulated that the MAC of SOA depends mainly on the pH and the [H+]free/[SOA mass] ratio of the aqueous SOA phase.

(Invited) One-Dimensional Features of Electron Transport in Single-Walled Carbon Nanotube Thin Films

Single-walled carbon nanotubes (SWCNTs) are excellent conductors with high flexibility, high thermal conductivity, and high transparency. Flexible and transparent SWCNT thin films and SWCNT yarns with high mechanical strength have been produced, and in particular, the improvement of electrical conduction characteristics of these SWCNT aggregates has been studied intensively. The electrical conductivity of SWCNT aggregates have improved year by year, but it is worse than those of a single SWCNT, so far. SWCNT aggregates contain complex structures such as SWCNTs with different chirality structures, many junctions, and bundle structures, which could be the cause of deterioration of transport characteristics, however, it has not been clarified.In this study, we focused on low-density SWCNT thin films and investigated their electron transport characteristics. The low-density SWCNT thin film has a simple network structure since the network consists of the bundles of a small number of long SWCNTs. Here, the magnetic field dependence, temperature dependence, and gate voltage dependence of the electrical conductivity were measured and analyzed.The SWCNT thin films were synthesized by a floating catalyst CVD method, and they were transparent (90%T), and electrically conductive [1]. The thin film consisted of a network structure of bundles, which consisted of about 10 SWCNTs. The films were mixtures with metallic and semiconducting SWCNTs. The electrical resistivity of the SWCNT thin film was measured by the four-point probes method, and the gate voltage (Vg) was applied using an ionic liquid. The direction of the magnetic field was perpendicular to the thin film surface. The areal density of SWCNT length was estimated from the light absorption cross-section of the SWCNT thin films, and then the electrical resistivity was calculated from the actual volume of SWCNTs excluding the void space.SWCNTs generally show p-type characteristics in the atmosphere in the back-gate configuration due to the dope effects of oxygen and/or water molecules. However, the Vg dependence of the electrical resistivity of the thin film showed a bipolar behavior under the ionic liquid gate. The change ratio of the resistivity in the Vg range (-3 to +3 V) was more than 10, which suggested that not only did the non-conductive semiconducting SWCNT become conductive, but the number of percolation paths increased accordingly. Raman scattering spectroscopy also exhibited that semi-conducting SWCNTs were heavily doped by the ionic liquid gating. The electrical resistivity decreased down to approximately 20 μΩcm at room temperature with Vg=-3 V. The temperature dependence in the temperature range (30-110 K) with Vg=-3 V was explained by the variable range hopping (VRH) model with the dimensionality of one, although the SWCNT thin films are two-dimensional structures. Hall resistivity of the thin film slightly changed at different Vg, however, it was almost negligible. It is probably because most of the SWCNT thin films were linear bundle parts, and the bundle diameter was a few nm, which is much smaller than the cyclotron radius [2]. Additionally, the thermoelectric measurement was performed. The Vg dependence of thermoelectrical conductivity showed one-dimensional characteristics [3]. These measurements showed one-dimensional features of electron transport properties of SWCNT thin films. A single SWCNT can be regarded as a one-dimensional system, but in general, one-dimensional features do not appear in the electron transport of SWCNTs in the form of thin films or yarns. In this study, probably because the thin film has a very low density (light transmittance 90% T) and forms a network consisting of a thin bundle structure, the one-dimensional features clearly appeared. The one-dimensionality is one of the origins of the excellent properties of SWCNTs and it is could be a useful index for improving electrical conductivity.AcknowledgmentsI would like to thank H. Date (Univ. of Tokyo) for the experiments and measurements, Prof. T. Fujii (Univ. of Tokyo) for the measurements, and Prof. E. I. Kauppinen for the sample supply.[1] A.G. Nasibulin, et al., ACS Nano, 5 (2011) 3214.[2] M. L. Roukes, et al., Phys. Rev. Lett., 59 (1987) 3011.[3] Y. Ichinose, et al., Phys. Rev. Mater., 5 (2021) 025404.

1D NiO–3D Fe2O3 mixed dimensional heterostructure for fast response flexible broadband photodetector

Conventional heterojunction photodetectors rely on planar junction architecture which suffer from low interfacial contact area, inferior light absorption characteristics and complex fabrication schemes. Heterojunctions based on mixed dimensional nanostructures such as 0D-1D, 1D-2D, 1D-3D etc have recently garnered exceptional research interest owing to their atomically sharp interfaces, tunable junction properties such as enhanced light absorption cross-section. In this work, a flexible broadband UV–vis photodetector employing mixed dimensional heterostructure of 1D NiO nanofibers and 3D Fe2O3 nanoparticles is fabricated. NiO nanofibers were synthesized via economical and scalable electro-spinning technique and made composite with Fe2O3 nanoclusters for hetero-structure fabrication. The optical absorption spectra of NiO nanofibers and Fe2O3 nanoparticles exhibit peak absorption in UV and visible spectra, respectively. The as-fabricated photodetector displays quick response times of 0.09 s and 0.18 s and responsivities of 5.7 mA W−1 (0.03 mW cm−2) and 5.2 mA W−1 (0.01 mW cm−2) for UV and visible spectra, respectively. The fabricated NiO–Fe2O3 device also exhibits excellent detectivity in the order of 1012 jones. The superior performance of the device is ascribed to the type-II heterojunction between NiO–Fe2O3 nanostructures, which results in the localized built-in potential at their interface, that aids in the effective carrier separation and transportation. Further, the flexible photodetector displays excellent robustness when bent over ∼1000 cycles thereby proving its potential towards developing reliable, diverse functional opto-electronic devices.

(Invited) Optically-Active Zero-Dimensional Graphene Quantum Dots with MoS2 for Photodetection

With its superior electronic properties, large surface area, high mechanical strength-to-weight ratio, exceptional charge carrier mobility reaching the ballistic limit in certain cases, graphene is a material of immense technological importance. However, compared to other two-dimensional (2D) van der Waals solids, such as transition metal dichalcogenides (TMDCs) and black phosphorus, an atomic membrane of graphene absorbs less than about 2% of the incoming light due to its low light absorption cross-section, and lack of a bandgap. However, when sheets of graphene are physically confined into nanoscale dimensions, either as graphene nanoribbons or zero-dimensional (0D) structures, such as graphene quantum dots (GQDs), a band gap in such structures is induced due to quantum confinement. Additionally, semiconducting 2D materials such as MoS2, exhibit a distinct and well defined band gap ranging from 1.3 eV to 1.8 eV, from bulk to monolayers. In this work, the hybrid structure of 0D graphene quantum dots (GQDs) and semiconducting 2D MoS2 has been investigated that exhibit outstanding properties for optoelectronic devices surpassing the limitations of MoS2 photodetectors where the GQDs extend the optical absorption into the near-UV regime. A tunable laser revealed the photocurrent to be maximal at lower wavelengths in the near ultra-violet (UV) over the 400 – 1100 nm spectral range, where the responsivity of the hybrid GQDs/MoS2 was ~ 775 AW-1. Time-resolved measurements of the photocurrent for the hybrid devices also resulted in enhancement of the switching dynamics with switching time constants far improved compared to bare MoS2. From our promising results, we conclude that the GQDs exhibit a sizable bandgap upon optical excitation, where photocarriers are injected into the MoS2 films, endowing the hybrids with long carrier life-times to enable efficient light absorption beyond the visible and into the near-UV regime. The GQD-MoS2 structure is thus an enabling platform for high-performance photodetectors, optoelectronic circuits and quantum devices.

(Invited) Optically-Active Zero-Dimensional Graphene Quantum Dots with MoS2 for Photodetection

With its superior electronic properties, large surface area, high mechanical strength-to-weight ratio, exceptional charge carrier mobility reaching the ballistic limit in certain cases, graphene is a material of immense technological importance. However, compared to other two-dimensional (2D) van der Waals solids, such as transition metal dichalcogenides (TMDCs) and black phosphorus, an atomic membrane of graphene absorbs less than about 2% of the incoming light due to its low light absorption cross-section, and lack of a bandgap. However, when sheets of graphene are physically confined into nanoscale dimensions, either as graphene nanoribbons or zero-dimensional (0D) structures, such as graphene quantum dots (GQDs), a band gap in such structures is induced due to quantum confinement. Additionally, semiconducting 2D materials such as MoS2, exhibit a distinct and well-defined band gap ranging from 1.3 eV to 1.8 eV, from bulk to monolayers. In this work, the hybrid structure of 0D graphene quantum dots (GQDs) and semiconducting 2D MoS2 has been investigated that exhibit outstanding properties for optoelectronic devices surpassing the limitations of bare MoS2 photodetectors.

UV and VUV-induced fragmentation of tin-oxo cage ions.

Photoresist materials are being optimized for the recently introduced Extreme Ultraviolet (EUV) photolithographic technology. Organometallic compounds are potential candidates for replacing the ubiquitous polymer-based chemically amplified resists. Tin (Sn) has a particularly large absorption cross section for EUV light (13.5 nm, 92 eV), which could lead to a lower required EUV dose for achieving the desired solubility change (improved sensitivity). However, the fundamental interaction between organometallic materials and higher energy photons is poorly understood. In this work, we exposed n-butyltin-oxo cage dications (M2+) in the gas phase to photons in the energy range 4-35 eV to explore their fundamental photoreactivity. Photoproducts were detected using mass spectrometry. Homolytic cleavage of tin-carbon bonds was observed for all photon energies above the onset of electronic absorption at ∼5 eV (∼250 nm), leading to photoproducts which have lost one or more of the attached butyl groups (Bu). Above 12 eV (<103 nm), dissociative photoionization occurred for the dication (M2+), competing with the neutral loss channels. The photoionization threshold is lowered by approximately 2 eV when one counterion (triflate, OTf- or tosylate, OTs-) is attached to the tin-oxo cage (MOTf+ and MOTs+). This threshold is expected to be even lower if each tin-oxo cage is attached to two counterions, as is the case in a solid film of tin-oxo cages. Addition of counterions also affected the fragmentation pathways; photoexcitation of (MX)+ (X = counterion, OTf or OTs) always led to formation of (MX-2Bu)+ rather than (MX-Bu)+. MOTs+ was much more reactive than MOTf+ in terms of reaction products per absorbed photon. A possible explanation for this is proposed, which involves the counterion reacting with the initially formed tin-based radical.

Photophysics of Isolated Rose Bengal Anions

Dye molecules based on the xanthene moiety are widely used as fluorescent probes in bioimaging and technological applications due to their large absorption cross-section for visible light and high fluorescence quantum yield. These applications require a clear understanding of the dye's inherent photophysics and the effect of a condensed-phase environment. Here, the gas-phase photophysics of the rose bengal doubly deprotonated dianion [RB - 2H]2-, deprotonated monoanion [RB - H]-, and doubly deprotonated radical anion [RB - 2H]•- is investigated using photodetachment, photoelectron, and dispersed fluorescence action spectroscopies, and tandem ion mobility spectrometry (IMS) coupled with laser excitation. For [RB - 2H]2-, photodetachment action spectroscopy reveals a clear band in the visible (450-580 nm) with vibronic structure. Electron affinity and repulsive Coulomb barrier (RCB) properties of the dianion are characterized using frequency-resolved photoelectron spectroscopy, revealing a decreased RCB compared with that of fluorescein dianions due to electron delocalization over halogen atoms. Monoanions [RB - H]- and [RB - 2H]•- differ in nominal mass by 1 Da but are difficult to study individually using action spectroscopies that isolate target ions using low-resolution mass spectrometry. This work shows that the two monoanions are readily distinguished and probed using the IMS-photo-IMS and photo-IMS-photo-IMS strategies, providing distinct but overlapping photodissociation action spectra in the visible spectral range. Gas-phase fluorescence was not detected from photoexcited [RB - 2H]2- due to rapid electron ejection. However, both [RB - H]- and [RB - 2H]•- show a weak fluorescence signal. The [RB - H]- action spectra show a large Stokes shift of ∼1700 cm-1, while the [RB - 2H]•- action spectra show no appreciable Stokes shift. This difference is explained by considering geometries of the ground and fluorescing states.

Optical absorption by electron states in nanosystem containing dielectric quantum dots

In the framework of dipole approximation, it is shown that the oscillator strengths of transitions as well as the dipole moments for transitions for one-particle electron quantum-confined states emerging above the spherical surface quantum dot of aluminum oxide assume giant values considerably (by two orders of magnitude) exceeding the typical values of the corresponding quantities for dielectrics. It has been established that the giant values of the light absorption cross section in the nanosystems under investigation make it possible to use such nanosystems as strongly absorbing nanomaterials in a wide range of infrared waves with a wavelength that can be varied in a wide range depending in the type of contacting materials.

Impact of one step alloying on the carrier relaxation and charge separation dynamics of CdxZn1-xSe graded nanocrystals

Slow carrier relaxation and extent of charge separation in semiconductor nanocrystals (NCs) are the desired parameters, which control the power conversion efficiency in photovoltaic. Although several synthesis approaches have explored, the spectroscopic analysis of the fundamental understanding of charge carrier dynamics in the quantum confined states of cadmium zinc selenide (CdxZn1-xSe) graded alloy NCs remain relatively unexplored. Here, we study the charge carrier dynamics of a series of CdxZn1-xSe alloy NCs by changing the metal (Cd and Zn; M) to selenide ratio adopting one-step synthesis. Our findings underline that both excitonic absorption and band edge photoluminescence (PL) of all the alloys are red shifted concerning the binary analogs (CdSe and ZnSe), which implies the formation of gradient alloy structure where the core is CdSe rich that leads to increasing light absorption cross-section in the solar spectrum. Femtosecond transient absorption (fs-TA) measurements of the alloy NCs reveal that the CdxZn1-xSe alloy show three distinct bleaches due to the different electronic transition like 1S (1Se-1S3/2), 2S (1Se-2S3/2), and 1P (1Pe-1P3/2) while only CdSe shows two bleaches due to 1S, and 1P. The distinctive band structure (quasi type-II) of the alloy leads to slow down the intraband carrier cooling time and prolonging the charge separation due to specially decoupled photo-excited electron and hole. This finding offers new insights to understand the photophysical behavior and suggest that CdxZn1-xSe graded NCs can be used as efficient light harvesting materials in quantum dot solar cell.

Efficient Luminescence Enhancement of Mg2TiO4:Mn4+ Red Phosphor by Incorporating Plasmonic Ag@SiO2 Nanoparticles

One of prospective ways for boosting efficiency of luminescent materials is their combination with noble metal nanoparticles. Collective, so-called plasmon, oscillations of surface electrons in a nanoparticle can resonantly interact with incident or fluorescent light and cause an increase in the light absorption cross section or radiative rate for an adjacent emitter. Plasmonic inorganic phosphors require gentle host crystallization at which added noble nanoparticles will not suffer from aggregation or oxidation. The prospective plasmonic Mg2TiO4:Mn4+ phosphor containing core@shell Ag@SiO2 nanoparticles is prepared here by spare low-temperature annealing of a sol-gel host precursor. It is revealed that Mn4+ luminescence nonmonotonously depends on the size and concentration of 40 and 70 nm silver nanoparticles. It is demonstrated that luminescence of the Mg2TiO4:Mn4+ phosphor can be up to a 1.5 times increase when Mn4+ excitation is supported by localized surface plasmon resonance in Ag@SiO2 nanoparticles.

Absorption of pulsed laser radiation by composites based on hexogen and aluminium nanoparticles

Absorption of the second-harmonic radiation from a pulsed YAG : Nd 3+ laser by composites based on hexogen and aluminium nanoparticles (of a diameter 100 nm) is theoretically and experimentally investigated. The absorption efficiency factor (the ratio of the light absorption cross section to the geometrical cross section) is calculated by using the Mie theory for Al inclusions in a hexogen medium for various particle diameters and wavelengths corresponding to laser fundamental and second-harmonic radiation. Dependences of the absorption coefficient and amplitude of an acoustic signal on the concentration of inclusions under laser irradiation of composite samples are measured by using a piezo-acoustic transducer. It is shown that the radiation is directly absorbed by nanoparticles. The optimal concentration is found, which provides the maximal signal of the piezo-acoustic transducer.

Photo-induced Fragmentation of a Tin-oxo Cage Compound

Tin-oxo cage materials are of interest for use as photoresists for EUV (Extreme­ Ultraviolet) lithography (13.5 run, 92 eV), owing to their large absorption cross section for EUV light. In this work we exposed an n-butyl tin-oxo cage dication in the gas phase to photons in the energy range 4-14 eV to explore its fundamental photoreactivity. At all energies above the onset of electronic absorption at 5 eV (250 run) cleavage of tin-carbon bonds was observed. With photon energies >12 eV (<103 run) photoionization can occur, leading to 3+ ions. Besides the higher charge promotion, butyl chain loss without electron ejection (leading to 2+ fragments) still occurs. Keywords: Tin-oxo cage, Photoresist, Mass spectrometry, Photochemistry

Dark Field Scattering Spectroelectrochemistry of Single Au Nanoparticles at Transparent Planar and Micro-Sized Electrodes

Boron dipyrromethene (BODIPY) molecules with donor-acceptor configurations are of great interests for harvesting and converting solar energy in a solar cell. Au nanoparticles have been applied to enhance solar energy harvesting and conversion efficiency of organic solar cells because of their surface plasmon properties for increasing light absorption cross-section of an organic dye. Electrochemical properties of single BODIPY dyes and plasmonic Au nanoparticles (NPs) are studied using combined optical and electrochemical methods to reveal their structure-function relationship at the nanometer scale. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-doped tin oxide (ITO) surfaces. Dark field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are used to probe local redox reactions of single Au nanoparticles at transparent planar and micro-sized electrode. Our study shows that these optical responses at individual plasmonic NPs are strongly dependent on particle size, and are affected by the local chemical and charge transfer environment of the NPs.

Suppressed power saturation due to optimized optical confinement in 9xx nm high-power diode lasers that use extreme double asymmetric vertical designs

Broad area lasers with novel extreme double asymmetric structure (EDAS) vertical designs featuring increased optical confinement in the quantum well, Γ, are shown to have improved temperature stability without compromising series resistance, internal efficiency or losses. Specifically, we present here vertical design considerations for the improved continuous wave (CW) performance of devices operating at 940 nm, based on systematically increasing Γ from 0.26% to 1.1%, and discuss the impact on power saturation mechanisms. The results indicate that key power saturation mechanisms at high temperatures originate in high threshold carrier densities, which arise in the quantum well at low Γ. The characteristic temperatures, T0 and T1, are determined under short pulse conditions and are used to clarify the thermal contribution to power limiting mechanisms. Although increased Γ reduces thermal power saturation, it is accompanied by increased optical absorption losses in the active region, which has a significant impact on the differential external quantum efficiency, . To quantify the impact of internal optical losses contributed by the quantum well, a resonator length-dependent simulation of is performed and compared to the experiment, which also allows the estimation of experimental values for the light absorption cross sections of electrons and holes inside the quantum well. Overall, the analysis enables vertical designs to be developed, for devices with maximized power conversion efficiency at high CW optical power and high temperatures, in a trade-off between absorption in the well and power saturation. The best balance to date is achieved in devices using EDAS designs with , which deliver efficiencies of 50% at 14 W optical output power at an elevated junction temperature of 105 °C.

Field effect transistor photodetector based on graphene and perovskite quantum dots

Graphene is an attractive optoelectronic material for various optoelectronic devices, especially in the field of photoelectric detection due to its high carrier mobility and fast response time. However, the relatively low light absorption cross-section and fast electron-hole recombination rate can lead to rapid exciton annihilation and small light gain, which restrict the commercial applications of pure graphene-based photodetector. The perovskite has attracted much attention because of its high photoelectric conversion efficiency in the field of solar cells. The perovskite has the advantages of long carrier diffusion distance and high optical absorption coefficient, which can effectively make up for the shortcomings of pure graphene-based field-effect transistor. In this work, a field-effect transistor photodetector is demonstrated with the combination of graphene and halide perovskite quantum dots (CsPbI3) serving as conductive channel materials. The graphene is prepared by plasma enhanced chemical vapor deposition, and the quantum dots are CsPbI3 perovskite. The electrical properties of graphene and pure graphene-based field-effect transistor are detected and analyzed by using the Raman spectrum. The results show that the graphene has good intrinsic electrical properties. Unlike previous report in which bulk perovskite was used, the perovskite quantum dot field-effect transistor photodetector has an obvious light response to 400 nm signal light, and shows the excellent photoelectrical performance. Under the illumination of 400 nm light, the signal light could be detected steadily and repeatedly by the graphene-perovskite quantum dot photodetector and converted into photocurrent. The photocurrent of the photodetector has a rapid rise, and the maximum value can reach 64 A at a light power of 12 W. The corresponding responsivity is 6.4 AW-1, which is two orders of magnitude higher than that of the general single graphene photodetector (10-2 AW-1), and it is also higher than that of perovskite-based photodetector (0.4 AW-1). In addition, the photoconductive gain and detectivity arrive at 3.7104 and 6107 Jones (1 Jones=1 cmHz1/2W-1), respectively. The results of this study demonstrate that the graphene-perovskite quantum dot photodetector can be a promising candidate for commercial UV light detectors.

Toward high performance nanoscale optoelectronic devices: super solar energy harvesting in single standing core-shell nanowire.

Single nanowire solar cells show great promise for next-generation photovoltaics and for powering nanoscale devices. Here, we present a detailed study of light absorption in a single standing semiconductor-dielectric core-shell nanowire (CSNW). We find that the CSNW structure can not only concentrate the incident light into the structure, but also confine most of the concentrated light to the semiconductor core region, which boosts remarkably the light absorption cross-section of the semiconductor core. The CSNW can support multiple higher-order HE modes, as well as Fabry-Pérot (F-P) resonance, compared to the bare nanowire (BNW). Overlapping of the adjacent higher-order HE modes results in broadband light absorption enhancement in the solar radiation spectrum. Results based on detailed balance analysis demonstrate that the super light concentration of the single CSNW gives rise to higher short-circuit current and open-circuit voltage, and thus higher apparent power conversion efficiency (3644.2%), which goes far beyond that of the BNW and the Shockley-Queisser limit that restricts the performance of a planar counterparts. Our study shows that the single CSNW can be a promising platform for construction of high performance nanoscale photodetectors, nanoelectronic power sources, super miniature cells, and diverse integrated nanosystems.