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Research on the defect types transformation induced by growth temperature of vertical graphene nanosheets
摘要： The in?uence factors on the defect types in vertical graphene nanosheets (VGNs) are widely researched while few systematic research has been reported on the growth temperature, which should play an important role in the transformation of defects types. In this work, VGNs were grown via plasma enhanced chemical vapor deposition (PECVD) method in the atmosphere of CH4, H2 and Ar. Based on SEM, Raman, XPS, NEXAFS and UPS spectrum analysis, we found that the types of defects in VGNs have clearly transformed from vacancy-like to boundary-like, corresponding to the rising growth temperature. Moreover, NEXAFS suggests that features near 7.7 eV are attributed to boundary-like defects, as well as (cid:1)6.7 eV in UPS, providing an intuitive and half-quantitative direction to characterize boundary-like defects in VGNs. Additionally, the sheet resistance (from 1386 to 175 Ohm/Sq) and the wetting angle (from 148(cid:3) to 121(cid:3)) decrease as the temperature rises. It shows that changing the growth temperature, as the easy and effective method, is crucial of modulating the properties of VGNs owning to the transition of defects types from vacancy-like to boundary-like.
关键词： Vertical graphene nanosheets,Near-edge X-ray absorption ?ne structure,Defects type,Ultraviolet photoemission spectroscopy,Modulate properties
更新于2025-09-23 15:22:29
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Optical absorption via intersubband transition of electrons in GaAs/Al <sub/>x</sub> Ga <sub/>1?x</sub> As multi-quantum wells in an electric field
摘要： Based on the effective mass approximation, the Schr?dinger equation and Poisson equation in GaAs/AlxGa1?xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
关键词： multi-quantum wells,optical absorption of electronic intersubband transition,refractive index changes,lateral electric field
更新于2025-09-23 15:22:29
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Direct observation of cross-polarized excitons in aligned single-chirality single-wall carbon nanotubes
摘要： Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been studied extensively, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, by using a macroscopic film of highly aligned single-chirality (6,5) SWCNTs, we performed a systematic polarization-dependent optical absorption spectroscopy study. In addition to the commonly observed angular-momentum-conserving interband absorption of parallel-polarized light, which generates E11 and E22 excitons, we observed a small but unambiguous absorption peak whose intensity is maximum for perpendicular-polarized light. We attribute this feature to the lowest-energy cross-polarized interband absorption processes that change the angular momentum along the nanotube axis by ±1, generating E12 and E21 excitons. Unlike previous observations of cross-polarized excitons in polarization-dependent photoluminescence and circular dichroism spectroscopy experiments, our direct observation using absorption spectroscopy allowed us to quantitatively analyze this resonance. Specifically, we determined the energy and oscillator strength of this resonance to be 1.54 and 0.05, respectively, compared with the values for the E11 exciton peak. These values, in combination with a comparison with theoretical calculations, in turn led to an assessment of the environmental effect on the strength of Coulomb interactions in this aligned single-chirality SWCNT film.
关键词： polarization-dependent,single-wall carbon nanotubes,cross-polarized excitons,aligned film,optical absorption spectroscopy,Coulomb interactions
更新于2025-09-23 15:22:29
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Physical conditions in high? <i>z</i> optically thin C? <scp>iii</scp> absorbers: Origin of cloud sizes and associated correlations
摘要： We present detailed photoionization models of well aligned optically thin C iii absorption components at 2.1 < z < 3.4. Using our models we estimate density (nH), metallicity ([C/H]), total hydrogen column density and line-of-sight thickness (L) in each C iii components. We estimate the systematic errors in these quantities contributed by the allowed range of the quasar spectral index used in the ultraviolet background radiation calculations. Our inferred nH and overdensity (?) are much higher than the measurements available in the literature and favor the absorption originating from gas associated with circumgalactic medium and probably not in hydrostatic equilibrium. We also notice nH, L and [C/H] associated with C iii components show statistically signi?cant redshift evolution. To some extent, these redshift evolutions are driven by the appearance of compact, high nH and high [C/H] components only in the low?z end. We ?nd more than 5σ level correlation between [C/H] and L, L and neutral hydrogen column density (N (H i)), N (H i) and [C/H]. We show L versus [C/H] correlation can be well reproduced if L is governed by the product of gas cooling time and sound speed as expected in the case of cloud fragmentation under thermal instabilities. This allows us to explain other observed correlations by simple photoionization considerations. Studying the optically thin C iii absorbers over a large z range and probably correlating their z evolution with global star formation rate density evolution can shed light into the physics of cold clump formation and their evolution in the circumgalactic medium.
关键词： galaxies: haloes,galaxies : evolution,quasars: absorption lines
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Hong Kong, China (2018.11.5-2018.11.9)] 2018 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Designing thin-film metamaterials by tuning effective ENZ behavior
摘要： Using an effective refractive index calculation, we demonstrate the ability to efficiently tune epsilon-near-zero (ENZ) behavior within compact thin-film stacks. Results show the desired effect of broadening the reflectivity profile and improving absorption for an all-oxide ENZ metamaterial.
关键词： near-zero index,metamaterials,perfect absorption,plasmonic,thin film,ENZ tuning,effective index
更新于2025-09-23 15:22:29
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The Transitional Transmittance Response of ZIF-8 Gas Adsorption Observed Using Terahertz Waves
摘要： In this study, we recorded the transitional response in terms of terahertz transmittance of zeolitic imidazole framework-8 [Zn(2-methylimidazolate)2, ZIF-8] at 2.0 THz as a function of exposure time to gaseous propane and n-butane. The transmittance at 2.0 THz increased as gas adsorbed onto the ZIF-8. Conversely, during a nitrogen purge, transmittance decreased as the alkane gas desorbed. We estimated time constants for the adsorption and desorption of the two gases by comparing the plots of their responses. We also demonstrated the potential of using a combination of ZIF materials and terahertz technology as a novel gas analyzer.
关键词： Adsorption kinetics,Terahertz vibration,Metal-organic frameworks,Porous solids,Infrared absorption spectroscopy
更新于2025-09-23 15:22:29
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Peroxy radical detection for airborne atmospheric measurements using absorption spectroscopy of NO<sub>2</sub>
摘要： Development of an airborne instrument for the determination of peroxy radicals (PeRCEAS – peroxy radical chemical enhancement and absorption spectroscopy) is reported. Ambient peroxy radicals (HO2 and RO2, R being an organic chain) are converted to NO2 in a reactor using a chain reaction involving NO and CO. Provided that the amplification factor, called effective chain length (eCL), is known, the concentration of NO2 can be used as a proxy for the peroxy radical concentration in the sampled air. The eCL depends on radical surface losses and must thus be determined experimentally for each individual setup. NO2 is detected by continuous-wave cavity ring-down spectroscopy (cw-CRDS) using an extended cavity diode laser (ECDL) at 408.9 nm. Optical feedback from a V-shaped resonator maximizes transmission and allows for a simple detector setup. CRDS directly yields absorption coefficients, thus providing NO2 concentrations without additional calibration. The optimum 1σ detection limit is 0.3 ppbv at an averaging time of 40 s and an inlet pressure of 300 hPa. Effective chain lengths were determined for HO2 and CH3O2 at different inlet pressures. The 1σ detection limit at an inlet pressure of 300 hPa for HO2 is 3 pptv for an averaging time of 120 s.
关键词： peroxy radicals,NO2,cavity ring-down spectroscopy,airborne measurements,absorption spectroscopy,chemical amplification
更新于2025-09-23 15:22:29
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Study on Five Porphyrin-Based Photosensitizers for Singlet Oxygen Generation
摘要： Five porphyrin derivatives were synthesized and characterized in order to be utilized as photosensitizers for singlet oxygen generation. UV-Vis absorption properties of porphyrins were experimentally and theoretically discussed. The results indicated that the increase in π-conjugation of porphyrin core can lower the S1-T1 energy gap and is favorable for efficient energy transfer. The singlet oxygen generation ability of porphyrins was measured and compared under both simulated sunlight and yellow light. As for the results using simulated sunlight, EBHPP and CEBHPP exhibited best and similar performance because they bear strong near-IR absorption and S1-T1 interactions. However, under yellow light conditions CEBHPP has better ability for singlet oxygen generation because of strong absorbance from 650–750 nm. The DNA photocleavage measurements were performed to evaluate the biological activity of the porphyrin derivatives. The photocleavage activities were in the order of TPP < TPP-NO2 < BHPP < EBHPP < CEBHPP, and the possible reasons were discussed. This work is useful for the design of more efficient photosensitizers.
关键词： Photosensitizer,Porphyrin,Singlet oxygen,UV-Vis absorption,Photodynamic therapy
更新于2025-09-23 15:22:29
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Microscopic FCA System for Depth-Resolved Carrier Lifetime Measurement in SiC
摘要： For high voltage SiC bipolar devices, carrier lifetime is an important parameter, and for optimization of device performance, we need to control the distribution of the carrier lifetime in a wafer. So far, there have been limited systems for depth-resolved carrier lifetime measurements without the necessity of making a cross sectional cut. In this study, we adopted a free carrier absorption technique and made local overlapping of the probe laser light with excitation laser light to develop depth-resolved carrier lifetime measurements. We named the developed system a microscopic FCA system and demonstrated measurement results for samples with and without intentional carrier lifetime distribution.
关键词： free carrier absorption,4H-SiC,carrier lifetime
更新于2025-09-23 15:22:29
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Axiolitic ZnO rods wrapped with reduced graphene oxide: Fabrication, microstructure and highly efficient microwave absorption
摘要： Axiolitic Zinc oxide/reduced graphene oxide (ZnO/r-GO) hybrid was achieved by a facile one-step hydrothermal route in this work. The axiolitic ZnO rods with uniform size were equally implanted in r-GO nanosheets. The composites exhibit prominent microwave absorption performance with the Min. RL of -55.7 dB for a thickness of merely 2.0 mm and effective absorption bandwidth covering the whole Ku band, which benefits by the introducing of axiolitic ZnO rods and constructing distinct structures. The synergistic effect of dipole polarization, interface polarization and conductivity manifestly boost the microwave attenuation capacity. The results indicated that the axiolitic ZnO/r-GO hybrid is a promising candidate for application in the field of microwave absorption, electromagnetic interference shielding, communication and safety information, etc.
关键词： polarization,microwave absorption,reduced graphene oxide,axiolitic ZnO rods
更新于2025-09-23 15:22:29