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Tunable plasmonic HfN nanoparticles and arrays
摘要： We present the fabrication of tunable plasmonic hafnium nitride (HfN) nanoparticles. HfN is a metallic refractory material with the potential of supporting plasmon resonances in the visible range, similar to silver and gold, but with the additional benefits of high melting point, chemical stability, and mechanical hardness. However, the preparation of HfN nanoparticles and the experimental demonstration of their plasmonic potential are still in their infancy. Here, high quality HfN thin films were fabricated, for which ellipsometry shows their plasmonic potential. From these thin films, nanorods and nanotriangles were milled using a focused ion beam and the plasmon resonances were identified using cathodoluminescence mapping. As an alternative fabrication strategy, an optimized electron-beam lithography procedure was used to prepare arrays of HfN nanoparticles, which also exhibited clear surface plasmon resonances. These results pave the way to further explore HfN nanoparticles in plasmonically-powered applications where materials robustness is essential.
关键词： electron-beam lithography,plasmonic,cathodoluminescence,nanoparticles,hafnium nitride
更新于2025-09-16 10:30:52
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Non-radiative recombination at dislocations in InAs quantum dots grown on silicon
摘要： We study the impact of misfit dislocations on the luminescence from InAs quantum dots (QDs) grown on Si substrates. Electron channeling contrast imaging is used together with cathodoluminescence mapping to locate misfit dislocations and characterize the resulting nonradiative recombination of carriers via near-infrared light emission profiles. With a 5 kV electron beam probe, the dark line defect width due to a typical misfit dislocation in a shallow QD active layer is found to be approximately 1 lm, with a 40%–50% peak emission intensity loss at room temperature. Importantly, we find that at cryogenic temperatures, the dislocations affect the QD ground state and the first excited state emission significantly less than the second excited state emission. At the same time, the dark line defect width, which partially relates to carrier diffusion in the system, is relatively constant across the temperature range of 10 K–300 K. Our results suggest that carrier dynamics in the QD wetting layer control emission intensity loss at dislocations, and that these defects reduce luminescence only at those temperatures where the probability of carriers thermalizing from the dots into the wetting layer becomes significant. We discuss the implications of these findings toward growing dislocation-tolerant, reliable quantum dot lasers on silicon.
关键词： silicon substrates,nonradiative recombination,quantum dot lasers,InAs quantum dots,cathodoluminescence,misfit dislocations
更新于2025-09-16 10:30:52
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Two-dimensional analysis of the nonuniform quantum yields of multiple quantum wells for AlGaN-based deep-ultraviolet LEDs grown on AlN templates with dense macrosteps using cathodoluminescence spectroscopy
摘要： AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) incorporating uneven multiple quantum wells (MQWs) with inclined and terrace zones, which were fabricated on an AlN template with dense macrosteps, have exhibited a high internal quantum efficiency (IQE). To investigate the microscopic structure of uneven MQWs, cathodoluminescence (CL) mapping characterization was carried out, and the maps of the CL intensity at 300 K relative to that at 38 K were obtained for uneven MQWs that targeted 265 and 285 nm LEDs. At an electron beam current of less than 1.0 nA, the signals from inclined and terrace zones of the uneven MQWs were confirmed to satisfy the non-saturated excitation condition at 300 K. Nonradiative recombination (NR) was insufficiently frozen even at 38 K, specifically on the terraces in the 265 nm MQW, suggesting high concentrations of NR centers due to point defects (PDs). In contrast, NR in the 285 nm MQW at 38 K was closer to freeze-out. The concentration of PDs in the 285 nm MQW was likely to be lower than that in the 265 nm MQW. Finally, the ratios of the CL intensity at 300 K to those at 38 K were mapped, demonstrating an approach to creating an approximate map of IQE. The values in the CL intensity ratio maps are discussed by considering the analytical error factors. The results support the model of localized current injection through Ga-rich stripe zones in the n-AlGaN cladding layer.
关键词： AlGaN,cathodoluminescence spectroscopy,internal quantum efficiency,deep-ultraviolet LEDs,multiple quantum wells
更新于2025-09-12 10:27:22
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Far-field radiation of three-dimensional plasmonic gold tapers near apices
摘要： Three-dimensional plasmonic gold tapers are widely used structures in nano-optics for achieving imaging at the nanometer-scale, enhanced spectroscopy, confined light sources, and ultrafast photoelectron emission. To understand their radiation properties further, especially in the proximity of the apex at the nanoscale, we employ cathodoluminescence spectroscopy with high spatial and energy resolution. The plasmon-induced radiation in the visible spectral range from three-dimensional gold tapers with opening angles of 13° and 47° is investigated under local electron excitation. We observe a much weaker radiation from the apex of the 13° taper than from that of the 47° taper. By means of finite-difference time-domain simulations we show that for small opening angles plasmon modes that are created at the apex are efficiently guided along the taper shaft. In contrast for tapers with larger opening angles, generated plasmon polaritons experience larger radiation damping. Interestingly, we find for both tapers that the most intense radiation comes from locations a few hundreds of nanometers behind the apices, instead of exactly at the apices. Our findings provide useful details for the design of plasmonic gold tapers as confined light sources or light absorbers.
关键词： plasmonics,surface plasmon coupled emission,cathodoluminescence,gold taper
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Annealing Influence on Structural and Luminescencent Properties of ZnSe:Fe
摘要： Zinc Selenide crystals doped with Iron are promising material to be used as an active media in tunable mid-IR lasers (4 ? 5 μm) [1]. The ZnSe:Fe lasing characteristics close to the theatrical maximum are obtained by optical excitation [2]. Nowadays other pumping methods are also being explored. Previously we have observed luminescence in the mid-IR spectral region with the maximum at the wavelength of 3.9 μm under electron-impact excitation. The present research is focused on the in?uence of annealing process in Zn atmosphere on defective-impurity compound (DIC) and intensity of mid-IR cathodoluminescence (CL). We studied DIC by two-photon confocal microscopy (TPCM) on Carl Zeiss LSM NLO 710 (commercially available equipment). The TPCM allows detecting edge luminescence (EL) (460-480 nm) and DIC (480 - 725 nm) as well as mapping luminescence distribution [3]. In the CL experiments, the crystals were excited by a pulsed electron gun with the accelerated electron energy of 36 kV [4]. A series of ZnSe single crystals doped with Fe by thermal diffusion from surface was subjected to the DIC and CL studies. The initial ZnSe plates were cut from boules grown from the melt by the Bridgman method with an addition of Tellurium. Iron concentrations varied from 0.01 to 14 wt.% as determined by XDR. The samples were observed by TPCM and CL before and after annealing in Zn atmosphere.
关键词： mid-IR lasers,ZnSe:Fe,two-photon confocal microscopy,cathodoluminescence,annealing
更新于2025-09-12 10:27:22
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European Microscopy Congress 2016: Proceedings || Angle-resolved cathodoluminescence of plasmonic crystal waveguide
摘要： Slow-light manipulation in a photonic crystal (PhC) waveguide is expected to improve future optical information processing and communication technologies such as optical buffering and light compression [T. Baba, Nat. Photon. 2, 465-473 (2008)]. Waveguiding using bandgap of plasmonic crystal (PlC) has also been demonstrated [S. I. Bozhevolnyi et al. Phys. Rev. Lett. 86, 3008-3001 (2001)]. However, the dispersion characteristics of the guided modes, which are essential to control surface plasmon polariton (SPP) pulses, have not yet been understood. Electron beam spectroscopies at high spatial resolution are powerful characterization tools to observe electromagnetic modes nowadays. Momentum-resolved spectroscopy in electron microscopy is especially useful to investigate detailed optical properties of locally-modified structures introduced into a PhC [R. Sapienza et al. Nat. Mater. 11, 781-787 (2012)] and a PlC [H. Saito and N. Yamamoto, Nano Lett. 15, 5764-5769 (2015)]. We have studied the dispersion characteristics of SPPs in a PlC waveguide by angle-resolved chatodoluminescence performed in a STEM. The guided SPP modes were found to have two unique features : i) energy dependence of the phase shift at the wall, and ii) waveguide bandgap (WBG) due to the periodicity originating from PlC structure, which resulted in small group velocity of the guided SPP modes over a wide energy range.
关键词： Slow light,Plasmonic crystal,Cathodoluminescence,Waveguide,Momentum-resolved spectroscopy
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Angle-resolved cathodoluminescence polarimetry on plasmonic nanostructures
摘要： Plasmonic metamaterials and metasurfaces have the ability to influence the propagation, confinement, and emission of light on a deep-subwavelength scale. Many of the optical properties of such materials are encoded in the spectrum, the angular intensity distribution, and the polarization of the far-field emission. Angle-resolved cathodoluminescence (CL) imaging spectroscopy (ARCIS) is a powerful platform for studying these properties, as it combines nanoscale excitation resolution, with the capability to measure both spectra and the angular emission intensity distribution. In particular, we use a 30 keV electron beam as a well-defined broad-band excitation source which is sensitive to the optical density of states. This method has been used to study the spectral and angular optical properties of a large variety of dielectric and plasmonic nanostructures. However, thus far we were only able to measure emission intensities and had to disregard the vectorial polarization nature of the light emission. The emission polarization contains valuable information, which can be used to identify multipoles, separate TM and TE modes in waveguides, characterize the coherence of an emission source etc. Here, we demonstrate a novel CL polarimetry technique in which we retrieve the Stokes vector, i.e. the full polarization state of the far-field emission, as function of angle [1]. To that end, we extend our setup to include a quarter-wave plate (QWP) and a linear polarizer in the beam path (see Figure 1 for a schematic representation of the setup). By taking six measurements with the appropriate combinations of QWP and polarizer angle we retrieve the polarization distribution in the detection plane. By applying a correction for the aluminum parabolic mirror optic we then find the emission polarization distribution. This approach is applied to gold plasmonic bull’s eye gratings which were fabricated using focused-ion-beam milling in a single-crystal gold substrate (see Figure 2(a) for an SEM image). These bull’s eyes can coherently couple out the Surface Plasmon Polaritons (SPPs) that are excited by the electron beam. Because the electron beam can be positioned at will, we can study the effect of exciting the bull’s eye at different positions. For central excitation, the grating is driven in phase leading to an azimuthally symmetric pattern and a radial polarization distribution, as expected from symmetry (see Figure 2(b-c)). However, when we excite off-center the patterns become significantly more complex, showing multiple lobes and alternating regions in angular space in which the polarization goes from circular to linear. To demonstrate the applicability to chiral structures, we move to spiral bull’s eyes with different handedness, and show that their chirality is reflected in the field distributions. The validity of the polarimetry technique is verified by measuring transition radiation which has a characteristic radial polarization distribution, similar to a vertical dipole source. This work paves the way for polarimetry measurements on a myriad of metallic and semiconductor nanophotonic geometries for characterization and better understanding of their optical properties.
关键词： Cathodoluminescence,plasmonics,polarization,nanophotonics
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Cathodoluminescence for in situ plasmonic sensing of beam effects
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关键词： plasmon,effects,sensing,beam,cathodoluminescence,localized,surface
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || SEM based electro-optical characterization of core-shell LEDs and simulation of imaging including CL and EBIC excitation inside ensembles
摘要： Three dimensional (3D) nano- and microstructures (NAMs) are attracting a lot of attention and are discussed regarding several applications, especially in optoelectronics and sensors. For example GaN based 3D light emitting diodes (LEDs) with a core-shell geometry are supposed to have substantial advantages over conventional planar LEDs: The active area along the sidewalls of hexagonal GaN pillars can considerably be increased by high aspect ratios - leading to a lower current density inside the InGaN quantum well (QW) at the same operation current per substrate area. [1] Thus related methods are requested for characterization of local electro-optical properties with a high spatial resolution on single structures as well as in ensembles. Usually, electron microscopy is employed to investigate the geometry and properties of such 3D-NAMs and for mapping of vertical features by an SEM a certain sample tilt (e.g. about 30°) is needed. Investigation of single 3D-LEDs by electron beam induced current (EBIC) using an SEM based manipulator setup proves the presence of a pn-junction and doping type of the core and shell, while cathodoluminescence (CL) gives an insight to the optical properties of the QW [2]. But in contrast to SEM on planar regions the interactions of the electron probe are significantly affected by the 3D geometry and the surrounding of the NAMs. In ensembles of 3D-NAMs a certain portion of incident electrons are scattered into neighbor structures and conventional SEM signals (SE, BSE, CL, X-ray emission) are partly shadowed. This interaction is affecting the SEM imaging contrast and the probed signal also includes contributions which are not related to the material properties at the electron beam spot. As such parasitic signals are generated quite close to the original region of the interaction most (global) SEM detectors cannot separate them from the original source. In particular scattering events occur in an enlarged volume of the sample (of the substrate and NAMs) leading to a reduced excitation density and parasitic effects, e.g. this causes a significant contribution of defect related yellow luminescence (YL) We present results of InGaN/GaN core-shell LEDs obtained with an FE-SEM which is equipped with SE, In-Beam SE, low-kV BSE, EBIC and monochromatic CL detection as well as a piezo controlled manipulator setup, see Figure 1. A modified parabolic collection mirror enables measuring luminescence from planar samples up to 4’’ in a tilted view up to 30°. For a quantitative interpretation of CL and EBIC measurement values and image contrasts, the physical modeling of SEM images and spatially resolved energy transfer by a probe spot is necessary. This is performed using the simulation program MCSEM [3]. It models the different stages of image formation and generates SEM images of complex NAM shapes using e.g. GaN as model material. Aspects of the simulation are the electron probe formation, a 3D model of the specimen structure, the interaction of electron probe and solid state by means of scattering trajectories, the emission of secondary electrons, and different types of electron detectors, see Figure 2 and Figure 3. An insight to CL and EBIC imaging is gained by evaluating the scattering energy deposited in a distinct volume inside the NAMs as an imaging signal - this is related to the generation rate of electron-hole pairs inside the respective volume of the semiconductor. Consent to the experiments this simulation reveals an edge contrast and shadowing of signals by the ensemble as well as scattering of primary electrons inside the ensemble of 3D-NAMs. A quantitative comparison is possible by the absorbed current (EBAC). Artefacts of the EBIC are also demonstrated by the simulation, in particular edge contrast by a reduced generation rate and parasitic signals by scattering from neighbor structures.
关键词： EBIC,cathodoluminescence,electron beam induced current,SEM simulation,core-shell LED
更新于2025-09-11 14:15:04
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Hybridization of Gap Modes and Lattice Modes in a Plasmonic Resonator Array with a Metal-Insulator-Metal Structure
摘要： Plasmonic resonator arrays have attracted a great interest as a platform to enhance light-matter interaction, and have been examined for their applicability to various types of optical devices, such as sensors, light emitter, photocatalyst, to name a few. In a plasmonic resonator array, localized and propagating plasmon modes can hybridize, which is known to result in an anti-crossing of the plasmon bands in the dispersion curves. However, it was so far unclear how the modal symmetry affects such a hybridization, especially when it occurs at a specific reciprocal lattice point with a high degree of symmetry e.g. the Γ point. In this work, we used momentum-resolved cathodoluminescence-scanning transmission electron microscopy to comprehensively characterize the modal hybridization at the Γ point. Our study reveals theoretically and experimentally the existence of mode symmetry selection rules that specify hybrid pairs of the lattice mode and localized mode.
关键词： mode hybridization,plasmonic crystal,dispersion relation,triangular lattice,cathodoluminescence,momentum resolved spectroscopy
更新于2025-09-11 14:15:04