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Probing of Thermal Transport in 50-nm Thick PbTe Nanocrystal Film by Time-Domain Thermoreflectance
摘要： Bottom-up fabrication of thermoelectric (TE) materials from colloidal nanocrystal (NC) building blocks can substantially increase their TE efficiency, e.g., by reducing lattice thermal conductivity. In this work, 10-nm spherical phase-pure oleate-capped PbTe NCs with narrow size distribution were synthesized and employed to fabricate 50-nm thick films on insulating SiO2/Si substrates. The spin-coating, with subsequent ligand exchange procedure, was applied to enhance coupling interactions between the NCs. Using dark conductivity measurements, we confirmed the semiconducting behavior and the Schottky-type electrical field-dependent conductivity mechanism in the resultant thin films. The thermal transport in the thin-film was probed by means of a time-domain thermoreflectance (TDTR) method. For this purpose, we used a customized state-of-the-art system based on a picosecond thermoreflectance instrument, which enables area-selective analysis with spatial resolution down to 5 μm. The results show that as-fabricated PbTe NC films exhibit ultralow thermal conductivity of 0.9 W m–1 K–1 at 300 K. The transport property findings suggest potential in the proposed quick and cost-effective spin-coating strategy for bottom-up fabrication of nanostructured TE films from high-quality colloidal NC building blocks.
关键词： colloidal nanocrystals,spin-coating,thermoelectric materials,thermal conductivity,time-domain thermoreflectance,PbTe
更新于2025-09-23 15:21:01
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Silicon Quantum Dots Metal Enhanced Photoluminescence by Gold Nanoparticles in Colloidal Ensembles: Effect of Surface Coating
摘要： In the present study we report the photophysical properties of colloidal ensembles of silicon quantum dots (SiD) and gold nanoparticles (AuNP), particularly focused on investigating metal-enhanced photoluminescence effects. AuNP with different sizes, (27 ± 10) and (88 ± 12) nm, and ca. 3.4 nm size SiD with different surface groups, either covered with an oxidized surface film bearing Si-OH surface groups or grafted with propylamine leading to Si-(CH2)2-CH2-NH2 terminal functionalities, were tested to evaluate gold enhancement of SiD photoluminescence. Nanoparticles were characterized by HRTEM, FTIR, XPS, ICP-AES, and gel electrophoresis, while photophysical properties of nanoparticles alone and in colloidal ensembles at different concentrations were investigated by absorption and steady-state and time-resolved photoluminescence studies, including quantum yield determinations. Enhanced absorption and photoluminescence of SiD in the presence of AuNP was evidenced, leading in the most favorable cases to ca. 10-times increase in SiD brightness. This effect depends strongly on the SiD surface coating and its interaction with citrate-capped gold surfaces, where these interactions govern particles aggregation and relative distance distributions among SiD and AuNP in the ensembles. The nature of these interactions and how they affect metal-enhanced luminescence is thoroughly discussed. The present study provides significant information on the effect of SiD surface groups and surface charge on the metal-enhanced luminescence phenomenon in colloidal aqueous suspensions.
关键词： gold nanoparticles,colloidal ensembles,metal-enhanced photoluminescence,silicon quantum dots,surface coating
更新于2025-09-23 15:21:01
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Hybrid Nanostructures of 2D CdSe Nanoplatelets for High-Performance Photodetector Using Charge Transfer Process
摘要： Two-dimensional (2D) semiconductor colloidal nanoplatelets (NPLs) have shown great potential as light-harvesting materials due to their advanced optical properties. Here, we have designed hybrid nanostructures of 2D CdSe nanoplatelets with phenothiazine (PTZ) for high-performance photodetector with varying thickness of CdSe NPLs by controlling charge transfer process. Significant photoluminescence quenching and the shortening of the average decay time of CdSe NPLs in presence of PTZ reveal the charge transfer process. Transient absorption (TA) spectroscopic analysis reveals the hot carrier cooling dynamics varies with changing the thickness of monolayers (ML) of CdSe NPLs. Furthermore, the slow exciton recombination of CdSe NPLs in presence of PTZ indicates the efficient charge separation. The optimized CdSe NPLs-PTZ hybrid exhibits a significant enhancement of photocurrent (~4.7×103 fold photo-to-dark current ratio) as compared to pure 3 ML CdSe NPLs (~10 fold) at the applied voltage of 1.5V. The measured external quantum efficiency, maximum detectivity and response time for the optimized hybrid are found to be ~40%, 4×1011 Jones and 107 milliseconds, with the responsivity value of 160 mA/W. These highly efficient measured parameters clearly suggest that CdSe NPLs-PTZ hybrid systems are promising alternate for ultrasensitive photodetector.
关键词： 2D colloidal nanoplatelets,photodetectors,hole transfer,hybrids,photocurrent
更新于2025-09-23 15:19:57
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Dual-Wavelength Lasing in Quantum-Dot Plasmonic Lattice Lasers
摘要： Arrays of metallic particles patterned on a substrate have emerged as a promising design for on-chip plasmonic lasers. In past examples of such devices, the periodic particles provided feedback at a single resonance wavelength, and organic dye molecules were used as the gain material. Here, we introduce a flexible template-based fabrication method that allows a broader design space for Ag particle-array lasers. Instead of dye molecules, we integrate colloidal quantum dots (QDs), which offer better photostability and wavelength tunability. Our fabrication approach also allows us to easily adjust the refractive index of the substrate and the QD-film thickness. Exploiting these capabilities, we demonstrate not only single-wavelength lasing but dual-wavelength lasing via two distinct strategies. First, by using particle arrays with rectangular lattice symmetries, we obtain feedback from two orthogonal directions. The two output wavelengths from this laser can be selected individually using a linear polarizer. Second, by adjusting the QD-film thickness, we use higher-order transverse waveguide modes in the QD film to obtain dual-wavelength lasing at normal and off-normal angles from a symmetric square array. We thus show that our approach offers various design possibilities to tune the laser output.
关键词： surface lattice resonances,dual-wavelength laser,colloidal quantum dots,plasmonics,nanolaser,template stripping,polarization
更新于2025-09-23 15:19:57
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[Institution of Engineering and Technology 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Lecce, Italy (23-25 May 2018)] 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Colloidal quantum dots for optoelectronic applications: fundamentals and recent progress
摘要： In this work, we present highlights and major milestones in the field of CQDs, starting from their optical and electronic properties that can be tailored not only by the atomic composition but also by the size, shape, and surface functionalization. We will also touch on CQD synthesis, processing and assembly, emphasizing their flexibility, low cost, low temperature and scalability. We will review recent advances in the design and fabrication of optoelectronic devices based on colloidal semiconductor quantum dots, with emphasis on light emitters, detectors and solar cells. We conclude with a short discussion on the large potentialities of this new class of materials as well as the challenges that must be addressed towards solution-processed functional optoelectronic nanomaterials for their practical applications in various fields.
关键词： semiconductor nanostructures,optoelectronic devices,colloidal quantum dots
更新于2025-09-23 15:19:57
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Magnetic Layer-by-Layer Assembly: From Linear Plasmonic Polymers to Oligomers
摘要： One-dimensional (1D) nanostructures with controllable aspect ratios are essential for a wide range of applications. An approach for magnetic superparticle (SP) assembly over large areas (55 mm × 25 mm) is introduced via co-assistance of electrostatic and magnetic fields, so-called magnetic layer-by-layer (MLBL) assembly, on an arbitrary hydrophilic substrate within minutes. The SP structures (diameter (d.) = 120-350 nm) of Fe3O4 or Ag@Fe3O4 composites composed of hundreds of magnetite nanocrystals (d. 10–20 nm) are used as colloidal monomers to fabricate arrays of high-aspect-ratio (up to 102) linear nanochains, viz. colloidal polymers, where thermal disturbances were minimized. The arrays of colloidal polymers exhibit strong optical polarization effects owing to their geometrical anisotropy, which can be used as a simple optical filter. Furthermore, by using the binary colloidal mixture of different magnetic colloids including different-sized Fe3O4 and magnetoplasmonic Ag@Fe3O4, low-aspect-ratio (2~15) colloidal chains, viz. magnetic/plasmonic oligomers, with tunable lengths were fabricated, affording a facile but effective approach to modulate the optical properties of the chains. The scalable fabrication of well-aligned, linear colloidal polymers and oligomers opens up appealing opportunities for the development of sensors, sub-wavelength waveguides, optical tweezers, and enhanced solar harvesting devices.
关键词： nanochain array,layer-by-layer,linear nanochain,colloidal oligomer,plasmonic oligomer,magnetic field induced assembly
更新于2025-09-23 15:19:57
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Ultrathin Plasmonic Tungsten Oxide Quantum Wells with Controllable Free Carrier Densities
摘要： We report the colloidal synthesis of ~3 tungsten-oxygen (W-O) layer thick (~1 nm), two-dimensional (2D) WO3-x nanoplatelets (NPLs) (x ~ 0.55 — 1.03), which display tunable near-infrared localized surface plasmon resonances (LSPR) spectra and high free electron density (Ne) that arises predominantly from their large shape factor. Importantly, the W to O composition ratios inferred from their LSPR measurements show much higher percentage of oxygen vacancies than those determined by X-ray diffraction analysis, suggesting that the aspect ratio of ultrathin WO3-x NPLs is the key to producing an unprecedentedly large Ne, although synthesis temperature is also an independent factor. We find that NPL formation is kinetically controlled, whereas thermodynamic parameter manipulation leads to Ne as high as 4.13 X 1022 cm-3, which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. The unique structural properties of 2D nanomaterials along with the high Ne of WO3-x NPLs provide an attractive alternative to plasmonic noble metal nanostructures for energy conversions.
关键词： Ultrathin Plasmonic Tungsten Oxide,Quantum Wells,Colloidal Synthesis,Localized Surface Plasmon Resonances,Free Carrier Densities
更新于2025-09-23 15:19:57
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High quality silicon: Colloidal quantum dot heterojunction based infrared photodetector
摘要： The integration of silicon (Si) and nanomaterials with infrared light harvesting capability is a promising approach to fabricate large area infrared light detecting arrays. However, the construction of a high quality junction between Si and small bandgap colloidal quantum dots (CQDs) remains a challenge, which limited their photodetecting performance in the short wavelength infrared region (1.4 lm–3 lm). Herein, a layer of solution processed ZnO nanoparticles was inserted between silicon and CQDs to passivate the surface dangling bond of silicon. This signi?cantly reduces the carrier recombination between Si and CQDs. Meanwhile, the formation of the Si:CQD heterojunction structure enables effective carrier extraction. As a result, the photodetector shows the detecting range to the short wavelength infrared region (0.8 eV) and achieves a standard detectivity of 4.08 (cid:2) 1011 Jones at a bias of (cid:3)0.25 V at room temperature.
关键词： colloidal quantum dot,heterojunction,infrared photodetector,silicon
更新于2025-09-23 15:19:57
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Long carrier lifetime in faceted PbS quantum dot superlattice fabricated by sedimentation method
摘要： We fabricated colloidal quantum dot (QD) superlattice films and investigated their primal optical properties. The films were prepared by depositing faceted PbS QDs on pyramidal-microhole-array template and flat substrate in solution. The red shift in the quantum state emission of QDs was observed in photoluminescence spectra after film formation, which suggested the weakened quantum confinement of carriers in intermediate bands. Emission decay curves at the excited states in the QD superlattice film were double exponential. The longer lifetime was several tens of nanoseconds and attributed to the carrier delocalization in the intermediate bands. The emission lifetime of the QD film prepared on the template was found to be more than twice as long as that on the flat substrate, which suggested that the template helped to form large area QD superlattice.
关键词： sedimentation method,colloidal quantum dot,PbS,superlattice,carrier lifetime
更新于2025-09-23 15:19:57
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Influence of photoactivation on luminescent properties of colloidal InP@ZnS quantum dots
摘要： The use of photo- and thermoactivation during the liquid-phase synthesis of colloidal quantum dots was found to yield luminescing InP@ZnS quantum dots with a luminescence quantum yield close to unity. Activation mode was found to have little or no influence on the maximal luminescent efficiency but affect particle size distribution. Compared to thermal activation, photoactivation ensures the formation of more monodispersed particles.
关键词： Colloidal quantum dots,Thermoactivation,Indium phosphide,Luminescence quantum yield,Photoactivation
更新于2025-09-23 15:19:57