ABSTRACT
Owing to their excellent electrical conductivity and robust mechanical properties, carbon-based nanocomposites are being used in a wide range of applications and devices, such as electromagnetic wave interference shielding, electronic devices, and fuel cells. While several approaches have been developed for synthesizing carbon nanotubes and carbon-black-based polymer nanocomposites, most studies have focused on the simple blending of the carbon material with a polymer matrix. However, this results in uncontrolled interactions between the carbon filler and the polymer chains, leading to the agglomeration of the carbon filler. Herein, we report a new strategy for synthesizing sulfonated polystyrene (PSS)-grafted carbon black nanoparticles (NPs) via surface-initiated atom-transfer radical polymerization. Treatments with O2 plasma and H2O2 result in the effective attachment of the appropriate initiator to the carbon black NPs, thus allowing for the controlled formation of the PSS brushes. The high polymeric processability and desirable mechanical properties of the PSS-grafted carbon black NPs enable them suitable for use in nonfluorinated-hydrocarbon-based polymer electrolyte membranes for fuel cells, which must exhibit high proton conductivity without interrupting the network of channels consisting of ionic clusters (i.e., sulfonic acid moieties).
ABSTRACT
The additional (CH3NH3)2MnCl4 phase was observed upon increasing the Mn2+ dopant concentration, preventing the formation of Mn2+-doped CH3NH3PbCl3 NCs. We introduce an approach to avoid the formation of an impurity phase by switching the sequence for the addition of MnCl2 in the crystal growth process.
ABSTRACT
Organolead halide perovskite nanocrystals (NCs) have emerged as promising materials for various optoelectronic applications. However, their practical applications have been limited due to low structural integrity and poor luminescence stability associated with fast attachment-detachment dynamics of surface capping molecules during postprocessing. At present, a framework for understanding how the functional additives interact with surface moieties of organolead halide perovskites is not available. Methylammonium lead bromide NCs without surfactants on their surface provide an ideal system to investigate the direct interactions of the perovskite with functional molecules. When the oleic acid is used in a combination with n-octylamine, its contribution to surface passivation is significantly increased by protonating the alkyl amine to the corresponding ammonium ion. Our results demonstrate that the Br vacancies at the nonpassivated surface result in a reduction of Pb2+ to Pb0 by trapping electrons generated from the exciton dissociation, which provides a main pathway for exciton trapping.
ABSTRACT
Recently developed electronic packaging materials based on low dimensional materials such as carbon nanotubes, graphene, and hexagonal boron nitride (h-BN) exhibit advantageous electrical, thermal, and mechanical properties for protecting electronic devices as well as dissipating heat flux from highly integrated circuits or high power electronic devices. Their thermal transport is mainly achieved by precise control of the nanostructure for nano-fillers to form the thermally conductive pathway. However, due to the viscoelastic behaviors of host polymeric materials, their phase or structural stability is significantly reduced by enhanced molecular motion at high temperature, resulting in poor thermal transport and mechanical strength. Here, we introduce flexible and robust h-BN foam sheets with a three-dimensional network structure, which exhibit much enhanced thermostability at high temperature. Furthermore, the additional infiltration of Fe3O4 nanoparticles into those structures results in relatively high electromagnetic absorbing performance. The combination of thermostability and mechanical strength based on the h-BN foam sheets provides novel opportunities for multifunctional thermally conductive materials in coatings and films without severely compromising auxiliary characteristics such as mechanical strength and thermal stability.
ABSTRACT
Organohalide perovskite nanocrystals (NCs) with a variety of nano-scale structures and morphologies have shown promising potential owing to their size- and composition-dependent optoelectronic properties. Despite extensive studies on their size-dependent optical properties, a lack of understanding on their morphological transformation and the relevant stability issues limits a wide range of applications. Herein, we hypothesize a mechanism for the morphological transformation of perovskite NCs, which leads to dissolving NCs and forming microscale rectangular grains, resulting in a reduction of photoluminescence. We found that the morphological transformation from nanocrystal solids to microscale rectangular solids occurs via Ostwald ripening. A surface treatment with a surfactant suppresses the transformation, resulting in nearly monodisperse NCs with a square shape (â¼20 nm edge size), and thus improves the stability of NC solution, as well as their photoluminescence performance and quantum yield (PLQY = 82%). Furthermore, we employed similar amine derivatives to investigate the effect of a molecular architecture (i.e. steric hindrance) on perovskite NC stability, which exhibited much enhanced PLQY (93%). These experimental results provide new insights into the fundamental relationship between the physical properties and the structure of perovskite nanocrystals required to understand their diverse optoelectronic properties.
ABSTRACT
A thermally stable 2D array of spheres and their morphology control become important for the fabrication of novel nanostructures. Here, a simple method is presented for fabrication of large-area and well-ordered arrays of carbonized polystyrene (PS) hollow spheres with a controlled (close-packed or non-close-packed hexagonal) morphology, prepared by combining the self-assembly of PS-grafted silica nanoparticles, etching, electron irradiation, and subsequent thermal annealing. Fine control in the 2D or 3D nanostructure of carbon materials can open up new opportunities for high-performance nanoscale applications that require an efficient fabrication method for preparation of the porous carbon array.
Subject(s)
Carbon/chemistry , Electrons , Nanospheres/chemistry , Polymers/chemistry , Particle Size , Porosity , Surface PropertiesABSTRACT
Electrostatically stabilized InP quantum dots (QDs) showing a high luminescence yield of 16% without any long alkyl chain coordinating ligands on their surface are demonstrated. This is achieved by UV-etching the QDs in the presence of fluoric and sulfuric acids. Fluoric acid plays a critical role in selectively etching nonradiative sites during the ligand-exchange process and in relieving the acidity of the solution to prevent destruction of the QDs. Given that the InP QDs show high luminescence without any electrical barriers, such as long alkyl ligands or inorganic shells, this method can be applied for QD treatment for application to highly efficient QD-based optoelectronic devices.
ABSTRACT
A series of single-phased emission-tunable Na(0.34)Ca(0.66)Al(1.66)Si(2.34)O(8):Eu(2+),Mn(2+) phosphors were successfully synthesized by a wet-chemical synthesis method. Photoluminescence excitation (PLE) spectra indicate that the phosphor can be efficiently excited by UV radiation from 250 to 420 nm. Also, NCASO:Eu(2+),Mn(2+) phosphor exhibit a broad blue emission band at 440 nm and an orange emission band at 570 nm, which originate from Eu(2+) and Mn(2+) ions, respectively. Therefore, overall emission color can be tuned from blue to white by increasing the concentration of Mn(2+) ions in the host lattice utilizing energy transfer from Eu(2+) to Mn(2+) ions. This energy transfer phenomenon was demonstrated to be a resonant type through dipole-dipole interaction determined with the help of PL spectra, decay time measurement, and energy transfer efficiency of the phosphor. These results indicate that NCASO:Eu(2+),Mn(2+) can be a promising single-phased white-emitting phosphor for white-light UV LEDs.
