The upconversion luminescence ͑UCL͒ of the hexagonal ͑͒-phase NaYF 4 : Yb, Er nanophosphors as a... more The upconversion luminescence ͑UCL͒ of the hexagonal ͑͒-phase NaYF 4 : Yb, Er nanophosphors as a function of temperature ͑300-450 K͒ was examined under 978 nm light excitation. The thermal sensitivity was evaluated based on the UCL intensity ratio between 2 H 11/2-4 I 15/2 and 4 S 3/2-4 I 15/2 transitions ͑R HS ͒. Excitation power, particle sizes ͑37, 65, and 140 nm͒, ion doping concentrations, and with and without silica coating were studied. It was found that R HS is only dependent on temperature at the low excitation power, and has no direct relation with the particle size and surface effects. Silica coating was found to enhance the thermal stability significantly without altering the thermal sensitivity.
Supported Pt-metal catalysts are of immense commercial importance for hydrogenation reactions. Th... more Supported Pt-metal catalysts are of immense commercial importance for hydrogenation reactions. The fine chemicals industry relies on special catalysts that selectively hydrogenate specific bonds or chemical functions on molecules. The activity, selectivity, lifetime, etc. of a supported hydrogenation catalyst is wellknown to depend strongly on the chosen support, but systematic studies of the role of the support and of support-metal interactions are lacking in the literature. The purpose of this work is to examine in detail the function of single-wall carbon nanotubes (SWNT) as support for a Pt catalyst, in the context of a selective hydrogenation reaction. The test reaction consists of the hydrogenation of the carbonyl group on 3-methyl-2- butenal, a reaction extensively studied on well-characterized Pt surfaces and also unsupported polycrystalline Pt. This reaction, which follows a parallel/consecutive reaction network (Fig. 1), represents a class of selective hydrogenation reacti...
New materials are now being fabricated with greater geometric complexity and smaller feature size... more New materials are now being fabricated with greater geometric complexity and smaller feature sizes. Such complexity is inherent to most biomaterials and their synthetic analogues, as well as to nanotechnology. Beyond complexity, phenomena occurring on even smaller length scales often adversely affect performance and reliability. Foremost among these phenomena are interface properties within the composite materials, resulting in chemical and structural gradients. Understanding and improving the performance and durability of these systems requires highresolution structural, chemical and geometric analysis of cross sections through the layers. The ability to perform such analysis on precisely located cross sections is one of the key attributes of the dual beam focused ion beam (FIB). This FIB system has been developed to combine the imaging capabilities of a typical scanning electron microscope (SEM) with the imaging and fabrication capabilities of a highly focused ion beam. As focused ion beam technology has advanced, focused ion beam systems have been gaining more attention as an alternative method for micro-and nanoscale machining and fabrication. Presently, the preparation of sections by mechanical polishing, dimpling and ion milling is either excessively time consuming or possible only with highly trained metrology experts or, in some cases, totally impossible. In other cases, the compliance of the constituents prevents the formation of undamaged/undistorted cross sections: certain shell-like biological structures exemplify this problem. The FIB system obviates these problems and also provides unique high precision etching and deposition for micromanipulation as well as imaging and analysis. This instrument provides unique capabilities for advanced materials research connected to nanoscale, biological, photonic and multifunctional materials.
Extremely low energy consumption neuromorphic computing is required to achieve massively parallel... more Extremely low energy consumption neuromorphic computing is required to achieve massively parallel information processing on par with the human brain. To achieve this goal, resistive memories based on materials with ionic transport and extremely low operating current are required. Extremely low operating current allows for low power operation by minimizing the program, erase, and read currents. However, materials currently used in resistive memories, such as defective HfOx, AlOx, TaOx, etc., cannot suppress electronic transport (i.e., leakage current) while allowing good ionic transport. Here, we show that 2D Ruddlesden-Popper phase hybrid lead bromide perovskite single crystals are promising materials for low operating current nanodevice applications because of their mixed electronic and ionic transport and ease of fabrication. Ionic transport in the exfoliated 2D perovskite layer is evident via the migration of bromide ions. Filaments with a diameter of approximately 20 nm are visu...
The supramolecular assembly of surfactant molecules at a solidliquid interface can produce tubula... more The supramolecular assembly of surfactant molecules at a solidliquid interface can produce tubular structures with diameters of around 10 nm (refs 1-4), which can be used for the templated polymerization of mesoporous silica thin films 3-5. The orientation of the tubules depends primarily on the nature of the substratesurfactant interaction. These nanostructured films hold much promise for applications such as their use as orientated nanowires 6 , sensor/actuator arrays 7-9 and optoelectronic devices 10. But a method of patterning the tubules and orientating them into designed arrangements is required for many of these possibilities to be realized. Here we describe a method that allows the direction of growth of these tubules to be guided by infiltrating a reaction fluid into the microcapillaries of a mould in contact with a substrate 11. An electric field applied tangentially to the surface within the capillaries induces electro-osmotic flow, and also enhances the rates of silica polymerization around the tubules by localized Joule heating. After removal of the mould, patterned bundles of orientated nanotubules remain on the surface. This method permits the formation of orientated mesoporous channels on a non-conducting substrate with an arbitrary microscopic pattern. The development of low-cost lithographic techniques to pattern materials with structural features on the nanometre scale is important for the miniaturization of electronic, optoelectronic and magnetic devices. Existing approaches include technologies involving scanning electron beams 12,13 , X-ray lithography 14,15 , scanning probe microscopes 16,17 and imprinting methods 18. The 'micromoulding in capillaries' (MIMIC) technique 11 provides a low-cost approach to thin-film patterning. In this method, a network of patterned capillaries is formed by placing an elastomeric stamp (typically made of polydimethyl siloxane, PDMS) possessing designed relief features on its surface in contact with a flat substrate (see Fig. 1). Second, an acidified aqueous reacting solution of tetraethoxysilane (TEOS) and cetyltrimethylammonium chloride (CTAC) is placed in contact with the edge of the mould and is transferred by 'wicking' into the networked channels. Typical molar ratios for the reacting solution are 1 TEOS : 1.2 CTAC : 9.2 HCl : 1,000 H 2 O. As has been shown previously 4 , the formation of a mesoscopic silica film begins to occur immediately on contact of this solution with any interface onto which the surfactant can adsorb. A dilute solution of the TEOS silica source is specifically used to prevent homogeneous nucleation of inorganic material in bulk solution, and to promote heterogeneous nucleation and growth of a mesoscopic film at the substrate-solution interface 4. Within the capillaries, because the reacting solution is dilute, reactants are quickly depleted, and film growth ceases if wicking occurs only through capillary suction. Moreover, the growth of mesoscopic film at the edges of the mould seals the capillaries and prevents diffusion of reacting species to the interior of the mould.
Solid phase crystallization (SPC) of a-Si: H at 600°C was investigated by transmission electron m... more Solid phase crystallization (SPC) of a-Si: H at 600°C was investigated by transmission electron microscopy (TEM) and Raman spectroscopy in a cantilever structure, where the underlying SiO2 was removed prior to the crystallization. The absence of the underlying oxide leads to both a higher grain size and a lower intragranular defect density. The grain size increases from 0.6 μm in regions with the underlying oxide to 3.0 μm without the underlying oxide, and the intragranular defect density decreases one order of magnitude from ∼ 1011 cm-2 to ∼ 1010 cm-2. The improvements in material quality without the lower a-Si/SiO2 interface are thought to be due to a lower nucleation rate and a lower tensile stress with an easier silicon atomic rearrangement at the lower silicon interface.
Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron... more Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm(2), is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the m...
Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively mod... more Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively modifies the optical properties. Such nanostructured materials could play an important role in optoelectronic devices, catalysis and imaging applications. In this work, we fabricate and characterize germanium nanocrystals (Ge NCs) embedded in arsenic sulfide thin films by pulsed laser ablation in aliphatic amine solutions. Unstable surface termination of aliphatic groups and stable termination by amine on Ge NCs are indicated by Raman and Fourier-transform infrared spectroscopy measurements, respectively. A broadband photoluminescence (PL) in the visible range is observed for the amine functionalized Ge NCs. A noticeable enhancement of fluorescence is observed for Ge NCs in arsenic sulfide, after annealing to remove the residual solvent of the glass matrix.
Advanced materials (Deerfield Beach, Fla.), Jan 24, 2017
Organic-inorganic hybrid perovskite materials are emerging as semiconductors with potential appli... more Organic-inorganic hybrid perovskite materials are emerging as semiconductors with potential application in optoelectronic devices. In particular, perovskites are very promising for light-emitting devices (LEDs) due to their high color purity, low nonradiative recombination rates, and tunable bandgap. Here, using pure CH3 NH3 PbI3 perovskite LEDs with an external quantum efficiency (EQE) of 5.9% as a platform, it is shown that electrical stress can influence device performance significantly, increasing the EQE from an initial 5.9% to as high as 7.4%. Consistent with the enhanced device performance, both the steady-state photoluminescence (PL) intensity and the time-resolved PL decay lifetime increase after electrical stress, indicating a reduction in nonradiative recombination in the perovskite film. By investigating the temperature-dependent characteristics of the perovskite LEDs and the cross-sectional elemental depth profile, it is proposed that trap reduction and resulting device...
Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelect... more Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH3NH3PbI3 and CH3NH3PbBr3 perovskite nanocrystals with an avera...
International journal of pharmaceutics, Jan 30, 2016
The blood brain barrier (BBB) is a major obstacle to drug delivery for diseases of the central ne... more The blood brain barrier (BBB) is a major obstacle to drug delivery for diseases of the central nervous system (CNS). This brief review highlights the current invasive and non-invasive technologies available to address this problem. In particular, nanomedicine has shown much promise as a non-invasive strategy due to its drug loading capabilities, ease of targeting to the BBB, and small size. The versatility of this technology in terms of type of drug and imaging agent, carrier material, and targeting mechanism is highlighted in this review. The recent inclusion of imaging agents in the nanocarriers has important consequences for the field of theranostics.
Understanding the mechanism of charge generation, distribution, and transfer between surfaces is ... more Understanding the mechanism of charge generation, distribution, and transfer between surfaces is very important for energy harvesting applications based on triboelectric effect. Here, we demonstrate dynamic nanotriboelectrification with torsional resonance (TR) mode atomic force microscopy (AFM). Experiments on rubbing the sample surface using TR mode for the generation of triboelectric charges and in-situ characterization of the charge distribution using scanning Kelvin probe microcopy (SKPM) were performed. This method allows the tip to perform lateral oscillation and maintains the tip-sample interaction in the attractive region to ensure high efficiency of the charge generation during the rubbing process. The measured efficiency of generating triboelectric charges can achieve ~10.53 times higher than conventional static/contact mode in the triboelectrification experiments. In addition to the charge generation, local discharging experiments were also performed. This work would pro...
Cu3Ge has been pursued as next-generation interconnection/contact material due to its high therma... more Cu3Ge has been pursued as next-generation interconnection/contact material due to its high thermal stability, low bulk resistivity and diffusion barrier property. Improvements in electrical performance and structure of Cu3Ge have attracted great attention in the past decades. Despite the remarkable progress in Cu3Ge fabrication on various substrates by different deposition methods, polycrystalline films with excess Ge were frequently obtained. Moreover, the characterization of nanoscale electrical properties remains challenging. Here we show the fabrication of epitaxial Cu3Ge thin film and its nanoscale electrical properties, which are directly correlated with localized film microstructures and supported by HRTEM observations. The average resistivity and work function of epitaxial Cu3Ge thin film are measured to be 6 ± 1 μΩ cm and ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to Cu.
Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface el... more Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He þ) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He þ beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the "Z 2-oscillations" of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets. V
We have prepared a novel material, consisting of Pt particles supported on purified single-walled... more We have prepared a novel material, consisting of Pt particles supported on purified single-walled carbon nanotubes (SWNTs), representing the first reported metal-loaded SWNT material. The material contains 10 wt % Pt on entangled SWNT bundles consisting of 20−100 ...
The upconversion luminescence ͑UCL͒ of the hexagonal ͑͒-phase NaYF 4 : Yb, Er nanophosphors as a... more The upconversion luminescence ͑UCL͒ of the hexagonal ͑͒-phase NaYF 4 : Yb, Er nanophosphors as a function of temperature ͑300-450 K͒ was examined under 978 nm light excitation. The thermal sensitivity was evaluated based on the UCL intensity ratio between 2 H 11/2-4 I 15/2 and 4 S 3/2-4 I 15/2 transitions ͑R HS ͒. Excitation power, particle sizes ͑37, 65, and 140 nm͒, ion doping concentrations, and with and without silica coating were studied. It was found that R HS is only dependent on temperature at the low excitation power, and has no direct relation with the particle size and surface effects. Silica coating was found to enhance the thermal stability significantly without altering the thermal sensitivity.
Supported Pt-metal catalysts are of immense commercial importance for hydrogenation reactions. Th... more Supported Pt-metal catalysts are of immense commercial importance for hydrogenation reactions. The fine chemicals industry relies on special catalysts that selectively hydrogenate specific bonds or chemical functions on molecules. The activity, selectivity, lifetime, etc. of a supported hydrogenation catalyst is wellknown to depend strongly on the chosen support, but systematic studies of the role of the support and of support-metal interactions are lacking in the literature. The purpose of this work is to examine in detail the function of single-wall carbon nanotubes (SWNT) as support for a Pt catalyst, in the context of a selective hydrogenation reaction. The test reaction consists of the hydrogenation of the carbonyl group on 3-methyl-2- butenal, a reaction extensively studied on well-characterized Pt surfaces and also unsupported polycrystalline Pt. This reaction, which follows a parallel/consecutive reaction network (Fig. 1), represents a class of selective hydrogenation reacti...
New materials are now being fabricated with greater geometric complexity and smaller feature size... more New materials are now being fabricated with greater geometric complexity and smaller feature sizes. Such complexity is inherent to most biomaterials and their synthetic analogues, as well as to nanotechnology. Beyond complexity, phenomena occurring on even smaller length scales often adversely affect performance and reliability. Foremost among these phenomena are interface properties within the composite materials, resulting in chemical and structural gradients. Understanding and improving the performance and durability of these systems requires highresolution structural, chemical and geometric analysis of cross sections through the layers. The ability to perform such analysis on precisely located cross sections is one of the key attributes of the dual beam focused ion beam (FIB). This FIB system has been developed to combine the imaging capabilities of a typical scanning electron microscope (SEM) with the imaging and fabrication capabilities of a highly focused ion beam. As focused ion beam technology has advanced, focused ion beam systems have been gaining more attention as an alternative method for micro-and nanoscale machining and fabrication. Presently, the preparation of sections by mechanical polishing, dimpling and ion milling is either excessively time consuming or possible only with highly trained metrology experts or, in some cases, totally impossible. In other cases, the compliance of the constituents prevents the formation of undamaged/undistorted cross sections: certain shell-like biological structures exemplify this problem. The FIB system obviates these problems and also provides unique high precision etching and deposition for micromanipulation as well as imaging and analysis. This instrument provides unique capabilities for advanced materials research connected to nanoscale, biological, photonic and multifunctional materials.
Extremely low energy consumption neuromorphic computing is required to achieve massively parallel... more Extremely low energy consumption neuromorphic computing is required to achieve massively parallel information processing on par with the human brain. To achieve this goal, resistive memories based on materials with ionic transport and extremely low operating current are required. Extremely low operating current allows for low power operation by minimizing the program, erase, and read currents. However, materials currently used in resistive memories, such as defective HfOx, AlOx, TaOx, etc., cannot suppress electronic transport (i.e., leakage current) while allowing good ionic transport. Here, we show that 2D Ruddlesden-Popper phase hybrid lead bromide perovskite single crystals are promising materials for low operating current nanodevice applications because of their mixed electronic and ionic transport and ease of fabrication. Ionic transport in the exfoliated 2D perovskite layer is evident via the migration of bromide ions. Filaments with a diameter of approximately 20 nm are visu...
The supramolecular assembly of surfactant molecules at a solidliquid interface can produce tubula... more The supramolecular assembly of surfactant molecules at a solidliquid interface can produce tubular structures with diameters of around 10 nm (refs 1-4), which can be used for the templated polymerization of mesoporous silica thin films 3-5. The orientation of the tubules depends primarily on the nature of the substratesurfactant interaction. These nanostructured films hold much promise for applications such as their use as orientated nanowires 6 , sensor/actuator arrays 7-9 and optoelectronic devices 10. But a method of patterning the tubules and orientating them into designed arrangements is required for many of these possibilities to be realized. Here we describe a method that allows the direction of growth of these tubules to be guided by infiltrating a reaction fluid into the microcapillaries of a mould in contact with a substrate 11. An electric field applied tangentially to the surface within the capillaries induces electro-osmotic flow, and also enhances the rates of silica polymerization around the tubules by localized Joule heating. After removal of the mould, patterned bundles of orientated nanotubules remain on the surface. This method permits the formation of orientated mesoporous channels on a non-conducting substrate with an arbitrary microscopic pattern. The development of low-cost lithographic techniques to pattern materials with structural features on the nanometre scale is important for the miniaturization of electronic, optoelectronic and magnetic devices. Existing approaches include technologies involving scanning electron beams 12,13 , X-ray lithography 14,15 , scanning probe microscopes 16,17 and imprinting methods 18. The 'micromoulding in capillaries' (MIMIC) technique 11 provides a low-cost approach to thin-film patterning. In this method, a network of patterned capillaries is formed by placing an elastomeric stamp (typically made of polydimethyl siloxane, PDMS) possessing designed relief features on its surface in contact with a flat substrate (see Fig. 1). Second, an acidified aqueous reacting solution of tetraethoxysilane (TEOS) and cetyltrimethylammonium chloride (CTAC) is placed in contact with the edge of the mould and is transferred by 'wicking' into the networked channels. Typical molar ratios for the reacting solution are 1 TEOS : 1.2 CTAC : 9.2 HCl : 1,000 H 2 O. As has been shown previously 4 , the formation of a mesoscopic silica film begins to occur immediately on contact of this solution with any interface onto which the surfactant can adsorb. A dilute solution of the TEOS silica source is specifically used to prevent homogeneous nucleation of inorganic material in bulk solution, and to promote heterogeneous nucleation and growth of a mesoscopic film at the substrate-solution interface 4. Within the capillaries, because the reacting solution is dilute, reactants are quickly depleted, and film growth ceases if wicking occurs only through capillary suction. Moreover, the growth of mesoscopic film at the edges of the mould seals the capillaries and prevents diffusion of reacting species to the interior of the mould.
Solid phase crystallization (SPC) of a-Si: H at 600°C was investigated by transmission electron m... more Solid phase crystallization (SPC) of a-Si: H at 600°C was investigated by transmission electron microscopy (TEM) and Raman spectroscopy in a cantilever structure, where the underlying SiO2 was removed prior to the crystallization. The absence of the underlying oxide leads to both a higher grain size and a lower intragranular defect density. The grain size increases from 0.6 μm in regions with the underlying oxide to 3.0 μm without the underlying oxide, and the intragranular defect density decreases one order of magnitude from ∼ 1011 cm-2 to ∼ 1010 cm-2. The improvements in material quality without the lower a-Si/SiO2 interface are thought to be due to a lower nucleation rate and a lower tensile stress with an easier silicon atomic rearrangement at the lower silicon interface.
Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron... more Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm(2), is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the m...
Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively mod... more Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively modifies the optical properties. Such nanostructured materials could play an important role in optoelectronic devices, catalysis and imaging applications. In this work, we fabricate and characterize germanium nanocrystals (Ge NCs) embedded in arsenic sulfide thin films by pulsed laser ablation in aliphatic amine solutions. Unstable surface termination of aliphatic groups and stable termination by amine on Ge NCs are indicated by Raman and Fourier-transform infrared spectroscopy measurements, respectively. A broadband photoluminescence (PL) in the visible range is observed for the amine functionalized Ge NCs. A noticeable enhancement of fluorescence is observed for Ge NCs in arsenic sulfide, after annealing to remove the residual solvent of the glass matrix.
Advanced materials (Deerfield Beach, Fla.), Jan 24, 2017
Organic-inorganic hybrid perovskite materials are emerging as semiconductors with potential appli... more Organic-inorganic hybrid perovskite materials are emerging as semiconductors with potential application in optoelectronic devices. In particular, perovskites are very promising for light-emitting devices (LEDs) due to their high color purity, low nonradiative recombination rates, and tunable bandgap. Here, using pure CH3 NH3 PbI3 perovskite LEDs with an external quantum efficiency (EQE) of 5.9% as a platform, it is shown that electrical stress can influence device performance significantly, increasing the EQE from an initial 5.9% to as high as 7.4%. Consistent with the enhanced device performance, both the steady-state photoluminescence (PL) intensity and the time-resolved PL decay lifetime increase after electrical stress, indicating a reduction in nonradiative recombination in the perovskite film. By investigating the temperature-dependent characteristics of the perovskite LEDs and the cross-sectional elemental depth profile, it is proposed that trap reduction and resulting device...
Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelect... more Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH3NH3PbI3 and CH3NH3PbBr3 perovskite nanocrystals with an avera...
International journal of pharmaceutics, Jan 30, 2016
The blood brain barrier (BBB) is a major obstacle to drug delivery for diseases of the central ne... more The blood brain barrier (BBB) is a major obstacle to drug delivery for diseases of the central nervous system (CNS). This brief review highlights the current invasive and non-invasive technologies available to address this problem. In particular, nanomedicine has shown much promise as a non-invasive strategy due to its drug loading capabilities, ease of targeting to the BBB, and small size. The versatility of this technology in terms of type of drug and imaging agent, carrier material, and targeting mechanism is highlighted in this review. The recent inclusion of imaging agents in the nanocarriers has important consequences for the field of theranostics.
Understanding the mechanism of charge generation, distribution, and transfer between surfaces is ... more Understanding the mechanism of charge generation, distribution, and transfer between surfaces is very important for energy harvesting applications based on triboelectric effect. Here, we demonstrate dynamic nanotriboelectrification with torsional resonance (TR) mode atomic force microscopy (AFM). Experiments on rubbing the sample surface using TR mode for the generation of triboelectric charges and in-situ characterization of the charge distribution using scanning Kelvin probe microcopy (SKPM) were performed. This method allows the tip to perform lateral oscillation and maintains the tip-sample interaction in the attractive region to ensure high efficiency of the charge generation during the rubbing process. The measured efficiency of generating triboelectric charges can achieve ~10.53 times higher than conventional static/contact mode in the triboelectrification experiments. In addition to the charge generation, local discharging experiments were also performed. This work would pro...
Cu3Ge has been pursued as next-generation interconnection/contact material due to its high therma... more Cu3Ge has been pursued as next-generation interconnection/contact material due to its high thermal stability, low bulk resistivity and diffusion barrier property. Improvements in electrical performance and structure of Cu3Ge have attracted great attention in the past decades. Despite the remarkable progress in Cu3Ge fabrication on various substrates by different deposition methods, polycrystalline films with excess Ge were frequently obtained. Moreover, the characterization of nanoscale electrical properties remains challenging. Here we show the fabrication of epitaxial Cu3Ge thin film and its nanoscale electrical properties, which are directly correlated with localized film microstructures and supported by HRTEM observations. The average resistivity and work function of epitaxial Cu3Ge thin film are measured to be 6 ± 1 μΩ cm and ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to Cu.
Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface el... more Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He þ) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He þ beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the "Z 2-oscillations" of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets. V
We have prepared a novel material, consisting of Pt particles supported on purified single-walled... more We have prepared a novel material, consisting of Pt particles supported on purified single-walled carbon nanotubes (SWNTs), representing the first reported metal-loaded SWNT material. The material contains 10 wt % Pt on entangled SWNT bundles consisting of 20−100 ...
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