Shape-Control and Doping of Lanthanides and Transition Metal Oxide Nanocrystals With Tailored Properties and Their Shape-Directed Self-Assembly

Lanthanide and transition metal oxides are widely used in various applications such phosphors, lasers, magnets, and catalysts, and have formed an important platform for biomedical research and clinical medicine. The synthesis of highly uniform nanomaterials with controlled size, shape, and compositions is paramount to precisely understanding their physical properties and to arrange them into highly ordered arrays to design functional metamaterials. Herein, I describe novel chemistry to synthesize highly uniform lanthanide and transition metal oxide nanocrystals. The size, shape, and compositions of lanthanide-based nanocrystals are systematically controlled with the addition of alkali metal salts. The reaction mechanism is investigated to understand the nanocrystal growth and characterized by X-ray measurements and microscopic analysis. The magnetic resonance relaxometry and the optical properties including phosphorescece, upconversion, and X-ray excited optical luminescence are investigated, which make these nanocrystals a promising platform for multimodal imaging in biomedical applications. The shape-controlled synthesis of isotopically labeled rare earth fluoride nanocrystals is also demonstrated, which is designed for in vitro and ex vivo radioisotopic detection, as well as non-invasive nuclear, optical radioluminescence, and magnetic resonance imaging. Using anisotropic nanocrystal building blocks, shape-directed liquid crystalline self-assembly is presented to understand how complex anisotropic superstructures can be designed with single and binary components in a predictable manner. Finally, transition metal oxides such as tungsten, oxide, titanium oxide, and vanadium oxide are synthesized using non-injection heating up method. In addition, I demonstrate that vanadium oxide nanocrystal can be utilized as the precursors to fabricate thermochromic VO2, which is an important building block for energy research, optics, and electronic devices

Photocatalytic Hydrogen Evolution from Sub-Stoichiometric Colloidal WO3-xNanowires

We report direct photocatalytic hydrogen evolution from substoichiometric highly reduced tungsten oxide (WOx) nanowires (NWs) using sacrificial alcohol. WOx NWs are synthesized via nonaqueous colloidal synthesis with a diameter of about 4 nm and an average length of about 250 nm. As-synthesized WOx NWs exhibit a broad absorption across the visible to infrared regions attributed to the presence of oxygen vacancies. The optical band gap is increased in these WOx NWs compared to stoichiometric bulk tungsten oxide (WO3) powders as a result of the Burstein\u2013Moss shift. As a consequence of this increase, we demonstrate direct photocatalytic hydrogen production from WOx NWs through alcohol photoreforming. The stable H2 evolution on platinized WOx NWs is observed under conditions in which platinized bulk WO3 and bulk WO2.9 powders either do not show activity or show very low rates, suggesting that increased surface area and specific exposed facets are key for the improved performance of WOx NWs. This work demonstrates that control of size and composition can lead to unexpected and beneficial changes in the photocatalytic properties of semiconductor materials

Colloidal Self-Assembly of Inorganic Nanocrystals into Superlattice Thin-Films and Multiscale Nanostructures

The self-assembly of colloidal inorganic nanocrystals (NCs) offers tremendous potential for the design of solution-processed multi-functional inorganic thin-films or nanostructures. To date, the self-assembly of various inorganic NCs, such as plasmonic metal, metal oxide, quantum dots, magnetics, and dielectrics, are reported to form single, binary, and even ternary superlattices with long-range orientational and positional order over a large area. In addition, the controlled coupling between NC building blocks in the highly ordered superlattices gives rise to novel collective properties, providing unique optical, magnetic, electronic, and catalytic properties. In this review, we introduce the self-assembly of inorganic NCs and the experimental process to form single and multicomponent superlattices, and we also describe the fabrication of multiscale NC superlattices with anisotropic NC building blocks, thin-film patterning, and the supracrystal formation of superlattice structures

Recent Advances in Fabrication of Flexible, Thermochromic Vanadium Dioxide Films for Smart Windows

Monoclinic-phase VO2 (VO2(M)) has been extensively studied for use in energy-saving smart windows owing to its reversible insulator–metal transition property. At the critical temperature (Tc = 68 °C), the insulating VO2(M) (space group P21/c) is transformed into metallic rutile VO2 (VO2(R) space group P42/mnm). VO2(M) exhibits high transmittance in the near-infrared (NIR) wavelength; however, the NIR transmittance decreases significantly after phase transition into VO2(R) at a higher Tc, which obstructs the infrared radiation in the solar spectrum and aids in managing the indoor temperature without requiring an external power supply. Recently, the fabrication of flexible thermochromic VO2(M) thin films has also attracted considerable attention. These flexible films exhibit considerable potential for practical applications because they can be promptly applied to windows in existing buildings and easily integrated into curved surfaces, such as windshields and other automotive windows. Furthermore, flexible VO2(M) thin films fabricated on microscales are potentially applicable in optical actuators and switches. However, most of the existing fabrication methods of phase-pure VO2(M) thin films involve chamber-based deposition, which typically require a high-temperature deposition or calcination process. In this case, flexible polymer substrates cannot be used owing to the low-thermal-resistance condition in the process, which limits the utilization of flexible smart windows in several emerging applications. In this review, we focus on recent advances in the fabrication methods of flexible thermochromic VO2(M) thin films using vacuum deposition methods and solution-based processes and discuss the optical properties of these flexible VO2(M) thin films for potential applications in energy-saving smart windows and several other emerging technologies

Shape-Directed Binary Assembly of Anisotropic Nanoplates: A Nanocrystal Puzzle with Shape-Complementary Building Blocks

We present the binary self-assembly of two anisotropic nanoplate building blocks mediated by shape complementarity. We use rhombic GdF₃ and tripodal Gd₂O₃ nanoplates as building blocks in which the size and shape are designed to be optimal for complementary organization. A liquid interfacial assembly technique allows the formation of self-assembled binary superlattices from two anisotropic nanoplates over a micrometer length scale. Shape-directed self-assembly guides the position of each anisotropic nanoplate in the binary superlattices, allowing for long-range orientational and positional order of each building block. The design of shape complementary anisotropic building blocks offers the possibility to self-assemble binary superlattices with predictable and designable structures

Facile Sulfurization under Ambient Condition with Na2S to Fabricate Nanostructured Copper Sulfide

The sulfurization reaction was investigated as a promising fabrication method for preparing metal sulfide nanomaterials. Traditional sulfurization processes generally require high vacuum systems, high reaction temperatures, and toxic chemicals, utilizing complicated procedures with poor composition and morphology controllability. Herein, a facile method is reported for synthesizing nanostructured copper sulfide using a sulfurization reaction with Na2S at room temperature under non-vacuum conditions. Moreover, we demonstrate that the morphology, composition, and optical properties of nanostructured copper sulfides could be controlled by the Na2S solution concentration and the reaction time. Nanostructured copper sulfides were synthesized in nanospheres, nanoplates, and nanoplate-based complex morphologies with various oxidation states. Furthermore, by comparing the optical properties of nanostructured copper sulfides with different oxidation states, we determined that reflectivity in the near infrared (NIR) region decreases with increasing oxidation states. These results reveal that the Na2S solution concentration and reaction time are key factors for designing nanostructured copper sulfides, providing new insights for synthesis methods of metal sulfide nanomaterials

Realization of Reflective Color Generation and Controllable absorption in Near-Infrared Based on Active Nanocrystal Metamaterials Absorber

The conventional color was realized by dye or organic paints. But these colors be vulnerable to Ultra-Violet light, discoloration occurs over time. To solve this problem, the structural color was proposed. To implement the structural color, An absorber is needed that can reflect a selective wavelength. The representative optical absorber is used Fabry-Perot structure. Conventional absorber has fixed optical properties after fabricated. To make up for these limitations, researchers used to Nanocrystal to tune material properties [1] or, an intuitive approach using phase change material (PCM) [2,3]. In the case of nanocrystals, the optical properties of the material can be changed, only in before fabrication, and the bulk PCM has a disadvantageous that is difficult to apply due to its large optical loss. In this study, we demonstrated a flexible reflective color filter with changeable Near-Infrared (NIR) absorption based on the solution-processable that without annealing process Vanadium dioxide (VO2) nanocrystal absorber. In this case, the optical loss can be controlled by only the nanocrystal size, and thickness without lost a phase change property. Based on these advantages, the main additive colors with NIR controllable absorption has been demonstrated. Furthermore, we exploit advanced VO2 that W-doped in which phase change temperature can be drastically reduced, it can be expected for anti-counterfeiting technology and display industry.2

Binary and Ternary Superlattices Self-Assembled from Colloidal Nanodisks and Nanorods

Self-assembly of multicomponent anisotropic nanocrystals with controlled orientation and spatial distribution allows the design of novel metamaterials with unique shape- and orientation-dependent collective properties. Although many phases of binary structures are theoretically proposed, the examples of multicomponent assemblies, which are experimentally realized with colloidal anisotropic nanocrystals, are still limited. In this report, we demonstrate the formation of binary and ternary superlattices from colloidal two-dimensional LaF₃ nanodisks and one-dimensional CdSe/CdS nanorods via liquid interfacial assembly. The colloidal nanodisks and nanorods are coassembled into AB-, AB₂-, and AB₆-type binary arrays determined by their relative size ratio and concentration to maximize their packing density. The position and orientation of anisotropic nanocrystal building blocks are tightly controlled in the self-assembled binary and ternary lattices. The macroscopic orientation of the superlattices is further tuned by changing the liquid subphase used for self-assembly, resulting in the formation of lamellar-type binary liquid crystalline superlattices. In addition, we demonstrate a novel ternary superlattice self-assembled from two different sizes of nanodisks and a nanorod, which offers the unique opportunity to design multifunctional metamaterials

Nanobiosensing Platforms for Real-Time and Non-Invasive Monitoring of Stem Cell Pluripotency and Differentiation

Breakthroughs in the biomedical and regenerative therapy fields have led to the influential ability of stem cells to differentiate into specific types of cells that enable the replacement of injured tissues/organs in the human body. Non-destructive identification of stem cell differentiation is highly necessary to avoid losses of differentiated cells, because most of the techniques generally used as confirmation tools for the successful differentiation of stem cells can result in valuable cells becoming irrecoverable. Regarding this issue, recent studies reported that both Raman spectroscopy and electrochemical sensing possess excellent characteristics for monitoring the behavior of stem cells, including differentiation. In this review, we focus on numerous studies that have investigated the detection of stem cell pluripotency and differentiation in non-invasive and non-destructive manner, mainly by using the Raman and electrochemical methods. Through this review, we present information that could provide scientific or technical motivation to employ or further develop these two techniques for stem cell research and its application

Sub-100-nm Nearly Monodisperse n-Paraffin/PMMA Phase Change Nanobeads

In this study, we demonstrate the colloidal synthesis of nearly monodisperse, sub-100-nm phase change material (PCM) nanobeads with an organic n-paraffin core and poly(methylmethacrylate) (PMMA) shell. PCM nanobeads are synthesized via emulsion polymerization using ammonium persulfate as an initiator and sodium dodecylbenzenesulfonate as a surfactant. The highly uniform n-paraffin/PMMA PCM nanobeads are sub-100 nm in size and exhibit superior colloidal stability. Furthermore, the n-paraffin/PMMA PCM nanobeads exhibit reversible phase transition behaviors during the n-paraffin melting and solidification processes. During the solidification process, multiple peaks with relatively reduced phase change temperatures are observed, which are related to the phase transition of n-paraffin in the confined structure of the PMMA nanobeads. The phase change temperatures are further tailored by changing the carbon length of n-paraffin while maintaining the size uniformity of the PCM nanobeads. Sub-100-nm-sized and nearly monodisperse PCM nanobeads can be potentially utilized in thermal energy storage and drug delivery because of their high colloidal stability and solution processability