Tin-doped Indium Oxide Nanocrystals Research Articles

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers.

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability. Here we propose, demonstrate, and analyze a mid-infrared absorber architecture leveraging monolayer films of nanoplasmonic colloidal tin-doped indium oxide nanocrystals (ITO NCs). We fabricate a series of ITO NC monolayer films using the liquid-air interface method; by synthetically varying the Sn dopant concentration in the NCs, we achieve spectrally selective perfect absorption tunable between wavelengths of two and five micrometers. We achieve monolayer thickness-controlled coupling strength tuning by varying NC size, allowing access to different coupling regimes. Furthermore, we synthesize a bilayer film that enables broadband absorption covering the entire midwave IR region (λ = 3-5 μm). We demonstrate a scalable platform, with perfect absorption in monolayer films only hundredths of a wavelength in thickness, enabling strong light-matter interaction, with potential applications for molecular detection and ultrafast nonlinear optical applications.

Structural Study of alumino(boro)silicate glasses containing tin-doped indium oxide (ITO) nanocrystals with nonlinear optical and enhanced UV/ NIR-shielding properties

Transparent alumino(boro)silicate glasses containing tin-doped indium oxide nanocrystals were fabricated using conventional melt-casting and heat treatment. Structural characterization was carried out by Raman spectroscopy to study glass-forming species, coordination, type and number of oxygens, and possible connectivity of silicate, aluminate, and borate species. A changing role of indium, acting as a modifier in the glass structure, but leaving a less modified glass after clustering and crystallization was also revealed. X-ray photoelectron spectroscopy confirmed that indium was in the trivalent state only. HR-TEM provided insights into the distribution and morphology of the nanocrystals in the glass ceramic sample, yielding a mean size of 4.75 nm. The nonlinear optical behavior of aluminoborosilicate glass samples was evaluated using the Z-scan technique, demonstrating high third-order nonlinear optical susceptibility for both glass and glass ceramic samples, accompanied by a change in the signs of nonlinear refractive indices before and after crystallization from negative to positive.

Dipolar Ligands Tune Plasmonic Properties of Tin-Doped Indium Oxide Nanocrystals.

Surface functionalization with dipolar molecules is known to tune the electronic band alignment in semiconductor films and colloidal quantum dots. Yet, the influence of surface modification on plasmonic nanocrystals and their properties remains little explored. Here, we functionalize tin-doped indium oxide nanocrystals (ITO NCs) via ligand exchange with a series of cinnamic acids with different electron-withdrawing and -donating dipolar characters. Consistent with previous reports on semiconductors, we find that withdrawing (donating) ligands increase (decrease) the work function caused by an electrostatic potential shift across the molecular layer. Quantitative analyses of the plasmonic extinction spectra reveal that varying the ligand molecular dipole affects the near-surface depletion layer, with an anticorrelated trend between the electron concentration and electronic volume fraction, factors that are positively correlated in as-synthesized NCs. Electronic structure engineering through surface modification provides access to distinctive combinations of plasmonic properties that could enable optoelectronic applications, sensing, and hot electron-driven processes.

Electrochemistry-Induced Restructuring of Tin-Doped Indium Oxide Nanocrystal Films of Relevance to CO2 Reduction

The electrochemical reduction of CO2 into fuels using renewable electricity presents an opportunity to utilize captured CO2. Electrocatalyst development has been a primary focus of research in this area. This is especially true at the nanoscale, where researchers have focused on understanding nanostructure-property relationships. However, electrocatalyst structure may evolve during operation. Indium- and tin-based oxides have been widely studied as electrocatalysts for CO2 reduction to formate, but evolution of these catalysts during operation is not well-characterized. Here, we report the evolution of nanoscale structure of precise tin-doped indium oxide nanocrystals under CO2 reduction conditions. We show that sparse monolayer nanocrystal films desorb from the electrode upon charging, but thicker nanocrystal films remain, likely due to an increased number of physical contacts. Upon applying a cathodic voltage of −1.0 V vs RHE or greater, the original 10-nm diameter nanocrystals are no longer visible, and instead form a larger microstructural network. Elemental analysis suggests the network is an oxygen-deficient indium-tin metal alloy. We hypothesize that this morphological evolution is the result of nanocrystal sintering due to oxide reduction. These data provide insights into the morphological evolution of tin-doped indium oxide nanocrystal electrocatalysts under reducing conditions and highlight the importance of post-electrochemical structural characterization of electrocatalysts.

Aqueous Processing and Spray Deposition of Polymer-Wrapped Tin-Doped Indium Oxide Nanocrystals as Electrochromic Thin Films

Plasmonic metal oxide nanocrystals are interesting electrochromic materials because they display high modulation of infrared light, fast switching kinetics, and durability. Nanocrystals facilitate solution-based and high-throughput deposition, but typically require handling hazardous nonaqueous solvents and further processing of the as-deposited film with energy-intensive or chemical treatments. We report on a method to produce aqueous dispersions of tin-doped indium oxide (ITO) by refunctionalizing the nanocrystal surface, previously stripped of its native hydrophobic ligands, with a hydrophilic poly(acrylic acid) polymer featuring a low density of methoxy-terminated poly(ethylene oxide) grafts (PAA-mPEO4). To determine conditions favoring the adsorption of PAA-mPEO4 on ITO, we varied the pH and chemical species present in the exchange solution. The extent of polymer wrapping on the nanocrystal surface can be tuned as a function of the pH to prevent aggregation in solution and deposit uniform, smooth, and optical quality spray coated thin films. We demonstrate the utility of polymer-wrapped ITO nanocrystal thin films as an electrochromic material and achieve fast, stable, and reversible near-infrared modulation without the need to remove the polymer after deposition provided that a wrapping density of ∼20% by mass is not exceeded.

Electron Beam Infrared Nano-Ellipsometry of Individual Indium Tin Oxide Nanocrystals.

Leveraging recent advances in electron energy monochromation and aberration correction, we record the spatially resolved infrared plasmon spectrum of individual tin-doped indium oxide nanocrystals using electron energy-loss spectroscopy (EELS). Both surface and bulk plasmon responses are measured as a function of tin doping concentration from 1-10 atomic percent. These results are compared to theoretical models, which elucidate the spectral detuning of the same surface plasmon resonance feature when measured from aloof and penetrating probe geometries. We additionally demonstrate a unique approach to retrieving the fundamental dielectric parameters of individual semiconductor nanocrystals via EELS. This method, devoid from ensemble averaging, illustrates the potential for electron-beam ellipsometry measurements on materials that cannot be prepared in bulk form or as thin films.

A temperature and electric field-responsive flexible smart film with full broadband optical modulation

This study provides a flexible multi-responsive smart film with a broadband optical modulation containing tin doped indium oxide nanocrystals and a phase-separated liquid crystal-polymer.

Composite for smarter windows

Glass has been prepared that selectively absorbs visible and near-infrared light when an electrochemical voltage is applied. This opens the way to 'smart' windows that block heat on demand, with or without optical transparency. See Letter p.323 Glass windows let in light and keep out extreme heat and cold, but with the advance of the field of electrochromism — the reversible change of optical transmittance in response to electrochemical charge and discharge — they could do much more. Delia Milliron and co-workers have made a step towards producing windows that can greatly reduce lighting and heating costs with the demonstration of a composite film composed of tin-doped indium oxide nanocrystals embedded in a niobium oxide glass matrix. By varying an applied voltage over a 2.5-volt range, the charged nanocrystals selectively block near-infrared light, while the glass strongly modulates visible light owing to its reconstructed bonding near the nanocrystal–glass interface. Practical 'smart windows' and other devices are still some way off, but this solution-processed nanocrystal-in-glass approach is modular and permits extensive tuning of structure and composition, and so provides a solid platform for further refinement.

Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites

Amorphous metal oxides are useful in optical, electronic and electrochemical devices. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials. This 'nanocrystal-in-glass' approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties-its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.

Molecular mechanism of monodisperse colloidal tin-doped indium oxide nanocrystals by a hot-injection approach

Molecular mechanisms and precursor conversion pathways associated with the reactions that generate colloidal nanocrystals are crucial for the development of rational synthetic protocols. In this study, Fourier transform infrared spectroscopy technique was employed to explore the molecular mechanism associated with the formation of tin-doped indium oxide (ITO) nanocrystals. We found that the reaction pathways of the indium precursor were not consistent with simple ligand replacements proposed in the literature. The resulting understanding inspired us to design a hot-injection approach to separate the ligand replacements of indium acetate and the aminolysis processes, generating quality ITO nanocrystals with decent size distributions. The hot-injection approach was readily applied to the synthesis of ITO nanocrystals with a broad range of tin doping. Structural, chemical, and optical analyses revealed effective doping of Sn4+ ions into the host lattices, leading to characteristic and tunable near-infrared surface plasmon resonance peaks. The size control of ITO nanocrystals by multiple hot-injections of metal precursors was also demonstrated.

Near‐Infrared Spectrally Selective Plasmonic Electrochromic Thin Films

A plasmonic electrochromic effect in which electrochemical doping reversibly modulates near-infrared surface plasmon absorption of aluminium-doped zinc oxide and tin-doped indium oxide nanocrystals is reported. Optical performance, switching kinetics, and cycling durability point to high-performance NIR selective plasmonic electrochromic coatings based on earth-abundant materials.