ITO Nanocrystals Research Articles

Assembly of ITO Nanocrystals into Nanotubes Using Polycarbonate Membranes for Dual-Band Electrochromic Modulation

Assembly of ITO Nanocrystals into Nanotubes Using Polycarbonate Membranes for Dual-Band Electrochromic Modulation

Surface-Enhanced Infrared Absorption Spectroscopy by Resonant Vibrational Coupling with Plasmonic Metal Oxide Nanocrystals.

Coupling between plasmonic resonances and molecular vibrations in nanocrystals (NCs) offers a promising approach for detecting molecules at low concentrations and discerning their chemical identities. Metallic NC superlattices can enhance vibrational signals under far-field detection by generating a myriad of intensified electric field hot spots between the NCs. Yet, their effectiveness is limited by the fixed electron concentration dictated by the metal composition and inefficient hot spot creation due to the large mode volume. Doped metal oxide NCs, such as tin-doped indium oxide (ITO), could overcome these limitations by enabling broad tunability of resonance frequencies in the mid-infrared range through independent variation of size and doping concentration. This study investigates the potential of close-packed ITO NC monolayers for surface-enhanced infrared absorption by quantifying trends in the coupling between their plasmon modes and various molecular vibrations. We show that maximum vibrational signal intensity occurs in monolayers composed of larger, more highly doped NCs, where the plasmon resonance peak lies at higher frequency than the molecular vibration. Using finite element and mutual polarization methods, we establish that near-field enhancement is stronger on the low-frequency side of the plasmon resonance and for more strongly coupled plasmonic NCs, thus rationalizing the design rules we experimentally uncovered. Our results can guide the development of optimal metal oxide NC-based superstructures for sensing target molecules or modifying their chemical properties through vibrational coupling.

Towards photoelectrochromic modulation of NIR absorption in plasmonic ITO using pentacene films

Pentacene molecules are deposited onto plasmonic ITO nanocrystals as hybrid organic–inorganic bilayers, holding promise as prospective NIR-modulating electrochromic systems being self-powered by VIS-light-driven photocharging.

Electrochemical Characteristics of Reconstructed WO3 Electrodes by Embedding ITO Nanocrystals

ITO nanocrystal-embedded WO3 electrodes (ITO@WO3) have been successfully fabricated with a facile solution process, and the structure and electrochromic properties were studied by transmission electron microscope, scanning electron microscope, X-ray diffraction and electrochemical methods. The results show that moderate embedding of ITO nanocrystals (NCs) effectively improves the electrochromic performance that the optical modulation and coloration efficiency are increased from about 20.86% and 30.18 cm2 C−1 to about 29.37% and 33.49 cm2 C−1, respectively. Further analysis of the cyclic voltammetry and chronoamperometry indicate that the diffusion-controlled reactions associating with the electrochromic of the electrodes are enhanced with the increasing ITO NCs at the low content, while the excessive ITO NCs inhibit them. On the other hand, the capacitive contribution to the total insertion/extraction charges keep steady with various ITO NCs contents in the considering range of the present work, suggesting that ITO NCs affect little on the capacitive nature of the WO3 matrix. These results provide a better understanding of the electrochemical kinetics of the nanocrystal embedded electrodes and are helpful to design more efficient electrochromic devices.

Multi-charge transfer from photodoped ITO nanocrystals.

Metal oxide nanocrystals are emerging as an extremely versatile material for addressing many of the current challenging demands of energy-conversion technology. Being able to exploit their full potential is not only an advantage but also a scientific and economic ambition for a more sustainable energy development. In this direction, the photodoping of metal oxide nanocrystals is a very notable process that allows accumulating multiple charge carriers per nanocrystal after light absorption. The reactivity of the photodoped electrons is currently the subject of an intense study. In this context, the possibility to extract efficiently the stored electrons could be beneficial for numerous processes, from photoconversion and sunlight energy storage to photocatalysis and photoelectrochemistry. In this work we provide, via oxidative titration and optical spectroscopy, evidence for multi-electron transfer processes from photodoped Sn : In2O3 nanocrystals to a widely employed organic electron acceptor (F4TCNQ). The results of this study disclose the potential of photodoped electrons to drive chemical reactions involving more than one electron.

Dual-Band Electrochromic Devices with a Transparent Conductive Capacitive Charge-Balancing Anode.

Dual-band electrochromic devices (DBEDs), which can selectively modulate near-infrared (NIR) and visible (VIS) light transmittance through electrochromism, have gained increasing interest as a building energy saving technology. The technology is strongly dependent on the progress in electrochromic materials. Most current research has focused on the dual-band properties of the cathode materials, leaving the charge-balancing anode materials under-explored by comparison. This is a report of our study on the suitability of tin-doped indium oxide (ITO) nanocrystals (NCs) as a capacitive anode material for DBEDs. The ITO NCs are electrically conductive and VIS light transparent throughout the device operating range. As a result, they would not affect the NIR-selective modulation of the electrochromic device like most other anode materials do. The high surface area and good conductivity of the ITO NCs facilitate the adsorption/desorption of anions; thereby increasing their effectiveness as an ion storage thin film on the anode to balance the cathode charge. The best DBED prototype assembled from an ITO NC anode and a WO3-x cathode showed effective and independent control of VIS light and NIR transmittance with high optical modulation (71.1% at 633 nm, 58.1% at 1200 nm), high coloration efficiency (95 cm2 C-1 at 633 nm, 220 cm2 C-1 at 1200 nm), fast switching speed, good bistability, and cycle stability.

Quantitative Analysis of Extinction Coefficients of Tin-Doped Indium Oxide Nanocrystal Ensembles.

The optical extinction coefficients of localized surface plasmon resonance (LSPR) in doped semiconductor nanocrystals (NCs) have intensities determined by the density and damping mechanisms of free charge carriers. We investigate the dependence of the extinction coefficient of tin-doped indium oxide (ITO) NCs on size and dopant concentration and find extinction coefficients as high as 56.6 μm-1 in the near-infrared for 20 nm diameter ITO NCs with 7.5 atomic% Sn. We find ITO NCs to be more efficient infrared light absorbers than metal nanoparticles or molecular dyes. We also find the intensive, volume-normalized extinction coefficient increases significantly with NC doping and NC diameter, but only up to the point of saturation in both cases. We qualitatively analyze trends in LSPR peak position and width to explain the effect of doping and size on extinction.

Transport in ITO Nanocrystals with Short- to Long-Wave Infrared Absorption for Heavy-Metal-Free Infrared Photodetection

Nanocrystals are often described as interesting materials for the design of low-cost optoelectronic devices, especially in the infrared range. However, the driving materials reaching infrared absor...

Improvement of Electrochromic Performance by Embedding ITO Nanocrystals in Amorphous WO3 Film

The electrochromic films featuring the well dispersed ITO nanocrystal (about 10 nm) in amorphous WO3 (ITO@WO3) have been successfully fabricated with a solution process. The structure and electrochromic properties of the as-prepared films were studied by high resolution transmission electron microscope, scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical methods. The measured coloration/bleach time decreases from 10.5/27.8 s to 5.7/0.9 s with the increasing of ITO/AMT ratio indicating that embedded ITO nanocrystals induce the nanocrystal/glassy interface effect remarkably improving the ion diffusion coefficient and electrochemical activity. The optimal ΔT at 633 nm of 0.1 ITO@WO3 films is about 53.80% much higher than that of pure WO3 (about 42.09%). But in near-infrared (NIR) range the pure WO3 films show the best transmittance modulation rather than the composite films. The above stated results are indicative that the interface effects of embedded ITO nanocrystals play the key role while its plasmon-induced electrochromic effects are limited because of not only excellent NIR modulation capability of amorphous WO3 itself but also the relative large size of ITO nanocrystals used, demonstrating that smaller nanocrystal size (∼5 nm) are required for better electrochromic performance of the composite films.

Gelation of plasmonic metal oxide nanocrystals by polymer-induced depletion attractions

Gelation of colloidal nanocrystals emerged as a strategy to preserve inherent nanoscale properties in multiscale architectures. However, available gelation methods to directly form self-supported nanocrystal networks struggle to reliably control nanoscale optical phenomena such as photoluminescence and localized surface plasmon resonance (LSPR) across nanocrystal systems due to processing variabilities. Here, we report on an alternative gelation method based on physical internanocrystal interactions: short-range depletion attractions balanced by long-range electrostatic repulsions. The latter are established by removing the native organic ligands that passivate tin-doped indium oxide (ITO) nanocrystals while the former are introduced by mixing with small PEG chains. As we incorporate increasing concentrations of PEG, we observe a reentrant phase behavior featuring two favorable gelation windows; the first arises from bridging effects while the second is attributed to depletion attractions according to phase behavior predicted by our unified theoretical model. Our assembled nanocrystals remain discrete within the gel network, based on X-ray scattering and high-resolution transmission electron microscopy. The infrared optical response of the gels is reflective of both the nanocrystal building blocks and the network architecture, being characteristic of ITO nanocrystals' LSPR with coupling interactions between neighboring nanocrystals.

Synthesis of highly dispersible IZO and ITO nanocrystals for the fabrication of transparent nanocomposites in UV- and near IR-blocking

Indium-doped zinc oxide (IZO) nanocrystals were successfully synthesized via the alcohol-assisted pyrolysis of a mixture of indium stearate and zinc stearate, which were fabricated by the direct reaction between the metals and molten stearic acid at a temperature of 260–270 °C. The ~ 10 nm IZO nanocrystals could be dispersed homogeneously in non-polar solvents such as hexane or chloroform, forming an optically clear solution. Transparent IZO-ITO (indium tin oxide)/polyvinyl butyral (PVB) nanocomposite with 10% IZO and 2% ITO loading shows more than 75% visible light transmittance, 100% UV-blocking (below 380 nm), and 100% blocking of NIR from 1600 to 2500 nm. Equilibrium molecular dynamic simulation results clearly stated the stearic acid wrapped IZO nanocrystals in PVB matrix would hardly affect the solubility parameter of PVB composite, indicating their good compatibility and guaranteeing the high transparency of PVB-based composites. Our strategy paves the way to facile synthesize non-polar solvent soluble nanocrystals and fabricate transparent PVB-based functional nanocomposite.

Tunable Charge Transport in Hybrid Superlattices of Indium Tin Oxide Nanocrystals and Metal Phthalocyanines—Toward Sensing Applications

AbstractMacroscopic superlattices of tin‐doped indium oxide (ITO) nanocrystals (NCs) are prepared by self‐assembly at the air/liquid interface followed by simultaneous ligand exchange with the organic semiconductors M‐4,4′,4″,4″′‐tetraaminophthalocyanine (M4APc, M = Cu, Co, Fe, Ni, Zn). Transport measurements, focusing on the effect of the metal center of the ligand, reveal a ligand‐dependent increase in electrical conductance by six to nine orders of magnitude, suggesting that M4APc provides efficient electronic coupling for neighboring ITO NCs. The resulting I–V characteristics as well as the temperature dependence (7–300 K) of the zero‐voltage conductance indicates that at low temperatures, transport across the arrays occurs via a sequence of inelastic cotunneling events, each involving ≈3 ITO NCs. At higher temperatures, a crossover to 3D Mott‐variable range hopping mechanism is observed. Finally, the vapor sensitivity of chemiresistors is investigated made from ITO NCs coupled via Cu‐ and Zn4APc by dosing the sensors with 4‐methyl‐2‐pentanone (4M2P), toluene, 1‐propanol, and water in the concentration range of 100–5000 ppm at 0% relative humidity. The nanocrystal superlattices respond with an increase in resistance to these analytes with the highest sensitivity to 4M2P.

Localized Surface Plasmon Coupling between Mid-IR-Resonant ITO Nanocrystals.

Sn-doped indium oxide (ITO) nanocrystals (NC) provide tunable localized surface plasmon resonance in the mid-infrared. To evaluate the applicability of these n-doped plasmonic semiconductors in field-enhanced spectroscopies, it is necessary to assess how the low, free-electron density affects the E-field localization and plasmon coupling in NC films when compared to metal nanoparticles (NP). In this article, we investigate plasmon coupling between approximate 6 nm diameter ITO NC on the collective resonance and quantify the effect of the electromagnetic field enhancement on the absorbance signal of surface-attached ligands in NC films and monolayers with different ratios of doped and undoped indium oxide NC.

Surface Functionalization with Copper Tetraaminophthalocyanine Enables Efficient Charge Transport in Indium Tin Oxide Nanocrystal Thin Films.

Macroscopic superlattices of tin-doped indium oxide (ITO) nanocrystals (NCs) are prepared by self-assembly at the air/liquid interface followed by simultaneous ligand exchange with the organic semiconductor copper 4,4',4″,4‴-tetraaminophthalocyanine (Cu4APc). By using X-ray photoelectron spectroscopy (XPS), grazing-incidence small-angle X-ray scattering (GISAXS), and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, we demonstrate that the semiconductor molecules largely replace the native surfactant from the ITO NC surface and act as cross-linkers between neighboring particles. Transport measurements reveal an increase in electrical conductance by 9 orders of magnitude, suggesting that Cu4APc provides efficient electronic coupling for neighboring ITO NCs. This material provides the opportunity to study charge and spin transport through phthalocyanine monolayers.

Triangle-, tripod-, and tetrapod-branched ITO nanocrystals for anisotropic infrared plasmonics.

While many sophisticated geometries of metallic nanoparticles have been explored for plasmon resonance in the visible light waveband, similar structures for infrared plasmonics have seldom been studied. Herein, for the first time, we report branched colloidal Sn-doped In2O3 (ITO) NCs prepared through heating metal organic precursors in a high boiling solvent and surfactants via a simple one-pot method and their interesting anisotropic infrared plasmonics. Shaped ITO NCs were anisotropically grown into triangles, tripods, and tetrapods from spherical particles by tuning the composition of the surfactants. Interestingly, such anisotropic ITO NCs exhibit shape-dependent localized surface plasmon resonances. A new peak emerged at a low energy band, and the peak intensity increases when the particles become more anisotropic. Meanwhile, a redshift of this newly emerging peak and a blueshift of the original peak can also be observed. The proposed overlapping spheroid model successfully explained those features and the calculated extinction spectra matched excellently with the experimental data. Moreover, the origins of those peaks were also revealed and assigned to in-plane longitudinal and out-of-plane transverse modes, respectively. This work may help design more sophisticated structures for infrared plasmonics and broaden its applications in various areas.

Electrical and Plasmonic Properties of Ligand-Free Sn(4+) -Doped In2 O3 (ITO) Nanocrystals.

Sn(4+) -doped In2 O3 (ITO) is a benchmark transparent conducting oxide material. We prepared ligand-free but colloidal ITO (8 nm, 10 % Sn(4+) ) nanocrystals (NCs) by using a post-synthesis surface-modification reaction. (CH3 )3 OBF4 removes the native oleylamine ligand from NC surfaces to give ligand-free, positively charged NCs that form a colloidal dispersion in polar solvents. Both oleylamine-capped and ligand-free ITO NCs exhibit intense absorption peaks, due to localized surface plasmon resonance (LSPR) at around λ=1950 nm. Compared with oleylamine-capped NCs, the electrical resistivity of ligand-free ITO NCs is lower by an order of magnitude (≈35 mΩ cm(-1) ). Resistivity over a wide range of temperatures can be consistently described as a composite of metallic ITO grains embedded in an insulating matrix by using a simple equivalent circuit, which provides an insight into the conduction mechanism in these systems.

Development of waterborne oil spill sensor based on printed ITO nanocrystals

Oil spill accidents occasionally occur in coastal and ocean environments, and cause critical environmental damage, spoiling the marine habitats and ecosystems. To mitigate the damages, the species and amount of spilled oil should be monitored. In this study, we developed a waterborne oil spill sensor using a printed ITO layer. ITO is a compatible material for salty environments such as oceans because ITO is strong against corrosion. The fabricated sensor was tested using three oils, gasoline, lubricant and diesel, and different oil thicknesses of 0, 5, 10, and 15mm. The results showed that the resistance of the sensor clearly increased with the oil thickness and its electrical resistance. For sustainable sensing applications in marine environments, XRD patterns confirmed that the crystal structure of the ITO sensor did not change and FE-SEM images showed that the surface was clearly maintained after tests.

Redox chemistries and plasmon energies of photodoped In2O3 and Sn-doped In2O3 (ITO) nanocrystals.

Plasmonic doped semiconductor nanocrystals promise exciting opportunities for new technologies, but basic features of the relationships between their structures, compositions, electronic structures, and optical properties remain poorly understood. Here, we report a quantitative assessment of the impact of composition on the energies of localized surface plasmon resonances (LSPRs) in colloidal tin-doped indium oxide (Sn:In2O3, or ITO) nanocrystals. Using a combination of aliovalent doping and photodoping, the effects of added electrons and impurity ions on the energies of LSPRs in colloidal In2O3 and ITO nanocrystals have been evaluated. Photodoping allows electron densities to be tuned post-synthetically in ITO nanocrystals, independent of their Sn content. Because electrons added photochemically are easily titrated, photodoping also allows independent quantitative determination of the dependence of the LSPR energy on nanocrystal composition and changes in electron density. The data show that ITO LSPR energies are affected by both electron and Sn concentrations, with composition yielding a broader plasmon tuning range than achievable by tuning carrier densities alone. Aspects of the photodoping energetics, as well as magneto-optical properties of these ITO LSPRs, are also discussed.

Effect of fatty acid on the formation of ITO nanocrystals via one-pot pyrolysis reaction

ITO nanocrystal dispersions were synthesized by direct pyrolysis of the as-synthesized indium–tin carboxylate precursors without using additional organic solvents.

A novel surface modification scheme for ITO nanocrystals by acetylene: a combined experimental and DFT study.

Many applications of Sn-doped indium oxide (ITO) films in organic electronics require appropriate surface modifications of ITO nanocrystals with small organic molecules, such as silanes, phosophonic acids and carboxylic acids, to improve interfacial contacts and charge transfer. Here, we propose a new surface modification strategy via adsorption of acetylene molecules on an oxygen-terminated ITO(100) surface using a slab crystalline model to represent the nanocrystal surface. The adsorption was first studied using density functional theory. It was found that the chemisorption of C2H2 on two types of surface oxygen dimers is highly exothermic with the calculated adsorption energies of 3.80 eV and 5.19 eV, respectively. Electron population analysis reveals the origin of the strong interaction between the adsorbate and the ITO(100) surface. Experimental studies on the synthesized ITO nanocrystals using X-ray photoelectron spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy confirm the predicted strong adsorption of C2H2 on ITO surfaces.