Indium Tin Oxide Nanocrystals Research Articles

Crystallization and optical properties of alumino-silicate and alumino-borosilicate glasses containing indium tin oxide

Transparent alumino-borosilicate based glass-ceramics containing indium tin oxide (ITO) nano-crystals were synthesized through melt casting method. The results showed that the SiO2-B2O3-Al2O3-Na2O glass system were crystallized more intensively than the other, due to a more extensive liquid-liquid phase separation. Thermal behavior and crystallinity of the specimens were investigated by conducting DTA and XRD analysis, respectively. FE-SEM images were used for microstructural evaluation of the specimens. Optical properties of the samples were studied by UV–vis and Near-IR spectroscopy. Furthermore, FTIR was utilized to identify various bonds in the specimens. The crystallized glasses of the alumino-borosilicate system showed transmittance up to 50 % in the visible wavelength, whereas they showed a significant absorption in the UV and near infrared wavelength ranges (>95%). According to the measurement, the mean crystallite size of the precipitated ITO in the optimum sample of the alumino-borosilicate system was less than 20 nm, which was obtained by heat treatment at 650 ℃ for 10 h.

Clear and transparent nanocrystals for infrared-responsive carrier transfer

Infrared-light-induced carrier transfer is a key technology for ‘invisible’ optical devices for information communication systems and energy devices. However, clear and colourless photo-induced carrier transfer has not yet been demonstrated in the field of photochemistry, to the best of our knowledge. Here, we resolve this problem by employing short-wavelength-infrared (1400–4000 nm) localized surface plasmon resonance-induced electron injection from indium tin oxide nanocrystals to transparent metal oxides. The time-resolved infrared measurements visualize the dynamics of the carrier in this invisible system. Selective excitation of localized surface plasmon resonances causes hot electron injection with high efficiency (33%) and long-lived charge separation (~ 2–200 μs). We anticipate our study not only provides a breakthrough for plasmonic carrier transfer systems but may also stimulate the invention of state-of-the-art invisible optical devices.

Multiaxial and Transparent Strain Sensors Based on Synergetically Reinforced and Orthogonally Cracked Hetero‐Nanocrystal Solids

AbstractWearable strain sensors are widely researched as core components in electronic skin. However, their limited capability of detecting only a single axial strain, and their low sensitivity, stability, opacity, and high production costs hinder their use in advanced applications. Herein, multiaxially highly sensitive, optically transparent, chemically stable, and solution‐processed strain sensors are demonstrated. Transparent indium tin oxide and zinc oxide nanocrystals serve as metallic and insulating components in a metal–insulator matrix and as active materials for strain gauges. Synergetic sensitivity‐ and stability‐reinforcing agents are developed using a transparent SU‐8 polymer to enhance the sensitivity and encapsulate the devices, elevating the gauge factor up to over 3000 by blocking the reconnection of cracks caused by the Poisson effect. Cross‐shaped patterns with an orthogonal crack strategy are developed to detect a complex multiaxial strain, efficiently distinguishing strains applied in various directions with high sensitivity and selectivity. Finally, all‐transparent wearable strain sensors with Ag nanowire electrodes are fabricated using an all‐solution process, which effectively measure not only the human motion or emotion, but also the multiaxial strains occurring during human motion in real time. The strategies can provide a pathway to realize cost‐effective and high‐performance wearable sensors for advanced applications such as bio‐integrated devices.

Investigation of compositionally tunable localized surface plasmon resonances (LSPRs) of a series of indium tin oxide nanocrystals prepared by one-step solvothermal synthesis

A series of novel nonmetallic plasmonic materials, indium tin oxide (ITO) nanocrystals (NCs), with tunable doping ratios of tin (from 0 up to 25%), were synthesized through a one-step solvothermal method. Cubic-shaped NCs with good crystallinity and uniform-size distribution (~ 17 nm), for all doping ratios, were confirmed through the X-ray diffraction patterns and transmission electron microscopy images. As inferred from X-ray photoelectron spectroscopy and inductively coupled plasma measurements, Sn is preferentially distributed close to the surface of ITO NCs. In particular, localized surface plasmon resonances (LSPRs) were tuned from near- to mid-infrared regions only by varying the doping ratios, which is of interest, for example, to avoid high-loss levels associated with metallic nanoparticles in LSPR biosensing applications. Our work provides a series of reliable and accessible materials for the researchers who need different wavelengths of LSPR frequencies in near-infrared and/or mid-infrared regions. It will benefit the research and development of nonmetallic plasmonic materials in a wider application scope.

Enhanced photodesorption from near- and mid-infrared plasmonic nanocrystal thin films

The authors show that the desorption rate of two model molecules, indole and benzoic acid, from thin films of indium tin oxide nanocrystals supporting near- and mid-infrared (0.33–0.48 eV) localized surface plasmon resonances (LSPRs) is enhanced by as much as 60% upon illumination with broadband infrared light. The desorption rate increases linearly with light intensity. No increase in the desorption rate is detected for undoped In2O3 nanocrystal thin films or when photons resonant with the LSPR are blocked. The authors study the desorption rate enhancement as a function of illumination intensity, LSPR energy, and isotopic substitution. Importantly, the authors demonstrate the accelerated desorption via in-coupling of light to LSPRs with energies well within the mid-infrared. Their work opens the door to using these low energy photons as choreographers of chemical processes and sets the stage for future mechanistic studies.

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.

Optical Properties of Colloidal Indium Tin Oxide Suspended in a Thermal Fluid

We investigated changes in the optical properties of indium tin oxide (ITO) nanocrystals as a function of temperature. ITO is a plasmonic, wide bandgap semiconductor capable of absorbing UV and IR radiation. The nanoparticles were made using a standard two-pot synthesis, which resulted in the formation of ITO nanoparticles with myristic acid and oleylamine as surface passivation ligands. Ligand exchange with (6-7% aminopropylmethylsiloxane) dimethylsiloxane-copolymer was allowed dispersion of the particles into a thermal fluid, Duratherm S, which is capable of withstanding working temperatures of 300°C. Nanoparticles suspended in the fluid were heated over a range of temperatures and the properties investigated using IR spectrometry, UV-VIS, TEM, and particle size analysis. Although heating showed no change in particle size, spectral changes were clearly observed in the form of a strong blue shift and increased absorb-ance. These temperature-dependent changes in the spectral properties of ITO were attribu...

Combined redox and plasmonic electrochromic effects in WO3/ITO double-layer films

In this paper, a double-layer coating with both redox and plasmonic electrochromic properties has been designed and deposited on fluorine doped tin oxide (FTO) substrates by sol-gel method. This coating consists of an amorphous WO3 film and a nanocrystalline indium tin oxide (ITO) film. Both the valence of W atoms in WO3 and the localized surface plasmon resonance (LSPR) frequency of ITO nanocrystals can be tuned reversibly and persistently by electrochemical process. Due to the LSPR electrochromism, the double-layer films can block near-infrared (NIR) and visible (Vis) light selectively and independently by applying different voltages, which is better and more functional than the traditional electrochromic films. High transmittance of WO3/ITO films is obtained both in Vis and NIR for positive applied voltages. When a weakly negative voltage is applied, the transmittance of WO3/ITO films in visible region is still high, while the transmittance in NIR decreases. The transmittance of the double-layer films in both Vis and NIR further decreases for increasingly more negative voltages.

Novel preparation of ITO nanocrystalline films with plasmon electrochromic properties by the sol-gel method using benzoylacetone as a chemical modifier

In this paper, benzoylacetone (BzAcH) was introduced as a chelating agent to the sol-gel technique to fabricate indium tin oxide (ITO) nanocrystalline films. BzAcH was found to decrease the grain size of the ITO film, and the growth of ITO nanocrystals was controlled by varying the BzAcH content. ITO nanocrystalline films prepared by this method showed significant localized surface plasmon resonance (LSPR) absorption features that could be manipulated electrically by electrochemical doping. Plasmonic electrochromism realized in ITO films indicated a strongly reversible and persistent variation of the film transmittance in the near-infrared region (NIR). Furthermore, the plasmon electrochromic mechanism of ITO nanocrystals is discussed in this paper.

Indium tin oxide nanocrystals as saturable absorbers for passively Q-switched erbium-doped fiber laser

A new type of saturable absorber (SA) based on indium tin oxide (ITO) nanocrystals for passively Q-switched erbium-doped fiber (EDF) laser has been demonstrated experimentally. High quality ITO nanocrystals were prepared by the coprecipitation method. As a degenerate oxide semiconductor, the ITO has a wide range of saturable absorption regions, strong plasmonic absorption peaks, and ultra-fast recovery time. The nonlinear absorption properties of ITO are investigated by a balanced twin-detector measurement system. The saturation intensity and modulation depths are 9.87 MW/cm2 and 0.83%, respectively. We successfully fabricated ITO SAs by depositing the ITO dispersion solution at the end of a fiber connector. By inserting the ITO SAs into an EDF fiber cavity, stable passively Q-switched pulses with the minimum pulse width of 1.15 μs under a repetition rate of 81.28 kHz were obtained. The maximum output power of 1722 μW and pulse energy of 21.19 nJ were realized when the pump power was 480 mW at the wavelength of 1530.3 nm. The results suggest that ITO nanocrystals are expected to develop into another effective SA for ultrafast photonics.

Reversible Tuning of the Surface Plasmon Resonance of Indium Tin Oxide Nanocrystals by Gas-Phase Oxidation and Reduction

Heavily doped oxide nanocrystals exhibit a tunable localized surface plasmon resonance (LSPR) in the infrared, a property that is promising for applications in photonics, spectroscopy, and photochemistry. Nanocrystal carrier density and, thus, spectral response are adjustable via chemical reaction; however, the fundamental processes that govern this behavior are poorly understood. Here, we study the time dependence of the LSPR supported by indium tin oxide (ITO) nanocrystals during O2 and N2 annealing with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We show that the LSPR red-shifts upon oxidation in O2 and blue-shifts to its original position upon reduction in N2. A reaction–diffusion model allows us to rationalize the underlying physicochemical processes and quantitatively connect nanocrystal redox chemistry, solid-state diffusion, carrier density, and the LSPR.

A Solution-Processed Ultrafast Optical Switch Based on a Nanostructured Epsilon-Near-Zero Medium.

All the optical properties of materials are derived from dielectric function. In spectral region where the dielectric permittivity approaches zero, known as epsilon-near-zero (ENZ) region, the propagating light within the material attains a very high phase velocity, and meanwhile the material exhibits strong optical nonlinearity. The interplay between the linear and nonlinear optical response in these materials thus offers unprecedented pathways for all-optical control and device design. Here the authors demonstrate ultrafast all-optical modulation based on a typical ENZ material of indium tin oxide (ITO) nanocrystals (NCs), accessed by a wet-chemistry route. In the ENZ region, the authors find that the optical response in these ITO NCs is associated with a strong nonlinear character, exhibiting sub-picosecond response time (corresponding to frequencies over 2 THz) and modulation depth up to ≈160%. This large optical nonlinearity benefits from the highly confined geometry in addition to the ENZ enhancement effect of the ITO NCs. Based on these ENZ NCs, the authors successfully demonstrate a fiber optical switch that allows switching of continuous laser wave into femtosecond laser pulses. Combined with facile processibility and tunable optical properties, these solution-processed ENZ NCs may offer a scalable and printable material solution for dynamic photonic and optoelectronic devices.

Influence of Binders and Solvents on Stability of Ru/RuOx Nanoparticles on ITO Nanocrystals as Li-O2 Battery Cathodes.

Fundamental research on Li-O2 batteries remains critical, and the nature of the reactions and stability are paramount for realising the promise of the Li-O2 system. We report that indium tin oxide (ITO) nanocrystals with supported 1-2 nm oxygen evolution reaction (OER) catalyst Ru/RuOx nanoparticles (NPs) demonstrate efficient OER processes, reduce the recharge overpotential of the cell significantly and maintain catalytic activity to promote a consistent cycling discharge potential in Li-O2 cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuOx nanoparticles lower the charge overpotential compared with those for ITO and carbon-only cathodes and have the greatest effect in DMSO electrolytes with a solution-processable F-free carboxymethyl cellulose (CMC) binder (<3.5 V) instead of polyvinylidene fluoride (PVDF). The Ru/RuOx /ITO nanocrystalline materials in DMSO provide efficient Li2 O2 decomposition from within the cathode during cycling. We demonstrate that the ITO is actually unstable from the first cycle and is modified by chemical etching, but the Ru/RuOx NPs remain effective OER catalysts for Li2 O2 during cycling. The CMC binders avoid PVDF-based side-reactions and improve the cyclability. The deterioration of the ITO nanocrystals is mitigated significantly in cathodes with a CMC binder, and the cells show good cycle life. In mixed DMSO-EMITFSI [EMITFSI=1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide] ionic liquid electrolytes, the Ru/RuOx /ITO materials in Li-O2 cells cycle very well and maintain a consistently very low charge overpotential of 0.5-0.8 V.

Low-temperature and solution-processed indium tin oxide films and their applications in flexible transparent capacitive pressure sensors

It is of great interest to fabricate indium tin oxide (ITO) films by solution-based techniques at low temperatures. Here, we combined the use of colloidal ITO nanoflowers synthesized by the strategy of limited ligand protection and oxygen plasma treatment which effectively remove the surface ligands of ITO nanocrystals to meet this goal. These efforts led to high-quality ITO films with resistivity as low as 2.33 × 10−2 Ω cm, which is the best result for solution-processed ITO nanocrystal films deposited at temperatures lower than 200 °C. The annealing-free processing allowed us to deposit ITO nanoflower films onto plastic substrates and apply them in flexible capacitive pressure sensors. The single-pixel device showed decent sensitivity and reproducibility, and the arrayed sensors exhibited good spatial resolution.

Nanoparticle enhanced spectral filtration of insolation from trough concentrators

A nanoparticle fluid filter consisting of gold nanoparticles and indium tin oxide nanocrystals was fabricated and the optical properties were assessed. Results were integrated against the AM 1.5 solar spectrum to determine solar weighted efficiency of the filter for light energies transmitted above the bandgap to a photovoltaic cell for direct electrical generation while absorbing light below the bandgap that is converted to heat for thermal storage or processing. Temperature dependent bandgaps for both GaAs and cSi were used for optimization of the filter design. GaAs is preferred based upon its higher IR reflectivity, lower temperature coefficient, and greater high-temperature efficiency. However, cSi is significantly cheaper than current and projected GaAs costs. It was found that the experimental filter efficiency was 62% for GaAs and 56% for cSi which was within 6% of previous theoretical predictions.

Single-step preparation of indium tin oxide nanocrystals dispersed in ionic liquids via oxidation of molten In-Sn alloys.

Oxidation of molten In-Sn alloys was carried out in ionic liquids by heat treatment with vigorous stirring, resulting in the formation of indium tin oxide (ITO) nanocrystals. The ITO nanocrystals exhibited a plasmon peak, the peak wavelength of which was blue-shifted with an increase in the Sn fraction in ITO.

A transparent flexible z-axis sensitive multi-touch panel based on colloidal ITO nanocrystals.

Bottom-up fabrication of a flexible multi-touch panel prototype based on transparent colloidal indium tin oxide (ITO) nanocrystal (NC) films is presented. A series of 7% Sn(4+) doped ITO NCs protected by oleate, octanoate and butanoate ligands are synthesized and characterized by a battery of techniques including, high resolution transmission electron microscopy, X-ray diffraction, (1)H, (13)C and (119)Sn nuclear magnetic resonance spectroscopy, and the related diffusion ordered spectroscopy. Electrical resistivities of transparent films of these NCs assembled on flexible polyethylene terephthalate substrates by convective self-assembly from their suspension in toluene decrease with the ligand length, from 220 × 10(3) for oleate ITO to 13 × 10(3)Ω cm for butanoate ITO NC films. A highly transparent, flexible touch panel based on a matrix of strain gauges derived from the least resistive film of 17 nm butanoate ITO NCs sensitively detects the lateral position (x, y) of the touch as well as its intensity over the z-axis. Being compatible with a stylus or bare/gloved finger, a larger version of this module may be readily implemented in upcoming flexible screens, enabling navigation capabilities over all three axes, a feature highly desired by the display industry.

Synthesis and application of non-agglomerated ITO nanocrystals via pyrolysis of indium–tin stearate without using additional organic solvents

Indium–tin stearate precursor was successfully synthesized by a direct reaction between metals (indium and tin) and molten stearic acid under a nitrogen atmosphere at 260 °C for 3 h for the first time. Nearly, monodisperse ~7 nm indium tin oxide (ITO) nanocrystals without any agglomeration were efficiently synthesized by pyrolysis of the as-synthesized precursors without using additional organic solvents under different conditions. It was found that both pyrolysis temperature and Sn doping level significantly influenced the particle size and size distribution of the ITO nanocrystals. A lower pyrolysis temperature and a higher Sn doping level resulted in a smaller particle size of the ITO nanocrystals. Addition of 1-octadecene solvent in the pyrolysis reaction could lead to a narrow particle size distribution of the ITO nanocrystals. In addition, all the as-synthesized ITO nanocrystals could be dispersed homogeneously in non-polar solvents such as n-hexane and chloroform without using surfactants forming optically clear solutions, which were used to prepare ITO/PVB nanocomposite film as interlayer for making laminated glass in solar control glazing.

Surface Modification and Assembly of Transparent Indium Tin Oxide Nanocrystals for Enhanced Conductivity

In a solution-phase synthesis of nanocrystals (NCs), organic surfactants play an important role in size and shape control as well as in facilitating the stable dispersion of NCs in solvents. However, in order to use these NCs for electrical applications, the surfactants must be removed effectively. Here we report that monodisperse indium tin oxide (ITO) NCs were synthesized and stabilized with oleate/oleylamine ligands, and these long-chain surfactants were readily substituted with tetrabutylammonium hydroxide (TBAOH), forming a stable methanol dispersion. Uniform assemblies of ITO NCs were made by spin-coating the ITO–TBAOH NC dispersions with an assembly thickness controllable from 68 to 260 nm by the NC solution concentration. An annealing treatment at 120 °C and 300 °C under Ar + 5% H2 for 1 h effectively removed the TBAOH, and the ITO NC assemblies showed high transparency (>88%) and low resistivity (2.6 × 10–3 Ω·cm). Our new approach to surface modification of ITO NCs with a volatile surfactant foll...

Influence of dopant distribution on the plasmonic properties of indium tin oxide nanocrystals.

Doped metal oxide nanocrystals represent an exciting frontier for colloidal synthesis of plasmonic materials, displaying unique optoelectronic properties and showing promise for a variety of applications. However, fundamental questions about the nature of doping in these materials remain. In this article, the strong influence of radial dopant distribution on the optoelectronic properties of colloidal indium tin oxide nanocrystals is reported. Comparing elemental depth-profiling by X-ray photoelectron spectroscopy (XPS) with detailed modeling and simulation of the optical extinction of these nanocrystals using the Drude model for free electrons, a correlation between surface segregation of tin ions and the average activation of dopants is observed. A strong influence of surface segregation of tin on the line shape of the localized surface plasmon resonance (LSPR) is also reported. Samples with tin segregated near the surface show a symmetric line shape that suggests weak or no damping of the plasmon by ionized impurities. It is suggested that segregation of tin near the surface facilitates compensation of the dopant ions by electronic defects and oxygen interstitials, thus reducing activation. A core-shell model is proposed to explain the observed differences in line shape. These results demonstrate the nuanced role of dopant distribution in determining the optoelectronic properties of semiconductor nanocrystals and suggest that more detailed study of the distribution and structure of defects in plasmonic colloidal nanocrystals is warranted.