Polycrystalline Indium Tin Oxide Research Articles

Multilayer Fe3O4-doped ITO indium saving indium tin oxide thin films

Multilayer Fe3O4-doped indium saving indium-tin oxide (ITO) thin films were fabricated by sputtering method. Double-layered Fe3O4-doped indium saving indium-tin oxide (ITO) thin films consisted of 12 nm layer of conventional indium tin oxide (90 mass% In2O3 and 10 mass% SnO2) and 138 nm layer of indium saving indium-tin oxide (50 mass% In2O3, 50 mass% SnO2 and Fe3O4-doped) were grown on preheated at 523 K glass substrates. Obtained polycrystalline ITO thin films exhibit volume resistivity of 416 µΩcm, electron mobility 28 cm2/V·s, carrier density 5.3 × 1020 cm−3 and average optical transmittance above 85% in visible range of spectrum.

Optoelectronic and structural properties of ITO/Ag/ITO transparent electrodes using ultraviolet laser annealing

Indium tin oxide (ITO) is widely used in the optoelectronic industry as a transparent conductive oxide owing to its excellent optical and electrical properties. To improve the physical properties of ITO, highly conductive ITO/Ag/ITO multilayer electrodes were prepared using radio frequency (RF) magnetron sputtering at room temperature. Then, laser annealing was performed on the multilayer electrodes with scanning intervals of 0.01, 0.02, 0.05 and 0.1 mm. The structural properties of the multilayer electrodes were characterized by X-ray diffraction, and their optical and electrical properties were characterized by ultraviolet (UV) visible spectrophotometry and a four-point probe station, respectively. The results demonstrated that the multilayer films had a polycrystalline structure, and ITO (222) and Ag (111) preferred orientations were identified after laser annealing. In addition, the crystalline size of the Ag layers increased slightly, implying that the defect density within the Ag layers was reduced, resulting in a significant increase in its conductivity. A significantly low electrical resistivity of 5.35 [Formula: see text]/sq and high optical transmittance of 85% were achieved. The Haacke index value was [Formula: see text], which was much better than the value of [Formula: see text] before laser annealing.

Single-beam ion source enhanced growth of transparent conductive thin films

A single-beam ion source was developed and used in combination with magnetron sputtering to modulate the film microstructure. The ion source emits a single beam of ions that interact with the deposited film and simultaneously enhances the magnetron discharge. The magnetron voltage can be adjusted over a wide range, from approximately 240 to 130 V, as the voltage of the ion source varies from 0 to 150 V, while the magnetron current increases accordingly. The low-voltage high-current magnetron discharge enables a ‘soft sputtering mode’, which is beneficial for thin-film growth. Indium tin oxide (ITO) thin films were deposited at room temperature using a combined single-beam ion source and magnetron sputtering. The ion beam resulted in the formation of polycrystalline ITO thin films with significantly reduced resistivity and surface roughness. Single-beam ion-source-enhanced magnetron sputtering has many potential applications in which low-temperature growth of thin films is required, such as coatings for organic solar cells.

Correction to “Tailoring of Point Defects in Polycrystalline Indium Tin Oxide Films with Postirradiation of Electronegative Oxygen Ions”

Correction to “Tailoring of Point Defects in Polycrystalline Indium Tin Oxide Films with Postirradiation of Electronegative Oxygen Ions”

High-temperature optical properties of indium tin oxide thin-films

Indium tin oxide (ITO) is one of the most widely used transparent conductors in optoelectronic device applications. We investigated the optical properties of ITO thin films at high temperatures up to 800 °C using spectroscopic ellipsometry. As temperature increases, amorphous ITO thin films undergo a phase transition at ~ 200 °C and develop polycrystalline phases with increased optical gap energies. The optical gap energies of both polycrystalline and epitaxial ITO thin films decrease with increasing temperature due to electron–phonon interactions. Depending on the background oxygen partial pressure, however, we observed that the optical gap energies exhibit reversible changes, implying that the oxidation and reduction processes occur vigorously due to the low oxidation and reduction potential energies of the ITO thin films at high temperatures. This result suggests that the electronic structure of ITO thin films strongly depends on temperature and oxygen partial pressure while they remain optically transparent, i.e., optical gap energies > 3.6 eV.

Multilayer indium saving ITO thin films produced by sputtering method

Deposition of multilayer indium saving indium-tin oxide (ITO) thin films was attempted to achieve both low volume resistivity and high transmittance. Double-layered structures consisting of very thin layer of conventional indium tin oxide (In2O3-10 mass % SnO2) and indium saving indium-tin oxide (In2O3-50 mass % SnO2) layer were grown by DC sputtering on glass substrates preheated at 523 K. It was found that this method can produce polycrystalline ITO thin films having volume resistivity as low as 281 μΩcm, mobility 28 cm2/V·s and carrier concentration 5.32 1020 cm−3. Average optical transmittances exhibited above 85% in visible range of spectrum. Arithmetical mean height (Sa) and root mean square height (Sq) of films deposited at optimum conditions were 1.09 and 1.40 nm, respectively.

Tailoring of Point Defects in Polycrystalline Indium Tin Oxide Films with Postirradiation of Electronegative Oxygen Ions

We have developed a state-of-the-art technology to tailor oxygen-related point defects such as oxygen vacancies (VO) and structural defects of polycrystalline highly conductive Sn-doped In2O3 (ITO) films by a postirradiation of electronegative oxygen (O–) ions. The intentional oxygen doping that would annihilate VO decreases carrier density (ne) from 9.3 × 1020 to 7.1 × 1020 cm–3 with an increase of Hall mobility (μH) from 44 to 51 cm2·V−1·s−1, and subsequently, ne drastically decreases down to 1.2 × 1019 cm–3 together with a decrease in μH owing to a formation of Sn–O neutral complexes with a further increase in the amount of oxygen atoms that should fill the structural defects while retaining their crystal structure. Upon the filling of the structural vacancies, the successful control of intrinsic point defects is probably caused by almost no difference in the ionic radii between In3+ having six-coordination and Sn4+ having eight-coordination. The O–-ion-irradiation technology enables one to tailor the ...

Highly stable semi-transparent MAPbI3 perovskite solar cells with operational output for 4000 h

We present high stability of semi-transparent methyl ammonium (MA) lead triiodide perovskite (MAPbI3) solar cells with sputter–deposited polycrystalline NiOx hole transport layer (HTL) and indium tin oxide (ITO) back contact. We have demonstrated high thermal stability of the MAPbI3 perovskite devices with the NiOx HTL and glass encapsulations, showing no performance degradation at 85 °C over 1000 h in dark. They showed instability, however, under 1 sun illumination at ∼30 °C. Here, we demonstrate that the combination of the NiOx HTL and the ITO for both top and bottom electrodes of the perovskite solar cells can solve this instability problem. This approach resulted in highly stable semitransparent devices with the average visible light transmittance (AVT) above 11% and the power conversion efficiency (PCE) of 12.5%, showing steady power output nearly 4000 h of continuous operation at MPPT under 1 sun illumination. While the use of poly[bis(4-phenyl)(2,4,6-trimethylphenyl) (PTAA) HTL resulted in the semitransparent devices with higher PCE of 13.6%, their device stabilities were much inferior to the NiOx HTL based devices. These results indicated that a rather classical MA based perovskite, MAPbI3, is indeed a stable photovoltaic material with the proper choice of the interface layers and electrode materials, and the use of the sputter–deposited NiOx HTL together with the ITO back contact is one of the key elements to overcome the stability problem in the lead halide perovskite solar cells.

The resistance temperature stability of ITO film strain gauge: detailed investigate the influence mechanism of (100) preferred orientation of ITO film

The indium tin oxide (ITO) film is one of the ideal candidates for optical transparent film strain gauge. Thus, the temperature stability of electrical properties is most important for ITO film strain gauge. In this work, the film strain gauge consisted of polycrystalline ITO film with and without (100) preferred orientation. Total 25 temperature circles in range of 20–200–20 °C were carried out on ITO film and ITO film strain gauge. After 25 temperature circles, the carrier concentration and carrier mobility of polycrystalline ITO film without preferred orientation decreased (38.1 ± 1.7)% and (15.4 ± 3.3)%, respectively. Then, the resistivity of polycrystalline ITO film without preferred orientation increased (90.7 ± 6.4)% after 25 temperature circles. As result, the resistance of film strain gauge monotonously increased with the increase of temperature circles, which consisted of the polycrystalline ITO film without preferred orientation. On the contrary, the carrier mobility and carrier concentration of polycrystalline ITO film with (100) preferred orientation was fixed at the constant after each temperature circle. Similarly, the resistivity of ITO film and the resistance of ITO restrain gauge was fixed at the constant after each temperature circle, which consisted of the polycrystalline ITO film with (100) preferred orientation. Finally, based on the theories of film growth and crystallography, the relationship between resistance temperature stability of ITO film strain gauge and (100) preferred orientation, as well as the physicochemical mechanism behind them, were systematically investigated. With above results, ITO film with (100) preferred orientation could be an ideal candidate for optical transparent film strain gauge, especially for film strain gauge worked at variable temperature condition.

Coherent Phonon Transport Measurement and Controlled Acoustic Excitations Using Tunable Acoustic Phonon Source in GHz-sub THz Range with Variable Bandwidth

We experimentally demonstrated a narrowband acoustic phonon source with simultaneous tunabilities of the centre frequency and the spectral bandwidth in the GHz-sub THz frequency range based on photoacoustic excitation using intensity-modulated optical pulses. The centre frequency and bandwidth are tunable from 65 to 381 GHz and 17 to 73 GHz, respectively. The dispersion of the sound velocity and the attenuation of acoustic phonons in silicon dioxide (SiO2) and indium tin oxide (ITO) thin films were investigated using the acoustic phonon source. The sound velocities of SiO2 and ITO films were frequency-independent in the measured frequency range. On the other hand, the phonon attenuations of both of SiO2 and ITO films showed quadratic frequency dependences, and polycrystalline ITO showed several times larger attenuation than those in amorphous SiO2. In addition, the selective excitation of mechanical resonance modes was demonstrated in nanoscale tungsten (W) film using acoustic pulses with various centre frequencies and spectral widths.

Ultralow-power on-chip all-optical Fano diode based on uncoupled nonlinear photonic-crystal nanocavities

We achieved an ultralow-power Fano-like diode in integrated photonic circuits through two cascaded and uncoupled photonic-crystal microcavities, coated with a nonlinear layer constructed from polycrystalline indium-tin oxide doped with gold nanoparticles. The multicomponent nanocomposite layer helps to obtain an extremely large nonlinearity enhancement on account of the quantum confinement effect, hot-electron injection, and local-field enhancement effect. Thus, the strong nonlinearity enhancement, asymmetric Fano-like spectrum lineshape, and asymmetric light confinement for the forward and backward incidence cases guarantee the nonreciprocal transmission of signal light. A compact size of 7 μm is maintained for the photonic-crystal microcavities and the transmission contrast reached 15 dB. Besides, we achieved 1.5 kW cm−2 operating threshold intensity (cut down by a thousand times). This work assists chip-integrated optical computing on the basis of nonlinear photonic-crystal microcavities.

Electrochemical microfluidic devices for evaluation of drug metabolism

An electrochemical drug metabolizing sensor device was fabricated with a patterned electrode of polycrystalline indium tin oxide (pITO) film and a poly(dimethylsiloxane) (PDMS) thin layer microchannel. The pITO film is known to be suitable as an electrode for detecting direct electron transfer (DET) from cytochrome P450 (CYP) without any surface modification. However, the ITO surface is hydrophilic and this causes the CYP to detach from it, resulting in poor repeatability. This manuscript describes the simultaneous electrochemical measurement of drug metabolizing reactions that is achieved by continuously supplying the pITO electrode surface with a small amount of microsome CYP. To achieve this, the microchannel was evaluated for its flow uniformity and reproducibility, and the shape and dimensions needed for good performance were determined by using a highly uniform nickel mold obtained by employing a polishing process after electroplated mold fabrication. A clearly separated dual flow was established with the microchannel. Using dual pITO working electrodes arranged in parallel (dual flow measurement) and subtraction process, the current from only the drug metabolism reaction was obtained by introducing drugs and microsome CYP at one pITO electrode and introducing only microsome CYP at the other pITO electrode. We also performed a kinetic analysis of the CYP activity in our electrochemical microfluidic device.

Influence of surface properties on the structure of granular silver films and excitation of localized plasmons

Granular silver films deposited on a thin insulating film of amorphous hydrogenated carbon (a-C:H) and transparent conducting electrode (polycrystalline indium tin oxide (ITO) layer) have been investigated by spectroscopy and microscopy methods. The extinction spectra of silver films on the surface of these materials are found to be significantly different. An annealing of silver films causes a blue shift of the peak of plasmon resonance band in the spectrum of silver nanoparticles: by 16 nm on the a-C:H surface and by 94 nm on the ITO surface. Silver films on the surface of a-C:H films are characterized by a narrower band in the extinction spectrum, which is peaked at 446 nm. The changes observed in the optical density of Ag films are related to the change in size and area of nanoparticles. The results of spectral studies of Ag films are in agreement with the data on the nanostructure obtained by scanning electron microscopy and statistical image processing. The spectra of granular silver films are shown to correlate well with the nanoparticle distribution function over the film area.

Simultaneous high-resolution scanning Bragg contrast and ptychographic imaging of a single solar cell nanowire.

Simultaneous scanning Bragg contrast and small-angle ptychographic imaging of a single solar cell nanowire are demonstrated, using a nanofocused hard X-ray beam and two detectors. The 2.5 µm-long nanowire consists of a single-crystal InP core of 190 nm diameter, coated with amorphous SiO2 and polycrystalline indium tin oxide. The nanowire was selected and aligned in real space using the small-angle scattering of the 140 × 210 nm X-ray beam. The orientation of the nanowire, as observed in small-angle scattering, was used to find the correct rotation for the Bragg condition. After alignment in real space and rotation, high-resolution (50 nm step) raster scans were performed to simultaneously measure the distribution of small-angle scattering and Bragg diffraction in the nanowire. Ptychographic reconstruction of the coherent small-angle scattering was used to achieve sub-beam spatial resolution. The small-angle scattering images, which are sensitive to the shape and the electron density of all parts of the nanowire, showed a homogeneous profile along the nanowire axis except at the thicker head region. In contrast, the scanning Bragg diffraction microscopy, which probes only the single-crystal InP core, revealed bending and crystalline inhomogeneity. Both systematic and non-systematic real-space movement of the nanowire were observed as it was rotated, which would have been difficult to reveal only from the Bragg scattering. These results demonstrate the advantages of simultaneously collecting and analyzing the small-angle scattering in Bragg diffraction experiments.

Active control of chirality in nonlinear metamaterials

An all-optical tunabe chirality is realized in a photonic metamaterial, the metamolecule of which consists of a nonlinear nano-Au:polycrystalline indium-tin oxide layer sandwiched between two L-shaped gold nano-antennas twisted 90° with each other. The maximum circular dichroism reached 30%. Under excitation of a 40 kW/cm2 weak pump light, the peak in the circular dichroism shifts 45 nm in the short-wavelength direction. An ultrafast response time of 35 ps is maintained. This work not only opens up the possibility for the realization of ultralow-power and ultrafast all-optical tunable chirality but also offers a way to construct ultrahigh-speed on-chip biochemical sensors.

Ultralow-power all-optical tunable double plasmon-induced transparencies in nonlinear metamaterials

An all-optical tunable double plasmon-induced transparency is realized in a photonic metamaterial coated on the surface of a nanocomposite layer made of polycrystalline indium-tin oxide doped with gold nanoparticles. The local-field effect, quantum confinement effect, and hot-electron injection ensure a large optical nonlinearity for the nanocomposite. A shift of 120 nm in the central wavelength of transparency windows is reached under excitation with a weak pump laser with an intensity of 21 kW/cm2. Compared with previous reports, the threshold pump intensity is reduced by five orders of magnitude, while an ultrafast response time of 34.9 ps is maintained.

Structural and optical properties of ITO/TiO2 anti-reflective films for solar cell applications.

Indium tin oxide (ITO) and titanium dioxide (TiO2) anti-reflective coatings (ARCs) were deposited on a (100) P-type monocrystalline Si substrate by a radio-frequency (RF) magnetron sputtering. Polycrystalline ITO and anatase TiO2 films were obtained at room temperature (RT). The thickness of ITO (60 to 64 nm) and TiO2 (55 to 60 nm) films was optimized, considering the optical response in the 400- to 1,000-nm wavelength range. The deposited films were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). The XRD analysis showed preferential orientation along (211) and (222) for ITO and (200) and (211) for TiO2 films. The XRD analysis showed that crystalline ITO/TiO2 films could be formed at RT. The crystallite strain measurements showed compressive strain for ITO and TiO2 films. The measured average optical reflectance was about 12% and 10% for the ITO and TiO2 ARCs, respectively.

Effects of annealing temperature on mechanical durability of indium-tin oxide film on polyethylene terephthalate substrate

Effects of the annealing temperature on mechanical durability of indium-tin oxide (ITO) thin films deposited on polyethylene terephthalate (PET) substrates were investigated. The ITO films were annealed at the range from 150°C to 195°C after the DC sputtering deposition for the production of polycrystalline ITO layers on the substrates. The onset strains of cracking in the annealed ITO films were evaluated by the uniaxial stretching tests with electrical resistance measurements during film stretching. The results indicate that the onset strain of cracking in the ITO film is clearly increased by increasing the annealing temperature. The in-situ measurements of the inter-planer spacing of the (222) plane in the crystalline ITO films during film stretching by using synchrotron radiation strongly suggest that the large compressive stress in the ITO film increases the onset strain of cracking in the film. X-ray stress analyses of the annealed ITO films and thermal mechanical analyses of the PET substrates also clarifies that the residual compressive stress in the ITO film is enhanced with increasing the annealing temperature due to the considerably larger shrinkage of the PET substrate.

Cytochrome P450 Modified Polycrystalline Indium Tin Oxide Film as a Drug Metabolizing Electrochemical Biosensor with a Simple Configuration

The development of a biocatalytic electrode consisting of cytochrome P450 (CYP) proteins would be a key technology with which to establish simple drug metabolizing biosensors or screening devices for drug inhibitors. We have successfully detected the direct electron transfer (DET) from a human CYP layer or a CYP microsome adsorbed on a bare indium tin oxide (ITO) film electrode without any modification layers and applied it to drug metabolism evaluation. We compared the electrocatalytic properties of the two ITO films with different surface nanostructures (polycrystalline or amorphous). CYP on polycrystalline ITO film enhanced the electron transfer rate of oxygen reduction about fifteen times more than with amorphous film. The polycrystalline ITO film was a suitable electrode for the adsorption of CYP proteins while maintaining efficient DET and enzymatic activity, probably because of its larger surface area and negatively charged surface. The oxygen reduction current at the polycrystalline ITO film electrodes had increased 3- to 4-fold, specifically coupled with the oxidation of drugs (testosterone and quinidine) by the monooxygenase activity of CYP. In contrast, the oxygen reduction current completely disappeared in the presence of the CYP inhibitor (ketoconazole). Similar results could be obtained from the CYP microsome with sufficiently clear responses. These results indicate that the CYP modified polycrystalline ITO electrode offers the potential for electrochemically evaluating CYP activity for drug metabolism with a simple configuration.

Ultraflexible Polymer Solar Cells Using Amorphous Zinc−Indium−Tin Oxide Transparent Electrodes

Polymer solar cells are fabricated on highly conductive, transparent amorphous zinc indium tin oxide (a-ZITO) electrodes. For two representative active layer donor polymers, P3HT and PTB7, the power conversion efficiencies (PCEs) are comparable to reference devices using polycrystalline indium tin oxide (ITO) electrodes. Benefitting from the amorphous character of a-ZITO, the new devices are highly flexible and can be repeatedly bent to a radius of 5 mm without significant PCE reduction.