Mechanical reliability of transparent conducting IZTO film electrodes for flexible panel displays

The mechanical reliability of transparent In-Zn-Sn-O (IZTO) films grown using pulsed DC magnetron sputtering with a single oxide alloyed ceramic target on a transparent polyimide (PI) substrate at room temperature is investigated. All IZTO films deposited at room temperature have an amorphous structure. However, their optical and electrical properties change depending on the oxygen partial pressure applied during depositing process. At an oxygen partial pressure of 3%, the films exhibit a resistivity of 8.3 × 10⁻⁴ Ω cm and an optical transmittance of 86%. Outer bending tests show that the critical bending radius decreases from 10 mm to 7.5 mm when the oxygen partial pressure increases from 1% to 3%. In the inner bending test, the critical bending radius is independent of oxygen partial pressure at 3.5 mm, indicating excellent film flexibility. In the dynamic fatigue test, the electrical resistance of the films reduces by less than 1% for more than 2000 bending cycles. These results suggest that IZTO films have excellent mechanical durability and flexibility in comparison to ITO films.     

Highly flexible,transparent, conductive and antibacterial films made of spin-coated silver nanowires and a protective ZnO layer

We prepared highly flexible, transparent, conductive and antibacterial film by spin coating a silver nanowire suspension on a poly (ethylene terephthalate) (PET) substrate. The ZnO layer covered the conductive silver nanowire (AgNW) network to protect the metal nanowires from oxidization and enhance both wire-to-wire adhesion and wire-to-substrate adhesion. It is found that the number of AgNW coatings correlates with both the sheet resistance (R_s) and the transmittance of the AgNW/ZnO composite films. An excellent 92% optical transmittance in the visible range and a surface sheet resistance of only 9 Ω sq⁻¹ has been achieved, respectively. Even after bending 1000 times (5 mm bending radius), we found no significant change in the sheet resistance or optical transmittance. The real-time sheet resistance measured as a function of bending radius also remains stable even at the smallest measured bending radius (1 mm). The AgNW/ZnO composite films also show antibacterial effects which could be useful for the fabrication of wearable electronic devices.     

Enhanced electrical stability of flexible indium tin oxide films prepared on stripe SiO2 buffer layer-coated polymer substrates by magnetron sputtering

The electrical stability of flexible indium tin oxide (ITO) films fabricated on stripe SiO₂ buffer layer-coated polyethylene terephthalate (PET) substrates by magnetron sputtering was investigated by the bending test. The ITO thin films with stripe SiO₂ buffer layer under bending have better electrical stability than those with flat SiO₂ buffer layer and without buffer layer. Especially in inward bending text, the ITO thin films with stripe SiO₂ buffer layer only have a slight resistance change when the bending radius r is not less than 8 mm, while the resistances of the films with flat SiO₂ buffer layer and without buffer layer increase significantly at r = 16 mm with decreasing bending radius. This improvement of electrical stability in bending test is due to the small mismatch factor α in ITO-SiO₂, the enhanced interface adhesion and the balance of residual stress. These results indicate that the stripe SiO₂ buffer layer is suited to enhance the electrical stability of flexible ITO film under bending.     

Effect of the twisting chirality configuration on the electromechanical behavior of multilayer superconducting tapes

Seeking a geometry that can withstand greater transverse loads based on the electromechanical material properties of high-temperature superconducting (HTS) tape is an effective way of improving the transport performance of HTS cables. The cabling method requires the determination of the optimum twist angle of the HTS tape for withstanding transverse loads. This paper investigates the critical current characteristics of HTS tapes under combined deformation. The limit range of the twist angle under the combined deformation is measured and the optimum twist angle of the HTS tape is determined. The results show that the twisting chirality configuration obviously affects the bending strength of the HTS tape. In the elastic range, increasing the pre-twist angle increases the bending strength of the HTS tape, thereby improving the transport performance. In addition, a numerical model is built to further investigate the effect of the twisting chirality configuration on the electromechanical properties of the HTS tape, and the experimental results are explained. The experimental and simulation results generally agree well, and calculations show that there is always a sharp change in stress at the interface of different materials. These findings explain the mechanism of the effect of the twisting chirality configuration on the mechanical behavior and critical current of the HTS tape. They also provide a reference for cabling methodologies for the HTS cable configuration.     

Small variations in the sheet resistance of graphene layers with compressive and tensile bending

We synthesized graphene on copper foil by chemical vapor deposition using H₂ and CH₄ gases, followed by transferring the synthesized graphene onto various substrates. Controlling the number of layers was achieved through the variation of transfer times, and the variations of sheet resistance and transmittance with the number of layers were measured. We also investigated the variation of resistance with the radius of curvature of graphene film. As the radius decreased, the resistance increased with tensile bending and decreased with compressive bending. However, the degree of changing resistance is small enough to be applicable into flexible devices. The resistance of monolayer graphene was found to be varied in the range of as small as ±3% by the tensile or compressive bending. It was further found that although the degree of changing resistance gets larger with increasing number of graphene, the tensile bending increased the resistance by less than 20% even in case of four layer graphene.     

基于石墨烯/PEDOT：PSS叠层薄膜的柔性OLED器件

石墨烯具有独特的电学性能、优异的机械延展性和良好的化学稳定性,是制备高性能导电薄膜的理想材料,但是当前石墨烯的高电阻率限制了它的实际应用。本文采用喷涂方法制备了石墨烯/聚（3,4-亚乙二氧基噻吩）-聚（苯乙烯磺酸）（PEDOT：PSS）复合导电薄膜,对复合薄膜的表面形貌与光电性能进行了研究。PEDOT：PSS的引入不仅降低了石墨烯薄膜的表面电阻,同时还平滑了薄膜表面。在此基础上,成功制备了柔性黄光有机电致发光器件,器件在12 V时达到效率最大值0.9 cd/A。器件在曲率半径为10 mm时弯曲了100次后,发光亮度并无明显变化。该复合薄膜可实际应用于柔性有机电致发光显示器件。     

Transparent conductive reduced graphene oxide thin films produced by spray coating

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,N-Dimethylformamide.The dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray volume.AFM measurements revealed that the thin films have near-atomically flat surface.The chemical and structural parameters of the samples were analyzed by Raman and XPS studies.It was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared region.The sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 nm.The conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.     

纳米晶氧化锡薄膜的接触特性

在 Ar和 O2 气体中 ,基片温度在 15 0～ 40 0℃的条件下 ,用直流磁控溅射的方法可以制备纳米晶透明导电薄膜。实验利用 TL M模型测试了纳米晶 Sn O2 透明导电薄膜的方块电阻、单位面积薄膜的接触电阻和电极与薄膜的结合力随热处理温度的变化情况     

Flexible NiO nanocrystal-based resistive memory device fabricated by low-temperature solution-process

In this study, a nickel oxide (NiO) nanocrystal (NC) based flexible resistive memory device is demonstrated at temperature as low as 180 °C by ligand exchange process. The fabricated device for flexible application with structure Ni/NiO/Ni on PI substrate exhibits excellent switching characteristics with low set/reset voltages and stable resistance values in both ON and OFF states for over 100 switching cycles of memory operation. Also, this flexible memory device shows stable resistive switching properties under compressive stress with bending radius to 10 mm and consecutive bending cycles. The ReRAM fabricated by a low-temperature solution-process shows potential for next generation flexible electronics.     

Formation of topological domain walls and quantum transport properties of zero-line modes in commensurate bilayer graphene systems

We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twisting angles. We find that the smaller is the twisting angle, the more significant the lattice reconstruction would be, so that sharper domain boundaries declare their existence. We subsequently study the quantum transport properties of topological zero-line modes which can exist because of the said domain boundaries via Green’s function method and Landauer−Büttiker formalism, and find that in scattering regions with tri-intersectional conducting channels, topological zero-line modes both exhibit robust behavior exemplified as the saturated total transmissionG_tot ≈ 2e²/h and obey a specific pseudospin-conserving current partition law among the branch transport channels. The former property is unaffected by Aharonov−Bohm effect due to a weak perpendicular magnetic field, but the latter is not. Results from our genuine bilayer hexagonal system suggest a twisting angle aroundθ ≈ 0.1° for those properties to be expected, consistent with the existing experimental reports.     

Direct growth of graphene films without catalyst on flexible glass substrates by PECVD

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition(PECVD) synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed. The quality of the prepared graphene films is evaluated by scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. In a radio frequency(RF) power range of50 W–300 W, the graphene growth rate increases with RF power increasing, while the intensity ratio of D-to G-Raman peak(ID/IG) decreases. When the RF power is higher than 300 W, the ID/IGrises again. By optimizing experimental parameters of hydrogen plasma etching and RF power, the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene's transparency, good electrical conductivity, and better macroscopic uniformity.Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.     

Carbon nanostructure–aSi:H photovoltaic cells with high open-circuit voltage fabricated without dopants

Recently discovered production techniques allow the synthesis of carbon nanostructured films with large surface areas. The abundance of carbon and the unique properties of these nanostructures, including high transparency and excellent electrical conductivity, make these materials very interesting for photovoltaic applications, in particular in combination with amorphous silicon. We examine the properties of thin carbon nanotube films (buckypaper) and graphene in junctions with undoped amorphous silicon thin films. The observed open-circuit voltages, 390 mV for the carbon nanotube film and 150 mV for graphene, suggest that solar cells with high efficiency can be produced without expensive processing steps like doping, multilayer film deposition in high vacuum, or transparent conducting oxide deposition. The buckypaper cells are stable in ambient conditions for many weeks, at least.     

Electrical and mechanical properties of graphene oxide on flexible substrate

Graphene oxide (GO) was deposited via the electrophoretic deposition (EPD) method to lower the oxygen concentration of graphene sheets for large-scale production. In addition, the direct synthesis of large-scale GO films using transfer processes on a polydimethylsiloxane (PDMS) substrate was conducted. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties. The Young's modulus values of films with thicknesses of 100–200 nm were 324–529 GPa. Moreover, the GO films exhibited excellent conductivity, with a sheet resistance of 276–2024 Ω/sq at 23–77% transparency. Experiments show that transfer processes for flexible substrates can produce high-quality cost-effective transparent conductive films.     

Vacuum-deposited, nonpolymeric flexible organic light-emitting devices

We demonstrate mechanically flexible, organic light-emitting devices (OLED's) based on the nonpolymetric thin-film materials tris-(8-hydroxyquinoline) aluminum (Alq(3)) and N, N(?) -diphenyl- N, N(?) -bis(3-methylphenyl)1- 1(?) biphenyl-4, 4(?) diamine (TPD). The single heterostructure is vacuum deposited upon a transparent, lightweight, thin plastic substrate precoated with a transparent, conducting indium tin oxide thin film. The flexible OLED performance is comparable with that of conventional OLED's deposited upon glass substrates and does not deteriorate after repeated bending. The large-area (~1 - cm>(2)) devices can be bent without failure even after a permanent fold occurs if they are on the convex substrate surface or over a bend radius of ~0.5>cm if they are on the concave surface. Such devices are useful for ultralightweight, flexible, and comfortable full-color flat panel displays.     

Applications of femtosecond Bessel beams to laser ablation

We demonstrate the fabrication of graphene-carbon nanotubes (CNTs) composite-based flexible transparent conductive films (GC-TCFs) and their improved durability on repetitive strain. The graphene and CNTs are synthesized using thermal chemical vapor deposition. To fabricate GC-TCFs, the graphenes are transferred and the CNTs are successively spray-deposited on polymer substrates, respectively. The change of electrical property of the TCFs is investigated as the response of repetitive strain loading and unloading. The sheet resistance of the GC-TCFs is much lower than CNT-based TCFs, owing to the lower contact resistance. In addition, when the cyclic strain is applied on the GC-TCFs, the films show improved durability in electrical property compared to graphene-based TCFs. Finally, the coated CNTs act as one dimensional conductive path across the cracks, which prevent electrical degradation during the repetitive strain application.     

Alternative transparent conducting electrode materials for flexible optoelectronic devices

Transparent Conductive Electrode (TCE) is an essential part of the optoelectronic and display devices such as Liquid Crystal Displays (LCDs), Solar Cells, Light Emitting Diodes (LEDs), Organic Light Emitting Diodes (OLEDs) and touch screens. Indium Tin Oxide (ITO) is a commonly used TCE in these devices because of its high transparency and low sheet resistance. However, scarcity of indium and brittle nature of ITO limit its use in future flexible electronics. In order to develop flexible optoelectronic devices with improved performance, there is a requirement of replacing the ITO with a better alternate TCE. In this work, several alternative TCEs including transparent conductive oxides, carbon nanotubes, conducting polymers, metal nanowires, graphene and composites of these materials are studied with their properties such as sheet resistance, transparency and flexibility. The advantage and current challenges of these materials are also presented in this work.     

An experimental set-up for the study of electromechanical properties of conducting polymer films

An experimental set-up have been designed and fabricated to study the electromechanical properties of a thick film of conducting polymer under load. Extension of the films versus voltage has been measured in terms of change in capacitance of parallel plate capacitor constituted by metal pan and a fixed metal plate. HP 4284A impedance analyzer measures absolute value of the capacitance. Change in capacitance is related to change in distance by pre-calibrating the assembly using traveling microscope. A computer programme is developed to convert the capacitance value with the corresponding distance and simultaneously plotting the graph between changes in length of polymer film versus applied voltage.The assembly has been used to study the electrochemomechanical behavior of solution cast polyaniline films (∼50 μ thick). During first cycle the length is enhanced by about 6% of original value, while repetitive value of extension is ≅2.8%, in subsequent cycles. This value closely matches to that reported in literatures.     

Transmission of 1.6 J Er:YAG laser light by ZnS-coated silver hollow waveguides

A maximum energy of 1.6 J at 5 pps of Er:YAG laser light has been transmitted through a flexible ZnS-coated silver hollow waveguide which has an inner diameter of 800 μm and is 116 cm long. The straight waveguide loss is 0.6 dB m⁻¹ and no significant loss and mechanical changes have been found after an endurance test of 10000 pulse transmissions and bending 400 times with a bending radius of 30 cm.     

Nanotube devices: A microscopic model

A microscopic model is developed for calculating electrostatic properties of nanotube devices. It is shown that the quantum-mechanical approach yields the same results as the statistical calculation in the limit of a thin tube suspended over a conducting gate at a distance exceeding the nanotube radius. A closed analytic expression is obtained for the atomistic capacitance of a straight nanotube and for a nanotube with a modest curvature. This method allows the fast and exact calculation of device parameters for the nanotube electromechanical systems and nanotube electronic devices.     

Nanoscale formation mechanism of conducting filaments in NiO thin films

We have studied the nanoscale electrical properties of NiO thin films by using conducting atomic force microscopy (CAFM) to understand the mechanism of resistance change of the NiO thin films as we changed the applied voltage. We observed that inhomogeneous conducting filaments were generated by external voltage bias; in addition, some of the inhomogeneous conducting filaments were durable while some of them were not, and they disappeared. We deduced that the resistance change of the NiO thin films was related to inhomogeneous filamentary conducting paths generated by both Ni ions in thermodynamically unstable NiO and the existence of conducting filament segments generated by high voltage bias.