Uniform graphene oxide films fabrication via spray-coating for sensing application

Abstract

A spray-coating technique for deposition of thin uniform graphene oxide films with a thickness of several tens of nanometers was developed. Among distinctive features of the technique is the low substrate heating temperature, which allows preserving most oxygen-containing functional groups and coat a wide range of substrates. The morphology of the spray-coated graphene oxide films with flakes of different lateral sizes was investigated. The local laser-induced photo-thermal reduction of thin graphene oxide thin films was demonstrated. The sensitivity of reduced graphene oxide to water vapor was also measured. Spray-coating and laser reduction techniques can be further applied for humidity sensor fabrication.     

Polypyrrole nanotube/ferrocene-modified graphene oxide composites: From fabrication to EMI shielding application

Polypyrrole nanotube/ferrocene-modified graphene oxide composites (PNT/GO-Fc, PNT/GO-Fc-GO, PNT/GO-EDA-Fc and PNT/GO-EDA-Fc-EDA-GO) were fabricated via in situ chemical oxidative polymerization. The prepared composites were characterized by FTIR, XRD, XPS, Raman, TGA, SEM, TEM and EDS. The electromagnetic interference shielding performance of the prepared composites was evaluated by a coaxial method within the frequency range of 1.0–4.5 GHz. The results demonstrated that the composite of PNT/GO-EDA-Fc-EDA-GO-7:1 exhibited the best electromagnetic interference shielding property with 28.73 dB (at the frequency of 1.0175 GHz with the thickness of 3.0 mm) of total shielding effectiveness by adding 50 wt% of the composite in the paraffin matrix. And the composite of PNT/GO-EDA-Fc-EDA-GO-7:1 exhibited good conductivity with a value of 1.320 S/cm. The relationship between the conductivities of prepared samples and the EMI shielding performance was investigated.

     

Randomly oriented graphene flakes film fabrication from graphite dispersed in N-methyl-pyrrolidone by using electrohydrodynamic atomization technique

In this work, we report the deposition of graphene flakes exfoliated through graphite dispersion in N-methyl-pyrrolidone using non-vacuum electrohydrodynamic atomization (EHDA) technique. Stable cone jet mode of EHDA is used to deposit graphene flakes on silicon substrate. The deposited graphene flakes film is characterized by Raman spectroscopy, microscopy, 3D-Nanomap, scanning electron microscope, and UV–visible spectroscopy. Through characterizations it is evident that a randomly oriented graphene flakes film has shown good transparency, conductivity and suitable work function. For electrical characterization of film, it is employed as cathode in a simple diode indium tin oxide/(poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)/polydioctylfluorene-benzothiadiazole/graphene. It is observed that at voltage of 0.3 V, the current density in device is at low value of 2.67 A/cm² however as the voltage is increased to a value of 4 V the current density is increased by almost 100 times and reaches up to 2.65 × 10² A/cm². We believe that by further optimizing parameters of EHDA techniques for graphene deposition, more uniform and defect free graphene film can be obtained.     

Flower-like zinc oxide deposited on the film of graphene oxide and its photoluminescence

The graphene oxide films have been fabricated by simply filtering the graphene oxide solution through the micropore filter. Then the flower-like ZnO grows on the graphene layer by immersing the seed-coated graphene oxide films in the dilute growing solution containing NH₃·H₂O and Zn(NO₃)₂·6H₂O. The morphologies of the as-obtained ZnO deposited on the graphene oxide layer are characterized by using scanning electron microscope (SEM), X-ray powder diffraction (XRD) and photoluminescence (PL). The formation mechanism of the flower-like ZnO has also been investigated. The results show that the morphology of the finally-obtained ZnO is tunable by seeds, the concentration of growing solution and the reaction time.     

Co-sputtered oxide thin film encapsulated organic electronic devices with prolonged lifetime

Effective top-side thin film encapsulation for organic light-emitting devices (OLEDs) was achieved by deposition of a multi-layer water diffusion barrier stack to protect the device against moisture permeation. The barrier stack was formed by alternative depositions of co-oxide and fluorocarbon (CF_x) films. The co-oxide layer was fabricated by magnetron co-sputtering of silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃). While the CF_x layer was formed by plasma enhanced chemical vapor deposition. The water vapor transmission rate of the optimized diffusion barrier stack can be down to 10^− 6 g/m²/day. The OLEDs encapsulated with the multilayer stack have been shown to have operation lifetime of over 18,000 h which is nearly the same as devices with conventional glass-cover encapsulation.     

ZnO压电薄膜的生长与应用

本文实验研究了ZnO压电薄膜的生长与表征,运用XRD和SEM测试了磁控溅射生长的ZnO压电薄膜的C轴择优取向生长情况和晶粒质量,比较了Si、覆盖在si基底上的Al薄膜和SixNy薄膜三种材料衬底以及退火处理对ZnO薄膜的结晶质量的影响.还开发了仍然采用Al作为底电极但用一层SixNy薄膜与ZnO层隔离的MEMS压电器件的微制造工艺,以满足生长高质量的ZnO压电薄膜并与CMOS工艺兼容的要求.     

Wafer-scale reduced graphene oxide films for nanomechanical devices

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( =185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit ( f x Q>10(11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite.     

Synergistic graphene/aluminum surface plasmon coupling for zinc oxide lasing improvement

Collective oscillations of free electrons generate plasmons on the surface of a material.A whispering-gallery microcavity effectively confines the light field on its surface based on the total reflection from its internal wall.When these two kinds of electromagnetic waves meet each other,the stimulated emissions from an individual ZnO microrod were enhanced more than 50-fold and the threshold was reduced after the whispering-gallery microcavity was coated with a monolayer of graphene and A1 nanoparticles.The improvement of the lasing performance was attributed to the synergistic energy coupling of the graphene/Al surface plasmons with ZnO excitons.The lasing characteristics and the coupling mechanism were investigated systematically.     

Nanostructured zinc oxide film for urea sensor

Nanostructured zinc oxide (Nano-ZnO) film has been electrochemically deposited onto indium-tin-oxide (ITO) coated glass plate to co-immobilized urease (Urs) and glutamate dehydrogenase (GLDH) for urea detection. The observed reflection planes corresponding to wurtzite ZnO nanoparticles (~25 nm) in XRD diffraction pattern and UV-visible absorption band at 338 nm reveal the formation of Nano-ZnO. Urs-GLDH/Nano-ZnO/ITO bioelectrode shows high sensitivity for urea detection within 10-80 mg/dL and limit of detection as 13.5 mg/dL with regression coefficient as 0.994 and Michaelis-Menten constant (K_m, 6.1 mg/dL) indicating good affinity of Urs-GLDH to urea.     

Information approach to estimating the accuracy of analog electronic devices and its application

A method is proposed for estimating the accuracy of analog devices which is based on an entropy approach. The loss of information by an analog device is sought as the limit of the information loss of an analog-to-digital device as its word length approaches infinity. Applications of the method are considered for an angle-parameter-number converter and for a measuring system.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 6–8, July, 1994.     

Transparent, luminescent, antibacterial and patternable film forming composites of graphene oxide/reduced graphene oxide

Multifunctional graphene oxide/reduced graphene oxide (GO/RGO) composites were prepared through electrostatic interaction using biocompatible ingredients. Different functionalities were added to GO/RGO by anchoring materials such as native lactoferrin (NLf), NLf protected Au clusters (designated as Au@NLf), chitosan (Ch) and combinations thereof. Anchoring of Ch and NLf enhances the antibacterial property of RGO/GO. The addition of Ch to RGO/GO not only helped in forming stable dispersions but also helped in fabricating large (cm(2)) area films through a simple solvent evaporation technique. Functionalities such as photoluminescence were added to Ch-RGO/GO composites by anchoring Au@NLf on it. The composites thus formed showed stable luminescence in presence of various metal ions in the solid state. The composite showed reasonable stability against pH and temperature variations as well. The as-prepared films were transparent and the transparency could be modulated by controlling the concentration of RGO/GO in the composite. The antibacterial property and ability to form stable thin films may provide an opportunity to use such composites for medical and environmental remediation applications as well. Erasable patterns were fabricated on the film by stamping required patterns under compressive pressure. Luminescent patterns can be inscribed on the film and can be erased by simply wetting it. Such films with erasable information may be useful for security applications.     

Ultrasound-assisted fabrication of dispersed two-dimensional copper/reduced graphene oxide nanosheets nanocomposites

Graphene oxide nanosheets (GOS) were employed as template and hydrazine hydrate was used as reductant for GOS and cupric ion. Highly dispersed two-dimensional (2D) copper/reduced graphene oxide nanosheets (Cu/RGOS) nanocomposites were effectively fabricated by ultrasound-assisted electroless copper plating process. Sandwich-like 2D Cu/RGOS nanocomposites consist of uniform Cu layer on the both side of centric RGOS. The Cu layer with thickness of about 60 nm exhibits almost single-crystalline with (1 1 1) preferred crystalline direction and have tight binding with RGOS. The effect of ultrasound on electroless Cu plating includes: accelerating deposition rate, enhancing interfacial bonding and preventing 2D Cu/RGOS nanocomposites from aggregating.     

Low-resistivity Cu film electrodeposited with 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonate for the application to the interconnection of electronic devices

In this study, we analyzed the properties of Cu films electrodeposited with 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonate (DPS) as an organic additive in damascene Cu electrodeposition, in comparison with bis(sulfopropyl) disulfide (SPS). It was observed that the resistivity of Cu film electrodeposited with DPS was lower than that with SPS. Spectroscopic analyses showed that the impurity level and crystallinity of Cu films are almost the same, but the difference was found in the film roughness. Low roughness of Cu film electrodeposited with DPS led to the low resistivity, and it was speculated that the low roughness is related to the strong adsorption through the nitrogen atom in the DPS molecule.     

Formation of zinc oxide film by boiling metallic zinc film in ultrapure water

A simple method for forming zinc oxide (ZnO) films has been discovered. Radio-frequency (rf) sputtered metallic zinc (Zn) film is boiled in ultrapure water at 368 K. The opaque Zn film changes into a transparent film. It is confirmed by transmission electron microscopy and X-ray diffraction that the transparent film is hexagonal ZnO. Optical and morphological properties of the ZnO film are discussed.     

Improved zinc oxide film for gas sensor applications

Zinc oxide (ZnO) is a versatile material for different commercial applications such as transparent electrodes, piezoelectric devices, varistors, SAW devices etc because of its high piezoelectric coupling, greater stability of its hexagonal phase and its pyroelectric property. In fact, ZnO is a potential material for gas sensor applications. Good quality ZnO films were deposited on glass and quartz substrates by a novel CVD technique using zinc acetate as the starting solution. X-ray diffraction confirmed the crystallinity of the zinc oxide film and SEM study revealed uniform deposition of fine grains. Undoped ZnO films were used for detection of dimethylamine (DMA) and H₂ at different temperatures by recording the change in resistivity of the film in presence of the test gases. The response was faster and the sensitivity was higher compared to the earlier reported ZnO based sensors developed in our laboratory. The main objective of this work was to study the selectivity of the ZnO film for a particular gas in presence of the others. The operating temperature was found to play a key role in the selectivity of such sensors.     

Titanium dichalcogenide-decorated reduced graphene oxide nanocomposite for high-performance photovoltaic cell fabrication

Journal of Materials Science: Materials in Electronics - This study describes the flexible DSSC devices based on efficient TiS2/Reduced Graphene Oxide (TiS2/RGO) hybrid photoanodes that have been...     

氧化石墨烯/聚酰亚胺复合薄膜的制备及阻水性能

以石墨粉为原料,采用改进的Hummers法制备氧化石墨烯（GO）,采用原位聚合法制备GO/聚酰亚胺酸（PAA）前驱体,GO/PAA前驱体经高温固化处理后得到GO/聚酰亚胺（PI）复合薄膜;采用XRD、Raman、FTIR、AFM等表征手段对GO的结构进行表征;此外,研究了不同固化温度下PI薄膜的结构;最后测试了GO/PI复合薄膜的透湿率和力学性能。结果表明:GO为单层结构,厚度为1.26 nm。GO/PI复合薄膜表现出良好的阻水性能,当GO/PI复合薄膜中GO的添加量为0.025wt%、薄膜厚度为50 μm时,GO/PI复合薄膜的透湿率低至56.7 g（m2·d）-1。此外,0.025wt% GO/PI复合薄膜拉伸强度和断裂伸长率分别为150.8 MPa和13.5%,与PI薄膜（分别为126.9 MPa和8.1%）相比,分别增加了18.8%和66.7%。      

氧化石墨烯/纳米纤维素复合薄膜的制备及表征

目的 热带水果由于其特殊的生理特点不能像普通蔬果一样进行低温贮藏,极易由于高温导致果体的腐烂变质,能量触发式变色薄膜是一种新型的功能型材料,新型的示温标签可以警示不合适的贮藏温度,达到延长热带水果保鲜期的作用。 方法 通过在聚乙烯醇( PVA) 母胶中加入助剂,采用基板成膜制得能量触发式标签薄膜,并研究了温度、变色剂浓度、薄膜厚度、吐温 80 含量对标签性能的影响。 结果 实验的影响显著性大小依次为变色剂质量分数、薄膜厚度、温度、吐温 80 含量。 结论摇45 益 下向原有配料中加入质量分数为 2% 的变色剂、0 . 2% 的吐温 80 母液制备平均厚度为 0 . 09 mm的样本变色标签膜,各项性能达到最佳。