Solution-based fabrication of a graphene–ZnO nanocomposite

Johra, Fatima Tuz,Lee, Mi-Jung,Jung, Woo-Gwang Springer-Verlag 2013 Journal of sol-gel science and technology Vol.66 No.3

Effect of Fabricating Nanopatterns on GaN-Based Light Emitting Diodes by a New Way of Nanosphere Lithography

Johra, Fatima Tuz,Jung, Woo-Gwang Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.3

Nanosphere lithography is an inexpensive, simple, high-throughput nanofabrication process. NSL can be done in different ways, such as drop coating, spin coating or by means of tilted evaporation. Nitride-based light-emitting diodes (LEDs) are applied in different places, such as liquid crystal displays and traffic signals. The characteristics of gallium nitride (GaN)-based LEDs can be enhanced by fabricating nanopatterns on the top surface of the LEDs. In this work, we created differently sized (420, 320 and 140 nm) nanopatterns on the upper surfaces of GaN-based LEDs using a modified nanosphere lithography technique. This technique is quite different from conventional NSL. The characterization of the patterned GaN-based LEDs revealed a dependence on the size of the holes in the pattern created on the LED surface. The depths of the patterns were 80 nm as confirmed by AFM. Both the photoluminescence and electroluminescence intensities of the patterned LEDs were found to increase with an increase in the size of holes in the pattern. The light output power of the 420-nm hole-patterned LED was 1.16 times higher than that of a conventional LED. Moreover, the current-voltage characteristics were improved with the fabrication of differently sized patterns over the LED surface using the proposed nanosphere lithography method.

Facile Synthesis and Characterization of Reduced Graphene Oxide-Zinc Ferrite Nanocomposite as Adsorbent in Aqueous Media

Johra, Fatima Tuz,Jung, Woo-Gwang Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.4

Here, Zn ferrite is synthesized along with reduced graphene oxide (rGO) by a facile one-step hydrothermal method. The difference between the synthesized nanocomposites with those in other reported work is that the reaction conditions in this work are 160 ℃ for 12 h. The synthesized products are characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and attenuated total reflection. Further, the adsorption property of rGO-Zn ferrite (rGZF) nanocomposite is studied after confirming its successful synthesis. The adsorption capacity of rGZFs toward rhodamine B (RB) is > 9.3 mg/g, whereas that of bare ZF nanoparticles is 1.8 mg/g in aqueous media. The efficiencies of rGZF and bare ZF to remove RB are 99 % and 20 %, respectively. Employing rGZF, 60 % of RB is decomposed within 5 min. The kinetic study reveals that the adsorption process of removing RB by bare Zn ferrite follows pseudo-first-order kinetics. However, after zinc ferrite is incorporated with rGO, the kinetics changes to pseudo-second-order. Furthermore, the Langmuir isotherm is accomplished by the adsorption process employing rGZF, indicating that a monolayer adsorption process occurs. The thermodynamic parameters of the process are also calculated.

Facile and safe graphene preparation on solution based platform

Johra, Fatima Tuz,Lee, Jee-Wook,Jung, Woo-Gwang Elsevier 2014 Journal of industrial and engineering chemistry Vol.20 No.5

<P><B>Abstract</B></P> <P>Graphene has attracted increasing attention because of its interesting properties. In this study, graphene was prepared from graphite by a very simple and easy process. The two-step protocol involves conversion of graphite to graphene oxide (GO) by oxidation, and subsequent reduction of GO to graphene. The structures and properties of the obtained GO and graphene were characterized via X-ray diffraction, and Raman, NMR, UV–vis absorption, and X-ray photoelectron spectroscopic techniques. The morphologies of these products were observed via field emission scanning electron microscopy. The preparation protocol is simple, easy, environmental friendly, i.e., nontoxic, and the yield of graphene is high.</P> <P><B>Graphical abstract</B></P> <P>We have fabricated high quality grapheme material with facile and safe method. Graphene oxide (GO) was prepared by means of improved Hummers’ method, then subsequent reduction of GO was made with hydrothermal method to fabricate the grapheme material. The quality of graphene was characterized by many analytical measurements. We optimized the process condition on the basis of the quality of graphene.</P>

RGO-TiO₂-ZnO composites: Synthesis, characterization, and application to photocatalysis

Johra, F.T.,Jung, W.G. Elsevier 2015 Applied Catalysis A Vol.491 No.-

Chemical approaches to the reduction of graphene oxide (GO) for large-scale production of reduced graphene oxide (RGO) sheets have become a reality, speeding up the availability of graphene. In this work, an RGO-TiO<SUB>2</SUB>-ZnO composite was synthesized through the hydrothermal reduction of GO in a deionized (DI) water solution containing TiO<SUB>2</SUB> and ZnO precursors at 180<SUP>o</SUP>C. Morphological and structural characterizations using several techniques are reported. The photocatalytic activity of the synthesized RGO-TiO<SUB>2</SUB>-ZnO composite is approximately 63% at 120min under 100W UV irradiation, which is much higher than that of pure ZnO (11%). The enhanced properties are described in terms of increased light absorption intensity and the reduction of electron-hole pair recombination in the composite owing to the stepwise energy level structure in the composite.

Effect of Light-Ions Implantation on Resistivity of GaN Thin Film

Fatima Tuz Johra,정우광 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.4

GaN is a very well-known semiconductor because of its properties, making it useful in different types of electronic devices. In electronics applications, the resistivity of the starting materials is very important. In this study, the resistivity of GaN thin films has been investigated upon its modification with ion implantation using both n-type and p-type GaN. Ionic implantation was performed with H, He, and Ar ions. The ion beam energy (60 and 120 keV) and flux (1.0 × 1012 and 1.0 × 1015 cm−2·s−1), as well as post-implantation annealing temperature (100°C - 500°C), were varied to analyze their influence on GaN resistivity. It was observed that the resistivity changed in all samples with the change in ion beam flux and energy. At room temperature, the resistivity of ntype GaN increased from 1.9 × 10−2 to 17.7 × 10−2 Ω·cm. Among all modified samples, He-ion-implanted samples show higher resistivity. During the post-annealing treatment, n-type GaN implanted with He showed more consistency compared to p-type GaN. On the contrary, p-type showed some anomalous character upon postannealing.

Facile and safe graphene preparation on solution based platform

Fatima Tuz Johra,이지욱,정우광 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5

Graphene has attracted increasing attention because of its interesting properties. In this study, graphene was prepared from graphite by a very simple and easy process. The two-step protocol involves conversion of graphite to graphene oxide (GO) by oxidation, and subsequent reduction of GO to graphene. The structures and properties of the obtained GO and graphene were characterized via X-ray diffraction, and Raman, NMR, UV–vis absorption, and X-ray photoelectron spectroscopic techniques. The morphologies of these products were observed via field emission scanning electron microscopy. The preparation protocol is simple, easy, environmental friendly, i.e., nontoxic, and the yield of graphene is high.

Synthesis of Black Phosphorus via a Facile Vapor Transfer Method

Fatima Tuz Johra,Woo-Gwang Jung 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.5

Single-layer black phosphorus (BP), known as phosphorene, has recently attracted interest in research due to itsexceptional properties, similar to those of other 2D materials. BP is the most stable allotrope of phosphorus with highdensity. BP can be obtained from other phosphorus allotropes by a number of ways. Due to white phosphorus beinghighly reactive at ≥ 30 °C, researchers tend to work with red phosphorus (RP). In this work, RP powder was heatedunder an argon atmosphere inside a muffle furnace along with tin and iodine at sequential temperatures for differenttimes. All elements were placed inside a quartz ampoule evacuated with a vacuum pump. The ampoule was sealedafter substituting it with argon gas. This method, known as the vapor transfer method, allows to synthesize BP witha ribbon-like structure. FE-SEM analyses revealed that the morphological structure of BP comprised clearly-stackedsheets. The structural analysis of the as-synthesized BP, conducted by XRD, TEM and Raman, showed the successfultransformation of RP into BP.

Improvement of On/Off Ratio in Solution-Processed Graphene-Zinc Oxide Resistive Switching Memory by Blending with Polystyrene

Kim, Chaewon,Johra, Fatima Tuz,Kim, Jiyoung,Lee, Jaegab,Jung, Woo-Gwang,Lee, Mi Jung American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.12

<P>Resistive switching (RS) memory devices are fabricated using solution processed graphene-zinc oxide (G-ZnO) and polystyrene (PS). G-ZnO is synthesized through solution processing at a low temperature. G-ZnO or G-ZnO:PS blended solution in a ratio of 1:5 by weight is spin-coated as the RS layer, and aluminum (Al) is adopted as the top and bottom electrode. Through UV-visible absorption, scanning electron microscopy (SEM), energy dispersive diffraction, and X-ray diffraction (XRD) analysis, G-ZnO and G-ZnO:PS films are confirmed as well-blended thin films. In the RS operation, the on/off ratio of low resistive state (LRS) and high resistive state (HRS) of G-ZnO device is approximately 10(4), which is increases to 10(8) in G-ZnO:PS device. PS, the insulating polymer, helps to improve the on/off ratio by reducing the off current in HRS. By analyzing the I-V curves in the HRS of G-ZnO device, the conduction mechanism is changed from ohmic conduction to space charge limited current (SCLC) in G-ZnO, while G-ZnO:PS shows the formation of a conductive path in insulators.</P>