Synthesis and Characterization of Reduced Graphene
Oxide/Rhodamine 101 (rGO-Rh101) Nanocomposites
and Their Heterojunction Performance in rGO-Rh101/p-Si
Device Configuration
G. GU¨ VEN BATIR,1 MUSTAFA ARIK,1,5ZAKIR CALDIRAN,2 ABDULMECIT TURUT,3and SAKIR AYDOGAN2,4
1.—Department of Chemistry, Faculty of Science, Atatu¨rk University, 25240 Erzurum, Turkey. 2.—Department of Physics, Faculty of Science, Atatu¨ rk University, 25240 Erzurum, Turkey. 3.—Department of Physics Engineering, Faculty of Science, Istanbul Medeniyet University, Istanbul, Turkey. 4.—Department of Environmental Engineering, Faculty of Engineering, Ardahan University, Ardahan, Turkey. 5.—e-mail: [email protected]
Reduced graphene oxide (rGO)-rhodamine 101 (Rh101) nanocomposites with different ratios of rGO have been synthesized in aqueous medium by ultra-sonic homogenization. The fluorescence of Rh101 as measured using a laser dye with high fluorescence quantum yield was substantially quenched with increasing amount of rGO in the nanocomposite. Formation of rGO-Rh101 nanocomposites was confirmed by x-ray diffraction analysis, scanning electron microscopy, ultraviolet–visible (UV–Vis) spectroscopy, and fluorescence mi-croscopy. Furthermore, rGO-Rh101 nanocomposite/p-Si heterojunctions were synthesized, all of which showed good rectifying behavior. The electrical characteristics of these devices were analyzed using current–voltage (I–V) measurements to determine the ideality factor and barrier height. The experimental results confirmed the presence of lateral inhomogeneity in the effective barrier height of the rGO-Rh101 nanocomposite/p-Si heterojunctions. In addition to I–V measurements, one device was analyzed in more detail using frequency-dependent capacitance–voltage measurements. All electrical measurements were carried out at room temperature and in the dark. Key words: Reduced graphene oxide, rhodamine 101, quenching,
heterojunction
INTRODUCTION
Graphene oxide (GO) is a two-dimensional gra-phitic material, being attractive due to the ability to tune its mechanical, electrical, and optical proper-ties.1,2 This tuning effect depends on the oxygen density in GO. GO can be easily dispersed in water due to the presence of oxygen functional groups; GO is a hydrophilic material, whereas graphene is hydrophobic. This property can improve the optical, electrical, and mechanical properties of a ceramic
matrix or polymer material when combined with graphene oxide, enabling large-scale production of such materials. When graphene oxide is reduced, its conductivity may increase significantly.3,4 Reduced graphene oxide (rGO) is currently one of the most interesting research materials in nanotechnology. It is known by various names, including chemically modified graphene (CMG), functionalized graphene (FG), chemically converted graphene (CCG), and graphene. rGO has excellent thermal, electrical, and mechanical properties.5–7 It has been widely investigated for use in many applications, e.g., for improvement of energy-storage capacitors,8–10 field-effect transistors,11 energy-related materials,12
(Received February 11, 2017; accepted August 19, 2017; published online September 8, 2017)
Journal of ELECTRONIC MATERIALS, Vol. 47, No. 1, 2018
DOI: 10.1007/s11664-017-5758-4
Ó2017 The Minerals, Metals & Materials Society
sensors,13 heavy-metal removal,14 drug delivery,15 and biomedical applications.16 Methods for rGO synthesis include mechanical or chemical exfolia-tion from graphite, chemical vapor deposiexfolia-tion (CVD), and epitaxial growth. The most popular method, which enables mass production at low cost, is a chemical method by which graphene sheets are produced from natural graphite.
The rhodamine 101 (Rh101) molecule is a cationic xanthene dye, showing high fluorescence quantum yield (in ethanol) and high photostability,17–19 which makes it a preferred choice for use in quantum counters for spectrofluorometers. Its fluo-rescence quantum yield is higher than that of rhodamine B. Rhodamine derivatives are often pre-ferred as active media for dye laser applications.20 Rh101 is also a candidate material for use in optical and electronic applications because of its stability.21 The main purpose of this study is the synthesis and characterization of reduced graphene oxide, and analysis of heterojunction devices using reduced graphene oxide (rGO)-rhodamine 101 (Rh101) nanocomposites.
EXPERIMENTAL PROCEDURES p-Si wafer was chemically cleaned using the well-known RCA1 and RCA2 processes before drying with N2gas. Natural graphite powders with average particle size of 325 mesh were purchased from Alfa Aesar. H2SO4 (98%), H2O2 (30%), KMnO4, NaNO3, N,N-dimethylformamide (DMF) were purchased from Sigma to use for preparing rGO. Rhodamine (Rh101) was obtained from Merck and prepared as stock solution of Rh101 (1.0 9 103M) in water. All experiments were carried out at room temperature. GO was synthesized from powder graphite using the modified Hummers’ method.22 In this reaction, graphite (1 g), NaNO3 (1 g), and concentrated H2SO4(50 mL) were stirred together in an ice bath until the temperature reached approximately 0°C to 3°C. To keep the reaction temperature below 5°C, KMnO4(6 g) was slowly added in fractions and the mixture was stirred for 30 min. In the next step, the mixture was moved to a 35°C water bath and stirred for 3 h. Distilled water (50 mL) was added slowly to produce a strongly exothermic reaction to 80°C. Additional heat was provided to maintain the reaction temperature at 80°C for 30 min. The mixture slowly turned brown in color. Water (100 mL) was added to produce an exothermic reaction, then 8 ml H2O2 (30%) was slowly added to reduce the residual manganese dioxide and permanganate. The mixture gradually turned from dark brown to yellow. This yellow solution was then filtered and washed three times with water (100 ml). The prepared filtrate was dried at 80°C in a vacuum oven, and graphite oxide (GO) was obtained. GO was dispersed in N, N-dimethylfor-mamide (DMF) with sonication in an ultrasonic bath, which enabled complete dispersion. The GO
solution was heated to 150°C under reflux and mixed for 6 h to reduce GO to rGO. The synthesized substance was cooled to room temperature, then filtered and washed with ethanol to remove DMF; finally, ethanol was evaporated using a rotary evaporator.
Reduced graphene oxide (rGO) sheets were syn-thesized from graphite powder using the modified Hummers’ method described above. rGO sheets were sonicated with different amounts of rhodamine 101 for 2 h in pure water, and rGO-Rh101 nanocom-posites were obtained. TableI presents the results for synthesis of rGO-Rh101 with different rGO ratios.
Next, Au metal was evaporated on the p-Si wafer at 1.33 9 106kPa after deposition of rGO-Rh101 using spin coating. We fabricated rGO-Rh101/p-Si heterojunctions, and all devices showed good recti-fying behavior. The current–voltage characteristics of the rGO-Rh101/p-Si heterojunctions are shown in Fig.1.
RESULTS AND DISCUSSION
The structural properties of the rGO-Rh101 nanocomposites were investigated using x-ray diffraction (XRD) analysis, scanning electron micro-scopy (SEM), ultraviolet–visible (UV–Vis) spec-troscopy, and fluorescence spectroscopy. XRD patterns of the samples were collected using a Rigaku D/Max-2000 diffractometer. Absorption and fluorescence spectra of the composites were analyzed using a PerkinElmer Lambda 35 UV–Vis spectrophotometer and Shimadzu RF-5301PC spec-trofluorophotometer, respectively.
The water-soluble rGO-Rh101 nanocomposites were synthesized simply by sonication of Rh101 and rGO in aqueous medium at room temperature. The structure of the rGO-Rh101 nanocomposites was characterized by UV–Vis absorption spectroscopy and fluorescence spectroscopy. The absorption and fluorescence spectra of rGO-Rh101 nanocomposites in aqueous solution are shown in Fig.1.
Figure1 shows the UV–Vis and fluorescence spectra recorded from rGO-Rh101 nanocomposites obtained using different amounts of rGO. In absence of rGO, the peak was located at 575 nm, indicating formation of Rh101 in the solution. With increasing
Table I. Synthesis of rGO-Rh101 with different ratios of rGO Sample Concentration (M) Amount of rGO (mg) Rh101 1 9 105 – rGO/Rh101-1 1 9 105 0.5 rGO/Rh101-2 1 9 105 1.2 rGO/Rh101-3 1 9 105 2.3
Batır, Arık, Caldıran, Turut, and Aydogan 330
