Cengiz Ozkan

The optimization of the electrode/electrolyte double-layer interface is a key factor for improving electrode performance of aqueous electrolyte based supercapacitors (SCs). Here, we report the improved functionality of carbon materials via a non-invasive, high-throughput, and inexpensive UV generated ozone (UV-ozone) treatment. This process allows precise tuning of the GM foam transitionally from ultrahydrophobic to hydrophilic within 60 sec. The continuous tuning of surface energy can be… Show more

The optimization of the electrode/electrolyte double-layer interface is a key factor for improving electrode performance of aqueous electrolyte based supercapacitors (SCs). Here, we report the improved functionality of carbon materials via a non-invasive, high-throughput, and inexpensive UV generated ozone (UV-ozone) treatment. This process allows precise tuning of the GM foam transitionally from ultrahydrophobic to hydrophilic within 60 sec. The continuous tuning of surface energy can be controlled by varying the UV-ozone exposure time, while the ozone-oxidized carbon nanostructure maintains its integrity. Symmetric SCs based on the UV-ozone treated GM foams demonstrated enhanced rate performance. This technique can be readily applied to other CVD-grown carbonaceous materials by taking advantage of its ease of processing, low cost, scalability, and controllability. Show less

Silicate particle formation on Cu foil during the synthesis of graphene by the commonly used thermal
chemical vapor deposition inside of a quartz tube was studied and characterized. The formation of
these particles was shown to form simultaneously alongside graphene layers. It is argued that the
phase transition of quartz at 573 C allows copper and hydrocarbon to diffuse into the quartz tube,
which in turn causes silicate to precipitate onto the copper foil during the CVD process… Show more

Silicate particle formation on Cu foil during the synthesis of graphene by the commonly used thermal
chemical vapor deposition inside of a quartz tube was studied and characterized. The formation of
these particles was shown to form simultaneously alongside graphene layers. It is argued that the
phase transition of quartz at 573 C allows copper and hydrocarbon to diffuse into the quartz tube,
which in turn causes silicate to precipitate onto the copper foil during the CVD process. Scanning
electron microscopy was used to image the contamination and its evolution during prolonged growth
times, and energy dispersive X-ray spectroscopy is utilized to identify and trace the potential source
of the contamination. Raman spectroscopy and mapping was utilized to demonstrate the negative
effects the contamination has on the graphene’s quality and uniformity by showing an increase in
the D peak and the development of the D peak. A simple method of avoiding Cu foil exposure
to turbulent flow during the growth is reported and verified to be an effective way of eliminating
contamination from the quartz tube.
Show less

Silicate particle formation on Cu foil during the synthesis of graphene by the commonly used thermal
chemical vapor deposition inside of a quartz tube was studied and characterized. The formation of
these particles was shown to form simultaneously alongside graphene layers. It is argued that the
phase transition of quartz at 573 C allows copper and hydrocarbon to diffuse into the quartz tube,
which in turn causes silicate to precipitate onto the copper foil during the CVD process… Show more

Silicate particle formation on Cu foil during the synthesis of graphene by the commonly used thermal
chemical vapor deposition inside of a quartz tube was studied and characterized. The formation of
these particles was shown to form simultaneously alongside graphene layers. It is argued that the
phase transition of quartz at 573 C allows copper and hydrocarbon to diffuse into the quartz tube,
which in turn causes silicate to precipitate onto the copper foil during the CVD process. Scanning
electron microscopy was used to image the contamination and its evolution during prolonged growth
times, and energy dispersive X-ray spectroscopy is utilized to identify and trace the potential source
of the contamination. Raman spectroscopy and mapping was utilized to demonstrate the negative
effects the contamination has on the graphene’s quality and uniformity by showing an increase in
the D peak and the development of the D peak. A simple method of avoiding Cu foil exposure
to turbulent flow during the growth is reported and verified to be an effective way of eliminating
contamination from the quartz tube.
Show less

Herein, porous nano-silicon has been synthesized via a highly scalable heat scavenger-assisted magnesiothermic reduction of beach sand. This environmentally benign, highly abundant, and low cost SiO2 source allows for production of nano-silicon at the industry level with excellent electrochemical performance as an anode material for Li-ion batteries. The addition of NaCl, as an effective heat scavenger for the highly exothermic magnesium reduction process, promotes the formation of an… Show more

Herein, porous nano-silicon has been synthesized via a highly scalable heat scavenger-assisted magnesiothermic reduction of beach sand. This environmentally benign, highly abundant, and low cost SiO2 source allows for production of nano-silicon at the industry level with excellent electrochemical performance as an anode material for Li-ion batteries. The addition of NaCl, as an effective heat scavenger for the highly exothermic magnesium reduction process, promotes the formation of an interconnected 3D network of nano-silicon with a thickness of 8-10 nm. Carbon coated nano-silicon electrodes achieve remarkable electrochemical performance with a capacity of 1024 mAhg−1 at 2 Ag−1 after 1000 cycles. Show less

Atomically thin molybdenum disulfide (MoS2) triangles and hexagrams were prepared by a two-step growth ambient pressure chemical vapor deposition (APCVD) process. Molybdenum Trioxide (MoO3) nanobelts, a few microns in length and width, were prepared using a hydrothermal technique and utilized as the starting material. High temperature treatment of the MoO3 nanobelts followed by a rigorous sulfurization via APCVD processing provided different morphologies of MoS2 monolayers and bi-layer sheets… Show more

Atomically thin molybdenum disulfide (MoS2) triangles and hexagrams were prepared by a two-step growth ambient pressure chemical vapor deposition (APCVD) process. Molybdenum Trioxide (MoO3) nanobelts, a few microns in length and width, were prepared using a hydrothermal technique and utilized as the starting material. High temperature treatment of the MoO3 nanobelts followed by a rigorous sulfurization via APCVD processing provided different morphologies of MoS2 monolayers and bi-layer sheets. Triangle and hexagram morphologies were characterized using Raman spectroscopy, photoluminescence (PL) measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The regrowth step in the CVD process was proven to be ideal in enlarging the grain size. PL and Raman spectroscopy and AFM results confirmed the presence of monolayer and bilayer regions in the regrowth growth process. Triangle and hexagram domains are observed to be cooperatively nucleating and coalescing together to form large-area layers. Furthermore, the electrical transport properties of the synthesized MoS2 layers were studied. Electron mobility based on back gated field effect transistors was measured to be approximately 0.02 cm2/Vs. Show less

In this work, we report the synthesis of an three-dimensional (3D) cone-shape CNT clusters (CCC) via chemical vapor deposition (CVD) with subsequent inductively coupled plasma (ICP) treatment. An innovative silicon decorated cone-shape CNT clusters (SCCC) is prepared by simply depositing amorphous silicon onto CCC via magnetron sputtering. The seamless connection between silicon decorated CNT cones and graphene facilitates the charge transfer in the system and suggests a binder-free technique… Show more

In this work, we report the synthesis of an three-dimensional (3D) cone-shape CNT clusters (CCC) via chemical vapor deposition (CVD) with subsequent inductively coupled plasma (ICP) treatment. An innovative silicon decorated cone-shape CNT clusters (SCCC) is prepared by simply depositing amorphous silicon onto CCC via magnetron sputtering. The seamless connection between silicon decorated CNT cones and graphene facilitates the charge transfer in the system and suggests a binder-free technique of preparing lithium ion battery (LIB) anodes. Lithium ion batteries based on this novel 3D SCCC architecture demonstrates high reversible capacity of 1954 mAh g−1 and excellent cycling stability (>1200 mAh g−1 capacity with ≈100% coulombic efficiency after 230 cycles). Show less

In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a… Show more

In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to an exceptionally high energy density of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications. Show less

We report on an innovative approach to fabricate lithium ion battery anodes based on optimized growth of hybrid carbon nanotube (CNT) and graphene nanostructures directly on copper foil substrates by an ambient pressure chemical vapor deposition process. Seamlessly connected graphene and CNT pillars provide a relatively strong active material-current collector integrity, which facilitates charge transfer in the system. This innovative architecture provides a binder-free technique for preparing… Show more

We report on an innovative approach to fabricate lithium ion battery anodes based on optimized growth of hybrid carbon nanotube (CNT) and graphene nanostructures directly on copper foil substrates by an ambient pressure chemical vapor deposition process. Seamlessly connected graphene and CNT pillars provide a relatively strong active material-current collector integrity, which facilitates charge transfer in the system. This innovative architecture provides a binder-free technique for preparing electrodes for lithium ion batteries. Show less

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a… Show more

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a fluorescence microscope. A large-area fluorescence montage image of the dyed graphene sample is collected and processed to identify the graphene and indicate the graphene layer thickness throughout the entire graphene sample. Using this metrology method, the effect of different transfer techniques on the quality of the graphene sheet is studied. It is shown that small-area characterization is insufficient to truly evaluate the effect of the transfer technique on the graphene sample. The results indicate that introducing a drop of acetone or liquid poly(methyl methacrylate) (PMMA) on top of the transfer PMMA layer before soaking the graphene sample in acetone improves the quality of the graphene dramatically over immediately soaking the graphene in acetone. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates. This metrology technique is well suited for many industrial applications due to its repeatability and flexibility.
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hree dimensional pillared graphene nanostructures were grown on metal substrates through a one-step chemical vapor deposition (CVD) by introducing a mixture precursor gases (H2, C2H4). We further explored sputtering evaporation system to uniformly deposited a layer of amorphous silicon on the as grown 3D carbon nanostructure. The surface morphologies of the carbon-silicon nanocomposites were investigated by scanning electron microscopy (SEM). Cyclic voltammetry and charge-discharge are… Show more

hree dimensional pillared graphene nanostructures were grown on metal substrates through a one-step chemical vapor deposition (CVD) by introducing a mixture precursor gases (H2, C2H4). We further explored sputtering evaporation system to uniformly deposited a layer of amorphous silicon on the as grown 3D carbon nanostructure. The surface morphologies of the carbon-silicon nanocomposites were investigated by scanning electron microscopy (SEM). Cyclic voltammetry and charge-discharge are conducted to determine the performance of the 3D hybrid carbon-silicon nanostructure for lithium ion battery anode. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. Show less