19 research outputs found
Single layer graphene film by ethanol chemical vapor deposition: Highly efficient growth and clean transfer method
The choice of ethanol (C2H5OH) as carbon source in the Chemical Vapor Deposition (CVD) of graphene on copper foils can be considered as an attractive alternative among the commonly used hydrocarbons, such as methane (CH4) [1]. Ethanol, a safe, low cost and easy handling liquid precursor, offers fast and efficient growth kinetics with the synthesis of fullyformed graphene films in just few seconds [2]. In previous studies of graphene growth from ethanol, various research groups explored temperature ranges lower than 1000 °C, usually reported for methane-assisted CVD. In particular, the 650â850 °C and 900 °C ranges were investigated, respectively for 5 and 30 min growth time [3, 4]. Recently, our group reported the growth of highly-crystalline, few-layer graphene by ethanol-CVD in hydrogen flow (1â 100 sccm) at high temperatures (1000â1070 °C) using growth times typical of CH4-assisted synthesis (10â30 min) [5]. Furthermore, a synthesis time between 20 and 60 s in the same conditions was explored too. In such fast growth we demonstrated that fully-formed graphene films can be grown by exposing copper foils to a low partial pressure of ethanol (up to 2 Pa) in just 20 s [6] and we proposed that the rapid growth is related to an increase of the Cu catalyst efficiency due weak oxidizing nature of ethanol. Thus, the employment of such liquid precursor, in small concentrations, together with a reduced time of growth and very low pressure leads to highly efficient graphene synthesis. By this way, the complete coverage of a copper catalyst surface with high spatial uniformity can be obtained in a considerably lower time than when using methane
On the CVD Growth of C Nanotubes Over Fe-Loaded Montmorillonite Catalysts
The synthesis of carbon nanotubes (CNTs) by
chemical vapor deposition (CVD) of isobutane (iâC4H10)
over sodiumâexchanged K10âmontmorillonite based ironâ
catalysts is investigated. By studying the influence of
ironâaddition (5â25wt%) on the catalyst performances, at
700 °C, an empirical relationship is derived relating the
mass of CNTs synthesized with the exposed surface of
loaded iron, as resulting from simultaneous change of
number, size and dispersion of Feânanoparticles available
for the growth
Interactions between Primary Neurons and Graphene Films with Different Structure and Electrical Conductivity
Graphene-based materials represent a useful tool for the realization of novel
neural interfaces. Several studies have demonstrated the biocompatibility of
graphene-based supports, but the biological interactions between graphene and
neurons still pose open questions. In this work, the influence of graphene films
with different characteristics on the growth and maturation of primary cortical
neurons is investigated. Graphene films are grown by chemical vapor deposition
progressively lowering the temperature range from 1070 to 650 °C to change the
lattice structure and corresponding electrical conductivity. Two graphene-based
films with different electrical properties are selected and used as substrate for
growing primary cortical neurons: i) highly crystalline and conductive (grown
at 1070 °C) and ii) highly disordered and 140-times less conductive (grown at
790 °C). Electron and fluorescence microscopy imaging reveal an excellent
neuronal viability and the development of a mature, structured, and excitable
network onto both substrates, regardless of their microstructure and electrical
conductivity. The results underline that high electrical conductivity by itself is
not fundamental for graphene-based neuronal interfaces, while other physicoâ
chemical characteristics, including the atomic structure, should be also considered
in the design of functional, bio-friendly templates. This finding widens the
spectrum of carbon-based materials suitable for neuroscience applications.European Union (EU)
785219-Graphene Flagship-Core2Ministero degli Affari Esteri e Cooperazione Internazionale of Italy (Farnesina-MAECI)
MAE0057294Basic Science Research ProgramCreative Materials Discovery ProgramInternational Research & Development Program through the NRF of Korea
2016M3A7B4910940
2018M3D1A1058793
2019K1A3A1A25000267European Union's Horizon 2020 under the Marie Skodowska-Curie Action-COFUND Athenea3i grant
754446European Union's Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant
71364
Fast growth of polycrystalline graphene by chemical vapor deposition of ethanol on copper
High conductive graphene films can be grown on metal foils by chemical vapor deposition (CVD). We here analyzed the use of ethanol, an economic precursor, which results also safer than commonly-used methane. A comprehensive range of process parameters were explored in order to obtain graphene films with optimal characteristics in view of their use in optoelectronics and photovoltaics. Commercially-available and electro-polished copper foils were used as substrates. By finely tuning the CVD conditions, we obtained few-layer (2-4) graphene films with good conductivity (-500 Ohm/sq) and optical transmittance around 92-94% at 550 nm on unpolished copper foils. The growth on electro-polished copper provides instead predominantly mono-layer films with lower conductivity (>1000 Ohm/sq) and with a transmittance of 97.4% at 550 nm. As for the device properties, graphene with optimal properties as transparent conductive film were produced by CVD on standard copper with specific process conditions
Nitrogen-doped graphene films from chemical vapor deposition of pyridine: influence of process parameters on the electrical and optical properties
Graphene films were produced by chemical vapor deposition (CVD) of pyridine on copper substrates. Pyridine-CVD is expected to lead to doped graphene by the insertion of nitrogen atoms in the growing sp2 carbon lattice, possibly improving the properties of graphene as a transparent conductive film. We here report on the influence that the CVD parameters (i.e., temperature and gas flow) have on the morphology, transmittance, and electrical conductivity of the graphene films grown with pyridine. A temperature range between 930 and 1070 °C was explored and the results were compared to those of pristine graphene grown by ethanol-CVD under the same process conditions. The films were characterized by atomic force microscopy, Raman and X-ray photoemission spectroscopy. The optical transmittance and electrical conductivity of the films were measured to evaluate their performance as transparent conductive electrodes. Graphene films grown by pyridine reached an electrical conductivity of 14.3 à 105 S/m. Such a high conductivity seems to be associated with the electronic doping induced by substitutional nitrogen atoms. In particular, at 930 °C the nitrogen/carbon ratio of pyridine-grown graphene reaches 3%, and its electrical conductivity is 40% higher than that of pristine graphene grown from ethanol-CVD
Experimental characterization of the thermo-optic coefficient vs. temperature for 4H-SiC and GaN semiconductors at the wavelength of 632Â nm
Abstract The design of semiconductor-based photonic devices requires precise knowledge of the refractive index of the optical materials, a not constant parameter over the operating temperature range. However, the variation of the refractive index with the temperature, the thermo-optic coefficient, is itself temperature-dependent. A precise characterization of the thermo-optic coefficient in a wide temperature range is therefore essential for the design of nonlinear optical devices, active and passive integrated photonic devices and, more in general, for the semiconductor technology explored at different wavelengths, from the visible domain to the infrared or ultraviolet spectrum. In this paper, after an accurate ellipsometric and micro-Raman spectroscopy characterization, the temperature dependence of the thermo-optic coefficient ( â n â T ) for 4H-SiC and GaN in a wide range of temperature between room temperature to Tâ=â500 K in the visible range spectrum, at a wavelength of λâ=â632.8 nm, is experimentally evaluated. For this purpose, using the samples as a FabryâPerot cavity, an interferometric technique is employed. The experimental results, for both semiconductors, show a linear dependence with a high determination coefficient, R2 of 0.9648 and 0.958, for 4H-SiC and GaN, respectively, in the considered temperature range
Polylactide and carbon nanotubes/smectite-clay nanocomposites: Preparation, characterization, sorptive and electrical properties
Chemical Vapor Deposited Graphene-Based Derivative As High-Performance Hole Transport Material for Organic Photovoltaics
Rapid and highly efficient growth of graphene on copper by chemical vapor deposition of ethanol
The growth of graphene by chemical vapor deposition on metal foils is a promising technique to deliver large-area films with high electron mobility. Nowadays, the chemical vapor deposition of hydrocarbons on copper is the most investigated synthesis method, although many other carbon precursors and metal substrates are used too. Among these, ethanol is a safe and inexpensive precursor that seems to offer favorable synthesis kinetics. We explored the growth of graphene on copper from ethanol, focusing on processes of short duration (up to one min). We investigated the produced films by electron microscopy, Raman and X-ray photoemission spectroscopy. A graphene film with high crystalline quality was found to cover the entire copper catalyst substrate in just 20 s, making ethanol appear as a more efficient carbon feedstock than methane and other commonly used precursors