Molecular beam growth of graphene nanocrystals on dielectric substrates
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Germanium-Assisted Direct Growth of Graphene on Arbitrary Dielectric Substrates for Heating Devices
Direct growth of graphene on dielectric substrates is a prerequsite for the development of graphene-based electronic and optoelectronic devices. However, the current graphene synthesis directly on dielectric substrates always involves metal contamination problem, and the direct production of graphene patterns still remains unattainable and challenging. We propose herein a semiconducting Ge-assisted chemical vapor deposition approach to directly grow monolayer graphene on arbitrary dielectric substrates. By pre-patterning of catalytic Ge layer, the graphene with desired pattern can be achieved with extreme ease. Due to the catalysis of Ge, monolayer graphene is able to form on Ge covered dielectric substrates including SiO 2 /Si, quartz glass and sapphire substrates. Optimization of the process parameters leads to the complete sublimation of catalytic Ge layer during or immediately after monolayer graphene formation, thus resulting in direct deposition of large-area continuous graphene on dielectric substrates. The large-area, highly conductive graphene synthesized on transparent dielectric substrate using the proposed approach has exhibited wide applications, e.g., in defogger and in thermochromic displays, with both devices possessing excellent performances.
36 MATERIALS SCIENCE↗
Direct synthesis of reduced graphene oxide films on dielectric substrates
A method for coating a dielectric substrate with a R-GO film includes positioning the dielectric substrate in a chamber which is purged with a first gas to adjust a pressure of the chamber to a first pressure. A second gas at a second flow rate and a third gas at a third flow rate is inserted into the chamber to increase the chamber pressure to a second pressure greater than the first pressure. A chamber temperature is increased to a first temperature. The flow of the second gas and the third gas is stopped. The chamber is purged to a third pressure higher than the first pressure and lower than the second pressure. The pressure of the chamber is set at a fourth pressure greater than the first pressure and the third pressure. A fourth gas is inserted into the chamber at a fourth flow rate for a first time.
36 MATERIALS SCIENCE↗
Scalable and Direct Growth of Graphene Micro Ribbons on Dielectric Substrates
Here we report on a scalable and direct growth of graphene micro ribbons on SiO2 dielectric substrates using a low temperature chemical vapor deposition. Due to the fast annealing at low temperature and dewetting of Ni, continuous few-layer graphene micro ribbons grow directly on bare dielectric substrates through Ni assisted catalytic decomposition of hydrocarbon precursors. These high quality graphene micro ribbons exhibit low sheet resistance of ,700 V 22100 V, high on/off current ratio of ,3, and high carrier mobility of ,655 cm2 V21 s21 at room temperature, all of which have shown significant improvement over other lithography patterned CVD graphene micro ribbons. This direct approach can in principle form graphene ribbons of any arbitrary sizes and geometries. It allows for a feasible methodology towards better integration with semiconductor materials for interconnect electronics and scalable production for graphene based electronic and optoelectronic applications where the electrical gating is the key enabling factor.
SYNTHESIS OF GRAPHENE↗
Control of optical response of a supported cluster on different dielectric substrates
We develop a computational method for optical response of a supported cluster on a dielectric substrate. The substrate is approximated by a dielectric continuum with a frequency-dependent dielectric function. The computational approach is based on our recently developed first-principles simulation method for photoinduced electron dynamics in real-time and real-space. The approach allows us to treat optical response of an adsorbate explicitly taking account of interactions at an interface between an adsorbate and a substrate. We calculate optical absorption spectra of supported Ag{sub n} (n = 2, 54) clusters, changing the dielectric function of a substrate. By analyzing electron dynamics in real-time and real-space, we clarify the mechanisms for variations in absorption spectra, such as peak shifts and intensity changes, relating to various experimental results for optical absorption of supported clusters. Attractive and repulsive interactions between an adsorbate and a substrate result in red and blue shifts, respectively, and the intensity decreases by energy dissipation into a substrate. We demonstrate that optical properties can be controlled by varying the dielectric function of a substrate.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Spatially resolved absolute densities of reactive species and positive ion flux in He-O 2 RF-driven atmospheric pressure plasma jet: touching and non-touching with dielectric substrate
Atmospheric pressure plasma jets (APPJs) are operating in direct contact with dielectric substrates for many applications. Nonetheless, many studies have been focusing on free jets. In this letter, we report spatially resolved measurements of reactive species including neutral and ionic species in an He + 1% O 2 RF-driven APPJ by molecular beam mass spectrometry equipped with a dielectric sampling plate, enabling to detect species densities for APPJ operating remotely or in direct contact with a substrate. Here, the spatially resolved distribution of O, O 2 (a 1 Δ g ) and O 3 is dominated by convection and, remarkably, shows minimum differences between touching and non-touching conditions.
74 ATOMIC AND MOLECULAR PHYSICS↗
Tunable directional radiation of a dipole inside a cuboid slot on a dielectric substrate
Far-field directional radiation of a single dipole in a cuboid slot is investigated in the presence of a dielectric substrate. Due to strong near field coupling between the dipole source and the surfaces of the slot and the dielectric, the far-field radiation shows strongly anisotropic pattern depending on the dipole radiation energy. By tuning local resonances within the air-slot interface or the substrate-slot interface, highly directional radiation either to free space or to the substrate space can be obtained. In the visible spectrum ranging from 1.2 eV to 3.5 eV, up to 18 fold directivity can be obtained. The up-to-down ratio can be tuned from −7.5 dB to 10 dB. We identify induced eigenmodes responsible for highly unidirectional radiations as a function of the emitter spectrum and slot thickness to assess controllability of radiation power and direction.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Substrate dielectric effects on graphene field effect transistors
Graphene is emerging as a promising material for future electronics and optoelectronics applications due to its unique electronic structure. Understanding the graphene-dielectric interaction is of vital importance for the development of graphene field effect transistors (FETs) and other novel graphene devices. Here, we extend the exploration of substrate dielectrics from conventionally used thermally grown SiO{sub 2} and hexagonal boron nitride films to technologically relevant deposited dielectrics used in semiconductor industry. A systematic analysis of morphology and optical and electrical properties was performed to study the effects of different substrates (SiO{sub 2}, HfO{sub 2}, Al{sub 2}O{sub 3}, tetraethyl orthosilicate (TEOS)-oxide, and Si{sub 3}N{sub 4}) on the carrier transport of chemical vapor deposition-derived graphene FET devices. As baseline, we use graphene FETs fabricated on thermal SiO{sub 2} with a relatively high carrier mobility of 10 000 cm{sup 2}/(V s). Among the deposited dielectrics studied, silicon nitride showed the highest mobility, comparable to the properties of graphene fabricated on thermal SiO{sub 2}. We conclude that this result comes from lower long range scattering and short range scattering rates in the nitride compared those in the other deposited films. The carrier fluctuation caused by substrates, however, seems to be the main contributing factor for mobility degradation, as a universal mobility-disorder density product is observed for all the dielectrics examined. The extrinsic doping trend is further confirmed by Raman spectra. We also provide, for the first time, correlation between the intensity ratio of G peak and 2D peak in the Raman spectra to the carrier mobility of graphene for different substrates.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Direct growth of nanocrystalline hexagonal boron nitride films on dielectric substrates
Atomically thin hexagonal-boron nitride (h-BN) films are primarily synthesized through chemical vapor deposition (CVD) on various catalytic transition metal substrates. In this work, a single-step metal-catalyst-free approach to obtain few- to multi-layer nanocrystalline h-BN (NCBN) directly on amorphous SiO{sub 2}/Si and quartz substrates is demonstrated. The as-grown thin films are continuous and smooth with no observable pinholes or wrinkles across the entire deposited substrate as inspected using optical and atomic force microscopy. The starting layers of NCBN orient itself parallel to the substrate, initiating the growth of the textured thin film. Formation of NCBN is due to the random and uncontrolled nucleation of h-BN on the dielectric substrate surface with no epitaxial relation, unlike on metal surfaces. The crystallite size is ∼25 nm as determined by Raman spectroscopy. Transmission electron microscopy shows that the NCBN formed sheets of multi-stacked layers with controllable thickness from ∼2 to 25 nm. The absence of transfer process in this technique avoids any additional degradation, such as wrinkles, tears or folding and residues on the film which are detrimental to device performance. This work provides a wider perspective of CVD-grown h-BN and presents a viable route towards large-scale manufacturing of h-BN substrates and for coating applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
High-Voltage Superconducting Fault Current Limiters Based on High-Diffusivity Dielectric Substrates
High-temperature superconducting (HTS) tapes currently used for the manufacture of resistive fault current limiters use metallic substrates upon which the HTS film is grown. Because the alloys used for these substrates, such as Hastelloy, have a rather high resistivity and low thermal conductivity, the HTS film must be protected by a more conducting metallic layer acting as a shunt to avoid burn out during a fault. This shunt layer limits severely the electric field generated during the fault to values smaller than 100 V/m. A long length of tape is then necessary to achieve the desired high voltage. We show here that by using a high thermal diffusivity dielectric substrate such as sapphire, it is possible to obtain much higher electric fields of up to several kilovolts per meter.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Estimation of mean electron energy in helium surface ionization waves on dielectric substrates
Abstract The determination of basic plasma parameters in atmospheric pressure discharges is critical to advancing their use in applications. Atmospheric pressure plasma jets have found use in the fields of medicine, agriculture, material modification and others. Atmospheric pressure plasma jets often generate plasma surface ionization waves (SIW) which interact with and propagate over surfaces. Electrical diagnostics are challenging in SIW due to high collision frequencies and small scale of the plasma discharge. This work employs a passive optical emission line ratio technique to estimate the mean electron energy in SIW over planar dielectric substrates. The method uses an intensity ratio of two helium triplet lines: He( 3 3 S ) at 706.5 nm and He( 3 3 D ) at 587.56 nm. A collisional-radiative model is used to correlate line ratio to mean electron energy and determine dependencies on electron density and He/air gas mixture. Mean electron energies ranging from 3–8 eV are determined in He/air mixtures and are found to remain constant as the surface wave propagates radially. This work provides a 2D, time-resolved, mean electron energy diagnostic for surface ionization wave propagation and validation of numerical modeling in atmospheric pressure systems with spatially varying He/air gas mixtures. The model in question is designed for use with any He line ratio in the n = 3 excitation level.
Morsell, Joshua (ORCID:0000000331073002)↗
Nickel enhanced graphene growth directly on dielectric substrates by molecular beam epitaxy
The efficacy of Ni as a surfactant to improve the crystalline quality of graphene grown directly on dielectric Al{sub 2}O{sub 3}(0001) substrates by molecular beam epitaxy is examined. Simultaneously exposing the substrate to a Ni flux throughout C deposition at 950 °C led to improved charge carrier mobility and a Raman spectrum indicating less structural disorder in the resulting nanocrystalline graphene film. X-ray photoelectron spectroscopy confirmed that no residual Ni could be detected in the film and showed a decrease in the intensity of the defect-related component of the C1s level. Similar improvements were not observed when a lower substrate temperature (850 °C) was used. A close examination of the Raman spectra suggests that Ni reduces the concentration of lattice vacancies in the film, possibly by catalytically assisting adatom incorporation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Correction to: High-Voltage Superconducting Fault Current Limiters Based on High-Diffusivity Dielectric Substrates
The original version of this article contains the following mistakes: On the second page 1st paragraph under heading “The Role of the Substrate Diffusivity” second and third sentences, 90 K, 300 cm{sup 2}/s and 5 mm, should be replaced with 65 K, 100 cm{sup 2}/s and 3 mm.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Infrared surface phonon nanospectroscopy of an interacting dielectric-particle–dielectric-substrate dimer using fast electrons
Refinements in energy monochromation and aberration correction in state-of-the-art scanning transmission electron microscopes has opened access to the far infrared regime for spectroscopic characterization at the nanoscale. At these low energies, the dielectric environment, such as a dielectric slab adjacent to the target specimen, may no longer play a passive role in the spectrum. Instead, the environment may itself host resonances that mix with those of the target and complicate interpretation of its spectral responses. This article explores a theoretical description of the coupling between the collective vibrational surface modes of a dielectric particle and dielectric slab of varying thickness for the purpose of elucidating the interacting phononic excitations in dielectric materials typical of inelastic electron scattering measurements in the infrared. Dynamical coordinates and a governing Hamiltonian are rigorously defined in the quasistatic limit to account for phonon mode mixing and forcing by an aloof electron probe, which travels along a grazing trajectory, parallel to the dielectric slab. As the spectral window of interrogation by fast electron probes has been extended down to thermal energies with unprecedented meV energy resolution, theoretical models like that presented herein are crucial for accurate interpretation of experimental data.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Laser-stimulated photodetachment of electrons from the negatively charged dielectric substrates
The photon-stimulated emission of bulk electrons has been extensively studied for various types of materials, while the photodetachment of surplus surface electrons has not been fully explored. The photodetachment barrier energy is commonly defined by the surface electron affinity of material, which is typically less than the work function and more pronounced for non-conducting substrates and in environments with a continuous flux of electrons to the surface, such as in gas discharge plasmas. Herein, it is experimentally shown that the photodetachment yield of surplus electrons created by plasma-induced charging of non-conductive surfaces of dielectric materials depends on the initial surface charge density and do not correlate with the tabulated affinity values of these materials under gas discharge charging conditions. In cocnclusion, this result obtained using laser-stimulated photodetachment for fused silica, boron nitride, and alumina, is critically important for the understanding of charging and discharging dynamics, secondary electron emission, and photo emission effects affecting plasma–wall interactions relevant to surface and capacitively coupled discharges, dusty plasmas, electrostatic probe diagnostics, and applications for plasma processing of materials, plasma propulsion, and gas breakdown.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Synthesis of graphene-like transparent conductive films on dielectric substrates using a modified filtered vacuum arc system
Here, we present a reliable process to deposit transparent conductive films on silicon oxide, quartz, and sapphire using a solid carbon source. This layer consists of partially ordered graphene flakes with a lateral dimension of about 5 nm. The process does not require any catalytic metal and exploits a high current arc evaporation (Φ-HCA) to homogeneously deposit a layer of carbon on heated substrates. A gas atmosphere consisting of Argon or Argon/Hydrogen blend acting as a buffer influences the morphology of the growing film. scanning tunneling microscopy, transmission electron microscopy, and Raman spectra were used for a thorough characterization of the samples in order to optimize the growth parameters. The best carbon layers have a surface resistance of 5.7 × 10{sup 3} Ω{sub ◻} whereas the optical transparency of the coatings is 88% with an excellent homogeneity over areas of several cm{sup 2}. Such results are compatible with most semiconductor fabrication processes and make this method very promising for various industrial applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Temperature-dependent Spectral Emission of Hexagonal Boron Nitride Quantum Emitters on Conductive and Dielectric Substrates
We report a reduction in the linewidth and suppression of spectral diffusion of quantum emitters in hexagonal boron nitride supported on a conductive substrate. In this work, we observe a temperature-dependent reduction in the spectral emission linewidth for CVD-grown and exfoliated crystals on conductive ITO relative to those seen on silicon dioxide (SiO 2 ) substrates. We show that the inhomogeneous linewidth can be suppressed by 45% as a result of using a conductive substrate. We investigate the zero-phonon line profile at temperatures ranging from 4 to 300 K and decompose the effects of thermal broadening and spectral diffusion at each temperature by Voigt fitting. The temperature dependence of homogeneous and inhomogeneous components of the broadening is discussed.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗