skip to main content

Explore Research Products in the NSF-PAR

Title: Graphene Film Growth on Silicon Carbide by Hot Filament Chemical Vapor Deposition
The electrical properties of graphene on dielectric substrates, such as silicon carbide (SiC), have received much attention due to their interesting applications. This work presents a method to grow graphene on a 6H-SiC substrate at a pressure of 35 Torr by using the hot filament chemical vapor deposition (HFCVD) technique. The graphene deposition was conducted in an atmosphere of methane and hydrogen at a temperature of 950 °C. The graphene films were analyzed using Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray, and X-ray photoelectron spectroscopy. Raman mapping and AFM measurements indicated that few-layer and multilayer graphene were deposited from the external carbon source depending on the growth parameter conditions. The compositional analysis confirmed the presence of graphene deposition on SiC substrates and the absence of any metal involved in the growth process.  more » « less
Award ID(s):
1849243
NSF-PAR ID:
10407191
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Nanomaterials
Volume:
12
Issue:
17
ISSN:
2079-4991
Page Range / eLocation ID:
3033
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ( , Coatings)
    We report a comparative spectroscopic study on the thin films of epitaxial aluminum nitride (AlN) on basal plane sapphire (Al2O3) substrates grown in hydrogen (H2) and nitrogen (N2) gas reaction environments. AlN films of similar thicknesses (~3.0 µm) were grown by metal-organic chemical vapor deposition (MOCVD) for comparison. The impact of the gas environment on the AlN epilayers was characterized using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS), secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The study showed that AlN layers grown in a N2 environment have 50% less stress (~0.5 GPa) and similar total dislocation densities (~109/cm2) as compared to the films grown in a H2 environment. On the other hand, AlN films grown in a H2 gas environment have about 33% lesser carbon and 41% lesser oxygen impurities than films grown in a N2 growth environment. The possible mechanisms that influenced the structural quality and impurity incorporation for two different gas environments to grow AlN epilayers in the MOCVD system on sapphire substrates were discussed. 
    more » « less
  2. ; ; ; ; ; ( , Nanomaterials)
    We report the first direct synthesis of graphene on SiO2/Si by hot-filament chemical vapor deposition. Graphene deposition was conducted at low pressures (35 Torr) with a mixture of methane/hydrogen and a substrate temperature of 970 °C followed by spontaneous cooling to room temperature. A thin copper-strip was deposited in the middle of the SiO2/Si substrate as catalytic material. Raman spectroscopy mapping and atomic force microscopy measurements indicate the growth of few-layers of graphene over the entire SiO2/Si substrate, far beyond the thin copper-strip, while X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy showed negligible amounts of copper next to the initially deposited strip. The scale of the graphene nanocrystal was estimated by Raman spectroscopy and scanning electron microscopy. 
    more » « less
  3. ; ; ; ; ; ( , Advanced Materials)
    Abstract

    Post‐growth graphene transfer to a variety of host substrates for circuitry fabrication has been among the most popular subjects since its successful development via chemical vapor deposition in the past decade. Fast and reliable evaluation tools for its morphological characteristics are essential for the development of defect‐free transfer protocols. The implementation of conventional techniques, such as Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy in production quality control at an industrial scale is difficult because they are limited to local areas, are time consuming, and their operation is complex. However, through a one‐shot measurement within a few seconds, phase‐shifting interferometry (PSI) successfully scans ≈1 mm2of transferred graphene with a vertical resolution of ≈0.1 nm. This provides crucial morphological information, such as the surface roughness derived from polymer residues, the thickness of the graphene, and its adhesive strength with respect to the target substrates. Graphene samples transferred via four different methods are evaluated using PSI, Raman spectroscopy, and AFM. Although the thickness of the nanomaterials measured by PSI can be highly sensitive to their refractive indices, PSI is successfully demonstrated to be a powerful tool for investigating the morphological characteristics of the transferred graphene for industrial and research purposes.

     
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al ( , Advanced Materials Interfaces)
    Abstract

    This study reports successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb photocathodes on graphene films. The results pave the way for an ultimate goal of encapsulating technologically relevant photocathodes for accelerator technology with an atomically thin protecting layer to enhance lifetime while minimizing QE losses. A QE of 17% at ≈3.1 eV (405 nm) is the highest value reported so far on graphene substrates and is comparable to that obtained on stainless steel and nickel reference substrates. The spectral responses of the photocathodes on graphene exhibit signature features of K2CsSb including the characteristic absorption at ≈2.5 eV. Materials characterization based on X‐ray fluorescence and X‐ray diffraction reveals that the composition and crystal quality of these photocathodes deposited on graphene is comparable to those deposited on a reference substrate. Quantitative agreement between optical calculations and QE measurements for the K2CsSb on free suspended graphene and a graphene‐coated metal substrate further confirms the high‐quality interface between the photocathodes and graphene. Finally, a correlation between the QE and graphene quality as characterized by Raman spectroscopy suggests that a lower density of atomistic defects in the graphene films leads to higher QE of the deposited K2CsSb photocathodes.

     
    more » « less
  5. ; ; ; ; ; ; ; ( , APL Materials)
    Phase pure β-(Al x Ga 1−x ) 2 O 3 thin films are grown on (001) oriented β-Ga 2 O 3 substrates via metalorganic chemical vapor deposition. By systematically tuning the precursor molar flow rates, the epitaxial growth of coherently strained β-(Al x Ga 1−x ) 2 O 3 films is demonstrated with up to 25% Al compositions as evaluated by high resolution x-ray diffraction. The asymmetrical reciprocal space mapping confirms the growth of coherent β-(Al x Ga 1−x ) 2 O 3 films (x < 25%) on (001) β-Ga 2 O 3 substrates. However, the alloy inhomogeneity with local segregation of Al along the ([Formula: see text]) plane is observed from atomic resolution STEM imaging, resulting in wavy and inhomogeneous interfaces in the β-(Al x Ga 1−x ) 2 O 3 /β-Ga 2 O 3 superlattice structure. Room temperature Raman spectra of β-(Al x Ga 1−x ) 2 O 3 films show similar characteristics peaks as the (001) β-Ga 2 O 3 substrate without obvious Raman shifts for films with different Al compositions. Atom probe tomography was used to investigate the atomic level structural chemistry with increasing Al content in the β-(Al x Ga 1−x ) 2 O 3 films. A monotonous increase in chemical heterogeneity is observed from the in-plane Al/Ga distributions, which was further confirmed via statistical frequency distribution analysis. Although the films exhibit alloy fluctuations, n-type doping demonstrates good electrical properties for films with various Al compositions. The determined valence and conduction band offsets at β-(Al x Ga 1−x ) 2 O 3 /β-Ga 2 O 3 heterojunctions using x-ray photoelectron spectroscopy reveal the formation of type-II (staggered) band alignment. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email