skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Facile synthesis of highly fluorescent free-standing films comprising graphitic carbon nitride (g-C 3 N 4 ) nanolayers
Astounding graphitic carbon nitride (g-C 3 N 4 ) nanostructures have attracted huge attention due to their unique electronic structures, suitable band gap, and thermal and chemical stability, and are insinuating as a promising candidate for photocatalytic and energy harvesting applications. The growth of a free-standing film is desirable for widespread electronic devices and electrochemical applications. Here, we present a facile approach to prepare free-standing films (15 mm × 10 mm × 0.5 mm) comprising g-C 3 N 4 nanolayers by the pyrolysis of dicyandiamide (C 2 H 4 N 4 ) utilizing the chemical vapor deposition (CVD) technique. The synthesis is done under low-pressure conditions of argon (∼3 Torr) and at a temperature of 600 °C. The as-synthesized g-C 3 N 4 films are systematically studied for their structural/microstructural characterization using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR) and UV-visible spectroscopy techniques. The excitation-dependent photoluminescence (PL) spectra of the as-synthesized g-C 3 N 4 film exhibited an intense, stable and broad emission peak in the visible region at ∼459 nm. The emission spectra of free-standing g-C 3 N 4 films show a blue shift and band sharpening compared to that of the g-C 3 N 4 powder.  more » « less
Award ID(s):
1807737
PAR ID:
10186207
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
New Journal of Chemistry
Volume:
44
Issue:
6
ISSN:
1144-0546
Page Range / eLocation ID:
2644 to 2651
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    A free-standing film composed of bilayered vanadium oxide nanoflakes is for the first time synthesized using a new low-energy process. The precursor powder, δ-Li x V 2 O 5 · n H 2 O, was prepared using a simple sol–gel based chemical preintercalation synthesis procedure. δ-Li x V 2 O 5 · n H 2 O was dispersed and probe sonicated in N -methyl pyrrolidone to exfoliate the bilayers followed by vacuum filtration resulting in the formation of a free-standing film with obsidian color. X-ray diffraction showed lamellar ordering of a single-phase material with a decreased interlayer distance compared to that of the precursor powder. Scanning electron microscopy images demonstrated stacking of the individual nanoflakes. This morphology was further confirmed with scanning transmission electron microscopy that showed highly malleable nanoflakes consisting of ∼10–100 vanadium oxide bilayers. One of the most important consequences of this morphological rearrangement is that the electronic conductivity of the free-standing film, measured by the four-probe method, increased by an order of magnitude compared to conductivity of the pressed pellet made of precursor powder. X-ray photoelectron spectroscopy measurements showed the coexistence of both V 5+ and V 4+ oxidation states in the exfoliated sample, possibly contributing to the change in electronic conductivity. The developed approach provides the ability to maintain the phase purity and crystallographic order during the exfoliation process, coupled with the formation of a free-standing film of enhanced conductivity. The produced bilayered vanadium oxide nanoflakes can be used as the building blocks for the synthesis of versatile two-dimensional heterostructures to create innovative electrodes for electrochemical energy storage applications. 
    more » « less
  2. The chemical structures of Co oxynitrides – in particular, interactions among N and O atoms bonded to the same cobalt – are of great importance for an array of catalytic and materials applications. X-ray diffraction (XRD), core and valence band X-ray photoelectron spectroscopy (XPS) and plane wave density functional theory (DFT) calculations are used to probe chemical and electronic interactions of nitrogen-rich CoO1-xNx (x > 0.7) films deposited on Si(100) using NH3 or N2 plasma-based sputter deposition or surface nitridation. Total energy calculations indicate that the zincblende (ZB) structure is energetically favored over the rocksalt (RS) structure for x > ~ 0.2, with an energy minimum observed in the ZB structure for x ~ 0.8 - 0.9. This is in close agreement with XPS-derived film compositions when corrected for surface oxide/hydroxide layers. XRD data indicate that films deposited on Si (100) at room temperature display either a preferred (220) orientation or no diffraction pattern, and are consistent with either rocksalt (RS) or zincblende (ZB) structure. Comparison between experimental and calculated X-ray excited valence band densities of states – also similar for all films synthesized herein – demonstrates a close agreement with a ZB, but not an RS structure. Core level XPS spectra exhibit systematic differences between films deposited in NH3 vs N2 plasma environments. Films deposited by N2 plasma magnetron sputtering exhibit greater O content as evidenced by systematic shifts in N 1s binding energies. Excellent agreement with experiment for core level binding energies is obtained for DFT calculations based on the ZB structure, but not for the RS structure. The agreement between theory and experiment demonstrates that these N-rich Co oxynitride films exhibit the ZB structure, and forms the basis of a predictive model for understanding how N and O interactions impact the electronic, magnetic and catalytic properties of these materials. 
    more » « less
  3. Abstract Single‐atom catalysts have demonstrated interesting activity in a variety of applications. In this study, we prepared single Co2+sites on graphitic carbon nitride (C3N4), which was doped with carbon for enhanced activity in visible‐light CO2reduction. The synthesized materials were characterized with a variety of techniques, including microscopy, X‐ray powder diffraction, UV‐vis spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, and X‐ray absorption spectroscopy. Doping C3N4with carbon was found to have profound effect on the photocatalytic activity of the single Co2+sites. At relatively low levels, carbon doping enhanced the photoresponse of C3N4in the visible region and improved charge separation upon photoactivation, thereby enhancing the photocatalytic activity. High levels of carbon doping were found to be detrimental to the photocatalytic activity of the single Co2+sites by altering the structure of C3N4and generating defect sites responsible for charge recombination. 
    more » « less
  4. 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
  5. We present a review of the use of selected nanofabricated thin films to deliver a host of capabilities and insights spanning bioanalytical and biophysical chemistry, materials science, and fundamental molecular-level research. We discuss approaches where thin films have been vital, enabling experimental studies using a variety of optical spectroscopies across the visible and infrared spectral range, electron microscopies, and related techniques such as electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and single molecule sensing. We anchor this broad discussion by highlighting two particularly exciting exemplars: a thin-walled nanofluidic sample cell concept that has advanced the discovery horizons of ultrafast spectroscopy and of electron microscopy investigations of in-liquid samples; and a unique class of thin-film-based nanofluidic devices, designed around a nanopore, with expansive prospects for single molecule sensing. Free-standing, low-stress silicon nitride membranes are a canonical structural element for these applications, and we elucidate the fabrication and resulting features—including mechanical stability, optical properties, X-ray and electron scattering properties, and chemical nature—of this material in this format. We also outline design and performance principles and include a discussion of underlying material preparations and properties suitable for understanding the use of alternative thin-film materials such as graphene. 
    more » « less