13 research outputs found
One-Step Process for High-Performance, Adhesive, Flexible Transparent Conductive Films Based on p‑Type Reduced Graphene Oxides and Silver Nanowires
This
work demonstrates a one-step process to synthesize uniformly dispersed
hybrid nanomaterial containing silver nanowires (AgNWs) and p-type
reduced graphene (p-rGO). The hybrid nanomaterial was coated onto
a polyethylene terephthalate (PET) substrate for preparing high-performance
flexible transparent conductive films (TCFs). The p-rGO plays the
role of bridging discrete AgNWs, providing more electron holes and
lowering the resistance of the contacted AgNWs; therefore, enhancing
the electrical conductivity without sacrificing too much transparence
of the TCFs. Additionally, the p-rGO also improves the adhesion between
AgNWs and substrate by covering the AgNWs on the substrate tightly.
The study shows that coating of the hybrid nanomaterials on the PET
substrate demonstrates exceptional optoelectronic properties with
a transmittance of 94.68% (at a wavelength of 550 nm) and a sheet
resistance of 25.0 ± 0.8 Ω/sq. No significant variation
in electric resistance can be detected even when the film was subjected
to a bend loading with a radius of curvature of 5.0 mm or the film
was loaded with a reciprocal tension or compression for 1000 cycles.
Furthermore, both chemical corrosion resistance and haze effect were
improved when p-rGO was introduced. The study shows that the fabricated
flexible TCFs have the potential to replace indium tin oxide film
in the optoelectronic industry
Enhancing the Electrical Properties of a Flexible Transparent Graphene-Based Field-Effect Transistor Using Electropolished Copper Foil for Graphene Growth
Flexible
transparent graphene-based field-effect transistors (Gr-FETs)
were fabricated using large-area single-layer graphene synthesized
through low-pressure chemical vapor deposition on a pretreated copper
(Cu) foil, followed by transfer of the graphene from the Cu foil to
a polyÂ(ethylene terephthalate) (PET) substrate. The electropolishing
method was adopted to smooth the surface of the Cu foil, which is
a crucial factor because it affects the defect density of graphene
films on the PET substrate after transfer and the electronic transport
property of the graphene-based devices. The influence of the electropolishing
process on the graphene properties was examined using a Raman spectroscope,
a scanning electron microscope, and an optical microscope. When the
electropolishing process was adopted to improve the graphene quality,
the carrier mobility of the flexible transparent Gr-FETs was enhanced
from 90 to 340 cm<sup>2</sup>/(V s). Furthermore, variation of the
carrier mobility was lower than 10% when the bending radius of the
flexible device was decreased from 6.0 to 1.0 cm
Flexible Solar Cells Using Doped Crystalline Si Film Prepared by Self-Biased Sputtering Solid Doping Source in SiCl<sub>4</sub>/H<sub>2</sub> Microwave Plasma
We developed an innovative approach
of self-biased sputtering solid doping source process to synthesize
doped crystalline Si film on flexible polyimide (PI) substrate via
microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using
SiCl<sub>4</sub>/H<sub>2</sub> mixture. In this process, P dopants
or B dopants were introduced by sputtering the solid doping target
through charged-ion bombardment in situ during high-density microwave
plasma deposition. A strong correlation between the number of solid
doping targets and the characteristics of doped Si films was investigated
in detail. The results show that both P- and B-doped crystalline Si
films possessed a dense columnar structure, and the crystallinity
of these structures decreased with increasing the number of solid
doping targets. The films also exhibited a high growth rate (>4.0
nm/s). Under optimal conditions, the maximum conductivity and corresponding
carrier concentration were, respectively, 9.48 S/cm and 1.2 ×
10<sup>20</sup> cm<sup>–3</sup> for P-doped Si film and 7.83
S/cm and 1.5 × 10<sup>20</sup> cm<sup>–3</sup> for B-doped
Si film. Such high values indicate that the incorporation of dopant
with high doping efficiency (around 40%) into the Si films was achieved
regardless of solid doping sources used. Furthermore, a flexible crystalline
Si film solar cell with substrate configuration was fabricated by
using the structure of PI/Mo film/<i>n</i>-type Si film/<i>i</i>-type Si film/<i>p</i>-type Si film/ITO film/Al
grid film. The best solar cell performance was obtained with an open-circuit
voltage of 0.54 V, short-circuit current density of 19.18 mA/cm<sup>2</sup>, fill factor of 0.65, and high energy conversion of 6.75%.
According to the results of bending tests, the critical radius of
curvature (<i>R</i><sub>C</sub>) was 12.4 mm, and the loss
of efficiency was less than1% after the cyclic bending test for 100
cycles at <i>R</i><sub>C</sub>, indicating superior flexibility
and bending durability. These results represent important steps toward
a low-cost approach to high-performance flexible crystalline Si film-based
photovoltaic devices
Fast Process To Decorate Silver Nanoparticles on Carbon Nanomaterials for Preparing High-Performance Flexible Transparent Conductive Films
This work demonstrates a fast process
to decorate silver (Ag) nanoparticles
onto the functionalized few-walled carbon nanotubes (f-FWCNTs) and
graphene nanosheets (f-GNs). The Ag-coated carbon nanomaterials were
used as fillers, which mixed with polyÂ(3,4-ethylenedioxythiophene)–polyÂ(4-stryensulfonate)
(PEDOT:PSS) for preparing high optoelectronic performances of flexible
transparent conductive films (TCFs). The Ag nanoparticles with a particle
size of approximate 5 nm were uniformly distributed on the surfaces
of the f-FWCNTs (Ag@f-FWCNTs) and the f-GNs (Ag@f-GNs). The Ag ions
play the role of electron acceptors during the reduction process,
which increases the hole concentrations in PEDOT:PSS, f-FWCNTs, and
f-GNs, therefore enhancing the electrical conductivity of the TCFs.
Additionally, the Schottky barrier was decreased because of the increase
of work functions of the carbon fillers caused by Ag decoration. The
X-ray diffraction spectrum of Ag@f-GNs depicts the formations of the
face-centered cubic Ag nanoparticles, and the peak of the (002) graphene
plane slightly shifted to the lower frequency, indicating that the
f-GN interlayer was intercalated with Ag ions or Ag nanoparticles.
When the mixture of 2.0 wt % Ag@f-FWCNTs and 8.0 wt % Ag@f-GNs containing
PEDOT:PSS dispersant was coated onto a polyÂ(ethylene terephthalate)
(PET) substrate, outstanding optoelectronic properties with a sheet
resistance of 50.3 Ω/sq and a transmittance of 79.73% at a wavelength
of 550 nm were achieved
High Mobility of Graphene-Based Flexible Transparent Field Effect Transistors Doped with TiO<sub>2</sub> and Nitrogen-Doped TiO<sub>2</sub>
Graphene
with carbon atoms bonded in a honeycomb lattice can be
tailored by doping various species to alter the electrical properties
of the graphene for fabricating p-type or n-type field-effect transistors
(FETs). In this study, large-area and single-layer graphene was grown
on electropolished Cu foil using the thermal chemical vapor deposition
method; the graphene was then transferred onto a polyÂ(ethylene terephthalate)
(PET) substrate to produce flexible, transparent FETs. TiO<sub>2</sub> and nitrogen-doped TiO<sub>2</sub> (N-TiO<sub>2</sub>) nanoparticles
were doped on the graphene to alter its electrical properties, thereby
enhancing the carrier mobility and enabling the transistors to sense
UV and visible light optically. The results indicated that the electron
mobility of the graphene was 1900 cm<sup>2</sup>/(V·s). Dopings
of TiO<sub>2</sub> and N-doped TiO<sub>2</sub> (1.4 at. % N) lead
to n-type doping effects demonstrating extremely high carrier mobilities
of 53000 and 31000 cm<sup>2</sup>/(V·s), respectively. Through
UV and visible light irradiation, TiO<sub>2</sub> and N-TiO<sub>2</sub> generated electrons and holes; the generated electrons transferred
to graphene channels, causing the FETs to exhibit n-type electric
behavior. In addition, the Dirac points of the graphene recovered
to their original state within 5 min, confirming that the graphene-based
FETs were photosensitive to UV and visible light. In a bending state
with a radius of curvature greater than 2.0 cm, the carrier mobilities
of the FETs did not substantially change, demonstrating the application
possibility of the fabricated graphene-based FETs in photosensors
Heterogranular-Structured Diamond–Gold Nanohybrids: A New Long-Life Electronic Display Cathode
In the age of hand-held portable
electronics, the need for robust,
stable and long-life cathode materials has become increasingly important.
Herein, a novel heterogranular-structured diamond–gold nanohybrids
(HDG) as a long-term stable cathode material for field-emission (FE)
display and plasma display devices is experimentally demonstrated.
These hybrid materials are electrically conductive that perform as
an excellent field emitters, viz. low turn-on field of 2.62 V/μm
with high FE current density of 4.57 mA/cm<sup>2</sup> (corresponding
to a applied field of 6.43 V/μm) and prominently high lifetime
stability lasting for 1092 min revealing their superiority on comparison
with the other commonly used field emitters such as carbon nanotubes,
graphene, and zinc oxide nanorods. The process of fabrication of these
HDG materials is direct and easy thereby paving way for the advancement
in next generation cathode materials for high-brightness FE and plasma-based
display devices
Enhanced Electron Field Emission Properties of Conducting Ultrananocrystalline Diamond Films after Cu and Au Ion Implantation
The
effects of Cu and Au ion implantation on the structural and
electron field emission (EFE) properties of ultrananocrystalline diamond
(UNCD) films were investigated. High electrical conductivity of 186
(Ω•cm)<sup>‑1</sup> and enhanced EFE properties with
low turn-on field of 4.5 V/μm and high EFE current density of
6.70 mA/cm<sup>2</sup> have been detected for Au-ion implanted UNCD
(Au-UNCD) films that are superior to those of Cu-ion implanted UNCD
(Cu-UNCD) ones. Transmission electron microscopic investigations revealed
that Au-ion implantation induced a larger proportion of nanographitic
phases at the grain boundaries for the Au-UNCD films in addition to
the formation of uniformly distributed spherically shaped Au nanoparticles.
In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged
in the row-like pattern were formed, and only a smaller proportion
of nanographite phases along the grain boundaries was induced. From
current imaging tunneling spectroscopy and local current–voltage
curves of scanning tunneling spectroscopic measurements, it is observed
that the electrons are dominantly emitted from the grain boundaries.
Consequently, the presence of nanosized Au particles and the induction
of abundant nanographitic phases in the grain boundaries of Au-UNCD
films are believed to be the authentic factors, ensuing in high electrical
conductivity and outstanding EFE properties of the films
Investigations on Diamond Nanostructuring of Different Morphologies by the Reactive-Ion Etching Process and Their Potential Applications
We report the systematic studies
on the fabrication of aligned, uniform, and highly dense diamond nanostructures
from diamond films of various granular structures. Self-assembled
Au nanodots are used as a mask in the self-biased reactive-ion etching
(RIE) process, using an O<sub>2</sub>/CF<sub>4</sub> process plasma.
The morphology of diamond nanostructures is a close function of the
initial phase composition of diamond. Cone-shaped and tip-shaped diamond
nanostructures result for microcrystalline diamond (MCD) and nanocrystalline
diamond (NCD) films, whereas pillarlike and grasslike diamond nanostructures
are obtained for Ar-plasma-based and N<sub>2</sub>-plasma-based ultrananocrystalline
diamond (UNCD) films, respectively. While the nitrogen-incorporated
UNCD (N-UNCD) nanograss shows the most-superior electron-field-emission
properties, the NCD nanotips exhibit the best photoluminescence properties,
viz, different applications need different morphology of diamond nanostructures
to optimize the respective characteristics. The optimum diamond nanostructure
can be achieved by proper choice of granular structure of the initial
diamond film. The etching mechanism is explained by in situ observation
of optical emission spectrum of RIE plasma. The preferential etching
of sp<sup>2</sup>-bonded carbon contained in the diamond films is
the prime factor, which forms the unique diamond nanostructures from
each type of diamond films. However, the excited oxygen atoms (O*)
are the main etching species of diamond film
Role of Carbon Nanotube Interlayer in Enhancing the Electron Field Emission Behavior of Ultrananocrystalline Diamond Coated Si-Tip Arrays
We
improved the electron field emission properties of ultrananocrystalline
diamond (UNCD) films grown on Si-tip arrays by using the carbon nanotubes
(CNTs) as interlayer and post-treating the films in CH<sub>4</sub>/Ar/H<sub>2</sub> plasma. The use of CNTs interlayer effectively
suppresses the presence of amorphous carbon in the diamond-to-Si interface
that enhances the transport of electrons from Si, across the interface,
to diamond. The post-treatment process results in hybrid-granular-structured
diamond (HiD) films via the induction of the coalescence of the ultrasmall
grains in these films that enhanced the conductivity of the films.
All these factors contribute toward the enhancement of the electron
field emission (EFE) process for the HiD<sub>CNT/Si‑tip</sub> emitters,
with low turn-on field of <i>E</i><sub>0</sub> = 2.98 V/μm
and a large current density of 1.68 mA/cm<sup>2</sup> at an applied
field of 5.0 V/μm. The EFE lifetime stability under an operation
current of 6.5 μA was improved substantially to τ<sub>HiD/CNT/Si‑tip</sub> = 365 min. Interestingly, these HiD<sub>CNT/Si‑tip</sub> materials also show enhanced plasma illumination behavior, as well
as improved robustness against plasma ion bombardment when they are
used as the cathode for microplasma devices. The study concludes that
the use of CNT interlayers not only increase the potential of these
materials as good EFE emitters, but also prove themselves to be good
microplasma devices with improved performance
Macroscopic, Freestanding, and Tubular Graphene Architectures Fabricated <i>via</i> Thermal Annealing
Manipulation of individual graphene sheets/films into specific architectures at macroscopic scales is crucially important for practical uses of graphene. We present herein a versatile and robust method based on annealing of solid carbon precursors on nickel templates and thermo-assisted removal of poly(methyl methacrylate) under low vacuum of ∼0.6 Pa for fabrication of macroscopic, freestanding, and tubular graphene (TG) architectures. Specifically, the TG architectures can be obtained as individual and woven tubes with a diameter of ∼50 μm, a wall thickness in the range of 2.1–2.9 nm, a density of ∼1.53 mg·cm<sup>–3</sup>, a thermal stability up to 600 °C in air, an electrical conductivity of ∼1.48 × 10<sup>6</sup> S·m<sup>–1</sup>, and field emission current densities on the order of 10<sup>4</sup> A·cm<sup>–2</sup> at low applied electrical fields of 0.6–0.7 V·μm<sup>–1</sup>. These properties show great promise for applications in flexible and lightweight electronics, electron guns, or X-ray tube sources