8 research outputs found
The Essential Role of Cu Vapor for the Self-Limit Graphene via the Cu Catalytic CVD Method
Because of the inconsistent observations,
the Cu catalytic decomposition
of methane for graphene synthesis is reexamined, i.e., via the surface
absorption, decomposition to atomic carbon, and segregation. Here,
we experimentally show the quantity of ambient Cu vapor is the key
factor in graphene synthesis, which influences the dropwise condensations
for airborne Cu clusters during growth. The massive carburization
in Cu clusters and the calculation of carbon solubility in nanosized
clusters are performed, experimented, and further examined from the
growth of diamond-like-carbon films and ball-like diamonds via Cu
vapor assisted growth on SiO<sub>2</sub>. The affinitive interactions
between Cu vapor, ambient gases, and solid surface are embodied. By
combining the molecular dynamics for the redeposited Cu clusters to
surface, the vehicle theory of Cu clusters, which transports the atomic
carbon to the surface and completes the graphene growth, is thus proposed
as the essential puzzle we considered
Low Temperature Growth of Graphene on Glass by Carbon-Enclosed Chemical Vapor Deposition Process and Its Application as Transparent Electrode
A novel carbon-enclosed chemical
vapor deposition (CE-CVD) to grow
high quality monolayer graphene on Cu substrate at a low temperature
of 500 °C was demonstrated. The quality of the grown graphene
was investigated by Raman spectra, and the detailed growth mechanism
of high quality graphene by the CE-CVD process was investigated in
detail. In addition to growth of high quality monolayer graphene,
a transparent hybrid few-layer graphene/CuNi mesh electrode directly
synthesized by the CE-CVD process on a conventional glass substrate
at the temperature of 500 °C was demonstrated, showing excellent
electrical properties (∼5 Ω/□ @ 93.5% transparency)
and ready to be used for optical applications without further transfer
process. The few-layer graphene/CuNi mesh electrode shows no electrical
degradation even after 2 h annealing in pure oxygen at an elevated
temperature of ∼300 °C. Furthermore, the few-layer graphene/CuNi
mesh electrode delivers an excellent corrosion resistance in highly
corrosive solutions such as electroplating process and achieves a
good nucleation rate for the deposited film. Findings suggest that
the low temperature few-layer graphene/CuNi mesh electrode synthesized
by the CE-CVD process is an excellent candidate to replace indium
tin oxide (ITO) as transparent conductive material (TCM) in the next
generation
Large Scale and Orientation-Controllable Nanotip Structures on CuInS<sub>2</sub>, Cu(In,Ga)S<sub>2</sub>, CuInSe<sub>2</sub>, and Cu(In,Ga)Se<sub>2</sub> by Low Energy Ion Beam Bombardment Process: Growth and Characterization
One-step facile methodology to create
nanotip arrays on chalcopyrite materials (such as CuInS<sub>2</sub>, CuÂ(In,Ga)ÂS<sub>2</sub>, CuInSe<sub>2</sub>, and CuÂ(In,Ga)ÂSe<sub>2</sub>) via a low energy ion beam bombardment process has been demonstrated.
The mechanism of formation for nanotip arrays has been proposed by
sputtering yields of metals and reduction of metals induced by the
ion beam bombardment process. The optical reflectance of these chalcopyrite
nanotip arrays has been characterized by UV–vis spectrophotometer
and the efficient light-trapping effect has been observed. Large scale
(∼4′′) and high density (10<sup>10</sup> tips/cm<sup>2</sup>) of chalcopyrite nanotip arrays have been obtained by using
low ion energy (< 1 kV), short processing duration (< 30 min),
and template-free. Besides, orientation and length of these chalcopyrite
nanotip arrays are controllable. Our results can be the guide for
other nanostructured materials fabrication by ion sputtering and are
available for industrial production as well
Single CuO<sub><i>x</i></sub> Nanowire Memristor: Forming-Free Resistive Switching Behavior
CuO<sub><i>x</i></sub> nanowires
were synthesized by a low-cost and large-scale electrochemical process
with AAO membranes at room temperature and its resistive switching
has been demonstrated. The switching characteristic exhibits forming-free
and low electric-field switching operation due to coexistence of significant
amount of defects and Cu nanocrystals in the partially oxidized nanowires.
The detailed resistive switching characteristics of CuO<sub><i>x</i></sub> nanowire systems have been investigated and possible
switching mechanisms are systematically proposed based on the microstructural
and chemical analysis via transmission electron microscopy
Large-Scale Micro- and Nanopatterns of Cu(In,Ga)Se<sub>2</sub> Thin Film Solar Cells by Mold-Assisted Chemical-Etching Process
A reactive mold-assisted chemical etching (MACE) process through an easy-to-make agarose stamp soaked in bromine methanol etchant to rapidly imprint larger area micro- and nanoarrays on CIGS substrates was demonstrated. Interestingly, by using the agarose stamp during the MACE process with and without additive containing oil and triton, CIGS microdome and microhole arrays can be formed on the CIGS substrate. Detailed formation mechanisms of microstructures and the chemical composition variation after the etching process were investigated. In addition, various microand nanostructures were also demonstrated by this universal approach. The microstructure arrays integrated into standard CIGS solar cells with thinner thickness can still achieve an efficiency of 11.22%, yielding an enhanced efficiency of ∼18% compared with that of their planar counterpart due to an excellent absorption behavior confirmed by the simulation results, which opens up a promising way for the realization of high-efficiency micro- or nanostructured thin-film solar cells. Finally, the complete dissolution of agarose stamp into hot water demonstrates an environmentally friendly method by the mold-assisted chemical etching process through an easy-to-make agarose stamp
Enhanced Conversion Efficiency of Cu(In,Ga)Se<sub>2</sub> Solar Cells via Electrochemical Passivation Treatment
Defect control in CuÂ(In,Ga)ÂSe<sub>2</sub> (CIGS) materials, no matter what the defect type or density,
is a significant issue, correlating directly to PV performance. These
defects act as recombination centers and can be briefly categorized
into interface recombination and Shockley–Read–Hall
(SRH) recombination, both of which can lead to reduced PV performance.
Here, we introduce an electrochemical passivation treatment for CIGS
films that can lower the oxygen concentration at the CIGS surface
as observed by X-ray photoelectron spectrometer analysis. Temperature-dependent <i>J–V</i> characteristics of CIGS solar cells reveal that
interface recombination is suppressed and an improved rollover condition
can be achieved following our electrochemical treatment. As a result,
the surface defects are passivated, and the power conversion efficiency
performance of the solar cell devices can be enhanced from 4.73 to
7.75%
Non-antireflective Scheme for Efficiency Enhancement of Cu(In,Ga)Se<sub>2</sub> Nanotip Array Solar Cells
We present systematic works in characterization of CIGS nanotip arrays (CIGS NTRs). CIGS NTRs are obtained by a one-step ion-milling process by a direct-sputtering process of CIGS thin films (CIGS TF) without a postselenization process. At the surface of CIGS NTRs, a region extending to 100 nm in depth with a lower copper concentration compared to that of CIGS TF has been discovered. After KCN washing, removal of secondary phases can be achieved and a layer with abundant copper vacancy (V<sub>Cu</sub>) was left. Such compositional changes can be a benefit for a CIGS solar cell by promoting formation of Cd-occupied Cu sites (Cd<sub>Cu</sub>) at the CdS/CIGS interface and creates a type-inversion layer to enhance interface passivation and carrier extraction. The raised V<sub>Cu</sub> concentration and enhanced Cd diffusion in CIGS NTRs have been verified by energy dispersive spectrometry. Strengthened adhesion of Al:ZnO (AZO) thin film on CIGS NTRs capped with CdS has also been observed in SEM images and can explain the suppressed series resistance of the device with CIGS NTRs. Those improvements in electrical characteristics are the main factors for efficiency enhancement rather than antireflection
Surface Plasmon-Driven Water Reduction: Gold Nanoparticle Size Matters
Water reduction under two different
visible-light ranges (λ
> 400 nm and λ > 435 nm) was investigated in gold-loaded
titanium
dioxide (Au-TiO<sub>2</sub>) heterostructures with different sizes
of Au nanoparticles (NPs). Our study clearly demonstrates the essential
role played by Au NP size in plasmon-driven H<sub>2</sub>O reduction
and reveals two distinct mechanisms to clarify visible-light photocatalytic
activity under different excitation conditions. The size of the Au
NP governs the efficiency of plasmon-mediated electron transfer and
plays a critical role in determining the reduction potentials of the
electrons transferred to the TiO<sub>2</sub> conduction band. Our
discovery provides a facile method of manipulating photocatalytic
activity simply by varying the Au NP size and is expected to greatly
facilitate the design of suitable plasmonic photocatalysts for solar-to-fuel
energy conversion