Transmittance spectra of CuAlO2 coatings from both electrospray and. a) and (b) SE micrographs of CuAlO2:1%Y fibers electrospun on quartz; (c). The photoluminescence properties introduced by lanthanide ion doping and the effects of trivalent dopants on the electrical properties are investigated.
Background on p-type transparent conducting oxides (TCOs)
Delafossite and its anisotropic properties
At longer wavelengths, reflection occurs due to the plasma edge and light cannot be transmitted. Based on some calculation results2, it is predicted that the substitution doping will increase the density of states at the top of the valence band.
Optical properties of CuAlO 2
2,45,46 recently showed that the 3d states of the trivalent Al site and the involvement of trivalent ions in the formation of the valence band is important for the delocalization of the hole states of CuAlO2. The origin of the two bands derives from Cu 3d-4s hybridization, in which the 3d level split into two sub-bands.
Constructing a multifunctional nanomaterial
However, at both room and low temperatures, the FWHM of the UV emission was ∼34 nm. By up- and down-conversion of the IR and UV light, the p-type TCOs can convert the non-visible light into visible region, which can be secondarily used or collected by other devices.
Electrohydrodynamic fabrication of novel ceramics
Basic instrumentation
Although electrohydrodynamic processing was originally designed for polymeric products, it is also capable of producing ceramics from chemical solutions or suspensions. A general arrangement of electrohydrodynamic processing with droplets or a single fiber emerging from the capillary under the forward bias electric field.
Electrohydrodynamic processing on tuning the microstructures
In this regard, the scaling law of the average droplet size d can be expressed as a function of the electrical conductivity of the liquid liquid, K, and the flow rate Q77. The dimension of the fiber at the terminal is a function of the surface tension , the dielectric constant , the flow rate Q, the electric current I, the radius of curvature of the beat R and the radius of the starting current.
One-dimensional phosphors derived from electrospinning
The aligned fiber structure or other patterned microstructure requires the modification of the electric field distribution between the two electrodes. In fact, size and shape of the phosphor have an important influence on the emission intensity and the efficiency of the device.
Introduction
Experimental
- Acrylamide gelling route
- Sol-gel route
- Electrohydrodynamic setup
- Calcination and annealing equipments
- Materials Charaterizations
The feeding process of the syringe was controlled by an automatic pump (Single Syringe Infusion Pump, Cole-Parmer, Vernon Hills, IL). A Fourier transform Raman spectrometer (Thermo Nicolet 6700) was used to record room temperature Raman spectra of the delafossite samples.
Electrospray synthesis of CuAlO 2 thin films by acrylamide gelling route
The tilted view in Figure 10(b) shows some roughness on the ash spray film, indicating the coalescence and overlapping of the droplet. After calcination, the color of the film appeared dark brown and showed permeability of.
Electrospinning of CuAlO 2 fibers by a modified sol-gel method
Furthermore, the size of the spun polymer droplet is significantly larger than that of the electrospray, which further implies that the droplet size is increased due to the introduction of PVP. Due to the increase in viscosity, the point along the length direction was elongated in the electric field. The fiber dimension was measured with Nanomeasure software and is shown in Figure 21(c).
It could be seen that the average fiber diameter is ~160 nm and most of the fibers fall within a narrow range, indicating that the fibers prepared by electrospinning are quite uniform. SEM images of the CuAlO2 ceramic fibers calcined at 1100 ºC for 3 h, at low (a) and high (b) magnifications: (c) Fiber diameter distribution with.
Summary
The microstructure development as well as the influence of electrospinning parameters such as tension and viscosity on fiber morphologies have been discussed in the previous chapter. The electrohydrodynamic behavior of a drop during the electrospinning process is more complicated than the electrospray process. 111,112 suggested that the straight jet could be stabilized only at a small distance from the nozzle.
Several models have been developed to model the polymer jet electrospinning process, such as the Lattice Boltzmann method113, the linear Maxwell method112,114 and the nonlinear Maxwell method with top convection115. In the first part of this chapter, a mathematical model derived from Reneker's model was used to simulate the jet path.
Mathmatical model and coding
In Figure 23, there are two other force components acting on bead i, which are Coulombic force and surface tension of opposite direction. Given the electric force (4) viscoelastic force (5), Coulombic force (9) and surface tension (10), the total force applied to bead i during electrospinning can be written as:. beads position can be assigned ri=ixi+jyi+kzi). To solve this equation, a differential equation solver ode45 in MATLAB (version: . R2014a, MathWorks, Natick, MA) was used.
Based on equation (12), the position of the ball in a certain integrated time and the velocity can be calculated. The main program consists of initial conditions, electrospinning parameters and the partial differential equation derived from equation (12).
Predicting the terminal fiber diameter during electrospinning
In this case, the viscosity of the bead was modified and the simulation results were compared with the experimental results. CuAlO2 is a typical p-type transparent oxide that has a wide band gap (>3eV) and room temperature photoluminescence due to the UV near-band-edge emission through the recombination of free excitons 117-120. The direct transition of carriers from valence band to conduction band and the recombination of free excitons lead to the luminescence in the UV range.
The size of M3+ cation corresponds to the stretching or relaxation in the Cu-O bond and therefore affects the electronic density and photoluminescence spectra. Furthermore, near-band-edge emission at room temperature was identified and the dielectric constant could be estimated in the high-frequency region.
Charaterization of Y 3+ -doped CuAlO 2 thin films
In this work, ceramic EHD-treated CuAlO2 thin films and nanofibers have been fabricated in their shape on quartz substrates for luminescence characterizations. The effective mass along with band gap enhancement could be extracted from these transparent fiber coated samples to quantify the intercalation of yttrium affecting the host band edge. useful for a better understanding of the doping mechanisms compared to divalent doping, which may increase the charge complexity and obscure some underlying phenomena. Summary of electrical properties of electrosprayed CuAlO2 thin films:. a) Temperature dependent DC conductivity; (b) Four-probe V-I curve;.
The fortune of electrohydrodynamics is its simplicity in producing nanostructured coatings or thin films with high transparency in the visible region, which is greatly favored by transparent conducting oxides. Samples can be easily deposited on glass or quartz substrates due to the strong attractive force between the charged jet and the grounded collector.
Blueshift in near-band-edge emission in Y 3+- doped CuAlO 2 nanofibers
The degree of band gap enhancement is also consistent with the blue shift observed in the PL spectra. The bulk bandgap was measured as the optical direct bandgap of the diffuse UV reflection. Calculation of the band gap improvement based on theoretical estimates of UV-visible optical properties and the experimental data from both PL.
This would suggest that band gap enhancement values could be calculated solely from crystallite size. The 4d orbitals formed by the Y3+ dopant at the lower edge of the conduction band caused additional adjustments to the band gap.
Summary
Assuming that CuAlO2 and CuYO2 have similar electron density maps127, then the reduced mass may be the cause of the corresponding Burstein-Moss band gap enhancement (shown in the inset of Figure 33), which shows a similar magnitude of enhancement with the fit deviations from quantum size model. The prominent coupling between the reduced mass and the Cu-O distance shows that hole accumulation can be improved by the substitution of Y3+ in the M3+ site. CuAlO2 may be a promising host material in which the Al site can be replaced with various trivalent rare earth dopants, without changing the hole transport within the Cu+ level 128 .
Since the main conduction pathway in delafossite crystals is close-packed layers of Cu+129, electrical properties could be preserved in addition to photoluminescence properties. The Eu3+ activator center was successfully doped into the Al3+ site, and this delaphosite-type material could be used as a potential host for luminescence applications.
Down-conversion in Eu 3+ doped CuAlO 2
Above this doping level, the intensity drops significantly due to the concentration damping effect19,20 shown in Fig. 40(c). As the Eu3+ concentration increases, cross-relaxation becomes dominant due to the reduced distance between two Eu3+ activator ions. This could be attributed to the exchange of Eu cations, which caused lattice distortion and increased hole concentrations.
On the other hand, the substitution of Eu on the Al site can introduce a smaller band gap associated with CuEuO2, and this modification at the near band edge can also contribute to the improvement of the hole conductivity. 6 could lead to the conjecture that the change in thermal activation may be due to the different band gaps induced by Eu partial substitution, since the band gaps decrease with the increase in Eu concentration.
Photoluminescence of CuAlO 2 doped with selected trilavent ions
Following a similar trend of monotonic increase as shown in Figure 35, the partial co-substitution results in the expansion of the cell. The lattice change in the AlO6 octahedron also leads to a change in the ligand field, which is supported by photoluminescence spectra in the Eu-doped samples. When all Al sites were substituted with Mg and Si ions, no luminescence is detected in the visible region, probably due to the absence of delafossite phase.
Furthermore, compared to the previous Y- and Eu-doped samples, there is a clear blue shift in the co-doping scenarios. The plausible reasons may lie in the fact that the non-stoichiometric O defect that dominates the hole carrier conductivity is sensitive to oxygen partial pressure and the as-synthesized CuAlO2.
Results and discussion
Compared to the TG/DTA curves in flowing nitrogen with lower oxygen partial pressure, the onset temperature for CuAlO2 formation in SPS is even lower. This could be due to the secondary decomposition of the formed CuAlO2 due to the long residence time required to consolidate the pellets during the pressureless sintering. Due to the different phase configurations, the conductivity varies, with the Cu-rich sample showing the highest conductivity, followed by the phase-pure CuAlO2 by SPS reactive sintering at 800 ºC.
CuAlO2 can also emit light in the UV-blue region at room temperatures due to excitation near the band edge, which could be considered as a sensitive approach to confirm phase purity and examine crystallinity. There is a small band at ~600 nm that could be attributed to emission near the band edge from the CuAl2O4 phase.
Summary
Moralles, "Influence of Cd Impurity on the Electronic Properties of CuAlO2 Delafossite: First-Principles Calculations", J. 34; Effects of Citric Acid on Properties of Single-Phase CuAlO2 Thin Films Derived by Chemical Solution Deposition", J. Çelik, "Annealing Effects on the Properties of Copper Oxide Thin Films Prepared by Chemical Deposition", Semicond.
Yan, “Annealing effect on the structural, optical and electrical properties of CuAlO2 films deposited by Magnetron Sputtering,” J. Fu, “Effects of Mg substitution on the structural, optical and electrical properties of CuAlO2 thin films,” J.
Matlab code
Table of variables
Code using ODE45 solver
Publication list
Electrohydrodynamic processing and optical materials
Ceramics Sintering, Solid-state single crystal conversion and others
