Cleva W Ow-Yang

• Ph.D.
• Staff Scientist, TEM Field Applications at Thermo Fisher Scientific

Although ambient processing is the key to low-cost organic solar cell production, high-vacuum thermal evaporation of LiF is often a limiting step, motivating the exploration of solution processing of LiF as an alternative electrode interlayer. Submonolayer films are realized with the assistance of polymeric micelle reactors that enable LiF particle...

Long persistence phosphors are promising materials for energy‐saving applications, due to their ability to temporarily store and release light. While boron is known to dramatically extend the afterglow persistence to longer than 8 h in strontium aluminates, previous attempts to understand the role of boron neglected any nanoscale‐related effects an...

Ceramic pigments emitting long afterglow have enormous potential for emerging lighting applications that consume zero energy from the power grid. One of the most efficient compounds is strontium aluminate, when co-doped with 2 rare-earth elements — an optically active emitter, such as Eu2+, and an auxiliary ion, such as Dy3+— and B. To date, spectr...

Recent work has shown that the incorporation of electrically charged, non-bridging oxygen (NBO) species into the doped Sr4Al14O25 (S4A7ED) crystal structure, in the form of BØ2O-, induces the clustering of divalent Eu and trivalent Dy, which is manifested as PersiL. Because other ceramic compounds exhibiting persistent luminescence also contain Si,...

This work is the supplementary information for the publication, "Borate polyanions tuning persistent luminescence in Eu and Dy co-doped strontium aluminate".

The addition of boron oxide is well‐known to dramatically extend the afterglow persistence (PersiL) from minutes to hours in Sr4Al14O25 (S4A7) co‐doped with 1 at% Eu and 1 at% Dy (S4A7EDxB), while the longest duration occurs when 30–40 mol% B2O3 is used. To elucidate the influence of B2O3 on the S4A7EDxB structure supporting PersiL, the thermodynam...

Development of restorative materials capable of mimicking optical and mechanical performance of natural teeth is a quest in aesthetic density. Yttria-Stabilized Zirconia (YSZ) ceramics represent one of the most popular choices for dental restorations, owing to their biocompatibility, white colour, and the possibility to use CAD-CAM technologies. In...

Corundum and transition alumina powders are commonly produced through the Bayer process—that is, by digestion of bauxite in a sodium hydroxide solution, followed by gibbsite precipitation, which contains significant amounts of Na⁺ ions. During the de‐hydroxylation of gibbsite, Na⁺ is associated with retardation of the structural phase transformatio...

To lower solid oxide fuel cell operating temperatures down to ≤ 700°C, we fabricated La0.8Sr0.2MnO3–Bi1.44Y0.56O3 (LSM-YDB) cathode films from a “single-pot” mixture of polymeric LSM and YDB precursors, which yielded nanocomposite-structured films with long triple phase boundary lengths. Alternating nanolayers of LSM and YDB phases were revealed by...

A powder-free solid oxide cell electrode fabrication route is demonstrated, in which a polymeric precursor, containing the cations of electrocatalyst and ionic conductor phases, is deposited onto a dense electrolyte. By this approach, the formation of a La0.8Sr0.2FeO3-Ce0.8Sm0.2O2 (LSF-SDC) nanocomposite structure because of nanoscale phase separat...

To develop a more reactive pozzolan for supplementary cementitious materials (SCMs), the co-calcination of kaolinite and limestone was investigated for its contribution to hydration of blended cement. Kaolinite (with ~50 wt% quartz impurity) was calcined at 700·°C, and a mixture of kaolinite and limestone was calcined at 800 °C. These activated SCM...

Gadolinia doped ceria (GDC) interlayers have been widely used to avoid resistive phase formation at the mixed ionic electronic conductor (MIEC) (La,Sr)CoO3 (LSC) air electrode/ yttria stabilized zirconia (YSZ) electrolyte interfaces. Although MIEC electrodes fabricated by low-temperature metal organic precursor methods offer the highest electrochem...

This work describes the development of transparent high-strength Yttria-Stabilized Zirconia (YSZ) ceramics with ultra-fine grain size utilizing conventional pressure-less densification. Starting with nanoparticles with diameter <10 nm, it was possible to achieve full densification (>99.5% of theoretical density) at a sintering temperature of 1100–1...

The main objective of the study was to produce alternative binder materials, obtained with low cost, low energy consumption, and low CO2 production, by regenerating end-of-life (EOL) materials from mineral deposits, to replace ordinary Portland cement (OPC). The materials analyzed were ash and slag from the Turceni thermal power plant deposit, Roma...

The high capacity of silicon (Si) for lithium incorporation makes it a promising anode material for lithium-ion batteries; however, pulverization of Si due to huge volume changes during lithiation/delithiation leads to significant capacity loss during cycling. To address challenges in low cyclability, nanostructured Si in carbon nanocomposites offe...

Although the longest duration of persistent luminescence in Eu and Dy co-doped strontium aluminate (S4A7ED) is obtained by processing with 30 mol% B2O3 (S4A7EDB), this composition does not contain the highest amount of the long persistence phase. To elucidate how the structural arrangement of atoms in S4A7EDB induced by synthesis using 30–40 mol% B...

Molten salt methods enable the synthesis of Si nanostructures by moderating the thermal energy evolved in highly exothermic magnesiothermic reduction reactions (MRR) of silica. Due to their cost-effectiveness and scalability, these techniques are well suited for producing nanoscale Si for a number of applications including energy storage. To contro...

It is a generally accepted perspective that type-II nanocrystal quantum dots (QDs) have low quantum yield due to the separation of the electron and hole wavefunctions. Recently, high quantum yield levels were reported for cadmium-based type-II QDs. Hence, the quest for finding non-toxic and efficient type-II QDs is continuing. Herein, we demonstrat...

Capacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy-metal content in such architectures hinders their safe use. In this s...

The article “ Exciton recycling via InP quantum dot funnels for luminescent solar concentrators ” written by Houman Bahmani Jalali ¹ ,§, Sadra Sadeghi ² ,§, Isinsu Baylam 3,4 , Mertcan Han ⁵ , Cleva W. Ow-Yang ⁶ , Alphan Sennaroglu 3,4 , and Sedat Nizamoglu 1,2,5 (✉), was originally published Online First without Open Access. After publication onli...

Luminescent solar concentrators (LSC) absorb large-area solar radiation and guide down-converted emission to solar cells for electricity production. Quantum dots (QDs) have been widely engineered at device and quantum dot levels for LSCs. Here, we demonstrate cascaded energy transfer and exciton recycling at nanoassembly level for LSCs. The graded...

Reduction of auric acid with polyethyleneimine (PEI) provides a simple, low-cost alternative for the production of cationic gold nanoparticles (GNPs). However, linear PEI (lPEI) failed to produce small, colloidally stable GNPs, so far. Since lPEI is a polyelectrolyte, pH should be an important factor both in reduction and stabilization of GNPs and...

B has been proposed to extend persistent luminescence from minutes to > 10 h in Eu, Dy, and B co-doped Sr4Al14O25 (S4A7EDB) by facilitating the incorporation of Eu²⁺ and Dy³⁺ into adjacent Sr sub-lattice sites and enabling energy transfer between them. To evaluate additional influences of B on the kinetics of microstructural evolution and dopant di...

A sustainable solution for the global construction industry can be partial substitution of Ordinary Portland Cement (OPC) by use of supplementary cementitious materials (SCMs) sourced from industrial end-of-life (EOL) products that contain calcareous, siliceous and aluminous materials. Candidate EOL materials include fly ash (FA), silica fume (SF),...

In this research, a CoFe2O4/Fe magnetic nanocomposite was successfully produced through mechanical alloying. The effects of different Fe concentrations (10, 30, and 50 wt %) and milling time (1, 3, 5, and 10 h) on the characteristics of the nanocomposite samples were systematically investigated. Single-phase CoFe2O4 nanoparticles were produced with...

The transformation of mesoporous silica morphology from monoliths to spherical particles was investigated at room temperature in Pluronic F127/TEOS system as a function of HCl acid catalyst concentration to understand and control the mechanism. It is shown that the specific surface area and the size of mesoporous spherical silica particles can simp...

Conventional composite cathodes used in solid oxide fuel cells (SOFCs) are fabricated by co-sintering of electrocatalyst and ionic conductor powders at 1100-1250 °C. The relatively high heat treatment temperatures required to ensure bonding among the powders and between the powders and electrolyte results in the formation of resistive phases and co...

Quantum dots with type-II band alignments provide benefits for optical gain, photocurrent generation, and reabsorption suppression due to their charge carriers delocalization. To date, indium phosphide possesses a great potential for optical and photovoltaic applications as an environmentally benign and relatively non-toxic heavy-metal-free quantum...

Magnetron sputtering is widely used for deposition of silicon oxynitride (SiOxNy) coatings on glass in large‐area applications. Since repeated deposition simulates the factory‐scale in‐line processing, amorphous aluminum‐doped SiOxNy layers with thickness of about 250 nm were deposited by reactive pulsed DC sputtering in a multi‐pass process with r...

Fluorescence resonance energy transfer, one of the most powerful phenomena for elucidating molecular interactions, has been extensively utilized as a biosensing tool to provide accurate information at the nanoscale. Numerous aptamer- and nanomaterial-based FRET bioassays has been developed for detection of a large variety of molecules. Affinity pro...

Magic clusters have attracted significant interest to explore the dynamics of quantum dot (QD) nucleation and growth. At the same time, CdSe magic-sized QDs reveal broadband emission in the visible wavelength region, which advantageously offer simple integration of a single-type of nanomaterial and high color rendering ability for white light-emitt...

AlSb is a less-studied member of III−V semiconductor family and herein, we report the colloidal synthesis of AlSb quantum dots for the first time. Different sizes of colloidal AlSb QDs (5 nm to 9 nm) were produced by the controlled reaction of AlCl3 and Sb[N(Si(Me)3)2]3 in the presence of superhydride. These colloidal AlSb quantum dots showed excit...

The possibility to control the structural parameters of nanostructured spinel cobalt ferrite paves the way to prepare the ferrite with the anticipated magnetic properties for broad applications. This study is aimed at elucidating the correlation between structural parameters and magnetic properties of cobalt ferrite nanoparticles subjected to post-...

In this study, natural molar human tooth specimens were investigated for determining their micro- and nanoscale structural morphology, chemistry and crystallinity. The differences were tracked comparatively for both enamel and dentin layers and at their interfaces. Although dental material structures are hard and tough and the cross-sectioning of t...

Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements...

Herein, we demonstrate that the structural and optical control of InP-based quantum dots can lead to high-performance LEDs. Zinc sulphide (ZnS) shells passivate the InP quantum dot core and increase the quantum yield in green-emitting quantum dots by 13-fold and red-emitting quantum dots by 8-fold. The optimised quantum dots are integrated in the l...

Multiplex biosensing of four types of bacterial food pathogens in one pot is described. Stokes and anti‐Stokes type photoluminescence (PL) of two quantum dots (QD) and two upconverting nanoparticles (UCNP) were utilised for realisation of the multiplex detection. The biosensing system was composed of aptamer‐functionalized QD and UCNP nanoprobes th...

Emerging applications in nanotechnology, such as superresolution imaging, ultra-sensitive biomedical detection, and heat-assisted magnetic recording, require plasmonic devices that can generate intense optical spots beyond the diffraction limit. One of the important drawbacks of surface plasmon focusing structures is their complex design, which is...

H-bonded, pH-responsive poly(2-ethyl-2-oxazoline) (PEOX) and tannic acid (TA) multilayers were prepared by layer-by-layer deposition. Free-floating PEOX/TA multilayers were shown to restructure in a pH3 phosphate buffer solution to H-bonded, pH-responsive PEOX/TA fibers. This restructuring was also evident during the growth of multilayers thicker t...

Luminescent solar concentrators (LSCs) show promise due to its potential for low-cost, large-area and high-efficiency energy harvesting. Stokes shift engineering of luminescent quantum dots is a favorable approach to suppress reabsorption losses in LSCs; however, the use of highly-toxic heavy metals in quantum dots constitutes a serious concern for...

Polyethyleneimine (PEI) is rarely recognized as a luminescent polymer but is frequently used for the production of cationic nanoparticles and tagged with an organic fluorophore to be tracked optically. Herein, a strongly luminescent, branched PEI-superparamagnetic iron oxide nanoparticle (bPEI-SPION) without a traditional fluorophore is reported. A...

In this work, we investigated the influence of Al doping on the structure of the (ZnO)5In2O3 homologous phase and the thermoelectric characteristics of (ZnO)5(In1−xAlx)2O3 ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500°C for 2 hours. The Al substituted for In on both the primary si...

For the transfer of 2-D gold nanoparticle arrays between different substrates, we have developed a new method using thermo-responsive poly-N-isopropylacrylamide (pNIPAAm). By tuning the degree of surface hydrophilicity of pNIPAAm between 5°C and 50°C, we demonstrate the transfer of arrays extending over micron-scale areas with preservation of array...

Homopolymers, such as polyvinylpyrrolidone (PVP), are commonly used to passivate the surface of blue-light emitting ZnO nanoparticles during colloid nucleation and growth. However, although PVP is known to auto-fluoresce at 400 nm, which is near the absorption edge of ZnO, the impact of PVP adsorption characteristics on the surface of ZnO and the s...

It is known that thermoelectric properties, i.e. figure of merit ZT of oxide-based polycrystalline thermoelectric materials can be improved by introducing planar faults into the microstructure of these materials. It is assumed that in-grown planar faults will reduce thermal conductivity without reducing electrical properties which would consequentl...

Homopolymers, such as polyvinylpyrrolidone (PVP), are commonly used to passivate the surface of blue-light emitting ZnO nanoparticles during colloid nucleation and growth. However, although PVP is known to auto-fluoresce at 400 nm, which is near the absorption edge of ZnO, the impact of PVP adsorption characteristics on the surface of ZnO and the s...

Although tuning organic solar cell performance can be achieved in the design of nanostructured interlayers between the active layer and the anode, elucidating the actual photophysical effects of such buried interfaces during device operation is a challenge, for which impedance spectroscopy (IS) analysis offers pivotal insight. Herein we have used I...

For determining the areal density of the nanoparticles, silicon wafer substrates were used. Because the image processing algorithm [1] relies on implementing an intensity threshold filter to define nanoparticles, we used Si substrates, which provide a uniform background. In contrast, the grain-sub-grain microstructure of ITO films produced variatio...

Homologous In2O3 (ZnO) 5 thin films were produced on a synthetic quartz glass substrate by thermal annealing of magnetron sputtered In2O3-ZnO compound films. When the annealing temperature was increased to 700 °C, the sputtered In2O3-ZnO film with In2O3 microcrystalline changed to a c-oriented homologous In2O3 (ZnO) 5 structure, for which the cry...

12th Nanoscience and Nanotechnology Conference 3-5 June 2016- Gebze Technical University- Turkey 1st place for poster presentation performance

By varying the density of solution-processed lithium fluoride (sol-LiF) nanoparticles at the interface between tin-doped indium oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), we have demonstrated that the electronic hole collection efficiency of an organic photovoltaic cell can be optimized through tuning the e...

By varying the density of solution-processed lithium fluoride (sol-LiF) nanoparticles at the interface between tin-doped indium oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), we have demonstrated that the electronic hole collection efficiency of an organic photovoltaic cell can be optimized through tuning the e...

Representing a source of short-term stored energy, strontium aluminate phosphor compounds of nominal stoichiometry (SrO) • (Al2O3)2 co-doped with 1 mol% Eu 2+ and 1 mol% Dy 3+ (SA2ED) exhibit long persistence that is even further extended by the incorporation of boron 1. To elucidate the effect of boron on afterglow persistence, we synthesized the...

Solution-processed lithium fluoride (sol-LiF) nanoparticles synthesized in polymeric micelle nanoreactors enable tuning of the surface work function of tin-doped indium oxide (ITO) films. The micelle reactors provide the means for controlling surface coverage by progressively building up the interlayer through alternating deposition and plasma etch...

The indium-tin-oxide/active layer interface is critical to the performance of organic solar cell devices. In this study, submonolayer films of LiF nanoparticles are deposited on the electrode surface with the assistance of polymeric micelle reactors, with controlled nanoscale surface coverage. Incorporation of the solution-processed bi-layer electr...

Tapping mode atomic force microscopy (TM-AFM) enables mapping of chemical composition at the nanoscale by taking advantage of the variation in phase angle shift arising from an embedded second phase. We demonstrate that phase contrast can be attributed to the variation in elastic modulus during the imaging of zinc acetate (ZnAc)-loaded reverse poly...

Emerging plasmonic and photovoltaic applications benefit from effective interaction between optical antennas and unidirectional incident light over a wide spectrum. Here, we propose a honeycomb array of plasmonic nanoantennas with broken symmetry to obtain a unidirectional radiation pattern over a wide spectrum. The honeycomb nanoantenna array is b...

We have experimentally demonstrated that the interface between ITO and Si or Si0.85Ge0.15 is metastable, with silicon reducing ITO to form an amorphous oxide layer and In metal. A 400nm-thick ITO layer was deposited on two types of substrates: p-type, 〈100〉 silicon wafers and a silicon wafer with a 400nm-thick layer of Si0.85Ge0.15 grown by CVD. An...

SrAl4O7 (SA2) phosphor powders were synthesized by using a modified Pechini process. Varying amounts of boron was incorporated into the SA2 lattice to investigate the effects on crystal structure and optical properties. X-ray spectra showed that boron addition enhances phase purity of the powder at a calcination temperature of 1000 °C, whereas the...

Single crystal films of n-type 3C-SiC were hydrothermally processed at pressures ranging from 10 to 70 MPa at 550°C. To study the effects of initial thin film microstructure on hydrothermal processing, two different samples of CVD-grown SiC were studied: one, 200 nm thick, contained low angle boundaries and a high density of planar defects; the oth...

We have developed a novel solid-state method for forming interfacial silicon dioxide by a two step process of rf sputtering tin-doped indium oxide (ITO), a transparent conductor, onto Si substrates followed by annealing at 800'C in flowing ultra-high purity nitrogen. TEM, XRD, FTIR, and C-V measurements were used to characterize the microstructure...

We report the use of reverse PS-b-P2VP diblock copolymer micelles as true nanoscale-sized reactor vessels to synthesize ZnO nanoparticles. The reverse micelles were formed in toluene and then sequentially loaded with zinc acetate dihydrate and tetramethylammonium hydroxide reactants. Moreover, high spatial resolution Z-contrast imaging and EDX spec...

Under energy-dissipative cantilevered tip-sample interaction, phase imaging using tapping-mode atomic force microscopy enables compositional mapping of composites containing a harder inorganic phase at the nanometer scale, embedded in a polymer matrix. The contrast in the phase images is shown to be dependent on the variation in the elastic propert...

Amorphous ZnO–SnO2–In2O3 films were grown by direct current magnetron sputtering from vacuum hot pressed ceramic oxide targets of Zn:In:Sn cation ratios 1:2:1 and 1:2:1.5 onto glass substrates. X-ray diffraction analysis showed that the microstructure remained amorphous during annealing at 200 °C for up to 5 hours. By monitoring the electrical resi...

We have demonstrated the synthesis of lanthanide co-doped nominally SrAl2O4 powders that phosphoresce over long durations. Previous work has reported that the color of phosphorescence depends on the nature of the alkaline earth cation, and that extended phosphorescence in Eu2+ and other lanthanide co-doped MAl2O4 (M= Sr, Ca, Ba) systems occurred wi...

Amorphous ZITO films were deposited by dc magnetron sputtering onto glass substrates from ceramic oxide targets containing Zn:In:Sn cation ratios of 1:2:1 and 1:2:1.5. The microstructure, carrier density, mobility, and resistivity of as-deposited and annealed samples were evaluated using x-ray diffraction and Hall effect measurements. The as-deposi...

Dry films: An electrospinning process was used to form films with high water contact angles (166.7°) and low sliding-angles (4.3°). The electrospun films exhibit excellent superhydrophobic Cassie-regime stability: The figure shows a nonwetting water droplet, even after 400 Pa of uniaxial loading.

The stability of the interface formed by depositing indium tin oxide (ITO) thin films on Si and Si0.85Ge0.15 substrates was investigated. Cross-sectional transmission electron microscopy combined with Fourier-transform infrared spectroscopy, energy dispersive x-ray analysis, x-ray diffraction, and capacitance-voltage measurements were used to chara...

Tin-doped indium oxide thin films are broadly used in electronics deposited onto heat-sensitive substrates, and deposition at relatively low temperatures result in amorphous film. However, semiconductor devices heat during operation, and the relatively low crystallization temperatures mandate a deeper understanding of the crystallization kinetics a...

Deposition of tin-doped-indium-oxide (ITO) on unheated substrates via low energy processes such as electron-beam deposition can result in the formation of amorphous films. The amorphous-to-crystalline transformation was studied in this system using in situ resistivity, time resolved reflectivity, glancing incidence angle x-ray diffraction, and tran...

Tin-doped indium oxide (ITO) films were deposited by dc magnetron sputtering using oxide (ITO) or alloy ITO targets. The ITO films sputter-deposited using Ar at total pressure (P-tot) lower than 1.2 Pa showed polycrystalline structure, whereas entirely amorphous films were deposited at P-tot higher than 1.4 Pa, indicating that the crystallinity of...

Amorphous tin-doped indium oxide (ITO) was deposited to a thickness of 110 nm on [100]-oriented Si substrates at similar to 40-60 degrees C by dc-magnetron sputtering under a total Ar pressure of 2 Pa. The kinetics of crystallization of the a-ITO films in flowing N-2 were investigated by in situ time-resolved reflectivity. The microstructure of the...

As a semiconductor with a centrosymmetric crystal structure, bulk GaAs is nonbirefringent and is therefore rarely used for nonlinear frequency conversion despite its attractive nonlinear coefficient. By building a multilayer system GaAs/oxidized AlAs (Alox), we have shown that high form birefringences can be obtained in the composite material. To o...

Available in film copy from University Microfilms International. Thesis (Ph. D.)--Brown University, 1998. Vita. Includes bibliographical references (leaves 6-7, 16, 36-37, 71, 108).

Thesis (Sc. M.)--Brown University, 1994. Includes bibliographical references (leaves 43-45).

Bi(Pb)-Sr-Ca-Cu-O/Ag (BSCCO/Ag) superconducting microcomposites with zero-resistance temperatures from 102 to 108 K and critical current densities of ~ 600 A/cm2 at 77 K were produced by oxidation and annealing of metallic precursor alloys. The stabilities and degradation behavior of BSCCO/Ag specimens in various environments were studied by a comb...