Ayse Turak
McMaster University, Engineering Physics, Faculty Member
In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, using 3D-printing. As these types of devices are sensitive to moisture and oxygen,... more
In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, using 3D-printing. As these types of devices are sensitive to moisture and oxygen, such a chamber can aid researchers in characterizing the electronic and stability properties. The chamber is intended to be used as a temporary, reusable, and stable environment with controlled properties (including humidity, gas introduction, and temperature). It can be used to protect air-sensitive materials or to expose them to contaminants in a controlled way for degradation studies. To characterize the properties of the chamber, we outline a simple procedure to determine the water vapor transmission rate (WVTR) using relative humidity as measured by a standard humidity sensor. This standard operating procedure, using a 50% infill density of polylactic acid (PLA), results in a chamber that can be used for weeks without any significant loss of device properties. The versatility and ease of use of the chamber allows it to be adapted to any characterization condition that requires a compact-controlled atmosphere.
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The coordination environments of iron (Fe) in Fe-N-C catalysts determine their intrinsic activities toward oxygen reduction reactions (ORR). The precise atomic-level regulation of the local coordination environments is thus of critical... more
The coordination environments of iron (Fe) in Fe-N-C catalysts determine their intrinsic activities toward oxygen reduction reactions (ORR). The precise atomic-level regulation of the local coordination environments is thus of critical importance yet quite challenging to achieve. Here, atomically dispersed Fe-N-C catalyst with O-Fe-N2C2 moieties is thoroughly studied for ORR catalysis. Advanced synchrotron X-ray characterizations, along with theoretical modeling, explicitly unraveled the penta-coordinated nature of the Fe center in the catalytic domain and the energetically optimized ORR pathways on the well-tailored O-Fe-N2C2 moieties. The combined structure identification from both experiments and theory provides an opportunity to understand the role of the coordination environments in directing the catalytic activity of single-atom or single-site catalysts; not only the center metal atom but also the whole coordinating atoms participate in the catalytic cycle.
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Research Interests: Engineering, Materials Science, Thermodynamics, Chemistry, PHOTOELECTRON SPECTROSCOPY, and 12 moreX Rays, Diffusion, Reaction-Diffusion Systems, Physical sciences, Work Organization, Metal, Alloy, Chemical Reaction, X Ray Photoelectron Spectroscopy, Cathode, X Ray Spectroscopy, and Light Emitting Diode
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Laboratories are critical to undergraduate education in most STEM disciplines. In principle, they provide opportunities to apply theoretical knowledge, build psychomotor skills and engage in problem solving exercises with an emphasis on... more
Laboratories are critical to undergraduate education in most STEM disciplines. In principle, they provide opportunities to apply theoretical knowledge, build psychomotor skills and engage in problem solving exercises with an emphasis on experiential learning. As engineering laboratory modules require significant resources and physical laboratories are not well suited to on-line and blended learning approaches, there has been significant interest in producing virtual experiences that mimic, replace or supplement physical in-person labs. Designing these experiences poses challenges and opportunities for educators – particularly in finding the right balance of pedagogical value and student engagement. In this contribution, we examine the role of having students as partners in designing a virtual lab to be used for a second year engineering statistical thermodynamics class at McMaster University. In this we used a qualitative interview approach to examine how the student perspective can affect development of virtual labs. Though the instructor and student see similar goals in general for laboratory experiences, they have differing views on what constitutes the explicit and implicit goal. For the faculty member, the explicit goal is to foster a practical connection to abstract theoretical concepts, with the implicit goal of discovery and creativity. For the student, the opposite was the case. The lab gave an explicit opportunity for discovery, problem solving and critical thinking, with the generalizability of the concepts or connection to theory as of secondary importance. Having these two perspectives can allow the development of much more engaging experiences for the students with much less turmoil for the educator. By the end of the session, audiences should have an understanding of the benefits of incorporating student involvement, as well as tools, such as the student engagement-pedagogy nexus, as a guide to best practices in involving student input
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Micelle templating has emerged as a powerful method to produce monodisperse nanoparticles. Herein, we explore unconventional phase transformations in the synthesis of organo-halide perovskite nanoparticles utilizing reverse micelle... more
Micelle templating has emerged as a powerful method to produce monodisperse nanoparticles. Herein, we explore unconventional phase transformations in the synthesis of organo-halide perovskite nanoparticles utilizing reverse micelle templates. We employ diblock-copolymer reverse micelles to fabricate these nanoparticles, which confines ions within micellar nanoreactors, retarding reaction kinetics and facilitating perovskite cage manipulation. The confined micellar environment exerts pressure on both precursors and perovskite crystals formed inside, enabling stable phases not typically observed at room temperature in conventional synthesis. This provides access to perovskite structures that are otherwise challenging to produce. The hydrophobic shell of the micelle also enhances perovskite stability, particularly when combined with anionic exchange approaches or large aromatic cations. This synergy results in long-lasting stable optical properties despite environmental exposure. Rever...
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We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone... more
We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m2. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq)3 as phosphorescent red dopant in electron transport layer.
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X-ray photoelectron spectroscopy was used to study the growth of oxides on the surface of Al and Mg films with and without a thin LiF coating under ambient conditions. At thicknesses typically used in optoelectronic device cathodes, LiF... more
X-ray photoelectron spectroscopy was used to study the growth of oxides on the surface of Al and Mg films with and without a thin LiF coating under ambient conditions. At thicknesses typically used in optoelectronic device cathodes, LiF does not completely cover the surface, likely forming islands on the metal surface. On Al, 10 A LiF (61% coverage) is sufficient to significantly decrease oxidation. The passivation of Al surfaces is enhanced due to a diffusion dominated oxidation mechanism, with metal ions diffusing through the LiF islands. LiF coated Mg, on the other hand, shows preferential oxidation to form MgCO 3 on the surface. These changes in the oxidation of the surface due to the introduction of a LiF layer can be used to explain the recent results for organic light-emitting devices. Bulk lattice constants can be used as a guide to predicting oxidation resistance, with matching interlayers providing better resistance in devices than nonmatching ones.
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Both n and p-type Si(100) surfaces, treated by various methods, have been investigated as electrodes for hole injection in organic light-emitting devices. It was found that the Fermi level of silicon dictates the device characteristics.... more
Both n and p-type Si(100) surfaces, treated by various methods, have been investigated as electrodes for hole injection in organic light-emitting devices. It was found that the Fermi level of silicon dictates the device characteristics. The surface Fermi level, which can be varied by doping and surface states, has been found to be a good reference level for controlling the hole injection barrier.
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Al/LiF cathode/organic is known to form an excellent interface for electron injection into the organic active layer, resulting in excellent performing organic light-emitting diodes (OLEDs). Here, the chemical structure of the interface... more
Al/LiF cathode/organic is known to form an excellent interface for electron injection into the organic active layer, resulting in excellent performing organic light-emitting diodes (OLEDs). Here, the chemical structure of the interface between the Al/LiF bilayer cathode and tris (8-hydroxyquinoline) aluminum (Alq) of working OLED devices was investigated by using x-ray photoelectron spectroscopy (XPS). Using a in situ peel-off technique, we are able to characterize the buried interface structure without disturbing the chemical states of each element probed. The data show that there are two types of F at the interface; one is attributed to LiF and the other to F attached to the Alq. This F-doped Alq layer could induce a downshift in molecular orbital levels and thus leads to a reduced electron injection barrier. XPS depth profile results show significant O diffusion through Al layer to the interface, and the diffusion of O ends abruptly at the Al/LiF interface.
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ABSTRACT After efficiency, lifetime is the second most important parameter for organic devices. Interfaces play a major role in that lifetime. This article reviews the current state of the art with regards to interfacial stability and... more
ABSTRACT After efficiency, lifetime is the second most important parameter for organic devices. Interfaces play a major role in that lifetime. This article reviews the current state of the art with regards to interfacial stability and control of electrode/active layer interfaces to understand the performance of organic optoelectronic devices. From examples relating to interfacial chemical reactions, interfacial morphological changes, and interfacial electronic level modification, a comprehensive picture of the role of the organic–electrode interfaces in device stability can be formed. The review begins with a brief overview of degradation in organic devices, including definitions and measurement approaches. It is then broken into two sections. The first focuses on the bottom contact (substrate) interface, specifically chemical reactions and dewetting, as the two main mechanisms of device degradation. The second section examines the top contact interface, which is prone to oxidation, interdiffusion, blistering and delamination, and inhomogeneous loss of performance (dark spots). For both sections, various approaches to overcoming device instabilities are given, with special attention to the various interlayers that have been introduced into devices for improved stability. Each section also includes examples where the main degradation mechanism is used advantageously to produce novel device architectures and surprising solutions to device degradation.
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CO<inf>2</inf> at room temperature and up to 1100psi was used to change the phase of micellar polystyrene-block-poly (2-vinylpyridine). FeCl3 filled micelles subjected to the process formed a phase which resulted in α -... more
CO<inf>2</inf> at room temperature and up to 1100psi was used to change the phase of micellar polystyrene-block-poly (2-vinylpyridine). FeCl3 filled micelles subjected to the process formed a phase which resulted in α - Fe2O<inf>3</inf> nanowires after plasma etching. Particles which were subjected to only a brief CO<inf>2</inf> process formed γ- Fe<inf>2</inf>O<inf>3</inf>
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ABSTRACTThe electroluminescent characteristics of blue organic light-emitting diodes(BOLEDs) were fabricated with single emitting layer using host-dopant system and doped charge carrier transport layers. The structure of the high... more
ABSTRACTThe electroluminescent characteristics of blue organic light-emitting diodes(BOLEDs) were fabricated with single emitting layer using host-dopant system and doped charge carrier transport layers. The structure of the high efficiency BOLED device was; NPB(600Å)/NPB:BCzVBi-7%(100Å)/ADN:BCzVBi-7%(300Å)/BAlq:BCzVBi-7%(100Å)/BAlq(200Å)/Liq(20Å)/Al(1200Å) to optimize probability of exciton generation by doping BCzVBi in emitting layer and hole/electron transport layers(HTL/ETL) as well. Luminance and luminous efficiency of BOLED doped BCzVBi in EML and HTL/ETL improved from 10090 cd/m2 at 9.5V and 6.44 cd/A at 4.0V to 13190 cd/m2 at 9.5V and 7.64 cd/A at 4.0V about 30% and 18%, respectively, with CIE coordinates of (0.14, 0.17) comparing to BOLED doped BCzVBi in EML only
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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... more
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 properties.
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The effect of doped buffer layers at the anode/organic interface in small molecule organic light-emitting diodes was investigated. Appropriate doping of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and... more
The effect of doped buffer layers at the anode/organic interface in small molecule organic light-emitting diodes was investigated. Appropriate doping of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and Cu-phthalacyanine (CuPc) layers using LiF or C60 molecules leads to improved interfacial morphology and thermal stability for both standard indium tin oxide or metals anodes, such as Au and Ag. Graded interfaces remain stable at temperatures well above the hole transport layer (i.e., NPB) glass transition temperature.
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Nanoparticles synthesized by reverse micelle templating cannot be formed directly on the top of active layer in organic and perovskite devices. In this work, we show a method of transferring the synthesized nanoparticles on top of an... more
Nanoparticles synthesized by reverse micelle templating cannot be formed directly on the top of active layer in organic and perovskite devices. In this work, we show a method of transferring the synthesized nanoparticles on top of an organic layer using a graphene based transfer printing technique. To confirm the successful transfer of nanoparticles, perovskite based methylammonium lead bromide (MAPBr) nanoparticles were used and their presence confirmed by Photoluminescence (PL).
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The combination of molecularly imprinted polymers (MIPs) and inverse opals (IO) have been a point of interest in the past few years due to their potential in sensing applications. At the same time, peptide nucleic acid (PNA) is a stable... more
The combination of molecularly imprinted polymers (MIPs) and inverse opals (IO) have been a point of interest in the past few years due to their potential in sensing applications. At the same time, peptide nucleic acid (PNA) is a stable analogue to natural occurring genetic material. In this study, we describe the preparation and characterization of a PNA imprinted matrix, based on the controlled self-assembly of organized silica particles (SiPs) arrays. The degree of organization of the silica arrays are compared to the organization of the cavities after the removal of the SiPs, using spatial statistical analysis. This analysis of the Voronoi tessellations, pair correlation functions and bond order showed that the successfully formed arrays contain a high degree of quasi-hexagonal (hexatic) organization of the cavities, with both global and local order. The adsorption analysis of the materials show potential for developing future materials with tunable structural reflective propert...
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We report on silicon waveguide distributed Bragg reflector (DBR) cavities hybridized with a tellurium dioxide (TeO2) cladding and coated in plasma functionalized poly (methyl methacrylate) (PMMA) for label free biological sensors. We... more
We report on silicon waveguide distributed Bragg reflector (DBR) cavities hybridized with a tellurium dioxide (TeO2) cladding and coated in plasma functionalized poly (methyl methacrylate) (PMMA) for label free biological sensors. We describe the device structure and fabrication steps, including reactive sputtering of TeO2 and spin coating and plasma functionalization of PMMA on foundry processed Si chips, as well as the characterization of two DBR designs via thermal, water, and bovine serum albumin (BSA) protein sensing. Plasma treatment on the PMMA films was shown to decrease the water droplet contact angle from ∼70 to ∼35°, increasing hydrophilicity for liquid sensing, while adding functional groups on the surface of the sensors intended to assist with immobilization of BSA molecules. Thermal, water and protein sensing were demonstrated on two DBR designs, including waveguide-connected sidewall (SW) and waveguide-adjacent multi-piece (MP) gratings. Limits of detection of 60 and ...