Konstantinos Sierros | West Virginia University (original) (raw)

Papers by Konstantinos Sierros

ACS Applied Materials & Interfaces

TiO2 is an important material widely used in optoelectronic devices due to its semiconducting and... more TiO2 is an important material widely used in optoelectronic devices due to its semiconducting and photocatalytic properties, nontoxicity, and chemically inert nature. Some indicative applications include water purification systems and energy harvesting. The use of solution, water-based inks for the direct writing of TiO2 on flexible substrates is of paramount importance since it enables low-cost and low-energy intensive large-area manufacturing, compatible with roll-to-roll processing. In this work we study the effect of crystalline TiO2 and polymer addition on the rheological and direct writing properties of Ti-organic/TiO2 inks. We also report on the bridging crystallite formation from the Ti-organic precursor into the TiO2 crystalline phase, under ultraviolet (UV) exposure or mild heat treatments up to 150 °C. Such crystallite formation is found to be enhanced by polymers with strong polarity and pKα such as polyacrylic acid (PAA). X-ray diffraction (XRD) coupled with Raman and X-ray photoelectron (XPS) spectroscopy are used to investigate the crystalline-phase transformation dependence based on the initial TiO2 crystalline-phase concentration and polymer addition. Transmission electron microscopy imaging and selected area electron diffraction patterns confirm the crystalline nature of such bridging printed structures. The obtained inks are patterned on flexible substrates using nozzle-based robotic deposition, a lithography-free, additive manufacturing technique that allows the direct writing of material in specific, digitally predefined, substrate locations. Photocatalytic degradation of methylene blue solutions highlights the potential of the studied films for chemical degradation applications, from low-cost environmentally friendly materials systems.

Sid Symposium Digest of Technical Papers, 2010

Abstract Energy efficient solid state lighting flexible and lightweight devices can offer an attr... more Abstract Energy efficient solid state lighting flexible and lightweight devices can offer an attractive alternative to bulky traditional rigid lighting solutions. We demonstrate a highly durable solid state flexible light emitting diode device and we report on critical factors during device manufacturing and use. We also propose alternative materials in order to further enhance the operational lifetime of the device.

The primary objective of this work was the fabrication and testing of a wireless LC resonator bas... more The primary objective of this work was the fabrication and testing of a wireless LC resonator based on micro-patterned electroceramic materials for the monitoring of high-temperature systems. The two-dimensional planar LC resonator sensors were designed and simulated using ANSYS Maxwell software, and these sensors were then fabricated from electrically conductive La2NiO4/Al2O3 particulate inks. The patterning and deposition of the ink were completed using a novel micro-casting process onto Al2O3 ceramic substrates, and the final pattern was bonded onto the substrate at 1200oC for 2 h. The final patterned materials were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and four-point conductivity to characterize the phase and microstructure development, and the resultant electrical conductivity (at 500-1200oC), respectively. The frequency shift with respect to temperature was measured, which is directly related to changes in the sensor’s dielectric perm...

MRS Online Proceeding Library

Solution-based fabrication methods have been widely used for depositing uniform functional coatin... more Solution-based fabrication methods have been widely used for depositing uniform functional coatings. These coatings can be utilized in a variety of applications such as optoelectronics, biomedical, and energy. However, such fabrication techniques are not appropriate for directly depositing patterned micro/nano-scale features, which are required in many contact-based applications such as in MEMS. In this work we propose the direct writing of hydrophobic silica-based sol-gel patterns with sustained functionality and their subsequent tribological characterization. Such an approach may be an advantageous alternative to current lithography-based methods due to the relative ease of processing and low material waste. This investigation involves the abrasive wear and frictional analysis of patterned fluorinated silica sol-gel coatings that are directly printed onto glass substrates with a robotically controlled pneumatic nozzle system. Such work sheds light on the tribological properties of...

Surface and Coatings Technology

Hydrophobically functional coatings can be used to protect surfaces and therefore improve the per... more Hydrophobically functional coatings can be used to protect surfaces and therefore improve the performance and lifetime of a broad range of applications such as optoelectronics and touchscreens. Organic–inorganic hybrid materials such as silica sol–gel coatings are particularly effective for this purpose, but the functional molecules in these coatings are susceptible to abrasive wear and thus lose their performance over time in the harsh environments typically encountered. To combat these problems, a silica nanoparticle-reinforced matrix was developed to increase hardness and wear resistance of the overall coating.

Thin Solid Films, 2015

There is currently a great interest in developing flexible electrodes. Such components are used i... more There is currently a great interest in developing flexible electrodes. Such components are used in most electronic devices from displays to solar cells to flexible sensors.To date most of them are fabricated using expensive vacuum techniques, and are based on transparent conducting oxides. These oxides are not entirely compatible with flexible substrates under the application of mechanical stresses, due to their brittle nature. Therefore, there is a need to explore novel lowcost, large-area fabrication methods to deposit alternative conducting materials with enhanced electro-mechanical performance. This work focuses on Ag patterns fabricated at low temperatures (below 150 o C) on flexible polyethylene naphthalate utilizing a robotic printing approach. Such lithography-free method minimizes material waste by printing exact amounts of inks on digitally predefined locations. Additionally, it allows a broad feature size range, from a few m to a few mm, and a variety of ink viscosities for better pattern control. We investigate the synthesis and direct writing of Ag particle-based inks, patterned-on-flex as lines and grids in the m scale. We report on a high-yield ink synthesis method (~61.6%) with controlled particle size. It is found that the electrical resistivity (1.75*10-4 Ω cm) of the patterns is in the same range with similar particle-based conductive components. The correlation between annealing temperature, microstructural evolution, and electrical performance is established. Also,

ABSTRACT This study demonstrates the ability to combine the dip-pen nanolithography patterning of... more ABSTRACT This study demonstrates the ability to combine the dip-pen nanolithography patterning of ZnO solutions on a polymer release layer and their subsequent transfer, after heat-treatment, to a flexible substrate. It is found that ink viscosity plays an important role in controlling both the feature size and the total number of the fabricated features. In addition, the role of the dwell time is investigated and it is observed that higher dwell times lead to both larger printed dot sizes and smaller total numbers of fabricated features. Resulting dot size is ranging from 7.2 to 1.9 μm as observed using in-situ optical microscopy. Heat treatment is found to lead to a slight shrinkage of the as-deposited patterns due to the coarsening and sintering mechanisms that are active during firing. Then, using a 75 kPa pressure and a hot plate set at 190 °C for 10 min, the fired ZnO patterns are transferred on a flexible polyethylene naphthalate substrate. The ability to effectively transfer high temperature-treated functional nano/micro-patterns on polymer substrates may be proved vital for the development of large-area flexible optoelectronic device applications.

Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered o... more Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered on polyethylene terephthalate (PET) substrates, is an issue of paramount importance in flexible optoelectronic devices. These components, when used in flexible device stacks, can be in contact with acid containing pressure-sensitive adhesives or with conductive polymers doped in acids.

The effect of deposition temperature on pulsed laser deposition (PLD) fabricated flexible transpa... more The effect of deposition temperature on pulsed laser deposition (PLD) fabricated flexible transparent electrodes subjected to mechanical loading, after exposure to acrylic acid, and the combined effect of fatigue and corrosion on sputter-deposited polyester-based indium tin oxide (ITO) films are both investigated in this study. Acrylic acid containing pressure sensitive adhesives, which are commonly used in various flexible device stacks, can corrode the ITO film. In addition, fatigue due to cyclic loading can lead to film cracking.

Thin polyester films are currently used as substrates in thin flexible displays, touch-screens an... more Thin polyester films are currently used as substrates in thin flexible displays, touch-screens and flat panel displays. The advantages of using such films in various display technologies include excellent optical transparency, mechanical flexibility and they are light weight and low cost. However, little research has been reported to date on the tribological properties of such top-sheet display components.

Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films ... more Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films on polyethylene napthalate (PEN) flexible display substrates. The electrical, optical, microstructural, mechanical and adhesive properties of the functional thin layer were investigated as a function of a narrow range of background oxygen gas pressure at room temperature, which is the most desirable thermal condition for growing transparent conducting oxides on flexible display polymer substrates.

Disclosed are various embodiments of methods and systems related to stimulus responsive nanoparti... more Disclosed are various embodiments of methods and systems related to stimulus responsive nanoparticles. In one embodiment includes a stimulus responsive nanoparticle system, the system includes a first electrode, a second electrode, and a plurality of elongated electro-responsive nanoparticles dispersed between the first and second electrodes, the plurality of electro-responsive nanorods configured to respond to an electric field established between the first and second electrodes.

The efficiency and long term reliability of multilayered films of Ag/Ag-alloy based indium tin ox... more The efficiency and long term reliability of multilayered films of Ag/Ag-alloy based indium tin oxide (ITO) used in solar energy applications depend on the surface integrity of the film. Surface integrity can be breached due to exposure to a harsh outdoor environment and mishandling. It is therefore important to study the tribo-corrosion properties of such film systems. Reciprocating polytetrafluoroethylene (PTFE) ball-on-film tests are conducted in a NaCl solution under moderate loading conditions and increasing number of cycles.

This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical... more This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical properties. Films as thin as 10nm thick have properties approaching those of existing electrodes based on indium tin oxide (ITO) but with significantly improved mechanical properties. In uniaxial tension, strains as high as 25% are required for permanent damage and at lower strains resistance changes are slight and consistent with elastic deformation of the individual CNTs.

Abstract—Carbon nanotubes have quickly emerged over the last several years as a potential candida... more Abstract—Carbon nanotubes have quickly emerged over the last several years as a potential candidate material to replace metal oxides in devices which require transparent and conductive electrodes. Typically, these materials are coated onto substrates such as PET and PEN for flexible electrodes and glass for rigid electrodes. Recently, there has been interest in more durable and lightweight substrates to replace glass, one such substrate being polycarbonate.

ABSTRACT Hydrophobic-oleophobic coatings are often used to provide the transparent electrodes in ... more ABSTRACT Hydrophobic-oleophobic coatings are often used to provide the transparent electrodes in devices like touch panels and smart windows with protection from fingerprints and other contaminants which may degrade electronic and optical performance. Conventional fluorosilane monolayers or co-condensed films are often surface-enriched with fluorinated moieties due to the thermodynamic drive of these components to migrate to low-surface energy interfaces.

ABSTRACT Fabrication of truly flexible optoelectronic devices, such as flexible displays and flex... more ABSTRACT Fabrication of truly flexible optoelectronic devices, such as flexible displays and flexible photovoltaics, is highly dependent on the mechanical integrity of individual thin inorganic/organic hybrid device components. A common feature of almost all thin composite film components for flexible optoelectronic applications is indium tin oxide (ITO) coated on polyester.

Abstract—Despite efforts to replace them, ceramic-coated polymer electrodes are still enjoying an... more Abstract—Despite efforts to replace them, ceramic-coated polymer electrodes are still enjoying an extensive use in touch-screen applications. Their mechanical behavior is of importance and can have an effect on the structural integrity of the touch system. In this paper, the mechanical and tribological response of such electrodes, under cyclic loading conditions, is investigated. Controlled buckling experiments and reciprocating wear studies are performed.

ACS Applied Materials & Interfaces

TiO2 is an important material widely used in optoelectronic devices due to its semiconducting and... more TiO2 is an important material widely used in optoelectronic devices due to its semiconducting and photocatalytic properties, nontoxicity, and chemically inert nature. Some indicative applications include water purification systems and energy harvesting. The use of solution, water-based inks for the direct writing of TiO2 on flexible substrates is of paramount importance since it enables low-cost and low-energy intensive large-area manufacturing, compatible with roll-to-roll processing. In this work we study the effect of crystalline TiO2 and polymer addition on the rheological and direct writing properties of Ti-organic/TiO2 inks. We also report on the bridging crystallite formation from the Ti-organic precursor into the TiO2 crystalline phase, under ultraviolet (UV) exposure or mild heat treatments up to 150 °C. Such crystallite formation is found to be enhanced by polymers with strong polarity and pKα such as polyacrylic acid (PAA). X-ray diffraction (XRD) coupled with Raman and X-ray photoelectron (XPS) spectroscopy are used to investigate the crystalline-phase transformation dependence based on the initial TiO2 crystalline-phase concentration and polymer addition. Transmission electron microscopy imaging and selected area electron diffraction patterns confirm the crystalline nature of such bridging printed structures. The obtained inks are patterned on flexible substrates using nozzle-based robotic deposition, a lithography-free, additive manufacturing technique that allows the direct writing of material in specific, digitally predefined, substrate locations. Photocatalytic degradation of methylene blue solutions highlights the potential of the studied films for chemical degradation applications, from low-cost environmentally friendly materials systems.

Sid Symposium Digest of Technical Papers, 2010

Abstract Energy efficient solid state lighting flexible and lightweight devices can offer an attr... more Abstract Energy efficient solid state lighting flexible and lightweight devices can offer an attractive alternative to bulky traditional rigid lighting solutions. We demonstrate a highly durable solid state flexible light emitting diode device and we report on critical factors during device manufacturing and use. We also propose alternative materials in order to further enhance the operational lifetime of the device.

The primary objective of this work was the fabrication and testing of a wireless LC resonator bas... more The primary objective of this work was the fabrication and testing of a wireless LC resonator based on micro-patterned electroceramic materials for the monitoring of high-temperature systems. The two-dimensional planar LC resonator sensors were designed and simulated using ANSYS Maxwell software, and these sensors were then fabricated from electrically conductive La2NiO4/Al2O3 particulate inks. The patterning and deposition of the ink were completed using a novel micro-casting process onto Al2O3 ceramic substrates, and the final pattern was bonded onto the substrate at 1200oC for 2 h. The final patterned materials were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and four-point conductivity to characterize the phase and microstructure development, and the resultant electrical conductivity (at 500-1200oC), respectively. The frequency shift with respect to temperature was measured, which is directly related to changes in the sensor’s dielectric perm...

MRS Online Proceeding Library

Solution-based fabrication methods have been widely used for depositing uniform functional coatin... more Solution-based fabrication methods have been widely used for depositing uniform functional coatings. These coatings can be utilized in a variety of applications such as optoelectronics, biomedical, and energy. However, such fabrication techniques are not appropriate for directly depositing patterned micro/nano-scale features, which are required in many contact-based applications such as in MEMS. In this work we propose the direct writing of hydrophobic silica-based sol-gel patterns with sustained functionality and their subsequent tribological characterization. Such an approach may be an advantageous alternative to current lithography-based methods due to the relative ease of processing and low material waste. This investigation involves the abrasive wear and frictional analysis of patterned fluorinated silica sol-gel coatings that are directly printed onto glass substrates with a robotically controlled pneumatic nozzle system. Such work sheds light on the tribological properties of...

Surface and Coatings Technology

Hydrophobically functional coatings can be used to protect surfaces and therefore improve the per... more Hydrophobically functional coatings can be used to protect surfaces and therefore improve the performance and lifetime of a broad range of applications such as optoelectronics and touchscreens. Organic–inorganic hybrid materials such as silica sol–gel coatings are particularly effective for this purpose, but the functional molecules in these coatings are susceptible to abrasive wear and thus lose their performance over time in the harsh environments typically encountered. To combat these problems, a silica nanoparticle-reinforced matrix was developed to increase hardness and wear resistance of the overall coating.

Thin Solid Films, 2015

There is currently a great interest in developing flexible electrodes. Such components are used i... more There is currently a great interest in developing flexible electrodes. Such components are used in most electronic devices from displays to solar cells to flexible sensors.To date most of them are fabricated using expensive vacuum techniques, and are based on transparent conducting oxides. These oxides are not entirely compatible with flexible substrates under the application of mechanical stresses, due to their brittle nature. Therefore, there is a need to explore novel lowcost, large-area fabrication methods to deposit alternative conducting materials with enhanced electro-mechanical performance. This work focuses on Ag patterns fabricated at low temperatures (below 150 o C) on flexible polyethylene naphthalate utilizing a robotic printing approach. Such lithography-free method minimizes material waste by printing exact amounts of inks on digitally predefined locations. Additionally, it allows a broad feature size range, from a few m to a few mm, and a variety of ink viscosities for better pattern control. We investigate the synthesis and direct writing of Ag particle-based inks, patterned-on-flex as lines and grids in the m scale. We report on a high-yield ink synthesis method (~61.6%) with controlled particle size. It is found that the electrical resistivity (1.75*10-4 Ω cm) of the patterns is in the same range with similar particle-based conductive components. The correlation between annealing temperature, microstructural evolution, and electrical performance is established. Also,

ABSTRACT This study demonstrates the ability to combine the dip-pen nanolithography patterning of... more ABSTRACT This study demonstrates the ability to combine the dip-pen nanolithography patterning of ZnO solutions on a polymer release layer and their subsequent transfer, after heat-treatment, to a flexible substrate. It is found that ink viscosity plays an important role in controlling both the feature size and the total number of the fabricated features. In addition, the role of the dwell time is investigated and it is observed that higher dwell times lead to both larger printed dot sizes and smaller total numbers of fabricated features. Resulting dot size is ranging from 7.2 to 1.9 μm as observed using in-situ optical microscopy. Heat treatment is found to lead to a slight shrinkage of the as-deposited patterns due to the coarsening and sintering mechanisms that are active during firing. Then, using a 75 kPa pressure and a hot plate set at 190 °C for 10 min, the fired ZnO patterns are transferred on a flexible polyethylene naphthalate substrate. The ability to effectively transfer high temperature-treated functional nano/micro-patterns on polymer substrates may be proved vital for the development of large-area flexible optoelectronic device applications.

Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered o... more Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered on polyethylene terephthalate (PET) substrates, is an issue of paramount importance in flexible optoelectronic devices. These components, when used in flexible device stacks, can be in contact with acid containing pressure-sensitive adhesives or with conductive polymers doped in acids.

The effect of deposition temperature on pulsed laser deposition (PLD) fabricated flexible transpa... more The effect of deposition temperature on pulsed laser deposition (PLD) fabricated flexible transparent electrodes subjected to mechanical loading, after exposure to acrylic acid, and the combined effect of fatigue and corrosion on sputter-deposited polyester-based indium tin oxide (ITO) films are both investigated in this study. Acrylic acid containing pressure sensitive adhesives, which are commonly used in various flexible device stacks, can corrode the ITO film. In addition, fatigue due to cyclic loading can lead to film cracking.

Thin polyester films are currently used as substrates in thin flexible displays, touch-screens an... more Thin polyester films are currently used as substrates in thin flexible displays, touch-screens and flat panel displays. The advantages of using such films in various display technologies include excellent optical transparency, mechanical flexibility and they are light weight and low cost. However, little research has been reported to date on the tribological properties of such top-sheet display components.

Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films ... more Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films on polyethylene napthalate (PEN) flexible display substrates. The electrical, optical, microstructural, mechanical and adhesive properties of the functional thin layer were investigated as a function of a narrow range of background oxygen gas pressure at room temperature, which is the most desirable thermal condition for growing transparent conducting oxides on flexible display polymer substrates.

Disclosed are various embodiments of methods and systems related to stimulus responsive nanoparti... more Disclosed are various embodiments of methods and systems related to stimulus responsive nanoparticles. In one embodiment includes a stimulus responsive nanoparticle system, the system includes a first electrode, a second electrode, and a plurality of elongated electro-responsive nanoparticles dispersed between the first and second electrodes, the plurality of electro-responsive nanorods configured to respond to an electric field established between the first and second electrodes.

The efficiency and long term reliability of multilayered films of Ag/Ag-alloy based indium tin ox... more The efficiency and long term reliability of multilayered films of Ag/Ag-alloy based indium tin oxide (ITO) used in solar energy applications depend on the surface integrity of the film. Surface integrity can be breached due to exposure to a harsh outdoor environment and mishandling. It is therefore important to study the tribo-corrosion properties of such film systems. Reciprocating polytetrafluoroethylene (PTFE) ball-on-film tests are conducted in a NaCl solution under moderate loading conditions and increasing number of cycles.

This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical... more This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical properties. Films as thin as 10nm thick have properties approaching those of existing electrodes based on indium tin oxide (ITO) but with significantly improved mechanical properties. In uniaxial tension, strains as high as 25% are required for permanent damage and at lower strains resistance changes are slight and consistent with elastic deformation of the individual CNTs.

Abstract—Carbon nanotubes have quickly emerged over the last several years as a potential candida... more Abstract—Carbon nanotubes have quickly emerged over the last several years as a potential candidate material to replace metal oxides in devices which require transparent and conductive electrodes. Typically, these materials are coated onto substrates such as PET and PEN for flexible electrodes and glass for rigid electrodes. Recently, there has been interest in more durable and lightweight substrates to replace glass, one such substrate being polycarbonate.

ABSTRACT Hydrophobic-oleophobic coatings are often used to provide the transparent electrodes in ... more ABSTRACT Hydrophobic-oleophobic coatings are often used to provide the transparent electrodes in devices like touch panels and smart windows with protection from fingerprints and other contaminants which may degrade electronic and optical performance. Conventional fluorosilane monolayers or co-condensed films are often surface-enriched with fluorinated moieties due to the thermodynamic drive of these components to migrate to low-surface energy interfaces.

ABSTRACT Fabrication of truly flexible optoelectronic devices, such as flexible displays and flex... more ABSTRACT Fabrication of truly flexible optoelectronic devices, such as flexible displays and flexible photovoltaics, is highly dependent on the mechanical integrity of individual thin inorganic/organic hybrid device components. A common feature of almost all thin composite film components for flexible optoelectronic applications is indium tin oxide (ITO) coated on polyester.

Abstract—Despite efforts to replace them, ceramic-coated polymer electrodes are still enjoying an... more Abstract—Despite efforts to replace them, ceramic-coated polymer electrodes are still enjoying an extensive use in touch-screen applications. Their mechanical behavior is of importance and can have an effect on the structural integrity of the touch system. In this paper, the mechanical and tribological response of such electrodes, under cyclic loading conditions, is investigated. Controlled buckling experiments and reciprocating wear studies are performed.