ABSTRACT In this study, induced modification caused by silicon incorporation (up to 21 at.%) in t... more ABSTRACT In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the composition and microstructure of hydrogenated amorphous carbon (a-C:H) thin films synthesized by plasma-enhanced chemical vapour deposition (PECVD) technique has been studied. The effect of this new microstructure on gas barrier performance and optical properties has been studied.A small amount of silicon incorporation (8.5 at.%) into the a-C:H coatings significantly improves the barrier performance, giving a gas reduction factor of 98%. Moreover, silicon incorporation results in an enhancement of optical band gap (doubled its value) and in a reduction of film density, stress, and refractive index. The silicon inclusion in the a-C:H structure breaks down large size sp2 carbon clusters and enhances the sp3 bonding; however, the use of tetramethylsilane (TMS) precursor gas in the PECVD process also leads to the development of a more polymer-like structure due to the increasing hydrogen content. The development of sp3 bonding and the reduction of large sp2 graphitic clusters are responsible for the enhancement of the optical band gap.We have demonstrated that Si-a-C:H thin film coatings can be used as a transparent barrier coating on polymer substrates with barrier performance comparable to that of conventional metal oxides coatings.
In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silic... more In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silicon doped tetrahedral amorphous carbon (ta-C:Si:H), and silicon doped hydrogenated amorphous carbon (a-C:H:Si) films with thickness in the range 50-370 nm have been produced by PECVD (Plasma Enhanced Chemical Vapour Deposition) and FCVA (Filtered Cathodic Vacuum Arc) techniques on Polyethylene terepthalate (PET) and polycarbonate (PC) substrates. The paper is concerned with exploring the links between the atomic structure, gas barrier performance in carbon based films deposited on polymer substrates. A range of techniques including XRR, NEXAFS, Raman, surface profilometry, nano-indentation and water vapour permeation analysis were used to analyze the microstructure and properties of the films. The intensity and area of p* peak at the C K (carbon) edge of the NEXAFS spectra was lower in the FCVA films in comparison to that of PECVD ones confirming the higher sp 3 content of FCVA films. The surface of ta-C films showed a network of micro-cracks, which is detrimental for gas barrier application. However, the surfaces of both ta-C:H:Si and a-C:H:Si silicon-incorporated films were almost free of cracks. We also found that the incorporation of Si into both types of DLC films lead to a significant reduction of water vapour transmission rate.
Roll-to-roll (R2R) production of organic transistors and circuits require patterned deposition of... more Roll-to-roll (R2R) production of organic transistors and circuits require patterned deposition of organic layers at high deposition rate. Here we demonstrate a vapour-jet process for the rapid deposition of the organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). The deposition rate achieved, equivalent to ~200 nm/s onto a stationary substrate, was several orders of magnitude faster than ordinary thermal evaporation. Nevertheless, transistor yield was 100% with an average mobility of 0.4 cm 2 /Vs in a single pass deposition onto a substrate moving at 0.15 m/min. We also demonstrate a vacuum, high rate R2R-compatible process for surfacefunctionalising a gate dielectric layer with lauryl acrylate which enabled an all-vacuum route to the fabrication of a five-stage ring oscillator.
In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the compos... more In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the composition and microstructure of hydrogenated amorphous carbon (a-C:H) thin films synthesized by plasma-enhanced chemical vapour deposition (PECVD) technique has been studied. The effect of this new microstructure on gas barrier performance and optical properties has been studied. A small amount of silicon incorporation (8.5 at.%) into the a-C:H coatings significantly improves the barrier performance, giving a gas reduction factor of 98%. Moreover, silicon incorporation results in an enhancement of optical band gap (doubled its value) and in a reduction of film density, stress, and refractive index. The silicon inclusion in the a-C:H structure breaks down large size sp 2 carbon clusters and enhances the sp 3 bonding; however, the use of tetramethylsilane (TMS) precursor gas in the PECVD process also leads to the development of a more polymer-like structure due to the increasing hydrogen content. The development of sp 3 bonding and the reduction of large sp 2 graphitic clusters are responsible for the enhancement of the optical band gap. We have demonstrated that Si-a-C:H thin film coatings can be used as a transparent barrier coating on polymer substrates with barrier performance comparable to that of conventional metal oxides coatings.
In this study, we report on the electrical characteristics of all-vacuum-processed pentacene thin... more In this study, we report on the electrical characteristics of all-vacuum-processed pentacene thin film transistors, with stable and reproducible performance, using high throughput roll-toroll processing. The method allows a polymerised tripropyleneglycol diacrylate (TPGDA) insulator layer of thickness up to 1µm to be obtained in a single pass by ultrahigh flash evaporation of monomer onto a web travelling at 10 m min-1 and subsequent irradiation with an argon plasma emitted from a dc sputter cathode. From plots of I D 1/2 vs V G we deduce that the resulting OTFTs exhibited a field effect mobility of 0.12 cm 2 V-1 s-1 , a threshold voltage of-21 V, a turn-on voltage of-2V, and an on/off current ratio of 1x10 5. In an initial attempt to understand degradation effects and thus optimise device performance, we investigated the effect of ambient air on the I-V characteristics of our OTFTs by cycling the device-testing environment from ambient-air to vacuum and back to ambient-air. The moisture absorbed by the device during such cycling has a reversible effect on the performance of the OTFTs showing a shift in the turn-on voltage and deterioration in the on-off ratio. However, the effect was eliminated using a simple conventional encapsulation method. Our vacuum-based process thus demonstrates excellent potential for providing an alternative route to low-cost, large area organic electronics manufacturing.
Two sets of experiments were carried out for both ta-C and ta-C:N films prepared by filtered cath... more Two sets of experiments were carried out for both ta-C and ta-C:N films prepared by filtered cathodic vacuum arc deposition (FCVA). For the first experiment films were prepared as a function of arc current ranging from 30 to 100 A with a film thickness of approximately 70 nm. In the second experiment a series of films was prepared as a function of thickness ranging from 30 to 100 nm at 80 A arc current. Raman studies showed that for ta-C and ta-C:N films, an arc current of 100 A produced films with the lowest sp 2 configurations as well as the highest density values. The effect of thickness on ta-C and ta-C:N films revealed different trends. Raman and XRR analysis identified a decrease in sp 2 content and an increase in density as film thickness was increased for ta-C films. However ta-C:N films exceeding 70 nm showed an increasing trend in sp 2 content whilst a significant drop in density was observed.
In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silic... more In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silicon doped tetrahedral amorphous carbon (ta-C:Si:H), and silicon doped hydrogenated amorphous carbon (a-C:H:Si) films with thickness in the range 50-370 nm have been produced by PECVD (Plasma Enhanced Chemical Vapour Deposition) and FCVA (Filtered Cathodic Vacuum Arc) techniques on Polyethylene terepthalate (PET) and polycarbonate (PC) substrates. The paper is concerned with exploring the links between the atomic structure, gas barrier performance in carbon based films deposited on polymer substrates. A range of techniques including XRR, NEXAFS, Raman, surface profilometry, nano-indentation and water vapour permeation analysis were used to analyze the microstructure and properties of the films. The intensity and area of p* peak at the C K (carbon) edge of the NEXAFS spectra was lower in the FCVA films in comparison to that of PECVD ones confirming the higher sp 3 content of FCVA films. The surface of ta-C films showed a network of micro-cracks, which is detrimental for gas barrier application. However, the surfaces of both ta-C:H:Si and a-C:H:Si silicon-incorporated films were almost free of cracks. We also found that the incorporation of Si into both types of DLC films lead to a significant reduction of water vapour transmission rate.
High-resolution x-ray reflectivity ͑XRR͒ and heavy-ion elastic recoil detection were employed to ... more High-resolution x-ray reflectivity ͑XRR͒ and heavy-ion elastic recoil detection were employed to study the role of hydrogen on the softening behavior observed in Si-incorporated hydrogenated amorphous carbon ͑Si-a-C:H͒ films synthesized by plasma-enhanced chemical-vapor deposition using tetramethylsilane ͑TMS͒ precursor in C 2 H 2 / Ar plasma. An enhancement of the optical band gap and a massive reduction in the density of the films prepared at high TMS flow rate were revealed, respectively, by spectroscopic ellipsometry and XRR analysis with the development of a double critical angle. A hydrogenation process was responsible for a rise in the density of voids and an associated reduction in the connectivity of the carbon network and the release of its residual stress.
Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 a... more Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 at.%, have been produced by a double bend off-plane filtered cathodic vacuum arc system. X-ray photoelectron and Raman spectroscopies have been applied to study the effect of nitrogen in the bonding structure in the films. Deconvolution of the XPS spectra revealed a decrease in the amount of sp-bonded carbon in the ta-C:N films. A comparative study between the Raman parameters at 514 and at 633 nm 3 excitation wavelength was presented. Nitrogen (N) incorporation led to a lower G peak position and higher I yI ratios, indicating D G the development of larger sp domains. Q (yve) parameter (which measures the skewness of G line) increased sharply with the 2 increased of N content in the films. The hardness of the films was evaluated by nanoindentation.
We report on the performance of organic thin film transistors manufactured in an all-evaporated v... more We report on the performance of organic thin film transistors manufactured in an all-evaporated vacuum roll-to-roll process. We show that dinaphtho [2,3-b:2 0 ,3 0-f] thieno[3,2-b]thiophene (DNTT) is a suitable semiconductor material for deposition onto a flash evaporated polymer insulator layer to make bottom-gate top-contact transistors. Significantly, in batches of 90 transistors, the process approached a 100% yield of high mobility transistors with high on/off ratios and low gate-leakage. By contrast, a solution-deposited insulator layer led to significant gate leakage in a high proportion of transistors leading to poor yield. The performance of DNTT devices is shown to be superior to that of previously reported pentacene devices. Transistor performance is further enhanced by inclusion of a low-polarity surface modification, such as polystyrene, to the acrylate. The devices show good environmental stability but we demonstrate also that they can be in-line encapsulated with an acrylate and a SiOx overlayer without damaging the underlying transistor. Finally, a first demonstration is made of organic vapour jet printing of the DNTT to manufacture transistors with a high semiconductor deposition rate.
ABSTRACT An all-vacuum evaporated approach to the roll-to-roll (R2R) fabrication of organic elect... more ABSTRACT An all-vacuum evaporated approach to the roll-to-roll (R2R) fabrication of organic electronic circuits is being developed for potential applications in, for example, display backplanes and integrated security tagging for packaging. As part of an on-going development process, we are now addressing the question of circuit design and simulation. Here we describe the first step in this process, namely the extraction of parameters from experimentally-obtained output and transfer characteristics of vacuum produced, thin film transistors based on the organic semiconductors pentacene and dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]thiophene (DNTT). For this we use Silvaco's Universal Thin Film Transistor (UOTFT) Model (Level=37) so that the extracted parameters may be used directly with Silvaco's Gateway circuit simulation software.
ABSTRACTWe report our fabrication of pentacene field effect transistors (FETs) based on a vacuum ... more ABSTRACTWe report our fabrication of pentacene field effect transistors (FETs) based on a vacuum processed and e-beam cured polymer electrolyte (i.e., tripropylene glycol diacrylate (TRPGDA)) as a gate dielectric layer on flexible wide web substrates. The deposition of the semiconductor and gate insulator layers is carried out in Oxford's roll-to-roll vacuum web processing facility and could be combined in-line with roll-to-roll pattern metallization. The aim of the work is to demonstrate the ability to create all-evaporated transistors, exploiting the kind of technologies at present extensively used in the food packaging industry, for example, in which all layers can be deposited at high web speeds. Ours is a room temperature and a solvent-free method with an ultrahigh deposition rate (web speeds in excess of 100 m/min are possible).The performance of the pentacene and the polymer dielectric materials within devices was investigated, demonstrating (1) the ability to deposit goo...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights
This article reports results of endothelial cell interaction with atom beam source N-doped a-C:H ... more This article reports results of endothelial cell interaction with atom beam source N-doped a-C:H (diamond-like carbon, DLC) as it compares with that of Si-doped DLC thin films. The RF plasma source exhibits up to 40% N-dissociation and N-atomic fluxes of ϳ0.85 ؋ 10 18 atoms/s, which ensures better atomic nitrogen incorporation. Two different types of nitrogen species (with and without the use of sweep plates to remove charged ions) were employed for nitrogen doping. The number of attached endothelial cells is highest on Si-DLC, followed by the N-DLC (where the sweep plates were used to remove ions), the N-DLC (without the use of sweep plates), undoped DLC, and finally the uncoated sample. The contact angle values for these films suggest that water contact angle is higher in the atomic nitrogen neutral films and Si-DLC films compared to the ionized-nitrogen specie doped films and undoped DLC thin films, suggesting that the more hydrophobic films, semiconducting films, and film with relieved stress have better interaction with human microvascular endothelial cells. It seems evident that N-doping increases the Raman I D /I G ratios, whereas N-neutral doping decreases it slightly and Si-doping decreases it even further. In this study, lower Raman I D /I G ratios are associated with increased sp 3 /sp 2 ratio, an increased H concentration, photoluminescence intensity, and a higher endothelial cellular adhesion. These investigations could be relevant to biocompatibility assessment of nanostructured biomaterials and tissue engineering.
Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrat... more Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrate bias voltage) on Si substrates by an off-plane double bend filtered vacuum cathodic arc (FCVA) system. The influences of arc current on mass density, chemical bonding and nanomechanical response have been studied for coatings. Based on X-ray reflectivity spectra, the maximum density of FCVA films is 3.27 gycm. The hardness measurements performed as a function of indentation depth for 3 75-nm-thick films have a maximum hardness of 37.5 GPa and stress values up to 13 GPa. The sp content in the ta-C films as 3 determined by analysis of the C 1s core level spectra had a value of approximately 80% with standard deviation value 1.2% on 6-cm diameter Si waver. Therefore, these coatings have both structural and thickness uniformity, which can be used for large area coating applications (i.e. flat panel display units).
ABSTRACT In this study, induced modification caused by silicon incorporation (up to 21 at.%) in t... more ABSTRACT In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the composition and microstructure of hydrogenated amorphous carbon (a-C:H) thin films synthesized by plasma-enhanced chemical vapour deposition (PECVD) technique has been studied. The effect of this new microstructure on gas barrier performance and optical properties has been studied.A small amount of silicon incorporation (8.5 at.%) into the a-C:H coatings significantly improves the barrier performance, giving a gas reduction factor of 98%. Moreover, silicon incorporation results in an enhancement of optical band gap (doubled its value) and in a reduction of film density, stress, and refractive index. The silicon inclusion in the a-C:H structure breaks down large size sp2 carbon clusters and enhances the sp3 bonding; however, the use of tetramethylsilane (TMS) precursor gas in the PECVD process also leads to the development of a more polymer-like structure due to the increasing hydrogen content. The development of sp3 bonding and the reduction of large sp2 graphitic clusters are responsible for the enhancement of the optical band gap.We have demonstrated that Si-a-C:H thin film coatings can be used as a transparent barrier coating on polymer substrates with barrier performance comparable to that of conventional metal oxides coatings.
In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silic... more In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silicon doped tetrahedral amorphous carbon (ta-C:Si:H), and silicon doped hydrogenated amorphous carbon (a-C:H:Si) films with thickness in the range 50-370 nm have been produced by PECVD (Plasma Enhanced Chemical Vapour Deposition) and FCVA (Filtered Cathodic Vacuum Arc) techniques on Polyethylene terepthalate (PET) and polycarbonate (PC) substrates. The paper is concerned with exploring the links between the atomic structure, gas barrier performance in carbon based films deposited on polymer substrates. A range of techniques including XRR, NEXAFS, Raman, surface profilometry, nano-indentation and water vapour permeation analysis were used to analyze the microstructure and properties of the films. The intensity and area of p* peak at the C K (carbon) edge of the NEXAFS spectra was lower in the FCVA films in comparison to that of PECVD ones confirming the higher sp 3 content of FCVA films. The surface of ta-C films showed a network of micro-cracks, which is detrimental for gas barrier application. However, the surfaces of both ta-C:H:Si and a-C:H:Si silicon-incorporated films were almost free of cracks. We also found that the incorporation of Si into both types of DLC films lead to a significant reduction of water vapour transmission rate.
Roll-to-roll (R2R) production of organic transistors and circuits require patterned deposition of... more Roll-to-roll (R2R) production of organic transistors and circuits require patterned deposition of organic layers at high deposition rate. Here we demonstrate a vapour-jet process for the rapid deposition of the organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). The deposition rate achieved, equivalent to ~200 nm/s onto a stationary substrate, was several orders of magnitude faster than ordinary thermal evaporation. Nevertheless, transistor yield was 100% with an average mobility of 0.4 cm 2 /Vs in a single pass deposition onto a substrate moving at 0.15 m/min. We also demonstrate a vacuum, high rate R2R-compatible process for surfacefunctionalising a gate dielectric layer with lauryl acrylate which enabled an all-vacuum route to the fabrication of a five-stage ring oscillator.
In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the compos... more In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the composition and microstructure of hydrogenated amorphous carbon (a-C:H) thin films synthesized by plasma-enhanced chemical vapour deposition (PECVD) technique has been studied. The effect of this new microstructure on gas barrier performance and optical properties has been studied. A small amount of silicon incorporation (8.5 at.%) into the a-C:H coatings significantly improves the barrier performance, giving a gas reduction factor of 98%. Moreover, silicon incorporation results in an enhancement of optical band gap (doubled its value) and in a reduction of film density, stress, and refractive index. The silicon inclusion in the a-C:H structure breaks down large size sp 2 carbon clusters and enhances the sp 3 bonding; however, the use of tetramethylsilane (TMS) precursor gas in the PECVD process also leads to the development of a more polymer-like structure due to the increasing hydrogen content. The development of sp 3 bonding and the reduction of large sp 2 graphitic clusters are responsible for the enhancement of the optical band gap. We have demonstrated that Si-a-C:H thin film coatings can be used as a transparent barrier coating on polymer substrates with barrier performance comparable to that of conventional metal oxides coatings.
In this study, we report on the electrical characteristics of all-vacuum-processed pentacene thin... more In this study, we report on the electrical characteristics of all-vacuum-processed pentacene thin film transistors, with stable and reproducible performance, using high throughput roll-toroll processing. The method allows a polymerised tripropyleneglycol diacrylate (TPGDA) insulator layer of thickness up to 1µm to be obtained in a single pass by ultrahigh flash evaporation of monomer onto a web travelling at 10 m min-1 and subsequent irradiation with an argon plasma emitted from a dc sputter cathode. From plots of I D 1/2 vs V G we deduce that the resulting OTFTs exhibited a field effect mobility of 0.12 cm 2 V-1 s-1 , a threshold voltage of-21 V, a turn-on voltage of-2V, and an on/off current ratio of 1x10 5. In an initial attempt to understand degradation effects and thus optimise device performance, we investigated the effect of ambient air on the I-V characteristics of our OTFTs by cycling the device-testing environment from ambient-air to vacuum and back to ambient-air. The moisture absorbed by the device during such cycling has a reversible effect on the performance of the OTFTs showing a shift in the turn-on voltage and deterioration in the on-off ratio. However, the effect was eliminated using a simple conventional encapsulation method. Our vacuum-based process thus demonstrates excellent potential for providing an alternative route to low-cost, large area organic electronics manufacturing.
Two sets of experiments were carried out for both ta-C and ta-C:N films prepared by filtered cath... more Two sets of experiments were carried out for both ta-C and ta-C:N films prepared by filtered cathodic vacuum arc deposition (FCVA). For the first experiment films were prepared as a function of arc current ranging from 30 to 100 A with a film thickness of approximately 70 nm. In the second experiment a series of films was prepared as a function of thickness ranging from 30 to 100 nm at 80 A arc current. Raman studies showed that for ta-C and ta-C:N films, an arc current of 100 A produced films with the lowest sp 2 configurations as well as the highest density values. The effect of thickness on ta-C and ta-C:N films revealed different trends. Raman and XRR analysis identified a decrease in sp 2 content and an increase in density as film thickness was increased for ta-C films. However ta-C:N films exceeding 70 nm showed an increasing trend in sp 2 content whilst a significant drop in density was observed.
In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silic... more In this report, tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon (a-C:H), silicon doped tetrahedral amorphous carbon (ta-C:Si:H), and silicon doped hydrogenated amorphous carbon (a-C:H:Si) films with thickness in the range 50-370 nm have been produced by PECVD (Plasma Enhanced Chemical Vapour Deposition) and FCVA (Filtered Cathodic Vacuum Arc) techniques on Polyethylene terepthalate (PET) and polycarbonate (PC) substrates. The paper is concerned with exploring the links between the atomic structure, gas barrier performance in carbon based films deposited on polymer substrates. A range of techniques including XRR, NEXAFS, Raman, surface profilometry, nano-indentation and water vapour permeation analysis were used to analyze the microstructure and properties of the films. The intensity and area of p* peak at the C K (carbon) edge of the NEXAFS spectra was lower in the FCVA films in comparison to that of PECVD ones confirming the higher sp 3 content of FCVA films. The surface of ta-C films showed a network of micro-cracks, which is detrimental for gas barrier application. However, the surfaces of both ta-C:H:Si and a-C:H:Si silicon-incorporated films were almost free of cracks. We also found that the incorporation of Si into both types of DLC films lead to a significant reduction of water vapour transmission rate.
High-resolution x-ray reflectivity ͑XRR͒ and heavy-ion elastic recoil detection were employed to ... more High-resolution x-ray reflectivity ͑XRR͒ and heavy-ion elastic recoil detection were employed to study the role of hydrogen on the softening behavior observed in Si-incorporated hydrogenated amorphous carbon ͑Si-a-C:H͒ films synthesized by plasma-enhanced chemical-vapor deposition using tetramethylsilane ͑TMS͒ precursor in C 2 H 2 / Ar plasma. An enhancement of the optical band gap and a massive reduction in the density of the films prepared at high TMS flow rate were revealed, respectively, by spectroscopic ellipsometry and XRR analysis with the development of a double critical angle. A hydrogenation process was responsible for a rise in the density of voids and an associated reduction in the connectivity of the carbon network and the release of its residual stress.
Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 a... more Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 at.%, have been produced by a double bend off-plane filtered cathodic vacuum arc system. X-ray photoelectron and Raman spectroscopies have been applied to study the effect of nitrogen in the bonding structure in the films. Deconvolution of the XPS spectra revealed a decrease in the amount of sp-bonded carbon in the ta-C:N films. A comparative study between the Raman parameters at 514 and at 633 nm 3 excitation wavelength was presented. Nitrogen (N) incorporation led to a lower G peak position and higher I yI ratios, indicating D G the development of larger sp domains. Q (yve) parameter (which measures the skewness of G line) increased sharply with the 2 increased of N content in the films. The hardness of the films was evaluated by nanoindentation.
We report on the performance of organic thin film transistors manufactured in an all-evaporated v... more We report on the performance of organic thin film transistors manufactured in an all-evaporated vacuum roll-to-roll process. We show that dinaphtho [2,3-b:2 0 ,3 0-f] thieno[3,2-b]thiophene (DNTT) is a suitable semiconductor material for deposition onto a flash evaporated polymer insulator layer to make bottom-gate top-contact transistors. Significantly, in batches of 90 transistors, the process approached a 100% yield of high mobility transistors with high on/off ratios and low gate-leakage. By contrast, a solution-deposited insulator layer led to significant gate leakage in a high proportion of transistors leading to poor yield. The performance of DNTT devices is shown to be superior to that of previously reported pentacene devices. Transistor performance is further enhanced by inclusion of a low-polarity surface modification, such as polystyrene, to the acrylate. The devices show good environmental stability but we demonstrate also that they can be in-line encapsulated with an acrylate and a SiOx overlayer without damaging the underlying transistor. Finally, a first demonstration is made of organic vapour jet printing of the DNTT to manufacture transistors with a high semiconductor deposition rate.
ABSTRACT An all-vacuum evaporated approach to the roll-to-roll (R2R) fabrication of organic elect... more ABSTRACT An all-vacuum evaporated approach to the roll-to-roll (R2R) fabrication of organic electronic circuits is being developed for potential applications in, for example, display backplanes and integrated security tagging for packaging. As part of an on-going development process, we are now addressing the question of circuit design and simulation. Here we describe the first step in this process, namely the extraction of parameters from experimentally-obtained output and transfer characteristics of vacuum produced, thin film transistors based on the organic semiconductors pentacene and dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]thiophene (DNTT). For this we use Silvaco's Universal Thin Film Transistor (UOTFT) Model (Level=37) so that the extracted parameters may be used directly with Silvaco's Gateway circuit simulation software.
ABSTRACTWe report our fabrication of pentacene field effect transistors (FETs) based on a vacuum ... more ABSTRACTWe report our fabrication of pentacene field effect transistors (FETs) based on a vacuum processed and e-beam cured polymer electrolyte (i.e., tripropylene glycol diacrylate (TRPGDA)) as a gate dielectric layer on flexible wide web substrates. The deposition of the semiconductor and gate insulator layers is carried out in Oxford's roll-to-roll vacuum web processing facility and could be combined in-line with roll-to-roll pattern metallization. The aim of the work is to demonstrate the ability to create all-evaporated transistors, exploiting the kind of technologies at present extensively used in the food packaging industry, for example, in which all layers can be deposited at high web speeds. Ours is a room temperature and a solvent-free method with an ultrahigh deposition rate (web speeds in excess of 100 m/min are possible).The performance of the pentacene and the polymer dielectric materials within devices was investigated, demonstrating (1) the ability to deposit goo...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights
This article reports results of endothelial cell interaction with atom beam source N-doped a-C:H ... more This article reports results of endothelial cell interaction with atom beam source N-doped a-C:H (diamond-like carbon, DLC) as it compares with that of Si-doped DLC thin films. The RF plasma source exhibits up to 40% N-dissociation and N-atomic fluxes of ϳ0.85 ؋ 10 18 atoms/s, which ensures better atomic nitrogen incorporation. Two different types of nitrogen species (with and without the use of sweep plates to remove charged ions) were employed for nitrogen doping. The number of attached endothelial cells is highest on Si-DLC, followed by the N-DLC (where the sweep plates were used to remove ions), the N-DLC (without the use of sweep plates), undoped DLC, and finally the uncoated sample. The contact angle values for these films suggest that water contact angle is higher in the atomic nitrogen neutral films and Si-DLC films compared to the ionized-nitrogen specie doped films and undoped DLC thin films, suggesting that the more hydrophobic films, semiconducting films, and film with relieved stress have better interaction with human microvascular endothelial cells. It seems evident that N-doping increases the Raman I D /I G ratios, whereas N-neutral doping decreases it slightly and Si-doping decreases it even further. In this study, lower Raman I D /I G ratios are associated with increased sp 3 /sp 2 ratio, an increased H concentration, photoluminescence intensity, and a higher endothelial cellular adhesion. These investigations could be relevant to biocompatibility assessment of nanostructured biomaterials and tissue engineering.
Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrat... more Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrate bias voltage) on Si substrates by an off-plane double bend filtered vacuum cathodic arc (FCVA) system. The influences of arc current on mass density, chemical bonding and nanomechanical response have been studied for coatings. Based on X-ray reflectivity spectra, the maximum density of FCVA films is 3.27 gycm. The hardness measurements performed as a function of indentation depth for 3 75-nm-thick films have a maximum hardness of 37.5 GPa and stress values up to 13 GPa. The sp content in the ta-C films as 3 determined by analysis of the C 1s core level spectra had a value of approximately 80% with standard deviation value 1.2% on 6-cm diameter Si waver. Therefore, these coatings have both structural and thickness uniformity, which can be used for large area coating applications (i.e. flat panel display units).
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