Search

High surface area electrode materials are of interest for a wide range of potential applications such as super-capacitors and electrochemical cells. This paper describes a fabrication method of three-dimensional (3D) graphene conformally coated on nanoporous insulating substrate with uniform nanopore size. 3D graphene films were formed by controlled graphitization of diamond-like amorphous carbon precursor films, deposited by plasma-enhanced chemical vapour deposition (PECVD). Plasma-assisted graphitization was found to produce better quality graphene than a simple thermal graphitization process. The resulting 3D graphene/amorphous carbon/alumina structure has a very high surface area, good electrical conductivity and exhibits excellent chemically stability, providing a good material platform for electrochemical applications. Consequently very large electrochemical capacitance values, as high as 2.1 mF for a sample of 10 mm(3), were achieved. The electrochemical capacitance of the material exhibits a dependence on bias voltage, a phenomenon observed by other groups when studying graphene quantum capacitance. The plasma-assisted graphitization, which dominates the graphitization process, is analyzed and discussed in detail.

Fast and reliable DNA sequencing is a long-standing target in biomedical research. Recent advances in graphene-based electrical sensors have demonstrated their unprecedented sensitivity to adsorbed molecules, which holds great promise for label-free DNA sequencing technology. To date, the proposed sequencing approaches rely on the ability of graphene electric devices to probe molecular-specific interactions with a graphene surface. Here we experimentally demonstrate the use of graphene field-effect transistors (GFETs) as probes of the presence of a layer of individual DNA nucleobases adsorbed on the graphene surface. We show that GFETs are able to measure distinct coverage-dependent conductance signatures upon adsorption of the four different DNA nucleobases; a result that can be attributed to the formation of an interface dipole field. Comparison between experimental GFET results and synchrotron-based material analysis allowed prediction of the ultimate device sensitivity, and assessment of the feasibility of single nucleobase sensing with graphene.

© 2015 Macmillan Publishers Limited. All rights reserved. Fast and reliable DNA sequencing is a long-standing target in biomedical research. Recent advances in graphene-based electrical sensors have demonstrated their unprecedented sensitivity to adsorbed molecules, which holds great promise for label-free DNA sequencing technology. To date, the proposed sequencing approaches rely on the ability of graphene electric devices to probe molecular-specific interactions with a graphene surface. Here we experimentally demonstrate the use of graphene field-effect transistors (GFETs) as probes of the presence of a layer of individual DNA nucleobases adsorbed on the graphene surface. We show that GFETs are able to measure distinct coverage-dependent conductance signatures upon adsorption of the four different DNA nucleobases; a result that can be attributed to the formation of an interface dipole field. Comparison between experimental GFET results and synchrotron-based material analysis allowed prediction of the ultimate device sensitivity, and assessment of the feasibility of single nucleobase sensing with graphene.

© 2015 Macmillan Publishers Limited. All rights reserved. Fast and reliable DNA sequencing is a long-standing target in biomedical research. Recent advances in graphene-based electrical sensors have demonstrated their unprecedented sensitivity to adsorbed molecules, which holds great promise for label-free DNA sequencing technology. To date, the proposed sequencing approaches rely on the ability of graphene electric devices to probe molecular-specific interactions with a graphene surface. Here we experimentally demonstrate the use of graphene field-effect transistors (GFETs) as probes of the presence of a layer of individual DNA nucleobases adsorbed on the graphene surface. We show that GFETs are able to measure distinct coverage-dependent conductance signatures upon adsorption of the four different DNA nucleobases; a result that can be attributed to the formation of an interface dipole field. Comparison between experimental GFET results and synchrotron-based material analysis allowed prediction of the ultimate device sensitivity, and assessment of the feasibility of single nucleobase sensing with graphene.

© The Royal Society of Chemistry. Extracellular nucleic acids freely circulating in blood and other physiologic fluids are important biomarkers for non-invasive diagnostics and early detection of cancer and other diseases, yet difficult to detect because they exist in very low concentrations and large volumes. Here we demonstrate a new broad-range sensor platform for ultrasensitive and selective detection of circulating DNA down to the single-molecule level. The biosensor is based on a chemically functionalized nanoporous diamond-like carbon (DLC) coated alumina membrane. The few nanometer-thick, yet perfect and continuous DLC-coating confers the chemical stability and biocompatibility of the sensor, allowing its direct application in biological conditions. The selective detection is based on complementary hybridization of a fluorescently-tagged circulating cancer oncomarker (a 21-mer nucleic acid) with covalently immobilized DNA on the surface of the membrane. The captured DNAs are detected in the nanoporous structure of the sensor using confocal scanning laser microscopy. The flow-through membrane sensor demonstrates broad-range sensitivity, spanning from 1015 molecules per cm2 down to single molecules, which is several orders of magnitude improvement compared to the flat DNA microarrays. Our study suggests that these flow-through type nanoporous sensors represent a new powerful platform for large volume sampling and ultrasensitive detection of different chemical biomarkers. This journal is

© The Royal Society of Chemistry. Extracellular nucleic acids freely circulating in blood and other physiologic fluids are important biomarkers for non-invasive diagnostics and early detection of cancer and other diseases, yet difficult to detect because they exist in very low concentrations and large volumes. Here we demonstrate a new broad-range sensor platform for ultrasensitive and selective detection of circulating DNA down to the single-molecule level. The biosensor is based on a chemically functionalized nanoporous diamond-like carbon (DLC) coated alumina membrane. The few nanometer-thick, yet perfect and continuous DLC-coating confers the chemical stability and biocompatibility of the sensor, allowing its direct application in biological conditions. The selective detection is based on complementary hybridization of a fluorescently-tagged circulating cancer oncomarker (a 21-mer nucleic acid) with covalently immobilized DNA on the surface of the membrane. The captured DNAs are detected in the nanoporous structure of the sensor using confocal scanning laser microscopy. The flow-through membrane sensor demonstrates broad-range sensitivity, spanning from 1015 molecules per cm2 down to single molecules, which is several orders of magnitude improvement compared to the flat DNA microarrays. Our study suggests that these flow-through type nanoporous sensors represent a new powerful platform for large volume sampling and ultrasensitive detection of different chemical biomarkers. This journal is

© The Royal Society of Chemistry. Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids. This journal is

© The Royal Society of Chemistry. Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids. This journal is

Diamond surface termination with substitutional nitrogen is reported, leading to the formation of a stable surface which is essentially clear of sub-band surface states and has a positive electron affinity. This is predicted to be an ideal environment for near-surface nitrogen-vacancy centers in diamond and may enable magnetic and quantum sensing breakthroughs with these devices.

A finite element method is applied to study the coupling between a nitrogen vacancy (NV) single photon emitter in nanodiamond and surface plasmons in a silver nanowire embedded in an alumina nanochannel template. We investigate the effective parameters in the coupled system and present detailed optimization for the maximum transmitted power at a selected optical frequency (650 nm). The studied parameters include nanowire length, nanowire diameter, distance between the dipole and the nanowire, orientation of the emitter and refractive index of the surrounding. It is found that the diameter of the nanowire has a strong influence on the propagation of the surface plasmon polaritons and emission power from the bottom and top endings of the nanowire. © 2014 Optical Society of America.

We demonstrate a robust templated approach to pattern thin films of chemical vapor deposited nanocrystalline diamond grown from monodispersed nanodiamond (mdND) seeds. The method works on a range of substrates, and we herein demonstrate the method using silicon, aluminum nitride (AlN), and sapphire substrates. Patterns are defined using photo- and e-beam lithography, which are seeded with mdND colloids and subsequently introduced into microwave assisted chemical vapor deposition reactor to grow patterned nanocrystalline diamond films. In this study, we investigate various factors that affect the selective seeding of different substrates to create high quality diamond thin films, including mdND surface termination, zeta potential, surface treatment, and plasma cleaning. Although the electrostatic interaction between mdND colloids and substrates is the main process driving adherence, we found that chemical reaction (esterification) or hydrogen bonding can potentially dominate the seeding process. Leveraging the knowledge on these different interactions, we optimize fabrication protocols to eliminate unwanted diamond nucleation outside the patterned areas. Furthermore, we have achieved the deposition of patterned diamond films and arrays over a range of feature sizes. This study contributes to a comprehensive understanding of the mdND-substrate interaction that will enable the fabrication of integrated nanocrystalline diamond thin films for microelectronics, sensors, and tissue culturing applications. © 2014 American Chemical Society.

Hybrid composite nanomaterials provide an attractive and versatile material platform for numerous emerging nano- and biomedical applications by offering the possibility to combine diverse properties which are impossible to obtain within a single material. In this work, we present the fabrication of novel hybrid diamond and amorphous diamond-like carbon (DLC) coated nanoporous alumina materials that exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. These multifunctional nanohybrid materials are fabricated using the plasma-induced carbonization method that effectively modifies the surface and the inside of the nanopores of anodic alumina, producing a homogenous ultrathin DLC protecting layer over the whole external and internal surfaces of the membranes. We demonstrate that the interplay between internal and external carbon supply is a critical factor for the formation of the ultrathin sp3-bonded carbon layer in the nanopores. This study brings new insights in the DLC growth mechanisms in confined nanospaces and opens new avenues to fabricate hybrid, chemically resistant and biocompatible carbon-coated nanoarchitectures on other inorganic supports. © 2014 Elsevier Ltd. All rights reserved.

Hybrid composite nanomaterials provide an attractive and versatile material platform for numerous emerging nano- and biomedical applications by offering the possibility to combine diverse properties which are impossible to obtain within a single material. In this work, we present the fabrication of novel hybrid diamond and amorphous diamond-like carbon (DLC) coated nanoporous alumina materials that exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. These multifunctional nanohybrid materials are fabricated using the plasma-induced carbonization method that effectively modifies the surface and the inside of the nanopores of anodic alumina, producing a homogenous ultrathin DLC protecting layer over the whole external and internal surfaces of the membranes. We demonstrate that the interplay between internal and external carbon supply is a critical factor for the formation of the ultrathin sp3-bonded carbon layer in the nanopores. This study brings new insights in the DLC growth mechanisms in confined nanospaces and opens new avenues to fabricate hybrid, chemically resistant and biocompatible carbon-coated nanoarchitectures on other inorganic supports. © 2014 Elsevier Ltd. All rights reserved.

We demonstrate a robust templated approach to pattern thin films of chemical vapor deposited nanocrystalline diamond grown from monodispersed nanodiamond (mdND) seeds. The method works on a range of substrates, and we herein demonstrate the method using silicon, aluminum nitride (AlN), and sapphire substrates. Patterns are defined using photo- and e-beam lithography, which are seeded with mdND colloids and subsequently introduced into microwave assisted chemical vapor deposition reactor to grow patterned nanocrystalline diamond films. In this study, we investigate various factors that affect the selective seeding of different substrates to create high quality diamond thin films, including mdND surface termination, zeta potential, surface treatment, and plasma cleaning. Although the electrostatic interaction between mdND colloids and substrates is the main process driving adherence, we found that chemical reaction (esterification) or hydrogen bonding can potentially dominate the seeding process. Leveraging the knowledge on these different interactions, we optimize fabrication protocols to eliminate unwanted diamond nucleation outside the patterned areas. Furthermore, we have achieved the deposition of patterned diamond films and arrays over a range of feature sizes. This study contributes to a comprehensive understanding of the mdND-substrate interaction that will enable the fabrication of integrated nanocrystalline diamond thin films for microelectronics, sensors, and tissue culturing applications. © 2014 American Chemical Society.

A finite element method is applied to study the coupling between a nitrogen vacancy (NV) single photon emitter in nanodiamond and surface plasmons in a silver nanowire embedded in an alumina nanochannel template. We investigate the effective parameters in the coupled system and present detailed optimization for the maximum transmitted power at a selected optical frequency (650 nm). The studied parameters include nanowire length, nanowire diameter, distance between the dipole and the nanowire, orientation of the emitter and refractive index of the surrounding. It is found that the diameter of the nanowire has a strong influence on the propagation of the surface plasmon polaritons and emission power from the bottom and top endings of the nanowire. © 2014 Optical Society of America.

We report fabrication and optical properties of electrochemically deposited silver nanowires into nanoporous alumina template. A finite element method is used to study plasmonic coupling of dipole emitters with the silver nanowires.

We report fabrication and optical properties of electrochemically deposited silver nanowires into nanoporous alumina template. A finite element method is used to study plasmonic coupling of dipole emitters with the silver nanowires. © 2012 IEEE.

We report fabrication and optical properties of electrochemically deposited silver nanowires into nanoporous alumina template. A finite element method is used to study plasmonic coupling of dipole emitters with the silver nanowires. © 2012 IEEE.

The potential of strained DOTFET technology is demonstrated. This technology uses a SiGe island as a stressor for a Si capping layer, into which the transistor channel is integrated. The structure information of fabricated samples is extracted from atomic force microscopy (AFM) measurements. Strain on the upper surface of a 30 nm thick Si layer is in the range of 0.7%, as supported by finite element calculations. The Ge content in the SiGe island is 30% on average, showing an increase towards the top of the island. Based on the extracted structure information, three-dimensional strain profiles are calculated and device simulations are performed. Up to 15% enhancement of the NMOS saturation current is predicted

Local electronic structures of nanometer-sized patches of epitaxial graphene and its interface layer with SiC(0001) have been studied by atomically resolved scanning tunneling microscopy and spectroscopy. Localized states belonging to the interface layer of a graphene/SiC system show to have essential influence on the electronic structure of graphene. Giant enhancement of inelastic tunneling, reaching 50% of the total tunneling current, has been observed at the localized states on a nanometer-sized graphene monolayer surrounded by defects

Local electronic structures of nanometer-sized patches of epitaxial graphene and its interface layer with SiC(0001) have been studied by atomically resolved scanning tunneling microscopy and spectroscopy. Localized states belonging to the interface layer of a graphene/SiC system show to have essential influence on the electronic structure of graphene. Giant enhancement of inelastic tunneling, reaching 50% of the total tunneling current, has been observed at the localized states on a nanometer-sized graphene monolayer surrounded by defects

Contains fulltext : 75951.pdf (publisher's version ) (Closed access)

Graphene-based materials exhibit many unique physical properties that are intriguing for both fundamental science and application purposes. This thesis describes three systems of sp2 bonded carbon: graphite, graphene and fullerene, and studies the electron behavior in these materials and how it is affected by the presence of defects. It is shown here that by inducing specific defects, phenomena such as ferromagnetism and superconductivity can arise in these systems. Graphite and its structural defects are studied by scanning tunneling microscopy and spectroscopy in chapter 2. This chapter represents the first detailed analysis of the structural and electronic properties of grain boundaries in graphite. Grain boundaries are the most common defects in highly oriented pyrolytic graphite (HOPG) because of its polycrystalline character. They form periodic arrays of point defects that are arranged in planes perpendicular to the graphene planes. On the graphite surface, grain boundaries manifest themselves as one-dimensional chains of point defects with a width around 1 nm and a length up to several micrometers. The periodic structure within a single grain boundary displays only two possible distances between point defects. This periodicity was found to be 0.5-10 nm in different grain boundaries. Atomically resolved STM images showed that grain boundaries are tilt grain boundaries, which are created between two rotated graphite grains. A new proposed structural model of grain boundaries based on periodically repeated point defects could explain all observed periodicities in STM. The electronic structure of grain boundaries has been studied locally with scanning tunneling spectroscopy (STS). Grain boundaries possess enhanced charge densities and localized electron states in comparison to the bare graphite surface. These states extend up to 4 nm from grain boundaries. Two localized electron states have been observed on grain boundaries having small periodicities (<4 nm)

Contains fulltext : 75951.pdf (publisher's version ) (Closed access)

Contains fulltext : 75951.pdf (publisher's version ) (Closed access)

We report on scanning tunneling microscopy and spectroscopy of grain boundaries in highly oriented pyrolytic graphite. Grain boundaries showed a periodic structure and an enhanced charge density compared to the bare graphite surface. Two possible periodic structures have been observed along grain boundaries. A geometrical model producing periodically distributed point defects on the basal plane of graphite has been proposed to explain the structure of grain boundaries. Scanning tunneling spectroscopy on grain boundaries revealed two strong localized states at -0.3 and 0.4 V which extended up to a 4 nm distance from grain boundaries.

Graphene-based materials exhibit many unique physical properties that are intriguing for both fundamental science and application purposes. This thesis describes three systems of sp2 bonded carbon: graphite, graphene and fullerene, and studies the electron behavior in these materials and how it is affected by the presence of defects. It is shown here that by inducing specific defects, phenomena such as ferromagnetism and superconductivity can arise in these systems. Graphite and its structural defects are studied by scanning tunneling microscopy and spectroscopy in chapter 2. This chapter represents the first detailed analysis of the structural and electronic properties of grain boundaries in graphite. Grain boundaries are the most common defects in highly oriented pyrolytic graphite (HOPG) because of its polycrystalline character. They form periodic arrays of point defects that are arranged in planes perpendicular to the graphene planes. On the graphite surface, grain boundaries manifest themselves as one-dimensional chains of point defects with a width around 1 nm and a length up to several micrometers. The periodic structure within a single grain boundary displays only two possible distances between point defects. This periodicity was found to be 0.5-10 nm in different grain boundaries. Atomically resolved STM images showed that grain boundaries are tilt grain boundaries, which are created between two rotated graphite grains. A new proposed structural model of grain boundaries based on periodically repeated point defects could explain all observed periodicities in STM. The electronic structure of grain boundaries has been studied locally with scanning tunneling spectroscopy (STS). Grain boundaries possess enhanced charge densities and localized electron states in comparison to the bare graphite surface. These states extend up to 4 nm from grain boundaries. Two localized electron states have been observed on grain boundaries having small periodicities (<4 nm)

The work provides methods for non-linear structural analysis and fatigue safety evaluation in assessment of existing railway bridges. The use of non-linear analysis leads to higher load carrying capacities, but also to improved understanding of the structural response, forming a better basis for decisions in the assessment. The methods for fatigue assessment lead to increased remaining service life of reinforced concrete railway bridges. The achievements of the work are: • Models for assessment of concrete bridges by non-linear analysis are described, and examples and general recommendations for practical application of the methods aregiven. • An overview of the effect of corrosion on the bond properties has been developed through non-linear analyses and tests found in literature. Recommendations for practical assessment of anchorage capacity in corroded railway concrete bridges are presented. • The determination of reliable in-situ material properties in old concrete bridges is described,including properties for fully probabilistic analysis. A particular aim was to develop better methods to describe development of concrete properties with age and degree of hydration. • Recommendations are given regarding re-distribution of sectional forces and moments, obtained through linear structural analysis (with FEM). In a case study, a typical slab bridge was designed using different methods, and its response evaluated through nonlinearanalyses. • A good understanding of the load-carrying mechanisms in combined bending-shear-torsion gives a possibility to make more accurate assessments than with standard code methods. Methods and examples are presented. • A state-of-the-art review of fatigue behaviour of reinforced concrete railway bridges is presented and a methodology to assess the remaining fatigue life of existing reinforced concrete bridges subjected to railway traffic is developed., EC Sixth Framework Program, Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives, TIP3-CT-2003-001653

The work provides methods for non-linear structural analysis and fatigue safety evaluation in assessment of existing railway bridges. The use of non-linear analysis leads to higher load carrying capacities, but also to improved understanding of the structural response, forming a better basis for decisions in the assessment. The methods for fatigue assessment lead to increased remaining service life of reinforced concrete railway bridges. The achievements of the work are: • Models for assessment of concrete bridges by non-linear analysis are described, and examples and general recommendations for practical application of the methods aregiven. • An overview of the effect of corrosion on the bond properties has been developed through non-linear analyses and tests found in literature. Recommendations for practical assessment of anchorage capacity in corroded railway concrete bridges are presented. • The determination of reliable in-situ material properties in old concrete bridges is described,including properties for fully probabilistic analysis. A particular aim was to develop better methods to describe development of concrete properties with age and degree of hydration. • Recommendations are given regarding re-distribution of sectional forces and moments, obtained through linear structural analysis (with FEM). In a case study, a typical slab bridge was designed using different methods, and its response evaluated through nonlinearanalyses. • A good understanding of the load-carrying mechanisms in combined bending-shear-torsion gives a possibility to make more accurate assessments than with standard code methods. Methods and examples are presented. • A state-of-the-art review of fatigue behaviour of reinforced concrete railway bridges is presented and a methodology to assess the remaining fatigue life of existing reinforced concrete bridges subjected to railway traffic is developed., EC Sixth Framework Program, Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives, TIP3-CT-2003-001653

The work provides methods for non-linear structural analysis and fatigue safety evaluation in assessment of existing railway bridges. The use of non-linear analysis leads to higher load carrying capacities, but also to improved understanding of the structural response, forming a better basis for decisions in the assessment. The methods for fatigue assessment lead to increased remaining service life of reinforced concrete railway bridges. The achievements of the work are: • Models for assessment of concrete bridges by non-linear analysis are described, and examples and general recommendations for practical application of the methods aregiven. • An overview of the effect of corrosion on the bond properties has been developed through non-linear analyses and tests found in literature. Recommendations for practical assessment of anchorage capacity in corroded railway concrete bridges are presented. • The determination of reliable in-situ material properties in old concrete bridges is described,including properties for fully probabilistic analysis. A particular aim was to develop better methods to describe development of concrete properties with age and degree of hydration. • Recommendations are given regarding re-distribution of sectional forces and moments, obtained through linear structural analysis (with FEM). In a case study, a typical slab bridge was designed using different methods, and its response evaluated through nonlinearanalyses. • A good understanding of the load-carrying mechanisms in combined bending-shear-torsion gives a possibility to make more accurate assessments than with standard code methods. Methods and examples are presented. • A state-of-the-art review of fatigue behaviour of reinforced concrete railway bridges is presented and a methodology to assess the remaining fatigue life of existing reinforced concrete bridges subjected to railway traffic is developed., EC Sixth Framework Program, Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives, TIP3-CT-2003-001653