Tin monoxide (SnO) has attracted attention due to its p-type character and capability of ambipola... more Tin monoxide (SnO) has attracted attention due to its p-type character and capability of ambipolar conductivity when properly doped, properties that are beneficial for the realization of complementary oxide thin film transistors technology, transparent flexible circuits and optoelectronic applications in general. However, its small fundamental band gap (0.7 eV) limits its applications as a solar energy material, therefore tuning its electronic properties is necessary for optimal performance. In this work, we use density functional theory (DFT) calculations to examine the electronic properties of the Sn1−xPbxO ternary oxide system. Alloying with Pb by element substitution increases the band gap of SnO without inducing defect states in the band gap retaining the anti-bonding character of the valence band maximum which is beneficial for p-type conductivity. We also examine the properties of the SnO/PbO heterojunction system in terms of band alignment and the effect of the most common i...
Interest in the Mn+1AXn phases (M = early transition metal; A = group 13–16 elements, and X = C o... more Interest in the Mn+1AXn phases (M = early transition metal; A = group 13–16 elements, and X = C or N) is driven by their ceramic and metallic properties, which make them attractive candidates for numerous applications. In the present study, we use the density functional theory to calculate the elastic properties and the incorporation of lithium atoms in the 312 MAX phases. It is shown that the energy to incorporate one Li atom in Mo3SiC2, Hf3AlC2, Zr3AlC2, and Zr3SiC2 is particularly low, and thus, theoretically, these materials should be considered for battery applications.
Anatase titanium oxide is important for its high chemical stability and photocatalytic properties... more Anatase titanium oxide is important for its high chemical stability and photocatalytic properties, however, the latter are plagued by its large band gap that limits its activity to only a small percentage of the solar spectrum. In that respect, straining the material can reduce its band gap increasing the photocatalytic activity of titanium oxide. We apply density functional theory with the introduction of the Hubbard + U model, to investigate the impact of stress on the electronic structure of anatase in conjunction with defect engineering by intrinsic defects (oxygen/titanium vacancies and interstitials), metallic dopants (iron, chromium) and non-metallic dopants (carbon, nitrogen). Here we show that both biaxial and uniaxial strain can reduce the band gap of undoped anatase with the use of biaxial strain being marginally more beneficial reducing the band gap up to 2.96 eV at a tensile stress of 8 GPa. Biaxial tensile stress in parallel with doping results in reduction of the band gap but also in the introduction of states deep inside the band gap mainly for interstitially doped anatase. Dopants in substitutional positions show reduced deep level traps. Chromium-doped anatase at a tensile stress of 8 GPa shows the most significant reduction of the band gap as the band gap reaches 2.4 eV.
Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for la... more Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for large scale graphene application. We propose here an etching process of graphene which can be applied immediately after growth to control the number of layers. We use nickel (Ni) foil at high temperature (T = 900 °C) to produce multilayer-AB-stacked-graphene (MLG). The etching process is based on annealing the samples in a hydrogen/argon atmosphere at a relatively low temperature (T = 450 °C) inside the growth chamber. The extent of etching is mainly controlled by the annealing process duration. Using Raman spectroscopy we demonstrate that the number of layers was reduced, changing from MLG to few-layer-AB-stacked-graphene and in some cases to randomly oriented few layer graphene near the substrate. Furthermore, our method offers the significant advantage that it does not introduce defects in the samples, maintaining their original high quality. This fact and the low temperature our method uses make it a good candidate for controlling the layer number of already grown graphene in processes with a low thermal budget.
Epitaxial, highly ordered Sb: SnO2 nanowires were grown by the vapor-liquid-solid mechanism on m-... more Epitaxial, highly ordered Sb: SnO2 nanowires were grown by the vapor-liquid-solid mechanism on m-, r- and a-Al2O3 between 700°C and 1000°C using metallic Sn and Sb with a mass ratio...
Journal of Materials Science: Materials in Electronics
density functional theory (DFT) simulations in conjunction with experimental nuclear magnetic res... more density functional theory (DFT) simulations in conjunction with experimental nuclear magnetic resonance (NMR) in order to investigate the Li ion migration mechanisms. Disorder in the anion sublattice can impact the material properties and the diffusion of point defects [14, 15]. This is a common future in energy related materials where intrinsic disorder and doping can influence the formation (i.e. concentration of point defects mediating diffusion) and the migration (i.e. the energy barriers for diffusion) [16-19]. Controlling point defects such as vacancies is important for semiconductors, superconductors, and oxides [20-28]. A way to defect engineer the concentration and clustering of point defects in the anion sublattice (for example oxygen vacancies) is via the introduction of dopants. This is effectively to maintain charge balance in the lattice [29]. For example the introduction of two trivalent dopants in the tetravalent cerium site in CeO 2 can be charge balanced by the formation of an oxygen vacancy. Therefore the introduction of trivalent dopants in CeO 2 is an efficient way to form oxygen vacancies at concentrations higher than the equilibrium concentration [29]. Atomistic simulation is an efficient and powerful way to understand the energetics of point defects in energy materials [30-32]. The main aim of the present study is to systematically investigate the intrinsic defect processes and impact of doping in Li 2 ZrO 3 using DFT. In particular, we consider here divalent (Mg, Zn, Ca, Cd, Sr, Ba), trivalent (Al, Ga, Sc, In, Y) and tetravalent (Si, Ge, Ti, Sn, Pb, Ce) substitutionals and their association with oxygen vacancies.
Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for la... more Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for large scale graphene application. We propose here an etching process of graphene which can be applied immediately after growth to control the number of layers. We use nickel (Ni) foil at high temperature (T = 900 °C) to produce multilayer-AB-stacked-graphene (MLG). The etching process is based on annealing the samples in a hydrogen/argon atmosphere at a relatively low temperature (T = 450 °C) inside the growth chamber. The extent of etching is mainly controlled by the annealing process duration. Using Raman spectroscopy we demonstrate that the number of layers was reduced, changing from MLG to few-layer-AB-stacked-graphene and in some cases to randomly oriented few layer graphene near the substrate. Furthermore, our method offers the significant advantage that it does not introduce defects in the samples, maintaining their original high quality. This fact and the low temperature our method...
ABSTRACT In this work we use a wafer-level, High Resolution Resistance Measuring Technique (HRRMT... more ABSTRACT In this work we use a wafer-level, High Resolution Resistance Measuring Technique (HRRMT) to detect fabrication faults of Al-Cu interconnections. Experiments have been performed on two distinct sets of metal lines. The first set includes two lots of 4 μm wide lines which, once tested at moderately accelerated stress conditions, gave largely different life times. A microstructural analysis confirmed a major defectivity of the lot with shorter life time. An accurate examination of the early resistance variations revealed the presence of two distinct and subsequent phases, namely an initial pseudo-parabolic resistance increase followed by a linear resistance drop. Significant differences between the resistance behaviour of the two lots were detected during the first stage, lasting a few hours. Measurable differences could even be detected in the first few minutes. A second group of experiments was launched in order to assess the capability of HRRMT as in-line monitors. Samples from four wafers, one reference wafer and three wafers with intentional process variations, have been tested using our HRRMT at constant temperature and current, simulating an in-line production test. The standard life time of the four wafers have also been collected. Preliminary measurements highlight that a change of life time due to process variation corresponds to changes of the resistance behaviour in the first hours of test. These results pave the way for a new application of high resolution methods to assess the quality of a metallization system in a reasonable amount of time.
In this work we examine the influence of thermal oxidation on the electrical characteristics of u... more In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si 0.78 Ge 0.22 substrates under moderate to high thermal budget conditions in N 2 O ambient at 800°C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si 0.78 Ge 0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si 0.78 Ge 0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO 2 -strained silicon interface and the rear strained silicon-Si 0.78 Ge 0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration-as a result of the thermal treatment-to the interfacial properties of the structure is discussed.
The dierential high-resolution electromigration (EM) measurement technique requires special test ... more The dierential high-resolution electromigration (EM) measurement technique requires special test patterns since for the implementation of this technique the presence of two metal lines is necessary, one metal line to be stressed with a high current density (`test' or`stressed' resistor) and a second line (`monitor' or`reference' resistor) to compensate for the thermal instabilities of the stressed one. It is accepted that due to Joule heating the stressed line always acquires higher temperature than the reference line and, therefore, additional resistance changes due to thermally induced phenomena, like precipitation of additional elements, will aect the measurement. In order to minimize these unwanted eects, an optimal high-resolution EM test structure should show a minimum temperature dierence between the stressed and the reference lines. Based on this requirement, in this work we simulated three dierent test structures being used by various research groups for high-resolution measurements and subsequently compared these test structures on account of their thermal behavior. Each test structure was examined for the case of two dierent widths of metal lines, 4 and 0.5 mm. The results obtained from the simulation of these test patterns demonstrated that the test pattern comprised of two parallel stress and reference lines shows better thermal behavior than the`lined-up' (continuous) metal lines where the stress and reference lines are actually part of the same line. In particular, the test pattern comprised of two parallel straight lines has slightly better behavior than the one with meandered lines in terms of minimization of the temperature dierence between the stressed and the reference resistors. The dierence between the thermal behavior of the two structures though is very small. For that reason, the parallel lines should be preferred from the meandered ones only if layout restrictions do not require the choice of a more compact (i.e., meandered) solution. Both test structures have shown a better thermal behavior than thè lined-up' metal lines. #
Tin monoxide (SnO) has attracted attention due to its p-type character and capability of ambipola... more Tin monoxide (SnO) has attracted attention due to its p-type character and capability of ambipolar conductivity when properly doped, properties that are beneficial for the realization of complementary oxide thin film transistors technology, transparent flexible circuits and optoelectronic applications in general. However, its small fundamental band gap (0.7 eV) limits its applications as a solar energy material, therefore tuning its electronic properties is necessary for optimal performance. In this work, we use density functional theory (DFT) calculations to examine the electronic properties of the Sn1−xPbxO ternary oxide system. Alloying with Pb by element substitution increases the band gap of SnO without inducing defect states in the band gap retaining the anti-bonding character of the valence band maximum which is beneficial for p-type conductivity. We also examine the properties of the SnO/PbO heterojunction system in terms of band alignment and the effect of the most common i...
Interest in the Mn+1AXn phases (M = early transition metal; A = group 13–16 elements, and X = C o... more Interest in the Mn+1AXn phases (M = early transition metal; A = group 13–16 elements, and X = C or N) is driven by their ceramic and metallic properties, which make them attractive candidates for numerous applications. In the present study, we use the density functional theory to calculate the elastic properties and the incorporation of lithium atoms in the 312 MAX phases. It is shown that the energy to incorporate one Li atom in Mo3SiC2, Hf3AlC2, Zr3AlC2, and Zr3SiC2 is particularly low, and thus, theoretically, these materials should be considered for battery applications.
Anatase titanium oxide is important for its high chemical stability and photocatalytic properties... more Anatase titanium oxide is important for its high chemical stability and photocatalytic properties, however, the latter are plagued by its large band gap that limits its activity to only a small percentage of the solar spectrum. In that respect, straining the material can reduce its band gap increasing the photocatalytic activity of titanium oxide. We apply density functional theory with the introduction of the Hubbard + U model, to investigate the impact of stress on the electronic structure of anatase in conjunction with defect engineering by intrinsic defects (oxygen/titanium vacancies and interstitials), metallic dopants (iron, chromium) and non-metallic dopants (carbon, nitrogen). Here we show that both biaxial and uniaxial strain can reduce the band gap of undoped anatase with the use of biaxial strain being marginally more beneficial reducing the band gap up to 2.96 eV at a tensile stress of 8 GPa. Biaxial tensile stress in parallel with doping results in reduction of the band gap but also in the introduction of states deep inside the band gap mainly for interstitially doped anatase. Dopants in substitutional positions show reduced deep level traps. Chromium-doped anatase at a tensile stress of 8 GPa shows the most significant reduction of the band gap as the band gap reaches 2.4 eV.
Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for la... more Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for large scale graphene application. We propose here an etching process of graphene which can be applied immediately after growth to control the number of layers. We use nickel (Ni) foil at high temperature (T = 900 °C) to produce multilayer-AB-stacked-graphene (MLG). The etching process is based on annealing the samples in a hydrogen/argon atmosphere at a relatively low temperature (T = 450 °C) inside the growth chamber. The extent of etching is mainly controlled by the annealing process duration. Using Raman spectroscopy we demonstrate that the number of layers was reduced, changing from MLG to few-layer-AB-stacked-graphene and in some cases to randomly oriented few layer graphene near the substrate. Furthermore, our method offers the significant advantage that it does not introduce defects in the samples, maintaining their original high quality. This fact and the low temperature our method uses make it a good candidate for controlling the layer number of already grown graphene in processes with a low thermal budget.
Epitaxial, highly ordered Sb: SnO2 nanowires were grown by the vapor-liquid-solid mechanism on m-... more Epitaxial, highly ordered Sb: SnO2 nanowires were grown by the vapor-liquid-solid mechanism on m-, r- and a-Al2O3 between 700°C and 1000°C using metallic Sn and Sb with a mass ratio...
Journal of Materials Science: Materials in Electronics
density functional theory (DFT) simulations in conjunction with experimental nuclear magnetic res... more density functional theory (DFT) simulations in conjunction with experimental nuclear magnetic resonance (NMR) in order to investigate the Li ion migration mechanisms. Disorder in the anion sublattice can impact the material properties and the diffusion of point defects [14, 15]. This is a common future in energy related materials where intrinsic disorder and doping can influence the formation (i.e. concentration of point defects mediating diffusion) and the migration (i.e. the energy barriers for diffusion) [16-19]. Controlling point defects such as vacancies is important for semiconductors, superconductors, and oxides [20-28]. A way to defect engineer the concentration and clustering of point defects in the anion sublattice (for example oxygen vacancies) is via the introduction of dopants. This is effectively to maintain charge balance in the lattice [29]. For example the introduction of two trivalent dopants in the tetravalent cerium site in CeO 2 can be charge balanced by the formation of an oxygen vacancy. Therefore the introduction of trivalent dopants in CeO 2 is an efficient way to form oxygen vacancies at concentrations higher than the equilibrium concentration [29]. Atomistic simulation is an efficient and powerful way to understand the energetics of point defects in energy materials [30-32]. The main aim of the present study is to systematically investigate the intrinsic defect processes and impact of doping in Li 2 ZrO 3 using DFT. In particular, we consider here divalent (Mg, Zn, Ca, Cd, Sr, Ba), trivalent (Al, Ga, Sc, In, Y) and tetravalent (Si, Ge, Ti, Sn, Pb, Ce) substitutionals and their association with oxygen vacancies.
Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for la... more Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for large scale graphene application. We propose here an etching process of graphene which can be applied immediately after growth to control the number of layers. We use nickel (Ni) foil at high temperature (T = 900 °C) to produce multilayer-AB-stacked-graphene (MLG). The etching process is based on annealing the samples in a hydrogen/argon atmosphere at a relatively low temperature (T = 450 °C) inside the growth chamber. The extent of etching is mainly controlled by the annealing process duration. Using Raman spectroscopy we demonstrate that the number of layers was reduced, changing from MLG to few-layer-AB-stacked-graphene and in some cases to randomly oriented few layer graphene near the substrate. Furthermore, our method offers the significant advantage that it does not introduce defects in the samples, maintaining their original high quality. This fact and the low temperature our method...
ABSTRACT In this work we use a wafer-level, High Resolution Resistance Measuring Technique (HRRMT... more ABSTRACT In this work we use a wafer-level, High Resolution Resistance Measuring Technique (HRRMT) to detect fabrication faults of Al-Cu interconnections. Experiments have been performed on two distinct sets of metal lines. The first set includes two lots of 4 μm wide lines which, once tested at moderately accelerated stress conditions, gave largely different life times. A microstructural analysis confirmed a major defectivity of the lot with shorter life time. An accurate examination of the early resistance variations revealed the presence of two distinct and subsequent phases, namely an initial pseudo-parabolic resistance increase followed by a linear resistance drop. Significant differences between the resistance behaviour of the two lots were detected during the first stage, lasting a few hours. Measurable differences could even be detected in the first few minutes. A second group of experiments was launched in order to assess the capability of HRRMT as in-line monitors. Samples from four wafers, one reference wafer and three wafers with intentional process variations, have been tested using our HRRMT at constant temperature and current, simulating an in-line production test. The standard life time of the four wafers have also been collected. Preliminary measurements highlight that a change of life time due to process variation corresponds to changes of the resistance behaviour in the first hours of test. These results pave the way for a new application of high resolution methods to assess the quality of a metallization system in a reasonable amount of time.
In this work we examine the influence of thermal oxidation on the electrical characteristics of u... more In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si 0.78 Ge 0.22 substrates under moderate to high thermal budget conditions in N 2 O ambient at 800°C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si 0.78 Ge 0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si 0.78 Ge 0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO 2 -strained silicon interface and the rear strained silicon-Si 0.78 Ge 0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration-as a result of the thermal treatment-to the interfacial properties of the structure is discussed.
The dierential high-resolution electromigration (EM) measurement technique requires special test ... more The dierential high-resolution electromigration (EM) measurement technique requires special test patterns since for the implementation of this technique the presence of two metal lines is necessary, one metal line to be stressed with a high current density (`test' or`stressed' resistor) and a second line (`monitor' or`reference' resistor) to compensate for the thermal instabilities of the stressed one. It is accepted that due to Joule heating the stressed line always acquires higher temperature than the reference line and, therefore, additional resistance changes due to thermally induced phenomena, like precipitation of additional elements, will aect the measurement. In order to minimize these unwanted eects, an optimal high-resolution EM test structure should show a minimum temperature dierence between the stressed and the reference lines. Based on this requirement, in this work we simulated three dierent test structures being used by various research groups for high-resolution measurements and subsequently compared these test structures on account of their thermal behavior. Each test structure was examined for the case of two dierent widths of metal lines, 4 and 0.5 mm. The results obtained from the simulation of these test patterns demonstrated that the test pattern comprised of two parallel stress and reference lines shows better thermal behavior than the`lined-up' (continuous) metal lines where the stress and reference lines are actually part of the same line. In particular, the test pattern comprised of two parallel straight lines has slightly better behavior than the one with meandered lines in terms of minimization of the temperature dierence between the stressed and the reference resistors. The dierence between the thermal behavior of the two structures though is very small. For that reason, the parallel lines should be preferred from the meandered ones only if layout restrictions do not require the choice of a more compact (i.e., meandered) solution. Both test structures have shown a better thermal behavior than thè lined-up' metal lines. #
Uploads
Papers by N. Kelaidis