Andreas Amann | University College Cork (original) (raw)
Papers by Andreas Amann
Metrology, Inspection, and Process Control for Microlithography XXVIII, 2014
ABSTRACT Different linear patterns obtained from the directed self-assembly of the block copolyme... more ABSTRACT Different linear patterns obtained from the directed self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) were analysed and compared. The hexagonal phase PS-b-PEO in a thin film exhibits linear pattern morphology, by conventional solvent annealing in an atmosphere saturated in chloroform. The surface energy of the silicon substrates was varied using surface functionalization of a self-assembly monolayer (SAM) and a polymer brush, chosen to investigate the influence of the surface energy on the self-assembly of the BCP. The linear patterns formed were analyzed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. The technique starts by performing dimensional metrology to calculate the pitch size and estimate the linewidth of the lines. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.
Charge accumulation in the quantum-well of a double-barrier resonant-tunneling diode (DBRT) may r... more Charge accumulation in the quantum-well of a double-barrier resonant-tunneling diode (DBRT) may result in bistability that provides a basis for formation of lateral current-density patterns. A typical pattern expected to appear is a current density front. Such fronts correspond to switching transitions and generally cannot be stabilized by a conventional external circuit. In this paper we discuss formation and stabilization
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
The double barrier resonant tunneling diode exhibits complex spatiotemporal patterns including lo... more The double barrier resonant tunneling diode exhibits complex spatiotemporal patterns including low-dimensional chaos when operated in an active external circuit. We demonstrate how autosynchronization by time-delayed feedback control can be used to select and stabilize specific current density patterns in a noninvasive way. We compare the efficiency of different control schemes involving feedback in either local spatial or global degrees of freedom. The numerically obtained Floquet exponents are explained by analytical results from linear stability analysis.
Physical Review E, 2003
We present a novel scheme to stabilize high-frequency domain oscillations in semiconductor superl... more We present a novel scheme to stabilize high-frequency domain oscillations in semiconductor superlattices by a time-delayed feedback loop. Applying concepts from chaos control theory we propose to control the spatio-temporal dynamics of fronts of accumulation and depletion layers which are generated at the emitter and may collide and annihilate during their transit, and thereby suppress chaos. The proposed method only requires the feedback of internal global electrical variables, viz current and voltage, which makes the practical implementation very easy.
Physical Review B, 2002
We analyze the dynamical evolution of the current and the charge density in a superlattice for fi... more We analyze the dynamical evolution of the current and the charge density in a superlattice for fixed external dc voltage in the regime of self-sustained current oscillations, using a microscopic sequential tunneling model. Fronts of accumulation and depletion layers which are generated at the emitter may collide and annihilate, thereby leading to a variety of different scenarios. We find complex chaotic regimes at high voltages and low contact conductivities.
Optics Express, 2014
We present a reliable and fast technique to experimentally categorise the dynamical state of opti... more We present a reliable and fast technique to experimentally categorise the dynamical state of optically injected two mode and single mode lasers. Based on the experimentally obtained time-traces locked, unlocked and chaotic states are distinguished for varying injection strength and detuning. For the two mode laser, the resulting experimental stability diagram provides a map of the various single mode and two mode regimes and the transitions between them. This stability diagram is in strong agreement with the theoretical predictions from low-dimensional dynamical models for two mode lasers. We also apply our method to the single mode laser and retain the close agreement between theory and experiment.
ABSTRACT form only given. Bursting is a striking feature found in a wide range of physical and bi... more ABSTRACT form only given. Bursting is a striking feature found in a wide range of physical and biological systems. It is characterized by periods of quiescence that are interspersed with periods of activity. We present an experimental and theoretical study of an interesting bursting mechanism in a two-mode semiconductor laser with single-mode optical injection. By tuning the strength and frequency of the injected light we find a transition from purely single-mode intensity oscillations to bursting in the intensity of the uninjected mode. We show that this bursting is organized by an interaction between a cusp and a pitchfork bifurcation of limit cycles. The underlying bursting mechanism is not specific to laser systems and was recently predicted theoretically on the basis of a simple two-dimensional dynamical system [1]. Here we experimentally confirm this new bursting mechanism.
ABSTRACT The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene... more ABSTRACT The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) was investigated. The hexagonal PS-b-PEO 42k-11.5k in a thin film was solvent annealed in a chlorophorm saturated atmosphere for three different annealing times. The microphase segregation of this BCP returned 18nm cylinders of PEO through the PS matrix, with an approximately 40 n periodicity, as expected. Under chlorophorm vapours, the PEO cylinders oriented perpendicular to the silicon substrate while increasing the annealing time. These cylinders formed linear patterns with different alignment. To achieve insights about the percentage of alignment, defect type pareto and density, and order quantification to compare the three annealing recipes, the samples were analysed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. From this technique, it was extracted dimensional metrology estimating pitch size and placement error, and the line-width of the lines was estimated. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.
We report a nonlinear stretching-based electromagnetic energy harvester using FR4 as a vibrating ... more We report a nonlinear stretching-based electromagnetic energy harvester using FR4 as a vibrating spring material due to its low Young's modulus. We show analytically that the nonlinearity is caused by the stretching, in addition to the bending, of the specially designed spring arms; this gives rise to a wider half-power bandwidth of 10 Hz at 1 g acceleration, which is almost 5 times higher than that of a comparable linear counterpart. The output spectra show the first reported experimental evidence of a symmetry broken nonlinear secondary peak in a single potential well system at frequencies close to the nonlinear jump frequency, which may appear to be due to the dynamic symmetry breaking of the oscillator or to the inherent asymmetry of the built prototype. The presence of this secondary peak is useful in generating a significant amount of power compared to the symmetric states, producing ∼3 times more power at the secondary peak than the nearby symmetric states. 110% of the peak power obtained for 0.5 g acceleration is achieved at the secondary peak during the frequency up-sweep. The experimental results are compared with a deterministic numerical model based on the Duffing oscillator, and we include a qualitative discussion on the influence of noise in an experimental energy harvesting system.
We derive a simple self-consistent model for the double-barrier resonant tunneling diode, which d... more We derive a simple self-consistent model for the double-barrier resonant tunneling diode, which describes the Zshaped current-voltage characteristic and includes the transverse re-distribution of electrons in the quantum well. In particular, we predict different regimes of spatio-temporal dynamics: stable uniform or filamentary current flow, and laterally uniform or nonuniform self-sustained current oscillations. Switching between the two stable uniform steady states (on and off) is explained in terms of transverse trigger fronts. Complex chaotic scenarios including spatiotemporal spiking are found. r
Recently, a number of attempts have been made to increase the operational bandwidth of the energy... more Recently, a number of attempts have been made to increase the operational bandwidth of the energy harvesting devices. Nonlinear mechanisms are one of them. In this paper, we report design and analytical formulation of stretching strain of an electromagnetic energy harvester on FR4 material under large deformation of the spring arms. It is found that nonlinearity has an inverse square dependence on thickness of the arms. Numerical solution of a monostable Duffing oscillator that governs the dynamics of such a large deformed nonlinear energy harvester showed that with decrease of load resistance, the average power output increases, where the output response depends strongly on the input force. For small input acceleration, the desired large amplitude vibration does not come into play and the response becomes linear. However, for higher input acceleration nonlinearity appears and the operational bandwidth increases, at the same time, output power level also increases.
We analyze the dynamics of charge distributions in weakly coupled, doped, dc voltage biased semic... more We analyze the dynamics of charge distributions in weakly coupled, doped, dc voltage biased semiconductor superlattices subject to voltage steps of different sizes. Qualitatively different current responses to voltage switching processes have been observed experimentally. We explain them by invoking distinct scenarios for electric-field domain formation, validated by numerical simulations. Furthermore, we investigate the transient from an unstable to a stable point in the current-voltage characteristics after a steplike or ramplike increase of the external voltage.
Ieee Photonics Journal, 2012
A proposal for an all-optical memory based on a bistability of single-mode states in a dualmode d... more A proposal for an all-optical memory based on a bistability of single-mode states in a dualmode diode laser with time-delayed optical feedback is presented. The system is modeled using a multimode extension of the Lang-Kobayashi equations with injected optical pulses. We uncover the bifurcation structure by deriving analytical expressions for the boundaries of the bistable region and demonstrate how the delay time in the external cavity determines an optimal pulse duration for efficient switching of the memory element. We also show the relevant role played by gain saturation and by the dual-mode solutions of the Lang-Kobayashi equations for the existence of the bistable regions. Our results demonstrate that feedback induced bistability can lead to significant performance improvements when compared to memory elements based on the injection locking bistability in dual-mode devices.
Scientific reports, 2014
Assertions that a new material may offer particularly advantageous properties should always be su... more Assertions that a new material may offer particularly advantageous properties should always be subjected to careful critical evaluation, especially when those properties can be affected by the presence of inclusions at trace level. This is particularly important for claims relating to new multiferroic compounds, which can easily be confounded by unobserved second phase magnetic inclusions. We demonstrate an original methodology for the detection, localization and quantification of second phase inclusions in thin Aurivillius type films. Additionally, we develop a dedicated statistical model and demonstrate its application to the analysis of Bi(6)Ti(2.8)Fe(1.52)Mn(0.68)O18 (B6TFMO) thin films, that makes it possible to put a high, defined confidence level (e.g. 99.5%) to the statement of 'new single phase multiferroic materials'. While our methodology has been specifically developed for magnetic inclusions, it can easily be adapted to any other material system that can be affe...
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
Metrology, Inspection, and Process Control for Microlithography XXVIII, 2014
ABSTRACT Different linear patterns obtained from the directed self-assembly of the block copolyme... more ABSTRACT Different linear patterns obtained from the directed self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) were analysed and compared. The hexagonal phase PS-b-PEO in a thin film exhibits linear pattern morphology, by conventional solvent annealing in an atmosphere saturated in chloroform. The surface energy of the silicon substrates was varied using surface functionalization of a self-assembly monolayer (SAM) and a polymer brush, chosen to investigate the influence of the surface energy on the self-assembly of the BCP. The linear patterns formed were analyzed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. The technique starts by performing dimensional metrology to calculate the pitch size and estimate the linewidth of the lines. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.
Charge accumulation in the quantum-well of a double-barrier resonant-tunneling diode (DBRT) may r... more Charge accumulation in the quantum-well of a double-barrier resonant-tunneling diode (DBRT) may result in bistability that provides a basis for formation of lateral current-density patterns. A typical pattern expected to appear is a current density front. Such fronts correspond to switching transitions and generally cannot be stabilized by a conventional external circuit. In this paper we discuss formation and stabilization
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
The double barrier resonant tunneling diode exhibits complex spatiotemporal patterns including lo... more The double barrier resonant tunneling diode exhibits complex spatiotemporal patterns including low-dimensional chaos when operated in an active external circuit. We demonstrate how autosynchronization by time-delayed feedback control can be used to select and stabilize specific current density patterns in a noninvasive way. We compare the efficiency of different control schemes involving feedback in either local spatial or global degrees of freedom. The numerically obtained Floquet exponents are explained by analytical results from linear stability analysis.
Physical Review E, 2003
We present a novel scheme to stabilize high-frequency domain oscillations in semiconductor superl... more We present a novel scheme to stabilize high-frequency domain oscillations in semiconductor superlattices by a time-delayed feedback loop. Applying concepts from chaos control theory we propose to control the spatio-temporal dynamics of fronts of accumulation and depletion layers which are generated at the emitter and may collide and annihilate during their transit, and thereby suppress chaos. The proposed method only requires the feedback of internal global electrical variables, viz current and voltage, which makes the practical implementation very easy.
Physical Review B, 2002
We analyze the dynamical evolution of the current and the charge density in a superlattice for fi... more We analyze the dynamical evolution of the current and the charge density in a superlattice for fixed external dc voltage in the regime of self-sustained current oscillations, using a microscopic sequential tunneling model. Fronts of accumulation and depletion layers which are generated at the emitter may collide and annihilate, thereby leading to a variety of different scenarios. We find complex chaotic regimes at high voltages and low contact conductivities.
Optics Express, 2014
We present a reliable and fast technique to experimentally categorise the dynamical state of opti... more We present a reliable and fast technique to experimentally categorise the dynamical state of optically injected two mode and single mode lasers. Based on the experimentally obtained time-traces locked, unlocked and chaotic states are distinguished for varying injection strength and detuning. For the two mode laser, the resulting experimental stability diagram provides a map of the various single mode and two mode regimes and the transitions between them. This stability diagram is in strong agreement with the theoretical predictions from low-dimensional dynamical models for two mode lasers. We also apply our method to the single mode laser and retain the close agreement between theory and experiment.
ABSTRACT form only given. Bursting is a striking feature found in a wide range of physical and bi... more ABSTRACT form only given. Bursting is a striking feature found in a wide range of physical and biological systems. It is characterized by periods of quiescence that are interspersed with periods of activity. We present an experimental and theoretical study of an interesting bursting mechanism in a two-mode semiconductor laser with single-mode optical injection. By tuning the strength and frequency of the injected light we find a transition from purely single-mode intensity oscillations to bursting in the intensity of the uninjected mode. We show that this bursting is organized by an interaction between a cusp and a pitchfork bifurcation of limit cycles. The underlying bursting mechanism is not specific to laser systems and was recently predicted theoretically on the basis of a simple two-dimensional dynamical system [1]. Here we experimentally confirm this new bursting mechanism.
ABSTRACT The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene... more ABSTRACT The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) was investigated. The hexagonal PS-b-PEO 42k-11.5k in a thin film was solvent annealed in a chlorophorm saturated atmosphere for three different annealing times. The microphase segregation of this BCP returned 18nm cylinders of PEO through the PS matrix, with an approximately 40 n periodicity, as expected. Under chlorophorm vapours, the PEO cylinders oriented perpendicular to the silicon substrate while increasing the annealing time. These cylinders formed linear patterns with different alignment. To achieve insights about the percentage of alignment, defect type pareto and density, and order quantification to compare the three annealing recipes, the samples were analysed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. From this technique, it was extracted dimensional metrology estimating pitch size and placement error, and the line-width of the lines was estimated. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.
We report a nonlinear stretching-based electromagnetic energy harvester using FR4 as a vibrating ... more We report a nonlinear stretching-based electromagnetic energy harvester using FR4 as a vibrating spring material due to its low Young's modulus. We show analytically that the nonlinearity is caused by the stretching, in addition to the bending, of the specially designed spring arms; this gives rise to a wider half-power bandwidth of 10 Hz at 1 g acceleration, which is almost 5 times higher than that of a comparable linear counterpart. The output spectra show the first reported experimental evidence of a symmetry broken nonlinear secondary peak in a single potential well system at frequencies close to the nonlinear jump frequency, which may appear to be due to the dynamic symmetry breaking of the oscillator or to the inherent asymmetry of the built prototype. The presence of this secondary peak is useful in generating a significant amount of power compared to the symmetric states, producing ∼3 times more power at the secondary peak than the nearby symmetric states. 110% of the peak power obtained for 0.5 g acceleration is achieved at the secondary peak during the frequency up-sweep. The experimental results are compared with a deterministic numerical model based on the Duffing oscillator, and we include a qualitative discussion on the influence of noise in an experimental energy harvesting system.
We derive a simple self-consistent model for the double-barrier resonant tunneling diode, which d... more We derive a simple self-consistent model for the double-barrier resonant tunneling diode, which describes the Zshaped current-voltage characteristic and includes the transverse re-distribution of electrons in the quantum well. In particular, we predict different regimes of spatio-temporal dynamics: stable uniform or filamentary current flow, and laterally uniform or nonuniform self-sustained current oscillations. Switching between the two stable uniform steady states (on and off) is explained in terms of transverse trigger fronts. Complex chaotic scenarios including spatiotemporal spiking are found. r
Recently, a number of attempts have been made to increase the operational bandwidth of the energy... more Recently, a number of attempts have been made to increase the operational bandwidth of the energy harvesting devices. Nonlinear mechanisms are one of them. In this paper, we report design and analytical formulation of stretching strain of an electromagnetic energy harvester on FR4 material under large deformation of the spring arms. It is found that nonlinearity has an inverse square dependence on thickness of the arms. Numerical solution of a monostable Duffing oscillator that governs the dynamics of such a large deformed nonlinear energy harvester showed that with decrease of load resistance, the average power output increases, where the output response depends strongly on the input force. For small input acceleration, the desired large amplitude vibration does not come into play and the response becomes linear. However, for higher input acceleration nonlinearity appears and the operational bandwidth increases, at the same time, output power level also increases.
We analyze the dynamics of charge distributions in weakly coupled, doped, dc voltage biased semic... more We analyze the dynamics of charge distributions in weakly coupled, doped, dc voltage biased semiconductor superlattices subject to voltage steps of different sizes. Qualitatively different current responses to voltage switching processes have been observed experimentally. We explain them by invoking distinct scenarios for electric-field domain formation, validated by numerical simulations. Furthermore, we investigate the transient from an unstable to a stable point in the current-voltage characteristics after a steplike or ramplike increase of the external voltage.
Ieee Photonics Journal, 2012
A proposal for an all-optical memory based on a bistability of single-mode states in a dualmode d... more A proposal for an all-optical memory based on a bistability of single-mode states in a dualmode diode laser with time-delayed optical feedback is presented. The system is modeled using a multimode extension of the Lang-Kobayashi equations with injected optical pulses. We uncover the bifurcation structure by deriving analytical expressions for the boundaries of the bistable region and demonstrate how the delay time in the external cavity determines an optimal pulse duration for efficient switching of the memory element. We also show the relevant role played by gain saturation and by the dual-mode solutions of the Lang-Kobayashi equations for the existence of the bistable regions. Our results demonstrate that feedback induced bistability can lead to significant performance improvements when compared to memory elements based on the injection locking bistability in dual-mode devices.
Scientific reports, 2014
Assertions that a new material may offer particularly advantageous properties should always be su... more Assertions that a new material may offer particularly advantageous properties should always be subjected to careful critical evaluation, especially when those properties can be affected by the presence of inclusions at trace level. This is particularly important for claims relating to new multiferroic compounds, which can easily be confounded by unobserved second phase magnetic inclusions. We demonstrate an original methodology for the detection, localization and quantification of second phase inclusions in thin Aurivillius type films. Additionally, we develop a dedicated statistical model and demonstrate its application to the analysis of Bi(6)Ti(2.8)Fe(1.52)Mn(0.68)O18 (B6TFMO) thin films, that makes it possible to put a high, defined confidence level (e.g. 99.5%) to the statement of 'new single phase multiferroic materials'. While our methodology has been specifically developed for magnetic inclusions, it can easily be adapted to any other material system that can be affe...
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011