Quantum Channel FETs for Advanced Biosensors

Experimental determination of the effect of polarization of the heating laser pulse on the characteristic decay time constant and focal length of thermal lenses, and on the thermal diffusivities in pure liquids

ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silicon associated with trapping and generation – recombination processes, which appear to predict very different noise spectra. In one approach the broad noise spectrum observed is assumed to be composed of a distribution of Lorentzian noise spectra, each associated with traps at a given energy depth, with appropriate weighting according to the energy distribution of characteristic time constants. This latter weighting is taken to mirror the energy distribution of states in the gap. This represents a linear superposition of the (weighted) contribution from individual trapping levels, each with its own characteristic time constant. This approach thus assumes that each trap level is an independent source of fluctuation in free carrier number, unaffected by the presence of other traps in the material. At first sight this assertion seems plausible, since in the multi-trapping situation envisaged, cross-correlation effects must be very small. However, the presence of several groups of traps, or, in the limit, a continuum, results in a distribution of characteristic time constants, which is not a simple linear superposition of the time constants for each level. Thus the assertion that a flat density of states, or a region which is flat, such as the top of a broadened level, results in a region of 1/f slope in the noise spectrum, may not be valid. We present an alternative model in which the distribution of time constants is appropriately incorporated, and compare the predictions of this model with the ‘superposition’ approach, using computed noise spectra.

Adsorption chillers can substitute the electric energy demand of conventional compression chillers with low-temperature heat. The efficiency and power density of adsorption chillers depend on their adsorbent and refrigerant, which form the working pair. Novel working pairs are therefore actively developed and characterized in dynamic small-scale experiments using a characteristic time constant. However, this evaluation by only few characteristic time constants, does not resolve the trade-off between efficiency and power density of adsorption chillers and novel materials are challenging to compare due to varying size, shape, and density. To fill these gaps, we investigate the trade-off between efficiency and power density by quantifying all characteristic time constants and transferring them to specific mean powers. We perform Large-Temperature-Jump experiments with water as the refrigerant on the two metal–organic frameworks CAU–10–H and aluminum fumarate for a chilling/recooling/regeneration temperature triple of 10/30/80 °C. We compare the metal–organic frameworks’ specific mean powers to the commercially available RD type silica gels Siogel and SG123. Siogel performed best in terms of area-specific mean powers with a maximum value of 3.2 kW/m². For low time constants up to 20% relative loading, corresponding to high power density but lower efficiency, Siogel also provided the highest volume-specific mean power at 8.1 MW/m³. CAU–10–H had the highest mass- and volume-specific mean powers at 19.0–19.9 kW/kg and 7.2–8.6 MW/m3 for characteristic time constants of 35% relative loading and higher. Aluminum fumarate and SG123 showed low specific mean powers for all chosen characteristic time constants. The results show that studying specific mean powers is a useful tool to benchmark adsorption working pairs as they would perform in an adsorption chiller, regardless of mass, shape, or density.

We introduce a simple micro-fluidic device containing an actuated flexible membrane, which allows the viscoelastic characterization of cells in small volumes of suspension by loading them in compression and observing the cell deformation in time. From this experiment, we can determine the characteristic time constant of recovery of the cell. To validate the device, two cell types known to have different cytoskeletal structures, 3T3 fibroblasts and HL60 cells, are tested. They show a substantially different response in the device and can be clearly distinguished on the basis of the measured characteristic recovery time constant. Also, the effect of breaking down the actin network, a main mechanical component of the cytoskeleton, by a treatment with Cytochalasin D, results in a substantial increase of the measured characteristic recovery time constant. Experimental variations in loading force, loading time, and surface treatment of the device also influence the measured characteristic recovery time constant significantly. The device can therefore be used to distinguish between cells with different mechanical structure in a quantitative way, and makes it possible to study changes in the mechanical response due to cell treatments, changes in the cell’s micro-environment, and mechanical loading conditions.

In this paper, state-of-the-art dynamic models for solid oxide fuel cells (SOFCs) in the open literature are reviewed. The review also includes the transient modeling of SOFC systems with reformers. In the transients of a SOFC, three characteristic time constants are observed. One of the challenges in transient modeling is to capture these characteristic times. The first characteristic time is on the order of milliseconds and is mostly neglected, because it is too small, from the viewpoint of practical applications. The second time constant is on the order of seconds and arises mainly because of the mass-transport dynamics. The third characteristic time is on the order of minutes or hours and is dependent on the energy transport characteristics of the system. These characteristic times are extremely system-specific and, therefore, must be identified on a case-to-case basis. In this paper, the existing literature on dynamic studies are reviewed, focusing mainly on the fidelity of the model that is required to capture these time constants. The dynamic modeling of SOFC is still not as rich as the steady-state modeling. Therefore, steady-state models are also reviewed, whenever required. The utility of the dynamic models in design, control, and operation is discussed. A dynamic model from the literature is chosen for this purpose.

We compare the predictions of several analytical models for conductivity fluctuations in a homogeneous semiconductor containing discrete and distributed traps, using a Monte-Carlo simulation of the relevant multi – trapping (MT) transitions. The simulation directly embodies the statistical features associated with such processes, in a simple ‘model - independent’ approach, free of approximations and assumptions. We compare the results with those of several analytical approaches. In one, the noise spectrum is assumed to reflect separately, the characteristic individual release time constants of the various trapping centers in the material. In another, the trapping time into the ensemble of electron traps is taken to be the dominant time constant, and hence, in a material such as a-Si:H, where the trapping time into tail sates is of order 1ps, this is taken to imply that this component of the conductivity noise spectrum is unobservable in practice. Our own analytical approach, incorporates coupling (albeit weak) between traps, which necessarily communicate via the extended states. Preliminary results of the simulation support our thesis, and verify that the same information is contained in the real part of the modulated photoconductivity (MPC) spectrum. A ‘full Monte’ – Carlo simulation incorporating all gap states and spatial inhomogeneities is now a priority.

In the production of integrated circuits (e.g. computer chips), optical lithography is used to transfer a pattern onto a semiconductor substrate (wafer). For lithographic systems using light in the ultraviolet band (EUV) with a 13.5nm nm wavelength, only reflective optics with multi-layers can reflect that light by means of interlayer interference, but these mirrors absorb around 30% of the incident light. Depending on pattern and beam shape, there is a nonuniform light distribution over the surface of the mirrors. This causes temperature gradients and therefore local deformations, due to different thermal expansions. To improve the throughput (wafers per hour), there is a demand to increase the source power, that will increase these deformations even further. Active mirrors are a solution to correct these deformations by reshaping the surface. This thesis addresses the challenges to accurate deform a mirror with high repeatability, meeting the requirements for implementation in a lithographic illumination machine. The main design criteria are vacuum compatibility, actuator stroke and the distance between actuators. Four different experimental mirrors, with increasing complexity, are successfully designed, realized and validated. All mirrors are equipped with thermomechanical actuators to either bend, or axially deform them. These actuators are free from mechanical hysteresis and therefore have a high position resolution with high reproducibility. Extensive finite element analysis is done, to maximize actuator stroke and minimize input power. All mirrors are tested and validated with interferometer surface measurements and thermocouple temperature measurements. The first experimental mirror with one thermo-mechanical bending actuator is successfully built and tested (chapter 2). To obtain a high mirror deflection at a given inserted actuator power, aluminum is chosen as the actuator material. The mirror is made from Zerodur® like the mirrors in the first EUV lithographic demonstration machines. A mirror deformation of 4:7 nm/C is achieved, where the inserted actuator power is 0.044 C/mW, meaning 0:21 nm/mW. The measured characteristic time constant is 10 s, meaning that for a given input, 63% of the steady state stroke is reached within that time scale. All values are close to the predicted ones from the models and also meet the requirements for implementation. To further investigate the concept and to measure the mechanical and thermal actuator coupling, an experimental mirror with four actuators is designed, developed and validated (chapter 3). It is an extension of the mirror with one actuator. In a single actuator step-response, a mirror deflection of 3.4 nm/C is achieved. A design optimization is proposed and successfully tested which reduces the actuator coupling from 30% to 10%, while the mirror deflection at the same input is reduced to 55%. Actuator speed is demonstrated while simultaneously heating all actuators with 3mW, which correspond with a mirror deformation of 33 pm/s. When using an adaptive mirror in an EUV lithography system, actuator strokes of 1 nm/min are required. The demonstrated actuator speed of 33 pm/s = 2 nm/min meets that requirement. The third and fourth mirror have actuators placed perpendicular to the surface (chapter 4). By placing the actuators on a thin back plate, the force loop is localized and therefore a lower actuator coupling is achieved. The results obtained from the third mirror with 7 actuators are close to the predicted values from the static and thermal models. Based on these good results, this actuation principle is implemented in a smaller deformable mirror with 19 actuators inside a 25mm beam diameter. A linear relation between actuator power and temperature of 0.190 C/mW and between power and averaged interactuator stroke of 0.13 nm/mW is achieved. So, the successfully realized mirror deflection is 0:68 nm/ C and no hysteresis is observed. For both mirrors a support frame is developed, that minimizes introduced surface deformations by temperature variations. Thermal step responses are fitted and both heating and cooling characteristic time constants are 2:5 s. The thermal actuator coupling from an energized actuator to its direct neighbor is 6:0, to their neighbors it is 1:3%. The total actuator coupling is approximated around 10%, based on the good agreement between simulated and measured inter-actuator stroke. Finally, chapter 5 summarizes the main findings from the different deformable mirrors and compares them. Also, suggestions for future research are given for implementation into a lithographic machine.

Inspired by the seminal work of A. J. Bard in electroanalytical chemistry during more than half of a century, we are trying to apply novel electroanalytical tools in conjunction with in-situ spectro-electrochemical techniques for the study of the most reactive electrochemical systems, related to energy storage and conversion. A variety of electroanalytical methods are widely used in advanced batteries and super-capacitors research for screening and optimization of electrode materials including their characteristic electrochemical windows, onset potentials of ions insertion and extraction, formation of protective surface-solution interphases etc. These parameters affect the electrodes stability, capacity retention, cycling efficiency and rate capability. Electroanalytical methods have their own intrinsic accessible time windows and different amplitude of electric perturbation (potential or current). Among these methods electrochemical impedance spectroscopy (EIS) has the widest time window from ca. 10-5 to 103 s and small potential amplitude which enables the probing the kinetics of a large variety of processes accompanying electrochemical insertion of Li , Na and Mg ions into battery electrodes separating them by the characteristic time constants of these processes. In contrast, cyclic voltammetry (CV) effectively probes kinetic steps in the long time window (from 102 to 105 s) close to either quasi-equilibrium intercalation or intercalation process in the form of first-order phase transition. CV is a large-amplitude technique, and attempts to apply it for a shorter time domain, e.g. corresponding to characteristic solid-state diffusion time constants inevitably results in lack of their resolution with respect to electrode potential (or intercalation level). The niche between EIS and CV is effectively bridged by intermittent titration techniques (PITT, GITT) ensuring highly resolved separation between the different sequential phase transitions in the long time domain, and potential-resolved chemical diffusion coefficients of intercalated ions. [1] The area-averaged responses of battery electrodes obtained by electroanalytical techniques depend on the local chemical or porous electrode structure: very often this information is required for correct interpretation of the electrochemical characteristics (e.g. chemical diffusion coefficients).Recent progress in electroanalytical methods adapted for application in LIB , NIB and Mg batteries research relates to development of non-gravimetric EQCM-D (electrochemical quartz-crystal microbalance with dissipation monitoring) techniques , which in contrast to classical EQCM, tracks not only resonant frequency change DF/n (n is overtone order) but also dissipation of the oscillation energy (or equivalently, resonance peak width change, DW/n). Tracking complex frequency change, DF*/n = DF/n + iDW/n, for rigid porous battery electrodes as a function of the penetration depth of transverse oscillation wave in the electrolyte solution, d (dependent on the overtone order and liquid’s density and viscosity) over multiple harmonics ,allows the characterization of the complex electric and mechanical properties of thin electrode coatings in electrolyte solutions (using the most relevant materials for advanced rechargeable batteries and super-capacitors) under applied potential. Intercalation-induced changes of dimensional and porous electrodes’ structure can be quantified in terms of hydrodynamic admittance models by fitting well developed models for momentum transfer to the experimental RQCM-D data retrieving structural parameters in way similar to fitting experimental EIS data (e.g. Nyquist plots) by equivalent electrical circuit analogs. Validation of the extracted parameters for their internal consistency and comparison with the results from complimentary other in-situ techniques (e.g. scanning probe microscopes) is required. The methodology of hydrodynamic spectroscopy of porous solids and composite electrodes that we develop in recent years is inexpensive, noninvasive and highly useful in a broad spectrum of applications including deeper insights into the dynamic build-up and subsequent development of solid-electrolyte interfaces in Li and Na battery electrodes and stresses-volume changes-stability interrelation of ion intercalation electrodes.[3] References [1] M.D. Levi and D. Aurbach, Electrochim. Acta 45 (1999) 167-185. [2] N. Shpigel, M.D. Levi, S. Sigalov, O. Girshevitz, D. Aurbach, L. Daikhin, P. Pikma, M. Marandi, A. Janes, E. Lust, N. Jackel, V. Presser, Nat. Mater. 15 (2016) 570-575.[3] S. Sigalov, N. Shpigel, M. D. Levi, M. Feldberg, L. Daikhin, D. Aurbach, Anal. Chem. 88, (2016) 10151–10157.

As a fundamental consideration in hydraulic valve dynamics, transient flow through a pipe orifice has been studied via numerical analysis. Steady axisymmetric viscous fluid flow was first investigated to confirm the present SIMPLER-based finite volume methodology. Time-dependent calculation for a suddenly imposed pressure gradient has shown two distinct characteristic time constants for the transient state. The first characteristic time constant is commonly considered corresponding to the flow rate change, while the second one concerning the variation of flow structure has not been investigated in earlier studies. The final settling of the flow is established through the second characteristic time which is almost ten times larger than the first one for the present condition.

Polarization relaxation was studied in Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) single crystals that show fatigue anisotropy. To excite prepoled crystals, a modest dc voltage (<1/2 of the coercive field) was applied along the poling direction. Upon removal of the voltage, the polarization decay in the time domain was measured. Experimental data were modeled with a stretched exponential function. Stretching exponent (β〈hkl〉) and characteristic time (τ〈hkl〉) constants for polarization relaxation were determined from data over four decades in the time domain at different stages of bipolar cycling. β〈hkl〉 values after 101 cycles were 0.146±0.002 and 0.247±0.0004 in the 〈001〉 and 〈111〉 orientations, respectively. The β〈111〉 constant increased up to 0.453±0.104 after 105 cycles in 〈111〉 oriented crystals that show fatigue. However, much less change is observed in β〈001〉 as a function of cycling for 〈001〉 crystals. Characteristic time constants for relaxation (τ〈hkl〉) were calculated for 〈001〉 and 〈111〉 orientations as 0.401±0.048 s and 57.46±0.10 s, respectively. These results suggest a faster polarization relaxation in 〈001〉 than in the 〈111〉 orientation of rhombohedral PZN-PT ferroelectric crystals.

PurposeThe paper aims at proposing a uniform and demonstrative description of two well‐known and widely used approximations of slowly time‐varying electromagnetic fields, i.e. the electro‐quasistatic and the magneto‐quasistationary approximation to Maxwell's equations.Design/methodology/approachUnder both approximations, the orders of magnitude of the relative errors of the dominant fields are analyzed by using three characteristic time constants. These time constants are determined by considering the material properties, the characteristic length scale and the characteristic time scale.FindingsLimiting curves which show the domains of applicability of the two approximations are retrieved from the estimation of their relative errors. The relation between the domains of validity of the electro‐quasistatic and magneto‐quasistationary approximations was found and depicted in a combined diagram.Research limitations/implicationsThe study is restricted to slowly time‐varying electromagnetic fields. Heuristic and local estimates based on local material properties were used for the analysis. Rigorous estimations of the errors (e.g. also considering the field problem's topology) of the magneto‐quasistationary approximation are already known in the literature. A rigorous estimation of the error of the electro‐quasistatic approximation is, therefore, suggested for future research.Originality/valueThe combined diagram showing the domains of validity of both approximations considered here in a uniform way is novel. It gives rise to an intuitive and easily accessible understanding of their applicability.

The P/Si-TiO2 thin films, with a molar ratio [P+Si]/[P/Si-TiO2]=0.03, were synthesized by the sol–gel method and spin-coating technique. Effects of relative ratios of dopants (i.e., R≡[P]/([ P+Si]) and calcination temperatures on phase transformation, grain growth, film thickness, surface morphology, light transmittance, energy gap and photocatalytic activity of the gel-derived P/Si-TiO2 thin films were examined and their results were compared with those of the undoped TiO2 thin films. By simultaneously doping Si and P elements into the Ti-O framework, the P/Si-TiO2 (i.e., 0.33≤ R ≤0.67) thin films calcined at ≦900℃ adhered strongly to the surface of fused-silica substrate and were composed of anatase-TiO2 only. The photocatalytic activities of the thin films were measured and represented using a characteristic time constant (τ) for the MB degradation. The small τ stands for high photocatalytic ability. The P/Si-TiO2 thin film prepared at R = 0.5 and 800℃ gave the best photocatalytic activity; this thin film decomposed about 90 mole% of MB in the water (the corresponding τ = 5.7 h), after 365-nm UV light irradiation for 12 h.

Clinical acceptance of laser-Doppler perfusion monitoring (LDPM) of microcirculation suffers from lack of quantitatively reliable signal data, due to varying tissue constitution, temperature, hydration, etc. In this article, we show that a novel approach using physiological models for response upon provocations provides quantitatively and clinically relevant time constants. We investigated this for two provocation protocols: postocclusive reactive hyperemia (PORH) and iontophoresis shots, measured with LDPM on extremities. PORH experiments were performed on patients with peripheral arterial occlusive disease (PAOD) or diabetes mellitus (DM), and on healthy controls. Iontophoresis experiments were performed on pre-eclamptic patients and healthy controls. We developed two dynamical physical models, both based on two characteristic time constants: for PORH, an "arterial" and a "capillary" time constant and, for iontophoresis, a "diffusion" and a "decay" time constant. For the different subject groups, we could extract time constants that could probably be related to physiological differences. For iontophoresis, a shot saturation constant was determined, with very different values for different groups and administered drugs. With these models, the dynamics of the provocations can be investigated and quantitative comparisons between experiments and subject groups become available. The models offer a quantifiable standard that is independent of the type of LDPM instrumentation.

ABSTRACTBacteria in the biofilm mode of growth are protected against chemical and mechanical stresses. Biofilms are composed, for the most part, of extracellular polymeric substances (EPSs). The extracellular matrix is composed of different chemical constituents, such as proteins, polysaccharides, and extracellular DNA (eDNA). Here we aimed to identify the roles of different matrix constituents in the viscoelastic response of biofilms. Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, and Pseudomonas aeruginosa biofilms were grown under different conditions yielding distinct matrix chemistries. Next, biofilms were subjected to mechanical deformation and stress relaxation was monitored over time. A Maxwell model possessing an average of four elements for an individual biofilm was used to fit the data. Maxwell elements were defined by a relaxation time constant and their relative importance. Relaxation time constants varied widely over the 104 biofilms included and were divided into seven ranges (<1, 1 to 5, 5 to 10, 10 to 50, 50 to 100, 100 to 500, and >500 s). Principal-component analysis was carried out to eliminate related time constant ranges, yielding three principal components that could be related to the known matrix chemistries. The fastest relaxation component (<3 s) was due to the presence of water and soluble polysaccharides, combined with the absence of bacteria, i.e., the heaviest masses in a biofilm. An intermediate component (3 to 70 s) was related to other EPSs, while a distinguishable role was assigned to intact eDNA, which possesses a unique principal component with a time constant range (10 to 25 s) between those of EPS constituents. This implies that eDNA modulates its interaction with other matrix constituents to control its contribution to viscoelastic relaxation under mechanical stress.

The solutions of the two-degree-pf-freedom aeroelastic system of an airfoil about different elastic axes are shown to be algebraically homomorphic. A simple aerodynamic model allows the characterization of this system by the lift and moment slopes and two characteristic time constants from the indicia! response to pitch, in addition to the usual structural parameters. Algebraic expressions for the flutter speed and frequency in terms of these parameters are thus derived. For flutter frequencies that are small compared with the characteristic time constants or for time constants that are close in magnitude, these expressions can be further simplified to uncoupled, explicit expressions. Many characteristics of flutter and their parametric dependency are readily discernible from these expressions, including the condition for flutter. It is shown that the flutter speed reaches the minimum (the so-called transonic dip) as the slope of pitching (about midchord) moment curve Cma becomes maximum. Hence, the Mach number of the transonic dip is predictable using quasisteady aerodynamics. Examples are also given to show the applicability of this simple criterion for the transonic dip of supercritical wings.