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This paper gives an overall review of the working principle of the inertial response from the synchronous condenser for frequency support in the grid. In addition to this, four proposed frequency control strategies for improvement of network frequency response by static energy storage devices, such as the Static Synchronous Compensator (STATCOM) with suitable energy storage elements or the battery energy storage system (BESS), are presented. The proposed frequency control strategies are evaluated and benchmarked with the synchronous condenser in the same network. It is shown that a power electronic converter based system with energy storage can be designed with lower rating, still providing the same or better frequency support than the synchronous condenser. more...

Analytic investigations of interarea oscillation damping of an idealized two-machine system using active-power modulation of three- and four-terminal high-voltage dc (HVDC) transmissions are presented. It is shown that, generally, the pairing of two terminals gives the highest damping. Based on the analytical results, recommendations for how the pairing should be made are developed. Simulations, both on a two-machine system and on a more realistic 23-machine system, verify the analytical results. more...

This paper introduces a new method for the preliminary design of power controllers (PCs) in the electric power grid. The method, which is denoted the ideal phase-shifter (IPS) method, utilizes the concept of the power controller plane where the active power of the PC line is plotted versus the difference in voltage angle between the PC terminals. The power controller plane makes it possible to graphically visualize the working area of a PC in a power grid and thus determine the grid situations which are dimensioning for the PC. The IPS method offers the possibility of plotting the grid characteristics in the power controller plane which are unbiased with respect to the reactive properties of the PC. This makes the method suitable for comparison and preliminary design of PCs of different types and with different characteristics by simple geometrical considerations. In this process, the IPS method uses the power-flow control method for deriving the PC characteristics. This paper includes an application example of the method where it is used for dimensioning of two different PCs in a 26-bus test system. more...

The ability of microorganisms to perform dissimilatory (per)chlorate reduction is, for most species, known to be oxygen sensitive. Consequently, bioremediation processes for the removal of oxochlorates will be disturbed if oxygen is present. We measured the expression of chlorite dismutase and chlorate reductase in the presence of different terminal electron acceptors in the chlorate reducer Ideonella dechloratans . Enzyme activity assays and mRNA analyses by real-time quantitative reverse transcription (qRT)-PCR were performed on cell extracts from cells grown aerobically with and without chlorate and on cells grown anaerobically in the presence of chlorate. Our results showed that both chlorite dismutase and chlorate reductase are expressed during aerobic growth. However, transfer to anaerobic conditions with chlorate resulted in significantly enhanced enzyme activities and mRNA levels for both enzymes. Absence of oxygen was necessary for the induction to occur, since chlorate addition under aerobic conditions produced neither increased enzyme activities nor higher relative levels of mRNA. For chlorite dismutase, the observed increase in activity was on the same order of magnitude as the increase in the relative mRNA level, indicating gene regulation at the transcriptional level. However, chlorate reductase showed about 200 times higher enzyme activity in anaerobically induced cells, whereas the increase in mRNA was only about 10-fold, suggesting additional mechanisms influence the enzyme activity. more...

This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important. more...

In this paper, a controller for a thyristor switched series capacitor (TSSC) is presented. The controller aims to stabilize the power system by damping interarea power oscillations and by improving the transient stability of the system. In addition to this, a power flow control feature is included in the controller. The power oscillation damping controller is designed based on a nonlinear control law, while the transient stability improvement feature works in open loop. The damping controller is adaptive and estimates the power system parameters according to a simplified generic model of a two-area power system. It is designed for systems where one poorly damped dominant mode of power oscillation exists. In the paper, a verification of the controller by means of digital simulations of one two-area, four-machine power system, and one 23-machine power system is presented. The results show that the controller improves the stability of both test systems significantly in a number of fault cases at different levels of interarea power flow. more...

This paper compares three different methods to limit the active power gradient of a renewable energy plant. The methods are based on the utilization of an Energy Storage System (ESS) to absorb and release power required in the case of fast power ramp-up or ramp-down, respectively. The paper presents analytical solutions for the required energy storage capacity in case of an ideal ramp event, using each of the three methods. The control methods are verified by simulations, using an active power time-series of a 6 MW wind farm. The novelty of this study lies in the inclusion of non-ideal power forecasts and evaluation of the control methods under varying forecast accuracies. The performance of the control methods when including a simple energy storage state controller was also studied. The controller prevents any drifts in the energy storage state. more...

With increasing utilization of high power-electronic converters, power-system modeling and stability analysis become ever more challenging. This paper introduces a transfer-matrix-based modeling method for power-system stability analysis. The method has previously been applied for studying the dynamic interaction between voltage-source converters and ac systems. In this paper, the modeling method is used to analyze some conventional power-system stability issues. It is demonstrated that the proposed modeling method gives a new interpretation of conventional power-system stability from a feedback-control point of view. The poles and zeros of the so-called Jacobian transfer matrix (JTM) are useful for understanding the properties of ac/dc systems. more...

The electronic structure of the propeller-shaped spiro-type molecules 2,2′, 7,7′-tetraphenyl-9,9′- spirobifluorene (spiro-quarterphenyl) and 2,2′, 7,7′-tetrakis(biphenyl-4-yl)-9,9-spirobifluorene (spiro-sexiphenyl) and its evolution upon doping with Li atoms or Na atoms have been studied by means of photoelectron spectroscopy. With lithium atoms as the dopant, two charges are stored on the same spiro branch in the form of bipolarons, for both spiro-quarterphenyl and spiro-sexiphenyl. In contrast, for doping with sodium atoms, the size of the counter ion makes it less energetically desirable to store two charges onto a single branch, and the charged species are polarons independent of the level of doping; this result is confirmed by optical absorption data. more...

The electronic structure of the conjugated polymer poly(9,9-dioctylfluorene) and the charge storage mechanism upon doping with lithium atoms have been studied using a combined experimental–theoretical approach. The density of states in the valence band region was measured using ultraviolet photoelectron spectroscopy, and the spectra interpreted with the help of the results of quantum-chemical calculations carried out at the Austin Model 1/Valence Effective Hamiltonian level. The valence band spectra as well as the calculated band structure and derived density of valence states of poly(9,9-dioctylfluorene) are compared to those of poly(p-phenylene) and a ladder-type derivative of poly(p-phenylene). The deposition of lithium atoms, in situ, onto the surface of the polymer films resulted in uniform (bulk) diffusion of the lithium atoms, charge transfer to the polymer (resulting in lithium ions), and the appearance of new electronic states in the gap. At low doping levels (up to about 0.1 Li-atom per repeat unit of the polymer), these states are polarons, and, as the doping level increases, they evolve into bipolarons. more...

The chemical and electronic structure of three different, strictly alternating copolymers, poly(2,5-diheptyl-1,4-phenylene- alt -1,4-naphthylene) (P14NHP), poly(2,5-diheptyl-1,4-phenylene- alt -2,6-naphthylene) (P26NHP) and poly(2,5-diheptyl-1,4-phenylene- alt -9,10-anthrylene) (P910AHP), have been studied by photoelectron spectroscopy and optical absorption spectroscopy. The experimental results have been analyzed using the results of quantum chemical calculations. In the geometrical structure of all three of the polymers there are large torsion angles between the phenylene unit and the naphthylene or anthrylene units. These large torsion angles lead to localization of the π-electron wave functions, and minimal conjugation along the polymer backbone. For all three polymers, the highest occupied molecular orbital is completely localized to the naphthylene or anthrylene unit. The frontier molecular orbital wave functions are very reminiscent of the highest occupied orbitals of the isolated naphthalene or anthracene molecules. The optical absorption spectra of all three polymers verify the existence of large optical band gaps, consistent with the large torsion angels. The first several optical transitions in the polymers are also very reminiscent of the transitions in single naphthalene and anthracene molecules. more...

The electronic structure of pristine and sodium-doped poly(p-pyridine) has been studied using both ultraviolet and x-ray photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum-chemical calculations. Electronic band-structure calculations are performed for isolated chains with different connectivity patterns (head-to-tail and head-to-head), using the valence effective Hamiltonian (VEH) method, with geometries derived from optimizations using the Austin Model 1 Hamiltonian. The density-of-valence-states are derived directly from the VEH band structure. Excellent agreement is obtained between the theoretical simulations and the experimental data, which allows for a detailed assignment of the different peaks in the spectra. The C(1s) and N(1s) shake-up spectra of poly(p-pyridine) are analyzed on the basis of corresponding data for pyridine in the gas phase. Upon sodium doping of poly(p-pyridine), new states are observed within the otherwise forbidden energy gap. These ... more...

We report a comparison of the work functions of thin films of indium tin oxide (ITO), carried out by means of ultraviolet photoelectron spectroscopy (UPS) and by measurements of the contact potential difference with respect to a gold reference electrode (Kelvin probe (KP) method). We investigated commercially available ITOs both “as-received”, and after certain surface treatments, such as oxygen plasma. First, we find measurable discrepancies between KP values measured with three different instruments, and between the KP and the UPS values. Secondly, and unexpectedly, we find that the KP, although more sensitive than UPS, does not detect certain differences between ITOs with different surface treatments. We discuss the results in view of the different environments in which the measurements are carried out (UHV for the UPS and air/Ar for the Kelvin method), of the effects which may be induced by the high-energy photon irradiation in the UPS measurement, and of the stability of the gold probe work function in gas ambient. We conclude that UPS is better-suited for absolute work function determination, although KP remains a convenient and inexpensive tool for fast screening of contact potential differences. more...

The behavior of lithium atoms deposited on the surfaces of ultra-thin spin-coated films of poly(dioctylfluorene), and of condensed molecular solid films of tris(8-hydroxyquinoline) aluminum, have b ... more...

Here are presented initial results on spectral narrowing in submicron thick neat films, of 2,2′,7,7′-tetraphenyl-9,9′-spirobifluorene (spiro-quarterphenyl) and 2,2′,7,7′-tetrakis(biphenyl-4-yl)-9,9-spirobiflourene (spiro-sexiphenyl). The luminescence effects reported here are common to several other molecules which belong the class of molecules known as the spiro-type molecules. The Amplified Spontaneous Emission (ASE) is evidenced by a dramatic collapse of the line width, when pumped with sufficient energy, down to 2.2 and 2.9 nm for spiro-quarterphenyl and spiro-sexiphenyl, respectively. These molecules have the ability to form stable, amorphous films with glass transition temperatures at around 200 °C. Thus, these molucules are suitable candidates as the active material in molecular solid state injection lasers. more...

We report combined studies of the influence of chemical and physical treatments on the properties of indium–tin oxide (ITO) thin films. The ITO films were also used as transparent anodes of polymeric light-emitting diodes (LEDs) incorporating poly(p-phenylene vinylene) (PPV) as the emitter material, with, or without, doped poly(3,4-ethylene dioxythiophene) (PEDOT) as a hole-injection/transport layer. Structures based on a soluble green derivative of PPV, poly(4,4′-diphenylene diphenylvinylene) were also tested. We studied chemical (aquaregia, degreasing, RCA protocol) and physical (oxygen and argon plasmas, Teflon, and paper rubbing) treatments and, in contrast to recently published work, we find that for Balzer Baltracon ITO, oxygen plasma and not aquaregia yields the highest efficiencies and luminances and the lowest drive voltages. For oxygen-plasma-treated anodes, the device efficiency clearly correlates with the value of the ITO surface work function, which in turn depends on the time of treatment. I... more...

Here are presented initial results on spectral narrowing in submicron thick neat films, of 2,2′,7,7′-tetraphenyl-9,9′-spirobifluorene (spiro-quarterphenyl) and 2,2′,7,7′-tetrakis(biphenyl-4-yl)-9,9-spirobiflourene (spiro-sexiphenyl). The luminescence effects reported here are common to several other molecules which belong the class of molecules known as the spiro-type molecules. The Amplified Spontaneous Emission (ASE) is evidenced by a dramatic collapse of the line width, when pumped with sufficient energy, down to 2.2 and 2.9 nm for spiro-quarterphenyl and spiro-sexiphenyl, respectively. These molecules have the ability to form stable, amorphous films with glass transition temperatures at around 200 °C. Thus, these molucules are suitable candidates as the active material in molecular solid state injection lasers. more...

Angle-dependent photoelectron spectroscopy has been used to study some details of the chemistry at the interface between indium-tinoxide, deposited by argon plasma sputtering, and poly( p -phenylene vinylene). We find chemical species corresponding to different oxidized states of poly( p -phenylene vinylene) and we discuss their assignment with reference to those produced in photo-oxidation experiments. more...

The electronic structure and optical properties of the propeller-shaped spiro molecules, 2,2′-bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)-9,9′-spirobifluorene, and 2,2′,7,7′-tetrakis (biphenyl-4-yl)-9,9-spirobifluorene, have been studied by photoelectron spectroscopy, Raman spectroscopy, and spectroscopic ellipsometry. The experimental spectra are analyzed with the help of results from quantum-chemical calculations. The excellent agreement between experiment and theory allows for a detailed characterization of the frontier electronic structure and lowest-energy optical transitions in these novel compounds. It follows that most of the electronic and optical properties of the these spiro-molecules can be deduced by consideration of a single branch; in this case a sexi-phenyl and PBD branch. In particular, although the branches in the spiro molecules are perpendicular to each other, there is considerable interaction at the spiro-center between the π-electron systems of the two branches, indicating, amon... more...

The electronic structure of cyano‐substituted poly(2,5‐dihexyloxy‐p‐phenylene‐vinylene), or CN‐PPV, has been studied in both pristine and doped states. Ultraviolet photoelectron spectroscopy (UPS) and x‐ray photoelectron spectroscopy (XPS), as well as optical absorption spectroscopy have been carried out under ultrahigh vacuum (UHV) conditions, and the results have been interpreted with the help of quantum‐chemical calculations. For the pristine polymer, the addition of cyano groups to the vinylene units does not affect the width of the π‐bands closest to the Fermi level; however, the positions of the flat parts of the upper π‐bands are shifted by approximately 0.4 eV towards higher binding energies relative to the Fermi energy, as compared with the corresponding bands of other alkoxy‐substituted poly(p‐phenylenevinylene)s. On the other hand, there are only marginal differences in the optical absorption spectra; the interband absorption onset is comparable to the values for alkoxy‐substituted poly(p‐pheny... more...

The equilibrium geometry of an isolated chain of poly(3,3′-phthalidylidene-4,4′-biphenylene), or PPB, has been studied using quantum chemical calculations based upon the Austin Model 1 (AM1) method. The band structure of an isolated PPB chain has been calculated, using the AM1 geometry as input, with the help of the valence-effective Hamiltonian (VEH) model. From the electronic structure results, the density of valence states has been derived for comparison with experimental data. Both the neutral and the n-doped polymer chains have been simulated. The results are compared with features of the polymer deduced through other measurements reported in the literature. more...

The valence band structure of poly(3,3′-phthalidylidene-4,4′-biphenylene) has been studied using ultraviolet photoelectron spectroscopy (UPS). This polymer exhibits a dielectric-to-metal phase transition under the influence of external forces and is therefore a good candidate for studying charge instabilities in conjugated polymers. Interpretation of the UPS spectra is facilitated using quantum chemical calculations based on the semi-empirical Austin Model 1 (AM1) method, for geometry optimization, and the valence effective Hamiltonian (VEH) method, for calculating the energy band structure diagram, from which the density of valence states (DOVS) in the solid material is derived. The calculated DOVs is in good agreement with the experimental UPS spectra, enabling an identification of features in the experimental data in terms of specific features in the energy band structure. more...

This paper describes an adaptive method for control of a TCSC device for power oscillation damping. The aim is to mitigate power oscillations in power systems with one dominating oscillation mode. To design the controller, a simple generic model of the power system with only a few variables is used. Initially, a fixed-parameter controller which is based on a pole-placement technique is designed. The controller is then implemented in a digital simulator and tested in a four-machine power system. The fixed-parameter controller performs well in most cases but in some contingencies, a performance decay is seen. To improve the controller performance, an adaptive control design has been investigated. The investigated controller is a self-tuning regulator and a recursive least-squares method is used to estimate the system model parameters. An open-loop controller for transient stability improvement and a closed-loop PI-controller for power flow control are also presented. The adaptive controller has been validated with good results by means of simulations of a number of contingencies in different operating conditions of the four-machine system. more...

Primary frequency control is often added to the control system of a high-voltage DC (HVDC) transmission that interconnects two nonsynchronous ac grids. As the active-power actuation lag is typically in the range of hundreds of milliseconds, the HVDC primary frequency control can be made fast enough to permit inertia sharing among the interconnected ac grids. This reduces the maximum frequency fall after a loss-of-generation contingency (the nadir). A fast HVDC primary frequency control may affect the interarea modes of the interconnected grids. To this end, it is shown that, at least for the cases studied, the modal damping never decreases through the introduction of the mentioned control. more...

This paper describes the design and verification of a time-discrete adaptive controller for damping of inter-area power oscillations, power flow control, and transient stability improvement. Only locally measured signals are used as inputs to the controller. The controller may be used with any FACTS device which operates as a variable series reactance in the power grid, such as for example the TCSC. The controller is based on a reduced system model which relies on the assumption of one dominating inter-area oscillation mode in the power system where the FACTS device is placed. Verification of the controller is performed by means of digital simulations of a four-machine system commonly used to study inter-area oscillations. more...

This paper describes an adaptive method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. Here, a reduced model of the power system with only two rotating masses is used as a basis for the control design. The model parameters are updated using local measurements of the active power on the controlled line. An adaptive closed loop controller is developed based on the principle that it is possible to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line in a small number of steps. The reduced model parameters are recomputed when new information of the system response is known making the control scheme an adaptive one. The paper also includes the derivation of a damping controller with a power flow control feature and a verification of the controllers using digital simulations of power system models of different complexities. more...

This paper describes an open loop method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. The principle of the method is to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line, thereby changing the total reactance between the areas participating in the oscillation. In order to stabilize the system during an oscillation, the stationary voltage angle difference between the areas is changed to coincide with the present angle at a point where the speed of the lumped machine representations of the areas is nominal. This is the case at the peaks of the oscillation. To determine the required size of the reactance step, a reduced model of the power system is used. The model parameters are continuously updated using local measurements of the active power on the reactance controlled line. Several approaches for damping with different numbers of steps are presented and verified using digital simulations of power system models. more...

For high performance control of flexible AC transmission system (FACTS) devices with controllable reactances, a representation of the surrounding grid is essential. Using such a model, an adaptive control strategy can be developed which optimizes the control in real time as the grid parameters change. This paper proposes such a generic grid model and derives the theory of how to estimate the main parameters using measurements of the line active power response from small step reactance changes. The estimation methods are verified using simple grid models in PSCAD simulations and more advanced grid models using SIMPOW simulations of a modified version of the CIGRE Nordic 32 grid. This work should be thought of as a foundation for developing control systems for variable series reactance FACTS devices. more...

The qualitative results of a study of the fabrication of Ca/CN-PPV/ITO polymer light-emitting diodes (LEDs) in ultrahigh vacuum (UHV) are reported, where CN-PPV is a cyano-substituted poly(p-phenylenevinylene). If the calcium electrode is deposited on a clean polymer surface under UHV conditions, the device yield is very low, and, for the devices that do function, the electroluminescence lifetimes are extremely short. If the calcium electrode is deposited in the presence of a high partial pressure of oxygen, the diodes are much better in terms of yield, lifetime and luminescence. more...

Electronic devices based on organic materials are presently being developed. In these devices, the cathode interface and the nature of the charge carrying species are often of crucial importance. In that context, the behavior of lithium atoms deposited on the surfaces of ultra-thin spin-coated films of poly(dioctyl-fluorene), PFO, and of condensed molecular solid films of tris(8-hydroxyquinoline) aluminum, Alq3, have been studied. The Li-atoms donate charges to the organic systems, leading to doping-induced electronic states in the otherwise forbidden energy gap. The changes in the electronic structure induced by charge transfer from the Li-atoms are different in the two materials studied, and depend upon the localization of the electronic states to which the electrons are transferred. In the case of the delocalized wave functions of the ∼-system of PFO, at low doping levels, the added charges lead to the formation of polaron states, while at higher doping concentrations, bipolaron states are formed. In the case of Alq3, however, up to a level of three added electrons per molecule, the added electrons reside in states localized on each of the three ligands. The role of thin (∼5 Å) interfacial layers of LiF or CsF between poly(9,9- dioctylfluorene) polymer film and an aluminum electrode was studied as well. LiF-deposition on poly(9,9-dioctyl-fluorene) did not cause doping of the polymer films, nor did the LiF dissociate at the interface. No significant shifts in the binding energy of the core levels nor any changes in the work function occurred. Al-deposition on LiF/PFO films did not cause dissociation of LiF, unlike the case for Alq3. We found that CsF does not dissociate when deposited on a polymer film. However, deposition of aluminum on CsF will cause dissociation with cesium n-doping the PFO film at the interface and fluorine likely reacting with aluminum to form AlF3. When deposited onto either of sputter-cleaned Al surface or Al with native oxide layer (AlxOy), CsF also was found to dissociate at the interface. CsF does not dissociate for Au/CsF/PFO and CsF/Au interfaces, which emphasizes the crucial role aluminum plays in the process. The observed decomposition of CsF occurring upon Al deposition and following Cs-doping of the surface region of PFO likely enhances injection of electrons into organic layer improving device performance. Since CsF dissociation is independent of the underlying material, the Al/CsF/emissive-material structure could be effective for almost all types of polymer/organic based electronic devices. more...

Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer. more...

The electronic structure of tris(8-hydroxyquinoline) aluminum (Alq(3)) has been studied in the pristine molecular solid state as well as upon interaction (doping) with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq(3) molecule, resulting in a new spectral feature (peak) in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq(3) molecule. (C) 1999 American Institute of Physics. [S0021-9606(99)50628-4]. more...

Organic conjugated polymers have the electronic structure of semiconductors and can be doped to become good conductors (1). Conjugated polymers are now used as active materials in a wide variety of ... more...

The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds. more...

The electronic and geometric structures of poly [3-(4-octylphenyl)thiophene] have been studied by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS, respectively). Thermochromic effects, and new charge induced states generated by potassium doping, have been observed by direct UPS measurements. The experimental results are in very good agreement with the results of theoretical quantum chemical calculations performed with the Austin Model 1 semi-empirical model and the valence-effective Hamiltonian pseudo-potential model. more...

An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC) (vol 25, pg 381, 2010)

The electronic structure of the interfacial region between tris(8-hydroxy-quinoline) aluminum (Alq) and alkali metal (Li and K) was studied by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). Condensed molecular solid films of Alq were doped by alkali metal deposited on the surface. The alkali metal atoms were found to distribute uniformly through out the depth to which the sample could be studied. A new feature of the density of states was observed in the band gap, 1.7eV higher than the HOMO of the pristine Alq. The binding energy of N(1s) core level of the quinoline ligand of Alq was shifted by doping to lower binding energies, of 1.6 eV and 1.8 eV from the original peak for Li and K doping, respectively. The intensity of the new shifted peak was saturated when Alq was fully doped. The full doping level, determined by chemical analysis (XPS), was Alq:metal=1:3. more...

The chemical and electronic structure of a highly luminescent conjugated polymer poly(4,4′-diphenylene diphenyl-vinylene) has been investigated using a combined experimental and theoretical approach based on photoelectron spectroscopy, optical absorption and semiempirical AM1 and INDO/SCI, as well as Valence Effective Hamiltonian (VEH), calculations. Details are presented on the ground state geometry, calculated electronic band structure, comparisons between the calculated and experimental, as obtained by UPS, density-of-valence-states, and nature of the optical transitions. more...

We studied the surface properties of indium-tin oxide (ITO) modified by wet (aquaregia, ultrasonication, RCA) and dry (oxygen and argon plasmas) treatments. The influence of surface treatment on ITO was investigated by surface energy, surface roughness, sheet resistance, and workfunction measurements. We report that oxygen plasma treatment induces: (1) the highest surface energy with the highest polarity, (2) the smoothest surface, (3) the lowest sheet resistance, and (4) the highest workfunction. We also observe that the PL efficiencies of PPV, PDPV and PEDOT/PPV on ITO are affected by the surface treatment of ITO. more...

We studied the surface properties of indium-tin oxide (ITO) modified by wet (aquaregia, ultrasonication, RCA) and dry (oxygen- and argon-plasma) treatments. The surface modification was investigated by surface energy, surface morphology, sheet resistance, carrier concentration, carrier mobility, and workfunction measurements. We report that the studied oxygen-plasma treatment induces: the highest surface energy with the highest polarity, the smoothest surface, the highest carrier density but the lowest mobility, the lowest sheet resistance, and the highest workfunction (stable in air). Polymer light-emitting diodes fabricated with the oxygen plasma treated substrates give the best performance in terms of electroluminescence efficiency and device lifetime. This is attributed to a favorable surface modification of ITO anodes by oxygen-plasma. more...