Electrically Excited Research Articles

Electroluminescence efficiencies of erbium in silicon-based hosts

We report on room-temperature 1.5 μm electroluminescence from trivalent erbium (Er3+) ions embedded in three different CMOS-compatible silicon-based hosts: SiO2, Si3N4, and SiNx. We show that although the insertion of either nitrogen or excess silicon helps enhance electrical conduction and reduce the onset voltage for electroluminescence, it drastically decreases the external quantum efficiency of Er3+ ions from 2% in SiO2 to 0.001% and 0.0004% in SiNx and Si3N4, respectively. Furthermore, we present strong evidence that hot carrier injection is significantly more efficient than defect-assisted conduction for the electrical excitation of Er3+ ions. These results suggest strategies to optimize the engineering of on-chip electrically excited silicon-based nanophotonic light sources.

An Electrically Excited Nanoscale Light Source with Active Angular Control of the Emitted Light

We report on the angular distribution, polarization, and spectrum of the light emitted from an electrically controlled nanoscale light source. This nanosource of light arises from the local, low-energy, electrical excitation of localized surface plasmons (LSP) on individual gold nanoparticles using a scanning tunneling microscope (STM). The gold nanoparticles (NP) are chemically synthesized truncated bitetrahedrons. The emitted light is collected through the transparent substrate and the emission characteristics (angular distribution, polarization, and spectrum) are analyzed. These three observables are found to strongly depend on the lateral position of the STM tip with respect to the triangular upper face of the gold NP. In particular, the resulting light emission changes orientation when the electrical excitation via the STM tip is moved from the base to the vertex of the triangular face. On the basis of the comparison of the experimental observations with an analytical dipole model and finite-difference time-domain (FDTD) calculations, we show that this behavior is linked to the selective excitation of the out-of-plane and in-plane dipolar LSP modes of the NP. This selective excitation is achieved through the lateral position of the tip with respect to the symmetry center of the NP.

Electromagnetic Field Analysis of Hybrid Excitation Vehicle Generator with Low Voltage and High Current

In order to further improve the power supply system reliability of low voltage high current vehicle generator, hybrid excitation is used and the permanent magnets are added between the main magnetic poles body and pole shoes. Aiming at reply the problem of limited installation space, the asymmetric pole structure, non-uniform commutating pole, single wave windings playing a role of the pressure line and oblique brush etc are investigated for improving commutation. This paper researched on the distribution of the flux line, the waveform of the air gap magnetic field, and analysis inner magnetic field at the loading by hybrid excitation and no loading by permanent magnet excitation alone respectively with the method of finite element. The results reveal that the magnetic field established by several excitation systems is still symmetric and uniform although the asymmetric structure, so it ensures the provision of suitable medium space for mechanical and electrical energy conversion. By comparing the permanent magnets excitation alone and hybrid excitation in a generator magnetic field distribution and air gap magnetic field waveform, the permanent magnet excitation and electricity excitation realized the superposition of magnetic field, and common establish main generator magnetic field. Hybrid excitation also reduces the current density of excitation coils and improves the heat dissipating performance compared with electrically excited alone. Through the performance analysis of the hybrid excitation, the output voltage waveform is very stable. The curve of auxiliary excitation current along with velocity variation provide important basis for excitation control devices and the development of control algorithm. It will help to improve the stability, reliability and security of the generator, the results can provide key technical support to the development of low-voltage high-current hybrid excitation vehicle generator.

Structural Damage Detection with Piezoelectric Wafer Active Sensors

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of damage detection and structural health monitoring (SHM) applications. This paper starts with a brief review of PWAS physical principles and basic modelling and continues by considering the various ways in which PWAS can be used for damage detection: (a) embedded guided-wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays, thickness mode; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; (c) passive detection, i.e., acoustic emission and impact detection. An example of crack-like damage detection and localization with PWAS phased arrays on a small metallic plate is given. The modelling of PWAS detection of disbond damage in adhesive joints is achieved with the analytical transfer matrix method (TMM). The analytical methods offer the advantage of fast computation which enables parameter studies and carpet plots. A parametric study of the effect of crack size and PWAS location on disbond detection is presented. The power and energy transduction between PWAS and structure is studied analytically with a wave propagation method. Special attention is given to the mechatronics modeling of the complete transduction cycle from electrical excitation into ultrasonic acoustic waves by the piezoelectric effect, the transfer through the structure, and finally reverse piezoelectric transduction to generate the received electric signal. It is found that the combination of PWAS size and wave frequency/wavelength play an important role in identifying transduction maxima and minima that could be exploited to achieve an optimum power-efficient design. The multi-physics finite element method (MP-FEM), which permits fine discretization of damaged regions and complicated structural geometries, is used to study the generation of guided waves in a plate from an electrically excited transmitter PWAS and the capture of these waves as electric signals at a receiver PWAS. Wave diffraction from a hole damage is illustrated through time-frame snapshots. The paper ends with conclusions and suggestions for further work.

Injection efficiency in AlGaN‐based UV laser diodes

AbstractWe evaluated AlGaN‐based 355 nm UV laser diodes prepared under two different Mg activation conditions. The annealing processes for Mg activation in p‐layers were carried out under N2 or O2 ambient to investigate the effect of the ambient gas on the laser characteristics. The threshold current densities and operating voltages of the UV laser diodes were improved by annealing under O2 compared with those under N2. We then estimated the injection efficiencies of the laser diode structures by considering the internal quantum efficiencies of optical excitation and electrical excitation. The internal quantum efficiency of the electrically excited spontaneous emission from the laser structure annealed under O2 reached 50% at a carrier density of 7.0×1018 cm‐3, while the structure annealed under N2 required a 1.8‐fold higher carrier density of 1.2×1019 cm‐3 to reach the same internal quantum efficiency. In addition, the internal quantum efficiency estimated from optical excitation reached 50% even at a carrier density of 3.0×1018 cm‐3. This implies that the injection efficiencies in the UV laser diode structures annealed under N2 and O2 were 25% and 45%, respectively. Mg activation by O2 annealing is effective for increasing the injection efficiency. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Triggered single-photon emission from electrically excited quantum dots in the red spectral range

Pulsed electrical excitation was used to excite single InP/Ga0.51In0.49P quantum dots and obtain triggered single-photon emission in the red spectral range at an excitation repetition rate of up to 200 MHz. Increased repetition rates are prevented by the finite decay-time, and autocorrelation measurements look similar to what is expected for dc injection above 1 GHz. Finally, it is shown that negative voltage pulses can increase the decay-rate considerably such that 1 GHz excitation rates should be possible.

Influence of the character of electric excitation on the parameters of transient processes in piezoelectric transducers with plate elements

A pulsed operating mode of a piezoelectric plate placed into a liquid is considered. The problem is solved for the application of exciting electric pulses with a duration that is a multiple of the duration of a sinusoid half-period at the natural frequency of a piezoelectric plate. For different degrees of plate damping, the dynamics of changes in the shape of an acoustic pulse are studied as a function of an electrically excited pulse duration. The durations and amplitudes of acoustic signals are evaluated. The problem is solved by the calculation-theoretical method via application of both the apparatus of schemes-analogues of piezoelectric transducers and the spectral method based on a Fourier transform.

Time-resolved studies of individual molecular rotors

Thioether molecular rotors show great promise as nanoscale models for exploringthe fundamental limits of thermally and electrically driven molecular rotation.By using time-resolved measurements which increase the time resolution of thescanning tunneling microscope we were able to record the dynamics of individualthioether molecular rotors as a function of surface structure, rotor chemistry,thermal energy and electrical excitation. Our results demonstrate that the localsurface structure can have a dramatic influence on the energy landscape that themolecular rotors experience. In terms of rotor structure, altering the length of therotor’s alkyl tails allowed the origin of the barrier to rotation to be more fullyunderstood. Finally, time-resolved measurement of electrically excited rotation revealedthat vibrational excitation of a C–H bond in the rotor’s alkyl tail is an efficientchannel with which to excite rotation, and that the excitation is a one-electronprocess.

Coherent electrically excited organic semiconductors: coherent or laser emission?

Recent experimental results demonstrating coherent emission from an electrically-excited pulsed dye-doped organic semiconductor interferometric emitter, are discussed from a coherence and a laser perspective. Examination of available results indicates that there is sufficient evidence to classify the reported emission as being equivalent to broadband dye laser radiation. From a practical perspective, however, this is an interferometric organic semiconductor emitter that yields a spatially coherent beam (Δθ≈ 2.53 mrad or 1.1 times the diffraction limit) and an emission linewidth comparable with broadband dye lasers (Δλ≈ 11 nm at half width). Geometrical dimensions, and electrical excitation parameters, for a significantly smaller interferometric organic emitter are suggested.

Electrically excited oxygen generator produces 30% transfer from O2 into O2(aΔ1) with 40% electrical efficiency

An electrically excited O2(aΔ1) generator packages a bundle of plasma containment tubes into a heat exchanger configuration. Chilled fluorinert circulates rapidly through the structure, and gases (O2, Ar, and He mix at 60–100Torr) flow transonically through the plasma tubes. An externally sustained, sub-breakdown discharge is ionized by means of applying overvolted [∼150Td(1Td=10−17Vcm2)] ∼10–30ns pulses at 50000pulses∕s. The plasma is preionized by UV radiation, iminating from a dielectric barrier discharge plasma. A dc electric field of E∕N=10Td conducts current longitudinally along the tubes. This process accomplishes: (1) O2(aΔ1) fractional extraction of 30%, (2) electrical excitation efficiency of 40%, (3) specific power loading up to 150kJ∕m O2, and (4) a minimal plasma temperature rise of <125°K. The O2(aΔ1) flow stream carries 2400W.

Intracellular Axial Current in Chara corallina Reflects the Altered Kinetics of Ions in Cytoplasm under the Influence of Light

Recent experiments demonstrate that the concentration of Ca 2+ in cytoplasm of Chara corallina internodal cells plays important role in electrical excitation of the plasma membrane. The concentration of free Ca 2+ in the cytoplasm −[Ca 2+] c is also sensitive to visible light. Both phenomena were simultaneously studied by noninvasive measuring action potential (AP) and magnetic field with a superconducting quantum interference device magnetometer in very close vicinity of electrically excited internodal C. corallina cells. A temporal shift in the depolarization maximum, which progressively occurred after transferring cells from the dark into the light, can be explained by the extended Othmer model. Assuming that the change in membrane voltage during the depolarization part of AP is the direct consequence of an activation of [Ca 2+] c sensitive Cl − channels, the model simulations compare well with the experimental data. We can say that we have an example of electrically elicited AP that is of biochemical nature. Electric and magnetic measurements are in good agreement.

Eigenfunction analysis of radially polarized piezoelectric cylindrical shells of finite length

An eigenfunction approach is presented to determine the response of radially polarized piezoelectric cylindrical shells of finite length to electrical excitation. The equations of motion of the piezoelectric cylinder are first derived by using the membrane approximation. Then they are solved by expressing the displacement distribution as the sum of the static solution and a weighted sum of a complete set of functions—the eigenfunctions of the short-circuited cylinder. The static solution is necessary to exactly satisfy the boundary conditions of the electrically excited cylinder. Moreover, in some cases, the series solution does not converge to the correct displacement distribution when some other terms, instead of the static solution, are used to satisfy the boundary conditions. The weights or displacement coefficients are determined by using the orthogonal property of the eigenfunctions. Finally, the input electrical admittance is determined by using the equation of state and the displacement distribution. Analyses of cylinders with various boundary conditions are presented to illustrate the approach. Numerical results are used to show that the series solutions converge very rapidly to the closed form solutions.

Catheters for imaging, sensing electrical potentials, and ablating tissue

An acoustic imaging system for use within a heart has a catheter, an ultrasound device incorporated into the catheter, and an electrode mounted on the catheter. The ultrasound device directs ultrasonic signals toward an internal structure in the heart to create an ultrasonic image, and the electrode is arranged for electrical contact with the internal structure. A chemical ablation device mounted on the catheter ablates at least a portion of the internal structure by delivery of fluid to the internal structure. The ablation device includes a material that vibrates in response to electrical excitation, the ablation being at least assisted by vibration of the material. The ablation device may alternatively be a transducer incorporated into the catheter, arranged to convert electrical signals into radiation and to direct the radiation toward the internal structure. The electrode may be a sonolucent structure incorporated into the catheter, through which the ultrasound device is arranged to direct signals. An acoustic marker mounted on the catheter emits a sonic wave when electrically excited. A central processing unit creates a graphical representation of the internal structure, and super-imposes items of data onto the graphical representation at locations that represent the respective plurality of locations within the internal structure corresponding to the plurality of items of data. A display system displays the graphical representation onto which the plurality of items of data are super-imposed.

Coulomb Excitation of Elements of Medium and Heavy Mass

Yields of gamma rays from thick targets of In, I 127 , Ta 181 , Re 185,187 , Ir 191,193 , Hg 198,199,200,202 , Th, and U were investigated under proton or alpha-particle bombardment in the energy range 2 to 4 Mev. By using the theory for electric excitation, reduced matrix elements for all electrically excited radiations were computed and compared with single-particle estimates. The results are interpreted in terms of the strong-coupling collective model of Bohr and Mottelson and compared with the systematic trends in the region of the closed shell at 126 neutrons. A 512-kev gamma ray excited in In by proton bombardment must result from a nuclear reaction. From excitation curves, gamma rays in I 127 at 60, 208, 392, 438, 631, 751, and 941 kev appear to arise from Coulomb excitation. No cascade radiations are observed. The radiations from Ta, Re, Ir, and Hg show the effects of a transition from the strong collective rotational motion to a collective vibrational nuclear motion or single-particle excitation as one approaches the closed neutron shell. Only the first excited states of Th 232 and U 238 were excited with alpha particles. No evidence for other levels was observed with proton excitation. The results agree within experimental error with other excitation measurements and with radiative lifetime measurements.