Temporary Charge Research Articles

Minimization of ion micromotion using ultracold atomic probes

We report on a sensitive method to minimize excess micromotion of an ion in a Paul trap. The ion is placed in an ultracold cloud of neutral Rb atoms in which ionic micromotion induces atomic losses and heating. Micromotion is minimized by applying static electric offset fields such that both loss and heating are minimized. We achieve a compensation on the level of the most precise compensation methods to date. In contrast to these methods, our scheme is applicable even for ions that cannot be optically probed. Furthermore, it avoids the formation of temporary patch charges which are a main issue for the long-term stability of micromotion minimization.

Investigation of the Gate Bias Stress Instability in ZnO Thin Film Transistors by Low-Frequency Noise Analysis

To investigate the electrical instability mechanism under the application of gate bias stress and relaxation, the 1/f noise spectra of two different ZnO thin-film transistors (TFTs) were analyzed. In terms of gate bias dependence (SIDS/IDS), both devices followed a mobility fluctuation model based on the traps in their channel layers prior to and after stress. Device A (channel thickness: 20 nm), recovered its initial noise parameter (αapp) after relaxation, in exact agreement with the current–voltage (I–V) measurement results; this shows that in device A, the dominant phenomenon under the application of stress was temporary charge trapping at grain boundary traps. However, in device B (channel thickness: 80 nm), αapp did not recover its initial values after relaxation, and transfer parameters, such as VTH, mobility, SS, and Nt, degraded after the gate bias stress. Moreover, after the stress, device B showed a reduced gate insulator breakdown voltage. The electrical degradation seen in device B can be explained by trap creation and/or charge injection near channel/gate oxide interfaces, including those within the channel layer.

Chemical Vapor Sensing with Monolayer MoS2

Two-dimensional materials such as graphene show great potential for future nanoscale electronic devices. The high surface-to-volume ratio is a natural asset for applications such as chemical sensing, where perturbations to the surface resulting in charge redistribution are readily manifested in the transport characteristics. Here we show that single monolayer MoS(2) functions effectively as a chemical sensor, exhibiting highly selective reactivity to a range of analytes and providing sensitive transduction of transient surface physisorption events to the conductance of the monolayer channel. We find strong response upon exposure to triethylamine, a decomposition product of the V-series nerve gas agents. We discuss these results in the context of analyte/sensor interaction in which the analyte serves as either an electron donor or acceptor, producing a temporary charge perturbation of the sensor material. We find highly selective response to electron donors and little response to electron acceptors, consistent with the weak n-type character of our MoS(2). The MoS(2) sensor exhibits a much higher selectivity than carbon nanotube-based sensors.

Model for oscillations in the guidance of ions through insulating nanocapillaries

The pre-equilibrium period of the ion guiding through insulating nanocapillaries is characterized by the production of temporary charge patches inside the capillaries. The dynamics of the charge patch creation is revealed by oscillations of the mean emission angle of the emerging ions. To understand the oscillations, we propose a phenomenological model based on the retardation between charging and discharging of the patches.

Electrical Characteristic Analysis of Postannealed ZnO Thin-Film Transistors under O2 Ambient

An electrical characteristic analysis of postannealed ZnO thin-film transistors (TFTs) under O2 ambient from 200 to 300 °C for 1 h was carried out. The 250-°C-annealed device showed the best electrical characteristics, which can be explained by crystallinity improvement on the basis of X-ray diffraction (XRD) analysis. However, although having an active layer of the best crystal quality, the electrical properties of the 300-°C-annealed device were degraded, which can be due to the higher ΦB0 resulting from the oxidation of Ti used as the S/D electrodes. Next, the stability of ZnO TFTs was investigated. Under a positive bias stress of 20 V, it was found that the annealed devices showed smaller threshold voltage shifts (ΔVTH) than the as-grown device. In addition, with the stress bias removed, all devices recover their original characteristics, which can be explained by temporary charge trapping into preexisting traps. Therefore, the post-thermal annealing under O2 ambient can improve the electrical and reliability characteristics of ZnO TFTs, which can be explained by a fewer grain boundary traps and a lower grain boundary potential barrier, as determined by 1/f noise analysis, closely related to the crystallinity improvement of the active layer and fewer zinc interstitials and/or oxygen vacancies near the grain boundary in the active layer.

The Performance of “Pious Fraud”: Reading Passive Obedience in Dryden’s Don Sebastian (1689)

Th is essay examines how obedience to authority structures John Dryden's Don Sebastian, a tragicomedy produced after William of Orange deposed James II in the Revolution of 1688. Because Dryden resigned his position as Poet Laureate after the Revolution rather than swear an oath of allegiance to the new monarch, scholars have interpreted Don Sebastian as the work of a defeated loyalist hoping for the return of the exiled James II. Th e depiction of obedience in the play, however, goes beyond the question of who should pos- sess the throne to comment more broadly on the agency available to individu- als in relations of submission. Specifi cally, the subplot in which the rebel Dorax becomes an obedient subject shows Dryden continuing to engage with passive obedience and non-resistance, a Stuart doctrine associated with divine right ideology and the established church. Dryden affi rms this extreme form of obe- dience, I argue, not to call for the return of absolutism but to respond to con- temporary charges that submission posed grave dangers to the self. Th rough a contextual reading, this essay shows how Dryden imbues submission with the potential for ethical transformation. Dorax receives praise for performing a pi- ous fraud that both confi rms his submissive will and conveys his disagreement with the sovereign. In this, Don Sebastian proves useful for engaging recent attempts to explore how individuals may demonstrate autonomy by willingly accepting limits on their freedom.

Role of charge patches in ion guiding through nanocapillaries in a PET polymer

We studied the dynamic properties of ion guiding through nanocapillaries in insulating polyethylene terephthalate (PET). The angular distribution of the transmitted ions was measured as a function of time. The temporal evolution of the angular transmission profiles was acquired for the capillary diameters of 200 and 400 nm. The tilt angle was varied from 0° to 6.5°. The transmission profiles exhibit significant changes in position as time varies. This observation is explained by the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.

Performance and Stability Characterization of Bottom Gated Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Grown by RF and DC Sputtering

In this paper, the performance and the gate bias stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with different channel sputtering conditions, RF and DC are studied. DC devices show excellent electrical characteristics but larger charge trapping and slower detrapping in relaxation period under the same gate bias stress. To understand the cause of stress behavior, traps are extracted by subthreshold slop and low-high frequency dependent capacitance measurement and compared before and after gate bias stress. The extracted trap densities well explain the process-dependent device properties like as threshold voltage, mobility and on/off current ratio, but are not dependent on bias stress. From current–voltage (I–V) and capacitance–voltage (C–V) measurement, we can conclude that the threshold voltage instability arises due to the process of temporary charge trapping which is dominant only at gate bias stress and the trapping/detrapping behavior is strongly dependent on the channel layer deposition condition.

Dynamic properties of ion guiding through nanocapillaries in an insulating polymer

We studied the dynamic properties of ion guiding through nanocapillaries in insulating polyethylene terephthalate. The angular distribution of the transmitted ions was measured as a function of the charge deposited on the sample surface, which is a measure of time. The time evolution of the angular transmission profiles was acquired for the capillary diameters of 200 and $400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The tilt angle was varied from 0\ifmmode^\circ\else\textdegree\fi{} to 6.5\ifmmode^\circ\else\textdegree\fi{}. The transmission profiles appear as a superposition of essentially three localized peaks which exhibit significant changes in intensity as time varies. This observation provides evidence for the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.

Time evolution of ion guiding through nanocapillaries in a PET polymer

We measured the time evolution of the guided transmission of 3keV Ne7+ ions through nanocapillaries in insulating PET polymers. Capillaries with a diameter of 200nm and a density of 4×106cm−2 were used. The angular distribution of the transmitted ions was measured as a function of the charge deposited on the sample surface, which is a measure of time. The evolution of the angular transmission profiles was acquired for different tilt angles ranging from 0° to 5°. The transmission profiles appear as a superposition of essentially 3 localized peaks which exhibit significant changes in intensity as time varies. This observation provides evidence for the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.

Modeling of electrochemical noise transients

AbstractStarting from the elementary corrosion reactions on a passive metal surface a model is developed for the origin of electrochemical noise. The ion currents flowing at the electrochemical reactions are described by the electrons remaining in the metal and then interpreted as a measuring signal. The measurable sum current is composed of the superimposition of the electron currents of the partial reactions. Due to the inhomogeneity of the metal surface, local metal dissolutions take place in preferential areas until the area is consumed or repassivated after short times. The short‐time surplus of free electrons leads for every metal dissolution event to a current transient, which itself consists of the partial currents of the elementary anodic and cathodic reactions. Due to the different reaction speeds, there are temporary charge disequilibria and thus measurable noise transients. In model calculations the influence of the diffusion of the oxygen on the sum signal as well as the variation of the anodic current is shown. Furthermore, the results show that a measurable noise signal can only arise under certain conditions. This signal arisen directly at the metal surface is not, however, ascertainable without further amplification. In the measurement amplifiers filter stages play an important role for signal conditioning. The influence of the measuring technique is shown at the filtration of a simulated test signal in different frequency domains. It is discussed how the signal distortion affects the detectability of the partial reactions described at the beginning and in which way the noise signal is estimated. Indications for the layout of suitable measuring parameters are given.

Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding. In some cases it may be desirable to reversibly bond devices to the Corning No. 1 cover glass. This could be due, perhaps, to a plasma cleaner not being available. In other instances, it may be desirable to remove the device from the glass after the culturing of neurons for certain types of microscopy or for immunostaining, though it is not necessary to remove the device for immunostaining since the neurons can be stained in the device. Some researchers, however, still prefer to remove the device. In this case, reversible bonding of the device to the cover glass makes that possible. There are some disadvantages to non-plasma bonding of the devices in that not as tight of a seal is formed. In some cases axons may grow under the grooves rather than through them. Also, because the glass and PDMS are hydrophobic, liquids do not readily enter the device making it necessary at times to force media and other reagents into the device. Liquids will enter the device via capillary action, but it takes significantly longer as compared to devices that have been plasma bonded. The plasma cleaner creates temporary hydrophilic charges on the glass and device that facilitate the flow of liquids through the device after bonding within seconds. For non-plasma bound devices, liquid flow through the devices takes several minutes. It is also important to note that the devices to be used with non-plasma bonding need to be sterilized first, whereas plasma treated devices do not need to be sterilized prior to use because the plasma cleaner will sterilize them.

Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding. In some cases it may be desirable to reversibly bond devices to the Corning No. 1 cover glass. This could be due, perhaps, to a plasma cleaner not being available. In other instances, it may be desirable to remove the device from the glass after the culturing of neurons for certain types of microscopy or for immunostaining, though it is not necessary to remove the device for immunostaining since the neurons can be stained in the device. Some researchers, however, still prefer to remove the device. In this case, reversible bonding of the device to the cover glass makes that possible. There are some disadvantages to non-plasma bonding of the devices in that not as tight of a seal is formed. In some cases axons may grow under the grooves rather than through them. Also, because the glass and PDMS are hydrophobic, liquids do not readily enter the device making it necessary at times to force media and other reagents into the device. Liquids will enter the device via capillary action, but it takes significantly longer as compared to devices that have been plasma bonded. The plasma cleaner creates temporary hydrophilic charges on the glass and device that facilitate the flow of liquids through the device after bonding within seconds. For non-plasma bound devices, liquid flow through the devices takes several minutes. It is also important to note that the devices to be used with non-plasma bonding need to be sterilized first, whereas plasma treated devices do not need to be sterilized prior to use because the plasma cleaner will sterilize them.

Dyes and other colorants in microtechnique and biomedical research

Dyes and other colorants in microtechnique and biomedical research

The Impact of Fermi Pinning on Thermal Properties of the Instabilities in ZnO TFTs

ABSTRACTIn this paper we describe gate bias and temperature induced device instabilities of inverted-staggered ZnO-TFTs. It is shown that low positive and negative gate bias results in the transfer characteristics shifting in a positive and negative direction respectively. It is suggested that this is a consequence of temporary charge trapping at or close to the channel/insulator interface. The degradation of device parameters such as the threshold voltage, subthreshold slope and effective channel mobility is demonstrated at elevated measurement temperatures, suggesting the generation of defects and/or trap states in the interfacial region. In addition, it is postulated from the extracted activation energy of the drain current that the Fermi-level is pinned during the operation of the devices due to the high level of states close to the conduction band edge. These results highlight the relatively ease with which defects could be created at the interface, indicating a high concentration of weak or strained bonds. Both charge trapping and defect creation-induced instabilities appear to be reversible, as all devices regain their original characteristics after a period of relaxation at room temperature.

Time projection chambers (TPC) in heavy ion experiments

In this paper the performance of TPCs in heavy ion experiments in terms of tracking and particle identification via dE/dx is reviewed. The principle of operation - drift, readout chambers and front end electronics, is illustrated. A few of the TPCs used are presented, along with a short description of the experiments. 1 TPC working principle A TPC is a three-dimensional almost continuous track- ing detector. It also provides information on the specific energy loss, dE/dx, of the particles traversing the drift volume. A TPC can be divided into three main parts: - The drift volume - The readout chambers - The readout electronics The charged particles produced in the collision pass through a gas mixture in the drift volume and release elec- trons from the gas atoms. These electrons drift in an ex- ternal electric field to the readout chambers. The drifting electrons initiate avalanches in the high fields at the an- ode wires providing an amplification. The electron cloud disappear immediately. The positive ions created in the avalanche induce a temporary image charge on the read- out pads which disappears as the ions move away from the anode wire. The image charge is measured by the readout electronics.

Ultrafast temporary charge transfer in pyrrolidinyl-benzonitrile and pyrrolyl-benzonitrile in the gas phase.

4-(N-pyrrolidinyl)benzonitrile and 4-(N-pyrrolyl)benzonitrile were excited by an ultrashort pulse at 270 nm to their La (S2) states and then probed by ionization at long wavelengths. Parent and fragment ion signals show components with time constants < 100 fs which we attribute to ultrafast relaxation to the Lb (S1) state. From this short time we infer a conical intersection between the Lb and La surfaces. The wave packet can branch there, one part going temporarily to a strongly displaced state. Its shift was concluded from an anisotropy observed only there. The only excited state known to have a large displacement is the charge-transfer (CT) state. The positive anisotropy indicates that the CT state belongs to the 2A species for both molecules. For pyrrolylbenzonitrile, this is in contrast to previous assignments. The anisotropy, and a coherent oscillation observed in pyrrolidinylbenzonitrile, support the idea that the amino-group twist is an important component of the CT reaction coordinate.

Spectral analysis of pigment photobleaching in photosynthetic antenna complex LHCIIb

Light-induced photooxidation of chlorophyll (Chl) a, b and xanthophylls was investigated in LHCIIb, the antenna pigment–protein complex of photosystem II. Absorption difference spectra at normal and low temperatures show initially (at less than 25% Chl a decay) a selective bleaching of a red-shifted Chl b with absorption bands at 487 and 655 nm, Chl b (460/650 nm) and Chl a (433/670 nm), which changes to a less selective photooxidation pattern at deeper bleaching stages. Difference absorption spectra and HPLC analyses indicate different photooxidation rates of pigments in the order neoxanthin>Chl a>lutein≈Chl b. Despite significant pigment loss as monitored with absorption spectra, CD spectra indicate an essentially complete persistence of the protein secondary structure. Fluorescence excitation spectra suggest the conversion of a small fraction of Chl a into pheophytin a which acts as a fluorescence quencher, possibly through temporary charge separation process. The strong features in the electroabsorption (Stark effect) spectra due to chlorophyll b at 655 nm and a xanthophyll at 510 nm, and the spectral changes mentioned above are assigned to Chl molecules located at several binding sites in LHCIIb protein and are discussed in the context of spatial configuration and interactions of pigment molecules.

Excess electron transfer in flavin-capped, thymine dimer-containing DNA hairpins.

The transfer of an excess electron through DNA was investigated with DNA hairpins, which contain a flavin cap functioning as an electron donor. A thymine dimer with an open backbone acts as the electron acceptor. The dimer translates the electron capture into a strand break, which is readily detectable by HPLC. Analysis of four hairpins, in which the distance between the flavin donor and the dimer acceptor was systematically increased, revealed a flat distance dependence of the repair efficiency supporting the view that excess electrons hop through DNA using intermediate A-T base pairs as temporary charge carriers.

Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile.

The L(a)-like S2 state (2A) of 4-(dimethylamino)benzonitrile was pumped at 267 nm in the gas phase at 130 degrees C. Nonresonant multiphoton ionization at 800 nm with mass-selective detection then probed the subsequent processes. Whereas ionization at the Franck-Condon geometry only gave rise to the parent ion, fragmentation increased on motion towards the charge-transfer (CT) state. This useful difference is ascribed to a geometry-dependent resonance in the ion. The time constants found are interpreted by ultrafast (approximately 68 fs) relaxation through a conical intersection to both the CT and the L(b)-type S1 state (1B). Then the population equilibrates between these two states within 1 ps. From there the molecule relaxes within 90 ps to a lower excited state which can only be a triplet state (T(n)) and then decomposes within 300 ps. Previous experiments either investigated only 1B --> CT relaxation-which does not take place in the gas phase or nonpolar solvents for energetic reasons--or, starting from S2 excitation, typically had insufficient time resolution (>1 ps) to detect the temporary charge transfer. Only recently temporary population of the CT state was found in a nonpolar solvent (Kwok et al., J. Phys. Chem. A. 2000, 104, 4188), a result fully consistent with our mechanism. We also show that S2 --> S1 relaxation does not occur vertically but involves an intermediate strong geometrical distortion, passing through a conical intersection.