Metastable Electron Research Articles

Outer Valence Ionic States of Cr(CO)6and (η5-C5H5)Co(CO)2Observed by Two-Dimensional Penning Ionization Electron Spectroscopy

Outer valence ionic states of Cr(CO)(6) and (eta(5)-C(5)H(5))Co(CO)(2) were investigated by means of Penning ionization electron spectroscopy (PIES) upon collision with metastable He*(2(3)S) excited atoms as well as high-level ab initio molecular orbital calculations taking electron correlation effects into consideration. By the 2D measurement combining the collision-energy-resolved technique of the metastable atomic beam and electron spectroscopy, ionic-state-resolved measurement of collision energy dependence of partial ionization cross sections (CEDPICS) was carried out. Because partial Penning ionization cross sections can be connected to the spatial extent of corresponding molecular orbitals (MOs) outside the boundary surface of colliding He* atoms, different slopes of CEDPICS were related to anisotropic interaction around the MO region. The observed CEDPICS and PIES band intensity were consistent with the order of calculated ionic states.

Thermally excited tunneling from a metastable electronic state in a single-Cooper-pair transistor

Metastable electron traps and two-level systems (TLSs) are common in solid-state devices and lead to background charge movement and charge noise in single-electron and single-Cooper-pair transistors. We present measurements of the real-time capture and escape of individual electrons in metastable trapped states at very low temperatures, leading to charge offsets close to 1e. The charge movement exhibits thermal excitation to a hysteretic tunneling transition. The temperature dependence and hysteresis can be explained by the coupling of a TLS to a quasiparticle trap.

Following electron attachment to CS ([formula omitted]): Quantum scattering calculations of the lowest resonant state

Parameter-free scattering calculations are carried out for the CS (Σ1+) molecular target interacting with slow electrons (<10eV) using a quantum dynamical approach in the molecular reference frame and varying the internuclear distance over a sizeable range of values. The calculations find a resonant state of CS−(Π2) in the low-energy region and the resonance is seen to stabilize as a bound CS− molecule when the bond is stretched beyond the CS equilibrium value, in agreement with existing experiments and calculations. An analysis of the excess, metastable electron is able to show that the initially occupied d π∗-orbital of the molecular resonance evolves into a more localized p*-orbital on the sulphur fragment. The results from the calculations are related to the existing experimental data for the title system and to the information we have on the target molecule electron affinity.

Absolute intensity calibration of emission spectra: application to the forbidden 346 nm nitrogen line for N(2P°) metastable atoms density measurement in flowing afterglow

A novel method, based on emission signal from the excitation transfer reaction: Ar*( 3 P 2 ) + N 2 ( X ) N 2 *( C 3 ) + Ar, is proposed for the intensity calibration of the spectroscopic optical detection system in absolute scale. It is applied for the measurement of N( 2 P°) metastable atoms density in the Short Lived Afterglow (SLA) of a 440 Pa nitrogen discharge produced by a 433 MHz resonant cavity. This density is deduced from the absolute intensity of the forbidden N( 2 P°– 4 S°) line at 346.65 nm, whose transition probability is only 0.005 s −1 . The N( 2 P°) density variation in the SLA resembles those of N 2 ( A 3 ) metastable molecules and electrons or the emission intensities of first positive (1 + ), second positive (2 + ) and first negative (1 − ) systems of N 2 . It first decays after the discharge zone up to a minimum and hence increases by almost a factor of thirty to reach a maximum value of 6 × 10 17 m −3 at the maximum of the SLA. It is proposed that N( 2 P°) density results from a local equilibrium between its production: N 2 ( A 3 ) + N( 4 S) N( 2 P) + N 2 ( X 1 , v ) and loss: N 2 ( X 1 , v ≥ 10)+ N( 2 P) N 2 ( A 3 ) + N( 4 S) reactions, which strongly couple the atomic and molecular metastable states and hence recycle N 2 ( A 3 ) metastable molecules produced in the SLA. The balance equation of N( 2 P°) density provides a N 2 ( X 1 ; v ≥ 10) density of 6.5 × 10 20 m −3 at the maximum of the SLA. This corresponds to 1% of the total N 2 molecules in vibrationally excited levels v ≥ 10.

Modelling dissociative dynamics of biosystems after metastable electron attachment: the sugar backbones

The damage induced by radiation in cells is currently described via low-energy attachment of electrons produced in the biological medium by the primary radiation. Therefore the corresponding metastable anionic states are obtained in this work from multichannel quantum calculations which, in the present study, involve β-D-ribose and β-D-deoxyribose molecular fragments from RNA and DNA structures. The scattering attributes associated with the resonant processes are derived from the computed total, elastic cross sections by means of a high-level Breit-Wigner analysis of the calculated phase shifts. The present procedure is shown to provide a powerful tool for extracting the resonance parameters from the scattering data even in the presence of broad, overlapping resonances which typically occur in the resonant dynamics of complicated biosystems after electron attachment effects.

Research on metastable electron traps in the modified SOI materials induced by Si ion implantation

Silicon-On-Insulator (SOI) materials were modified by Si ion implantation with different doses, as reported in this letter. The electrical performance was studied and the effect of a modification technique on the SOI materials was investigated. The characteristic, obtained by pseudo-metal-oxide-semiconductor (pseudo-MOS) method, showed that the drain ID current versus gate voltage VG(ID−VG) curves shifted along the axis of VG with the change of Si ion implantation doses. The results of electron paramagnetic resonance (EPR), x-ray photoelectron spectroscopy (XPS), and electronic test suggested that the parameters of implantation affect the electrical performance and that the metastable electron traps are introduced into the buried oxide layers of SOI materials.

Investigation of a radio-frequency inductive- coupled-plasma discharge afterglow in noble gases

It has been shown (Demidov et al 2005 Phys. Rev. Lett. 95 215002) that even a small number of nonlocal fast electrons, which do not significantly affect the overall mean electron energy, can dramatically change both the plasma and near-wall sheath properties. In this work, Langmuir probe measurements of the electron energy distribution function (EEDF) show the presence of fast electrons created due to collisions of pairs of metastable atoms and collisions of the second kind between metastable atoms and bulk electrons. These measurements were made in the afterglow of a 100% modulated radio-frequency inductive-coupled-plasma discharge in argon, neon and helium. It is shown that this fast component of the EEDF can be controlled independently of the slow electrons, which is a direct consequence of the EEDF nonlocality. Both EEDF and plasma emission spectroscopy measurements are presented for the helium afterglow. These data allow us to determine the absolute density of metastable atoms and their temporal decay during the afterglow. It is shown that under the experimental conditions, stepwise excitation of helium metastable atoms is the primary process for populating excited states and, therefore, decay of the excited atoms is governed by the decay of metastable states. The presence of a trace amount of nitrogen in the system, which does not significantly change the properties of the helium discharge, allowed us to independently measure the decay of helium metastables by monitoring the N+2(B–X) emission resulting from Penning ionization of N2(X) and confirmed the above conclusions regarding the presence and importance of metastable atoms.

On the nature of infrared absorbing trapped electron center in low-temperature ice-I h

Ionization of polar liquids and glasses often yields metastable electron centers known as ‘weakly bound’ (wb) electrons that absorb to the red of the ground state of the solvated/trapped electron. In this Letter, we address the structure of the wb electron in low-temperature ice-I h theoretically. The comparison with the observed properties suggests that this species is an s-like electron filling a water vacancy.

Effects of Switched-bias Annealing on Charge Trapping in HfO$_{2}$ Gate Dielectrics

Charge trapping characteristics are investigated for MOS capacitors with 6.8 nm HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers and 1.0 nm interfacial silicon oxynitrides; the effective oxide thickness of the high-kappa gate dielectric layers is 2.1 nm. These devices were irradiated with 10-keV X-rays or subjected to constant voltage stress, and then annealed for ten minute intervals of alternating positive and negative gate bias at temperatures between 25 and 150degC. The resulting oxide-trap and interface-trap charge densities exhibit reversible buildup and annealing that depend strongly on bias and temperature. Additional defect-density growth with time was observed as a result of charge injection into the gate stack during the annealing process. This defect-density growth increases with increasing annealing time and temperature. After irradiation, the most of the reversibility in the charge trapping is due to metastable electron traps in the near-interfacial dielectric layers. After constant voltage stress, the motion, reactions, and trapping of protons at or near the Si/oxynitride interface are more important to the observed device response than are metastable electron traps. This is a result of reduced electron-hole pair creation during low-energy constant-voltage stress, as compared to high-energy X-ray irradiation. These results illustrate the importance of both electron traps and protons to the ionizing radiation response and long-term reliability of MOS devices with high-kappa gate dielectrics

Method to determine argon metastable number density and plasma electron temperature from spectral emission originating from four 4p argon levels

A simple model and method is proposed here to determine argon metastable number densities and electron temperature with the assumption of a Maxwell-Boltzmann electron energy distribution. This method is based on the availability of experimental relative emission intensities of only four argon lines that originate from any of the 4p argon levels. The proposed model has a relatively wide range of validity for laboratory plasmas that contain argon gas and can be a valuable tool for the emerging field of atmospheric microplasmas, for which diagnostics is still limited.

Electron dynamics and kinetics during the formation of a virtual cathode in different media

Results are presented from the first systematic investigation of how various factors in material media influence electron kinetics during the formation of a virtual cathode in an overcritical-current electron beam. A study is made of such factors as the viscous frictional force acting on the electrons in the medium, the dielectric constant of the medium, and ionization processes induced by the electrons in the medium. The dynamics of formation of a virtual cathode and the kinetics of the so-called metastable electrons in the cathode are considered.

準安定原子電子放射顕微鏡の開発とそのNi(111)初期酸化反応への適用

準安定原子電子放射顕微鏡の開発とそのNi(111)初期酸化反応への適用

Nanostructuring of crystalline grains of natural diamond using ionizing radiation

Crystalline grains of type IIa natural diamond (the average grain mass is ∼1 mg) are studied after their irradiation with neutrons in a nuclear reactor at a neutron fluence of ∼1021 cm−2. The irradiation is found to bring about a decrease in the macroscopic density of the grains by 40%. A quadrature signal of electron spin resonance (ESR) with a gfactor equal to 2.00006 and a paramagnetic-relaxation time > 10−5 s is detected for the first time. Metastable uncompensated electron spins residing at the inner surface of the nanovoids may be the cause of the appearance of this signal. A similar signal is also observed for C60 fullerite powder. The results of an ESR spectroscopy study of the irradiated diamonds are consistent with data obtained from Raman scattering spectroscopy (the appearance of an anomalously broad band peaked at 950 cm−1 instead of a narrow single line at 1332 cm−1 in the initial sample) and electron microscopy (the appearance of nanostructuring). It is established that nanostructuring of diamond under the effect of ionizing radiation brings about the appearance of dc electrical conductivity with an activation energy of 0.17 eV in the temperature range 30 to 300°C.

Measurement of metastable state densities and electron temperatures in an electron cyclotron resonance argon plasma

The number of metastable state densities obtained ranges from 1×1015to 4×1015 m-3 in the electron cyclotron resonance (ECR) argon plasma by measuring the optical absorption of the 8115 nm spectral line under the conditions of 02—08 Pa and 500—800 W. Taking into account the c ontribution of both the ground state and the 1s5 metastable state to the emiss ions, the electron temperature Te is measured by the ratio of emissio n lines. Results show that there are obvious differences compared with only considering t he metastable state densities.

Measurement of the Active Species Density for the Synthesis of Amorphous Carbon Nitrides I. Metastable Atoms and Electrons in the Microwave Discharge Flow of Ar

The densities of Ar(3P2) metastable atoms and free electrons produced in the microwave (MW) discharge flow of Ar were measured. The 3P1–3P2 (λ=696.5 nm) and 3P2–3P2 (λ=706.7 nm) transitions of Ar were observed by laser-induced fluorescence (LIF) spectroscopy. The LIF intensities were calibrated against Rayleigh scattering intensity by Ar atoms. The electron density was measured by a single-probe method. The number densities of Ar(3P2) atoms and electrons were determined to be (4.05±0.05)×1014 m-3 and (8.5±1.5)×1015 m-3, respectively, under the condition of PAr=0.1 Torr, where PAr denotes Ar pressure. When BrCN was introduced into the reaction system, the Ar(3P2) density became negligibly small, and the electron density was reduced to (2.0±0.8)×1015 m-3. On the basis of these observations, the decomposition process of BrCN in the MW discharge flow of Ar is discussed.

Generation of metastable electron traps in the near interfacial region of SOI buried oxides by ion implantation and their effect on device properties

Implanting the buried oxide of silicon-on-insulator technologies can create electron traps throughout the buried oxide that can compensate the buildup of radiation-induced positive charge. These can be used as an effective method for total-dose hardening buried oxides in SOI devices. In this work, we show that implanting buried oxides can also create thermally activated metastable electron traps near the top Si/SiO 2 border. These metastable electron traps can produce significant bias instabilities in the back-gate transistor characteristics and lead to threshold voltage instabilities in fully-depleted devices.

Growth of CuPc Thin Films on Structured SiO2/Si(100) Studied by Metastable Electron Emission Microscopy and Photoelectron Emission Microscopy

A combined metastable electron emission microscopy (MEEM) and photoelectron emission microscopy (PEEM) study has been performed for copper phthalocyanine (CuPc) thin films vacuum deposited on Si(100) with a lithographic SiO2 pattern. The MEEM image of SiO2 pattern edges changed considerably upon deposition of a very small amount of CuPc on the SiO2/Si(100) substrate, whereas no such changes were observed in the PEEM images. The different contrast features in MEEM and PEEM can be the result of different surface sensitivities of these microscopy techniques. The MEEM contrast characteristic for the pattern edges after the CuPc deposition may be ascribed to the difference of the molecular orientation of CuPc which cannot be observed by PEEM.

Microfabricated inductively coupled plasma-on-a-chip for molecular SO2 detection: a comparison between global model and optical emission spectrometry

In this work the molecular SO2 detection limit obtained using a microfabricated inductively coupled plasma-on-a-chip (mICP) system is compared with a volume-averaged plasma model. The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminium vacuum chamber. The plasma operates from 0.1 to 10 Torr, and requires less than 4 W of power at a frequency of 493 MHz. Molecular detection limits were measured using the SO2 MUV2 band (A(1B1), a(3B1) → X(1A1)). Detection limits improve with increase of both the operating power and pressure due to increases in electron and metastable state Ar densities, with the best DL value being 45 ppb. A global plasma model is developed to calculate the metastable Ar density, electron temperature, and SO2 excitation rates in the mICP. Excitation rates for electron-impact collisions and the quenching reaction with Ar metastables, together with the known sensitivity of the optical system, allow one to calculate detection limits for molecular SO2 excitation. Calculated DLs are in reasonable agreement with experimental OES results.

Unified model of hole trapping, 1/f noise, and thermally stimulated current in MOS devices

Capture cross-section data from the literature and recent density-functional theory (DFT) calculations strongly suggest that the 1/f noise of MOS devices is caused by the thermally activated capture and emission of carriers at O vacancy centers near the Si-SiO/sub 2/ interface. At least two kinds of defects can contribute to the noise of unirradiated and irradiated devices. The first is a "dimer" vacancy associated with the E/sub /spl delta//' center, which is shown by DFT to be a metastable electron trap when the Si-Si spacing is stretched beyond its equilibrium value, as likely can occur in strained SiO/sub 2/ near the Si-SiO/sub 2/ interface. The second is a neutral or positively charged E/spl gamma/' center, which has two configurations. One is puckered (one of the Si atoms relaxes through its local bonding plane) and forms a dipole after electron capture (E(/spl gamma//sup 4/)'). The other is shown via DFT to be a different kind of puckered configuration, including a fivefold coordinated Si (E(/spl gamma//sup 5/)'); this does not form a dipole. These results strongly suggest a common model of charge exchange with O vacancies can account for much of the oxide-trap charge and 1/f noise in MOS devices. Applying this model to thermally stimulated current (TSC) experiments suggests hole emission in TSC may well be due to the thermal relaxation of a puckered E/spl gamma/' into a dimer E/sub /spl delta//'. This can explain literature discrepancies between optical and thermal estimates of trapped-hole energies.

Electron–hole liquid formation by exciton and biexciton resonant excitation in CuCl

The dynamics of a cold photoexcited electron–hole system created by resonant excitation with picosecond optical pulses are studied by time-resolved emission and pump–probe measurements. A rapid build-up of strong metallic reflection in the mid-infrared region was observed, which indicates the creation of electron–hole plasma via the exciton or biexciton Mott transition. Transient reflection spectra clearly show the transformation of high-density electron–hole plasma into a metallic colloid-like state within 10 ps. In the meantime, broad plasma emission turns to a narrow emission band, in which the spectral profile does not change within several tens of picoseconds. These features in the emission spectra disappear when switched to the band-to-band excitation. An analysis of the reflection and emission spectra reveals that the density of metastable electron–hole liquid is as high as 10 20 cm −3. This indicates that the plasma formation via the Mott transition is crucial to eliminate excess heating for reaching the low-temperature states of an electron–hole ensemble.