Measurement Of Energy Distribution Research Articles

The high-resolution electron–ion collision facility at TSR

A new electron beam facility at the storage ring TSR is presented which makes electron–ion collision experiments possible without using the existing electron cooler device as an electron target. A long adiabatic acceleration section combined with magnetic adiabatic expansion (factor up to ≈90) is used to reduce the longitudinal and transverse electron temperatures. The facility can be operated with either a thermionic or a photocathode. Results from two-dimensional electron beam profile measurements and longitudinal electron energy distribution measurements are discussed.

Electron transport mechanisms in thin boron-doped diamond films

Electron transmission spectroscopy is used to examine the effect of transport distance, diamond nanostructure, and electron affinity on the cold emission characteristics of thin nanocrystalline diamond films. Energy distribution and intensity measurements are taken from films having different thicknesses (∼0.15, 2, and 4 μm) and surface properties (hydrogenated, cesiated), and two distinct transmission regimes are identified that exhibit fundamentally different characteristics. In measurements taken at sufficiently high beam energy Eo, electrons are transported through the conduction band of the diamond and emitted at a low-affinity surface, with transmission yields generally greater than 1. In this regime, the dependence on Eo results from the finite escape depth of the conduction-band electrons, which is determined to be ∼1 μm for these films based on a Monte Carlo analysis of the incident electron range. In measurements taken at lower values of Eo, electrons are generated outside of this escape range and are unable to reach the surface via conduction-band transport. In this regime, the transmission data are dominated by a much broader, low-intensity distribution, and the transmission yields are substantially lower than 1. The transmission is furthermore completely insensitive to changes in the surface properties of the diamond. Based on the nanostructure of the films, electrons are most likely transported along grain boundaries that propagate through the films.

Model of auroral electron acceleration by dissipative nonlinear inertial Alfvén wave

In a recent work [Wu, 2003a, 2003b], a dissipative nonlinear inertial Alfvén wave (DNIAW) were proposed as the physical explanation for the formation of the strong electric spikes often observed in the auroral ionosphere and the magnetosphere. DNIAW can also lead to the field_aligned electron acceleration. In the present paper, dynamical characteristics of DNIAW acceleration are discussed and its possible role in auroral electron acceleration is further investigated. The effective acceleration region for auroral electrons with energies of the order of keV produced by DNIAW acceleration is between 0.5 and 2.5 RE above the ionosphere, and the most efficient acceleration occurs around 0.8 RE where both the Alfvén velocity and the produced auroral electron energy peak, and the peak energy is around 10 keV. We suggest that this could explain the precipitous decrease of the auroral electron energy spectrum toward energies above 10 keV, which can be inferred from measurements of energy distribution of precipitating auroral electrons. Typical widths of auroral arcs caused by the DNIAW acceleration are in scales of the order of 1 km.

Sputtering of a polycyclic hydrocarbon molecule: TOF–SIMS experiments and molecular dynamic simulations

This study focuses on the desorption and ionization processes of an aromatic molecule containing several phenyl rings, 1,2,3,4-tetraphenylnaphthalene (TPN), adsorbed on a Au surface, via the comparison of experimental secondary ion mass spectrometry (SIMS) data and molecular dynamic (MD) simulations. The mass spectra and kinetic energy distribution (KED) measurements were obtained using both TOF–SIMS and MD simulation methods. For entire TPN molecules, a good agreement is observed between the calculated and experimental KEDs, except for high energies, where they start diverging. This difference is partly caused by the unimolecular dissociation of internally excited molecules over larger time intervals than those considered in the simulation. In turn, using an internal energy threshold to remove the most excited molecules from the calculated KEDs provides a better agreement with the experiment. The MD simulations also show that molecules surrounding the impact point of the projectile are sputtered with more kinetic energy and shorter emission times than molecules located farther away from it. The distinct emission mechanisms inducing these different energy spectra are identified by the analysis of the simulation results.

Development of an advanced high efficiency electro-emission device

In this article, we describe the improvement in cold emission characteristics of a device termed HEED (high efficiency electro-emission device) by optimizing the emission site structures. The advanced HEED consists of a bottom electrode, a Si layer, a SiOx layer, a top electrode, and a carbon layer. The electron emission properties were significantly improved by appropriately arranging emission sites of “dimplelike” forms with a diameter of 1 μm on the device surface. The applied voltage was significantly lowered to 20 V (1/5 of that in the previously reported HEED), and a high emission current density of 1.8 mA/cm2 was obtained at a applied voltage of 20 V with an electron emission efficiency of 1% under a pulse operation. The energy distribution measurement of emitted electrons showed that the device emits considerably high-energy electrons as compared with conventional field emitters. Using this emitter as an excitation source, a 4 in. prototype flat display panel has been fabricated with a vacuum spacing of 9 mm between glass substrates. The panel operates well at a practical brightness of 2000 cd/m2.

Experimental Study on Stress-Strain Curve of Concrete Considering Localized Failure in Compression

One of the important factors for compressive stress-strain curves of concrete is the localization of failure. The stress-strain curve of concrete strongly depends on the aspect ratio of the concrete specimen; therefore, a unique stress-strain curve is not adequate to express the softening behavior of concrete. To overcome the problem related to the localization of failure, a series of uniaxial compressive tests of concrete specimens was conducted. From the measured energy distribution, the failed specimen was assumed to be composed of 2 or 3 zones. Then, an equation for an envelope curve involving a characteristic of compressive strength of concrete was formulated so as to match the experimental curve of each zone. Combining 2 or 3 proposed equations considering the extent of each zone could express the experimental stress-strain curve of the specimen regardless of the aspect ratio.

The electron-impact dissociative ionization ofCCl2F2

An investigation of the formation channels and properties of ionfragments following electron-impact dissociative ionization of theCCl2F2 molecule using electron kinetic energies in the 0–100 eV range isreported. Measurements of ion appearance potentials (APs) and nascenttranslational energy distributions were made on a supersonic expansion ofCCl2F2 in a time-of-flight mass spectrometer. A discussion of the correlation betweenthe channel APs, the precursor bond characters as calculated from thepopulation analysis, and the low-resolution photoelectron spectrum of theCCl2F2 molecule is presented.

Low density plasma-assisted electron and ion emission from LATGS single crystals

Energy distribution measurements for a weak plasma-assisted emission of electrons and ions, generated at the surface of l-α alanine doped TGS (LATGS) single crystals under driving (10 3 to 10 4 V/cm) ac electric field, have been carried out. These plasma-assisted emission processes are produced during positive charging of the emitting sample surface due to switching of the spontaneous polarization or normal charging of the dielectric sample. The energy of electrons monitored under our experimental conditions were focused at about 200 eV; contrary to the energy of electrons, the ions have broad energy spectra with energies up to a few hundreds of eV. Moreover, the influence of internal bias on the energy spectra registered for electrons is observed.

Measurement of the astrophysical S factor for dd interaction at ultralow deuteron-collision energies using the inverse Z pinch

This paper is devoted to measurement of the astrophysical S factor and cross sections of the d + d → 3He + n reaction at ultralow deuteron-collision energies. Formation of the flow of the accelerated deuterons incident on the CD2 solid-state target was made within the scheme of the inverse Z pinch. The liner in the initial state was a hollow supersonic deuterium jet of radius of 15 mm and length of 20 mm. The experiment was carried out at the pulsed high-current accelerator (I=950 kA, τ=80 ns) of the Institute of High-Current Electronics (Tomsk, Russia). Measurement of the deuteron energy distribution was performed through an analysis of the time distributions of the intensity of the liner radiation (Hα and Hβ lines) generated during the liner radial movement from the axis. Recording of this radiation was carried out by optical detectors placed along the direction of the liner moving from its axis. The measured value of the astrophysical S factor for the dd reaction at the average deuteron collision energy E coll=3.69 keV was equal to S(E coll=3.69 keV)=58.2±18.1 keV b. The dd-reaction cross section calculated using the found value of the S factor and known representation of the reaction cross section as the product of the barrier factor and the astrophysical S factor was σ dd n (E coll=3.69 keV)=(1.33±0.41)×10−30 cm2.

Ion energy distribution and optical measurements in high-density, inductively coupled C4F6 discharges

Hexafluoro-1,3 butadiene (C4F6) is a potential etching gas with a very low global warming potential for the manufacturing of semiconductors, unlike commonly used fluorocarbon gases such as CF4 and c−C4F8. We report ion energy distributions, relative ion intensities and absolute total ion current densities measured at the edge of an inductively coupled gaseous electronics conference radio-frequency reference cell for discharges generated in pure C4F6 and C4F6:Ar mixtures. In addition, the ratio of radical densities relative to CF measured using submillimeter absorption spectroscopy and optical emission spectroscopy measurements are presented. These measurements of the C4F6 plasmas were made for several different gas pressures (0.67, 1.33, and 2.66 Pa) and gas mixture ratios (25%, 50%, 75%, and 100% C4F6 volume fractions).

Photodissociation of Methacrylonitrile at 193 nm: The CN Radical Product Channel

Photodissociation dynamics of methacrylonitrile (H2CC(CH3)CN) and 2-butenenitrile at 193 nm have been investigated by measuring laser induced fluorescence spectra of CN fragments. From the spectra, internal and translational energy distributions of CN have been obtained. For both molecules, the measured energy distributions are well represented by statistical prior calculations, assuming the CN and allyl radical products rather than the propenyl isomer. Ab initio calculations were performed for the relevant product species and transition states for isomerization and CN elimination. It has been concluded that methacrylonitrile dissociates in the ground electronic state via allyl cyanide formed by CN and H atom migration prior to dissociation. The quantum yield of the CN channel from methacrylonitrile was measured to be 0.012 ± 0.001.

Possible test of the thermodynamic approach to granular media.

We study the steady state distribution of the energy of the Sherrington-Kirkpatrick model driven by a tapping mechanism which mimics the mechanically driven dynamics of granular media. The dynamics consists of two phases: a zero temperature relaxation phase which leads the system to a metastable state, then a tapping which excites the system thus reactivating the relaxational dynamics. Numerically, we investigate whether the distribution of the energies of the blocked states obtained agrees with a simple canonical form of the Edwards measure. It is found that this canonical measure is in good agreement with the dynamically measured energy distribution. A possible experimental test of the Edwards measure based on the study here is proposed.

A Monte Carlo simulation of ballistic transport in nanocrystalline silicon diode

Nanocrystalline silicon (nc-Si) diodes, composed of thin Au films, structure controlled nc-Si layers, n-type Si substrates, and ohmic back contacts, efficiently emit ballistic electrons when positive bias voltages are applied to the Au electrode with respect to the substrate. In this study, the characteristics of ballistic electron transport in nc-Si diodes are investigated using the Monte Carlo simulation. Both the calculated and measured energy distributions are far from that expected from the thermal equilibrium condition. We can see that a good agreement between two results is obtained on the higher energy side relating to quasi-ballistic and ballistic transport. The ballistic behavior is evident from the peaks of two distributions that correspond to 70-80% of the applied voltage. This is an indication that very few collisions occur in the higher energy region in nc-Si layer. We compared the characteristics of electron transport in nc-Si layer to that of electron transport in the superlattice structure in order to investigate the effects of the electric field in the ballistic transport in the nc-Si layer. The electrons injected into the nc-Si layer are preferentially conducted to the interfaces between nanocrystallites as into drain by a concentrated electric field. The effective thickness of the barrier at the interstice significant decreases, so the probability of sequential tunneling in nc-Si layer becomes larger than that in the superlattice. The energy distributions of electrons in the superlattice are relatively broad because the probability of tunneling is lower than that in nc-Si. The ballistic electron transport by geometry-sensitive like multiple tunneling in the interconnected nc-Si system is shown in this study. These results support that electrons can travel ballistically in nanocrystalline layers under a high electric field. The ballistic transport indicates the further technological potential of silicon nanocrystallites.

Highly efficient time-of-flight spectrometer for studying low-energy secondary emission from dielectrics: Secondary-electron emission from LiF film

A highly efficient time-of-flight electron spectrometer is described. An incident electron current of the order of 10−14 A makes it suitable for studying secondary emission from dielectric surfaces. A microchannel plate position-sensitive detector allows flight distance correction while keeping a large acceptance angle. Measured energy distribution curves of secondary electrons generated from a LiF film by 19–31 eV incident electrons demonstrate good energy resolution and reveal reproducible and stable emission features at 2.6±0.3 eV, 7.2±0.3 eV, and 10.3±0.3 eV.

Computer-Controlled System for Plasma Ion Energy Auto-Analyzer

A computer-controlled system for plasma ion energy auto-analyzer was technically studied for rapid and online measurement of plasma ion energy distribution. The system intelligently controls all the equipments via a RS-232 port, a printer port and a home-built circuit. The software designed by Lab VIEW G language automatically fulfils all of the tasks such as system initializing, adjustment of scanning-voltage, measurement of weak-current, data processing, graphic export, etc. By using the system, a few minutes are taken to acquire the whole ion energy distribution, which rapidly provides important parameters of plasma process techniques based on semiconductor devices and microelectronics.

The Measurements of Ion Currents and Ion Energy Distributions in the Hanbit Mirror Plasma Heated by ICRF

Ion cyclotron resonant heating (ICRH) experiments have been carried out on the central cell of the HANBIT magnetic mirror. In these experiments were tested startup, heating, electrostatic ion confinement and electric potential modification which makes use of the electron cyclotron resonant heating (ECRH).The ions heated by the wave are generally either reflected near magnetic field or are eventually disappeared into the loss cone. The small Faraday cup is used to measure the ions heated by the RF wave. End loss analyzers, types of electrostatic potential multi-grid Faraday cup have been used to measure the current and the axial energy distribution of ions escaping along magnetic field lines in the magnetic mirror machine. The change of the end loss ion current was shown to be consistent with the measured changes in the plasma potential when the ECRH occurred at the Plug region.

1428 超希薄気体流における温度非平衡現象の解析

In highly rarefied gas flows, there appear deviation of rotational energy distribution from the Boltzmann distribution. In this study, to analyze the nonequilibrium phenomena, we applied 2R+2 N_2-REMPI to the measurement of rotational energy distributions along the axial center line in a supersonic free molecular flow of nitrogen. As a result, strong nonequilibrium in the rotational energy mode has been found in the flow. The Boltzmann plot obtained from the measured REMPI spectra cannot be fitted by one line, revealing the non-Boltzmann distribution of the rotational energy. The transition from the equilibrium to the nonequilibrium is also discussed by showing the dependence of the rotational energy distribution on the distance from the nozzle exit in the flow.

Field-Induced and Surface-Catalyzed Formation of N2H Ions

Using H2-N2 mixed gases, high-electric-field-induced formation of ions such as N2+ and N2H+ on a surface of gold has been investigated in the pulsed-laser time-of-flight atom-probe field ion microscope. The N2H+ ions are found from the lattice steps of the surface in the range (30-40) V/nm. The formation of the ions depends not only on the applied field strength, but also on the atomic structure of the substrate. By applying theoretical values of the binding energy and ionization potentials of N2H, as calculated by the ab initio method and using measurements of the energy distributions of the N2+ and N2H+ ions, several conclusions can be drawn.

A Deep JI Survey of the Pleiades for Freely-Floating Superplanets and Brown Dwarfs at the Deuterium Burning Limit

We present preliminary results from a deep near-infrared J-band and I-band photometric survey of the Pleiades for freely-floating superplanets and brown dwarfs (BD) near the deuterium burning limit (DBL). With limiting magnitudes of J=20.5 and I=23.5, we have selected candidate Pleiads on the basis of evolutionary tracks, color-magnitudes, and I-J color lower limits (non-detections at deep I-band). Likelihoods of membership will be ultimately determined by a combination of image profile analysis, spectral energy distribution, proper motion, and low-resolution measurements of near-infrared water and/or methane absorption slopes. If confirmed, our faintest candidates are predicted to have made the transition from L to T spectral types with temperatures down to 820 K, and masses approaching 10 MJup.

Behavior of the solid-state field-controlled planar emitters under extreme working conditions

In this article we present the emission properties of planar solid-state field-controlled emission cold cathodes under extreme conditions, in particular about the highest limit for current densities on one hand and on the other hand about the highest gas pressures that can be supported by these cathodes under continuous electron emission. The experimental results are discussed in correlation with the measured energy distribution of the emitted electrons.