Star-unitary transformations as a tool in single-atom pulse spectroscopy

Star-unitary transformations, of the type developed by I. Prigogine and his group, are used to study the pulse excitation and subsequent decay of a single atom coupled to the electromagnetic field. A systematic perturbation scheme is proposed for atomic properties, valid without limitation of time scale or strength of pulse irradiation, provided that the total duration of the pulses is shorter than the radiative lifetimes. In the absence of irradiation, Bloch-like rate equations are obtained as an exact result (in the thermodynamic limit of a large box enclosing the field).     

Study of elastic electron collisions by plasma electron spectroscopy

In this work we study elastic electron collisions by using the plasma electron spectroscopy method, which is based on the study of the electron energy distribution function in a plasma afterglow. We give the results of this method for the electron-electron collision frequency, and the frequency and cross section of the elastic collision of electrons with helium atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 7–11, February, 1987.In conclusion, the authors express their gratitude to Professor N. P. Penkin for useful discussions concerning this work.     

Near-field Raman spectroscopy of biological nanomaterials by in situ laser-induced synthesis of tip-enhanced Raman spectroscopy tips

We report a new approach in tip-enhanced Raman spectroscopy (TERS) in which TERS-active tips with enhancement factors of ～10(-5)× can be rapidly (1-3 min) produced in situ by laser-induced synthesis of silver nanoparticles at the tip apex. The technique minimizes the risks of tip contamination and damage during handling and provides in situ feedback control, which allows the prediction of the tip performance. We show that TERS tips produced by this technique enable the measurement of spatially resolved TERS spectra of self-assembled peptide nanotubes with a spatial resolution of ～20 nm.     

Spin-up and spin-down electron transport through a single-atom imperfect metallic wire: An analytical picture

Within a new perspective which includes the consideration of spin-up and spin-down electrons, a quantum-box approach is used to find a closed mathematical expression for the quantized electrical conductance of an imperfect point–metal contact. From this expression, both proper and improper fractions of the fundamental conductance quantum are obtained and discussed in the light of both resonant and off-resonant conduction states. Issues concerning Fermi energy and electrochemical potential are discussed. In addition, essential aspects related to the atom–lead coupling are examined; in particular, a tensor–dyadic formalism is introduced. Our results are found to be in excellent agreement with previous theoretical results and with experimental observations.     

Conversion electron spectroscopy at IGISOL

Conversion elecron spectroscopy has been an important part of the nuclear spectrocopy research at the Department of Physics of the University of Jyväskylä since the commissioning of the first cyclotron in the mid 1970s. At the IGISOL facility a specialiced conversion electron spectrometer ELLI was developed in the late 1980s. The first results with ELLI were obtained using the beams from the old MC-20 cyclotron to study newly discovered isotopes of refractory fission products. In the present K130 cyclotron laboratory ELLI has been utilized in many decay-spectroscopy experiments both neutron-deficient and neutron-rich side of the valley of stability. In the early 2000s the new JYFLTRAP ion trap system overthrew ELLI from its permanent place in the IGISOL beamline. Conversion electron spectroscopy has continued with the new Penning trap that has been used in in-trap electron spectroscopy tests and post-trap electron spectroscopy is foreseen.     

Continuous X-ray-induced Auger electron spectroscopy

Bremsstrahlung emission from a tungsten anode has been used, for the first time, to obtain X-ray-induced Auger electron spectra (CXAES) in a conventional X-ray photoelectron spectrometer. Auger KLL signal and background intensities obtained from a silicon—aluminium sample have been compared with those obtained un der the same experimental conditions but using a standard aluminium anode. For such an aluminium anode, the respective contributions of the bremsstrahlung and the characteristic radiation to the C_KVV intensity have also been established.     

Field-emission properties of transparent tungsten oxide nano-urchins

The field-emission properties of transparent tungsten oxide nano-urchin (NU) films deposited on conducting glass substrates were examined. The novel crystalline tungsten oxide NUs consisted of nanowires added to a spherical shell. The WO_2.72 NUs showed better field-emission properties than the WO₃ NUs with a low turn-on field of approximately 5.8 V/μm and a current density as high as 1.3 mA/cm² at 7.2 V/mm. The WO _x NUs films could be used in FE applications using a large-area glass substrate without the need for a catalyst and a mechanical rubbing or lift-up process. These results have implications for the enhancement of FE properties by further tuning the WO _x phases.     

Mechanisms of charging in electron spectroscopy

From the use of physical arguments based on classical electrostatics and elementary solid state physics, the role of the various parameters involved in the charging mechanisms of insulating materials is analysed in detail when these insulating specimens are investigated by surface analytical techniques (mainly XPS and e⁻AES). The role of the sub-surface composition and structure is outlined and the strong correlations between charging effects and some radiation damage effects are pointed out. Some strategies are also deduced to minimise these effects.     

Auger electron spectroscopy of silicon surfaces

The measurements of the spectra of Auger electrons of the silicon surfaces performed at the pressure of (2–5)×10^?7 Torr are described. In this pressure range rapid oxidation and carbonization of the uppermost layers take place. The changes of characteristic energies in Auger and loss spectra are related to the change of chemical composition of the surface. The combination of the characteristic loss spectroscopy with Auger electron spectroscopy makes possible the determination of the chemical shifts. The measurements of the chemical shifts of the individual energy levels of the silicon atoms in both the pure and contaminated silicon surfaces, in quartz and Fe∶Si alloy are given. Finally, the possibilities and limitations of the heating for the silicon surface cleaning are examined.     

Core electron spectroscopy of water solutions

O1s spectra from water in glycol, dimethylformamide and LiCl solutions have been recorded. The liquid/vapour shift is found to differ between the three solutions and from that measured for the pure organic solvents. The correlation of the shifts with molecular size and polarizability is discussed. The O1s binding energy for H₂O in the LiCl solution is measured to be 538.0 eV. From the liquid/vapour shift in this solution an estimate is obtained of. the electronic polarization contribution to the solvation energy of the K⁺ ion in water.     

Field-emission in the presence of a magnetic field

Transverse effective-mass effects are studied in a pseudo-one-dimensional Kronig-Penney model. Three-dimensional effects are discussed qualitatively. It is shown that the current must be analyzed in terms of the normal, and not the total energy, of electrons in the vacuum and that band effets appear via a structural dependent modulation which does not reduce to the “simplified effective-mass” approximation.     

Detection limits in Auger electron spectroscopy

The sources of background noise in Auger electron microanalysis are analyzed in order to evaluate the minimum detectable concentration x_m and the minimum number of detectable atoms y_m that can be reached. The best choices of operating conditions (the energy E₀, intensity I₀, and spot size d₀ of the incident electron beam, and the duration of the experiment t_e) are deduced for bulk and thin film analysis. The main results are: (i) The choice of E₀ is not very stringent, at least when E₀ ? 5E_i(A), where E_i(A) is the ionization energy, (ii) For a given electron dose received by the sample, x_m is improved by the use of the largest incident spot size while y_m is improved by the use of the finest spot size. The results also hold for other microanalytical techniques such as electron energy loss spectroscopy or electron probe microanalysis. (iii) Chemical identification of a single atom will be possible on samples able to tolerate very large electron doses by using incident electron beams 10 nm or less in diameter. The expected performance of a coincidence technique first suggested by Wittry is also discussed.     

Low-power electron paramagnetic resonance spin-echo spectroscopy

Electron spin-echo experiments generally require microwave power levels of hundreds of watts to produce the 5–10 G of RF field to generate 90° and 180° pulses in 10 ns. A low-power (i.e., less than I W) EPR spectrometer using a loop-gap resonator can generate the full range of time-domain experiments on samples with submicrosecond recovery times; 90° pulses are generated in 40 ns, and relaxation times as short as 22 ns are measured. Appropriate time-domain experiments were performed to independently measure the spinspin relaxation time, phase memory time, and spin-lattice relaxation time; the results were compared with CW saturation. It was found that the spin-spin and spin-lattice relaxation rates do differ by about 5%. The entire CW signal of PADS is reconstructed from a pulse experiment at a single field position. Small differences in linewidths among the three lines were seen in accordance with theory.