On the field penetration into semiconductors in the field ion microscope

The calculation of field penetration in semiconductors and consequent band bending during field ionization/evaporation is discussed. The shielding by surface states is also taken into account. The Si(111) face example demonstrates that neglection of surface states may give unrealistic high band bending values. Because of the lack of reliable data for the density of surface states, a possible maximal band bending has been calculated for GaAs. Its value in the case of an external applied field of $\text{1}\text{V}\text{A}\text{?}$ may be such smaller as formerly assumed in recent works.     

Direct observation of reconstructed surfaces in the field ion microscope

Both the Ir(110)1×2 and the Ir(100)1×5 reconstructed surfaces have been imaged in the field ion microscope. The observations agree with results obtained on macroscopic single crystal surfaces. Evidence for a possible 1×2 reconstruction of the Ir(113) surface is shown.     

Neon gas imaging of gold in the field ion microscope

An improved field ion microscope (FIM) technique has been developed for the neon gas imaging of gold specimens. The technique produces images which are stable at best image voltage at a tip temperature (T_T) of 30 K or less. The first stage of the technique consisted of the development of an end form at 55 K in the presence of a partial pressure of air (～ 2 × 10^?8 Torr gauge pressure) and neon gas (～ 3 × 10^?5 Torr gauge pressure) followed by further field evaporation at 28 K. The second stage involved neon gas imaging of the previously developed end form in a baked FIM in a background pressure of (0.5 to 3) × 10^?9 Torr. The FIM images obtained in conjunction with the field ionization characteristic curves showed that there is a working range (in the sense defined by Southon and Brandon). A detailed study was made of artifact vacancies detected in the {203}, {321}, {315}, {421}, {671} and {731} planes, and it was found that at 28 K their concentration was < 2.5 × 10^?3 at.fr. Approximately 191,000 atomic sites were examined for artifact vacancies. The artifact vacancy concentrations measured in the present study were a factor of 13 to 60 lower than those measured earlier by Schmid and Balluffi who employed a background pressure of ～ 5 × 10^?8 Torr in their FIM. Hence, the artifact vacancy concentrations detected in gold are dependent upon the background partial pressure employed in the FIM. This latter result plus the result that the images are only stable in ultra-high vacuum (UHV) conditions indicates the need for UHV conditions for the successful imaging of gold surfaces.     

The in situ cleaning of specimens in the field ion microscope by argon ion bombardment

The extensive adoption of argon bombardment cleaning techniques for specimens used in LEED and Auger studies, and the frequent, and often difficult, requirement of preparing field ion emitters, and their supports, free from contamination, led to the investigation of in situ argon ion bombardment of specimens in the field of ion microscope, both from the point of view of the efficiency of the cleaning process, and the investigation of ensuing surface and lattice damage, a task to which the technique of field ion microscopy is particularly appropriate.Experiments were carried out in some detail for tungsten specimens, and subsequently extended to the hexagonal metal, rhenium, with a view to obtain information on the thermally annealed end forms of such metals. In both cases, very small radius clean thermally annealed specimens could be prepared.     

Hydrogen promoted corrosion of tungsten by oxygen in an electric field: A field ion microscope study

The extensive changes in surface topography observed to occur on tungsten field ion emitters as a result of exposure to oxygen in presence of hydrogen at 78°K and at fields of 2 V/Å have been studied in detail. Field promoted diffusion of gas from the low field region of the emitter shank over the imaged area of the surface removes kink site metal atoms and subsequently deposits them on either side of the well defined diffusion paths along close packed zones; field evaporation of such atoms may also occur when the change in local surface contour causes sufficient field enhancement. Although oxygen is primarily responsible for the corrosion effects, its diffusion at such temperatures is promoted by the presence of hydrogen, and the rate of reaction is dependent, inter alia, on hydrogen pressure.     

Kinetics of microplasma atmospheric ion generation correlated with discharge current

The conditions necessary for achieving a stable bipolar ion generation (in the order of 10⁶ ion/cm³) and lower ozone concentration (less than 50 ppb) using a surface discharge microplasma device (SMD) by adjusting the applied voltage and frequency were experimentally determined and investigated. Measurements of the discharge current characteristics of the SMD revealed saturation against the frequency (1.5–2.5 kHz, depending on the applied voltage). The ion and ozone concentrations both increased in step with the discharge current in the lower frequency region. The ion concentration reached equilibrium in the frequency range of 200–500 Hz, and the point of equilibrium within that range depended on the applied voltage. The ozone concentration did not reach equilibrium under our experimental conditions (ozone concentration < 100 ppb). The kinetics of the ion/ozone generation rate with a focus on the plasma reaction and recombination of bipolar ions is discussed.     

The Bohm approach to cavity quantum scalar field dynamics. Part I: The free field

Bohm 's approach to quantum field theory is illustrated through its application to cavity quantum scalar field dynamics. Specific calculations demonstrate how the evolution of the well-defined scalar field is governed by the nature of its quantum state. The implications of the nonlocality inherent in quantum mechanics and the meaning of the classical limit are discussed in this context.     

Probing dynamic interference in high-order harmonic generation from long-range molecular ion:Bohmian trajectory investigation

Using Bohmlan trajectory （151） method, we investigate the dynamic interference in nlgn-orcter narmonlc generauon from diatomic molecular ions. It is demonstrated that the main characteristics of the molecular harmonic spectrum can be well reproduced by only two BTs which are located at the two ions. This haiapens because these two localized trajectories can receive and store the whole collision information coming from all of the other re-collision trajectories. Therefore, the amplitudes and frequencies of these two trajectories represent the intensity and frequency distribution of the harmonic generation. Moreover, the interference between these two trajectories shows a dip in the harmonic spectrum, which reveals the molecular structure information.     

Influence of the current density longitudinal distribution in current sheets on their magnetic field structure and formation dynamics. I: Calculation of the magnetic field of current sheets with different configurations

The structure of the current sheet magnetic fields are numerically calculated for different distributions of the current density across the current sheet width. The structural features of the magnetic fields of current sheets with current density double-humped distributions are revealed.     

Low-order harmonic generation of hydrogen molecular ion in laser field studied by the two-state model

The low-order harmonic generation of hydrogen molecular ion interacting with a linearly polarized laser field has been investigated theoretically by using a simple two-state model. The validity of the two-state model is carefully examined by comparing the harmonic spectra of hydrogen molecular ion obtained from this model with those from the three-dimensional time-dependent Schr¨odinger equation. When combined with the Morlet transform of quantum time-frequency spectrum,the two-state model can be used to study the dynamical origin of the low-order harmonic generation of hydrogen molecular ion driven by low-frequency pulses. In addition, some interesting structures of the time profiles for low order harmonics are obtained.     

Scanning helium ion microscope: Distribution of secondary electrons and ion channeling

The principles and features of operation of a scanning helium microscope are reviewed briefly. The measurement data on the energy distribution of secondary electrons excited by the ion beam in an Au film and on the angular dependence of the backscattered ion yield are obtained and presented for the first time. The effect of ion channeling in silicon single crystal with the (110) orientation is demonstrated.     

Ion implantation: Measurement of ion pressure

The paper deals with a simple technique of measurement of ion pressure which is created when accelerated ions strike a solid target.     

Mean field approach to pion production in intermediate energy heavy ion collisions

The pion production in intermediate-energy heavy ion collisions is studied in the mean field approximation. Pion spectra are calculated in the slab geometry for various incident energies. It is found that the one-nucleon process cannot explain the observed cross section and that two-nucleon processes are important.     

Calibration parameters for the probing tip of a magnetic force microscope in the field of a test current loop

The subject of discussion is calibration of the tip of a magnetic force microscope using the field of a ring-shaped current loop. To calculate the calibration parameters, the magnetic contribution from the extended tip of the probe in the field of the current loop to the rigidity of the cantilever is approximated by the contribution from a point magnetic dipole and magnetic “charge” in terms of the theoretical model adopted. Three simplified models of the conic tip (with a sharpened, blunted, and rounded top) are considered. The calculated dependences of the effective calibration parameters on the radius of the current loop are compared with experimental data. It is found that the model of a uniformly magnetized tip in the form of a blunted cone provides the best fit to the experiment. The calculation results may be helpful in simulating images obtained with a magnetic force microscope and numerically testing magnetic objects.