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The nucleation and growth of silver nanoclusters on TiO2(110) surfaces with on-top O adatoms (oxidized TiO2), surface O vacancies and H adatoms (reduced TiO2) have been studied. From the interplay of scanning tunneling microscopy/photoelectron spectroscopy experiments and density functional theory calculations, it is found that silver clusters are much more strongly bonded to oxidized TiO2(110) surfaces than to reduced TiO2(110) model supports. It is shown that electronic charge can be transferred from silver clusters to the oxidized TiO2(110) surface, as evidenced by the reappearance of the Ti3d defect state upon silver exposure. Furthermore, from both scanning tunneling microscopy data and density functional theory calculations the most favorable adsorption site of silver monomers on oxidized TiO2(110) is one that bridges between on-top O adatoms and regular surface O atoms nearby.

Titanium dioxide (TiO 2 ) has a number of uses in catalysis, photochemistry, and sensing that are linked to the reducibility of the oxide. Usually, bridging oxygen (O br ) vacancies are assumed to cause the Ti 3d defect state in the band gap of rutile TiO 2 (110). From high-resolution scanning tunneling microscopy and photoelectron spectroscopy measurements, we propose that Ti interstitials in the near-surface region may be largely responsible for the defect state in the band gap. We argue that these donor-specific sites play a key role in and may dictate the ensuing surface chemistry, such as providing the electronic charge required for O 2 adsorption and dissociation. Specifically, we identified a second O 2 dissociation channel that occurs within the Ti troughs in addition to the O 2 dissociation channel in O br vacancies. Comprehensive density functional theory calculations support these experimental observations.

We present an extensive investigation of CO-induced structural transformations occurring on the reconstructed Pt(110)-(1×2) surface while bridging the so-called pressure gap between surface science and industrial catalysis. The structural changes are followed on the atomic scale as a function of CO pressure over 12 orders of magnitude, up to 1 bar, by the use of a novel high-pressure scanning tunneling microscope (HP-STM). The transition between the low-coverage and saturation-coverage structures is found to proceed through local displacements of substrate Pt atoms. The structural transformations of the Pt surface as observed by STM can be explained within a very simple picture governed by the gain in CO binding energy when CO binds to low-coordinated metal atoms.

We have studied the adsorption of decacyclene (DC) molecules on a Cu(110) surface. The results are compared to previous studies of hexa-tert-butyl decacyclene (HtBDC) also on Cu(110). Opposite to HtBDC, the DC molecules do not induce any restructuring of the Cu(110) surface and no ordered structures are observed at low coverages. This difference is discussed in terms of molecule–substrate and molecule–molecule interactions. Close to full monolayer coverage, DC molecules are forced into ordered arrangements. The ordered structures with different molecule density are described in a model.

The adsorption of a large organic molecule, named Lander, has been studied on a Cu(110) substrate by scanning tunneling microscopy (STM). At low temperatures three different conformations of the molecule are observed on the flat surface terraces. At room temperature the Lander molecules are highly mobile and anchor preferentially to step edges. There the molecules cause a rearrangement of the Cu step atoms leading to the formation of Cu nanostructures that are adapted to the dimension of the molecule, as revealed directly by STM manipulation experiments. Upon annealing to 500 K the molecules order at higher coverages partially into small domains. In all cases the exact adsorption conformation of the molecules was identified through an interplay with elastic scattering quantum chemistry calculations.

We present the design and performance of a high-pressure scanning tunneling microscope (HP–STM), which allows atom-resolved imaging of metal surfaces at pressures ranging from ultrahigh vacuum (UHV) to atmospheric pressures (1×10−10–1000 mbar) on a routine basis. The HP–STM is integrated in a gold-plated high-pressure cell with a volume of only ∼0.5 l, which is attached directly to an UHV preparation/analysis chamber. The latter facilitates quick sample transfer between the UHV chamber and the high-pressure cell, and allows for in situ chemical and structural analysis by a number of analytical UHV techniques incorporated in the UHV chamber. Reactant gases are admitted to the high-pressure cell via a dedicated gas handling system, which includes several stages of gas purification. The use of ultrapure gasses is essential when working at high pressures in order to achieve well-defined experimental conditions. The latter is demonstrated in the case of H/Cu(110) at atmospheric H2 pressures where impurity-rela...

We present a new method for measuring the coefficient of restitution between a steel ball and a flat, smooth surface, based on the recording of sound files with a PC. We demonstrate how a simple and straightforward analysis of the sound files yields the coefficient of restitution as a function of velocity. The time resolution of many PC sound cards allows us to measure the collision time and hence to estimate the average impulsive force and the stress exerted on the surface. This in turn provides a basis for a discussion of energy loss mechanisms.

The diffusion, nucleation, and growth of Pt on the hexagonally reconstructed Pt(100)-hex surface are investigated. By means of Scanning Tunneling Microscopy (STM), the positions, sizes, and number densities of monoatomically high, rectangular, reconstructed Pt islands, formed in the submonolayer coverage regime, have been determined for substrate temperatures in the range T = 318-497 K and adatom deposition rates from R = 4 × 10 -5 to 7 × 10 -3 site -1 s -1 . The measurements are compared to the results of kinetic Monte Carlo (KMC) simulations and rate equation theory. The Pt(100)-hex surface exhibits a height modulation caused by the misfit between the topmost quasi-hexagonal layer and the quadratic substrate, resulting in a highly anisotropic large scale surface morphology with six-atom wide channels running along the [110] direction. From an autocorrelation analysis of the determined island positions, it is revealed that the islands are distributed with long/short correlation lengths along/perpendicular to the reconstruction channels. The autocorrelation analysis allows us to quantify the degree of anisotropy in adatom diffusion. Island size distributions obtained at different temperatures are found to collapse onto a single scaling curve also in the present case of strongly anisotropic diffusion. By comparison to similar curves derived from KMC simulations in a model incorporating anisotropic diffusion and finite island sizes, it is concluded that the critical island size is i = 1 and that the mobility of dimers is negligible. Furthermore, an early onset of island coalescence is revealed. From the scaling of the measured saturation island density, N x ∼ (R/h) χ , where h = v exp(-E d /k B T) is the adatom hopping rate, an effective fround to be influenced by the finite extent of the islands when diffusion is anisotropic. This is due to the increased ability of the islands to capture adatoms as they grow to cover more diffusion channels. Rate equations incorporating this effect are solved, and a scaling exponent of χ = 1/. is derived in contrast to the χ = 1/4 obtained for a 1-D point-island model.

The reaction of CO2 with an oxygen precovered Ag(110) surface leading to the formation of carbonate has been studied by scanning tunneling microscopy (STM) for different oxygen precoverages. For coverages below 0.5 monolayers (ML), the reaction is initiated preferentially at steps and defects and spreads uniaxially along the [001] directed, added ‐Ag–O‐ rows. For initial oxygen coverages below 0.25 ML, complete transformation to the carbonate structure is observed. For higher initial oxygen coverage, the unreacted rows are compressed to a (2×1) structure. In all cases, the ratio of carbonate ions formed to oxygen atoms consumed from added rows is close to 1:2. The reaction leads to a new reconstruction of the surface in which the carbonate ions are seen to reside preferentially on top of [110] directed triplet structures.

We have studied the interaction of ethanol with reduced TiO(2)(110)-(1 × 1) by high-resolution scanning tunneling microscopy (STM) measurements and density functional theory calculations. The STM data revealed direct evidence for the coexistence of molecularly and dissociatively adsorbed ethanol species on surface Ti sites. In addition, we found evidence for dissociation of ethanol at bridge-bonded O vacancies. The density functional theory calculations support these findings and rationalize the distinct diffusion behaviors of molecularly and dissociatively adsorbed ethanol species, as revealed in time-lapsed STM images.

A missing-row reconstruction of an fcc (111) metal surface has been observed for the first time. Direct observation of many small islands formed at the surface during S adsorption on Ni(111) indicates that a long-range mass transport takes place and that the surface undergoes a reconstruction. We present evidence that this reconstruction corresponds to a model in which every fifth Ni surfaces row is missing, with a total of 0.4 monolayer of S atoms adsorbed in threefold hollow positions on the surface and in the created troughs. The driving force for this novel missing-row reconstruction is proposed to be adsorption-induced surface stress

In this study, through the choice of the well-known G-K biological coordination system, bioligand-alkali metal coordination has for the first time been brought onto an inert Au(111) surface. Using the interplay between high-resolution scanning tunneling microscopy and density functional theory calculations, we show that the mobile G molecules on Au(111) can effectively coordinate with the K atoms, resulting in a metallosupramolecular porous network that is stabilized by a delicate balance between hydrogen bonding and metal-organic coordination.

Two samples of illite-smectite (I-S) isolated from Upper Jurassic clays in well 2/7-3 (3365 m) and well 2/11-1 (4548 m) have been investigated by scanning tunnelling microscopy (STM), and the particle shape and dimensions have been correlated to results from transmission electron microscopy (TEM) on shadowed specimens and results from atomic-force microscopy (AFM). By STM, lath-like and equant particles were observed in both samples, some of the particles having sharp edges. In the I-S from well 2/11-1, spiral-shaped particles were also seen. For both samples, the most frequent particle diameter was 100–200 Å. Particle-thickness distributions from STM and TEM were similar for the I-S from well 2/7-3, being dominated by 10 Å thick particles. For I-S from 2/11-1, the STM particle-thickness distribution has a predominance of 20 Å thick particles, but the TEM particle-thickness distribution is broad, with about equal amounts of 20, 30, 40, 50 and 60 Å thick particles. The AFM particle-thickness distribution for this I-S resembles the TEM thickness distribution. It is concluded that mainly thin (10 and 20 Å) particles are seen by STM. Failure of AFM to show sharp particle edges (seen in STM and TEM) might be attributed to the AFM tip movement or tip shape. In STM, I-S particles from well 2/7-3 have peaks along edges, whereas I-S particles from well 2/11-1 have rims. These rims are also seen in AFM and are therefore real geometrical features, probably a result of two-dimensional growth, whereas the spirals in the I-S from well 2/11-1 demonstrate three-dimensional growth. The minimum thickness of most particles is 10 Å.

From an interplay of time-lapsed high resolution scanning tunneling microscopy and density functional theory calculations we reveal the formation and diffusion of water dimers on hydrated rutile TiO2(110)-(1x1) surfaces, i.e., surfaces containing OH_{br} groups. At temperatures between approximately 150 and approximately 210 K water monomers diffusing along the Ti troughs were found to form stable water dimers that diffuse faster than the water monomers. An H bond mediated rollover mechanism operating for the water dimers explains the experimental findings.

Spectroscopy of channeling radiation from 3.5 MeV electrons along a 〈111〉 axis in Si has been applied to derive effective Debye temperatures at room temperature and at 110 K. The results are in good agreement with values obtained from measurements of planar-channeling radiation at 54 MeV and with recent measurements of high-order Bragg reflection of X-rays, but they are inconsistent with determinations from Bragg scattering of neutrons. We obtain Debye temperatures of about 510 K, much lower than the standard value of 543 K usually applied for Si.

The SPECTRUM - X-GAMMA mission is being developed by the Space Research Institute (IKI), USSR, together with many other countries and is scheduled for launch in 1993 ( Sunyaev,1990; Schnopper,1990). Mission objectives include broad and narrow band imaging spectroscopy over a wide range of energies from the EUV through gamma rays, with an emphasis on studying galactic and extragalactic X-ray sources. The Danish Space Research Institute (DSRI) and IKI will provide two thin-foil X-ray telescopes (SODART), each with an aperture of 60 cm and focal length of 8 m. They are designed to have a half-power width of less than 2 arc minutes and will have collecting areas of 1700, 1200 and 100 cm2 at 1, 8 and 20 keV, respectively. Images and polarization will be recorded by position-sensitive proportional counters. Moderate resolution spectroscopy will be done by the segmented solid state detector SIXA (Silicon X-ray Array), designed and to be constructed by a consortium in Finland, Denmark and USSR. Finland will have the main responsibility in financing and delivering the detector. The Institute of Electromechanics in Moscow will provide its passive cooling system (110 K). The detector will consist of 19 segments (Si(Li)), each with a diameter of about 8 mm. The spectral resolution of 160 eV (at 6 keV), combined with the large collecting area, provide good opportunities for time-resolved iron line spectroscopy ( 6-8 keV). The potential observing program includes stellar coronae, cataclysmic variables and X-ray binaries, accretion discs and coronae of neutron stars and black hole candidates, supernova-remnants, active galactic nuclei, clusters of galaxies and the diffuse cosmic X-ray background. We demonstrate the instrument’s power through some astrophysical simulations.

Scanning tunneling microscopy shows that a nanopattern forms as the Pt(110)-(1 x 2) surface is exposed to oxygen at room temperature or above. The nanopattern consists of [11[over]0] oriented O-induced stripes assembling into a (11 x 2) superstructure at high O coverage. The stripes form because the O adsorption energy increases by expanding the Pt lattice along the ridges of the surface as compared to the bulk. From interplay with density functional theory calculations, we show that the O-induced nanoscale periodicity is caused by short-ranged elastic relaxations confined to the surface.

Scanning tunneling microscopy (STM) and density-functional theory are used to reexamine the structure of the renowned p(4 x 4)-O/Ag(111) surface oxide. The accepted structural model [C. I. Carlisle, Phys. Rev. Lett. 84, 3899 (2000)10.1103/PhysRevLett.84.3899] is incompatible with the enhanced resolution of the current STM measurements. An "Ag6 model" is proposed that is more stable than its predecessor and accounts for the coexistence of the p(4 x 4) and a novel c(3 x 5log3)rect phase. This coexistence is an indication of the dynamic complexity of the system that until now has not been appreciated.

Through an interplay between scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that bridging oxygen vacancies are the active nucleation sites for Au clusters on the rutile TiO2(110) surface. We find that a direct correlation exists between a decrease in density of vacancies and the amount of Au deposited. From the DFT calculations we find that the oxygen vacancy is indeed the strongest Au binding site. We show both experimentally and theoretically that a single oxygen vacancy can bind 3 Au atoms on average. In view of the presented results, a new growth model for the TiO2(110) system involving vacancy-cluster complex diffusion is presented.

Adsorbate diffusion has been observed directly and atthe atomic scale in a large number of instances by eitherfield ion microscopy (FIM) for metals on metals [1] or byscanning tunneling microscopy (STM) for metal, semicon-ductor, or simple gaseous adatoms [2,3] on a wide range ofsurfaces. Similar, detailed studies on the surface mobilityof larger organic molecules are still very scarce [4]. Theyare, however, strongly warranted both due to a fundamen-tal scientific interest [5,6] and because of the importantrole played by the diffusion of such species in the forma-tion of, e.g., self-assembled monolayer molecular films orsurface-bound nanostructures [7].In the simplest picture of surface diffusion, the migra-tion of adsorbates occurs by random jumps between near-est neighbor (

The interaction of largish molecules with metal surfaces has been studied by combining the imaging and manipulation capabilities of the scanning tunneling microscope (STM). At the atomic scale, the STM results directly reveal that the adsorption of a largish organic molecule can induce a restructuring of a metal surface underneath. This restructuring anchors the molecules on the substrate and is the driving force for a self-assembly process of the molecules into characteristic molecular double rows.

Nucleation and growth of Pt on the reconstructed Pt(100)-hex surface was studied by scanning tunneling microscopy. A detailed autocorrelation analysis of island positions reveals direct evidence for strongly anisotropic diffusion, and from the island size distribution, which obeys a simple scaling relation, we conclude that the mobility of dimers is negligible. Finally, kinetic Monte Carlo simulations, incorporating anisotropy in diffusion and finite island sizes, yield new insight into how these two factors affect the island size distribution and the scaling behavior of island density with temperature and deposition rate.

The growth of one monolayer of Au on Ni(111) is shown to lead to an ordered array of misfit dislocation loops in the underlying Ni(111) surface. The signature of these loops is observed by scanning tunneling microscopy, and atomistic simulations are used to relate the observed surface structure to that of the buried interface. The new interface structure is different from normal misfit dislocation structures in three respects: (i) it forms already during growth of a single Au monolayer, (ii) it forms in the substrate and not in the overlayer, and (iii) it is controlled by the interface energy rather than by the strain in the two phases.

Violet Lander (C(108)H(104)) is a large organic molecule that when deposited on Cu(110) surface exhibits lock-and-key like behavior [Otero et al., Nature Mater. 3, 779 (2004)]. In this work, we report a detailed fully atomistic molecular mechanics and molecular dynamics study of this phenomenon. Our results show that it has its physical basis on the interplay of the molecular hydrogens and the Cu(110) atomic spacing, which is a direct consequence of the matching between molecule and surface dimensions. This information could be used to find new molecules capable of displaying lock-and-key behavior with new potential applications in nanotechnology.

The design and performance of a fast-scanning, low- and variable-temperature, scanning tunneling microscope (STM) incorporated in an ultrahigh vacuum system is described. The sample temperature can be varied from 25 to 350 K by cooling the sample using a continuous flow He cryostat and counter heating by a W filament. The sample temperature can be changed tens of degrees on a time scale of minutes, and scanning is possible within minutes after a temperature change. By means of a software implemented active drift compensation the drift rate can be as low as 1 nm/day. The STM is rigid, very compact, and of low weight, and is attached firmly to the sample holder using a bayonet-type socket. Atomic resolution on clean metal surfaces can be achieved in the entire temperature range. The performance of the instrument is further demonstrated by images of adsorbed hexa-tert-butyl-decacyclene molecules on Cu(110), by STM movies, i.e., sequential STM images with a time resolution down to 1 s/image (100×100 A2 with 256×256 pixels), of the mobility of these molecules, and finally by constant current images of standing waves in the electronic local density of states on Cu(110).

Recent novel results concerning the applicability of the scanning tunneling microscope for atom‐resolved studies of chemical reactions, discrimination of chemically different elements, and alloying of nonmiscible metals at metal surfaces are discussed.

The 2p-1s and 3p-1s lines of channeling radiation have been measured at three different temperatures, 110 K, 300 K, and 500 K, for 3.5 MeV electrons channeled along a 〈111〉 direction in silicon. A variation of about 20% of the photon energy is observed, in good agreement with calculations. The variation reflects a temperature dependence of the 1s level due to the thermal smearing of the continuum string potential. The measured linewidths also agree with theoretical estimates. They are dominated by thermal scattering, with an estimated contribution of ~ 10% from electronic scattering.

Neutron-induced fission of 238 U has been studied by the crystal-blocking technique for neutron energies just below and above the threshold for second-chance fission. In agreement with earlier measurements, in this energy range the lifetime for first-chance fission is found to be too short to have an observable effect on the blocking dips. Above the threshold, however, an appreciable filling-in of the dips is observed. The results are analyzed in terms of a two-component lifetime distribution and then indicate an average lifetime of a few fsec for second-chance fission at a neutron energy of E n ≈ 7.2 MeV, in agreement with results from a simple calculation. It is shown that in this analysis it is important to take into account the anisotropy of the fission-fragment distribution and, in particular, the difference between the angular distributions for first- and second-chance fission.

Solid-state radiation detectors for simultaneous determination of charged particle position and energy are reviewed. Particular emphasis is devoted to the operational conditions, which are of importance for the performance of such devices, and examples of distortion and resolution reflecting inherent limitations are given for one- as well as for two-dimensional detectors. Several applications of such detectors are considered, and illustrations of the present status are given with relevant results obtained with various detectors.

The impact-parameter-dependent probability of K-shell ionization by protons has been measured in the energy range 0.5–2.5 MeV for copper, silver, and gold targets. The data are used to test the scaling relations predicted from semiclassical calculations in first Born approximation, with unperturbed projectile trajectory and nonrelativistic hydrogenic electron wave functions. A systematic procedure is described for correcting such calculations for the inadequacy of these approximations, and the correction scheme is tested by comparison partly with experiments, partly with more complete theoretical treatments. The relation between ionization by scattered particles and by particles emitted in nuclear decays or absorbed in compound-nucleus reactions is discussed, and quantitative estimates are derived for the monopole term, which dominates for projectile velocities much lower than the K-shell electron velocity.

The radiation from MeV electrons penetrating a single crystal has been studied. Coherent bremsstrahlung and channeling radiation are discussed theoretically with particular emphasis on the relation between the two phenomena. The close connection becomes clear when the coherent bremsstrahlung is interpreted as radiation from transitions between free states of motion relative to a set of planes, while the planar-channeling radiation is due to transitions between bound states in the planar averaged potential. Detailed calculations of the one-dimensional band structure for such states have been carried out for the case of 4 MeV electrons in silicon, which has also been studied experimentally. In the measured forward-radiation spectra, free-to-free, bound-to-bound, and also free-to-bound transitions have been identified, and the observed energies and intensities are in good agreement with the predictions.

Axially channeled electrons are captured into bound states of the ''atomic-string'' potential. When two rows lie in close proximity as in the direction of diamond, the potentials overlap, forming a saddle point between the rows. For 4-MeV electrons in the diamond potential, the 2p level lies above the saddle point, and molecular states are formed. The observation of radiation arising from transitions of these states is reported. Spectral information is used to deduce electron-density enhancement in the C-C bond.

Coherent bremsstrahlung with sidebands has been observed for 3.5-MeV electrons channeled through a thin Si crystal along the (110) plane close to the [110] axis. Both energies and intensities of the radiation are in good agreement with predictions.

A new high‐stability scanning tunneling microscope (STM) has been developed. Its key design feature is the application of two, concentrically aligned, piezoelectric ceramic tubes, allowing x–y–z motion of the tungsten tip as well as sample mounting to be cast into a single compact unit. The construction is small, very rigid, and temperature compensated, yielding reduced sensitivity to mechanical and acoustic vibrations and temperature variations. Other advantages of this ‘‘thimble‐size’’ STM include easy sample mounting and, at a later stage, operation under UHV conditions with access to other surface‐analysis (UHV) tools. At present, the microscope is operated in air, and its performance is tested by imaging a highly oriented pyrolytic graphite surface and a Si(111) surface on which a 100‐A‐thick Au layer has been deposited.

The Z 1 dependence of inner-shell ionization has been investigated by measuring the impact-parameter dependence of Cu-K-shell ionization by H, Be, C, and O, at energies corresponding to 2 MeV/amu. Large deviations from a scaling with Z 1 2 are observed. By scaling results for ionization of Cu by protons, it is attempted to test quantitatively an explanation based upon the modification of the K-electron binding and wavefunction, due to the proximity of the projectile to the Cu nucleus. The scaling is successful for close collisions, but significant discrepancies are found at larger impact parameters. From measurements with oxygen at different energies, the deviations are found to depend strongly on projectile velocity, almost disappearing at the lowest bombarding energy. Possible explanations are considered in connection with a discussion of the binding correction, based on adiabatic perturbation theory. Also the origin of the charge-state effect observed for oxygen (≈20% difference between O 8+ and O 6+ ) is discussed.

The probability of proton-induced Cu K-shell ionization has been investigated for small impact parameters by measuring coincidences between K X-rays and 0.5-20 MeV protons scattered through large angles. In such measurements, corrections for random coincidences are important, and it is shown that high-frequency time structure of the beam current can lead to large systematic errors. After elimination of these problems, the measured ionization probability for 2 MeV protons was nearly constant at large scattering angles, in agreement with predictions from semiclassical approximation (SCA) calculations with straight-line trajectories. At lower energies, however, a significant increase in the ionization probability has been found for the largest scattering angles. It is shown that these results may be explained in the SCA model when the deflection of the projectile is taken into account.

A theoretical description of planar-channeling radiation is given, with special emphasis on the scattering processes contributing to the radiation linewidth. Owing to coherence between scattering in the initial and final states for the radiation process, the contribution to the linewidth from processes with small momentum transfer (e.g., plasmon excitation) is strongly suppressed, and the linewidth is dominated by thermal interband scattering. Also contributions from nonsystematic reflections and from finite crystal thickness are evaluated. Experimentally, planarchanneling radiation has been studied for 4 MeV electrons in nickel, at different target temperatures, and the radiation energies and linewidths confirm the predictions. The influence of correlation of vibrations is revealed by a variation of the linewidth with the angle to a major axis in the plane. The radiation intensity as a function of incidence angle to the plane is strongly modified by multiple interband scattering, and a comparison between measured and calculated intensities serves as a further check on the theoretical treatment.

Axial channeling radiation from MeV electrons in Si resulting from spontaneous transitions between transverse energy states is studied theoretically and experimentally. Transitions between tightly bound states are well described within the single-string approximation with a thermally averaged Hartree-Fock continuum potential. This applies both for line energies and for absolute intensities as functions of incidence direction for the electron beam. For weakly bound states the extension of the calculations to describe itinerant states in the tight-binding approximation reproduces the band widths obtained from more complete many-beam calculations. For a thick crystal the discrete lines are Lorentzians with widths determined by incoherent scattering, whereas the finite crystal thickness modifies the line shape and the line width in thinner specimens. For tightly bound states the incoherent scattering is due to thermal displacements of atoms, and the formula presented for the scattering probabilities gives satisfactory agreement with observed line widths when correlations of displacements are included.

A line spectrum of channeling radiation from MeV electrons penetrating thin crystals has been observed for both planar and axial channeling. In diamond-type crystals, the atomic strings are for certain axes arranged in close-lying pairs, and the channeling states of MeV electrons may then be of molecular type. Measurements for 3 to 4 MeV electrons channeled along a 〈211〉 axis in Si show a splitting into four lines of the 2p-1s transition. The different 2p levels can be populated preferentially by a proper choice of incidence direction, and the measured line yields as well as the line energies agree with calculations based on atomic Hartree-Fock potentials, modified to include electron displacements into bonds.

Precise (3–10%) measurements of K-shell-ionization cross sections for protons have been performed for Ti, Fe, Cu, Se, Zr, and Ag. Experimental conditions are emphasized and possible errors are discussed. Comparison with theoretical values corrected for binding, Coulomb, and relativistic effects show good agreement.

The advantages and problems associated with the use of ion implantation for the fabrication of position-sensitive particle detectors are discussed. Analysis of the noise and pulse risetime properties of such devices shows the desirability of using a high sheet resistance in the distributing resistive layer for optimum position resolution while restricting the RC of the detector to values approximately equal to the clipping times used in the measuring circuits in order to obtain good position linearity. From both detector noise and pulse rise-time considerations it is found desirable to use equal pulse shaping in the energy and the position signal measuring systems. Detectors were made by implantation of 60 keV boron and phosphorus ions into 4000 ohm-cm n-type silicon. Representative results are shown for a 4×32 mm2 one dimensional detector which shows integral and differential position nonlinearity of less than one percent and position resolution of less than 0.2 mm. Extension to one dimensional detectors up to 50 mm and to 10×10mm two dimensional detectors is discussed.

Equilibrium charge distributions have been measured for 2≦Z≦18 ions with energies from 100 to 400 keV. Equilibrium was established by passing accelerated ions through a helium gas. The different charge states of the beam were separated in an electric field and detected by an open position-sensitive electron multiplier, constructed for this experiment. The results show that the equilibrium charge distribution depends strongly on the atomic number of the projectile and that the mean charge ι is an oscillating function of Z at fixed velocity. For ions with Z ι is larger in helium than after passage through a carbon foil.

Implanted dopant ions are used to form the resistive layer in position sensitive p-n junction particle detectors. Position resolution of 0.2 mm fwhm and linearity of ±0.3 mm are obtained.

The IBEC theory has been tested for the case of 193Pt. The QEC value is 56.3 ± 0.3 keV, and the data make it possible to give an upper limit on the electron neutrino mass of 500 eV (90% CL). The partial beta‐decay half‐life for M capture in 163Ho is (4.0±1.2) × 104 y and the 163Ho − 163Dy mass difference is 2.3 ± 1.0 keV. From these independent Ho results a half‐life of (7±2) × 103 y and an upper limit on mνe of 1.3 keV can be deduced.