Ultralow energy ion beam surface modification of low density polyethylene

Ultralow energy Ar+ and O+ ion beam irradiation of low density polyethylene has been carried out under controlled dose and monoenergetic conditions. XPS of Ar+-treated surfaces exposed to ambient atmosphere show that the bombardment of 50 eV Ar+ ions at a total dose of 10(16) cm(-2) gives rise to very reactive surfaces with oxygen incorporation at about 50% of the species present in the upper surface layer. Using pure O+ beam irradiation, comparatively low O incorporation is achieved without exposure to atmosphere (approximately 13% O in the upper surface). However, if the surface is activated by Ar+ pretreatment, then large oxygen contents can be achieved under subsequent O+ irradiation (up to 48% O). The results show that for very low energy (20 eV) oxygen ions there is a dose threshold of about 5 x 10(15) cm(-2) before surface oxygen incorporation is observed. It appears that, for both Ar+ and O+ ions in this regime, the degree of surface modification is only very weakly dependent on the ion energy. The results suggest that in the nonequilibrium plasma treatment of polymers, where the ion flux is typically 10(18) m(-2) s(-1), low energy ions (<50 eV) may be responsible for surface chemical modification.     

The resolution obtained from low energy ion scattering using an ion cyclotron resonance spectrometer

The resolving power of the low energy ion scattering technique with FT-ICR spectrometry is discussed. Resolution improvement due to simultaneous registration of scattered ions with different masses is shown.     

Chemical effects on oscillatory cross sections in low energy ion scattering

Oscillatory structure in the scattered ion yield for He⁺ scattering from In has been observed to depend upon the chemical environmental of the In. Fourier analysis of the oscillatory structure indicates two major components whose relative amplitudes vary significantly with chemical environment.     

Probing interatomic potentials by ion translational energy spectrometry: A new crossed molecular beams apparatus

This report presents details of the development of a new crossed molecular beams apparatus designed and fabricated to carry out high sensitivity ion translational energy spectrometric investigations of the potential energy surfaces of small molecular species. The translational energy spectrometer is used to carry out experimental studies of ion-neutral reactions resulting in charge stripping of CS⁺ radicals and dissociation of metastable CO²⁺ dications. These results are interpreted in the light of high-levelab initia molecular orbital calculations of the pertinent molecular potential energy functions. New results for the double ionisation energy of CS and the kinetic energy released upon dissociation of specific electronic states of CO²⁺ are presented.     

Chemical modification of fluorinated self-assembled monolayer surfaces by low energy reactive ion bombardment

Reactive collisions of low energy (<100-eV) mass-selected ions are used to chemically modify fluorinated self-assembled monolayer surfaces comprised of alkanethiolate chains CF₃(CF₂)₁₁(CH₂)₂S— bound to Au. Typical experiments were done by using 1-nA/cm² beams and submonolayer doses of reactant ions. Characterization of the modified surface was achieved by in situ chemical sputtering (60-eV Xe^+·) and by independent high mass resolution time-of-flight-secondary ionization mass spectrometry (TOF-SIMS) (15–25-keV, Ga⁺) experiments. Treatment with Si³⁵C1 ₄ ^+· produced a surface from which Xe⁺ sputtering liberated CF₂ ³⁵C1⁺ ions, which suggested Cl-for-F halogen exchange at the surface. Isotopic labeling studies that used Si³⁵Cl₂ ³⁷Cl ₂ ^+· ; and experiments with bromine-containing and iodine-containing projectiles, confirmed this reaction. High mass resolution TOF-SIMS spectra, as well as high spatial resolution images, provided further evidence as to the existence of halogen-exchanged species at the bombarded surface. Analogous Cl-for-F halogen substitution was observed in a model gas-phase reaction. The ion-surface reaction is suggested to proceed through an intermediate fluoronium ion in which the projectile is bonded to the target molecule. The most significant conclusion of the study is that selective chemical modification of monolayer surfaces can be achieved by using reactive ion beams, which lead to new covalent bonds at the surface and in the scattered ions.     

Experimental apparatus for investigation of sputtering and secondary ion emission induced by energetic ion beams

The construction of an experimental apparatus, for investigation of implantation, secondary ion emission and sputtering processes, during irradiation of samples with an ion beam of up to 70 keV energy, is described. The basis of the apparatus is an electromagnetic mass separator equipped with a quadrupole mass spectrometer located in the collector chamber. The computer data acquisition control system makes it possible to perform the experimental measurements with high accuracy and precision. Preliminary results of secondary ion mass spectral measurements, obtained for C, Al, Si and Cu targets bombarded with Ar(+) and Kr(+) ions, are presented.     

Z-pinch used as a plasma lens for heavy ion beams

Focusing of a heavy ion beam by the azimuthal magnetic field of a z-pinch discharge was observed. The experiment was carried out with a device, which has been designed to generate controlled plasma states for the investigation of the interaction of heavy ion beams with hot matter. A focusing factor of 5 in beam diameter was detected with high speed photographic methods. The experimental results are in agreement with numerical calculations.     

The structural and compositional analysis of single crystal surfaces using low energy ion scattering

The use of ion scattering for surface composition and structure analysis has been reviewed. The extreme surface specificity of this technique has been widely used to obtain qualitative information in a straightforward way, but the occurrence of charge exchange processes, thermal lattice vibrations and multiple scattering have precluded quantitative analysis of experimental data. Examples are quoted to illustrate the progress that has been made in understanding these fundamental processes and in applying this knowledge to the development of the analytical capabilities of the technique.     

Structural modification of nanocrystalline ceria by ion beams

Exceptional size-dependent electronic-ionic conductivity of nanostructured ceria can significantly alter materials properties in chemical, physical, electronic and optical applications. Using energetic ions, we have demonstrated effective modification of interface volume and grain size in nanocrystalline ceria from a few nm up to ～25 nm, which is the critical region for controlling size-dependent material property. The grain size increases and follows an exponential law as a function of ion fluence that increases with temperature, while the cubic phase is stable under the irradiation. The unique self-healing response of radiation damage at grain boundaries is utilized to control the grain size at the nanoscale. Structural modification by energetic ions is proposed to achieve desirable electronic-ionic conductivity.     

Optical and dielectric properties of fluorinated ethylene propylene and tetrafluoroethylene–perfluoro(alkoxy vinyl ether) copolymer films modified by low energy N and C ion beams

Fluorinated ethylene propylene (FEP) and tetrafluoroethylene–perfluoro(alkoxy vinyl ether) (PFA) copolymer films were irradiated in vacuum with 60 keV C⁴⁺ and N⁴⁺ ions to fluences ranging from 1.0×10¹² to 5.0×10¹⁵ cm⁻². Changes in optical and dielectric properties were analyzed by spectroscopic ellipsometry and ultraviolet–visible (UV–vis), Raman and dielectric relaxation spectroscopies. Direct and indirect energy band gap values were determined from the absorption edge in the 200–800 nm region using Tauc's relation. The values of the direct energy gap have been found to be greater than the corresponding values of the indirect energy gap. Significant changes in the index of refraction, and β and γ dielectric relaxations were observed in the case of N⁴⁺ irradiated FEP and PFA samples.     

Secondary ion images of the rodent brain

Sections of biologic tissue obtained from laboratory rodents are prepared and analyzed by secondary ion mass spectrometry. The intensity of phosphocholine secondary ions is used to identify anatomical features of the brain from secondary ion images and to evaluate the effectiveness of procedures developed. Secondary ion emission of phosphocholine (m/z 184), is found to be abundant and its intensity is heterogeneous. Effects of sample thickness are addressed. Correspondence between conventional optical images of stained tissue and secondary ion images shows that successive ion images may be used to produce a three-dimensional map of the brain, i.e., an atlas.     

Axial focusing following low kinetic energy pulsed extraction from a miniature linear ion trap

Using an axial focusing miniature linear ion trap with tubular end cap lenses (MLIT) we have investigated spatial focusing on ion ejection using low kinetic energy pulsed extraction methods. Ion packet widths focused to ca. 1 mm (in both the radial and axial planes) are produced following collisional cooling with helium buffer gas in an MLIT. Small axial and radial packet widths as well as application of DC extraction voltages allow different ion focusing techniques to be used on batch ion extraction. In particular, controlling the position of the space focus plane (commonly used in time-of-flight mass spectrometry) following low kinetic energy ( approximately 10 eV) ion ejection from an MLIT through the application of DC extraction voltages is illustrated. Prior to simultaneous ion ejection, induced axial ion oscillation through a change in the DC potential well shape is also shown to be useful for separating and controlling different mass/charge ion packet spatial distributions in the region of an orthogonal time-of-flight (o-TOF) push pulse.     

Production of iodine radionuclides using 7Li ion beams

Journal of Radioanalytical and Nuclear Chemistry - This is the first attempt to generate baseline data on the level of Naturally Occurring Radioactive Materials, (NORMs) 238U, 232Th and...     

Secondary ion images of the developing rat brain

Secondary ion images were obtained from sections of rat brain over a 21 day postnatal period, using the intensity of m/z 184, phosphocholine. When compared with corresponding optical images of similar, but stained sections from the same animal, the secondary ion images appear to reflect less developed brains. During development, myelination occurs after axon extension. Apparently, myelination obscures the source of secondary m/z 184, phosphatidylcholine, from the analyzing ion probe; absenting myelination, secondary ion images show no physiological features.     

A computerized system for the digital image processing of ion microscope images

A general program for the digital image processing of ion microscope images is described. The program IONPIX and the accompanying aggregate of related subprograms comprise a basis for the process of extracting the large amount of compositional morphological information contained in ion images. Previous practical applications of the IONPIX software system are also described.     

Micrometer-scale transient ion transport for real-time pH assay in living rat brains

Ion transport has been widely used for various applications such as sensing, desalination and energy conversion; however, nearly all applications are based on steady-state ion transport. Herein, we for the first time demonstrate the capability of transient ion transport for in vivo sensing with both high spatial (∼μm) and temporal (∼ms) resolution by using pH as the model target. Transient ion transport behavior (i.e., time-dependent ion current change) was observed by applying high-frequency pulse potential. Importantly, we proposed the ion distribution transient model for this time-dependent ion transport behavior. With this model, the temporal resolution of the as-developed pH microsensor based on ion current was improved to the ms level, thus satisfying the requirement of neurochemical recording. Moreover, our microsensor features good reproducibility, selectivity, and reversibility, and can thus real-time monitor the pH change in living rat brains. This study demonstrates the first example of in vivo sensing based on ion transport, opening a new way to neurochemical monitoring with ultrahigh spatiotemporal resolution. This study is also helpful to understand the transient process of asymmetric ion transport.

Micrometer-scale transient ion transport has been successfully used for constructing a high spatiotemporal resolution and performance microsensor, which could be used for real-time monitoring the change of pH in rat brains.     

A high transmission hemispherical energy analyzer for ion spectrometry

A hemispherical energy analyzer was constructed by using a novel approach to control the fringing electrostatic field. It provides several properties useful in ion spectrometers: namely, rather simple fabrication and compact size, high transmission efficiency at moderate resolution, and the capability to adjust resolution by changing the intersphere potentials. A computer program was developed to evaluate ion trajectories through the hemispherical analyzer. Data obtained from the trajectories were used to predict the characteristics of the analyzer. Experiments performed to determine the kinetic energy dependence of the absolute transmission and the resolution functions are in accord with theoretical calculations.