B.U.R. Sundqvist

Electronic Sputtering: From Atomic Physics to Continuum Mechanics

The surprising fact that even very complex molecules can be ejected intact into the vapor phase when a material is electronically excited by incident particles provides a new probe of the behavior of condensed matter at high excitation densities. The physics of the conversion of the electronic excitation energy into mechanical and chemical energy links atomic physics in a solid at low excitation densities to nanometer‐scale continuum mechanics at high excitation densities

Acceleration of Cn+60 molecules to high energy

Abstract For the first time fullerene ions have been accelerated to high energy (4–36 MeV). Negative ions of C − 60 were produced in an ion source with a Cs gun and injected into a tandem accelerator. The change of charge from negative to positive was achieved by collisions with N 2 molecules in a gas cell at the high voltage terminal before the second acceleration step. To identify the accelerated molecular ions, the injected beam was pulsed, and time-of-flight measurements combined with energy measurements allowed mass and charge assignments.

Modifications in the chemical bonding and optical absorption of PPS by ion bombardment

Abstract Commercial-grade thin poly(p-phenylene sulphide) (PPS) foils, 2 μm thick, have been bombarded with 1H+ (380 keV), and with 0.61 MeV/amu 4He+, 12C2+, 16O3+, 32S3+, 79Br9+ and 127I14+ ions. The completely modified foils have been analyzed by Fourier transform infrared absorption spectroscopy (FTIR) and by ultraviolet-visible absorption spectroscopy (UV-VIS). The bond breaking and rearrangement processes were followed by using the FTIR results. The absorbance of bands related to CS, SS, CH and most of the ring carbon bonds show an exponential decrease as a function of fluence. The absorption bands most sensitive to the ion bombardment are those assigned to CS and SS bonds. The CC and CH bonds are less sensitive and certain absorption band changes indicate carbon-carbon aliphatic and or aromatic conjugation, due to their increasing intensity as a function of the ion fluence. Damage cross sections have been extracted from the plots of IR absorbance versus fluence. The values of the damage cross sections obtained scale roughly with the square of d E d x (independent of the nature of the chemical bond). The optical absorption coefficient has also been followed as a function of the ion fluence.

Deep level transient spectroscopy analysis of fast ion tracks in silicon

Deep level transient spectroscopy measurements of electron traps in MeV proton‐ and alpha‐irradiated n‐type silicon have been performed. Six deep levels are found in proton‐irradiated samples, while only three appear after alpha irradiation. The influence of the irradiation dose on the defect production is investigated together with the depth concentration profiles. The profiles scale with the nuclear energy deposition, but in the case of the doubly negative charged state of the divacancy at EC −0.24 eV, the peak concentration at the end of the track is less pronounced relative to the tail region towards the surface. It is proposed that the singly negative charged state at EC −0.42 is more probable in a highly distorted lattice and it is shown that the formation of the singly negative charged state of the divacancy dominates the defect production for higher doses.

Radiation damage features on mica and L-valine probed by scanning force microscopy

The radiation damage tracks on the surface of muscovite mica due to single 78.2 MeV 127I ions from the Uppsala EN tandem accelerator have been studied using tapping mode scanning force microscopy (TM-SFM). Conically-shaped hillocks having nearly circular bases were observed on a sample irradiated at normal incidence. Samples irradiated at grazing angles of incidence displayed wider and taller hillocks, and each hillock was accompanied by a raised tail over the bulk ion track. First SFM results are also presented from a study of radiation damage features on mica and single crystals of L-valine induced by single 23 MeV C60 ions from the Orsay tandem accelerator. Brief comments are made on the scaling laws that could link results obtained with atomic and cluster ions.

Photochemical versus thermal mechanisms in matrix-assisted laser desorption/ionization probed by back side desorption

The contribution of photochemical and thermal effects in the formation and ejection of biomolecular ions in matrix-assisted laser desorption/ionization; (MALDI) is studied by comparing desorption from one-and-the-same sample in two incident laser geometries—irradiating the sample front, or irradiating the back side through a 2000 A gold layer. Such a set-up results in the efficient decoupling of photoexcitation from thermal processes. Our results indicate that laser-induced photochemistry, e.g. charge transfer reactions between electronically-excited matrix molecules and the analyte, plays a major role in the MALDI process.

The influence of ion flux on defect production in MeV proton‐irradiated silicon

The production of stable vacancy‐related point defects in silicon irradiated with 1.3 MeV protons has been studied as a function of ion flux (protons s−1 cm−2), while keeping the total fluence constant. Since the total fluence was very low (5 × 109 protons cm−2), no interference between neighboring ion tracks was expected. The defect concentrations have been measured by deep‐level transient spectroscopy, and a decrease in the resulting defect density is found for increasing flux. This effect was unexpected and shows that there is an overlap between ion tracks, in spite of the low fluence. The behavior is attributed to the rapidly diffusing silicon interstitials, which overlap the vacancy distributions produced in adjacent ion tracks. When the ion flux is low, the distribution of vacancies from one ion becomes diluted and recombination with interstitials from ions impacting at a later time is rare. As the flux is increased the vacancy distribution from one ion will still be confined to a small volume when ...

An MeV-ion implanter for large area applications

Abstract A facility for MeV ion irradiation of large areas (10 × 10 cm2) is described. Irradiation with a variety of ion beams at fluences ranging from 108 to 1015 ions/cm2 can be conducted with less than 5% variation in dose. The system is presently used for charge-carrier lifetime control in semiconductors and for studies of thin film adhesion enhancement.

Hydrogen-related electron traps in proton-bombarded float zone silicon

Abstract P + n diodes have been irradiated at nominal room temperature by 1.3 MeV H + or 5.0 MeV He 2+ ions to doses in the range 10 8 –10 10 cm −2 . The diodes were analysed with respect to electron traps in the forbidden band gap by applying deep level transient spectroscopy. It is found that two levels, at approximately 0.32 and 0.45 eV below the conduction band, originate from irradiation-induced defects involving hydrogen. The levels appear at low doses and are presumably caused by low order complexes. On the basis of the experimental results and of computer simulations of the H + implantation profile it is speculated that the two peaks may originate from vacancy-oxygen and divacancy configurations which are partly saturated with hydrogen.

Total molecular yields for fast heavy ion induced desorption of biomolecules

Abstract The total desorption yield for intact molecules of the amino acid leucine (131 amu) induced by 90MeV 127I14+ ions has been studied. A collector method was used where the collector samples were analysed using both an amino acid analyzer (via optical absorption) for absolute measurements and Plasma Desorption Mass Spectroscopy for relative measurements of the total number of unfragmented molecules. Results indicate high yields of intact molecules of the order of one thousand which corresponds to a removal of about 1 × 105 A3 of sample material per incident ion. It has been shown that fast heavy ion induced desorption of leucine is essentially a “neutral ejection” process with the generally studied ionized portion constituting a very small fraction (≈1:104).