Ion dose

The bombardment of a sample with a dose of high energetic primary ions (1 to 20 keV) results in the destruction of the initial surface and near-surface regions (Sect. 3.1.1). If the primary ion dose is higher than 10 ions mm the assumption of an initial, intact surface is no longer true. A sputter equilibrium is reached at a depth greater than the implantation depth of the primary ions. The permanent bombardment of the sample with primary ions leads to several sputter effects more or less present on any sputtered surface, irrespective of the instrumental method (AES, SIMS, GDOES. ..). 

Cu/ Zn0/Si02 catalyst obtained with different doses of 5 keV Ne" ions (see insert, spectra are shifted vertically for clarity). Catalyst reduction temperature 700 K. Solid lines fitted Gauss peaks [3.147]. (b) The relative coverage of Cu and ZnO on the silica-supported catalyst, reduced at 700 K, as a function of the ion dose [3.147]. 

Cu/ Zn0/Si02 catalyst reduced at 700 K [3.147]. These LEIS spectra were obtained at three different ion doses - 3 x 3.41 x 10 and 8.67 x 10 Ne" cm . Because of the use of isotopically enriched Cu and Zn, and of Ne" ions as projectiles, Cu and Zn can clearly be separated in the LEIS spectrum. Strong dose-dependence is apparent. Eig. 3.60b shows the dose-dependent surface concentrations of Cu and Zn. At low doses (<1.5 x lO " Ne cm ) the Zn concentration remains constant whereas the Cu concentration increases. At these low doses a hydroxyl layer on top of the catalyst is sputtered. The Zn signal stays constant despite removal of the adsorbate, indicating that at the virgin surface the Zn concentration was even higher. 

As an electrolyte, Nafion 112 (Du Pont, Inc) membrane was pretreated using H2O2, H2SO4 and deionized water before ion beam bombardment. The prepared membranes with a size of 8 X 8 cm were mounted on a bombardment frame with a window size of 5 x 5 cm, equal to the active area of the test fuel cells, and dried up at 80 C for 2 hr. Then, the mounted membrane was brought in a vacuum chamber equipped with a hollow cathode ion beam source as described in the previous study [1]. Ion dose was measured using a Faraday cup. Ion density... 

Fig. 1 shows SEM images for the surface of the untreated and the surface treated Nafion 112 membranes with ion dose density from lO to lO ions/cm at ion beam energy of 1 keV. With increasing the ion dose density, surface of the membrane was clearly roughened. Surfece of the membrane seemed to have a nodule-like structure at ion dose densities of lO and lO ... 

Study [1], it was reported that with increasing ion dose density from 10" to lO ions/cm, RMS roughness of the ion beam bombarded membrane increased from 21 to 204 nm without changing ionic conductivity of the membrane. 

Fig. 2. Effects of ion dose density on i-V curves. Cathode catalyst loading = 0.2 mg-Pt/cm, H2/air.

The experimental data presented confirm that - at least after the disappearance of the smallest elements at the beginning of the sputtering - the particle sizes can indeed be adjusted by the applied ion dose, which allows us to follow the size dependent changes of the physical properties of the particles from the bulk limit. 

In situ measurements of electrical sheet resistance provide another clue to the composition of the films. A plot of the sheet resistance as a function of dose is shown in Figure 8. The decrease in sheet resistance trails the loss of carbon and oxygen by a factor of 10 in terms of ion dose and reaches a limiting value of 2xl04 uto-cm. This is two orders of magnitude greater than the lowest value measured in the laser-exposed material, at least qualitatively consistent with the relative purity of the metals in each case. 

Figure 5. Infrared spectra of 0.90 nm palladium acetate film on silicon as a function of 2 MeV He+ ion dose. Dose range 0-6x 1014 ions/cm2.

Figure 8. Sheet resistance of 0.90 fim palladium acetate film as a function of 2 MeV He+ and Ne+ ion dose.

Figure 9. The quadrupole mass spectrometer signal for volatile species released from 0.90 nm palladium acetate film as a function of 2 MeV He+ ion dose. Mass 15 is shown for both CH3 and CH4 because of overlap at m/e 16 with oxygen. Mass 31 is shown for C2H6 (13C isotope) because of overlap at m/e 30 with major fragments of other parent ions.

Figure 11. Carbon and oxygen content of 0.12/im palladium acetate film, measured by Rutherford backscattering spectroscopy as a function of 2 MeV Ne+ ion dose.

The intrinsic flexibility involved in being able to select and vary the ion energy, ion type and ion dose enables complex interfaces to be "tailored" to specific requirements. 

The time necessary for removing one monolayer during a SIMS experiment depends not only on the sputter yield, but also on the type of sample under study. We will make an estimate for two extremes. First, the surface of a metal contains about 1015 atoms/cm2. If we use an ion beam with a current density of 1 nA/cm2, then we need some 150 000 s - about 40 h - to remove one monolayer if the sputter yield is 1, and 4 h if the sputter rate is 10. However, if we are working with polymers we need significantly lower ion doses to remove a monolayer. It is believed [4] that one impact of a primary ion affects an area of about 10 nm2, which is equivalent to a circle of about 3.5 nm diameter. Hence if the sample consists, for example, of a monolayer film of polymer material, a dose of 10n ions/cm2 could in principle be sufficient to remove or alter all material on the surface. With a current density of 1 nA this takes about 1500 s or 25 min only. For adsorbates such as CO adsorbed on a metal surface, we estimate that the monolayer lifetime is at least a factor of 10 higher than that for polymer samples. Thus for static SIMS, one needs primary ion current densities on the order of 1 nA/cm2 or less, and one should be able to collect all spectra of one sample within a quarter of an hour. 

Ion conducting glasses, 12 585-586 Ion-cut process, 14 448-449 Ion cyclotron (ICR) analyzers, 15 663-664 Ion cyclotron resonance instrument, 15 664 Ion-dipole interactions, 14 411-418 Ion doping, in photocatalysis, 19 94-95 Ion doses, measuring, 14 444—445 Ion engines, cesium application, 5 705 Ion exchange, 14 380-426... 

Group 14 (IV) elements as, 22 232 high throughput experimentation, 7 382t, 414t hydrides in, 13 609 introduction of dopants into, 14 428 ion dose for, 14 427 photon interaction with, 23 33—34 as photosensitive materials, 22 716 scanning capacitance microscopy,... 

RBS spectra were obtained using a 2.120 MeV He+2 ion beam at a backscattering angle of 162. The spectra were accumulated for a total ion dose of 40 uC using a 10 nA beam current. The number of Ti atoms/cm2 in the sample was calculated by comparison to spectra for a standard Si wafer implanted with a known dose of Sb. 

Figure 22. Human embryonic kidney cells (A), rat vascular smooth muscle cells (B, C) and human osteoblast-like MG 63 cells (D) in cultures on micropattemed surfaces. A, B PTFE irradiated with UV light produced by a Xe2 -excimer lamp for 30 min in an ammonia atmosphere through a mask with holes 100 pm in diameter and center-to-center distance 300 pm C PE irradiated with Ar ions (energy 150 keV, ion dose lO ions/cm ) through a mask with holes 100 pm in diameter and center-to-center distance 200 pm fullerenes Qo deposited through a mask with rectangular holes with an average size of 128 3 pm per 98 8 pm on glass coverslips. Day 7 after seeding. A native cells in an inverted phase-contrast microscope B, C cells stained with hematoxylin and eosin, Olympus microscope IX 50 D cells stained with fluorescence-based LIVE/DEAD viability/cytotoxicity kit (Invitrogen), Olympus microscope IX 50. Bars 300 pm (A), 200 pm (B, D), Imm (C) [10,11].

Figure 4.4 Evolution of the damage in the C and Si sublattices versus the ion dose (i.e., fluence) at the peak damage position, (a) From the early damaging up to the amorphous state. (From [55]. 2000 Elsevier B.V. Reprinted with permission.) (b) Low damage level (From [59]. 2001 American Institute of Physics. Reprinted with permission.) (c) Very early damage. (From [60]. 2001 American Physical Society. Reprinted with permission.)...

Figure 4.5 (a) Comparison between the computed and measured displaced profiles SRIM-97 simulation versus experimental data. (From [63]. 1999 Elsevier B.V. Reprinted with permission.) (b) values for the C and Si sublattices in 6H-SiC versus ion dose for 300K implantation temperature. (From [31]. 2002 Elsevier B.V. Reprinted with permission.) (c) for the Si sublattice in 6H-SiC versus ion dose and ion mass for 180-190K implantation temperature. (From [63]. 1999 Elsevier B.V. Reprinted with permission.)... 

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