Sputtering yield measurements at glancing incidence using a quartz crystal microbalance

Abstract

Low energy sputtering yields at grazing incidence have been investigated experimentally using a quartz crystal microbalance ͑QCM͒ technique. This method involved precoating the QCM with a thin film of the desired target material and relating the resonance frequency shift directly to mass loss during ion bombardment. A highly focused, low divergence ion beam provided a well defined incidence angle. Focusing most of the ion current on the center of the target allowed for higher sensitivity by taking into account the radial mass sensitivity of the QCM. Measurements of Mo, Cu, and W sputtering yields were taken for low energy ͑80-1000 eV͒ Xe + and Ar + to validate this experimental method. The target films ranged from 3.5 to 8.0 m in thickness and were deposited so that their crystal structure and density would match those of the bulk material as closely as possible. These properties were characterized using a combination of scanning electron microscope imagery, profilometry, and x-ray diffraction. At normal incidence, the sputtering yields demonstrated satisfactory agreement with previously published work. At angles of incidence up to 40°off normal, the data agreed well with predictions from existing theoretical models. Sputtering yields were found to increase by a factor of 1.6 over this range. The optimum angle for sputtering occurred at 55°, after which the yields rapidly decreased. Measurements were taken up to 80°from the surface normal.

Tuning the surface properties of hydrogel at the nanoscale with focused ion irradiation

“…Some additional effects such as charging during the irradiation of insulated hydrogel as well as redeposition may also have contributed to the variations in simulation. 21,22,32,33 The experimentally determined yield of this study (0.47 mm 3 nC À1 ), however, is close to the reported yield of polymethyl methacrylate (PMMA) with the same ion energy, 34 and will provide a reference value for future tasks.…”

Sputtering and crystalline structure modification of bismuth thin films deposited onto silicon substrates under the impact of 20–160keV Ar+ ions

“…Notice that the whole irradiated Bi area is much larger compared to that corresponding to the global size of the grains and granular structures created on the Bi sample surface. Therefore, one expects that such structures would have only minor effects on the measured sputtering yields [30,31]. A behavior characterized by similar but magnified effects is observed when the Bi sample surface is irradiated by 120 keV Ar + ions of increasing fluence up to 1.2 Â 10 16 cm À2 (Fig.…”

“…The inter-atomic spacing in the deposited film was directly determined from the peak locations in the diffracted patterns as in Ref. [30]. One finds a value of 3.914 Å, larger than that for bulk bismuth (d = 3.734 Å) by less than 4%.…”

“…However, it amounts up to $70% in the very low ion fluence region. The measured sputtering yields in this region are very sensitive to ion fluence variation and to the important variation of the target areal density upon primary ion-irradiation, i.e., to errors affecting the sputtered depths [30,34].…”

Modelling radio-frequency plasma cleaning of fusion optics

“…Voltage and frequency remain as variables which can tailor the IEDF to ideal values between 35 eV (threshold for Mo) and 25 eV (the estimated threshold for BeO), with the frequency being most significant due to narrower IEDFs at higher frequencies. However there is the consideration that metals, such as Mo, have been shown to have order of magnitude higher sputtering yields than oxides, such as BeO, when compared at higher energies [40]. With sputtering being a complicated process it is also known that threshold energies have an angular dependence which can cause sputtering below the threshold energy (usually measured with perpendicular ions) [41].…”