Electrodeposited Au/Si(111) (t = 14.1 nm or 60 ML) after 5 months: (a) STM and (b) corresponding BEEM images (Vb = −1 V and It = 2 nA. Scanned area: 200 × 200 nm2). (c) and (d) height and BEEM current profiles along the indicated lines in the corresponding STM and BEEM images.
Cross-sectional TEM image 〈110〉 beam direction of an electrodeposited Au/Si (111) contact (t = 14.1 nm or 60 ML) after 11 months in air (a) bright-field, low-magnification with associated selected area diffraction pattern, (b) high magnification lattice image of the interfacial region. The circled diffraction spots are from Au while the others are from Si.
Electrodeposited Au/Si(111) (t = 7.0 nm or 30 ML) after 1 week in air: (a) STM image (200 nm x 200 nm) obtained at a tip bias Vb = −1.0 V, tip current It = 2 nA, (b) height profile along the indicated line in STM image in (a). No BEEM signal was detectable.
Cross-sectional 〈110〉 TEM lattice image, with an associated selected area diffraction pattern, of an electrodeposited Au/Si (111) contact (t = 7.0 nm or 30 ML) after 11 months in air. The circled diffraction spots are from Au and the others Si.
Evaporated (fresh) Au/Si(111) (t = 8 nm or 30 ML): (a) (200 nm x 200 nm) STM and (b) corresponding BEEM image (Vb = −2.0 V, It = 4 nA) (from Ref. 10 ). (c) and (d) height and BEEM current profiles along the indicated lines in the STM and BEEM images. Note that the BEEM signal disappeared after 1 day. (Images in (a) and (b) are reprints from Ref. 12 with permission. Copyright 2008 American Chemical Society.)
Electrodeposited Au/Si(001) (t = 6.7 nm) one month after deposition: (a) (200 nm × 200 nm) STM and (b) corresponding BEEM image (Vb = −1.0 V, It = 2 nA). The edges of the images are parallel to 〈110〉 Si directions. (c) and (d) height and BEEM current profiles along the indicated lines in the STM and BEEM images.
Average BEEM spectra (It = 2 nA) of electrodeposited Au/Si diodes after 5 months as a function of Au thickness and Si orientation: Si (100) Δ 6.7 nm (33 ML), ◻ 13.5 nm (66 ML); Si (111) ▪ 14.1 nm (60 ML). The solid lines are fits to these spectra giving the BEEM thresholds listed in Table I .
Log (IB /It ) versus Au thickness, t, for Au/Si(111) diodes (closed symbols) and Au/Si(100) diodes (open symbols). Room temperature with a tip bias −1.2 V. Solid lines are best linear fits. ED = Electrodeposited; Vac = EV on chemically etched Si, secondary vacuum 10−7 Torr, UHV = EV in UHV (10−10 Torr); SP = sputtered (physical vapour deposition using an Ar ion beam).
Summary of Au/Si diode properties as a function of surface orientation and Au layer thickness, t. The electrical barrier height, φIV , ideality factor, n, and zero bias resistance, Ro , are extracted from macroscopic current-density voltage measurements. The local BEEM thresholds (or barrier height), φB and BEEM transmission current, IB , are extracted from averaged BEEM spectra (measured at a tip bias of −2 V, tip current 2 nA). The last column lists whether STM imaging was feasible (Y = stable; N = not stable). Bracketed data is for diodes aged 5 months, otherwise the results are for diodes measured within 1 day (EV) or within a week (ED).
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