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(Color online) Upper part: sketch of the photoelectrochemical cell used for the photocurrent measurements. The electrons and holes generated by photoexcitation are referred to as and , respectively. One of these charge carriers is collected at the electrode surface and the other one is scavenged by the oxidized (ox) or reduced (red) form of the redox couple in the electrolyte. Lower part: typical photocurrent on-off cycles upon photoirradiation in the energy range between 2.0 and .
(Color online) (a) STM image of the Ge average diameter. and ; (b) conductance curves obtained by differentiating the curves recorded on Ge dots of about (solid line) and (dotted line). In the inset, the energy band gap vs the Ge dot size is shown.
(Color online) Photocurrent action spectra of (a) large Ge dot sample (mean diameter of ) (triangles) and Ge dot sample (black circles). The right scale refers to the former sample, while the left scale refers to the latter; (c) (black circles) and (triangles) Ge nominal thickness samples. The open circles report the photocurrent data for a Ge amorphous ultrathin film. (b) Experimental optical absorption coefficient for Ge bulk, as reported in Ref. 20
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