In situ interface characterization of silicon surface in fluoride media

Dopant-Induced Electronic Structure Modification of HOPG Surfaces: Implications for High Activity Fuel Cell Catalysts

“…In addition, a fourth capacitance associated with surface state charges may be present in parallel with the space charge capacitance if the solid surface is not atomically smooth. For electrolytes of relatively moderate concentrations, diffuse ionic layer and compact layer capacitance are usually much larger (typically by at least an order of magnitude) than the space charge capacitance (at least at the flat band voltage), and hence their contribution to the total capacitance at the capacitance minimum is usually negligible. , For our undoped HOPG substrates, as with stress annealed pyrolitic graphite, it appears that the surface state capacitance is also negligible. This is not surprising given the near atomically smooth character of the undoped HOPG surface.…”

“…This is evident from the behavior in the positive-potential (depletion) region of the capacitance−voltage curve, where for both the Ar-doped and N-doped substrates, the capacitance decreases with voltage. The decrease in capacitance with voltages positive of the flat-band potential is characteristic of n-type semiconductor behavior. ,, For both samples, n-type semiconductor behavior is verified by replotting the capacitance−voltage data as C −2 vs. V . According to the Mott−Schottky theory, the capacitance of the space charge region ( C sc ) in an extrinsic semiconductor as a function of electrode potential under depletion conditions is given by: 1 C 2 = true( 2 ε ε 0 e N true) true[ V − true( V fb + k T e true) true] where e is the electron charge, N is the electronic charge carrier density, ε is the dielectric constant, ε 0 is the permittivity in vacuum, V is the applied potential, k is the Boltzmann constant, and kTq −1 is the temperature ( T )-dependent term (∼26 meV at room temperature).…”

“…These surface-state capacitance contributions can be considered to be in parallel with the space charge capacitance, as shown in the equivalent circuit models in Figure . , While the simple schematic in Figure depicts the defects and dopants as simple volume elements, we recognize that the true physical picture is certainly more complicated. As depicted in the schematic, the defect/dopant zone is confined to the near-surface region of the HOPG substrate, a consequence of the low-angle, low-energy ion implantation used to dose the samples.…”