A highly sensitive potentiometric technique generally applicable for detection of gases utilizing adsorption-induced changes in surface work function is demonstrated. This technique is applied to sense hydrogen based on work function change of a Pt thin film. The surface work function changes of Pt upon exposure to pure and 1000ppm hydrogen were found to be ∼900 and ∼270mV, respectively. These work function changes are much higher than corresponding changes in the Schottky barrier height in Pt-semiconductor based amperometric sensor devices for similar hydrogen concentration. Using this technique, detection down to 8ppm hydrogen concentration is demonstrated.

Surface electronic properties of GaN nanowires have been investigated using scanning probe microscopy and correlated with metal/nanowire contact characteristics. Surface current map of the nanowire was observed to be highly nonuniform, resulting from a large variation in surface barrier of the nanowire, on the order of a few tenths of an eV. The surface barrier non‐uniformity, which most likely determines the formation of an ohmic or Schottky contact, is increased dramatically with the nanowire surface deformation. Current–voltage characteristics and scanning gate microscopy of the nanowires also indicate significant carrier trapping at the nanowire and silicon dioxide surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple technique for quantitative nanoscale capacitance–voltage (C–V) measurements has been developed and used to characterize the two-dimensional electron gas (2DEG) at the interface of AlGaN/GaN heterostructures. The measurements indicate change in confinement of the 2DEG at the AlGaN/GaN interface depending on the direction of the dc voltage sweep during C–V measurements, indicating surface state charging and discharging. Under UV illumination, the 2DEG increased significantly as inferred from the increase in threshold voltage of the nanoscale C–V scans, while no change in 2DEG confinement was observed.

Perturbation of charges at the surface and interface of AlGaN/GaN heterostructures has been studied by quantitative nanoscale capacitance-voltage (C-V) measurements. The nanoscale C-V curves were found to have different slopes in the forward and reverse directions. These measurements indicate a change in confinement of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface depending on the direction of the dc voltage sweep during C-V measurements, which can be explained by surface state charging and discharging during the bias sweep. Under UV illumination, the density of the 2DEG increased significantly as inferred from the increase in threshold voltage of the nanoscale C-V scans, and no change in 2DEG confinement, depending on the direction of the bias sweep, was observed.

Shrinking gate lengths have led to increased challenges in isolating defects using conventional physical failure analysis methods. Conducting atomic force microscopy (CAFM) has been proven to be a powerful tool to isolate gate oxide defects in silicon-on-insulator devices. Some sample preparation techniques of exposing polysilicon and gate oxide, which were critical to perform CAFM scan, are discussed in this paper.