A systematic study of local-density-of-states ͑LDOS͒ deconvolution from tip-surface tunneling spectra is reported. The one-dimensional WKB approximation is used to simulate the process. A technique for DOS deconvolution from the electron-tunneling spectroscopy data is proposed. The differential conductivity normalized to its fit to the tunneling probability function is used as a method of recovering sample DOS. This explicit procedure does not use unconstrained parameters and reveals a better DOS deconvolution in comparison with other techniques. The advantage of this method is its feasibility for extracting two important physical parameters from experimental tunneling spectra: ͑i͒ local surface potential, and ͑ii͒ tip-sample distance. These values are the parameters used in the proposed fitting procedure. The local surface potential and the tip-sample distance retrieval are demonstrated by means of numerical simulations. Comparative scanning tunneling spectroscopy is proposed as an approach to eliminate the influence of the tip condition on the surface LDOS recovery.

A statistical model of activated dissociative adsorption is developed using microcanonical, unimolecular rate theory. Dissociation is treated as occurring through energy randomizing collisions between incident molecules and local clusters of surface atoms. The predictions of the statistical model are found to be in remarkable accord with existent experimental data for methane dissociative adsorption and the thermal hydrogenation of methyl radicals on Pt(ll1). Perhaps surprisingly, the "over the barrer" statistical model adequately describes the known kinetics of these reactions without any explicit provision for quantum tunneling.

Scanning capacitance spectroscopy (SCS), a variant of scanning capacitance microscopy (SCM), is presented. By cycling the applied dc bias voltage between the tip and sample on successive scan lines, several points of the high-frequency capacitance–voltage characteristic C(V) of the metal–oxide–semiconductor capacitor formed by the tip and oxidized Si surface are sampled throughout an entire image. By numerically integrating dC/dV, spatially resolved C(V) curves are obtained. Physical interpretation of the C(V) curves is simpler than for a dC/dV image as in a single-voltage SCM image, so that the pn junction may be unambiguously localized inside a narrow and well-defined region. We show SCS data of a transistor in which the pn junction is delineated with a spatial resolution of ±30 nm. This observation is consistent with the conclusion that SCS can delineate the pn junction to a precision comparable to the Si depletion width, in other words, the actual size of the electrical pn junction. A physical model to explain the observed SCS data near the pn junction is presented.

Angle-resolved, photofragment translational energy distributions, Pϑ(ET)s, arising from 308 nm laser irradiation of CH3Br adsorbed on Pt(111) are presented. Methyl photofragments were observed with translational energies extending to 2 eV and with Pϑ(ET)s which varied sharply with angle of exit from the surface. The fragmentation dynamics were consistent with a mechanism of dissociative electron attachment of subvacuum level, photoexcited substrate electrons to adsorbed CH3Br. The CH3 Pϑ(ET)s and the angular variation of the CH3 yield gave evidence that submonolayers of CH3Br form islands on Pt(111).

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Nanosecond laser pulses, with 2.33 eV photon energy and ∼0.6 MW/cm2 radiation flux, have been used to initiate a transient increase of tunneling current between a W tip and a Si sample surface in an ultrahigh vacuum scanning tunneling microscope (STM) apparatus. As the laser power is increased to ∼2.5 MW/cm2, single atom transfer from the tip to a silicon surface occurs. For both polarities, the laser induced tunneling current is linear with laser pulse energy up to ∼0.6 MW/cm2. A transient tunneling current up to 15 μA has been observed. The similarity of the laser induced transient tunneling for both polarities, and hence its independence on material, suggest that the same mechanism is operative in both directions of tunneling. Both ballistic electron tunneling and band bending effects have been considered in the analysis of the electron transfer. It is proposed, however, that pulse laser heating of the tip causes this transient increase of the tunneling current due to a transient thermal expansion, reducing the tip-sample tunneling distance. The increase in tunneling current may lead to additional Nottingham heating of the tip apex. At a laser flux of 2.5 MW/cm2, single atom transfer between the W tip and the silicon surface occurs. The number of atoms transferred can be controlled by the laser flux, and the transfer process is virtually independent of the tip-sample bias polarity. Since a maximum tip temperature of 650 K is estimated during the pulse, W atom transfer must occur under the influence of strong W–Si chemical interaction. The speed of the pulse laser atom transfer (8 ns) exceeds by orders of magnitude the transfer speed that could be achieved by pulsing the STM piezodrive.

The transient tunneling current induced by pulsed laser irradiation of a scanning tunneling microscope (STM) tunneling gap was observed to occur over a 100 μs time scale range in response to a 20 ns duration of the laser pulse. The amplitude of the transient current varies exponentially with laser power, confirming our previous suggestion that thermal expansion of the STM tip is the main source of the transient increase of tunneling current. This thermal expansion mechanism is also supported by the observation of a qualitatively similar variation of the tunneling current during the piezo-driven decrease of the tip-sample separation.

The scanning capacitance microscope ͑SCM͒ is a carrier-sensitive imaging tool based upon the well-known scanning-probe microscope ͑SPM͒. As reported in Edwards et al. ͓Appl. Phys. Lett. 72, 698 ͑1998͔͒, scanning capacitance spectroscopy ͑SCS͒ is a new data-taking method employing an SCM. SCS produces a two-dimensional map of the electrical pn junctions in a Si device and also provides an estimate of the depletion width. In this article, we report a series of microelectronics applications of SCS in which we image submicron transistors, Si bipolar transistors, and shallow-trench isolation structures. We describe two failure-analysis applications involving submicron transistors and shallow-trench isolation. We show a process-development application in which SCS provides microscopic evidence of the physical origins of the narrow-emitter effect in Si bipolar transistors. We image the depletion width in a Si bipolar transistor to explain an electric field-induced hot-carrier reliability failure. We show two sample geometries that can be used to examine different device properties.