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We report a new method of achieving tip-sample distance regulation in an atomic force microscope ͑AFM͒. A piezoelectric quartz tuning fork serves as both actuator and sensor of tip-sample interactions, allowing tip-sample distance regulation without the use of a diode laser or dither piezo. Such a tuning fork has a high spring constant so a dither amplitude of only 0.1 nm may be used to perform AFM measurements. Tuning-fork feedback is shown to operate at a noise level as low as that of a cantilever-based AFM. Using phase-locked-loop control to track excursions in the resonant frequency of a 32 kHz tuning fork, images are acquired at scan rates which are fast enough for routine AFM measurements. Magnetic force microscopy using tuning-fork feedback is demonstrated.

We report Raman studies of the Si–Si phonon band in Si1−xGex alloys, where the excitation is by visible and ultraviolet (351 nm) light. At a wavelength 351 nm, the optical penetration depth is extremely shallow (≈5 nm). By varying the excitation from 351 to 514 nm, the optical penetration depth spans from 5 to 300 nm. Two sets of samples were examined. Thin layers grown using molecular beam epitaxy were coherently strained to match the lattice constant of the silicon substrate. Thick layers grown using organo–metallic chemical vapor deposition were strain relaxed. For the thin, strained layers, visible excitation produces a spectrum, which is a superposition of the substrate and the epilayer phonon bands. Reducing the wavelength (and, consequently, penetration depth) allows us to isolate the epilayer spectrum. Phonon energies obtained using all excitation wavelengths agree. We conclude that Raman scattering from these alloys using 351 nm laser light gives us bulk alloy properties pertinent to the near-surface composition and strain. The epilayers show no evidence of compositional variance or strain relaxation near the surface.

We present results of the fabrication and investigation of totally spatially localized crystalline structures. Low temperature photoluminescence exhibits structure that is best explained by a bottleneck for hole energy loss. This bottleneck is believed to be a direct consequence of the modification of the band structure by the fabrication-imposed potential and is believed to be the first evidence for total spatial quantization in a fabricated heterojunction system.

We identify the four allowable phonon modes in InxGa1−xAs on InP:InAs-like transverse optical (TO) (225±2 cm−1), InAs-like longitudinal optical (LO) (233±1 cm−1), GaAs-like TO (255±2 cm−1), and GaAs-like LO (269±1 cm−1), using the selectivity of first-order Raman scattering off the (100) normal surface and the (011) cleaved plane and detailed line-shape analysis employing a sequential simplex optimization procedure. Raman scattering off the (011) cleaved plane was achieved for the first time in thin-film InGaAs using microprobing capabilities (∼1 μm). We also identify another phonon mode R* at 244 cm−1 which is attributed to an alloy disorder mode in these films. For the five identified phonon modes, a linear relationship between the Raman frequencies and composition determined from x-ray diffraction was determined for near-lattice-matched conditions (0.42<1−x<0.52).