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We measure the conductance variations of submicrometer inversion-layer segments in silicon devices, systematically changing the length, width, inelastic diffusion length, gate voltage, magnetic field, and temperature. Results agree with the theory of universal conductance fluctuations, demonstrating that random quantum interference causes rms conductance changes AG^^^e^/h in each phase-coherent subunit of each segment. The random quantum interference is extremely sensitive to change of a single scatterer.PACS numbers: 72.20. My, 72.20.Dp, 73.40.Qv It is now well understood that low-temperature conductance changes due to weak localization (coherent backscattering) are an example of electron quantum interference in disordered metals.^ In recent theoretical investigations,^"^ a new type of sample-specific random quantum interference of a surprisingly universal character is asserted to affect to varying degrees all conductance measurements on disordered metals. In this Letter, we experimentally confirm key predictions of this theory of ''universal conductance fluctuations."' Random quantum interference arises from the scattering of electron waves by the particular disordered configuration of scatterers ("impurities") in each specimen. A single specimen should exhibit different conductances G corresponding to changes of magnetic field (phase) and electron energy (wavelength) sufficient to rerandomize the interference. Macroscopically similar specimens-having the same dimensions, electron density, and average density of scatterers-should show a similar range of specimento-specimen variation due to microscopic differences of configuration. In both cases, for phase-coherent specimens, the theory predicts an rms variation 8G with a universal magnitude of approximately e^/h = (25.8 kfi)"^ For specimens consisting of A^ phase-coherent subunits, it predicts that the fractional fluctuations are smaller by A^^^^ because of selfaveraging.Two manifestations of this random interference are the aperiodic magnetoresistance fluctuations observed in small metal wires^*^^ and narrow Si inversion layers,^^'^^ and the periodic A/^ Aharonov-Bohm oscillations observed in metal^^"^^ and quantum-well^^ rings. Prior comparisons between theory and the aperiodic phenomena have been based on one or two devices with very small fractional effects. In the present Letter, we systematically confirm a broad range of key predictions of the universal conductance fluctuations theory, including systems in which the fractional effect is of order unity.We have fabricated dozens of Si inversion-layer segments of various lengths and widths in the range 0.04-1.0 fxm and have measured the conductance of each at a variety of gate voltages, magnetic fields, and temperatures. Our devices are /^channel metaloxide-silicon field-effect transistors (MOSFETs) with multiple contacts and narrow channel segments. The device structure and fabrication is described in Mankiewich.^^ Each device contains a narrow channel of width W with several side branches that are used ...

Multiterminal measurements of magnetoresistance fluctuations in silicon inversion-layer nanostructures are extended to probe spacings L<^L^, the phase-preserving diff'usion length. Unlike for L>L^^ the sizes of the voltage fluctuations are independent of L, and have novel correlations consistent with independent potential fluctuations of each probe. The corresponding ^'conductance" fluctuations SG(L) are ^e^/h\ however, this can be understood if each pair of probes eff*ectively measures voltage fluctuations at scale L^, determined by the condition 5G(L^) =e^/h.

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High-frequency gratings with rectangular-groove profiles are used to generate high-efficiency beam splitters and beam deflectors. The effects of the grating design parameters, i.e., period, groove depth, duty cycle, number of phase levels, and polarization state (TE and TM) of the incoming signal, are considered. The case of the binary beam splitter grating is analyzed by using rigorous electromagnetic grating analysis. Fabrication techniques are presented in which three different lithographic techniques are considered (optical contact, deep-UV stepper reduction, and electron-beam direct write). Experimental results of 97% efficiency for the beam splitter grating and up to 80% for the beam deflector grating are reported.