The model of a multiple-quantum-well (MQW) structure in the vicinity of a high surface potential is studied to understand the interaction between the Tamm states and the unperturbed interior states of near-surface MQW’s. A finite number of wells, different degrees of interwell coupling, and the influence of the cap-layer thickness are considered.

In order to investigate the formation and the time evolution of Na oxidation states, a thin layer of sodium was deposited on oxidized substrates and exposed to oxygen at ${10}^{\mathrm{-}9}$ Torr. In the Na 2p core-level spectrum, several chemically shifted components have been observed, denoting the presence of nonstoichiometric Na oxidation states, whose binding energy is substrate independent. Modification of these states, with oxygen exposure has been observed by detecting the increase in intensity of the corresponding shifted components and the consequent decrease of the clean features: the stationary configuration is reached in a time τ=${10}^3$ s.

The number of silver atoms incorporated into a Si(111) 3×1(6×1)-Ag structure is determined by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Silver MNN Auger intensities from surfaces with two different compositions were compared between clean 7×7, (√3 × √3 )R30°-Ag, and 3×1(6×1)-Ag structures, which were determined from scanning tunneling microscopy images. From the AES intensity ratio and known occupancies of each reconstruction, the number of Ag atoms incorporated into the 3×1(6×1)-Ag structure was determined to be 0.36±0.16 ML. This value is close to 1/3 ML, suggesting that one of the two rows observed by STM does not consist of Ag atoms.

The optical response of one Ag monolayer deposited on different Si surfaces has been studied by differential reflectance spectroscopy. The observation of the plasma resonance in the Ag deposits and its energy position, or the nonobservation of this plasma resonance, allows a qualitative determination of the morphology of the thin Ag film: either continuous or formed by quasispherical particles or by flattened three-dimensional particles.

Resonant-valence-band as well as core-level-photoemission measurements have been performed for depositions of Ce (∼0.6-14 Å) onto a Rh(100) substrate. The core-level spectra indicate formation of a mixed interface as Ce is deposited on Rh. The Rh 3d core-level emission could be deconvolved into three components, which are assigned to bulk Rh, surface Rh, and rhodium that has reacted with cerium. The Ce 4f emission intensity at the Fermi level is observed to move away from the Fermi level with increased Ce deposition in the submonolayer regime. The f-d hybridization is argued to increase with increasing amounts of Ce in the low-coverage regime. The present findings seem to favor the picture of bandlike behavior of strongly hybridized f electrons.

We calculate the bulk (infinite system), (100)-bulk-projected and (100)-surface-projected Green’s functions using the surface-Green’s-function matching method and an empirical tight-binding Hamiltonian with tight-binding parameters that describe well the bulk band structure of CdTe. In particular, we analyze the band (B-4) arising at -4.4 eV from the top of the valence band at Γ according to the results of Niles and Höchst and at -4.6 eV according to Gawlik et al., both obtained by angle-resolved photoelectron spectroscopy. We give a theoretical description of this band.

We have studied the sound velocity in the quasi-one-dimensional organic conductor (TMTSF${)}_2$${\mathrm{ClO}}_4$, where TMTSF is tetramethyltetraselenafulvalene. The system shows profound magnetoacoustic oscillations at low temperatures and in high magnetic fields. At the reentrant transition from the field-induced spin-density-wave (FISDW) state to the metallic state, the sound velocity shows a discontinuous jump. In the reentrant metallic phase, the amplitude of the oscillations is greatly enhanced and their phase is different by 180° from that in the FISDW state. Above ∼20 T the sound velocity shows complex, temperature-dependent structure, which may indicate sharp oscillations of the phase boundary as predicted in some recent theories.

We found that a whole class of structures with rhombohedral symmetry possesses sizable photonic gaps. These structures can be generated by connecting lattice points in an A7 structure by cylinders and a few structures that are known to possess photonic band gaps are in fact members of this ‘‘parent’’ structure. This class of structures also allows us to explore more systematically the criteria favorable for gap formation.

The electronic structure and optical properties of rhombohedral ${\mathrm{LiNbO}}_3$ have been studied by a first-principles method in the local-density approximation (LDA). An approximate k-dependent and energy-dependent self-energy-correction scheme is then applied to the LDA result, yielding a direct band gap of 3.56 eV at Γ. It is shown that the calculated dielectric function with the self-energy-corrected eigenvalues is in much better agreement with the optical and refractive index data than those from LDA. The calculated negative optical birefringence is in excellent agreement with experiment. Valence-charge analysis indicates the ionic formula for ${\mathrm{LiNbO}}_3$ to be ${\mathrm{Li}}^{0.98}$${\mathrm{Nb}}^{3.67}$(${\mathrm{O}}^{\mathrm{-}1.55}$${)}_3$.

We report the passivation of two deep copper-related acceptor levels in Cu-diffused p-type GaAs by the group-I element lithium. The deep-level-transient-spectroscopy (DLTS) signals of the well-known Cu-related levels with apparent activation energies 0.15 eV and 0.40 eV disappear in Cu-diffused samples when they are diffused with Li, but can be reactivated by annealing. Photoluminescence measurements show a corresponding disappearance and reappearance of the copper-related luminescence at 1.36 eV. Also we observe with DLTS an energy level at ${\mathit{E}}_{\mathit{V}}$ + 0.32 eV in the Cu-Li-diffused samples. The level is neither present in the Cu-diffused samples before Li diffusion nor in Cu-Li-diffused samples after annealing. As the level is not observed in starting materials or solely Li-diffused samples we suggest that it is related to a Cu-Li complex.

The presence of Si donors in GaAs exerts a strong influence on the charge state and diffusion of muonium at the tetrahedral interstitial site (${\mathrm{Mu}}_{\mathit{T}}^0$), while it has relatively weak effect on the bond-center muonium (${\mathrm{Mu}}_{\mathrm{BC}}^0$). In metallic GaAs:Si, the highly mobile ${\mathrm{Mu}}_{\mathit{T}}^0$ center observed in nonmetallic GaAs is replaced by a charged species (probably ${\mathrm{Mu}}^{\mathrm{-}}$) which shows a diffusion rate at least ${10}^{\mathrm{-}2}$ times smaller than the ${\mathrm{Mu}}_{\mathit{T}}^0$ center. The ${\mathrm{Mu}}_{\mathrm{BC}}^0$ center is metastable and its transition to ${\mathrm{Mu}}_{\mathit{T}}^0$ or ${\mathrm{Mu}}^{\mathrm{-}}$ centers (depending on doping concentration) is seen in the 50–150-K range. The current results also suggest that the ${\mathrm{Mu}}_{\mathit{T}}^0$ state undergoes fast spin-exchange interaction with conductive carriers prior to the transition ${\mathrm{Mu}}_{\mathit{T}}^0$→${\mathrm{Mu}}^{\mathrm{-}}$.

We report the development of a ${\mathrm{Mn}}^{2+}$ focused ion beam for use in the direct fabrication of submicrometer magnetic structures. Mn-implanted GaAs bulk epilayers and quantum wells are studied by low-temperature cathodoluminescence and polarization-resolved photoluminescence. The data demonstrate that Mn ions are magnetically active, producing optical polarizations of 70% at 8 T.

Photoluminescence experiments detecting the occupation of higher subbands in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superlattices are used to determine the field strengths of electric-field domains. While the magnitude of the electric field in the low-field domain corresponds to resonant alignment of subbands in adjacent wells, the field strength in the high-field domain is below the value corresponding to the resonant field. These results are interpreted in terms of a simple model based on current conservation.

The normal (${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te grown on CdTe) and inverted (CdTe on ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te) interfaces are studied separately using a quantitative model of the Zeeman effect of excitons in asymmetric CdTe quantum wells with a magnetic ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te barrier on one side and a nonmagnetic ${\mathrm{Cd}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Zn}}_{\mathit{y}}$Te barrier on the opposite side. The extrinsic effect (dilution of Mn) is dominant at the inverted interface, while the normal interface allows a rather low upper bound to the intrinsic interface effect (due to missing nearest neighbors). Experimental results agree well with model profiles assuming a complete Cd/Mn exchange during growth between the surface layer and the subsurface layer.

We report first-principles total-energy calculations for the GaAs(001) surface. Our results indicate that the 2×4 reconstruction corresponds to the β2(2×4) structure, which exhibits two As dimers in the top layer and a third As dimer in the third layer. This structure has a lower surface energy than the β(2×4) model, which has three As dimers in the top layer. We also find that a model recently proposed by Skala et al. [Phys. Rev. B 48, 9138 (1993)] for the structure of the Ga-rich 4×2 phase is energetically unfavorable. From our results we conclude that electrostatic interactions between the charged building blocks of polar semiconductor surfaces play an important role in determining the equilibrium structure. We introduce a simple model for estimating these interactions.

We study single-electron tunneling in a two-junction device in the presence of microwave radiation. We introduce a model for numerical simulations that extends the Tien-Gordon theory for photon-assisted tunneling to encompass correlated single-electron tunneling. We predict sharp current jumps which reflect the discrete photon energy hf, and a zero-bias current whose sign changes when an electron is added to the central island of the device. Measurements on split-gate quantum dots show microwave-induced features that are in good agreement with the model.

The transition from a two-dimensional to a quasi-three-dimensional electron system has been studied in multiple quantum wells, by varying the barrier thickness ${\mathit{L}}_{\mathit{b}}$ for a constant 100-Å well width. Dramatic differences in electron-hole correlation are observed due to the different extension of electron and hole wave functions. The 1S-2S energy separation of the heavy-hole exciton decreases from 8.3 meV for ${\mathit{L}}_{\mathit{b}}$=150 Å to 3.1 meV for ${\mathit{L}}_{\mathit{b}}$=10 Å. The acceptor-bound-exciton binding energy is constant, while the bound-exciton decay time increases dramatically with decreasing ${\mathit{L}}_{\mathit{b}}$.

We have measured the Brillouin spectrum in p-p polarization of a bilayer of Si/${\mathrm{SiO}}_2$ produced by low-dose oxygen implantation on the Si (001) surface. The spectra show two strong resonances close to the longitudinal threshold of silicon, which are explained by a full calculation of the Brillouin cross section. In particular the resonance below the threshold is a guided mode of the buried layer (${\mathrm{SiO}}_2$), which originates from the localization in the layer of the surface longitudinal resonance of the matrix (Si). The theory takes into account in a supported double layer both the ripple and the elasto-optic scattering mechanisms.

Strong interlayer correlations generate a long-wavelength energy gap in the acoustic-excitation spectrum of a superlattice, whose magnitude is determined by the interlayer correlation function. We establish an iterative scheme for the calculation of the latter, starting from the well-known correlation function of the isolated two-dimensional electron layer. The gap size is displayed as a function of the layer-layer separation and of the coupling parameter within a layer.

We discuss the heating of electrons by a steady-state electric field in an unbounded thin metal film by considering the energy flow from the electron system to the acoustic modes of the film. Using the dispersion relationships and the resulting density of states for the acoustic modes calculated from a non-Debye model, and a deformation potential coupling between the electrons and the acoustic modes, it is shown that the relationship between the electric field and the electron temperature is dependent on the coupling between acoustic modes at the surface of the film. At low excitation we show the energy relaxation is dominated by the antisymmetric Rayleigh mode.