Using high-temperature annealing of thin gold nanofilms deposited onto the (001) surface of doped p-GaAs crystal with an ultrathin oxide layer, the nanoclusters of gold (Au2Ga alloy) are fabricated. The gold clusters have the wedge shapes with rectangular bases elongated in [110] direction at GaAs(001) surface. This assertion is confirmed by the data of diagnostics of Au/p-GaAs(001) structures. Anisotropic plasmons localized on equally oriented wedge-shaped Au (Au2Ga) clusters are investigated with the optical reflectance anisotropy spectroscopy and spectroscopy of polarized light reflection. It is shown that the spectral peak at the energy about 0.9 eV in the near infrared range is associated with plasmons polarized along the longest sides of clusters in crystallographic direction [110]. Another peak—at the energy of 1.8 eV—is due to plasmons having polarization in direction [11̅0] .

A theory of two-dimensional non-radiative (Coulomb) plasmon-excitons in metal and semiconductor nanolayers located nearby is presented. Electrodynamics of damped harmonic oscillators is developed for polarization waves related to Coulomb plasmons, excitons and mixed (hybrid) plasmon-excitons excited via the near field of an external oscillating dipole. For polarization fields of the collective electronic excitations in question, the equations of motion are deduced within the classical electrodynamics with the constitutive relations conditioned by quantum theory. The dispersion relations derived for the normal plasmon-exciton modes are found to reveal the anticrossing effect due to resonant energy interchange between plasmons and excitons. The time-dependent regimes of excitation and relaxation of the two-dimensional plasmon-excitons are thoroughly investigated in terms of the forced steady and concomitant transient waves. The developed analytical theory reveals practically valuable dynamical analogies of plasmon-excitons with some other kinds of mixed modes known for various objects of linear oscillations theory.

Wedge-shaped nanoclusters of gold (Au2Ga) are fabricated by high-temperature annealing of a gold nanofilm deposited onto (001) surface of p-doped GaAs crystal with a very thin overlayer of natural oxide. The data of diagnostics confirm the presence in prepared Au/p-GaAs(001) structures of the wedge-shaped Au-intermetallic nanoclusters elongated in [110] direction at GaAs surface. A crystallographic model of the wedge-shaped Au (Au2Ga) nanoclusters conditioned by GaAs(001) surface is discussed in relation with their physicochemical nature. Anisotropic plasmons localized on equally oriented Au-based nanoclusters are detected optically with the reflectance anisotropy spectroscopy and investigated thoroughly with the spectroscopy of polarized light reflection. It is proved experimentally and theoretically that the inhomogeneously broadened infrared spectral peak at the energy about 1.1 eV is associated with plasmons polarized along the wedge-shaped clusters in [110] crystal direction. Another peak - at the energy approximately of 1.8 eV - is due to plasmons having orthogonal polarization in direction [110].

This work demonstrates how to create the structures Au/GaAs with perfect on-surface gold nanoclusters. In doing so, used is covering the GaAs substrate with chemically stable atomic monolayers of sulphur to prevent subsequently a chemical reaction of Au with GaAs. The structures Au/S/GaAs with monolayers of chemisorbed sulphur atoms are fabricated, characterized and studied by polarized reflection spectroscopy. The anisotropy of on-surface gold nanoclusters is established, and the anisotropic plasmons localized in Au clusters are investigated using the spectra of polarized reflection and interpreted theoretically.

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [11̅0] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [11̅0] of crystal.

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [110] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [110] of crystal. Keywords: semiconductor surface, nitride passivation, gold nanoclusters, anisotropic plasmons, polarized reflectance.

Herein, the formation of Au nanoclusters on nitridized GaAs(001) surface is described, as well as the structure diagnostics and spectroscopic studies which reveal a strong anisotropy of the plasmons localized on the clusters. Principal aspects of the work are the following. Technologically, structures of Au/N/GaAs are fabricated with a monolayer of nitrogen atoms chemisorbed preliminary onto GaAs substrate to prevent its reaction with subsequently deposited Au film. Annealing of the structures Au/N/GaAs results in the appearance of anisotropic nanoclusters of chemically clean gold on GaAs surface. Experimentally, the existence of in‐surface anisotropy of Au clusters is verified with the atomic force microscopy and it is investigated with the resonant optical spectroscopies of anisotropy reflectance and polarized reflection. All the methods are applied jointly for the detailed study of anisotropic plasmons revealed in gold nanocluster arrays. Theoretically, the plasmon‐conditioned features observed in optical polarized spectra are interpreted using an optical model of in‐surface anisotropic plasmons in Au nanospheroids. As a result, the macroscopic anisotropy and orientation of gold nanoclusters and their plasmons relative to the crystallographic axes of GaAs substrate are unambiguously established and reliably specified.

A principal role of chemical passivation of GaAs surface in the formation of oriented anisotropic on-surface nanoclusters of gold is discussed. The gold nanoclusters are fabricated by thermal annealing of the gold film deposited onto GaAs(001) surface passivated preliminary by an atomic monolayer of nitrogen or sulphur. These atoms forming a crystal lattice are bonded chemically to gallium atoms of the crystal surface to prevent chemical interaction of Au with GaAs. Annealing Au on passivated GaAs(001) surface results in formation of arrays of anisotropic (elongated) nanolusters of chemically pure Au oriented preferably in crystal direction. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and the optical techniques of reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Within an optical model of plasmon polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons polarized in Au nanoclusters predominantly in direction on GaAs(001) surface.

A theory is developed for the relaxation of two-dimensional non-radiative (Coulomb) plasmon-excitons in closely located thin layers of a metal and a semiconductor. In the framework of classical electrodynamics, the equations of motion are formulated for the polarization waves of non-radiative plasmons and excitons with taking account of their Coulomb coupling and of an external near-field polarization. In the model of coupled harmonic oscillators represented by the polarization fields of excitations, the problem of relaxation is solved for Coulomb plasmons, excitons and plasmon-excitons. The dispersion branches of normal plasmon-exciton modes are shown to undergo anticrossing (repulsion) at the resonance between plasmon and exciton. Allowing for dissipative damping and energy transfer between the excitations under study, the time-dependent process of plasmon-exciton relaxation is investigated. The theory reveals the principal analogies between dynamics of plasmon-excitons and oscillations typical of other objects of linear vibration theory, such as mechanical oscillators, resonant electric chains, etc.

The Schottky nanostructures Au/GaAs with Au nanoclusters are prepared by annealing of thin gold films deposited on nitridized GaAs(001) surface. The nanostructures are diagnosed nanoscopically and investigated by optical reflection anisotropy spectroscopy. The Au nanoclusters arrays of two types are found to be formed respectively under and over GaAs surface. The energies of local plasmons of the arrays are detected at 1.6 and 2.15 eV, respectively. The latter plasmons possess in-surface anisotropy which causes in optical anisotropy spectra the intensive resonant feature at energy about 2 eV. The plasmon anisotropy is studied comprehensively, and the results are interpreted theoretically.

A theory of Coulomb (non-radiative) plasmons-excitons in a semiconductor with adjacent quantum well and ultrathin metal film is presented. The equations of motion are formulated for the polarization waves of surface plasmons and quasi-two-dimensional excitons with taking account of Coulomb interaction between them. Within a model of coupled harmonic oscillators, solved are the problems of Coulomb plasmon, exciton and plasmon-exciton excitations in the presence of an external dipole force. The coupling constant is calculated for plasmon-excitons, their optical spectra are investigated, and the relative contributions of plasmons and excitons to the normal modes are found. It is concluded that near the resonance between plasmon and exciton the spectrum of plasmon-exciton excitations consists of two peaks whose behavior in passing through the resonance shows the signs of anti-crossing effect (repulsion of frequencies).

A procedure is developed for controlled creation of Au nanoclusters by annealing of a gold film deposited onto GaAs(0 0 1) crystal surface. The nanoclusters of Au are formed at GaAs surfaces covered by either a natural oxide layer or a monolayer of gallium nitride. Surface morphology of the Au/GaAs structures with Au nanoclusters is characterized by scanning probe diagnostics and localized plasmons of the nanoclusters are investigated by optical reflection spectroscopy. In annealing Au film dissimilar gold nanoclusters are found to occur on oxidized or nitridized GaAs(0 0 1) surface via chemical transformation or recrystallization of Au film, respectively. Gold nanoclusters of the two types cause resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of optical spectroscopy and their theoretical analysis we assign the former peak to localized plasmons of prolate Au nanoclusters buried into GaAs crystal near its surface. Another peak at 2.15 eV is attributed to plasmons of oblate Au nanoislands appearing on nitride overlayer which prevents any chemical contact of Au with GaAs bulk. The asserted existence of Au nanoclusters in the bulk of GaAs crystal near its oxidized surface is expected to be helpful in elucidating the nature and structure of Ohmic Au-GaAs contacts.

The structures Au/GaAs(001) with gold nanoclusters are created by annealing of Au films deposited onto GaAs surface. The samples are diagnosed stepwise by scanning probe microscopy. Using reflectance anisotropy spectroscopy, Au clusters are established to possess plasmons with the in-surface anisotropy. The measured anisotropy spectrum consists of a resonant feature near the energy of 2 eV typical of local plasmons of Au clusters. The results are explained theoretically, and the new spectral feature is assigned to anisotropic plasmons of Au nanoclusters located on GaAs surface.

The structure of the optical spectra related to the resonant interaction of quasi-two-dimensional excitons and localized plasmons is investigated theoretically. The constant of plasmon–exciton coupling is estimated in a model considering a semiconductor quantum well close to a layer of metal nanoparticles in an adjacent dielectric medium. Numerical calculations carried out for GaAs/Ag and ZnO/Al nanosystems indicate that near the plasmon–exciton resonance the spectrum features a double-peak structure which exhibits the plasmon-excitonic anticrossing behavior upon detuning from exact resonance.

Gold nanoclusters of two different kinds are found to occur on annealing of thin Au films deposited on either oxidized or nitridized GaAs(001) surfaces. The morphology of Au/GaAs interfaces is characterized, and the gold nanoclusters are established to cause two resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of reflection spectroscopy and theoretical analysis, we assign the latter peak to localized plasmons of Au nanoislands located on Au/GaAs surface. The former peak is attributed to plasmons of prolate Au nanoclusters buried in GaAs crystal just near its surface. As well, plasmonic anisotropy of Au nanoclusters formed on nitridized GaAs surfaces is detected using reflectance anisotropy spectroscopy.

AbstractThe structure of the optical spectra related to the resonant interaction of quasi-two-dimensional excitons and localized plasmons is investigated theoretically. The constant of plasmon–exciton coupling is estimated in a model considering a semiconductor quantum well close to a layer of metal nanoparticles in an adjacent dielectric medium. Numerical calculations carried out for GaAs/Ag and ZnO/Al nanosystems indicate that near the plasmon–exciton resonance the spectrum features a double-peak structure which exhibits the plasmon-excitonic anticrossing behavior upon detuning from exact resonance.

A theory of plasmon-exciton coupling and its spectroscopy is developed for metal-semiconductor nanostructures. Considered as a model is a periodic superlattice with cells consisting of a quantum well and a layer of metal nanoparticles. The problem is solved self-consistently using the electrodynamic Green's functions taking account of resonant polarization. Coulomb plasmon-exciton interaction is associated with the dipole surface plasmons of particles and their image charges due to excitonic polarization of neighboring quantum well. Optical reflection spectra are numerically investigated for superlattices with GaAs/AlGaAs quantum wells and silver nanoparticles. Superradiant regime caused by one-dimensional Bragg diffraction is studied for plasmonic, excitonic and plasmon-excitonic polaritons depending on the number of supercells. The plasmon-excitonic Rabi splitting is shown to occur in reflectivity spectra of resonant Bragg structures.

The results of the theory considering mixed plasmon-excitonic modes and their spectroscopy are presented. The plasmon-excitons are formed owing to strong Coulomb coupling between quasi-two-dimensional excitons of a quantum well and dipole plasmons of nanoparticles. The effective polarizability associated with a nanoparticle is calculated in a self-consistent approximation taking into account the local field determined by in-layer dipole plasmons and their image charges due to the excitonic polarization of a near quantum well. The spectra of elastic scattering and specular reflection of light are investigated in cases of a single silver nanoparticle and a monolayer of such particles situated in close proximity to a quantum well GaAs/AlGaAs. The optical spectra show a two-peak structure with a deep and narrow dip in the resonant range of plasmon-excitons. Propagation of plasmon-excitonic polaritons is discussed for periodic superlattices whose unit cell consists of a quantum well and a layer of metal nanoparticles. The superradiance regime originating in the Bragg diffraction of plasmon-excitonic polaritons by the superlattice is investigated. It is shown that the broad spectrum of plasmonic reflection depending on the number of unit cells in a superlattice also has a narrow dip at the exciton frequency.

Local plasmons of gold nanoclusters formed at Au/GaAs interface are observed and investigated. The gold nanoclusters are prepared by thermal annealing of thin Au films deposited on GaAs(001) surface. In order to prevent chemical interaction between Au and GaAs at high temperatures, a thin layer of GaN is formed on GaAs substrate surface by chemical nitridation in hydrazine sulfide solution prior to deposition of Au. Typical shapes and sizes of Au nanoclusters are obtained from STM characterization of samples in ultrahigh vacuum followed by measuring and calculating their optical reflectivity spectra. In general, the reflectivity spectra of Au/GaAs samples reveal two resonant peaks at the energies about 1.55 and 2.15 eV. The former peak dominates for oxidized GaAs(001) substrates, while the latter peak is clearly visible for nitridized GaAs substrates. Theoretical analysis of the optical spectra of Au/GaAs interface using a model of Au nanospheroids allows us to assign the reflectance peak at 2.15 eV to local plasmons of Au nanoclusters which look like oblate islands on a Au/GaAs(001) sample. In turn, the peak at 1.55 eV is assigned to plasmons of Au nanoclusters prolate perpendicularly to the surface of GaAs crystal in whose near-surface region these Au clusters are buried.

A theory of plasmonic reflectance anisotropy spectroscopy (RAS) is developed for nanocluster layer at an interface. The model of identical ellipsoidal metal particles occupying the sites of rectangular lattice is used to calculate the effective plasmonic polarizability of nanoparticles. The anisotropic local field due to optically induced dipole plasmons and their interface-conditioned images is taken into account. Within the theory, resonant reflectance anisotropy spectra recently observed for In nanoclusters on InAs surface are explained, the anisotropy being associated with the difference between frequencies of plasmons with orthogonal in-layer polarizations. The frequency difference is treated in terms of anisotropy of the particles shape or/and the layer structure, its sign being opposite for the two types of anisotropy. The plasmonic RAS is concluded to serve as a method for investigating the anisotropy of nanocluster arrays.