Experimental observation of photonic and polaritonic gaps in a silica opal

Experimental observations of the simultaneous presence of a polaritonic and a photonic gap in a three-dimensional photonic crystal is reported, to the best of our knowledge, for the first time. The photonic crystal was made of monodispersed silica microspheres sedimented into a face-centered-cubic structure. Silica has a polaritonic gap for wavelengths between 8 and 9.35 microm. Four different sphere sizes were used, with diameters of d=0.49, 0.73, 0.99, and 1.57 microm. The photonic crystals were studied by normal incidence infrared reflectance measurements in the wavelength interval 0.8-12 microm. Four peaks with the a magnitude of approximately 0.6, originating from the periodicity of the crystal, were recorded in the interval between 1 and 4 microm. Another peak, the polaritonic reflectance peak (approximately 0.4), is observed for wavelengths around 9 microm for all four crystals.     

Reflection spectra of uninfiltrated and Ba(NO3)2-infiltrated synthetic opal photonic crystals

The reflection spectra of uninfiltrated and Ba(NO₃)₂-infiltrated synthetic opal crystals have been measured using a halogen lamp with a quasi-continuous near-UV through IR spectrum as the light source. The spectra have been analyzed in a specular geometry at angles of incidence from 5° to 45°. The specular reflection spectra show a prominent maximum whose position depends on the angle of incidence. The infiltration of opal with barium nitrate shifts the maximum to longer wavelengths by 50 to 100 nm, depending on the angle of incidence. This effect has been interpreted in terms of the photonic band gap, which depends on the angle of incidence and the refractive index of the material filling the pores. The experimental data are in reasonable agreement with the peak-reflectance wavelengths calculated using well-known relations for Bragg diffraction.     

Local spectroscopy of band gaps in ferroelectric photonic crystals

We have measured visible to near-UV reflection spectra of opal photonic crystals infiltrated with ferroelectrics: barium titanate, sodium nitrite, potassium iodate, and triglycine sulfate. An experimental procedure has been developed for the infiltration of various ferroelectrics into opal pores through laser ablation and laser implantation. Using a fiber-optic probe, we were able to analyze surface reflection spectra of photonic crystals with a 0.2-mm resolution. A deuterium lamp was used as a broadband UV source, which allowed us to observe both the first and second [111] photonic band gaps in the reflection spectrum of opal crystals.     

Control over the spectral position of the band gap of opal photonic crystals

We demonstrate that the width and spectral position of the band gap of opal photonic crystals can be controlled by varying the concentration of solution in the opal pores. An experimental technique is proposed which enables identification of both the first and second photonic band gaps in the reflection spectrum of opal. The ability to observe the second band gap allows a dispersion relation to be derived for the refractive index of the infiltrated substance. The calculations are performed using a model for a one-dimensional periodic layered medium with two refractive indices. We obtain an ω(k) dispersion relation and the reflection spectra of a photonic crystal in the [111] direction at different solution concentrations.     

Dispersion relation of surface plasmons near photonic band gaps: Influence of the interaction with light

Abstract

We present an experimental and theoretical study of the photonic band gap in the propagation of surface plasmons (SPs) on periodically corrugated surfaces. Our main purpose is to investigate the case where the band gap width is larger than the energy distance between the SP dispersion curve for a flat surface and the light line. We introduce a physical model of the interaction of light waves with SPs and derive an analytical expression for the SP wave vector near band gaps based on the coupled-mode approach involving three interacting modes (two of them are SP modes and one is a light mode). By using the interferometric measurement we have studied, for the first time, the SP propagation parameters in the vicinity of the photonic band gap (10 μm wavelength region). The predictions of our theory are in good agreement with the experimental data.     

Secondary electron spectra of graphene on Ni(111) surface

We report on kinetic energy distributions of electrons emitted during bombardment of graphene adsorbed on a Ni(111) surface by 0.5-0.9 keV electrons. The spectra reveal several peaks superimposed on the background of cascade electrons. The position of these peaks does not depend significantly on primary electron energy but show a remarkable angular dependence, indicating that they are directly related to the empty bands above the vacuum level of the sample.     

Observation of electromagnetically induced photonic band gaps in hot two-level atoms

In this paper, two-level thermal Cs atoms are used to observe electromagnetically induced photonic band gaps with a strong symmetric and two types of asymmetric standing-wave (SW) driving fields. One main band and two sidebands are measured for the transmitted and reflected spectra. We carry out physical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations for hot two-level system to simulate the experimental results. The numerical analyses are consistent with the experimental observations for properties of electromagnetically induced photonic band gaps.     

Controllable preparation of the ordered pore arrays anodic alumina with high-quality photonic band gaps

High-quality photonic crystals (PCs) based on the ordered pore arrays anodic alumina are fabricated by the anodic oxidation method using the newly-designed periodic oxidation voltage wave. The obtained PCs own uniform narrow photonic band gaps (PBGs), steep photonic band edges, zero transmittances inside of the PBGs and high transmittances outside of the PBGs. Importantly, the high-quality PBGs of the anodic alumina PCs are tunable and controllable in the range from 350 nm to 1330 nm by modifying the anodizing voltage waveform. The benefit of newly-designed periodic oxidation voltage wave is to improve the optical properties of anodic alumina PCs.     

Studying natural oxide on the surface of n-Si(111), n-Si(100), and p-Si(111) single crystal wafers by X-ray reflection spectroscopy

The state of the surface of standard phosphorus-doped n-Si(111) and n-Si(100) (KEF grade) and boron-doped p-Si(111) (KDB grade) single-crystal wafers treated in a 50% HF–70% HNO₃ (1: 3, v/v) polishing solution has been studied using soft X-ray reflection spectroscopy. The fine structure of the reflection spectra in the region of the Si L _2,3 ionization threshold has been analyzed. The dependence of the natural oxide thickness on the orientation of a silicon single crystal surface is established.     

Double stripe reconstruction of the Pt(111) surface

We have studied the reconstruction of the Pt(111) surface theoretically, using a 2D generalization of the Frenkel-Kontorova model. The parameters in the model are obtained by performingab initio density functional theory calculations. The Pt(111) surface does not reconstruct under normal conditions but experiments have shown that there are two ways to induce the reconstruction: by increasing the temperature, or by depositing adatoms on the surface. The basic motif of this reconstruction is a ‘double stripers with an increased surface density and alternatinghcp andfcc domains, arranged to form a honeycomb pattern with a very large repeat distance of 100–300 Å. In this paper, we have studied the ‘double stripe’ reconstruction of the Pt(111) surface. In agreement with experiment, we find that it is favourable for the surface to reconstruct in the presence of adatoms, but not otherwise.     

The adsorbate induced facetting of the Mo(111) surface

The adsorption of S,N,O, and CO on the Mo(111) surface has been observed to induce facetting to produce a surface formed of (111) and (112) planes. The formation of the facets is an activated process requiring heating to temperatures of ±700K. The orientation of the facets produced depends upon the adsorbate and has been related to the electronegativity of the adatom.     

Passivation of the GaP(111) surface by treatment in selenium vapors

Results of examination of structural phase transitions on the GaP(111) surface after heat treatment in selenium vapors in a vacuum chamber with a quasi-closed volume are described. The electrophysical characteristics of Schottky-barrier diodes on GaP(111) are studied before and after treatment in selenium vapors by measuring the current-voltage characteristics and by deep-level transient spectroscopy. It is found that, after treatment in selenium vapors, the Schottky-barrier height becomes dependent on the work function of the metal in accordance with the Schottky-Mott rule for an ideal diode. It is shown that a decrease in the density of surface electronic states in GaP(111) results from the formation of a Ga₂Se₃(111)(√3 × √3)-R30° surface phase with ordered stoichiometric gallium vacancies.     

The nucleation and growth of borophene on the Ag (111) surface

B sheets have been intently studied, and various candidates with vacancies have been reported in theoretical investigations, including their possible growth on metal surfaces. However, a recent experiment reported that the borophene formed on a Ag (111) surface consisted of a buckled triangular lattice without vacancies. Our calculations propose a novel nucleation mechanism of B clusters and emphasize the B–Ag interaction in the growth process of borophene, demonstrating the structural evolution of triangular fragments with various profiles and vacancy distributions. Compared with the triangular lattice without vacancies, we have confirmed that the sheet energetically favored during the nucleation and growth is that containing 1/6 vacancies in a stripe pattern, whose scanning tunneling microscopy image is in better agreement with the experimental observation.

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Anisotropic electric conductivity of In-Si(111) surface phases

The dependence of the electric conductivity of Si(111)√3 × √3-In and Si(111)4 × 1-In surface phases on the substrate surface orientation has been studied using low-energy electron diffraction, scanning tunneling microscopy, and four-point probe conductivity measurements. It is established that the directions of maximum conductivity in the Si(111)√3 × √3-In superlattice coincide with the directions of the maximum number density of In atoms, and in the Si(111)4 × 1-ln superlattice, with the directions of one-dimensional In atomic chains.     

Orientation of ethyl mercaptan on Cu(111) surface

X-Ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) studies have been performed on ethyl mercaptan adsorbed on a clean Cu(111) surface at 85 K. At submonolayer coverage (0.36 ML), two different states of sulfur (thiolate) are identified with the aid of XPS investigations. Polarization dependence of S K-edge NEXAFS of the submonolayer phase indicates that the S---C bond for the two thiolate phases are tilted 33±7° and 30±7° from the surface.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

A study of the electrical properties of the porous GaP (111) surface

Local electrical properties of the surface of porous GaP have been measured by the method of tunneling spectroscopy in ultrahigh vacuum. Two surface areas with different electrical properties were found. The effect of anomalous field-induced photoemission was observed. The most probable reason for this effect is the presence of Ga₂O₃ and GaP nanoclusters and the high density of acceptor-type surface states associated with these clusters. Integral characteristics of the field electron emission from the sample surface were obtained by using a computerized recording system with online processing of current–voltage characteristics.     

Theoretical study of melamine superstructures and their interaction with the Au(111) surface

Using a systematic method, based on considering all possible hydrogen bond connections between two melamine molecules, and ab initio density functional theory (DFT) calculations, we consider the possible planar superstructures that the molecules can form in two dimensions. This is relevant to the assembly of melamine on flat metal surfaces with a small lateral corrugation of the molecule-surface interaction energy. The structures considered include small clusters as well as periodic structures, such as one-dimensional filaments and two-dimensional monolayers. Then, the interaction of melamine structures with the Au(111) surface is considered in detail to elucidate the possible effect of the surface on the formed structures, including the influence of the van der Waals interaction, which is not taken into account in DFT-based methods. The problem of commensurability between the lattices of the gas-phase monolayer and of the substrate is also discussed.     

Investigations of surface structure for thermally evaporated silicon on a Cu(111) surface

The surface structure and composition of semiconductor/Cu(111) films prepared by thermal evaporation in an ultrahigh vacuum condition have been investigated. As Si atoms were deposited on a Cu(111) surface, diffused spots were observed up to 2 monolayers while 1 × 1 spots become dimmer as revealed using low-energy electron diffraction technique. Because of a larger electron affinity of Si than that of Cu, the Cu L₃M₄₅M₄₅ Auger line shifts to a lower kinetic energy. Annealing treatments at 425 K causes a splitting of the Cu L₃M₄₅M₄₅ line. This shows the interdiffusion at the Si/Cu interface and the formation of a Cu-rich surface layer. After annealing treatments, the domains grow and aggregate to form larger domains as revealed by the decreasing full-width at half maximum of diffraction spots. Ge/Cu(111) shows 1 × 1 structure as annealing up to 500 K. Lack of a dominant structure and a large valence diameter of Ge result in different structures as compared to Si/Cu(111).     

Field-induced surface transport of indium adatoms on Si(111) surfaces

Reflection high energy electron diffraction and resistivity measurements were performed on an In/Si(111) system. The deposition of about one monolayer of indium onto a clean Si(111) surface produces a 4 × 1 superstructure at temperatures from 500 to 740 K. Further deposition of one or two monolayers causes the 4 × 1 structure to disappear and only a 1 × 1 structure remains. This 1 × 1 In surface is found to have the characteristic property that the 1 × 1 area moves in an electric field like a positive carrier with a much higher mobility than that of conventional electromigration and the sheet conductance of the substrate increases markedly on the formation of the 1 × 1 In surface.