Tamm Surface States Research Articles

Surface Tamm States of 2-5 nm Nanodiamond via Raman Spectroscopy.

We observed resonance effects in the Raman scattering of nanodiamonds with an average size of 2-5 nm excited at a wavelength of 1064 nm (1.16 eV). The resonant Raman spectrum of the 2-5 nm nanodiamonds consists of bands at wavelengths of 1325 and 1600 cm-1, a band at 1100-1250 cm-1, and a plateau in the range from 1420 to 1630 cm-1. When excited away from the resonance (at a wavelength of 405 nm, 3.1 eV), the Raman spectrum consists of only three bands at 1325, 1500, and 1600 cm-1. It is important to note that the additional lines (1500 and 1600 cm-1) belong to the sp3-hybridized carbon bonds. The phonon density of states for the nanodiamonds (~1 nm) was calculated using moment tensor potentials (MTP), a class of machine-learning interatomic potentials. The presence of these modes in agreement with the lattice dynamics indicates the existence of bonds with force constants higher than in single-crystal diamonds. The observed resonant phenomena of the Raman scattering and the increase in the bulk modulus are explained by the presence of Tamm states with an energy of electronic transitions of approximately 1 eV, previously observed on the surface of single-crystal diamonds.

Effect of Tamm Surface States on Landau Damping in Metal–Semiconductor Nanostructures

AbstractThe hot electron generation in plasmonic nanoparticles is the key to efficient plasmonic photocatalysis. Here, the effect of Tamm states (TSs) at the metal–semiconductor interface on hot electron generation and Landau damping (LD) in metal nanoparticles is studied theoretically for the first time. TSs can lead to resonant hot electron generation and to the LD rate enhanced by several times. The resonant hot electron generation is reinforced by thetransitionabsorption due to the jump of the permittivity at the metal–semiconductor interface. Since electron states in the metal and the quasi‐discrete TS are coupledcoherently(“bound state in continuum”), the absorption spectrum of light by electrons has a Fano‐type shape. The results demonstrate clearly the importance of taking into account details of the semiconductor band structure and surface states at the metal–semiconductor interface, including Tamm surface states, for a proper description of the hot carrier generation and LD. The results are in correspondence with earlier experimental works on coherent electron transport and chemical‐induced damping in plasmonic nanostructures. Thus, by judicious selection of semiconductor materials with Tamm surface states one can engineer decay rates and hot carrier production for important applications, such as photodetection and photochemistry.

Distinct Tamm and Shockley surface states on Re(0001) mixed by spin-orbit interaction

Tamm and Shockley states, these two paradigmatic concepts are used to describe surface states not only in electronic systems but also in photonic and phononic crystals. The Re(0001) surface hosts both types of electronic surface states in neighboring but qualitatively different energy gaps. Interestingly, spin-orbit interaction generates a double W-shaped energy vs ${\mathbf{k}}_{\ensuremath{\parallel}}$ dispersion by mixing both types of states and lifting their spin degeneracy. By combining spin- and angle-resolved photoemission, tight-binding model calculations, as well as density functional theory including the photoemission process, we develop verifiable criteria to distinguish between the two types of surface states and arrive at a consistent picture of the role of spin-orbit interaction in such a scenario.

High performance mid infrared temperature sensor based on resonance excitation of hybrid Tamm surface states

Theoretical design of mid infrared temperature sensor based on the resonance excitation of hybrid Tamm surface state (HTSS) is presented. An excellent sensing performance is attained by the coupling of graphene plasmon polaritons and hexagonal boron nitride (hBN) phonon polaritons that forms hybrid polariton modes at the interface. In one dimensional ternary photonic crystal (1D TPC), terminated by hBN layer sandwiched between graphene monolayers, the coupling between Bloch surface waves and hybrid polariton modes leads to the formation of HTSS or Tamm plasmon-phonon modes. Employing Kretschmann configuration coupling mechanism, the excitation of the HTSSs at the truncated interface is manifested for transverse magnetic (TM) polarized wave. The structure supports excited HTSS between 7.14μm to 10.34μm that allows astounding control over the sensing ability by varying the number of unit cells and the resonant angles. The sensor has a high detection accuracy of 1010 at room temperature (300K). It is proved that for 50 unit cells and at 49° angle, a high quality factor of 372176, detection limit of 5K and sensitivity of 0.20pm/K is attained with operating range between 280K to 380K. The operating range is widened from 300K to 900K by changing the resonant angle from 49° to 53°. Further, for 30 unit cells and at 53° angle, the temperature sensing ability of the sensor extends from 100K to 900K with a sensitivity of 0.80pm/K and detection limit of 54.16K.

Resonance photogeneration of hot electrons through Tamm surface states.

Internal surface photoemission of electrons from 1D crystal into a barrier with participation of Tamm state (TS) at the interface crystal barrier is considered theoretically for the first time, to the best of our knowledge. It is shown that resonant tunneling of electrons through a TS could lead to substantial enhancement of the quantum efficiency and lowering the red border to a value defined by the TS. In contrast to the Fowler quadratic law, the photocurrent scales linearly with photon energy near the red border. The results suggest that the efficiency of hot electron generation with plasmonic metal nanoparticles could reach several tens of percent, which is very attractive for application in energy conversion technologies such as water splitting.

Polaritonic Tamm states induced by cavity photons

Abstract We consider a periodic chain of oscillating dipoles, interacting via long-range dipole–dipole interactions, embedded inside a cuboid cavity waveguide. We show that the mixing between the dipolar excitations and cavity photons into polaritons can lead to the appearance of new states localized at the ends of the dipolar chain, which are reminiscent of Tamm surface states found in electronic systems. A crucial requirement for the formation of polaritonic Tamm states is that the cavity cross section is above a critical size. Above this threshold, the degree of localization of the Tamm states is highly dependent on the cavity size since their participation ratio scales linearly with the cavity cross-sectional area. Our findings may be important for quantum confinement effects in one-dimensional systems with strong light–matter coupling.

Engineering zero modes, Fano resonance, and Tamm surface states in the waveguide-array realization of the modified Su-Schrieffer-Heeger model.

In this article, we developed a generalized coupled-mode theory for mixing an isolated state with a continuum having an intrinsic energy gap, which dubbed as "the bound states in the gapped continuum" (BIGC). We investigated the mixture interaction by mimicking the Su-Schrieffer-Heeger model in an optical coupled waveguide array (WA), and presented a unified engineering mechanism for topologically-protected zero modes, Fano resonance, and Tamm surface states, even though those phenomena are diverse in topological insulators, atomic physics and semiconductors, respectively. By tuning the on-site potential and coupling strength of the isolated state, we found the unified operating characteristics for zero modes, Fano resonance, and Tamm states, with demonstrating their localization, transmission spectra, and distinct evolution dynamics explicitly. As an extension for triple-modes coupling, two special sandwich-like configurations are studied: the isolated-continuous-isolated and continuous-isolated-continuous configurations lead to adiabatic eliminations and domain walls, respectively, revealing possible applications and wide connections in many fields of physics and optics.

Charge Transfer on a Two-Dimensional Lattice with Impurity Sites

The quantum dynamics of charge transfer along a two-dimensional lattice with impurity sites at the lattice edges is considered. These sites simulate the surface (Tamm) states. In the tight-binding approximation, the nonstationary problem of the evolution of quantum excitation along impurity sites at the lattice perimeter is solved. The solution is obtained as an expansion in eigenfunctions of the unperturbed Hamiltonian. Analytical results are obtained for the propagation of the wave function over impurity sites.

Tamm States in Bragg Heterostructures on Waveguide Slot Lines

Tamm surface states are experimentally studied and calculated for a Bragg heterostructure consisting of two groups of periodic fragments of waveguide slot transmission line with finite sizes. The Tamm surface states are not observed in a perfect Bragg heterostructure. The Tamm surface states emerge in the presence of an interface element at the interface of two Bragg structures when the characteristics of the element differ from the characteristics of both Bragg structures.

Tamm states of fractal surfaces

The theory of modification of surface Tamm states on fractal surfaces is developed, and manifestations of such phenomena are analyzed. The obtained results suggest that the fractality of free and inner surfaces of nanoobjects affects their electronic spectrum, which may lead to modification of the physical and chemical properties of nanostructures.

Unconventional optical Tamm states in metal-terminated three-dimensional photonic crystals

Unconventional optical Tamm surface states have been demonstrated in transmission and reflectance spectra of three-dimensional opal photonic crystals coated by thin metal films. These states appear in registry with diffraction resonances and localize the electromagnetic energy in asymmetric resonators formed by stacks of lattice planes and metal semishells. Tamm defect states provide the bypass for light at the edges of the Bragg diffraction resonances and thus reduce the diffraction efficiency. Despite the hidden nature of this effect, its magnitude is comparable to the extraordinary transmission associated with the surface-plasmon polaritons that are simultaneously excited at the surfaces of the corrugated metal films.

Discrete solitons in graphene metamaterials

We study nonlinear properties of multilayer metamaterials created by graphene sheets separated by dielectric layers. We demonstrate that such structures can support localized nonlinear modes described by the discrete nonlinear Schr\"{o}dinger equation and that its solutions are associated with stable discrete plasmon solitons. We also analyze the nonlinear surface modes in truncated graphene metamaterials being a nonlinear analog of surface Tamm states.

Electronic Tamm states of metamaterial-like semiconductor composite structures

In a semi-infinite crystal, the periodic potential is destroyed at the surface, and the electronic wave functions exponentially decay from the surface to both sides. Such localized electronic states in the vicinity of the surface are known as Tamm surface states. In analogy to the electronic Tamm states, in recent years, optical Tamm states have been found at the surface of the truncated photonic crystal composed of two kinds of dielectrics. Very recently, novel types of optical Tamm states including backward Tamm states in which the phase velocity and the group velocity of optical waves are in the opposite direction have been discovered in the photonic structures containing metamaterials. In fact, the concepts in electronic field and photonic field can inspire each other. Many unique phenomena in photonic systems can also be mapped to the electronic systems. In this paper, we study the novel types of electronic Tamm states in electronic systems, inspired by the novel types of optical Tamm states in photonic structures. #br#At first, comparing Maxwell equations with Schrodinger equations, one can see a correspondence between the parameters in electromagnetic system and the parameters in the electronic system. In particular, Hg1-xCdxTe semiconductors with special electronic band structures can realize various electronic materials in analogy to the optical metamaterials with various values of permittivity and permeability. By tuning the parameter x of Hg1-xCdxTe, we obtain a variety of metamaterial-like electronic materials, in analogy to the single-negative metamaterials, the double-negative metamaterials and the near-zero-index metamaterials in optical systems. Then, inspired by the one-dimensional heterostructures with metamaterials that generate optical Tamm states, we design a one-dimensional electronic heterostructure consisting of Hg0.847Cd0.153Te and CdTe/HgTe superlattice. When Hg0.847Cd0.153Te is analogous to the double-negative metamaterial, we find the backward electronic Tamm states in which the phase velocity and the group velocity of electronic waves are in the opposite directions. When Hg0.847Cd0.153Te is analogous to the near-zero-index metamaterial, we find a novel electronic Tamm states in which the amplitude of the electronic probability decays very slowly in Hg0.847Cd0.153Te. The discovery of these new types of electronic Tamm states enlarges our knowledge of electronic surface states.

Invisible surface defects in a tight-binding lattice

Surface Tamm states arise in one-dimensional lattices from some defects at the lattice edge and their energy generally falls in a gap of the crystal. The defects at the surface change rather generally the phase of propagative Bloch waves scattered off at the lattice edge, so that an observer, far from the surface, can detect the existence of edge defects from e.g. time-of-flight measurements as a delay or an advancement of a Bloch wave packet. Here we show that a special class of defects can sustain surface Tamm states which are invisible, in a sense that reflected waves acquire the same phase as in a fully homogeneous lattice with no surface state. Surface states have an energy embedded into the tight-binding lattice band and show a lower than exponential (algebraic) localization. Like most of bound states in the continuum of von Neumann - Wigner type, such states are fragile and decay into resonance surface states in presence of perturbations or lattice disorder. The impact of structural lattice imperfections and disorder on the invisibility of the defects is investigated by numerical simulations.

Electrical and magnetic properties of nanodiamond and pyrocarbon composites

The electrical and magnetic properties of the nanodiamond composites comprising nanodiamond, pyrolytic carbon, and nanosized pores were studied. The composites are p-type semiconductors and their resistance decreases by 12 orders of magnitude as the pyrocarbon-to-diamond ratio γ increases from 0 to 80 wt %. Evidence for paramagnetic properties of the nanodiamond composites was obtained. The observed properties are explained by increased concentration of surface Tamm states. The paramagnetic properties are explained in terms of the electron spins localized on the nanodiamond surface in the composite.

Tunable Microcavity Based on Macroporous Silicon: Feasibility of Fabrication

Simultaneous electrochemical etching of deep pores and trenches in silicon was used to fabricate a two-dimensional, photonic crystal slab (PCS). The structure consists of five rows of macro-pores on both sides of a trench-defect, filled with a nematic liquid crystal. Polarized reflection and transmission spectra from the fabricated structure were investigated in the mid-infrared spectral range and were compared with spectra calculated using a scattering matrix method. In order to obtain agreement between the experimental and calculated spectra, a model structure with a complex refractive index of silicon was introduced. This enabled us to take into account losses related to light scattering at the inner surfaces of pores and trenches within the structure. The influence of these losses on the amplitude of the defects and surface Tamm states was analysed using this model. The Tamm states originate from the unstructured Si layer at the interface of the structure and the external medium, air in this case. A quantitative evaluation of the losses was performed by extracting a coefficient from a fit to the experimental spectra. This coefficient was utilised to determine the dependence of the micro-cavity parameters on the number of periods in the PCS. We conclude that a micro-cavity based on macro-porous silicon should not have more than three periods on each side of a defect.

Surface Tamm states in a photonic crystal slab with asymmetric termination

AbstractThe reflection and transmission spectra of a finite thickness 2D photonic crystal slab (PCS) based on macroporous silicon are investigated. Periodic photonic crystal region is separated from air by homogeneous silicon interfacial layers. These interfacial layers at the silicon/air boundary being defects of the photonic crystal lattice, define the properties of surface Tamm states in the photonic stop‐bands (PSBs). It is demonstrated experimentally and theoretically that the reflection spectra of a structure with different thicknesses of the interfacial layers on both sides of the PCS depend on the illuminated side. At the same time, the transmission spectra are identical for both light directions in agreement with the reciprocity principle. Analysis shows that the dependence of the reflection spectrum on the side of light entrance is due to scattering losses in the real structure. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface Tamm states in one-dimensional photonic crystals containing anisotropic indefinite metamaterials

We present a theoretical study of surface Tamm states localized at an interface that separates a semi-infinite isotropic left-handed metamaterial (LHM) and one-dimensional photonic crystal made of anisotropic indefinite metamaterial (IMM) (always-cutoff material). We discuss the dispersion properties of the Tamm states in different bandgaps and demonstrate that the cap layer, angular frequency, and arrangement of photonic crystal can provide flexible control for the dispersive properties of the Tamm states.

Surface states in the optical spectra of two-dimensional photonic crystals with various surface terminations

Reflection and transmission spectra of two-dimensional photonic crystal slabs, fabricated by photoelectrochemical etching of deep macropores and trenches in Si, are investigated theoretically and experimentally. It is shown that the presence of an unstructured silicon interfacial layer between the air and the photonic crystal structure can give rise to surface (Tamm) states within the TE and TM photonic stop bands. In the presence of roughness of inner surfaces of air pores, the surface states show up as dips within the stop bands in the reflection spectrum. The calculated electromagnetic near-field distribution demonstrates the vortices between the upper pores at the frequency of the surface mode. The experimental reflection and transmission spectra are in a good agreement with theoretical calculations performed by the Fourier modal method in the scattering matrix form.

Investigation of optical properties of Tamm states in higher bands of multilayer stacks including right and left handed materials

We study the electromagnetic surface wave localizing, the so-called surface Tamm states, at an interface separating a left-handed metamaterial (LHM) and a semi-infinite one-dimensional photonic crystal made of alternative left-handed metamaterial and right-handed materials. We show that the existence of metamaterial causes the Tamm states with backward energy flow and allows flexible control of dispersion properties of the surface modes. We study the effect of the physical parameters of the photonic crystal on the dispersion properties and the group velocity of the Tamm states. We also study dispersion properties of the Tamm states in higher order photonic band gaps of the photonic crystal and compare our results with the case when the LHM medium is replaced by a right-handed material (RHM).