Thermally driven sensitive surface phonon polariton modes in thin-film SiC

The results of this work show that significant changes to the spectral properties of thermal emission may be accomplished by taking advantage of surface phonon polariton (SPP) modes that are very sensitive to small refractive index changes. Surface phonon polaritons are interface restricted wave modes that do not usually participate in thermal radiative energy exchange. In this work, the possibility of varying the spectral properties by using a thin-film surface active material, layered between dielectrics, is explored. Unlike surface gratings, the multilayered structure discussed in this work couples the surface modes into radiative modes using subtle changes in refractive index. The proposed multilayer effect is studied by first developing the SPP mode dispersion relation to identify the spectral location of the surface modes. The relationship between SPP coupling and refractive index change is then developed. The fluctuation-dissipation theorem and an impedance boundary condition is used to theoretically show how thermal radiation can excite SPP modes. Results are then presented that show how film thickness and substrate properties act to support SPP modes that are particularly sensitive to changes in refractive index and therefore offers opportunities for dramatic changes to the spectral properties.     

Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.     

Field expulsion and reconfiguration in polaritonic photonic crystals

We uncover a rich set of optical phenomena stemming from the incorporation of polar materials exhibiting transverse phonon polariton excitations into a photonic crystal structure. We identify in the frequency spectrum two regimes in which the dielectric response of the polaritonic medium can induce extreme localization of the electromagnetic energy. Our analysis of the effect of polarization and the interaction between the polariton and photonic band gaps on the Bloch states leads to a pair of mechanisms for sensitive frequency-controlled relocation and/or reconfiguration of the fields.     

Surface effects on optical phonons and on phonon-plasmon modes

The size and shape dependence of the properties of long wave optical phonons in polar crystals is discussed. The main effect occurring due to the presence of surfaces is the appearance of a surface optical phonon band in the frequency region between the frequencies ω_t and ω_l of the long wave transverse and longitudinal bulk modes. The surface modes give rise to strong absorption peaks in the infrared absorption spectra of small samples. For very small crystallites the surface mode absorption is dominant, and as the size of the specimens is increased, the ratio of surface to bulk mode absorption decreases. It is shown that the large spread in particle sizes usually encountered in experimental work and the increased damping of the phonon modes in small samples both tend to obscure the fine structure of the absorption spectrum. The surface phonon-plasmon modes in polar crystals containing free carriers are treated in an analogous manner.     

The Investigation of Bulk and Surface Polariton Modes in Ga1?xNxAs by Using Infrared Magneto Spectroscopy

We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga_1–xN_xAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm^-1. The origin of sharp feature in p-polarization reflectivity about 300 cm^–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration.     

Analysis of surface and guided wave plasmon polariton modes in insulator–metal–insulator planar plasmonic waveguides

Theoretical and experimental study of the surface plasmon–polariton and guided wave plasmon polariton modes is presented for the Sapphire/Ag/Polycarbonate/Air structure. Theoretical results are obtained by solving complex multilayer eigenvalue equations as well as the reflectivity equation for this structure. It is proposed that the mode attenuation can be significantly reduced by inserting a low index dielectric buffer between the metal and the guiding dielectric layer. The dispersion and attenuation curves are generated. Both the surface plasmon and guided wave plasmon polariton modes are studied experimentally. The experimental values of the effective refractive indices agree well with the theoretical values. The electric field profiles are generated and used to examine the nature of modes. After optimization of various parameters the condition for low loss single mode guiding is obtained for the proposed structure. Effect of metal thickness on surface plasmon mode is also discussed. It is inferred that in a properly optimized plasmonic waveguide, the losses can be reduced by a factor of 4.     

Surface phonon polariton characteristics of bulk wurtzite ZnO crystal

The surface phonon polariton (SPP) mode of bulk wurtzite (α-) zinc oxide (ZnO) crystal is investigated by means of p-polarized infrared attenuated total reflection (ATR) spectroscopy. From the ATR spectrum, a strong absorption dip corresponds to the SPP mode of bulk α-ZnO is clearly observed at 529 cm⁻¹. The experimental SPP mode showed good agreement with the theoretical SPP mode deduced from the surface polariton dispersion curve generated by the semi-infinite anisotropic crystal model.     

Dielectric constant of porous ultra low-k dielectrics by fractal-Monte Carlo simulations

The effective dielectric constant of porous ultra low-k dielectrics is simulated by applying the fractal geometry and Monte Carlo technique in this work. Based on the fractal character of pore size distribution in porous media, the probability models for pore diameter and for effective dielectric constant are derived. The proposed model for the effective dielectric constant is expressed as a function of the dielectric coefficient of base medium and the volume fractions of pores and base medium, fractal dimension for pores, the pore size, as well as random number. The Monte Carlo simulations combined with the fractal geometry are performed. The predictions by the present simulations are shown in good accord with the available experimental data. The proposed technique may have the potential in analyzing other properties such as electrical conductivity and thermal conductivity in porous ultra low-k dielectrics.     

Experimental simulation and theoretical analysis of the thermal deformation of dielectric plates under submicrosecond radiation heating

The flexural deformation of dielectric plates subjected to submicrosecond thermal stresses generated by volume and surface sources is studied. The action of such stresses is simulated by laser irradiation of colored glass plates with different optical absorption factors. Such an approach to simulating the thermomechanical action of radiation on dielectric materials allows researchers to visualize the qualitative and quantitative thermoelastic response of the plates to the action of pulsed sources of thermal stresses with different spatial parameters. For volume sources of thermal stresses, it is shown that the thermal deformation of a dielectric plate can be viewed as a set of quasi-harmonic extension-compression wave processes combined with the quasi-static bend of the plate. Under the action of surface sources of submicrosecond thermal stresses, the deformation mechanism is a superposition of the thermal deformation of a thin surface layer and a pulse wave process resulting in the bend of the plate when the pulses reverberate between the surfaces of the plate. Approximate analytical models of thermal deformation due to pulsed thermal disturbances are suggested that make it possible to predict the extent of bend versus the absorbed energy dose under the action of both volume and surface sources of thermal stresses.     

Apertureless SNOM imaging of the surface phonon polariton waves: what do we measure?

The apertureless scanning near-field microscope (ASNOM) mapping of surface phonon polariton (SPP) waves being excited at the surface of the SiC polar crystal at a frequency corresponding to the lattice resonance was investigated. The wave with well-defined direction and source position, as well as a well-known propagation law, was used to calibrate the signal of an ASNOM. An experimental proof is presented showing that the signal collected by the ASNOM in such a case is proportional (as a complex number) to the local field amplitude above the surface, regardless of the tip response model. It is shown that the expression describing an ASNOM response, which is, in general case, rather complicated nonlinear function of a surface/tip dielectric constants, wavelength, tip vibration amplitude, tip shape etc., can be dramatically simplified in the case of the SPP waves mapping in a mid-IR range, due to a lucky combination of the tip and surface parameters for the case being considered. A tip vibration amplitude is much less than a running SPP wave field decay height in a normal direction. At the same time, the tip amplitude is larger than a characteristic distance at which a tip–surface electromagnetic near-field interaction plays a significant role.     

Van der Waals interactions between atoms and dispersive surfaces at finite temperature

The long-range interactions between an atomic system in an arbitrary energy level and dispersive surfaces in thermal equilibrium at non-zero temperature are revisited within the framework of the quantum-mechanical linear response theory, using generalized susceptibilities for both atom and electromagnetic field. After defining the observables of interest, one presents a general analysis of the atomic level shift valid for any number and form of dielectric surfaces. It is shown that, at zero temperature, one recovers well-known results previously obtained in the linear response regime. The case of a plane dispersive surface is elaborated on in the non-retarded regime. Calculations are given in detail for a dielectric surface exhibiting a single polariton resonance. Theoretical predictions are presented within a physical viewpoint allowing one to discriminate between the various interaction processes: on one hand, the level shift induced by non-resonant quantum fluctuations, on the other hand, two potentially resonant atom-surface couplings. The first resonant process appears for excited-state atoms and originates in an atomic de-excitation channel resonantly coupled to the surface polariton mode. It exists also at zero temperature, and has been studied and observed previously. The second physical process, which exists at non-zero temperature only, corresponds to the reverse process in which a thermal quantum excitation of a surface polariton resonantly couples to an atomic absorption channel. This novel phenomenon is predicted as well for a ground state atom, and can turn the ordinary long-range van der Waals attraction of atoms into a surface repulsion at increasing temperatures. This opens the way to the control and engineering of the sign and amplitude of van der Waals forces via surface temperature adjustment.     

两耦合半无限超晶格中的局域界面声子-极化激元

采用转移矩阵方法，研究了含结构缺陷层的两耦合半无限超晶格(GaAs/AlAs)中的局域界面声子-极化激元模性质. 研究发现，含不同介电特性的缺陷超晶格结构中的局域界面声子-极化激元模在剩余射线区［ω_TO, ω_LO］的分布情况与数量存在不同，而且反对称模表现出不同的特征. 文中着重研究了缺陷层介电常数与角频率无关的缺陷超晶格，发现该结构中的局域界面声子-极化激元模对组分层的排列顺序与厚度、缺陷层的厚度以及横向波数有着不同程度的依赖.     

Quantum Theory of Surface Polaritons on a Rough Surface

In this paper, we present the quantum field theory of the surface phonon-polaritolis on a rough polar crystal surface. The dispersion relations of the surface phonon-polaritons and the dispersion relations of polariton leaking modes owing to the interaction between bulk TO mode with the surface effect and photons are derived. We also study the k-dependence of the electric field strength in each polariton branch. The numerical calculations for the dispersion relations and the k-dependence of the electric field strength are carried out for a stepped Gap surface. The results show that the surface roughness depressed the frequency of the surface phonon-polariton below its values in the absence of the surface roughness. For the frequencies of the polariton leaking modes, the photon-like one is enhanced by the surface roughness and the phonon-like one b depressed. Our evaluations also illustrate that the surface roughness introduces a strong dependence on the k-dependence of the electric field strength in each polariton branch.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for Al_xGa_1−xAs and Zn_xCd_1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed.     

Phonon-induced polariton superlattices

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.     

金属/介质薄膜中声子热辐射的空间和各向异性研究

基于理论、实验和仿真相结合的方式,着重研究了金属/介质(MD)薄膜中声子热辐射的空间特性和各向异性。声子是由于晶格振动产生的元激发,是物质的内在属性。尽管声子不易调控,但是声子与其他光学激发的耦合会产生奇异的光学现象。特别是红外到太赫兹范围内的光子与极性介质中的声子强耦合产生表面声子激元（SPhP）。SPhP具有强局域、低损耗等特点,与等离子体（plasmon polaritons）形成互补,使得深亚波长光学成为可能。为了进一步了解声子吸收的内在理论基础,首先通过黄昆方程和超晶格连续介电模型在理论上分析了声子吸收。实验上,主要以SiO₂声子作为研究对象,利用等离子体增强化学气相沉积(PECVD)方法,分别在Si/Al（150 nm）薄膜和Si衬底上制备出500 nm厚的SiO₂薄膜。基于傅里叶红外光谱仪(FTIR),在垂直入射下得到热辐射光谱,通过热辐射光谱分析,并结合由时域有限差分算法（finite-difference time-domain,FDTD）计算得出的仿真光谱图,对比了MD薄膜结构和非MD薄膜结构中声子的热辐射,发现MD薄膜结构更能够有利于声子和SPhP的激发。根据Berreman效应,纵光学波（LO）声子只在倾斜入射时产生。光谱线没有呈现洛伦兹线型,因此,虽然LO声子在垂直入射时测得的热辐射图中不辐射,但同样影响横光学波（TO）声子辐射谱的线型。另外,利用FTIR对金属（Si/Al）/介质（SiO₂薄膜）进行热辐射转角测试,对热辐射转角图分析证明,Si/Al/SiO₂薄膜中SiO₂声子遵循LST(lyddano-sachs-teller)关系,纵横声子成对出现,且两种声子的空间辐射特性不同。改变偏振,发现在S偏振和P偏振下,声子热辐射呈现不同的模式, 体现出声子的空间各向异性。并且,声子与光子耦合可以激发SPhP,反过来,SPhP可以增强声子的吸收。基于MD结构,能够激发并调控SPhP和声子辐射行为,为红外器件的实现奠定了基础。     

太赫兹表面极化激元

作为束缚于表面或界面的电磁波与极性元激发的耦合模量子,表面极化激元是克服衍射极限的核心物理.在紫外、可见以及近红外波段,表面等离子极化激元展现出了亚波长特性,具有高分辨成像等应用,并发展成为"表面等离子极化激元亚波长光学"学科;在中红外波段,表面声子极化激元发挥着同样的作用.太赫兹波段曾是人类认识的空白区域,近三十年来得以高速发展,其战略意义重大.具有克服衍射极限能力的太赫兹表面极化激元同样是小型化与集成化太赫兹器件,以及太赫兹超高分辨成像的重要物理基础.近几年来,对以石墨烯为代表的二维材料的研究突飞猛进,诞生了"石墨烯表面等离子极化激元亚波长光学"这门学科,并贡献于太赫兹领域.本文对可在太赫兹波段工作的人工超构材料、掺杂半导体、二维电子气、二维材料、拓扑绝缘体等结构材料的表面极化激元进行了较为全面的总结与介绍,为研制克服衍射极限的太赫兹集成光子学器件提供可资借鉴的物理基础.     

Entanglement dynamics for a solid polariton system at zero and finite temperatures

The dynamics of the entanglement for a solid polariton system is investigated. The polariton system is a photon-phonon complex and its time-dependent characteristic function in the Wigner representation for the system is obtained analytically. It is found that when the photon field is initially prepared in the squeezed vacuum state, and the phonon in the thermal state, the polariton system can evolve into a two-mode Gaussian mixed state. The entanglement between photon and phonon turns out to be apparently dependent on the squeezing parameter and exhibits a critical behavior with respect to the temperature.     

Surface polaritons in a dielectric at a boundary with a metal in crossed electric and magnetic fields

AbstractThe spectrum of surface polaritons in a dielectric at a boundary with an ideal metal or a super-conductor in crossed constant electric and magnetic fields is studied. It is shown that the polariton spectrum possesses strong nonreciprocity (polaritons with fixed frequency propagate only in one direction; this is the rectification effect) and depends strongly on the directions of the external fields and their ratios H ₀/E ₀.     

带孔硅纳米薄膜热整流及声子散射特性研究

本文基于非平衡的分子动力学模拟方法计算了带有三角形孔的硅纳米薄膜的界面热阻特性,结果表明300-1100 K范围内随着热流方向的改变,在含有三角形孔的硅纳米薄膜中存在热整流效应,热整流系数达28％.同时借助于声子波包动力学模拟方法,获得了不同频率下的纵波声子在三角形孔处的散射特性,结果表明纵波声子在散射过程中产生了横波声子,并且从三角形底部向顶部入射的声子能量透射系数比反向时平均低22％.不对称结构引起的声子透射率的差异是引起热整流效应的主要因素.