Double Plasmon Research Articles

Configuration interaction study of single and double dipole plasmon excitations in Na 8

We carry out a microscopic analysis of the ground and excited states of the Na 8 metal cluster within the jellium model. We perform a series of configuration interaction calculations on a Hartree–Fock basis and construct eigenstates of the Hamiltonian which carry up to 4-particle 4-hole components. Based on the analysis of the dipole transition strengths, we single out those states which can be interpreted as the collective dipole plasmon and its double excitations. These modes are found to possess a high degree of harmonicity, deviations from the harmonic limit remaining, however, of the order of 10%.

Submicron/nanostructure plasma physics: double quantum wire plasmons interacting with semi-infinite host optical phonons

A brief survey of collisionless plasma phenomenology and nanostructure plasma physics, replete with quantum effects, is presented in conjunction with the determination of the joint collective modes of double quantum wire plasmons interacting with semi-infinite host optical phonons.

Hybridization of optical phonons with double quantum-wire plasmons including drift instabilities

We examine the collective mode spectrum for a double quantum-wire system embedded in semi-infinite polar medium, taking account of the role of optical phonons in interaction with the double quantum-wire plasmons and bulk/surface plasmons. The collective mode frequencies are exhibited as functions of q x (wavenumber parallel to the wires) and as functions of z 0 (distance of first wire from the interface). We also find that the region of drift instability of the collective modes is split into two disjoint regions of instability by the optical phonons, with a region of stability between them.

Coherence in electron energy loss spectrometry

Coherence effects in electron energy loss spectrometry (EELS) and in energy filtering are largely neglected although they occur frequently due to Bragg scattering in crystals. We discuss how coherence in the inelastically scattered wave field can be described by the mixed dynamic form factor (MDFF), and how it relates to the density matrix of the scattered electrons. Among the many aspects of “inelastic coherence” are filtered high-resolution images, dipole-forbidden transitions, coherence in plasma excitations, errors in chemical microanalysis, coherent double plasmons, and circular dichroism.

Tunable multiple plasmon resonance wavelengths response from multicomponent polymer-metal nanocomposite systems

A method of vapor phase codeposition has been used at elevated target temperature coupled with selective masking technique to produce a multicomponent optical material with seven different ultraviolet-visible optical active planes. Such a system consists of different nanocomposites of Teflon AF/Ag, Teflon AF/Au, and Teflon AF/Cu with sharp interfaces. The fabricated system has regions of single nanocomposite plane together with multilayer structures facilitating tunable multiple particle plasmon resonance wavelength response from a single system. Distinct double and triple plasmon wavelength resonance absorptions could be obtained from such interfaces forming multilayers of either two or three nanocomposite structures.

Terahertz quantum cascade lasers.

Recent developments in terahertz quantum cascade lasers are reviewed. Structures operating from a wavelength of lambda = 66 microm down to lambda = 87 microm are demonstrated. These devices used either a three-quantum-well chirped-superlattice active region or an active region based on a bound-to-continuum transition. The comparison between structures grown in a waveguide based on a single interface plasmon and a buried contact and (non-lasing) structures using a double plasmon waveguide demonstrates the importance of waveguide design on the operation of such devices. Continuous-wave operation up to a maximum temperature of 55 K with up to 15 mW output power at 10 K was demonstrated.

InAs/AlSb quantum cascade lasers operating at 10 μm

InAs/AlSb intersubband quantum cascade lasers based on bound-to-continuum transitions are fabricated and operation at 10 μm is demonstrated. A spatially indirect intersubband transition together with a double plasmon waveguide structure is employed. Threshold current density is 4.9 kA/cm2 at 4 K. Temperature dependence of the threshold current density is also presented.

InAs-based quantum cascade light emitting structures containing a double plasmon waveguide

Molecular beam epitaxy and electroluminescence properties of InAs-based quantum cascade light emitting structure containing an InAs double plasmon waveguide are reported. Samples are prepared using low group-V flux and controlled interface bonds during molecular beam epitaxy resulting in high structural and optical qualities. Electroluminescence measurements indicate that it is necessary to reduce the operating electric fields to avoid band-to-band tunneling in narrow gap semiconductor cascade devices.

High performance single mode GaAs quantum cascade lasers

We report on the realization of distributed feedback quantum cascade lasers in the AlGaAs/GaAs material system. Strong coupling is achieved by the use of a metalized surface relief grating, allowing the realization of short lasers. Continuous wave operation was achieved for an AlAs/GaAs chirped superlattice laser with an emission wavelength of 11.8 μm . The used double plasmon enhanced optical waveguide consists only of the binary material GaAs and not of a ternary compound which results in a small thermal resistance. Further, the emission wavelength of the distributed feedback laser is continuously tunable according to the temperature dependence of the refractive index. Additionally, we want to report about pulsed single mode operation up to 335 K for a laser material, where Al 0.45Ga 0.55As is used for the barriers and GaAs for the wells. The emission wavelength is 9.5 μm and the optical peak power in pulsed mode operation from one facet of the distributed feedback laser is 0.3 W at a temperature of 0°C.

Preparation of a 10 nm thick single-crystal silicon membrane self-supporting over a diameter of 1 mm

We report the fabrication of a 10 nm thick, self-supporting, single-crystal silicon membrane. The fabrication process can be broken up into four major stages. First, a buried SiO 2 layer was formed by implantation of oxygen at a depth of 200 nm into a (100) silicon wafer. The size of the membrane was then established by removing the bulk of the silicon over a 1 mm area using a fast acid etch. After this the sample was etched in a hot EDP solution which stops at the buried SiO 2 layer. The sample was then cleaned and the SiO 2 layers removed, after which it was introduced into a plasma-etching chamber. The membrane was thinned down to a final thickness of 10 nm by RF plasma etching in a gas mixture of carbon tetrafluoride and oxygen. The thickness was monitored during plasma etching by measuring the intensity of He–Ne laser light transmitted through the membrane. The electron energy loss spectrum of the membrane has been measured and shows two features due to single and double plasmon excitation. The plasmon energy was 17.05 eV, in good agreement with previous measurements. Membrane thickness has also been estimated from the area of the plasmon energy loss peak. The final sample had good crystalline quality, was of even thickness over the membrane diameter and showed only a small amount of surface contamination due to the plasma etching stage.

Electrically pumped Terahertz quantum well sources

Far infrared emission from quantum cascade structures is presented. Surface emission from a grating coupler show that the intersubband luminescence of our vertical transition structure is limited at low temperature by electron–electron scattering. As the temperature is increased, the limitation comes from the emission of optical phonons. In order to check for material gain, waveguide loss and differential gain measurements have been performed using a single-pass-type measurement. We report waveguide losses of 110 cm −1 and differential gain of 23 cm −1 . Our results strongly suggest the possibility of far-infrared lasers using the quantum cascade technology coupled to double plasmon waveguides.

Cluster ionization via two-plasmon excitation

We calculate the two-photon ionization of clusters for photon energies near the surface plasmon resonance. The results are expressed in terms of the ionization rate of a double plasmon excitation, which is calculated perturbatively. For the conditions of the experiment by Schlipper et al., we find an ionization rate of the order of 0.05-0.10 fs^(-1). This rate is used to determine the ionization probability in an external field in terms of the number of photons absorbed and the duration of the field. The probability also depends on the damping rate of the surface plasmon. Agreement with experiment can only be achieved if the plasmon damping is considerably smaller than its observed width in the room-temperature single-photon absorption spectrum.

Image Conservation in Inelastically Scattered Electrons in Reflection Electron Microscopy

Energy-filtered reflection electron microscope (REM) images of well-defined surfaces were taken for the first time using an ultrahigh vacuum electron microscope equipped with an omega filter. Si(111)7×7 and Si(111)5×2-Au surfaces were imaged. Images using electrons with energy losses of 11.3 and 22.6 eV (single and double surface plasmon excitation) showed lattice fringes of Si(111)7×7(2.3 nm in spacing) and Si(111) 5×2-Au(1.7 nm). The observation gave the first experimental evidence that diffraction image contrast is conserved in images formed by electrons inelastically scattered by small angles in REM, as in the case of transmission electron microscopy.

Surface plasmon satellite in the X-ray emission spectra of magnesium

An expression for the surface plasmon high energy satellite in the X-ray emission spectra has been obtained by extending the Bohm-Pines Hamiltonian and using many body theory. It has been shown that the surface plasmon satellite observed by the Krause and Ferreira is due to the surface plasmon oscillations in the Mg. It has also been shown that the several other satellites observed by Krause and Ferreira are due to surface, double and triple plasmon losses or a combination of these losses.

Plural-scattering deconvolution of electron energy-loss spectra recorded with an angle-limiting aperture

We examine the validity of Fourier-logarithmic deconvolution for removing plural-scattering peaks from a transmission-electron energy-loss spectrum, in the case where the spectrum has been recorded in the presence of an angle-limiting collection aperture. Experimental results indicate that the procedure is accurate to better than 3% within the plasmon-loss region, for apertures commonly used in a transmission electron microscope. This degree of accuracy implies that the fraction F n of electrons which pass through the aperture (after inelastic scattering of order n) obeys the relation F n ≈( F 1) n . Computer calculations of the angular distributions of double and triple scattering support this relationship, taking the single-scattering distribution to be Lorentzian and the collection semi-angle to be large compared to the characteristic angle θ E . Extending our analysis to the deconvolution of inner-shell ionization edges, the error in the subtraction of double (plasmon+inner-shell) scattering is predicted to be less than 10% for edge energies below 5 keV, assuming 10 mrad collection semi-angle and 100 keV incident electrons.

Effect of geometry on the collective electron oscillations in the X-ray absorption spectra of various metal compounds

The effect of collective electron oscillations at the surface of the metal compounds has been discussed in the X-ray absorption spectra of several metal compounds. The effect of double plasmon oscillations has also been discussed on the X-ray K or L-absorption edges. As a result of our work, various unexplained chemical shifts have been explained.

Double plasmon oscillations during X-ray emission

The role of double plasmon oscillations in X-ray emission can be theoretically explained by obtaining expressions for the dispersion relation and relative intensity. The calculated values of relative intensities from our expression are fairly close to the observed relative intensities for Na and Cu. The present expression for the relative intensity has been compared with the Langreth and Pardee formulae. It is shown that for high electron density our expression turns into the Pardee et al. expression. It is also shown that the present expression works best for intrinsic double plasmon satellites.

Low-energy double plasmon satellites in the X-ray spectra of metals

Bohm and Pines' Hamiltonian and their dispersion relation have been extended up to second order to account for double plasmon oscillations in the X-ray emission spectra of solids. The effect of interaction between electrons and plasmons has also been taken into account in the dispersion relation. An expression for the relative intensity of low-energy double plasmon satellites has been derived. Fairly good agreement is obtained between values of the relative intensity calculated using this expression and values observed experimentally by Jenkins and Chung.

An attempt to observe the double plasmon loss by electron spectroscopy

The technique of electron energy loss has been applied to an investigation of the theoretical predictions of Ashley and Ritchie (1970) on the double plasmon excitation process. Electron energy loss spectra of evaporated silicon and aluminium films have been recorded at an incident electron energy of 60 keV and these spectra have been corrected for plural scattering effects. After this correction, no spectra exhibited a prominent loss in the region 31 to 33 eV, where the double plasmon loss would be expected. It is concluded that for amorphous silicon and polycrystalline aluminium films, the cross section for the double plasmon excitation is less than 0.02 of the cross section for the single plasmon excitation process.