Normal Incidence Condition Research Articles

Fabrication of cone-shaped subwavelength structures by utilizing a confined convective self-assembly technique and inductively coupled-plasma reactive-ion etching

Cone-shaped subwavelength structures (SWSs) were fabricated on a GaAs substrate by utilizing a confined convective self-assembly process followed by inductively coupled-plasma reactive-ion etching. A self-assembled polystyrene monolayer was used as an etch mask for pattern transfer onto the GaAs substrate. The fabricated SWS, having a cone profile with an aspect ratio of 1.5 and a 300 nm pitch, exhibited very low reflectance throughout the solar spectrum range and exhibited wide tolerance to different optical incidence angles. Reflectance of the cone-shaped SWS on the GaAs surface was less than 4% in a spectral range of 300–1000 nm under a normal incidence condition.

Grazing incidence scattering of vibrationally excited H 2 molecules from metal surfaces

We have studied the scattering of vibrationally excited H 2 molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H 2 molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.

Optical transmission anomalies in a double-layered metallic slit array

We theoretically predicted the existence of an anomalous optical transmittance dip, which must be observed for a metamaterial structure with two metallic slabs with cut-through slit arrays of a constant period d under a normal incident condition. By changing the relative lateral displacement l between the two slabs, the dip frequency varies across that of a so-called Rayleigh-Wood's (RW) anomaly frequency. The mechanism of this anomaly is quite different from that of the RW anomaly and interpreted in terms of the interference between the propagating and evanescent waves. For the present double-layered system, furthermore, it is suggested that the RW anomaly vanishes for l = 0 and d/2. In experiments in the terahertz region, we observe that the fundamental features agree with these theoretical predictions.

Angular dependence of the intensity of light beams diffracted by colloidal crystals

An experimental and theoretical analysis of the angular dependence of the diffracted light beams emerging from three-dimensional colloidal photonic crystals is herein presented. Diffracted beams are identified according to their associated reciprocal-lattice vectors, and their intensities are obtained as a function of the zenithal and azimuthal incidence angles. Significant changes in the beam intensities are observed for large zenithal incidence angles as the azimuthal angle is varied. This phenomenon is related to the excitation of new resonant modes inside the photonic crystal which cannot be observed under normal incidence conditions.

Polypropylene-substrate-based SRR- and CSRR- metasurfaces for submillimeter waves

In this paper it is presented the fabrication of low loss millimeter wave metamaterials based on patterning on polypropylene substrates by conventional contact photolitography. We study numerically and experimentally the transmission and reflection properties of two dimensional arrays of split ring resonators (SRRs), or metasurfaces, and their complementary structure (CSRRs) for co- and cross-polarization excitations up to submillimeter frequencies under normal incidence conditions. The obtained results suggest the possibility of scaling them at terahertz frequencies based on this substrate where other lossy substrates degrade the resonators quality. Left-handed metamaterials derived from these SRRs and CSRRs metasurfaces could be feasible.

Fabrication of Mo/Si multilayer mirrors for extreme ultraviolet lithography by means of superconducting bulk magnet magnetron sputtering

The fabrication of a highly reflective multi-layer film is an urgent need in the next-generation extreme ultraviolet (EUV) lithography to print ever-smaller circuit patterns onto semiconductor wafers by using extremely short wavelength (13.5 nm) light. For this purpose, we have synthesized the Mo/Si multi-layer films by employing the two-cathode superconducting bulk magnet magnetron sputtering apparatus. The films were made by repeatedly depositing a pair of 4.5 nm thick Si and then 2.5 nm thick Mo layer up to 40 or 50 pairs on the Si wafer with its root-mean square (rms) surface roughness of 0.1 nm. The resulting rms surface roughness of the Mo/Si multi-layer film turned out to be 0.12 nm. The transmission electron microscope (TEM) studies revealed the inter-diffusion layer thicknesses of Si-on-Mo and Mo-on-Si layers to be 0.5 and 1.5 nm, respectively. The EUV-reflectivity was theoretically calculated to reach the value of 70%, when these structural data are inserted into the reflectivity formula. However, the highest EUV-reflectivity so far observed was 67% in the normal incident condition. The 2–3% shortage of the reflectivity is attributed to the presence of residual Xe gas atoms incorporated into the film during deposition in the reduced Xe gas atmosphere.

The optimization of incident angles of low-energy oxygen ion beams for increasing sputtering rate on silicon samples

In order to determine an appropriate incident angle of low-energy (350-eV) oxygen ion beam for achieving the highest sputtering rate without degradation of depth resolution in SIMS analysis, a delta-doped sample was analyzed with incident angles from 0° to 60° without oxygen bleeding. As a result, 45° incidence was found to be the best analytical condition, and it was confirmed that surface roughness did not occur on the sputtered surface at 100-nm depth by using AFM. By applying the optimized incident angle, sputtering rate becomes more than twice as high as that of the normal incident condition.

Construction of superconducting bulk magnet magnetron sputtering apparatus for fabrication of highly reflective optical mirrors

We have developed the two-cathode magnetron sputtering apparatus equipped with superconducting permanent magnet to produce Mo/Si multi-layer films, which would potentially serve as a high-quality optical mirror at extreme ultraviolet (EUV) wavelength of 13.5 nm. The best deposition condition was searched by analyzing the structure of the inter-diffusion layer formed in the Mo/Si bi-layer film prepared under different deposition conditions. It was found that (1) Xe gas should be used as inert gas species, (2) its pressure is lower than 4 × 10 −2 Pa, (3) a throw distance is longer than 250 mm and (4) discharge voltage around 2 kV. By making full use of these data, we synthesized Mo/Si multi-layer films and analyzed the structure and its effect on the reflectivity. The highest EUV-reflectivity so far obtained is 67% in the normal incident condition.

Onset of shadowing-dominated growth in glancing angle deposition

We demonstrate that shadowing instabilities can dramatically alter the very early stages of growth of amorphous thin films on nominally smooth surfaces. These observations are made by comparing the porosity and morphological evolutions of thin films grown under conditions of normal and glancing incidences of the vapor flux. At conditions of normal incidence, we see evidence of nucleation, followed by coalescence and growth of a continuous film; at glancing incidence, we observe the development of a mounded surface morphology before deposition of the first nanometer, followed by growth of isolated nanopillars.

Normal Incidence Intersubband Absorption in GaN/AlN Superlattices Grown on Facet-Controlled Epitaxial Lateral Overgrown GaN/Sapphire Templates

GaN/AlN superlattice structures along the (1122) facet were grown on facet-controlled epitaxial lateral overgrown (FACELO) GaN/sapphire templates by metal organic chemical vapor deposition (MOCVD). The as-grown GaN/AlN superlattice shows abrupt interfaces and good periodicity, as characterized by high-resolution transmission electron microscopy (TEM). The intersubband transition peak at a wavelength of 1.9 µm was observed for an AlN (1.5 nm)/GaN (1 nm) superlattice grown on the FACELO GaN (1122) facet with the propagation direction of the incident light normal to the (0001) facet of sapphire, called the normal incidence condition. The full width at half-maximum of the absorption peak is as narrow as 65 meV, implying the high quality of the interfaces, good thickness uniformity, and the reduced polarization effect in the structures. This result shows the promising feasibility for realizing two-dimensional (2D) arrays of nitride-based quantum-well infrared photodetectors (QWIPs) using GaN/AlN superlattices grown on FACELO GaN/sapphire templates.

Infrared response of a metamaterial made of gold wires and split ring resonators deposited on silicon

Periodic arrays of gold wires and split ring resonators (SRR) with a minimum feature size of 50 nm are fabricated on low-doped silicon. To our knowledge, the periodic arrangement of SRRs and wires considered in this work has not been studied in the near-infrared domain yet. For normal-incidence conditions, this metamaterial structure exhibits resonances at 70 and 170 THz (i.e., at λ ≈ 4.3 and 1.75 μm), which are identified as LC- and Mie resonances, respectively. These resonances are also observed for the SRRs alone, but the amplitude of the Mie resonance is reinforced due to the coupling between the SRRs and wires. The structure is simulated using finite-element software, while transmission and reflection measurements are performed with a Fourier transform infrared spectrometer. Numerical simulations are found to be in very good agreement with experimental characterizations, thereby showing that the Drude model used in calculations is well suited to simulate gold structures at near-infrared frequencies. Theoretical calculations predict that the metamaterial has a negative permittivity and a negative permeability near each resonance.

Characteristics of a cluster‐ion beam of Os3(CO)n+ (n = 7 or 8) for low‐damage sputtering

AbstractA cluster‐ion source has been developed to produce stable ion beams of metal‐cluster‐complex ions. As a metal cluster complex, triosmium dodecacarbonyl, Os3(CO)12, was used, which has a molecular weight of 906.7. Using the ion source, energy dependence of beam current and sputtering yield of silicon bombarded with Os3(CO)n+ (n = 7–8) were investigated at beam energies from 2 to 10 keV under the normal incidence condition. By high‐resolution Rutherford backscattering spectrometry (HR‐RBS), a silicon target bombarded with the normally incident Os3(CO)7–8+ ions at 10 keV with oxygen flooding at 5 × 10−4 Pa was analyzed. The experimental results showed that the ion‐beam current increased almost linearly with the acceleration voltage. It was found that the sputtering yields of silicon with Os3(CO)7–8+ ions varied substantially with beam energy. The sputtering yield with Os3(CO)7–8+ at 10 keV was higher than that with SF5+ or Ar+ by a factor of 3–20, whereas the yield at 3 keV was lower than that with Ar+. In the case of 2 keV, deposition was found to occur on the silicon surface. The substantial variation in the sputtering yield with beam energy would arise from the lower kinetic energy of each atom constituting the metal‐cluster‐complex ions. From HR‐RBS results, it was confirmed that the constituent atoms of the Os3(CO)7–8+ ions, Os, C, and O, were implanted into the silicon target. The observed depth profiles of Os and C atoms were in good agreement with results of TRIM simulation, while that of the O atom was significantly different from the simulation results. The depth profile of the O atom was examined in terms of oxygen diffusion and implantation. Copyright © 2006 John Wiley & Sons, Ltd.

High-temperature operation normal incident 256/spl times/256 InAs-GaAs quantum-dot infrared photodetector focal plane array

In this letter, a 256/spl times/256 midwavelength infrared focal plane array (FPA) based on 30-period InAs-GaAs quantum-dot infrared photodetectors (QDIPs) is fabricated. The demonstrated original real-time nonuniformity corrected thermal images of hot soldering iron head with 30-Hz frame rate for the FPA are observed. Without additional light-coupling scheme, the QDIP FPA module is first operated at temperatures higher than 135 K under normal-incident condition with a 30/spl deg/ field of view and f/2 optics. For single device performances, a similar QDIP device with a 30-period InAs-GaAs QD structure is fabricated under the same processing procedure. High specific detectivity D/sup */ 1.5/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W and low noise current density 5.3/spl times/10/sup -13/ A/Hz/sup 1/2/ at applied voltage 0.3 V are observed.

Phase resonances in obliquely illuminated compound gratings

The existence of phase resonances in obliquely illuminated, perfectly conducting compound gratings is investigated. The diffraction problem of a p-polarized plane wave impinging on the structure is solved using the modal approach. The results show that even under oblique illumination, where no symmetry is imposed by the incident field, there are resonant wavelengths that are clearly associated with a certain degree of symmetry in the phase distribution of the magnetic field inside the cavities. New configurations of this phase distribution take place, that were not allowed under normal incidence conditions. It was found that the interior field is intensified in the resonances, and the specularly reflected efficiency is maximized. In particular, this efficiency is optimized for Littrow mount.

Magnetic Metamaterials at Telecommunication and Visible Frequencies

Arrays of gold split rings with a 50-nm minimum feature size and with an LC resonance at 200 THz frequency (1.5 microm wavelength) are fabricated. For normal-incidence conditions, they exhibit a pronounced fundamental magnetic mode, arising from a coupling via the electric component of the incident light. For oblique incidence, a coupling via the magnetic component is demonstrated as well. Moreover, we identify a novel higher-order magnetic resonance at around 370 THz (800 nm wavelength) that evolves out of the Mie resonance for oblique incidence. Comparison with theory delivers good agreement and also shows that the structures allow for a negative magnetic permeability.

Angular Resolved Energy and Particle Flux Measurements in a Magnetized Plasma

AbstractA flat probe allowing simultaneous energy flux and current density measurements as functions of an applied voltage was rotated in a homogeneous plasma. The probe dimensions (a) were larger or comparable to the ion gyro radius (ri).Current density (ji), floating potential (Uf ), energy flux density (q), ion energy reflection coefficient RE and the sheath energy transmission coefficient γ were determined as functions of the angle α between the probe surface normal and the magnetic field. For normal incidence conditions (α = 0) all measured quantities do agree well with the theoretical predictions. With |α| approaching 90°, finite gyro‐radii effects of the ions become important. To lowest order the angular variations can be understood by assuming Γe,i ∝ cos α + 2re,i/a for the ion particle flux density.Most remarkably, a pronounced reduction of the floating potential and the ion impact energy was found experimentally at shallow angles. In contrast, relatively small angular dependencies were found for γ and RE. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stark absorption spectroscopy of indole and 3-methylindole.

Indole and 3-methylindole (3-MI) doped into a polymethylmethacrylate (PMMA) film are studied by the Stark absorption (electroabsorption) spectroscopy. The 1La and 1Lb absorption bands are distinguished and the change in permanent dipole moment on 1La excitation is determined by a model fit to the measured absorption and electroabsorption spectra. Analysis of the spectra, measured at normal incidence and magic angle conditions, proved the essential role of the electric-field-induced orientation/alignment effects for polar indole and 3-MI molecules in the PMMA environment at room temperature.

Site-Specific Neutralization of Slow Multicharged Ions Incident on Solid Surfaces

Recent measurements of projectile neutralization during 120° binary collision backscattering from Au(110) and RbI(100), performed at the ORNL Multicharged Ion Research Facility, are described. A common feature of the Au(110) and RbI(100) results is that the observed scattered charge state distributions show significant dependences on the target azimuthal orientation, even for normal or close to normal incidence conditions. The observed target azimuth dependences originate in part from the fact that for the 120° backscattering geometry, quasi-binary double collisions make significant contributions to the total binary scattering collision flux. For the Au(110) target, the types of possible quasi-binary collisions vary with target azimuth because of the corrugation of the reconstructed surface and the number of layers of atoms exposed in a (110) fcc lattice. For the RbI(100) surface, quasi-binary collisions vary with azimuth because of the ordered, two-component nature of the surface even when scattering from deeper layers is blocked. Sample data for few-keV incident F, Ne, and Ar multicharged incident projectiles are presented to illustrate the underlying concepts.

Experimental study of the free spectral range (FSR) in FPI with a small plate gap

In this paper we investigate the variation of free spectral range (FSR) for the Fabry-Perot interferometer (FPI) consisting of mirrors with phase shift dispersion. The reflection phase shift on a mirror has been calculated employing the Transfer-Matrix Method and the values of FSR have been calculated under the condition of normal incidence of light beam. Fabry-Perot (FP) cavities have been fabricated employing bulk micromachining technology, and silicon wafers coated with multiplayer dielectric films were used as mirrors. FSR of these FP cavities have been experimentally measured. The experimental data match the calculated results very well. The conclusion is that FSR shortening effect must be taken into account for the FPIs with a small plate gap, as the finesse and the tunable range of tunable FPI can be affected by the shortening effect greatly.

The instability of the surface of helium crystal in a superfluid flow

The problem on crystal growth under conditions of normal incidence of fluid on the boundary is investigated for stability. The threshold velocity of the emergence of instability is found; at low temperatures, this velocity proves to be much lower than the sound velocity. The stability is examined of the shape of cylindrical crystal in a fluid flow parallel to the crystal axis. The behavior of the atomically rough surface of crystal helium is experimentally investigated in a jet of fluid in the temperature range from 1 to 1.4 K, where the emergence is observed of an instability of the type previously predicted by Kagan, as well as by Nozieres and Uwaha. Observations reveal that, below the roughening transition, the (0001) basal face is stable in a jet of fluid.