Optical Properties Of Ultrathin Films Research Articles

Investigation of the Optical Properties of Ultrathin Films Based on Metal Silicide

Investigation of the Optical Properties of Ultrathin Films Based on Metal Silicide

Investigation of the Optical Properties of Ultrathin Films Based on Metal Silicide

When studying the optical properties of thin films, in order to obtain reliable information about the magnitude of their optical constants, it is necessary to accurately measure the thickness of the metal. Thickness 600 d 1500 Å is measured by the method of multibeam interferometry and the resonant-frequency method.

Evolution of epsilon-near-zero plasmon with surface roughness and demonstration of perfect absorption in randomly rough indium tin oxide thin films

Any degree of surface roughness could play a significant role in determining the optical properties of ultra-thin films required for epsilon-near-zero (ENZ) applications. In this report, we have provided a systematic analysis of the evolution of an ENZ mode with increasing surface roughness values and established both experimentally and theoretically that roughness acts as a supporting mechanism for achieving a strong ENZ plasmon resonance response in randomly rough indium tin oxide thin films. For pulsed laser deposited indium tin oxide thin films, ENZ plasmon-mediated absorption is enhanced monotonically with the increasing surface roughness. A value of 99.75%, depicting near-perfect absorption, at a wavelength of 1335 nm for the incidence angle of 50° is demonstrated experimentally via Kretschmann–Raether configuration for the film with the highest surface roughness. A modified transfer matrix method based on the anisotropic Bruggemann effective medium approximation is being used to effectively simulate the experimental spectra, and based on this analysis, an even higher absorption is predicted at lower angles outside the experimentally viable domain. Such a high value of absorption just above the ENZ wavelength is due to the strong electric field enhancement inside the film layer, while in terms of absorption loss, surface roughness leads the way and contributes immensely toward the occurrence of perfect absorption in the collective media. Modification of the ENZ mode dispersion in the presence of a surface roughness layer is also discussed, and observed perfect absorption is recognized as the outcome of the crossover between the internal damping and radiation damping terms.

Pseudo-refractive index and excitonic features of single layer CdSe/CdS core–shell nanoplatelet films

Semiconductor CdSe/CdS core–shell nanoplatelets exhibit narrow and intense absorption and photoluminescence spectra in the visible range, which makes them suitable for numerous applications in optoelectronics. Of particular interest is the preparation and optical characterization of thin films with an accurately controlled amount of nanoplatelets. Here we report on the use of spectroscopic ellipsometry for investigating the optical properties of ultrathin films composed of a single layer of negatively charged CdSe/CdS core–shell nanoplatelets prepared by the electrostatic layer-by-layer deposition on SiO2/Si substrates. Combining the ellipsometric spectra with atomic force microscopy measurements, we were able to infer the nanoplatelet film extinction spectra which was found to exhibit the two characteristic exciton peaks albeit blueshifted relative to the colloidal nanoplatelets.

Optical response and activity of ultrathin films of topological insulators

We investigate the optical properties of ultrathin film of a topological insulator in the presence of an in-plane magnetic field. We show that due to the combination of the overlap between the surface states of the two layers and the magnetic field, the optical conductivity can show strong anisotropy. This leads to the effective optical activity of the ultrathin film by influencing the circularly polarized incident light. Intriguingly, for a range of magnetic fields, the reflected and transmitted lights exhibit elliptic character. Even for certain values almost linear polarizations are obtained, indicating that the thin film can act as a polaroid in reflection. All these features are discussed in the context of the time-reversal symmetry breaking as one of the key ingredients for the optical activity.

Changes in the optical properties of ultrathin films of liquid crystals during phase transitions

The temperature dependences of diffuse reflection spectra and the polarization of light reflected from ultrathin Langmuir films based on liquid crystals are studied. The results are compared to the experimental data obtained on thicker liquid films. The dependences of the electric capacity of metal-film-metal structures on temperature are measured. The maximum for ultrathin films lies near 75°C, indicating the occurrence of a ferroelectric phase transition. Features in the intensity and polarization of the reflected light are registered at the phase transition temperature. It is concluded that the generality of the results obtained using samples of both types indicates the existence of a mesomorphic phase in Langmuir films. The observed differences could be associated with either dimensional effects or differences in the structures of the films.

Thickness-dependence of optical constants for Ta2O5 ultrathin films

An effective method for determining the optical constants of Ta2O5 thin films deposited on crystal silicon (c-Si) using spectroscopic ellipsometry (SE) measurement with a two-film model (ambient–oxide–interlayer–substrate) was presented. Ta2O5 thin films with thickness range of 1–400 nm have been prepared by the electron beam evaporation (EBE) method. We find that the refractive indices of Ta2O5 ultrathin films less than 40 nm drop with the decreasing thickness, while the other ones are close to those of bulk Ta2O5. This phenomenon was due to the existence of an interfacial oxide region and the surface roughness of the film, which was confirmed by the measurement of atomic force microscopy (AFM). Optical properties of ultrathin film varying with the thickness are useful for the design and manufacture of nano-scaled thin-film devices.

Optical characterization of polyethylene and cobalt phthalocyanine ultrathin films by means of the ATR technique at surface plasmon resonance

AbstractIt is well known that the development and determination of optical properties of ultrathin films is an important issue in many technological areas. In this work organic polyethylene (PE) and cobalt phthalocyanines (CoPc) ultrathin films were deposited over metal films using the r.f. sputtering and thermal evaporation techniques, respectively. Attenuated total reflection (ATR) measurements for the system organic film/metal at the surface plasmon resonance (SPR) were used for determining the thicknesses and optical properties of the PE and CoPc thin films. Thicknesses of the order of some nanometers were found, fitting the theoretical multilayer ATR model, for p polarization monochromatic light, to the experimental reflection data. The dielectric function of CoPc ultrathin films was determined at a wavelength of 632.8 nm. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical properties of ultra-thin films fabricated by layer-by-layer adsorption process depending on dipping time

The layer-by-layer (LBL) self-assembled polyelectrolytes adsorption process is a very slow process. For the fabrication of low-cost application, fabrication time must be decreased. In this work, we measured optical properties of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) thin films depending on deposition time and added impurities. As dipping time was short from 900 s to 180 s, thickness was almost the same. The reason for this was that adsorption quantity was almost the same between 900 s and 180 s from frequency shift of the quartz crystal microbalance measurement. When dipping time was 900 s and 180 s, the refractive index dispersion curves were different before HCl treatment. However, the refractive index dispersion curves were almost the same after HCl treatment. The total fabrication time of the anti-reflection (AR) film decreased from about 6 h (dipping time 900 s) to 2 h (dipping time 180 s), three times faster. Luminous reflection of the film decreased from 0.5 to 0.2, performing 2.5 times better. We propose a high-performance AR film fabrication method for LBL process by the optimization of the film thickness.

Third-Order Nonlinear Optical Properties of an Ultrathin Film Containing a Porphyrin Derivative

An ultrathin nanoscopic multilayer film has been fabricated through the electrostatic layer-by-layer self-assembly of negatively charged 5,10,15,20-tetrakis(3,4,5-trihydroxyphenyl)porphyrin (DHP) and oppositely charged polyethylenimine (PEI). UV-vis spectra showed a continuous and uniform deposition process of PEI and DHP. The film structure was characterized by small-angle X-ray diffraction measurement and AFM images. The nonlinear optical properties of ultrathin film were studied by Z-scan technique with laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited strong nonlinear saturated absorption and a self-defocusing effect. The nonlinear absorption coefficient and refractive index of the self-assembly ultrathin film are -9.7 x 10(-5) m/W and -7.56 x 10(-12) m(2)/W, respectively.

Dielectric polarization and refractive indices of ultrathin barium titanate films on strontiumtitanate single crystals

The electrical and optical properties of ultrathin films of tetragonal barium titanate(BaTiO3) on strontiumtitanate (SrTiO3) single-crystal substrates are theoretically investigated using a microscopic quantummechanical model based on the orbital approximation in correlation with thedipole–dipole interaction. First-, second-, and third-order electronic polarizabilitieshad to be considered in this calculation in order to obtain accurate results forboth the dielectric spontaneous polarization and the refractive indices of theBaTiO3 overlayer. The spontaneous polarization is drastically reduced in the film as itsthickness decreases. However, an electronic polarization appears within theSrTiO3 substratein the neighbourhood of the interface. This polarization, which vanishes far away from the interface into theSrTiO3 bulk, is induced bythe polarization of the BaTiO3 film. Furthermore, we find the refractive index for both theBaTiO3 filmand the SrTiO3 substrate to be deeply reduced for light polarized perpendicular to the surface.

Fabrication and nonlinear optical properties of ultrathin films containing sulfonate functionalized fullerenes

An ultrathin composite film containing both poly(diallyldimethyl ammonium chloride) (PDDA) and hexa(sulfobutyl)fullerenes (C 60-HS) has been fabricated by the electrostatic layer-by-layer self-assembly technique. UV–Vis spectra showed a continuous deposition process of PDDA and C 60-HS. The film structure was characterized by small angle X-ray diffraction measurement and AFM image. The nanothick film showed an effective third-order nonlinear refractive index n 2=1.56×10 −8 esu.

Optical Properties of Ultrathin Films: Evidence for a Dielectric Anomaly at the Insulator-to-Metal Transition

Optical properties of ultrathin layers (<50 A) of Au and Pb quench condensed on amorphous germanium (alpha-Ge) have been measured in situ at 10 K. The development of these films from an insulating state to a metallic state is traced as a function of the film thickness as well as the sheet resistance, R(square). Of particular interest is the regime of R(square) near 3000 Omega where there is an anomaly in the optical transmission. This anomaly is due to a singularity in the dielectric function when the system undergoes an electronic percolation or insulator-to-metal (I/M) transition.

Superconducting and optical properties of ultrathin films of Bi2(Sr,Ca)3Cu2Ox formed at 673 K

Electronic properties of ultrathin films of Bi2(Sr,Ca)3Cu2Ox, successively formed on MgO(100) at a substrate temperature of 673 K using atomic layering deposition of metals followed by oxidation with a 8×10−7 Torr NO2 are studied. It was revealed that the film formed at 673 K showed a semiconductive property, whereas the film annealed at 1093 K with 760 Torr O2 shows a superconducting transition with the onset Tc of 90 K and the zero-resistance Tc of 40 K. Optical absorption and x-ray diffraction studies indicate that the electronic structure of Bi2(Sr,Ca)3Cu2Ox ultrathin film changes from charge-transfer type semiconductor to a superconductor with an in-gap band, due to the increase in carrier concentration caused by annealing with O2.

In situ ellipsometric study of optical properties of ultrathin films

A method has been developed for analysis of a series of ellipsometric data taken in situ during deposition. With this method the optical constants n and k and thickness d of growing ion-beam-sputtered films of C, Si, Ni, Nb, Mo, Ru, Rh, Pd, Ag, W, Re, and Au have been determined as a function of deposition time t. The minimum critical thickness d(i) needed for a film to become optically isotropic has been determined from the n, k, d-versus-t curves. Anomalous behavior of these curves appears in the region d less, similar d(c) resulting from a breakdown of the isotropic film model employed. This is shown, by transmission electron micrographs, to have a correlation with a transition region from island/anisotropic to continuous/isotropic.