A fully automated multi-target reactive magnetron sputtering (MS) process is presented in which real-time modeling and in situ standard or Mueller matrix ellipsometry is combined demonstrating growth of nanoscale multi-layer optical thin films having desired properties such as thickness, while observing properties such as index of refraction (n), extinction coefficient (k), and complex permittivity throughout growth. For each material layer isotropic or anisotropic properties as required can be modeled automatically in real-time, allowing for the development of hyperbolic metamaterials. In situ use of an RC2 ellipsometer from JA Woollam is presented, having a spectral range of 210nm - 2500nm. TEM measurements of the thin films are presented.
In previous work, we have introduced an analytical approach that utilizes the dispersion relation for an infinite periodic multilayer structure to predict the performance of finite multilayer structures. We have validated the accuracy of our predictions by demonstrating numerical agreement with other established simulation methods, such as the transfer matrix method, and through experimental confirmation. In this work, we employ dispersion relations to first illustrate that metallo-dielectric structures, as opposed to multilayer dielectric-dielectric structures, can efficiently yield a sharp-edge transmittance spectrum profile, with control over both sides of the bandpass cutoff edges. Our approach also enables the calculation of effective permittivity without relying on traditional homogenization techniques. Next, utilizing the concept of effective permittivity, we illustrate that increasing the thickness of specific dielectric layers within MD structures leads to narrower passbands without significant loss in transmission, demonstrating the potential of this approach for engineering the transmittance spectrum of bandpass filters in the visible and near-IR regions. The capability to achieve a sharp-edge filter with a limited number of layers further underscores the cost-effectiveness of such bandpass filters.
Extreme adaptive optics (ExAO) systems are optimized for high-contrast imaging and coronagraphy. ExAO systems are currently limited to wavefront sensing using a bright natural guide star (NGS) due to the need for high precision wavefront control. Recent advances in sodium laser guide star (LGS) technology such as high power, efficient laser sources and pre-compensation of the laser uplink overcome previous limitations in LGS technology, opening up the potential for LGS technology to improve ExAO system performance with dim targets. The LAser guide Star Sensor Integrated Extreme adaptive optics (LASSIE) project at the Starfire Optical Range will explore the trade space in beacon size, brightness, coherence, and wavefront sensor design to preform path-finding research on the potential performance of an uplink-corrected LGS-ExAO system. In this presentation we will discuss the current progress of the LASSIE project.
We show applications of our analytical approach to predict the performance of multilayer metallo-dielectric bandpass filters, which also enables estimation of their effective permittivity without relying on homogenization techniques. The approach is based on the one-dimensional dispersion relation for an infinite metallo-dielectric structure that accounts for the complex nature of the permittivities for the metal and dielectric constituents. The dispersion relation clearly reveals the band structure (often comprising multiple passbands), directly provides transmittance characteristics such as center wavelengths and bandwidths and enables the calculation of effective propagation constant and effective attenuation. In this work, we evaluate the dispersion relations for metallo-dielectric structures with complex refractive index data for the metal, viz., Ag, acquired from different sources to show the differences in the center wavelength and the cutoff wavelengths. We verify the accuracy of our method numerically by comparing the transmittance spectrum of finite metallo-dielectric structures using the transfer matrix method. We also plot the dispersion relation using Al as the metal and show the differences in the dispersion relations of the infinite structure and the transmittances of the finite structures relative to Ag. Extension to determination of dispersion relations for other polarizations, viz., transverse magnetic, is discussed, along with corresponding transmittance spectra for oblique incidence.
The co-sputtered Cu-Si-O and Cu-Ge-O thin films were prepared using reactive DC, pulse DC and modulated pulse power magnetron sputtering (MPPMS) on two separate Cu and Si or Cu and Ge targets simultaneously. The powers on each target and Oxygen/Argon flow ratio f(O2) were varied to have different stoichiometies determined by XPS. The film thickness, refractive index n and extinction coefficient k were extracted from in situ ellipsometry and the reactive plasma discharge was monitored by optical emission spectroscopy in real time during film growth. The grazing incident x-ray diffraction measurements reveal that the films deposited at low f(O2) have the nanocrystalline structure of cuprous Cu2O with diffraction peaks of (111) and (200). The films deposited at high f(O2) (≥ 1) have cupric oxide CuO phase. The optical constant n and k, film density and band gap of the co-sputtered film were investigated and determined by in situ ellipsometry, X-ray reflectivity and UV-Vis-NIR spectroscopy. Their structural, chemical and optical properties are able to be tuned by incorporating Cu2O, CuO and the mixtures of them into Silicon oxide or Germanium oxide matrix with varying target powers and oxygen/Argon ratio for applications in optical coatings and optical filters.
John Jones, Jonathan Goldstein, Steven Smith, Gerald Landis, Lawrence Grazulis, Neil Murphy, Gregory Kozlowski, Rachel Jakubiak, Charles Stutz, Lirong Sun
Oxide materials of desired stoichiometry are challenging to make in small quantities. Nanostructured thin films of multiple oxide materials were obtained by using pulsed laser deposition and multiple independent targets consisting of Si, BaTiO3, and B. Programmable stoichiometry of nanostructured thin films was achieved by synchronizing a 248-nm krypton fluoride excimer laser at an energy of 300 mJ/pulse, a galvanometer mirror system, and the three independent target materials with a background pressure of oxygen. Island growth occurred on a per pulse basis; some 500 pulses are required to deposit 1 nm of material. The number of pulses on each target was programmed with a high degree of precision. Trends in material properties were systematically identified by varying the stoichiometry of multiple nanostructured thin films and comparing the resulting properties measured using in situ spectroscopic ellipsometry, capacitance measurements including relative permittivity and loss, and energy dispersive spectroscopy (EDS). Films were deposited ∼150 to 907 nm thickness, and in situ ellipsometry data were modeled to calculate thickness n and k. A representative atomic force microscopy measurement was also collected. EDS, ellipsometry, and capacitance measurements were all performed on each of the samples, with one sample having a calculated permittivity greater than 20,000 at 1 kHz.
This article [J. Nanophoton.. 8, (1 ), 083890 ( Feb 5 , 2014)] mistakenly appeared in the Special Section on Metamaterials and Photonic Nanostructures. It was republished in the Special Section on Nanostructured Thin Films VI with a corrected CID on 10 February 2014. The updated citation is shown below:
Pulsed laser deposition is an energetic deposition technique in which thin films are deposited when a laser pulse at 248-nm wavelength strikes a target and material is subsequently deposited onto a substrate with ideally the same stoichiometry. By synchronizing a high-speed mirror system with the pulsing of the laser, and using two separate targets, thin films having tunable stoichiometry have been deposited. Depositions were performed in a high vacuum environment to obtain as much kinetic energy as possible during growth. Typically, some 150 pulses at 300 mJ/pulse were required to deposit 1 nm. Island growth must occur on a per pulse basis since over 100 pulses are required to deposit a 1 nm film thickness. Films were deposited to ∼100-nm thickness, and in situ ellipsometry data were modeled to calculate thickness, n and k . X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy (AFM) were all performed on each of the films. XPS demonstrated change in film composition with change in laser pulse ratio; ellipsometry displayed thickness from the model generated as well as the optical properties from 370 to 1690 nm. AFM thickness measurements were in agreement with independently modeled ellipsometry thickness values.
The spectral radiative properties of coherent thermal emission in the mid- and far-IR from two metal-semiconductor
resonating structures were demonstrated experimentally. Using an efficient implementation of Rigorous Coupled-Wave
Analysis, a truncated resonator was designed to selectively emit at mid-IR and far-IR wavelengths. A High Impulse
Power Magnetron Sputtering deposition technique was used to fabricate two Ag-Ge-Ag resonating structures with layer
thicknesses of 6-240-160 nm for one sample and 6-700-200 nm for the other. Reflectance measurements demonstrated
spectrally selective absorption at the designed mid- and far-IR wavelengths whose general behavior was largely
unaffected by a wide range of incident angles. Further, radiance measurements were taken at various high temperatures,
up to 601 K, where spectrally selective emission was achieved through wave interference effects due to thermally excited
surface waves. From these radiance measurements, spectral emittance was directly derived and compared to the
emittance inferred from reflectance measurements. It was established that inferring emittance through Kirchhoff’s law
can help to approximate the expected emission from a structure, but it is not an exact method of determining the actual
emittance of a thermal source at higher temperatures due to the temperature dependence of material parameters.
Current work on deep-reactive ion etching has primarily focused on creating vertical sidewalls for microelectromechanical system and electronics applications. For micro-optical and micro-optoelectromechanical system structures control of the sidewall angles other than vertical is as important as the ultimate depth. In this work, we investigate the control of sidewall profiles using an inductively coupled plasma technique. The material systems being investigated on blanket samples are silicon and silicon dioxide with CF4, CHF3, and SF6 chemistries. Micro-optic structures are created by photolithography and CHF3 gas has been explored to achieve a wide range of etch rates, smooth etch profiles, and sidewall angles. The etch profiles are characterized by scanning electron microscopy.
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