Benn Gleason

Performance Evaluation of a Bench-Top Precision Glass Molding Machine

A Dyna Technologies Inc. GP-5000HT precision glass molding machine has been found to be a capable tool for bridging the gap between research-level instruments and the higher volume production machines typically used in industry, providing a means to apply the results of rigorous instrumentation analysis performed in the lab to industrial PGM applications. The GP-5000HTs thermal and mechanical functionality is explained and characterized through the measurement baseline functionality and the associated error. These baseline measurements were used to determine the center thickness repeatability of pressed glass parts, which is the main metric used in industrial pressing settings. The baselines and the repeatability tests both confirmed the need for three warm-up pressing cycles before the press reaches a thermal steady state. The baselines used for pressing a 2 mm glass piece to a 1 mm target center thickness yielded an average center thickness of 1.001 mm and a standard deviation of thickness of 0.0055 mm for glass samples pressed over 3 consecutive days. The baseline tests were then used to deconvolve the sources of error of final pressed piece center thickness.

Processing and properties of arsenic trisulfide chalcogenide glasses for direct laser writing of 3D microstructures

Arsenic trisulfide (As2S3) is a transparent material from ~620 nm to 11 μm with direct applications in sensors, photonic waveguides, and acousto-optics. As2S3 may be thermally deposited to form glassy films of molecular chalcogenide (ChG) clusters. It has been shown that linear and multi-photon exposure can be used to photo-pattern thermally deposited As2S3. Photo-exposure cross-links the film into a network solid. Treating the photo-patterned material with a polarsolvent removes the unexposed material leaving behind a structure that is a negative-tone replica of the photo-pattern. In this work, nano-structure arrays were photo-patterned in As2S3 films by multi-photon direct laser writing (DLW) and the resulting structure, morphology, and chemical composition were characterized and correlated with the conditions of the thermal deposition, patterned irradiation, and etch processing. Raman spectroscopy was used to characterize the chemical structure of the unexposed and photo-exposed material, and near infrared ellipsometry was used to measure the refractive index. Physical characterization including structure size and surface adhesion of nano-scale features is related to the processing conditions.

Nanoscale optical features via hot-stamping of As2Se3 glass

Here we show our ability to fabricate two-dimensional (2D) gratings on chalcogenide glasses with peak-to-valley amplitude of ~200 nm. The fabrication method relies on the thermal nano-imprinting of the glass substrate or film in direct contact with a patterned stamp. Stamping experiments are carried out using a bench-top precision glass-molding machine, both on As2Se3 optically-polished bulk samples and thermally-evaporated thin films. The stamps consist of silicon wafers patterned with sub-micron lithographically defined features. We demonstrate that the fabrication method described here enables precise control of the glass’ viscosity, mitigates risks associated with internal structural damages such as dewetting, or parasitic crystallization. The stamping fidelity as a function of the Time-Force-Temperature regime is discussed, and further developments and potential applications are presented.

Fabrication and characterization of micro-structures created by direct laser writing in multi-layered chalcogenide glasses

Arsenic trisulfide (As2S3) is a chalcogenide (ChG) material with excellent infrared (IR) transparency (620 nm to 11 μm), low phonon energies, and large nonlinear refractive indices. These properties directly relate to commercial and industrial applications including sensors, photonic waveguides, and acousto-optics. Multi-photon exposure can be used to photopattern thermally deposited As2S3 ChG glassy films of molecular clusters. Immersing the photo-patterned cross-linked material into a polar-solvent removes the unexposed material leaving behind a structure that is a negative-tone replica of the photo-pattern. Nano-structure arrays that were photo-patterned in single-layered As2S3 films through multi-photon direct laser writing (DLW) resulted in the production of nano-beads as a consequence of a standing wave effect. To overcome this effect, an anti-reflective (AR) layer of arsenic triselenide (As2Se3) was thermally deposited between the silicon substrate and the As2S3 layer, creating a multi-layered film. The chemical composition of the unexposed and photo-exposed multi-layered film was examined through Raman spectroscopy. Nano-structure arrays were photopatterned in the multi-layered film and the resulting structure, morphology, and chemical composition were characterized, compared to results from the single-layered film, and correlated with the conditions of the thermal deposition, patterned irradiation, and etch processing.

Using design of experiments to improve precision glass moulding

A design of experiments (DOE) approach was used to characterise the effect of process parameters, including heating and cooling rates, soaking times, moulding viscosities, and forces applied during the moulding and cooling stages on the repeatability of the final thickness of moulded N-BK7 and LBAL35 glasses using a precision glass moulding (PGM) machine. Analysis of the DOE showed that process parameters that lengthen the overall time of the moulding process tend toward more repeatable final thicknesses. Using the ideal parameters found by the DOE, the error in the final thickness was held within ±0.05 mm.

Fabrication and characterization of microstructures created in thermally deposited arsenic trisulfide by multiphoton lithography

Abstract. A detailed study of multiphoton lithography (MPL) in arsenic trisulfide (As2S3) films and the effects on nanoscale morphology, chemical networking, and the appearance of the resulting features by the chemical composition, deposition rate, etch processing, and inclusion of an antireflection (AR) layer of As2Se3 between the substrate and the As2S3 layer is reported. MPL was used to photo-pattern nanostructured arrays in single- and multilayer films. The variation in chemical composition for laser-exposed, UV-exposed, and unexposed films is correlated with the etch response, nanostructure formation, and deposition conditions. Reflection of the focused beam at the substrate back into the film produces standing wave interference that modulates the exposure with distance from the substrate and produces nanobead structures. The interference and the modulation can be controlled by the addition of an AR layer of As2Se3 deposited between the substrate and the As2S3 film. Relative to structures produced in a single-layer As2S3 film having no AR layer, photo-patterning in the multilayer As2S3-on-As2Se3 film yields pillar-shaped structures that are closer to the targeted shape and are narrower (120 versus 320 nm), more uniform, and better adhering to the substrate. Processing methods are demonstrated for fabricating large-area arrays with diffractive optical function.

Multi-photon lithography of 3D micro-structures in As2S3 and Ge5(As2Se3)95 chalcogenide glasses

This work reports a detailed study of the processing and photo-patterning of two chalcogenide glasses (ChGs) − arsenic trisulfide (As2S3) and a new composition of germanium-doped arsenic triselenide Ge5(As2Se3)95 − as well as their use for creating functional optical structures. ChGs are materials with excellent infrared (IR) transparency, large index of refraction, low coefficient of thermal expansion, and low change in refractive index with temperature. These features make them well suited for a wide range of commercial and industrial applications including detectors, sensors, photonics, and acousto-optics. Photo-patternable films of As2S3 and Ge5(As2Se3)95 were prepared by thermally depositing the ChGs onto silicon substrates. For some As2S3 samples, an anti-reflection layer of arsenic triselenide (As2Se3) was first added to mitigate the effects of standing-wave interference during laser patterning. The ChG films were photo-patterned by multi-photon lithography (MPL) and then chemically etched to remove the unexposed material, leaving free-standing structures that were negative-tone replicas of the photo-pattern in networked-solid ChG. The chemical composition and refractive index of the unexposed and photo-exposed materials were examined using Raman spectroscopy and near-IR ellipsometry. Nano-structured arrays were photo-patterned and the resulting nano-structure morphology and chemical composition were characterized and correlated with the film compositions, conditions of thermal deposition, patterned irradiation, and etch processing. Photo-patterned Ge5(As2Se3)95 was found to be more resistant than As2S3 toward degradation by formation of surface oxides.

Designing mid-wave infrared (MWIR) thermo-optic coefficient (dn/dT) in chalcogenide glasses

Seventeen infrared-transmitting GeAsSe chalcogenide glasses were fabricated to determine the role of chemistry and structure on mid-wave infrared (MWIR) optical properties. The refractive index and thermoptic coefficients of samples were measured at λ = 4.515 μm using an IR-modified Metricon prism coupler, located at University of Central Florida. Thermo-optic coefficient (dn/dT) values were shown to range from approximately -40 ppm/°C to +65 ppm/°C, and refractive index was shown to vary between approximately 2.5000 and 2.8000. Trends in refractive index and dn/dT were found to be related to the atomic structures present within the glassy network, as opposed to the atomic percentage of any individual constituent. A linear correlation was found between the quantity (n-3•dn/dT) and the coefficient of thermal expansion (CTE) of the glass, suggesting the ability to compositionally design chalcogenide glass compositions with zero dn/dT, regardless of refractive index or dispersion performance. The tunability of these novel glasses offer increased thermal and mechanical stability as compared to the current commercial zero dn/dT options such as AMTIR-5 from Amorphous Materials Inc. For IR imaging systems designed to achieve passive athermalization, utilizing chalcogenide glasses with their tunable ranges of dn/dT (including zero) can be key to addressing system size, weight, and power (SWaP) limitations.

Optimization of Manufacturability of Chalcogenide Glasses for Mid-infrared Optical Components

Next generation optical components will require materials that possess unique, spectral-specific optical functions and forming compatible attributes defined by their chemistry, structure and properties. Trade-offs in the optimization of these variables for manufacturability are discussed.

Compositional-tailoring of optical properties in IR transparent chalcogenide glasses for precision glass molding

The structural and optical properties of AsSe chalcogenide glass, starting with As40Se60, were studied as a function of Ge or Se additions. These elements provide broad glass forming options when combined with the host matrix to allow for compositional tuning of properties. Optimization of glass composition has been shown to produce bulk glasses with a thermoptic coefficient (dn/dT) equal to zero, as well as a composition which could demonstrate a net zero change in index after precision glass molding (PGM). The bulk glass density, coefficient of thermal expansion (CTE), refractive index, and dn/dT were measured for all bulk compositions, as was the refractive index after PGM. For the bulk glasses examined, both the refractive index (measured at discrete laser wavelengths from 3.4 to10.6 μm) and dn/dT were observed to decrease as the molecular percentage of either Ge or Se is increased. Compared to the starting glass’ network, additions of either Ge or Se lead to a deviation from the “optimally constrained” binary glass’ average coordination number = 2.4. Additions of Se or Ge serve to decrease or increase the average coordination number (CN) of the glass, respectively, while also changing the network’s polarizability. After a representative PGM process, glasses exhibited an “index drop” consistent with that seen for oxide glasses.1 Based on our evaluation, both the Gecontaining and Ge-free tielines show potential for developing unique compositions with either a zero dn/dT for the unmolded, bulk glass, as well as the potential for a glass that demonstrates a net zero “index drop” after molding. Such correlation of glass chemistry, network, physical and optical properties will enable the tailoring of novel compositions suitable for prototyping towards targeted molding behavior and final properties.