Browsing by Author "Nakagawa, Wataru"

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Auger electron spectroscopy mapping of lithium niobate ferroelectric domains with nano-scale resolution
(Optica Publishing Group, 2022-12) McLoughlin, Torrey; Babbitt, Wm. Randall; Nakagawa, Wataru
The +/−Z ferroelectric domains in periodically poled lithium niobate are characterized with Auger electron spectroscopy. The -Z domains have a higher Auger O-KLL transition amplitude than the +Z domains. Based on this, Auger electron spectroscopy mapping can be used on the O-KLL peak to image the +/-Z domain structure. This new characterization technique is confirmed with HF etching, and compared to SEM imaging. Spatial resolution down to 68 nm is demonstrated.
Development and Optimization of Surface Plasmon-Polariton Based Sensing System
(2013-03) Drummond, Krista; Nakagawa, Wataru
Techniques based on the Surface Plasmon-Polariton (SPP) phenomenon are a common approach to realizing high-performance refractive index sensors. In our laboratory, we have designed and built such a system which is capable of measuring the refractive index of liquid samples. This is done by injecting a sample liquid into a fluidic system, consisting of a Polydimethylsiloxane (PDMS) walled chamber designed to hold the sample flush to the surface of a gold coated glass slide. This boundary is then illuminated with a laser beam and the excited SPP is observed. The current SPP-based sensor is capable of detecting refractive index changes (Δ n) of about 0.0022. Our goal is to increase sensor performance by investigating several improvements to system components. This includes evaluating enhancements to the fluidic system layout to reduce the required sample volume to make a measurement, modifying the optical layout to increase system angular resolution, and improving the quality of the gold film which will improve the sensitivity of the sensor. This includes testing alternate gold adhesion layer compositions, improving the smoothness of the gold surface, or comparing different deposition methods to achieve the highest quality SPP. This investigation documents an improvement in overall system performance by showing an increase in system sensitivity through a decrease in measureable change in refractive index. Measuring this optical property can help determine the identity of a liquid, along with determining solute concentrations. Future investigation involving PDMS microfluidics will facilitate interdisciplinary collaboration, including chemical, biological, and medical applications.
Fabrication of Optical Nanostructures using HSQ Masks
(2013-03) Rydberg, Skyler; Rydberg, Skyler; Nakagawa, Wataru; Dickensheets, David
Subwavelength-scale nanostructures hold great promise for the development of new, useful optical devices. One of the challenges in realizing such devices is the creation of the desired nanoscale patterns in materials such as silicon with the required precision. Recently, a new resist material for electron-beam lithography, Hydrogen Silsesquioxane (HSQ), has emerged as a solution to this challenge. The purpose of this project is to create a recipe for a 100 nm layer of HSQ to be applied to a silicon substrate by means of spin-coating. After formulation of a recipe to achieve the desired 100 nm thickness, tests were performed to determine which electron beam dosages produced the best features in terms of resolution and contrast. Grating patterns were created with varying periods while maintaining a constant 50% fill factor. Characterization of the gratings was performed to determine the optimal dosage for these features. The optimal dose was found to be 95 μC/cm2. After determining an ideal recipe, the HSQ was used as an etch mask to create hybrid HSQ-silicon gratings with nanoscale features. This capability will enable the development of a number of new optical devices based on nanostructures, for a range of interdisciplinary applications.
Nano-scale ferroelectric domain differentiation in periodically poled lithium niobate with auger electron spectroscopy
(Optica Publishing Group, 2022-03) McLoughlin, Torrey; Babbitt, Wm. Randall; Nakagawa, Wataru
A new method for characterizing lithium niobate +/-Z ferroelectric polarization domains using Auger electron spectroscopy (AES) is presented. The domains of periodically poled samples are found to be differentiable using the peak amplitude of the Auger oxygen KLL transition, with -Z domains having a larger peak-amplitude as compared to +Z domains. The peak amplitude separation between domains is found to be dependent on the primary beam current, necessitating a balance between the insulating samples charging under the primary beam and achieving sufficient signal to noise in amplitude separation. AES amplitude-based domain characterization is demonstrated for fields of view (FOV) ranging from 1 𝜇m to 78 𝜇m. Domain spatial resolution of 91 nm is demonstrated at 1 𝜇m FOV.
Near-Infrared Polarization Optics using Nanostructured Silicon
(2013-03) Keeler, Ethan; Nakagawa, Wataru; Dickensheets, David
Silicon structures with sub-micron size features can have interesting optical properties, and have been explored in a number of application areas. In addition, these silicon nanostructures can be fabricated using standard materials and processes adapted from the semiconductor industry, streamlining their construction and enabling eventual integration with other silicon-based devices such as micro-electro-mechanical systems (MEMS) or electronic circuitry. The goal of this work is to investigate an optical device realized using a silicon nanostructure: a polarizing beam splitter (PBS), a device that reflects one linear polarization state while transmitting the other. This device consists of a grating in a silicon substrate with a thin layer of gold atop its peaks and inside its troughs. In order to evaluate the optical characteristics of this device in detail, several simpler but related devices, such as subwavelength-period gold gratings (wire-grid polarizers) and silicon gratings (form-birefrignent structures), are also investigated. We present the design, fabrication, and preliminary characterization of this family of devices fabricated in our laboratory. In creating all of these devices, the project successfully demonstrated that an optical PBS can be realized using engineered silicon nanostructures. It also quantitatively compared the new PBS device to well known structures of the same nature, and it provided an excellent side-by-side comparison of the different structures used to achieve polarization selectivity. As this work suggests, silicon is an excellent material for creating optical nanostructures, but also potentially enables large-scale integration of electrical and optical systems, which will have boundless possibilities as technology progresses into the future.