skip to main content

Title: Hyperspectral imaging for high-throughput, spatially resolved spectroscopic scatterometry of silicon nanopillar arrays

Modern high-throughput nanopatterning techniques, such as nanoimprint lithography, make it possible to fabricate arrays of nanostructures (features with dimensions of 10’s to 100’s of nm) over large area substrates (cm2to m2scale) such as Si wafers, glass sheets, and flexible roll-to-roll webs. The ability to make such large-area nanostructure arrays (LNAs) has created an extensive design space, enabling a wide array of applications including optical devices, such as wire-grid polarizers, transparent conductors, color filters, and anti-reflection surfaces, and building blocks for electronic components, such as ultracapacitors, sensors, and memory storage architectures. However, existing metrology methods will have trouble scaling alongside fabrication methods. Scanning electron microscopy (SEM) and atomic force microscopy (AFM), for instance, have micron scale fields of view (FOV) that preclude comprehensive characterization of LNAs, which may be manufactured at m2per minute rates. Scatterometry approaches have larger FOVs (typically 100’s of µm to a few mm), but traditional scatterometry systems measure samples one point at a time, which also makes them too slow for large-scale LNA manufacturing. In this work, we demonstrate parallelization of the traditional spectroscopic scatterometry approach using hyperspectral imaging, increasing the throughput of the technique by a factor of 106-107. We demonstrate this approach by using hyperspectral imaging and inverse modeling of reflectance spectra to derive 3-dimensional geometric data for Si nanopillar array structures over both mm and cm-scale with µm-scale spatial resolution. This work suggests that geometric measurements for a variety of LNAs can be performed with the potential for high speed over large areas which may be critical for future LNA manufacturing.

more » « less
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Optical Society of America
Date Published:
Journal Name:
Optics Express
1094-4087; OPEXFF
Page Range / eLocation ID:
Article No. 14209
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Surface recombination is a major bottleneck for realizing highly efficient micro/nanostructure solar cells. Here, parametric studies of the influence of Si microwire (SiMW) surface‐facet orientation (rectangular with flat‐facets, {110}, {100} and circular), with a fixed height of 10 µm, diameter (D= 1.5–9.5 µm), and sidewall spacing (S= 2.5–8.5 µm), and mesh‐grid density (1–16 mm−2) on recombination and carrier collection in SiMW solar cells with radial p‐n junctions are reported. An effective surface passivation layer composed of thin thermally grown silicon dioxide (SiO2) and silicon nitride (SiNx) layers is employed. For a fixedDof 1.5 µm, tight SiMW spacing results in improved short‐circuit current density (Jsc= 30.1 mA cm−2) and sparse arrays result in open‐circuit voltages (Voc= 0.552 V) that are similar to those of control Si planar cells. For a fixedS, smallerDresults in better light trapping at shorter wavelengths and higherJscwhile largerDexhibits better light trapping at larger wavelengths and a higherVoc. With a mesh‐grid electrode the power conversion efficiency increases to 15.3%. These results provide insights on the recombination mechanisms in SiMW solar cells and provide general design principles for optimizing their performance.

    more » « less
  2. Abstract

    To exploit their charge transport properties in transistors, semiconducting carbon nanotubes must be assembled into aligned arrays comprised of individualized nanotubes at optimal packing densities. However, achieving this control on the wafer‐scale is challenging. Here, solution‐based shear in substrate‐wide, confined channels is investigated to deposit continuous films of well‐aligned, individualized, semiconducting nanotubes. Polymer‐wrapped nanotubes in organic ink are forced through sub‐mm tall channels, generating shear up to 10 000 s−1uniformly aligning nanotubes across substrates. The ink volume and concentration, channel height, and shear rate dependencies are elucidated. Optimized conditions enable alignment within a ±32° window, at 50 nanotubes µm−1, on 10 × 10 cm2substrates. Transistors (channel length of 1–5 µm) are fabricated parallel and perpendicular to the alignment. The parallel transistors perform with 7× faster charge carrier mobility (101 and 49 cm2V−1s−1assuming array and parallel‐plate capacitances, respectively) with high on/off ratio of 105. The spatial uniformity varies ±10% in density, ±2° in alignment, and ±7% in mobility. Deposition occurs within seconds per wafer, and further substrate scaling is viable. Compared to random networks, aligned nanotube films promise to be a superior platform for applications including sensors, flexible/stretchable electronics, and light emitting and harvesting devices.

    more » « less
  3. Abstract

    Solution‐processable organic semiconductors can serve as the basis for new products including rollable displays, tattoo‐like smart bandages for real‐time health monitoring, and conformable electronics integrated into clothing or even implanted in the human body. For such exciting commercial applications to become a reality, good device performance and uniformity over large areas are necessary. The design of new materials has progressed at an astonishing pace, but accessing their intrinsic, efficient electrical properties in large‐area flexible device arrays is difficult. The development of protocols that allow integration with industrial‐scale processing for high‐throughput manufacturing, without the need to compromise on performance, is the key for transitioning these materials to real‐life applications. In this work, large‐area arrays of organic thin‐film transistors obtained by spray‐coating the high‐mobility polymer indacenodithiophene‐co‐benzothiadiazole (IDTBT) are demonstrated. A maximum charge carrier mobility of 2.3 cm2V−1s−1, with a very narrow performance distribution, is obtained over surface areas of 10 cm × 10 cm. The devices retain their electrical properties when bent multiple times and at different curvatures. In addition, large arrays of highly sensitive (0.25% change in mobility for 1% humidity variation), reusable, near‐identical humidity sensors are produced in a one‐step fabrication and calibrated from 0% to 94% relative humidity.

    more » « less
  4. Metal oxide (MO) semiconductor thin films prepared from solution typically require multiple hours of thermal annealing to achieve optimal lattice densification, efficient charge transport, and stable device operation, presenting a major barrier to roll-to-roll manufacturing. Here, we report a highly efficient, cofuel-assisted scalable combustion blade-coating (CBC) process for MO film growth, which involves introducing both a fluorinated fuel and a preannealing step to remove deleterious organic contaminants and promote complete combustion. Ultrafast reaction and metal–oxygen–metal (M-O-M) lattice condensation then occur within 10–60 s at 200–350 °C for representative MO semiconductor [indium oxide (In2O3), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO)] and dielectric [aluminum oxide (Al2O3)] films. Thus, wafer-scale CBC fabrication of IGZO-Al2O3thin-film transistors (TFTs) (60-s annealing) with field-effect mobilities as high as ∼25 cm2V−1s−1and negligible threshold voltage deterioration in a demanding 4,000-s bias stress test are realized. Combined with polymer dielectrics, the CBC-derived IGZO TFTs on polyimide substrates exhibit high flexibility when bent to a 3-mm radius, with performance bending stability over 1,000 cycles.

    more » « less
  5. Abstract

    In the field of optical imaging, the ability to image tumors at depth with high selectivity and specificity remains a challenge. Surface enhanced resonance Raman scattering (SERRS) nanoparticles (NPs) can be employed as image contrast agents to specifically target cells in vivo; however, this technique typically requires time-intensive point-by-point acquisition of Raman spectra. Here, we combine the use of “spatially offset Raman spectroscopy” (SORS) with that of SERRS in a technique known as “surface enhanced spatially offset resonance Raman spectroscopy” (SESORRS) to image deep-seated tumors in vivo. Additionally, by accounting for the laser spot size, we report an experimental approach for detecting both the bulk tumor, subsequent delineation of tumor margins at high speed, and the identification of a deeper secondary region of interest with fewer measurements than are typically applied. To enhance light collection efficiency, four modifications were made to a previously described custom-built SORS system. Specifically, the following parameters were increased: (i) the numerical aperture (NA) of the lens, from 0.2 to 0.34; (ii) the working distance of the probe, from 9 mm to 40 mm; (iii) the NA of the fiber, from 0.2 to 0.34; and (iv) the fiber diameter, from 100 µm to 400 µm. To calculate the sampling frequency, which refers to the number of data point spectra obtained for each image, we considered the laser spot size of the elliptical beam (6 × 4 mm). Using SERRS contrast agents, we performed in vivo SESORRS imaging on a GL261-Luc mouse model of glioblastoma at four distinct sampling frequencies: par-sampling frequency (12 data points collected), and over-frequency sampling by factors of 2 (35 data points collected), 5 (176 data points collected), and 10 (651 data points collected). In comparison to the previously reported SORS system, the modified SORS instrument showed a 300% improvement in signal-to-noise ratios (SNR). The results demonstrate the ability to acquire distinct Raman spectra from deep-seated glioblastomas in mice through the skull using a low power density (6.5 mW/mm2) and 30-times shorter integration times than a previous report (0.5 s versus 15 s). The ability to map the whole head of the mouse and determine a specific region of interest using as few as 12 spectra (6 s total acquisition time) is achieved. Subsequent use of a higher sampling frequency demonstrates it is possible to delineate the tumor margins in the region of interest with greater certainty. In addition, SESORRS images indicate the emergence of a secondary tumor region deeper within the brain in agreement with MRI and H&E staining. In comparison to traditional Raman imaging approaches, this approach enables improvements in the detection of deep-seated tumors in vivo through depths of several millimeters due to improvements in SNR, spectral resolution, and depth acquisition. This approach offers an opportunity to navigate larger areas of tissues in shorter time frames than previously reported, identify regions of interest, and then image the same area with greater resolution using a higher sampling frequency. Moreover, using a SESORRS approach, we demonstrate that it is possible to detect secondary, deeper-seated lesions through the intact skull.

    more » « less