We provide an overview of NIST efforts related to the development of optical medical imaging standards. Specifically, we introduce the planar NIST-certified standard reference material (SRM) appropriate for calibrating depth-resolving 3D optical systems such as optical coherent tomography. We also present the development of an optical measurement facility for the characterization of the optical properties of materials used in such standards such as an integrating sphere system for broadband measurements of the absorption coefficients and the reduced scattering coefficients of potential phantom materials. Lastly, we report on our progress toward the development of a realistic, validated 3D retinal eye phantom.
Metal oxide thin-film transistors (MOTFTs) are expected to play a vital role in enabling printed transparent, plastic electronics. Compatibility with plastics, however, requires MOTFTs to be scalably processed at low temperatures (T). Herein, we explore blade-coating of indium oxide (In2O3) TFTs via sol-gel and combustion chemistries. We find that the sol-gel process enables amorphous In2O3 TFTs at 200°C with moderate electronic mobility (ca. 1 cm2V-1s-1) which increases to 5 cm2V-1s-1 for 212°C. Combustion synthesis is found to bypass the electronically-active amorphous state leading to an early crystallization onset. Paradoxically, combustion TFTs are found to possess poor charge transport at low-T of 200-250°C. Early nucleation during combustion forms nanocrystalline domains that are deleterious to charge transport. Our results highlight that surprisingly it is not crystallization, rather the absence of it that is required to fabricate high-mobility, low-T bladed In2O3 TFTs.
We report on optics contamination rates induced by exposure to broad-bandwidth, high-intensity EUV radiation peaked
near 8 nm in a new beamline at the NIST synchrotron. The peak intensity of 50 mW/mm2 allows extension of previous
investigations of contamination by in-band 13.5 nm radiation at intensities an order of magnitude lower. We report nonlinear
pressure and intensity scaling of the contamination rates which is consistent with the earlier lower-intensity
studies. The magnitude of the contamination rate per unit EUV dose, however, was found to be significantly lower for
the lower wavelength exposures. We also report an apparent dose-dependent correlation between the thicknesses as
measured by spectroscopic ellipsometry and XPS for the carbon deposits created using the higher doses available on the
new beamline. It is proposed that this is due to different sensitivities of the metrologies to variations in the density of the
deposited C induced by prolonged EUV irradiation.
Before being used in an extreme-ultraviolet (EUV) scanner, photoresists must be qualified to
ensure that they will not excessively contaminate the scanner optics or other parts of the vacuum
environment of the scanner. At the National Institute of Standards and Technology we have
designed and constructed a high-throughput beamline on the Synchrotron Ultraviolet Radiation
Facility (SURF III) in order to provide data on the contamination potential of the outgas products
of a candidate resist by simultaneously irradiating a witness substrate and a nearby resist-coated
wafer with EUV radiation, the so called witness sample test that is currently the resist
qualification method required by ASML. We will present results from four sample resists that
were subjected to the test.
Although the witness-sample test based on irradiating the resist with EUV radiation at 13.5 nm
most closely reproduces conditions in a scanner, the limited availability of suitable EUV sources
to conduct such tests has led to development of an alternative method which uses e-beam
irradiation in place of EUV radiation. We will also present the results of a comparison of these
two methods.
We describe a null-field ellipsometric imaging system (NEIS) that provides for the real-time imaging of carbon
deposition profiles on extreme-ultraviolet (EUV) optics in a vacuum system. NEIS has been demonstrated at NIST on a
small chamber that is used for EUV optics lifetime testing. The system provides images of carbon deposition spots with
sub-nanometer resolution thickness measurements that maintain good agreement with those from ex-situ spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). The system will be implemented on several synchrotron beamlines for real-time monitoring of carbon film growth on optics during EUV irradiation.
The goal of our ongoing optics-contamination program is to estimate the magnitude and scaling laws of the
contamination rates of optics exposed to extreme-ultraviolet (EUV) radiation in the presence of various contaminant
species expected in the EUV-lithography-tool environment by exposing samples to in-band 13.5 nm light from our
synchrotron in the presence of fixed partial pressures of admitted gases. We report contamination rate measurements on
TiO2-capped samples for species observed in separate resist-outgassing measurements (benzene, isobutene, toluene and
tert-butylbenzene) in the pressure range (10-8 to 10-5) Pa. We use two spatially-resolved surface probe techniques,
spectroscopic ellipsometry and X-ray photoelectron spectroscopy, to determine the thickness of deposited carbon. The
correlation and sensitivities of these techniques are discussed. The high sensitivity of ellipsometry shows that
contamination rates for some species have a pronounced non-linear intensity dependence and can be strongly influenced
by admixtures of water vapor, while the rates for other species are linear over the same intensity range and are less
affected by ambient water. Understanding scaling laws is critical when estimating optic lifetimes or cleaning cycles by
extrapolating over the 3-to-6 orders of magnitude between accelerated-testing and tool-environment partial pressures.
Thermal embossing nanoimprint lithography (NIL) is an area of continuing interest because it allows direct patterning of nanoscale structures into a wide variety of functional polymer materials. Measuring the shape evolution of nanoimprinted lines during thermal annealing can provide insights into mechanisms of polymer stability and the dynamics of polymer flow. Recently, we have used optical scatterometry to extract the profile of nanoimprinted lines in low- and high-molecular mass polymer gratings during annealing of the gratings at the glass transition temperature. The data are obtained in situ using a spectroscopic ellipsometer and analyzed using a rigorous-coupled-wave scatterometry model. The results obtained from scatterometry are in very good agreement with those measured ex situ by atomic force microscopy and specular x-ray reflectivity, revealing very different decay mechanisms for gratings in low- and high-molecular mass polymers. The role of the selection of grating model in determining the uncertainties the grating line profile extracted from scatterometry is also discussed.
We investigate charge injection and transport in organic field-effect transistors fabricated by using poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) or poly(3-hexylthiophene) (P3HT) as the active polymer
layer. We show that in high mobility devices where the channel resistances are low compared to the contact resistances,
the device performance can be dominated by the metal/organic semiconductor (OSC) contacts. However, in sets of
devices where the channel resistance is dominant over the contacts (usually the lower mobility devices), we see
pronounced field dependence in the saturation regime mobilities consistent with a Poole-Frenkel model of charge
transport within the channel. The field-dependent mobility in short-channel devices produces nonlinear output current-voltage
characteristics which can be modeled consistently in the Poole-Frenkel framework.
Near-field Raman spectroscopy can be used to obtain images with both chemical specificity and the subwavelength spatial resolution of near-field scanning optical microscopy. In the absence of signal intensification factors, such as `surface enhancement' or electronic resonance in the specimen, Raman scattering suffers from a small cross section ((sigma) equals 10-28 cm2 to 10-31 cm2). Since most reports of Raman-NSOM to date involve exploitation of a specimen-specific intensification, an assessment of the general applicability of Raman-NSOM to a wider variety of `un-enhanced' samples is of great interest. We report here on several approaches to increasing the sensitivity of near- field Raman spectroscopy that do not rely on specimen properties. The use of chemically etched aperture probes as an illumination source has been investigated and compared to probes fabricated by the traditional heat and pull method.
KEYWORDS: Near field, Infrared radiation, Near field scanning optical microscopy, Infrared imaging, Spatial resolution, Near field optics, Microscopes, Gold, Silicon, Infrared microscopy
The development of a scanning near-field microscope that utilizes infrared absorption as the optical contrast mechanism is described. This instrument couples the nanoscale spatial resolution of a scanning probe microscope with the chemical specificity of vibrational spectroscopy. This combination allows the in situ mapping of chemical functional groups with subwavelength spatial resolution. Key elements of this infrared microscope include: a broadly tunable infrared light source producing ultrafast pulses with a FWHM bandwidth of 150 cm-1, an infrared focal plane array-based spectrometer which allows parallel detection of the entire pulse bandwidth with 8 cm-1 resolution, and a single mode fluoride glass fiber probe which supports transmission from 2200 to 4500 cm-1. A novel chemical etching protocol for the fabrication of near-field aperture probes is described. Infrared transmission images of a micropatterned thin gold film are presented that demonstrate spatial resolution of (lambda) /8 at 2900 cm-1, in the absence of artifacts due to topography induced contrast. Images of thin film polymer blends and nanocomposites acquired in the C-H stretching region are used to benchmark the chemical imaging capabilities of this microscope, focusing particularly on the absorption sensitivity of the spectrometer.
Vibrational spectra of biomimetic membranes have been obtained using a broad-band approach to sum frequency generation (SFG). A new innovation, broad band SFG (BBSFG) allows for high quality SFG spectra with rapid collection times. With the BBSFG approach, we have followed in situ the formation of a hybrid bilayer membrane from the reorganization of phospholipid vesicles at akanethiol monolayers.
KEYWORDS: Laser induced damage, Platinum, Metals, Data modeling, Chemical analysis, Molecules, Ions, Molecular lasers, Semiconductors, Chemical species
Laser induced molecular desorption which is mediated by optically generated substrate carriers is considered. State-specific diagnostics are combined with desorption-laser wavelength dependence studies to clarify the excitation and desorption dynamics involved. Results from NO desorption from both metallic and semiconductor substrates are presented, along with theoretical models of the desorption processes.
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