Eungman Lee

Plasmonic nano lithography with a high scan speed contact probe

We demonstrate plasmonic lithography with an optical contact probe to achieve high speed patterning without external gap distance control between the probe and the photoresist. The bottom surface of the probe is covered with a 10 nm thickness silica glass film for the gap distance control and coated with self-assembled monolayer (SAM) to reduce friction between the probe and the photoresist. We achieve a patterning resolution of ~50 nm and a patterning speed of ~10 mm/s. We obtain the quality of line patterning comparable to that in conventional optical lithography.

Stabilization of p21 (Cip1/WAF1) following Tip60-dependent acetylation is required for p21-mediated DNA damage response

The molecular mechanisms controlling post-translational modifications of p21 have been pursued assiduously in recent years. Here, utilizing mass-spectrometry analysis and site-specific acetyl-p21 antibody, two lysine residues of p21, located at amino-acid sites 161 and 163, were identified as Tip60-mediated acetylation targets for the first time. Detection of adriamycin-induced p21 acetylation, which disappeared after Tip60 depletion with concomitant destabilization of p21 and disruption of G1 arrest, suggested that Tip60-mediated p21 acetylation is necessary for DNA damage-induced cell-cycle regulation. The ability of 2KQ, a mimetic of acetylated p21, to induce cell-cycle arrest and senescence was significantly enhanced in p21 null MEFs compared with those of cells expressing wild-type p21. Together, these observations demonstrate that Tip60-mediated p21 acetylation is a novel and essential regulatory process required for p21-dependent DNA damage-induced cell-cycle arrest.

The effect of photoresist contrast on the exposure profiles obtained with evanescent fields of nanoapertures

We propose a simple theoretical model to predict the exposure profiles of a photoresist obtained with evanescent fields of nanoapertures. Assuming the electric field intensity to be a Gaussian distribution function with an exponential decay, the top critical dimension and the depth of the photoresist profile are described with analytic formulas. The profiles are analyzed as a function of the photoresist contrast and the electric field intensity decay length.

Wave propagation characteristics of a figure-eight shaped nanoaperture

Wave propagation characteristics of apertures were analyzed to explain the light transmission of metallic nanoapertures. Based on Maxwell’s equations, the wave dispersion relations of wave propagation modes in nanoapertures were derived. The resonance frequency shift of the aperture and the variation of the spot size are explained with the dispersion relations. The relationship between near-field and far-field light transmission power throughput and spot size is also shown with the wave mode change predicted by the dispersion relations.

SU-F-T-294: The Analysis of Gamma Criteria for Delta4 Dosimetry Using Statistical Process Control

PURPOSE To evaluate the sensitivity of gamma criteria for patient-specific volumetric modulated arc therapy(VMAT) quality assurance of the Delta4 dosimetry program using the statistical process control(SPC) methodology. METHODS The authors selected 20 patient-specific VMAT QA cases which were undertaken MapCHECK and ArcCHECK with gamma pass rate better than 97%. The QAs data were collected Delta4 Phantom+ and Elekta Agility six megavolts without using an angle incrementer. The gamma index(GI) were calculated in 2D planes with normalizing deviation to local dose(local gamma). The sensitivity of the GI methodology using criterion of 3%/3mm, 3%/2mm and 2%/3mm was analyzed with using process acceptability indices. We used local confidence(LC) level, the upper control limit(UCL) and lower control limit(LCL) of I-MR chart for process capability index(Cp) and a process acceptability index (Cpk). RESULTS The lower local confidence levels of 3%/3mm, 3%/2mm and 2%/3mm were 92.0%, 83.6% and 78.8% respectively. All of the calculated Cp and Cpk values that used LC level were under 1.0 in this study. The calculated LCLs of I-MR charts were 89.5%, 79.0% and 70.5% respectively. These values were higher than 1.0 which means good quality of QA. For the generally used lower limit of 90%, we acquired over 1.3 of Cp value for the gamma index of 3%/3mm and lower than 1.0 in the rest of GI. CONCLUSION We applied SPC methodology to evaluate the sensitivity of gamma criteria and could see the lower control limits of VMAT QA for the Delta 4 dosimetry and could see that Delta 4 phantom+ dosimetry more affected by the position error and the I-MR chart derived values are more suitable for establishing lower limits. Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (No. 2015R1D1A1A01060463).

SU-E-J-64: Feasibility Study of Surgical Clips for Fiducial Tracking in CyberKnife System

Purpose: To investigate the ability of CyberKnife to track surgical clips used as fiducial markers. Methods: The Octavius 1000SRS detector and solid water (RW3) slab phantom were used with motion platform to evaluate the study. The RW3 slab phantom was set up to measure the dose distribution from coronal plane. It consists of 9 plates and the thickness of each plate is 10mm. Among them, one plate was attached with 3 surgical clips, which are orthogonally positioned on outer region of array. The length of attached clip was represented as 1cm on planning CT. The clip plate was placed on the 1000SRS detector and 3 slabs were stacked up on the plate to build the measuring depth. Below the detector, 5 slabs were set. The two-axis motion platform was programmed with 1D sinusoidal movement (20mm peak-to-peak, 3s period) toward superior/inferior and left/right directions to simulate target motion. During delivery, two clips were extracted by two X-ray imagers, which led to translational error correction only. Synchrony was also used for dynamic tracking. After the irradiation, the measured dose distribution of coronal plane was compared with the planar dose distribution calculated by the CyberKnife treatment planning system (Multiplan) for cross verification. The results were assessed by comparing the absolute Gamma (γ) index. Results: The dose distributions measured by the 1000SRS detector were in good agreements with those calculated by Multiplan. In the dosimetric comparison using γ-function criteria based on the distance-to-agreement of 3mm and the local dose difference of 3%, the passing rate with γ- parameter ≤1 was 91% in coronal plane. Conclusion: The surgical clips can be considered as new fiducials for robotic radiosurgery delivery by considering the target margin with less than 5mm.

TU‐F‐CAMPUS‐I‐03: Enhancement of 4D CBCT Image Quality Using An Adaptive Prior Image Constrained Compressed Sensing

Purpose: To develop an iterative reconstruction algorithm using a compressed sensing with adaptive prior image constraints to solve 4D CBCT reconstruction problem. Methods: The images reconstructed by the FDK algorithm with a full set of unsorted projections are served as prior images for partial projections in each phase group and are utilized as an initial guess. Additionally, the prior images are clustered into several regions by applying intensity-based thresholding, which is referred to as the segmented prior images. The segmented prior images are employed to detect any possible mismatched areas compared with the target images generated by partial projection data. With these two prior images, our algorithm alternately performs the simultaneous algebraic reconstruction technique and anisotropic total variation regularization while adjusting a weighted relaxation map during the iterative reconstruction process. The weighted relaxation map depends on binary images created by the voxel-dependent comparison between the segmented prior and segmented target images. For the segmented target images, the k-means clustering with a geometric weighting is applied on the reconstruction images generated in each iteration step. The inverse values of the distance map converted from binary images are assigned to be the values of the relaxation map. Evaluations using Catphan504 phantom with a motion platform were carried out. Results: Qualitative and quantitative analyses showed that the method provides high-quality CBCT reconstruction images when compared with those generated by the FDK, CS, and PICCS algorithms, with higher contrast-to-noise ratio and faster convergence caused by minimizing data fidelity. Especially, the proposed method was superior to PICCS in the aspect of updating locally-mismatched region. Conclusion: The proposed method not only improves the image quality of 4D CBCT by adaptive updates during the reconstruction process, but also leads to a lower imaging dose and faster acquisition time by using a regular 3D CBCT scan.

Nano patterning with a single high-transmission nano-metal aperture system

We design a C-shaped aperture which overcomes the diffraction limit of light to produce a high-brightness nano-size light spot. For optical nano lithography, we construct a nano patterning system using an optical probe which adopts a solid immersion lens (SIL), the 120 nm thickness aluminum film on the bottom surface of the SIL and the C-shaped aperture engraved in the metal film. Light source is a diode laser of 405nm wavelength to expose h-line photoresist(PR). A linear stage holding the optical probe makes the nano aperture contact with the PR coated on silicon wafer. Using this patterning system, we obtain sub 100nm array patterns and measure the system performance in various exposure conditions to verify the feasibility of plasmonic lithography.

Design of metal slits for higher harmonic fringe patterns generated with surface plasmon interference lithography

In this paper, based on numerical study using the finite difference time domain method, we designed metal slits for higher harmonic fringe patterns generated with surface plasmon interference lithography. The slits were designed to generate higher fringe patterns having high intensity output, high contrast and good uniformity in sub-100nm scale. After fabricating several types of slits on aluminum film mask according to the calculated designs with a focused ion beam facility, lithography experiments using the aluminum slits were performed to record the near-filed fringe patterns using i-line Hg lamp and SU-8 negative photoresist.

Spectrally investigated optimization for high optical transmission of the C-shaped nano apertures

Due to the maturity of current laser technology, the limitation of empirical wavelengths of lasers useful for optical microlithography makes spectrally investigated optimization very important for the design of C-shaped nano apertures; in order to achieve high optical transmission as well as tight focusing, the resonant transmission of nano apertures depends on the incident lights wavelength. The optically propagating transmission through the nano aperture, determined by the effects of the propagating field and evanescent field, is also important in order to achieve deep patterning. High power throughput and decaying behaviors of propagating light through nano apertures depend on their resonance condition which is affected by geometric parameters and material properties as well as the wavelength of incident light. In this report, we analyze the spectral properties of resonant transmission of light through a C-shaped nano aperture in a metal film using a finite-difference time-domain (FDTD) simulation. These simulations may be helpful for the design of C-shaped nano apertures for high power throughput with tight focusing. Furthermore, we show that power dissipation of propagating light through the C-shaped nano aperture depends on metals.