Correlation between surface tension and fatigue properties of Ti-6Al-4V alloy fabricated by EBM additive manufacturing

Choi, Youngsin,Lee, Dong-Geun Elsevier BV * North-Holland 2019 Applied Surface Science Vol.481 No.-

<P><B>Abstract</B></P> <P>The powder bed fusion method using a heat source for 3D printing can be applied to fabricate the geometrical shapes of some parts, and enables rapid melting and cooling. 3D EBM additive manufacturing can supply a near-net-shape or net-shape and precise parts better than micro scale casting and precision casting. Casting parts have residual stress in the matrix and their microstructure, which can affect the dynamic properties, but if they are heat-treated under the optimal conditions, the residual stress can be reduced to enhance the dynamic-mechanical properties of 3D printed parts. In this study, Ti-6Al-4V bulk bars were fabricated by EBM additive manufacturing, and the microstructures, residual stress, and various interior defects of the specimens were analyzed. The residual stress and surface tension were measured and calculated in different specimens heat-treated at 850–950 °C. The relationship between the residual stress and surface tension was explained using the related equations and the influence on the high cycle fatigue properties was evaluated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> AM parts with residual stress and surface tension </LI> <LI> Influences of post treatment on residual stress and fatigue properties </LI> </UL> </P>

Linear analysis of signal and noise characteristics of a nonlinear CMOS active-pixel detector for mammography

Yun, Seungman,Kim, Ho Kyung,Han, Jong Chul,Kam, Soohwa,Youn, Hanbean,Cunningham, Ian A. Elsevier BV * North-Holland 2017 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>The imaging properties of a complementary metal-oxide-semiconductor (CMOS) active-pixel photodiode array coupled to a thin gadolinium-based granular phosphor screen with a fiber-optic faceplate are investigated. It is shown that this system has a nonlinear response at low detector exposure levels (<10mR), resulting in an over-estimation of the detective quantum efficiency (DQE) by a factor of two in some cases. Errors in performance metrics on this scale make it difficult to compare new technologies with established systems and predict performance benchmarks that can be achieved in practice and help understand performance bottlenecks. It is shown the CMOS response is described by a power-law model that can be used to linearize image data. Linearization removed an unexpected dependence of the DQE on detector exposure level.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A nonlinear response of a CMOS detector at low exposure levels can overestimate DQE. </LI> <LI> A power-law form can model the response of a CMOS detector at low exposure levels, and can be used to linearize image data. </LI> <LI> Performance evaluation of nonlinear imaging systems must incorporate adequate linearizations. </LI> </UL> </P>

Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature

Park, J.W.,Kim, E.S.,Kim, J.U.,Kim, Y.,Windes, W.E. Elsevier BV * North-Holland 2016 Applied Surface Science Vol.378 No.-

The potential of reducing the oxidation of the supporting graphite components during normal and/or accident conditions in the Very High Temperature Reactor (VHTR) design has been studied. In this work efforts have been made to slow the oxidation process of the graphite with a thin SiC coating (~10μm). Upon heating at≥1173K in air, the spallations and cracks were formed in the dense columnar structured SiC coating layer grown on the graphite with a functionally gradient electron beam physical vapor deposition (EB-PVD. In accordance with the formations of these defects, the sample was vigorously oxidized, leaving only the SiC coating layer. Then, efforts were made to heal the surface defects using additional EB-PVD with ion beam bombardment and chemical vapor deposition (CVD). The EB-PVD did not effectively heal the cracks. But, the CVD was more appropriate for crack healing, likely due to its excellent crack line filling capability with a high density and high aspect ratio. It took~34min for the 20% weight loss of the CVD crack healed sample in the oxidation test with annealing at 1173K, while it took~8min for the EB-PVD coated sample, which means it took ~4 times longer at 1173K for the same weight reduction in this experimental set-up.

Electrical bistabilities and memory mechanisms of nonvolatile organic bistable devices based on exfoliated muscovite-type mica nanoparticle/poly(methylmethacrylate) nanocomposites

Lim, Won Gyu,Lee, Dea Uk,Na, Han Gil,Kim, Hyoun Woo,Kim, Tae Whan Elsevier BV * North-Holland 2018 Applied Surface Science Vol.432 No.2

<P><B>Abstract</B></P> <P>Organic bistable devices (OBDs) with exfoliated mica nanoparticles (NPs) embedded into an insulating poly(methylmethacrylate) (PMMA) layer were fabricated by using a spin-coating method. Current–voltage (I–V) curves for the Al/PMMA/exfoliated mica NP/PMMA/indium-tin-oxide/glass devices at 300K showed a clockwise current hysteresis behavior due to the existence of the exfoliated muscovite-type mica NPs, which is an essential feature for bistable devices. Write-read-erase-read data showed that the OBDs had rewritable nonvolatile memories and an endurance number of ON/OFF switching for the OBDs of 10<SUP>2</SUP> cycles. An ON/OFF ratio of 1×10<SUP>3</SUP> was maintained for retention times larger than 1×10<SUP>4</SUP> s. The memory mechanisms of the fabricated OBDs were described by using the trapping and the tunneling processes within a PMMA active layer containing exfoliated muscovite-type mica NPs on the basis of the energy band diagram and the I–V curves.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organic bistable devices (OBDs) with exfoliated mica NPs embedded into an insulating PMMA layer were fabricated. </LI> <LI> Current–voltage curves for the devices showed a bistability with an ON/OFF ratio of 1×10<SUP>3</SUP>. </LI> <LI> ON and the OFF states for the devices endured for 10<SUP>2</SUP> cycles. </LI> <LI> ON/OFF ratio of 1×10<SUP>3</SUP> was maintained for retention times larger than 1×10<SUP>4</SUP> s. </LI> <LI> Memory mechanisms for the devices were attributed to the F-N tunneling process. </LI> </UL> </P>

The neutralino sector in the U(1)-extended supersymmetric Standard Model

Choi, S.Y.,Haber, H.E.,Kalinowski, J.,Zerwas, P.M. Elsevier BV * North-Holland 2007 Nuclear Physics, Section B Vol.778 No.1-2

Motivated by grand unified theories and string theories we analyze the general structure of the neutralino sector in the USSM, an extension of the minimal supersymmetric Standard Model that involves a broken extra U(1) gauge symmetry. This supersymmetric U(1)-extended model includes an Abelian gauge superfield and a Higgs singlet superfield in addition to the standard gauge and Higgs superfields of the MSSM. The interactions between the MSSM fields and the new fields are in general weak and the mixing is small, so that the coupling of the two subsystems can be treated perturbatively. As a result, the mass spectrum and mixing matrix in the neutralino sector can be analyzed analytically and the structure of this 6-state system is under good theoretical control. We describe the decay modes of the new states and the impact of this extension on decays of the original MSSM neutralinos, including radiative transitions in cross-over zones. Production channels in cascade decays at the LHC and pair production at e<SUP>+</SUP>e<SUP>-</SUP> colliders are also discussed.

Crystalline beryllium oxide on Si (100) deposited using E-beam evaporator and thermal oxidation

Yoon, Seonno,Lee, Seung Min,Yum, Jung Hwan,Bielawski, Christopher W.,Lee, Hi-Deok,Oh, Jungwoo Elsevier BV * North-Holland 2019 Applied Surface Science Vol.479 No.-

<P><B>Abstract</B></P> <P>The growth characteristics and electrical properties of thin films of crystalline beryllium oxide (BeO) on Si (100) substrates grown using electron beam evaporation (EBE) are described. To expand the commercial viability of BeO, a combination of EBE with thermal oxidation was optimized to facilitate its use in nanoscale semiconductor devices. The surfaces of the EBE BeO films were found to be smooth with limited quantities of native oxides or metal silicates, as determined using atomic force measurements and X-ray photoelectron spectroscopy, respectively. Moreover, high-resolution transmission electron microscopy revealed that the films were highly crystalline. Excellent insulator properties, including a dielectric constant of 6.77 and a breakdown voltage of 8.3 MV/cm, were deduced from a series of capacitance–voltage and leakage current measurements. Reflection electron energy loss spectroscopy and ultraviolet photoelectron spectroscopy indicated that the films exhibited a high band gap of 8.6 eV and a high conduction band offset of 3.43 eV. Collectively, these results indicate that EBE BeO films hold promise for use as electrical insulators in Si CMOS and nanoscale device applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Crystalline BeO film on Si (100) was deposited using E-beam evaporator and thermal oxidation. </LI> <LI> Excellent insulator properties, including a dielectric constant of 6.77 and a breakdown voltage of 8.3 MV/cm were deduced. </LI> <LI> Band alignment of EBE BeO/Si was analyzed by REELS and UPS. </LI> <LI> BeO/Si exhibits a very high CBO value (3.43 eV). </LI> <LI> Physical details of the band structure provide a good basis for applying EBE BeO to Si(100) MOSFETs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Characteristics of fabricated si PIN-type radiation detectors on cooling temperature

Kim, Han Soo,Jeong, Manhee,Kim, Young Soo,Lee, Dong Hun,Cho, Seung Yeon,Ha, Jang Ho Elsevier BV * North-Holland 2015 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>Si PIN photodiode radiation detectors with three different active areas (3×3mm<SUP>2</SUP>, 5×5mm<SUP>2</SUP>, and 10×10mm<SUP>2</SUP>) were designed and fabricated at the Korea Atomic Energy Research Institute (KAERI) for low energy X- and gamma-ray detection. In Si-based semiconductor radiation detectors, one of the noise sources is thermal noise, which degrades their energy resolution performance. In this study, the temperature effects on the energy resolution were investigated using a 3×3mm<SUP>2</SUP> active area PIN photodiode radiation detector using a Thermoelectric Module (TEM) from room temperature to −23°C. Energy resolutions from 25keV auger electrons to 81keV gamma-ray from a Ba-133 calibration source were measured and compared at every 10°C interval. At −23°C, energy resolutions were improved by 15.6% at 25keV, 4.0% at 31keV, and 1.2% at 81keV in comparison with resolutions at room temperature. CsI(Tl)/PIN photodiode radiation detectors were also fabricated for relatively high energy gamma-ray detection. Energy resolutions for Cs-137, Co-60, and Na-22 sources were measured and compared with the spectral responsivity.</P>

Improvement in interfacial characteristics of low-voltage carbon nanotube thin-film transistors with solution-processed boron nitride thin films

Jeon, Jun-Young,Ha, Tae-Jun Elsevier BV * North-Holland 2017 Applied Surface Science Vol.413 No.-

<P><B>Abstract</B></P> <P>In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We demonstrate the potential of solution-processed boron nitride (BN) thin films for nanoelectronics. </LI> <LI> Improved interfacial characteristics reduced the leakage current by three orders of magnitude. </LI> <LI> The BN encapsulation improves all the device key metrics of low-voltage SWCNT-TFTs. </LI> <LI> Such improvements were achieved by reduced interaction of interfacial localized states. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Flipped SU(5) from Z_12-I orbifold with Wilson line

Kim, J.E.,Kyae, B. Elsevier BV * North-Holland 2007 Nuclear Physics, Section B Vol.770 No.1-2

We construct a three family flipped SU(5) model from the heterotic string theory compactified on the Z<SUB>12-I</SUB> orbifold with one Wilson line. The gauge group is SU(5)xU(1)<SUB>X</SUB>xU(1)<SUP>3</SUP>x[SU(2)xSO(10)xU(1)<SUP>2</SUP>]<SUP>'</SUP>. This model does not derive any non-Abelian group except SU(5) from E<SUB>8</SUB>, which is possible only for two cases in case of one shift V, one in Z<SUB>12-I</SUB> and the other in Z<SUB>12-II</SUB>. We present all possible Yukawa couplings. We place the third quark family in the twisted sectors and two light quark families in the untwisted sector. From the Yukawa couplings, the model provides the R-parity, the doublet-triplet splitting, and one pair of Higgs doublets. It is also shown that quark and lepton mixings are possible. So far we have not encountered a serious phenomenological problem. There exist vector-like flavor SU(5) exotics (including Q<SUB>em</SUB>=+/-16 color exotics and Q<SUB>em</SUB>=+/-12 electromagnetic exotics) and SU(5) vector-like singlet exotics with Q<SUB>em</SUB>=+/-12 which can be removed near the GUT scale. In this model, sin<SUP>2</SUP>θ<SUB>W</SUB><SUP>0</SUP>=38 at the full unification scale.

Evaluation of high grid strip densities based on the moiré artifact analysis for quality assurance: Simulation and experiment

Je, U.K.,Park, C.K.,Lim, H.W.,Cho, H.S.,Lee, D.Y.,Lee, H.W.,Kim, K.S.,Park, S.Y.,Kim, G.A.,Kang, S.Y.,Park, J.E.,Kim, W.S.,Jeon, D.H.,Woo, T.H. Elsevier BV * North-Holland 2017 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>We have recently developed precise x-ray grids having strip densities in the range of 100 – 250 lines/inch by adopting the precision sawing process and carbon interspace material for the demands of specific x-ray imaging techniques. However, quality assurance in the grid manufacturing has not yet satisfactorily conducted because grid strips of a high strip density are often invisible through an x-ray nondestructive testing with a flat-panel detector of an ordinary pixel resolution (>100 μ m). In this work, we propose a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. We performed a systematic simulation and experiment with several sample grids and a detector having a 143- μ m pixel resolution to verify the proposed quality assurance method. According to our results, the relative differences between the nominal and the evaluated grid strip densities were within 0.2% and 1.8% in the simulation and experiment, respectively, which demonstrates that the proposed method is viable with an ordinary detector having a moderate pixel resolution for quality assurance in grid manufacturing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The precise carbon-interspaced antiscatter grids have been studied. </LI> <LI> It is proposed for a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. </LI> <LI> The simulation and experimental results demonstrate that the proposed method is viable with an ordinary detector having a moderate pixel resolution (>100 μ m) for quality assurance in grid manufacturing. </LI> </UL> </P>