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(1 - 8 of 8)
- Title
- Ultrafast lattice dynamics in lead selenide quantum dot induced by laser excitation.
- Creator
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Wang, Xuan, Rahmani, Hamidreza, Zhou, Jun, Gorfien, Matthew, Plaskus, Joshua Mendez, Li, Dong, Voss, Ryan, Nelson, Cory A., Lei, Kin Wai, Wolcott, Abraham, Zhu, Xiaoyang, Li,...
Show moreWang, Xuan, Rahmani, Hamidreza, Zhou, Jun, Gorfien, Matthew, Plaskus, Joshua Mendez, Li, Dong, Voss, Ryan, Nelson, Cory A., Lei, Kin Wai, Wolcott, Abraham, Zhu, Xiaoyang, Li, Junjie, Cao, Jianming
Show less - Abstract/Description
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We directly monitored the lattice dynamics in PbSe quantum dots (QD) induced by laser excitation using ultrafast electron diffraction. The energy relaxation between the carriers and the lattice took place within 10 ps, showing no evidence of any significant phonon bottleneck effect. Meanwhile, the lattice dilation exhibited some unusual features that could not be explained by the available mechanisms of photon-induced acoustic vibrations in semiconductors alone. The heat transport between the...
Show moreWe directly monitored the lattice dynamics in PbSe quantum dots (QD) induced by laser excitation using ultrafast electron diffraction. The energy relaxation between the carriers and the lattice took place within 10 ps, showing no evidence of any significant phonon bottleneck effect. Meanwhile, the lattice dilation exhibited some unusual features that could not be explained by the available mechanisms of photon-induced acoustic vibrations in semiconductors alone. The heat transport between the QDs and the substrate deviates significantly from Fourier's Law, which opens questions about the heat transfer under nonequilibrium conditions in nanoscale materials. Published by AIP Publishing.
Show less - Date Issued
- 2016-10-10
- Identifier
- FSU_libsubv1_wos_000386534800044, 10.1063/1.4964269
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- Citation
- Title
- Geometric dependence of transport and universal behavior in three dimensional carbon nanostructures.
- Creator
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Wang, Leizhi, Yin, Ming, Jaroszynski, Jan, Park, Ju-Hyun, Mbamalu, Godwin, Datta, Timir
- Abstract/Description
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Carbon nanostructures with the spherical voids exhibit interesting temperature and magnetic field dependent transport properties. By increasing the void size, the structures are tuned from metallic to insulating; in addition, the magnetoresistance (MR) is enhanced. Our investigation in the magnetic fields (B) up to 18 T at temperatures (T) from 250 mK to 20K shows that at high temperatures (T>2 K), the MR crosses over from quadratic to a non-saturating linear dependence with increasing...
Show moreCarbon nanostructures with the spherical voids exhibit interesting temperature and magnetic field dependent transport properties. By increasing the void size, the structures are tuned from metallic to insulating; in addition, the magnetoresistance (MR) is enhanced. Our investigation in the magnetic fields (B) up to 18 T at temperatures (T) from 250 mK to 20K shows that at high temperatures (T>2 K), the MR crosses over from quadratic to a non-saturating linear dependence with increasing magnetic field. Furthermore, all MR data in this temperature regime collapse onto a single curve as a universal function of B/T, following Kohler's rule. Remarkably, the MR also exhibits orientation insensitivity, i.e., it displays a response independent of the direction on the magnetic field. Published by AIP Publishing.
Show less - Date Issued
- 2016-09-19
- Identifier
- FSU_libsubv1_wos_000384558700054, 10.1063/1.4963261
- Format
- Citation
- Title
- Persistent-current switch for pancake coils of rare earth-barium-copper-oxide high-temperature superconductor: Design and test results of a double-pancake coil operated in liquid nitrogen (77-65 K) and in solid nitrogen (60-57 K).
- Creator
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Qu, Timing, Michael, Philip C., Voccio, John, Bascunan, Juan, Hahn, Seungyong, Iwasa, Yukikazu
- Abstract/Description
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We present design and test results of a superconducting persistent current switch (PCS) for pancake coils of rare-earth-barium-copper-oxide, REBCO, high-temperature superconductor (HTS). Here, a REBCO double-pancake (DP) coil, 152-mm ID, 168-mm OD, 12-mm high, was wound with a no-insulation technique. We converted a similar to 10-cm long section in the outermost layer of each pancake to a PCS. The DP coil was operated in liquid nitrogen (77-65 K) and in solid nitrogen (60-57 K). Over the...
Show moreWe present design and test results of a superconducting persistent current switch (PCS) for pancake coils of rare-earth-barium-copper-oxide, REBCO, high-temperature superconductor (HTS). Here, a REBCO double-pancake (DP) coil, 152-mm ID, 168-mm OD, 12-mm high, was wound with a no-insulation technique. We converted a similar to 10-cm long section in the outermost layer of each pancake to a PCS. The DP coil was operated in liquid nitrogen (77-65 K) and in solid nitrogen (60-57 K). Over the operating temperature ranges of this experiment, the normal-state PCS enabled the DP coil to be energized; thereupon, the PCS resumed the superconducting state and the DP coil field decayed with a time constant of 100 h, which would have been nearly infinite, i.e., persistent-mode operation, were the joint across the coil terminals superconducting. Published by AIP Publishing.
Show less - Date Issued
- 2016-08-22
- Identifier
- FSU_libsubv1_wos_000383849000032, 10.1063/1.4961622
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- Citation
- Title
- Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material.
- Creator
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Li, Junjie, Wang, Xuan, Zhou, Haidong, Zhou, Jun, Cheng, J. G., Cao, Jianming
- Abstract/Description
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We report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. The fast process is designated as the initial...
Show moreWe report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. The fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. The slow process is attributed to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites. Published by AIP Publishing.
Show less - Date Issued
- 2016-07-25
- Identifier
- FSU_libsubv1_wos_000381688900016, 10.1063/1.4960100
- Format
- Citation
- Title
- Magnetic-field-induced changes in superparamagnetic cluster dynamics in the martensitic phase of Ni43Co7Mn40Sn10.
- Creator
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Kuhns, P. L., Hoch, M. J. R., Yuan, S., Reyes, A. P., Srivastava, V., James, R. D., Leighton, C.
- Abstract/Description
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The off-stoichiometric Heusler alloys, such as Ni50Mn25+yX25-y (X = Sn, In, Ga, etc.), have been extensively investigated using a variety of experimental techniques to probe their interesting and potentially useful magnetic properties. Recent Mn-55 nuclear magnetic resonance (NMR) experiments, carried out largely in zero field (ZF) and making use of the large internal hyperfine field at the nuclear sites, have demonstrated the power of this approach in determining the ground state magnetic...
Show moreThe off-stoichiometric Heusler alloys, such as Ni50Mn25+yX25-y (X = Sn, In, Ga, etc.), have been extensively investigated using a variety of experimental techniques to probe their interesting and potentially useful magnetic properties. Recent Mn-55 nuclear magnetic resonance (NMR) experiments, carried out largely in zero field (ZF) and making use of the large internal hyperfine field at the nuclear sites, have demonstrated the power of this approach in determining the ground state magnetic characteristics of these materials. In particular, the results reveal that distinct nanoscale ferromagnetic and antiferromagnetic phases coexist. A key parameter used in interpreting the NMR data is the transverse relaxation time T-2 which, inter alia, determines the NMR blocking temperature T-B(NMR) of magnetic regions. The present experiments on a polycrystalline sample of a specific illustrative alloy, Ni43Co7Mn40Sn10, which has received considerable attention, show that the application of relatively small external fields, comparable to or greater than the local anisotropy field in the ferromagnetic cluster regions, produces dramatic changes in T-2 and hence T-B(NMR). The experimental findings are discussed using an extended version of a recently proposed nanocluster model for superparamagnetic systems. It is demonstrated that the field and temperature induced changes in T-2 provide a significant test of the model and lead to a notable advance in applying the NMR technique to the investigation of the magnetic properties of this type of alloy. Published by AIP Publishing.
Show less - Date Issued
- 2016-06-20
- Identifier
- FSU_libsubv1_wos_000379039900023, 10.1063/1.4954732
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- Citation
- Title
- Gate-modulated conductance of few-layer WSe2 field-effect transistors in the subgap regime.
- Creator
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Wang, Junjie, Rhodes, Daniel, Feng, Simin, Nguyen, Minh An T., Watanabe, K., Taniguchi, T., Mallouk, Thomas E., Terrones, Mauricio, Balicas, Luis, Zhu, J.
- Date Issued
- 2016-02-08
- Identifier
- FSU_libsubv1_wos_000373056300060, 10.1063/1.4941993
- Format
- Citation
- Title
- Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn.
- Creator
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Tarantini, C., Sung, Z.-H., Lee, P. J., Ghosh, A. K., Larbalestier, D. C.
- Abstract/Description
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Nb3Sn wire is now very close to its final optimization, but despite its classical nature, a detailed understanding of the role of Ta and Ti doping in the A15 is not fully developed. Long thought to be essentially equivalent in their influence on H-c2, they were interchangeably applied. Here, we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher T-c onset in zero-field, they always have a wider T-c...
Show moreNb3Sn wire is now very close to its final optimization, but despite its classical nature, a detailed understanding of the role of Ta and Ti doping in the A15 is not fully developed. Long thought to be essentially equivalent in their influence on H-c2, they were interchangeably applied. Here, we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher T-c onset in zero-field, they always have a wider T-c-distribution. In particular, whereas the Ta-doped A15 has a T-c-distribution extending from 18 down to 5-6 K (the lowest expected T-c for the binary A15 phase), the Ti-doped samples have no A15 phase with T-c below similar to 12 K. The much narrower T-c distribution in the Ti-doped samples has a positive effect on their in-field T-c-distribution too, leading to an extrapolated mu H-0(c2)(0) 2 T larger than the Ta-doped wire. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high J(c) conductors. The enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase. (C) 2016 AIP Publishing LLC.
Show less - Date Issued
- 2016-01-25
- Identifier
- FSU_libsubv1_wos_000375217200044, 10.1063/1.4940726
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- Citation
- Title
- Micro-architecture Embedding Ultra-thin Interlayer To Bond Diamond And Silicon Via Direct Fusion.
- Creator
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Kim, Jong Cheol, Kim, Jongsik, Xin, Yan, Lee, Jinhyung, Kim, Young-Gyun, Subhash, Ghatu, Singh, Rajiv K., Arjunan, Arul C., Lee, Haigun
- Abstract/Description
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The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus...
Show moreThe continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (similar to 3 nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry. Published by AIP Publishing.
Show less - Date Issued
- 2018-05-21
- Identifier
- FSU_libsubv1_wos_000433140900009, 10.1063/1.5030580
- Format
- Citation
