Topological Insulator State in Thin Bismuth Films Subjected to Plane Tensile Strain

NASA Astrophysics Data System (ADS)

Demidov, E. V.; Grabov, V. M.; Komarov, V. A.; Kablukova, N. S.; Krushel'nitskii, A. N.

2018-03-01

The results of experimental examination of galvanomagnetic properties of thin bismuth films subjected to plane tensile strain resulting from the difference in thermal expansion coefficients of the substrate material and bismuth are presented. The resistivity, the magnetoresistance, and the Hall coefficient were studied at temperatures ranging from 5 to 300 K in magnetic fields as strong as 0.65 T. Carrier densities were calculated. A considerable increase in carrier density in films thinner than 30 nm was observed. This suggests that surface states are more prominent in thin bismuth films on mica substrates, while the films themselves may exhibit the properties of a topological insulator.

A metal-insulator transition study of VO 2 thin films grown on sapphire substrates

DOE PAGES

Yu, Shifeng; Wang, Shuyu; Lu, Ming; ...

2017-12-15

In this paper, vanadium thin films were deposited on sapphire substrates by DC magnetron sputtering and then oxidized in a tube furnace filled with oxygen under different temperatures and oxygen flow rates. The significant influence of the oxygen flow rate and oxidation temperature on the electrical and structural properties of the vanadium oxide thin films were investigated systematically. It shows the pure vanadium dioxide (VO 2) state can only be obtained in a very narrow temperature and oxygen flow rate range. The resistivity change during the metal-insulator transition varies from 0.2 to 4 orders of magnitude depending on the oxidationmore » condition. Large thermal hysteresis during the metal-insulator phase transition was observed during the transition compared to the results in literature. Proper oxidation conditions can significantly reduce the thermal hysteresis. Finally, the fabricated VO 2 thin films showed the potential to be applied in the development of electrical sensors and other smart devices.« less

Enhancement on crystallinity property of low annealed PbTiO3 thin films for metal-insulator-metal capacitor

NASA Astrophysics Data System (ADS)

Nurbaya, Z.; Wahid, M. H.; Rozana, M. D.; Alrokayan, S. A. H.; Khan, H. A.; Rusop, M.

2018-05-01

This study presents the investigation on crystallinity property of PbTiO3 thin films towards metal-insulator-metal capacitor device fabrication. The preparation of the thin films utilizes sol-gel spin coating method with low annealing temperature effect. Hence, structural and electrical characterization is brought to justify the thin films consistency.

Metal-insulator transition in tin doped indium oxide (ITO) thin films: Quantum correction to the electrical conductivity

NASA Astrophysics Data System (ADS)

Kaushik, Deepak Kumar; Kumar, K. Uday; Subrahmanyam, A.

2017-01-01

Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films (prepared at 300 K and subsequently annealed at 673 K in vacuum for 60 minutes) in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (kFl˜1; kF is the Fermi wave vector and l is the electron mean free path) and degenerate semiconductors. The transport of charge carriers (electrons) in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well-known `metal-insulator transition' (MIT) which is observed at 110 K in these ITO thin films. The MIT in ITO thin films is explained by the quantum correction to the conductivity (QCC); this approach is based on the inclusion of quantum-mechanical interference effects in Boltzmann's expression of the conductivity of the disordered systems. The insulating behaviour observed in ITO thin films below the MIT temperature is attributed to the combined effect of the weak localization and the electron-electron interactions.

Outline and comparison of the possible effects present in a metal-thin-film-insulator-semiconductor solar cell

NASA Technical Reports Server (NTRS)

Fonash, S. J.

1976-01-01

The advantages possible with the insertion of a thin-film insulating or semi-insulating layer between a metal and a semiconductor to form the MIS photovoltaic device have been presented previously in the literature. This MIS configuration may be considered as a specific example of a more general class of photovoltaic devices: electrode-thin-film-insulator-semiconductor devices. Since the advantages of the configuration were pointed out, there has been considerable experimental interest in these photovoltaic devices. Because the previous analysis showed that the introduction of the insulator layer could produce several different but advantageous effects, this paper presents a further outline giving a comparison of these effects together with their ramifications.

Large Enhancement of Thermal Conductivity and Lorenz Number in Topological Insulator Thin Films.

PubMed

Luo, Zhe; Tian, Jifa; Huang, Shouyuan; Srinivasan, Mithun; Maassen, Jesse; Chen, Yong P; Xu, Xianfan

2018-02-27

Topological insulators (TI) have attracted extensive research effort due to their insulating bulk states but conducting surface states. However, investigation and understanding of thermal transport in topological insulators, particularly the effect of surface states, are lacking. In this work, we studied thickness-dependent in-plane thermal and electrical conductivity of Bi 2 Te 2 Se TI thin films. A large enhancement in both thermal and electrical conductivity was observed for films with thicknesses below 20 nm, which is attributed to the surface states and bulk-insulating nature of these films. Moreover, a surface Lorenz number much larger than the Sommerfeld value was found. Systematic transport measurements indicated that the Fermi surface is located near the charge neutrality point (CNP) when the film thickness is below 20 nm. Possible reasons for the large Lorenz number include electrical and thermal current decoupling in the surface state Dirac fluid, and bipolar diffusion transport. A simple computational model indicates that the surface states and bipolar diffusion indeed can lead to enhanced electrical and thermal transport and a large Lorenz number.

Photoinduced metal-to-insulator transition in a manganite thin film.

PubMed

Takubo, N; Onishi, I; Takubo, K; Mizokawa, T; Miyano, K

2008-10-24

A persistent photoinduced metal-to-insulator transition has been confirmed in a manganite thin film, Pr_(0.55)(Ca_(0.75)Sr_(0.25))_(0.45)MnO3, near a multicritical point by monitoring with transport measurements and x-ray photoemission spectroscopy. Together with the previously reported reverse effect, the photoinduced insulator-to-metal transition, it is found that the relative stability of the metallic and insulating phases interchanges around 80 K in the middle of a very wide hysteresis loop, which is a manifestation of the large potential barrier due to the long-range elastic energy. It is shown that photons are much more effective in overcoming the barrier via the electronically excited intermediate states than via the heat mode.

Metal-insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

NASA Astrophysics Data System (ADS)

Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

2016-06-01

We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal-insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

Metal-insulator transition characteristics of VO2 thin films grown on Ge(100) single crystals

NASA Astrophysics Data System (ADS)

Yang, Z.; Ko, C.; Ramanathan, S.

2010-10-01

Phase transitions exhibited by correlated oxides could be of potential relevance to the emerging field of oxide electronics. We report on the synthesis of high-quality VO2 thin films grown on single crystal Ge(100) substrates by physical vapor deposition and their metal-insulator transition (MIT) properties. Thermally triggered MIT is demonstrated with nearly three orders of magnitude resistance change across the MIT with transition temperatures of 67 °C (heating) and 61 °C (cooling). Voltage-triggered hysteretic MIT is observed at room temperature at threshold voltage of ˜2.1 V for ˜100 nm thickness VO2 films. Activation energies for electron transport in the insulating and conducting states are obtained from variable temperature resistance measurements. We further compare the properties of VO2 thin films grown under identical conditions on Si(100) single crystals. The VO2 thin films grown on Ge substrate show higher degree of crystallinity, slightly reduced compressive strain, larger resistance change across MIT compared to those grown on Si. Depth-dependent x-ray photoelectron spectroscopy measurements were performed to provide information on compositional variation trends in the two cases. These results suggest Ge could be a suitable substrate for further explorations of switching phenomena and devices for thin film functional oxides.

Thin-film topological insulators for continuously tunable terahertz absorption

NASA Astrophysics Data System (ADS)

West, D.; Zhang, S. B.

2018-02-01

One of the defining characteristics of a three-dimensional topological insulator (TI) is the appearance of a Dirac cone on its surface when it creates an interface with vacuum. For thin film TIs, however, the Dirac cones on opposite surfaces interact forming a small gap. For the case of three quintuple layers of Bi2Se3, we show that this gap can be continuously tuned between 128 meV and 0 meV with the application of modest perpendicular electric fields of less than 30 meV Å-1. Through both the Hamiltonian model and first-principles density functional theory calculations, we show that the inherent nonlinearity in realistic Dirac cone interaction leads to a gap which can be continuously tuned through the application of an external electric field. This tunability, coupled with the high optical absorption of thin film TIs, make this a very promising platform for terahertz and infrared detection.

Chromium-induced ferromagnetism with perpendicular anisotropy in topological crystalline insulator SnTe (111) thin films

NASA Astrophysics Data System (ADS)

Wang, Fei; Zhang, Hongrui; Jiang, Jue; Zhao, Yi-Fan; Yu, Jia; Liu, Wei; Li, Da; Chan, Moses H. W.; Sun, Jirong; Zhang, Zhidong; Chang, Cui-Zu

2018-03-01

Topological crystalline insulator is a recently discovered topological phase of matter. It possesses multiple Dirac surface states, which are protected by the crystal symmetry. This is in contrast to the time-reversal symmetry that is operative in the well-known topological insulators. In the presence of a Zeeman field and/or strain, the multiple Dirac surface states are gapped. The high-Chern-number quantum anomalous Hall (QAH) state is predicted to emerge if the chemical potential resides in all the Zeeman gaps. Here, we use molecular-beam epitaxy to grow 12 double-layer (DL) pure and Cr-doped SnTe (111) thin film on heat-treated SrTi O3 (111) substrate using a quintuple layer of insulating (Bi0.2Sb0.8 ) 2T e3 topological insulator as a buffer film. The Hall traces of Cr-doped SnTe film at low temperatures display square hysteresis loops indicating long-range ferromagnetic order with perpendicular anisotropy. The Curie temperature of the 12 DL S n0.9C r0.1Te film is ˜110 K. Due to the chemical potential crossing the bulk valence bands, the anomalous Hall resistance of 12 DL S n0.9C r0.1Te film is substantially lower than the predicted quantized value (˜1 /4 h /e2 ). It is possible that with systematic tuning the chemical potential via chemical doping and electrical gating, the high-Chern-number QAH state can be realized in the Cr-doped SnTe (111) thin film.

Tc depression and superconductor-insulator transition in molybdenum nitride thin films

NASA Astrophysics Data System (ADS)

Ichikawa, F.; Makise, K.; Tsuneoka, T.; Maeda, S.; Shinozaki, B.

2018-03-01

We have studied that the Tc depression and the superconductor-insulator transition (SIT) in molybdenum nitride (MoN) thin films. Thin films were fabricated by reactive DC magnetron sputtering method onto (100) MgO substrates in the mixture of Ar and N2 gases. Several dozen MoN thin films were prepared in the range of 3 nm < thickness d < 60 nm. The resistance was measured by a DC four-probe technique. It is found that Tc decreases from 6.6 K for thick films with increase of the normal state sheet resistance {R}{{sq}}{{N}} and experimental data were fitted to the Finkel’stein formula using the bulk superconducting transition temperature Tc 0 = 6.45 K and the elastic scattering time of electron τ = 1.6 × 10‑16 s. From this analysis the critical sheet resistance Rc is found about 2 kΩ, which is smaller than the quantum sheet resistance R Q. This value of Rc is almost the same as those for 2D NbN films. The value of τ for MoN films is also the similar value for NbN films 1.0 × 10‑16 s, while Tc 0 is different from that for NbN films 14.85 K. It is indicated that the mechanism of SIT for MoN films is similar to that of NbN films, while the mean free path ℓ for MoN films is larger than that for NbN films.

Voltage-induced Metal-Insulator Transitions in Perovskite Oxide Thin Films Doped with Strongly Correlelated Electrons

NASA Astrophysics Data System (ADS)

Wang, Yudi; Gil Kim, Soo; Chen, I.-Wei

2007-03-01

We have observed a reversible metal-insulator transition in perovskite oxide thin films that can be controlled by charge trapping pumped by a bipolar voltage bias. In the as-fabricated state, the thin film is metallic with a very low resistance comparable to that of the metallic bottom electrode, showing decreasing resistance with decreasing temperature. This metallic state switches to a high-resistance state after applying a voltage bias: such state is non-ohmic showing a negative temperature dependence of resistance. Switching at essentially the same voltage bias was observed down to 2K. The metal-insulator transition is attributed to charge trapping that disorders the energy of correlated electron states in the conduction band. By increasing the amount of charge trapped, which increases the disorder relative to the band width, increasingly more insulating states with a stronger temperature dependence of resistivity are accessed. This metal-insulator transition provides a platform to engineer new nonvolatile memory that does not require heat (as in phase transition) or dielectric breakdown (as in most other oxide resistance devices).

Giant spin Hall angle from topological insulator BixSe(1 - x) thin films

NASA Astrophysics Data System (ADS)

Dc, Mahendra; Jamali, Mahdi; Chen, Junyang; Hickey, Danielle; Zhang, Delin; Zhao, Zhengyang; Li, Hongshi; Quarterman, Patrick; Lv, Yang; Mkhyon, Andre; Wang, Jian-Ping

Investigation on the spin-orbit torque (SOT) from large spin-orbit coupling materials has been attracting interest because of its low power switching of the magnetization and ultra-fast driving of the domain wall motion that can be used in future spin based memory and logic devices. We investigated SOT from topological insulator BixSe(1 - x) thin film in BixSe(1 - x) /CoFeB heterostructure by using the dc planar Hall method, where BixSe(1 - x) thin films were prepared by a unique industry-compatible deposition process. The angle dependent Hall resistance was measured in the presence of a rotating external in-plane magnetic field at bipolar currents. The spin Hall angle (SHA) from this BixSe(1 - x) thin film was found to be as large as 22.41, which is the largest ever reported at room temperature (RT). The giant SHA and large spin Hall conductivity (SHC) make this BixSe(1 - x) thin film a very strong candidate as an SOT generator in SOT based memory and logic devices.

Scaling analysis of field-tuned superconductor-insulator transition in two-dimensional tantalum thin films.

PubMed

Park, Sungyu; Shin, Junghyun; Kim, Eunseong

2017-02-20

The superconductor-insulator (SI) transition in two-dimensional Ta thin films is investigated by controlling both film thickness and magnetic field. An intriguing metallic phase appears between a superconducting and an insulating phase within a range of film thickness and magnetic field. The temperature and electric field scaling analyses are performed to investigate the nature of the SI transition in the thickness-tuned metallic and superconducting samples. The critical exponents product of νz obtained from the temperature scaling analysis is found to be approximately 0.67 in the entire range of film thickness. On the other hand, an apparent discrepancy is measured in the product of ν(z + 1) by the electric filed analysis. The product values are found to be about 1.37 for the superconducting films and about 1.86 for the metallic films respectively. We find that the discrepancy is the direct consequence of electron heating that introduces additional dissipation channels in the metallic Ta films.

Enhanced performance of solution-processed organic thin-film transistors with a low-temperature-annealed alumina interlayer between the polyimide gate insulator and the semiconductor.

PubMed

Yoon, Jun-Young; Jeong, Sunho; Lee, Sun Sook; Kim, Yun Ho; Ka, Jae-Won; Yi, Mi Hye; Jang, Kwang-Suk

2013-06-12

We studied a low-temperature-annealed sol-gel-derived alumina interlayer between the organic semiconductor and the organic gate insulator for high-performance organic thin-film transistors. The alumina interlayer was deposited on the polyimide gate insulator by a simple spin-coating and 200 °C-annealing process. The leakage current density decreased by the interlayer deposition: at 1 MV/cm, the leakage current densities of the polyimide and the alumina/polyimide gate insulators were 7.64 × 10(-7) and 3.01 × 10(-9) A/cm(2), respectively. For the first time, enhancement of the organic thin-film transistor performance by introduction of an inorganic interlayer between the organic semiconductor and the organic gate insulator was demonstrated: by introducing the interlayer, the field-effect mobility of the solution-processed organic thin-film transistor increased from 0.35 ± 0.15 to 1.35 ± 0.28 cm(2)/V·s. Our results suggest that inorganic interlayer deposition could be a simple and efficient surface treatment of organic gate insulators for enhancing the performance of solution-processed organic thin-film transistors.

Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

DOE PAGES

Si, W.; Zhang, C.; Wu, L.; ...

2015-09-01

Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk.more » With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Si, Weidong, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov; Zhang, Cheng; Wu, Lijun

2015-08-31

Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF{sub 2} crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. Withmore » large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

Microstructural and magneto-transport characterization of Bi2SexTe3-x topological insulator thin films grown by pulsed laser deposition method

NASA Astrophysics Data System (ADS)

Jin, Zhenghe; Kumar, Raj; Hunte, Frank; Narayan, Jay; Kim, Ki Wook; North Carolina State University Team

Bi2SexTe3-x topological insulator thin films were grown on Al2O3 (0001) substrate by pulsed laser deposition (PLD). XRD and other structural characterization measurements confirm the growth of the textured Bi2SexTe3-x thin films on Al2O3 substrate. The magneto-transport properties of thick and thin Þlms were investigated to study the effect of thickness on the topological insulator properties of the Bi2SexTe3 - x films. A pronounced semiconducting behavior with a highly insulating ground state was observed in the resistivity vs. temperature data. The presence of the weak anti-localization (WAL) effect with a sharp cusp in the magnetoresistance measurements confirms the 2-D surface transport originating from the TSS in Bi2SexTe3-x TI films. A high fraction of surface transport is observed in the Bi2SexTe3-x TI thin films which decreases in Bi2SexTe3-x TI thick films. The Cosine (θ) dependence of the WAL effect supports the observation of a high proportion of 2-D surface state contribution to overall transport properties of the Bi2SexTe3-x TI thin films. Our results show promise that high quality Bi2SexTe3-x TI thin films with significant surface transport can be grown by PLD method to exploit the exotic properties of the surface transport in future generation spintronic devices. This work was supported, in part, by National Science Foundation ECCS-1306400 and FAME.

Thin film three-dimensional topological insulator metal-oxide-semiconductor field-effect-transistors: A candidate for sub-10 nm devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akhavan, N. D., E-mail: nima.dehdashti@uwa.edu.au; Jolley, G.; Umana-Membreno, G. A.

2014-08-28

Three-dimensional (3D) topological insulators (TI) are a new state of quantum matter in which surface states reside in the bulk insulating energy bandgap and are protected by time-reversal symmetry. It is possible to create an energy bandgap as a consequence of the interaction between the conduction band and valence band surface states from the opposite surfaces of a TI thin film, and the width of the bandgap can be controlled by the thin film thickness. The formation of an energy bandgap raises the possibility of thin-film TI-based metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this paper, we explore the performance of MOSFETs basedmore » on thin film 3D-TI structures by employing quantum ballistic transport simulations using the effective continuous Hamiltonian with fitting parameters extracted from ab-initio calculations. We demonstrate that thin film transistors based on a 3D-TI structure provide similar electrical characteristics compared to a Si-MOSFET for gate lengths down to 10 nm. Thus, such a device can be a potential candidate to replace Si-based MOSFETs in the sub-10 nm regime.« less

ZnO thin-film transistors with a polymeric gate insulator built on a polyethersulfone substrate

NASA Astrophysics Data System (ADS)

Hyung, Gun Woo; Park, Jaehoon; Koo, Ja Ryong; Choi, Kyung Min; Kwon, Sang Jik; Cho, Eou Sik; Kim, Yong Seog; Kim, Young Kwan

2012-03-01

Zinc oxide (ZnO) thin-film transistors (TFTs) with a cross-linked poly(vinyl alcohol) (c-PVA) insulator are fabricated on a polyethersulfone substrate. The ZnO film, formed by atomic layer deposition, shows a polycrystalline hexagonal structure with a band gap energy of about 3.37 eV. The fabricated ZnO TFT exhibits a field-effect mobility of 0.38 cm2/Vs and a threshold voltage of 0.2 V. The hysteresis of the device is mainly caused by trapped electrons at the c-PVA/ZnO interface, whereas the positive threshold voltage shift occurs as a consequence of constant positive gate bias stress after 5000 s due to an electron injection from the ZnO film into the c-PVA insulator.

A thin polymer insulator for Josephson tunneling applications

NASA Technical Reports Server (NTRS)

Wilmsen, C. M.

1973-01-01

The use of an organic monolayer formed from a vapor as an insulating barrier for thin film Josephson junctions is considered, and the effect of an organic monolayer on the transition temperature of a thin film superconductor is investigated. Also analyzed are the geometric factors which influence Josephson junctions and Josephson junction interferometers.

Thin-Film Power Transformers

NASA Technical Reports Server (NTRS)

Katti, Romney R.

1995-01-01

Transformer core made of thin layers of insulating material interspersed with thin layers of ferromagnetic material. Flux-linking conductors made of thinner nonferromagnetic-conductor/insulator multilayers wrapped around core. Transformers have geometric features finer than those of transformers made in customary way by machining and mechanical pressing. In addition, some thin-film materials exhibit magnetic-flux-carrying capabilities superior to those of customary bulk transformer materials. Suitable for low-cost, high-yield mass production.

Metal insulator transitions in perovskite SrIrO{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biswas, Abhijit; Jeong, Yoon Hee, E-mail: yhj@postech.ac.kr; Kim, Ki-Seok

Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO{sub 3} thin films, containing a strong spin orbit coupled 5d element Ir, on various substrates such as GdScO{sub 3} (110), DyScO{sub 3} (110), SrTiO{sub 3} (001), and NdGaO{sub 3} (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We foundmore » that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO{sub 3}, unusual non-Fermi liquid characteristics emerge in resistivity as Δρ ∝ T{sup ε} with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.« less

Localized superconductivity in the quantum-critical region of the disorder-driven superconductor-insulator transition in TiN thin films.

PubMed

Baturina, T I; Mironov, A Yu; Vinokur, V M; Baklanov, M R; Strunk, C

2007-12-21

We investigate low-temperature transport properties of thin TiN superconducting films in the vicinity of the disorder-driven superconductor-insulator transition. In a zero magnetic field, we find an extremely sharp separation between superconducting and insulating phases, evidencing a direct superconductor-insulator transition without an intermediate metallic phase. At moderate temperatures, in the insulating films we reveal thermally activated conductivity with the magnetic field-dependent activation energy. At very low temperatures, we observe a zero-conductivity state, which is destroyed at some depinning threshold voltage V{T}. These findings indicate the formation of a distinct collective state of the localized Cooper pairs in the critical region at both sides of the transition.

Topological transitions induced by antiferromagnetism in a thin-film topological insulator

NASA Astrophysics Data System (ADS)

Yin, Gen; He, Qinglin; Yu, Luyan; Pan, Lei; Wang, Kang

Ferromagnetism introduced in topological insulators (TIs) opens a non-trivial exchange band gap, providing an exciting platform to control the topological order through an external magnetic field. The magnetization induces a topological transition that breaks time-reversal symmetry, resulting in anomalous Hall effects. Recently, it was experimentally shown that the surface of an antiferromagnetic (AFM) thin film can magnetize the surface Dirac fermions in a TI thin film similar to the case induced by ferromagnetism. Here, we show that when a TI thin film is sandwiched between two antiferromagnetic layers, an unsynchronized magnetic reversal introduces two intermediate spin configurations during the scan of the external field, resulting in a new topological phase with second Chern numbers. This topological phase introduces two counter-propagating chiral edge modes inside the exchange gap, changing the total number of transport channels drastically when the fermi level is close to the Dirac point. Induced by this change, the magnetoresistance of the channel presents an antisymmetric feature during the field scan. With the the help of the high ordering temperature of AFM layers, this transport signature of the phase transition persists up to 90K experimentally. This work is supported by (i) SHINES, an EFRC by US-DOE, Office of Science, BES, #SC0012670. (ii) US-NSF (DMR-1411085), (iii) ARO program W911NF-15-1-10561, and (iv) FAME Center in STARnet, an SRC program by MARCO and DARPA.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Bilayer Photoresist Insulator for High Performance Organic Thin-Film Transistors on Plastic Films

NASA Astrophysics Data System (ADS)

Wang, He; Li, Chun-Hong; Pan, Feng; Wang, Hai-Bo; Yan, Dong-Hang

2009-11-01

A novel bilayer photoresist insulator is applied in flexible vanadyl-phthalocyanine (VOPc) organic thin-film transistors (OTFTs). The micron-size patterns of this photoresisit insulator can be directly defined only by photolithography without the etching process. Furthermore, these OTFTs exhibit high field-effect mobility (about 0.8 cm2/Vs) and current on/off ratio (about 106). In particular, they show rather low hysteresis (< 1 V). The results demonstrate that this bilayer photoresist insulator can be applied in large-area electronics and in the facilitation of patterning insulators.

Low-Temperature Fabrication of Robust, Transparent, and Flexible Thin-Film Transistors with a Nanolaminated Insulator.

PubMed

Kwon, Jeong Hyun; Park, Junhong; Lee, Myung Keun; Park, Jeong Woo; Jeon, Yongmin; Shin, Jeong Bin; Nam, Minwoo; Kim, Choong-Ki; Choi, Yang-Kyu; Choi, Kyung Cheol

2018-05-09

The lack of reliable, transparent, and flexible electrodes and insulators for applications in thin-film transistors (TFTs) makes it difficult to commercialize transparent, flexible TFTs (TF-TFTs). More specifically, conventional high process temperatures and the brittleness of these elements have been hurdles in developing flexible substrates vulnerable to heat. Here, we propose electrode and insulator fabrication techniques considering process temperature, transmittance, flexibility, and environmental stability. A transparent and flexible indium tin oxide (ITO)/Ag/ITO (IAI) electrode and an Al 2 O 3 /MgO (AM)-laminated insulator were optimized at the low temperature of 70 °C for the fabrication of TF-TFTs on a polyethylene terephthalate (PET) substrate. The optimized IAI electrode with a sheet resistance of 7 Ω/sq exhibited the luminous transmittance of 85.17% and maintained its electrical conductivity after exposure to damp heat conditions because of an environmentally stable ITO capping layer. In addition, the electrical conductivity of IAI was maintained after 10 000 bending cycles with a tensile strain of 3% because of the ductile Ag film. In the metal/insulator/metal structure, the insulating and mechanical properties of the optimized AM-laminated film deposited at 70 °C were significantly improved because of the highly dense nanolaminate system, compared to those of the Al 2 O 3 film deposited at 70 °C. In addition, the amorphous indium-gallium-zinc oxide (a-IGZO) was used as the active channel for TF-TFTs because of its excellent chemical stability. In the environmental stability test, the ITO, a-IGZO, and AM-laminated films showed the excellent environmental stability. Therefore, our IGZO-based TFT with IAI electrodes and the 70 °C AM-laminated insulator was fabricated to evaluate robustness, transparency, flexibility, and process temperature, resulting in transfer characteristics comparable to those of an IGZO-based TFT with a 150 °C Al 2 O 3

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction.

PubMed

Sokolowski-Tinten, K; Shen, X; Zheng, Q; Chase, T; Coffee, R; Jerman, M; Li, R K; Ligges, M; Makasyuk, I; Mo, M; Reid, A H; Rethfeld, B; Vecchione, T; Weathersby, S P; Dürr, H A; Wang, X J

2017-09-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels.

Thermal conductivity of thin insulating films determined by tunnel magneto-Seebeck effect measurements and finite-element modeling

NASA Astrophysics Data System (ADS)

Huebner, Torsten; Martens, Ulrike; Walowski, Jakob; Münzenberg, Markus; Thomas, Andy; Reiss, Günter; Kuschel, Timo

2018-06-01

In general, it is difficult to access the thermal conductivity of thin insulating films experimentally by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl2O4 (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO (0.7 W (K · m)‑1) and MgO (5.8 W (K · m)‑1), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films.

Electrolysis-induced protonation of VO2 thin film transistor for the metal-insulator phase modulation

NASA Astrophysics Data System (ADS)

Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

2016-02-01

Compared to state-of-the-art modulation techniques, protonation is the most ideal to control the electrical and optical properties of transition metal oxides (TMOs) due to its intrinsic non-volatile operation. However, the protonation of TMOs is not typically utilized for solid-state devices because of imperative high-temperature annealing treatment in hydrogen source. Although one solution for room temperature (RT) protonation of TMOs is liquid-phase electrochemistry, it is unsuited for practical purposes due to liquid-leakage problem. Herein we demonstrate solid-state RT-protonation of vanadium dioxide (VO2), which is a well-known thermochromic TMO. We fabricated the three terminal thin-film-transistor structure on an insulating VO2 film using a water-infiltrated nanoporous glass, which serves as a solid electrolyte. For gate voltage application, water electrolysis and protonation/deprotonation of VO2 film surface occurred, leading to reversible metal-insulator phase conversion of ~11-nm-thick VO2 layer. The protonation was clearly accompanied by the structural change from an insulating monoclinic to a metallic tetragonal phase. Present results offer a new route for the development of electro-optically active solid-state devices with TMO materials by engineering RT protonation.

Proximity-Induced Superconductivity and Quantum Interference in Topological Crystalline Insulator SnTe Thin-Film Devices.

PubMed

Klett, Robin; Schönle, Joachim; Becker, Andreas; Dyck, Denis; Borisov, Kiril; Rott, Karsten; Ramermann, Daniela; Büker, Björn; Haskenhoff, Jan; Krieft, Jan; Hübner, Torsten; Reimer, Oliver; Shekhar, Chandra; Schmalhorst, Jan-Michael; Hütten, Andreas; Felser, Claudia; Wernsdorfer, Wolfgang; Reiss, Günter

2018-02-14

Topological crystalline insulators represent a new state of matter, in which the electronic transport is governed by mirror-symmetry protected Dirac surface states. Due to the helical spin-polarization of these surface states, the proximity of topological crystalline matter to a nearby superconductor is predicted to induce unconventional superconductivity and, thus, to host Majorana physics. We report on the preparation and characterization of Nb-based superconducting quantum interference devices patterned on top of topological crystalline insulator SnTe thin films. The SnTe films show weak anti-localization, and the weak links of the superconducting quantum interference devices (SQUID) exhibit fully gapped proximity-induced superconductivity. Both properties give a coinciding coherence length of 120 nm. The SQUID oscillations induced by a magnetic field show 2π periodicity, possibly dominated by the bulk conductivity.

Ultralow Damping in Nanometer-Thick Epitaxial Spinel Ferrite Thin Films.

PubMed

Emori, Satoru; Yi, Di; Crossley, Sam; Wisser, Jacob J; Balakrishnan, Purnima P; Khodadadi, Behrouz; Shafer, Padraic; Klewe, Christoph; N'Diaye, Alpha T; Urwin, Brittany T; Mahalingam, Krishnamurthy; Howe, Brandon M; Hwang, Harold Y; Arenholz, Elke; Suzuki, Yuri

2018-06-08

Pure spin currents, unaccompanied by dissipative charge flow, are essential for realizing energy-efficient nanomagnetic information and communications devices. Thin-film magnetic insulators have been identified as promising materials for spin-current technology because they are thought to exhibit lower damping compared with their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping insulators. Here, we demonstrate a new class of nanometer-thick ultralow-damping insulating thin films based on design criteria that minimize orbital angular momentum and structural disorder. Specifically, we show ultralow damping in <20 nm thick spinel-structure magnesium aluminum ferrite (MAFO), in which magnetization arises from Fe 3+ ions with zero orbital angular momentum. These epitaxial MAFO thin films exhibit a Gilbert damping parameter of ∼0.0015 and negligible inhomogeneous linewidth broadening, resulting in narrow half width at half-maximum linewidths of ∼0.6 mT around 10 GHz. Our findings offer an attractive thin-film platform for enabling integrated insulating spintronics.

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction

PubMed Central

Sokolowski-Tinten, K.; Shen, X.; Zheng, Q.; Chase, T.; Coffee, R.; Jerman, M.; Li, R. K.; Ligges, M.; Makasyuk, I.; Mo, M.; Reid, A. H.; Rethfeld, B.; Vecchione, T.; Weathersby, S. P.; Dürr, H. A.; Wang, X. J.

2017-01-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels. PMID:28795080

Electric-field induced spin accumulation in the Landau level states of topological insulator thin films

NASA Astrophysics Data System (ADS)

Siu, Zhuo Bin; Chowdhury, Debashree; Basu, Banasri; Jalil, Mansoor B. A.

2017-08-01

A topological insulator (TI) thin film differs from the more typically studied thick TI system in that the former has both a top and a bottom surface where the states localized at both surfaces can couple to one other across the finite thickness. An out-of-plane magnetic field leads to the formation of discrete Landau level states in the system, whereas an in-plane magnetization breaks the angular momentum symmetry of the system. In this work, we study the spin accumulation induced by the application of an in-plane electric field to the TI thin film system where the Landau level states and inter-surface coupling are simultaneously present. We show, via Kubo formula calculations, that the in-plane spin accumulation perpendicular to the magnetization due to the electric field vanishes for a TI thin film with symmetric top and bottom surfaces. A finite in-plane spin accumulation perpendicular to both the electric field and magnetization emerges upon applying either a differential magnetization coupling or a potential difference between the two film surfaces. This spin accumulation results from the breaking of the antisymmetry of the spin accumulation around the k-space equal-energy contours.

Superconductor-Insulator transition in sputtered amorphous MoRu and MoRuN thin films

NASA Astrophysics Data System (ADS)

Makise, K.; Shinozaki, B.; Ichikawa, F.

2018-03-01

This work shows the experimental results of the superconductor-insulator (S-I) transition for amorphous molybdenum ruthenium (MoRu) and molybdenum ruthenium nitride (MoRuN) films. These amorphous films onto c-plane sapphire substrates have been interpreted to be homogeneous by XRD and AFM measurements. Electrical and superconducting properties measurements were carried out on MoRu and MoRuN thin films deposited by reactive sputtering technique. We have analysed the data on R sq (T) based on excess conductivity of superconducting films by the AL and MT term and weak localization and electron-electron interaction for the conductance. MoRu films which offer the most homogeneous film morphology, showed a critical sheet resistance of transition, Rc, of ∼ 2 kΩ. This values is smaller than those previously our reported for quench-condensed MoRu films on SiO underlayer held at liquid He temperature.

Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

PubMed Central

Torriss, B.; Margot, J.; Chaker, M.

2017-01-01

Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing. PMID:28098240

Quantum Size Effects in Transport Properties of Bi2Te3 Topological Insulator Thin Films

NASA Astrophysics Data System (ADS)

Rogacheva, E. I.; Budnik, A. V.; Nashchekina, O. N.; Meriuts, A. V.; Dresselhaus, M. S.

2017-07-01

Bi2Te3 compound and Bi2Te3-based solid solutions have attracted much attention as promising thermoelectric materials for refrigerating devices. The possibility of enhancing the thermoelectric efficiency in low-dimensional structures has stimulated studies of Bi2Te3 thin films. Now, interest in studying the transport properties of Bi2Te3 has grown sharply due to the observation of special properties characteristic of three-dimensional (3D) topological insulators in Bi2Te3. One of the possible manifestations of quantum size effects in two-dimensional structures is an oscillatory behavior of the dependences of transport properties on film thickness, d. The goal of this work is to summarize our earlier experimental results on the d-dependences of transport properties of Bi2Te3 thin films obtained by thermal evaporation in a vacuum on glass substrates, and to present our new results of theoretical calculations of the oscillations periods within the framework of the model of an infinitely deep potential well, which takes into account the dependence of the Fermi energy on d and the contribution of all energy subbands below the Fermi level to the conductivity. On the basis of the data obtained, some general regularities and specificity of the quantum size effects manifestation in 3D topological insulators are established.

Ultrahigh sensitivity of anomalous Hall effect sensor based on Cr-doped Bi 2Te 3 topological insulator thin films

DOE PAGES

Ni, Y.; Zhang, Z.; Nlebedim, I. C.; ...

2016-07-01

Anomalous Hall effect (AHE) was recently discovered in magnetic element-doped topological insulators (TIs), which promises low power consumption and high efficiency spintronics and electronics. This discovery broadens the family of Hall sensors. In this paper, AHE sensors based on Cr-doped Bi 2Te 3 topological insulator thin films are studied with two thicknesses (15 and 65 nm). It is found, in both cases, that ultrahigh Hall sensitivity can be obtained in Cr-doped Bi 2Te 3. Hall sensitivity reaches 1666 Ω/T in the sensor with the 15 nm TI thin film, which is higher than that of the conventional semiconductor HE sensor.more » The AHE of 65 nm sensors is even stronger, which causes the sensitivity increasing to 2620 Ω/T. Furthermore, after comparing Cr-doped Bi 2Te 3 with the previously studied Mn-doped Bi 2Te 3 TI Hall sensor, the sensitivity of the present AHE sensor shows about 60 times higher in 65 nm sensors. Furthermore, the implementation of AHE sensors based on a magnetic-doped TI thin film indicates that the TIs are good candidates for ultrasensitive AHE sensors.« less

Metal-oxide assisted surface treatment of polyimide gate insulators for high-performance organic thin-film transistors.

PubMed

Kim, Sohee; Ha, Taewook; Yoo, Sungmi; Ka, Jae-Won; Kim, Jinsoo; Won, Jong Chan; Choi, Dong Hoon; Jang, Kwang-Suk; Kim, Yun Ho

2017-06-14

We developed a facile method for treating polyimide-based organic gate insulator (OGI) surfaces with self-assembled monolayers (SAMs) by introducing metal-oxide interlayers, called the metal-oxide assisted SAM treatment (MAST). To create sites for surface modification with SAM materials on polyimide-based OGI (KPI) surfaces, the metal-oxide interlayer, here amorphous alumina (α-Al 2 O 3 ), was deposited on the KPI gate insulator using spin-coating via a rapid sol-gel reaction, providing an excellent template for the formation of a high-quality SAM with phosphonic acid anchor groups. The SAM of octadecylphosphonic acid (ODPA) was successfully treated by spin-coating onto the α-Al 2 O 3 -deposited KPI film. After the surface treatment by ODPA/α-Al 2 O 3 , the surface energy of the KPI thin film was remarkably decreased and the molecular compatibility of the film with an organic semiconductor (OSC), 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C 10 ), was increased. Ph-BTBT-C 10 molecules were uniformly deposited on the treated gate insulator surface and grown with high crystallinity, as confirmed by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. The mobility of Ph-BTBT-C 10 thin-film transistors (TFTs) was approximately doubled, from 0.56 ± 0.05 cm 2 V -1 s -1 to 1.26 ± 0.06 cm 2 V -1 s -1 , after the surface treatment. The surface treatment of α-Al 2 O 3 and ODPA significantly decreased the threshold voltage from -21.2 V to -8.3 V by reducing the trap sites in the OGI and improving the interfacial properties with the OSC. We suggest that the MAST method for OGIs can be applied to various OGI materials lacking reactive sites using SAMs. It may provide a new platform for the surface treatment of OGIs, similar to that of conventional SiO 2 gate insulators.

Metal-Insulator crossover in SrVO3 thin film

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Wang, Zhen; Saghayezhian, Mohammad; Chen, Chen; Chen, Lina; Guo, Hangwen; Zhu, Yimei; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3 (SVO) represents a prototype system for the study of the mechanism behind thickness-induced metal-to-insulator transition (MIT) or crossover due to its simple structure and itinerancy. Here SrVO3 thin films with different thicknesses were obtained through the layer-by-layer growth by laser Molecular Beam Epitaxy on SrTiO3 (001) surface. Ultraviolet Photoemission Spectroscopy and Scanning Tunneling Spectroscopy measurements confirm a MIT at the thickness of 3 unit cell, while atomically resolved Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy analysis reveal the depletion of Sr, change of V-valence and expansion of the out-of-plane lattice constant in the first three unit cell above the interface, thus different from the rest of the films. The existence of significant amount of oxygen vacancies is proposed, which is also supported by X-ray Photoelectron Spectroscopy, therefore providing a possible explanation of MIT. This work is primarily supported by U.S. DOE under Grant No. DOE DE-SC0002136. G.W. was supported by U.S. NSF under Grant No. DMR 16088865.

Optimization of a Solution-Processed SiO2 Gate Insulator by Plasma Treatment for Zinc Oxide Thin Film Transistors.

PubMed

Jeong, Yesul; Pearson, Christopher; Kim, Hyun-Gwan; Park, Man-Young; Kim, Hongdoo; Do, Lee-Mi; Petty, Michael C

2016-01-27

We report on the optimization of the plasma treatment conditions for a solution-processed silicon dioxide gate insulator for application in zinc oxide thin film transistors (TFTs). The SiO2 layer was formed by spin coating a perhydropolysilazane (PHPS) precursor. This thin film was subsequently thermally annealed, followed by exposure to an oxygen plasma, to form an insulating (leakage current density of ∼10(-7) A/cm(2)) SiO2 layer. Optimized ZnO TFTs (40 W plasma treatment of the gate insulator for 10 s) possessed a carrier mobility of 3.2 cm(2)/(V s), an on/off ratio of ∼10(7), a threshold voltage of -1.3 V, and a subthreshold swing of 0.2 V/decade. In addition, long-term exposure (150 min) of the pre-annealed PHPS to the oxygen plasma enabled the maximum processing temperature to be reduced from 180 to 150 °C. The resulting ZnO TFT exhibited a carrier mobility of 1.3 cm(2)/(V s) and on/off ratio of ∼10(7).

Comparison of Classical and Charge Storage Methods for Determining Conductivity of Thin Film Insulators

NASA Technical Reports Server (NTRS)

Swaminathan, Prasanna; Dennison, J. R.; Sim, Alec; Brunson, Jerilyn; Crapo, Eric; Frederickson, A. R.

2004-01-01

Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode attached to the other side of the insulator. Data are obtained by capacitive coupling to measure both the resulting voltage on the open surface and emission of electrons from the exposed surface, as well monitoring currents to the electrode. Instrumentation for both classical and charge storage decay methods has been developed and tested at Jet Propulsion Laboratory (JPL) and at Utah State University (USU). Details of the apparatus, test methods and data analysis are given here. The JPL charge storage decay chamber is a first-generation instrument, designed to make detailed measurements on only three to five samples at a time. Because samples must typically be tested for over a month, a second-generation high sample throughput charge storage decay chamber was developed at USU with the capability of testing up to 32 samples simultaneously. Details are provided about the instrumentation to measure surface charge and current; for charge deposition apparatus and control; the sample holders to properly isolate the mounted samples; the sample carousel to rotate samples into place; the control of the sample environment including sample vacuum, ambient gas, and sample temperature; and the computer control and data acquisition systems. Measurements are compared here for a number of thin film insulators using both

A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection.

PubMed

Liu, Junshan; Wang, Junyao; Chen, Zuanguang; Yu, Yong; Yang, Xiujuan; Zhang, Xianbin; Xu, Zheng; Liu, Chong

2011-03-07

A three-layer poly (methyl methacrylate) (PMMA) electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection is presented. A 50 μm-thick PMMA film is used as the insulating layer and placed between the channel plate (containing the microchannel) and the electrode plate (containing the microelectrode). The three-layer structure facilitates the achievement of a thin insulating layer, obviates the difficulty of integrating microelectrodes on a thin film, and does not compromise the integration of microchips. To overcome the thermal and chemical incompatibilities of polymers and photolithographic techniques, a modified lift-off process was developed to integrate Pt microelectrodes onto the PMMA substrate. A novel two-step bonding method was created to assemble the complete PMMA microchip. A low limit of detection of 1.25 μg ml(-1) for Na(+) and high separation efficiency of 77,000 and 48,000 plates/m for Na(+) and K(+) were obtained when operating the detector at a low excitation frequency of 60 kHz.

Influence of oxygen flow rate on metal-insulator transition of vanadium oxide thin films grown by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Ma, Xu; Liu, Xinkun; Li, Haizhu; Zhang, Angran; Huang, Mingju

2017-03-01

High-quality vanadium oxide ( VO2) films have been fabricated on Si (111) substrates by radio frequency (RF) magnetron sputtering deposition method. The sheet resistance of VO2 has a significant change (close to 5 orders of magnitude) in the process of the metal-insulator phase transition (MIT). The field emission-scanning electron microscope (FE-SEM) results show the grain size of VO2 thin films is larger with the increase of oxygen flow. The X-ray diffraction (XRD) results indicate the thin films fabricated at different oxygen flow rates grow along the (011) crystalline orientation. As the oxygen flow rate increases from 3 sccm to 6 sccm, the phase transition temperature of the films reduces from 341 to 320 K, the width of the thermal hysteresis loop decreases from 32 to 9 K. The thin films fabricated in the condition of 5 sccm have a high temperature coefficient of resistance (TCR) -3.455%/K with a small resistivity of 2.795 ρ/Ω cm.

Thin-film composite materials as a dielectric layer for flexible metal-insulator-metal capacitors.

PubMed

Tiwari, Jitendra N; Meena, Jagan Singh; Wu, Chung-Shu; Tiwari, Rajanish N; Chu, Min-Ching; Chang, Feng-Chih; Ko, Fu-Hsiang

2010-09-24

A new organic-organic nanoscale composite thin-film (NCTF) dielectric has been synthesized by solution deposition of 1-bromoadamantane and triblock copolymer (Pluronic P123, BASF, EO20-PO70-EO20), in which the precursor solution has been achieved with organic additives. We have used a sol-gel process to make a metal-insulator-metal capacitor (MIM) comprising a nanoscale (10 nm-thick) thin-film on a flexible polyimide (PI) substrate at room temperature. Scanning electron microscope and atomic force microscope revealed that the deposited NCTFs were crack-free, uniform, highly resistant to moisture absorption, and well adhered on the Au-Cr/PI. The electrical properties of 1-bromoadamantane-P123 NCTF were characterized by dielectric constant, capacitance, and leakage current measurements. The 1-bromoadamantane-P123 NCTF on the PI substrate showed a low leakage current density of 5.5 x 10(-11) A cm(-2) and good capacitance of 2.4 fF at 1 MHz. In addition, the calculated dielectric constant of 1-bromoadamantane-P123 NCTF was 1.9, making them suitable candidates for use in future flexible electronic devices as a stable intermetal dielectric. The electrical insulating properties of 1-bromoadamantane-P123 NCTF have been improved due to the optimized dipole moments of the van der Waals interactions.

Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

PubMed

Tsuyama, T; Chakraverty, S; Macke, S; Pontius, N; Schüßler-Langeheine, C; Hwang, H Y; Tokura, Y; Wadati, H

2016-06-24

We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150  ps) to fast (<70  ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

Positive Bias Instability of Bottom-Gate Zinc Oxide Thin-Film Transistors with a SiOx/SiNx-Stacked Gate Insulator

NASA Astrophysics Data System (ADS)

Furuta, Mamoru; Kamada, Yudai; Hiramatsu, Takahiro; Li, Chaoyang; Kimura, Mutsumi; Fujita, Shizuo; Hirao, Takashi

2011-03-01

The positive bias instabilities of the zinc oxide thin-film transistors (ZnO TFTs) with a SiOx/SiNx-stacked gate insulator have been investigated. The film quality of a gate insulator of SiOx, which forms an interface with the ZnO channel, was varied by changing the gas mixture ratio of SiH4/N2O/N2 during plasma-enhanced chemical vapor deposition. The positive bias stress endurance of ZnO TFT strongly depended on the deposition condition of the SiOx gate insulator. From the relaxations of the transfer curve shift after imposition of positive bias stress, transfer curves could not be recovered completely without any thermal annealing. A charge trapping in a gate insulator rather than that in bulk ZnO and its interface with a gate insulator is a dominant instability mechanism of ZnO TFTs under positive bias stress.

Electric-field driven insulator-metal transition and tunable magnetoresistance in ZnO thin film

NASA Astrophysics Data System (ADS)

Zhang, Le; Chen, Shanshan; Chen, Xiangyang; Ye, Zhizhen; Zhu, Liping

2018-04-01

Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to -2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.

Superconductor to weak-insulator transitions in disordered tantalum nitride films

NASA Astrophysics Data System (ADS)

Breznay, Nicholas P.; Tendulkar, Mihir; Zhang, Li; Lee, Sang-Chul; Kapitulnik, Aharon

2017-10-01

We study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents z ν ≈1.3 , with a corresponding critical field Hc≪Hc 2 , the upper critical field. The Hall effect exhibits a crossing point near Hc, but with a nonuniversal critical value ρxy c comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.

Thin Film Transistors On Plastic Substrates

DOEpatents

Carey, Paul G.; Smith, Patrick M.; Sigmon, Thomas W.; Aceves, Randy C.

2004-01-20

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The silicon based thin film transistor produced by the process includes a low temperature substrate incapable of withstanding sustained processing temperatures greater than about 250.degree. C., an insulating layer on the substrate, a layer of silicon on the insulating layer having sections of doped silicon, undoped silicon, and poly-silicon, a gate dielectric layer on the layer of silicon, a layer of gate metal on the dielectric layer, a layer of oxide on sections of the layer of silicon and the layer of gate metal, and metal contacts on sections of the layer of silicon and layer of gate metal defining source, gate, and drain contacts, and interconnects.

Role of geometric parameters in electrical measurements of insulating thin films deposited on a conductive substrate

NASA Astrophysics Data System (ADS)

Kumar, S.; Gerhardt, R. A.

2012-03-01

The effects of film thickness, electrode size and substrate thickness on the impedance parameters of alternating frequency dielectric measurements of insulating thin films deposited on conductive substrates were studied through parametric finite-element simulations. The quasi-static forms of Maxwell's electromagnetic equations in a time harmonic mode were solved using COMSOL Multiphysics® for several types of 2D models (linear and axisymmetric). The full 2D model deals with a configuration in which the impedance is measured between two surface electrodes on top of a film deposited on a conductive substrate. For the simplified 2D models, the conductive substrate is ignored and the two electrodes are placed on the top and bottom of the film. By comparing the full model and the simplified models, approximations and generalizations are deduced. For highly insulating films, such as the case of insulating SiO2 films on a conducting Si substrate, even the simplified models predict accurate capacitance values at all frequencies. However, the edge effects on the capacitance are found to be significant when the film thickness increases and/or the top electrode contact size decreases. The thickness of the substrate affects predominantly the resistive components of the dielectric response while having no significant effect on the capacitive components. Changing the electrode contact size or the film thickness determines the specific values of the measured resistance or capacitance while the material time constant remains the same, and thus this affects the frequency dependence that is able to be detected. This work highlights the importance of keeping in mind the film thickness and electrode contact size for the correct interpretation of the measured dielectric properties of micro/nanoscale structures that are often investigated using nanoscale capacitance measurements.

Topological Magnon Modes in Patterned Ferrimagnetic Insulator Thin Films.

PubMed

Li, Yun-Mei; Xiao, Jiang; Chang, Kai

2018-05-09

Manipulation of magnons opens an attractive direction in the future energy-efficient information processing devices. Such quasi-particles can transfer and process information free from the troublesome Ohmic loss in conventional electronic devices. Here, we propose to realize topologically protected magnon modes using the interface between the patterned ferrimagnetic insulator thin films of different configurations without the Dzyaloshinskii-Moriya interaction. The interface thus behaves like a perfect waveguide to conduct the magnon modes lying in the band gap. These modes are immune to backscattering even in sharply bent tracks, robust against the disorders, and maintain a high degree of coherence during propagation. We design a magnonic Mach-Zehnder interferometer, which realizes a continuous change of magnon signal with varying external magnetic field or driving frequency. Our results pave a new way for realizing topologically protected magnon waveguide and finally achieving a scalable low-dissipation spintronic devices and even the magnonic integrated circuit.

Field-tuned superconductor-insulator transitions and Hall resistance in thin polycrystalline MoN films

NASA Astrophysics Data System (ADS)

Makise, Kazumasa; Ichikawa, Fusao; Asano, Takayuki; Shinozaki, Bunju

2018-02-01

We report on the superconductor-insulator transitions (SITs) of disordered molybdenum nitride (MoN) thin films on (1 0 0) MgO substrates as a function of the film thickness and magnetic fields. The T c of the superconducting MoN films, which exhibit a sharp superconducting transition, monotonically decreases as the normal state R sq increases with a decreasing film thickness. For several films with different thicknesses, we estimate the critical field H c and the product zν  ≃  0.6 of the dynamical exponent z and the correlation length exponent ν using a finite scaling analysis. The value of this product can be explained by the (2  +  1) XY model. We found that the Hall resistance ΔR xy (H) is maximized when the magnetic field satisfies H HP(T) \\propto |1  -  T/T C0| in the superconducting state and also in the normal states owning to the superconducting fluctuation corresponding to the ghost critical magnetic field. We measured the Hall conductivity δσ xy (H)  =  σ xy (H)  -  σ xyn and fit the Gaussian approximation theory for δσ xy (H) to the experimental data. Agreement between the data and the theory beyond H c suggests the survival of the Cooper pair in the insulating region of the SIT.

Field-tuned superconductor-insulator transitions and Hall resistance in thin polycrystalline MoN films.

PubMed

Makise, Kazumasa; Ichikawa, Fusao; Asano, Takayuki; Shinozaki, Bunju

2018-02-14

We report on the superconductor-insulator transitions (SITs) of disordered molybdenum nitride (MoN) thin films on (1 0 0) MgO substrates as a function of the film thickness and magnetic fields. The T c of the superconducting MoN films, which exhibit a sharp superconducting transition, monotonically decreases as the normal state R sq increases with a decreasing film thickness. For several films with different thicknesses, we estimate the critical field H c and the product zν  ≃  0.6 of the dynamical exponent z and the correlation length exponent ν using a finite scaling analysis. The value of this product can be explained by the (2  +  1) XY model. We found that the Hall resistance ΔR xy (H) is maximized when the magnetic field satisfies H HP (T) [Formula: see text] |1  -  T/T C0 | in the superconducting state and also in the normal states owning to the superconducting fluctuation corresponding to the ghost critical magnetic field. We measured the Hall conductivity δσ xy (H)  =  σ xy (H)  -  [Formula: see text] and fit the Gaussian approximation theory for δσ xy (H) to the experimental data. Agreement between the data and the theory beyond H c suggests the survival of the Cooper pair in the insulating region of the SIT.

Superconductor to weak-insulator transitions in disordered tantalum nitride films

DOE PAGES

Breznay, Nicholas P.; Tendulkar, Mihir; Zhang, Li; ...

2017-10-31

Here, we study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents zν ≈ 1.3, with a corresponding critical field H c << H c2, the upper critical field. The Hall effect exhibits a crossing point near H c, but with a nonuniversal critical valuemore » ρ c xy comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.« less

Advanced thin film thermocouples

NASA Technical Reports Server (NTRS)

Kreider, K. G.; Semancik, S.; Olson, C.

1984-01-01

The fabrication, materials characterization, and performance of thin film platinum rhodium thermocouples on gas turbine alloys was investigated. The materials chosen for the study were the turbine blade alloy systems MAR M200+Hf with NiCoCrAlY and FeCrAlY coatings, and vane alloy systems MAR M509 with FeCrAlY. Research was focussed on making improvements in the problem areas of coating substrate stability, adhesion, and insulation reliability and durability. Diffusion profiles between the substrate and coating with and without barrier coatings of Al2O3 are reported. The relationships between fabrication parameters of thermal oxidation and sputtering of the insulator and its characterization and performance are described. The best thin film thermocouples were fabricated with the NiCoCrAlY coatings which were thermally oxidized and sputter coated with Al2O3.

Epitaxy, strain, and composition effects on metal-insulator transition characteristics of SmNiO{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aydogdu, Gulgun H.; Ha, Sieu D.; Viswanath, B.

SmNiO{sub 3} (SNO) thin films were deposited on LaAlO{sub 3} (LAO), SrTiO{sub 3}, SrLaAlO{sub 4}, Si, and Al{sub 2}O{sub 3} (sapphire) substrates by RF magnetron sputtering and studies were conducted to understand how film structure and composition influence the insulator-metal transition properties. It is observed that the compressive strain induces the insulator to metal transition (MIT), while tensile strain suppresses it. In the case of non-epitaxial films, semiconducting behavior is obtained on sapphire over a broad temperature range, while on heavily-doped Si substrate; an MIT is seen in out-of-plane resistance measurement. In addition, thickness dependence on the resistance behavior andmore » nickel oxidation state has been examined for epitaxial SNO films on LAO substrates. Fine control of the MIT by modifications to the mismatch strain and thickness provides insights to enhance the performance and the functionality of these films for emerging electron devices.« less

Nonvolatile memory thin-film transistors using biodegradable chicken albumen gate insulator and oxide semiconductor channel on eco-friendly paper substrate.

PubMed

Kim, So-Jung; Jeon, Da-Bin; Park, Jung-Ho; Ryu, Min-Ki; Yang, Jong-Heon; Hwang, Chi-Sun; Kim, Gi-Heon; Yoon, Sung-Min

2015-03-04

Nonvolatile memory thin-film transistors (TFTs) fabricated on paper substrates were proposed as one of the eco-friendly electronic devices. The gate stack was composed of chicken albumen gate insulator and In-Ga-Zn-O semiconducting channel layers. All the fabrication processes were performed below 120 °C. To improve the process compatibility of the synthethic paper substrate, an Al2O3 thin film was introduced as adhesion and barrier layers by atomic layer deposition. The dielectric properties of biomaterial albumen gate insulator were also enhanced by the preparation of Al2O3 capping layer. The nonvolatile bistabilities were realized by the switching phenomena of residual polarization within the albumen thin film. The fabricated device exhibited a counterclockwise hysteresis with a memory window of 11.8 V, high on/off ratio of approximately 1.1 × 10(6), and high saturation mobility (μsat) of 11.5 cm(2)/(V s). Furthermore, these device characteristics were not markedly degraded even after the delamination and under the bending situration. When the curvature radius was set as 5.3 cm, the ION/IOFF ratio and μsat were obtained to be 5.9 × 10(6) and 7.9 cm(2)/(V s), respectively.

Metal-insulator transition in CaVO3 thin films: Interplay between epitaxial strain, dimensional confinement, and surface effects

NASA Astrophysics Data System (ADS)

Beck, Sophie; Sclauzero, Gabriele; Chopra, Uday; Ederer, Claude

2018-02-01

We use density functional theory plus dynamical mean-field theory (DFT+DMFT) to study multiple control parameters for tuning the metal-insulator transition (MIT) in CaVO3 thin films. We focus on separating the effects resulting from substrate-induced epitaxial strain from those related to the reduced thickness of the film. We show that tensile epitaxial strain of around 3%-4% is sufficient to induce a transition to a paramagnetic Mott-insulating phase. This corresponds to the level of strain that could be achieved on a SrTiO3 substrate. Using free-standing slab models, we then demonstrate that reduced film thickness can also cause a MIT in CaVO3, however, only for thicknesses of less than 4 perovskite units. Our calculations indicate that the MIT in such ultrathin films results mainly from a surface-induced crystal-field splitting between the t2 g orbitals, favoring the formation of an orbitally polarized Mott insulator. This surface-induced crystal-field splitting is of the same type as the one resulting from tensile epitaxial strain, and thus the two effects can also cooperate. Furthermore, our calculations confirm an enhancement of correlation effects at the film surface, resulting in a reduced quasiparticle spectral weight in the outermost layer, whereas bulklike properties are recovered within only a few layers away from the surface.

Superconductor-Insulator Transition in NbTiN Films

NASA Astrophysics Data System (ADS)

Burdastyh, M. V.; Postolova, S. V.; Baturina, T. I.; Proslier, T.; Vinokur, V. M.; Mironov, A. Yu.

2017-12-01

Experimental results indicating a direct disorder-induced superconductor-insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition T c according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii-Kosterlitz-Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.

Tuning thermoelectricity in a Bi 2Se 3 topological insulator via varied film thickness

DOE PAGES

Guo, Minghua; Wang, Zhenyu; Xu, Yong; ...

2016-01-12

We report thermoelectric transport studies on Bi 2Se 3 topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi 2Se 3 thin films. Lastly, this work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

Spin Seebeck effect in insulating epitaxial γ-Fe2O3 thin films

NASA Astrophysics Data System (ADS)

Jiménez-Cavero, P.; Lucas, I.; Anadón, A.; Ramos, R.; Niizeki, T.; Aguirre, M. H.; Algarabel, P. A.; Uchida, K.; Ibarra, M. R.; Saitoh, E.; Morellón, L.

2017-02-01

We report the fabrication of high crystal quality epitaxial thin films of maghemite (γ-Fe2O3), a classic ferrimagnetic insulating iron oxide. Spin Seebeck effect (SSE) measurements in γ-Fe2O3/Pt bilayers as a function of sample preparation conditions and temperature yield a SSE coefficient of 0.5(1) μV/K at room temperature. Dependence on temperature allows us to estimate the magnon diffusion length in maghemite to be in the range of tens of nanometers, in good agreement with that of conducting iron oxide magnetite (Fe3O4), establishing the relevance of spin currents of magnonic origin in magnetic iron oxides.

Geometric confinement effects on the metal-insulator transition temperature and stress relaxation in VO2 thin films grown on silicon

NASA Astrophysics Data System (ADS)

Viswanath, Changhyun Ko, B.; Yang, Zheng; Ramanathan, Shriram

2011-03-01

VO2 undergoes a sharp metal-insulator transition at ˜67 °C with several orders of change in conductivity and optical transmittance. Understanding and control of the properties of vanadium oxide layers grown on technologically relevant substrates such as Si (100) single crystals is therefore of great interest. In this work, we show tunability of metal-insulator transition temperature as well as recoverable stress in VO2 thin films grown on Si substrate by introducing nanoscale atomic layer deposited HfO2 interfacial layers with no degradation in the resistance ratio. For a confined VO2 film, the metal-insulator transition temperature is suppressed by ˜16 °C and the recoverable stress is 150 MPa, compared to 400 MPa for a bare film. These observations are further correlated with in situ variable temperature measurement of stress changes occurring during the phase transition. Structural and microstructural studies on the various samples have been carried out by x ray diffraction and cross-sectional transmission electron microscopy. The strategy of tuning the metal-insulator transition characteristics by nanoscale interfacial dielectrics is of broader relevance in design of programmable materials and integration into solid state devices for electronics.

A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films on insulating substrates and single crystals.

PubMed

Kamlapure, Anand; Saraswat, Garima; Ganguli, Somesh Chandra; Bagwe, Vivas; Raychaudhuri, Pratap; Pai, Subash P

2013-12-01

We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350 mK and in magnetic fields up to 9 T, with thin film deposition and in situ single crystal cleaving capabilities. The main focus lies on the simple design of STM head and a sample holder design that allows us to get spectroscopic data on superconducting thin films grown in situ on insulating substrates. Other design details on sample transport, sample preparation chamber, and vibration isolation schemes are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe2 single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.

Resistivity and resistivity fluctuations of thin-film platinum-aluminum oxide granular metal-insulator composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantese, J.V.

1986-01-01

Thin film metal-insulator composites were used to study how the resistivity and fluctuations in the resistivity were altered by changes in conduction mechanism so as to understand the source of the fluctuations and to better understand the conduction processes themselves. Metal-insulator composites were prepared by co-evaporation of platinum and aluminum oxide in a high vacuum system to create a series of films which had a range of metal volume fill fractions, p, from 23 to 100%. The samples were patterned using standard photolithographic techniques to form sample geometries of typical dimensions, length approx.40 ..mu..m, width approx.2 ..mu..m, and thickness approx.1500more » A. The resistivity rho, and power spectral density of the resistivity fluctuations, S/sub rho/(f), were measured as a function of p and temperature, T. Rho(p,T) was found to be a rapidly increasing function of decreasing p, rising monotonically by more than 7 orders of magnitude as p was decreased from 100% to 23%. For p greater than or equal to 59% the resistivity decreased linearly with decreasing temperature until limited by impurity scattering. The resistivities for the low metal fill fraction materials (P greater than or equal to 50%) increased as the temperature was reduced as expected of thermally assisted tunneling conduction in metal-insulator composites. The transition from metallic conduction to thermally assisted tunneling occurred at a critical value, p/sub c/, between 59% and 50% Pt.« less

Organic Field Effect Transistor Using Amorphous Fluoropolymer as Gate Insulating Film

NASA Astrophysics Data System (ADS)

Kitajima, Yosuke; Kojima, Kenzo; Mizutani, Teruyoshi; Ochiai, Shizuyasu

Organic field effect transistors are fabricated by the active layer of Regioregular poly (3-hexylthiophene-2,5-diy)(P3HT) thin film. CYTOP thin film made from Amorphous Fluoropolymer and fabricated by spin-coating is adopted to a gate dielectric layer on Polyethylenenaphthalate (PEN) thin film that is the substrate of an organic field effect transistor. The surface morphology and molecular orientation of P3HT thin films is observed by atomic force microscope (AFM) and X-Ray diffractometer (XRD). Grains are observed on the CYTOP thin film via an AFM image and the P3HT molecule is oriented perpendicularly on the CYTOP thin film. Based on the performance of the organic field effect transistor, the carrier mobility is 0.092 cm2/Vs, the ON/OFF ratio is 7, and the threshold voltage is -12 V. The ON/OFF ratio is relatively low and to improve On/Off ratio, the CYTOP/Polyimide double gate insulating layer is adopted to OFET.

Solution-derived SiO2 gate insulator formed by CO2 laser annealing for polycrystalline silicon thin-film transistors

NASA Astrophysics Data System (ADS)

Hishitani, Daisuke; Horita, Masahiro; Ishikawa, Yasuaki; Ikenoue, Hiroshi; Uraoka, Yukiharu

2017-05-01

The formation of perhydropolysilazane (PHPS)-based SiO2 films by CO2 laser annealing is proposed. Irradiation with a CO2 laser with optimum fluence transformed a prebaked PHPS film into a SiO2 film with uniform composition in the thickness direction. Polycrystalline silicon thin-film transistors (poly-Si TFTs) with a SiO2 film as the gate insulator were fabricated. When the SiO2 film was formed by CO2 laser annealing (CO2LA) at the optimum fluence of 20 mJ/cm2, the film had fewer OH groups which was one-twentieth that of the furnace annealed PHPS film and one-hundredth that of the SiO2 film deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethyl orthosilicate (TEOS). The resulting TFTs using PHPS showed a clear transistor operation with a field-effect mobility of 37.9 ± 1.2 cm2 V-1 s-1, a threshold voltage of 9.8 ± 0.2 V, and a subthreshold swing of 0.76 ± 0.02 V/decade. The characteristics of such TFTs were as good as those of a poly-Si TFT with a SiO2 gate insulator prepared by PECVD using TEOS.

Thickness-dependent carrier and phonon dynamics of topological insulator Bi2Te3 thin films.

PubMed

Zhao, Jie; Xu, Zhongjie; Zang, Yunyi; Gong, Yan; Zheng, Xin; He, Ke; Cheng, Xiang'ai; Jiang, Tian

2017-06-26

As a new quantum state of matter, topological insulators offer a new platform for exploring new physics, giving rise to fascinating new phenomena and new devices. Lots of novel physical properties of topological insulators have been studied extensively and are attributed to the unique electron-phonon interactions at the surface. Although electron behavior in topological insulators has been studied in detail, electron-phonon interactions at the surface of topological insulators are less understood. In this work, using optical pump-optical probe technology, we performed transient absorbance measurement on Bi 2 Te 3 thin films to study the dynamics of its hot carrier relaxation process and coherent phonon behavior. The excitation and dynamics of phonon modes are observed with a response dependent on the thickness of the samples. The thickness-dependent characteristic time, amplitude and frequency of the damped oscillating signals are acquired by fitting the signal profiles. The results clearly indicate that the electron-hole recombination process gradually become dominant with the increasing thickness which is consistent with our theoretical calculation. In addition, a frequency modulation phenomenon on the high-frequency oscillation signals induced by coherent optical phonons is observed.

Thin-film metal hydrides.

PubMed

Remhof, Arndt; Borgschulte, Andreas

2008-12-01

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well-defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye-catching hydrogen switchable mirror effect, the visualization of solid-state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin-metal hydride films are used as model systems to study metal-insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis.

Origins of enhanced thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070; Chi, Hang

2016-01-25

In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materialsmore » with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m{sup −1} K{sup −2} is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films.« less

Conduction at domain walls in insulating Pb(Zr0.2 Ti0.8)O3 thin films.

PubMed

Guyonnet, Jill; Gaponenko, Iaroslav; Gariglio, Stefano; Paruch, Patrycja

2011-12-01

Domain wall conduction in insulating Pb(Zr(0.2) Ti(0.8))O(3) thin films is demonstrated. The observed electrical conduction currents can be clearly differentiated from displacement currents associated with ferroelectric polarization switching. The domain wall conduction, nonlinear and highly asymmetric due to the specific local probe measurement geometry, shows thermal activation at high temperatures, and high stability over time. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface modification of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors.

PubMed

Jang, Kwang-Suk; Wee, Duyoung; Kim, Yun Ho; Kim, Jinsoo; Ahn, Taek; Ka, Jae-Won; Yi, Mi Hye

2013-06-11

We report a simple approach to modify the surface of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors. It is expected that the yttrium oxide interlayer will provide a surface that is more chemically compatible with the ZnO semiconductor than is bare polyimde. The field-effect mobility and the on/off current ratio of the ZnO TFT with the YOx/polyimide gate insulator were 0.456 cm(2)/V·s and 2.12 × 10(6), respectively, whereas the ZnO TFT with the polyimide gate insulator was inactive.

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

NASA Astrophysics Data System (ADS)

Jeon, Jun-Young; Ha, Tae-Jun

2017-08-01

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.

Broadband and wide angle near-unity absorption in graphene-insulator-metal thin film stacks

NASA Astrophysics Data System (ADS)

Zhang, H. J.; Zheng, G. G.; Chen, Y. Y.; Xu, L. H.

2018-05-01

Broadband unity absorption in graphene-insulator-metal (GIM) structures is demonstrated in the visible (VIS) and near-infrared (NIR) spectra. The spectral characteristics possess broadband absorption peaks, by simply choosing a stack of GIM, while no nanofabrication steps and patterning are required, and thus can be easily fabricated to cover a large area. The electromagnetic (EM) waves can be entirely trapped and the absorption can be greatly enhanced are verified with the finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA) methods. The position and the number of the absorption peak can be totally controlled by adjusting the thickness of the insulator layer. The proposed absorber maintains high absorption (above 90%) for both transverse electric (TE) and transverse magnetic (TM) polarizations, and for angles of incidence up to 80°. This work opens up a promising approach to realize perfect absorption (PA) with ultra-thin film, which could implicate many potential applications in optical detection and optoelectronic devices.

Topological insulator thin films starting from the amorphous phase-Bi{sub 2}Se{sub 3} as example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barzola-Quiquia, J., E-mail: j.barzola@physik.uni-leipzig.de; Lehmann, T.; Stiller, M.

We present a new method to obtain topological insulator Bi{sub 2}Se{sub 3} thin films with a centimeter large lateral length. To produce amorphous Bi{sub 2}Se{sub 3} thin films, we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing, the samples transform into the rhombohedral Bi{sub 2}Se{sub 3} crystalline structure which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared tomore » the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance and the Hall effect at different temperatures between 2 K and 275 K. At temperatures T ≲ 50 K and fields B ≲ 1 T, we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.« less

Thin films of topological Kondo insulator candidate SmB6: Strong spin-orbit torque without exclusive surface conduction

PubMed Central

Li, Yufan; Ma, Qinli; Huang, S. X.; Chien, C. L.

2018-01-01

The advent of topological insulators (TIs), a novel class of materials that harbor a metallic spin-chiral surface state coexisting with band-insulating bulk, opens up new possibilities for spintronics. One promising route is current-induced switching of an adjacent magnetic layer via spin-orbit torque (SOT), arising from the large spin-orbit coupling intrinsically possessed by TIs. The Kondo insulator SmB6 has been recently proposed to be a strongly correlated TI, supported by the observation of a metallic surface state in bulk SmB6, as evidenced by the thickness independence of the low-temperature resistance plateau. We report the synthesis of epitaxial (001) SmB6/Si thin films and a systematic thickness-dependent electrical transport study. Although the low-temperature resistance plateau is observed for all films from 50 to 500 nm in thickness, the resistance is distinctively thickness-dependent and does not support the notion of surface conduction and interior insulation. On the other hand, we demonstrate that SmB6 can generate a large SOT to switch an adjacent ferromagnetic layer, even at room temperature. The effective SOT generated from SmB6 is comparable to that from β-W, one of the strongest SOT materials. PMID:29376125

Tuning metal-insulator transitions in epitaxial V2O3 thin films

NASA Astrophysics Data System (ADS)

Thorsteinsson, Einar B.; Shayestehaminzadeh, Seyedmohammad; Arnalds, Unnar B.

2018-04-01

We present a study of the synthesis of epitaxial V2O3 films on c-plane Al2O3 substrates by reactive dc-magnetron sputtering. The results reveal a temperature window, at substantially lower values than previously reported, wherein epitaxial films can be obtained when deposited on [0001] oriented surfaces. The films display a metal-insulator transition with a change in the resistance of up to four orders of magnitude, strongly dependent on the O2 partial pressure during deposition. While the electronic properties of the films show sensitivity to the amount of O2 present during deposition of the films, their crystallographic structure and surface morphology of atomically flat terraced structures with up to micrometer dimensions are maintained. The transition temperature, as well as the scale of the metal-insulator transition, is correlated with the stoichiometry and local strain in the films controllable by the deposition parameters.

Ferromagnetic insulating state in tensile-strained LaCoO3 thin films from LDA + U calculations

NASA Astrophysics Data System (ADS)

Hsu, Han; Blaha, Peter; Wentzcovitch, Renata M.

2012-04-01

With local density approximation+Hubbard U (LDA+U) calculations, we show that the ferromagnetic (FM) insulating state observed in tensile-strained LaCoO3 epitaxial thin films is most likely a mixture of low-spin (LS) and high-spin (HS) Co, namely, a HS/LS mixture state. Compared with other FM states, including the intermediate-spin (IS) state (metallic within LDA+U), which consists of IS Co only, and the insulating IS/LS mixture state, the HS/LS state is the most favorable one. The FM order in the HS/LS state is stabilized via the superexchange interactions between adjacent LS and HS Co. We also show that the Co spin state can be identified by measuring the electric field gradient at the Co nucleus via nuclear magnetic resonance spectroscopy.

The effect of Argon pressure dependent V thin film on the phase transition process of (020) VO2 thin film

NASA Astrophysics Data System (ADS)

Meng, Yifan; Huang, Kang; Tang, Zhou; Xu, Xiaofeng; Tan, Zhiyong; Liu, Qian; Wang, Chunrui; Wu, Binhe; Wang, Chang; Cao, Juncheng

2018-01-01

It has been proved challenging to fabricate the single crystal orientation of VO2 thin film by a simple method. Based on chemical reaction thermodynamic and crystallization analysis theory, combined with our experimental results, we find out that when stoichiometric number of metallic V in the chemical equation is the same, the ratio of metallic V thin film surface average roughness Ra to thin film average particle diameter d decreases with the decreasing sputtering Argon pressure. Meanwhile, the oxidation reaction equilibrium constant K also decreases, which will lead to the increases of oxidation time, thereby the crystal orientation of the VO2 thin film will also become more uniform. By sputtering oxidation coupling method, metallic V thin film is deposited on c-sapphire substrate at 1 × 10-1 Pa, and then oxidized in the air with the maximum oxidation time of 65s, high oriented (020) VO2 thin film has been fabricated successfully, which exhibits ∼4.6 orders sheet resistance change across the metal-insulator transition.

Delocalized metallic state on insulating, disordered BiSbTeSe2 thin films - a test of Z2 protection.

NASA Astrophysics Data System (ADS)

Gopal, Rk; Singh, Sourabh; Sarkar, Jit; Patro, Reshma; Roy, Subhadip; Mitra, Chiranjib; Quantum computation; Topological matter Group Team

We present thickness and temperature dependent magneto transport properties of bulk insulating and granular BiSbTeSe2 thin films, grown by pulsed laser deposition technique. The temperature dependent resistivity (R-T) of these films is found to be insulating (d ρ/dT <0) and resistivity changes thrice the magnitude measured at room temperature as temperature is varied from 300K to 1.8K. On application of small perpendicular magnetic field in the low temperature regime, the R-T takes an upward shift from the zero field R-T - a trademark signature of a metallic state on an insulating bulk film. The grain boundaries in these films, as seen by scanning electron microscopy, present an additional disorder and hence confinement/trapping centers to the surface Dirac states in comparison to the films grown by molecular beam epitaxy and single crystals, which have atomically flat surface. Therefore these films present real test for the topological protection of surface Dirac states and their immunity against localization which is known as Z2 protection. From the magnetoresistance (MR) measurements at low temperatures a sharp and relatively large rise in MR is found a signature of weak - antilocalization (WAL) -a signature of topologically protected surface states. The WAL analysis of the MR data reveals a phase breaking length of the order of grain size suggesting that grain Author is grateful to the Government of India and IISER-Kolkata for providing funding and experimental facilities for the following research work.

Flexible Thin Metal Film Thermal Sensing System

NASA Technical Reports Server (NTRS)

Thomsen, Donald Laurence (Inventor)

2012-01-01

A flexible thin metal film thermal sensing system is provided. A thermally-conductive film made from a thermally-insulating material is doped with thermally-conductive material. At least one layer of electrically-conductive metal is deposited directly onto a surface of the thermally-conductive film. One or more devices are coupled to the layer(s) to measure an electrical characteristic associated therewith as an indication of temperature.

Bulk contribution to magnetotransport properties of low-defect-density Bi2Te3 topological insulator thin films

NASA Astrophysics Data System (ADS)

Ngabonziza, P.; Wang, Y.; Brinkman, A.

2018-04-01

An important challenge in the field of topological materials is to carefully disentangle the electronic transport contribution of the topological surface states from that of the bulk. For Bi2Te3 topological insulator samples, bulk single crystals and thin films exposed to air during fabrication processes are known to be bulk conducting, with the chemical potential in the bulk conduction band. For Bi2Te3 thin films grown by molecular beam epitaxy, we combine structural characterization (transmission electron microscopy), chemical surface analysis as function of time (x-ray photoelectron spectroscopy) and magnetotransport analysis to understand the low defect density and record high bulk electron mobility once charge is doped into the bulk by surface degradation. Carrier densities and electronic mobilities extracted from the Hall effect and the quantum oscillations are consistent and reveal a large bulk carrier mobility. Because of the cylindrical shape of the bulk Fermi surface, the angle dependence of the bulk magnetoresistance oscillations is two dimensional in nature.

Uncooled thin film pyroelectric IR detector with aerogel thermal isolation

DOEpatents

Ruffner, Judith A.; Bullington, Jeff A.; Clem, Paul G.; Warren, William L.; Brinker, C. Jeffrey; Tuttle, Bruce A.; Schwartz, Robert W.

1999-01-01

A monolithic infrared detector structure which allows integration of pyroelectric thin films atop low thermal conductivity aerogel thin films. The structure comprises, from bottom to top, a substrate, an aerogel insulating layer, a lower electrode, a pyroelectric layer, and an upper electrode layer capped by a blacking layer. The aerogel can offer thermal conductivity less than that of air, while providing a much stronger monolithic alternative to cantilevered or suspended air-gap structures for pyroelectric thin film pixel arrays. Pb(Zr.sub.0.4 Ti.sub.0.6)O.sub.3 thin films deposited on these structures displayed viable pyroelectric properties, while processed at 550.degree. C.

Metal-Insulator Transition in Epitaxial Pyrochlore Iridates Bi2Ir2O7 thin Films

NASA Astrophysics Data System (ADS)

Chu, Jiun-Haw; Liu, Jian; Yi, Di; Rayan-Serrao, C.; Suresha, S.; Marti, Xavi; Riggs, Scott; Shapiro, Max; Ian, Fisher; Ramesh, R.

2013-03-01

Recently there is a surge of interest in searching for topological order in correlated electronic systems such as transition metal oxides. The strong spin-orbit interaction of 5d electrons and the geometric frustration in the crystal lattice make the pyrochlore iridate(A2Ir2O7) an ideal candidate to achieve this goal. Pioneering experiments on bulk polycrystalline and single crystal samples revealed a temperature dependent metal-insulator transition coupled to a long range magnetic order, and the transition temperature can be tuned by either A-site ionic radius or an external pressure. In this talk we present our efforts to understand and control the metal-insulator transition and the underlying electronic structure of pyrochlore iridates via epitaxial Bi2Ir2O7 thin films. Bulk Bi2Ir2O7 is located at the metallic side of the phase diagram. However as the film's thickness decreases the transport evolves from a metallic to a strongly localized character. Resonant X-ray spectroscopy suggests that the density of states near Fermi level is dominated by the Ir Je ff =1/2 states. Intriguingly, the magnetoresistance shows a linear field dependence over a wide range of fields at low temperatures, which is possibly consistent with the existence of Dirac nodes.

Thermal conductivity model for nanoporous thin films

NASA Astrophysics Data System (ADS)

Huang, Congliang; Zhao, Xinpeng; Regner, Keith; Yang, Ronggui

2018-03-01

Nanoporous thin films have attracted great interest because of their extremely low thermal conductivity and potential applications in thin thermal insulators and thermoelectrics. Although there are some numerical and experimental studies about the thermal conductivity of nanoporous thin films, a simplified model is still needed to provide a straightforward prediction. In this paper, by including the phonon scattering lifetimes due to film thickness boundary scattering, nanopore scattering and the frequency-dependent intrinsic phonon-phonon scattering, a fitting-parameter-free model based on the kinetic theory of phonon transport is developed to predict both the in-plane and the cross-plane thermal conductivities of nanoporous thin films. With input parameters such as the lattice constants, thermal conductivity, and the group velocity of acoustic phonons of bulk silicon, our model shows a good agreement with available experimental and numerical results of nanoporous silicon thin films. It illustrates that the size effect of film thickness boundary scattering not only depends on the film thickness but also on the size of nanopores, and a larger nanopore leads to a stronger size effect of the film thickness. Our model also reveals that there are different optimal structures for getting the lowest in-plane and cross-plane thermal conductivities.

Growth of magnesium diboride thin films on boron buffered Si and silicon-on-insulator substrates by hybrid physical chemical vapor deposition

NASA Astrophysics Data System (ADS)

Withanage, Wenura K.; Penmatsa, Sashank V.; Acharya, Narendra; Melbourne, Thomas; Cunnane, D.; Karasik, B. S.; Xi, X. X.

2018-07-01

We report on the growth of high quality MgB2 thin films on silicon and silicon-on-insulator substrates by hybrid physical chemical vapor deposition. A boron buffer layer was deposited on all sides of the Si substrate to prevent the reaction of Mg vapor and Si. Ar ion milling at a low angle of 1° was used to reduce the roughness of the boron buffer layer before the MgB2 growth. An Ar ion milling at low angle of 1° was also applied to the MgB2 surface to reduce its roughness. The resultant MgB2 films showed excellent superconducting properties and a smooth surface. The process produces thin MgB2 films suitable for waveguide-based superconducting hot electron bolometers and other MgB2-based electronic devices.

A Study of Electrical and Optical Stability of GSZO THin Film Transisitors

DTIC Science & Technology

2014-01-01

introduces an overview of the research carried out on IGZO , ZnO, and GSZO thin film transistors that is relevant to the work discussed in this...dangling bonds or electron trapping near the gate insulator interface in IGZO thin film transistors . Mathews et al. [13] indicated that subjecting TFTs to...Ping David Shieh, Hideo Hosono, and Jerzy Kanicki, Photofield-Effect in Amporphous In-Ga-Zn-O (a- IGZO ) Thin - Film Transistors . Journal of Information

Thin film hydrogen sensor

DOEpatents

Lauf, Robert J.; Hoffheins, Barbara S.; Fleming, Pamela H.

1994-01-01

A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed.

Fabrication and Characterization of ZnO Langmuir-Blodgett Film and Its Use in Metal-Insulator-Metal Tunnel Diode.

PubMed

Azad, Ibrahim; Ram, Manoj K; Goswami, D Yogi; Stefanakos, Elias

2016-08-23

Metal-insulator-metal tunnel diodes have great potential for use in infrared detection and energy harvesting applications. The quantum based tunneling mechanism of electrons in MIM (metal-insulator-metal) or MIIM (metal-insulator-insulator-metal) diodes can facilitate rectification at THz frequencies. In this study, the required nanometer thin insulating layer (I) in the MIM diode structure was fabricated using the Langmuir-Blodgett technique. The zinc stearate LB film was deposited on Au/Cr coated quartz, FTO, and silicon substrates, and then heat treated by varying the temperature from 100 to 550 °C to obtain nanometer thin ZnO layers. The thin films were characterized by XRD, AFM, FTIR, and cyclic voltammetry methods. The final MIM structure was fabricated by depositing chromium/nickel over the ZnO on Au/Cr film. The current voltage (I-V) characteristics of the diode showed that the conduction mechanism is electron tunneling through the thin insulating layer. The sensitivity of the diodes was as high as 32 V(-1). The diode resistance was ∼80 Ω (at a bias voltage of 0.78 V), and the rectification ratio at that bias point was about 12 (for a voltage swing of ±200 mV). The diode response exhibited significant nonlinearity and high asymmetry at the bias point, very desirable diode performance parameters for IR detection applications.

Poly(4-vinylphenol) gate insulator with cross-linking using a rapid low-power microwave induction heating scheme for organic thin-film-transistors

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Shang, Ming-Chi; Hsia, Mao-Yuan; Wang, Shea-Jue; Huang, Bohr-Ran; Lee, Win-Der

2016-03-01

A Microwave-Induction Heating (MIH) scheme is proposed for the poly(4-vinylphenol) (PVP) gate insulator cross-linking process to replace the traditional oven heating cross-linking process. The cross-linking time is significantly decreased from 1 h to 5 min by heating the metal below the PVP layer using microwave irradiation. The necessary microwave power was substantially reduced to about 50 W by decreasing the chamber pressure. The MIH scheme is a good candidate to replace traditional thermal heating for cross-linking of PVP as the gate insulator for organic thin-film-transistors.

Emergent Topological Phenomena in Thin Films of Pyrochlore Iridates

NASA Astrophysics Data System (ADS)

Yang, Bohm-Jung; Nagaosa, Naoto

2014-06-01

Because of the recent development of thin film and artificial superstructure growth techniques, it is possible to control the dimensionality of the system, smoothly between two and three dimensions. In this Letter we unveil the dimensional crossover of emergent topological phenomena in correlated topological materials. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that the thin film can have a giant anomalous Hall conductance, proportional to the thickness of the film, even though there is no Hall effect in 3D bulk material. Moreover, in the case of ultrathin films, a quantized anomalous Hall conductance can be observed, despite the fact that the system is an antiferromagnet. In addition, we uncover the emergence of a new topological phase, the nontrivial topological properties of which are hidden in the bulk insulator and manifest only in thin films. This shows that the thin film of correlated topological materials is a new platform to search for unexplored novel topological phenomena.

Growth and characterization of MnGa thin films with perpendicular magnetic anisotropy on BiSb topological insulator

NASA Astrophysics Data System (ADS)

Duy Khang, Nguyen Huynh; Ueda, Yugo; Yao, Kenichiro; Hai, Pham Nam

2017-10-01

We report on the crystal growth as well as the structural and magnetic properties of Bi0.8Sb0.2 topological insulator (TI)/MnxGa1-x bi-layers grown on GaAs(111)A substrates by molecular beam epitaxy. By optimizing the growth conditions and Mn composition, we were able to grow MnxGa1-x thin films on Bi0.8Sb0.2 with the crystallographic orientation of Bi0.8Sb0.2(001)[1 1 ¯ 0]//MnGa (001)[100]. Using magnetic circular dichroism (MCD) spectroscopy, we detected both the L10 phase ( x < 0.6 ) and the D022 phase ( x > 0.6 ) of MnxGa1-x. For 0.50 ≤ x ≤ 0.55 , we obtained ferromagnetic L10-MnGa thin films with clear perpendicular magnetic anisotropy, which were confirmed by MCD hysteresis, anomalous Hall effect as well as superconducting quantum interference device measurements. Our results show that the BiSb/MnxGa1-x bi-layer system is promising for perpendicular magnetization switching using the giant spin Hall effect in TIs.

Electronic Devices Based on Oxide Thin Films Fabricated by Fiber-to-Film Process.

PubMed

Meng, You; Liu, Ao; Guo, Zidong; Liu, Guoxia; Shin, Byoungchul; Noh, Yong-Young; Fortunato, Elvira; Martins, Rodrigo; Shan, Fukai

2018-05-30

Technical development for thin-film fabrication is essential for emerging metal-oxide (MO) electronics. Although impressive progress has been achieved in fabricating MO thin films, the challenges still remain. Here, we report a versatile and general thermal-induced nanomelting technique for fabricating MO thin films from the fiber networks, briefly called fiber-to-film (FTF) process. The high quality of the FTF-processed MO thin films was confirmed by various investigations. The FTF process is generally applicable to numerous technologically relevant MO thin films, including semiconducting thin films (e.g., In 2 O 3 , InZnO, and InZrZnO), conducting thin films (e.g., InSnO), and insulating thin films (e.g., AlO x ). By optimizing the fabrication process, In 2 O 3 /AlO x thin-film transistors (TFTs) were successfully integrated by fully FTF processes. High-performance TFT was achieved with an average mobility of ∼25 cm 2 /(Vs), an on/off current ratio of ∼10 7 , a threshold voltage of ∼1 V, and a device yield of 100%. As a proof of concept, one-transistor-driven pixel circuit was constructed, which exhibited high controllability over the light-emitting diodes. Logic gates based on fully FTF-processed In 2 O 3 /AlO x TFTs were further realized, which exhibited good dynamic logic responses and voltage amplification by a factor of ∼4. The FTF technique presented here offers great potential in large-area and low-cost manufacturing for flexible oxide electronics.

Thin film photovoltaic device and process of manufacture

DOEpatents

Albright, S.P.; Chamberlin, R.

1997-10-07

Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells. 13 figs.

Thin film photovoltaic device and process of manufacture

DOEpatents

Albright, Scot P.; Chamberlin, Rhodes

1999-02-09

Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells.

Thin film photovoltaic device and process of manufacture

DOEpatents

Albright, S.P.; Chamberlin, R.

1999-02-09

Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells. 13 figs.

Thin film photovoltaic device and process of manufacture

DOEpatents

Albright, Scot P.; Chamberlin, Rhodes

1997-10-07

Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells.

Helium ion beam induced electron emission from insulating silicon nitride films under charging conditions

NASA Astrophysics Data System (ADS)

Petrov, Yu. V.; Anikeva, A. E.; Vyvenko, O. F.

2018-06-01

Secondary electron emission from thin silicon nitride films of different thicknesses on silicon excited by helium ions with energies from 15 to 35 keV was investigated in the helium ion microscope. Secondary electron yield measured with Everhart-Thornley detector decreased with the irradiation time because of the charging of insulating films tending to zero or reaching a non-zero value for relatively thick or thin films, respectively. The finiteness of secondary electron yield value, which was found to be proportional to electronic energy losses of the helium ion in silicon substrate, can be explained by the electron emission excited from the substrate by the helium ions. The method of measurement of secondary electron energy distribution from insulators was suggested, and secondary electron energy distribution from silicon nitride was obtained.

Epitaxial Ba2IrO4 thin-films grown on SrTiO3 substrates by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Nichols, J.; Korneta, O. B.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A.

2014-03-01

We have synthesized epitaxial Ba2IrO4 (BIO) thin-films on SrTiO3 (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metal-insulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr2IrO4. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting physical properties predicted in layered iridates.

Magnetic Proximity Effect in a Transferred Topological Insulator Thin Film on a Magnetic Insulator

NASA Astrophysics Data System (ADS)

Che, Xiaoyu; Murata, Koichi; Pan, Lei; He, Qinglin; Yin, Gen; Fan, Yabin; Bi, Lei; Wang, Kang Lung

Exotic physical phenomena such as the quantum anomalous Hall effect (QAHE) arise by breaking the time-reversal symmetry (TRS) in topological insulators. However, substantial efforts have been made in improving the temperature for realizing the QAHE via magnetically doping, while the proximity coupling is another approach to develop the magnetic order without the introduction of additional carriers or the presence of local Fermi level fluctuation. Here we demonstrate the experimental signature of magnetic proximity effect in a molecular beam epitaxy-grown TI thin film of Bi2Se3 transferred to a magnetic substrate of yttrium iron garnet using a wet transfer technique. Comparing to the TI/GaAs control sample, the magnetic order is manifested by the anomalous Hall effect in magneto-transport characterization. Furthermore, due to TRS breaking by the proximity effect we observed a constituent weak localization component accompanied with the weak antilocalization behavior. The present work takes a step further toward realizing QAHE at higher temperature and opens up a new path in TI device designs for applications. We acknowledge the support from the ARO program under contract 15-1-10561, the SHINES Center under Award # S000686, NSF DMR-1350122, and the FAME Center, one of six centers of STARnet, sponsored by MARCO and DARPA.

Ferroelectricity in epitaxial Y-doped HfO2 thin film integrated on Si substrate

NASA Astrophysics Data System (ADS)

Lee, K.; Lee, T. Y.; Yang, S. M.; Lee, D. H.; Park, J.; Chae, S. C.

2018-05-01

We report on the ferroelectricity of a Y-doped HfO2 thin film epitaxially grown on Si substrate, with an yttria-stabilized zirconia buffer layer pre-deposited on the substrate. Piezoresponse force microscopy results show the ferroelectric domain pattern, implying the existence of ferroelectricity in the epitaxial HfO2 film. The epitaxially stabilized HfO2 film in the form of a metal-ferroelectric-insulator-semiconductor structure exhibits ferroelectric hysteresis with a clear ferroelectric switching current in polarization-voltage measurements. The HfO2 thin film also demonstrates ferroelectric retention comparable to that of current perovskite-based metal-ferroelectric-insulator-semiconductor structures.

Thin film hydrogen sensor

DOEpatents

Lauf, R.J.; Hoffheins, B.S.; Fleming, P.H.

1994-11-22

A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed. 6 figs.

Photo-oxidation-modulated refractive index in Bi2Te3 thin films

NASA Astrophysics Data System (ADS)

Yue, Zengji; Chen, Qinjun; Sahu, Amit; Wang, Xiaolin; Gu, Min

2017-12-01

We report on an 800 nm femtosecond laser beam induced giant refractive index modulation and enhancement of near-infrared transparency in topological insulator material Bi2Te3 thin films. An ultrahigh refractive index of up to 5.9 was observed in the Bi2Te3 thin film in near-infrared frequency. The refractive index dramatically decreases by a factor of ~3 by an exposure to the 800 nm femtosecond laser beam. Simultaneously, the transmittance of the Bi2Te3 thin films markedly increases to ~96% in the near-infrared frequency. The Raman spectra provides strong evidences that the observed both refractive index modulation and transparency enhancement result from laser beam induced photooxidation effects in the Bi2Te3 thin films. The Bi2Te3 compound transfers into Bi2O3 and TeO2 under the laser beam illumination. These experimental results pave the way towards the design of various optical devices, such as near-infrared flat lenses, waveguide and holograms, based on topological insulator materials.

Fabrication of amorphous InGaZnO thin-film transistor with solution processed SrZrO3 gate insulator

NASA Astrophysics Data System (ADS)

Takahashi, Takanori; Oikawa, Kento; Hoga, Takeshi; Uraoka, Yukiharu; Uchiyama, Kiyoshi

2017-10-01

In this paper, we describe a method of fabrication of thin film transistors (TFTs) with high dielectric constant (high-k) gate insulator by a solution deposition. We chose a solution processed SrZrO3 as a gate insulator material, which possesses a high dielectric constant of 21 with smooth surface. The IGZO-TFT with solution processed SrZrO3 showed good switching property and enough saturation features, i.e. field effect mobility of 1.7cm2/Vs, threshold voltage of 4.8V, sub-threshold swing of 147mV/decade, and on/off ratio of 2.3×107. Comparing to the TFTs with conventional SiO2 gate insulator, the sub-threshold swing was improved by smooth surface and high field effect due to the high dielectric constant of SrZrO3. These results clearly showed that use of solution processed high-k SrZrO3 gate insulator could improve sub-threshold swing. In addition, the residual carbon originated from organic precursors makes TFT performances degraded.

Thin-film encapsulation of organic electronic devices based on vacuum evaporated lithium fluoride as protective buffer layer

NASA Astrophysics Data System (ADS)

Peng, Yingquan; Ding, Sihan; Wen, Zhanwei; Xu, Sunan; Lv, Wenli; Xu, Ziqiang; Yang, Yuhuan; Wang, Ying; Wei, Yi; Tang, Ying

2017-03-01

Encapsulation is indispensable for organic thin-film electronic devices to ensure reliable operation and long-term stability. For thin-film encapsulating organic electronic devices, insulating polymers and inorganic metal oxides thin films are widely used. However, spin-coating of insulating polymers directly on organic electronic devices may destroy or introduce unwanted impurities in the underlying organic active layers. And also, sputtering of inorganic metal oxides may damage the underlying organic semiconductors. Here, we demonstrated that by utilizing vacuum evaporated lithium fluoride (LiF) as protective buffer layer, spin-coated insulating polymer polyvinyl alcohol (PVA), and sputtered inorganic material Er2O3, can be successfully applied for thin film encapsulation of copper phthalocyanine (CuPc)-based organic diodes. By encapsulating with LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films, the device lifetime improvements of 10 and 15 times can be achieved. These methods should be applicable for thin-film encapsulation of all kinds of organic electronic devices. Moisture-induced hole trapping, and Al top electrode oxidation are suggest to be the origins of current decay for the LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films encapsulated devices, respectively.

PLD of metal insulator and relaxor electroceramic thin films

NASA Astrophysics Data System (ADS)

Bowman, Robert M.; Catalan, Gustau; Corbett, Michael H.; O'Neill, Dierdre; Gregg, J. M.

2001-04-01

In this paper we describe the use of pulsed laser deposition (PLD) for the growth of thin film VxOy, NdNiO3 and Pb(Mg1/3Nb2/3)O3. We begin by briefly describing our growth system. By showing case studies of the three materials systems we identify some important aspects and conditions that we believe are of crucial importance to oxide film growth in general.

TI--CR--AL--O thin film resistors

DOEpatents

Jankowski, Alan F.; Schmid, Anthony P.

2000-01-01

Thin films of Ti--Cr--Al--O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti--Cr--Al--O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti--Cr--Al--O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti--Cr--Al--O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

A flexible amorphous Bi(5)Nb(3)O(15) film for the gate insulator of the low-voltage operating pentacene thin-film transistor fabricated at room temperature.

PubMed

Cho, Kyung-Hoon; Seong, Tae-Geun; Choi, Joo-Young; Kim, Jin-Seong; Kwon, Jae-Hong; Shin, Sang-Il; Chung, Myung-Ho; Ju, Byeong-Kwon; Nahm, Sahn

2009-10-20

The amorphous Bi(5)Nb(3)O(15) film grown at room temperature under an oxygen-plasma sputtering ambient (BNRT-O(2) film) has a hydrophobic surface with a surface energy of 35.6 mJ m(-2), which is close to that of the orthorhombic pentacene (38 mJ m(-2)), resulting in the formation of a good pentacene layer without the introduction of an additional polymer layer. This film was very flexible, maintaining a high capacitance of 145 nF cm(-2) during and after 10(5) bending cycles with a small curvature radius of 7.5 mm. This film was optically transparent. Furthermore, the flexible, pentacene-based, organic thin-film transistors (OTFTs) fabricated on the poly(ether sulfone) substrate at room temperature using a BNRT-O(2) film as a gate insulator exhibited a promising device performance with a high field effect mobility of 0.5 cm(2) V(-1) s(-1), an on/off current modulation of 10(5), and a small subthreshold slope of 0.2 V decade(-1) under a low operating voltage of -5 V. This device also maintained a high carrier mobility of 0.45 cm(2) V(-1 )s(-1) during the bending with a small curvature radius of 9 mm. Therefore, the BNRT-O(2) film is considered a promising material for the gate insulator of the flexible, pentacene-based OTFT.

Tunneling probe of fluctuating superconductivity in disordered thin films

NASA Astrophysics Data System (ADS)

Dentelski, David; Frydman, Aviad; Shimshoni, Efrat; Dalla Torre, Emanuele G.

2018-03-01

Disordered thin films close to the superconductor-insulator phase transition (SIT) hold the key to understanding quantum phase transition in strongly correlated materials. The SIT is governed by superconducting quantum fluctuations, which can be revealed, for example, by tunneling measurements. These experiments detect a spectral gap, accompanied by suppressed coherence peaks, on both sides of the transition. Here we describe the insulating side in terms of a fluctuating superconducting field with finite-range correlations. We perform a controlled diagrammatic resummation and derive analytic expressions for the tunneling differential conductance. We find that short-range superconducting fluctuations suppress the coherence peaks even in the presence of long-range correlations. Our approach offers a quantitative description of existing measurements on disordered thin films and accounts for tunneling spectra with suppressed coherence peaks.

Welding Wires To Thin Thermocouple Films

NASA Technical Reports Server (NTRS)

Holanda, Raymond; Kim, Walter S.; Danzey, Gerald A.; Pencil, Eric; Wadel, Mary

1993-01-01

Parallel-gap resistance welding yields joints surviving temperatures of about 1,000 degrees C. Much faster than thermocompression bonding. Also exceeds conductive-paste bonding and sputtering thin films through porous flame-sprayed insulation on prewelded lead wires. Introduces no foreign material into thermocouple circuit and does not require careful control of thickness of flame-sprayed material.

Disorder-dominated linear magnetoresistance in topological insulator Bi2Se3 thin films

NASA Astrophysics Data System (ADS)

Wang, Wen Jie; Gao, Kuang Hong; Li, Qiu Lin; Li, Zhi-Qing

2017-12-01

The linear magnetoresistance (MR) effect is an interesting topic due to its potential applications. In topological insulator Bi2Se3, this effect has been reported to be dominated by the carrier mobility (μ) and hence has a classical origin. Here, we study the magnetotransport properties of Bi2Se3 thin films and observe the linear MR effect, which cannot be attributed to the quantum model. Unexpectedly, the linear MR does not show the linear dependence on μ, in conflict with the reported results. However, we find that the observed linear MR is dominated by the inverse disorder parameter 1 /kFl , where kF and l are the Fermi wave vector and the mean free path, respectively. This suggests that its origin is also classical and that no μ-dominated linear MR effect is observed which may be due to the very small μ values in our samples.

Fabrication of high performance thin-film transistors via pressure-induced nucleation.

PubMed

Kang, Myung-Koo; Kim, Si Joon; Kim, Hyun Jae

2014-10-31

We report a method to improve the performance of polycrystalline Si (poly-Si) thin-film transistors (TFTs) via pressure-induced nucleation (PIN). During the PIN process, spatial variation in the local solidification temperature occurs because of a non-uniform pressure distribution during laser irradiation of the amorphous Si layer, which is capped with an SiO2 layer. This leads to a four-fold increase in the grain size of the poly-Si thin-films formed using the PIN process, compared with those formed using conventional excimer laser annealing. We find that thin films with optimal electrical properties can be achieved with a reduction in the number of laser irradiations from 20 to 6, as well as the preservation of the interface between the poly-Si and the SiO2 gate insulator. This interface preservation becomes possible to remove the cleaning process prior to gate insulator deposition, and we report devices with a field-effect mobility greater than 160 cm(2)/Vs.

Direct observation of the lattice precursor of the metal-to-insulator transition in V2O3 thin films by surface acoustic waves

NASA Astrophysics Data System (ADS)

Kündel, J.; Pontiller, P.; Müller, C.; Obermeier, G.; Liu, Z.; Nateprov, A. A.; Hörner, A.; Wixforth, A.; Horn, S.; Tidecks, R.

2013-03-01

A surface acoustic wave (SAW) delay line is used to study the metal-to-insulator (MI) transition of V2O3 thin films deposited on a piezoelectric LiNbO3 substrate. Effects contributing to the sound velocity shift of the SAW which are caused by elastic properties of the lattice of the V2O3 films when changing the temperature are separated from those originating from the electrical conductivity. For this purpose the electric field accompanying the elastic wave of the SAW has been shielded by growing the V2O3 film on a thin metallic Cr interlayer (coated with Cr2O3), covering the piezoelectric substrate. Thus, the recently discovered lattice precursor of the MI transition can be directly observed in the experiments, and its fine structure can be investigated.

Studies of electronic and magnetic properties of LaVO3 thin film

NASA Astrophysics Data System (ADS)

Jana, Anupam; Karwal, Sharad; Choudhary, R. J.; Phase, D. M.

2018-04-01

We have investigated the electronic and magnetic properties of pulsed laser deposited Mott insulator LaVO3 (LVO) thin film. Structural characterization revels the single phase [00l] oriented LVO thin film. Enhancement of out of plane lattice parameter indicates the compressively strained LVO film. Electron spectroscopic studies demonstrate that vanadium is present in V3+ state. An energy dispersive X-ray spectroscopic study ensures the stoichiometric growth of the film. Very smooth surface is observed in scanning electron micrograph. Colour mapping for elemental distribution reflect the homogeneity of LVO film. The bifurcation between zero-field-cooled and Field-cooled curves clearly points towards the weak ferromagnetic phase presence in compressively strained LVO thin film. A finite value of coercivity at 300 K reflects the possibility of room temperature ferromagnetism of LVO thin film.

Aluminum induced crystallization of amorphous Ge thin films on insulating substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Ch. Kishan, E-mail: kisn@igcar.gov.in; Tah, T.; Sunitha, D. T.

2016-05-23

Aluminium (metal) induced crystallization of amorphous Ge in bilayer and multilayer Ge/Al thin films deposited on quartz substrate at temperature well below the crystallization temperature of bulk Ge is reported. The crystallization of poly-Ge proceeds via formations of dendritic crystalline Ge grains in the Al matrix. The observed phases were characterized by Raman spectroscopy and X-ray diffraction. The microstructure of Al thin film layer was found to have a profound influence on such crystallization process and formation of dendritic grains.

Surface modification of polyimide gate insulators for solution-processed 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) thin-film transistors.

PubMed

Jang, Kwang-Suk; Kim, Won Soo; Won, Jong-Myung; Kim, Yun-Ho; Myung, Sung; Ka, Jae-Won; Kim, Jinsoo; Ahn, Taek; Yi, Mi Hye

2013-01-21

The surface property of a polyimide gate insulator was successfully modified with an n-octadecyl side-chain. Alkyl chain-grafted poly(amic acid), the polyimide precursor, was synthesized using the diamine comonomer with an alkyl side-chain. By adding a base catalyst to the poly(amic acid) coating solution, the imidization temperature of the spin-coated film could be reduced to 200 °C. The 350 nm-thick polyimide film had a dielectric constant of 3.3 at 10 kHz and a leakage current density of less than 8.7 × 10(-10) A cm(-2), while biased from 0 to 100 V. To investigate the potential of the alkyl chain-grafted polyimide film as a gate insulator for solution-processed organic thin-film transistors (TFTs), we fabricated C(10)-BTBT TFTs. C(10)-BTBT was deposited on the alkyl chain-grafted polyimide gate insulator by spin-coating, forming a well-ordered crystal structure. The field-effect mobility and the on/off current ratio of the TFT device were measured to be 0.20-0.56 cm(2) V(-1) s(-1) and >10(5), respectively.

Electromagnetic waves in a topological insulator thin film stack: helicon-like wave mode and photonic band structure.

PubMed

Inoue, Jun-ichi

2013-09-09

We theoretically explore the electromagnetic modes specific to a topological insulator superlattice in which topological and conventional insulator thin films are stacked periodically. In particular, we obtain analytic formulas for low energy mode that corresponds to a helicon wave, as well as those for photonic bands. We illustrate that the system can be modeled as a stack of quantum Hall layers whose conductivity tensors alternately change signs, and then we analyze the photonic band structures. This subject is a natural extension of a previous study by Tselis et al., which took into consideration a stack of identical quantum Hall layers but their discussion was limited into a low energy mode. Thus we provide analytic formulas for photonic bands and compare their features between the two systems. Our central findings in the topological insulator superlattice are that a low energy mode corresponding to a helicon wave has linear dispersion instead of the conventional quadratic form, and that a robust gapless photonic band appears although the system considered has spacial periodicity. In addition, we demonstrate that the photonic bands agree with the numerically calculated transmission spectra.

Record surface state mobility and quantum Hall effect in topological insulator thin films via interface engineering

DOE PAGES

Koirala, Nikesh; Han, Myung -Geun; Brahlek, Matthew; ...

2015-11-19

Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In 2Se 3/(Bi 0.5In 0.5) 2Se 3 heterostructure, we introduce a quantum generation of Bi 2Se 3 films with an order of magnitude enhanced mobilities than before. Furthermore, this scheme has led to the first observation of the quantum Hallmore » effect in Bi 2Se 3.« less

Thin Film Physical Sensor Instrumentation Research and Development at NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Wrbanek, John D.; Fralick, Gustave C.

2006-01-01

A range of thin film sensor technology has been demonstrated enabling measurement of multiple parameters either individually or in sensor arrays including temperature, strain, heat flux, and flow. Multiple techniques exist for refractory thin film fabrication, fabrication and integration on complex surfaces and multilayered thin film insulation. Leveraging expertise in thin films and high temperature materials, investigations for the applications of thin film ceramic sensors has begun. The current challenges of instrumentation technology are to further develop systems packaging and component testing of specialized sensors, further develop instrumentation techniques on complex surfaces, improve sensor durability, and to address needs for extreme temperature applications. The technology research and development ongoing at NASA Glenn for applications to future launch vehicles, space vehicles, and ground systems is outlined.

Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

NASA Astrophysics Data System (ADS)

Pergolesi, Daniele; Roddatis, Vladimir; Fabbri, Emiliana; Schneider, Christof W.; Lippert, Thomas; Traversa, Enrico; Kilner, John A.

2015-02-01

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.

Hydrothermal Barium Titanate Thin-Film Characteristics and their Suitability as Decoupling Capacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raj, P. Markondeya; Lee, Baik-Woo; Kang, Nam-Kee

System integration and miniaturization demands are driving integrated thin film capacitor technologies towards ultrahigh capacitance densities for noise-free power supply, power conversion and efficient power management. Hydrothermal route can deposit crystalline ferroelectric films at low temperatures of less than 150 C. It is hence an attractive route for integrating high permittivity thin film capacitors on organic, silicon or flex substrates. However, hydrothermal films are not commercialized so far because of their inferior insulation characteristics. Embedded hydroxyl groups are attributed to be the cause for high leakage currents, temperature dependent properties and lower Breakdown Voltages (BDVs). This paper discusses the dielectricmore » characteristics such as capacitance density, leakage currents and Temperature Coefficient of Capacitance (TCC) of hydrothermal barium titanate films and correlates them to the embedded water and OH groups, film morphology, stoichiometry and crystallinity. With thermal treatment, majority of the OH groups can be removed leading to improved insulation characteristics. The room temperature I-V characteristics agreed with ionic conduction models for films baked at 160 C while higher baking temperatures of above 300 C resulted in Poole-Frenkel type conduction. A brief perspective is provided on the suitability of hydrothermal thin film capacitors for power supply applications.« less

Fabrication of thin film heat flux sensors

NASA Technical Reports Server (NTRS)

Will, Herbert

1991-01-01

Thin-film heat-flux sensors have been constructed in the form of arrays of thermocouples on upper and lower surfaces of an insulating layer, so that flux values are proportional to the temperature difference across the upper and lower surface of the insulation material. The sensor thermocouples are connected in thermopile arrangement, and the structure is patterned with photolithographic techniques. Both chromel-alumel and Pt-Pt/Rh thermocouples have been devised; the later produced 28 microvolts when exposed to the radiation of a 1000 C furnace.

Topological insulator film growth by molecular beam epitaxy: A review

DOE PAGES

Ginley, Theresa P.; Wang, Yong; Law, Stephanie

2016-11-23

In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V 2-VI 3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have amore » high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. Furthermore, we close by discussing the bright future for TI film growth by MBE.« less

Ferroelectric domain inversion and its stability in lithium niobate thin film on insulator with different thicknesses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Guang-hao; Bai, Yu-hang; Cui, Guo-xin

2016-07-15

Ferroelectric domain inversion and its effect on the stability of lithium niobate thin films on insulator (LNOI) are experimentally characterized. Two sets of specimens with different thicknesses varying from submicron to microns are selected. For micron thick samples (∼28 μm), domain structures are achieved by pulsed electric field poling with electrodes patterned via photolithography. No domain structure deterioration has been observed for a month as inspected using polarizing optical microscopy and etching. As for submicron (540 nm) films, large-area domain inversion is realized by scanning a biased conductive tip in a piezoelectric force microscope. A graphic processing method is takenmore » to evaluate the domain retention. A domain life time of 25.0 h is obtained and possible mechanisms are discussed. Our study gives a direct reference for domain structure-related applications of LNOI, including guiding wave nonlinear frequency conversion, nonlinear wavefront tailoring, electro-optic modulation, and piezoelectric devices.« less

Quantum transport in new two-dimensional heterostructures: Thin films of topological insulators, phosphorene

NASA Astrophysics Data System (ADS)

Majidi, Leyla; Zare, Moslem; Asgari, Reza

2018-06-01

The unusual features of the charge and spin transport characteristics are investigated in new two-dimensional heterostructures. Intraband specular Andreev reflection is realized in a topological insulator thin film normal/superconducting junction in the presence of a gate electric field. Perfect specular electron-hole conversion is shown for different excitation energy values in a wide experimentally available range of the electric field and also for all angles of incidence when the excitation energy has a particular value. It is further demonstrated that the transmission probabilities of the incoming electrons from different spin subbands to the monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid structure have different behavior with the angle of incidence and perfect transmission occurs at defined angles of incidence to the proposed structure with different length of the N region, and different alignments of magnetization vectors. Moreover, the sign change of the spin-current density is demonstrated by tuning the chemical potential and exchange field of the F region.

Domain switching kinetics in ferroelectric-resistive BiFeO3 thin film memories

NASA Astrophysics Data System (ADS)

Meng, Jianwei; Jiang, Jun; Geng, Wenping; Chen, Zhihui; Zhang, Wei; Jiang, Anquan

2015-02-01

We fabricated (00l) BiFeO3 (BFO) thin films in different growth modes on SrRuO3/SrTiO3 substrates using a pulsed laser deposition technique. X-ray diffraction patterns show an out-of-plane lattice constant of 4.03 Å and ferroelectric polarization of 82 µC/cm2 for the BFO thin film in a layer-by-layer growth mode (2D-BFO), larger than 3.96 Å and 51 µC/cm2 for the thin film in the 3D-island formation growth mode (3D-BFO). The 2D-BFO thin film at 300 K shows switchable on/off diode currents upon polarization flipping near a negative coercive voltage, which is nevertheless absent from the above 3D-BFO thin film. From a positive-up-negative-down pulse characterization technique, we measured domain switching current transients as well as polarization-voltage (Pf-Vf) hysteresis loops in both semiconducting thin films. Pf-Vf hysteresis loops after 1 µs-retention time show the preferred domain orientation pointing to bottom electrodes in a 3D-BFO thin film. The poor retention of the domains pointing to top electrodes can be improved considerably in a 2D-BFO thin film. From these measurements, we extracted domain switching time dependence of coercive voltage at temperatures of 78-300 K. From these dependences, we found coercive voltages in semiconducting ferroelectric thin films much higher than those in insulating thin films, disobeying the traditional Merz equation. Finally, an equivalent resistance model in description of free-carrier compensation of the front domain boundary charge is developed to interpret this difference. This equivalent resistance can be coincidently extracted either from domain switching time dependence of coercive voltage or from applied voltage dependence of domain switching current, which drops almost linearly with the temperature until down to 0 in a ferroelectric insulator at 78 K.

Nondestructive Memory Elements Based on Polymeric Langmuir-Blodgett Thin Films

NASA Astrophysics Data System (ADS)

Reece, T. J.; Ducharme, S.

2007-03-01

Ferroelectric field effect transistors (FeFETs) have attracted much attention recently because of their low power consumption and fast nondestructive readout. Among the ferroelectric thin films used in FET devices; the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C2H2F2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, low cost and compatibility with organic semiconductors. By employing the Langmuir-Blodgett technique, we are able to deposit films as thin as 1.8 nm. We discuss the characterization, modeling and fabrication of metal-ferroelectric-insulator-semiconductor (MFIS) structures incorporating these films.

Strong modification of thin film properties due to screening across the interface

NASA Astrophysics Data System (ADS)

Altendorf, S. G.; Reisner, A.; Tam, B.; Meneghin, F.; Wirth, S.; Tjeng, L. H.

2018-04-01

We report on our investigation of the influence of screening across the interface on the properties of semiconducting thin films. Using EuO as a well-defined model material, layers of various thickness deposited on yttria-stabilized zirconia (100) substrates were covered half with Mg metal and half with the wide-band-gap insulator MgO. We observed that the Curie temperature for the thinnest films is significantly higher for the part which is interfaced with the metal compared to the part which is interfaced with the insulator. We infer that the proximity of a polarizable medium reduces the energies of virtual charge excitations and thus increases the effective exchange interactions, a strong effect that can be utilized systematically for the design of thin film and multilayer systems.

Fabrication and evaluation of dispersed-Ag nanoparticles-in-polyimide thin films

NASA Astrophysics Data System (ADS)

Sonehara, Makoto; Watanabe, Yuki; Yamaguchi, Sota; Kato, Takanori; Yoshisaku, Yasuaki; Sato, Toshiro; Itoh, Eiji

2017-10-01

A thin-film common-mode filter (TF-CMF) for cell phones in the UHF band was fabricated and evaluated. The TF-CMF consisted of multiple metal-insulator-metal (MIM) capacitors and inductors. The sizes of the 0.70-1.0 GHz band-type and 1.8-2.0 GHz band-type TF-CMFs are 1,140 × 1,260 × 10.5 µm3, and 1,060 × 1,060 × 10.5 µm3, respectively. The footprint in both types of TF-CMFs is over 1 mm2. In order to miniaturize the TF-CMF, we proposed to change a polyimide-only to a polyimide with dispersed Ag nanoparticles with high permittivity in the insulator layer for the MIM capacitor of the TF-CMF. A polyimide (\\text{polyimide precursor}:\\text{toluene with dispersed Ag nanoparticles} = 100:1) thin film with dispersed high-density Ag nanoparticles has a relative permittivity of about 8, which is twice as high as that of the polyimide-only thin film. If the capacitance and distance between electrodes are the same, then the capacitor footprint may be halved.

Spin accumulation in disordered topological insulator ultrathin films

NASA Astrophysics Data System (ADS)

Siu, Zhuo Bin; Ho, Cong Son; Tan, Seng Ghee; Jalil, Mansoor B. A.

2017-08-01

Topological insulator (TI) ultrathin films differ from the more commonly studied semi-infinite bulk TIs in that the former possess both top and bottom surfaces where the surface states localized at different surfaces can couple to one another across the finite thickness of the film. In the presence of an in-plane magnetization, the TI thin films display two distinct phases depending on which of the inter-surface coupling or the magnetization is stronger. In this work, we consider a Bi2Se3 TI thin film system with an in-plane magnetization and numerically calculate the resulting spin accumulation on both surfaces of the film due to an in-plane electric field to linear order. We describe a numerical scheme for performing the Kubo formula calculation in which we include impurity scattering and vertex corrections. We find that the sums of the spin accumulation over the two surfaces in the in-plane direction perpendicular to the magnetization and in the out of plane direction are antisymmetric in Fermi energy around the charge neutrality point and are non-vanishing only when the symmetry between the top and bottom TI surfaces is broken. The impurity scattering, in general, diminishes the magnitude of the spin accumulation.

Resistivity behavior of optimized PbTiO3 thin films prepared by spin coating method

NASA Astrophysics Data System (ADS)

Nurbaya, Z.; Wahid, M. H.; Rozana, M. D.; Alrokayan, S. A. H.; Khan, H. A.; Rusop, M.

2018-05-01

Th is study presents the resistivity behavior of PbTiO3 thin films which were prepared towards metal-insulator-metal capacitor device fabrication. The PbTiO3 thin films were prepared through sol-gel spin coating method that involved various deposition parameters that is (1) different molar concentration of PbTiO3 solutions, (2) various additional PbAc-content in PbTiO3 solutions, and (3) various annealing temperature on PbTiO3 thin films. Hence, an electrical measurement of current versus voltage was done to determine the resistivity behavior of PbTiO3 thin films.

Thin-film decoupling capacitors for multi-chip modules

NASA Astrophysics Data System (ADS)

Dimos, D.; Lockwood, S. J.; Schwartz, R. W.; Rogers, M. S.

Thin-film decoupling capacitors based on ferroelectric lead lanthanum zirconate titanate (PLZT) films are being developed for use in advanced packages, such as multi-chip modules. These thin-film decoupling capacitors are intended to replace multi-layer ceramic capacitors for certain applications, since they can be more fully integrated into the packaging architecture. The increased integration that can be achieved should lead to decreased package volume and improved high-speed performance, due to a decrease in interconnect inductance. PLZT films are fabricated by spin coating using metal carboxylate/alkoxide solutions. These films exhibit very high dielectric constants ((var epsilon) greater than or equal to 900), low dielectric losses (tan(delta) = 0.01), excellent insulation resistances (rho greater than 10(exp 13) (Omega)-cm at 125 C), and good breakdown field strengths (E(sub B) = 900 kV/cm). For integrated circuit applications, the PLZT dielectric is less than 1 micron thick, which results in a large capacitance/area (8-9 nF/sq mm). The thin-film geometry and processing conditions also make these capacitors suitable for direct incorporation onto integrated circuits and for packages that require embedded components.

Low-Temperature-Processed Zinc Oxide Thin-Film Transistors Fabricated by Plasma-Assisted Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Kawamura, Yumi; Tani, Mai; Hattori, Nozomu; Miyatake, Naomasa; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu

2012-02-01

We investigated zinc oxide (ZnO) thin films prepared by plasma assisted atomic layer deposition (PA-ALD), and thin-film transistors (TFTs) with the ALD ZnO channel layer for application to next-generation displays. We deposited the ZnO channel layer by PA-ALD at 100 or 300 °C, and fabricated TFTs. The transfer characteristic of the 300 °C-deposited ZnO TFT exhibited high mobility (5.7 cm2 V-1 s-1), although the threshold voltage largely shifted toward the negative (-16 V). Furthermore, we deposited Al2O3 thin film as a gate insulator by PA-ALD at 100 °C for the low-temperature TFT fabrication process. In the case of ZnO TFTs with the Al2O3 gate insulator, the shift of the threshold voltage improved (-0.1 V). This improvement of the negative shift seems to be due to the negative charges of the Al2O3 film deposited by PA-ALD. On the basis of the experimental results, we confirmed that the threshold voltage of ZnO TFTs is controlled by PA-ALD for the deposition of the gate insulator.

Controllable film densification and interface flatness for high-performance amorphous indium oxide based thin film transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ou-Yang, Wei, E-mail: OUYANG.Wei@nims.go.jp, E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Mitoma, Nobuhiko; Kizu, Takio

2014-10-20

To avoid the problem of air sensitive and wet-etched Zn and/or Ga contained amorphous oxide transistors, we propose an alternative amorphous semiconductor of indium silicon tungsten oxide as the channel material for thin film transistors. In this study, we employ the material to reveal the relation between the active thin film and the transistor performance with aid of x-ray reflectivity study. By adjusting the pre-annealing temperature, we find that the film densification and interface flatness between the film and gate insulator are crucial for achieving controllable high-performance transistors. The material and findings in the study are believed helpful for realizingmore » controllable high-performance stable transistors.« less

In-Plane Impedance Spectroscopy measurements in Vanadium Dioxide thin films

NASA Astrophysics Data System (ADS)

Ramirez, Juan; Patino, Edgar; Schmidt, Rainer; Sharoni, Amos; Gomez, Maria; Schuller, Ivan

2012-02-01

In plane Impedance Spectroscopy measurements have been done in Vanadium Dioxide thin films in the range of 100 Hz to 1 MHz. Our measurements allows distinguishing between the resistive and capacitive response of the Vanadium Dioxide films across the metal-insulator transition. A non ideal RC behavior was found in our thin films from room temperature up to 334 K. Around the MIT, an increase of the total capacitance is observed. A capacitor-network model is able to reproduce the capacitance changes across the MIT. Above the MIT, the system behaves like a metal as expected, and a modified equivalent circuit is necessary to describe the impedance data adequately.

Thin Film Approaches to the SRF Cavity Problem Fabrication and Characterization of Superconducting Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beringer, Douglas

Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory’s CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater performance benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency – 1.5more » GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m – there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (≈ 45 MV/m for Nb) where inevitable thermodynamic breakdown occurs. With state of the art Nb based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio frequency applications. Correlated studies on structure, surface morphology and superconducting properties of epitaxial Nb and MgB2 thin films are presented.« less

Gate insulator effects on the electrical performance of ZnO thin film transistor on a polyethersulphone substrate.

PubMed

Lee, Jae-Kyu; Choi, Duck-Kyun

2012-07-01

Low temperature processing for fabrication of transistor backplane is a cost effective solution while fabrication on a flexible substrate offers a new opportunity in display business. Combination of both merits is evaluated in this investigation. In this study, the ZnO thin film transistor on a flexible Polyethersulphone (PES) substrate is fabricated using RF magnetron sputtering. Since the selection and design of compatible gate insulator is another important issue to improve the electrical properties of ZnO TFT, we have evaluated three gate insulator candidates; SiO2, SiNx and SiO2/SiNx. The SiO2 passivation on both sides of PES substrate prior to the deposition of ZnO layer was effective to enhance the mechanical and thermal stability. Among the fabricated devices, ZnO TFT employing SiNx/SiO2 stacked gate exhibited the best performance. The device parameters of interest are extracted and the on/off current ratio, field effect mobility, threshold voltage and subthreshold swing are 10(7), 22 cm2/Vs, 1.7 V and 0.4 V/decade, respectively.

Epitaxial strain effect on the physical properties of layered ruthenate and iridate thin films

NASA Astrophysics Data System (ADS)

Miao, Ludi

Transition metal oxides have attracted widespread attention due to their broad range of fascinating exotic phenomena such as multiferroicity, superconductivity, colossal magnetoresistance and metal-to-insulator transition. Due to the interplay between spin, charge, lattice and orbital degrees of freedom of strongly correlated d electrons, these physical properties are extremely sensitive to the external perturbations such as magnetic field, charge carrier doping and pressure, which provide a unique chance in search for novel exotic quantum states. Ruthenate systems are a typical strongly correlated system, with rich ordered states and their properties are extremely sensitive to external stimuli. Recently, the experimental observation of spin-orbit coupling induced Mott insulator in Sr2IrO4 as well as the theoretical prediction of topological insulating state in other iridates, have attracted tremendous interest in the physics of strong correlation and spin-orbit coupling in 4d/5d compounds. We observe an itinerant ferromagnetic ground state of Ca2 RuO4 film in stark contrast to the Mott-insulating state in bulk Ca2RuO4. We have also established the epitaxial strain effect on the transport and magnetic properties for the (Ca,Sr) 2RuO4 thin films. For Sr2IrO4 thin films, we will show that the Jeff = 1/2 moment orientation can be modulated by epitaxial strain. In addition, we discovered novel Ba 7Ir3O13+x thin films which exhibit colossal permittivity.

Thin film heat flux sensor for Space Shuttle Main Engine turbine environment

NASA Technical Reports Server (NTRS)

Will, Herbert

1991-01-01

The Space Shuttle Main Engine (SSME) turbine environment stresses engine components to their design limits and beyond. The extremely high temperatures and rapid temperature cycling can easily cause parts to fail if they are not properly designed. Thin film heat flux sensors can provide heat loading information with almost no disturbance of gas flows or of the blade. These sensors can provide steady state and transient heat flux information. A thin film heat flux sensor is described which makes it easier to measure small temperature differences across very thin insulating layers.

Understanding the Origin of Ferromagnetism in Strained LaCoO3 Thin Films

NASA Astrophysics Data System (ADS)

Ma, J. X.; Shi, J.; Freeland, J. W.

2009-03-01

Using strain to control the behavior of strongly correlated materials offers new opportunities to control fundamental properties. For the case of magnetism, LaCoO3 offers the ability to use strain through thin film growth to manipulate directly the spin-state of Co in this system. Here we present the results of a detailed polarized x-ray spectroscopy study of LaCoO3 thin films grown on SrTiO3(001) and LaAlO3 (001) substrates. X-ray diffraction from 25 nm thin films confirm the films are fully strained in both cases and, for films under tensile strain, total moment magnetometry shows a clear transition to ferromagnetic state at ˜80K. X-ray absorption shows that the films grown from a LaCoO3 target are slightly hole doped due to non-stoichiometry generated during growth (effective doping ˜ 0.1 holes per unit cell), which in the bulk is sufficient to destroy the low-spin state. However, even though the films are slightly hole doped, the films under tensile strain show long range ferromagnetic order unlike the bulk system. Since the films are insulating, these results are consistent with a ferromagnetic insulating state arising due to superexchange. Work at UCR is supported by ONR/DMEA under award H94003-08-2-0803.

Thickness dependent quantum oscillations of transport properties in topological insulator Bi2Te3 thin films

NASA Astrophysics Data System (ADS)

Rogacheva, E. I.; Budnik, A. V.; Sipatov, A. Yu.; Nashchekina, O. N.; Dresselhaus, M. S.

2015-02-01

The dependences of the electrical conductivity, the Hall coefficient, and the Seebeck coefficient on the layer thickness d (d = 18-600 nm) of p-type topological insulator Bi2Te3 thin films grown by thermal evaporation in vacuum on glass substrates were obtained at room temperature. In the thickness range of d = 18-100 nm, sustained oscillations with a substantial amplitude were revealed. The observed oscillations are well approximated by a harmonic function with a period Δd = (9.5 ± 0.5) nm. At d > 100 nm, the transport coefficients practically do not change as d is increased. The oscillations of the kinetic properties are attributed to the quantum size effects due to the hole confinement in the Bi2Te3 quantum wells. The results of the theoretical calculations of Δd within the framework of a model of an infinitely deep potential well are in good agreement with the experimental results. It is suggested that the substantial amplitude of the oscillations and their sustained character as a function of d are connected with the topologically protected gapless surface states of Bi2Te3 and are inherent to topological insulators.

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

PubMed Central

Ahn, Cheol Hyoun; Senthil, Karuppanan; Cho, Hyung Koun; Lee, Sang Yeol

2013-01-01

High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm2/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers. PMID:24061388

Unusual terahertz spectral weight and conductivity dynamics of the insulator-metal transition in Pr0.5Nd0.5NiO3 thin films

NASA Astrophysics Data System (ADS)

Santhosh Kumar, K.; Das, Sarmistha; Eswara Phanindra, V.; Rana, D. S.

2017-12-01

The metal-insulator transition (MIT) in correlated systems is a central phenomenon that possesses potential for several emerging technologies. We investigate the kinetics of such MIT in perovskite nickelates by studying the terahertz (THz) low-energy charge dynamics in orthorhombic and tetragonal symmetries of Pr0.5Nd0.5NiO3 thin films. The THz conductivity of the orthorhombic thin film is dominated by Drude behavior in the entire temperature range, albeit a dominant anomaly at and around the MIT region. The tetragonal thin film exhibits different overall THz conductivity dynamics though, i.e. of a Drude-Smith (DS) type in the entire temperature range, the DS coefficient signifying dominant backscattering peaks in the MIT region. While the overall THz dynamics profile is different for the two films, a unique yet similar sensitivity of the I-M transition regions of both films to THz frequencies underlines the fundamental origin of the bi-critical phase around MIT of the nickelates. The peculiar behavior around the I-M transition, as evaluated in the framework of a percolative path approximation based Dyre expression, emphasizes the importance of critical metallic volume fraction (f c) for the percolation conduction, as an f c of ~0.645 obtained for the present case, along with evidence for the absence of super-heating.

Deposition of SiC x H y O z thin film on epoxy resin by nanosecond pulsed APPJ for improving the surface insulating performance

NASA Astrophysics Data System (ADS)

Qing, XIE; Haofan, LIN; Shuai, ZHANG; Ruixue, WANG; Fei, KONG; Tao, SHAO

2018-02-01

Non-thermal plasma surface modification for epoxy resin (EP) to improve the insulation properties has wide application prospects in gas insulated switchgear and gas insulated transmission line. In this paper, a pulsed Ar dual dielectrics atmospheric-pressure plasma jet (APPJ) was used for SiC x H y O z thin film deposition on EP samples. The film deposition was optimized by varying the treatment time while other parameters were kept at constants (treatment distance: 10 mm, precursor flow rate: 0.6 l min-1, maximum instantaneous power: 3.08 kW and single pulse energy: 0.18 mJ). It was found that the maximum value of flashover voltages for negative and positive voltage were improved by 18% and 13% when the deposition time was 3 min, respectively. The flashover voltage reduced as treatment time increased. Moreover, all the surface conductivity, surface charge dissipation rate and surface trap level distribution reached an optimal value when thin film deposition time was 3 min. Other measurements, such as atomic force microscopy and scanning electron microscope for EP surface morphology, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy for EP surface compositions, optical emission spectra for APPJ deposition process were carried out to better understand the deposition processes and mechanisms. The results indicated that the original organic groups (C-H, C-C, C=O, C=C) were gradually replaced by the Si containing inorganic groups (Si-O-Si and Si-OH). The reduction of C=O in ester group and C=C in p-substituted benzene of the EP samples might be responsible for shallowing the trap level and then enhancing the flashover voltage. However, when the plasma treatment time was longer than 3 min, the significant increase of the surface roughness might increase the trap level depth and then deteriorate the flashover performance.

A Low Temperature, Solution-Processed Poly(4-vinylphenol), YO(x) Nanoparticle Composite/Polysilazane Bi-Layer Gate Insulator for ZnO Thin Film Transistor.

PubMed

Shin, Hyeonwoo; Kang, Chan-Mo; Chae, Hyunsik; Kim, Hyun-Gwan; Baek, Kyu-Ha; Choi, Hyoung Jin; Park, Man-Young; Do, Lee-Mi; Lee, Changhee

2016-03-01

Low temperature, solution-processed metal oxide thin film transistors (MEOTFTs) have been widely investigated for application in low-cost, transparent, and flexible electronics. To enlarge the application area, solution-processed gate insulators (GI) have been investigated in recent years. We investigated the effects of the organic/inorganic bi-layer GI to ZnO thin film transistors (TFTs). PVP, YO(x) nanoparticle composite, and polysilazane bi-layer showed low leakage current (-10(-8) A/cm2 in 2 MV), which are applicable in low temperature processed MEOTFTs. Polysilazane was used as an interlayer between ZnO and PVP, YO(x) nanoparticle composite as a good charge transport interface with ZnO. By applying the PVP, YO(x), nanoparticle composite/polysilazane bi-layer structure to ZnO TFTs, we successfully suppressed the off current (I(off)) to -10(-11) and fabricated good MEOTFTs in 180 degrees C.

Composition spread studies of Nd1-xLaxNiO3 combinatorial thin films

NASA Astrophysics Data System (ADS)

Suchoski, Richard; Jin, Kui; Yasui, Shintaro; Greene, Richard; Takeuchi, Ichiro

2013-03-01

Rare earth nickelates have attracted a great deal of attention in recent years due to a host of interesting features, one being a transition from paramagnetic metal to antiferromagnetic insulator through distortions from the ideal perovskite unit cell. This metal-to-insulator transition (MIT) can be manipulated by modifying variables such as temperature, rare earth ion size, oxygen content, or stress from lattice-mismatched epitaxial thin film growth. Research on this family has been extensive, though there still exists an absence of thin film studies focusing on intermediate compositions. We have fabricated epitaxial thin film composition spreads of Nd1-xLaxNiO3 grown via combinatorial PLD to investigate these transitional compositions. While our films exhibit a smooth composition progression, we observe a composition threshold where orthorhombic NdNiO3 transforms to rhombohedral LaNiO3, correlating with disappearance of the MIT, and displays a non-Vegard evolution of the film's in-plane lattice constant in HRXRD and Raman scattering data of the A1g rotational mode. This work was performed at the Center for Nanophysics and Advanced Materials (CNAM) at UMD, and supported by AFO SR MURI Grant #FA95500910603.

Thin Film Approaches to the SRF Cavity Problem: Fabrication and Characterization of Superconducting Thin Films

NASA Astrophysics Data System (ADS)

Beringer, Douglas B.

Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory's CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency - 1.5 GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m - there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (approximately 45 MV/m for Niobium) where inevitable thermodynamic breakdown occurs. With state of the art niobium based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio-frequency applications.

Comparison of the agglomeration behavior of thin metallic films on SiO2

NASA Astrophysics Data System (ADS)

Gadkari, P. R.; Warren, A. P.; Todi, R. M.; Petrova, R. V.; Coffey, K. R.

2005-07-01

The stability of continuous metallic thin films on insulating oxide surfaces is of interest to applications such as semiconductor interconnections and gate engineering. In this work, we report the study of the formation of voids and agglomeration of initially continuous Cu, Au, Ru and Pt thin films deposited on amorphous thermally grown SiO2 surfaces. Polycrystalline thin films having thicknesses in the range of 10-100 nm were ultrahigh vacuum sputter deposited on thermally grown SiO2 surfaces. The films were annealed at temperatures in the range of 150-800 °C in argon and argon+3% hydrogen gases. Scanning electron microscopy was used to investigate the agglomeration behavior, and transmission electron microscopy was used to characterize the microstructure of the as-deposited and annealed films. The agglomeration sequence in all of the films is found to follow a two step process of void nucleation and void growth. However, void growth in Au and Pt thin films is different from Cu and Ru thin films. Residual stress and adhesion were observed to play an important part in deciding the mode of void growth in Au and Pt thin films. Last, it is also observed that the tendency for agglomeration can be reduced by encapsulating the metal film with an oxide overlayer.

Strain dependence of the electronic properties of LaTiO3 thin films

NASA Astrophysics Data System (ADS)

Moon, S. J.; Kim, Y. S.

2014-11-01

We report on the transport and the core-level X-ray photoemission spectroscopy data of fully-strained LaTiO3 thin films grown on GdScO3 and SrTiO3 substrates. We observed that LaTiO3 thin film grown on GdScO3 showed insulating behavior but that grown on SrTiO3 exhibited a metallic character. We found that while the La 4 d photoemission spectra of the two films were nearly the same, their Ti 2 p and O 1 s data revealed a difference. Our results suggest that strain-induced changes in the Ti-O bonding play an important role in the electronic properties of LaTiO3 thin films.

Process for producing Ti-Cr-Al-O thin film resistors

DOEpatents

Jankowski, Alan F.; Schmid, Anthony P.

2001-01-01

Thin films of Ti-Cr-Al-O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti-Cr-Al-O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti-Cr-Al-O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti-Cr-Al-O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

Flat panel display using Ti-Cr-Al-O thin film

DOEpatents

Jankowski, Alan F.; Schmid, Anthony P.

2002-01-01

Thin films of Ti--Cr--Al--O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti--Cr--Al--O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti--Cr--Al--O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti--Cr--Al--O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

Inelastic deformation of plasma polymerised thin films facilitated by transient dense plasma focus irradiation

NASA Astrophysics Data System (ADS)

Grant, Daniel S.; Rawat, Rajdeep S.; Bazaka, Kateryna; Jacob, Mohan V.

2017-09-01

The high degree of crosslinking present in plasma polymerised thin films, coupled with their high molecular weight, imbues these films with properties similar to those of thermosetting polymers. For instance, such films tend to be relatively hard, insoluble, and to date have not exhibited plasticity when subjected to elevated temperatures. In this paper it is demonstrated that plasma polymers can, in fact, undergo plastic deformation in response to the application of extremely short-lived thermal treatment delivered by a dense plasma focus device, as evidenced by the evolution of bubble-like structures from the thin film. This finding suggests new avenues for texturing plasma thin films, and synthesising cavities that may find utility as thermal insulators or domains for material encapsulation.

Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel

2015-06-30

Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb) 2Te 3 (CBST) films grown on SrTiO 3 (1 1 1) substrates with and without a Te capping layer. We find that bothmore » the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures.« less

Structural, magnetic, and electronic properties of GdTiO{sub 3} Mott insulator thin films grown by pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grisolia, M. N.; Bruno, F. Y.; Sando, D.

2014-10-27

We report on the optimization process to synthesize epitaxial thin films of GdTiO{sub 3} on SrLaGaO{sub 4} substrates by pulsed laser deposition. Optimized films are free of impurity phases and are fully strained. They possess a magnetic Curie temperature T{sub C} = 31.8 K with a saturation magnetization of 4.2 μ{sub B} per formula unit at 10 K. Transport measurements reveal an insulating response, as expected. Optical spectroscopy indicates a band gap of ∼0.7 eV, comparable to the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of perovskite materials for the design of emergent strongly correlated states at oxide interfaces using a versatile growthmore » technique such as pulsed laser deposition.« less

Fabrication of Thin Film Heat Flux Sensors

NASA Technical Reports Server (NTRS)

Will, Herbert A.

1992-01-01

Prototype thin film heat flux sensors have been constructed and tested. The sensors can be applied to propulsion system materials and components. The sensors can provide steady state and fast transient heat flux information. Fabrication of the sensor does not require any matching of the mounting surface. Heat flux is proportional to the temperature difference across the upper and lower surfaces of an insulation material. The sensor consists of an array of thermocouples on the upper and lower surfaces of a thin insulating layer. The thermocouples for the sensor are connected in a thermopile arrangement. A 100 thermocouple pair heat flux sensor has been fabricated on silicon wafers. The sensor produced an output voltage of 200-400 microvolts when exposed to a hot air heat gun. A 20 element thermocouple pair heat flux sensor has been fabricated on aluminum oxide sheet. Thermocouples are Pt-Pt/Rh with silicon dioxide as the insulating material. This sensor produced an output of 28 microvolts when exposed to the radiation of a furnace operating at 1000 C. Work is also underway to put this type of heat flux sensor on metal surfaces.

Hidden landscapes in thin film topological insulators: between order and disorder, 2D and 3D, normal and topological phases

NASA Astrophysics Data System (ADS)

Oh, Seongshik

Topological insulator (TI) is one of the rare systems in the history of condensed matter physics that is initiated by theories and followed by experiments. Although this theory-driven advance helped move the field quite fast despite its short history, apparently there exist significant gaps between theories and experiments. Many of these discrepancies originate from the very fact that the worlds readily accessible to theories are often far from the real worlds that are available in experiments. For example, the very paradigm of topological protection of the surface states on Z2 TIs such as Bi2Se3, Bi2Te3, Sb2Te3, etc, is in fact valid only if the sample size is infinite and the crystal momentum is well-defined in all three dimensions. On the other hand, many widely studied forms of TIs such as thin films and nano-wires have significant confinement in one or more of the dimensions with varying level of disorders. In other words, many of the real world topological systems have some important parameters that are not readily captured by theories, and thus it is often questionable how far the topological theories are valid to real systems. Interestingly, it turns out that this very uncertainty of the theories provides additional control knobs that allow us to explore hidden topological territories. In this talk, I will discuss how these additional knobs in thin film topological insulators reveal surprising, at times beautiful, landscapes at the boundaries between order and disorder, 2D and 3D, normal and topological phases. This work is supported by Gordon and Betty Moore Foundation's EPiQS Initiative (GBMF4418).

Electronic and optical properties of La-doped S r3I r2O7 epitaxial thin films

NASA Astrophysics Data System (ADS)

Souri, M.; Terzic, J.; Johnson, J. M.; Connell, J. G.; Gruenewald, J. H.; Thompson, J.; Brill, J. W.; Hwang, J.; Cao, G.; Seo, A.

2018-02-01

We have investigated structural, transport, and optical properties of tensile strained (Sr1-xL ax ) 3I r2O7 (x =0 , 0.025, 0.05) epitaxial thin films. While high-Tc superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped S r3I r2O7 thin films is presumably due to disorder-induced localization and ineffective electron doping of La, which brings to light the intriguing difference between epitaxial thin films and bulk single crystals of the iridates.

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films

PubMed Central

2011-01-01

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated. PMID:21711646

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Fiorenza, Patrick; Lo Nigro, Raffaella; Raineri, Vito

2011-12-01

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated.

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films.

PubMed

Fiorenza, Patrick; Lo Nigro, Raffaella; Raineri, Vito

2011-02-04

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated.

Investigation of Rapid Low-Power Microwave-Induction Heating Scheme on the Cross-Linking Process of the Poly(4-vinylphenol) for the Gate Insulator of Pentacene-Based Thin-Film Transistors

PubMed Central

Fan, Ching-Lin; Shang, Ming-Chi; Wang, Shea-Jue; Hsia, Mao-Yuan; Lee, Win-Der; Huang, Bohr-Ran

2017-01-01

In this study, a proposed Microwave-Induction Heating (MIH) scheme has been systematically studied to acquire suitable MIH parameters including chamber pressure, microwave power and heating time. The proposed MIH means that the thin indium tin oxide (ITO) metal below the Poly(4-vinylphenol) (PVP) film is heated rapidly by microwave irradiation and the heated ITO metal gate can heat the PVP gate insulator, resulting in PVP cross-linking. It is found that the attenuation of the microwave energy decreases with the decreasing chamber pressure. The optimal conditions are a power of 50 W, a heating time of 5 min, and a chamber pressure of 20 mTorr. When suitable MIH parameters were used, the effect of PVP cross-linking and the device performance were similar to those obtained using traditional oven heating, even though the cross-linking time was significantly decreased from 1 h to 5 min. Besides the gate leakage current, the interface trap state density (Nit) was also calculated to describe the interface status between the gate insulator and the active layer. The lowest interface trap state density can be found in the device with the PVP gate insulator cross-linked by using the optimal MIH condition. Therefore, it is believed that the MIH scheme is a good candidate to cross-link the PVP gate insulator for organic thin-film transistor applications as a result of its features of rapid heating (5 min) and low-power microwave-irradiation (50 W). PMID:28773101

Investigation of Rapid Low-Power Microwave-Induction Heating Scheme on the Cross-Linking Process of the Poly(4-vinylphenol) for the Gate Insulator of Pentacene-Based Thin-Film Transistors.

PubMed

Fan, Ching-Lin; Shang, Ming-Chi; Wang, Shea-Jue; Hsia, Mao-Yuan; Lee, Win-Der; Huang, Bohr-Ran

2017-07-03

In this study, a proposed Microwave-Induction Heating (MIH) scheme has been systematically studied to acquire suitable MIH parameters including chamber pressure, microwave power and heating time. The proposed MIH means that the thin indium tin oxide (ITO) metal below the Poly(4-vinylphenol) (PVP) film is heated rapidly by microwave irradiation and the heated ITO metal gate can heat the PVP gate insulator, resulting in PVP cross-linking. It is found that the attenuation of the microwave energy decreases with the decreasing chamber pressure. The optimal conditions are a power of 50 W, a heating time of 5 min, and a chamber pressure of 20 mTorr. When suitable MIH parameters were used, the effect of PVP cross-linking and the device performance were similar to those obtained using traditional oven heating, even though the cross-linking time was significantly decreased from 1 h to 5 min. Besides the gate leakage current, the interface trap state density (Nit) was also calculated to describe the interface status between the gate insulator and the active layer. The lowest interface trap state density can be found in the device with the PVP gate insulator cross-linked by using the optimal MIH condition. Therefore, it is believed that the MIH scheme is a good candidate to cross-link the PVP gate insulator for organic thin-film transistor applications as a result of its features of rapid heating (5 min) and low-power microwave-irradiation (50 W).

Thin-film morphology of inkjet-printed single-droplet organic transistors using polarized Raman spectroscopy: effect of blending TIPS-pentacene with insulating polymer.

PubMed

James, David T; Kjellander, B K Charlotte; Smaal, Wiljan T T; Gelinck, Gerwin H; Combe, Craig; McCulloch, Iain; Wilson, Richard; Burroughes, Jeremy H; Bradley, Donal D C; Kim, Ji-Seon

2011-12-27

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π-π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm(2)/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm(2)/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes.

Spreading Resistance on Thin Film Contacts

NASA Astrophysics Data System (ADS)

Zhang, Peng; Lau, Y. Y.; Hung, D.; Gilgenbach, R. M.

2012-10-01

Electrical contact [1] is important to wire-array z-pinches, metal-insulator-vacuum junctions, and high power microwave sources, etc. Contact problems account for 40 percent of all electrical failures, from small scale consumer electronics to large scale defense and aerospace systems. The crowding of the current lines at contacts leads to enhanced localized heating, a measure of which is the spreading resistance (Rs). For a microscopic area of contact (the ``a-spot'' [1]) on a thin film, we calculate Rs in both Cartesian and cylindrical geometries [2]. In the limit of small film thickness, h, the normalized thin film spreading resistance converges to the finite values, 2.77 for the Cartesian case and 0.28 for the cylindrical case. These same finite limits are found to be applicable to the a-spot between bulk solids in the high frequency limit if the skin depth is identified with h. Extension to a general a-spot geometry is proposed [2]. [4pt] [1] R. Holm, Electric Contacts, 4th ed., Springer (1967). [0pt] [2] P. Zhang et al., IEEE Trans. Electron Devices 59, 1936 (2012).

Memory switches based on metal oxide thin films

NASA Technical Reports Server (NTRS)

Ramesham, Rajeshuni (Inventor); Thakoor, Anilkumar P. (Inventor); Lambe, John J. (Inventor)

1990-01-01

MnO.sub.2-x thin films (12) exhibit irreversible memory switching (28) with an OFF/ON resistance ratio of at least about 10.sup.3 and the tailorability of ON state (20) resistance. Such films are potentially extremely useful as a connection element in a variety of microelectronic circuits and arrays (24). Such films provide a pre-tailored, finite, non-volatile resistive element at a desired place in an electric circuit, which can be electrically turned OFF (22) or disconnected as desired, by application of an electrical pulse. Microswitch structures (10) constitute the thin film element, contacted by a pair of separate electrodes (16a, 16b) and have a finite, pre-selected ON resistance which is ideally suited, for example, as a programmable binary synaptic connection for electronic implementation of neural network architectures. The MnO.sub.2-x microswitch is non-volatile, patternable, insensitive to ultraviolet light, and adherent to a variety of insulating substrates (14), such as glass and silicon dioxide-coated silicon substrates.

Visualizing ferromagnetic domains in magnetic topological insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wenbo; Gu, G. D.; Yang, Fang

2015-05-13

We report a systematic study of ferromagnetic domains in both single-crystal and thin-film specimens of magnetic topological insulators Cr doped (Bi 0.1Sb 0.9) 2Te 3 using magnetic force microscopy (MFM). The temperature and field dependences of MFM and in situ resistance data are consistent with previous bulk transport and magnetic characterization. Bubble-like ferromagnetic domains were observed in both single crystals and thin films. Significantly, smaller domain size (~500 nm) with narrower domain wall (~150 – 300 nm) was observed in thin films of magnetic topological insulators, likely due to vertical confinement effect. As a result, these results suggest that thinmore » films are more promising for visualization of chiral edge states.« less

UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

2016-08-01

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent

Role of microstructures on the M1-M2 phase transition in epitaxial VO2 thin films

PubMed Central

Ji, Yanda; Zhang, Yin; Gao, Min; Yuan, Zhen; Xia, Yudong; Jin, Changqing; Tao, Bowan; Chen, Chonglin; Jia, Quanxi; Lin, Yuan

2014-01-01

Vanadium dioxide (VO2) with its unique sharp resistivity change at the metal-insulator transition (MIT) has been extensively considered for the near-future terahertz/infrared devices and energy harvesting systems. Controlling the epitaxial quality and microstructures of vanadium dioxide thin films and understanding the metal-insulator transition behaviors are therefore critical to novel device development. The metal-insulator transition behaviors of the epitaxial vanadium dioxide thin films deposited on Al2O3 (0001) substrates were systematically studied by characterizing the temperature dependency of both Raman spectrum and Fourier transform infrared spectroscopy. Our findings on the correlation between the nucleation dynamics of intermediate monoclinic (M2) phase with microstructures will open a new avenue for the design and integration of advanced heterostructures with controllable multifunctionalities for sensing and imaging system applications. PMID:24798056

The effects of layering in ferroelectric Si-doped HfO{sub 2} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lomenzo, Patrick D.; Nishida, Toshikazu, E-mail: nishida@ufl.edu; Takmeel, Qanit

2014-08-18

Atomic layer deposited Si-doped HfO{sub 2} thin films approximately 10 nm thick are deposited with various Si-dopant concentrations and distributions. The ferroelectric behavior of the HfO{sub 2} thin films are shown to be dependent on both the Si mol. % and the distribution of Si-dopants. Metal-ferroelectric-insulator-semiconductor capacitors are shown to exhibit a tunable remanent polarization through the adjustment of the Si-dopant distribution at a constant Si concentration. Inhomogeneous layering of Si-dopants within the thin films effectively lowers the remanent polarization. A pinched hysteresis loop is observed for higher Si-dopant concentrations and found to be dependent on the Si layering distribution.

Investigation of Gas-Sensing Property of Acid-Deposited Polyaniline Thin-Film Sensors for Detecting H2S and SO2

PubMed Central

Dong, Xingchen; Zhang, Xiaoxing; Wu, Xiaoqing; Cui, Hao; Chen, Dachang

2016-01-01

Latent insulation defects introduced in manufacturing process of gas-insulated switchgears can lead to partial discharge during long-time operation, even to insulation fault if partial discharge develops further. Monitoring of decomposed components of SF6, insulating medium of gas-insulated switchgear, is a feasible method of early-warning to avoid the occurrence of sudden fault. Polyaniline thin-film with protonic acid deposited possesses wide application prospects in the gas-sensing field. Polyaniline thin-film sensors with only sulfosalicylic acid deposited and with both hydrochloric acid and sulfosalicylic acid deposited were prepared by chemical oxidative polymerization method. Gas-sensing experiment was carried out to test properties of new sensors when exposed to H2S and SO2, two decomposed products of SF6 under discharge. The gas-sensing properties of these two sensors were compared with that of a hydrochloric acid deposited sensor. Results show that the hydrochloric acid and sulfosalicylic acid deposited polyaniline thin-film sensor shows the most outstanding sensitivity and selectivity to H2S and SO2 when concentration of gases range from 10 to 100 μL/L, with sensitivity changing linearly with concentration of gases. The sensor also possesses excellent long-time and thermal stability. This research lays the foundation for preparing practical gas-sensing devices to detect H2S and SO2 in gas-insulated switchgears at room temperature. PMID:27834895

Effects of Structural and Electronic Disorder in Topological Insulator Sb2Te3 Thin Films

NASA Astrophysics Data System (ADS)

Korzhovska, Inna

Topological quantum matter is a unique and potentially transformative protectorate against disorder-induced backscattering. The ultimate disorder limits to the topological state, however, are still not known - understanding these limits is critical to potential applications in the fields of spintronics and information processing. In topological insulators spin-orbit interaction and time-reversal-symmetry invariance guarantees - at least up to a certain disorder strength - that charge transport through 2D gapless Dirac surface states is robust against backscattering by non-magnetic disorder. Strong disorder may destroy topological protection and gap out Dirac surface states, although recent theories predict that under severe electronic disorder a quantized topological conductance might yet reemerge. Very strong electronic disorder, however, is not trivial to install and quantify, and topological matter under such conditions thus far has not been experimentally tested. This thesis addresses the behavior of three-dimensional (3D) topological insulator (TI) films in a wide range of structural and electronic disorder. We establish strong positional disorder in thin (20-50 nm) Sb2Te 3 films, free of extrinsic magnetic dopants. Sb 2Te3 is a known 2nd generation topological insulator in the low-disorder crystalline state. It is also a known phase-change material that undergoes insulator-to-metal transition with the concurrent orders of magnitude resistive drop, where a huge range of disorder could be controllably explored. In this work we show that even in the absence of magnetic dopants, disorder may induce spin correlations detrimental to the topological state. Chapter 1 contains a brief introduction to the topological matter and describes the role played by disorder. This is followed by theory considerations and a survey of prior experimental work. Next we describe the motivation for our experiments and explain the choice of the material. Chapter 2 describes deposition

Novel Thin Film Sensor Technology for Turbine Engine Hot Section Components

NASA Technical Reports Server (NTRS)

Wrbanek, John D.; Fralick, Gustave C.

2007-01-01

Degradation and damage that develops over time in hot section components can lead to catastrophic failure of the turbine section of aircraft engines. A range of thin film sensor technology has been demonstrated enabling on-component measurement of multiple parameters either individually or in sensor arrays including temperature, strain, heat flux, and flow. Conductive ceramics are beginning to be investigated as new materials for use as thin film sensors in the hot section, leveraging expertise in thin films and high temperature materials. The current challenges are to develop new sensor and insulation materials capable of withstanding the extreme hot section environment, and to develop techniques for applying sensors onto complex high temperature structures for aging studies of hot propulsion materials. The technology research and development ongoing at NASA Glenn Research Center for applications to future aircraft, launch vehicles, space vehicles, and ground systems is outlined.

Periodic domain inversion in x-cut single-crystal lithium niobate thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mackwitz, P., E-mail: peterm@mail.upb.de; Rüsing, M.; Berth, G.

2016-04-11

We report the fabrication of periodically poled domain patterns in x-cut lithium niobate thin-film. Here, thin films on insulator have drawn particular attention due to their intrinsic waveguiding properties offering high mode confinement and smaller devices compared to in-diffused waveguides in bulk material. In contrast to z-cut thin film lithium niobate, the x-cut geometry does not require back electrodes for poling. Further, the x-cut geometry grants direct access to the largest nonlinear and electro-optical tensor element, which overall promises smaller devices. The domain inversion was realized via electric field poling utilizing deposited aluminum top electrodes on a stack of LNmore » thin film/SiO{sub 2} layer/Bulk LN, which were patterned by optical lithography. The periodic domain inversion was verified by non-invasive confocal second harmonic microscopy. Our results show domain patterns in accordance to the electrode mask layout. The second harmonic signatures can be interpreted in terms of spatially, overlapping domain filaments which start their growth on the +z side.« less

Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

NASA Technical Reports Server (NTRS)

Wilson, Scott D.; Fralick, Gus c.; Wrbanek, John D.; Sayir, Ali

2010-01-01

The NASA Glenn Research Center (GRC) has been testing high-efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multiyear missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test setup to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging micro-porous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-film heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slipcasting and using Physical Vapor Deposition (PVD). One-micron-thick noble metal thermocouples measure temperature on the surface of an alumina ceramic disk and heat flux is calculated. Fabrication, integration, and test results of a thin-film heat flux sensor are presented.

Resistivity and Resistivity Fluctuations of Thin Film Platinum-Aluminum Oxide Granular Metal-Insulator Composites

NASA Astrophysics Data System (ADS)

Mantese, Joseph Vito

Thin film metal-insulator composites were used to study how the resistivity and fluctuations in the resistivity were altered by changes in conduction mechanism so as to understand the source of the fluctuations and to better understand the conduction processes themselves. Metal-insulator composites were prepared by co -evaporation of platinum and aluminum oxide in a high vacuum system to create a series of films which had a range of metal volume fill fractions, p, from 23% to 100%. The samples were patterned using standard photolithographic techniques to form sample geometries of typical dimensions, length (TURN) 40(mu)m, width (TURN) 2(mu)m and thickness (TURN) 1500(ANGSTROM). The resistivity, (rho), and power spectral density of the resistivity fluctuations, S(,(rho))(f), were measured as a function of p and temperature, T. (rho)(p,T) was found to be a rapidly increasing function of decreasing p, rising monotonically by more than 7 orders of magnitude as p was decreased from 100% to 23%. For p (GREATERTHEQ) 59% the resistivity decreased linearly with decreasing temperature until limited by impurity scattering. The resistivities for the low metal fill fraction materials (p (LESSTHEQ) 50%) increased as the temperature was reduced as expected of thermally assisted tunneling conduction in metal-insulator composites. The transition from metallic conduction to thermally assisted tunneling occurred at a critical value, p(,c), between 59% and 50% Pt. For all samples at all p and T, S(,(rho))(f)(PROPORTIONAL)1/f('(alpha)) (1/f noise) with 0.8 (LESSTHEQ) (alpha) (LESSTHEQ) .1.2 and f the frequency in Hertz. No systematic dependence upon either p or T was found. The normalized noise intensity fS(,(rho))(f)/(rho)('2) (,1) (,Hz) was found to increase monotonically by 5 orders of magnitude with decreasing p then saturate at p(,c) where the conduction mechanism changed from metallic conduction to thermally assisted tunneling. Effective medium theory was used to analyze the role

Strain-controlled electronic properties and magnetorelaxor behaviors in electron-doped CaMnO3 thin films

NASA Astrophysics Data System (ADS)

Xiang, P.-H.; Yamada, H.; Sawa, A.; Akoh, H.

2009-02-01

We have fabricated epitaxial thin films of electron-doped manganite Ca1-xCexMnO3 (CCMO) with 0≤x≤0.08. The transport properties of CCMO films are very sensitive to substrate-controlled epitaxial strain. For the CCMO(x =0.05) film, the metallic transport characteristic is observed only on a nearly lattice-matched NdAlO3 (NAO) substrate, while tensilely and compressively stressed films are insulating. The CCMO(x =0.06) film on the NAO substrate shows a large magnetoresistance characteristic of a magnetorelaxor. This behavior can be explained in terms of the phase separation and the irreversible growth of the metallic domain in antiferromagnetic insulating matrix.

Thin-film optical initiator

DOEpatents

Erickson, Kenneth L.

2001-01-01

A thin-film optical initiator having an inert, transparent substrate, a reactive thin film, which can be either an explosive or a pyrotechnic, and a reflective thin film. The resultant thin-film optical initiator system also comprises a fiber-optic cable connected to a low-energy laser source, an output charge, and an initiator housing. The reactive thin film, which may contain very thin embedded layers or be a co-deposit of a light-absorbing material such as carbon, absorbs the incident laser light, is volumetrically heated, and explodes against the output charge, imparting about 5 to 20 times more energy than in the incident laser pulse.

Magnetoresistance Versus Oxygen Deficiency in Epi-stabilized SrRu1 - x Fe x O3 - δ Thin Films

NASA Astrophysics Data System (ADS)

Dash, Umasankar; Acharya, Susant Kumar; Lee, Bo Wha; Jung, Chang Uk

2017-03-01

Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu1 - x Fe x O3 - δ epitaxial thin films ( x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu1 - x Fe x O3 - δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal-insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2-300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR ( 36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies ( δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr1 - x La x )(Ru1 - x Fe x )O3. These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu1 - x Fe x O3 - δ thin films.

Periodic oxidation for fabricating titanium oxynitride thin films via atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iwashita, Shinya, E-mail: shinya.iwashita@tel.com; Aoyama, Shintaro; Nasu, Masayuki

2016-01-15

This paper demonstrates thermal atomic layer deposition (ALD) combined with periodic oxidation for synthesizing titanium oxynitride (TiON) thin films. The process used a typical ALD reactor for the synthesis of titanium nitride (TiN) films wherein oxygen was supplied periodically between the ALD-TiN cycles. The great advantage of the process proposed here was that it allowed the TiN films to be oxidized efficiently. Also, a uniform depth profile of the oxygen concentration in the films could be obtained by tuning the oxidation conditions, allowing the process to produce a wide variety of TiON films. The resistivity measurement is a convenient methodmore » to confirm the reproducibility of metal film fabrication but may not be applicable for TiON films depending upon the oxidation condition because the films can easily turn into insulators when subjected to periodic oxidation. Therefore, an alternative reproducibility confirmation method was required. In this study, spectroscopic ellipsometry was applied to monitor the variation of TiON films and was able to detect changes in film structures such as conductor–insulator transitions in the TiON films.« less

Combinatorial screening of organic electronic materials: thin film stability

NASA Astrophysics Data System (ADS)

Chattopadhyay, Santanu; Carson Meredith, J.

2005-01-01

Dewetting of thin polymeric semiconducting-insulating (and conducting-insulating) bilayers is a serious fundamental problem facing the fabrication of organic electronic devices such as transistors, light-emitting diodes and supercapacitors. This paper describes a high-throughput characterization method that utilizes orthogonal thickness-gradient libraries of the bilayer components poly(3-octylthiophene) (semiconductor) and poly(styrene) (insulator). The technique allows simultaneous observation of hundreds of combinations of thicknesses and has permitted rapid discovery of a previously-unknown VDW instability transition. We observe that the onset of VDW instability in the PS-P3OT bilayer is a complex function of P3OT thickness that cannot be predicted by Hamaker constant models for free energy. At low P3OT thickness, the semiconductor acts to stabilize the PS insulator. But above a P3OT thickness of 175 nm, this behaviour is switched and P3OT destabilizes the PS. These thickness-dependent effects are correlated very well with dramatic transitions in P3OT optical spectra and the P3OT-AFM tip interaction forces. This unusual behaviour places critical limitations on practical device thicknesses and interfacial combinations, and points to the need for a thin-film stability theory that accounts for thickness-dependent molecular-electronic effects.

Controlling phase separation in vanadium dioxide thin films via substrate engineering

NASA Astrophysics Data System (ADS)

Gilbert Corder, Stephanie N.; Jiang, Jianjuan; Chen, Xinzhong; Kittiwatanakul, Salinporn; Tung, I.-Cheng; Zhu, Yi; Zhang, Jiawei; Bechtel, Hans A.; Martin, Michael C.; Carr, G. Lawrence; Lu, Jiwei; Wolf, Stuart A.; Wen, Haidan; Tao, Tiger H.; Liu, Mengkun

2017-10-01

The strong electron-lattice interactions in correlated electron systems provide unique opportunities for altering the material properties with relative ease and flexibility. In this Rapid Communication, we use localized strain control via a focused-ion-beam patterning of Ti O2 substrates to demonstrate that one can selectively engineer the insulator-to-metal transition temperature, the fractional component of the insulating and metallic phases, and the degree of optical anisotropy down to the length scales of the intrinsic phase separation in V O2 thin films without altering the quality of the films. The effects of localized strain control on the strongly correlated electron system are directly visualized by state-of-the-art IR near-field imaging and spectroscopy techniques and x-ray microdiffraction measurements.

Formation of Fe2SiO4 thin films on Si substrates and influence of substrate to its thermoelectric transport properties

NASA Astrophysics Data System (ADS)

Choi, Jeongyong; Nguyen, Van Quang; Duong, Van Thiet; Shin, Yooleemi; Duong, Anh Tuan; Cho, Sunglae

2018-03-01

Fe2SiO4 thin films have been grown on n-type, p-type and semi-insulating Si(100) substrates by molecular beam epitaxy. When Fe-O thin films were deposited on Si(100) substrate at 300 °C, the film reacted with Si, resulting in a Fe2SiO4 film because of the high reactivity between Fe and Si. The electrical resistance and Seebeck coefficient of Fe2SiO4 thin films grown were different in different doping states. On n-type and p-type Si(100), the electrical resistance decreased suddenly and increased again at 350 and 250 K, respectively, while on semi-insulating Si(100), it exhibited typical semiconducting resistance behavior. We observed similar crossovers at 350 and 250 K in temperature dependent Seebeck coefficients on n-type and p-type Si(100), respectively. These results suggest that the measured electrical and thermoelectric properties originate from Si substrate.

Thickness dependent properties of CMR Manganite thin films on lattice mismatched substrates: Distinguishing Strain and Interface Effects

NASA Astrophysics Data System (ADS)

Davidson, Anthony, III; Kolagani, Rajeswari; Bacharova, Ellisaveta; Yong, Grace; Smolyaninova, Vera; Schaefer, David; Mundle, Rajeh

2007-03-01

Epitaxial thin films of CMR manganite materials have been known to show thickness dependent electrical and magnetic properties on lattice mismatched substrates. Below a critical thickness, insulator-metal transition is suppressed. These effects have been largely attributed to the role of bi-axial lattice mismatch strain. Our recent results of epitaxial thin films of La0.67Ca0.33MnO3 (LCMO) on two substrates with varying degrees of compressive lattice mismatch indicate that, in addition to the effect of lattice mismatch strain, the thickness dependence of the properties are influenced by other factors possibly related to the nature of the film substrate interface and defects such as twin boundaries. We have compared the properties of LCMO films on (100) oriented LaAlO3 and (001) oriented NdCaAlO4 both of which induce compressive bi-axial strain. Interestingly, the suppression of the insulator-metal transition is less in films on NCAO which has a larger lattice mismatch. We will present results correlating the electrical and magneto transport properties with the structure and morphology of the films.

Characterization of thin solid films and surfaces by infrared spectroscopy

NASA Astrophysics Data System (ADS)

Grosse, Peter

Thin solid films and surfaces are characterized by means of IR-spectroscopy. Properties under consideration are geometric structures of layers and stacks of layers, chemical composition and incorporation of impurities, and parameters of free electrons and holes. The method is based on reflectance and transmittance measurements, in particular with polarized light at oblique incidence. Thus the interaction of the electromagnetic waves with thin films is enhanced and two independent data sets for s- and p-polarization are available. The interpretation of the measured spectra is carried out by a fit procedure, simulating the observed spectra by an adequate model. For fitting we use an ansatz of a dielectric function which is a sum of susceptibilities taking into account the contributions of valence electrons, optical phonons, free carriers, and of impurities. As examples for the method we discuss the following systems: insulating and percolating films of Ag deposited on glass, epitactic III-V-heterostructures, oxide films as used for MOS-structures, diffusion and implantation profiles, and adsorbates on metals. All examples are relevant for application in technology, as microelectronics, thin film technology, catalysis e.g. The reliability of the non-destructive IR-method is compared with other relevant analytic methods as SIMS, RBS, and AES.

Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Middey, S.; Rivero, P.; Meyers, D.

2014-10-29

In this study, we address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO 3 on the band insulator SrTiO 3 along the pseudo cubic [111] direction. While in general the metallic LaNiO 3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, andmore » synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La 2Ni 2O 5 (Ni 2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO 3/SrTiO 3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.« less

Integrated Electrical Wire Insulation Repair System

NASA Technical Reports Server (NTRS)

Williams, Martha; Jolley, Scott; Gibson, Tracy; Parks, Steven

2013-01-01

An integrated system tool will allow a technician to easily and quickly repair damaged high-performance electrical wire insulation in the field. Low-melt polyimides have been developed that can be processed into thin films that work well in the repair of damaged polyimide or fluoropolymer insulated electrical wiring. Such thin films can be used in wire insulation repairs by affixing a film of this low-melt polyimide to the damaged wire, and heating the film to effect melting, flow, and cure of the film. The resulting repair is robust, lightweight, and small in volume. The heating of this repair film is accomplished with the use of a common electrical soldering tool that has been modified with a special head or tip that can accommodate the size of wire being repaired. This repair method can furthermore be simplified for the repair technician by providing replaceable or disposable soldering tool heads that have repair film already "loaded" and ready for use. The soldering tool heating device can also be equipped with a battery power supply that will allow its use in areas where plug-in current is not available

Thin-film solar cell fabricated on a flexible metallic substrate

DOEpatents

Tuttle, John R.; Noufi, Rommel; Hasoon, Falah S.

2006-05-30

A thin-film solar cell (10) is provided. The thin-film solar cell (10) comprises a flexible metallic substrate (12) having a first surface and a second surface. A back metal contact layer (16) is deposited on the first surface of the flexible metallic substrate (12). A semiconductor absorber layer (14) is deposited on the back metal contact. A photoactive film deposited on the semiconductor absorber layer (14) forms a heterojunction structure and a grid contact (24) deposited on the heterjunction structure. The flexible metal substrate (12) can be constructed of either aluminium or stainless steel. Furthermore, a method of constructing a solar cell is provided. The method comprises providing an aluminum substrate (12), depositing a semiconductor absorber layer (14) on the aluminum substrate (12), and insulating the aluminum substrate (12) from the semiconductor absorber layer (14) to inhibit reaction between the aluminum substrate (12) and the semiconductor absorber layer (14).

Thin-Film Solar Cell Fabricated on a Flexible Metallic Substrate

DOEpatents

Tuttle, J. R.; Noufi, R.; Hasoon, F. S.

2006-05-30

A thin-film solar cell (10) is provided. The thin-film solar cell (10) comprises a flexible metallic substrate (12) having a first surface and a second surface. A back metal contact layer (16) is deposited on the first surface of the flexible metallic substrate (12). A semiconductor absorber layer (14) is deposited on the back metal contact. A photoactive film deposited on the semiconductor absorber layer (14) forms a heterojunction structure and a grid contact (24) deposited on the heterjunction structure. The flexible metal substrate (12) can be constructed of either aluminium or stainless steel. Furthermore, a method of constructing a solar cell is provided. The method comprises providing an aluminum substrate (12), depositing a semiconductor absorber layer (14) on the aluminum substrate (12), and insulating the aluminum substrate (12) from the semiconductor absorber layer (14) to inhibit reaction between the aluminum substrate (12) and the semiconductor absorber layer (14).

Effect of tip polarity on Kelvin probe force microscopy images of thin insulator CaF2 films on Si(111)

NASA Astrophysics Data System (ADS)

Yurtsever, Ayhan; Sugimoto, Yoshiaki; Fukumoto, Masaki; Abe, Masayuki; Morita, Seizo

2012-08-01

We investigate thin insulating CaF2 films on a Si (111) surface using a combination of noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). Atomic-scale NC-AFM and KPFM images are obtained in different imaging modes by employing two different tip polarities. The KPFM image contrast and the distance-dependent variation of the local contact potential difference (LCPD) give rise to a tip-polarity-dependent contrast inversion. Ca2+ cations had a higher LCPD contrast than F- anions for a positively terminated tip, while the LCPD provided by a negatively charged tip gave a higher contrast for F- anions. Thus, this result implies that it is essential to determine the tip apex polarity to correctly interpret LCPD signals acquired by KPFM.

Pyrolyzed thin film carbon

NASA Technical Reports Server (NTRS)

Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor); Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor)

2010-01-01

A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

Spin–orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

DOE PAGES

Li, Peng; Liu, Tao; Chang, Houchen; ...

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe 12O 19 bilayer where the BaFe 12O 19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control themore » up and down states of the remnant magnetization in the BaFe 12O 19 film when the film is magnetized by an in-plane magnetic field. Furthermore, it can reduce or increase the switching field of the BaFe 12O 19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.« less

Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; Demann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

Superconductivity-related insulating behavior.

PubMed

Sambandamurthy, G; Engel, L W; Johansson, A; Shahar, D

2004-03-12

We present the results of an experimental study of superconducting, disordered, thin films of amorphous indium oxide. These films can be driven from the superconducting phase to a reentrant insulating state by the application of a perpendicular magnetic field (B). We find that the high-B insulator exhibits activated transport with a characteristic temperature, TI. TI has a maximum value (TpI) that is close to the superconducting transition temperature (Tc) at B=0, suggesting a possible relation between the conduction mechanisms in the superconducting and insulating phases. Tp(I) and Tc display opposite dependences on the disorder strength.

Structural and electrical properties of sputter deposited ZnO thin films

NASA Astrophysics Data System (ADS)

Muhammed Shameem P., V.; Mekala, Laxman; Kumar, M. Senthil

2018-05-01

The growth of zinc oxide thin films having different oxygen content was achieved at ambient temperature by reactive dc magnetron sputtering technique and their structural and electrical properties are studied. The structural studies show that the films are polycrystalline with a preferential orientation of the grains along the c-axis [002], which increases with increase in oxygen partial pressure. The grain size and the surface roughness of the zinc oxide films are found to decrease with increasing oxygen partial pressure. It is observed that the resistivity of the zinc oxide films can be tuned from semiconducting to insulating regime by varying the oxygen content.

Controlling phase separation in vanadium dioxide thin films via substrate engineering

DOE PAGES

Gilbert Corder, Stephanie N.; Jiang, Jianjuan; Chen, Xinzhong; ...

2017-10-23

The strong electron-lattice interactions in correlated electron systems provide unique opportunities for altering the material properties with relative ease and flexibility. Here in this Rapid Communication, we use localized strain control via a focused-ion-beam patterning of TiO 2 substrates to demonstrate that one can selectively engineer the insulator-to-metal transition temperature, the fractional component of the insulating and metallic phases, and the degree of optical anisotropy down to the length scales of the intrinsic phase separation in VO 2 thin films without altering the quality of the films. The effects of localized strain control on the strongly correlated electron system aremore » directly visualized by state-of-the-art IR near-field imaging and spectroscopy techniques and x-ray microdiffraction measurements.« less

High performance inkjet-printed metal oxide thin film transistors via addition of insulating polymer with proper molecular weight

NASA Astrophysics Data System (ADS)

Sun, Dawei; Chen, Cihai; Zhang, Jun; Wu, Xiaomin; Chen, Huipeng; Guo, Tailiang

2018-01-01

Fabrication of metal oxide thin film transistor (MOTFT) arrays using the inkjet printing process has caused tremendous interest for low-cost and large-area flexible electronic devices. However, the inkjet-printed MOTFT arrays usually exhibited a non-uniform geometry due to the coffee ring effect, which restricted their commercial application. Therefore, in this work, a strategy is reported to control the geometry and enhance device performance of inkjet-printed MOTFT arrays by the addition of an insulating polymer to the precursor solution prior to film deposition. Moreover, the impact of the polymer molecular weight (MW) on the geometry, chemical constitution, crystallization, and MOTFT properties of inkjet-printed metal oxide depositions was investigated. The results demonstrated that with an increase of MW of polystyrene (PS) from 2000 to 200 000, the coffee ring was gradually faded and the coffee ring effect was completely eliminated when MW reached 200 000, which is associated with the enhanced viscosity with the insulating polymer, providing a high resistance to the outward capillary flow, which facilitated the depinning of the contact line, leading to the elimination of the coffee ring. More importantly, the carrier mobility increased significantly from 4.2 cm2 V-1 s-1 up to 13.7 cm2 V-1 s-1 as PS MW increased from 2000 to 200 000, which was about 3 times that of the pristine In2O3 TFTs. Grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy results indicated that PS doping of In2O3 films not only frustrated crystallization but also altered chemical constitution by enhancing the formation of the M-O structure, both of which facilitated the carrier transport. These results demonstrated that the simple polymer additive process provides a promising method that can efficiently control the geometry of MO arrays during inkjet printing and maximize the device performance of MOTFT arrays, which showed great potential for the application in next

Physical aspects of colossal dielectric constant material CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Deng, Guochu; He, Zhangbin; Muralt, Paul

2009-04-01

The underlying physical mechanism of the so-called colossal dielectric constant phenomenon in CaCu3Ti4O12 (CCTO) thin films were investigated by using semiconductor theories and methods. The semiconductivity of CCTO thin films originated from the acceptor defect at a level ˜90 meV higher than valence band. Two contact types, metal-semiconductor and metal-insulator-semiconductor junctions, were observed and their barrier heights, and impurity concentrations were theoretically calculated. Accordingly, the Schottky barrier height of metal-semiconductor contact is about 0.8 eV, and the diffusion barrier height of metal-insulator-semiconductor contact is about 0.4-0.7 eV. The defect concentrations of both samples are quite similar, of the magnitude of 1019 cm-3, indicating an inherent feature of high defect concentration.

Growth of electronically distinct manganite thin films by modulating cation stoichiometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Sangkyun; Lee, Joonhyuk; Ahn, Eunyoung

Nd 1-xSr xMnO 3 (NSMO) is a well-known manganite due to close connection between structure, transport, magnetism, and chemistry. Thus, it would be an ideal system to study modification of physical properties by external stimuli including control of stoichiometry in growth. In this work, we show that abrupt change of electronic and magnetic properties can be achieved by subtle change of oxygen partial pressure in pulsed laser deposition. Interestingly, the pressure indeed modulates cation stoichiometry. We clearly observed that the films grown at 150 mTorr and higher showed clear insulator to metal transition and stronger magnetism, commonly found in lessmore » hole doping, while the films grown at 130 mTorr and lower showed insulating behavior and weak magnetism. From soft x-ray spectroscopic methods, we clearly observed the compositional difference in those thin films. This result is further supported by scattering of lighter elements in high oxygen partial pressure but not by anion deficiency in growth.« less

Growth of electronically distinct manganite thin films by modulating cation stoichiometry

DOE PAGES

Ryu, Sangkyun; Lee, Joonhyuk; Ahn, Eunyoung; ...

2017-06-26

Nd 1-xSr xMnO 3 (NSMO) is a well-known manganite due to close connection between structure, transport, magnetism, and chemistry. Thus, it would be an ideal system to study modification of physical properties by external stimuli including control of stoichiometry in growth. In this work, we show that abrupt change of electronic and magnetic properties can be achieved by subtle change of oxygen partial pressure in pulsed laser deposition. Interestingly, the pressure indeed modulates cation stoichiometry. We clearly observed that the films grown at 150 mTorr and higher showed clear insulator to metal transition and stronger magnetism, commonly found in lessmore » hole doping, while the films grown at 130 mTorr and lower showed insulating behavior and weak magnetism. From soft x-ray spectroscopic methods, we clearly observed the compositional difference in those thin films. This result is further supported by scattering of lighter elements in high oxygen partial pressure but not by anion deficiency in growth.« less

Surface-State-Dominated Spin-Charge Current Conversion in Topological-Insulator-Ferromagnetic-Insulator Heterostructures.

PubMed

Wang, Hailong; Kally, James; Lee, Joon Sue; Liu, Tao; Chang, Houchen; Hickey, Danielle Reifsnyder; Mkhoyan, K Andre; Wu, Mingzhong; Richardella, Anthony; Samarth, Nitin

2016-08-12

We report the observation of ferromagnetic resonance-driven spin pumping signals at room temperature in three-dimensional topological insulator thin films-Bi_{2}Se_{3} and (Bi,Sb)_{2}Te_{3}-deposited by molecular beam epitaxy on Y_{3}Fe_{5}O_{12} thin films. By systematically varying the Bi_{2}Se_{3} film thickness, we show that the spin-charge conversion efficiency, characterized by the inverse Rashba-Edelstein effect length (λ_{IREE}), increases dramatically as the film thickness is increased from two quintuple layers, saturating above six quintuple layers. This suggests a dominant role of surface states in spin and charge interconversion in topological-insulator-ferromagnet heterostructures. Our conclusion is further corroborated by studying a series of Y_{3}Fe_{5}O_{12}/(Bi,Sb)_{2}Te_{3} heterostructures. Finally, we use the ferromagnetic resonance linewidth broadening and the inverse Rashba-Edelstein signals to determine the effective interfacial spin mixing conductance and λ_{IREE}.

Dewetting of Thin Polymer Films

NASA Astrophysics Data System (ADS)

Dixit, P. S.; Sorensen, J. L.; Kent, M.; Jeon, H. S.

2001-03-01

DEWETTING OF THIN POLYMER FILMS P. S. Dixit,(1) J. L. Sorensen,(2) M. Kent,(2) H. S. Jeon*(1) (1) Department of Petroleum and Chemical Engineering, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, jeon@nmt.edu (2) Department 1832, Sandia National Laboratories, Albuquerque, NM. Dewetting of thin polymer films is of technological importance for a variety of applications such as protective coatings, dielectric layers, and adhesives. Stable and smooth films are required for the above applications. Above the glass transition temperature (Tg) the instability of polymer thin films on a nonwettable substrate can be occurred. The dewetting mechanism and structure of polypropylene (Tg = -20 ^circC) and polystyrene (Tg = 100 ^circC) thin films is investigated as a function of film thickness (25 Åh < 250 Åand quenching temperature. Contact angle measurements are used in conjunction with optical microscope to check the surface homogeneity of the films. Uniform thin films are prepared by spin casting the polymer solutions onto silicon substrates with different contact angles. We found that the stable and unstable regions of the thin films as a function of the film thickness and quenching temperature, and then constructed a stability diagram for the dewetting of thin polymer films. We also found that the dewetting patterns of the thin films are affected substantially by the changes of film thickness and quenching temperature.

Metal insulator transition and magnetotransport anomalies in perovskite SrIr{sub 0.5}Ru{sub 0.5}O{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biswas, Abhijit; Lee, Yong Woo; Kim, Sang Woo

2015-03-21

We investigated the nature of transport and magnetic properties in SrIr{sub 0.5}Ru{sub 0.5}O{sub 3} (SIRO), which has characteristics intermediate between a correlated non-Fermi liquid state and an itinerant Fermi liquid state, by growing perovskite thin films on various substrates (e.g., SrTiO{sub 3} (001), (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}TaAlO{sub 6}){sub 0.7} (001), and LaAlO{sub 3} (001)). We observed systematic variation of underlying substrate dependent metal-to-insulator transition temperatures (T{sub MIT} ∼ 80 K on SrTiO{sub 3}, ∼90 K on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}TaAlO{sub 6}){sub 0.7}, and ∼100 K on LaAlO{sub 3}) in resistivity. At temperature 300 K ≥ T ≥ T{sub MIT}, SIRO is metallic and its resistivity follows a T{supmore » 3/2} power law, whereas insulating nature at T < T{sub MIT} is due to the localization effect. Magnetoresistance (MR) measurement of SIRO on SrTiO{sub 3} (001) shows negative MR at T < 25 K and positive MR at T > 25 K, with negative MR ∝ B{sup 1/2} and positive MR ∝ B{sup 2}; consistent with the localized-to-normal transport crossover dynamics. Furthermore, observed spin glass like behavior of SIRO on SrTiO{sub 3} (001) at T < 25 K in the localized regime validates the hypothesis that (Anderson) localization favors glassy ordering. These remarkable features provide a promising approach for future applications and of fundamental interest in oxide thin films.« less

Electrochemically Induced Insulator-Metal-Insulator Transformations of Vanadium Dioxide Nanocrystal Films

NASA Astrophysics Data System (ADS)

Milliron, Delia; Dahlman, Clayton; Leblanc, Gabriel; Bergerud, Amy

Vanadium dioxide (VO2) undergoes significant optical, electronic, and structural changes as it transforms between the low-temperature monoclinic and high-temperature rutile phases. The low-temperature state is insulating and transparent, while the high-temperature state is metallic and IR blocking. Alternative stimuli have been utilized to trigger insulator-to-metal transformations in VO2, including electrochemical gating. Here, VO2 nanocrystal films have been prepared by solution deposition of V2O3 nanocrystals followed by oxidative annealing. Nanocrystalline VO2 films are electrochemically reduced, inducing changes in their electronic and optical properties. We observe a reversible transition between infrared transparent insulating phases and a darkened metallic phase by in situ visible-near-infrared spectroelectrochemistry and correlate these observations with structural and electronic changes monitored by X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, and conductivity measurements. Reduction causes an initial transformation to a metallic, IR-colored distorted monoclinic phase. However, an unexpected reversible transition from conductive, reduced monoclinic VO2 to an infrared-transparent insulating phase is observed upon further reduction.

Design and evaluation of thin metal surface insulation for hypersonic flight

NASA Technical Reports Server (NTRS)

Miller, R. C.; Petach, A. M.

1976-01-01

An all-metal insulation was studied as a thermal protection system for hypersonic vehicles. Key program goals included fabricating the insulation in thin packages which are optimized for high temperature insulation of an actively cooled aluminum structure, and the use of state-of-the-art alloys. The insulation was fabricated from 300 series stainless steel in thicknesses of 0.8 to 12 mm. The outer, 0.127 mm thick, skin was textured to accommodate thermal expansion and oxidized to increase emittance. The thin insulating package was achieved using an insulation concept consisting of foil radiation shields spaced within the package, and conical foil supports to carry loads from the skin and maintain package dimensions. Samples of the metal-insulation were tested to evaluate thermal insulation capability, rain and sand erosion resistance, high temperature oxidation resistance, applied load capability, and high temperature emittance.

Thin film superconductor magnetic bearings

DOEpatents

Weinberger, Bernard R.

1995-12-26

A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

Amorphous silicon Schottky barrier solar cells incorporating a thin insulating layer and a thin doped layer

DOEpatents

Carlson, David E.

1980-01-01

Amorphous silicon Schottky barrier solar cells which incorporate a thin insulating layer and a thin doped layer adjacent to the junction forming metal layer exhibit increased open circuit voltages compared to standard rectifying junction metal devices, i.e., Schottky barrier devices, and rectifying junction metal insulating silicon devices, i.e., MIS devices.

Fabrication and characterization of high mobility spin-coated zinc oxide thin film transistors

NASA Astrophysics Data System (ADS)

Singh, Shaivalini; Chakrabarti, P.

2012-10-01

A ZnO based thin film transistor (TFT) with bottom-gate configuration and SiO2 as insulating layer has been fabricated and characterized. The ZnO thin film was prepared by spin coating the sol-gel solution on the p-type Si wafers. The optical and structural properties of ZnO films were investigated using UV measurements and scanning electron microscope (SEM). The result of UV-visible study confirms that the films have a good absorbance in UV region and relatively low absorbance in the visible region. The TFT exhibited an off-current of 2.5×10-7 A. The values of field effect channel mobility and on/off current ratio extracted for the device, measured 11 cm2/V.s and ~102 respectively. The value of threshold voltage was found to be 1.3 V.

Effect of Al2O3 insulator thickness on the structural integrity of amorphous indium-gallium-zinc-oxide based thin film transistors.

PubMed

Kim, Hak-Jun; Hwang, In-Ju; Kim, Youn-Jea

2014-12-01

The current transparent oxide semiconductors (TOSs) technology provides flexibility and high performance. In this study, multi-stack nano-layers of TOSs were designed for three-dimensional analysis of amorphous indium-gallium-zinc-oxide (a-IGZO) based thin film transistors (TFTs). In particular, the effects of torsional and compressive stresses on the nano-sized active layers such as the a-IGZO layer were investigated. Numerical simulations were carried out to investigate the structural integrity of a-IGZO based TFTs with three different thicknesses of the aluminum oxide (Al2O3) insulator (δ = 10, 20, and 30 nm), respectively, using a commercial code, COMSOL Multiphysics. The results are graphically depicted for operating conditions.

[Spectral emissivity of thin films].

PubMed

Zhong, D

2001-02-01

In this paper, the contribution of multiple reflections in thin film to the spectral emissivity of thin films of low absorption is discussed. The expression of emissivity of thin films derived here is related to the thin film thickness d and the optical constants n(lambda) and k(lambda). It is shown that in the special case d-->infinity the emissivity of thin films is equivalent to that of the bulk material. Realistic numerical and more precise general numerical results for the dependence of the emissivity on d, n(lambda) and k(lambda) are given.

Ceramic Composite Thin Films

NASA Technical Reports Server (NTRS)

Dikin, Dmitriy A. (Inventor); Nguyen, SonBinh T. (Inventor); Ruoff, Rodney S. (Inventor); Stankovich, Sasha (Inventor)

2013-01-01

A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

PZT Thin-Film Micro Probe Device with Dual Top Electrodes

NASA Astrophysics Data System (ADS)

Luo, Chuan

should be less than 3 mm in order to guarantee the first resonant frequency above 60 kHz. Finally, a package for the PZT thin-film micro probe device is developed to ensure its proper function in an aqueous environment, such as inside of cochlea. The package is an insulation layer of parylene coating on the probe. A finite element analysis indicates that a coating thickness of less than 1 mum will reduce the PZT diaphragm displacement by less than 10%. A special fixture is designed to hold a large number of probes for parylene deposition of a thickness of 250 nm. A packaged probe is then submerged in deionized water and functions properly for at least 55 hours. Displacement and impedance of the probe are measured via a laser Doppler vibrometer and an impedance analyzer, respectively. Experimental results show that displacement of the PZT diaphragm increases about 30% in two hours, after the probe is submerged in the deionized water. The impedance measurement shows consistent trends. A hypothesis to explain this unusual phenomenon is diffusion of water molecules into the PZT thin film. High-resolution SEM images of the probe indicate presence of numerous nano-pores in the surface of the PZT thin film, indirectly confirming the hypothesis. Keywords: PZT, Thin-Film, Dual Electrodes, Parylene Coating, Aqueous Environment, Cochlear Implant

Spin-Orbit Torque-Assisted Switching in Magnetic Insulator Thin Films with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Wu, Mingzhong

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque that can induce magnetization switching in a neighboring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. This presentation reports the SOT-assisted switching in heavy metal/magnetic insulator systems.1 The experiments made use of Pt/BaFe12O19 bi-layered structures. Thanks to its strong spin-orbit coupling, Pt has been widely used to produce pure spin currents in previous studies. BaFe12O19 is an M-type barium hexagonal ferrite and is often referred as BaM. It is one of the few magnetic insulators with strong magneto-crystalline anisotropy and shows an effective uniaxial anisotropy field of about 17 kOe. It's found that the switching response in the BaM film strongly depends on the charge current applied to the Pt film. When a constant magnetic field is applied in the film plane, the charge current in the Pt film can switch the normal component of the magnetization (M⊥) in the BaM film between the up and down states. The current also dictates the up and down states of the remnant magnetization when the in-plane field is reduced to zero. When M⊥ is measured by sweeping an in-plane field, the response manifests itself as a hysteresis loop, which evolves in a completely opposite manner if the sign of the charge current is flipped. When the coercivity is measured by sweeping an out-of-plane field, its value can be reduced or increased by as much as about 500 Oe if an appropriate charge current is applied. 1. P. Li, T. Liu, H. Chang, A. Kalitsov, W. Zhang, G. Csaba, W. Li, D. Richardson, A. Demann, G. Rimal, H. Dey, J. S. Jiang, W. Porod, S. Field, J. Tang, M. C. Marconi, A. Hoffmann, O. Mryasov, and M. Wu, Nature Commun. 7:12688 doi: 10.1038/ncomms12688 (2016).

Synthesis of zinc oxide thin films prepared by sol-gel for specific bioactivity

NASA Astrophysics Data System (ADS)

Adam, Tijjani; Basri, B.; Dhahi, Th. S.; Mohammed, Mohammed; Hashim, U.; Noriman, N. Z.; Dahham, Omar S.

2017-09-01

Zinc oxide (ZnO) thin films this device to used for many application like chemical sensor, biosensor, solar energy, etc but my project to use for bioactivity(biosensor). Zinc oxide (ZnO) thin films have been grown using sol-gel technique. Characterization was done using Scanning Electron Microscope (SEM), Energy Dispersive X-ray(EDX) and Electrical Measurement(I-V). ZnO thin film was successfully synthesized using low cost sol-gel spin coating method. The coupling of DNA probe to ZnO thin film supports modified with carboxylic acid (COOH) is certainly the best practical method to make DNA immobilization and it does not require any coupling agent which could be a source of variability during the spotting with an automatic device. So, selected this coupling procedure for further experiments. The sensor was tested with initial trial with low concentrated DNA and able to detect detection of the disease effectively. Silicon-on-insulator (SOI) wafer device with ZnO can detect at different concentration in order to valid the device capabilities for detecting development. The lowest concentration 1 µM HPV DNA probe can detect is 0.1 nM HPV target DNA.

Fabrication of Vertical Organic Light-Emitting Transistor Using ZnO Thin Film

NASA Astrophysics Data System (ADS)

Yamauchi, Hiroshi; Iizuka, Masaaki; Kudo, Kazuhiro

2007-04-01

Organic light-emitting diodes (OLEDs) combined with thin film transistor (TFT) are well suitable elements for low-cost, large-area active matrix displays. On the other hand, zinc oxide (ZnO) is a transparent material and its electrical conductivity is controlled from conductive to insulating by growth conditions. The drain current of ZnO FET is 180 μA. The OLED uses ZnO thin film (Al-doped) for the electron injection layer and is controlled by radio frequency (rf) and direct current (dc) sputtering conditions, such as Al concentration and gas pressure. Al concentration in the ZnO film and deposition rate have strong effects on electron injection. Furthermore, the OLED driven by ZnO FET shows a luminance of 13 cd/m2, a luminance efficiency of 0.7 cd/A, and an on-off ratio of 650.

Zinc nitride thin films: basic properties and applications

NASA Astrophysics Data System (ADS)

Redondo-Cubero, A.; Gómez-Castaño, M.; García Núñez, C.; Domínguez, M.; Vázquez, L.; Pau, J. L.

2017-02-01

Zinc nitride films can be deposited by radio frequency magnetron sputtering using a Zn target at substrate temperatures lower than 250°C. This low deposition temperature makes the material compatible with flexible substrates. The asgrown layers present a black color, polycrystalline structures, large conductivities, and large visible light absorption. Different studies have reported about the severe oxidation of the layers in ambient conditions. Different compositional, structural and optical characterization techniques have shown that the films turn into ZnO polycrystalline layers, showing visible transparency and semi-insulating properties after total transformation. The oxidation rate is fairly constant as a function of time and depends on environmental parameters such as relative humidity or temperature. Taking advantage of those properties, potential applications of zinc nitride films in environmental sensing have been studied in the recent years. This work reviews the state-of-the-art of the zinc nitride technology and the development of several devices such as humidity indicators, thin film (photo)transistors and sweat monitoring sensors.

LPCVD homoepitaxy of Si doped β-Ga2O3 thin films on (010) and (001) substrates

NASA Astrophysics Data System (ADS)

Rafique, Subrina; Karim, Md Rezaul; Johnson, Jared M.; Hwang, Jinwoo; Zhao, Hongping

2018-01-01

This paper presents the homoepitaxy of Si-doped β-Ga2O3 thin films on semi-insulating (010) and (001) Ga2O3 substrates via low pressure chemical vapor deposition with a growth rate of ≥1 μm/h. Both high resolution scanning transmission electron microscopy and X-ray diffraction measurements demonstrated high crystalline quality homoepitaxial growth of these thin films. Atomic resolution STEM images of the as-grown β-Ga2O3 thin films on (010) and (001) substrates show high quality material without extended defects or dislocations. The charge carrier transport properties of the as-grown Si-doped β-Ga2O3 thin films were characterized by the temperature dependent Hall measurement using van der Pauw patterns. The room temperature carrier concentrations achieved for the (010) and (001) homoepitaxial thin films were ˜1.2 × 1018 cm-3 and ˜9.5 × 1017 cm-3 with mobilities of ˜72 cm2/V s and ˜42 cm2/V s, respectively.

NMR characterization of thin films

DOEpatents

Gerald II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

2010-06-15

A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

NMR characterization of thin films

DOEpatents

Gerald, II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

2008-11-25

A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

Nucleation-controlled low-temperature solid-phase crystallization for Sn-doped polycrystalline-Ge film on insulator with high carrier mobility (˜550 cm2/V s)

NASA Astrophysics Data System (ADS)

Xu, Chang; Gao, Hongmiao; Sugino, Takayuki; Miyao, Masanobu; Sadoh, Taizoh

2018-06-01

High-speed thin-film transistors (TFTs) are required to develop the next generation of electronics, such as three-dimensional large-scale integrated circuits and advanced system-in-displays. For this purpose, high-carrier-mobility semiconductor films on insulator structures should be fabricated with low-temperature processing conditions (≤500 °C). To achieve this, we investigate solid-phase crystallization of amorphous-GeSn (a-GeSn) films (Sn concentration: 2% and thickness: 50-200 nm) on insulating substrates, where thin a-Si under-layers (thickness: 0-20 nm) are introduced between a-GeSn films and insulating substrates. The GeSn films are polycrystallized by annealing (450 °C, 20 h) for all samples irrespective of a-GeSn and a-Si thickness conditions, while the Si films remain amorphous. Analysis of crystal structures of GeSn films (thickness: 50 nm) reveals that grain sizes decrease from ˜10 μm to 2-3 μm by the introduction of a-Si under-layers (thickness: 3-20 nm). This phenomenon is attributed to the change in dominant nucleation sites from the interface to the bulk, which significantly decreases grain-boundary scattering of carriers through a decrease in the barrier heights at grain boundaries. Bulk-nucleation further becomes dominant by increasing the GeSn film thickness. As a result, a high carrier mobility of ˜550 cm2/V s is realized for GeSn films (thickness: 100 nm) grown with a-Si under-layers. This mobility is the largest among ever reported data for Ge and GeSn grown on an insulator. This technique will facilitate realization of high-speed TFTs for use in the next generation of electronics.

Specific heat measurement set-up for quench condensed thin superconducting films.

PubMed

Poran, Shachaf; Molina-Ruiz, Manel; Gérardin, Anne; Frydman, Aviad; Bourgeois, Olivier

2014-05-01

We present a set-up designed for the measurement of specific heat of very thin or ultra-thin quench condensed superconducting films. In an ultra-high vacuum chamber, materials of interest can be thermally evaporated directly on a silicon membrane regulated in temperature from 1.4 K to 10 K. On this membrane, a heater and a thermometer are lithographically fabricated, allowing the measurement of heat capacity of the quench condensed layers. This apparatus permits the simultaneous thermal and electrical characterization of successively deposited layers in situ without exposing the deposited materials to room temperature or atmospheric conditions, both being irreversibly harmful to the samples. This system can be used to study specific heat signatures of phase transitions through the superconductor to insulator transition of quench condensed films.

Thin film cell development workshop report

NASA Technical Reports Server (NTRS)

Woodyard, James R.

1991-01-01

The Thin Film Development Workshop provided an opportunity for those interested in space applications of thin film cells to debate several topics. The unique characteristics of thin film cells as well as a number of other issues were covered during the discussions. The potential of thin film cells, key research and development issues, manufacturing issues, radiation damage, substrates, and space qualification of thin film cells were discussed.

Photo-Patterned Ion Gel Electrolyte-Gated Thin Film Transistors

NASA Astrophysics Data System (ADS)

Choi, Jae-Hong; Gu, Yuanyan; Hong, Kihyun; Frisbie, C. Daniel; Lodge, Timothy P.

2014-03-01

We have developed a novel fabrication route to pattern electrolyte thin films in electrolyte-gated transistors (EGTs) using a chemically crosslinkable ABA-triblock copolymer ion gel. In the self-assembly of poly[(styrene-r-vinylbenzylazide)-b-ethylene oxide-b-(styrene-r-vinylbenzylazide)] (SOS-N3) triblock copolymer and the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), the azide groups of poly(styrene-r-vinylbenzylazide) (PS-N3) end-blocks in the cores can be chemically cross-linked via UV irradiation (λ = 254 nm). Impedance spectroscopy and small-angle X-ray scattering confirmed that ion transport and microstructure of the ion gel are not affected by UV cross-linking. Using this chemical cross-linking strategy, we demonstrate a photo-patterning of ion gels through a patterned mask and the fabricated electrolyte-gated thin film transistors with photo-patterned ion gels as high-capacitance gate insulators exhibited high device performance (low operation voltages and high on/off current ratios).

Growth control of the oxidation state in vanadium oxide thin films

NASA Astrophysics Data System (ADS)

Lee, Shinbuhm; Meyer, Tricia L.; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung

2014-12-01

Precise control of the chemical valence or oxidation state of vanadium in vanadium oxide thin films is highly desirable for not only fundamental research but also technological applications that utilize the subtle change in the physical properties originating from the metal-insulator transition (MIT) near room temperature. However, due to the multivalent nature of vanadium and the lack of a good understanding on growth control of the oxidation state, stabilization of phase pure vanadium oxides with a single oxidation state is extremely challenging. Here, we systematically varied the growth conditions to clearly map out the growth window for preparing phase pure epitaxial vanadium oxides by pulsed laser deposition for providing a guideline to grow high quality thin films with well-defined oxidation states of V2 + 3 O 3 , V + 4 O 2 , and V2 + 5 O 5 . A well pronounced MIT was only observed in VO2 films grown in a very narrow range of oxygen partial pressure P(O2). The films grown either in lower (<10 mTorr) or higher P(O2) (>25 mTorr) result in V2O3 and V2O5 phases, respectively, thereby suppressing the MIT for both cases. We have also found that the resistivity ratio before and after the MIT of VO2 thin films can be further enhanced by one order of magnitude when the films are further oxidized by post-annealing at a well-controlled oxidizing ambient. This result indicates that stabilizing vanadium into a single valence state has to compromise with insufficient oxidation of an as grown thin film and, thereby, a subsequent oxidation is required for an improved MIT behavior.

Resistance noise in epitaxial thin films of ferromagnetic topological insulators

NASA Astrophysics Data System (ADS)

Bhattacharyya, Semonti; Kandala, Abhinav; Richardella, Anthony; Islam, Saurav; Samarth, Nitin; Ghosh, Arindam

2016-02-01

We report detailed temperature and gate-voltage dependence of 1/f resistance noise in magnetically doped topological insulators (TI) Crx(Bi,Sb)2-xTe3. The noise is remarkably sensitive to the gate voltage, increasing rapidly as the chemical potential is moved towards the charge neutrality point. Unlike in identically prepared (Bi,Sb)2Te3 films, where mobility-fluctuations in the surface states is the dominant mechanism, the noise in the magnetic Crx(Bi,Sb)2-xTe3 originates from transport in the localized band tail of the bulk valence band. A strong increase in noise with decreasing temperature supports this scenario. At higher temperature (≥10 K), we observed large noise peaks at gate voltage-dependent characteristic temperature scales. In line with similar observations in other non-magnetic TI systems, we attribute these peaks to generation-recombination in the Cr-impurity band.

Thermoelectric properties of an ultra-thin topological insulator.

PubMed

Islam, S K Firoz; Ghosh, T K

2014-04-23

Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor.

Low work function, stable thin films

DOEpatents

Dinh, Long N.; McLean, II, William; Balooch, Mehdi; Fehring, Jr., Edward J.; Schildbach, Marcus A.

2000-01-01

Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

Drop dynamics on a thin film: Thin film rupture

NASA Astrophysics Data System (ADS)

Carlson, Andreas; Kim, Pilnam; Stone, Howard A.

2011-11-01

The spreading of a water drop on an oil film that covers a solid substrate is a common event in many industrial processes. We study in experiments the dynamics of a water drop on a thin silicone oil film and quantify its interaction with the solid substrate that supports the film. The oil film becomes unstable and ruptures for solids that are hydrophilic. We determine the ``waiting time,'' the time it takes the water drop to drain the silicone film. This timescale is found to highly depend on how well water wets the solid, illustrating the interplay between intermolecular and hydrodynamic forces in the phenomenon. A phase diagram for the thin film stability is extracted based on waters equilibrium contact angle on the solid, which shows that we can either promote or inhibit de-wetting. As water comes in direct contact with the solid, it spreads and peels off the silicone film. We show the influence of viscosity, equilibrium contact angle and film height on the opening radius of the hole formed as the solid de-wets.

Structure of disordered gold-polymer thin films using small angle x-ray scattering

NASA Astrophysics Data System (ADS)

Teixeira, F. S.; Salvadori, M. C.; Cattani, M.; Brown, I. G.

2010-11-01

We have investigated the structure of disordered gold-polymer thin films using small angle x-ray scattering and compared the results with the predictions of a theoretical model based on two approaches—a structure form factor approach and the generalized Porod law. The films are formed of polymer-embedded gold nanoclusters and were fabricated by very low energy gold ion implantation into polymethylmethacrylate (PMMA). The composite films span (with dose variation) the transition from electrically insulating to electrically conducting regimes, a range of interest fundamentally and technologically. We find excellent agreement with theory and show that the PMMA-Au films have monodispersive or polydispersive characteristics depending on the implanted ion dose.

Improving yield and performance in ZnO thin-film transistors made using selective area deposition.

PubMed

Nelson, Shelby F; Ellinger, Carolyn R; Levy, David H

2015-02-04

We describe improvements in both yield and performance for thin-film transistors (TFTs) fabricated by spatial atomic layer deposition (SALD). These improvements are shown to be critical in forming high-quality devices using selective area deposition (SAD) as the patterning method. Selective area deposition occurs when the precursors for the deposition are prevented from reacting with some areas of the substrate surface. Controlling individual layer quality and the interfaces between layers is essential for obtaining good-quality thin-film transistors and capacitors. The integrity of the gate insulator layer is particularly critical, and we describe a method for forming a multilayer dielectric using an oxygen plasma treatment between layers that improves crossover yield. We also describe a method to achieve improved mobility at the important interface between the semiconductor and the gate insulator by, conversely, avoiding oxygen plasma treatment. Integration of the best designs results in wide design flexibility, transistors with mobility above 15 cm(2)/(V s), and good yield of circuits.

A thin film nitinol heart valve.

PubMed

Stepan, Lenka L; Levi, Daniel S; Carman, Gregory P

2005-11-01

In order to create a less thrombogenic heart valve with improved longevity, a prosthetic heart valve was developed using thin film nitinol (NiTi). A "butterfly" valve was constructed using a single, elliptical piece of thin film NiTi and a scaffold made from Teflon tubing and NiTi wire. Flow tests and pressure readings across the valve were performed in vitro in a pulsatile flow loop. Bio-corrosion experiments were conducted on untreated and passivated thin film nitinol. To determine the material's in vivo biocompatibility, thin film nitinol was implanted in pigs using stents covered with thin film NiTi. Flow rates and pressure tracings across the valve were comparable to those through a commercially available 19 mm Perimount Edwards tissue valve. No signs of corrosion were present on thin film nitinol samples after immersion in Hank's solution for one month. Finally, organ and tissue samples explanted from four pigs at 2, 3, 4, and 6 weeks after thin film NiTi implantation appeared without disease, and the thin film nitinol itself was without thrombus formation. Although long term testing is still necessary, thin film NiTi may be very well suited for use in artificial heart valves.

Spin Currents and Ferromagnetic Resonance in Magnetic Thin Films

NASA Astrophysics Data System (ADS)

Ellsworth, David

Spin currents represent a new and exciting phenomenon. There is both a wealth of new physics to be discovered and understood, and many appealing devices which may result from this area of research. To fully realize the potential of this discipline it is necessary to develop new methods for realizing spin currents and explore new materials which may be suitable for spin current applications. Spin currents are an inherently dynamic phenomenon involving the transfer of angular momentum within and between different thin films. In order to understand and optimize such devices the dynamics of magnetization must be determined. This dissertation reports on novel approaches for spin current generation utilizing the magnetic insulators yttrium iron garnet (YIG) and M-type barium hexagonal ferrite (BaM). First, the light-induced spin Seebeck effect is reported for the first time in YIG. Additionally, the first measurement of the spin Seebeck effect without an external magnetic field is demonstrated. To accomplish this the self-biased BaM thin films are utilized. Second, a new method for the generation of spin currents is presented: the photo-spin-voltaic effect. In this new phenomenon, a spin current may be generated by photons in a non-magnetic metal that is in close proximity to a magnetic insulator. On exposure to light, there occurs a light induced, spin-dependent excitation of electrons in a few platinum layers near the metal/magnetic insulator interface. This excitation gives rise to a pure spin current which flows in the metal. This new effect is explored in detail and extensive measurements are carried out to confirm the photonic origin of the photo-spin-voltaic effect and exclude competing effects. In addition to the spin current measurements, magnetization dynamics were probed in thin films using ferromagnetic resonance (FMR). In order to determine the optimal material configuration for magnetic recording write heads, FMR measurements were used to perform damping

Leakage current and charging/discharging processes in barrier-type anodic alumina thin films for use in metal-insulator-metal capacitors

NASA Astrophysics Data System (ADS)

Hourdakis, E.; Koutsoureli, M.; Papaioannou, G.; Nassiopoulou, A. G.

2018-06-01

Barrier-type anodic alumina thin films are interesting for use in high capacitance density metal-insulator-metal capacitors due to their excellent dielectric properties at small thickness. This thickness is easily controlled by the anodization voltage. In previous papers we studied the main parameters of interest of the Al/barrier-type anodic alumina/Al structure for use in RF applications and showed the great potential of barrier-type anodic alumina in this respect. In this paper, we investigated in detail charging/discharging processes and leakage current of the above dielectric material. Two different sets of metal-insulator-metal capacitors were studied, namely, with the top Al electrode being either e-gun deposited or sputtered. The dielectric constant of the barrier-type anodic alumina was found at 9.3. Low leakage current was observed in all samples studied. Furthermore, depending on the film thickness, field emission following the Fowler-Nordheim mechanism was observed above an applied electric field. Charging of the anodic dielectric was observed, occurring in the bulk of the anodic layer. The stored charge was of the order of few μC/cm2 and the calculated trap density ˜2 × 1018 states/cm3, the most probable origin of charge traps being, in our opinion, positive electrolyte ions trapped in the dielectric during anodization. We do not think that oxygen vacancies play an important role, since their existence would have a more important impact on the leakage current characteristics, such as resistive memory effects or significant changes during annealing, which were not observed. Finally, discharging characteristic times as high as 5 × 109 s were measured.

Characterization of crystallographic properties of thin films using X-ray diffraction

NASA Astrophysics Data System (ADS)

Zoo, Yeongseok

2007-12-01

Silver (Ag) has been recognized as one of promising candidates in Ultra-Large Scale Integrated (ULSI) applications in that it has the lowest bulk electrical resistivity of all pure metals and higher electromigration resistance than other interconnect materials. However, low thermal stability on Silicon Dioxide (Si02) at high temperatures (e.g., agglomeration) is considered a drawback for the Ag metallization scheme. Moreover, if a thin film is attached on a substrate, its properties may differ significantly from that of the bulk, since the properties of thin films can be significantly affected by the substrate. In this study, the Coefficient of Thermal Expansion (CTE) and texture evolution of Ag thin films on different substrates were characterized using various analytical techniques. The experimental results showed that the CTE of the Ag thin film was significantly affected by underlying substrate and the surface roughness of substrate. To investigate the alloying effect for Ag meatallization, small amounts of Copper (Cu) were added and characterized using theta-2theta X-ray Diffraction (XRD) scan and pole figure analysis. These XRD techniques are useful for investigating the primary texture of a metal film, (111) in this study, which (111) is the notation of a specific plane in the orthogonal coordinate system. They revealed that the (111) textures of Ag and Ag(Cu) thin films were enhanced with increasing temperature. Comparison of texture profiles between Ag and Ag(Cu) thin films showed that Cu additions enhanced (111) texture in Ag thin films. Accordingly, the texture enhancement in Ag thin films by Cu addition was discussed. Strained Silicon-On-Insulator (SSOI) is being considered as a potential substrate for Complementary Metal-Oxide-Semiconductor (CMOS) technology since the induced strain results in a significant improvement in device performance. High resolution X-ray diffraction (XRD) techniques were used to characterize the perpendicular and parallel

Ultra-thin smart acoustic metasurface for low-frequency sound insulation

NASA Astrophysics Data System (ADS)

Zhang, Hao; Xiao, Yong; Wen, Jihong; Yu, Dianlong; Wen, Xisen

2016-04-01

Insulating low-frequency sound is a conventional challenge due to the high areal mass required by mass law. In this letter, we propose a smart acoustic metasurface consisting of an ultra-thin aluminum foil bonded with piezoelectric resonators. Numerical and experimental results show that the metasurface can break the conventional mass law of sound insulation by 30 dB in the low frequency regime (<1000 Hz), with an ultra-light areal mass density (<1.6 kg/m2) and an ultra-thin thickness (1000 times smaller than the operating wavelength). The underlying physical mechanism of such extraordinary sound insulation performance is attributed to the infinite effective dynamic mass density produced by the smart resonators. It is also demonstrated that the excellent sound insulation property can be conveniently tuned by simply adjusting the external circuits instead of modifying the structure of the metasurface.

Electron-beam induced damage in thin insulating films on compound semiconductors. M.S. Thesis, 1988

NASA Technical Reports Server (NTRS)

Pantic, Dragan M.

1989-01-01

Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron-beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectric. The electron-beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry.

PubMed

Williams, Calum; Rughoobur, Girish; Flewitt, Andrew J; Wilkinson, Timothy D

2016-11-10

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF₂ (75-250 nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.

Nonlinear optical observation of coherent acoustic Dirac plasmons in thin-film topological insulators

NASA Astrophysics Data System (ADS)

Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

2016-09-01

Low-energy collective electronic excitations exhibiting sound-like linear dispersion have been intensively studied both experimentally and theoretically for a long time. However, coherent acoustic plasmon modes appearing in time-domain measurements are rarely observed due to Landau damping by the single-particle continua. Here we report on the observation of coherent acoustic Dirac plasmon (CADP) modes excited in indirectly (electrostatically) opposite-surface coupled films of the topological insulator Bi2Se3. Using transient second-harmonic generation, a technique capable of independently monitoring the in-plane and out-of-plane electron dynamics in the films, the GHz-range oscillations were observed without corresponding oscillations in the transient reflectivity. These oscillations were assigned to the transverse magnetic and transverse electric guided CADP modes induced by the evanescent guided Lamb acoustic waves and remained Landau undamped due to fermion tunnelling between the opposite-surface Dirac states.

Coating of plasma polymerized film

NASA Technical Reports Server (NTRS)

Morita, S.; Ishibashi, S.

1980-01-01

Plasma polymerized thin film coating and the use of other coatings is suggested for passivation film, thin film used for conducting light, and solid body lubrication film of dielectrics of ultra insulators for electrical conduction, electron accessories, etc. The special features of flow discharge development and the polymerized film growth mechanism are discussed.

Epitaxial thin films

DOEpatents

Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

2006-04-25

Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

Photocurrent Suppression of Transparent Organic Thin Film Transistors

NASA Astrophysics Data System (ADS)

Chuang, Chiao-Shun; Tsai, Shu-Ting; Lin, Yung-Sheng; Chen, Fang-Chung; Shieh, Hang-Ping D.

2007-12-01

Organic thin-film transistors (OTFTs) with high transmittance and low photosensitivity have been demonstrated. By using titanium dioxide nanoparticles as the additives in the polymer gate insulators, the level of device photoresponse has been reduced. The device shows simultaneously a high transparence and a minimal threshold voltage shift under white light illumination. It is inferred that the localized energy levels deep in the energy gap of pentacene behave as the recombination centers, enhancing substantially the recombination process in the conducting channel of the OTFTs. Therefore, the electron trapping is relieved and the shift of threshold voltage is reduced upon illumination.

Growth control of the oxidation state in vanadium oxide thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Shinbuhm; Meyer, Tricia L.; Lee, Ho Nyung, E-mail: hnlee@ornl.gov

2014-12-01

Precise control of the chemical valence or oxidation state of vanadium in vanadium oxide thin films is highly desirable for not only fundamental research but also technological applications that utilize the subtle change in the physical properties originating from the metal-insulator transition (MIT) near room temperature. However, due to the multivalent nature of vanadium and the lack of a good understanding on growth control of the oxidation state, stabilization of phase pure vanadium oxides with a single oxidation state is extremely challenging. Here, we systematically varied the growth conditions to clearly map out the growth window for preparing phase puremore » epitaxial vanadium oxides by pulsed laser deposition for providing a guideline to grow high quality thin films with well-defined oxidation states of V{sub 2}{sup +3}O{sub 3}, V{sup +4}O{sub 2}, and V{sub 2}{sup +5}O{sub 5}. A well pronounced MIT was only observed in VO{sub 2} films grown in a very narrow range of oxygen partial pressure P(O{sub 2}). The films grown either in lower (<10 mTorr) or higher P(O{sub 2}) (>25 mTorr) result in V{sub 2}O{sub 3} and V{sub 2}O{sub 5} phases, respectively, thereby suppressing the MIT for both cases. We have also found that the resistivity ratio before and after the MIT of VO{sub 2} thin films can be further enhanced by one order of magnitude when the films are further oxidized by post-annealing at a well-controlled oxidizing ambient. This result indicates that stabilizing vanadium into a single valence state has to compromise with insufficient oxidation of an as grown thin film and, thereby, a subsequent oxidation is required for an improved MIT behavior.« less

Magnetoresistance Versus Oxygen Deficiency in Epi-stabilized SrRu1 - x Fe x O3 - δ Thin Films.

PubMed

Dash, Umasankar; Acharya, Susant Kumar; Lee, Bo Wha; Jung, Chang Uk

2017-12-01

Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu 1 - x Fe x O 3 - δ epitaxial thin films (x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu 1 - x Fe x O 3 - δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal-insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2-300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR (~36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies (δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr 1 - x La x )(Ru 1 - x Fe x )O 3 . These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu 1 - x Fe x O 3 - δ thin films.

Wafer-scale growth of VO2 thin films using a combinatorial approach

PubMed Central

Zhang, Hai-Tian; Zhang, Lei; Mukherjee, Debangshu; Zheng, Yuan-Xia; Haislmaier, Ryan C.; Alem, Nasim; Engel-Herbert, Roman

2015-01-01

Transition metal oxides offer functional properties beyond conventional semiconductors. Bridging the gap between the fundamental research frontier in oxide electronics and their realization in commercial devices demands a wafer-scale growth approach for high-quality transition metal oxide thin films. Such a method requires excellent control over the transition metal valence state to avoid performance deterioration, which has been proved challenging. Here we present a scalable growth approach that enables a precise valence state control. By creating an oxygen activity gradient across the wafer, a continuous valence state library is established to directly identify the optimal growth condition. Single-crystalline VO2 thin films have been grown on wafer scale, exhibiting more than four orders of magnitude change in resistivity across the metal-to-insulator transition. It is demonstrated that ‘electronic grade' transition metal oxide films can be realized on a large scale using a combinatorial growth approach, which can be extended to other multivalent oxide systems. PMID:26450653

Asymmetries in surface waves and reflection/transmission characteristics associated with topological insulators

NASA Astrophysics Data System (ADS)

Mackay, Tom G.; Chiadini, Francesco; Fiumara, Vincenzo; Scaglione, Antonio; Lakhtakia, Akhlesh

2017-08-01

Three numerical studies were undertaken involving the interactions of plane waves with topological insulators. In each study, the topologically insulating surface states of the topological insulator were represented through a surface admittance. Canonical boundary-value problems were solved for the following cases: (i) Dyakonov surface-wave propagation guided by the planar interface of a columnar thin film and an isotropic dielectric topological insulator; (ii) Dyakonov-Tamm surface-wave propagation guided by the planar interface of a structurally chiral material and an isotropic dielectric topological insulator; and (iii) reflection and transmission due to the planar interface of a topologically insulating columnar thin film and vacuum. The nonzero surface admittance resulted in asymmetries in the wave speeds and decay constants of the surface waves in studies (i) and (ii). The nonzero surface admittance resulted in asymmetries in the reflectances and transmittances in study (iii).

The Effects of Postprocessing on Physical and Solution Deposition of Complex Oxide Thin Films for Tunable Applications

DTIC Science & Technology

2016-02-01

BST barium strontium titanate εr dielectric constant MIM metal /insulator/ metal MOSD metal organic spin deposition PtSi platinum silicide RF...improvement. In addition, BST films processed via solution metal organic spin deposition, which yield a lower dielectric range of 150–335, also...layers. This report details how we used solution and physical deposition to fabricate thin films via radio frequency (RF) sputtering and metal

Thin film hydrogen sensor

DOEpatents

Cheng, Y.T.; Poli, A.A.; Meltser, M.A.

1999-03-23

A thin film hydrogen sensor includes a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end. 5 figs.

Thin film hydrogen sensor

DOEpatents

Cheng, Yang-Tse; Poli, Andrea A.; Meltser, Mark Alexander

1999-01-01

A thin film hydrogen sensor, includes: a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end.

Stoichiometry and thickness dependence of superconducting properties of niobium nitride thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beebe, Melissa R., E-mail: mrbeebe@email.wm.edu; Beringer, Douglas B.; Burton, Matthew C.

2016-03-15

The current technology used in linear particle accelerators is based on superconducting radio frequency (SRF) cavities fabricated from bulk niobium (Nb), which have smaller surface resistance and therefore dissipate less energy than traditional nonsuperconducting copper cavities. Using bulk Nb for the cavities has several advantages, which are discussed elsewhere; however, such SRF cavities have a material-dependent accelerating gradient limit. In order to overcome this fundamental limit, a multilayered coating has been proposed using layers of insulating and superconducting material applied to the interior surface of the cavity. The key to this multilayered model is to use superconducting thin films tomore » exploit the potential field enhancement when these films are thinner than their London penetration depth. Such field enhancement has been demonstrated in MgB{sub 2} thin films; here, the authors consider films of another type-II superconductor, niobium nitride (NbN). The authors present their work correlating stoichiometry and superconducting properties in NbN thin films and discuss the thickness dependence of their superconducting properties, which is important for their potential use in the proposed multilayer structure. While there are some previous studies on the relationship between stoichiometry and critical temperature T{sub C}, the authors are the first to report on the correlation between stoichiometry and the lower critical field H{sub C1}.« less

Waterproof Silicone Coatings of Thermal Insulation and Vaporization Method

NASA Technical Reports Server (NTRS)

Cagliostro, Domenick E. (Inventor)

1999-01-01

Thermal insulation composed of porous ceramic material can be waterproofed by producing a thin silicone film on the surface of the insulation by exposing it to volatile silicone precursors at ambient conditions. When the silicone precursor reactants are multi-functional siloxanes or silanes containing alkenes or alkynes carbon groups higher molecular weight films can be produced. Catalyst are usually required for the silicone precursors to react at room temperature to form the films. The catalyst are particularly useful in the single component system e.g. dimethylethoxysilane (DNMS) to accelerate the reaction and decrease the time to waterproof and protect the insulation. In comparison to other methods, the chemical vapor technique assures better control over the quantity and location of the film being deposited on the ceramic insulation to improve the waterproof coating.

Piezoelectric actuated micro-resonators based on the growth of diamond on aluminum nitride thin films.

PubMed

Hees, J; Heidrich, N; Pletschen, W; Sah, R E; Wolfer, M; Williams, O A; Lebedev, V; Nebel, C E; Ambacher, O

2013-01-18

Unimorph heterostructures based on piezoelectric aluminum nitride (AlN) and diamond thin films are highly desirable for applications in micro- and nanoelectromechanical systems. In this paper, we present a new approach to combine thin conductive boron-doped as well as insulating nanocrystalline diamond (NCD) with sputtered AlN films without the need for any buffer layers between AlN and NCD or polishing steps. The zeta potentials of differently treated nanodiamond (ND) particles in aqueous colloids are adjusted to the zeta potential of AlN in water. Thereby, the nucleation density for the initial growth of diamond on AlN can be varied from very low (10(8) cm(-2)), in the case of hydrogen-treated ND seeding particles, to very high values of 10(11) cm(-2) for oxidized ND particles. Our approach yielding high nucleation densities allows the growth of very thin NCD films on AlN with thicknesses as low as 40 nm for applications such as microelectromechanical beam resonators. Fabricated piezo-actuated micro-resonators exhibit enhanced mechanical properties due to the incorporation of boron-doped NCD films. Highly boron-doped NCD thin films which replace the metal top electrode offer Young's moduli of more than 1000 GPa.

Carbon Nanotube Thin-Film Antennas.

PubMed

Puchades, Ivan; Rossi, Jamie E; Cress, Cory D; Naglich, Eric; Landi, Brian J

2016-08-17

Multiwalled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) dipole antennas have been successfully designed, fabricated, and tested. Antennas of varying lengths were fabricated using flexible bulk MWCNT sheet material and evaluated to confirm the validity of a full-wave antenna design equation. The ∼20× improvement in electrical conductivity provided by chemically doped SWCNT thin films over MWCNT sheets presents an opportunity for the fabrication of thin-film antennas, leading to potentially simplified system integration and optical transparency. The resonance characteristics of a fabricated chlorosulfonic acid-doped SWCNT thin-film antenna demonstrate the feasibility of the technology and indicate that when the sheet resistance of the thin film is >40 ohm/sq no power is absorbed by the antenna and that a sheet resistance of <10 ohm/sq is needed to achieve a 10 dB return loss in the unbalanced antenna. The dependence of the return loss performance on the SWCNT sheet resistance is consistent with unbalanced metal, metal oxide, and other CNT-based thin-film antennas, and it provides a framework for which other thin-film antennas can be designed.

Internal stresses and formation of switchable nanowires at thin silica film edges

NASA Astrophysics Data System (ADS)

Phillips, J. C.

2011-02-01

At vertical edges, thin films of silicon oxide (SiO2-x) can contain defect-free semiconductive c-Si layered nanocrystals (Si NC) embedded in and supported by an insulating g-SiO2 matrix. Yaoet al. [Appl. Phys. A (in press)] have shown that a trenched thin film geometry enables the NC to form switchable nanowires (SNW) when trained by an applied field. The field required to form SNW decreases rapidly within a few cycles, or by annealing at 600 °C in even fewer cycles, and is stable to 700 °C. Here we describe the intrinsic evolution of Si NC and SNW in terms of the competition between internal stresses and electro-osmosis. The analysis relies heavily on experimental data from a wide range of thin film studies, and it explains why a vertical edge across the planar polySi-SiO2-x interface is necessary to form SNW. The discussion also shows that the formation mechanisms of Si NC and polySi/SiO2-x SNW are intrinsic and result from optimization of nanowire connectivity in the presence of residual host misfit stresses.

Harnessing the metal-insulator transition for tunable metamaterials

NASA Astrophysics Data System (ADS)

Charipar, Nicholas A.; Charipar, Kristin M.; Kim, Heungsoo; Bingham, Nicholas S.; Suess, Ryan J.; Mathews, Scott A.; Auyeung, Raymond C. Y.; Piqué, Alberto

2017-08-01

The control of light-matter interaction through the use of subwavelength structures known as metamaterials has facilitated the ability to control electromagnetic radiation in ways not previously achievable. A plethora of passive metamaterials as well as examples of active or tunable metamaterials have been realized in recent years. However, the development of tunable metamaterials is still met with challenges due to lack of materials choices. To this end, materials that exhibit a metal-insulator transition are being explored as the active element for future metamaterials because of their characteristic abrupt change in electrical conductivity across their phase transition. The fast switching times (▵t < 100 fs) and a change in resistivity of four orders or more make vanadium dioxide (VO2) an ideal candidate for active metamaterials. It is known that the properties associated with thin film metal-insulator transition materials are strongly dependent on the growth conditions. For this work, we have studied how growth conditions (such as gas partial pressure) influence the metalinsulator transition in VO2 thin films made by pulsed laser deposition. In addition, strain engineering during the growth process has been investigated as a method to tune the metal-insulator transition temperature. Examples of both the optical and electrical transient dynamics facilitating the metal-insulator transition will be presented together with specific examples of thin film metamaterial devices.

DC current induced metal-insulator transition in epitaxial Sm{sub 0.6}Nd{sub 0.4}NiO{sub 3}/LaAlO{sub 3} thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Haoliang; CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026; Luo, Zhenlin, E-mail: zlluo@ustc.edu.cn

2014-05-15

The metal-insulator transition (MIT) in strong correlated electron materials can be induced by external perturbation in forms of thermal, electrical, optical, or magnetic fields. We report on the DC current induced MIT in epitaxial Sm{sub 0.6}Nd{sub 0.4}NiO{sub 3} (SNNO) thin film deposited by pulsed laser deposition on (001)-LaAlO{sub 3} substrate. It was found that the MIT in SNNO film not only can be triggered by thermal, but also can be induced by DC current. The T{sub MI} of SNNO film decreases from 282 K to 200 K with the DC current density increasing from 0.003 × 10{sup 9} A•m{sup −2}more » to 4.9 × 10{sup 9} A•m{sup −2}. Based on the resistivity curves measured at different temperatures, the MIT phase diagram has been successfully constructed.« less

Growth and Etch Rate Study of Low Temperature Anodic Silicon Dioxide Thin Films

PubMed Central

Ashok, Akarapu; Pal, Prem

2014-01-01

Silicon dioxide (SiO2) thin films are most commonly used insulating films in the fabrication of silicon-based integrated circuits (ICs) and microelectromechanical systems (MEMS). Several techniques with different processing environments have been investigated to deposit silicon dioxide films at temperatures down to room temperature. Anodic oxidation of silicon is one of the low temperature processes to grow oxide films even below room temperature. In the present work, uniform silicon dioxide thin films are grown at room temperature by using anodic oxidation technique. Oxide films are synthesized in potentiostatic and potentiodynamic regimes at large applied voltages in order to investigate the effect of voltage, mechanical stirring of electrolyte, current density and the water percentage on growth rate, and the different properties of as-grown oxide films. Ellipsometry, FTIR, and SEM are employed to investigate various properties of the oxide films. A 5.25 Å/V growth rate is achieved in potentiostatic mode. In the case of potentiodynamic mode, 160 nm thickness is attained at 300 V. The oxide films developed in both modes are slightly silicon rich, uniform, and less porous. The present study is intended to inspect various properties which are considered for applications in MEMS and Microelectronics. PMID:24672287

Influence of magnetic disorders on quantum anomalous Hall effect in magnetic topological insulator films beyond the two-dimensional limit

NASA Astrophysics Data System (ADS)

Xing, Yanxia; Xu, Fuming; Cheung, King Tai; Sun, Qing-feng; Wang, Jian; Yao, Yugui

2018-04-01

Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetic topological insulator (MTI) thin films fabricated on magnetically doped {({{Bi}},{{Sb}})}2{{{Te}}}3. In an MTI thin film with the magnetic easy axis along the normal direction (z-direction), orientations of magnetic dopants are randomly distributed around the magnetic easy axis, acting as magnetic disorders. With the aid of the non-equilibrium Green's function and Landauer–Büttiker formalism, we numerically study the influence of magnetic disorders on QAHE in an MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is found that, due to the existence of gapless side surface states, QAHE is protected even in the presence of magnetic disorders as long as the z-component of magnetic moment of all magnetic dopants are positive. More importantly, such magnetic disorders also suppress the dissipation of the chiral edge states and enhance the quality of QAHE in MTI films. In addition, the effect of magnetic disorders depends very much on the film thickness, and the optimal influence is achieved at certain thickness. These findings are new features for QAHE in three-dimensional systems, not present in two-dimensional systems.

Angle-independent VO2 Thin Film on Glass Fiber Cloth as a Soft-Smart-Mirror (SSM)

PubMed Central

Cai, Nianjin; Zhang, Wang; Wang, Wanlin; Zhu, Yuchen; Zada, Imran; Gu, Jiajun; Liu, Qinglei; Su, Huilan; Guo, Cuiping; Zhang, Zhijian; Zhang, Jianzhong; Wu, Liping; Zhang, Di

2016-01-01

Designing materials with a negative feedback function is beneficial for achieving temperature regulation inside a greenhouse. VO2 has been studied extensively because of its low insulator-to-metal transition temperature (IMT). In this study, reflection changes during a VO2 phase transition were investigated. Glass fiber cloth was used as a substrate, as it is stable and soft. A VO2 thin film on a glass fiber cloth whose surface contained 96% V4+ and 4% V5+ was prepared using an inorganic sol-gels method. The insulator-to-metal transition temperature was decreased by 38 °C, which was observed from the reflection curve detected using an angle-resolved spectrometer. This decrease in IMT occurred mainly because of the presence of V5+, which causes destabilization of the monoclinic phase of VO2. When the greenhouse temperature was increased from 30 °C to 40 °C, the reflected intensity of VO2 on glass fiber cloth decreased by 22% for the wavelength range of 400 nm to 800 nm. In addition, the angle-independent property of the VO2 thin film was observed using an angle-resolved spectrometer. Owing to its thermo-reflective properties, the thin film can serve as a soft-smart-mirror (SSM) inside a greenhouse to stabilize the temperature, playing a negative feedback role. PMID:27849051

Angle-independent VO2 Thin Film on Glass Fiber Cloth as a Soft-Smart-Mirror (SSM)

NASA Astrophysics Data System (ADS)

Cai, Nianjin; Zhang, Wang; Wang, Wanlin; Zhu, Yuchen; Zada, Imran; Gu, Jiajun; Liu, Qinglei; Su, Huilan; Guo, Cuiping; Zhang, Zhijian; Zhang, Jianzhong; Wu, Liping; Zhang, Di

2016-11-01

Designing materials with a negative feedback function is beneficial for achieving temperature regulation inside a greenhouse. VO2 has been studied extensively because of its low insulator-to-metal transition temperature (IMT). In this study, reflection changes during a VO2 phase transition were investigated. Glass fiber cloth was used as a substrate, as it is stable and soft. A VO2 thin film on a glass fiber cloth whose surface contained 96% V4+ and 4% V5+ was prepared using an inorganic sol-gels method. The insulator-to-metal transition temperature was decreased by 38 °C, which was observed from the reflection curve detected using an angle-resolved spectrometer. This decrease in IMT occurred mainly because of the presence of V5+, which causes destabilization of the monoclinic phase of VO2. When the greenhouse temperature was increased from 30 °C to 40 °C, the reflected intensity of VO2 on glass fiber cloth decreased by 22% for the wavelength range of 400 nm to 800 nm. In addition, the angle-independent property of the VO2 thin film was observed using an angle-resolved spectrometer. Owing to its thermo-reflective properties, the thin film can serve as a soft-smart-mirror (SSM) inside a greenhouse to stabilize the temperature, playing a negative feedback role.

Angle-independent VO2 Thin Film on Glass Fiber Cloth as a Soft-Smart-Mirror (SSM).

PubMed

Cai, Nianjin; Zhang, Wang; Wang, Wanlin; Zhu, Yuchen; Zada, Imran; Gu, Jiajun; Liu, Qinglei; Su, Huilan; Guo, Cuiping; Zhang, Zhijian; Zhang, Jianzhong; Wu, Liping; Zhang, Di

2016-11-16

Designing materials with a negative feedback function is beneficial for achieving temperature regulation inside a greenhouse. VO 2 has been studied extensively because of its low insulator-to-metal transition temperature (IMT). In this study, reflection changes during a VO 2 phase transition were investigated. Glass fiber cloth was used as a substrate, as it is stable and soft. A VO 2 thin film on a glass fiber cloth whose surface contained 96% V 4+ and 4% V 5+ was prepared using an inorganic sol-gels method. The insulator-to-metal transition temperature was decreased by 38 °C, which was observed from the reflection curve detected using an angle-resolved spectrometer. This decrease in IMT occurred mainly because of the presence of V 5+ , which causes destabilization of the monoclinic phase of VO 2 . When the greenhouse temperature was increased from 30 °C to 40 °C, the reflected intensity of VO 2 on glass fiber cloth decreased by 22% for the wavelength range of 400 nm to 800 nm. In addition, the angle-independent property of the VO 2 thin film was observed using an angle-resolved spectrometer. Owing to its thermo-reflective properties, the thin film can serve as a soft-smart-mirror (SSM) inside a greenhouse to stabilize the temperature, playing a negative feedback role.

Installing fiber insulation in tight spaces

NASA Technical Reports Server (NTRS)

Patel, B. C.; Wang, D. S.; Warren, A. D.

1978-01-01

Two techniques using organic resin binders or thin clear-burning plastic film have been successfully used to simplify, and facilitate handling of aluminum/zirconia fiber batting as insulation material for high temperature seals.

Thin Films

NASA Astrophysics Data System (ADS)

Khorshidi, Zahra; Bahari, Ali; Gholipur, Reza

2014-11-01

Effect of annealing temperature on the characteristics of sol-gel-driven Ta ax La(1- a) x O y thin film spin-coated on Si substrate as a high- k gate dielectric was studied. Ta ax La(1- a) x O y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta0.3 x La0.7 x Oy film had an amorphous structure. Therefore, Ta0.3 x La0.7 x O y film was chosen to continue the present studies. The morphology of Ta0.3 x La0.7 x O y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta0.3 x La0.7 x O y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance-voltage ( C- V) and current density-voltage ( J- V) measurements and the Tauc method. The obtained results demonstrated that Ta0.3 x La0.7 x O y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10-6 A/cm2 at 1 V).

Tuning Magnetic Order in Transition Metal Oxide Thin Films

NASA Astrophysics Data System (ADS)

Grutter, Alexander John

In recent decades, one of the most active and promising areas of condensed matter research has been that of complex oxides. With the advent of new growth techniques such as pulsed laser deposition and molecular beam epitaxy, a wealth of new magnetic and electronic ground states have emerged in complex oxide heterostructures. The wide variety of ground states in complex oxides is well known and generally attributed to the unprecedented variety of valence, structure, and bonding available in these systems. The tunability of this already diverse playground of states and interactions is greatly multiplied in thin films and heterostructures by the addition of parameters such as substrate induced strain and interfacial electronic reconstruction. Thus, recent studies have shown emergent properties such as the stabilization of ferromagnetism in a paramagnetic system, conductivity at the interface of two insulators, and even exchange bias at the interface between a paramagnet and a ferromagnet. Despite these steps forward, there remains remarkable disagreement on the mechanisms by which these emergent phenomena are stabilized. The contributions of strain, stoichiometry, defects, intermixing, and electronic reconstruction are often very difficult to isolate in thin films and superlattices. This thesis will present model systems for isolating the effects of strain and interfacial electronic interactions on the magnetic state of complex oxides from alternative contributions. We will focus first on SrRuO3, an ideal system in which to isolate substrate induced strain effects. We explore the effects of structural distortions in the simplest case of growth on (100) oriented substrates. We find that parameters including saturated magnetic moment and Curie temperature are all highly tunable through substrate induced lattice distortions. We also report the stabilization of a nonmagnetic spin-zero configuration of Ru4+ in tetragonally distorted films under tensile strain. Through

Temperature dependent infrared nano-imaging of La0.67Sr0.33MnO3 thin film

NASA Astrophysics Data System (ADS)

Xu, Peng; Huffman, T. J.; Hae Kwak, In; Biswas, Amlan; Qazilbash, M. M.

2018-01-01

We investigate the temperature dependence of infrared properties at nanometer length scales in La0.67Sr0.33MnO3 (LSMO) thin film with a thickness of 47 unit cells grown on SrTiO3 substrate. The infrared nano-imaging experiments were performed using a near-field optical microscope in conjunction with a variable temperature heating stage. The near-field infrared data is consistent with the bulk of the LSMO film undergoing the thermally-driven non-percolative second-order transition from a metallic, ferromagnetic phase to an insulating, paramagnetic phase. We find persistent infrared contrast on the nanoscale that is independent of temperature and which we attribute to two novel phases with different conductivities coexisting in the vicinity of the film-substrate interface. These two coexisting phases at the film-substrate interface do not undergo the metal-insulator transition (MIT) and hence are different from the metallic, ferromagnetic and insulating, paramagnetic phases in the bulk of the film. At temperatures approaching the nominal MIT temperature, repeated scans of the same microscopic area at constant temperature reveal bimodal fluctuation of the near-field infrared amplitude. We interpret this phenomenon as slow, critical fluctuations of the conductivity in the bulk of the LSMO film.

Film and membrane-model thermodynamics of free thin liquid films.

PubMed

Radke, C J

2015-07-01

In spite of over 7 decades of effort, the thermodynamics of thin free liquid films (as in emulsions and foams) lacks clarity. Following a brief review of the meaning and measurement of thin-film forces (i.e., conjoining/disjoining pressures), we offer a consistent analysis of thin-film thermodynamics. By carefully defining film reversible work, two distinct thermodynamic formalisms emerge: a film model with two zero-volume membranes each of film tension γ(f) and a membrane model with a single zero-volume membrane of membrane tension 2γ(m). In both models, detailed thermodynamic analysis gives rise to thin-film Gibbs adsorption equations that allow calculation of film and membrane tensions from measurements of disjoining-pressure isotherms. A modified Young-Laplace equation arises in the film model to calculate film-thickness profiles from the film center to the surrounding bulk meniscus. No corresponding relation exists in the membrane model. Illustrative calculations of disjoining-pressure isotherms for water are presented using square-gradient theory. We report considerable deviations from Hamaker theory for films less than about 3 nm in thickness. Such thin films are considerably more attractive than in classical Hamaker theory. Available molecular simulations reinforce this finding. Copyright © 2014 Elsevier Inc. All rights reserved.

Substrate spacing and thin-film yield in chemical bath deposition of semiconductor thin films

NASA Astrophysics Data System (ADS)

Arias-Carbajal Reádigos, A.; García, V. M.; Gomezdaza, O.; Campos, J.; Nair, M. T. S.; Nair, P. K.

2000-11-01

Thin-film yield in the chemical bath deposition technique is studied as a function of separation between substrates in batch production. Based on a mathematical model, it is proposed and experimentally verified in the case of CdS thin films that the film thickness reaches an asymptotic maximum with increase in substrate separation. It is shown that at a separation less than 1 mm between substrates the yield, i.e. percentage in moles of a soluble cadmium salt deposited as a thin film of CdS, can exceed 50%. This behaviour is explained on the basis of the existence of a critical layer of solution near the substrate, within which the relevant ionic species have a higher probability of interacting with the thin-film layer than of contributing to precipitate formation. The critical layer depends on the solution composition and the temperature of the bath as well as the duration of deposition. An effective value for the critical layer thickness has been defined as half the substrate separation at which 90% of the maximum film thickness for the particular bath composition, bath temperature and duration of deposition is obtained. In the case of CdS thin films studied as an example, the critical layer is found to extend from 0.5 to 2.5 mm from the substrate surface, depending on the deposition conditions.

Improvement in negative bias illumination stress stability of In-Ga-Zn-O thin film transistors using HfO2 gate insulators by controlling atomic-layer-deposition conditions

NASA Astrophysics Data System (ADS)

Na, So-Yeong; Kim, Yeo-Myeong; Yoon, Da-Jeong; Yoon, Sung-Min

2017-12-01

The effects of atomic layer deposition (ALD) conditions for the HfO2 gate insulators (GI) on the device characteristics of the InGaZnO (IGZO) thin film transistors (TFTs) were investigated when the ALD temperature and Hf precursor purge time were varied to 200, 225, and 250 °C, and 15 and 30 s, respectively. The HfO2 thin films showed low leakage current density of 10-8 A cm-2, high dielectric constant of over 20, and smooth surface roughness at all ALD conditions. The IGZO TFTs using the HfO2 GIs showed good device characteristics such as a saturation mobility as high as 11 cm2 V-1 s-1, a subthreshold swing as low as 0.10 V/dec, and all the devices could be operated at a gate voltage as low as  ±3 V. While there were no marked differences in transfer characteristics and PBS stabilities among the fabricated devices, the NBIS instabilities could be improved by increasing the ALD temperature for the formation of HfO2 GIs by reducing the oxygen vacancies within the IGZO channel.

Surface Termination Conversion during SrTiO3 Thin Film Growth Revealed by X-ray Photoelectron Spectroscopy

PubMed Central

Baeumer, Christoph; Xu, Chencheng; Gunkel, Felix; Raab, Nicolas; Heinen, Ronja Anika; Koehl, Annemarie; Dittmann, Regina

2015-01-01

Emerging electrical and magnetic properties of oxide interfaces are often dominated by the termination and stoichiometry of substrates and thin films, which depend critically on the growth conditions. Currently, these quantities have to be measured separately with different sophisticated techniques. This report will demonstrate that the analysis of angle dependent X-ray photoelectron intensity ratios provides a unique tool to determine both termination and stoichiometry simultaneously in a straightforward experiment. Fitting the experimental angle dependence with a simple analytical model directly yields both values. The model is calibrated through the determination of the termination of SrTiO3 single crystals after systematic pulsed laser deposition of sub-monolayer thin films of SrO. We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film. We show that this termination conversion results in insulating properties of interfaces between polar perovskites and SrTiO3 thin films. These insights about oxide thin film growth can be utilized for interface engineering of oxide heterostructures. In particular, they suggest a recipe for obtaining two-dimensional electron gases at thin film interfaces: SrTiO3 should be deposited slightly Ti-rich to conserve the TiO2-termination. PMID:26189436

Revealing topological Dirac fermions at the surface of strained HgTe thin films via quantum Hall transport spectroscopy

NASA Astrophysics Data System (ADS)

Thomas, C.; Crauste, O.; Haas, B.; Jouneau, P.-H.; Bäuerle, C.; Lévy, L. P.; Orignac, E.; Carpentier, D.; Ballet, P.; Meunier, T.

2017-12-01

We demonstrate evidences of electronic transport via topological Dirac surface states in a thin film of strained HgTe. At high perpendicular magnetic fields, we show that the electron transport reaches the quantum Hall regime with vanishing resistance. Furthermore, quantum Hall transport spectroscopy reveals energy splittings of relativistic Landau levels specific to coupled Dirac surface states. This study provides insights in the quantum Hall effect of topological insulator (TI) slabs, in the crossover regime between two- and three-dimensional TIs, and in the relevance of thin TI films to explore circuit functionalities in spintronics and quantum nanoelectronics.

Naphthacene Based Organic Thin Film Transistor With Rare Earth Oxide

NASA Astrophysics Data System (ADS)

Konwar, K.; Baishya, B.

2010-12-01

Naphthacene based organic thin film transistors (OTFTs) have been fabricated using La2O3, as the gate insulator. All the OTFTs have been fabricated by the process of thermal evaporation in vacuum on perfectly cleaned glass substrates with aluminium as source-drain and gate electrodes. The naphthacene film morphology on the glass substrate has been studied by XRD and found to be polycrystalline in nature. The field effect mobility, output resistance, amplification factor, transconductance and gain bandwidth product of the OTFTs have been calculated by using theoretical TFT model. The highest value of field effect mobility is found to be 0.07×10-3 cm2V-1s-1 for the devices annealed in vacuum at 90° C for 5 hours.

Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor.

PubMed

Nomura, Kenji; Ohta, Hiromichi; Ueda, Kazushige; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo

2003-05-23

We report the fabrication of transparent field-effect transistors using a single-crystalline thin-film transparent oxide semiconductor, InGaO3(ZnO)5, as an electron channel and amorphous hafnium oxide as a gate insulator. The device exhibits an on-to-off current ratio of approximately 106 and a field-effect mobility of approximately 80 square centimeters per volt per second at room temperature, with operation insensitive to visible light irradiation. The result provides a step toward the realization of transparent electronics for next-generation optoelectronics.

Ultrafast terahertz spectroscopy study of a Kondo insulating thin-film Sm B6 : Evidence for an emergent surface state

NASA Astrophysics Data System (ADS)

Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard L.; Averitt, Richard D.

2018-04-01

We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound Sm B6 , a prototype Kondo insulator. Temperature-dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ˜T*=20 K , well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20 K) suggests the emergence of a surface state with an effective electron mass of 0.1 me . The conductivity dynamics following optical excitation is also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20 K, indicative of another channel opening up in the low-energy electrodynamics. Taken together, these results are consistent with the onset of a surface state well below the crossover temperature (100 K) after long-range coherence of the f -electron Kondo lattice is established.

Temperature Behavior of Thin Film Varactor

DTIC Science & Technology

2012-01-01

Temperature Behavior of Thin Film Varactor By Richard X. Fu ARL-TR-5905 January 2012...Thin Film Varactor Richard X. Fu Sensors and Electron Devices Directorate, ARL...DD-MM-YYYY) January 2012 2. REPORT TYPE Final 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Temperature Behavior of Thin Film Varactor 5a

Self-Limited Growth in Pentacene Thin Films

PubMed Central

2017-01-01

Pentacene is one of the most studied organic semiconducting materials. While many aspects of the film formation have already been identified in very thin films, this study provides new insight into the transition from the metastable thin-film phase to bulk phase polymorphs. This study focuses on the growth behavior of pentacene within thin films as a function of film thickness ranging from 20 to 300 nm. By employing various X-ray diffraction methods, combined with supporting atomic force microscopy investigations, one crystalline orientation for the thin-film phase is observed, while three differently tilted bulk phase orientations are found. First, bulk phase crystallites grow with their 00L planes parallel to the substrate surface; second, however, crystallites tilted by 0.75° with respect to the substrate are found, which clearly dominate the former in ratio; third, a different bulk phase polymorph with crystallites tilted by 21° is found. The transition from the thin-film phase to the bulk phase is rationalized by the nucleation of the latter at crystal facets of the thin-film-phase crystallites. This leads to a self-limiting growth of the thin-film phase and explains the thickness-dependent phase behavior observed in pentacene thin films, showing that a large amount of material is present in the bulk phase much earlier during the film growth than previously thought. PMID:28287698

Self-Limited Growth in Pentacene Thin Films.

PubMed

Pachmajer, Stefan; Jones, Andrew O F; Truger, Magdalena; Röthel, Christian; Salzmann, Ingo; Werzer, Oliver; Resel, Roland

2017-04-05

Pentacene is one of the most studied organic semiconducting materials. While many aspects of the film formation have already been identified in very thin films, this study provides new insight into the transition from the metastable thin-film phase to bulk phase polymorphs. This study focuses on the growth behavior of pentacene within thin films as a function of film thickness ranging from 20 to 300 nm. By employing various X-ray diffraction methods, combined with supporting atomic force microscopy investigations, one crystalline orientation for the thin-film phase is observed, while three differently tilted bulk phase orientations are found. First, bulk phase crystallites grow with their 00L planes parallel to the substrate surface; second, however, crystallites tilted by 0.75° with respect to the substrate are found, which clearly dominate the former in ratio; third, a different bulk phase polymorph with crystallites tilted by 21° is found. The transition from the thin-film phase to the bulk phase is rationalized by the nucleation of the latter at crystal facets of the thin-film-phase crystallites. This leads to a self-limiting growth of the thin-film phase and explains the thickness-dependent phase behavior observed in pentacene thin films, showing that a large amount of material is present in the bulk phase much earlier during the film growth than previously thought.

Metallic Thin-Film Bonding and Alloy Generation

NASA Technical Reports Server (NTRS)

Peotter, Brian S. (Inventor); Fryer, Jack Merrill (Inventor); Campbell, Geoff (Inventor); Droppers, Lloyd (Inventor)

2016-01-01

Diffusion bonding a stack of aluminum thin films is particularly challenging due to a stable aluminum oxide coating that rapidly forms on the aluminum thin films when they are exposed to atmosphere and the relatively low meting temperature of aluminum. By plating the individual aluminum thin films with a metal that does not rapidly form a stable oxide coating, the individual aluminum thin films may be readily diffusion bonded together using heat and pressure. The resulting diffusion bonded structure can be an alloy of choice through the use of a carefully selected base and plating metals. The aluminum thin films may also be etched with distinct patterns that form a microfluidic fluid flow path through the stack of aluminum thin films when diffusion bonded together.

Molecular beam epitaxy growth of SmB6+/-δ thin films

NASA Astrophysics Data System (ADS)

Hoffman, Jason; Saleem, Muhammad; Day, James; Bonn, Doug; Hoffman, Jennifer

SmB6 has emerged as a leading candidate in the search for exotic topological states generated by strong interactions. The synthesis of epitaxial SmB6 thin films presents new avenues to control surface termination, thickness, and strain in this system. In this work, we use molecular beam epitaxy (MBE) to deposit SmB6+/-δ films on insulating (001)-oriented MgO substrates. We use ex-situ x-ray diffraction and magnetotransport measurements to assess the properties of the samples and compare them to previously reported values for single crystals. We also discuss the prospects of using rare-earth substitution to control the correlation strength and alter the topology of the bulk and surface electronic states.

Air-stable solution-processed n-channel organic thin film transistors with polymerenhanced morphology

DOE PAGES

He, Zhengran; Shaik, Shoieb; Bi, Sheng; ...

2015-05-04

N,N 0-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN 2) is an n-type semiconductor exhibiting high electron mobility and excellent air stability. However, the reported electron mobility based on spin-coated PDIF-CN 2 film is much lower than the value of PDIF-CN 2 single crystals made from vapor phase deposition, indicating significant room for mobility enhancement. In this study, various insulating polymers, including poly(vinyl alcohol), poly(methyl methacrylate) (PMMA), and poly(alpha-methylstyrene) (PaMS), are pre-coated on silicon substrate aiming to enhance the morphology of the PDIF-CN 2 thin film, thereby improving the charge transport and air stability. Atomic force microscopy images reveal that with the pre-deposition of PaMSmore » or PMMA polymers, the morphology of the PDIF-CN 2 polycrystalline films is optimized in semiconducting crystal connectivity, domain size, and surface roughness, which leads to significant improvement of organic thin-film transistor (OTFT) performance. Particularly, an electron mobility of up to 0.55 cm 2/V s has been achieved from OTFTs based on the PDIF-CN 2 film with the pre-deposition of PaMS polymer.« less

Engineering Electronic Properties of Strongly Correlated Metal Thin Films

NASA Astrophysics Data System (ADS)

Eaton, Craig

residual resistivity ration complex vanadate thin films have been demonstrated. Methods for growing minimally strained SrVO3 films on (LaAlO 3)0.3(Sr2AlTaO6)0.7 substrates (0.7% tensile) were expanded to other substrates with different lattice mismatches, namely SrTiO3 (1.8% tensile) and LaAlO3 (1.3% compressive). Varying strain modifies bond angles or overlap, and can give rise to an insulating ground state. Changes in the film surface morphology derived from atomic force microscopy (AFM) was used to discriminate optimal growth conditions on each substrate. Films grown at each strain state remain strongly metallic at 10 nm thickness. Low temperature resistivity measurements, which demonstrates a marked increase in low temperature resistivity with respect to those films grown at optimized growth parameters, were found to be substrate dependent. The thickness of films grown on SrTiO3 are optimized for maximum thickness without cracking. Use of epitaxial strain as a mechanism for enabling a Mott transition was not demonstrated at strains and conditions attempted within this study. The experimental support of this hypothesis could not be experimentally confirmed within the range of strains studied here. Finally, high quality epitaxial SrTiO3-SrVO3-SrTiO 3 heterostructures are grown on (LaAlO3)0.3(Sr 2AlTaO6)0.7 substrates by hybrid MBE. RHEED, XRD, and TEM showed that these structures are of high structural quality, with atomically and chemically abrupt interfaces. By fixing the thickness of the SrTiO3 confinement layers to be 15 nm and decreasing the thickness of the SrVO3 from 50 nm down to 1.2 nm, it has been demonstrated that the system transitions from a strongly-correlated metal to an insulating state, as shown by temperature dependent resistivity and carrier concentration measurements. For films with thickness larger than 1.2 nm, the resistivity versus temperature is described by Fermi liquid behavior. Below this critical thickness the material undergoes an electronic

Printable CIGS thin film solar cells

NASA Astrophysics Data System (ADS)

Fan, Xiaojuan

2014-03-01

Among the various thin film solar cells in the market, CuInGaSe thin film cells have been considered as the most promising alternatives to silicon solar cells because of their high photo-electricity efficiency, reliability, and stability. However, many fabrication of CIGS thin film are based on vacuum processes such as evaporation sputtering techniques which are not cost efficient. This work develops a method using paste or ink liquid spin-coated on glass that would be to conventional ways in terms of cost effective, non-vacuum needed, quick processing. A mixture precursor was prepared by dissolving appropriate amounts of chemicals. After the mixture solution was cooled, a viscous paste prepared and ready for spin-coating process. A slight bluish CIG thin film substrate was then put in a tube furnace with evaporation of metal Se by depositing CdS layer and ZnO nanoparticle thin film coating to a solar cell fabrication. Structure, absorption spectrum, and photo-conversion efficiency for the as-grown CIGS thin film solar cell under study.

Comparative DMFT study of the eg-orbital Hubbard model in thin films

NASA Astrophysics Data System (ADS)

Rüegg, Andreas; Hung, Hsiang-Hsuan; Gull, Emanuel; Fiete, Gregory A.

2014-02-01

Heterostructures of transition-metal oxides have emerged as a new route to engineer electronic systems with desired functionalities. Motivated by these developments, we study a two-orbital Hubbard model in a thin-film geometry confined along the cubic [001] direction using the dynamical mean-field theory. We contrast the results of two approximate impurity solvers (exact diagonalization and one-crossing approximation) to the results of the numerically exact continuous-time quantum Monte Carlo solver. Consistent with earlier studies, we find that the one-crossing approximation performs well in the insulating regime, while the advantage of the exact-diagonalization-based solver is more pronounced in the metallic regime. We then investigate various aspects of strongly correlated eg-orbital systems in thin-film geometries. In particular, we show how the interfacial orbital polarization dies off quickly a few layers from the interface and how the film thickness affects the location of the interaction-driven Mott transition. In addition, we explore the changes in the electronic structure with varying carrier concentration and identify large variations of the orbital polarization in the strongly correlated regime.

Time-resolved terahertz dynamics in thin films of the topological insulator Bi 2Se 3

DOE PAGES

Valdés Aguilar, R.; Qi, J.; Brahlek, M.; ...

2015-01-07

We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi 2Se 3 films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. Furthermore, these different dynamics aremore » attributed to the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.« less

Growth and characterization of ultra thin vanadium oxide films

NASA Astrophysics Data System (ADS)

Song, Fangfang

This dissertation focuses on the growth and characterization of ultra thin VO2 films on technologically relevant Si/SiO2 substrate. The samples were prepared by magnetron sputtering with varying deposition and post annealing conditions. VO2(M1) films prepared under optimal condition with thickness around 42nm shows a continuous micro-structure and a metal insulator transition with resistivity change of two orders of magnitude. The transition temperature is determined to be 345K with a hysteresis width of approximately 8°C. The activation energy of the low temperature semiconducting VO2 monoclinic phase is determined to be 0.16+/-0.03ev. These properties are found to be fairly stable over time under ambient atmosphere. Temperature dependent hall measurements suggest that the decrease of the resistivity with increasing temperature is mainly caused by the increase of the number density of charge carriers, the energy gap of VO2 film in the semiconducting phase is 0.4ev and phonon scattering is the dominant scattering mechanism in the temperature range from 195K to 340K. Analysis based on composite model suggested that the sample has some untransitional phases with a length that is 1/4 of the grain size. Stress measurements using X-ray diffraction indicate that the ultra thin VO2 film has a large tensile stress of 2.0+/-0.2GPa. This value agrees well with that calculated thermal stress assuming the stress is due to differential thermal expansion between VO2 film and substrate. The stress is expected to lead to a shift of the transition temperature in the film, as observed. Using magnetron sputtering, VO2(B) film was able to obtained on Si substrate. The temperature dependent current voltage measurement on VO2(B) film did not show any abrupt change in the electrical resistivity. W - VO2(B) thin film - W metal semiconductor-metal I-V properties were found to be determined by reverse biased Schottky barrier at the W/VO 2(b) interface. And the Schottky height between VO2(B

Thin film temperature sensor

NASA Technical Reports Server (NTRS)

Grant, H. P.; Przybyszewski, J. S.

1980-01-01

Thin film surface temperature sensors were developed. The sensors were made of platinum-platinum/10 percent rhodium thermocouples with associated thin film-to-lead wire connections and sputtered on aluminum oxide coated simulated turbine blades for testing. Tests included exposure to vibration, low velocity hydrocarbon hot gas flow to 1250 K, and furnace calibrations. Thermal electromotive force was typically two percent below standard type S thermocouples. Mean time to failure was 42 hours at a hot gas flow temperature of 1250 K and an average of 15 cycles to room temperature. Failures were mainly due to separation of the platinum thin film from the aluminum oxide surface. Several techniques to improve the adhesion of the platinum are discussed.

Pulsed—Laser Deposition Of Oxide Thin Films And Laser—Induced Breakdown Spectroscopy Of Multi—Element Materials

NASA Astrophysics Data System (ADS)

Pedarnig, Johannes D.

2010-10-01

New results of the Linz group on pulsed—laser deposition (PLD) of oxide thin films and on laser—induced breakdown spectroscopy (LIBS) of multi-element materials are reported. High-Tc superconducting (HTS) films with enhanced critical current density Jc are produced by laser ablation of novel nano-composite ceramic targets. The targets contain insulating nano-particles that are embedded into the YBa2Cu3O7 matrix. Epitaxial double-layers of lithium-doped and aluminum-doped ZnO are deposited on r-cut sapphire substrates. Acoustic over-modes in the GHz range are excited by piezoelectric actuation of layers. Smooth films of rare-earth doped glass are produced by F2—laser ablation. The transport properties of HTS thin films are modified by light—ion irradiation. Thin film nano—patterning is achieved by masked ion beam irradiation. LIBS is employed to analyze trace elements in industrial iron oxide powder and reference polymer materials. Various trace elements of ppm concentration are measured in the UV/VIS and vacuum-UV spectral range. Quantitative LIBS analysis of major components in oxide materials is performed by calibration-free methods.

Analysis of Hard Thin Film Coating

NASA Technical Reports Server (NTRS)

Shen, Dashen

1998-01-01

Marshall Space Flight Center (MSFC) is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) to deposit hard thin film on stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

Analysis of Hard Thin Film Coating

NASA Technical Reports Server (NTRS)

Shen, Dashen

1998-01-01

MSFC is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using electron cyclotron resonance chemical vapor deposition (ECRCVD) to deposit hard thin film an stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

Surface structural reconstruction of SrVO3 thin films on SrTiO3 (001)

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Saghayezhian, Mohammad; Chen, Lina; Guo, Hangwen; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3>(SVO) is an itinerant system known to undergo thickness-induced metal-insulator-transition (MIT) in ultrathin film form, which makes it a prototype system for the study of the mechanism behind metal-insulator-transition like structure distortion, electron correlations and disorder-induced localization. We have grown SrVO3 thin film with atomically flat surface through the layer-by-layer deposition by laser Molecular Beam Epitaxy (laser-MBE) on SrTiO3 (001) surface. Low Energy Electron Diffraction (LEED) measurements reveal that there is a (√2X √2) R45°surface reconstruction independent of film thickness. By using LEED-I(V) structure refinement, we determine the surface structure. In combination with X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM), we discuss the implication on the MIT in ultrathin films below 2-3 unit cell thickness. This work is supported by the National Science Foundation under the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

Miniaturized and reconfigurable notch antenna based on a BST ferroelectric thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Hung Viet; CEA-LETI, Minatec, 17 avenue des Martyrs, 38054 Grenoble Cedex 9; Benzerga, Ratiba, E-mail: ratiba.benzerga@univ-rennes1.fr

Highlights: • A miniature and agile antenna based on a BST MIM capacitor is simulated and made. • Mn{sup 2+} doped BST thin films are synthesized by chemical deposition and spin coating. • Permittivity and losses of the BST thin film are respectively 225 and 0.02 at 1 GHz. • A miniaturization rate of 70% is obtained with a MIM capacitance of 3.7 pF. • A frequency tunability of 14.5% and a tunability performance of 0.04 are measured. - Abstract: This work deals with the design, realization and characterization of a miniature and frequency agile antenna based on a ferroelectricmore » Ba{sub 0,80}Sr{sub 0,20}TiO{sub 3} thin film. The notch antenna is loaded with a variable metal/insulator/metal (MIM) capacitor and is achieved by a monolithic method. The MIM capacitance is 3.7 pF, which results in a resonant frequency of 670 MHz compared to 2.25 GHz for the unloaded simulated antenna; the resulting miniaturization rate is 70%. The characterization of the antenna prototype shows a frequency tunable rate of 14.5% under an electric field of 375 kV/cm, with a tunability performance η = 0.04.« less

Thin Thermal-Insulation Blankets for Very High Temperatures

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2003-01-01

Thermal-insulation blankets of a proposed type would be exceptionally thin and would endure temperatures up to 2,100 C. These blankets were originally intended to protect components of the NASA Solar Probe spacecraft against radiant heating at its planned closest approach to the Sun (a distance of 4 solar radii). These blankets could also be used on Earth to provide thermal protection in special applications (especially in vacuum chambers) for which conventional thermal-insulation blankets would be too thick or would not perform adequately.

Nanocrystal thin film fabrication methods and apparatus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kagan, Cherie R.; Kim, David K.; Choi, Ji-Hyuk

Nanocrystal thin film devices and methods for fabricating nanocrystal thin film devices are disclosed. The nanocrystal thin films are diffused with a dopant such as Indium, Potassium, Tin, etc. to reduce surface states. The thin film devices may be exposed to air during a portion of the fabrication. This enables fabrication of nanocrystal-based devices using a wider range of techniques such as photolithography and photolithographic patterning in an air environment.

Thin-film rechargeable lithium batteries

NASA Astrophysics Data System (ADS)

Dudney, N. J.; Bates, J. B.; Lubben, D.

1994-11-01

Small thin-film rechargeable cells have been fabricated with a lithium phosphorus oxynitride electrolyte, Li metal anode, and Li(1-x)Mn2O4 as the cathode film. The cathode films were fabricated by several different techniques resulting in both crystalline and amorphous films. These were compared by observing the cell discharge behavior. Estimates have been made for the scale-up of such a thin-film battery to meet the specifications for the electric vehicle application. The specific energy, energy density, and cycle life are expected to meet the USABC mid-term criteria. However, the areas of the thin-films needed to fabricate such a cell are very large. The required areas could be greatly reduced by operating the battery at temperatures near 100 C or by enhancing the lithium ion transport rate in the cathode material.

Thin film-coated polymer webs

DOEpatents

Wenz, Robert P.; Weber, Michael F.; Arudi, Ravindra L.

1992-02-04

The present invention relates to thin film-coated polymer webs, and more particularly to thin film electronic devices supported upon a polymer web, wherein the polymer web is treated with a purifying amount of electron beam radiation.

Thin film solar cell workshop

NASA Technical Reports Server (NTRS)

Armstrong, Joe; Jeffrey, Frank

1993-01-01

A summation of responses to questions posed to the thin-film solar cell workshop and the ensuing discussion is provided. Participants in the workshop included photovoltaic manufacturers (both thin film and crystalline), cell performance investigators, and consumers.

Low-temperature electron cyclotron resonance plasma-enhanced chemical-vapor deposition silicon dioxide as gate insulator for polycrystalline silicon thin-film transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maiolo, L.; Pecora, A.; Fortunato, G.

2006-03-15

Silicon dioxide films have been deposited at temperatures below 270 deg. C in an electron cyclotron resonance (ECR) plasma reactor from O{sub 2}, SiH{sub 4}, and He gas mixture. Pinhole density analysis as a function of substrate temperature for different microwave powers was carried out. Films deposited at higher microwave power and at room temperature show defect densities (<7 pinhole/mm{sup 2}), ensuring low-temperature process integration on large area. From Fourier transform infrared analysis and thermal desorption spectrometry we also evaluated very low hydrogen content if compared to conventional rf-plasma-enhanced chemical-vapor-deposited (PECVD) SiO{sub 2} deposited at 350 deg. C. Electrical propertiesmore » have been measured in metal-oxide-semiconductor (MOS) capacitors, depositing SiO{sub 2} at RT as gate dielectric; breakdown electric fields >10 MV/cm and charge trapping at fields >6 MV/cm have been evaluated. From the study of interface quality in MOS capacitors, we found that even for low annealing temperature (200 deg. C), it is possible to considerably reduce the interface state density down to 5x10{sup 11} cm{sup -2} eV{sup -1}. To fully validate the ECR-PECVD silicon dioxide we fabricated polycrystalline silicon thin-film transistors using RT-deposited SiO{sub 2} as gate insulator. Different postdeposition thermal treatments have been studied and good device characteristics were obtained even for annealing temperature as low as 200 deg. C.« less

Optical switching and photoluminescence in erbium-implanted vanadium dioxide thin films

NASA Astrophysics Data System (ADS)

Lim, Herianto; Stavrias, Nikolas; Johnson, Brett C.; Marvel, Robert E.; Haglund, Richard F.; McCallum, Jeffrey C.

2014-03-01

Vanadium dioxide (VO2) is under intensive consideration for optical switching due to its reversible phase transition, which features a drastic and rapid shift in infrared reflectivity. Classified as an insulator-to-metal transition, the phase transition in VO2 can be induced thermally, electrically, and optically. When induced optically, the transition can occur on sub-picosecond time scales. It is interesting to dope VO2 with erbium ions (Er3+) and observe their combined properties. The first excited-state luminescence of Er3+ lies within the wavelength window of minimal transmission-loss in silicon and has been widely utilized for signal amplification and generation in silicon photonics. The incorporation of Er3+ into VO2 could therefore result in a novel photonic material capable of simultaneous optical switching and amplification. In this work, we investigate the optical switching and photoluminescence in Er-implanted VO2 thin films. Thermally driven optical switching is demonstrated in the Er-implanted VO2 by infrared reflectometry. Photoluminescence is observed in the thin films annealed at ˜800 °C or above. In addition, Raman spectroscopy and a statistical analysis of switching hysteresis are carried out to assess the effects of the ion implantation on the VO2 thin films. We conclude that Er-implanted VO2 can function as an optical switch and amplifier, but with reduced switching quality compared to pure VO2.

Infrared radiation of thin plastic films.

NASA Technical Reports Server (NTRS)

Tien, C. L.; Chan, C. K.; Cunnington, G. R.

1972-01-01

A combined analytical and experimental study is presented for infrared radiation characteristics of thin plastic films with and without a metal substrate. On the basis of the thin-film analysis, a simple analytical technique is developed for determining band-averaged optical constants of thin plastic films from spectral normal transmittance data for two different film thicknesses. Specifically, the band-averaged optical constants of polyethylene terephthalate and polyimide were obtained from transmittance measurements of films with thicknesses in the range of 0.25 to 3 mil. The spectral normal reflectance and total normal emittance of the film side of singly aluminized films are calculated by use of optical constants; the results compare favorably with measured values.

Charge trapping phenomena of tetraethylorthosilicate thin film containing Si nanocrystals synthesized by solid-state reaction.

PubMed

Lau, H W; Tan, O K; Liu, Y; Trigg, D A; Chen, T P

2006-08-28

In this work, we report on the fabrication of tetraethylorthosilicate (TEOS) thin dielectric film containing silicon nanocrystals (Si nc), synthesized by solid-state reaction, in a capacitor structure. A metal-insulator-semi-conductor (MIS) capacitor, with 28 nm thick Si nc in a TEOS thin film, has been fabricated. For this MIS, both electron and hole trapping in the Si nc are possible, depending on the polarity of the bias voltage. A V(FB) shift greater than 1 V can be experienced by a bias voltage of 16 V applied to the metal electrode for 1 s. Though there is no top control oxide, the discharge time for 10% of charges can be up to 4480 s when it is biased at 16 V for 1 s. It is further demonstrated that charging and discharging mechanisms are due to the Si nc rather than the TEOS oxide defects. This form of Si nc in a TEOS thin film capacitor provides the possibility of memory applications at low cost.

Integration of strained and relaxed silicon thin films on silicon wafers via engineered oxide heterostructures: Experiment and theory

NASA Astrophysics Data System (ADS)

Seifarth, O.; Dietrich, B.; Zaumseil, P.; Giussani, A.; Storck, P.; Schroeder, T.

2010-10-01

Strained and relaxed single crystalline Si on insulator systems is an important materials science approach for future Si-based nanoelectronics. Layer transfer techniques are the dominating global integration approach over the whole wafer system but are difficult to scale down for local integration purposes limited to the area of the future device. In this respect, the heteroepitaxy approach by two simple subsequent epitaxial deposition steps of the oxide and the Si thin film is a promising way. We introduce tailored (Pr2O3)1-x(Y2O3)x oxide heterostructures on Si(111) as flexible heteroepitaxy concept for the integration of either strained or fully relaxed single crystalline Si thin films. Two different buffer concepts are explored by a combined experimental and theoretical study. First, the growth of fully relaxed single crystalline Si films is achieved by the growth of mixed PrYO3 insulators on Si(111) whose lattice constant is matched to Si. Second, isomorphic oxide-on-oxide epitaxy is exploited to grow strained Si films on lattice mismatched Y2O3/Pr2O3/Si(111) support systems. A thickness dependent multilayer model, based on Matthew's approach for strain relaxation by misfit dislocations, is presented to describe the experimental data.

Thermally tunable VO2-SiO2 nanocomposite thin-film capacitors

NASA Astrophysics Data System (ADS)

Sun, Yifei; Narayanachari, K. V. L. V.; Wan, Chenghao; Sun, Xing; Wang, Haiyan; Cooley, Kayla A.; Mohney, Suzanne E.; White, Doug; Duwel, Amy; Kats, Mikhail A.; Ramanathan, Shriram

2018-03-01

We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing continuous temperature tunability of the dielectric constant. The smooth thermal tunability is a result of the insulator-metal transition in the VO2 inclusions dispersed within an insulating matrix. We present a detailed comparison of the dielectric characteristics of this nanocomposite with those of a VO2 control layer and of VO2/SiO2 laminate multilayers of comparable overall thickness. We demonstrated a nanocomposite capacitor that has a thermal capacitance tunability of ˜60% between 25 °C and 100 °C at 1 MHz, with low leakage current. Such thermally tunable capacitors could find potential use in applications such as sensing, thermal cloaks, and phase-change energy storage devices.

Tuning the Curie temperature of epitaxial Nd0.6Sr0.4MnO3 thin films

NASA Astrophysics Data System (ADS)

Bhat, Shwetha G.; Kumar, P. S. Anil

2018-02-01

NdxSr1-xMnO3 (0.2 ≤ x ≤ 0.5) systems are widely studied in magnetism, popular for high colossal magnetoresistance and are ferromagnetic oxides with TC ranging from 200 K to 300 K. Recently, many of such compounds are re-visited for exploring the correlation of spin, charge and lattice degrees of freedom. Although, manganite thin films are the ideal candidates for studying the electron-correlation effects, the puzzle of obtaining a high quality epitaxial thin films of NdxSr1-xMnO3 are still unsolved contrary to its sister compound LaxSr1-xMnO3. Hence, in this study, we demonstrate the growth of best quality of Nd0.6Sr0.4MnO3 (NSMO) epitaxial thin films. This is evident from the TC and a sharp insulator-to-metal transition (IMT) coinciding at as high as ∼255 K against the bulk TC (∼270 K). It is the highest reported TC in Nd0.6Sr0.4MnO3 thin films to date. Moreover, as-deposited films with in situ oxygen annealing are not enough to relax the lattice of NSMO films due to the significant Jahn-Teller distortion in the film. With ex situ annealing processes alongside the various deposition and in situ annealing conditions, we have extensively studied the growth of epitaxial NSMO thin films on LaAlO3 (0 0 1) and SrTiO3 (0 0 1) to investigate the evolution of lattice and its one-to-one correspondence with the magnetism and the electrical properties of thin films. Accordingly, the enhanced magnetization, reduced resistivity and the higher TC and IMT of the NSMO films obtained from our extensive growth analysis looks promising for the future applications across the TC and IMT.

Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

NASA Technical Reports Server (NTRS)

Wilson, Scott D.; Fralick, Gustave; Wrbanek, John; Sayir, Ali

2009-01-01

The NASA Glenn Research Center (GRC) has been testing high efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multi-year missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test set up to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging microporous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-mm heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slip casting and using Physical Vapor Deposition (PVD). One micron thick noble metal thermocouples measure temperature on the surface of an Alumina ceramic disc and heat flux is calculated. Fabrication, integration, and test results of a thin film heat flux sensor are presented.

Permanent laser conditioning of thin film optical materials

DOEpatents

Wolfe, C. Robert; Kozlowski, Mark R.; Campbell, John H.; Staggs, Michael; Rainer, Frank

1995-01-01

The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold.

Voltage-Controlled Spray Deposition of Multiwalled Carbon Nanotubes on Semiconducting and Insulating Substrates

NASA Astrophysics Data System (ADS)

Maulik, Subhodip; Sarkar, Anirban; Basu, Srismrita; Daniels-Race, Theda

2018-05-01

A facile, cost-effective, voltage-controlled, "single-step" method for spray deposition of surfactant-assisted dispersed carbon nanotube (CNT) thin films on semiconducting and insulating substrates has been developed. The fabrication strategy enables direct deposition and adhesion of CNT films on target samples, eliminating the need for substrate surface functionalization with organosilane binder agents or metal layer coatings. Spray coating experiments on four types of sample [bare silicon (Si), microscopy-grade glass samples, silicon dioxide (SiO2), and polymethyl methacrylate (PMMA)] under optimized control parameters produced films with thickness ranging from 40 nm to 6 μm with substantial surface coverage and packing density. These unique deposition results on both semiconducting and insulator target samples suggest potential applications of this technique in CNT thin-film transistors with different gate dielectrics, bendable electronics, and novel CNT-based sensing devices, and bodes well for further investigation into thin-film coatings of various inorganic, organic, and hybrid nanomaterials on different types of substrate.

High carrier mobility of Sn-doped polycrystalline-Ge films on insulators by thickness-dependent low-temperature solid-phase crystallization

NASA Astrophysics Data System (ADS)

Sadoh, Taizoh; Kai, Yuki; Matsumura, Ryo; Moto, Kenta; Miyao, Masanobu

2016-12-01

To realize the advanced thin-film transistors (TFTs), high-carrier-mobility semiconductor films on insulator structures should be fabricated with low-temperature processing conditions (≤500 °C). To achieve this, we investigated the solid-phase crystallization of amorphous-GeSn films on insulating substrates under a wide range of Sn concentrations (0%-20%), film thicknesses (30-500 nm), and annealing temperatures (380-500 °C). Our results reveal that a Sn concentration close to the solid solubility of Sn in Ge (˜2%) is effective in increasing the grain-size of poly-GeSn. In addition, we discovered that the carrier mobility depends on the film thickness, where the mobilities are determined by the counterbalance between two different carrier scattering mechanisms. Here, vacancy-related defects dominate the carrier scattering near the insulating substrates (≤˜120 nm), and grain-size determined by bulk nucleation dominates the grain-boundary scattering of thick films (≥˜200 nm). Consequently, we obtained the maximum mobilities in samples with a Sn concentration of 2% and a film thickness of 200 nm. The effect of increasing the grain-size of poly-GeSn by lowering the annealing temperature was also clarified. By combining these results, a very high carrier mobility of 320 cm2/Vs was obtained at a low temperature of 380 °C. This mobility is about 2.5 times as high as previously reported data for Ge and GeSn films grown at low temperatures (≤500 °C). Our technique therefore opens up the possibility of high-speed TFTs for use in the next generation of electronics.

Permanent laser conditioning of thin film optical materials

DOEpatents

Wolfe, C.R.; Kozlowski, M.R.; Campbell, J.H.; Staggs, M.; Rainer, F.

1995-12-05

The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold. 9 figs.

Scalable planar fabrication processes for chalcogenide-based topological insulators

NASA Astrophysics Data System (ADS)

Sharma, Peter; Henry, M. David; Douglas, Erica; Wiwi, Michael; Lima Sharma, Ana; Lewis, Rupert; Sugar, Joshua; Salehi, Maryam; Koirala, Nikesh; Oh, Seongshik

Surface currents in topological insulators are expected to have long spin diffusion lengths, which could lead to numerous applications. Experiments that show promising transport properties were conducted on exfoliated flakes from bulk material, thin films on substrates of limited dimensions, or bulk material, with limited yield. A planar thin film-based technology is needed to make topological insulator devices at scale and could also lead to new device designs. We address two problems related to fabricating chalcogenide-based topological insulator devices on 3'' wafers in the Sandia Microfabrication Facility using Bi2Te3 films. (2) Implantation damage and its subsequent mitigation through annealing is characterized. (2) The degradation in dielectric layers used to manipulate surface potential for elucidating topological surface state transport is characterized under different processing conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. Funded by the Office of Naval Research (N0001416IP00098-0).

Thin Film Photovoltaic Partnership Project | Photovoltaic Research | NREL

Science.gov Websites

Thin Film Photovoltaic Partnership Project Thin Film Photovoltaic Partnership Project NREL's Thin Film Photovoltaic (PV) Partnership Project led R&D on emerging thin-film solar technologies in the National Laboratory developed low-cost transparent encapsulation schemes for CIGS cells that reduced power

Semiconductor-insulator transition in VO{sub 2} (B) thin films grown by pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rúa, Armando; Díaz, Ramón D.; Lysenko, Sergiy

2015-09-28

Thin films of B-phase VO{sub 2} were grown by pulsed-laser deposition on glass and (100)-cut MgO substrates in a temperature range from 375 to 425 °C and at higher gas pressures than usual for this technique. The films were strongly oriented, with ab-planes parallel to the substrate surface. Detailed study of surface morphology through Atomic Force Microscopy images suggest significant differences in evolution as a function of growth temperature for films on the two types of substrates. Measurements of electrical conductivities through cooling-heating cycles from room temperature to 120 K showed changes of five orders of magnitude, with steeper changes between roommore » temperature and ∼150 K, which corresponds with the extended and reversible phase transition known to occur for this material. At lower temperatures conductivities exhibited Arrhenius behavior, indicating that no further structural change was occurring and that conduction is thermally activated. In this lower temperature range, conductivity of the samples can be described by the near-neighbor hopping model. No hysteresis was found between the cooling and heating braches of the cycles, which is at variance with previous results published for VO{sub 2} (B). This apparent lack of hysteresis for thin films grown in the manner described and the large conductivity variation as a function of temperature observed for the samples suggests this material could be of interest for infrared sensing applications.« less

Multifunctional thin film surface

DOEpatents

Brozik, Susan M.; Harper, Jason C.; Polsky, Ronen; Wheeler, David R.; Arango, Dulce C.; Dirk, Shawn M.

2015-10-13

A thin film with multiple binding functionality can be prepared on an electrode surface via consecutive electroreduction of two or more aryl-onium salts with different functional groups. This versatile and simple method for forming multifunctional surfaces provides an effective means for immobilization of diverse molecules at close proximities. The multifunctional thin film has applications in bioelectronics, molecular electronics, clinical diagnostics, and chemical and biological sensing.

Thin film tritium dosimetry

DOEpatents

Moran, Paul R.

1976-01-01

The present invention provides a method for tritium dosimetry. A dosimeter comprising a thin film of a material having relatively sensitive RITAC-RITAP dosimetry properties is exposed to radiation from tritium, and after the dosimeter has been removed from the source of the radiation, the low energy electron dose deposited in the thin film is determined by radiation-induced, thermally-activated polarization dosimetry techniques.

Epitaxial VO2 thin-film-based radio-frequency switches with electrical activation

NASA Astrophysics Data System (ADS)

Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

2017-09-01

Vanadium dioxide (VO2) is a correlated material exhibiting a sharp insulator-to-metal phase transition (IMT) caused by temperature change and/or bias voltage. We report on the demonstration of electrically triggered radio-frequency (RF) switches based on epitaxial VO2 thin films. The highly epitaxial VO2 and SnO2 template layer was grown on a (001) TiO2 substrate by pulsed laser deposition (PLD). A resistance change of the VO2 thin films of four orders of magnitude was achieved with a relatively low threshold voltage, as low as 13 V, for an IMT phase transition. VO2 RF switches also showed high-frequency responses of insertion losses of -3 dB at the on-state and return losses of -4.3 dB at the off-state over 27 GHz. Furthermore, an intrinsic cutoff frequency of 17.4 THz was estimated for the RF switches. The study on electrical IMT dynamics revealed a phase transition time of 840 ns.

Deposition and thermal characterization of nano-structured aluminum nitride thin film on Cu-W substrate for high power light emitting diode package.

PubMed

Cho, Hyun Min; Kim, Min-Sun

2014-08-01

In this study, we developed AlN thick film on metal substrate for hybrid type LED package such as chip on board (COB) using metal printed circuit board (PCB). Conventional metal PCB uses ceramic-polymer composite as electrical insulating layer. Thermal conductivities of such type dielectric film are typically in the range of 1~4 W/m · K depending on the ceramic filler. Also, Al or Cu alloy are mainly used for metal base for high thermal conduction to dissipate heat from thermal source mounted on metal PCB. Here we used Cu-W alloy with low thermal expansion coefficient as metal substrate to reduce thermal stress between insulating layer and base metal. AlN with polyimide (PI) powder were used as starting materials for deposition. We could obtain very high thermal conductivity of 28.3 W/m · K from deposited AlN-PI thin film by AlN-3 wt% PI powder. We made hybrid type high power LED package using AlN-PI thin film. We tested thermal performance of this film by thermal transient measurement and compared with conventional metal PCB substrate.

Thermo-optically tunable thin film devices

NASA Astrophysics Data System (ADS)

Domash, Lawrence H.

2003-10-01

We report advances in tunable thin film technology and demonstration of multi-cavity tunable filters. Thin film interference coatings are the most widely used optical technology for telecom filtering, but until recently no tunable versions have been known except for mechanically rotated filters. We describe a new approach to broadly tunable components based on the properties of semiconductor thin films with large thermo-optic coefficients. The technology is based on amorphous silicon deposited by plasma-enhanced chemical vapor deposition (PECVD), a process adapted for telecom applications from its origins in the flat-panel display and solar cell industries. Unlike MEMS devices, tunable thin films can be constructed in sophisticated multi-cavity, multi-layer optical designs.

Understanding mobility degeneration mechanism in organic thin-film transistors (OTFT)

NASA Astrophysics Data System (ADS)

Wang, Wei; Wang, Long; Xu, Guangwei; Gao, Nan; Wang, Lingfei; Ji, Zhuoyu; Lu, Congyan; Lu, Nianduan; Li, Ling; Liu, Miwng

2017-08-01

Mobility degradation at high gate bias is often observed in organic thin film transistors. We propose a mechanism for this confusing phenomenon, based on the percolation theory with the presence of disordered energy landscape with an exponential density of states. Within a simple model we show how the surface states at insulator/organic interface trap a portion of channel carriers, and result in decrease of mobility as well as source/drain current with gate voltage. Depending on the competition between the carrier accumulation and surface trapping effect, two different carrier density dependences of mobility are obtained, in excellent agreement with experiment data.

Effects of postdeposition annealing on the metal-insulator transition of VO2-x thin films prepared by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Liu, Shiu-Jen; Su, Yu-Tai; Hsieh, Juang-Hsin

2014-03-01

We report the fabrication of textured VO2-x films on c-cut sapphire substrates by postdeposition annealing of V2O3 films prepared by RF magnetron sputtering using V2O3 as the target. Although the prepared VO2-x films are expected to be oxygen-deficient, overoxidation on the film surface was revealed by X-ray photoelectron spectroscopy. The metal-insulator transition (MIT) characteristics of the VO2-x films were investigated. MIT parameters including the transition temperature, transition sharpness, and hysteresis width of the VO2-x films were manipulated by varying the oxygen pressure during postdeposition annealing. The suppression of optical transmittance in the near-infrared region was observed by increasing the temperature through the MIT.

High-Performance Ink-Synthesized Cu-Gate Thin-Film Transistor with Diffusion Barrier Formation

NASA Astrophysics Data System (ADS)

Woo, Whang Je; Nam, Taewook; Oh, Il-Kwon; Maeng, Wanjoo; Kim, Hyungjun

2018-02-01

The improved electrical properties of Cu-gate thin-film transistors (TFTs) using an ink-synthesizing process were studied; this technology enables a low-cost and large area process for the display industry. We investigated the film properties and the effects of the ink-synthesized Cu layer in detail with respect to device characteristics. The mobility and reliability of the devices were significantly improved by applying a diffusion barrier at the interface between the Cu gate and the gate insulator. By using a TaN diffusion barrier layer, considerably improved and stabilized ink-Cu gated TFTs could be realized, comparable to sputtered-Cu gated TFTs under positive bias temperature stress measurements.

High-Performance Ink-Synthesized Cu-Gate Thin-Film Transistor with Diffusion Barrier Formation

NASA Astrophysics Data System (ADS)

Woo, Whang Je; Nam, Taewook; Oh, Il-Kwon; Maeng, Wanjoo; Kim, Hyungjun

2018-05-01

The improved electrical properties of Cu-gate thin-film transistors (TFTs) using an ink-synthesizing process were studied; this technology enables a low-cost and large area process for the display industry. We investigated the film properties and the effects of the ink-synthesized Cu layer in detail with respect to device characteristics. The mobility and reliability of the devices were significantly improved by applying a diffusion barrier at the interface between the Cu gate and the gate insulator. By using a TaN diffusion barrier layer, considerably improved and stabilized ink-Cu gated TFTs could be realized, comparable to sputtered-Cu gated TFTs under positive bias temperature stress measurements.

Two dimensional simulation of patternable conducting polymer electrode based organic thin film transistor

NASA Astrophysics Data System (ADS)

Nair, Shiny; Kathiresan, M.; Mukundan, T.

2018-02-01

Device characteristics of organic thin film transistor (OTFT) fabricated with conducting polyaniline:polystyrene sulphonic acid (PANi-PSS) electrodes, patterned by the Parylene lift-off method are systematically analyzed by way of two dimensional numerical simulation. The device simulation was performed taking into account field-dependent mobility, low mobility layer at the electrode-semiconductor interface, trap distribution in pentacene film and trapped charge at the organic/insulator interface. The electrical characteristics of bottom contact thin film transistor with PANi-PSS electrodes and pentacene active material is superior to those with palladium electrodes due to a lower charge injection barrier. Contact resistance was extracted in both cases by the transfer line method (TLM). The extracted charge concentration and potential profile from the two dimensional numerical simulation was used to explain the observed electrical characteristics. The simulated device characteristics not only matched the experimental electrical characteristics, but also gave an insight on the charge injection, transport and trap properties of the OTFTs as a function of different electrode materials from the perspectives of transistor operation.

Comparison of full 3-D, thin-film 3-D, and thin-film plate analyses of a postbuckled embedded delamination

NASA Technical Reports Server (NTRS)

Whitcomb, John D.

1989-01-01

Strain-energy release rates are often used to predict when delamination growth will occur in laminates under compression. Because of the inherently high computational cost of performing such analyses, less rigorous analyses such as thin-film plate analysis were used. The assumptions imposed by plate theory restrict the analysis to the calculation of total strain energy, G(sub t). The objective is to determine the accuracy of thin-film plate analysis by comparing the distribution of G(sub t) calculated using fully three dimensional (3D), thin-film 3D, and thin-film plate analyses. Thin-film 3D analysis is the same as thin-film plate analysis, except 3D analysis is used to model the sublaminate. The 3D stress analyses were performed using the finite element program NONLIN3D. The plate analysis results were obtained from published data, which used STAGS. Strain-energy release rates were calculated using variations of the virtual crack closure technique. The results demonstrate that thin-film plate analysis can predict the distribution of G(sub t) quite well, at least for the configurations considered. Also, these results verify the accuracy of the strain-energy release rate procedure for plate analysis.

Thin film ion conducting coating

DOEpatents

Goldner, Ronald B.; Haas, Terry; Wong, Kwok-Keung; Seward, George

1989-01-01

Durable thin film ion conducting coatings are formed on a transparent glass substrate by the controlled deposition of the mixed oxides of lithium:tantalum or lithium:niobium. The coatings provide durable ion transport sources for thin film solid state storage batteries and electrochromic energy conservation devices.

Identification of Mott insulators and Anderson insulators in self-assembled gold nanoparticles thin films

NASA Astrophysics Data System (ADS)

Jiang, Cheng-Wei; Ni, I.-Chih; Tzeng, Shien-Der; Wu, Cen-Shawn; Kuo, Watson

2014-05-01

How the interparticle tunnelling affects the charge conduction of self-assembled gold nanoparticles is studied by three means: tuning the tunnel barrier width by different molecule modification and by substrate bending, and tuning the barrier height by high-dose electron beam exposure. All approaches indicate that the metal-Mott insulator transition is governed predominantly by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on the strength of disorder. The charge conduction is from nearest-neighbour hopping to co-tunnelling between nanoparticles in Mott insulators whereas it is from variable-range hopping through charge puddles in Anderson insulators. When the two-dimensional nanoparticle network is under a unidirectional strain, the interparticle coupling becomes anisotropic so the average sheet resistance is required to describe the charge conduction.How the interparticle tunnelling affects the charge conduction of self-assembled gold nanoparticles is studied by three means: tuning the tunnel barrier width by different molecule modification and by substrate bending, and tuning the barrier height by high-dose electron beam exposure. All approaches indicate that the metal-Mott insulator transition is governed predominantly by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on the strength of disorder. The charge conduction is from nearest-neighbour hopping to co-tunnelling between

Temperature dependence of LRE-HRE-TM thin films

NASA Astrophysics Data System (ADS)

Li, Zuoyi; Cheng, Xiaomin; Lin, Gengqi; Li, Zhen; Huang, Zhixin; Jin, Fang; Wang, Xianran; Yang, Xiaofei

2003-04-01

Temperature dependence of the properties of RE-TM thin films is very important for MO recording. In this paper, we studied the temperature dependence of the magnetic and magneto-optical properties of the amorphous LRE-HRE-TM single layer thin films and LRE-HRE-TM/HRE-TM couple-bilayered thin films. For LRE-HRE-TM single layer thin films, the temperature dependence of the magnetization was investigated by using the mean field theory. The experimental and theoretical results matched very well. With the LRE substitution in HRE-TM thin film, the compensation temperature Tcomp decreased and the curie temperature Tc remained unchanged. Kerr rotation angle became larger and the saturation magnetization Ms at room temperature increased. For LRE-HRE-TM/HRE-TM couple-bilayered thin films, comparisons of the temperature dependences of the coercivities and Kerr rotation angles were made between isolated sublayers and couple-bilayered thin film.

Chemical and thermal stability of the characteristics of filtered vacuum arc deposited ZnO, SnO2 and zinc stannate thin films

NASA Astrophysics Data System (ADS)

Çetinörgü, E.; Goldsmith, S.

2007-09-01

ZnO, SnO2 and zinc stannate thin films were deposited on commercial microscope glass and UV fused silica substrates using filtered vacuum arc deposition system. During the deposition, the substrate temperature was at room temperature (RT) or at 400 °C. The film structure and composition were determined using x-ray diffraction and x-ray photoelectron spectroscopy, respectively. The transmission of the films in the VIS was 85% to 90%. The thermal stability of the film electrical resistance was determined in air as a function of the temperature in the range 28 °C (RT) to 200 °C. The resistance of ZnO increased from ~ 5000 to 105 Ω when heated to 200 °C, that of SnO2 films increased from 500 to 3900 Ω, whereas that of zinc stannate thin films increased only from 370 to 470 Ω. During sample cooling to RT, the resistance of ZnO and SnO2 thin films continued to rise considerably; however, the increase in the zinc stannate thin film resistance was significantly lower. After cooling to RT, ZnO and SnO2 thin films became practically insulators, while the resistance of zinc stannate was 680 Ω. The chemical stability of the films was determined by immersing in acidic and basic solutions up to 27 h. The SnO2 thin films were more stable in the HCl solution than the ZnO and the zinc stannate thin films; however, SnO2 and zinc stannate thin films that were immersed in the NaOH solution did not dissolve after 27 h.

Surface Modification of Solution-Processed ZrO2 Films through Double Coating for Pentacene Thin-Film Transistors

NASA Astrophysics Data System (ADS)

Kwon, Jin-Hyuk; Bae, Jin-Hyuk; Lee, Hyeonju; Park, Jaehoon

2018-03-01

We report the modification of surface properties of solution-processed zirconium oxide (ZrO2) dielectric films achieved by using double-coating process. It is proven that the surface properties of the ZrO2 film are modified through the double-coating process; the surface roughness decreases and the surface energy increases. The present surface modification of the ZrO2 film contributes to an increase in grain size of the pentacene film, thereby increasing the field-effect mobility and decreasing the threshold voltage of the pentacene thin-film transistors (TFTs) having the ZrO2 gate dielectric. Herein, the molecular orientation of pentacene film is also studied based on the results of contact angle and X-ray diffraction measurements. Pentacene molecules on the double-coated ZrO2 film are found to be more tilted than those on the single-coated ZrO2 film, which is attributed to the surface modification of the ZrO2 film. However, no significant differences are observed in insulating properties between the single-and the double-coated ZrO2 dielectric films. Consequently, the characteristic improvements of the pentacene TFTs with the double-coated ZrO2 gate dielectric film can be understood through the increase in pentacene grain size and the reduction in grain boundary density.

Method of producing amorphous thin films

DOEpatents

Brusasco, Raymond M.

1992-01-01

Disclosed is a method of producing thin films by sintering which comprises: a. coating a substrate with a thin film of an inorganic glass forming parulate material possessing the capability of being sintered, and b. irridiating said thin film of said particulate material with a laser beam of sufficient power to cause sintering of said material below the temperature of liquidus thereof. Also disclosed is the article produced by the method claimed.

Method of producing amorphous thin films

DOEpatents

Brusasco, R.M.

1992-09-01

Disclosed is a method of producing thin films by sintering which comprises: (a) coating a substrate with a thin film of an inorganic glass forming material possessing the capability of being sintered; and (b) irradiating said thin film of said particulate material with a laser beam of sufficient power to cause sintering of said material below the temperature of liquidus thereof. Also disclosed is the article produced by the method claimed. 4 figs.

iCVD Cyclic Polysiloxane and Polysilazane as Nanoscale Thin-Film Electrolyte: Synthesis and Properties.

PubMed

Chen, Nan; Reeja-Jayan, B; Liu, Andong; Lau, Jonathan; Dunn, Bruce; Gleason, Karen K

2016-03-01

A group of crosslinked cyclic siloxane (Si-O) and silazane (Si-N) polymers are synthesized via solvent-free initiated chemical vapor deposition (iCVD). Notably, this is the first report of cyclic polysilazanes synthesized via the gas-phase iCVD method. The deposited nanoscale thin films are thermally stable and chemically inert. By iCVD, they can uniformly and conformally cover nonplanar surfaces having complex geometry. Although polysiloxanes are traditionally utilized as dielectric materials and insulators, our research shows these cyclic organosilicon polymers can conduct lithium ions (Li(+) ) at room temperature. The conformal coating and the room temperature ionic conductivity make these cyclic organosilicon polymers attractive for use as thin-film electrolytes in solid-state batteries. Also, their synthesis process and properties have been systemically studied and discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Barium ferrite thin-film recording media

NASA Astrophysics Data System (ADS)

Sui, Xiaoyu; Scherge, Matthias; Kryder, Mark H.; Snyder, John E.; Harris, Vincent G.; Koon, Norman C.

1996-03-01

Both longitudinal and perpendicular barium ferrite thin films are being pursued as overcoatless magnetic recording media. In this paper, prior research on thin-film Ba ferrite is reviewed and the most recent results are presented. Self-textured high-coercivity longitudinal Ba ferrite thin films have been achieved using conventional rf diode sputtering. Microstructural studies show that c-axis in-plane oriented grains have a characteristic acicular shape, while c-axis perpendicularly oriented grains have a platelet shape. Extended X-ray absorption fine structure (EXAFS) measurements indicate that the crystal orientations are predetermined by the structural anisotropy in the as-sputtered 'amorphous' state. Recording tests on 1500 Oe coercivity longitudinal Ba ferrite disks show performance comparable with that of a 1900 Oe Co alloy disk. To further improve the recording performance, both grain size and aspect ratio need to be reduced. Initial tribological tests indicate high hardness of Ba ferrite thin films. However, surface roughness needs to be reduced. For future ultrahigh-density contact recording, it is believed that perpendicular recording may be used. A thin Pt underlayer has been found to be capable of producing Ba ferrite thin films with excellent c-axis perpendicular orientation.

Gas Permeation in Thin Glassy Polymer Films

NASA Astrophysics Data System (ADS)

Paul, Donald

2011-03-01

The development of asymmetric and composite membranes with very thin dense ``skins'' needed to achieve high gas fluxes enabled the commercial use of membranes for molecular level separations. It has been generally assumed that these thin skins, with thicknesses of the order of 100 nm, have the same permeation characteristics as films with thicknesses of 25 microns or more. Thick films are easily made in the laboratory and have been used extensively for measuring permeation characteristics to evaluate the potential of new polymers for membrane applications. There is now evidence that this assumption can be in very significant error, and use of thick film data to select membrane materials or predict performance should be done with caution. This presentation will summarize our work on preparing films of glassy polymers as thin as 20 nm and characterizing their behavior by gas permeation, ellipsometry and positron annihilation lifetime spectroscopy. Some of the most important polymers used commercially as gas separation membranes, i.e., Matrimid polyimide, polysulfone (PSF) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), have been made into well-defined thin films in our laboratories by spin casting techniques and their properties studied using the techniques we have developed. These thin films densify (or physically age) much faster than thicker films, and, as result, the permeability decreases, sometimes by several-fold over weeks or months for thin films. This means that the properties of these thin films can be very different from bulk films. The techniques, interpretations and implications of these observations will be discussed. In a broader sense, gas permeation measurements can be a powerful way of developing a better understanding of the effects of polymer chain confinement and/or surface mobility on the behavior of thin films.

Novel Electrically Tunable Microwave Solenoid Inductor and Compact Phase Shifter Utilizing Permaloy and PZT Thin Films

DOE PAGES

Wang, Tengxing; Jiang, Wei; Divan, Ralu; ...

2017-08-03

A Permalloy (Py) thin film enabled tunable 3-D solenoid inductor is designed and fabricated. The special configuration of magnetic core is discussed and by selectively patterning Py thin film, the proposed tunable inductor can work at frequency up to several GHz range. The inductance of the solenoid inductor can be electrically tuned by dc current and the tunability is above 10%. Utilizing the implemented Py enabled tunable solenoid inductor and Lead Zirconate Titanate (PZT) thin film enabled metal-insulator-metal (MIM) capacitor, a compact fully electrically tunable lumped elements phase shifter is achieved. The tunable phase shifter has both inductive and capacitivemore » tunability and the dual tunability significantly improves the tuning range and design flexibility. Moreover, the dual tunability is able to retain the equivalent characteristic impedance of the device in the process of the phase being tuned. Here, the phase of the device can be tuned by fully electrical methods and when dc current and dc voltage are provided, the length normalized phase tunability is up to 210°/cm« less

Composition dependence of charge and magnetic length scales in mixed valence manganite thin films

PubMed Central

Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.

2016-01-01

Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1−yPry)1−xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1−xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties. PMID:27461993

Polycrystalline silicon thin-film transistors fabricated by Joule-heating-induced crystallization

NASA Astrophysics Data System (ADS)

Hong, Won-Eui; Ro, Jae-Sang

2015-01-01

Joule-heating-induced crystallization (JIC) of amorphous silicon (a-Si) films is carried out by applying an electric pulse to a conductive layer located beneath or above the films. Crystallization occurs across the whole substrate surface within few tens of microseconds. Arc instability, however, is observed during crystallization, and is attributed to dielectric breakdown in the conductor/insulator/transformed polycrystalline silicon (poly-Si) sandwich structures at high temperatures during electrical pulsing for crystallization. In this study, we devised a method for the crystallization of a-Si films while preventing arc generation; this method consisted of pre-patterning an a-Si active layer into islands and then depositing a gate oxide and gate electrode. Electric pulsing was then applied to the gate electrode formed using a Mo layer. The Mo layer was used as a Joule-heat source for the crystallization of pre-patterned active islands of a-Si films. JIC-processed poly-Si thin-film transistors (TFTs) were fabricated successfully, and the proposed method was found to be compatible with the standard processing of coplanar top-gate poly-Si TFTs.

Fabrication of ZnO Thin Films by Sol-Gel Spin Coating and Their UV and White-Light Emission Properties

NASA Astrophysics Data System (ADS)

Kumar, Mirgender; Dubey, Sarvesh; Rajendar, Vanga; Park, Si-Hyun

2017-10-01

ZnO thin films have been fabricated by the sol-gel spin-coating technique and annealed under different conditions, and their ultraviolet (UV) and white-light emission properties investigated. Different ambient conditions including oxygen, nitrogen, zinc-rich nitrogen, and vacuum were used to tune the main properties of the ZnO thin films. The resistivity varied from the conductive to semi-insulating regime, and the luminescence emission from fairly intense UV to polychromatic. The emission intensity was also found to be a function of the annealing conditions. Possible routes to compensate the loss of emission characteristics are discussed. X-ray photoelectron spectroscopy (XPS) analysis was carried out to detect the chemical states of the zinc/oxygen species. The changes in the electrical and emission properties are explained based on annihilation/formation of inherent donor/acceptor-type defects. Such ZnO thin films could have potential applications in solid-state lighting.

Broadly tunable thin-film intereference coatings: active thin films for telecom applications

NASA Astrophysics Data System (ADS)

Domash, Lawrence H.; Ma, Eugene Y.; Lourie, Mark T.; Sharfin, Wayne F.; Wagner, Matthias

2003-06-01

Thin film interference coatings (TFIC) are the most widely used optical technology for telecom filtering, but until recently no tunable versions have been known except for mechanically rotated filters. We describe a new approach to broadly tunable TFIC components based on the thermo-optic properties of semiconductor thin films with large thermo-optic coefficients 3.6X10[-4]/K. The technology is based on amorphous silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD), a process adapted for telecom applications from its origins in the flat-panel display and solar cell industries. Unlike MEMS devices, tunable TFIC can be designed as sophisticated multi-cavity, multi-layer optical designs. Applications include flat-top passband filters for add-drop multiplexing, tunable dispersion compensators, tunable gain equalizers and variable optical attenuators. Extremely compact tunable devices may be integrated into modules such as optical channel monitors, tunable lasers, gain-equalized amplifiers, and tunable detectors.

Semiconductor-nanocrystal/conjugated polymer thin films

DOEpatents

Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

2014-06-17

The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

Semiconductor-nanocrystal/conjugated polymer thin films

DOEpatents

Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

2010-08-17

The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

Thin film absorber for a solar collector

DOEpatents

Wilhelm, William G.

1985-01-01

This invention pertains to energy absorbers for solar collectors, and more particularly to high performance thin film absorbers. The solar collectors comprising the absorber of this invention overcome several problems seen in current systems, such as excessive hardware, high cost and unreliability. In the preferred form, the apparatus features a substantially rigid planar frame with a thin film window bonded to one planar side of the frame. An absorber in accordance with the present invention is comprised of two thin film layers that are sealed perimetrically. In a preferred embodiment, thin film layers are formed from a metal/plastic laminate. The layers define a fluid-tight planar envelope of large surface area to volume through which a heat transfer fluid flows. The absorber is bonded to the other planar side of the frame. The thin film construction of the absorber assures substantially full envelope wetting and thus good efficiency. The window and absorber films stress the frame adding to the overall strength of the collector.

Self-assembly of dodecaphenyl POSS thin films

NASA Astrophysics Data System (ADS)

Handke, Bartosz; Klita, Łukasz; Niemiec, Wiktor

2017-12-01

The self-assembly abilities of Dodecaphenyl Polyhedral Oligomeric Silsesquioxane thin films on Si(1 0 0) surfaces were studied. Due to their thermal properties - relatively low sublimation temperature and preservation of molecular structure - cage type silsesquioxanes are ideal material for the preparation of a thin films by Physical Vapor Deposition. The Ultra-High Vacuum environment and the deposition precision of the PVD method enable the study of early stages of thin film growth and its molecular organization. X-ray Reflectivity and Atomic Force Microscopy measurements allow to pursuit size-effects in the structure of thin films with thickness ranges from less than a single molecular layer up to several tens of layers. Thermal treatment of the thin films triggered phase change: from a poorly ordered polycrystalline film into a well-ordered multilayer structure. Self-assembly of the layers is the effect of the π-stacking of phenyl rings, which force molecules to arrange in a superlattice, forming stacks of alternating organic-inorganic layers.

Thin-film Rechargeable Lithium Batteries

DOE R&D Accomplishments Database

Dudney, N. J.; Bates, J. B.; Lubben, D.

1995-06-01

Thin film rechargeable lithium batteries using ceramic electrolyte and cathode materials have been fabricated by physical deposition techniques. The lithium phosphorous oxynitride electrolyte has exceptional electrochemical stability and a good lithium conductivity. The lithium insertion reaction of several different intercalation materials, amorphous V{sub 2}O{sub 5}, amorphous LiMn{sub 2}O{sub 4}, and crystalline LiMn{sub 2}O{sub 4} films, have been investigated using the completed cathode/electrolyte/lithium thin film battery.

An overview of thin film nitinol endovascular devices.

PubMed

Shayan, Mahdis; Chun, Youngjae

2015-07-01

Thin film nitinol has unique mechanical properties (e.g., superelasticity), excellent biocompatibility, and ultra-smooth surface, as well as shape memory behavior. All these features along with its low-profile physical dimension (i.e., a few micrometers thick) make this material an ideal candidate in developing low-profile medical devices (e.g., endovascular devices). Thin film nitinol-based devices can be collapsed and inserted in remarkably smaller diameter catheters for a wide range of catheter-based procedures; therefore, it can be easily delivered through highly tortuous or narrow vascular system. A high-quality thin film nitinol can be fabricated by vacuum sputter deposition technique. Micromachining techniques were used to create micro patterns on the thin film nitinol to provide fenestrations for nutrition and oxygen transport and to increase the device's flexibility for the devices used as thin film nitinol covered stent. In addition, a new surface treatment method has been developed for improving the hemocompatibility of thin film nitinol when it is used as a graft material in endovascular devices. Both in vitro and in vivo test data demonstrated a superior hemocompatibility of the thin film nitinol when compared with commercially available endovascular graft materials such as ePTFE or Dacron polyester. Promising features like these have motivated the development of thin film nitinol as a novel biomaterial for creating endovascular devices such as stent grafts, neurovascular flow diverters, and heart valves. This review focuses on thin film nitinol fabrication processes, mechanical and biological properties of the material, as well as current and potential thin film nitinol medical applications. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fully Solution-Processed Flexible Organic Thin Film Transistor Arrays with High Mobility and Exceptional Uniformity

PubMed Central

Fukuda, Kenjiro; Takeda, Yasunori; Mizukami, Makoto; Kumaki, Daisuke; Tokito, Shizuo

2014-01-01

Printing fully solution-processed organic electronic devices may potentially revolutionize production of flexible electronics for various applications. However, difficulties in forming thin, flat, uniform films through printing techniques have been responsible for poor device performance and low yields. Here, we report on fully solution-processed organic thin-film transistor (TFT) arrays with greatly improved performance and yields, achieved by layering solution-processable materials such as silver nanoparticle inks, organic semiconductors, and insulating polymers on thin plastic films. A treatment layer improves carrier injection between the source/drain electrodes and the semiconducting layer and dramatically reduces contact resistance. Furthermore, an organic semiconductor with large-crystal grains results in TFT devices with shorter channel lengths and higher field-effect mobilities. We obtained mobilities of over 1.2 cm2 V−1 s−1 in TFT devices with channel lengths shorter than 20 μm. By combining these fabrication techniques, we built highly uniform organic TFT arrays with average mobility levels as high as 0.80 cm2 V−1 s−1 and ideal threshold voltages of 0 V. These results represent major progress in the fabrication of fully solution-processed organic TFT device arrays. PMID:24492785

Chemical sensing employingpH sensitive emeraldine base thin film for carbon dioxide detection

NASA Astrophysics Data System (ADS)

Irimia-Vladu, Mihai

impedance spectroscopy measurements, revealed valuable information about conduction mechanisms at pH levels were the overall conductivity of the film remained unchanged. Typical impedance spectra for the emeraldine thin films for a frequency sweep between 3.2 E7 to 1 Hz shows a single semicircle. The overall conductivity of the film (5x10-4 S/cm) does not change when CO 2 is bubbled through the water in which the sensor is immersed, but an additional semicircle starts to appear at low (less than 200 Hz) frequency corresponding to lowering the pH of the solution below 5.0. The original semicircle diminishes in size but maintains its initial peak frequency. The EB film is very sensitive to pH changes, therefore an additional semicircle appears in unpurified argon gas due to the reduction of the pH of water solution to 4.65. The same mechanism is displayed in hydrochloric acid solutions of various pH. The formation of the second semicircle depends on the initial conductivity of the emeraldine base film, a film displaying an initial conductivity of 4.8 x 10-3 S/cm forming the second semicircle at a pH of 5.85. The appearance of the second semicircle is most likely due to a preferential protonation in the insulating matrix of the polymer film. The overall conductivity of the film increases when the level of protonation in the insulating portion of the film reached a level close to the protonation level in the scattered metallic islands, allowing the electron-hopping mechanism to became active. The sensor output is stable and reproducible even after 11 months passed from the polymer film deposition.

Piezoelectric thin films and their applications for electronics

NASA Astrophysics Data System (ADS)

Yoshino, Yukio

2009-03-01

ZnO and AlN piezoelectric thin films have been studied for applications in bulk acoustic wave (BAW) resonator. This article introduces methods of forming ZnO and AlN piezoelectric thin films by radio frequency sputtering and applications of BAW resonators considering the relationship between the crystallinity of piezoelectric thin films and the characteristics of the BAW resonators. Using ZnO thin films, BAW resonators were fabricated for a contour mode at 3.58 MHz and thickness modes from 200 MHz to 5 GHz. The ZnO thin films were combined with various materials, substrates, and thin films to minimize the temperature coefficient of frequency (TCF). The minimum TCF of BAW resonators was approximately 2 ppm/°C in the range -20 to 80 °C. The electromechanical coupling coefficient (k2) in a 1.9 GHz BAW resonator was 6.9%. Using AlN thin films, 5-20 GHz BAW resonators with an ultrathin membrane were realized. The membrane thickness of a 20 GHz BAW resonator was about 200 nm, k2 was 6.1%, and the quality factor (Q) was about 280. Q decreased with increasing resonant frequency. The value of k2 is almost the same for 5-20 GHz resonators. This result could be obtained by improving the thickness uniformity, by controlling internal stress of thin films, and by controlling the crystallinity of AlN piezoelectric thin film.

Fabrication and characterization of Aerogel-Polydimethyl siloxane (PDMS) Insulation Film

NASA Astrophysics Data System (ADS)

Noh, Yeoung ah; Song, Sinae; Taik Kim, Hee

2018-03-01

The building has a large impact on the space heating demand and the indoor environment is affected by climate or daylight. Hence, silica aerogel has generally used as a film to reduce the coefficient of the window in the building. Silica aerogel is a suitable material to apply for insulation material with lower thermal conductivity than that of air to save interior energy. However expensive precursor and drying process were the main issue of the silica aerogel synthesis and practical usage. We attempt to fabricate aerogel insulation film for energy saving through the economic process under ambient pressure. Silica aerogel was synthesized from rice husk ash, which was an agricultural waste to be able to recycle. Taguchi design was used to optimize the parameters (amount of rice husk ash, pH, aging time) controlling the surface area of silica aerogel. The silica aerogel is prepared by sol-gel processing through acidic treatment and aging. The silica aerogel was obtained by modification of silica hydrogel surface and dry at ambient pressure. Finally, aerogel film was respectively fabricated by the different content of aerogel in polydimethylsiloxane (PDMS). Silica aerogel obtained 21 – 24nm average particle size was analyzed by SEM and silica aerogel with high surface area (832.26 m2/g), pore size ( 3.30nm ) was characterized by BET. Then silica Aerogel – PDMS insulation film with thermal conductivity (0.002 W/mK) was analyzed by thermal wave system. The study demonstrates an eco-friendly and low-cost route toward silica – PDMS insulation film with low thermal conductivity (0.002 W/mK).

Stretchable, adhesive and ultra-conformable elastomer thin films.

PubMed

Sato, Nobutaka; Murata, Atsushi; Fujie, Toshinori; Takeoka, Shinji

2016-11-16

Thermoplastic elastomers are attractive materials because of the drastic changes in their physical properties above and below the glass transition temperature (T g ). In this paper, we report that free-standing polystyrene (PS, T g : 100 °C) and polystyrene-polybutadiene-polystyrene triblock copolymer (SBS, T g : -70 °C) thin films with a thickness of hundreds of nanometers were prepared by a gravure coating method. Among the mechanical properties of these thin films determined by bulge testing and tensile testing, the SBS thin films exhibited a much lower elastic modulus (ca. 0.045 GPa, 212 nm thickness) in comparison with the PS thin films (ca. 1.19 GPa, 217 nm thickness). The lower elastic modulus and lower thickness of the SBS thin films resulted in higher conformability and thus higher strength of adhesion to an uneven surface such as an artificial skin model with roughness (R a = 10.6 μm), even though they both have similar surface energies. By analyzing the mechanical properties of the SBS thin films, the elastic modulus and thickness of the thin films were strongly correlated with their conformability to a rough surface, which thus led to a high adhesive strength. Therefore, the SBS thin films will be useful as coating layers for a variety of materials.

Dynamics of solid thin-film dewetting in the silicon-on-insulator system

NASA Astrophysics Data System (ADS)

Bussmann, E.; Cheynis, F.; Leroy, F.; Müller, P.; Pierre-Louis, O.

2011-04-01

Using low-energy electron microscopy movies, we have measured the dewetting dynamics of single-crystal Si(001) thin films on SiO2 substrates. During annealing (T>700 °C), voids open in the Si, exposing the oxide. The voids grow, evolving Si fingers that subsequently break apart into self-organized three-dimensional (3D) Si nanocrystals. A kinetic Monte Carlo model incorporating surface and interfacial free energies reproduces all the salient features of the morphological evolution. The dewetting dynamics is described using an analytic surface-diffusion-based model. We demonstrate quantitatively that Si dewetting from SiO2 is mediated by surface-diffusion driven by surface free-energy minimization.

The Thin Oil Film Equation

NASA Technical Reports Server (NTRS)

Brown, James L.; Naughton, Jonathan W.

1999-01-01

A thin film of oil on a surface responds primarily to the wall shear stress generated on that surface by a three-dimensional flow. The oil film is also subject to wall pressure gradients, surface tension effects and gravity. The partial differential equation governing the oil film flow is shown to be related to Burgers' equation. Analytical and numerical methods for solving the thin oil film equation are presented. A direct numerical solver is developed where the wall shear stress variation on the surface is known and which solves for the oil film thickness spatial and time variation on the surface. An inverse numerical solver is also developed where the oil film thickness spatial variation over the surface at two discrete times is known and which solves for the wall shear stress variation over the test surface. A One-Time-Level inverse solver is also demonstrated. The inverse numerical solver provides a mathematically rigorous basis for an improved form of a wall shear stress instrument suitable for application to complex three-dimensional flows. To demonstrate the complexity of flows for which these oil film methods are now suitable, extensive examination is accomplished for these analytical and numerical methods as applied to a thin oil film in the vicinity of a three-dimensional saddle of separation.

Development of High Resistive and High Magnetization Soft Thin Film and Fabrication of Thin Film Inductors

DTIC Science & Technology

2004-11-01

properties of Co- doped ZnO nanocluster films", .J. of Appl. Phys. in press, 2005 2. Presentations (contributed): Conference Contributions: 1) Y. Qiang...gigahertz band applications. The effects of substrates bias, sputter parameters, and seed-layer have thoroughly been investigated. The magnetic...Adequate properties of soft magnetic thin film were evaluated by an analytical calculation [1] to meet the requirement for gigahertz band thin-film

Black thin film silicon

NASA Astrophysics Data System (ADS)

Koynov, Svetoslav; Brandt, Martin S.; Stutzmann, Martin

2011-08-01

"Black etching" has been proposed previously as a method for the nanoscale texturing of silicon surfaces, which results in an almost complete suppression of reflectivity in the spectral range of absorption relevant for photovoltaics. The method modifies the topmost 150 to 300 nm of the material and thus also is applicable for thin films of silicon. The present work is focused on the optical effects induced by the black-etching treatment on hydrogenated amorphous and microcrystalline silicon thin films, in particular with respect to their application in solar cells. In addition to a strong reduction of the reflectivity, efficient light trapping within the modified thin films is found. The enhancement of the optical absorption due to the light trapping is investigated via photometric measurements and photothermal deflection spectroscopy. The correlation of the texture morphology (characterized via atomic force microscopy) with the optical effects is discussed in terms of an effective medium with gradually varying optical density and in the framework of the theory of statistical light trapping. Photoconductivity spectra directly show that the light trapping causes a significant prolongation of the light path within the black silicon films by up to 15 μm for ˜1 μm thick films, leading to a significant increase of the absorption in the red.

Thin-Film Photovoltaic Solar Array Parametric Assessment

NASA Technical Reports Server (NTRS)

Hoffman, David J.; Kerslake, Thomas W.; Hepp, Aloysius F.; Jacobs, Mark K.; Ponnusamy, Deva

2000-01-01

This paper summarizes a study that had the objective to develop a model and parametrically determine the circumstances for which lightweight thin-film photovoltaic solar arrays would be more beneficial, in terms of mass and cost, than arrays using high-efficiency crystalline solar cells. Previous studies considering arrays with near-term thin-film technology for Earth orbiting applications are briefly reviewed. The present study uses a parametric approach that evaluated the performance of lightweight thin-film arrays with cell efficiencies ranging from 5 to 20 percent. The model developed for this study is described in some detail. Similar mass and cost trends for each array option were found across eight missions of various power levels in locations ranging from Venus to Jupiter. The results for one specific mission, a main belt asteroid tour, indicate that only moderate thin-film cell efficiency (approx. 12 percent) is necessary to match the mass of arrays using crystalline cells with much greater efficiency (35 percent multi-junction GaAs based and 20 percent thin-silicon). Regarding cost, a 12 percent efficient thin-film array is projected to cost about half is much as a 4-junction GaAs array. While efficiency improvements beyond 12 percent did not significantly further improve the mass and cost benefits for thin-film arrays, higher efficiency will be needed to mitigate the spacecraft-level impacts associated with large deployed array areas. A low-temperature approach to depositing thin-film cells on lightweight, flexible plastic substrates is briefly described. The paper concludes with the observation that with the characteristics assumed for this study, ultra-lightweight arrays using efficient, thin-film cells on flexible substrates may become a leading alternative for a wide variety of space missions.

Thin film atomic hydrogen detectors

NASA Technical Reports Server (NTRS)

Gruber, C. L.

1977-01-01

Thin film and bead thermistor atomic surface recombination hydrogen detectors were investigated both experimentally and theoretically. Devices were constructed on a thin Mylar film substrate. Using suitable Wheatstone bridge techniques sensitivities of 80 microvolts/2x10 to the 13th power atoms/sec are attainable with response time constants on the order of 5 seconds.

Hybrid Physical-Chemical Vapor Deposition of Bi2Se3 Thin films on Sapphire

NASA Astrophysics Data System (ADS)

Brom, Joseph; Ke, Yue; Du, Renzhong; Gagnon, Jarod; Li, Qi; Redwing, Joan

2012-02-01

High quality thin films of topological insulators continue to garner much interest. We report on the growth of highly-oriented thin films of Bi2Se3 on c-plane sapphire using hybrid physical-chemical vapor deposition (HPCVD). The HPCVD process utilizes the thermal decomposition of trimethyl bismuth (TMBi) and evaporation of elemental selenium in a hydrogen ambient to deposit Bi2Se3. Growth parameters including TMBi flow rate and decomposition temperature and selenium evaporation temperature were optimized, effectively changing the Bi:Se ratio, to produce high quality films. Glancing angle x- ray diffraction measurements revealed that the films were c-axis oriented on sapphire. Trigonal crystal planes were observed in atomic force microscopy images with an RMS surface roughness of 1.24 nm over an area of 2μmx2μm. Variable temperature Hall effect measurements were also carried out on films that were nominally 50-70 nm thick. Over the temperature range from 300K down to 4.2K, the carrier concentration remained constant at approximately 6x10^18 cm-3 while the mobility increased from 480 cm^2/Vs to 900 cm^2/Vs. These results demonstrate that the HPCVD technique can be used to deposit Bi2Se3 films with structural and electrical properties comparable to films produced by molecular beam epitaxy.

Indium local geometry in In-Sb-Te thin films using XANES and DFT calculations

NASA Astrophysics Data System (ADS)

Bilovol, V.; Gil Rebaza, A. V.; Mudarra Navarro, A. M.; Errico, L.; Fontana, M.; Arcondo, B.

2017-12-01

In-Sb-Te when is a thin film presents a huge difference in its electrical resistivity when transform from the amorphous (insulating) to the crystalline (conducting) phase. This property made this system one of the main phase-change materials used in the data storage industry. The change in the electrical conductivity is probably associated to a change in the bonding geometry of some of its constituents. To explore this point, we present in this work an study of the bonding geometry of In atoms in In-Sb-Te films by means of In K-edge X-ray absorption near edge structure (XANES) spectroscopy using synchrotron radiation in both as deposited (amorphous) and crystalline thin films obtained as a result of resistance (R) vs temperature (T) measurements. Comparison of the XANES spectra obtained for ternary amorphous films and binary crystalline reference films suggests that in amorphous films the bonding geometry of In atoms is tetrahedral-like. After the thermal annealing has been carried out the differences in the XANES spectra of the as deposited and the annealed films indicate that the bonding geometry of In atoms changes. Based on X-ray diffraction results and ab initio calculations in the framework of the Density Functional Theory (DFT) we show that the new coordination geometry is associated with a tendency of In atoms towards octahedral-like.

Influence of Mn concentration on magnetic topological insulator Mn xBi 2−xTe 3 thin-film Hall-effect sensor

DOE PAGES

Ni, Y.; Zhang, Z.; Nlebedim, I. C.; ...

2015-06-11

Hall-effect (HE) sensors based on high-quality Mn-doped Bi 2Te 3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi 2Te 3. The sensors with low Mn concentrations, Mn xBi 2-xTe 3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almostmore » eight times as high as that of the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.« less

Dynamic delamination of patterned thin films

NASA Astrophysics Data System (ADS)

Kandula, Soma S. V.; Tran, Phuong; Geubelle, Philippe H.; Sottos, Nancy R.

2008-12-01

We investigate laser-induced dynamic delamination of a patterned thin film on a substrate. Controlled delamination results from our insertion of a weak adhesion region beneath the film. The inertial forces acting on the weakly bonded portion of the film lead to stable propagation of a crack along the film/substrate interface. Through a simple energy balance, we extract the critical energy for interfacial failure, a quantity that is difficult and sometimes impossible to characterize by more conventional methods for many thin film/substrate combinations.

APCVD hexagonal boron nitride thin films for passive near-junction thermal management of electronics

NASA Astrophysics Data System (ADS)

KC, Pratik; Rai, Amit; Ashton, Taylor S.; Moore, Arden L.

2017-12-01

The ability of graphene to serve as an ultrathin heat spreader has been previously demonstrated with impressive results. However, graphene is electrically conductive, making its use in contact with electronic devices problematic from a reliability and integration perspective. As an alternative, hexagonal boron nitride (h-BN) is a similarly structured material with large in-plane thermal conductivity but which possesses a wide band gap, thereby giving it potential to be utilized for directing contact, near-junction thermal management of electronics without shorting or the need for an insulating intermediate layer. In this work, the viability of using large area, continuous h-BN thin films as direct contact, near-junction heat spreaders for electronic devices is experimentally evaluated. Thin films of h-BN several square millimeters in size were synthesized via an atmospheric pressure chemical vapor deposition (APCVD) method that is both simple and scalable. These were subsequently transferred onto a microfabricated test device that simulated a multigate transistor while also allowing for measurements of the device temperature at various locations via precision resistance thermometry. Results showed that these large-area h-BN films with thicknesses of 77-125 nm are indeed capable of significantly lowering microdevice temperatures, with the best sample showing the presence of the h-BN thin film reduced the effective thermal resistance by 15.9% ± 4.6% compared to a bare microdevice at the same power density. Finally, finite element simulations of these experiments were utilized to estimate the thermal conductivity of the h-BN thin films and identify means by which further heat spreading performance gains could be attained.

Enhanced electrical properties of oxide semiconductor thin-film transistors with high conductivity thin layer insertion for the channel region

NASA Astrophysics Data System (ADS)

Nguyen, Cam Phu Thi; Raja, Jayapal; Kim, Sunbo; Jang, Kyungsoo; Le, Anh Huy Tuan; Lee, Youn-Jung; Yi, Junsin

2017-02-01

This study examined the performance and the stability of indium tin zinc oxide (ITZO) thin film transistors (TFTs) by inserting an ultra-thin indium tin oxide (ITO) layer at the active/insulator interface. The electrical properties of the double channel device (ITO thickness of 5 nm) were improved in comparison with the single channel ITZO or ITO devices. The TFT characteristics of the device with an ITO thickness of less than 5 nm were degraded due to the formation of an island-like morphology and the carriers scattering at the active/insulator interface. The 5 nm-thick ITO inserted ITZO TFTs (optimal condition) exhibited a superior field effect mobility (∼95 cm2/V·s) compared with the ITZO-only TFTs (∼34 cm2/V·s). The best characteristics of the TFT devices with double channel layer are due to the lowest surface roughness (0.14 nm) and contact angle (50.1°) that result in the highest hydrophicility, and the most effective adhesion at the surface. Furthermore, the threshold voltage shifts for the ITO/ITZO double layer device decreased to 0.80 and -2.39 V compared with 6.10 and -6.79 V (for the ITZO only device) under positive and negative bias stress, respectively. The falling rates of EA were 0.38 eV/V and 0.54 eV/V for the ITZO and ITO/ITZO bi-layer devices, respectively. The faster falling rate of the double channel devices suggests that the trap density, including interface trap and semiconductor bulk trap, can be decreased by the ion insertion of a very thin ITO film into the ITZO/SiO2 reference device. These results demonstrate that the double active layer TFT can potentially be applied to the flat panel display.

Improvements in the bias illumination stability of amorphous InGaZnO thin-film transistors by using thermal treatments

NASA Astrophysics Data System (ADS)

Kim, Woo-Byung; Lee, Dong Keun; Ryu, Sang Ouk

2014-07-01

The a-IGZO deposited by using the rf sputtering method features a conductive or an insulator characteristic based on amount of oxygen. We demonstrated that a post-treatment affects the resistance patterns of particular-sized InGaZnO(IGZO) thin films in a-IGZO thin-film transistors (TFTs). Post-annealing shifted the driving voltage of a-IGZO TFT to positive or negative values, depending on the annealing temperatures. Post-annealing may introduce oxygen vacancies or desorbed oxygen in the IGZO thin film. The changed driving voltage of IGZO TFTs coincides with the shift of the resistance pattern of IGZO. The fabricated a-IGZO TFTs exhibited a field effect mobility of 6.2 cm2/Vs, an excellent subthreshold gate swing of 0.32 V/decade, and a high I on/off ratio of > 109. Under positive bias illumination stress (PBIS) and negative bias illumination stress (NBIS), after 3,600 seconds, the device threshold voltage shifted about 0.2 V and 0.3 V, respectively.

Composition dependence of electronic, magnetic, transport and morphological properties of mixed valence manganite thin films

DOE PAGES

Singh, Surendra; Freeland, J. W.; Fitzsimmons, Michael R.; ...

2016-07-27

Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La 1-yPr y) 1-xCaxMnO 3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La 0.4Pr 0.6) 1-xCaxMnO3 films with x = 0.33 and 0.375, across themore » MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.« less