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Sample records for ultrathin hfo2 dielectric

  1. High performance organic field-effect transistors with ultra-thin HfO2 gate insulator deposited directly onto the organic semiconductor

    NASA Astrophysics Data System (ADS)

    Ono, S.; Häusermann, R.; Chiba, D.; Shimamura, K.; Ono, T.; Batlogg, B.

    2014-01-01

    We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO2 gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm2/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO2 layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor.

  2. HfO2 dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Xie, Dan; Xu, Jian-Long; Li, Xin-Ming; Sun, Yi-Lin; Dai, Rui-Xuan; Li, Xian; Zhu, Hong-Wei

    2015-10-01

    We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids-Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id-Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-GFETs with different HfO2 dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO2 film from atomic layer deposition process, the concentration of which varies from the thickness of HfO2 layer.

  3. Atomic layer deposition HfO2 capping layer effect on porous low dielectric constant materials

    NASA Astrophysics Data System (ADS)

    Cheng, Yi-Lung; Kao, Kai-Chieh; Huang, Chi-Jia; Chen, Giin-Shan; Fang, Jau-Shiung

    2015-11-01

    Low dielectric constant (low-k) materials are used as inter-level insulators between copper (Cu) conductors to improve the characteristics of integrated circuits. This work proposes a new method for improving the characteristics of porous low-k dielectric film by capping it with an HfO2 film by atomic layer deposition (ALD). Experimental results revealed that capping a porous low-k dielectric film with a ?1.0 nm-thick HfO2 film increases its dielectric constant from 2.56 to 2.65 because the pores in the surface of the film are sealed by Hf precursors. The leakage current density and reliability of the porous low-k dielectrics are greatly improved. The HfO2 capping film also increased resistances against Cu diffusion and damage by oxygen plasma. Therefore, this ALD-deposited HfO2 capping film can be used as a pore-sealing layer and a Cu barrier layer for the porous low-k dielectric film in the future advanced technologies.

  4. Fabrication of Crystalline HfO2 High-? Dielectric Films Deposited on Crystalline ?-Al2O3 Films

    NASA Astrophysics Data System (ADS)

    Okada, Takayuki; Shahjahan, Mohammad; Sawada, Kazuaki; Ishida, Makoto

    2005-04-01

    Crystalline HfO2/?-Al2O3 gate stacks were successfully fabricated by evaporating the HfO2 film on crystalline ?-Al2O3/Si substrates at 500°C. In the fabrication, crystalline ?-Al2O3 assisted the crystallization of the HfO2 film, which was deposited without the degradation of surface morphology. The electrical characteristics of the crystalline HfO2/?-Al2O3 stacked dielectric and amorphous HfO2 unstacked dielectric were compared. The leakage current density of the stacked dielectric was lower than that of the unstacked dielectric. The HfO2 layer deposited on the crystalline ?-Al2O3/Si showed a higher dielectric constant than the amorphous HfO2 unstacked dielectric. It was also observed that the frequency dependence of the flat-band voltage shift of the stacked dielectric was negligible and different from that of the unstacked dielectric. These results indicate that crystalline ?-Al2O3 films prevented the formation of an interface layer between HfO2 and Si substrates. The crystalline ?-Al2O3 films work well as buffer layers and may be available for future high-? gate stack application.

  5. The effect of ultraviolet irradiation on the ultra-thin HfO2 based CO gas sensor

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Barin, Ã.-zlem; Y?ld?z, Dilber Esra; Acar, Selim

    2015-11-01

    In this work, an effort has been made to fabricate ultrathin HfO2/Al2O3 sample by atomic layer deposition method for the fast detection of CO gas at room temperature. The effect of the operating temperature and the UV light on the gas sensing characteristics has been studied. We investigated the optimum operating temperature for the sample by sensing 25 ppm CO and CO2 gases from room temperature to 150 °C for 10 °C steps. The maximum response was obtained at 150 °C for both gases in the measurement temperature range. Also, the photoresponse measurements clearly show the effect of UV light on the sample. At room temperature, sensor showed superior response (14%) for 5 ppm CO gas. The response time of sensor is 6 s to 5 ppm CO gas concentration. The ultrathin HfO2 based sample shows acceptable gas sensitivity for 5 ppm CO gas at room temperature under UV light irradiation.

  6. Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si

    NASA Astrophysics Data System (ADS)

    Dai, J. Y.; Lee, P. F.; Wong, K. H.; Chan, H. L. W.; Choy, C. L.

    2003-07-01

    Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf-Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance-voltage measurement on an as-grown 40-Å yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 Å. The leakage current density is 7.0×10-2 A/cm2 at 1 V gate bias voltage.

  7. Effect of Al addition in HfO2 on the optical properties of the dielectrics using spectroscopy ellipsometry

    NASA Astrophysics Data System (ADS)

    Fan, Xiaojiao; Liu, Hongxia; Zhong, Bo; Fei, Chenxi; Wang, Xing; Wang, Qianqiong

    2015-04-01

    The imaginary part of the dielectric functions (?2) and the band gap energy (Eg) of Al-HfO2 films with different Al incorporation levels prepared by atomic layer deposition (ALD) are extracted using variable angle spectroscopic ellipsometry (VASE). The analysis results show that pure HfO2 film exhibits crystallization features after annealing at 500 °C. When Al is incorporated, Al-HfO2 films can maintain amorphous at temperatures up to 700 °C after rapid thermal annealing, indicating a good thermal stability. In particular, as-deposition [1Al2O3 + 5HfO2] film shows similar optical properties to that of pure HfO2. Moreover, least disorder in the amorphous film structure and excellent thermal stability of Eg (5.5 ± 0.1 eV) during annealing are obtained for [1Al2O3 ± 5HfO2] films. However, increased Al incorporation levels induce more disorder in the amorphous film structure and thermal instability of Eg during the annealing procedure. Thus, [1Al2O3 ± 5HfO2] film displays the optimal optical properties and excellent thermal stability of Eg.

  8. Bias temperature instability comparison of CMOS LTPS-TFTs with HfO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Ma, William Cheng-Yu; Huang, Chi-Yuan

    2015-12-01

    In this paper, the positive and negative bias temperature instability (P/NBTI) of complementary metal-oxide-semiconductor (CMOS) low-temperature poly-Si thin-film transistors (LTPS-TFTs) with HfO2 gate dielectric are studied simultaneously. Significant threshold voltage shift ?VTH, degradation of the subthreshold swing S.S. and transconductance Gm are observed for both n-type LTPS-TFTs after PBTI stress and p-type LTPS-TFTs after NBTI stress. Moreover, the Gm degradation rate with the stress time of p-type devices during NBTI shows significantly different behavior from the PBTI of n-type devices. The PBTI of n-type device shows a saturation behavior of the Gm degradation with various stress bias and temperature. Conversely, the NBTI of p-type device shows an enhanced Gm degradation rate with the increase of stress time and stress temperature. In addition, the threshold voltage shift |?VTH| of PBTI does not obey the traditional empirical power law model, but the NBTI obeys it with higher time exponent. Consequently, the NBTI of the p-type device shows worse driving current Idrv degradation than the PBTI of the n-type device mainly due to the different Gm degradation behavior.

  9. Properties of HfO2/ultrathin SiO2/Si structures and their comparison with Si MOS structures passivated in KCN solution

    NASA Astrophysics Data System (ADS)

    Pin?ík, Emil; Kobayashi, Hikaru; Matsumoto, Taketoshi; Takahashi, Masao; Mikula, Milan; Brunner, Róbert

    2014-05-01

    Electrical, optical and partly structural properties are investigated on very thin ALD HfO2/ultrathin NAOS SiO2/n-type Si structures. An ALD layer was deposited at 250 °C and it contains amorphous and crystalline-probably monoclinic HfO2 phases. HfO2 films with both types of structural phases were not stable if thermal treatment above 200 °C was applied. On as- prepared samples, deep interface traps with activation energy of ?W = 0.23 eV have been determined. After annealing of the structure at 200 °C, the traps were partly transformed and a mid-gap level ?W = 0.49 eV was detected. FTIR and AFM measurements confirmed presence of HfO2 monoclinic phase in the HfO2 films. On the other side, the density of interface defect states of the structure decreased from approx. 1012 eV-1 cm-2 to 1011 eV-1 cm-2 after low temperature annealing of the reference structure. The results are compared with very similar (almost identical) development of interface defect states on the very thin thermal SiO2/Si structure before and after passivation in a 0.1 M KCN methanol solution.PACS: 78.55.Qr; 78.66.Jg; 81.16.Pr; 85.40Ls

  10. Solid-state dewetting of ultra-thin Au films on SiO2 and HfO2

    NASA Astrophysics Data System (ADS)

    Seguini, G.; Llamoja Curi, J.; Spiga, S.; Tallarida, G.; Wiemer, C.; Perego, M.

    2014-12-01

    Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO2 and HfO2. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h = 0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 1012 Au NPs cm-2 were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h ? 1.0 nm where the Au NPs diameter is in the 5-10 nm range and the density is around 1011 Au NPs cm-2. The effect of a subsequent high temperature (400-800 °C) annealing in N2 atmosphere on the Au NPs was investigated as well. For h ? 1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0 ? h ? 6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT.

  11. Germanium nanowire field-effect transistors with SiO2 and high-? HfO2 gate dielectrics

    NASA Astrophysics Data System (ADS)

    Wang, Dunwei; Wang, Qian; Javey, Ali; Tu, Ryan; Dai, Hongjie; Kim, Hyoungsub; McIntyre, Paul C.; Krishnamohan, Tejas; Saraswat, Krishna C.

    2003-09-01

    Single-crystal Ge nanowires are synthesized by a low-temperature (275 °C) chemical vapor deposition (CVD) method. Boron doped p-type GeNW field-effect transistors (FETs) with back-gates and thin SiO2 (10 nm) gate insulators are constructed. Hole mobility higher than 600 cm2/V s is observed in these devices, suggesting high quality and excellent electrical properties of as-grown Ge wires. In addition, integration of high-? HfO2 (12 nm) gate dielectric into nanowire FETs with top-gates is accomplished with promising device characteristics obtained. The nanowire synthesis and device fabrication steps are all performed below 400 °C, opening a possibility of building three-dimensional electronics with CVD-derived Ge nanowires.

  12. Grazing incidence-X-ray fluorescence spectrometry for the compositional analysis of nanometer-thin high-kappa dielectric HfO2 layers.

    PubMed

    Hellin, David; Delabie, Annelies; Puurunen, Riikka L; Beaven, Peter; Conard, Thierry; Brijs, Bert; De Gendt, Stefan; Vinckier, Chris

    2005-07-01

    In future microelectronic devices, SiO2 as a gate dielectric material will be replaced by materials with a higher dielectric constant. One such candidate material is HfO2. Thin layers are typically deposited from ligand-containing precursors in chemical vapor deposition (CVD) processes. In the atomic layer deposition (ALD) of HfO2, these precursors are often HfCl4 and H2O. Obviously, the material properties of the deposited films will be affected by residual ligands from the precursors. In this paper, we evaluate the use of grazing incidence--and total reflection-X-ray fluorescence spectrometry (GI-XRF and TXRF) for Cl trace analysis in nanometer-thin HfO2 films deposited using ALD. First, the results from different X-ray analysis approaches for the determination of Hf coverage are compared with the results from Rutherford backscattering spectrometry (RBS). Next, we discuss the selection of an appropriate X-ray excitation source for the analysis of traces within the high-kappa: layers. Finally, we combine both in a study on the accuracy of Cl determinations in HfO2 layers. PMID:16038507

  13. Thermal stability of TiN metal gate prepared by atomic layer deposition or physical vapor deposition on HfO2 high-K dielectric

    NASA Astrophysics Data System (ADS)

    Wu, L.; Yu, H. Y.; Li, X.; Pey, K. L.; Pan, J. S.; Chai, J. W.; Chiu, Y. S.; Lin, C. T.; Xu, J. H.; Wann, H. J.; Yu, X. F.; Lee, D. Y.; Hsu, K. Y.; Tao, H. J.

    2010-03-01

    In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples.

  14. Ferromagnetic HfO2/Si/GaAs interface for spin-polarimetry applications

    NASA Astrophysics Data System (ADS)

    Tereshchenko, O. E.; Golyashov, V. A.; Eremeev, S. V.; Maurin, I.; Bakulin, A. V.; Kulkova, S. E.; Aksenov, M. S.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.; Dmitriev, D. V.; Toropov, A. I.; Gutakovskii, A. K.; Khandarkhaeva, S. E.; Prosvirin, I. P.; Kalinkin, A. V.; Bukhtiyarov, V. I.; Latyshev, A. V.

    2015-09-01

    In this letter, we present electrical and magnetic characteristics of HfO2-based metal-oxide-semiconductor capacitors (MOSCAPs), along with the effect of pseudomorphic Si as a passivating interlayer on GaAs(001) grown by molecular beam epitaxy. Ultrathin HfO2 high-k gate dielectric films (3-15 nm) have been grown on Si/GaAs(001) structures through evaporation of a Hf/HfO2 target in NO2 gas. The lowest interface states density Dit at Au/HfO2/Si/GaAs(001) MOS-structures were obtained in the range of (6 -13 )×1011 eV-1 cm-2 after annealing in the 400-500 °C temperature range as a result of HfO2 crystallization and the Si layer preservation in non-oxidized state on GaAs. HfO2-based MOSCAPs demonstrated the ferromagnetic properties which were attributed to the presence of both cation and anion vacancies according to the first-principle calculations. Room-temperature ferromagnetism in HfO2 films allowed us to propose a structure for the ferromagnetic MOS spin-detector.

  15. Atomic layer deposition of Y2O3 and yttrium-doped HfO2 using a newly synthesized Y(iPrCp)2(N-iPr-amd) precursor for a high permittivity gate dielectric

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Seung; Kim, Woo-Hee; Oh, Il-Kwon; Kim, Min-Kyu; Lee, Gyeongho; Lee, Chang-Wan; Park, Jusang; Lansalot-Matras, Clement; Noh, Wontae; Kim, Hyungjun

    2014-04-01

    We systematically investigated the effects of Y doping in HfO2 dielectric layer, focusing on structural phase transformation and the dielectric properties of the resultant films. Y doping was carried out using atomic layer deposition (ALD) with a novel Y(iPrCp)2(N-iPr-amd) precursor, which exhibits good thermal stability without any decomposition and clean evaporation. As a result, the ALD process of the Y2O3 films showed well-saturated and linear growth characteristics of ˜0.45 Å/cycle without significant incubation delays and produced pure Y2O3 films. Then, yttrium-doped HfO2 films with various Y/(Y + Hf) compositions (yttrium content: 0.6- 4.8 mol%) were prepared by alternating Y2O3 and HfO2 growth cycles. Structural and electrical characterization revealed that the addition of yttrium to HfO2 induced phase transformations from the monoclinic to the cubic or tetragonal phases, even at low post-annealing temperatures of 600 °C, and improved leakage current densities by inducing oxygen vacancy-related complex defects. A maximum relative dielectric constant of ˜33.4 was obtained for films with a yttrium content of ˜1.2 mol%. Excellent EOT scalability was observed down to ˜1 nm without dielectric constant degradation.

  16. Field-effect modulation of conductance in VO2 nanobeam transistors with HfO2 as the gate dielectric

    E-print Network

    Wu, Junqiao

    as the gate dielectric. When heated up from low to high temperatures, VO2 undergoes an insulator-to-metal as it is heated, and the system breaks up into alternating insulator and metal domains.10 The metal domains first origins. VC 2011 American Institute of Physics. [doi:10.1063/1.3624896] VO2 undergoes an insulator-to-metal

  17. Effect of pre-deposition annealing on the performance of MIS capacitor formed using atomic layer deposition of ultrathin HfO2

    NASA Astrophysics Data System (ADS)

    Maurya, Savita; Singh, B. R.; Radhakrishna, M.

    2013-06-01

    In this work, we report the effect of pre-deposition annealing on electrical characteristics of metal-insulator-semiconductor (MIS) capacitors, with HfO2 as high-k insulator. HfO2 has been deposited via atomic layer deposition (ALD) using Tetrakis [Ethyl Methyl Amino] Hafnium, Hf[N(CH3)(C2H5(]4 (TEMAHf) as metal oxide precursor and water (H2O) as oxidizing precursor. The results obtained have shown that the pre-and post deposition annealing have profound effect on electrical characteristic of MIS Capacitors. This led us to hypothesize that the preparation of Silicon substrate with pre-deposition temperature treatment forms an interfacial layer between hafnium dioxide & substrate and that will have influence on the ALD deposition and consequentially on the electrical characteristic of the device formed through ALD. By controlling the post deposition conditions, the electrical characteristic behavior is ascribed to the predeposition treatment. The promising hypothesis of such a behavior, supported with some preliminary experimental data has been presented in this short communication.

  18. Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application

    PubMed Central

    2011-01-01

    Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching. PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea PMID:21711946

  19. Electrical characteristics of hydrogen-terminated diamond metal-oxide-semiconductor with atomic layer deposited HfO2 as gate dielectric

    NASA Astrophysics Data System (ADS)

    Liu, J. W.; Liao, M. Y.; Imura, M.; Oosato, H.; Watanabe, E.; Koide, Y.

    2013-03-01

    HfO2 films have been deposited on hydrogen-terminated diamond (H-diamond) by an atomic layer deposition (ALD) technique at 120 °C. Effect of rapid thermal annealing treatment on electrical properties of Au/Ti/Pd/ALD-HfO2/H-diamond metal-oxide-semiconductor (MOS) diodes has been investigated. The leakage current density of the MOS diode after annealing at 300 °C is as small as 10-8 A/cm2 at gate biases from -5.0 to 4.0 V. The capacitance-voltage curve in the depletion mode of the MOS diode after annealing is much sharper than that of the MOS diode before annealing and close to the theoretical dependence, which indicates the small interface state density. The annealed MOS diode is concluded to be more suitable for the fabrication of field effect transistors.

  20. Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application

    PubMed Central

    2011-01-01

    Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (?5 keV) ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices. PMID:21711708

  1. High temperature thermal stability of the HfO2/Ge (100) interface as a function of surface preparation studied by synchrotron radiation core level photoemission

    NASA Astrophysics Data System (ADS)

    Chellappan, Rajesh Kumar; Gajula, Durga Rao; McNeill, David; Hughes, Greg

    2014-02-01

    High resolution soft x-ray photoemission spectroscopy (SXPS) have been used to study the high temperature thermal stability of ultra-thin atomic layer deposited (ALD) HfO2 layers (?1 nm) on sulphur passivated and hydrofluoric acid (HF) treated germanium surfaces. The interfacial oxides which are detected for both surface preparations following HfO2 deposition can be effectively removed by annealing upto 700 °C without any evidence of chemical interaction at the HfO2/Ge interface. The estimated valence and conduction band offsets for the HfO2/Ge abrupt interface indicated that effective barriers exist to inhibit carrier injection.

  2. Characterization of Interfaces between HfO2 Thin Film and Metal Electrode with Pre-Post Treatments

    NASA Astrophysics Data System (ADS)

    Kim, Young-Nam

    2012-04-01

    We investigated the effects of post O3 feeding treatment and pre-post O2 plasma treatment on HfO2 dielectric films in the metal/insulator/metal (MIM) structure TiN/HfO2/TiN. The carbon contents of the HfO2 films decreases with increasing O3 feeding time, which leads to the improvement in leakage current. The O2 plasma and O3 feeding treatments produce Hf-Hf bonds in the bulk HfO2 film and a Ti oxide layer at the film/bottom electrode and HfO2/TiN interface, which prevent the out diffusion of nitrogen into the HfO2 layer. In addition, these treatments also create the local crystallization of HfO2 at the interface. In the case of rapid thermal annealing of an actual dynamic random access memory (DRAM) structure, TiN/HfO2/Al2O3/HfO2/TiN, a local crystallization is also observed in the HfO2 layer, which enhances leakage current.

  3. Permittivity increase of yttrium-doped HfO2 through structural phase transformation

    NASA Astrophysics Data System (ADS)

    Kita, Koji; Kyuno, Kentaro; Toriumi, Akira

    2005-03-01

    An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600°C. The yttrium-doped HfO2 films show higher permittivity than undoped HfO2, and the permittivity as high as 27 is obtained by 4at.% yttrium doping. The permittivity enhancement by yttrium doping can be explained by the shrinkage of molar volume due to the structural phase transformation. The advantage of yttrium doping is more pronounced at higher temperatures, since the permittivity of undoped HfO2 is reduced significantly, whereas that of 17at.% yttrium-doped film shows no change even at 1000°C.

  4. The effects of plasma treatment on the thermal stability of HfO 2 thin films

    NASA Astrophysics Data System (ADS)

    Chang, Kow-Ming; Chen, Bwo-Ning; Huang, Shih-Ming

    2008-07-01

    The thermal stability of pure HfO 2 thin films is not high enough to withstand thermal processes, such as S/D activation or post-metal annealing, in modern industrial CMOS production. In addition, plasma nitridation technology has been employed for increasing the dielectric constant of silicon dioxide and preventing boron penetration. In this experiment, atomic layer deposition (ALD) technology was used to deposit HfO 2 thin films and inductively coupled plasma (ICP) technology was used to perform plasma nitridation process. The C- V and J- V characteristics of the nitrided samples were observed to estimate the effect of the nitridation process. According to this study, plasma nitridation process would be an effective method to improve the thermal stability of HfO 2 thin films.

  5. Plasmonic excitations in ultrathin metal films on dielectric substrates

    NASA Astrophysics Data System (ADS)

    Li, Xiaoguang; Teng, Ao; Özer, Mustafa M.; Shen, Jian; Weitering, Hanno H.; Zhang, Zhenyu

    2014-06-01

    The optical properties of metals are mainly determined by their plasmonic excitations, with various intriguing phenomena associated with systems in reduced dimensions. In this paper, we present a systematic study of the plasmonic excitations in ultrathin metal films on dielectric substrates using two different theoretical approaches, and with Mg thin films on Si as prototype systems. The bulk of the results are obtained using the first approach within first-principles time-dependent local density approximation. We show that the presence of the substrate substantially modifies the plasmon hybridization of the metal films; in turn, the plasmon excitation in the films strongly enhances the absorption of the substrate. The detailed absorption spectra contain several intriguing features. Above the Mg surface plasmon mode, we observe a broad resonance due to the hybridization between the antisymmetric surface plasmon and multipole surface plasmon. Furthermore, below the Mg surface plasmon mode, there also exists a broad absorption feature, caused by individual electron-hole pair excitations. In the second approach, we use a semi-classical local optics model to reveal an intrinsic connection between the broad absorption feature and the multipole surface plasmon modes, which result from the single-particle and collective excitations of the same surface electrons, respectively. Our theoretical predictions on the plasmon dispersions and absorption spectra are also shown to be qualitatively consistent with the latest experimental observations using electron energy loss spectroscopy for Mg thin films grown on Si substrates.

  6. Mechanistic Insight into the Stability of HfO2 -Coated MoS2 Nanosheet Anodes for Sodium Ion Batteries.

    PubMed

    Ahmed, Bilal; Anjum, Dalaver H; Hedhili, Mohamed N; Alshareef, Husam N

    2015-09-01

    It is demonstrated for the first time that surface passivation of 2D nanosheets of MoS2 by an ultrathin and uniform layer of HfO2 can significantly improve the cyclic performance of sodium ion batteries. After 50 charge/discharge cycles, bare MoS2 and HfO2 coated MoS2 electrodes deliver the specific capacity of 435 and 636 mAh g(-1) , respectively, at current density of 100 mA g(-1) . These results imply that batteries using HfO2 coated MoS2 anodes retain 91% of the initial capacity; in contrast, bare MoS2 anodes retain only 63%. Also, HfO2 coated MoS2 anodes show one of the highest reported capacity values for MoS2 . Cyclic voltammetry and X-ray photoelectron spectroscopy results suggest that HfO2 does not take part in electrochemical reaction. The mechanism of capacity retention with HfO2 coating is explained by ex situ transmission electron microscope imaging and electrical impedance spectroscopy. It is illustrated that HfO2 acts as a passivation layer at the anode/electrolyte interface and prevents structural degradation during charge/discharge process. Moreover, the amorphous nature of HfO2 allows facile diffusion of Na ions. These results clearly show the potential of HfO2 coated MoS2 anodes, which performance is significantly higher than previous reports where bulk MoS2 or composites of MoS2 with carbonaceous materials are used. PMID:26061915

  7. Optical second harmonic generation studies of ultrathin high-k dielectric JILA, University of Colorado, Boulder, Colorado 80309

    E-print Network

    Borguet, Eric

    Optical second harmonic generation studies of ultrathin high-k dielectric stacks V. Fomenko JILA of Chemistry, Temple University, Philadelphia, Pennsylvania 19122 Received 24 March 2004; accepted 17 December 2004; published online 11 April 2005 We report an investigation of charge transfer in high-k dielectric

  8. Cross linking molecular systems to form ultrathin dielectric layers

    NASA Astrophysics Data System (ADS)

    Feng, Danqin

    Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1"-terphenyl]-4,4"-dimethanethiol, from the dispersion of the molecular orbitals with changing the wave vector k and from the changes with temperature. With the formation self assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g. in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT). Depending on molecular orientation, the effective Debye temperature can be comparable to that of graphite due to the 'stiffness' of the benzene rings, but follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature. This is not always the case. We find that a monomolecular film formed from [1,1';4',1"-terphenyl]-4,4"-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation. We also find evidence for the increase in dielectric character with polymerization (cross-linking) in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The changes in the HOMO-LUMO gap, with cross-linking, are roughly consistent with the band dispersion. The decomposition and cross-linking processes are also accompanied by changes in molecular orientation. The energetics of the three isomeric carborane cage compounds [ closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] decomposition are investigated. Thermodynamic Born-Haber cycles are constructed for neutral and ionic species in an attempt to systemically characterize closo-carborane decomposition process. The decomposition processes are in favor of lower energy decomposition processes. Among the ionic species the photon induced decomposition is dominated by BH+ and BH 2+ fragment loss, and associated with core to bound excitations. It has been observed that dehydrogenation of the closo-carboranes leads to possible cross-linking and formation of a boron rich semiconductor with good dielectric properties.

  9. Leakage current limit of time domain reflectometry in ultrathin dielectric characterization

    NASA Astrophysics Data System (ADS)

    Kim, Yonghun; Baek, Seung-heon Chris; Jeon, Changhoon; Lee, Young Gon; Kim, Jin Ju; Jung, Ukjin; Kang, Soo Cheol; Park, Woojin; Lee, Seok Hee; Lee, Byoung Hun

    2014-08-01

    The accurate characterization of highly leaky dielectrics has been a serious challenge in MOSFET and capacitor studies. We have shown that time domain reflectometry (TDR) can be used to measure the capacitance of ultrathin SiO2 MOS capacitors even at a leakage current density as high as ˜3000 A/cm2, which is approximately 103 times higher than the limit of a conventional impedance analyzer. The extremely short interaction time of the TDR C-V method makes the TDR capacitance measurement more immune to the leakage current. Since the TDR C-V method does not require special high-frequency test structures other than a ground-signal pad pattern, the TDR C-V method is a promising capacitance measurement method for leaky dielectrics.

  10. Electrical properties of radio-frequency sputtered HfO2 thin films for advanced CMOS technology

    NASA Astrophysics Data System (ADS)

    Sarkar, Pranab Kumar; Roy, Asim

    2015-08-01

    The Hafnium oxide (HfO2) high-k thin films have been deposited by radio frequency (rf) sputtering technique on p-type Si (100) substrate. The thickness, composition and phases of films in relation to annealing temperatures have been investigated by using cross sectional FE-SEM (Field Emission Scanning Electron Microscope) and grazing incidence x-ray diffraction (GI-XRD), respectively. GI-XRD analysis revealed that at annealing temperatures of 350°C, films phases change to crystalline from amorphous. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the annealed HfO2 film have been studied employing Al/HfO2/p-Si metal-oxide-semiconductor (MOS) structures. The electrical properties such as dielectric constant, interface trap density and leakage current density have been also extracted from C-V and I-V Measurements. The value of dielectric constant, interface trap density and leakage current density of annealed HfO2 film is obtained as 23,7.57×1011eV-1 cm-2 and 2.7×10-5 Acm-2, respectively. In this work we also reported the influence of post deposition annealing onto the trapping properties of hafnium oxide and optimized conditions under which no charge trapping is observed into the dielectric stack.

  11. Ferroelectricity in Simple Binary ZrO2 and HfO2.

    PubMed

    Müller, Johannes; Böscke, Tim S; Schröder, Uwe; Mueller, Stefan; Bräuhaus, Dennis; Böttger, Ulrich; Frey, Lothar; Mikolajick, Thomas

    2012-08-01

    The transition metal oxides ZrO(2) and HfO(2) as well as their solid solution are widely researched and, like most binary oxides, are expected to exhibit centrosymmetric crystal structure and therewith linear dielectric characteristics. For this reason, those oxides, even though successfully introduced into microelectronics, were never considered to be more than simple dielectrics possessing limited functionality. Here we report the discovery of a field-driven ferroelectric phase transition in pure, sub 10 nm ZrO(2) thin films and a composition- and temperature-dependent transition to a stable ferroelectric phase in the HfO(2)-ZrO(2) mixed oxide. These unusual findings are attributed to a size-driven tetragonal to orthorhombic phase transition that in thin films, similar to the anticipated tetragonal to monoclinic transition, is lowered to room temperature. A structural investigation revealed the orthorhombic phase to be of space group Pbc2(1), whose noncentrosymmetric nature is deemed responsible for the spontaneous polarization in this novel, nanoscale ferroelectrics. PMID:22812909

  12. Synthesis of freestanding HfO2 nanostructures

    PubMed Central

    2011-01-01

    Two new methods for synthesizing nanostructured HfO2 have been developed. The first method entails exposing HfTe2 powders to air. This simple process resulted in the formation of nanometer scale crystallites of HfO2. The second method involved a two-step heating process by which macroscopic, freestanding nanosheets of HfO2 were formed as a byproduct during the synthesis of HfTe2. These highly two-dimensional sheets had side lengths measuring up to several millimeters and were stable enough to be manipulated with tweezers and other instruments. The thickness of the sheets ranged from a few to a few hundred nanometers. The thinnest sheets appeared transparent when viewed in a scanning electron microscope. It was found that the presence of Mn enhanced the formation of HfO2 by exposure to ambient conditions and was necessary for the formation of the large scale nanosheets. These results present new routes to create freestanding nanostructured hafnium dioxide. PACS: 81.07.-b, 61.46.Hk, 68.37.Hk. PMID:21711786

  13. In-situ MBE and ALD deposited HfO2 on In0.53Ga0.47As

    NASA Astrophysics Data System (ADS)

    Lee, W. C.; Lin, C. A.; Huang, M. L.; Kwo, J.; Chang, Y. H.; Chang, P.; Lin, T. D.; Hong, M.

    2012-02-01

    The semiconductor industry is calling for innovative devices offering high performance with low power consumption. High-? dielectrics/metal gates on high carrier mobility channels are now strong contenders in the post Si CMOS application. Hafnium-based oxide has been employed as the gate dielectric in Si CMOS since 45 nm node and InGaAs is a leading candidate for channel materials. However, reports of HfO2 on InGaAs are scant, and surface treatments using H2S or trimethylaluminum are claimed to be required for achieving high quality HfO2(high-?)/InGaAs interface. In this work, HfO2 has been in-situ deposited on n- and p-In0.53Ga0.47As using both molecular-beam-epitaxy (MBE) and atomic-layer- deposition (ALD), without using any interfacial passivation layer or surface treatments. The HfO2/In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) all exhibit outstanding thermal stabilities (> 800^oC), low leakage currents (˜ 10-8 A/cm^2 at 1 MV/cm), and good CV characteristics. Moreover, the MOSCAPs have shown spectra of interfacial trap densities (Dit's) with no discernible peaks at mid-gap, confirmed by temperature-dependent conductance method.

  14. A high performance, visible to mid-infrared photodetector based on graphene nanoribbons passivated with HfO2.

    PubMed

    Yu, Xuechao; Dong, Zhaogang; Liu, Yanping; Liu, Tao; Tao, Jin; Zeng, Yongquan; Yang, Joel K W; Wang, Qi Jie

    2015-12-17

    Graphene has drawn tremendous attention as a promising candidate for electronic and optoelectronic applications owing to its extraordinary properties, such as broadband absorption and ultrahigh mobility. Nevertheless, the absence of a bandgap makes graphene unfavorable for digital electronic or photonic applications. Although patterning graphene into nanostructures with the quantum confinement effect is able to open a bandgap, devices based on these graphene nanostructures generally suffer from low carrier mobility and scattering losses. In this paper, we demonstrated that encapsulation of an atomic layer deposited high-quality HfO2 film will greatly enhance the carrier mobility and decrease the scattering losses of graphene nanoribbons, because this high-k dielectric layer weakens carrier coulombic interactions. In addition, a photodetector based on HfO2 layer capped graphene nanoribbons can cover broadband wavelengths from visible to mid-infrared at room temperature, exhibiting ?10 times higher responsivity than the one without a HfO2 layer in the visible regime and ?8 times higher responsivity in the mid-infrared regime. The method employed here could be potentially used as a general approach to improve the performance of graphene nanostructures for electronic and optoelectronic applications. PMID:26610363

  15. The structural and electronic properties of HfO2

    NASA Astrophysics Data System (ADS)

    Seema, Kumari; Kumar, Ranjan

    2012-06-01

    Electronic and structural properties of the cubic and tetragonal phases of HfO2 are calculated. SIESTA method within the framework of the density functional theory was used. For the cubic phase, the lattice constant was obtained through a total energy minimization. For the tetragonal phase, the lattice parameters were calculated from the equilibrium volume obtained by variation of the ratio c/a, besides the relaxation of internal atomic positions. Calculated results are in good agreement with previous studies.

  16. Atomic-layer-deposited silver and dielectric nanostructures for plasmonic enhancement of Raman scattering from nanoscale ultrathin films

    NASA Astrophysics Data System (ADS)

    Ko, Chung-Ting; Yang, Po-Shuan; Han, Yin-Yi; Wang, Wei-Cheng; Huang, Jhih-Jie; Lee, Yen-Hui; Tsai, Yi-Jen; Shieh, Jay; Chen, Miin-Jang

    2015-07-01

    Plasmonic silver nanostructures and a precise ZnO cover layer prepared by capacitively coupled plasma atomic layer deposition (ALD) were exploited to enhance the Raman scattering from nanoscale ultrathin films on a Si substrate. The plasmonic activity was supported by a nanostructured Ag (nano-Ag) layer, and a ZnO cover layer was introduced upon the nano-Ag layer to spectrally tailor the localized surface plasmon resonance to coincide with the laser excitation wavelength. Because of the optimized dielectric environment provided by the precise growth of ZnO cover layer using ALD, the intensity of Raman scattering from nanoscale ultrathin films was significantly enhanced by an additional order of magnitude, leading to the observation of the monoclinic and tetragonal phases in the nanoscale ZrO2 high-K gate dielectric as thin as ?6 nm on Si substrate. The excellent agreement between the finite-difference time-domain simulation and experimental measurement further confirms the so-called {{?ft| {\\overset{\\scriptscriptstyle\\rightharpoonup}{E}} \\right|}4} dependence of the surface-enhanced Raman scattering. This technique of plasmonic enhancement of Raman spectroscopy, assisted by the nano-Ag layer and optimized dielectric environment prepared by ALD, can be applied to characterize the structures of ultrathin films in a variety of nanoscale materials and devices, even on a Si substrate with overwhelming Raman background.

  17. Dielectric polarization and refractive indices of ultrathin barium titanate films on strontium titanate single crystals.

    PubMed

    Chaib, H; Eng, L M; Otto, T

    2005-01-12

    The electrical and optical properties of ultrathin films of tetragonal barium titanate (BaTiO(3)) on strontium titanate (SrTiO(3)) single-crystal substrates are theoretically investigated using a microscopic quantum mechanical model based on the orbital approximation in correlation with the dipole-dipole interaction. First-, second-, and third-order electronic polarizabilities had to be considered in this calculation in order to obtain accurate results for both the dielectric spontaneous polarization and the refractive indices of the BaTiO(3) overlayer. The spontaneous polarization is drastically reduced in the film as its thickness decreases. However, an electronic polarization appears within the SrTiO(3) substrate in the neighbourhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO(3) bulk, is induced by the polarization of the BaTiO(3) film. Furthermore, we find the refractive index for both the BaTiO(3) film and the SrTiO(3) substrate to be deeply reduced for light polarized perpendicular to the surface. PMID:21690676

  18. Spurious phenomena occurring during current measurement on ultra-thin dielectric layers: From electro-thermal effects to surface damage

    SciTech Connect

    Grandfond, A.; Gautier, B.; Militaru, L.; Albertini, D.; Descamps-Mandine, A.

    2014-04-07

    In this paper, the conduction properties of dielectric ultra-thin layers are studied using atomic force microscopy. Especially, the conductive-atomic force microscope allows to measure the leakage current at the nanoscale and to study the degradation mechanisms locally. Nonetheless, the dielectric layer seems to be damaged by a technique's specific phenomenon: hillocks appear when a positive tip bias is applied on different dielectrics. In this paper, the formation of these hillocks is studied. Contrary to what is observed during the dielectric breakdown, the conductivity is reduced after hillocks formation which occurs after the dielectric breakdown. Moreover, we have observed the formation of cavities in the silicon substrate linked to the formation of hillocks, which is not compatible with a swelling process (as dielectric breakdown induced epitaxy). We propose that these results may be explained by an electro-thermal effect due to the large dissipated energy, maybe combined with the oxidation of the substrate. Finally, the interdependence of measurements is demonstrated during serial acquisition.

  19. Using dual plasma treatment to improve electrical characteristics and reduce flicker noise of high-? HfO2 LTPS-TFTs

    NASA Astrophysics Data System (ADS)

    Chang, Kow-Ming; Huang, Bo-Wen; Wu, Chien-Hung; Deng, I.-Chung; Chang, Ting-Chia; Lin, Sheng-Chia

    2015-09-01

    This study demonstrated the application of a dual plasma treatment to low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) comprising a self-aligned phosphorus implantation source and drain, high-? HfO2 gate dielectric, and aluminum metal gate. The dual plasma treatment involves a pre-deposition CF4 plasma treatment at a high-?/poly-Si interface and post-deposition N2 plasma treatment at a high-? HfO2 gate dielectric; this treatment enables reducing the interface-trap-state defects at the high-?/poly-Si interface, grain boundary traps in the poly-Si channel film, and oxygen vacancy Vo in the high-? HfO2 gate dielectric. Thus, LTPS-TFTs with dual plasma treatment demonstrate excellent electrical characteristics such as threshold voltage, subthreshold swing, transconductance, driving current, and on/off current ratio. Flicker noise, also referred to as 1/f noise, caused by fluctuations of carriers transported in the grain boundary and the trapped carriers per unit oxide volume (Nt) can be suppressed. Therefore, high performance LTPS-TFTs subjected to dual plasma treatment can be appropriately applied to active matrix liquid phase-crystal display on system-on-panel technology.

  20. Electron mobility in ultra-thin InGaAs channels: Impact of surface orientation and different gate oxide materials

    NASA Astrophysics Data System (ADS)

    Krivec, Sabina; Poljak, Mirko; Suligoj, Tomislav

    2016-01-01

    Electron mobility is investigated in sub-20 nm-thick InGaAs channels, sandwiched between different gate oxides (SiO2, Al2O3, HfO2) and InP as substrate, using physics-based numerical modeling. Effects of body thickness downscaling to 2 nm, different gate oxides, and surface orientation [(1 0 0) and (1 1 1)] are examined by including all electron valleys and all relevant scattering mechanisms. We report that ultra-thin (1 1 1) Al2O3-InGaAs-InP devices offer greater electron mobility than (1 0 0) devices even in the extremely-thin channels. Furthermore, ultra-thin (1 0 0) InGaAs devices outperform SOI in terms of electron mobility for body thicknesses above ?4 nm, while (1 1 1) InGaAs channels are superior to SOI for all body thickness values above ?3 nm. The study of different gate oxides indicates that HfO2 is the optimum gate dielectric regardless of device orientation, offering a mobility improvement of up to 124% for (1 1 1) and 149% for (1 0 0) surface orientation, when compared to the initial Al2O3-InGaAs-InP structure. The (1 1 1) orientation offers improvement over (1 0 0) device irrespective of the body thickness and gate oxide material, with the highest difference reported for SiO2, followed by Al2O3 and HfO2.

  1. Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics

    PubMed Central

    Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

    2013-01-01

    Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10?8 A cm?2 and capacitance density of 0.62 µF cm?2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V?1 s?1. PMID:24288423

  2. Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

    1990-01-01

    An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

  3. Optical characteristics of H2O-based and O3-based HfO2 films deposited by ALD using spectroscopy ellipsometry

    NASA Astrophysics Data System (ADS)

    Fan, Xiaojiao; Liu, Hongxia; Zhong, Bo; Fei, Chenxi; Wang, Xing; Wang, Qianqiong

    2015-06-01

    Optical properties of thin atomic layer-deposited HfO2 films grown by H2O and O3 are analyzed by variable angle spectroscopic ellipsometry. By investigating the dielectric constant, it is found that a higher real part of the dielectric constant ( ? 1) value is observed for H2O-based film due to less silicate component in the film. Careful examination of the log scale of imaginary part of the dielectric constant ( ? 2) leads to the conclusion that the absorption features in the energy range of 3.2-5.35 eV originate from the interface layer between the silicon substrate and the native oxide. In particular, O3-based gate stacks have less sub-band gap defect states besides the silicon's critical features. Moreover, a larger high-frequency dielectric constant, direct and indirect band gap values are obtained for O3-based film. Meanwhile, suitable valence band offsets (3.38 and 3.55 eV) and conduction band offsets (1.58 and 1.47 eV) are obtained for H2O- and O3-based HfO2 gate stacks, respectively, indicating both type of dielectric films can provide sufficient tunneling barriers for both electrons and holes.

  4. Chemical structures and electrical properties of atomic layer deposited HfO2 thin films grown at an extremely low temperature (?100 °C) using O3 as an oxygen source

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Hwan; Park, Tae Joo; Kim, Seong Keun; Cho, Deok-Yong; Jung, Hyung-Suk; Lee, Sang Young; Hwang, Cheol Seong

    2014-02-01

    The properties of atomic layer deposited (ALD) HfO2 films grown at low temperatures (?100 °C) were examined for potential applications in flexible display and bioelectronics. A saturated ALD growth behavior was observed even at an extremely low temperature (30 °C) due to the strong oxidizing potential of O3. However, HfO2 films grown at low temperatures showed a low film density and high impurity concentration, because the thermal energy during film growth was insufficient to remove ligands completely from Hf ions in precursor molecule. This resulted in low dielectric constant and high leakage current density of the films. Nevertheless, HfO2 film grown at 100 °C using O3 gas with a high concentration (390 g/Nm3) showed a tolerable impurity concentration with the dielectric constant of ?16 and breakdown field of ?4 MV/cm, which are approximately two-thirds of those of HfO2 film grown at 250 °C.

  5. Incubation effect of laser-induced surface damage of HfO2/SiO2 HR coating in the femto-nanosecond region

    NASA Astrophysics Data System (ADS)

    Chen, Shunli; Zhao, Yuanan; Kong, Fanyu; Li, Dawei; He, Hongbo; Shao, Jianda

    2011-11-01

    This paper is devoted to a long-term investigation into the nature of incubation effect of multilayer dielectric HR mirror coatings. Accumulated damage behaviors of HfO2/SiO2 mirrors for 800nm, 1053nm, and 1064nm, both fabricated by conventional electron beam evaporation (EBE), were investigated by ultra-short pulse (800nm/~100fs), short pulse (1053nm/~1ps), and long pulse (1064nm/~10ns) lasers, respectively. Incubation effect was found to be a universal phenomenon for HfO2/SiO2 mirrors irradiating by the femto-nanosecond lasers. And when the shot number was about 100, the multi-pulse damage threshold of samples decreased to the level of 60~70% of the single-pulse threshold. Typical damage morphologies and depths information of HR samples were characterized by optical microscope and surface profiler. The results revealed that the electric field distribution within the mirrors had significant influence on the initial damage onset of the mirrors. In addition, theoretical simulation was carried out to describe the incubation behaviors of HfO2/SiO2 mirrors in the femto- and nano-second regions. It seemed reasonable that incubation effect was attributed to the accumulation of native or laser-induced electronic trapping states.

  6. Incubation effect of laser-induced surface damage of HfO2/SiO2 HR coating in the femto-nanosecond region

    NASA Astrophysics Data System (ADS)

    Chen, Shunli; Zhao, Yuanan; Kong, Fanyu; Li, Dawei; He, Hongbo; Shao, Jianda

    2012-01-01

    This paper is devoted to a long-term investigation into the nature of incubation effect of multilayer dielectric HR mirror coatings. Accumulated damage behaviors of HfO2/SiO2 mirrors for 800nm, 1053nm, and 1064nm, both fabricated by conventional electron beam evaporation (EBE), were investigated by ultra-short pulse (800nm/~100fs), short pulse (1053nm/~1ps), and long pulse (1064nm/~10ns) lasers, respectively. Incubation effect was found to be a universal phenomenon for HfO2/SiO2 mirrors irradiating by the femto-nanosecond lasers. And when the shot number was about 100, the multi-pulse damage threshold of samples decreased to the level of 60~70% of the single-pulse threshold. Typical damage morphologies and depths information of HR samples were characterized by optical microscope and surface profiler. The results revealed that the electric field distribution within the mirrors had significant influence on the initial damage onset of the mirrors. In addition, theoretical simulation was carried out to describe the incubation behaviors of HfO2/SiO2 mirrors in the femto- and nano-second regions. It seemed reasonable that incubation effect was attributed to the accumulation of native or laser-induced electronic trapping states.

  7. Room temperature ferromagnetism in un-doped amorphous HfO2 nano-helix arrays

    NASA Astrophysics Data System (ADS)

    Xie, Qian; Wang, Wei-Peng; Xie, Zheng; Zhan, Peng; Li, Zheng-Cao; Zhang, Zheng-Jun

    2015-05-01

    Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2. Project supported by the National Natural Science Foundation of China (Grant Nos. 51372135 and 61176003) and the Tsinghua University Initiative Scientific Research Program, China.

  8. III-Nitride grating grown on freestanding HfO2 gratings

    PubMed Central

    2011-01-01

    We report here the epitaxial growth of III-nitride material on freestanding HfO2 gratings by molecular beam epitaxy. Freestanding HfO2 gratings are fabricated by combining film evaporation, electron beam lithography, and fast atom beam etching of an HfO2 film by a front-side silicon process. The 60-?m long HfO2 grating beam can sustain the stress change during the epitaxial growth of a III-nitride material. Grating structures locally change the growth condition and vary indium composition in the InGaN/GaN quantum wells and thus, the photoluminescence spectra of epitaxial III-nitride grating are tuned. Guided mode resonances are experimentally demonstrated in fabricated III-nitride gratings, opening the possibility to achieve the interaction between the excited light and the grating structure through guided mode resonance. PACS: 78.55.Cr; 81.65.Cf; 81.15.Hi. PMID:21849084

  9. Phase diagrams, dielectric response, and piezoelectric properties of epitaxial ultrathin (001) lead zirconate titanate films under anisotropic misfit strains

    NASA Astrophysics Data System (ADS)

    Qiu, Q. Y.; Alpay, S. P.; Nagarajan, V.

    2010-06-01

    We develop a nonlinear thermodynamic model to predict the phase stability of ultrathin epitaxial (001)-oriented ferroelectric PbZr1-xTixO3 (PZT) films with x =1.0, 0.9, 0.8, and 0.7 on substrates which induce anisotropic in-plane strains. The theoretical formalism incorporates the relaxation by misfit dislocations at the film deposition temperature, the possibility of formation of ferroelectric polydomain structures, and the effect of the internal electric field that is generated due to incomplete charge screening at the film-electrode interfaces and the termination of the ferroelectric layer. This analysis allows the development of misfit strain phase diagrams that provide the regions of stability of monodomain and polydomain structures at a given temperature, film thickness, and composition. It is shown that the range of stability for rotational monodomain phase is markedly increased in comparison to the same ferroelectric films on isotropic substrates. Furthermore, the model finds a strong similarity between ultrathin PbTiO3 and relatively thicker PZT films in terms of phase stability. The combinations of the in-plane misfit strains that yield a phase transition sequence that results in a polarization rotation from the c-phase (polarization parallel to the [001] direction in the film) to the r-phase, and eventually to an in-plane polarization parallel to the [110] direction (the aa-phase) is determined to be the path with the most attractive dielectric and piezoelectric coefficients resulting in enhancements of 10 to 100 times in the dielectric permittivity and piezoresponse compared to bulk tetragonal ferroelectrics of the same PZT composition.

  10. Schottky barrier height reduction for metal/n-InP by inserting ultra-thin atomic layer deposited high-k dielectrics

    SciTech Connect

    Zheng, Shan; Yang, Wen; Sun, Qing-Qing E-mail: linchen@fudan.edu.cn; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David; Chen, Lin; Xiao, Fei

    2013-12-23

    Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (?{sub B,eff}) were optimized by inserting ultrathin dielectrics in this work. Comparing the inserted monolayer and bilayer high-k dielectrics, we demonstrated that the introduction of bilayer dielectrics can further reduce ?{sub B,eff} (from 0.49?eV to 0.22?eV) than the monolayer dielectric (from 0.49?eV to 0.32?eV) even though the overall dielectric thickness was thicker. The additional dipole formed at high-k/high-k interfaces could be used to expound the mechanism. This work proposed an effective solution to reduce resistance contacts for InP based transistors and Schottky barrier transistors.

  11. Detailed analysis of oxide related charges and metal-oxide barriers in terrace etched Al2O3 and HfO2 on AlGaN/GaN heterostructure capacitors

    NASA Astrophysics Data System (ADS)

    Winzer, A.; Szabó, N.; Ocker, J.; Hentschel, R.; Schuster, M.; Schubert, F.; Gärtner, J.; Wachowiak, A.; Mikolajick, T.

    2015-09-01

    In this work, we present the terrace etching technique to obtain excessive thickness series of atomic layer deposition (ALD) grown Al2O3 and HfO2 on GaN-cap/AlGaN/GaN heterostructures allowing for the detailed study of oxide charge distribution and its impact of the metal-insulator-semiconductor high electron mobility transistor (MISHEMT) threshold voltage. By modeling the experimental plot of threshold voltage versus oxide thickness on the basis of experimentally determined two-dimensional electron gas charge density in AlGaN/GaN MISHEMTs, we separated the interface and bulk charge components and determined the oxide-metal barrier height for the investigated gate dielectrics. In both Al2O3 and HfO2 gate dielectrics, the oxide charges are mainly located at the oxide/GaN interface. Determining the interface trap charges from comparison of the pulsed capacitance-voltage (CV) technique with very fast voltage sweep to the modulation type CV method with slow DC voltage ramp, we extracted positive fixed charges of NOx=2.7 ×1012 cm-2 for Al2O3 and NOx=7.8 ×1012 cm-2 for HfO2. We found a strong Vth shift of opposite direction for both high-k materials, corresponding to negatively charged up trap states at the HfO2/GaN interface and positively charged up trap states at the Al2O3/GaN interface. The evaluation of the metal-oxide barrier height in dependence of the metal work function followed the trend of the Schottky model, whereas HfO2 showed less Fermi level pinning compared to Al2O3 indicating the presence of an increased number of interface states in Al2O3 on GaN.

  12. Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium silicate dielectric films on silicon

    NASA Astrophysics Data System (ADS)

    Chambers, J. J.; Busch, B. W.; Schulte, W. H.; Gustafsson, T.; Garfunkel, E.; Wang, S.; Maher, D. M.; Klein, T. M.; Parsons, G. N.

    2001-09-01

    X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) are used to determine chemical bonding and composition of ultra-thin films of mixed yttrium, silicon, and oxygen, formed by oxidation of metal on clean and pre-treated silicon. XPS and MEIS analyses indicate that oxidation of yttrium on bare silicon results in a fully oxidized film with a significant fraction of Y-O-Si bonding. The mixed Y-O-Si structure results from the relatively rapid reaction between Y and the Si substrate to form yttrium silicide, followed by oxidation. The effect of various silicon pretreatments, including in situ oxidation and nitridation, on bulk and interface film composition are also examined. Transmission electron microscopy (TEM) of 40 Å thick films indicates that the yttrium silicate films are amorphous with uniform contrast throughout the layer. MEIS shows evidence for a graded metal concentration in the dielectric near the silicon interface, with uniform oxygen concentration (consistent with full oxidation) throughout the film. Angle resolved XPS (ARXPS) shows no significant signal related to Si +4, as would be expected from a substantial SiO 2 interface layer. Capacitance-voltage analysis demonstrates that a ˜10 Å equivalent oxide thickness can be achieved. The effects of ultra-thin silicon oxide, nitrided-oxide and nitrided silicon interfaces on silicon consumption during the oxidation of yttrium are investigated. When yttrium is deposited on a thin (˜10 Å) SiO 2 film and oxidized, a yttrium silicate film is formed with bonding and composition similar to films formed on bare silicon. However, when the interface is a thin nitride, the silicon consumption rate is significantly reduced, and the resulting film composition is closer to Y 2O 3. The consumption of the silicon substrate by metal is shown to occur during oxidation and during vacuum annealing of yttrium on silicon. The relatively rapid formation of metal-silicon bonds suggests that metal-silicon structures may also be important reactive intermediates in silicon/dielectric interface formation reactions during chemical vapor deposition. In addition to thermodynamic stability, understanding the relative rates of elementary reaction steps in film formation is critical to control composition and structure at the dielectric/Si interface.

  13. Large-Scale Precise Printing of Ultrathin Sol-Gel Oxide Dielectrics for Directly Patterned Solution-Processed Metal Oxide Transistor Arrays.

    PubMed

    Lee, Won-June; Park, Won-Tae; Park, Sungjun; Sung, Sujin; Noh, Yong-Young; Yoon, Myung-Han

    2015-09-01

    Ultrathin and dense metal oxide gate di-electric layers are reported by a simple printing of AlOx and HfOx sol-gel precursors. Large-area printed indium gallium zinc oxide (IGZO) thin-film transistor arrays, which exhibit mobilities >5 cm(2) V(-1) s(-1) and gate leakage current of 10(-9) A cm(-2) at a very low operation voltage of 2 V, are demonstrated by continuous simple bar-coated processes. PMID:26222338

  14. High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures.

    PubMed

    Lee, Sung-Min; Kwong, Anthony; Jung, Daehwan; Faucher, Joseph; Biswas, Roshni; Shen, Lang; Kang, Dongseok; Lee, Minjoo Larry; Yoon, Jongseung

    2015-10-27

    Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III-V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells formed hexagonal arrays of nanoscale posts that serve as lossless photonic nanostructures for antireflection, diffraction, and light trapping in conjunction with a co-integrated rear-surface reflector. Systematic studies on optical and electrical properties and photovoltaic performance in experiments, as well as numerical modeling, quantitatively describe the optimal design rules for ultrathin, nanostructured GaAs solar cells and their integrated modules. PMID:26376087

  15. Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O 3/HfO 2 tunnel oxide.

    PubMed

    El-Atab, Nazek; Turgut, Berk Berkan; Okyay, Ali K; Nayfeh, Munir; Nayfeh, Ammar

    2015-12-01

    In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics. PMID:26055483

  16. Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs . 2.85-nm Si nanoparticles with asymmetric Al2O3/HfO2 tunnel oxide

    NASA Astrophysics Data System (ADS)

    El-Atab, Nazek; Turgut, Berk Berkan; Okyay, Ali K.; Nayfeh, Munir; Nayfeh, Ammar

    2015-06-01

    In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.

  17. Light Coupling and Trapping in Ultrathin Cu(In,Ga)Se2 Solar Cells Using Dielectric Scattering Patterns.

    PubMed

    van Lare, Claire; Yin, Guanchao; Polman, Albert; Schmid, Martina

    2015-10-27

    We experimentally demonstrate photocurrent enhancement in ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells with absorber layers of 460 nm by nanoscale dielectric light scattering patterns printed by substrate conformal imprint lithography. We show that patterning the front side of the device with TiO2 nanoparticle arrays results in a small photocurrent enhancement in almost the entire 400-1200 nm spectral range due to enhanced light coupling into the cell. Three-dimensional finite-difference time-domain simulations are in good agreement with external quantum efficiency measurements. Patterning the Mo/CIGSe back interface using SiO2 nanoparticles leads to strongly enhanced light trapping, increasing the efficiency from 11.1% for a flat to 12.3% for a patterned cell. Simulations show that optimizing the array geometry could further improve light trapping. Including nanoparticles at the Mo/CIGSe interface leads to substantially reduced parasitic absorption in the Mo back contact. Parasitic absorption in the back contact can be further reduced by fabricating CIGSe cells on top of a SiO2-patterned In2O3:Sn (ITO) back contact. Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitransparent geometry. PMID:26348324

  18. Atomic layer deposition of HfO2 thin films using H2O2 as oxidant

    NASA Astrophysics Data System (ADS)

    Choi, Min-Jung; Park, Hyung-Ho; Jeong, Doo Seok; Kim, Jeong Hwan; Kim, Jin-Sang; Kim, Seong Keun

    2014-05-01

    HfO2 films were deposited by atomic layer deposition (ALD) using Hf[(C2H5)(CH3)N]4 and H2O2 at a temperature range of 175-325 °C. The growth per cycle of the HfO2 films decreased with increasing temperature up to 280 °C and then abruptly increased above 325 °C as a result of the thermal decomposition of the precursor. Although the HfO2 films grown with H2O2 exhibited slightly higher carbon contents than those grown with H2O, the leakage properties of the HfO2 films grown with H2O2 were superior to those of the HfO2 films grown with H2O. This is because the HfO2 films grown with H2O2 were fully oxidized as a result of the strong oxidation potential of H2O2. The use of the ALD process with H2O2 also revealed the conformal growth of HfO2 films on a SiO2 hole structure with an aspect ratio of ˜15. This demonstrates that using the ALD process with H2O2 shows great promise for growing robust HfO2 films.

  19. Enhancement of the blue photoluminescence intensity for the porous silicon with HfO2 filling into microcavities

    PubMed Central

    Jiang, Ran; Du, Xianghao; Sun, Weideng; Han, Zuyin; Wu, Zhengran

    2015-01-01

    With HfO2 filled into the microcavities of the porous single-crystal silicon, the blue photoluminescence was greatly enhanced at room temperature. On one hand, HfO2 contributes to the light emission with the transitions of the defect levels for oxygen vacancy. On the other hand, the special filling-into-microcavities structure of HfO2 leads to the presence of ferroelectricity, which greatly enhances the blue emission from porous silicon. Since both HfO2 and Si are highly compatible with Si-based electronic industry, combined the low-cost and convenient process, the HfO2-filled porous Si shows a promising application prospect. PMID:26503804

  20. Enhancement of the blue photoluminescence intensity for the porous silicon with HfO2 filling into microcavities

    NASA Astrophysics Data System (ADS)

    Jiang, Ran; Du, Xianghao; Sun, Weideng; Han, Zuyin; Wu, Zhengran

    2015-10-01

    With HfO2 filled into the microcavities of the porous single-crystal silicon, the blue photoluminescence was greatly enhanced at room temperature. On one hand, HfO2 contributes to the light emission with the transitions of the defect levels for oxygen vacancy. On the other hand, the special filling-into-microcavities structure of HfO2 leads to the presence of ferroelectricity, which greatly enhances the blue emission from porous silicon. Since both HfO2 and Si are highly compatible with Si-based electronic industry, combined the low-cost and convenient process, the HfO2-filled porous Si shows a promising application prospect.

  1. Temperature and stress polarity-dependent dielectric breakdown in ultrathin gate oxides

    NASA Astrophysics Data System (ADS)

    Eriguchi, Koji; Niwa, Masaaki

    1998-10-01

    Temperature and stress polarity-dependent dielectric breakdown in thin silicon dioxides has been carefully investigated. The experimental data show that the time to breakdown under a constant-current injection has two kinks around 330 and 230 K for 4- and 10-nm-thick oxides under both stress polarities. It has been found that thinner oxides have a stronger temperature dependence (a larger activation energy) even if the field dependence of the activation energy is taken into consideration, and also that, from the gate voltage shift during the constant-current injection, the postbreakdown characteristics strongly depends on the stress polarity for thinner oxides.

  2. Optimal migration path of Ag in HfO2: A first-principles study

    NASA Astrophysics Data System (ADS)

    Dai, Yue-Hua; Chen, Zhen; Jin, Bo; Li, Ning; Li, Xiao-Feng

    2015-07-01

    First-principles calculations are used to investigate the migration path of Ag in the HfO2-based resistive random access memory (ReRAM). The formation energy calculation suggests that there are two different sites (site 1 and site 3) for the incorporation of Ag atoms into the HfO2 unit cell. Thermodynamic analysis shows that the motion of Ag atom in the HfO2 supercell appears to be anisotropic, which is due to the fact that the Ag atom at site 3 moves along the orientation, but the Ag atom at site 1 moves along the [001] orientation. The migration barriers of the Ag atoms hopping between neighboring unit cells are calculated along five different orientations. Difficulty in producing motion of the Ag atom varies with the migration barrier: this motion is minimized along orientation. Furthermore, The optimal circulation path for Ag migration within the HfO2 supercells is obtained, and is found to be approximately along the orientation. Therefore, it is proposed that the positive voltage should be applied along this orientation, the conduction filament may form more easily, which could improve the response time and reduce the power consumption in ReRAM applications. Project supported by the National Natural Science Foundation of China (Grant No. 61376106).

  3. Thermal Conductivity and Water Vapor Stability of HfO2-based Ceramic Coating Materials

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Fox, Dennis S.; Bansal, Narottam P.; Miller, Robert A.

    2004-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2- 15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermaVenvironmenta1 barrier coating applications will also be discussed.

  4. Thermal Conductivity and Water Vapor Stability of Ceramic HfO2-Based Coating Materials

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Fox, Dennis S.; Bansal, Narottam P.; Miller, Robert A.

    2004-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2-15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications will also be discussed.

  5. Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium silicate dielectric films on silicon

    E-print Network

    Garfunkel, Eric

    1 Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium of ultra-thin films of mixed yttrium, silicon, and oxygen, formed by oxidation of metal on clean and pre-treated silicon. XPS and MEIS analyses indicate that oxidation of yttrium on bare silicon results in a fully

  6. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    PubMed Central

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-01-01

    Based on micro-Raman spectroscopy (?RS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, ?RS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors. PMID:26311131

  7. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    NASA Astrophysics Data System (ADS)

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-08-01

    Based on micro-Raman spectroscopy (?RS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, ?RS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  8. Thermodynamic mixing properties of the UO2-HfO2 solid solution: Density functional theory and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Yuan, Ke; Ewing, Rodney C.; Becker, Udo

    2015-03-01

    HfO2 is a neutron absorber and has been mechanically mixed with UO2 in nuclear fuel in order to control the core power distribution. During nuclear fission, the temperature at the center of the fuel pellet can reach above 1300 K, where hafnium may substitute uranium and form the binary solid solution of UO2-HfO2. UO2 adopts the cubic fluorite structure, but HfO2 can occur in monoclinic, tetragonal, and cubic structures. The distribution of Hf and U ions in the UO2-HfO2 binary and its atomic structure influence the thermal conductivity and melting point of the fuel. However, experimental data on the UO2-HfO2 binary are limited. Therefore, the enthalpies of mixing of the UO2-HfO2 binary with three different structures were calculated in this study using density functional theory and subsequent Monte Carlo simulations. The free energy of mixing was obtained from thermodynamic integration of the enthalpy of mixing over temperature. From the ?G of mixing, a phase diagram of the binary was obtained. The calculated UO2-HfO2 binary forms extensive solid solution across the entire compositional range, but there are a variety of possible exsolution phenomena associated with the different HfO2 polymorphs. As the structure of the HfO2 end member adopts lower symmetry and becomes less similar to cubic UO2, the miscibility gap of the phase diagram expands, accompanied by an increase in cell volume by 7-10% as the structure transforms from cubic to monoclinic. Close to the UO2 end member, which is relevant to the nuclear fuel, the isometric uranium-rich solid solutions exsolve as the fuel cools, and there is a tendency to form the monoclinic hafnium-rich phase in the matrix of the isometric, uranium-rich solid solution phase.

  9. Flexible FETs using ultrathin Si microwires embedded in solution processed dielectric and metal layers

    NASA Astrophysics Data System (ADS)

    Khan, S.; Yogeswaran, N.; Taube, W.; Lorenzelli, L.; Dahiya, R.

    2015-12-01

    This work presents a novel manufacturing route for obtaining high performance bendable field effect transistors (FET) by embedding silicon (Si) microwires (2.5 ?m thick) in layers of solution-processed dielectric and metallic layers. The objective of this study is to explore heterogeneous integration of Si with polymers and to exploit the benefits of both microelectronics and printing technologies. Arrays of Si microwires are developed on silicon on insulator (SOI) wafers and transfer printed to polyimide (PI) substrate through a polydimethylsiloxane (PDMS) carrier stamp. Following the transfer printing of Si microwires, two different processing steps were developed to obtain top gate top contact and back gate top contact FETs. Electrical characterizations indicate devices having mobility as high as 117.5?cm2 V?1 s?1. The fabricated devices were also modeled using SILVACO Atlas. Simulation results show a trend in the electrical response similar to that of experimental results. In addition, a cyclic test was performed to demonstrate the reliability and mechanical robustness of the Si ?-wires on flexible substrates.

  10. A thorough investigation of the progressive reset dynamics in HfO2-based resistive switching structures

    NASA Astrophysics Data System (ADS)

    Lorenzi, P.; Rao, R.; Irrera, F.; Suñé, J.; Miranda, E.

    2015-09-01

    According to previous reports, filamentary electron transport in resistive switching HfO2-based metal-insulator-metal structures can be modeled using a diode-like conduction mechanism with a series resistance. Taking the appropriate limits, the model allows simulating the high (HRS) and low (LRS) resistance states of the devices in terms of exponential and linear current-voltage relationships, respectively. In this letter, we show that this simple equivalent circuit approach can be extended to represent the progressive reset transition between the LRS and HRS if a generalized logistic growth model for the pre-exponential diode current factor is considered. In this regard, it is demonstrated here that a Verhulst logistic model does not provide accurate results. The reset dynamics is interpreted as the sequential deactivation of multiple conduction channels spanning the dielectric film. Fitting results for the current-voltage characteristics indicate that the voltage sweep rate only affects the deactivation rate of the filaments without altering the main features of the switching dynamics.

  11. Response-surface-based optimization of 0.1-?m PMOSFETs with ultrathin gate stack dielectrics

    NASA Astrophysics Data System (ADS)

    Srivastava, Anadi; Osburn, Carlton M.

    1998-09-01

    An optimal design for 0.1 micrometer PMOS, consistent with SIA-NTRS Roadmap projections, is developed using a Response Surface methodology (RSM). The impact of four different low thermal budget growth and deposition gate dielectric processes (Furnace oxidation, Rapid Thermal Oxidation (RTO), Rapid Thermal CVD (RTCVD) and Remote Plasma Enhanced CVD (RPECVD) on the design optimization is examined. A Design Of Experiments (DOE) approach was independently employed in each case with simulated baseline surface channel PMOSFET structures having a 2.0 nm gate oxide to statistically explore the channel and extension junction parameter spaces. Channel and extension junction parameters were separately optimized, with channel optimization performed for both doubly-implanted and uniformly doped channels. The condition for constrained optimization was the maximization of Isat at the NTRS Roadmap specified Ioff value of 3 nA/micrometer. A 20% manufacturing tolerance in channel length was factored into the optimization strategy by measuring both Isat and Ioff under their respective worst case tolerance conditions. Optimal designs with modestly differing implant specifications but exhibiting largely comparable performance characteristics were identified for each gate stack. Excellent current drivability of 279 (mu) A/micrometer was obtained at the nominal Leff of 70 nm. Optimized doubly-implanted channels provide 7.5% higher current than the uniformly doped ones. Optimum extension junction design was achieved by a high surface concentration of 2 X 1020 cm-3, extension depth of 32 nm and spacer width of 49 nm, and the analysis clearly revealed that a necessary condition for junction optimization was the onset of drain decoupling from the channel.

  12. Effect of calcination temperature on phase transformation of HfO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Tripathi, S. K.; Kaur, Charanpreet; Kaur, Ramneek; Kaur, Jagdish

    2015-08-01

    Oxides nanomaterials exhibit unique physical, chemical and structural properties and motivated a big research that focus in the integration of these materials for various optoelectronic device applications. In present work, hafnium oxide (HfO2) nanoparticles (NPs) have been synthesized using precipitation method. Hafnium tetrachloride and sodium hydroxide has been used as starting precursors. Prepared oxide material has been characterized by X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) and UV-Vis spectroscopy. The phase transformation from amorphous to monoclinic is observed with the increase in calcination temperature from 500 °C and 800 °C. In FTIR spectra, the characteristic bands at ? ˜ 758.53 and 509.57 cm-1 reveals the monoclinic phase of prepared HfO2 NPs. UV-Vis spectroscopy shows an absorption peak at 204 nm and the bandgap calculated is 6.07 eV.

  13. Design and Fabrication of Interdigital Nanocapacitors Coated with HfO2

    PubMed Central

    González, Gabriel; Kolosovas-Machuca, Eleazar Samuel; López-Luna, Edgar; Hernández-Arriaga, Heber; González, Francisco Javier

    2015-01-01

    In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers. PMID:25602271

  14. Mechanisms for plasma etching of HfO2 gate stacks with Si selectivity and photoresist trimming

    E-print Network

    Kushner, Mark

    Mechanisms for plasma etching of HfO2 gate stacks with Si selectivity and photoresist trimming its etching.4 In this article, the plasma etching of HfO2 gate stacks is computationally investigated with an as a replacement for SiO2. To speed the rate of processing, it is desirable to etch the gate stack e.g., metal gate

  15. Influence of phosphorous precursors on spectroscopic properties of Er3+-activated SiO2-HfO2-P2O5 planar waveguides

    NASA Astrophysics Data System (ADS)

    Vasilchenko, I.; Carpentiero, A.; Chiappini, A.; Chiasera, A.; Vaccari, A.; Lukowiak, A.; Righini, G. C.; Vereshagin, V.; Ferrari, M.

    2014-12-01

    (70-x)SiO2-30HfO2 -xP2O5 (x= 5, 10 mol %) glass planar waveguides activated by 0.5 mol% Er3+ ions were prepared by sol-gel route. Several phosphorous precursors have been investigated for the synthesis of a dielectric stable sol useful for the realization of planar waveguides. The waveguides were investigated by different diagnostic techniques. The optical properties such as refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 632.8 and 543.5 nm by prism coupling technique. Transmission measurements were carried out in order to assess the transparency of the deposited films. Photoluminescence measurements and lifetime decay curves of the Er3+ transition (4I13/2 ? 4I15/2) were performed in order to investigate the role of P2O5.

  16. Fabrication and Electrical Characterization of Ultrathin Crystalline Al2O3 Gate Dielectric Films on Si(100) and Si(111) by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Shahjahan, Mohammad; Takahashi, Nariya; Sawada, Kazuaki; Ishida, Makoto

    2002-12-01

    Fabrication of ultrathin crystalline Al2O3 (equivalent oxide thickness (EOT)=1.5--2 nm) on Si substrates by molecular beam epitaxy (MBE) and the electrical properties of these films were discussed. In the electrical measurements, a high breakdown field (8-10 MV/cm) and extremely low leakage current density ˜ 10-8 A/cm2 at a field of 3 MV/cm were obtained. The dielectric constant of these films was calculated from high-frequency C-V measurement and its value was obtained to be 7.5. The interface state density (Dit) at the crystalline Al2O3/Si interface was calculated from quasi-static capacitance-voltage (C-V) measurement and its value was obtained to be 1--3× 1011 eV-1{\\cdot}cm-2.

  17. High Performance ALD HfO2-Al2O3 Laminate MIM Capacitors for RF and Mixed Signal IC Applications

    E-print Network

    Fu, Li Ming

    High Performance ALD HfO2-Al2O3 Laminate MIM Capacitors for RF and Mixed Signal IC Applications ALD HfO2-Al2O3 laminate metal-insulator-metal (MIM) capacitor is demonstrated for the first time electrical properties and reliability suggest that the ALD HfO2-Al2O3 laminate is a very promising material

  18. Search for ferromagnetism in transition metal doped monoclinic HfO2

    NASA Astrophysics Data System (ADS)

    Seema, K.; Kumar, Ranjan

    2013-02-01

    Electronic and structural properties of the bulk monoclinic (m) phase of HfO2 are calculated using density functional theory as implemented in SIESTA code. We have considered substitutional doping of transition metals (TM) V and Cr in m-hafnia and studied electronic and magnetic properties of the resulting system. We found that TM doped systems are ferromagnetic. Also Cr doped m-hafnia exhibit half-metallic characteristics and posses Curie temperature above room temperature. Therefore TM doped m-hafnia offers the possibility of integration of CMOS with spintronic technology.

  19. Effects of different dopants on switching behavior of HfO2-based resistive random access memory

    NASA Astrophysics Data System (ADS)

    Deng, Ning; Pang, Hua; Wu, Wei

    2014-10-01

    In this study the effects of doping atoms (Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory (RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy (Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.

  20. Band offsets of a ruthenium gate on ultrathin high-oxide films on silicon Sylvie Rangan, Eric Bersch, and Robert Allen Bartynski

    E-print Network

    Garfunkel, Eric

    , and the ruthenium work function that have been directly measured on these samples, the experimental band offsetsBand offsets of a ruthenium gate on ultrathin high- oxide films on silicon Sylvie Rangan, Eric, HfO2, Hf0.7Si0.3O2, and Al2O3 grown on silicon and their shifts upon sequential metallization

  1. Morphology and Photoluminescence of HfO2Obtained by Microwave-Hydrothermal

    PubMed Central

    2009-01-01

    In this letter, we report on the obtention of hafnium oxide (HfO2) nanostructures by the microwave-hydrothermal method. These nanostructures were analyzed by X-ray diffraction (XRD), field-emission gum scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDXS), ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence (PL) measurements. XRD patterns confirmed that this material crystallizes in a monoclinic structure. FEG-SEM and TEM micrographs indicated that the rice-like morphologies were formed due to an increase in the effective collisions between the nanoparticles during the MH processing. The EDXS spectrum was used to verify the chemical compositional of this oxide. UV–vis spectrum revealed that this material have an indirect optical band gap. When excited with 488 nm wavelength at room temperature, the HfO2nanostructures exhibited only one broad PL band with a maximum at around 548 nm (green emission). PMID:20628455

  2. Electronic and magnetic properties of the cation vacancy defect in m -HfO2

    NASA Astrophysics Data System (ADS)

    McKenna, Keith P.; Ramo, David Muñoz

    2015-11-01

    The electronic and magnetic properties of cation vacancies in m -HfO2 are predicted using density functional theory. The hafnium vacancy is found to introduce a series of charge transition levels in the range 0.76-1.67 eV above the valence band maximum associated with holes localized on neighboring oxygen sites. The neutral defect adopts a S =2 spin state, and we compute corresponding g tensors to aid electron experimental identification of the defect by electron spin resonance spectroscopy. We find that separated vacancies exhibit weak ferromagnetic coupling and the interaction is highly anisotropic—being much stronger when mediated by planes of three-coordinated oxygen ions. Further, we characterize the process of thermal detachment of a hole from a neutral vacancy providing an atomistic model for the p -type conductivity observed experimentally at high temperature. These results provide invaluable information on the electronic and magnetic properties of cation vacancies in HfO2 and can aid future experimental identification of these complex defects.

  3. Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating

    NASA Astrophysics Data System (ADS)

    Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Seán. T.

    2014-09-01

    Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

  4. Statistical analysis of random telegraph noise in HfO2-based RRAM devices in LRS

    NASA Astrophysics Data System (ADS)

    Puglisi, Francesco Maria; Pavan, Paolo; Larcher, Luca; Padovani, Andrea

    2015-11-01

    In this work, we present a thorough statistical characterization of Random Telegraph Noise (RTN) in HfO2-based Resistive Random Access Memory (RRAM) cells in Low Resistive State (LRS). Devices are tested under a variety of operational conditions. A Factorial Hidden Markov Model (FHMM) analysis is exploited to extrapolate the properties of the traps causing multi-level RTN in LRS. The trapping and de-trapping of charge carriers into/out of defects located in the proximity of the conductive filament results in a shielding effect on a portion of the conductive filament, leading to the observed RTN current fluctuations. It is found that both oxygen vacancies and oxygen ions defects may be responsible for the observed RTN. The variations of the current observed at subsequent set/reset cycles are instead attributed to the stochastic variations in the filament due to oxidation/reduction processes during reset and set operations, respectively.

  5. Annealing Dependence of Solution-Processed Ultra-Thin ZrOx Films for Gate Dielectric Applications.

    PubMed

    Liu, G X; Liu, A; Meng, Y; Shan, F K; Shin, B C; Lee, W J; Cho, C R

    2015-03-01

    Ultra-thin ZrOx thin films on Si substrates were prepared by sol-gel technique and processed with different methods (baked on hot plate at 150 °C, annealed at 500 °C in furnace, and photo-annealed under UV light). The decomposition of the organic groups and the formation of Zr-O bonding in the ZrOx thin films were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It is found that the ZrOx thin film annealed under UV light shows decent characteristics, including an ultra-small surface roughness, a low leakage current density of 10(-9) A/cm2 at 1 MV/cm, a large breakdown electric field of 9.5 MV/cm, and a large areal capacitance of 775 nF/cm2. PMID:26413638

  6. Dynamics in ultrathin liquid films studied by simultaneous dielectric spectroscopy (DRS) and organic molecular beam deposition (OMBD)

    NASA Astrophysics Data System (ADS)

    Wübbenhorst, M.; Capponi, S.; Napolitano, S.; Rozanski, S.; Couderc, G.; Behrnd, N.-R.; Hulliger, J.

    2010-10-01

    Real-time dielectric relaxation spectroscopy for a molecular beam deposited glass forming liquids is proposed as a versatile approach for the study of the dynamic glass transition in geometric confinement. To achieve the highest sensitivity down to monomolecular organic layers in a wide frequency range (0.1-107 Hz) during simultaneous deposition and desorption, we have used ?m spaced interdigitated electrodes under ultrahigh vacuum conditions. Experiments using glycerol deposited on fused silica at - 40 ?C revealed a dielectric glass transition process for a layer thickness as low as 0.7 nm. While its peak position hardly changes upon thickness reduction, a clear broadening is observed that implies an increasing heterogeneous mobility scenario for the thinnest films caused by molecules being part of a reduced (at the substrate) or enhanced (free surface) mobility layer. This finding is supported by desorption experiments that reveal a strong retardation of the desorption rate for films below 1 nm.

  7. Optical constants of crystalline HfO2 for energy range 140-930 eV

    SciTech Connect

    Filatova, Elena; Sokolov, Andrey; Andre, Jean-Michel; Schaefers, Franz; Braun, Walter

    2010-05-10

    We calculated the optical constants of the monoclinic phase of a HfO2 film from reflection spectra measured using synchrotron radiation in the spectral region from 143 eV to 927 eV, which includes the HfN4,5{sup -}, HfN2,3{sup -}, and OK absorption edges. The calculations were carried out using the Kramers-Kronig relations. It could be shown that the relation R(E){approx}E{sup -4} can be used for extrapolation of the experimental reflection spectrum of HfO2 (and probably of other heavy elements) for energies such that {theta}/{theta}c>3.7.

  8. Pt/Ta2 O5 /HfO2- x /Ti resistive switching memory competing with multilevel NAND flash.

    PubMed

    Yoon, Jung Ho; Kim, Kyung Min; Song, Seul Ji; Seok, Jun Yeong; Yoon, Kyung Jean; Kwon, Dae Eun; Park, Tae Hyung; Kwon, Young Jae; Shao, Xinglong; Hwang, Cheol Seong

    2015-07-01

    Pt/Ta2 O5 /HfO2- x /Ti resistive switching memory with a new circuit design is presented as a feasible candidate to succeed multilevel-cell (MLC) NAND flash memory. This device has the following characteristics: 3 bit MLC, electroforming-free, self-rectifying, much higher cell resistance than interconnection wire resistance, low voltage operation, low power consumption, long-term reliability, and only an electronic switching mechanism, without an ionic-motion-related mechanism. PMID:25973913

  9. Comparative study of non-polar switching behaviors of NiO- and HfO 2-based oxide resistive-RAMs

    NASA Astrophysics Data System (ADS)

    Jousseaume, V.; Fantini, A.; Nodin, J. F.; Guedj, C.; Persico, A.; Buckley, J.; Tirano, S.; Lorenzi, P.; Vignon, R.; Feldis, H.; Minoret, S.; Grampeix, H.; Roule, A.; Favier, S.; Martinez, E.; Calka, P.; Rochat, N.; Auvert, G.; Barnes, J. P.; Gonon, P.; Vallée, C.; Perniola, L.; De Salvo, B.

    2011-04-01

    This paper presents a detailed comparative study of the switching characteristics of resistive memory devices, with NiO or HfO 2 active materials and Pt electrodes, based on identical integration schemes. Material screening and qualification are performed using structural and composition analyses. Preliminary electrical investigations outline the non-polar switching behavior of both HfO 2 and NiO devices. Then, by using a specific test setup, we present a systematic comparative study of HfO 2 and NiO devices, clearly showing the tunability of the electrical characteristics with material type and process. HfO 2 devices lead to largest High Resistance State/Low Resistance State ratios and higher forming voltages compared to NiO cells, while reset voltages are similar. Data retention of both materials show highly stable Low Resistance State, while High Resistance State increases over time under 85 °C baking.

  10. Interfacial and electrical characterization of HfO2/Al2O3/InAlAs structures

    NASA Astrophysics Data System (ADS)

    Wu, Li-fan; Zhang, Yu-ming; Lu, Hong-liang; Zhang, Yi-men

    2015-11-01

    The HfO2/Al2O3 double layer has been deposited by the atomic layer deposition (ALD) technique to a InAlAs epitaxial layer. The chemical composition at the interface was revealed by angle-resolved X-ray photoelectron spectroscopy (XPS). The electrical properties of the ALD-HfO2/Al2O3/InAlAs metal–oxide–semiconductor (MOS) capacitor have been investigated and compared with those of the ALD-HfO2/InAlAs capacitor. It is demonstrated that the insertion of the Al2O3 layer can decrease interfacial oxidation and trap charge formation. Compared with the HfO2/InAlAs capacitor, the HfO2/Al2O3/InAlAs capacitor exhibits better electrical properties with reduced hysteresis and decreasing stretch-out of the capacitance–voltage (C–V) characteristics, and the oxide trapped charge (Qot) value is significantly decreased after inserting the Al2O3 interlayer.

  11. Structural phase transformation of Y2O3 doped HfO2 films grown on Si using atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Majumder, Prodyut; Jursich, Gregory; Takoudis, Christos

    2009-05-01

    HfO2 and Y2O3 films, along with Y2O3-doped HfO2 composite films, have been deposited on Si by means of atomic layer deposition (ALD) using tetrakis(diethylamino)hafnium and tris(ethylcyclopentadienyl)yttrium with water vapor as the oxidizer. The growth rate and structural properties of these films have been investigated by spectral ellipsometry, grazing incidence x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). The film growth temperature dependence of both HfO2 and Y2O3 films indicate overlapping ALD windows in the 250-285°C region, which is critical for ALD of Y2O3-doped HfO2 films. The composition of such films is controlled by altering precursor cycle ratios, and XPS analyses of the resulting films indicate strong correlation between the precursor cycle ratio and the film composition. From structural analyses, the as-deposited HfO2 was found to be amorphous but after annealing at 600°C or higher, it became monoclinic. In contrast, all Y2O3 films whether annealed or not had evidence of cubic crystallinity. Having a cycle ratio of at least 2.5% in a Y2O3-doped HfO2 composite film is observed to induce cubic phase crystallinity in the film after postdeposition annealing at 600°C or greater.

  12. Transport properties of HfO2-x based resistive-switching memories

    NASA Astrophysics Data System (ADS)

    Wang, Zhongrui; Yu, HongYu; Tran, Xuan Anh; Fang, Zheng; Wang, Jinghao; Su, Haibin

    2012-05-01

    Transport measurements of both the dc and the low-frequency ac are performed on Pt/HfO2-x/TiN resistive-switching memory cells at various temperatures. The conductance of the pristine cells has a power law ?STN relationship with temperature and frequency. To account for the much larger conductance of both the high resistance states (HRSs) and the low resistance states (LRSs), an additional conductance term associated with oxygen vacancy filaments is added, which is independent of the cross-sectional area of the memory cell. This additional component of conductance in a HRS is frequency independent but temperature dependent, showing the small polaron originated transport, with an activation energy of 50 (2.1) meV at temperatures above (below) half of the Debye temperature, which agrees with the analysis of the electric field dependence data. The frequency- and temperature-dependent conduction of HRSs indicate the existence of polarization centers which facilitate the transport and make HfO2-x highly polarizable. However, the additional conductance term associated with filaments in LRS, of an order of ˜105 S m-1, exhibits a weak metallic behavior in temperature-dependent measurements. Properties of aligned oxygen vacancy chains on the (1¯11) surface are calculated by first-principles simulation. Through analysis of the partial density of states and spatial distribution of the wave function of impurity states generated by oxygen vacancies, this weak metallic behavior is attributed to the delocalization of the impurity band associated with aligned oxygen vacancies.

  13. The use of angle resolved XPS to measure the fractional coverage of high- k dielectric materials on silicon and silicon dioxide surfaces

    NASA Astrophysics Data System (ADS)

    Mack, P.; White, R. G.; Wolstenholme, J.; Conard, T.

    2006-09-01

    Angle resolved XPS (ARXPS) is a powerful tool for the determination of the thickness of ultra-thin films. In the case of high- k dielectric layers, the technique is capable of measuring the thickness of both the high- k layer and intermediate layers of silicon dioxide or metal silicate. The values for layer thickness are in close agreement with those generated by a variety of other techniques. As well as knowing the thickness of these layers, it is important to determine whether the layers are continuous or whether the coverage of the high- k layer is only partial. Using ARXPS, a method has been developed to determine whether the coverage of the high- k material is continuous and, if not, to calculate the fraction of the surface that is covered. The method is described with reference to the layers of Al 2O 3 grown on SiO 2 using atomic layer deposition (ALD). The method is then applied to HfO 2 layers produced using ALD on silicon wafers whose surfaces had received three different types of surface treatment. The way in which the layers grow and the nature of the resulting layer were found to depend upon the pre-treatment method. For example, growth on a thermal silicon dioxide surface resulted in complete coverage of HfO 2 after fewer ALD cycles than layers grown on an H-terminated surface. The results from ARXPS are compared with those obtained from ToF SIMS that have been shown earlier to be a valuable alternative to the LEIS analysis [1].

  14. Atomic Layer Deposition of HfO2 onto Si Using Hf(NMe2)4

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Chan; Cho, Yong Seok; Heup Moon, Sang

    2009-06-01

    The temperature window for the atomic layer deposition (ALD) of HfO2 onto Si using Hf(NMe2)4 [tetrakis(dimethylamino)hafnium] as an Hf precursor was determined based on the thermal decomposition characteristics of Hf(NMe2)4, as observed by temperature-programmed decomposition in an ultra-high vacuum. The growth rate of the HfO2 obtained in the temperature window was ca. 1.2 Å/cycle. The prepared film had electrical properties suitable for use in complementary metal-oxide-semiconductor (CMOS) devices, showing an equivalent-oxide thickness (EOT) of 2.5 nm and a leakage current density of 1.3 ×10-6 A/cm2 at -1 V. The leakage current was three orders of magnitude lower than that of SiO2 with the same EOT. The lower current leakage was obtained because N atoms in the Hf(NMe2)4 formed an SiNx interlayer by reaction with the Si substrate during the ALD, as confirmed by in-situ X-ray photoelectron spectroscopy (XPS) and by the analysis of residue on the substrate after the decomposition of the Hf precursor.

  15. An ultrathin Zr(Ge) alloy film as an exhaustion interlayer combined with Cu(Zr) seed layer for the Cu/porous SiOC:H dielectric integration

    SciTech Connect

    Liu, B.; Song, Z. X.; Li, Y. H.; Xu, K. W.

    2008-10-27

    A highly reliable interface of an ultrathin Zr(Ge) exhaustion interlayer between Cu(Zr) film and porous SiOC:H (p-SiOC:H) dielectric has been developed in the present work. After being processed at a moderate elevated temperature (say, 450 deg. C), a self-formed nanomultilayer of CuGe{sub x}/ZrO{sub x}(ZrSi{sub y}O{sub x}) was produced at the interface of Cu(Zr)/p-SiOC:H film stacks, which showed strong ability to effectively hinder Cu atoms diffusion into p-SiOC:H film and free Si atoms diffusion into Cu film. The mechanism involving the thermal stability of the films system is analyzed based on detailed characterization studies.

  16. Germanium nanowire field-effect transistors with SiO2 and high-HfO2 gate dielectrics

    E-print Network

    Javey, Ali

    Germanium nanowire field-effect transistors with SiO2 and high- HfO2 gate dielectrics Dunwei Wang­6 Currently, for further device scaling and miniatur- ization, germanium is of renewed interest characteristics are obtained with these de- vices. GeNWs were synthesized by CVD of germanium at 275 °C on Au

  17. Characterization of HfO2-SiO2 rugate multilayers deposited by ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Rauhut, R.; Nehls, K.; Mechold, L.

    2014-10-01

    Ion beam sputtering (IBS) is a deposition technique being well known for resulting in very dense and damage resistant coatings due to high kinetic energies of the sputtered atoms. While different layers are deposited homogeneously, abrupt interfaces between the materials are the most susceptible part of the stack. Therefore we aim for an improvement of the laser damage threshold by sputtering material mixtures. Using a target with high- and low-index material next to each other, arbitrary refractive indices can be realized by adjusting the target axis. Our material system of choice is HfO2- SiO2, already yielding good results with non-rugate coatings. A comparison in terms of laser damage threshold between these designs and varying refractive index coatings will be shown.

  18. Dual bipolar resistive switching in the sub-forming regime of HfO2 resistive switching devices

    NASA Astrophysics Data System (ADS)

    Recher, Shani; Yalon, Eilam; Ritter, Dan; Riess, Ilan; Salzman, Joseph

    2015-09-01

    Resistive switching in HfO2 in the sub-forming regime (before an electroforming step had been fully performed) is studied by electrical measurements using a very low current compliance of 1 ?A. Electroforming under low current limitation results in reduced self-heating and partial filament formation. Following the reset process in this sub-forming regime, the device fully recovers its pristine resistive state. Furthermore, a dual bipolar resistive switching (DBRS) effect is observed, which we model as two antiparallel bipolar resistive switches. We attribute this phenomenon to intermittent formation and rupture of filaments originating from opposite electrodes. Following the rupture of a filament, originating from one of the electrodes, another filament originating from the opposite electrode is formed.

  19. The Development of HfO2-Rare Earth Based Oxide Materials and Barrier Coatings for Thermal Protection Systems

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Harder, Bryan James

    2014-01-01

    Advanced hafnia-rare earth oxides, rare earth aluminates and silicates have been developed for thermal environmental barrier systems for aerospace propulsion engine and thermal protection applications. The high temperature stability, low thermal conductivity, excellent oxidation resistance and mechanical properties of these oxide material systems make them attractive and potentially viable for thermal protection systems. This paper will focus on the development of the high performance and high temperature capable ZrO2HfO2-rare earth based alloy and compound oxide materials, processed as protective coating systems using state-or-the-art processing techniques. The emphasis has been in particular placed on assessing their temperature capability, stability and suitability for advanced space vehicle entry thermal protection systems. Fundamental thermophysical and thermomechanical properties of the material systems have been investigated at high temperatures. Laser high-heat-flux testing has also been developed to validate the material systems, and demonstrating durability under space entry high heat flux conditions.

  20. Voltage and Power-Controlled Regimes in the Progressive Unipolar RESET Transition of HfO2-Based RRAM

    PubMed Central

    Long, Shibing; Perniola, Luca; Cagli, Carlo; Buckley, Julien; Lian, Xiaojuan; Miranda, Enrique; Pan, Feng; Liu, Ming; Suñé, Jordi

    2013-01-01

    Resistive switching (RS) based on the formation and rupture of conductive filament (CF) is promising in novel memory and logic device applications. Understanding the physics of RS and the nature of CF is of utmost importance to control the performance, variability and reliability of resistive switching memory (RRAM). Here, the RESET switching of HfO2-based RRAM was statistically investigated in terms of the CF conductance evolution. The RESET usually combines an abrupt conductance drop with a progressive phase ending with the complete CF rupture. RESET1 and RESET2 events, corresponding to the initial and final phase of RESET, are found to be controlled by the voltage and power in the CF, respectively. A Monte Carlo simulator based on the thermal dissolution model of unipolar RESET reproduces all of the experimental observations. The results contribute to an improved physics-based understanding on the switching mechanisms and provide additional support to the thermal dissolution model. PMID:24121547

  1. The role of pulse length in target poisoning during reactive HiPIMS: application to amorphous HfO2

    NASA Astrophysics Data System (ADS)

    Ganesan, R.; Murdoch, B. J.; Treverrow, B.; Ross, A. E.; Falconer, I. S.; Kondyurin, A.; McCulloch, D. G.; Partridge, J. G.; McKenzie, D. R.; Bilek, M. M. M.

    2015-06-01

    In conventional reactive magnetron sputtering, target poisoning frequently leads to an instability that requires the reactive gas flow rate to be actively regulated to maintain a constant composition of the deposited layers. Here we demonstrate that the pulse length in high power impulse magnetron sputtering (HiPIMS) is important for determining the surface conditions on the target that lead to poisoning. By increasing the pulse length, a smooth transition can be achieved from a poisoned target condition (short pulses) to a quasi-metallic target condition (long pulses). Appropriate selection of pulse length eliminates the need for active regulation, enabling stable reactive magnetron sputter deposition of stoichiometric amorphous hafnium oxide (HfO2) from a Hf target. A model is presented for the reactive HiPIMS process in which the target operates in a partially poisoned mode with a distribution of oxide on its surface that depends on the pulse length.

  2. Soft x-ray photoemission studies of the HfO2 SiO2 Si system S. Sayan and E. Garfunkela)

    E-print Network

    Garfunkel, Eric

    using the measured band-offset and work-function values. Lucovsky and co-workers studied band offsets- quality low-defect-density interface with silicon. When high- k materials such as ZrO2 , HfO2 , etc., are bonded directly to silicon they present higher interface state densities than are observed in the SiO2

  3. Journal of the Korean Physical Society, Vol. 51, No. 2, August 2007, pp. 647650 Band Alignments in Oxygen-Deficient HfO2/Si(100) Interfaces

    E-print Network

    Oh, Se-Jung

    in Oxygen-Deficient HfO2/Si(100) Interfaces Deok-Yong Cho School of Physics & Astronomy and Center and Si(100) by using photoelectron spectroscopy with X-ray and ultraviolet photon sources. The Fermi and from the onset energies of secondary electrons in the ultraviolet photoemission spectra. Considering

  4. Effect of Annealing on Physical and Electrical Properties of Ultrathin Crystalline ?-Al2O3 High-k Dielectric Deposited on Si Substrates

    NASA Astrophysics Data System (ADS)

    Shahjahan, Mohammad; Okada, Takayuki; Sawada, Kazuaki; Ishida, Makoto

    2004-08-01

    Ultrathin crystalline ?-Al2O3 films with an equivalent oxide thickness (EOT) of 1.3 nm to 2.5 nm have been fabricated on Si substrates by molecular beam epitaxy and annealed in various atmospheres at different temperatures (300-700°C). The effect of the annealing on the chemical composition, crystalline property, surface morphology and electrical properties of the ultrathin ?-Al2O3 films has been studied. An improvement in the electrical properties after annealing was observed. It was also observed that the nitrogen atoms were incorporated into the ?-Al2O3 (?-Al2O3:N) films during annealing at higher temperatures. No detectable pits or pinholes were observed on the surfaces after annealing and the crystalline property remained unchanged during annealing.

  5. Electrical active defects in HfO2 based metal/oxide/metal devices

    NASA Astrophysics Data System (ADS)

    El Kamel, F.

    2016-01-01

    Dielectric as well as thermally stimulated current measurements were performed on metal/HfO2/Pt capacitors in order to study the electrical active defects in hafnia thin films. Two thermally activated relaxation processes have been carried out from both measurements. At low temperatures, the relaxation process can be ascribed to the shallow traps level localized at 0.65?eV and generally evidenced by the second ionization of oxygen vacancies. At high temperatures, the relaxation process arises from the diffusion of positively charged oxygen vacancies by overcoming an energetic barrier of about 1?eV.

  6. High-performance self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors by in-situ atomic-layer-deposited HfO2

    NASA Astrophysics Data System (ADS)

    Lin, T. D.; Chang, W. H.; Chu, R. L.; Chang, Y. C.; Chang, Y. H.; Lee, M. Y.; Hong, P. F.; Chen, Min-Cheng; Kwo, J.; Hong, M.

    2013-12-01

    Self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors (MOSFETs) have been fabricated using the gate dielectrics of in-situ directly atomic-layer-deposited (ALD) HfO2 followed by ALD-Al2O3. There were no surface pretreatments and no interfacial passivation/barrier layers prior to the ALD. TiN/Al2O3 (4 nm)/HfO2 (1 nm)/In0.53Ga0.47As/InP MOS capacitors exhibited well-behaved capacitance-voltage characteristics with true inversion behavior, low leakage current densities of ˜10-8 A/cm2 at ±1 MV/cm, and thermodynamic stability at high temperatures. Al2O3 (3 nm)/HfO2 (1 nm)/In0.53Ga0.47As MOSFETs of 1 ?m gate length, with 700 °C-800 °C rapid thermal annealing in source/drain activation, have exhibited high extrinsic drain current (ID) of 1.5 mA/?m, transconductance (Gm) of 0.84 mS/?m, ION/IOFF of ˜104, low sub-threshold swing of 103 mV/decade, and field-effect electron mobility of 1100 cm2/V . s. The devices have also achieved very high intrinsic ID and Gm of 2 mA/?m and 1.2 mS/?m, respectively.

  7. Surface-directed spinodal decomposition in the pseudobinary alloy (HfO2)x(SiO2)1-x

    NASA Astrophysics Data System (ADS)

    Liu, J.; Wu, X.; Lennard, W. N.; Landheer, D.; Dharma-Wardana, M. W. C.

    2010-06-01

    Hf silicate films (HfO2)0.25(SiO2)0.75 with thicknesses in the range 4-20 nm were grown on silicon substrate by atomic layer deposition at 350 °C. Hf distributions in as-grown and 800 °C annealed films were investigated by high resolution transmission electron microscopy (HRTEM), angle-resolved x-ray photoelectron spectroscopy (ARXPS), and medium energy ion scattering (MEIS). HRTEM images show a layered structure in films thinner than 8 nm. The ARXPS data also reveal a nonuniform distribution of Hf throughout the film depth. Diffusion of SiO2 to the film surface after a longer time anneal was observed by MEIS. All these observations provide evidence for surface-directed spinodal decomposition in the pseudobinary (HfO2)x(SiO2)1-x alloy system.

  8. Modelling of oxygen vacancy aggregates in monoclinic HfO2: can they contribute to conductive filament formation?

    PubMed

    Bradley, Samuel R; Bersuker, Gennadi; Shluger, Alexander L

    2015-10-21

    Formation of metal rich conductive filaments and their rearrangements determine the switching characteristics in HfO2 based resistive random access memory (RRAM) devices. The initiation of a filament formation process may occur either via aggregation of pre-existing vacancies randomly distributed in the oxide or via generation of new oxygen vacancies close to the pre-existing ones. We evaluate the feasibility of vacancy aggregation processes by calculating the structures and binding energies of oxygen vacancy aggregates consisting of 2, 3 and 4 vacancies in bulk monoclinic (m)-HfO2 using density functional theory (DFT). We demonstrate that formation of neutral oxygen vacancy aggregates is accompanied by small energy gain, which depends on the size and shape of the aggregate. In the most strongly bound configurations, vacancies are unscreened by Hf cations and form voids within the crystal, with the larger aggregates having larger binding energy per vacancy (-0.11 to??-0.18?eV). The negatively charged di-vacancy was found to have similar binding energies to the neutral one, while the positively charged di-vacancy was found to be unstable. Thus aggregation process of either neutral or negatively charged oxygen vacancies is energetically feasible. PMID:26414778

  9. Wide band antireflective coatings Al2O3 / HfO2 / MgF2 for UV region

    NASA Astrophysics Data System (ADS)

    Winkowski, P.; Marsza?ek, Konstanty W.

    2013-07-01

    Deposition technology of the three layers antireflective coatings consists of hafnium compound are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5x10-5 mbar in presence of oxygen and fluoride films by thermal evaporation. Substrate temperature was 250°C. Coatings were deposited onto optical lenses made from quartz glass (Corning HPFS). Thickness and deposition rate were controlled by thickness measuring system Inficon XTC/2. Simulations leading to optimization of thickness and experimental results of optical measurements carried during and after deposition process were presented. Physical thickness measurements were made during deposition process and were equal to 43 nm/74 nm/51 nm for Al2O3 / HfO2 / MgF2 respectively. Optimization was carried out for ultraviolet region from 230nm to the beginning of visible region 400 nm. In this region the average reflectance of the antireflective coating was less than 0.5% in the whole range of application.

  10. Modelling of oxygen vacancy aggregates in monoclinic HfO2: can they contribute to conductive filament formation?

    NASA Astrophysics Data System (ADS)

    Bradley, Samuel R.; Bersuker, Gennadi; Shluger, Alexander L.

    2015-09-01

    Formation of metal rich conductive filaments and their rearrangements determine the switching characteristics in HfO2 based resistive random access memory (RRAM) devices. The initiation of a filament formation process may occur either via aggregation of pre-existing vacancies randomly distributed in the oxide or via generation of new oxygen vacancies close to the pre-existing ones. We evaluate the feasibility of vacancy aggregation processes by calculating the structures and binding energies of oxygen vacancy aggregates consisting of 2, 3 and 4 vacancies in bulk monoclinic (m)-HfO2 using density functional theory (DFT). We demonstrate that formation of neutral oxygen vacancy aggregates is accompanied by small energy gain, which depends on the size and shape of the aggregate. In the most strongly bound configurations, vacancies are unscreened by Hf cations and form voids within the crystal, with the larger aggregates having larger binding energy per vacancy (-0.11 to??-0.18?eV). The negatively charged di-vacancy was found to have similar binding energies to the neutral one, while the positively charged di-vacancy was found to be unstable. Thus aggregation process of either neutral or negatively charged oxygen vacancies is energetically feasible.

  11. Sub-30 nm InAs Quantum-Well MOSFETs with Self-aligned Metal Contacts and Sub-1 nm EOT HfO2 Insulator

    E-print Network

    del Alamo, Jesús A.

    budget, gate-last process that uses RIE extensively and an entirely lift-off free process in the frontend. This is the only lift-off step in the backend of the process. The final gate length is defined by the recess1 Sub-30 nm InAs Quantum-Well MOSFETs with Self-aligned Metal Contacts and Sub-1 nm EOT HfO2

  12. Subwavelength gratings on a free-standing HfO2 membrane for out-of-plane coupling of visible light

    NASA Astrophysics Data System (ADS)

    Liu, Qifa; Wang, Wei; Sa, Tongliang; He, Shumin; Li, Xin; Zhu, Gangyi; Wang, Yongjin

    2015-10-01

    Subwavelength grating couplers implemented on free-standing HfO2 membrane are proposed for out-of-plane coupling of visible light. The device is realized by double-side fabrication, which combines front patterning of grating grooves with a back-releasing of the Si substrate. The free-standing HfO2 membrane with diameter ~200 ?m and thickness 200 nm is fabricated by including an auxiliary structure into the membrane to release residual stress. The fabricated grating parameters are characterized by scanning electron microscope and atomic force microscope. TE and TM light coupling into and out of the planar membrane waveguide is thoroughly investigated by a numerical finite element method simulation and experiment. Two pairs of gratings with different periods 350 and 330 nm, and filling factors 0.4 and 0.6, but the same etching depth 70 nm, were prepared. TE and TM light entered and exited the planar membrane through the grating coupling. The removal of the substrate suppresses radiation leakage. The coupling can be tuned by controlling the grating period, filling factor, and light incident angles. Free-standing HfO2 planar photonics in the visible spectrum may be used to realize specialized or highly sensitive sensors, beam splitters, or display components, and for particular wavelength extraction.

  13. Atomic scale characterization of HfO2/Al2O3 thin films grown on nitrided and oxidized Si substrates

    NASA Astrophysics Data System (ADS)

    Nishimura, T.; Okazawa, T.; Hoshino, Y.; Kido, Y.; Iwamoto, K.; Tominaga, K.; Nabatame, T.; Yasuda, T.; Toriumi, A.

    2004-12-01

    One and three bilayers of HfO2(9Å )/Al2O3(3Å) thin films were grown by atomic layer chemical-vapor deposition on Si(001) substrates whose surfaces were nitrided or oxidized. The films as-grown and postannealed in an ultrahigh vacuum were analyzed by atomic force microscopy, photoelectron spectroscopy, and medium energy ion scattering. For the one- and three-bilayer films grown on the nitrided Si substrates, the HfO2 and Al2O3 layers are mixed to form Hf aluminates at temperatures above 600°C. The mixed Hf aluminate layer is partly decomposed into HfO2 and Al2O3 grains and Al2O3 segregates to the surface by postannealing at 900°C. Complete decomposition takes place at 1000°C and the surface is covered with Al2O3. The surfaces are uniform and almost flat up to 900°C but are considerably roughened at 1000°C due to the complete decomposition of the Hf aluminate layer. In contrast, for one- bilayer films stacked on the oxidized Si substrates, Hf silicate layers, including Hf aluminate, are formed by annealing at 600-800°C. At temperatures above 900°C, HfSi2 grows and Al oxide escapes from the surface.

  14. CMUTs with High-K Atomic Layer Deposition Dielectric Material Insulation Layer

    PubMed Central

    Xu, Toby; Tekes, Coskun; Degertekin, F. Levent

    2014-01-01

    Use of high-? dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SixNy) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2 such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD SixNy and 100-nm HfO2 insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure. PMID:25474786

  15. CMUTs with high-K atomic layer deposition dielectric material insulation layer.

    PubMed

    Xu, Toby; Tekes, Coskun; Degertekin, F

    2014-12-01

    Use of high-? dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (Six)Ny)) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2) such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD Six)Ny) and 100-nm HfO2) insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure. PMID:25474786

  16. Excellent resistive switching properties of atomic layer-deposited Al2O3/HfO2/Al2O3 trilayer structures for non-volatile memory applications

    NASA Astrophysics Data System (ADS)

    Wang, Lai-Guo; Qian, Xu; Cao, Yan-Qiang; Cao, Zheng-Yi; Fang, Guo-Yong; Li, Ai-Dong; Wu, Di

    2015-03-01

    We have demonstrated a flexible resistive random access memory unit with trilayer structure by atomic layer deposition (ALD). The device unit is composed of Al2O3/HfO2/Al2O3-based functional stacks on TiN-coated Si substrate. The cross-sectional HRTEM image and XPS depth profile of Al2O3/HfO2/Al2O3 on TiN-coated Si confirm the existence of interfacial layers between trilayer structures of Al2O3/HfO2/Al2O3 after 600°C post-annealing. The memory units of Pt/Al2O3/HfO2/Al2O3/TiN/Si exhibit a typical bipolar, reliable, and reproducible resistive switching behavior, such as stable resistance ratio (>10) of OFF/ON states, sharp distribution of set and reset voltages, better switching endurance up to 103 cycles, and longer data retention at 85°C over 10 years. The possible switching mechanism of trilayer structure of Al2O3/HfO2/Al2O3 has been proposed. The trilayer structure device units of Al2O3/HfO2/Al2O3 on TiN-coated Si prepared by ALD may be a potential candidate for oxide-based resistive random access memory.

  17. Positive-bias gate-controlled metal–insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics

    PubMed Central

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-01-01

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal–insulator transitions. Metal–insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal–insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal–insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal–insulator transitions, paving the pathway for developing functional field effect transistors. PMID:26657761

  18. Positive-bias gate-controlled metal-insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics.

    PubMed

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-01-01

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal-insulator transitions. Metal-insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal-insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal-insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal-insulator transitions, paving the pathway for developing functional field effect transistors. PMID:26657761

  19. Optical and Structural Properties of Ultra-thin Gold Films

    E-print Network

    Kossoy, Anna; Simakov, Denis; Leosson, Kristjan; Kéna-Cohen, Stéphane; Maier, Stefan A

    2014-01-01

    Realizing laterally continuous ultra-thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra-thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3-mercaptopropyl) trimethoxysilane prior to deposition. Void-free fi lms with deposition thickness as low as 5.4 nm are realized and remain structurally stable at room temperature. Based on detailed structural analysis of the fi lms by specular and diffuse X-ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra-thin films can be accounted for using the bulk dielectric function of gold. However, it is important to take into account the non-abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra-thin films (film thickness...

  20. Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

    NASA Astrophysics Data System (ADS)

    Marsza?ek, Konstanty; Winkowski, Pawe?; Jaglarz, Janusz

    2014-01-01

    Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

  1. Bandgap engineering of tunnel oxide with multistacked layers of Al2O3/HfO2/SiO2 for Au-nanocrystal memory application

    NASA Astrophysics Data System (ADS)

    Lo, Yun-Shan; Liu, Ke-Chih; Wu, Jyun-Yi; Hou, Cheng-Hao; Wu, Tai-Bor

    2008-09-01

    Charge storage characteristics of metal-oxide-semiconductor (MOS) structure containing Au nanocrystals on tunnel oxide composed of triply stacked SiO2, HfO2, and Al2O3 layers were studied. Significantly high charge injection and detrapping efficiency for program and erase operations along with a satisfactory long-term charge retention were obtained from the above MOS structure. It is attributed to the bandgap engineering of tunnel oxide with a multistacked concave barrier, from which the effective thickness of the tunneling barrier can be greatly reduced under a moderate bias, while a thick and high barrier is retained for charge retention.

  2. High Dose Neutron Irradiation Performance of Dielectric Mirrors

    SciTech Connect

    Nimishakavi, Anantha Phani Kiran Kumar; Leonard, Keith J; Jellison Jr, Gerald Earle; Snead, Lance Lewis

    2015-01-01

    The study presents the high-dose behavior of dielectric mirrors specifically engineered for radiation-tolerance: alternating layers of Al2O3/SiO2 and HfO2/SiO2 were grown on sapphire substrates and exposed to neutron doses of 1 and 4 dpa at 458 10K in the High Flux Isotope Reactor (HFIR). In comparison to previously reported results, these higher doses of 1 and 4 dpa results in a drastic drop in optical reflectance, caused by a failure of the multilayer coating. HfO2/SiO2 mirrors failed completely when exposed to 1 dpa, whereas the reflectance of Al2O3/SiO2 mirrors reduced to 44%, eventually failing at 4 dpa. Transmission electron microscopy (TEM) observation of the Al2O3/SiO2 specimens showed SiO2 layer defects which increases size with irradiation dose. The typical size of each defect was 8 nm in 1 dpa and 42 nm in 4 dpa specimens. Buckling type delamination of the interface between the substrate and first layer was typically observed in both 1 and 4 dpa HfO2/SiO2 specimens. Composition changes across the layers were measured in high resolution scanning-TEM mode using energy dispersive spectroscopy. A significant interdiffusion between the film layers was observed in Al2O3/SiO2 mirror, though less evident in HfO2/SiO2 system. The ultimate goal of this work is the provide insight into the radiation-induced failure mechanisms of these mirrors.

  3. Interface absorption versus film absorption in HfO2 SiO2 thin-film pairs in the near-ultraviolet and the relation to pulsed-laser damage

    NASA Astrophysics Data System (ADS)

    Papernov, S.; Kozlov, A. A.; Oliver, J. B.

    2014-10-01

    Near-ultraviolet absorption in hafnium oxide and silica oxide thin-film pairs in a configuration strongly departing from the regular quarter-wave-thickness approach has been studied with the goal of separating film and interfacial contributions to absorption and pulsed laser damage. For this purpose, we manufactured a model HfO2 SiO2 thin-film coating containing seven HfO2 layers separated by narrow SiO2 layers and a single-layer HfO2 film in one coating run. The two coatings were characterized by a one-wave total optical thickness for the HfO2 material and similar E-field peak intensity inside the film. Absorption in the electron-beam-deposited films was measured using photothermal heterodyne imaging. By comparing absorption for the seven-layer and single-layer films, one can estimate the partial HfO2 SiO2 interface contribution. Relevance of obtained data to the thin-film pulsed-laser damage was verified by conducting 351-nm, nanosecond-laser-damage measurements and damage-morphology characterization using atomic force microscopy.

  4. On the etching characteristics and mechanisms of HfO2 thin films in CF4/O2/Ar and CHF3/O2/Ar plasma for nano-devices.

    PubMed

    Lim, Nomin; Efremov, Alexander; Yeom, Geun Young; Kwon, Kwang-Ho

    2014-12-01

    The study of etching characteristics and mechanisms for HfO2 and Si in CF4/O2/Ar and CHF3/O2/Ar inductively-coupled plasmas was carried out. The etching rates of HfO2 thin films as well as the HfO2/Si etching selectivities were measured as functions of Ar content in a feed gas (0-50% Ar) at fixed fluorocarbon gas content (50%), gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). Plasma parameters as well as the differences in plasma chemistries for CF4- and CHF3-based plasmas were analyzed using Langmuir probe diagnostics and 0-dimensional plasma modeling. It was found that, in both gas systems, the non-monotonic (with a maximum at about 15-20% Ar) HfO2 etching rate does not correlate with monotonic changes of F atom flux and ion energy flux. It was proposed that, under the given set of experimental conditions, the HfO2 etching process is affected by the factors determining the formation and decomposition kinetics of the fluorocarbon polymer layer. These factor are the fluxes of CF(x) (x = 1, 2) radicals, O atoms and H atoms. PMID:25971118

  5. Integration of lead-free ferroelectric on HfO2/Si (100) for high performance non-volatile memory applications

    PubMed Central

    Kundu, Souvik; Maurya, Deepam; Clavel, Michael; Zhou, Yuan; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Priya, Shashank

    2015-01-01

    We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x = 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFM study reveals that the domains reversal occurs with 180° phase change by applying external voltage, demonstrating its effectiveness for NVM device applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ~106?s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology. PMID:25683062

  6. Ferroelectric-field-effect-enhanced resistance performance of TiN/Si:HfO2/oxygen-deficient HfO2/TiN resistive switching memory cells

    NASA Astrophysics Data System (ADS)

    Jiang, Ran; Wu, Zhengran; Du, Xianghao; Han, Zuyin; Sun, Weideng

    2015-07-01

    Greatly improved resistance performance, including high resistance ratio between the high resistance state and the low resistance state, long-time retention, and reliable endurance, was observed in TiN/Si:HfO2/oxygen-deficient HfO2/TiN memory cells. The enhanced resistance ratio is ascribed to the creation/elimination of an extra barrier in oxygen-deficient HfO2 layer in response to the polarization reversal in the ferroelectric Si:HfO2 layer. Along with the enhanced resistance ratio, the long retention and good endurance make the proposed device a promising candidate for non-volatile resistive memories.

  7. OH- absorption and one-color holographic recording in Ru:Fe:LiNbO3 crystals varied co-doped with HfO2

    NASA Astrophysics Data System (ADS)

    Dai, Li; Yan, Zhehua; Jiao, Shanshan; Xu, Chao; Xu, Yuheng

    2014-12-01

    A series of Ru:Fe:LiNbO3 crystals with various doping concentrations of HfO2 were grown by the Czochralski technique. Their defect structures were analyzed by the infrared absorption spectra and the Lorentzian fitting. The one-color holographic storage characteristics of these crystals were investigated by means of two-wavelength technology. The experimental results showed that fast response time of 12.7 s and high one-color holographic recording sensitivity of 0.53 cm/J were obtained in Hf(5 mol%):Ru:Fe:LiNbO3 crystal, meanwhile the fixed diffraction efficiency was as high as 44.3%. These results indicated Hf, Ru and Fe co-doped LiNbO3 crystals were outstanding media for holographic storage applications.

  8. Atomic layer deposited HfO2 gate dielectrics for low-voltage operating, high-performance poly-(3-hexythiophene) organic thin-film transistors

    E-print Network

    of the most popular channel materials in organic electronics due to its simple solution processibility.R. Berger). Organic Electronics 11 (2010) 1719­1722 Contents lists available at ScienceDirect Organic Elect

  9. HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition Martin M. Franka

    E-print Network

    Garfunkel, Eric

    , Center for Materials Research, Ithaca, New York 14853 Received 13 January 2005; accepted 26 February 2005 their fabrication. We have studied hafnium oxide and aluminum oxide grown on gallium arsenide by atomic layer of the absence of stable passivating native oxides and the high density of slow interface traps Dit

  10. Ultrathin Dielectric Oxide Films On Silicon

    DOEpatents

    Klemperer, Walter G. (Champaign, IL); Lee, Jason (Liverpool, GB); Mikalsen, Erik A. (Urbana, IL); Payne, David A. (Champaign, IL)

    2004-09-21

    A method of making a semiconductor structure includes contacting a surface of a semiconductor with a liquid including Zr.sub.4 (OPr.sup.n).sub.16 to form a modified surface, activating the modified surface, and repeating the contacting and activating to form a layer of zirconia on the semiconductor surface.

  11. Calculation of the electron mobility in III-V inversion layers with high-? dielectrics

    NASA Astrophysics Data System (ADS)

    O'Regan, T. P.; Fischetti, M. V.; Sorée, B.; Jin, S.; Magnus, W.; Meuris, M.

    2010-11-01

    We calculate the electron mobility for a metal-oxide-semiconductor system with a metallic gate, high-? dielectric layer, and III-V substrate, including scattering with longitudinal-optical (LO) polar-phonons of the III-V substrate and with the interfacial excitations resulting from the coupling of insulator and substrate optical modes among themselves and with substrate plasmons. In treating scattering with the substrate LO-modes, multisubband dynamic screening is included and compared to the dielectric screening in the static limit and with the commonly used screening model obtained by defining an effective screening wave vector. The electron mobility components limited by substrate LO phonons and interfacial modes are calculated for In0.53Ga0.47As and GaAs substrates with SiO2 and HfO2 gate dielectrics. The mobility components limited by the LO-modes and interfacial phonons are also investigated as a function of temperature. Scattering with surface roughness, fixed interface charge, and nonpolar-phonons is also included to judge the relative impact of each scattering mechanism in the total mobility for In0.53Ga0.47As with HfO2 gate dielectric. We show that InGaAs is affected by interfacial-phonon scattering to an extent larger than Si, lowering the expected performance, but probably not enough to question the technological relevance of InGaAs.

  12. ALD gate dielectrics for improved threshold voltage stability in AlGaN/GaN MOS-HFETs for power applications

    NASA Astrophysics Data System (ADS)

    Ramanan, Narayanan; Lee, Bongmook; Misra, Veena

    2015-12-01

    Dielectrics by atomic layer deposition (ALD) are sought after for fabricating AlGaN/GaN based metal oxide semiconductor heterojunction field effect transistors (MOS-HFETs) for power applications. The ideal gate dielectric is required to suppress gate leakage and minimize threshold voltage (V T) instability by hosting minimal interface traps. Additionally, with the need for an enhancement mode device, it is preferable if it minimizes V T shift in the negative direction. For the first time, we compare popular ALD dielectrics like SiO2, Al2O3, HfO2 and HfAlO with identical electrical thickness on AlGaN/GaN, thereby ensuring identical electrostatic conditions across different dielectrics. High-k ALD dielectrics (HfAlO, HfO2 and Al2O3) are found to suppress gate leakage but host a high density of interface traps with AlGaN, thereby resulting in significant V T instability. ALD SiO2 gate dielectric, annealed in N2 above 600 °C, is a promising gate dielectric candidate which provides the most stable and least negative shift in V T while also substantially suppressing gate leakage below that of an HFET.

  13. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Growth Related Carrier Mobility Enhancement of Pentacene Thin-Film Transistors with High-k Oxide Gate Dielectric

    NASA Astrophysics Data System (ADS)

    Yu, Ai-Fang; Qi, Qiong; Jiang, Peng; Jiang, Chao

    2009-07-01

    Carrier mobility enhancement from 0.09 to 0.59 cm2/Vs is achieved for pentacene-based thin-film transistors (TFTs) by modifying the HfO2 gate dielectric with a polystyrene (PS) thin film. The improvement of the transistor's performance is found to be strongly related to the initial film morphologies of pentacene on the dielectrics. In contrast to the three-dimensional island-like growth mode on the HfO2 surface, the Stranski-Krastanov growth mode on the smooth and nonpolar PS/HfO2 surface is believed to be the origin of the excellent carrier mobility of the TFTs. A large well-connected first monolayer with fewer boundaries is formed via the Stranski-Krastanov growth mode, which facilitates a charge transport parallel to the substrate and promotes higher carrier mobility.

  14. The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces

    NASA Astrophysics Data System (ADS)

    Kent, Tyler; Tang, Kechao; Chobpattana, Varistha; Negara, Muhammad Adi; Edmonds, Mary; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi; McIntyre, Paul; Kummel, Andrew C.

    2015-10-01

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher Cmax hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low Dit high Cox MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

  15. Influence of composition and seed dimension on the structure and laser damage of nodular defects in HfO2/SiO2 high reflectors.

    PubMed

    Wei, Chaoyang; Yi, Kui; Fan, Zhengxiu; Shao, Jianda

    2012-10-01

    Seeds are the sources for forming nodular defects that largely limit the improvement of laser-induced damage threshold of 1? laser mirrors in the nanosecond pulse regime. To shed more light of the composition and sizes of seeds on the associated structure of nodular defects and laser damage sensitivity, nodular defects were generated in 1064 nm HfO(2)/SiO(2) high reflectors with different sizes of absorbing Au and nonabsorbing SiO(2) nanoparticles located on the surfaces of substrates. The width dimensions, inner structures, and damage morphologies of nodular defects were characterized by an atomic force microscope, a field emission scanning electron microscope, and a focused ion beam. It was found that the composition and size both influenced the structure and the laser damage of nodular defects. The width of nodules from SiO(2) seeds were larger than that formed by the same size of Au seed. A nodule grown from a small seed generally tends to have a continuous and stable boundary. The ejection fluences of nodules generated from different size absorbing Au and nonabsorbing SiO(2) seeds were totally different. The results were interpreted from the aspects of absorption cross sections of seeds and mechanical stability of nodular structures. PMID:23033093

  16. Thermal Conductivity and Stability of HfO2-Y2O3 and La2Zr2O7 Evaluated for 1650 Deg C Thermal/Environmental Barrier Coating Applications

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Bansal, Narottam P.; Miller, Robert A.

    2003-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal and environmental barrier coating (T/EBC) materials for gas turbine ceramic matrix composite (CMC) combustor applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature stability of hot-pressed and plasma sprayed specimens with representative partially-stabilized and fully-cubic HfO2-Y2O3 compositions and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasmasprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC hexoloy or SiC/SiC CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications are also discussed.

  17. Atomic layer deposition of high-k dielectrics on single-walled carbon nanotubes: a Raman study

    NASA Astrophysics Data System (ADS)

    Suriyasena Liyanage, Luckshitha; Cott, Daire J.; Delabie, Annelies; Van Elshocht, Sven; Bao, Zhenan; Wong, H.-S. Philip

    2013-06-01

    Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, to realize a carbon nanotube field effect transistor (CNTFET) with excellent gate control, the high-k dielectrics between the CNT and the metal gate must have superb electrical properties and extremely high uniformity. Thus it is essential to understand the interactions between high-k materials and the SWCNTs to effectively control the transistor characteristics. In this study, we investigate the effects of atomic layer deposited (ALD) high-k dielectrics (Al2O3 and HfO2) on SWCNTs using Raman spectroscopy. We subjected the SWCNTs to various ALD cycles and studied the nucleation and growth of ALD dielectrics at defect sites using scanning electron microscopy and transmission electron microscopy images. We analyzed these samples using Raman spectroscopy and x-ray photoelectron spectroscopy. The Raman peak shifts of the G-peak and the 2D (G?) peaks suggest doping and stress induced effects on the CNTs by the surrounding high-k oxide environment. Trends in the G-peak FWHM and G/D-peak ratios were identified and compared between Al2O3 and HfO2. We confirmed the ALD-deposited HfO2 is polycrystalline using x-ray diffraction and analyzed dielectric-CNT bonding states using XPS measurements. This study provides insights on the effects of ALD high-k materials on SWCNTs for future high-speed transistor applications.

  18. The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces.

    PubMed

    Kent, Tyler; Tang, Kechao; Chobpattana, Varistha; Negara, Muhammad Adi; Edmonds, Mary; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi; McIntyre, Paul; Kummel, Andrew C

    2015-10-28

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher Cmax hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low Dit high Cox MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120?°C and 300?°C were compared. PMID:26520547

  19. Ultra-thin multilayer capacitors.

    SciTech Connect

    Renk, Timothy Jerome; Monson, Todd C.

    2009-06-01

    The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laboratories. The goal of this work was to increase the energy density of ceramic capacitors through the formation of a multilayer device with excellent materials properties, dielectric constant, and standoff voltage. For successful device construction, there are a number of challenging requirements including achieving correct stoichiometric and crystallographic composition of the deposited PLZT, as well as the creation of a defect free homogenous film. This report details some success in satisfying these requirements, although 900 C temperatures were necessary for PLZT perovskite phase formation. These temperatures were applied to a previously deposited multi-layer film which was then post-annealed to this temperature. The film exhibited mechanical distress attributable to differences in the coefficient of thermal expansion (CTE) of the various layers. This caused significant defects in the deposited films that led to shorts across devices. A follow-on single layer deposition without post-anneal produced smooth layers with good interface behavior, but without the perovskite phase formation. These issues will need to be addressed in order for ion beam deposited MLCCs to become a viable technology. It is possible that future in-situ heating during deposition may address both the CTE issue, and result in lowered processing temperatures, which in turn could raise the probability of successful MLCC formation.

  20. Advanced passivation techniques for Si solar cells with high-? dielectric materials

    NASA Astrophysics Data System (ADS)

    Geng, Huijuan; Lin, Tingjui; Letha, Ayra Jagadhamma; Hwang, Huey-Liang; Kyznetsov, Fedor A.; Smirnova, Tamara P.; Saraev, Andrey A.; Kaichev, Vasily V.

    2014-09-01

    Electronic recombination losses at the wafer surface significantly reduce the efficiency of Si solar cells. Surface passivation using a suitable thin dielectric layer can minimize the recombination losses. Herein, advanced passivation using simple materials (Al2O3, HfO2) and their compounds H(Hf)A(Al)O deposited by atomic layer deposition (ALD) was investigated. The chemical composition of Hf and Al oxide films were determined by X-ray photoelectron spectroscopy (XPS). The XPS depth profiles exhibit continuous uniform dense layers. The ALD-Al2O3 film has been found to provide negative fixed charge (-6.4 × 1011 cm-2), whereas HfO2 film provides positive fixed charge (3.2 × 1012 cm-2). The effective lifetimes can be improved after oxygen gas annealing for 1 min. I-V characteristics of Si solar cells with high-? dielectric materials as passivation layers indicate that the performance is significantly improved, and ALD-HfO2 film would provide better passivation properties than that of the ALD-Al2O3 film in this research work.

  1. In situ auger electron spectroscopy study of atomic layer deposition: growth initiation and interface formation reactions during ruthenium ALD on Si-H, SiO2, and HfO2 surfaces.

    PubMed

    Park, Kie Jin; Terry, David B; Stewart, S Michael; Parsons, Gregory N

    2007-05-22

    Growth initiation and film nucleation in atomic layer deposition (ALD) is important for controlling interface composition and achieving atomic-scale films with well-defined composition. Ruthenium ALD is studied here using ruthenocene and oxygen as reactants, and growth initiation and nucleation are characterized on several different growth surfaces, including SiO2, HfO2, and hydrogen terminated silicon, using on-line Auger electron spectroscopy and ex-situ X-ray photoelectron spectroscopy. The time needed to reach the full growth rate (typically approximately 1 A per deposition cycle) is found to increase as the surface energy of the starting surface (determined from contact angle measurements) decreased. Growth starts more readily on HfO2 than on SiO2 or Si-H surfaces, and Auger analysis indicates distinct differences in surface reactions on the various surfaces during film nucleation. Specifically, surface oxygen is consumed during ruthenocene exposure, so the nucleation rate will depend on the availability of oxygen and the energetics of surface oxygen bonding on the starting substrate surface. PMID:17461600

  2. Interface Electronic State Characterization of Plasma Enhanced Atomic Layer Deposited Dielectrics on GaN

    NASA Astrophysics Data System (ADS)

    Yang, Jialing

    In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25--220 °C). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O 3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H 2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO 2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction.

  3. Structural, electronic, vibrational and dielectric properties of selected high-shape K semiconductor oxides

    NASA Astrophysics Data System (ADS)

    Scolfaro, L. M. R.; Leite Alves, H. W.; Borges, P. D.; Garcia, J. C.; da Silva, E. F., Jr.

    2014-10-01

    The semiconductor oxides SnO2, HfO2, ZrO2, TiO2 and SrTiO3 are interesting materials for applications as high-K dielectric gate materials in silicon-based devices and spintronics, among others. Here we review our theoretical work about the structural, electronic and vibrational properties of these oxides in their most stable structural phases, including dielectric properties as derived from the electronic structure taking into account the lattice contribution. Finally, we address the recent role played by the presence of transition metal atoms in semiconductor oxides, considering in particular SnO2 as an example in forming diluted magnetic alloys.

  4. Development and Performance Evaluations of HfO2-Si and Rare Earth-Si Based Environmental Barrier Bond Coat Systems for SiC/SiC Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming

    2014-01-01

    Ceramic environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiCSiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si based EBC bond coat systems for SiCSiC CMC combustor and turbine airfoil applications are investigated. The coating design approach and stability requirements are specifically emphasized, with the development and implementation focusing on Plasma Sprayed (PS) and Electron Beam-Physic Vapor Deposited (EB-PVD) coating systems and the composition optimizations. High temperature properties of the HfO2-Si based bond coat systems, including the strength, fracture toughness, creep resistance, and oxidation resistance were evaluated in the temperature range of 1200 to 1500 C. Thermal gradient heat flux low cycle fatigue and furnace cyclic oxidation durability tests were also performed at temperatures up to 1500 C. The coating strength improvements, degradation and failure modes of the environmental barrier coating bond coat systems on SiCSiC CMCs tested in simulated stress-environment interactions are briefly discussed and supported by modeling. The performance enhancements of the HfO2-Si bond coat systems with rare earth element dopants and rare earth-silicon based bond coats are also highlighted. The advanced bond coat systems, when integrated with advanced EBC top coats, showed promise to achieve 1500 C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and long-term durability.

  5. Ultrathin flexible dual band terahertz absorber

    NASA Astrophysics Data System (ADS)

    Shan, Yan; Chen, Lin; Shi, Cheng; Cheng, Zhaoxiang; Zang, Xiaofei; Xu, Boqing; Zhu, Yiming

    2015-09-01

    We propose an ultrathin and flexible dual band absorber operated at terahertz frequencies based on metamaterial. The metamaterial structure consists of periodical split ring resonators with two asymmetric gaps and a metallic ground plane, separated by a thin-flexible dielectric spacer. Particularly, the dielectric spacer is a free-standing polyimide film with thickness of 25 ?m, resulting in highly flexible for our absorber and making it promising for non-planar applications such as micro-bolometers and stealth aircraft. Experimental results show that the absorber has two resonant absorption frequencies (0.41 THz and 0.75 THz) with absorption rates 92.2% and 97.4%, respectively. The resonances at the absorption frequencies come from normal dipole resonance and high-order dipole resonance which is inaccessible in the symmetrical structure. Multiple reflection interference theory is used to analyze the mechanism of the absorber and the results are in good agreement with simulated and experimental results. Furthermore, the absorption properties are studied under various spacer thicknesses. This kind of metamaterial absorber is insensitive to polarization, has high absorption rates (over 90%) with wide incident angles range from 0° to 45° and the absorption rates are also above 90% when wrapping it to a curved surface.

  6. All-dielectric metamaterials.

    PubMed

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces. PMID:26740041

  7. Chemical gating of epitaxial graphene through ultrathin oxide layers

    NASA Astrophysics Data System (ADS)

    Larciprete, Rosanna; Lacovig, Paolo; Orlando, Fabrizio; Dalmiglio, Matteo; Omiciuolo, Luca; Baraldi, Alessandro; Lizzit, Silvano

    2015-07-01

    We achieved a controllable chemical gating of epitaxial graphene grown on metal substrates by exploiting the electrostatic polarization of ultrathin SiO2 layers synthesized below it. Intercalated oxygen diffusing through the SiO2 layer modifies the metal-oxide work function and hole dopes graphene. The graphene/oxide/metal heterostructure behaves as a gated plane capacitor with the in situ grown SiO2 layer acting as a homogeneous dielectric spacer, whose high capacity allows the Fermi level of graphene to be shifted by a few hundreds of meV when the oxygen coverage at the metal substrate is of the order of 0.5 monolayers. The hole doping can be finely tuned by controlling the amount of interfacial oxygen, as well as by adjusting the thickness of the oxide layer. After complete thermal desorption of oxygen the intrinsic doping of SiO2 supported graphene is evaluated in the absence of contaminants and adventitious adsorbates. The demonstration that the charge state of graphene can be changed by chemically modifying the buried oxide/metal interface hints at the possibility of tuning the level and sign of doping by the use of other intercalants capable of diffusing through the ultrathin porous dielectric and reach the interface with the metal.We achieved a controllable chemical gating of epitaxial graphene grown on metal substrates by exploiting the electrostatic polarization of ultrathin SiO2 layers synthesized below it. Intercalated oxygen diffusing through the SiO2 layer modifies the metal-oxide work function and hole dopes graphene. The graphene/oxide/metal heterostructure behaves as a gated plane capacitor with the in situ grown SiO2 layer acting as a homogeneous dielectric spacer, whose high capacity allows the Fermi level of graphene to be shifted by a few hundreds of meV when the oxygen coverage at the metal substrate is of the order of 0.5 monolayers. The hole doping can be finely tuned by controlling the amount of interfacial oxygen, as well as by adjusting the thickness of the oxide layer. After complete thermal desorption of oxygen the intrinsic doping of SiO2 supported graphene is evaluated in the absence of contaminants and adventitious adsorbates. The demonstration that the charge state of graphene can be changed by chemically modifying the buried oxide/metal interface hints at the possibility of tuning the level and sign of doping by the use of other intercalants capable of diffusing through the ultrathin porous dielectric and reach the interface with the metal. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02936h

  8. Non-linear dielectric constant increase with Ti composition in high-k ALD-HfTiOx films after O2 crystallization annealing

    NASA Astrophysics Data System (ADS)

    Tomida, K.; Popovici, M.; Opsomer, K.; Menou, N.; Wang, W. C.; Delabie, A.; Swerts, J.; Steenbergen, J.; Kaczer, B.; Elshocht, S. V.; Detavernier, C.; Afanas'ev, V. V.; Wouters, D. J.; Kittl, J. A.

    2010-02-01

    HfTiOx films deposited on TiN, Pt and Al2O3/Si bottom electrodes (BE) by Atomic Layer Deposition (ALD) method were investigated in terms of the crystallization temperature, dielectric constant and leakage current. The as-deposited films show a linear increase of dielectric constant from 20 (HfO2) to 40 (TiO2) as a function of Ti content in the film. On the other hands, the dielectric constant of HfTiOx films with 64% - 30% Hf content increases up to 60 after crystallization annealing, which strongly correlates with the appearance of the orthorhombic HfTiO4 structure. Furthermore, the thermal treatment in O2 ambient is found to have a drastic effect to decrease the leakage current density (Jg). As a result, 10-8 A/cm2 at Vg = +1V with 0.8nm EOT is achieved with 30%-Hf contained film.

  9. Ultrathin Planar Graphene Supercapacitors

    SciTech Connect

    Huang, Jingsong; Meunier, Vincent; Sumpter, Bobby G; Ajayan, Pullikel M; Yoo, Jung Joon; Balakrishnan, Kaushik; Srivastava, Anchal; Conway, Michelle; Reddy, Arava Leela Mohan; Yu, Jin; Vajtai, Robert

    2011-01-01

    With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an in-plane fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multi-layer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 Fcm-2. While, much higher (394 Fcm-2) specific capacities are observed in case of multi-layered graphene oxide electrodes, owing to the better utilization of the available electrochemical surface area. The performances of devices with pristine as well as thicker graphene based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.

  10. Ultra-thin titanium oxide

    NASA Astrophysics Data System (ADS)

    Bareiß, M.; Kälblein, D.; Jirauschek, C.; Exner, A.; Pavlichenko, I.; Lotsch, B.; Zschieschang, U.; Klauk, H.; Scarpa, G.; Fabel, B.; Porod, W.; Lugli, P.

    2012-08-01

    We demonstrate the fabrication of ultra-thin titanium oxide films by plasma-induced surface oxidation. Ellipsometry measurements indicate an oxide thickness of about 2 nm. Electrical characterization was performed on microscale and nanoscale metal-insulator-metal tunneling diodes. Electrical fields up to 22 MV/cm were applied without destroying the titanium oxide films. The current-voltage-characteristic of the diodes are found to be asymmetric with respect to zero bias when employing electrodes with different work functions. The permittivity of the ultra-thin titanium oxide was determined to be less than 6, which is the smallest permittivity that has been reported for titanium oxide.

  11. Effect of high-k dielectric and ionic liquid gate on nanolayer black-phosphorus field effect transistors

    NASA Astrophysics Data System (ADS)

    Kamalakar, M. Venkata; Madhushankar, B. N.; Dankert, André; Dash, Saroj P.

    2015-09-01

    Nanolayer black phosphorus (BP) is a direct bandgap semiconducting two dimensional crystal, showing immense promise for future nanoelectronic devices. Here, we report the effect of high-k dielectric and ionic-liquid gate in BP field effect transistors (BP FET). An ambipolar behavior is observed in pristine BP FETs with current modulation of 104. With a high-k HfO2 encapsulation, we observed identical switching performance in the BP FETs, however, with noticeable enhancement in mobility at room temperature. In comparison to the pristine device, the HfO2 encapsulation showed a contrasting decrease in mobility at lower temperatures. BP FETs with electric double layer ionic liquid gate showed a drastic improvement in the subthreshold swing (SS) to 173 mV/dec and operation voltages less than 0.5 V in comparison to solid state SiO2 back gated devices. Our results elucidate the effect of different electrostatic conditions on BP transistor channels and open up ways for further exploration of their prospects for nanoelectronic devices and circuits.

  12. First-principles study of fission product (Xe, Cs, Sr) incorporation and segregation in alkaline earth metal oxides, HfO(2), and the MgO-HfO(2) interface.

    PubMed

    Liu, Xiang-Yang; Uberuaga, Blas P; Sickafus, Kurt E

    2009-01-28

    In order to close the nuclear fuel cycle, advanced concepts for separating out fission products are necessary. One approach is to use a dispersion fuel form in which a fissile core is surrounded by an inert matrix that captures and immobilizes the fission products from the core. If this inert matrix can be easily separated from the fuel, via e.g. solution chemistry, the fission products can be separated from the fissile material. We examine a surrogate dispersion fuel composition, in which hafnia (HfO(2)) is a surrogate for the fissile core and alkaline earth metal oxides are used as the inert matrix. The questions of fission product incorporation in these oxides and possible segregation behavior at interfaces are considered. Density functional theory based calculations for fission product elements (Xe, Sr, and Cs) in these oxides are carried out. We find smaller incorporation energy in hafnia than in MgO for Cs and Sr, and Xe if variation of charge state is allowed. We also find that this trend is reversed or reduced for alkaline earth metal oxides with large cation sizes. Model interfacial calculations show a strong tendency of segregation from bulk MgO to MgO-HfO(2) interfaces. PMID:21715804

  13. Low operation voltage and high thermal stability of a WSi2 nanocrystal memory device using an Al2O3/HfO2/Al2O3 tunnel layer

    NASA Astrophysics Data System (ADS)

    Uk Lee, Dong; Jun Lee, Hyo; Kyu Kim, Eun; You, Hee-Wook; Cho, Won-Ju

    2012-02-01

    A WSi2 nanocrystal nonvolatile memory device was fabricated with an Al2O3/HfO2/Al2O3 (AHA) tunnel layer and its electrical characteristics were evaluated at 25, 50, 70, 100, and 125 °C. The program/erase (P/E) speed at 125 °C was approximately 500 ?s under threshold voltage shifts of 1 V during voltage sweeping of 8 V/-8 V. When the applied pulse voltage was ±9 V for 1 s for the P/E conditions, the memory window at 125 °C was approximately 1.25 V after 105 s. The activation energies for the charge losses of 5%, 10%, 15%, 20%, 25%, 30%, and 35% were approximately 0.05, 0.11, 0.17, 0.21, 0.23, 0.23, and 0.23 eV, respectively. The charge loss mechanisms were direct tunneling and Pool-Frenkel emission between the WSi2 nanocrystals and the AHA barrier engineered tunneling layer. The WSi2 nanocrystal memory device with multi-stacked high-K tunnel layers showed strong potential for applications in nonvolatile memory devices.

  14. Accurate characterization and understanding of interface trap density trends between atomic layer deposited dielectrics and AlGaN/GaN with bonding constraint theory

    NASA Astrophysics Data System (ADS)

    Ramanan, Narayanan; Lee, Bongmook; Misra, Veena

    2015-06-01

    Many dielectrics have been proposed for the gate stack or passivation of AlGaN/GaN based metal oxide semiconductor heterojunction field effect transistors, to reduce gate leakage and current collapse, both for power and RF applications. Atomic Layer Deposition (ALD) is preferred for dielectric deposition as it provides uniform, conformal, and high quality films with precise monolayer control of film thickness. Identification of the optimum ALD dielectric for the gate stack or passivation requires a critical investigation of traps created at the dielectric/AlGaN interface. In this work, a pulsed-IV traps characterization method has been used for accurate characterization of interface traps with a variety of ALD dielectrics. High-k dielectrics (HfO2, HfAlO, and Al2O3) are found to host a high density of interface traps with AlGaN. In contrast, ALD SiO2 shows the lowest interface trap density (<2 × 1012 cm-2) after annealing above 600 °C in N2 for 60 s. The trend in observed trap densities is subsequently explained with bonding constraint theory, which predicts a high density of interface traps due to a higher coordination state and bond strain in high-k dielectrics.

  15. Magnetism in ultrathin film structures

    NASA Astrophysics Data System (ADS)

    Vaz, C. A. F.; Bland, J. A. C.; Lauhoff, G.

    2008-05-01

    In this paper, we review some of the key concepts in ultrathin film magnetism which underpin nanomagnetism. We survey the results of recent experimental and theoretical studies of well characterized epitaxial structures based on Fe, Co and Ni to illustrate how intrinsic fundamental properties such as the magnetic exchange interactions, magnetic moment and magnetic anisotropies change markedly in ultrathin films as compared with their bulk counterparts, and to emphasize the role of atomic scale structure, strain and crystallinity in determining the magnetic properties. After introducing the key length scales in magnetism, we describe the 2D magnetic phase transition and survey studies of the thickness dependent Curie temperature and the critical exponents which characterize the paramagnetic-ferromagnetic phase transition. We next discuss recent experimental and theoretical results on the determination of the exchange constant, followed by an overview of measurements of the magnetic moment in the elemental 3d transition metal thin films in the various crystal phases that have been successfully stabilized, thereby illustrating the sensitivity of the magnetic moment to the local symmetry and to the atomic environment. Finally, we discuss briefly the magnetic anisotropies of Fe, Co and Ni in the fcc crystalline phase, to emphasize the role of structure and the details of the interface in influencing the magnetic properties. The dramatic effect that adsorbates can have on the magnetic anisotropies of thin magnetic films is also discussed. Our survey demonstrates that the fundamental properties, namely, the magnetic moment and magnetic anisotropies of ultrathin films have dramatically different behaviour compared with those of the bulk while the comparable size of the structural and magnetic contributions to the total energy of ultrathin structures results in an exquisitely sensitive dependence of the magnetic properties on the film structure.

  16. Electron tunneling through ultrathin boron nitride crystalline barriers.

    PubMed

    Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio H Castro; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S

    2012-03-14

    We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. PMID:22380756

  17. Excitons in ultrathin organic-inorganic perovskite crystals

    NASA Astrophysics Data System (ADS)

    Yaffe, Omer; Chernikov, Alexey; Norman, Zachariah M.; Zhong, Yu; Velauthapillai, Ajanthkrishna; van der Zande, Arend; Owen, Jonathan S.; Heinz, Tony F.

    2015-07-01

    We demonstrate the formation of large sheets of layered organic-inorganic perovskite (OIPC) crystals, as thin as a single unit cell, prepared by mechanical exfoliation. The resulting two-dimensional OIPC nanosheets of 2.4 nm thickness are direct semiconductors with an optical band gap of 2.4 eV. They exhibit unusually strong light-matter interaction with an optical absorption as high as 25% at the main excitonic resonance, as well as bright photoluminescence. We extract an exciton binding energy of 490 meV from measurement of the series of excited exciton states. The properties of the excitons are shown to be strongly influenced by the changes in the dielectric surroundings. The environmental sensitivity of these ultrathin OIPC sheets is further reflected in the strong suppression of a thermally driven phase transition present in the bulk crystals.

  18. Metal mirrors with metal-dielectric HR-coating for ultrashort laser pulses applied in scanner applications

    NASA Astrophysics Data System (ADS)

    Schürmann, M.; Risse, S.; Kämmer, H.; Franke, C.; Schlegel, R.; Müller, S.; Damm, C.; Steinkopf, R.; Dreisow, F.; Nolte, S.; Eberhardt, R.; Kaiser, N.

    2015-03-01

    Metal mirrors are an attractive solution for scan mirrors working with ultra-short pulse lasers. Small mechanical inertia and a small mirror mass are required. Therefore, the mirrors have to be very stiff and a high quality optical surface has to be provided. This can be achieved with lightweight AlSi based mirrors with diamond-turned NiP polishable plating. Different coating options were evaluated in order to provide the necessary high reflectivity and a satisfactory laser damage threshold for ultrashort laser pulses in the few ps to fs regime at ? = 1030 nm. High-reflective metal layers enhanced by dielectric HfO2/SiO2 stacks were found to be the most advantageous coating option due to their comparatively small thickness and measured damage thresholds above 1 J/cm2@8ps.

  19. Preparation of patterned ultrathin polymer films.

    PubMed

    Yang, Huige; Su, Meng; Li, Kaiyong; Jiang, Lei; Song, Yanlin; Doi, Masao; Wang, Jianjun

    2014-08-12

    Though patterned ultrathin polymer films (<100 nm) are of great importance in the fields of sensors and nanoelectronic devices, the fabrication of patterned ultrathin polymer films remains a great challenge. Herein, patterned ultrathin polymer films are fabricated facilely on hydrophobic substrates with different hydrophilic outline patterns by the pinning of three-phase contact lines of polymer solution on the hydrophilic outlines. This method is universal for most of the water-soluble polymers, and poly(vinyl alcohol) (PVA) has been selected as a model polymer due to its biocompatibility and good film-forming property. The results indicate that the morphologies of ultrathin polymer films can be precisely adjusted by the size of the hydrophilic outline pattern. Specifically, patterned hydrophilic outlines with sizes of 100, 60, and 40 ?m lead to the formation of concave-shaped ultrathin PVA films, whereas uniform ultrathin PVA films are formed on 20 and 10 ?m patterned substrates. The controllabilities of morphologies can be interpreted through the influences of the slip length and coffee ring effect. Theoretical analysis shows that when the size of the hydrophilic outline patterns is smaller than a critical value, the coffee ring effect disappears and uniform patterned ultrathin polymer films can be formed for all polymer concentrations. These results provide an effective methodology for the fabrication of patterned ultrathin polymer films and enhance the understanding of the coffee ring effect. PMID:25066958

  20. UV protection filters by dielectric multilayer thin films on Glass BK-7 and Infrasil 301

    NASA Astrophysics Data System (ADS)

    Abdel-Aziz, M. M.; Azim, Osama A.; Abdel-Wahab, L. A.; Seddik, Mohamed M.

    2006-10-01

    The increasing use of Ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, four suitable protection filters were produced to block three UV bands (UVA, UVB, and UVC). The design structure of the required dielectric multilayer filters was done by optical thin film technology using the absorbing property of UV radiation for the substrates and dielectric materials. The computer analyses of the multilayer filter formulas were prepared using Macleod Software for the production processes. The deposition technique was achieved on optical substrates (Glass BK-7 and Infrasil 301) by dielectric material combinations including Titanium dioxide (Ti 2O 3), Hafnium dioxide (HfO 2), and Lima (mixture of oxides SiO 2/Al 2O 3); deposition being achieved using an electron beam gun. The output results of the theoretical and experimental transmittance values for spectral band from 200 nm to 800 nm were discussed in four processes. To analyze the suitability for use in 'real world' applications, the test pieces were subjected to the durability tests (adhesion, abrasion resistance, and humidity) according to Military Standard MIL-C-675C and MIL-C-48497A.

  1. Silicon nanowires with high-k hafnium oxide dielectrics for sensitive detection of small nucleic acid oligomers.

    PubMed

    Dorvel, Brian R; Reddy, Bobby; Go, Jonghyun; Duarte Guevara, Carlos; Salm, Eric; Alam, Muhammad Ashraful; Bashir, Rashid

    2012-07-24

    Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues, such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO(2)), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFETs has been small oligonucleotides, more specifically, microRNA (miRNA). MicroRNAs are small RNA oligonucleotides which bind to mRNAs, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO(2) dielectric-based silicon nanowires for biosensing applications. Here we demonstrate sensing of single-stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100 fM detection levels of the miR-10b DNA analogue, with a theoretical limit of detection of 1 fM. Moreover, the noncomplementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

  2. Ultrathin silicon dioxide films grown by photo-oxidation of silicon using 172 nm excimer lamps

    NASA Astrophysics Data System (ADS)

    Kaliwoh, Never; Zhang, Jun-Ying; Boyd, Ian W.

    2000-12-01

    We report the low temperature growth of ultrathin SiO2 films on crystalline Si by photo-oxidation with an array of Xe2? excimer vacuum ultraviolet (VUV) lamps operating at a wavelength of 172 nm. Ultrathin layers from 1.2 to 3.3 nm thickness were grown at time intervals from 5 to 40 min at 100-400°C at an O2 pressure of 1000 mbar. Growth rates of up to 0.2 nm min-1 have been achieved at 400°C, while the chemical bonding of the films has been analysed by Fourier transform infrared (FTIR) spectroscopy and found to be SiO2. The as-grown 3.3 nm films exhibited good dielectric properties, comparible to SiO2 films of identical thickness, grown by RTP at 800°C.

  3. Electrical properties of spin coated ultrathin titanium oxide films on GaAs

    NASA Astrophysics Data System (ADS)

    Dutta, Shankar; Pal, Ramjay; Chatterjee, Ratnamala

    2015-04-01

    In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (˜10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nm with thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be -0.1 V to -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10-4 A cm-2 at 3 V) compared to the unpassivated film (1.8 × 10-3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm-1 and 7.2 MV cm-1 respectively.

  4. Solid-state dewetting of ultra-thin Au films on SiO? and HfO?.

    PubMed

    Seguini, G; Curi, J Llamoja; Spiga, S; Tallarida, G; Wiemer, C; Perego, M

    2014-12-12

    Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO2 and HfO2. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h = 0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 10(12) Au NPs cm(-2) were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h ? 1.0 nm where the Au NPs diameter is in the 5-10 nm range and the density is around 10(11) Au NPs cm(-2). The effect of a subsequent high temperature (400-800 °C) annealing in N2 atmosphere on the Au NPs was investigated as well. For h ? 1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0 ? h ? 6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT. PMID:25410136

  5. Short channel field-effect transistors from ultrathin GaTe nanosheets

    NASA Astrophysics Data System (ADS)

    Xu, Kai; Zhang, Zhangyuan; Wang, Zhenxing; Wang, Feng; Huang, Yun; Liao, Lei; He, Jun

    2015-10-01

    The emergence of 2D layered materials provides a route for MOSFETs limited by short channel effects (SCEs). In this work, we investigate short channel transport behavior in ultrathin GaTe-based MOSFETs with channel lengths ranging from 1 ?m down to 50 nm and then reveal the onset of SCEs in GaTe MOSFETs. Moreover, electrical transport measurements as a function of temperature dependence and gas absorption were conducted to modulate the SCEs. In addition, the behavior of GaTe MOSFETs was suppressed, evidently, by decreasing dielectric thickness. Our research provides the experimental groundwork for future applications of MOSFETs based on layered materials.

  6. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, Harold K. (Bend, OR); Babcock, Walter C. (Bend, OR); Friensen, Dwayne T. (Bend, OR); Smith, Kelly L. (Bend, OR); Johnson, Bruce M. (Bend, OR); Wamser, Carl C. (West Linn, OR)

    1990-01-01

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

  7. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

    1990-08-14

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

  8. Depolarizing field in ultrathin electrocalorics

    NASA Astrophysics Data System (ADS)

    Glazkova, E.; Chang, C.-M.; Lisenkov, S.; Mani, B. K.; Ponomareva, I.

    2015-08-01

    Ferroelectric thin films are considered to be among the top candidates for room-temperature electrocaloric materials as they exhibit excellent electric properties and allow application of record high electric fields. At the same time, downsizing of ferroelectric electrocalorics brings about an unwanted but unavoidable depolarizing field that could critically alter or even destroy the films' electrocaloric properties. We use an atomistic first-principles-based computational approach that does not rely on the use of Maxwell relations (i) to reveal the critical role of the depolarizing field on the electrocaloric properties of ferroelectric ultrathin films, (ii) to demonstrate the contribution of nanodomains to the electrocaloric effect in such films, and (iii) to revisit the potential limitations of the indirect approach to study electrocaloric effect in nanoscale ferroelectrics.

  9. Ultra-Thin, Flexible Electronics

    NASA Technical Reports Server (NTRS)

    Holland, Brian; McPherson, Ryan; Zhang, Tan; Hou, Zhenwei; Dean, Robert; Johnson, R. Wayne; DelCastillo, Linda; Moussessian, Alina

    2008-01-01

    Thinned die can be used to realize ultra-thin flexible electronics for applications such as conformal and wearable electronics. Three techniques have been developed to achieve this goal using thinned die: die flip chip bonded onto flexible substrates, die laminated onto LCP films, and die embedded in polyimide. A key to achieving each of these techniques is the thinning of die to a thickness of 50 microns or thinner. Conventional CMP processing can be used to thin to 50 microns. At 50 microns, the active die become flexible and must be handled by temporarily bonding them to a holder die, for further processing. Once bonded face down to the holder die, the active die can be further thinned by DRIE etching the exposed backside. The thinned die can then been packaged in or on the flexible substrate.

  10. Characterization of ALD Beryllium Oxide as a Potential High- k Gate Dielectric for Low-Leakage AlGaN/GaN MOSHEMTs

    NASA Astrophysics Data System (ADS)

    Johnson, Derek W.; Yum, Jung Hwan; Hudnall, Todd W.; Mushinski, Ryan M.; Bielawski, Christopher W.; Roberts, John C.; Wang, Wei-E.; Banerjee, Sanjay K.; Harris, H. Rusty

    2014-01-01

    The chemical and electrical characteristics of atomic layer deposited (ALD) beryllium oxide (BeO) on GaN were studied via x-ray photoelectron spectroscopy, current-voltage, and capacitance-voltage measurements and compared with those of ALD Al2O3 and HfO2 on GaN. Radiofrequency (RF) and power electronics based on AlGaN/GaN high-electron-mobility transistors are maturing rapidly, but leakage current reduction and interface defect ( D it) minimization remain heavily researched. BeO has received recent attention as a high- k gate dielectric due to its large band gap (10.6 eV) and thermal stability on InGaAs and Si, but little is known about its performance on GaN. Unintentionally doped GaN was cleaned in dilute aqueous HCl immediately prior to BeO deposition (using diethylberyllium and H2O precursors). Formation of an interfacial layer was observed in as-deposited samples, similar to the layer formed during ALD HfO2 deposition on GaN. Postdeposition anneal (PDA) at 700°C and 900°C had little effect on the observed BeO binding state, confirming the strength of the bond, but led to increased Ga oxide formation, indicating the presence of unincorporated oxygen in the dielectric. Despite the interfacial layer, gate leakage current of 1.1 × 10-7 A/cm2 was realized, confirming the potential of ALD BeO for use in low-leakage AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors.

  11. Measurement of optical anisotropy in ultrathin films using surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Devanarayanan, V. P.; Manjuladevi, V.; Poonia, Monika; Gupta, R. K.; Gupta, Sanjeev K.; Akhtar, Jamil

    2016-01-01

    The optical phenomenon, surface plasmon resonance (SPR) is employed for the measurement of optical anisotropy in the ultrathin films fabricated through Langmuir-Blodgett (LB) and self-assembled monolayer (SAM) techniques onto 50 nm gold film supported on BK7 glass substrates. The resonance angle (RA) is measured using a home built setup in Kretschmann configuration. The LB films and SAM can provide a single layer of highly ordered and organized molecules on the two dimensional surface. If the film forming molecules are anisotropic, their organization in the LB films and SAM can yield an anisotropic film due to tilt of the molecules with respect to the surface normal. The SPR spectra are recorded for the two orthogonal directions of the film with respect to the plane of incidence. The spectra are simulated by modeling the Fresnel's reflection from 4-layers viz., prism, gold, ultrathin films and air; and the real and imaginary parts of refractive index are estimated. Our study shows the metallic and dielectric nature of the LB films of bundles of single walled carbon nanotubes (SWCNTs) when the long axis of SWCNTs are aligned parallel and perpendicular to plane of incidence, respectively. The optical anisotropy was estimated from the change in real part of refractive index (?nr) of the ultrathin films measured in the orthogonal directions. In addition, we have also studied such optical anisotropy in the LB film of cadmium-stearate and self-assembled monolayer of octadecanethiol.

  12. Ultrathin silicon wafer bonding: Physics and applications

    NASA Astrophysics Data System (ADS)

    Beggans, Michael Howard

    Ultrathin silicon wafer bonding is an emerging process that simplifies device fabrication, reduces manufacturing costs, increases yield, and allows the realization of novel devices. Ultrathin silicon wafers are between 3 and 200 microns thick with all the same properties of the thicker silicon wafers (greater than 300 microns) normally used by the semiconductor electronics industry. Wafer bonding is one technique by which multiple layers are formed. In this thesis, the history and practice of wafer bonding is described and applied to the manufacture of microelectomechanical systems (MEMS) devices with layer thickness on the scale of microns. Handling and processing problems specific to ultrathin silicon wafers and their bonding are addressed and solved. A model that predicts the conformal nature of these flexible silicon wafers and its impact on bonding is developed in terms of a relatively new description of surface quality, the Power Spectral Density (PSD). A process for reducing surface roughness of silicon is elucidated and a model of this process is described. A method of detecting particle contamination in chemical baths and other processes using wafer bonding is detailed. A final section highlights some recent work that has used ultrathin silicon wafer bonding to fabricate MEMS devices that have reduced existing design complexity and made possible novel, and otherwise difficult to produce, sensors. A new fabrication process that can reduce the required time for "proof-of-principle" devices using ultrathin silicon wafers is also described.

  13. Quantum chemistry study of dielectric materials deposition

    NASA Astrophysics Data System (ADS)

    Widjaja, Yuniarto

    The drive to continually decrease the device dimensions of integrated circuits in the microelectronics industry requires that deposited films approach subnanometer thicknesses. Hence, a fundamental understanding of the physics and chemistry of film deposition is important to obtain better control of the properties of the deposited film. We use ab initio quantum chemistry calculations to explore chemical reactions at the atomic level. Important thermodynamic and kinetic parameters are then obtained, which can then be used as inputs in constructing first-principles based reactor models. Studies of new systems for which data are not available can be conducted as well. In this dissertation, we use quantum chemistry simulations to study the deposition of gate dielectrics for metal-oxide-semiconductor (MOS) devices. The focus of this study is on heterogeneous reactions between gaseous precursors and solid surfaces. Adsorbate-surface interactions introduce additional degrees of complexity compared to the corresponding gas-phase or solid-state reactions. The applicability and accuracy of cluster approximations to represent solid surfaces are first investigated. The majority of our results are obtained using B3LYP density functional theory (DFT). The structures of reactants, products, and transition states are obtained, followed by calculations of thermochemical and kinetic properties. Whenever experimental data are available, qualitative and/or quantitative comparisons are drawn. Atomistic mechanisms and the energetics of several reactions leading to the deposition of SiO2, Si3N4, and potential new high-kappa materials such as ZrO2, HfO2, and Al 2O3 have been explored in this dissertation. Competing reaction pathways are explored for each of the deposition reactions studied. For example, the potential energy surface (PES) for ZrO2 ALD shows that the reactions proceed through a trapping-mediated mechanism, which results in a competition between desorption and decomposition of the gaseous reactants, i.e. ZrCl4 and H2O, on the ZrO2 surface. This competition results in relatively low saturation coverage, which consequently leads to a slow growth rate and possibly affects the thickness uniformity and conformality. The insights gained are then used to systematically improve deposition reactions. For instance, from the ZrO2 ALD PES, we are able to suggest the use of high temperature and pressure to obtain higher surface coverage.

  14. A study on the evolution of dielectric function of ZnO thin films with decreasing film thickness

    SciTech Connect

    Li, X. D.; Chen, T. P. Liu, P.; Liu, Y.; Liu, Z.; Leong, K. C.

    2014-03-14

    Dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry. As the film thickness decreases, both real (?{sub 1}) and imaginary (?{sub 2}) parts of the dielectric function decrease significantly, and ?{sub 2} shows a blue shift. The film thickness dependence of the dielectric function is shown related to the changes in the interband absorption, discrete-exciton absorption, and continuum-exciton absorption, which can be attributed to the quantum confinement effect on both the band gap and exciton binding energies.

  15. Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

    SciTech Connect

    Kinyanjui, M. K. Kaiser, U.; Benner, G.; Pavia, G.; Boucher, F.; Habermeier, H.-U.; Keimer, B.

    2015-05-18

    We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12?nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presented approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.

  16. High efficiency ultrathin silicon solar cells

    NASA Technical Reports Server (NTRS)

    Storti, G.; Wrigley, C. Y.

    1979-01-01

    This paper summarizes developments in ultrathin, (50 micron), silicon solar cells for high power-to-weight ratio space power systems. The fabrication technology developments included uniformly thinning oriented silicon slices, enhancement of internal reflection, optimizing high-temperature processes, surface texturing and back surface field enhancement. The best textured-surface ultrathin cells have achieved 14.3% AMO efficiency, while pilot-manufacturing quantities of smooth-surfaced cells have been fabricated with efficiencies of 12%. Data are presented on cell structure, fabrication collection efficiencies and optical properties.

  17. Dielectric and complex impedance properties of tetravalent hafnium (HF 4+) integrated cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Sanchez, Luis

    The work presented in this thesis was carried out to understand the effects of tetravalent hafnium (Hf4+) ion on the crystal structure and phase, surface morphology, electrical, dielectric and complex impedance properties of cobalt ferrite (CoFe2O4; CFO). Hafnium incorporated cobalt ferrite, CoFe2-xHfxO4, with x = 0.00, 0.05, 0.075, 0.10, 0.15 and 0.20 were prepared by the standard solid state ceramic synthesis method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations were performed to determine the structural properties. Most important aspect of this study is to explore the dielectric and complex impedance properties as a function of variable temperature (T=300-1000 K) and frequency (f=20 Hz -1 MHz). Room temperature and the temperature dependence of dielectric constant, loss factor, complex impedance, and the ac resistivity measurements enabled us to understand the effect of temperature and frequency on the electrical and dielectric properties on CoFe2-xHfxO4 and, thus, to derive structure-property relation. X-ray diffraction (XRD) patterns for Hf-incorporated CFO confirm the formation of majority of CFO spinel [with space group Fd3m (227)] phase, in addition to the small amount of HfO2 monoclinic [space group, P1 21/c (14)] phase leading to formation of CFO-Hf composites. The lattice constant values derived from XRD for CFO-Hf were found to increase from 8.374 A (x = 0.000) to 8.391 A (x = 0.200). The lattice expansion is significant at the very first step of Hf-incorporation and then slows down with progressive Hf-incorporation. SEM imaging analysis indicates that Hf resides at the grain boundaries for CFO-Hf. The dielectric constant (epsilon') of CFO-Hf is T-independent at T<450 K, at which point increasing trend prevails. A grain bulk-boundary based two-layer model, where semiconducting-grains separated by insulating-grain boundaries, satisfactorily accounts for epsilon- T (>450 K) variation. Correspondingly, electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also accounts for the observed two dielectric-relaxations. The results demonstrate that the dielectric phenomena in CFO-Hf can be tailored by tuning Hf-concentration.

  18. Measurement of effective carrier lifetime at the semiconductor-dielectric interface by Photoconductive Decay (PCD) Method

    NASA Astrophysics Data System (ADS)

    Drummond, P. J.; Bhatia, D.; Ruzyllo, J.

    2013-03-01

    The semiconductor-dielectric interface is of key importance to the performance of Metal-Oxide-Semiconductor transistors (MOSFETs). The near-surface Photoconductance Decay (ns-PCD) method using probe contacts is shown in this study to be very useful in measuring effective carrier lifetime at the semiconductor-dielectric interface. By doing so, it provides direct information on the condition of the charge transport environment in the MOSFET channel without a need to fabricate a transistor. The way measurement is implemented depends on the thickness of dielectric. For dielectric layers thicker than about 5 nm, etched windows in the dielectric layer are necessary to achieve an ohmic contact with the semiconductor layer. For dielectric layers thinner than about 5 nm, however, the ohmic contact to the semiconductor substrate, essential to the performance of this measurement, is established using probes and electrical contact formation process. The measurements were performed on thermally oxidized Si-SiO2 structures as well as Si-Al2O3 (3 nm) and Si-Ta2O5 (3 nm) structures formed by means of Atomic Layer Deposition (ALD). The results obtained demonstrate that the PCD method adapted as discussed in this work can be very useful in monitoring condition of semiconductor - ultra-thin (<5 nm) dielectric interface by measuring carrier lifetime in the as-processed samples, i.e. without subjecting it to any processing step beyond dielectric deposition.

  19. Interfacial phenomena in high-kappa dielectrics

    NASA Astrophysics Data System (ADS)

    Mathew, Anoop

    The introduction of novel high-kappa dielectric materials to replace the traditional SiO2 insulating layer in CMOS transistors is a watershed event in the history of transistor development. Further, replacement of the traditional highly-doped polycrystalline silicon gate electrode with a new set of materials for metal gates complicates the transition and introduces further integration challenges. A whole variety of new material surfaces and interfaces are thus introduced that merit close investigation to determine parameters for optimal device performance. Nitrogen is a key component that improves the performance of a variety of materials for the next generation of these CMOS transistors. Nitrogen is introduced into new gate dielectric materials such as hafnium silicates as well as in potential metal gate materials such as hafnium nitride. A photoemission study of the binding energies of the various atoms in these systems using photoemission reveals the nature of the atomic bonding. The current study compares hafnium silicates of various compositions which were thermally nitrided at different temperatures in ammonia, hafnium nitrides, and thin HfO2 films using photoelectron spectroscopy. A recurring theme that is explored is the competition between oxygen and nitrogen atoms in bonding with hafnium and other atoms. The N 1s photoemission peak is seen to have contributions from its bonding with hafnium, oxygen, and silicon atoms. The Hf 4f and O 1s spectra similarly exhibit signatures of their bonding environment with their neighboring atoms. Angle resolved photoemission and in-situ annealing/argon sputtering experiments are used to elucidate the nature of the bonding and its evolution with processing. A nondestructive profilitng of nitrogen distribution as a function of composition in nitrided hafnium silicates is also constructed using angle resolved photoemission as a function of the take-off angle. These results are corroborated with depth reconstruction obtained using medium energy ion scattering (MEIS). A comparison of samples nitrided at progressively increasing temperatures in an ammonia environment shows substitution of oxygen with nitrogen atoms and increasing penetration of nitrogen into the gate stack. Trends in the binding energy of the the as-prepared hafnium silicates suggest that they are non-phase separated, and the binding energy of the hafnium and silicon track the relative composition. Upon being subject to rapid thermal annealing, the samples are observed to show behavior consistent with phase separation. There is also the evidence of charges at the oxide/Si interface that modify the expected behavior of the shifts in binding energy. In another set of experiments, a one-cycle atomic layer deposition (ALD) growth reaction on the water terminated Si(100) -- (2x1) surface is shown to lead to successful nucleation, high metal oxide coverage, and an abrupt metal-oxide/silicon interface as confirmed by photoemission, reflection high energy electron diffraction (RHEED), and Rutherford back scattering (RBS) measurements. Photoemission results confirm the coordination states of the hafnium and oxygen atoms. A Hf 4f core level shift is observed and assigned to the presence of the Si-O-Hf bonding environment with the more electronegative Si atom inducing the binding energy shift. This Hf 4f shift is smaller than that reported previously for silicates because of the difference of the semiconductor bonding environment. The subspecies *(O)2HfCl2 and *OHfCl3 are seen to be the predominant intermediate species in these reactions and photoemission results provide corroborative evidence for their presence. Experiments indicate that the hydroxyl sites bound to Si(100) are active for adsorption. The abrupt interface could be useful for aggressive Effective Oxide Thickness (EOT) scaling.

  20. Ultrathin niobium nanofilms on fiber optical tapers – a new route towards low-loss hybrid plasmonic modes

    PubMed Central

    Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A.

    2015-01-01

    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10?nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15??m/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices. PMID:26593209

  1. Ultrathin niobium nanofilms on fiber optical tapers - a new route towards low-loss hybrid plasmonic modes.

    PubMed

    Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A

    2015-01-01

    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10?nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3-4 dB/mm in aqueous environment and a refractive index sensitivity up to 15??m/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices. PMID:26593209

  2. Investigation of band gap and permittivity of the perovskite CaTiO3 in ultrathin layers

    NASA Astrophysics Data System (ADS)

    Krause, A.; Weber, W. M.; Pohl, D.; Rellinghaus, B.; Kersch, A.; Mikolajick, T.

    2015-10-01

    Simulations and experimental results of ultrathin layers of the model perovskite CaTiO3 prove its suitability for integration as a novel dielectric in industrial applications due to an excellent compromise between band gap and permittivity. The computational approach relies on density functional theory in the local density approximation for CaTiO3 and comparable perovskites. With low-energy EELS measurements, the band gap of 3.8-4.38?eV for CaTiO3 was determined with exceptional precision, using a monochromatic electron beam (80?kV acceleration voltage, 0.18?eV FWHM) in a high resolution scanning transmission electron microscopy setup. Results of capacitance voltage measurements of ultrathin CaTiO3 capacitors show an excellent permittivity of 102.3 for 17.8?nm layer thickness. DUV-VIS ellipsometric measurements are carried out to complete the picture of band gap and permittivity of CaTiO3 as a competing perovskite to SrTiO3 or others for possible integration in ultrathin capacitor stacks.

  3. Atomically Flat Ultrathin Cobalt Ferrite Islands.

    PubMed

    Martín-García, Laura; Quesada, Adrián; Munuera, Carmen; Fernández, Jose F; García-Hernández, Mar; Foerster, Michael; Aballe, Lucía; de la Figuera, Juan

    2015-10-01

    A route for fabricating structurally perfect cobalt ferrite magnetic nanostructures is demonstrated. Ultrathin islands of up to 100 ?m(2) with atomically flat surfaces and free from antiphase boundaries are developed. The extremely low defect concentration leads to a robust magnetic order, even for thicknesses below 1 nm, and exceptionally large magnetic domains. This approach allows the evaluation of the influence of specific extrinsic effects on domain wall pinning. PMID:26306027

  4. Ultrathin silver nanowires produced by amyloid biotemplating.

    PubMed

    Malisauskas, Mantas; Meskys, Rolandas; Morozova-Roche, Ludmilla A

    2008-01-01

    By using a self-assembled amyloid from lysozyme as biotemplate we produced an ultrathin silver wire of 1 nm diameter and up to 2 mum in length, which is at the limit attainable in nanobiotechnological manufacturing. We showed that 2,2,2-trifluoroethanol produces a dual effect: it reduces ionic silver to colloidal nanoparticles with a regular size, depending on the length of incubation, and induces fibrillar assembly into the amyloid scaffold, forming the hollow channel filled with silver. PMID:19194928

  5. Photoresponsive properties of ultrathin silicon nanowires

    SciTech Connect

    Tran, Duy P.; Macdonald, Thomas J.; Nann, Thomas; Thierry, Benjamin E-mail: benjamin.thierry@unisa.edu.au; Wolfrum, Bernhard; Stockmann, Regina; Offenhäusser, Andreas E-mail: benjamin.thierry@unisa.edu.au

    2014-12-08

    Functional silicon nanowires (SiNWs) are promising building blocks in the design of highly sensitive photodetectors and bio-chemical sensors. We systematically investigate the photoresponse properties of ultrathin SiNWs (20?nm) fabricated using a size-reduction method based on e-beam lithography and tetramethylammonium hydroxide wet-etching. The high-quality SiNWs were able to detect light from the UV to the visible range with excellent sensitivity (?1 pW/array), good time response, and high photoresponsivity (R???2.5?×?10{sup 4?}A/W). Improvement of the ultrathin SiNWs' photoresponse has been observed in comparison to 40?nm counter-part nanowires. These properties are attributable to the predominance surface-effect due to the high surface-to-volume ratio of ultrathin SiNWs. Long-term measurements at different temperatures in both the forward and reverse bias directions demonstrated the stability and reliability of the fabricated device. By sensitizing the fabricated SiNW arrays with cadmium telluride quantum dots (QDs), hybrid QD SiNW devices displayed an improvement in photocurrent response under UV light, while preserving their performance in the visible light range. The fast, stable, and high photoresponse of these hybrid nanostructures is promising towards the development of optoelectronic and photovoltaic devices.

  6. Photoresponsive properties of ultrathin silicon nanowires

    NASA Astrophysics Data System (ADS)

    Tran, Duy P.; Macdonald, Thomas J.; Wolfrum, Bernhard; Stockmann, Regina; Nann, Thomas; Offenhäusser, Andreas; Thierry, Benjamin

    2014-12-01

    Functional silicon nanowires (SiNWs) are promising building blocks in the design of highly sensitive photodetectors and bio-chemical sensors. We systematically investigate the photoresponse properties of ultrathin SiNWs (20 nm) fabricated using a size-reduction method based on e-beam lithography and tetramethylammonium hydroxide wet-etching. The high-quality SiNWs were able to detect light from the UV to the visible range with excellent sensitivity (˜1 pW/array), good time response, and high photoresponsivity (R ˜ 2.5 × 104 A/W). Improvement of the ultrathin SiNWs' photoresponse has been observed in comparison to 40 nm counter-part nanowires. These properties are attributable to the predominance surface-effect due to the high surface-to-volume ratio of ultrathin SiNWs. Long-term measurements at different temperatures in both the forward and reverse bias directions demonstrated the stability and reliability of the fabricated device. By sensitizing the fabricated SiNW arrays with cadmium telluride quantum dots (QDs), hybrid QD SiNW devices displayed an improvement in photocurrent response under UV light, while preserving their performance in the visible light range. The fast, stable, and high photoresponse of these hybrid nanostructures is promising towards the development of optoelectronic and photovoltaic devices.

  7. Broadband frequency-selective spoof surface plasmon polaritons on ultrathin metallic structure.

    PubMed

    Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

    2015-01-01

    We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10?dB with the transmission loss around 1.5?dB in the selective frequency band from 7 to 10?GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band. PMID:25641730

  8. Spoof localized surface plasmons on ultrathin textured MIM ring resonator with enhanced resonances

    PubMed Central

    Zhou, Yong Jin; Xiao, Qian Xun; Jia Yang, Bao

    2015-01-01

    We numerically demonstrate that spoof localized surface plasmons (LSPs) resonant modes can be enhanced based on ultrathin corrugated metal-insulator-metal (MIM) ring resonator. Further enhancement of the LSPs modes has been achieved by incorporating an efficient and ease-of-integration exciting method. Quality factors of resonance peaks have become much larger and multipolar resonances modes can be easily observed on the textured MIM ring resonator excited by a microstrip line. Experimental results validate the high-efficiency excitation and resonance enhancements of spoof LSPs modes on the MIM ring resonator in the microwave frequencies. We have shown that the fabricated resonator is sensitive to the variation of both the dielectric constant and the thickness of surrounding materials under test. The spoof plasmonic resonator can be used as key elements to provide many important device functionalities such as optical communications, signal processing, and spectral engineering in the plasmonic integration platform. PMID:26420668

  9. Spoof localized surface plasmons on ultrathin textured MIM ring resonator with enhanced resonances

    NASA Astrophysics Data System (ADS)

    Zhou, Yong Jin; Xiao, Qian Xun; Jia Yang, Bao

    2015-09-01

    We numerically demonstrate that spoof localized surface plasmons (LSPs) resonant modes can be enhanced based on ultrathin corrugated metal-insulator-metal (MIM) ring resonator. Further enhancement of the LSPs modes has been achieved by incorporating an efficient and ease-of-integration exciting method. Quality factors of resonance peaks have become much larger and multipolar resonances modes can be easily observed on the textured MIM ring resonator excited by a microstrip line. Experimental results validate the high-efficiency excitation and resonance enhancements of spoof LSPs modes on the MIM ring resonator in the microwave frequencies. We have shown that the fabricated resonator is sensitive to the variation of both the dielectric constant and the thickness of surrounding materials under test. The spoof plasmonic resonator can be used as key elements to provide many important device functionalities such as optical communications, signal processing, and spectral engineering in the plasmonic integration platform.

  10. Resonant dielectric metamaterials

    DOEpatents

    Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

    2014-12-02

    A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

  11. Imaging Electrons in Ultra-thin Nanowires

    NASA Astrophysics Data System (ADS)

    Boyd, Erin E.

    2011-12-01

    Ultra-thin semiconductor nanowires are promising systems in which to explore novel low-dimensional physics and are attractive candidates for future nanoelectronics. Ultra-thin nanowires with diameters of 20 to 30 nm are essentially one-dimensional (ID) for moderate electron number, because only one radial subband is occupied. Low-temperature scanning gate microscopy is especially well suited for improving our understanding of nanowires in order to optimize the construction of nanowire systems. We use a home-built liquid-He cooled scanning gate microscope (SGM) to probe and manipulate electrons beneath the surface of devices. The SGM's conductance images are obtained by scanning the charged SGM tip above the sample and recording the change in conductance through the device as a function of tip position. We present simulations of extracting the amplitude of the 1D electron wavefunction along the length of the quantum dot in an ultra-thin InAs/InP heterostructure nanowire (diameter = 30 nm) using a SGM. A weakly perturbing SGM tip slightly dents the electron wavefunction inside the quantum dot, and we propose measuring the change in energy of the dot due to the perturbation as a function of tip position. By measuring the change in energy of the dot and by knowing the form of the tip potential, the amplitude of the wavefunction can be found. This extraction technique could serve as a powerful tool to improve our understanding of electron behavior in quasi-1 D systems. We have used our SGM to image the conductance through an ultra-thin (diameter ˜ 30 nm) 1nAs nanowire with two InP barriers. Our imaging technique provides detailed information regarding the position and flow of electrons in the nanowire. We demonstrate that the charged SPM tip's position or voltage can be used to control the number of electrons on the quantum dots. We spatially locate three quantum dots in series along the length of the ultra-thin nanowire. Using energy level spectroscopy and the conductance images, we find the length of all three of the dots, and we determine the dots' relative coupling strength.

  12. Request Information Download PDF Permalink Print Ultrathin Nanoporous Silicon Nitride

    E-print Network

    Heydari, Payam

    Request Information Download PDF Permalink Print Ultrathin Nanoporous Silicon Nitride and windows for transmission electron microscopy molecular sieves: separation/filtration of molecules by size the ultrathin character of these membranes in silicon nitride, they can be used as windows for high

  13. Thermal stability of precursors for atomic layer deposition of TiO2, ZrO2, and HfO2: an ab initio study of alpha-hydrogen abstraction in bis-cyclopentadienyl dimethyl complexes.

    PubMed

    Zydor, Aleksandra; Elliott, Simon D

    2010-02-01

    Thin film dielectrics based on hafnium and zirconium oxides are being introduced to increase the permittivity of insulating layers in nanoelectronic transistor and memory devices. Atomic layer deposition (ALD) is the process of choice for fabricating these films, and the success of this method depends crucially on the chemical properties of the precursor molecules. Designing new precursors requires molecular engineering and chemical tailoring to obtain specific physical properties and performance capabilities. A successful ALD precursor should be volatile, stable in the gas-phase, but reactive on the substrate and growing surface, leading to inert byproduct. This study is concerned with the thermal stability in the gas phase of Ti, Zr, and Hf precursors that contain cyclopentadienyl (Cp = C(5)H(5-x)R(x)) ligands. We use density functional theory (DFT) to probe the non-ALD decomposition pathway and find a mechanism via intramolecular alpha-H transfer that produces an alkylidene complex. The analysis shows that thermal stabilities of complexes of the type MCp(2)(CH(3))(2) increase down group 4 (M = Ti, Zr, and Hf) due to an increase in the HOMO-LUMO band gap of the reactants, which itself increases with the electrophilicity of the metal. Precursor decomposition via this pathway in the gas phase can therefore be avoided by replacing the alpha-H donor or acceptor ligands or by increasing the electrophilicity of the metal. This illustrates how the ALD process window can be widened by rational molecular design based on mechanistic understanding. PMID:20055493

  14. Dielectric Theory of the Vacuum

    E-print Network

    J. X. Zheng-Johansson

    2006-12-11

    The vacuum is proposed to be a dielectric medium constituted of neutral but polarizable vacuuons based on overall experimental observations in separate publications. In the present paper I formally develop the dielectric theory for this dielectric vacuum.

  15. Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy

    NASA Astrophysics Data System (ADS)

    Dols-Perez, A.; Gramse, G.; Calò, A.; Gomila, G.; Fumagalli, L.

    2015-10-01

    We measured and quantified the local electric polarization properties of ultrathin (~5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants ?r = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ~50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping.We measured and quantified the local electric polarization properties of ultrathin (~5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants ?r = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ~50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping. Electronic supplementary information (ESI) available: Modelling sharp probes on insulator substrates, probe geometry calibration. See DOI: 10.1039/c5nr04983k

  16. Design and Fabrication of Ultrathin Plasmonic Nanostructures for Photovoltaics, Color Filtering and Biosensing

    NASA Astrophysics Data System (ADS)

    Zeng, Beibei

    Since the first report of the extraordinary optical transmission (EOT) phenomenon through periodic subwavelength hole arrays milled in optically-thick metal film, plasmonics have generated considerable interest because they enable new fundamental science and application technologies. Central to this phenomenon is the role of surface plasmon polaritons (SPPs), which are essentially electromagnetic waves trapped at the interface between a metal and a dielectric medium through their interactions with free electrons at the metal surface. The resonant interaction between the incident light and surface charge oscillations enables the concentration and manipulation of light at deep subwavelength scales, opening up exciting application opportunities ranging from subwavelength optics and optoelectronics to bio/chemical sensing. Furthermore, additional phenomena arise as the thickness of metal film decreases to be comparable to its skin depth (optically-thin), and the single-interface SPPs on the top and bottom metal surfaces combine to form two coupled SPPs, the long-range and short-range SPPs. Until now, much less work has focused on the study of surface plasmon resonances (SPRs) in ultrathin nanostructured metals. This dissertation seeks to elucidate underlying physical mechanisms of SPRs in ultrathin nanostructured metals and tailor them for practical applications. Inspired by state-of-the-art advances on plasmonics in optically-thick nanostructured metals, one- (1D) and two-dimensional (2D) ultrathin plasmonic nanostructures are exploited for particular applications in three essential areas: photovoltaics, color filters and biosensors, achieving superior performances compared with their optically-thick counterparts. More specifically, this thesis is focused on systematic investigations on: (1) plasmonic transparent electrodes for organic photovoltaics and polarization-insensitive optical absorption enhancement in the active layer; (2) plasmonic subtractive color filters with record-high transmission efficiency and other unique properties; (3) rapid and highly-sensitive plasmonic bio-sensors employing ultrathin nanogratings. The successful development of these new plasmonic platforms have far-reaching impact on green energy technologies, next-generation displays and imagers, and label-free bio-sensing for point-of-care diagnostics.

  17. On the structural development during ultrathin amorphous Al2O3 film growth on Al(111) and Al(100) surfaces by thermal oxidation

    NASA Astrophysics Data System (ADS)

    Flötotto, D.; Wang, Z. M.; Mittemeijer, E. J.

    2015-03-01

    The structural developments during growth of ultrathin amorphous Al2O3 film on bare Al(100) and Al(111) surfaces, by dry thermal oxidation in the oxygen partial pressure range of 1 × 10- 5-1.0 Pa at 300 K, were investigated as function of the oxide-film thickness by (local) chemical state analysis using angle-resolved X-ray photoelectron spectroscopy in combination with low electron energy diffraction and cross-sectional high resolution transmission electron microscopy. The effect of the dielectric discontinuity, at the interfaces of the surficial Al2O3 film has been determined quantitatively and has been subtracted from the observed chemical shifts of the core level photoelectron binding energies as well as from the observed Auger transition kinetic energies. It is revealed that ultrathin amorphous Al2O3 films on the Al(111) and Al(100) surfaces experience remarkably different structural developments upon growth.

  18. Optical properties of ultrafine line and space polymeric nanogratings coated with metal and metal-dielectric-metal thin films.

    PubMed

    Leong, Eunice Sok Ping; Wu, Siji; Zhang, Nan; Loh, Wei Wei; Khoo, Eng Huat; Si, Guang Yuan; Dai, Hai Tao; Liu, Yan Jun

    2014-02-01

    Noble metal and metal-dielectric-metal ultrathin films were deposited on the surfaces of ultrafine polymeric nanogratings, which were fabricated using nanoimprint lithography. Experimental results showed dramatic differences of the surface morphologies for single metal and triple metal-dielectric-metal films deposited on flat and corrugated polymeric surfaces. The effect of the surface morphology on the optical properties was hence investigated and analyzed under linearly polarized light. The surface plasmon resonances of single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces were also characterized based on the Kretschmann prism-coupling method. The single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces are important for the study of photon-plasmon interactions (i.e. couplings and conversions) at the interfaces between a nanograting and metal films. PMID:24406796

  19. Arrays of ultrathin silicon solar microcells

    DOEpatents

    Rogers, John A.; Rockett, Angus A.; Nuzzo, Ralph; Yoon, Jongseung; Baca, Alfred

    2015-08-11

    Provided are solar cells, photovoltaics and related methods for making solar cells, wherein the solar cell is made of ultrathin solar grade or low quality silicon. In an aspect, the invention is a method of making a solar cell by providing a solar cell substrate having a receiving surface and assembling a printable semiconductor element on the receiving surface of the substrate via contact printing. The semiconductor element has a thickness that is less than or equal to 100 .mu.m and, for example, is made from low grade Si.

  20. The Reliability of Ultrathin Silicon Dioxide

    NASA Astrophysics Data System (ADS)

    Lee, Kyungho

    The kinetics of carrier trapping and breakdown in oxides of less than 5 nm was studied. It was found that electron trapping was negligible, but hole trapping was relatively high. An effective oxide trap density due to tunnel annealing was proposed. The rate equation of carrier trapping in the bulk oxide was presented in connection with the generated hole injection by anode surface plasmons. The voltage variation during a constant current test was analyzed using the hole trapping model and capacitance-voltage measured interface trap generation, and approximate values for the capture cross section and hole generation rate were extracted. Using the weak area breakdown model we found that the ratio of weak to robust area is about 5%. The electrical characteristics of ultrathin oxides used in an x-ray lithography n-channel metal-oxide-silicon (NMOS) process grown at 700^circC and 950^circC were studied. Oxides grown at 950^circC had a lower interface trap density than 700^circ C oxides, but 950^circC oxides are more sensitive to x-ray radiation damage. After 350^circC hydrogen annealing about 80% of the radiation damage in the form of interface traps was recovered. Charge trapping and device degradation by Fowler -Nordheim (F-N) stress was studied with ultrathin gate oxide (5.5 nm) MOSFETs. With positive and negative F-N stress it is found that ultrathin oxides show negligible electron trapping and relatively high hole trapping. These results are due to the effects of tunnel annealing and reduced electron trapping in these ultrathin layers. Oxide charge trapping and interface trap generation by hot carrier stress was studied with x-ray irradiated MOSFETs. Although the threshold voltage and transconductance were recovered after a hydrogen anneal at 450^ circC, the irradiated and annealed devices were more susceptible to damage under hot carrier stressing. The latent damage was quantified using the various gate voltage hot carrier stresses. It is found that the major part of latent damage is related to oxide hole traps and interface traps. Electron trapping is present, but is less significant.

  1. Ultrathin, epitaxial cerium dioxide on silicon

    SciTech Connect

    Flege, Jan Ingo Kaemena, Björn; Höcker, Jan; Schmidt, Thomas; Falta, Jens; Bertram, Florian; Wollschläger, Joachim

    2014-03-31

    It is shown that ultrathin, highly ordered, continuous films of cerium dioxide may be prepared on silicon following substrate prepassivation using an atomic layer of chlorine. The as-deposited, few-nanometer-thin Ce{sub 2}O{sub 3} film may very effectively be converted at room temperature to almost fully oxidized CeO{sub 2} by simple exposure to air, as demonstrated by hard X-ray photoemission spectroscopy and X-ray diffraction. This post-oxidation process essentially results in a negligible loss in film crystallinity and interface abruptness.

  2. Arrays of ultrathin silicon solar microcells

    DOEpatents

    Rogers, John A; Rockett, Angus A; Nuzzo, Ralph; Yoon, Jongseung; Baca, Alfred

    2014-03-25

    Provided are solar cells, photovoltaics and related methods for making solar cells, wherein the solar cell is made of ultrathin solar grade or low quality silicon. In an aspect, the invention is a method of making a solar cell by providing a solar cell substrate having a receiving surface and assembling a printable semiconductor element on the receiving surface of the substrate via contact printing. The semiconductor element has a thickness that is less than or equal to 100 .mu.m and, for example, is made from low grade Si.

  3. Ultra-thin silicate films on metals.

    PubMed

    Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2015-11-11

    Silica is one of the key materials in many modern technological applications. 'Surface science' approach for understanding surface chemistry on silica-based materials, on the one hand, and further miniaturization of new generation electronic devices, on the other, all these face the necessity of rational design of the ultrathin silica films on electrically conductive substrates. The review updates recent studies in this field. Despite the structural complexity and diversity of silica, substantial progress has recently been achieved in understanding of the atomic structure of truly 2D silicates. PMID:26459605

  4. Ultrathin Au nanowires and their transport properties.

    PubMed

    Wang, Chao; Hu, Yongjie; Lieber, Charles M; Sun, Shouheng

    2008-07-16

    This paper presents a facile synthesis of single-crystalline Au nanowires by reduction of HAuCl4 in oleic acid and oleylamine. The diameter of these micron-meter-long Au nanowires is controlled to be 3 and 9 nm by volume ratio of oleylamine and oleic acid. When linked between two gold electrodes, the 9 nm Au nanowire shows good electron conductivity with its breakdown current density reaching 3.5 x 10(12) A/m2. This demonstrates that the chemically made ultrathin Au nanowires can be used as a molecular-scale interconnect for nanoelectronic applications. PMID:18540579

  5. Ultra-thin silicate films on metals

    NASA Astrophysics Data System (ADS)

    Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2015-11-01

    Silica is one of the key materials in many modern technological applications. ‘Surface science’ approach for understanding surface chemistry on silica-based materials, on the one hand, and further miniaturization of new generation electronic devices, on the other, all these face the necessity of rational design of the ultrathin silica films on electrically conductive substrates. The review updates recent studies in this field. Despite the structural complexity and diversity of silica, substantial progress has recently been achieved in understanding of the atomic structure of truly 2D silicates.

  6. Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics.

    PubMed

    Li, Guanhong; Li, Qunqing; Jin, Yuanhao; Zhao, Yudan; Xiao, Xiaoyang; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

    2015-10-22

    Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors. PMID:26451806

  7. Medium energy ion scattering for the high depth resolution characterisation of high-k dielectric layers of nanometer thickness

    NASA Astrophysics Data System (ADS)

    van den Berg, J. A.; Reading, M. A.; Bailey, P.; Noakes, T. Q. C.; Adelmann, C.; Popovici, M.; Tielens, H.; Conard, T.; de Gendt, S.; van Elshocht, S.

    2013-09-01

    Medium energy ion scattering (MEIS) using, typically, 100-200 keV H+ or He+ ions derives it ability to characterise nanolayers from the fact that the energy after backscattering depends (i) on the elastic energy loss suffered in a single collision with a target atom and (ii) on the inelastic energy losses on its incoming and outgoing trajectories. From the former the mass of the atom can be determined and from the latter its depth. Thus MEIS yields depth dependent compositional and structural information, with high depth resolution (sub-nm near the surface) and good sensitivity for all but the lighter masses. It is particularly well suited for the depth analysis of high-k multilayers of nanometer thickness. Accurate quantification of the depth distributions of atomic species can be obtained using suitable spectrum simulation. In the present paper, important aspects of MEIS including quantification, depth resolution and spectrum simulation are briefly discussed. The capabilities of the technique in terms of the high depth resolution layer compositional and structural information it yields, is illustrated with reference to the detailed characterisation of a range of high-k nanolayer and multilayer structures for current microelectronic devices or those still under development: (i) HfO2 and HfSiOx for gate dielectric applications, including a TiN/Al2O3/HfO2/SiO2/Si structure, (ii) TiN/SrTiO3/TiN and (iii) TiO2/Ru/TiN multilayer structures for metal-insulator-metal capacitors (MIMcaps) in DRAM applications. The unique information provided by the technique is highlighted by its clear capability to accurately quantify the composition profiles and thickness of nanolayers and complex multilayers as grown, and to identify the nature and extent of atom redistribution (e.g. intermixing, segregation) during layer deposition, annealing and plasma processing. The ability makes it a valuable tool in the development of the nanostructures that will become increasingly important as device dimensions continue to be scaled down.

  8. Ultrathin inorganic molecular nanowire based on polyoxometalates.

    PubMed

    Zhang, Zhenxin; Murayama, Toru; Sadakane, Masahiro; Ariga, Hiroko; Yasuda, Nobuhiro; Sakaguchi, Norihito; Asakura, Kiyotaka; Ueda, Wataru

    2015-01-01

    The development of metal oxide-based molecular wires is important for fundamental research and potential practical applications. However, examples of these materials are rare. Here we report an all-inorganic transition metal oxide molecular wire prepared by disassembly of larger crystals. The wires are comprised of molybdenum(VI) with either tellurium(IV) or selenium(IV): {(NH4)2[XMo6O21]}n (X=tellurium(IV) or selenium(IV)). The ultrathin molecular nanowires with widths of 1.2?nm grow to micrometre-scale crystals and are characterized by single-crystal X-ray analysis, Rietveld analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, thermal analysis and elemental analysis. The crystals can be disassembled into individual molecular wires through cation exchange and subsequent ultrasound treatment, as visualized by atomic force microscopy and transmission electron microscopy. The ultrathin molecular wire-based material exhibits high activity as an acid catalyst, and the band gap of the molecular wire-based crystal is tunable by heat treatment. PMID:26139011

  9. Ultrathin inorganic molecular nanowire based on polyoxometalates

    PubMed Central

    Zhang, Zhenxin; Murayama, Toru; Sadakane, Masahiro; Ariga, Hiroko; Yasuda, Nobuhiro; Sakaguchi, Norihito; Asakura, Kiyotaka; Ueda, Wataru

    2015-01-01

    The development of metal oxide-based molecular wires is important for fundamental research and potential practical applications. However, examples of these materials are rare. Here we report an all-inorganic transition metal oxide molecular wire prepared by disassembly of larger crystals. The wires are comprised of molybdenum(VI) with either tellurium(IV) or selenium(IV): {(NH4)2[XMo6O21]}n (X=tellurium(IV) or selenium(IV)). The ultrathin molecular nanowires with widths of 1.2?nm grow to micrometre-scale crystals and are characterized by single-crystal X-ray analysis, Rietveld analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, thermal analysis and elemental analysis. The crystals can be disassembled into individual molecular wires through cation exchange and subsequent ultrasound treatment, as visualized by atomic force microscopy and transmission electron microscopy. The ultrathin molecular wire-based material exhibits high activity as an acid catalyst, and the band gap of the molecular wire-based crystal is tunable by heat treatment. PMID:26139011

  10. Flexible, Ultra-Thin, Embedded Die Packaging

    NASA Astrophysics Data System (ADS)

    McPherson, Ryan J.

    As thin, flexible electronics solutions become more robust, their integration into everyday life becomes more likely. With possible applications in wearable electronics, biomedical sensors, or 'peel and stick' sensors, the reliability of these ultra-thin packages becomes paramount. Likewise, the density achievable with stacked packages benefits greatly from thinner die stacks. To this end, techniques previously developed have demonstrated packages with die thinned to approximately 20mum. Covered in this work are methods for thinning and packaging silicon die, as well as information on common materials used in these processes. The author's contribution is a fabrication process for embedding ultra-thin (approximately 10mum) silicon die in polyimide substrates. This method is fully illustrated in Chapter 3 and enumerated in the Appendix as a quick reference. Additionally, thermal cycle testing of passive daisy chain assemblies has shown promising reliability data. Packages were mounted in three alignments: flat, concave, and convex, and placed into thermal shock testing. Finally, the author discusses possible applications for this fabrication process, including the fabrication of multi-chip-modules.

  11. Solution-Processed Dielectrics Based on Thickness-Sorted Two-Dimensional Hexagonal Boron Nitride Nanosheets.

    PubMed

    Zhu, Jian; Kang, Joohoon; Kang, Junmo; Jariwala, Deep; Wood, Joshua D; Seo, Jung-Woo T; Chen, Kan-Sheng; Marks, Tobin J; Hersam, Mark C

    2015-10-14

    Gate dielectrics directly affect the mobility, hysteresis, power consumption, and other critical device metrics in high-performance nanoelectronics. With atomically flat and dangling bond-free surfaces, hexagonal boron nitride (h-BN) has emerged as an ideal dielectric for graphene and related two-dimensional semiconductors. While high-quality, atomically thin h-BN has been realized via micromechanical cleavage and chemical vapor deposition, existing liquid exfoliation methods lack sufficient control over h-BN thickness and large-area film quality, thus limiting its use in solution-processed electronics. Here, we employ isopycnic density gradient ultracentrifugation for the preparation of monodisperse, thickness-sorted h-BN inks, which are subsequently layer-by-layer assembled into ultrathin dielectrics with low leakage currents of 3 × 10(-9) A/cm(2) at 2 MV/cm and high capacitances of 245 nF/cm(2). The resulting solution-processed h-BN dielectric films enable the fabrication of graphene field-effect transistors with negligible hysteresis and high mobilities up to 7100 cm(2) V(-1) s(-1) at room temperature. These h-BN inks can also be used as coatings on conventional dielectrics to minimize the effects of underlying traps, resulting in improvements in overall device performance. Overall, this approach for producing and assembling h-BN dielectric inks holds significant promise for translating the superlative performance of two-dimensional heterostructure devices to large-area, solution-processed nanoelectronics. PMID:26348822

  12. Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy.

    PubMed

    Dols-Perez, A; Gramse, G; Calò, A; Gomila, G; Fumagalli, L

    2015-10-29

    We measured and quantified the local electric polarization properties of ultrathin (?5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants ?r = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ?50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping. PMID:26488226

  13. Parallel-Plate Waveguide Terahertz Time Domain Spectroscopy for Ultrathin Conductive Films

    NASA Astrophysics Data System (ADS)

    Razanoelina, M.; Kinjo, R.; Takayama, K.; Kawayama, I.; Murakami, H.; Mittleman, Daniel M.; Tonouchi, M.

    2015-12-01

    Development of techniques for characterization of extremely thin films is an important challenge in terahertz (THz) science and applications. Spectroscopic measurements of materials on the nanometer scale or of atomic layer thickness (2D materials) require a sufficient terahertz wave-matter interaction length, which is challenging to achieve in conventional transmission geometry. Waveguide-based THz spectroscopy offers an alternative method to overcome this problem. In this paper, we investigate a new parallel-plate waveguide (PPWG) technique for measuring dielectric properties of ultrathin gold films, in which we mount the thin film sample at the center of the waveguide. We discuss a model of THz dielectric parameter extraction based on waveguide theory and analyze the response of thin films for both transverse magnetic (TM) and transverse electric (TE) waveguide modes. In contrast to other waveguide methods, our approach enables comparison of the material response with different electromagnetic field distributions without significantly changing the experimental setup. As a result, we demonstrate that TE modes have a better sensitivity to the properties of the thin film. For prototype test samples, optical parameters extracted using our method are in good agreement with literature values.

  14. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M. (Livermore, CA); Sampayan, Stephen (Manteca, CA); Slenes, Kirk (Albuquerque, NM); Stoller, H. M. (Albuquerque, NM)

    2009-11-10

    A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

  15. Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.

    DOEpatents

    Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchoque, NY); DeSanto, Leonard (Patchoque, NY); Veligdan, James T. (Manorville, NY)

    2005-02-15

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  16. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

    2003-02-11

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  17. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

    2001-10-09

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  18. Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.

    DOEpatents

    Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

    2005-05-17

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  19. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

    2002-01-01

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated With a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  20. Dielectric spectroscopy in agrophysics

    NASA Astrophysics Data System (ADS)

    Skierucha, W.; Wilczek, A.; Szyp?owska, A.

    2012-04-01

    The paper presents scientific foundation and some examples of agrophysical applications of dielectric spectroscopy techniques. The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which occur in agriculture. Dielectric spectroscopy, which describes the dielectric properties of a sample as a function of frequency, may be successfully used for examinations of properties of various materials. Possible test materials may include agrophysical objects such as soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc. Dielectric spectroscopy techniques enable non-destructive and non-invasive measurements of the agricultural materials, therefore providing tools for rapid evaluation of their water content and quality. There is a limited number of research in the field of dielectric spectroscopy of agricultural objects, which is caused by the relatively high cost of the respective measurement equipment. With the fast development of modern technology, especially in high frequency applications, dielectric spectroscopy has great potential of expansion in agrophysics, both in cognitive and utilitarian aspects.

  1. Accurate surface profilometry of ultrathin wafers

    NASA Astrophysics Data System (ADS)

    Weeks, A. E.; Litwin, D.; Galas, J.; Surma, B.; Piatkowski, B.; MacLaren, D. A.; Allison, W.

    2007-09-01

    Geometric characterization of 50 mm diameter, 50 µm thick single-crystal Si(1 1 1) wafers has been performed using complementary methods: industry-standard capacitance measurements of warp and total thickness variation (TTV), and a technique we term scanned chromatic confocal profilometry (SCCP). We compare the measurements made by the two techniques and demonstrate the limitations of capacitance measurements when applied to ultrathin wafers. The two-dimensional SCCP measurements are shown to enhance the description of wafer thickness variations beyond that generated by the standard test method. We discuss a Fourier transform-based analysis and show it to be useful in wafer quality assessment. Adding a summary of spatial frequencies in a wafer's thickness map to the conventional measures of warp and TTV provides a more complete summary of the salient features of a wafer's geometry.

  2. Self-Organized Ultrathin Oxide Nanocrystals

    SciTech Connect

    Huo, Ziyang; Tsung, Chia-kuang; Huang, Wenyu; Fardy, Melissa; Yan, Ruoxue; Li, Yadong; Yang, Piedong; Zhang, Xiaofeng

    2009-01-08

    Sub-2-nm (down to one-unit cell) uniform oxide nanocrystals and highly ordered superstructures were obtained in one step using oleylamine and oleic acid as capping and structure directing agents. The cooperative nature of the nanocrystal growth and assembly resulted in mesoscopic one-dimensional ribbon-like superstructures made of these ultrathin nanocrystals. The process reported here is general and can be readily extended to the production of many other transition metal (TiO2, ZnO, Nb2O5) and rare earth oxide (Eu2O3, Sm2O3, Er2O3, Y2O3, Tb2O3, and Yb2O3) systems.

  3. Ultra-thin microporous/hybrid materials

    DOEpatents

    Jiang, Ying-Bing (Albuquerque, NM); Cecchi, Joseph L. (Albuquerque, NM); Brinker, C. Jeffrey (Albuquerque, NM)

    2012-05-29

    Ultra-thin hybrid and/or microporous materials and methods for their fabrication are provided. In one embodiment, the exemplary hybrid membranes can be formed including successive surface activation and reaction steps on a porous support that is patterned or non-patterned. The surface activation can be performed using remote plasma exposure to locally activate the exterior surfaces of porous support. Organic/inorganic hybrid precursors such as organometallic silane precursors can be condensed on the locally activated exterior surfaces, whereby ALD reactions can then take place between the condensed hybrid precursors and a reactant. Various embodiments can also include an intermittent replacement of ALD precursors during the membrane formation so as to enhance the hybrid molecular network of the membranes.

  4. Magnetization and structure of ultrathin Fe films

    NASA Astrophysics Data System (ADS)

    Zdyb, R.; Mente?, T. O.; Locatelli, A.; Niño, M. A.; Bauer, E.

    2009-11-01

    The connection between magnetization and structure of ultrathin films is studied at room temperature for the case of Fe films on W(110) by inserting a 2-monolayer-thick growth-modifying Au layer between film and substrate using spin-polarized low-energy electron microscopy and low-energy electron diffraction. Ferromagnetic order with the easy axis pointing in the [11¯0] direction appears upon percolation at 1.6 monolayers. Shortly thereafter, the easy axis rotates into the [001] direction. With further increasing thickness the magnetization oscillates between the [001] and the [11¯0] direction with a maximum deviation from the [001] direction at seven monolayers where the magnetic signal has a maximum. The changes in the magnetization are associated with changes in the structure, strain, and morphology that are deduced from the diffraction patterns and which strongly influence the competition between interface anisotropy, magnetoelastic anisotropy, and dipolar surface anisotropy.

  5. Electric field effect in ultrathin black phosphorus

    SciTech Connect

    Koenig, Steven P.; Schmidt, Hennrik; Doganov, Rostislav A.; Castro Neto, A. H.; Özyilmaz, Barbaros

    2014-03-10

    Black phosphorus exhibits a layered structure similar to graphene, allowing mechanical exfoliation of ultrathin single crystals. Here, we demonstrate few-layer black phosphorus field effect devices on Si/SiO{sub 2} and measure charge carrier mobility in a four-probe configuration as well as drain current modulation in a two-point configuration. We find room-temperature mobilities of up to 300 cm{sup 2}/Vs and drain current modulation of over 10{sup 3}. At low temperatures, the on-off ratio exceeds 10{sup 5}, and the device exhibits both electron and hole conduction. Using atomic force microscopy, we observe significant surface roughening of thin black phosphorus crystals over the course of 1 h after exfoliation.

  6. Electric field effect in ultrathin black phosphorus

    NASA Astrophysics Data System (ADS)

    Koenig, Steven P.; Doganov, Rostislav A.; Schmidt, Hennrik; Castro Neto, A. H.; Özyilmaz, Barbaros

    2014-03-01

    Black phosphorus exhibits a layered structure similar to graphene, allowing mechanical exfoliation of ultrathin single crystals. Here, we demonstrate few-layer black phosphorus field effect devices on Si/SiO2 and measure charge carrier mobility in a four-probe configuration as well as drain current modulation in a two-point configuration. We find room-temperature mobilities of up to 300 cm2/Vs and drain current modulation of over 103. At low temperatures, the on-off ratio exceeds 105, and the device exhibits both electron and hole conduction. Using atomic force microscopy, we observe significant surface roughening of thin black phosphorus crystals over the course of 1 h after exfoliation.

  7. Chemical vapor deposition and characterization of zirconia films for high-k dielectric applications

    NASA Astrophysics Data System (ADS)

    Song, Zhe

    Due to the aggressive dimensional scaling of metal-oxide-semiconductor-field-effect-transistors (MOSFETs), direct tunneling current across the SiO2 gate dielectric layer has become a significant problem. High-k dielectric materials, such as ZrO2, HfO2, are expected to replace SiO2 as the gate dielectric layers to minimize direct tunneling currents. Development of the deposition processes and the characterization of high-k films have become significant challenges for the semiconductor industry. Based on multi-sample variable-angle spectroscopic ellipsometry (MS-VASE), we first developed a methodology to characterize ZrO2 films deposited on silicon. Results showed that proper modeling the optical properties of the interfacial layer is the key to accurate characterization. Using a stack model, consisting of an effective medium approximation (EMA) surface-roughness layer, a Tauc-Lorentz (TL) layer to represent the ZrO2 layer, and a second TL layer to represent the interfacial layer, we accurately extracted both thicknesses and optical constants of layers. The extracted surface-roughness and thickness values were confirmed by atomic force microscopy (AFM) and transmission electron microscopy (TEM) results. The following chapters cover studies of the initial-stage deposition of ZrO2 films from zirconium t-butoxide (ZTB) on both native silicon oxide and H-terminated silicon (H-Si) surfaces. In-situ SE was used to study the deposition process in real time. AFM, TEM, time of flight medium back scattering (ToF MEBS), and angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to investigate the properties of deposited films. We discovered that film properties are affected by the nucleation and coalescence processes on different surfaces. A 3-dimensional nucleation process is predominant on HSi surfaces due to the lack of reactive surface hydroxyl groups and high surface diffusivity of ZTB molecules. At temperatures about 350°C, a layer-by-layer deposition process on native oxide surfaces leads to smooth, uniform ZrO 2 films. An interfacial layer between the silicon substrate and ZrO 2 is formed through two independent mechanisms: reaction between the starting surfaces and ZTB or its decomposition intermediates, and the diffusion of reactive oxidants through the forming ZrO2 interfacial stack layer and their reaction with the substrate.

  8. Probing the ultrathin limit of hyperbolic metamaterial: nonlocality induced topological transitions (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Chen, Long; Zhang, Cheng; Zhou, Jing; Guo, L. Jay

    2015-09-01

    An ideal hyperbolic metamaterial (HMM), which has a perfect hyperbolic dispersion curve, theoretically can support modes with indefinite wavenumbers, leading to large photon local density of states (LDOS) and many applications such as enhancing light-matter interactions, spontaneous emission and thermal radiation. Here in this presentation, HMMs based on ultrathin metal-dielectric multilayers have been studied by considering the nonlocal response of electrons in metal. Based on the hydrodynamic model of the nonlocal response, we investigate the effect of nonlocality on the performance (dispersion relation, ray refraction, LDOS and spontaneous emission) of HMMs when gradually approaching the ultrathin limit of the unit cell. We show that nonlocality will induce topological transitions of the iso-frequency surfaces and limit the wavenumber as well as LDOS for both type I and type II HMMs. Under nonlocal treatment, the iso-frequency surface of type II HMM transforms from a hyperbola to a bullet shape, while for type I HMM, the surface splits into two branches: a cylindrical-like branch at high k region and an elliptical branch at the low k region. In the high k region, the nonlocality set a cut-off k for the allowed wavenumbers in both type I and type II HMMs. This cut-off k which is defined by the electron Fermi velocity of the metal intrinsically limits the LDOS and light-matter interactions. These results indicate that in the aim of achieving high performance HMMs, merely thinning the constituent films according to the local theories is no longer valid.

  9. High performance organic field-effect transistors with ultra-thin HfO{sub 2} gate insulator deposited directly onto the organic semiconductor

    SciTech Connect

    Ono, S.; Häusermann, R.; Laboratory for Solid State Physics, ETH Zurich, Zurich 8093 ; Chiba, D.; PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 322-0012; Department of Applied Physics, University of Tokyo, Tokyo 113-8656 ; Shimamura, K.; Ono, T.; Batlogg, B.

    2014-01-06

    We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO{sub 2} gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm{sup 2}/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO{sub 2} layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor.

  10. PREFACE: Dielectrics 2013

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, Sillas; Blackburn, John

    2013-11-01

    This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also pleased to express our thanks to the Conference Department of the Institute of Physics for their invaluable support in organizing this event. We are especially grateful to Dawn Stewart for her responsive and day-to-day handling of this conference, as well as Claire Garland for help in planning and managing this international event. We would also like to thank Dr Steve Welch, Director at ESP Central Ltd, representing the interest of the Electronics, Sensors, Photonics Knowledge Transfer Network, as well as Paul Naylor and Susan Matos for their contribution towards the KTN session of the Conference. Finally, we would like to thank Solartron Analytical, Ametek and Princeton Applied Research for demonstrating precision electrochemical impedance spectroscopy measurement techniques at the conference. We hope that the wider Dielectrics community will find these proceedings of interest and will use them as reference text in their future work. Programme committee R Pethig, University of Edinburgh J Blackburn, National Physical Laboratory J Swingler, Heriot Watt University S Hadjiloucas, University of Reading A West, University of Sheffiled M Hughes, University of Surrey S Dodd, University of Leicester D Almond, University of Bath M Cain, National Physical Laboratory D J Swaffield, University of Southampton N Green, University of Southampton A Vaughan, University of Southampton Sillas Hadjiloucas and John Blackburn (Summer 2013)

  11. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D. (Livermore, CA); Britten, Jerald A. (Oakley, CA); Nguyen, Hoang T. (Livermore, CA); Boyd, Robert (Livermore, CA); Shore, Bruce W. (Livermore, CA)

    1999-01-01

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

  12. Thermally switchable dielectrics

    DOEpatents

    Dirk, Shawn M.; Johnson, Ross S.

    2013-04-30

    Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a `built-in` safety mechanism for electronic devices.

  13. Absorption in dielectric models

    E-print Network

    Churchill, R J

    2015-01-01

    We develop a classical microscopic model of a dielectric. The model features nonlinear interaction terms between polarizable dipoles and lattice vibrations. The lattice vibrations are found to act as a pseudo-reservoir, giving broadband absorption of electromagnetic radiation without the addition of damping terms in the dynamics. The effective permittivity is calculated using a perturbative iteration method and is found to have the form associated with real dielectrics. Spatial dispersion is naturally included in the model and we also calculate the wavevector dependence of the permittivity.

  14. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

    1999-05-25

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

  15. A dielectric affinity microbiosensor

    NASA Astrophysics Data System (ADS)

    Huang, Xian; Li, Siqi; Schultz, Jerome S.; Wang, Qian; Lin, Qiao

    2010-01-01

    We present an affinity biosensing approach that exploits changes in dielectric properties of a polymer due to its specific, reversible binding with an analyte. The approach is demonstrated using a microsensor comprising a pair of thin-film capacitive electrodes sandwiching a solution of poly(acrylamide-ran-3-acrylamidophenylboronic acid), a synthetic polymer with specific affinity to glucose. Binding with glucose induces changes in the permittivity of the polymer, which can be measured capacitively for specific glucose detection, as confirmed by experimental results at physiologically relevant concentrations. The dielectric affinity biosensing approach holds the potential for practical applications such as long-term continuous glucose monitoring.

  16. 2015 IEEE, P. C. Jamison, Takaaki Tsunoda, T. Vo, J. Li, H. Jagannathan, S. R. Shinde, V. K. Paruchuri, D. Gall, "SiO2 Free HfO2 Gate Dielectrics by Physical Vapor Deposition," IEEE Trans. Electron Devices, 62, 2878 (2015).

    E-print Network

    Gall, Daniel

    2015-01-01

    No. 1309490. P. C. Jamison is with IBM Research at Albany Nanotech, Albany, NY 12203 USA Institute, Albany, NY 12203 USA (e- mail: tvo@sunycnse.com) J. Li is with IBM Research at Albany Nanotech, Albany, NY 12203 USA (e-mail: juntaoli@us.ibm.com H. Jagannathan is with IBM Research at Albany Nanotech

  17. Unconventional seed-mediated growth of ultrathin Au nanowires in aqueous solution

    E-print Network

    Lin, Zhiqun

    Unconventional seed-mediated growth of ultrathin Au nanowires in aqueous solution Bo Li,a Beibei seed-mediated growth of ultrathin Au nanowires induced by hydrophobic molecules. Quite intriguingly of Au nanorods, silver ions and Au seeds were crucially required to yield the water-soluble ultrathin Au

  18. Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers

    E-print Network

    Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers T. S March 2003; accepted 4 June 2003 The fabrication of ultrathin strained silicon directly on insulator is demonstrated and the thermal stability of these films is investigated. Ultrathin ( 13 nm) strained silicon

  19. Lightweight electrowetting display on ultra-thin glass substrate Andrew J. Steckl

    E-print Network

    Cincinnati, University of

    Lightweight electrowetting display on ultra-thin glass substrate Han You Andrew J. Steckl Abstract, and mechanical flexibility. Electrowetting (EW) devices fabricated on ultra-thin glass are demonstrated° when a 20 V direct current (or alternating current) voltage is applied. EW devices on ultra-thin glass

  20. Ultra-thin Co/Pd multilayers with enhanced high-temperature annealing M. Gottwald,1

    E-print Network

    Siegel, Paul H.

    Ultra-thin Co/Pd multilayers with enhanced high-temperature annealing stability M. Gottwald,1 K properties of ultra-thin Co/Pd multilayers deposited at room temperature. It is shown that perpendicular magnetic anisotropy of ultra-thin Co/Pd multilayers improves with increasing annealing temperature up

  1. Nanoscale Buckling of Ultrathin Low-k Dielectric Lines during Hard-Mask Patterning.

    PubMed

    Stan, Gheorghe; Ciobanu, Cristian V; Levin, Igor; Yoo, Hui J; Myers, Alan; Singh, Kanwal; Jezewski, Christopher; Miner, Barbara; King, Sean W

    2015-06-10

    Commonly known in macroscale mechanics, buckling phenomena are now also encountered in the nanoscale world as revealed in today's cutting-edge fabrication of microelectronics. The description of nanoscale buckling requires precise dimensional and elastic moduli measurements, as well as a thorough understanding of the relationships between stresses in the system and the ensuing morphologies. Here, we analyze quantitatively the buckling mechanics of organosilicate fins that are capped with hard masks in the process of lithographic formation of deep interconnects. We propose an analytical model that quantitatively describes the morphologies of the buckled fins generated by residual stresses in the hard mask. Using measurements of mechanical properties and geometric characteristics, we have verified the predictions of the analytical model for structures with various degrees of buckling, thus putting forth a framework for guiding the design of future nanoscale interconnect architectures. PMID:25950850

  2. MoS{sub 2} functionalization for ultra-thin atomic layer deposited dielectrics

    SciTech Connect

    Azcatl, Angelica; McDonnell, Stephen; Santosh, K.C.; Peng, Xin; Dong, Hong; Qin, Xiaoye; Addou, Rafik; Lu, Ning; Kim, Moon J.; Cho, Kyeongjae; Wallace, Robert M.; Mordi, Greg I.; Kim, Jiyoung

    2014-03-17

    The effect of room temperature ultraviolet-ozone (UV-O{sub 3}) exposure of MoS{sub 2} on the uniformity of subsequent atomic layer deposition of Al{sub 2}O{sub 3} is investigated. It is found that a UV-O{sub 3} pre-treatment removes adsorbed carbon contamination from the MoS{sub 2} surface and also functionalizes the MoS{sub 2} surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS{sub 2} surface and provides nucleation sites for atomic layer deposition of Al{sub 2}O{sub 3}. The enhanced nucleation is found to be dependent on the thin film deposition temperature.

  3. Substrate-assisted nucleation of ultra-thin dielectric layers on graphene by atomic layer deposition

    E-print Network

    Dlubak, Bruno; Kidambi, Piran R.; Weatherup, Robert S.; Hofmann, Stephan; Robertson, John

    2012-04-26

    We report on a large improvement in the wetting of Al2O3 thin films grown by unseeded atomic layer deposition on monolayer graphene, without creating point defects. This enhanced wetting is achieved by greatly increasing the nucleation density...

  4. Non-Destructive Characterization and Metrology for Ultra-Thin High-k Dielectric Layers

    NASA Astrophysics Data System (ADS)

    Champaneria, R.; Mack, P.; White, R.; Wolstenholme, J.

    2003-09-01

    Angle-resolved X-ray photoelectron spectroscopy (ARXPS) has been used to characterize non-destructively silicon oxynitride and high-k film samples. The ARXPS data have been processed to provide accurate and precise measurements of thickness of surface and interface layers. Concentration depth profiles have been reconstructed from the ARXPS data to provide elemental and chemical state distribution information. For silicon oxynitride samples, nitrogen doses have been calculated from the concentration profiles, thereby accounting for the distribution of the nitrogen within the oxynitride layer. A comparison of ARXPS with modeled single-angle XPS experiments illustrate the potential errors in calculation of both thickness and dose using the latter technique. Sputter depth profiles are also shown to contain potentially misleading information when compared to reconstructed ARXPS depth profiles.

  5. Resilience of ultra-thin oxynitride films to percolative wear-out and reliability implications for high-? stacks at low voltage stress

    NASA Astrophysics Data System (ADS)

    Raghavan, Nagarajan; Padovani, Andrea; Li, Xiang; Wu, Xing; Lip Lo, Vui; Bosman, Michel; Larcher, Luca; Leong Pey, Kin

    2013-09-01

    Localized progressive wear-out and degradation of ultra-thin dielectrics around the oxygen vacancy percolation path formed during accelerated time dependent dielectric breakdown tests is a well-known phenomenon documented for silicon oxynitride (SiON) based gate stacks in metal oxide semiconductor field effect transistors. This progressive or post breakdown stage involves an initial phase characterized by "digital" random telegraph noise fluctuations followed by the wear-out of the percolation path, which results in an "analog" increase in the leakage current, culminating in a thermal runaway and hard breakdown. The relative contribution of the digital and analog phases of degradation at very low voltage stress in ultra-thin SiON (16 Å´) is yet to be fully investigated, which represents the core of this study. We investigate the wear-out process by combining electrical and physical analysis evidences with modeling and simulation results using Kinetic Monte Carlo defect generation and multi-phonon trap assisted tunneling (PTAT) models. We show that the transition from the digital to the analog regime is governed by a critical voltage (VCRIT), which determines the reliability margin in the post breakdown phase. Our results have a significant impact on the post-breakdown operational reliability of SiON and advanced high-?-SiOx interfacial layer gate stacks, wherein the SiOx layer seems to be the weakest link for percolation event.

  6. Lunar permafrost - Dielectric identification.

    NASA Technical Reports Server (NTRS)

    Alvarez, R.

    1973-01-01

    A simulator of lunar permafrost at 100 K exhibits a dielectric relaxation centered at approximately 300 hertz. If permafrost exists in the moon between 100 and 213 K, it should present a relaxation peak at approximately 300 hertz. For temperatures up to 263 K it may go up to 20 kilohertz.

  7. Molds for cable dielectrics

    DOEpatents

    Roose, L.D.

    1996-12-10

    Molds for use in making end moldings for high-voltage cables are described wherein the dielectric insulator of a cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made. 5 figs.

  8. Ultrathin Silver Films on Ni(111)

    SciTech Connect

    Flege, J.I.; Senanayake, S.; Meyer, A.; Rettew, R.E.; Schmidt, T.; Alamgir, F.M.; Falta, J.

    2010-08-16

    The growth and atomic structure of ultrathin silver films on Ni(111) was investigated by low-energy electron microscopy and diffraction (LEEM/LEED) as well as intensity-voltage [I(V)]-LEEM in the growth temperature range between 470 and 850 K. We find that silver grows in a Stranski-Krastanov mode with a two monolayer thin wetting layer which takes on a p(7 x 7) reconstruction at temperatures lower than 700 K and a ({radical}52 x {radical}52)R13.9{sup o} reconstruction at higher temperatures. The occurrence of the two distinct reconstructions is shown to have profound implications for the growth characteristics of films exhibiting thicknesses of one and two monolayers. The nanoscale I(V) characteristics of the films were analyzed by means of multiple-scattering calculations based on dynamical LEED theory. Furthermore, the vertical interatomic spacing at the interface between the Ag film and the Ni substrate was determined to (2.8 {+-} 0.1) {angstrom} for all film thicknesses (<13 ML) while the uppermost silver layer relaxes by about (4 {+-} 1)% toward the crystal.

  9. Ultrathin Silver Films on Ni(111)

    SciTech Connect

    Meyer, A.; Flege, J; Rettew, R; Senanayake, S; Schmidt, T; Alamgir, F; Falta, J

    2010-01-01

    The growth and atomic structure of ultrathin silver films on Ni(111) was investigated by low-energy electron microscopy and diffraction (LEEM/LEED) as well as intensity-voltage [I(V)]-LEEM in the growth temperature range between 470 and 850 K. We find that silver grows in a Stranski-Krastanov mode with a two monolayer thin wetting layer which takes on a p(7 x 7) reconstruction at temperatures lower than 700 K and a ({radical}52 x {radical}52)R13.9{sup o} reconstruction at higher temperatures. The occurrence of the two distinct reconstructions is shown to have profound implications for the growth characteristics of films exhibiting thicknesses of one and two monolayers. The nanoscale I(V) characteristics of the films were analyzed by means of multiple-scattering calculations based on dynamical LEED theory. Furthermore, the vertical interatomic spacing at the interface between the Ag film and the Ni substrate was determined to (2.8 {+-} 0.1) {angstrom} for all film thicknesses (<13 ML) while the uppermost silver layer relaxes by about (4 {+-} 1)% toward the crystal.

  10. Dewetting observations of ultrathin metallic films

    NASA Astrophysics Data System (ADS)

    Han, G. C.; Wu, Y. H.; Luo, P.; Qiu, J. J.; Chong, T. C.

    2003-05-01

    Ultrathin metallic films like CoFe, Ta, Cu, Cr, and NiFe are widely used in magnetic devices such as magnetic random access memory (MRAM) and magnetic recording heads. Dewetting corrosions were often observed after O 2 plasma ashing in MRAM fabrications. The surface stability of these films was then examined. The results show that dewetting takes place when CoFe or Cu films are exposed to air after an O 2 plasma process. In contrast to the dewetting reported so far in organic or metallic liquid films on solid substrates, the observed dewetting does not occur in a liquid state but in a solid state. Several in situ and ex situ process methods were examined to control the dewetting. It is found that after ashing, the immediate immersion of wafer into acetone and ultrasonic cleaning some minutes after opening chamber can greatly suppress the occurrence of dewettings. Process examinations show that the heating is unimportant for the formation of the dewetting, while moisture in air may play an important role in the formation of the dewetting, acting as a necessary catalyst. Several dewetting patterns were observed, and the pattern shape depends not only on the thickness of the film, but also on the plasma parameters. Possible mechanisms responsible for the formation of these patterns are discussed.

  11. Tri-gate InGaAs-OI junctionless FETs with PE-ALD Al2O3 gate dielectric and H2/Ar anneal

    NASA Astrophysics Data System (ADS)

    Djara, Vladimir; Czornomaz, Lukas; Deshpande, Veeresh; Daix, Nicolas; Uccelli, Emanuele; Caimi, Daniele; Sousa, Marilyne; Fompeyrine, Jean

    2016-01-01

    We present a tri-gate In0.53Ga0.47As-on-insulator (InGaAs-OI) junctionless field-effect transistor (JLFET) architecture. The fabricated devices feature a 20-nm-thick n-In0.53Ga0.47As channel doped to 1018/cm3 obtained by metal organic chemical vapor phase deposition and direct wafer bonding along with a 3.5-nm-thick Al2O3 gate dielectric deposited by plasma-enhanced atomic layer deposition (PE-ALD). The PE-ALD Al2O3 presents a bandgap of 7.0 eV, a k-value of 8.1 and a breakdown field of 8-10.5 MV/cm. A post-fabrication H2/Ar anneal applied to the PE-ALD Al2O3/In0.53Ga0.47As-OI gate stack yielded a low density of interface traps (Dit) of 7 × 1011/cm2 eV at Ec - E = -0.1 eV along with lower border trap density values than recently reported PE-ALD bi-layer Al2O3/HfO2 and thermal ALD HfO2 gate stacks deposited on In0.53Ga0.47As. The H2/Ar anneal also improved the subthreshold performance of the tri-gate InGaAs-OI JLFETs. After H2/Ar anneal, the long-channel (10 ?m) device featured a threshold voltage (VT) of 0.25 V, a subthreshold swing (SS) of 88 mV/dec and a drain-induced barrier lowering (DIBL) of 65 mV/V, while the short-channel (160 nm) device exhibited a VT of 0.1 V, a SS of 127 mV/dec and a DIBL of 218 mV/V. Overall, the tri-gate InGaAs-OI JLFETs showed the best compromise in terms of VT, SS and DIBL compared to the other III-V JLFET architectures reported to date. However, a 15× increase in access resistance was observed after H2/Ar anneal, significantly degrading the maximum drain current of the tri-gate InGaAs-OI JLFETs.

  12. Swelling of ultrathin crosslinked polyamide water purification membranes

    NASA Astrophysics Data System (ADS)

    Chan, Edwin; Stafford, Christopher

    2013-03-01

    Polyamide (PA) ultrathin films represent the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these materials, such as permselectivity, is intimately linked with extent of swelling of the PA network. Thus, quantifying their swelling behavior would be a useful and simple route to understanding the specific network structural parameters that control membrane performance. In this work, we measure the swelling behavior of PA ultrathin films using X-ray reflectivity as a function of water hydration. By applying the Flory-Rehner theory used to describe the swelling behavior of polymer networks, we quantify the PA network properties including Flory interaction parameter and the monomer units between crosslinks. Finally, we demonstrate application of this measurement approach for characterizing the network properties of different types of PA ultrathin films relevant to water purification and discuss the relationship between network and transport properties. Materials Science and Engineering Division

  13. Nonlinear characteristics in fracture strength test of ultrathin silicon die

    NASA Astrophysics Data System (ADS)

    Liu, Zunxu; Huang, YongAn; Xiao, Lin; Tang, Pengpeng; Yin, Zhouping

    2015-04-01

    The precise evaluation of fracture strength of ultrathin (<50 ?m thick) silicon chips/ribbons plays a critical role in design of deformability and lifetime of flexible/stretchable electronics. In its three-point bending test, however, the classical linear theory used to convert the experimental fracture load into fracture strength value fails to match the emerged geometrically nonlinear characteristics for such an ultrathin silicon die. Here, we consider the geometric large deformation and present its nonlinear solution to more reliably evaluate the fracture stress of ultrathin specimen by virtue of the obtained experimental fracture load. A quite good agreement on experiments shows that the nonlinear analytical predictions allow a more comprehensive understanding for the effects of the silicon samples’ thickness on the transformation from linear relation to nonlinearity. The comparisons indicate that the fracture strength values are lower from linear evaluations, and to this the corresponding correction factor is defined to enhance the estimate precision.

  14. In situ electrical transport measurementof superconductive ultrathin films

    NASA Astrophysics Data System (ADS)

    Liu, Can-Hua; Jia, Jin-Feng

    2015-11-01

    The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform electrical transport measurement in ultra-high vaccum (UHV). Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films. The work in SJTU was supported by the National Basic Research Program of China (Grant Nos. 2013CB921902 and 2011CB922200) and the National Natural Science Foundation of China (Grant Nos. 11227404, 11274228, 11521404, 11174199, and 11134008).

  15. Printable Ultrathin Metal Oxide Semiconductor-Based Conformal Biosensors.

    PubMed

    Rim, You Seung; Bae, Sang-Hoon; Chen, Huajun; Yang, Jonathan L; Kim, Jaemyung; Andrews, Anne M; Weiss, Paul S; Yang, Yang; Tseng, Hsian-Rong

    2015-12-22

    Conformal bioelectronics enable wearable, noninvasive, and health-monitoring platforms. We demonstrate a simple and straightforward method for producing thin, sensitive In2O3-based conformal biosensors based on field-effect transistors using facile solution-based processing. One-step coating via aqueous In2O3 solution resulted in ultrathin (3.5 nm), high-density, uniform films over large areas. Conformal In2O3-based biosensors on ultrathin polyimide films displayed good device performance, low mechanical stress, and highly conformal contact determined using polydimethylsiloxane artificial skin having complex curvilinear surfaces or an artificial eye. Immobilized In2O3 field-effect transistors with self-assembled monolayers of NH2-terminated silanes functioned as pH sensors. Functionalization with glucose oxidase enabled d-glucose detection at physiologically relevant levels. The conformal ultrathin field-effect transistor biosensors developed here offer new opportunities for future wearable human technologies. PMID:26498319

  16. Antenna with Dielectric Having Geometric Patterns

    NASA Technical Reports Server (NTRS)

    Dudley, Kenneth L. (Inventor); Elliott, Holly A. (Inventor); Cravey, Robin L. (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Watson, Kent A. (Inventor); Smith, Jr., Joseph G. (Inventor)

    2013-01-01

    An antenna includes a ground plane, a dielectric disposed on the ground plane, and an electrically-conductive radiator disposed on the dielectric. The dielectric includes at least one layer of a first dielectric material and a second dielectric material that collectively define a dielectric geometric pattern, which may comprise a fractal geometry. The radiator defines a radiator geometric pattern, and the dielectric geometric pattern is geometrically identical, or substantially geometrically identical, to the radiator geometric pattern.

  17. Characterization of dielectric breakdown behavior by in situ transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Bonifacio, Cecile Semana

    Dielectric breakdown (BD) is the loss of capacitance upheld by an insulating material through defect formation and charge trapping. Dielectric BD is well-studied in the framework of reliability physics for semiconductor applications, and presents itself as a viable mechanism during materials processing by electric field assisted sintering (EFAS). So far a mechanistic understanding of dielectric BD is incomplete due to the limitations in nanoscale defect characterization techniques. The recent development of novel in situ transmission electron microscopy (TEM) capabilities enables the atomic-scale characterization of dielectric BD mechanisms, which was the subject of this dissertation. As the technology of semiconductor devices moves toward the sub-25 nm technology the electronic properties of gate oxide layers are affected eventually leading to device failure by dielectric BD. This study aimed to provide a systematic approach of simultaneous imaging and local application of electrical stress using in situ TEM by contacting an electrically biased Scanning Tunnelling Microscopy (STM) probe directly to the TEM sample. This experimental setup therefore allows a correlation of electrical signatures with defect structure evolution. In situ TEM experiments carried out with a single SiO2-based field effect transistor resulted to catastrophic failure of the dielectric layer consistent with descriptions of soft dielectric breakdown (SBD) and hard dielectric breakdown (HBD). A variety of in situ TEM techniques was further utilized to investigate whether electric field induced dielectric breakdown may contribute to densification of metallic powder particles during EFAS. In situ heating and STM-TEM experiments were systematically applied to separately study thermal and athermal effects during densification, respectively. Nanometric metal powders used for sintering typically possess surface oxides that affect the thermodynamics and kinetics of neck formation during the initial stage of sintering. The thermal effects were found to be driven by reduction-oxidation reactions of nickel oxide with carbon. The presence of carbon promotes the removal of surface oxides at lower temperatures and, therefore, can accelerate densification. By the controlled application of electrical bias, EFAS conditions were reproduced during in situ TEM and revealed reduction of ultra-thin nickel oxide surface layers by electric field-induced dielectric breakdown. The results provide evidence for previously suggested effects of local electric field amplification at inter-particle contact areas, which, hence, triggers surface cleaning through electric field-induced dielectric breakdown.

  18. Preparation and characterization of ultrathin free-standing carbon films

    NASA Astrophysics Data System (ADS)

    Lee, Hoikwan; Rajagopalan, Ramakrishnan

    2013-11-01

    Ultrathin free-standing carbon films with thicknesses of ˜8-14 nm were prepared by peeling from glass after pyrolization of the polyfurfuryl alcohol precursor at 700 °C. The carbon films were characterized by using optical profilometry, confocal Raman spectroscopy, transmission electron microscopy, UV-vis spectroscopy, and a two-point probe I - V station measurement. The results confirmed the formation of ultrathin free-standing carbon films with a polyaromatic domain structure. Those films had up to a 90% transmittance with respect to air and had an ohmic behavior. In this work, we also suggest that the most likely peeling mechanism of carbon films results from glass corrosion.

  19. Method for laser welding ultra-thin metal foils

    DOEpatents

    Pernicka, John C. (Fort Collins, CO); Benson, David K. (Golden, CO); Tracy, C. Edwin (Golden, CO)

    1996-01-01

    A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

  20. Method for laser welding ultra-thin metal foils

    DOEpatents

    Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

    1996-03-26

    A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

  1. Ultrathin Metallic Coatings Can Induce Quantum Levitation between Nanosurfaces

    E-print Network

    Mathias Boström; Barry W. Ninham; Iver Brevik; Clas Persson; Drew F. Parsons; Bo E. Sernelius

    2012-06-05

    There is an attractive Casimir-Lifshitz force between two silica surfaces in a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin (5-50{\\AA}) metallic nanocoating to one of the surfaces results in repulsive Casimir-Lifshitz forces above a critical separation. The onset of such quantum levitation comes at decreasing separations as the film thickness decreases. Remarkably the effect of retardation can turn attraction into repulsion. From that we explain how an ultrathin metallic coating may prevent nanoelectromechanical systems from crashing together.

  2. Surface-sensitive UHV dielectric studies of nanoscale organic thin films: Adsorption, crystallization, and sublimation

    NASA Astrophysics Data System (ADS)

    Underwood, Jason M.

    Nanoscale systems are small collections of atoms or molecules, which as a result of their limited extent, show measurable thermodynamic deviations from bulk samples of the same species. The deviations may result from purely finite-size effects, or may be due to an increased significance of the interaction between the nanoscale system and its container. Ultra-thin (<100 nm) films of organic molecules adsorbed on surfaces afford unique opportunities to study the interplay of forces relevant to nanoscale physics. This thesis describes the development of a novel ultra-high vacuum apparatus to study the behavior of adsorbed polar molecules via dielectric spectroscopy (UHV-DS). Ultra-thin films are grown and characterized in-situ. The use of interdigitated electrode capacitors and a ratio-transformer bridge technique yields resolutions of ˜1 aF and ˜10-5 ppm in the capacitance and loss tangent, respectively. Typical sensitivity is 10 aF per monolayer at 80 K. Results are given for studies on water, methanol, and Cp* (a synthetic molecular rotor). The desorption event in the dielectric spectra is correlated with thermal desorption spectroscopy. During growth of methanol films, we observe partial crystallization for temperatures above ? 100 K. Crystallization is also observed upon heating glassy films grown at 80 K. Finally, we discuss UHV-DS as a probe for solid thin-film vapor pressure measurements, and show that our data on methanol compare favorably with those in the literature.

  3. Temperature switchable polymer dielectrics.

    SciTech Connect

    Johnson, Ross Stefan

    2010-08-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  4. Linear optical properties from Ni ultrathin films in the diamagnetic domain

    NASA Astrophysics Data System (ADS)

    Villagómez, R.

    1998-05-01

    Optical properties of Ni ultrathin films deposited by radio-frequency sputtering on SiO 2 (glass) and Si substrates are obtained. Thickness dependence infrared (IR) reflectance ( R) measurements are used to characterize these metallic films. For our quantum well system the local field calculation of the optical diamagnetic response in a quantum well is made to correlate our experimental findings. Also, an experimental approximation (to the first order of d/ ?) for the imaginary part of the Ni dielectric function is given. Finally, we measure R in the presence of a fixed magnetic field ( B-field) in the direction perpendicular to the plane of the metallic film. From these results, quantum size effects revealed as fine oscillations in R are altered when the B-field is applied. In both cases, with and without the B-field, R from Ni/SiO 2 keeps its diamagnetic behavior unchanged. To insure the two conditions: d? ? and near normal incidence, an external field from a tunable CO 2 laser tuned to a p-polarized wavelength of 9.201 ?m and angle of incidence of 7° is chosen.

  5. Phase Formation Behavior in Ultrathin Iron Oxide.

    PubMed

    Jõgi, Indrek; Jacobsson, T Jesper; Fondell, Mattis; Wätjen, Timo; Carlsson, Jan-Otto; Boman, Mats; Edvinsson, Tomas

    2015-11-17

    Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and 50 nm were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 nm nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films. PMID:26506091

  6. Tunable Dielectric Properties of Ferrite-Dielectric Based Metamaterial

    PubMed Central

    Bi, K.; Huang, K.; Zeng, L. Y.; Zhou, M. H.; Wang, Q. M.; Wang, Y. G.; Lei, M.

    2015-01-01

    A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices. PMID:25993433

  7. Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics

    NASA Astrophysics Data System (ADS)

    Li, Guanhong; Li, Qunqing; Jin, Yuanhao; Zhao, Yudan; Xiao, Xiaoyang; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

    2015-10-01

    Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors.Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05036g

  8. Ultrathin Single-Walled Carbon Nanotube Network Framed Graphene Hybrids

    E-print Network

    Wikswo, John

    such as high charge- carrier mobility, remarkable thermal conductivity, and large surface-area-to-volume ratio utilizing the mechanical support from poly(methyl methacrylate) (PMMA), large-area SWNT-graphene hybrids can method is developed to synthesize ultrathin SWNT-graphene films through chemical vapor deposition

  9. Imaging Electrons in Ultra-thin Nanowires A thesis presented

    E-print Network

    -thin Nanowires Abstract Ultra-thin semiconductor nanowires are promising systems in which to explore novel low-dimensional of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Physics Harvard University Cambridge, Massachusetts January 2011 #12;©2011 ­ Erin E. Boyd All rights

  10. Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters

    E-print Network

    Krchnavek, Robert R.

    Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters Ryan W of the imprinter. Previous work on thick 100 nm diamondlike carbon DLC layers indicates that fluorinated DLC F interest is the plasma deposition of a layer of fluorinated diamondlike car- bon F-DLC . Diamondlike carbon

  11. Synthesis and Characterization of Zirconium Tungstate Ultra-Thin Fibers

    SciTech Connect

    Zhang, Lifeng; Howe, Jane Y; Fong, Hao; Zhang, Yan

    2009-01-01

    This study reports an innovative method of electrospinning followed by pyrolysis to synthesize zirconium tungstate (ZrW2O8), a material with negative coefficient of thermal expansion (CTE), in ultra-thin fiber form. Morphologies and microstructures of the as-electrospun precursor fibers, the heat-treated intermediate fibers, and the final ZrW2O8 ultra-thin fibers were characterized by SEM, XRD, and TEM. The ZrW2O8 ultra-thin fibers had diameters in the sub-micrometer range with aspect ratios larger than 100; these fibers were polycrystalline, and consisted of single crystalline ZrW2O8 crystallites with sizes of 30-50 nm and surface roughness of several nanometers. The ZrW2O8 ultra-thin fibers are expected to outperform spherically, cylindrically, and/or irregularly shaped polycrystalline ZrW2O8 particles for the development of composites with precisely controlled CTEs. Additionally, this reported method could be utilized as a general approach to convert nano-scaled inorganic particles into fibers.

  12. Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions.

    PubMed

    Zhou, Wenjun; Mandia, David J; Barry, Seán T; Albert, Jacques

    2014-12-29

    The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered. PMID:25607137

  13. Ultra-Thin Coatings Beautify Art

    NASA Technical Reports Server (NTRS)

    2013-01-01

    The craftsmen in the Roman Empire who constructed the Lycurgus Cup 17 centuries ago probably didn't think their artifact would survive for nearly 2,000 years as a prized possession. And they certainly couldn't have known that the technology they used to make it would eventually become an important part of space exploration. Carved from one solid mass, the cup is one of the few complete glass objects from that period, and the only one made from dichroic glass. Meaning "two-colored" in Greek, dichroic glass was originally created by adding trace amounts of gold and silver to a large volume of glass melt. The resulting medium partially reflects the light passing through it, causing an observer to see different colors depending on the direction of the light source. The Lycurgus Cup, for example, is famous for appearing green in daylight and red when lit at night, symbolic of the ripening grapes used to fill it with wine. NASA revitalized the production of dichroic glass in the 1950s and 1960s as a means of protecting its astronauts. Ordinary clear substances cannot protect human vision from the harsh rays of unfiltered sunlight, and everything from the human body to spacecraft sensors and computers are at risk if left unprotected from the radiation that permeates space. The microscopic amounts of metal present in dichroic glass make it an effective barrier against such harmful radiation. While the ancient manufacturing technique called for adding metals to glass melt, NASA developed a process in which metals are vaporized by electron beams in a vacuum chamber and then applied directly to surfaces in an ultra-thin film. The vapor condenses in the form of crystal structures, and the process is repeated for up to several dozen coatings. The resulting material, still only about 30 millionths of an inch thick, is sufficient to reflect radiation even while the glass, or polycarbonate, as in the case of space suit helmets, remains transparent to the human eye.

  14. Low Dielectric Polymers

    NASA Technical Reports Server (NTRS)

    Cassidy, Patrick E.

    2002-01-01

    This report summarizes results obtained through our current research effort entitled 'Low Dielectric Polymers'. Results are reported in four areas: (1) Development of an alkyne containing a crosslinking agent for 12F-PEK and its analogues; (2) Preparation and evaluation of new silicon- and/or fluorine-containing polymers for low temperature applications; (3) Polymers derived from a new highly fluorinated monomer; and (4) Continued evaluation of the scale-up of the preparation of 6FC11- and 6FC17-PEKs.

  15. Voltage sensor and dielectric material

    DOEpatents

    Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

    2006-10-17

    A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

  16. DIELECTRIC-BASED MULTIPARAMETER SENSOR

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the last few decades, microwave dielectric-based sensors were mainly developed for sensing moisture in different materials. The fact that these sensors rely on measurement of dielectric properties, which are also dependent on other physical properties of the material, make them potentially multi...

  17. Dielectric Composites for Naval Applications

    NASA Astrophysics Data System (ADS)

    Gorzkowski, E. P.; Pan, M.-J.

    2013-12-01

    As an integral part of the U.S. Navy's all-electric ship effort, the Naval Research Laboratory (NRL) has been developing advanced dielectrics to provide viable solutions for high energy density capacitors as well as high-dielectric-constant (K) filter capacitors. Our group at NRL has focused on ceramic and ceramic-based composite dielectrics, which are characterized by the high dielectric constant (from 200 to 4000) relative to polymer materials (typically <5) and high breakdown strengths (>200 kV/cm). This article details three approaches to creating high energy density and high-K-filter capacitor materials. These approaches use different processing routes to produce ceramic-based composite dielectrics and include freeze-casting, glass-ceramic, and nanocomposite technologies.

  18. Dielectric laser accelerators

    NASA Astrophysics Data System (ADS)

    England, R. Joel; Noble, Robert J.; Bane, Karl; Dowell, David H.; Ng, Cho-Kuen; Spencer, James E.; Tantawi, Sami; Wu, Ziran; Byer, Robert L.; Peralta, Edgar; Soong, Ken; Chang, Chia-Ming; Montazeri, Behnam; Wolf, Stephen J.; Cowan, Benjamin; Dawson, Jay; Gai, Wei; Hommelhoff, Peter; Huang, Yen-Chieh; Jing, Chunguang; McGuinness, Christopher; Palmer, Robert B.; Naranjo, Brian; Rosenzweig, James; Travish, Gil; Mizrahi, Amit; Schachter, Levi; Sears, Christopher; Werner, Gregory R.; Yoder, Rodney B.

    2014-10-01

    The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years. The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA). In the DLA scheme operating at typical laser pulse lengths of 0.1 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the GV /m regime. The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude. Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment. Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers. Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines.

  19. High dielectric constant oxides

    NASA Astrophysics Data System (ADS)

    Robertson, J.

    2004-12-01

    The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO{2} with a physically thicker layer of oxides of higher dielectric constant (kappa) or `high K' gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO{2}, such as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.

  20. Tunable ultrathin mantle cloak via varactor-diode-loaded metasurface.

    PubMed

    Liu, Shuo; Xu, He-Xiu; Zhang, Hao Chi; Cui, Tie Jun

    2014-06-01

    We propose a tunable strategy for the ultrathin mantle cloak via metasurface. The tunable cloak is implemented by loading varactor diodes between two neighboring horizontal metallic strips which constitute the metasurface. We demonstrate that the varactor diodes enable the capacitive reactance of the metasurface to be tunable from -157 ? to -3 ? when the DC bias voltage is properly changed. The active metasurface is then explored to cloak conformally a conducting cylinder. Both numerical and experiment results show that the cloaking frequency can be continuously controlled from 2.3 GHz to 3.7 GHz by appropriately adjusting the bias voltage. The flexible tunability and good cloaking performance are further examined by the measured field distributions. The advanced features of tunability, low profile, and conformal ability of the ultrathin cloak pave the way for practical applications of cloaking devices. PMID:24921534

  1. Ultrathin aluminum sample cans for single crystal inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Stone, M. B.; Loguillo, M. J.; Abernathy, D. L.

    2011-05-01

    Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to one's measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

  2. Structure-dependent mechanical properties of ultrathin zinc oxide nanowires

    PubMed Central

    2011-01-01

    Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability. PMID:21711876

  3. Ultrathin and lightweight organic solar cells with high flexibility

    PubMed Central

    Kaltenbrunner, Martin; White, Matthew S.; G?owacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2012-01-01

    Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2??m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date. PMID:22473014

  4. Observation of surface-state transport in ultrathin Sb

    NASA Astrophysics Data System (ADS)

    Cairns, S.; Teasdale, N.; Keay, J.; Gaspe, C. K.; Wickramasinghe, K. S.; Mishima, T. D.; Santos, M. B.; Murphy, S. Q.

    2015-05-01

    We report magnetotransport studies of ultrathin Sb films. Sb has been identified as a topologically nontrivial element; as a semimetal, however, the interior states dominate the transport in bulk samples. In the ultrathin films studied here, quantum confinement suppresses the interior transport such that surface transport accounts for about 15 % of the conduction in 10-bilayer-thick Sb structures. For thicknesses between 5 and 16 bilayers, the conduction increases linearly with film thickness, extrapolating to a finite remnant conductivity at zero film thickness. Weak antilocalization (WAL) is observed at low magnetic fields with thickness independent values of the phase breaking length and prefactor (? ) implying surface transport coupled to residual interior conduction. At high fields we see an evolution of the magnetoresistance (MR) field dependence from parabolic to sublinear as a function of film thickness. The data are reproduced by a simple model combining parallel parabolic MR from the interior and WAL from the surface.

  5. Magnetic excitations in ultrathin magnetic films: Temperature effects

    NASA Astrophysics Data System (ADS)

    Zakeri, Kh.; Prokop, J.; Zhang, Y.; Kirschner, J.

    2014-12-01

    The idea of investigating large wave-vector magnetic excitations in ultrathin films by spin-polarized electron spectroscopy is briefly reviewed. The historical background of the paper is based on the personal experience of the authors who collaborated and discussed with Douglas Mills regarding this subject. Douglas Mills' impact on the understanding of fundamental mechanisms involved in the excitation process and the development of the theory of magnetic excitations is outlined. In addition, the temperature effects on the large wave-vector magnetic excitations in ultrathin Fe films are addressed. The experimental results of magnon excitations in the pseudomorphic Fe monolayer on W(110) are presented. The temperature dependence of the magnon dispersion relation is discussed.

  6. Ultrathin zoom lens system based on liquid lenses

    NASA Astrophysics Data System (ADS)

    Li, Lei; Liu, Chao; Wang, Qiong-Hua

    2015-07-01

    In this paper, we propose an ultrathin zoom lens system based on liquid lenses. The proposed system consists of an annular folded lens and three electrowetting liquid lenses. The annular folded lens has several concentric surfaces. The annular folded lens is used to get the main power and correct aberrations. The three liquid lenses are used to change the focal length and correct aberration. An analysis of the proposed system is presented along with the design, fabrication, and testing of a prototype. All the elements in the proposed system are very thin, so the system is an ultrathin zoom lens system, which has potential application as lightweight, thin, high-quality imagers for aerospace, consumer, and military applications.

  7. Strain-Induced Water Dissociation on Supported Ultrathin Oxide Films

    E-print Network

    Song, Zhenjun; Xu, Hu

    2015-01-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this Letter, we have identified the enhanced chemical reactivity of ultrathin MgO(100) films deposited on Mo(100) substrate that causes water dissociation. We reveal that the ability to split water on insulating surface closely depends on the lattice mismatch between ultrathin films and the underlying substrate, and substrate-induced in-plane tensile strain dramatically results in water dissociation on MgO(100). Three dissociative adsorption configurations of water with lower energy are predicted, and the structural transition going from molecular form to dissociative form is almost barrierless. Our results provide an effective avenue to achieve water dissociation at the single-molecule level and shed light on how to tune the chemical reactions of insulating surfaces by choosing the suitable substrates.

  8. Ultrathin and lightweight organic solar cells with high flexibility.

    PubMed

    Kaltenbrunner, Martin; White, Matthew S; G?owacki, Eric D; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2012-01-01

    Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2 ?m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date. PMID:22473014

  9. Magnetoelectric transport and quantum interference effect in ultrathin manganite films

    SciTech Connect

    Wang, Cong; Jin, Kui-juan Gu, Lin; Lu, Hui-bin; Li, Shan-ming; Zhou, Wen-jia; Zhao, Rui-qiang; Guo, Hai-zhong; He, Meng; Yang, Guo-zhen

    2014-04-21

    The magnetoelectric transport behavior with respect to the thicknesses of ultrathin La{sub 0.9}Sr{sub 0.1}MnO{sub 3} films is investigated in detail. The metal-insulator phase transition, which has never been observed in bulk La{sub 0.9}Sr{sub 0.1}MnO{sub 3}, is found in ultrathin films with thicknesses larger than 6 unit cells. Low-temperature resistivity minima appeared in films with thicknesses less than 10 unit cells. This is attributed to the presence of quantum interference effects. These data suggest that the influence of the weak localization becomes much pronounced as the film thickness decreases from 16 to 8 unit cells.

  10. Evolution of the electronic structure in ultrathin Bi(111) films

    NASA Astrophysics Data System (ADS)

    Miao, Lin; Yao, Meng-Yu; Ming, Wenmei; Zhu, Fengfeng; Han, C. Q.; Wang, Z. F.; Guan, D. D.; Gao, C. L.; Liu, Canhua; Liu, Feng; Qian, Dong; Jia, Jin-Feng

    2015-05-01

    By combining angle-resolved photoemission spectroscopy and first-principles calculations, we systematically studied the electronic structures of ultrathin Bi(111) films (?5 bilayers) epitaxially grown on Bi2Te3. High-resolution low-energy band dispersions and Fermi surfaces of ultrathin Bi (111 )/Bi2Te3 films as a function of thickness were experimentally determined. Our results also indicate that the electronic structures of epitaxial Bi films are strongly influenced by the substrate compared with freestanding films. The substrate effects mainly include two aspects. First, the in-plane lattice constant of Bi(111) films is compressed, which increases the bandwidth of the surface-state-like bands. Furthermore, the band dispersion near the ? ¯ point is significantly modified as well. Second, there exists a strong hybridization at the Bi /Bi2Te3 interface, and the hybridization effects spatially extend to three Bi bilayers.

  11. Ultrathin and lightweight organic solar cells with high flexibility

    NASA Astrophysics Data System (ADS)

    Kaltenbrunner, Martin; White, Matthew S.; G?owacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2012-04-01

    Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2??m thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date.

  12. Color Switching with Enhanced Optical Contrast in Ultrathin Phase-Change Materials and Semiconductors Induced by Femtosecond

    E-print Network

    Color Switching with Enhanced Optical Contrast in Ultrathin Phase- Change Materials: Ultrathin semiconductors on metals constitute color filters, which selectively absorb wavelength ranges of incident light. This paper demonstrates that these coatings are attractive for tunable color devices

  13. Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.

    PubMed

    Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

    2014-09-17

    Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications. PMID:25042767

  14. Modelling study of phase transitions in amorphous ultrathin films

    NASA Astrophysics Data System (ADS)

    Leonid, Afremov; Aleksandr, Petrov

    2015-09-01

    The phase transition's critical temperature dependence of the thickness and critical magnetic concentration are studied using the method of configuration averaging over the interaction fields in the framework of the Ising model in amorphous ultrathin film to define the transition from ferromagnetic state to paramagnetic one. It is shown that the Curie temperature increases quickly with a rise in number of monolayers and critical magnetic concentration decreases to bulk material value.

  15. Multilayer optical dielectric coating

    DOEpatents

    Emmett, John L. (Pleasanton, CA)

    1990-01-01

    A highly damage resistant, multilayer, optical reflective coating includes alternating layers of doped and undoped dielectric material. The doping levels are low enough that there are no distinct interfaces between the doped and undoped layers so that the coating has properties nearly identical to the undoped material. The coating is fabricated at high temperature with plasma-assisted chemical vapor deposition techniques to eliminate defects, reduce energy-absorption sites, and maintain proper chemical stoichiometry. A number of differently-doped layer pairs, each layer having a thickness equal to one-quarter of a predetermined wavelength in the material are combined to form a narrowband reflective coating for a predetermined wavelength. Broadband reflectors are made by using a number of narrowband reflectors, each covering a portion of the broadband.

  16. THE DIELECTRIC WALL ACCELERATOR

    SciTech Connect

    Caporaso, G J; Chen, Y; Sampayan, S E

    2009-08-17

    The Dielectric Wall Accelerator (DWA), a class of induction accelerators, employs a novel insulating beam tube to impress a longitudinal electric field on a bunch of charged particles. The surface flashover characteristics of this tube may permit the attainment of accelerating gradients on the order of 100 MV/m for accelerating pulses on the order of a nanosecond in duration. A virtual traveling wave of excitation along the tube is produced at any desired speed by controlling the timing of pulse generating modules that supply a tangential electric field to the tube wall. Because of the ability to control the speed of this virtual wave, the accelerator is capable of handling any charge to mass ratio particle; hence it can be used for electrons, protons and any ion. The accelerator architectures, key technologies and development challenges will be described.

  17. Ultrathin (˜10 nm) carbon foils in space instrumentation

    NASA Astrophysics Data System (ADS)

    McComas, D. J.; Allegrini, F.; Pollock, C. J.; Funsten, H. O.; Ritzau, S.; Gloeckler, G.

    2004-11-01

    Over the past several decades, a number of groups have successfully developed and flown space instruments based on ultrathin (0.5-3.5 ?g cm-2 or ˜2-17 nm nominal thickness) carbon foils suspended on fine metallic grids. These foils have proven to be remarkably robust in surviving the rigors of the launch and space environments and have functioned as required over long mission lifetimes. This study examines the scientific basis of possible failure mechanisms and the actual flight histories of ultrathin carbon foils. In all, we were able to document 138 separate foils used in 17 independent space instruments on 16 different spacecraft with a cumulative functioning flight history of 93 foil-years in space. All of these foils clearly survived their launches, and there is no evidence for any significant degradation over their various flight histories. This successful flight heritage, combined with laboratory data on foil survivability, shows that properly implemented ultrathin carbon foils are a mature and reliable technology for space flight applications.

  18. Ultra-thin film nanostructured gallium arsenide solar cells

    NASA Astrophysics Data System (ADS)

    Kang, Yangsen; Chen, Yusi; Huo, Yijie; Zhao, Li; Jia, Jieyang; Deng, Huiyang; Harris, James S.

    2014-11-01

    State-of-the-art III-V cells have reached the highest energy conversion efficiency among all types of solar cells. However, these cells are not applicable to widespread terrestrial solar energy system yet due to the high cost of epitaxial growth. Ultra-thin film absorbers with advanced light management is one of the most promising solutions to drive down the cost. In this paper, we present an ultra-thin film nano-window gallium arsenide (GaAs) solar cell design. This ultrathin cell consists of a nano-structured Al0.8Ga0.2As window layer on the front side to reduce the reflection and to trap the light, and a metal reflector on the back side to further increase the light path. The 300 nm thick GaAs cell with Al0.8Ga0.2As nano-window shows a broad band absorption enhancement from visible to near infrared (NIR), achieving a spectrally averaged absorption of 94% under normal incidence. In addition, this cell shows excellent angular absorption properties, achieving over 85% spectral averaged absorption at up to 60 degree off normal incidence. Meanwhile, this structure with planar junction and nano-window has solved the issue of low fill factor and low open-circuit voltage in nano-structured GaAs solar cell. A nano-window cell with a 3 ?m thick GaAs junction demonstrated an open circuit voltage of 0.9V.

  19. Electric field effect in ultrathin zigzag graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Zhang, Wen-Xing; Liu, Yun-Xiao; Tian, Hua; Xu, Jun-Wei; Feng, Lin

    2015-07-01

    The electric field effect in ultrathin zigzag graphene nanoribbons containing only three or four zigzag carbon chains is studied by first-principles calculations, and the change of conducting mechanism is observed with increasing in-plane electric field perpendicular to the ribbon. Wider zigzag graphene nanoribbons have been predicted to be spin-splitted for both valence band maximum (VBM) and conduction band minimum (CBM) with an applied electric field and become half-metal due to the vanishing band gap of one spin with increasing applied field. The change of VBM for the ultrathin zigzag graphene nanoribbons is similar to that for the wider ones when an electric field is applied. However, in the ultrathin zigzag graphene nanoribbons, there are two kinds of CBMs, one is spin-degenerate and the other is spin-splitted, and both are tunable by the electric field. Moreover, the two CBMs are spatially separated in momentum space. The conducting mechanism changes from spin-degenerate CBM to spin-splitted CBM with increasing applied electric field. Our results are confirmed by density functional calculations with both LDA and GGA functionals, in which the LDA always underestimates the band gap while the GGA normally produces a bigger band gap than the LDA. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204201 and 11147142) and the Natural Science Foundation for Young Scientists of Shanxi Province, China (Grant No. 2013021010-1).

  20. Thermal characterization and modeling of ultra-thin silicon chips

    NASA Astrophysics Data System (ADS)

    Alshahed, Muhammad; Yu, Zili; Rempp, Horst; Richter, Harald; Harendt, Christine; Burghartz, Joachim N.

    2015-11-01

    Manufacturing ultra-thin chip is an emerging field in semiconductor technology that is driven by 3-D integrated circuits and flexible electronics. Unlike bulk silicon (Si) chips with thickness greater than 400 ?m, the thermal management of ultra-thin Si chips with thickness smaller than 20 ?m is challenging due to the increased lateral thermal resistance implying stringent cooling requirements. Therefore, a reasonable prediction of temperature gradients in such chips is necessary. In this work, a thermal chip is implemented in an ultra-thin 0.5 ?m CMOS technology to be employed in surface steady-state and transient temperature measurement. Test chips are either packaged in a Pin Grid Array (PGA) ceramic package or attached to a flexible polyimide substrate. The experimental results show an on-chip temperature gradient of ?15 °C for a dissipated power of 0.4 W in the case of the PGA package and ?30 °C for the polyimide substrate. The time constants are ?50 s and ?1 s for the PGA and the polyimide packages respectively. The measurements are complemented by FEM simulations using ANSYS 14.5 workbench and spice simulations using an equivalent lumped-component thermal circuit model. The lumped-element thermal circuit model is then used for the surface temperature prediction, which is compared to measurement results.

  1. Room Temperature Ferroelectricity in Ultrathin SnTe Films

    NASA Astrophysics Data System (ADS)

    Chang, Kai; Liu, Junwei; Lin, Haicheng; Zhao, Kun; Zhong, Yong; Ji, Shuai-Hua; He, Ke; Wang, Lili; Ma, Xucun; Fu, Liang; Chen, Xi; Xue, Qi-Kun

    2015-03-01

    The ultrathin SnTe films with several unit cell thickness grown on graphitized SiC(0001) surface have been studied by the scanning tunneling microscopy and spectroscopy (STM/S). The domain structures, local lattice distortion and the electronic band bending at film edges induced by the in-plane spontaneous polarization along < 110 > have been revealed at atomic scale. The experiments at variant temperature show that the Curie temperature Tc of the one unit cell thick (two atomic layers) SnTe film is as high as 280K, much higher than that of the bulk counterpart (~100K) and the 2-4 unit cell thick films even indicate robust ferroelectricity at room temperature. This Tc enhancement is attributed to the stress-free interface, larger electronic band gap and greatly reduced Sn vacancy concentration in the ultrathin films. The lateral domain size varies from several tens to several hundreds of nanometers, and the spontaneous polarization direction could be modified by STM tip. Those properties of ultrathin SnTe films show the potential application on ferroelectric devices. The work was financially supported by Ministry of Science and Technology of China, National Science Foundation and Ministry of Education of China.

  2. GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

    NASA Astrophysics Data System (ADS)

    Islam, Sk Masiul; Chowdhury, Sisir; Sarkar, Krishnendu; Nagabhushan, B.; Banerji, P.; Chakraborty, S.; Mukherjee, Rabibrata

    2015-06-01

    Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO2 and ZrO2, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×1011 cm-2, respectively. The device with a structure Metal/ZrO2/InAs QDs/HfO2/GaAs/Metal shows maximum memory window equivalent to 6.87 V. The device also exhibits low leakage current density of the order of 10-6 A/cm2 and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO2 deposition.

  3. Robust Ultrathin Oxynitride with High Nitrogen Diffusion Barrier near its Surface Formed by NH3 Nitridation of Chemical Oxide and Reoxidation with O2

    NASA Astrophysics Data System (ADS)

    Lai, Chiung Hui; Lin, Bo Chun; Chang, Kow Ming; Hsieh, Kuang Yeu; Lai, Yi Lung

    2006-06-01

    We have proposed an approach for growing robust ultrathin oxynitride using conventional thermal processes with the capability of preventing boron penetration. In this method, we obtain oxynitride with high nitrogen concentration (?13 at. %) on the top and low interface state density (Dit=2× 1010 cm-2 eV-1). The films demonstrate excellent properties in terms of low Dit, low leakage current, high endurance in stressing and superior boron diffusion blocking behavior. This method does not involve any additional capital equipment [such as decoupled plasma nitridation (DPN) or remote plasma nitridation (RPN)] or gas (NO or N2O). In addition, it obtains high-quality oxynitride film with low thermal budget. Most importantly, this process is simple and fully compatible with current process technology. It would be important and interesting for process engineers engaged in the field of gate dielectrics. It is suitable for the next generation of ULSI technology.

  4. Dielectric loss in microstrip lines

    NASA Technical Reports Server (NTRS)

    Simpson, T. L.; Tseng, B.

    1976-01-01

    A technique is presented for calculating dielectric loss in microstrip lines. Numerical results for several different substrates are included. These are compared with other available results and experimental data.

  5. Infrared cubic dielectric resonator metamaterial.

    SciTech Connect

    Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.

    2010-06-01

    Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.

  6. Effect of Dielectric and Liquid on Plasma Sterilization Using Dielectric Barrier Discharge Plasma

    E-print Network

    Roy, Subrata

    Effect of Dielectric and Liquid on Plasma Sterilization Using Dielectric Barrier Discharge Plasma Abstract Plasma sterilization offers a faster, less toxic and versatile alternative to conventional sterilization methods. Using a relatively small, low temperature, atmospheric, dielectric barrier discharge

  7. Graphene-graphite oxide field-effect transistors.

    PubMed

    Standley, Brian; Mendez, Anthony; Schmidgall, Emma; Bockrath, Marc

    2012-03-14

    Graphene's high mobility and two-dimensional nature make it an attractive material for field-effect transistors. Previous efforts in this area have used bulk gate dielectric materials such as SiO(2) or HfO(2). In contrast, we have studied the use of an ultrathin layered material, graphene's insulating analogue, graphite oxide. We have fabricated transistors comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. The graphite oxide layers show relatively minimal leakage at room temperature. The breakdown electric field of graphite oxide was found to be comparable to SiO(2), typically ~1-3 × 10(8) V/m, while its dielectric constant is slightly higher, ? ? 4.3. PMID:22380722

  8. Dimerization of 1,3-Butadiene on Highly Characterized Hydroxylated Surfaces of Ultrathin

    E-print Network

    Dimerization of 1,3-Butadiene on Highly Characterized Hydroxylated Surfaces of Ultrathin Films-cyclohexene on highly ordered hydroxylated ultrathin films of -Al2O3. High surface area, powdered -Al2O3 is widely used to prepare not only highly characterized surfaces of -Al2O3, but also to prepare hydroxylated -Al2O3

  9. Ultrathin, high-efficiency, broad-band, omni-acceptance, organic solar cells enhanced by

    E-print Network

    efficiency of solar-cells," Sol. Energy Mater. Sol. Cells 38(1-4), 45­ 55 (1995). 3. A. V. Shah, R. PlatzUltrathin, high-efficiency, broad-band, omni- acceptance, organic solar cells enhanced by plasmonic and demonstration of a new ultra-thin high- efficiency organic solar cell (SC), termed "plasmonic cavity

  10. Stick-slip friction and nucleation dynamics of ultrathin liquid films I. S. Aranson,1

    E-print Network

    Tsimring, Lev S.

    Stick-slip friction and nucleation dynamics of ultrathin liquid films I. S. Aranson,1 L. S'' of the confined fluid. This model successfully accounts for the observed phenomenology of friction in ultrathin.60. p I. INTRODUCTION The nature of sliding friction is a fundamental physical problem of prime

  11. Printed array of thin-dielectric metal-oxide-metal (MOM) tunneling diodes

    NASA Astrophysics Data System (ADS)

    Bareiß, Mario; Hochmeister, Andreas; Jegert, Gunther; Zschieschang, Ute; Klauk, Hagen; Huber, Rupert; Grundler, Dirk; Porod, Wolfgang; Fabel, Bernhard; Scarpa, Giuseppe; Lugli, Paolo

    2011-08-01

    A large area array of metal-oxide-metal (MOM) tunneling diodes with an ultrathin dielectric (˜3.6 nm aluminum oxide) have been fabricated via a transfer-printing process. The MOM diodes exhibit an excellent tunneling behavior that is suitable for rectifying high-frequency ac current into direct current (dc). Direct tunneling and Fowler-Nordheim tunneling have been observed over eight orders of magnitude in current density. The ratio between forward and reverse current is as large as two orders of magnitude. Simulations have been carried out to extract the static device parameters and have confirmed the existence of a dipole layer at the aluminum/aluminum oxide interface of the printed tunneling diodes. Capacitance measurements have shown that the permittivity of the ultrathin aluminum oxide film is smaller than that of bulk aluminum oxide. The mechanical yield of the transfer-printing process is better than 80%, confirming that transfer printing is a promising candidate for the efficient fabrication of quantum devices over large areas.

  12. Dielectric and permeability

    NASA Technical Reports Server (NTRS)

    Cole, K. D.

    1982-01-01

    Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular+B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in goephysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j*), which includes the well-known polarisation current, given by J*=d/dt (ExM)+(PxB)xB B(-2) where M and P are the magnetization and polarization vectors respectively.

  13. Metal-dielectric interactions

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1979-01-01

    Metal direlectric surface interactions and dielectric films on metal substrates were investigated. Since interfacial interaction depends so heavily on the nature of the surfaces, analytical surface tools such as Auger emission spectroscopy, X-ray photoelectron spectroscopy and field ion microscopy were used to assist in surface and interfacial characterization. The results indicate that with metals contacting certain glasses in the clean state interfacial, bonding produces fractures in the glasses while when a film such as water is present, fractures occur in the metal near the interface. Friction forces were used to measure the interfacial bond strengths. Studies with metals contacting polymers using field ion microscopy revealed that strong bonding forces could develop being between a metal and polymer surface with polymer transferring to the metal surface in various ways depending upon the forces applied to the surface in contact. With the deposition of refractory carbides, silicides and borides onto metal and alloy substrates the presence of oxides at the interface or active gases in the deposition plasma were shown to alter interfacial properties and chemistry. Auger ion depth profile analysis indicated the chemical composition at the interface and this could be related to the mechanical, friction, and wear behavior of the coating.

  14. Water absorption and interface reactivity of yttrium oxide gate dielectrics on silicon

    NASA Astrophysics Data System (ADS)

    Niu, D.; Ashcraft, R. W.; Parsons, G. N.

    2002-05-01

    High dielectric constant insulators deposited at low temperatures rapidly absorb water during exposure to the atmosphere, and the resulting OH leads to detrimental interface reactions. We report the effect of atmospheric exposure on ultrathin yttrium oxide, and details of silicon substrate reactions during postdeposition anneals. Infrared absorption analysis indicates significant absorption of water vapor during atmospheric exposure, even for very short times (<15 min). X-ray photoelectron spectroscopy demonstrates that after OH absorption, a thermally activated interface reaction proceeds with an activation energy of 0.33 eV, consistent with substrate reaction with OH present in the film. The OH absorption rate is reduced for annealed films or when capping layers are deposited in situ. Similar oxidation processes are expected to occur in other high-k materials of interest, where the rate of OH absorption will depend on the deposition process and material thermal history.

  15. Ferroelectric modulation of terahertz waves with graphene/ultrathin-Si:HfO2/Si structures

    NASA Astrophysics Data System (ADS)

    Jiang, Ran; Han, Zuyin; Sun, Weideng; Du, Xianghao; Wu, Zhengran; Jung, Hyung-Suk

    2015-10-01

    Ferroelectric-field-effect-tunable modulation of terahertz waves in graphene/Si:HfO2/Si stack structure was observed. The modulation shows distinct behaviors when the samples under different gate polarities. At a negative voltage, a transmission modulation depth up to ˜74% was present without depending on the photo illumination power, whereas, at a positive voltage, the modulation of Thz wave shows dependence on the illumination power, which is ascribed to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO2 layer. Considering the good compatibility of HfO2 on Si-based semiconductor process, the ferroelectricity layer of Si:HfO2 may open up an avenue for the tunable modulation of Thz wave.

  16. Chemical surface deposition of ultra-thin semiconductors

    DOEpatents

    McCandless, Brian E. (243 W. Main St., Elkton, MD 21921); Shafarman, William N. (1905 N. Van Buren St., Wilmington, DE 19802)

    2003-03-25

    A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

  17. Lifetimes of Confined Acoustic Phonons in Ultrathin Silicon Membranes

    NASA Astrophysics Data System (ADS)

    Cuffe, J.; Ristow, O.; Chávez, E.; Shchepetov, A.; Chapuis, P.-O.; Alzina, F.; Hettich, M.; Prunnila, M.; Ahopelto, J.; Dekorsy, T.; Sotomayor Torres, C. M.

    2013-03-01

    We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ˜4.7ns to 5 ps with decreasing membrane thickness from ˜194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures.

  18. Lifetimes of confined acoustic phonons in ultrathin silicon membranes.

    PubMed

    Cuffe, J; Ristow, O; Chávez, E; Shchepetov, A; Chapuis, P-O; Alzina, F; Hettich, M; Prunnila, M; Ahopelto, J; Dekorsy, T; Sotomayor Torres, C M

    2013-03-01

    We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures. PMID:23496722

  19. Ultrathin 2D Metal-Organic Framework Nanosheets.

    PubMed

    Zhao, Meiting; Wang, Yixian; Ma, Qinglang; Huang, Ying; Zhang, Xiao; Ping, Jianfeng; Zhang, Zhicheng; Lu, Qipeng; Yu, Yifu; Xu, Huan; Zhao, Yanli; Zhang, Hua

    2015-12-01

    A facile surfactant-assisted bottom-up synthetic method to prepare a series of freestanding ultrathin 2D M-TCPP (M = Zn, Cu, Cd or Co, TCPP = tetrakis(4-carboxyphenyl)porphyrin) nanosheets with a thickness of sub-10 nm is developed. As a proof-of-concept application, some of them are successfully used as new platforms for DNA detection. The Cu-TCPP nanosheet-based sensor shows excellent fluorescent sensing performance and is used for the simultaneous detection of multiple DNA targets. PMID:26468970

  20. Optical visualization of ultrathin mica flakes on semitransparent gold substrates

    PubMed Central

    2013-01-01

    We show that optical visualization of ultrathin mica flakes on metallic substrates is viable using semitransparent gold as substrates. This enables to easily localize mica flakes and rapidly estimate their thickness directly on gold substrates by conventional optical reflection microscopy. We experimentally demonstrate it by comparing optical images with atomic force microscopy images of mica flakes on semitransparent gold. Present results open the possibility for simple and rapid characterization of thin mica flakes as well as other thin sheets directly on metallic substrates. PMID:23819688

  1. Real-Time Deposition Monitor for Ultrathin Conductive Films

    NASA Technical Reports Server (NTRS)

    Hines, Jacqueline

    2011-01-01

    A device has been developed that can be used for the real-time monitoring of ultrathin (2 or more) conductive films. The device responds in less than two microseconds, and can be used to monitor film depositions up to about 60 thick. Actual thickness monitoring capability will vary based on properties of the film being deposited. This is a single-use device, which, due to the very low device cost, can be disposable. Conventional quartz/crystal microbalance devices have proven inadequate to monitor the thickness of Pd films during deposition of ultrathin films for hydrogen sensor devices. When the deposited film is less than 100 , the QCM measurements are inadequate to allow monitoring of the ultrathin films being developed. Thus, an improved, high-sensitivity, real-time deposition monitor was needed to continue Pd film deposition development. The new deposition monitor utilizes a surface acoustic wave (SAW) device in a differential delay-line configuration to produce both a reference response and a response for the portion of the device on which the film is being deposited. Both responses are monitored simultaneously during deposition. The reference response remains unchanged, while the attenuation of the sensing path (where the film is being deposited) varies as the film thickness increases. This device utilizes the fact that on high-coupling piezoelectric substrates, the attenuation of an SAW undergoes a transition from low to very high, and back to low as the conductivity of a film on the device surface goes from nonconductive to highly conductive. Thus, the sensing path response starts with a low insertion loss, and as a conductive film is deposited, the film conductivity increases, causing the device insertion loss to increase dramatically (by up to 80 dB or more), and then with continued film thickness increases (and the corresponding conductivity increases), the device insertion loss goes back down to the low level at which it started. This provides a continuous, real-time monitoring of film deposition. For use with different films, the device would need to be calibrated to provide an understanding of how film thickness is related to film conductivity, as the device is responding primarily to conductivity effects (and not to mass loading effects) in this ultrathin film regime.

  2. Switchable cross-polarization conversion in ultrathin metasurfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Yu; Hu, Xiaoyong; Yang, Hong; Gong, Qihuang

    2015-10-01

    An actively switchable cross-polarization conversion is realized in an ultrathin metasurface consisting of periodic arrays of 30 nm thick meta-molecules covered with a 50 nm thick vanadium dioxide layer. A cross-polarization conversion ratio of 45% is obtained for 45° linearly polarized light. A complete switching off of the cross-polarization conversion is achieved based on the insulator-to-metal phase transition of vanadium dioxide induced by increasing temperature. This may pave a way for the realization of multifunctional integrated photonic circuits and quantum solid chips based on metasurfaces.

  3. Ultrathin conformal coating for complex magneto-photonic structures.

    PubMed

    Pascu, Oana; Caicedo, José Manuel; López-García, Martín; Canalejas, Víctor; Blanco, Álvaro; López, Cefe; Arbiol, Jordi; Fontcuberta, Josep; Roig, Anna; Herranz, Gervasi

    2011-11-01

    We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer, yielding magneto-photonic crystals with excellent quality. The use of a ternary oxide for the ultrathin coating demonstrates the potential of this methodology to realize three-dimensional structures with complex materials that may find applications beyond photonics, such as energy, sensing or catalysis. PMID:21987109

  4. Wide-scale evolution of magnetization distribution in ultrathin films

    NASA Astrophysics Data System (ADS)

    Kisielewski, M.; Maziewski, A.; Polyakova, T.; Zablotskii, V.

    2004-05-01

    We show, combining simulations and analytical study, the evolution of magnetization distributions in ultrathin film with in-plane fields (H?) and changes of magnetic anisotropy characterized by the quality factor, Q. Reconstruction of the distributions and their new types near Q or H?-induced reorientation phase transitions, from a domain structure (DS) with perpendicular magnetization into a state with in-plane magnetization, are reported. Sinusoidal-like DS exist for H? larger than the anisotropy field and for Q<1. A minimal 8?lex DS period is predicted (lex is the exchange length).

  5. Extracellular ultrathin fibers sensitive to intracellular reactive oxygen species: Formation of intercellular membrane bridges

    SciTech Connect

    Jung, Se-Hui; Park, Jin-Young; Joo, Jung-Hoon; Kim, Young-Myeong; Ha, Kwon-Soo

    2011-07-15

    Membrane bridges are key cellular structures involved in intercellular communication; however, dynamics for their formation are not well understood. We demonstrated the formation and regulation of novel extracellular ultrathin fibers in NIH3T3 cells using confocal and atomic force microscopy. At adjacent regions of neighboring cells, phorbol 12-myristate 13-acetate (PMA) and glucose oxidase induced ultrathin fiber formation, which was prevented by Trolox, a reactive oxygen species (ROS) scavenger. The height of ROS-sensitive ultrathin fibers ranged from 2 to 4 nm. PMA-induced formation of ultrathin fibers was inhibited by cytochalasin D, but not by Taxol or colchicine, indicating that ultrathin fibers mainly comprise microfilaments. PMA-induced ultrathin fibers underwent dynamic structural changes, resulting in formation of intercellular membrane bridges. Thus, these fibers are formed by a mechanism(s) involving ROS and involved in formation of intercellular membrane bridges. Furthermore, ultrastructural imaging of ultrathin fibers may contribute to understanding the diverse mechanisms of cell-to-cell communication and the intercellular transfer of biomolecules, including proteins and cell organelles.

  6. All-dielectric bianisotropic nanoantennas

    E-print Network

    Alaee, Rasoul; Rahimzadegan, Aso; Mirmoosa, Mohammad S; Kivshar, Yuri S; Rockstuhl, Carsten

    2015-01-01

    The study of high-index dielectric nanoparticles and nanoantennas currently attracts a lot of attention. They do not suffer from absorption but promise to provide control on the properties of light comparable to plasmonic nanoantennas. To further advance the field, it is important to identify versatile dielectric nanoantennas with unconventional properties. Here, we show that breaking the symmetry of an all-dielectric nanoantenna leads to a geometrically tunable magneto-electric coupling, i.e. a strong bianisotropy. The suggested nanoantenna exhibits different backscatterings and, as an interesting consequence, different optical scattering forces for opposite illumination directions. An array of such nanoantennas provides different reflection phases when illuminated from opposite directions. With a proper geometrical tuning, this bianisotropic nanoantenna is capable of providing a $2\\pi$ phase change in the reflection spectrum while possessing a rather large and constant amplitude. This allows creating reflec...

  7. Polymer/metal oxide hybrid dielectrics for low voltage field-effect transistors with solution-processed, high-mobility semiconductors

    NASA Astrophysics Data System (ADS)

    Held, Martin; Schießl, Stefan P.; Miehler, Dominik; Gannott, Florentina; Zaumseil, Jana

    2015-08-01

    Transistors for future flexible organic light-emitting diode (OLED) display backplanes should operate at low voltages and be able to sustain high currents over long times without degradation. Hence, high capacitance dielectrics with low surface trap densities are required that are compatible with solution-processable high-mobility semiconductors. Here, we combine poly(methyl methacrylate) (PMMA) and atomic layer deposition hafnium oxide (HfOx) into a bilayer hybrid dielectric for field-effect transistors with a donor-acceptor polymer (DPPT-TT) or single-walled carbon nanotubes (SWNTs) as the semiconductor and demonstrate substantially improved device performances for both. The ultra-thin PMMA layer ensures a low density of trap states at the semiconductor-dielectric interface while the metal oxide layer provides high capacitance, low gate leakage and superior barrier properties. Transistors with these thin (?70 nm), high capacitance (100-300 nF/cm2) hybrid dielectrics enable low operating voltages (<5 V), balanced charge carrier mobilities and low threshold voltages. Moreover, the hybrid layers substantially improve the bias stress stability of the transistors compared to those with pure PMMA and HfOx dielectrics.

  8. Capacitive Cells for Dielectric Constant Measurement

    ERIC Educational Resources Information Center

    Aguilar, Horacio Munguía; Maldonado, Rigoberto Franco

    2015-01-01

    A simple capacitive cell for dielectric constant measurement in liquids is presented. As an illustrative application, the cell is used for measuring the degradation of overheated edible oil through the evaluation of their dielectric constant.

  9. CORRELATING HONEYDEW MELON QUALITY WITH DIELECTRIC PROPERTIES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Honeydew melons were grown and harvested with a range of maturities for measurement of tissue permittivities (dielectric constant and loss factor) to study possible correlations between the dielectric properties and soluble solids (sweetness) for nondestructive sensing of maturity. Permittivities of...

  10. Electric and Magnetic Walls on Dielectric Interfaces

    E-print Network

    Changbiao Wang

    2010-07-20

    Sufficient conditions of the existence of electric or magnetic walls on dielectric interfaces are given for a multizone uniform dielectric waveguiding system. If one of two adjacent dielectric zones supports a TEM field distribution while the other supports a TM (TE) field distribution, then the common dielectric interface behaves as an electric (magnetic) wall, that is, the electric (magnetic) field line is perpendicular to the interface while the magnetic (electric) field line is parallel to the interface.

  11. Dielectric crystal in the Planck blackbody

    E-print Network

    Miroslav Pardy

    2015-05-05

    The dielectric crystal with the index of refraction n is inserted in the Planck blackbody. The spectral formula for photons in such dielectric medium is derived with the equation for the temperature of internal photons. The derived equation is solved for the constant index of refraction. The photon ow initiates the osmotic pressure of he Debye phonons in the dielectric blackbody. Key words: Thermodynamics, blackbody, photons, phonons, dielectric medium, dispersion.

  12. Formation of hybrid hafnium oxide by applying sacrifacial silicon film

    NASA Astrophysics Data System (ADS)

    Lin, Chiung-Wei; Zheng, Bo-Shen; Huang, Jing-Wei

    2016-01-01

    In the fabrication of hafnium oxide (HfO2)-based metal–insulator–semiconductor (MIS) devices, a sacrificial amorphous silicon (a-Si) film was used as silicon source for facilitating the formation of hafnium silicate (Hf-silicate; HfSiO) between HfO2 and crystallized Si (c-Si). HfSiO can assist in changing the phase of the HfO2 film into the tetragonal phase and achieve high dielectric constant. The combination of HfSiO and HfO2 was named as “Hybrid HfO2”. When this Hybrid HfO2 insulator was applied to MIS devices, it can form a good insulator/semiconductor interface with c-Si. Hybrid HfO2 cannot only suppress the leakage current but also show high dielectric strength. The Hybrid HfO2 film in this work exhibited a high dielectric constant of 25.5 and a high dielectric strength of 17.9 MV/cm.

  13. Dielectric Properties of Piezoelectric Polyimides

    NASA Technical Reports Server (NTRS)

    Ounaies, Z.; Young, J. A.; Simpson, J. O.; Farmer, B. L.

    1997-01-01

    Molecular modeling and dielectric measurements are being used to identify mechanisms governing piezoelectric behavior in polyimides such as dipole orientation during poling, as well as degree of piezoelectricity achievable. Molecular modeling on polyimides containing pendant, polar nitrile (CN) groups has been completed to determine their remanent polarization. Experimental investigation of their dielectric properties evaluated as a function of temperature and frequency has substantiated numerical predictions. With this information in hand, we are then able to suggest changes in the molecular structures, which will then improve upon the piezoelectric response.

  14. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  15. Ultrathin films of TiO2 nanoparticles at interfaces.

    PubMed

    Choudhary, Keerti; Manjuladevi, V; Gupta, R K; Bhattacharyya, P; Hazra, A; Kumar, S

    2015-02-01

    The properties of a material change remarkably as a result of the scaling dimensions. The Langmuir-Blodgett (LB) film deposition technique is known to offer precise control over the film thickness and the interparticle separation. To form a well-ordered LB film, it is essential to form a stable Langmuir film at the air-water interface. Here, we report our studies on ultrathin films of TiO2 nanoparticles at air-water and air-solid interfaces. The Langmuir film of TiO2 nanoparticles at the air-water interface was found to be very stable, and it exhibits loose-packing and close-packing phases. The LB films were transferred onto solid substrates for characterization and application. The surface morphology of the LB film was obtained by a field emission scanning electron microscope. The optical and electronic properties of the LB films of TiO2 nanoparticles were studied using UV-vis spectroscopy and current-voltage measurements, respectively. The LB film of TiO2 nanoparticles was employed for ethanol gas sensing, and the sensing performance was compared to that of bulk material. Because of the enormous gain in the surface to volume ratio and the increase in crystalline defect density in the ultrathin LB film of TiO2 nanoparticles, the LB film is found to be a potential functional layer for ethanol sensing as compared to the bulk material. PMID:25557246

  16. Supersonically blown ultrathin thorny devil nanofibers for efficient air cooling.

    PubMed

    An, Seongpil; Lee, Changmin; Liou, Minho; Jo, Hong Seok; Park, Jung-Jae; Yarin, Alexander L; Yoon, Sam S

    2014-08-27

    The effect of the supersonically blown below-74 nm nanofibers on cooling of high-temperature surfaces is studied experimentally and theoretically. The ultrathin supersonically blown nanofibers were deposited and then copper-plated, while their surfaces resembled those of the thorny-devil nanofibers. Here, we study for the first time the enhancement of surface cooling in gas in the cases of the forced and natural convection with the help of ultrathin thorny-devil nanofibers. These polymer core-metal shell nanofibers in nanometric scale possess a relatively high thickness of the metal shell and a high effective thermal conductivity, which facilitates heat transfer. The additional surface temperature reduction close to 5 °C in the case of the forced convection in the impinging air jet and close to 17 °C in the case of the natural convection was achieved. Correspondingly, an increase in the value of the heat transfer coefficient of about 41% in the forced convection, and about 20% in the natural convection was achieved due to the presence of the thorny devil electrospun and/or supersonically blown nanofibers. PMID:25017392

  17. Processing and characterization of Ultrathin carbon coatings on glass

    SciTech Connect

    Lee, H.; Rajagopalan, R.; Robinson, J.; Pantano, C.G.

    2009-04-15

    Ultrathin carbon layers, on the order of 3-6 nm in thickness, were formed on glass substrates by spin coating and pyrolysis of polymer precursors. The organic precursors used were poly(furfuryl alcohol), coal tar pitch, and a photoresist. The carbon coatings were characterized by ellipsometry, optical profilometry, water contact angle, confocal Raman spectroscopy, UV-vis spectroscopy, and atomic force microscopy. We also report the transparency, hydrophobicity, friction, weathering resistance, and electrical conductivity of the carbon-coated glass. The results reveal that up to 97% transparent, ultrathin carbon films could be formed on glass substrates with a root-mean-square roughness of less than about to 0.3 nm. This carbon layer modified the otherwise hydrophilic surface of the glass to yield a water contact angle of 85{sup o}. The coatings were also found to provide a water barrier against weathering under hot and humid conditions. A 4.5-nm-thick carbon film on glass had a sheet resistance of 55.6 k {Omega} m and a conductivity of 40 S/cm.

  18. Resonant light trapping in ultrathin films for water splitting.

    PubMed

    Dotan, Hen; Kfir, Ofer; Sharlin, Elad; Blank, Oshri; Gross, Moran; Dumchin, Irina; Ankonina, Guy; Rothschild, Avner

    2013-02-01

    Semiconductor photoelectrodes for solar hydrogen production by water photoelectrolysis must employ stable, non-toxic, abundant and inexpensive visible-light absorbers. Iron oxide (?-Fe(2)O(3)) is one of few materials meeting these requirements, but its poor transport properties present challenges for efficient charge-carrier generation, separation, collection and injection. Here we show that these challenges can be addressed by means of resonant light trapping in ultrathin films designed as optical cavities. Interference between forward- and backward-propagating waves enhances the light absorption in quarter-wave or, in some cases, deeper subwavelength films, amplifying the intensity close to the surface wherein photogenerated minority charge carriers (holes) can reach the surface and oxidize water before recombination takes place. Combining this effect with photon retrapping schemes, such as using V-shaped cells, provides efficient light harvesting in ultrathin films of high internal quantum efficiency, overcoming the trade-off between light absorption and charge collection. A water photo-oxidation current density of 4 mA cm(-2) was achieved using a V-shaped cell comprising ~26-nm-thick Ti-doped ?-Fe(2)O(3) films on back-reflector substrates coated with silver-gold alloy. PMID:23142836

  19. Ultra-thin, light-trapping silicon solar cells

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.

    1989-01-01

    Design concepts for ultra-thin (2 to 10 microns) high efficiency single-crystal silicon cells are discussed. Light trapping allows more light to be absorbed at a given thickness, or allows thinner cells of a given Jsc. Extremely thin cells require low surface recombination velocity at both surfaces, including the ohmic contacts. Reduction of surface recombination by growth of heterojunctions of ZnS and GaP on Si has been demonstrated. The effects of these improvements on AM0 efficiency is shown. The peak efficiency increases, and the optimum thickness decreases. Cells under 10 microns thickness can retain almost optimum power. The increase of absorptance due to light trapping is considered. This is not a problem if the light-trapping cells are sufficiently thin. Ultra-thin cells have high radiation tolerance. A 2 microns thick light-trapping cell remains over 18 percent efficient after the equivalent of 20 years in geosynchronous orbit. Including a 50 microns thick coverglass, the thin cells had specific power after irradiation over ten times higher than the baseline design.

  20. Ultrathin nickel oxide nanosheets for enhanced sodium and lithium storage

    NASA Astrophysics Data System (ADS)

    Sun, Wenping; Rui, Xianhong; Zhu, Jixin; Yu, Linghui; Zhang, Yu; Xu, Zhichuan; Madhavi, Srinivasan; Yan, Qingyu

    2015-01-01

    Outstanding sodium and lithium storage capability is successfully demonstrated in ultrathin NiO nanosheets (4-5 nm in thickness) synthesized via a facile solvothermal process followed by annealing in air. For sodium storage, the NiO nanosheets deliver a high reversible specific capacity of 299 mA h g-1 at a current density of 1 A g-1, and the capacity still remains up to 154 mA h g-1 at 10 A g-1. Upon charge/discharge cycling, the specific capacity maintains to be as high as 266 mA h g-1 during the 100th cycle at 1 A g-1. Such sodium storage capability of NiO nanosheets is by far one of the best reported for transition metal oxides. For lithium storage, the cell achieves a high reversible specific capacity of 1242 and 250 mA h g-1 at 0.2 and 15 A g-1, respectively. The capacity for lithium storage maintains to be 851 mA h g-1 during the 170th cycle at 2 A g-1. The present results demonstrate that ultrathin NiO nanosheets are highly attractive for fast sodium/lithium diffusion with high-rate capability for rechargeable sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs).

  1. Curie temperature of ultrathin ferromagnetic layer with Dzyaloshinskii-Moriya interaction

    SciTech Connect

    You, Chun-Yeol

    2014-08-07

    We investigate the effect of the Dzyaloshinskii-Moriya interaction (DMI) on the Curie temperature of the ultrathin ferromagnetic layers. It has been known that the Curie temperature of the ferromagnet depends on spin wave excitation energies, and they are affected by DMI. Therefore, the ferromagnetic transition temperature of the ultrathin ferromagnetic layer must be sensitive on the DMI. We find that the Curie temperature depends on the DMI by using the double time Green's function method. Since the DMI is arisen by the inversion symmetry breaking structure, the DMI is always important in the inversion symmetry breaking ultrathin ferromagnetic layers.

  2. Linearly tapered slot antenna with dielectric superstrate

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Lee, Richard Q.

    1993-01-01

    The effect of dielectric superstrate on a linearly tapered slot antenna (LTSA) was investigated experimentally. It was observed that the dielectric superstrate improves the directivity but generally at the expense of higher sidelobe level. The dielectric superstrate could be used to reduce the physical length and to improve the radiation characteristics of the LTSA.

  3. DIELECTRIC METHODS FOR MULTIPARAMETER MICROWAVE SENSOR

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Three dielectric-based approaches are presented for predicting physical properties of grain and seed from measurement of their dielectric properties. In the first approach, regression analysis provided explicit direct relationships between the dielectric properties of these materials and their phys...

  4. Polarization of Dielectrics by Acceleration

    E-print Network

    L. A. Melnikovsky

    2006-08-23

    We argue that acceleration induces electric polarization in usual dielectrics. Both accelerations in superfluid participate in the medium polarization. Excitations contribution to the polarization is calculated at low temperatures. Estimates of the effect show order of magnitude agreement with recent experimental results on electric effect of superflow.

  5. Counteracting Gravitation In Dielectric Liquids

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E.; Jackson, Henry W.; Strayer, Donald M.

    1993-01-01

    Force of gravity in variety of dielectric liquids counteracted by imposing suitably contoured electric fields. Technique makes possible to perform, on Earth, variety of experiments previously performed only in outer space and at great cost. Also used similarly in outer space to generate sort of artificial gravitation.

  6. Optical dielectric function of silver

    NASA Astrophysics Data System (ADS)

    Yang, Honghua U.; D'Archangel, Jeffrey; Sundheimer, Michael L.; Tucker, Eric; Boreman, Glenn D.; Raschke, Markus B.

    2015-06-01

    The dielectric function of silver is a fundamental quantity related to its electronic structure and describes its optical properties. However, results published over the past six decades are in part inconsistent and exhibit significant discrepancies. The measurement is experimentally challenging with the values of dielectric function spanning over five orders of magnitude from the mid-infrared to the visible/ultraviolet spectral range. Using broadband spectroscopic ellipsometry, we determine the complex-valued dielectric function of evaporated and template stripped polycrystalline silver films from 0.05 eV (? =25 ? m ) to 4.14 eV (? =300 nm) with a statistical uncertainty of less than 1 % . From Drude analysis of the 0.1-3 eV range, values of the plasma frequency ? ?p=8.9 ±0.2 eV, dielectric function at infinite frequency ??=5 ±2 , and relaxation time ? =1 /? =17 ±3 fs are obtained, with the absolute uncertainties estimated from systematic errors and experimental repeatability. Further analysis based on the extended Drude model reveals an increase in ? with decreasing frequency in agreement with Fermi liquid theory, and extrapolates to ? ?22 fs for zero frequency. A deviation from simple Fermi liquid behavior is suggested at energies below 0.1 eV (? =12 ? m ) with the onset of a further increase in ? connecting to the DC value from transport measurements of ˜40 fs. The results are consistent with a wide range of optical and plasmonic experiments throughout the infrared and visible/ultraviolet spectral range. However, due to the polycrystalline nature of our sample, the values measured are not likely reaching the intrinsic limit of silver. The influence of grain boundaries, defect scattering, and surface oxidation is discussed. The results are compared with our previous measurements of the dielectric function of gold [Olmon et al., Phys. Rev. B 86, 235147 (2012)], 10.1103/PhysRevB.86.235147.

  7. Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 2. Fourier

    E-print Network

    Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 2. Fourier Transform SPR Place, Madison, Wisconsin, 53711 The application of surface plasmon resonance (SPR) measurements otherwise interfere with the analysis. Surface plasmon resonance (SPR) measurements are surface- sensitive

  8. Research Update: Synthesis, properties, and applications of ultrathin metallic nanowires and associated heterostructures

    NASA Astrophysics Data System (ADS)

    Liu, Haiqing; Li, Luyao; Scofield, Megan E.; Wong, Stanislaus S.

    2015-08-01

    The properties of one-dimensional (1D) nanostructured materials can change considerably and unexpectedly, when their diameters attain the "ultrathin" level, i.e., below 10 nm. Herein, we have summarized recent developments associated with not only the synthesis but also more importantly, the applications of ultrathin 1D nanowires. Specifically, various classes of ultrathin metallic nanowires have been shown to be excellent, high-performing structural motifs for electrocatalysts, superconducting materials, electrical devices, and nano-sized pressure sensors. Moreover, the fabrication of ultrathin-based 0D-1D, 1D-1D, and 1D-2D composite hybrid structures may represent one of the most promising designs for novel architectures in energy storage and conversion, photovoltaic devices, photoconductivity, and photoelectrocatalysis.

  9. Nearly Total Solar Absorption in Ultrathin Nanostructured Iron Oxide for Efficient Photoelectrochemical Water Splitting

    E-print Network

    Fan, Shanhui

    , photoelectrochemical cells Hematite (-iron oxide) is a promising material for the photoelectrochemical conversionNearly Total Solar Absorption in Ultrathin Nanostructured Iron Oxide for Efficient, United States § Department of Materials Science and Engineering, Stanford University, Stanford

  10. Stealth dicing characterization, optimization, integration, and operations management for ultra-thin stacked memory dies

    E-print Network

    Teh, Weng Hong

    2014-01-01

    This dissertation presents original work in the development of multi-strata subsurface infrared (1.342 [mu]m) nanosecond pulsed laser die singulation (stealth dicing) to enable defect-free ultra-thin stacked memory dies. ...

  11. Feasibility of Ultra-Thin Fiber-Optic Dosimeters for Radiotherapy Dosimetry.

    PubMed

    Lee, Bongsoo; Kwon, Guwon; Shin, Sang Hun; Kim, Jaeseok; Yoo, Wook Jae; Ji, Young Hoon; Jang, Kyoung Won

    2015-01-01

    In this study, prototype ultra-thin fiber-optic dosimeters were fabricated using organic scintillators, wavelength shifting fibers, and plastic optical fibers. The sensor probes of the ultra-thin fiber-optic dosimeters consisted of very thin organic scintillators with thicknesses of 100, 150 and 200 ?m. These types of sensors cannot only be used to measure skin or surface doses but also provide depth dose measurements with high spatial resolution. With the ultra-thin fiber-optic dosimeters, surface doses for gamma rays generated from a Co-60 therapy machine were measured. Additionally, percentage depth doses in the build-up regions were obtained by using the ultra-thin fiber-optic dosimeters, and the results were compared with those of external beam therapy films and a conventional fiber-optic dosimeter. PMID:26593917

  12. High performance thin film transistor with HfSiO x dielectric fabricated at room temperature RF-magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Cho, Dongkyu; Woo, Sanghyun; Yang, Jungil; Lee, Donghee; Lim, Yoosung; Kim, Daekuk; Park, Sungmin; Yi, Moonsuk

    2013-07-01

    In this work, we investigated the enhanced performance of IZO-based TFTs with HfSiO x gate insulators. Four types of HfSiO x gate insulators with different deposition powers were deposited by co-sputtering HfO2 and Si. To simplify the processing sequences, all of the layers of the TFTs were deposited by an RF-magnetron sputtering method using patterned shadow-masks without any intentional heating of the substrate or subsequent thermal annealing. The four different HfSiO x structural properties were investigated by x-ray Diffraction (XRD), Atomic Force Microscopy (AFM), and the electrical characteristics were also analyzed. There were some noticeable differences depending on the composition of the HfO2 and Si combination. The TFT based on the HfSiO x gate insulator comprised of HfO2 (100 W)-Si (100 W) showed the best results with a field effect mobility of 2.0 cm2/V·s, a threshold voltage of 0.6 V, an I on/off ratio of 3.18 × 105, and an insulator surface roughness of 0.16 nm RMS. This confirms that the composition of the HfO2 and Si is an important factor in an HfSiO x insulator. In addition, the effective bonding of the HfO2 and Si reduced the defects in the insulator bulk and also improved the interface quality between the channel and the gate insulator.

  13. Intrinsic microwave dielectric loss of lanthanum aluminate.

    PubMed

    Shimada, Takeshi; Ichikawa, Koji; Minemura, Tetsuro; Yamauchi, Hiroki; Utsumi, Wataru; Ishii, Yoshinobu; Breeze, Jonathan; Alford, Neil McN

    2010-10-01

    The intrinsic dielectric properties of LaAlO? were investigated to understand the microwave properties of several materials containing LaAlO?. In this study, LaAlO? single crystals were prepared by the Czochralski method. The temperature dependence of the dielectric properties and neutron inelastic scattering of the single crystals were measured. From these data, the intrinsic dielectric properties were evaluated and it was found that the dielectric loss of the LaAlO? includes two types of dielectric loss. One is a phonon absorption-related loss and the other is a component of the loss arising from Debye- type orientation polarization. The latter affects the room temperature dielectric loss in materials containing LaAlO?. The present study suggests that avoiding this polarization loss is an important goal in decreasing the total dielectric loss. PMID:20889412

  14. Modeling of dielectric charging in capacitive structures

    NASA Astrophysics Data System (ADS)

    Amiaud, A.-C.; Leuliet, A.; Loiseaux, B.; Ganne, J.-P.; Nagle, J.

    2015-11-01

    In this paper, we investigate dielectric charging process in capacitive structure dielectrics under bias voltage. We particularly focus on the case of Si 3 N 4 dielectric layers. The main defects in silicon nitride involved in electronic transport are identified as shallow traps. A new model for dielectric charging is presented with trap assisted tunneling effect as interfacial electronic transport mechanism and Frenkel-Poole and hopping current as bulk transport mechanisms. Thanks to this model, electric field and charge carrier distribution in the dielectric layer can be calculated. The actuation bias shift versus time, which is responsible for RF capacitive structure failure, can also be determined. We find that after a 300 s actuation, the charge is concentrated in few nm in the dielectric layer and a voltage shift of few volts is calculated, depending on dielectric characteristics.

  15. Dielectric properties and microstructure of sintered BaTiO3 fabricated by using mixed 150-nm and 80-nm powders with various additives

    NASA Astrophysics Data System (ADS)

    Oh, Min Wook; Kang, Jae Won; Yeo, Dong Hun; Shin, Hyo Soon; Jeong, Dae Yong

    2015-04-01

    Recently, the use of small-sized BaTiO3 particles for ultra-thin MLCC research has increased as a method for minimizing the dielectric layer's thickness in thick film process. However, when particles smaller than 100 nm are used, the reduced particle size leads to a reduced dielectric constant. The use of nanoparticles, therefore, requires an increase in the amount of additive used due to the increase in the specific surface area, thus increasing the production cost. In this study, a novel method of coating 150-nm and 80-nm BaTiO3 powders with additives and mixing them together was employed, taking advantage of the effect obtained through the use of BaTiO3 particles smaller than 100 nm, to conveniently obtain the desired dielectric constant and thermal characteristics. Also, the microstructure and the dielectric properties were evaluated. The additives Dy, Mn, Mg, Si, and Cr were coated on a 150-nm powder, and the additives Dy, Mn, Mg, and Si were coated on 80-nm powder, followed by mixing at a ratio of 1:1. As a result, the microstructure revealed grain formation according to the liquid-phase additive Si; additionally, densification was well realized. However, non-reducibility was not obtained, and the material became a semiconductor. When the amount of added Mn in the 150-nm powder was increased to 0.2 and 0.3 mol%, insignificant changes in the microstructure were observed, and the bulk density after mixing was found to have increased drastically in comparison to that before mixing. Also, non-reducibility was obtained for certain conditions. The dielectric property was found to be consistent with the densification and the grain size. The mixed composition #1-0.3 had a dielectric constant over 2000, and the result somewhat satisfied the dielectric constant temperature dependency for X6S.

  16. Improved high-field reliability for a SiC metal-oxide-semiconductor device by the incorporation of nitrogen into its HfTiO gate dielectric

    NASA Astrophysics Data System (ADS)

    Lin, L. M.; Lai, P. T.

    2007-09-01

    Materials with high dielectric constant (k) have been used in SiC-based metal-oxide-semiconductor (MOS) devices to reduce the electric field in the gate dielectric and thus suppress a high-field reliability problem. In this work, high-k gate dielectrics HfxTi1-xO2 and HfxTi1-xON are applied in SiC MOS devices and an ultrathin thermally grown SiO2 is used as an interlayer between SiC and the high-k materials to block electron injection from SiC into the low-barrier high-k materials. Incorporating nitrogen into the Hf-Ti oxide (by adding nitrogen gas during its sputtering) stacked with a SiO2 interlayer (HfxTi1-xO/SiO2) results in a better gate dielectric for the MOS capacitor, such as smaller frequency dispersion in the capacitance-voltage curve, less oxide charges, and better interface quality. Moreover, the nitrogen incorporation increases the dielectric constant of the oxide, but causes higher dielectric leakage, which can be suppressed by the SiO2 interlayer. High-field stress under constant electric field is performed on the stacked/nonstacked Hf-Ti oxides and oxynitrides, and it turns out that the two oxynitrides show a much smaller flatband shift and a less stress-induced leakage current compared with the two oxides. Based on these results, the HfxTi1-xON/SiO2 stack could be a promising high-k gate dielectric for SiC MOS devices with enhanced reliability.

  17. Two-phase mixed media dielectric with macro dielectric beads for enhancing resistivity and breakdown strength

    SciTech Connect

    Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary

    2014-06-10

    A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.

  18. Fluorescence Spectroscopy with Metal-Dielectric Waveguides

    PubMed Central

    Badugu, Ramachandram; Szmacinski, Henryk; Ray, Krishanu; Descrovi, Emiliano; Ricciardi, Serena; Zhang, Douguo; Chen, Junxue; Huo, Yiping; Lakowicz, Joseph R.

    2015-01-01

    We describe a hybrid metal-dielectric waveguide structures (MDWs) with numerous potential applications in the biosciences. These structures consist of a thin metal film coated with a dielectric layer. Depending on the thickness of the dielectric layer, the modes can be localized near the metal, within the dielectric, or at the top surface of the dielectric. The optical modes in a metal-dielectric waveguide can have either S (TE) or P (TM) polarization. The dielectric spacer avoids the quenching, which usually occurs for fluorophores within about 5 nm from the metal. Additionally, the resonances display a sharp angular dependence and can exhibit several hundred-fold increases in intensity (E2) at the silica-air interface relative to the incident intensity. Fluorophores placed on top of the silica layer couple efficiently with the metal, resulting in a sharp angular distribution of emission through the metal and down from the bottom of the structure. This coupling occurs over large distances to several hundred nm away from the metal and was found to be consistent with simulations of the reflectivity of the metal-dielectric waveguides. Remarkably, for some silica thicknesses, the emission is almost completely coupled through the structure with little free-space emission away from the metal-dielectric waveguide. The efficiency of fluorophore coupling is related to the quality of the resonant modes sustained by the metal-dielectric waveguide, resulting in coupling of most of the emission through the metal into the underlying glass substrates. Metal-dielectric waveguides also provide a method to resolve the emission from surface-bound fluorophores from the bulk-phase fluorophores. Metal-dielectric waveguides are simple to fabricate for large surface areas, the resonance wavelength can be adjusted by the dielectric thickness, and the silica surface is suitable for coupling to biomolecules. Metal-dielectric waveguides can have numerous applications in diagnostics and high-throughput proteomics or DNA analysis. PMID:26523157

  19. Energy Storage via Polyvinylidene Fluoride Dielectric on the Counterelectrode of Dye-Sensitized Solar Cells

    PubMed Central

    Huang, Xuezhen; Zhang, Xi

    2013-01-01

    To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I?/I3? redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (?) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g?1. Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density. PMID:24327797

  20. Simplified analytic formula for magneto-optical Kerr effects in ultrathin magnetic films.

    SciTech Connect

    You, C.-Y.

    1998-06-10

    Expressions are presented for various magneto-optical Kerr effects in the ultrathin film limit with arbitrary magnetization direction by considering the multiple reflections within an optically thin film. The Kerr effect of p- and s-polarization consists of products of two factors: the prefactor, dependent only on the optical parameters of the system, and the main factor of the polar Kerr effect for normal incidence in the ultrathin limit.

  1. Tailoring dielectric properties of ferroelectric-dielectric multilayers

    SciTech Connect

    Kesim, M. T.; Zhang, J.; Cole, M. W.; Misirlioglu, I. B.

    2014-01-13

    We develop a nonlinear thermodynamic model for multilayer ferroelectric heterostructures that takes into account electrostatic and electromechanical interactions between layers. We concentrate on the effect of relative layer fractions and in-plane thermal stresses on dielectric properties of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}-, BaTiO{sub 3}-, and PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT)-SrTiO{sub 3} (STO) multilayers on Si and c-sapphire. We show that dielectric properties of such multilayers can be significantly enhanced by tailoring the growth/processing temperature and the STO layer fraction. Our computations show that large tunabilities (?90% at 400?kV/cm) are possible in carefully designed barium strontium titanate-STO and PZT-STO even on Si for which there exist substantially large in-plane strains.

  2. Dielectric Breakdown of Cell Membranes

    PubMed Central

    Zimmermann, U.; Pilwat, G.; Riemann, F.

    1974-01-01

    With human and bovine red blood cells and Escherichia coli B, dielectric breakdown of cell membranes could be demonstrated using a Coulter Counter (AEG-Telefunken, Ulm, West Germany) with a hydrodynamic focusing orifice. In making measurements of the size distributions of red blood cells and bacteria versus increasing electric field strength and plotting the pulse heights versus the electric field strength, a sharp bend in the otherwise linear curve is observed due to the dielectric breakdown of the membranes. Solution of Laplace's equation for the electric field generated yields a value of about 1.6 V for the membrane potential at which dielectric breakdown occurs with modal volumes of red blood cells and bacteria. The same value is also calculated for red blood cells by applying the capacitor spring model of Crowley (1973. Biophys. J. 13:711). The corresponding electric field strength generated in the membrane at breakdown is of the order of 4 · 106 V/cm and, therefore, comparable with the breakdown voltages for bilayers of most oils. The critical detector voltage for breakdown depends on the volume of the cells. The volume-dependence predicted by Laplace theory with the assumption that the potential generated across the membrane is independent of volume, could be verified experimentally. Due to dielectric breakdown the red blood cells lose hemoglobin completely. This phenomenon was used to study dielectric breakdown of red blood cells in a homogeneous electric field between two flat platinum electrodes. The electric field was applied by discharging a high voltage storage capacitor via a spark gap. The calculated value of the membrane potential generated to produce dielectric breakdown in the homogeneous field is of the same order as found by means of the Coulter Counter. This indicates that mechanical rupture of the red blood cells by the hydrodynamic forces in the orifice of the Coulter Counter could also be excluded as a hemolysing mechanism. The detector voltage (or the electric field strength in the orifice) depends on the membrane composition (or the intrinsic membrane potential) as revealed by measuring the critical voltage in E. coli B harvested from the logarithmic and stationary growth phases. The critical detector voltage increased by about 30% for a given volume on reaching the stationary growth phase. PMID:4611517

  3. Homogeneous switching mechanism in pure polyvinylidene fluoride ultrathin films

    NASA Astrophysics Data System (ADS)

    Tian, B. B.; Chen, L. F.; Liu, Y.; Bai, X. F.; Wang, J. L.; Sun, Sh.; Yuan, G. L.; Sun, J. L.; Dkhil, B.; Meng, X. J.; Chu, J. H.

    2015-08-01

    Polarization switching kinetics is one of the key issues for future development of nanoelectronic devices based on ferroelectrics. Up to now, such kinetics still remains poorly studied despite its crucial impact on the device performances. Here, the switching mechanism in 11-nm-thick ferroelectric films of pure homopolymer of polyvinylidene fluoride is investigated. While the usual mechanism involves nucleation and growth of domains, a homogeneous ferroelectric switching is evidenced in such ultrathin films. Indeed, the dependence of the switching rate on applied voltage reveals a critical behavior with the existence of a true threshold field (of ˜0.26 GV /m ) which is required to overcome the energy barrier to reverse the whole polarization homogeneously as suggested by Landau-Ginzburg mean-field theory. Such finding not only supports few previous works but also raises the question on the general aspect of such homogeneous mechanism that might exist in any other nanoscale ferroelectric materials.

  4. An ultrathin invisibility skin cloak for visible light

    NASA Astrophysics Data System (ADS)

    Ni, Xingjie; Wong, Zi Jing; Mrejen, Michael; Wang, Yuan; Zhang, Xiang

    2015-09-01

    Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable for hiding macroscopic objects.

  5. Tuning the Quantum Stability and Superconductivity of Ultrathin Metal Alloys

    SciTech Connect

    Ozer, Mustafa M; Jia, Yu; Zhang, Zhenyu; Thompson, James R; Weitering, Harm H

    2007-01-01

    Quantum confinement of itinerant electrons in atomically smooth ultrathin lead films produces strong oscillations in the thickness-dependent film energy. By adding extra electrons via bismuth alloying, we showed that both the structural stability and the superconducting properties of such films can be tuned. The phase boundary (upper critical field) between the superconducting vortex state and the normal state indicates an anomalous suppression of superconducting order just below the critical temperature, Tc. This suppression varies systematically with the film thickness and the bismuth content and can be parameterized in terms of a characteristic temperature, Tc* (less than Tc), that is inversely proportional to the scattering mean free path. The results indicate that the isotropic nature of the superconductive pairing in bulk lead-bismuth alloys is altered in the quantum regime.

  6. Nonideal ultrathin mantle cloak for electrically large conducting cylinders.

    PubMed

    Liu, Shuo; Zhang, Hao Chi; Xu, He-Xiu; Cui, Tie Jun

    2014-09-01

    Based on the concept of the scattering cancellation technique, we propose a nonideal ultrathin mantle cloak that can efficiently suppress the total scattering cross sections of an electrically large conducting cylinder (over one free-space wavelength). The cloaking mechanism is investigated in depth based on the Mie scattering theory and is simultaneously interpreted from the perspective of far-field bistatic scattering and near-field distributions. We remark that, unlike the perfect transformation-optics-based cloak, this nonideal cloaking technique is mainly designed to minimize simultaneously several scattering multipoles of a relatively large geometry around considerably broad bandwidth. Numerical simulations and experimental results show that the antiscattering ability of the metasurface gives rise to excellent total scattering reduction of the electrically large cylinder and remarkable electric-field restoration around the cloak. The outstanding cloaking performance together with the good features of and ultralow profile, flexibility, and easy fabrication predict promising applications in the microwave frequencies. PMID:25401449

  7. Tailoring magnetic skyrmions in ultra-thin transition metal films.

    PubMed

    Dupé, Bertrand; Hoffmann, Markus; Paillard, Charles; Heinze, Stefan

    2014-01-01

    Skyrmions in magnetic materials offer attractive perspectives for future spintronic applications since they are topologically stabilized spin structures on the nanometre scale, which can be manipulated with electric current densities that are by orders of magnitude lower than those required for moving domain walls. So far, they were restricted to bulk magnets with a particular chiral crystal symmetry greatly limiting the number of available systems and the adjustability of their properties. Recently, it has been experimentally discovered that magnetic skyrmion phases can also occur in ultra-thin transition metal films at surfaces. Here we present an understanding of skyrmions in such systems based on first-principles electronic structure theory. We demonstrate that the properties of magnetic skyrmions at transition metal interfaces such as their diameter and their stability can be tuned by the structure and composition of the interface and that a description beyond a micromagnetic model is required in such systems. PMID:24893652

  8. Origin of the {Tc}-depression in ultrathin YBCO

    SciTech Connect

    Cieplak, M.Z.; Guha, S.; Vadlamannati, S.; Nien, C.H.; Lindenfeld, P.

    1994-12-31

    Conductance measurements on YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) between layers of Y{sub 1{minus}x}Pr{sub x}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} [(Y-Pr)BCO] show a transition from a bulk regime in the interior of the YBCO to a surface regime near the interfaces. The depression of the zero-resistance transition temperature in ultrathin YBCO is correlated with the depressed conductance in the surface layer. The results indicate that the changes are related to the presence of the interfaces, primarily to charge transfer between the layers, with little, if any, indication of a change in the intrinsic properties of the YBCO from bulk down to the thickness of a single unit cell.

  9. Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

    SciTech Connect

    Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.; Lee, Michael V.; Qi, Yabing; Joo Shin, Tae; Ahn, Docheon; Lee, Han-Koo; Baik, Jaeyoon; Shin, Hyun-Joon

    2015-03-15

    Ultrathin (<6?nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1?nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

  10. Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets

    NASA Astrophysics Data System (ADS)

    Narayanan, Tharangattu N.; Vusa, Chiranjeevi S. R.; Alwarappan, Subbiah

    2014-08-01

    Atomically thin molybdenum disulfide (MoS2) sheets were synthesized and isolated via solvent-assisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS2 sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS2 sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS2 electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS2. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS2 sheets, which will supplement their established electronic applications.

  11. Crossover behavior in hydrogen sensing mechanism for palladium ultrathin films.

    SciTech Connect

    Darling, S. B.; Ramanathan, M.; Skudlarek, G.; Wang, H. H.; Illinois Math and Science Academy

    2010-01-01

    Palladium has been extensively studied as a material for hydrogen sensors because of the simplicity of its reversible resistance change when exposed to hydrogen gas. Various palladium films and nanostructures have been used, and different responses have been observed with these diverse morphologies. In some cases, such as with nanowires, the resistance will decrease, whereas in others, such as with thick films, the resistance will increase. Each of these mechanisms has been explored for several palladium structures, but the crossover between them has not been systematically investigated. Here we report on a study aimed at deciphering the nanostructure-property relationships of ultrathin palladium films used as hydrogen gas sensors. The crossover in these films is observed at a thickness of {approx} 5 nm. Ramifications for future sensor developments are discussed.

  12. Optimal wrapping of liquid droplets with ultrathin sheets.

    PubMed

    Paulsen, Joseph D; Démery, Vincent; Santangelo, Christian D; Russell, Thomas P; Davidovitch, Benny; Menon, Narayanan

    2015-12-01

    Elastic sheets offer a path to encapsulating a droplet of one fluid in another that is different from that of traditional molecular or particulate surfactants. In wrappings of fluids by sheets of moderate thickness with petals designed to curl into closed shapes, capillarity balances bending forces. Here, we show that, by using much thinner sheets, the constraints of this balance can be lifted to access a regime of high sheet bendability that brings three major advantages: ultrathin sheets automatically achieve optimally efficient shapes that maximize the enclosed volume of liquid for a fixed area of sheet; interfacial energies and mechanical properties of the sheet are irrelevant within this regime, thus allowing for further functionality; and complete coverage of the fluid can be achieved without special sheet designs. We propose and validate a general geometric model that captures the entire range of this new class of wrapped and partially wrapped shapes. PMID:26322716

  13. Sintering of ultrathin gold nanowires for transparent electronics.

    PubMed

    Maurer, Johannes H M; González-García, Lola; Reiser, Beate; Kanelidis, Ioannis; Kraus, Tobias

    2015-04-22

    Ultrathin gold nanowires (AuNWs) with diameters below 2 nm and high aspect ratios are considered to be a promising base material for transparent electrodes. To achieve the conductivity expected for this system, oleylamine must be removed. Herein we present the first study on the conductivity, optical transmission, stability, and structure of AuNW networks before and after sintering with different techniques. Freshly prepared layers consisting of densely packed AuNW bundles were insulating and unstable, decomposing into gold spheres after a few days. Plasma treatments increased the conductivity and stability, coarsened the structure, and left the optical transmission virtually unchanged. Optimal conditions reduced sheet resistances to 50 ?/sq. PMID:25838194

  14. Iodide sensing via electrochemical etching of ultrathin gold films

    NASA Astrophysics Data System (ADS)

    Dielacher, Bernd; Tiefenauer, Raphael F.; Junesch, Juliane; Vörös, János

    2015-01-01

    Iodide is an essential element for humans and animals and insufficient intake is still a major problem. Affordable and accurate methods are required to quantify iodide concentrations in biological and environmental fluids. A simple and low cost sensing device is presented which is based on iodide induced electrochemical etching of ultrathin gold films. The sensitivity of resistance measurements to film thickness changes is increased by using films with a thickness smaller than the electron mean free path. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and resistance change measurements in a buffer solution. Iodide sensing is conducted in buffer solutions as well as in lake water with limits of detection in the range of 1 ?M (127 ?g L-1) and 2 ?M (254 ?g L-1), respectively. In addition, nanoholes embedded in the thin films are tested for suitability of optical iodide sensing based on localized surface plasmon resonance.

  15. Iodide sensing via electrochemical etching of ultrathin gold films.

    PubMed

    Dielacher, Bernd; Tiefenauer, Raphael F; Junesch, Juliane; Vörös, János

    2015-01-16

    Iodide is an essential element for humans and animals and insufficient intake is still a major problem. Affordable and accurate methods are required to quantify iodide concentrations in biological and environmental fluids. A simple and low cost sensing device is presented which is based on iodide induced electrochemical etching of ultrathin gold films. The sensitivity of resistance measurements to film thickness changes is increased by using films with a thickness smaller than the electron mean free path. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and resistance change measurements in a buffer solution. Iodide sensing is conducted in buffer solutions as well as in lake water with limits of detection in the range of 1 ?M (127 ?g L(-1)) and 2 ?M (254 ?g L(-1)), respectively. In addition, nanoholes embedded in the thin films are tested for suitability of optical iodide sensing based on localized surface plasmon resonance. PMID:25513753

  16. Long-living terahertz magnons in ultrathin metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Qin, H. J.; Zakeri, Kh.; Ernst, A.; Sandratskii, L. M.; Buczek, P.; Marmodoro, A.; Chuang, T.-H.; Zhang, Y.; Kirschner, J.

    2015-01-01

    The main idea behind magnonics is to use the elementary magnetic excitations (magnons) for information transfer and processing. One of the main challenges, hindering the application of ultrafast terahertz magnons in magnonics, has been the short lifetime of these excitations in metallic ferromagnets. Here, we demonstrate that the engineering of the electronic structure of a ferromagnetic metal, by reducing its dimensionality and changing its chemical composition, opens a possibility to strongly suppress the relaxation channels of terahertz magnons and thereby enhance the magnons’ lifetime. For the first time, we report on the long-lived terahertz magnons excited in ultrathin metallic alloy films. On the basis of the first-principles calculations, we explain the microscopic nature of the long lifetime being a consequence of the peculiar electronic hybridizations of the species. We further demonstrate a way of tailoring magnon energies (frequencies) by varying the chemical composition of the film.

  17. Transport properties of ultrathin black phosphorus on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Doganov, Rostislav A.; Koenig, Steven P.; Yeo, Yuting; Watanabe, Kenji; Taniguchi, Takashi; Özyilmaz, Barbaros

    2015-02-01

    Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO2 substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explain the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400 K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO2 substrates and reduces the hysteresis at room temperature.

  18. An ultrathin invisibility skin cloak for visible light.

    PubMed

    Ni, Xingjie; Wong, Zi Jing; Mrejen, Michael; Wang, Yuan; Zhang, Xiang

    2015-09-18

    Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable for hiding macroscopic objects. PMID:26383946

  19. Parasitic bipolar effect in ultra-thin FD SOI MOSFETs

    NASA Astrophysics Data System (ADS)

    Liu, F. Y.; Ionica, I.; Bawedin, M.; Cristoloveanu, S.

    2015-10-01

    The parasitic bipolar effect is investigated in fully-depleted silicon-on-insulator (FD SOI) n-type MOSFETs with ultra-thin films (5-10 nm). Our measurements show that at low drain bias the drain leakage current is governed by the gate current. Beyond VD > 1.0 V, leakage current amplification is observed in short-channel 10-nm thick devices. With film thickness shrinking, the current amplification is suppressed. We explain this amplification by the turn-on of the lateral parasitic bipolar transistor. TCAD simulations confirm that the parasitic bipolar is activated due to holes generated by band-to-band tunneling at the drain side and accumulated in the floating body. An effective method for the extraction of bipolar gain is proposed based on the comparison of leakage current in short- and long-channel devices. The experimental method is validated through simulations.

  20. Manipulation of transmitted wave front using ultrathin planar acoustic metasurfaces

    NASA Astrophysics Data System (ADS)

    Zhai, Shilong; Chen, Huaijun; Ding, Changlin; Shen, Fangliang; Luo, Chunrong; Zhao, Xiaopeng

    2015-09-01

    Nowadays, the acoustic devices are developing toward miniaturization. However, conventional materials can hardly satisfy the requirements because of their large size and complex manufacturing process. The introduction of acoustic metasurfaces has broken these restrictions, as they are able to manipulate sound waves at will by utilizing ultrathin planar metamaterials. Here, a simple acoustic metasurface is designed and characterized, whose microstructure is constructed with a cavity filled with air and two elastic membranes on the ends of cavity. By appropriately optimizing the configurations of microstructures, the steering of transmitted wave trajectory is demonstrated, and some extraordinary phenomena are realized at 3.5 kHz, such as planar acoustic axicon, acoustic lens, the conversion from spherical waves to plane waves, and the transformation from propagating waves to surface waves.

  1. Domain wall in ultrathin magnetic film: Internal structure and dynamics

    NASA Astrophysics Data System (ADS)

    Sobolev, V. L.; Ivanova, S. V.; Huang, H. L.

    2000-10-01

    Detailed micromagnetic study of internal structure and dynamics of domain wall in ultrathin magnetic film with thickness tf?lex (lex is the exchange length) is carried out. It is revealed that deviations of stationary magnetization distribution inside the wall from the one of the Bloch domain wall are small and proportional to (tf/lex)Q-1. The limiting velocity of uniform domain wall motion coincides with the same for the Bloch wall (Walker's critical velocity) with an accuracy of terms proportional to (tf/lex)2. It is also found that the same small parameter describes deviation of stationary distribution of magnetization in a vertical Bloch line and deviation of Bloch line velocity from the expressions found for films with tf>lex.

  2. Electrostatically Directed Self-Assembly of Ultrathin Supramolecular Polymer Microcapsules

    PubMed Central

    Parker, Richard M; Zhang, Jing; Zheng, Yu; Coulston, Roger J; Smith, Clive A; Salmon, Andrew R; Yu, Ziyi; Scherman, Oren A; Abell, Chris

    2015-01-01

    Supramolecular self-assembly offers routes to challenging architectures on the molecular and macroscopic scale. Coupled with microfluidics it has been used to make microcapsules—where a 2D sheet is shaped in 3D, encapsulating the volume within. In this paper, a versatile methodology to direct the accumulation of capsule-forming components to the droplet interface using electrostatic interactions is described. In this approach, charged copolymers are selectively partitioned to the microdroplet interface by a complementary charged surfactant for subsequent supramolecular cross-linking via cucurbit[8]uril. This dynamic assembly process is employed to selectively form both hollow, ultrathin microcapsules and solid microparticles from a single solution. The ability to dictate the distribution of a mixture of charged copolymers within the microdroplet, as demonstrated by the single-step fabrication of distinct core–shell microcapsules, gives access to a new generation of innovative self-assembled constructs. PMID:26213532

  3. Low voltage electrowetting-on-dielectric

    NASA Astrophysics Data System (ADS)

    Moon, Hyejin; Cho, Sung Kwon; Garrell, Robin L.; Kim, Chang-Jin ``Cj''

    2002-10-01

    This article discusses and experimentally verifies how to lower the operating voltage that drives liquid droplets by the principle of electrowetting on dielectric (EWOD). A significant contact angle change (120°?80°) is desired to reliably pump the droplet in microchannels for applications such as lab-on-a-chip or micrototal analysis systems. Typically, much higher voltages (>100 V) are used to change the wettability of an electrolyte droplet on a dielectric layer compared with a conductive layer. The required voltage can be reduced by increasing the dielectric constant and decreasing the thickness of the dielectric layer, thus increasing the capacitance of the insulating layer. This dependence of applied voltage on dielectric thickness is confirmed through EWOD experiments for three different dielectric materials of varying thickness: Amorphous fluoropolymer (Teflon® AF, Dupont), silicon dioxide (SiO2) and parylene. The dependence on the dielectric constant is confirmed with two different dielectric materials of similar thickness: SiO2 and barium strontium titanate. In all cases, the surface is coated with a very thin (200 Å) layer of amorphous fluoropolymer to provide initial hydrophobicity. Limiting factors such as the dielectric breakdown and electrolysis are also discussed. By using very thin (700 Å) and high dielectric constant (˜180) materials, a significant contact angle change (120°?80°) has been achieved with voltages as low as 15 V. Based on these results, a microfluidic device has been fabricated and tested, demonstrating successful transporting (pumping) of a 460 nL water droplet with only 15 V.

  4. Low dielectric constant materials and processes for interlayer dielectric applications

    NASA Astrophysics Data System (ADS)

    Vedula, Ramakrishna

    At 0.18 microns and below minimum device dimensions in Ultra Large Scale Integrated Circuits, signal net parasitic delay amounts to 80% of the overall path delay. This leads to serious problems relating to signal timing, crosstalk, noise and power consumption. Although Copper is being used as an alternative to Aluminum interconnects to reduce the resistive component of the RC delays, finding a suitable material to replace Silicon Dioxide (SiO2) as the interlayer dielectric poses serious challenges. Most of the inorganic candidates are variants of SiO2, while the most prominent among polymeric materials belong to the polyparaxylylene family. The primary disadvantage of polyparaxylylene materials is their low thermal stability. While SiO2 based inorganic films exhibit excellent thermal stability, they offer only incremental improvement in the dielectric constant. The thin film deposition technique for these materials is important as it directly impacts the cost of manufacturing. Chemical Vapor Deposition is known to make high purity, conformal thin films, and is compatible with current silicon manufacturing technology. This research is primarily focused to develop materials which have (i) Low dielectric Constant; (ii) High thermal stability, and to deposit them using Chemical Vapor Deposition technique. The vision was to develop a composite thin film material with the thermal stability of SiO2 and the low dielectric constant of paraxylylenes. The first objective of this research was to develop a technique to deposit SiO2 films at near room temperatures. Thin conformal films of SiO2 were deposited at temperatures around 50°C using Di-acetoxy-di-tertiary-butoxy silane (DADBS) as the precursor. The thermal stability, optical and electrical properties of the codeposited thin films were systematically studied. It was possible to control the composition of these films smoothly and these films were shown to be of nanocomposite type. However, the thermal stability of these nanocomposite thin films was only marginally better than that of paraxylylenes. These films were then heat treated under oxygen to 'burn off' the polymer content. It was shown that annealing these films in oxygen environment leaves porous SiO 2 which exhibits the thermal stability of SiO2 and the porosity results in lower dielectric constant.

  5. Asymmetric Dielectric Elastomer Composite Material

    NASA Technical Reports Server (NTRS)

    Stewart, Brian K. (Inventor)

    2014-01-01

    Embodiments of the invention provide a dielectric elastomer composite material comprising a plurality of elastomer-coated electrodes arranged in an assembly. Embodiments of the invention provide improved force output over prior DEs by producing thinner spacing between electrode surfaces. This is accomplished by coating electrodes directly with uncured elastomer in liquid form and then assembling a finished component (which may be termed an actuator) from coated electrode components.

  6. End moldings for cable dielectrics

    DOEpatents

    Roose, Lars D. (Albuquerque, NM)

    2000-01-01

    End moldings for high-voltage cables are described wherein the dielectric insulator of the cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made. Disclosed is a method for making the cable connectors either in the field or in a factory, molds suitable for use with the method, and the molded cable connectors, themselves.

  7. Carbon impurities in oxide dielectrics

    NASA Astrophysics Data System (ADS)

    Tailor, Hiral D.; Lyons, John L.; Choi, Minseok; Janotti, Anderson; van de Walle, Chris G.

    2015-03-01

    The high-k oxides ZrO2, and LaAlO3 can be used as dielectrics in metal-oxide-semiconductor (MOS) devices. Dielectrics are commonly grown with atomic layer deposition (ALD), often leading to unintentional incorporation of impurities such as carbon from the metal-organic precursors. Experiments indicated that carbon can be a significant cause of leakage current. We investigate this problem using density functional theory with a hybrid functional. Our results show that carbon substituting on the cation site undergoes an off-site displacement and forms close sp bonds with three oxygen atoms in ZrO2 and LaAlO3. We calculate the corresponding defect levels, and in order to determine the impact on MOS devices we align the band structures of the dielectrics with those of the semiconductor channel materials (including GaN, Si, and GaAs) . We find that carbon incorporation leads to defect levels near the conduction-band minimum of the channel materials, proving potentially detrimental for n-type devices. Intriguingly, we find that the defect levels of these carbon centers in a variety of oxides and semiconductors are aligned at roughly -3.5 eV below the vacuum level. Work supported by NSF, ONR, and ARO.

  8. High thermal robustness of molecularly thin perovskite nanosheets and implications for superior dielectric properties.

    PubMed

    Li, Bao-Wen; Osada, Minoru; Ebina, Yasuo; Akatsuka, Kosho; Fukuda, Katsutoshi; Sasaki, Takayoshi

    2014-06-24

    A systematic study has been conducted to examine the thermal stability of layer-by-layer assembled films of perovskite-type nanosheets, (Ca2Nb3O10(-))n (n = 1-10), which exhibit superior dielectric and insulating properties. In-plane and out-of-plane X-ray diffraction data as well as observations by atomic force microscopy and transmission electron microscopy indicated the high thermal robustness of the nanosheet films. In a monolayer film with an extremely small thickness of ?2 nm, the nanosheet was stable up to 800 °C, the temperature above which segregation into CaNb2O6 and Ca2Nb2O7 began. The critical temperature moderately decreased as the film thickness, or the number of nanosheet layers, increased, and reached 700 °C for seven- and 10-layer films, which is comparable to the phase transformation temperature for a bulk phase of the protonic layered oxide of HCa2Nb3O10·1.5H2O as a precursor of the nanosheet. This thermal stabilization of perovskite-type nanosheets should be associated with restricted nucleation and crystal growth peculiar to such ultrathin 2D bound systems. The stable high-k dielectric response (?r = 210) and highly insulating nature (J < 10(-7) A cm(-2)) remained substantially unchanged even after the nanosheet film was annealed up to 600 °C. This study demonstrates the high thermal stability of 2D perovskite-type niobate nanosheets in terms of structure and dielectric properties, which suggests promising potential for future high-k devices operable over a wide temperature range. PMID:24797417

  9. Study of the thickness effect on the dielectric functions by utilizing a wedge-shaped Ti film sample with continuously varied thickness

    NASA Astrophysics Data System (ADS)

    Hu, Er-Tao; Zhang, Rong-Jun; Cai, Qing-Yuan; Wang, Zi-Yi; Xu, Ji-Ping; Zheng, Yu-Xiang; Wang, Song-You; Wei, Yan-Feng; Huang, Ren-Zhong; Chen, Liang-Yao

    2015-09-01

    The dielectric functions of direct-current-sputtered wedge-shaped ultrathin titanium (Ti) film on K9 glass were investigated in this paper. The wedge-shaped Ti thin film was deposited under the identical conditions with continuously varied thickness. Atomic force microscope revealed that the thin film surface was very smooth with the surface roughness of about 0.5 nm. The dielectric functions of the wedge-shaped films in the wavelength range of 300-1200 nm were obtained by a focused-beam ellipsometer with the beam size on the sample about 200 ?m. Results show that ? 1, the real part of the dielectric function, is negative almost in the whole spectrum region, proving that the film at the measured area is continuous and shows metallic behavior. On the other hand, ? 1 decreases with the increase in the film thickness, while ? 2, the imaginary part of the dielectric function, has the opposite variation tendency. The changing of ? 1 with film thickness is due to the reduced electron-electron interactions and enhanced metallic behavior. While for ? 2, it gets larger with the increase in the film thickness, which is mainly owing to the decrease in the tensile stress in the film.

  10. Electromechanics of dielectric particles in dielectric liquids acted on by a microelectrode array 

    E-print Network

    Seo, Cheong Soo

    2006-04-12

    Arrays of microelectrodes were used to apply forces to dielectric (soda lime glass) spheres in a thin (200 micrometer thick) layer of a dielectric liquid polymer (EOPN 8021). The microelectrodes were fabricated using standard photolithographic...

  11. Dielectric relaxation of high-k oxides

    PubMed Central

    2013-01-01

    Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary. PMID:24180696

  12. Contact-free sheet resistance determination of large area graphene layers by an open dielectric loaded microwave cavity

    NASA Astrophysics Data System (ADS)

    Shaforost, O.; Wang, K.; Goniszewski, S.; Adabi, M.; Guo, Z.; Hanham, S.; Gallop, J.; Hao, L.; Klein, N.

    2015-01-01

    A method for contact-free determination of the sheet resistance of large-area and arbitrary shaped wafers or sheets coated with graphene and other (semi) conducting ultrathin layers is described, which is based on an open dielectric loaded microwave cavity. The sample under test is exposed to the evanescent resonant field outside the cavity. A comparison with a closed cavity configuration revealed that radiation losses have no significant influence of the experimental results. Moreover, the microwave sheet resistance results show good agreement with the dc conductivity determined by four-probe van der Pauw measurements on a set of CVD samples transferred on quartz. As an example of a practical application, correlations between the sheet resistance and deposition conditions for CVD graphene transferred on quartz wafers are described. Our method has a high potential as measurement standard for contact-free sheet resistance measurement and mapping of large area graphene samples.

  13. Dielectric behavior of semiconductors at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Dahiya, Jai N.

    1992-01-01

    A cylindrical microwave resonant cavity in TE(011) (Transverse Electric) mode is used to study the dielectric relaxation in germanium and silicon. The samples of these semiconductors are used to perturb the electric field in the cavity, and Slater's perturbation equations are used to calculate the real and imaginary parts of the dielectric constant. The dielectric loss of germanium and silicon is studied at different temperatures, and Debye's equations are used to calculate the relaxation time at these temperatures.

  14. Onsite Substitution Synthesis of Ultrathin Ni Nanofilms Loading Ultrafine Pt Nanoparticles for Hydrogen Evolution.

    PubMed

    Xiao, Mingshu; Cheng, Rui; Hao, Meifeng; Zhou, Mao; Miao, Yuqing

    2015-12-01

    Here, the ultrathin Ni nanofilms loading ultrafine Pt nanoparticles (Ni/Pt nanocomposites) were synthesized by a simple substitution method for the electrocatalysis of hydrogen evolution reaction (HER). First, the ultrathin Ni nanofilms were prepared by using NaBH4 to reduce Ni salt. Then the ultrafine Pt nanoparticles attached on the surface of the ultrathin Ni nanofilms through the onsite substitution reaction between PtCl6(2-) and Ni element. X-ray photoelectron spectroscopy (XPS) experiment confirmed that Ni in Ni/Pt nanocomposites exists in the form of Ni(OH)2. Transmission electro microscope (TEM) study showed that the ultrafine Pt nanoparticles were sufficiently dispersed and loaded at Ni ultrathin nanofilms. The obtained Ni/Pt nanocomposites exhibited superior activity of HER and good stability in acidic media. It obtained 10 and 100 mA/cm(2) with overpotential of only 36 and 115 mV, respectively. The stability experiment of 20?000 s gave nearly negligible current decrease. On the one hand, the ultrathin Ni nanofilms help to disperse and form the ultrafine Pt nanoparticles. On the other hand, the ultrathin Ni nanofilms help to load the ultrafine Pt nanoparticles as catalyst support and immobilize both of them onto the electrode surface because of the high surface free energy of ultrathin nanofilm and the leading high adsorption ability. In addition, Ni itself exhibited somewhat electrocatalytic activity of HER, which contributed to the whole HER electrocatalysis of Ni/Pt nanocomposites. The excellent electrocatalysis may lead to the decreased consumption of expensive Pt and open up new opportunities for applications in hydrogen energy. PMID:26551915

  15. Solar cell with silicon oxynitride dielectric layer

    DOEpatents

    Shepherd, Michael; Smith, David D

    2015-04-28

    Solar cells with silicon oxynitride dielectric layers and methods of forming silicon oxynitride dielectric layers for solar cell fabrication are described. For example, an emitter region of a solar cell includes a portion of a substrate having a back surface opposite a light receiving surface. A silicon oxynitride (SiO.sub.xN.sub.y, 0dielectric layer is disposed on the back surface of the portion of the substrate. A semiconductor layer is disposed on the silicon oxynitride dielectric layer.

  16. Computationally efficient dielectric calculations of molecular crystals

    SciTech Connect

    Schwarz, Kathleen A.; Sundararaman, Ravishankar; Arias, T. A.

    2015-06-07

    The microscopic dielectric response is a key quantity for electronic materials such as organic semiconductors. Calculations of this response for molecular crystals are currently either expensive or rely on extreme simplifications such as multipole expansions which lack microscopic detail. We present an alternate approach using a microscopic analogue of the Clausius-Mossotti equation, which constructs the dielectric response of a crystal from an eigenvalue decomposition of the dielectric response of individual molecules. This method can potentially be used to examine the effects of defects, disorder, and surfaces on the dielectric properties of molecular solids.

  17. Theory of epsilon-near-zero modes in ultrathin films

    NASA Astrophysics Data System (ADS)

    Campione, Salvatore; Brener, Igal; Marquier, Francois

    2015-03-01

    The physics of the epsilon-near-zero (ENZ) mode, which is supported by a nanolayer at the frequency where the dielectric permittivity vanishes, has recently been a subject of debate. In this Rapid Communication, we thoroughly investigate and clarify the physics of this mode, providing its main characteristics and its domain of existence. This understanding will benefit all the applications that rely on ENZ modes in semiconductor nanolayers, including directional perfect absorption, voltage-tunable devices, and ultrafast thermal emission.

  18. Tunable charge-trap memory based on few-layer MoS2.

    PubMed

    Zhang, Enze; Wang, Weiyi; Zhang, Cheng; Jin, Yibo; Zhu, Guodong; Sun, Qingqing; Zhang, David Wei; Zhou, Peng; Xiu, Faxian

    2015-01-27

    Charge-trap memory with high-? dielectric materials is considered to be a promising candidate for next-generation memory devices. Ultrathin layered two-dimensional (2D) materials like graphene and MoS2 have been receiving much attention because of their fantastic physical properties and potential applications in electronic devices. Here, we report on a dual-gate charge-trap memory device composed of a few-layer MoS2 channel and a three-dimensional (3D) Al2O3/HfO2/Al2O3 charge-trap gate stack. Because of the extraordinary trapping ability of both electrons and holes in HfO2, the MoS2 memory device exhibits an unprecedented memory window exceeding 20 V. Importantly, with a back gate the window size can be effectively tuned from 15.6 to 21 V; the program/erase current ratio can reach up to 10(4), allowing for multibit information storage. Moreover, the device shows a high endurance of hundreds of cycles and a stable retention of ? 28% charge loss after 10 years, which is drastically lower than ever reported MoS2 flash memory. The combination of 2D materials with traditional high-? charge-trap gate stacks opens up an exciting field of nonvolatile memory devices. PMID:25496773

  19. Ultra-thin solid oxide fuel cells: Materials and devices

    NASA Astrophysics Data System (ADS)

    Kerman, Kian

    Solid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 -- 1000 °C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O 2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y 2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 -- 500 °C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O 3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.

  20. Dielectric strength of parylene HT

    SciTech Connect

    Diaham, S. Bechara, M.; Locatelli, M.-L.; Khazaka, R.; Tenailleau, C.

    2014-02-07

    The dielectric strength of parylene HT (PA-HT) films was studied at room temperature in a wide thickness range from 500?nm to 50??m and was correlated with nano- and microstructure analyses. X-ray diffraction and polarized optical microscopy have revealed an enhancement of crystallization and spherulites development, respectively, with increasing the material thickness (d). Moreover, a critical thickness d{sub C} (between 5 and 10??m) is identified corresponding to the beginning of spherulite developments in the films. Two distinct behaviors of the dielectric strength (F{sub B}) appear in the thickness range. For d???d{sub C}, PA-HT films exhibit a decrease in the breakdown field following a negative slope (F{sub B}???d{sup ?0.4}), while for d?dielectric strength (F{sub B}???10 MV/cm) is obtained. A model of spherulite development in PA-HT films with increasing the thickness is proposed. The decrease in F{sub B} above d{sub C} is explained by the spherulites development, whereas its increase below d{sub C} is induced by the crystallites growth. An annealing of the material shows both an enhancement of F{sub B} and an increase of the crystallites and spherulites dimensions, whatever the thickness. The breakdown field becomes thickness-independent below d{sub C} showing a strong influence of the nano-scale structural parameters. On the contrary, both nano- and micro-scale structural parameters appear as influent on F{sub B} for d???d{sub C}.

  1. Dielectric strength of parylene HT

    NASA Astrophysics Data System (ADS)

    Diaham, S.; Bechara, M.; Locatelli, M.-L.; Khazaka, R.; Tenailleau, C.; Kumar, R.

    2014-02-01

    The dielectric strength of parylene HT (PA-HT) films was studied at room temperature in a wide thickness range from 500 nm to 50 ?m and was correlated with nano- and microstructure analyses. X-ray diffraction and polarized optical microscopy have revealed an enhancement of crystallization and spherulites development, respectively, with increasing the material thickness (d). Moreover, a critical thickness dC (between 5 and 10 ?m) is identified corresponding to the beginning of spherulite developments in the films. Two distinct behaviors of the dielectric strength (FB) appear in the thickness range. For d ? dC, PA-HT films exhibit a decrease in the breakdown field following a negative slope (FB ˜ d-0.4), while for d < dC, it increases with increasing the thickness (FB ˜ d0.3). An optimal thickness doptim ˜ 5 ?m corresponding to a maximum dielectric strength (FB ˜ 10 MV/cm) is obtained. A model of spherulite development in PA-HT films with increasing the thickness is proposed. The decrease in FB above dC is explained by the spherulites development, whereas its increase below dC is induced by the crystallites growth. An annealing of the material shows both an enhancement of FB and an increase of the crystallites and spherulites dimensions, whatever the thickness. The breakdown field becomes thickness-independent below dC showing a strong influence of the nano-scale structural parameters. On the contrary, both nano- and micro-scale structural parameters appear as influent on FB for d ? dC.

  2. Graphene ultrathin film electrode for detection of lead ions in acetate buffer solution.

    PubMed

    Wang, Zhaomeng; Liu, Erjia

    2013-01-15

    Few-layer graphene ultrathin films were synthesized via solid-state carbon diffusion from amorphous carbon (a-C) thin layers sputtering coated on Si substrates with or without a SiO(2) layer, which an a-C layer was covered by a nickel (Ni) layer as a catalyst. When the Ni/a-C bilayer coated samples were heated at 1000°C the carbon (C) atoms from the a-C layers diffused into the top Ni layers to form a C rich surface. Upon rapid cooling, the C atoms accumulated on the surface of the Ni layers and formed graphene ultrathin films through nucleation and growth processes. The formation of graphene ultrathin films was confirmed by Raman spectroscopy, high resolution transmission electron microscopy (HR-TEM), electron diffraction, field-emission scanning electron microscopy (FE-SEM) and 4-point probe. The synthesized graphene ultrathin films were used as working electrodes for detection of trace heavy metal ions (Pb(2+), as low as 7 nM) in acetate buffer solutions (pH 5.3) using square wave anodic stripping voltammetry (SWASV). The effects of substrate surface condition and Ni layer thickness on the structure and electrochemical properties of graphene ultrathin film electrodes were investigated in detail. Compared to conventional diamond-like carbon (DLC) electrodes, the graphene electrodes developed in this study had better repeatability, higher sensitivity and higher resistance to passivation caused by surface active species. PMID:23200357

  3. Ultrathin Nickel Hydroxide and Oxide Nanosheets: Synthesis, Characterizations and Excellent Supercapacitor Performances

    NASA Astrophysics Data System (ADS)

    Zhu, Youqi; Cao, Chuanbao; Tao, Shi; Chu, Wangsheng; Wu, Ziyu; Li, Yadong

    2014-08-01

    High-quality ultrathin two-dimensional nanosheets of ?-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin ?-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the ?-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g-1 at a current density of 1 A g-1. Even at higher rate of 16 A g-1, the specific capacitance is still maintained at 2680 F g-1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.

  4. Ultrathin Nickel Hydroxide and Oxide Nanosheets: Synthesis, Characterizations and Excellent Supercapacitor Performances

    PubMed Central

    Zhu, Youqi; Cao, Chuanbao; Tao, Shi; Chu, Wangsheng; Wu, Ziyu; Li, Yadong

    2014-01-01

    High-quality ultrathin two-dimensional nanosheets of ?-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2?nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin ?-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the ?-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5?F g?1 at a current density of 1?A g?1. Even at higher rate of 16?A g?1, the specific capacitance is still maintained at 2680?F g?1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications. PMID:25168127

  5. Effects of Adsorbed Pyridine Derivatives and Ultrathin Atomic-Layer-Deposited Alumina Coatings on the Conduction Band-Edge Energy

    E-print Network

    Effects of Adsorbed Pyridine Derivatives and Ultrathin Atomic-Layer- Deposited Alumina Coatings the adsorption of t-butylpyridine and the atomic- layer deposition of ultrathin conformal coatings of insulators and the concomitant suppression of dark current does not require the coordination of surface Ti(IV) or Al(III) atoms

  6. Ultrathin organic transistors for chemical sensing Richard D. Yang, T. Gredig, Corneliu N. Colesniuc, Jeongwon Park, Ivan K. Schuller,

    E-print Network

    Kummel, Andrew C.

    Ultrathin organic transistors for chemical sensing Richard D. Yang, T. Gredig, Corneliu N on the chemical environments.1­6 Herein, OTFTs employed for chemical sensing using small organic materials have been fabricated for chemical sensing. Compared to 50 ML devices, the ultrathin transistors show

  7. Ultra-thin silver films obtained by sequential quench-anneal processing S.B. Arnason a,

    E-print Network

    Hebard, Arthur F.

    Ultra-thin silver films obtained by sequential quench-anneal processing S.B. Arnason a, , A Ultra-thin films We have used the "two-step" growth technique, quench condensing followed by an anneal, to grow ultra- thin films of silver on glass substrates. As has been seen with semiconductor substrates

  8. Femtosecond laser structuring in dielectrics

    NASA Astrophysics Data System (ADS)

    Juodkazis, Saulius

    2008-03-01

    Three-dimensional (3D) structuring of glasses, crystals, and polymers by tightly focused femtosecond laser pulses is a promising technique for microfluidic, micro-optical, photonic crystal and micro-mechanical applications [1-4]. The 3D laser micro-structuring of resists is demonstrated by direct laser writing [1] and holographic recording using phase control of interfering pulses [2]. Tightly focused laser pulses can reach dielectric breakdown irradiance without self-focusing when sub-1 ps pulses are used for laser-structuring inside dielectrics. The limiting case of microstructuring, a void recording, can be achieved [3]. The mechanism of void formation has been explained as a result of dielectric breakdown and micro-explosion. The absorption is localized within a skin depth of tens-of-nanometers in the plasma at the focus. This defines an ultimate localization of the energy delivery by a laser pulse. The absorbance reaches 0.6 in a fully ionized solid state density breakdown plasma. The high temperature and pressure buildup is large enough to generate a shock wave (strong micro-explosion). For example, a single 100 nJ laser pulse forms a void under tight focusing conditions even in the high strength sapphire (Young modulus of 400 GPa). It is considered that material fails upon compression rather than tension for which the mechanical failure threshold is by an order of magnitude smaller. This scenario of breakdown by compression is corroborated by numerical modeling of the strong explosion at our experimental conditions. Modification of materials by tightly focused femtosecond pulses opens new material processing routes for inert dielectrics [4] and can possibly be used for creation of new high-temperature and pressure phases inside the volume of irradiated samples. These regions with altered nano-structure have different chemical properties as was found in silica glass, quartz, and sapphire by wet etching of the ``shocked'' regions in aqueous solution of hydrofluoric acid. Current challenges of structural characterization of micrometer-sized volumes of nano-structures materials are discussed. The achievable resolution limits and potential of the fabricated 3D patterns in photonics, micro-fluidics, and sensor applications will be presented. [1] K. K. Seet et al., Adv. Mat. 17, 541, 2005. [2] T. Kondo, et al., New J. Phys. 8, 250, 2006. [3] S. Juodkazis, et al., Phys. Rev. Lett. 96 166101 2006. [4] S. Juodkazis, et al., Adv. Mater. 18 1361 2006.

  9. Interaction of two dielectric macroparticles

    SciTech Connect

    Munirov, V. R.; Filippov, A. V.

    2013-11-15

    The electrostatic interaction of two charged dielectric spherical particles with a nonuniform freecharge distribution over their surfaces in an external homogeneous electric field is considered. An exact solution for the electric field potential is obtained, and an analytical expression for the interaction force between these two particles is found. The case of a uniform free-charge distribution is considered in detail, and the region of parameters in the plane “the ratio of the radii vs. the ratio of the charges,” where repulsion between two like-charged particles turns into attraction as the interparticle distance decreases is established.

  10. Crosslinked polymeric dielectric materials and electronic devices incorporating same

    NASA Technical Reports Server (NTRS)

    Marks, Tobin J. (Inventor); Facchetti, Antonio (Inventor); Wang, Zhiming (Inventor); Choi, Hyuk-Jin (Inventor); Suh, legal representative, Nae-Jeong (Inventor)

    2012-01-01

    Solution-processable dielectric materials are provided, along with precursor compositions and processes for preparing the same. Composites and electronic devices including the dielectric materials also are provided.

  11. High thermal conductivity lossy dielectric using a multi layer configuration

    DOEpatents

    Tiegs, Terry N. (Lenoir City, TN); Kiggans, Jr., James O. (Oak Ridge, TN)

    2003-01-01

    Systems and methods are described for loss dielectrics. A loss dielectric includes at least one high dielectric loss layer and at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. A method of manufacturing a loss dielectric includes providing at least one high dielectric loss layer and providing at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. The systems and methods provide advantages because the loss dielectrics are less costly and more environmentally friendly than the available alternatives.

  12. Dielectric liquid ionization chambers for detecting fast neutrons

    E-print Network

    Boyd, Erin M

    2008-01-01

    Three ionization chambers with different geometries have been constructed and filled with dielectric liquids for detection of fast neutrons. The three dielectric liquids studied were Tetramethylsilane (TMS), Tetramethylpentane ...

  13. Internal Dielectric Transduction in Bulk-Mode Resonators

    E-print Network

    Weinstein, Dana

    This paper investigates electrostatic transduction of a longitudinal-mode silicon acoustic resonator with internal dielectric films. Geometric optimization of internal dielectrically transduced resonators is derived ...

  14. Dielectric Loss Measurements on Raw Materials.

    ERIC Educational Resources Information Center

    Mwanje, J.

    1980-01-01

    Describes an experiment used to study dielectric properties of materials. Values of the dielectric loss tangent can be determined at low frequencies from Lissajous figures formed on an oscilloscope. Some mineral rock specimens show Debye-type relaxation peaks at frequencies in the region of 1 to 500 Hz. (Author/DS)

  15. Integrated Circuit / Microfluidic Chips for Dielectric Manipulation

    E-print Network

    Integrated Circuit / Microfluidic Chips for Dielectric Manipulation A THESIS PRESENTED BY THOMAS by Thomas Hunt All rights reserved. #12;iii Abstract Integrated Circuit / Microfluidic Chips for Dielectric of integrated circuit / microfluidic chips to move individual living cells and chemical droplets along

  16. Dielectric spectroscopy of watermelons for quality sensing

    NASA Astrophysics Data System (ADS)

    Nelson, Stuart O.; Guo, Wen-chuan; Trabelsi, Samir; Kays, Stanley J.

    2007-07-01

    Dielectric properties of four small-sized watermelon cultivars, grown and harvested to provide a range of maturities, were measured with an open-ended coaxial-line probe and an impedance analyser over the frequency range from 10 MHz to 1.8 GHz. Probe measurements were made on the external surface of the melons and also on tissue samples from the edible internal tissue. Moisture content and soluble solids content (SSC) were measured for internal tissue samples, and SSC (sweetness) was used as the quality factor for correlation with the dielectric properties. Individual dielectric constant and loss factor correlations with SSC were low, but a high correlation was obtained between the SSC and permittivity from a complex-plane plot of dielectric constant and loss factor, each divided by SSC. However, SSC prediction from the dielectric properties by this relationship was not as high as expected (coefficient of determination about 0.4). Permittivity data (dielectric constant and loss factor) for the melons are presented graphically to show their relationships with frequency for the four melon cultivars and for external surface and internal tissue measurements. A dielectric relaxation for the external surface measurements, which may be attributable to a combination of bound water, Maxwell-Wagner, molecular cluster or ion-related effects, is also illustrated. Coefficients of determination for complex-plane plots, moisture content and SSC relationship, and penetration depth are also shown graphically. Further studies are needed for determining the practicality of sensing melon quality from their dielectric properties.

  17. Microwave Dielectric Properties of Cereal Grains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectric properties of five cereal grains (wheat, corn, barley, oats, and grain sorghum) were 19 measured at 23 oC over broad microwave frequency range (5 GHz to 15 GHz) with a free-space-transmission 20 technique. Results of dielectric properties measurement are tabulated for each material for mo...

  18. Dielectric Study of Water Binding in Grain

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectric properties of wheat samples, in which moisture equilibrium was upset by adding water, were tracked versus time in the frequency range between 5 GHz and 15 GHz at room temperature (23 oC). Results presented at 10 GHz show an initial drop in the dielectric constant and loss factor, which r...

  19. Analysis of electron interactions in dielectric gases

    SciTech Connect

    Olivet, Aurelio; Duque, Daniel; Vega, Lourdes F.

    2007-01-15

    We present and discuss results concerning electron interactions processes of dielectric gases and their relationship with the macroscopic behavior of these gases, in particular, with their dielectric strength. Such analysis is based on calculating energies of reactions for molecular ionization, dissociative ionization, parent negative ion formation, and dissociative electron attachment processes. We hypothesize that the estimation of the required energy for a reduced number of processes that take place in electrically stressed gases could be related to the gas' capability to manage the electron flow during an electrical discharge. All calculations were done with semiempirical quantum chemistry methods, including an initial optimization of molecular geometry and heat of formation of the dielectric gases and all of species that appear during electron interaction reactions. The performance of semiempirical methods Austin model 1 and Parametric model 3 (PM3) was compared for several compounds, PM3 being superior in most cases. Calculations performed for a sample of nine dielectric gases show that electron attachment and detachment processes occur in different energy bands that do not overlap for any value of the dielectric strength. We have also analyzed the relationship between dielectric strength and two physical properties: electron affinity and ionization energy. Calculations performed for 43 dielectric gases show no clear correlation between them, although certain guidelines for the qualitative estimation of dielectric strength can still be assessed.

  20. Optical Response of High-Dielectric-Constant

    E-print Network

    Johnson, Peter D.

    Optical Response of High-Dielectric-Constant Perovskite-Related Oxide C. C. Homes,1 * T. Vogt,1 S dielectric con- stant 0 of a material will ultimately decide the degree of miniaturization. Perovskites. M. Shapiro,1 S. Wakimoto,1,2 A. P. Ramirez3 Optical conductivity measurements on the perovskite

  1. Dielectric Spectroscopy of Fresh Chicken Breast Meat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The dielectric properties of fresh chicken breast meat were measured at temperatures from 5 to 85 'C over the frequency range from 10 MHz to 1.8 GHz by dielectric spectroscopy techniques with an open-ended coaxial-line probe and impedance analyzer. Samples were cut from both the Pectoralis major an...

  2. DIELECTRIC SPECTROSCOPY OF HARD RED WINTER WHEAT

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The dielectric properties (components of the complex permittivity relative to free space) of ground hard red winter wheat of 11 to 25 percent moisture content were determined by dielectric spectroscopy measurements with an open-ended coaxial-line probe and impedance analyzer over the frequency range...

  3. Cadmium Telluride Solar Cells on Ultrathin Glass for Space Applications

    NASA Astrophysics Data System (ADS)

    Irvine, S. J. C.; Lamb, D. A.; Clayton, A. J.; Kartopu, G.; Barrioz, V.

    2014-08-01

    This paper details the preliminary findings of a study to achieve a durable thin-film CdTe photovoltaic (PV) device structure on ultrathin space-qualified cover glass. An aluminum-doped zinc oxide (AZO) transparent conducting oxide was deposited directly onto the cover glass using metalorganic chemical vapor deposition (MOCVD). The AZO demonstrated low sheet resistance of 10 ?/? and high optical transparency of 85% as well as excellent adherence and environmental stability. Preliminary deposition of PV layers onto the AZO on cover glass, by MOCVD, showed the possibility of such a structure, yielding a device conversion efficiency of 7.2%. High series resistance (10 ? cm2) and low V oc (586 mV) were identified as the limiting factors when compared with the authors' platform process on indium tin oxide-coated aluminosilicate. The coverage of the Cd1- x Zn x S window layer along with the front contacting of the device were shown to be the major causes of the low efficiency. Further deposition of AZO/CdTe employing an oxygen plasma cleaning step to the cover glass and evaporated gold front contacts significantly improved the device performance. With a highest conversion efficiency of 10.2%, series resistance improved to 4.4 ? cm2, open-circuit voltage ( V oc) up to 667 mV, and good adhesion, this represents the first demonstration of direct deposition of CdTe solar cells onto 100- ?m-thick space-qualified cover glass.

  4. Ultrathin-layer chromatography nanostructures modified by atomic layer deposition.

    PubMed

    Jim, S R; Foroughi-Abari, A; Krause, K M; Li, P; Kupsta, M; Taschuk, M T; Cadien, K C; Brett, M J

    2013-07-19

    Stationary phase morphology and surface chemistry dictate the properties of ultrathin-layer chromatography (UTLC) media and interactions with analytes in sample mixtures. In this paper, we combined two powerful thin film deposition techniques to create composite chromatography nanomaterials. Glancing angle deposition (GLAD) produces high surface area columnar microstructures with aligned macropores well-suited for UTLC. Atomic layer deposition (ALD) enables precise fabrication of conformal, nanometer-scale coatings that can tune surfaces of these UTLC films. We coated ?5?m thick GLAD SiO2 UTLC media with <10nm thick ALD metal oxides (Al2O3, ZrO2, and ZnO) to decouple surface chemistry from the underlying GLAD scaffold microstructure. The effects of ALD coatings on GLAD UTLC media were investigated using transmission electron microscopy (TEM), gas adsorption porosimetry, and lipophilic dye separations. The results collectively show that the most significant changes occur over the first few nanometers of ALD coating. They further demonstrate independent control of film microstructure and surface characteristics. ALD coatings can enhance complex GLAD microstructures to engineer new composite nanomaterials potentially useful in analytical chromatography. PMID:23768654

  5. A dual-stimuli-responsive fluorescent switch ultrathin film.

    PubMed

    Li, Zhixiong; Liang, Ruizheng; Liu, Wendi; Yan, Dongpeng; Wei, Min

    2015-10-01

    Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices. PMID:26400734

  6. Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials

    NASA Astrophysics Data System (ADS)

    Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

    2014-10-01

    Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential.

  7. The Physical and Chemical Properties of Ultrathin Oxide Films

    NASA Astrophysics Data System (ADS)

    Street, S. C.; Xu, C.; Goodman, D. W.

    1997-10-01

    Thin oxide films (from one to tens of monolayers) of SiO2, MgO, NiO, Al2O3, FexOy, and TiO2 supported on refractory metal substrates have been prepared by depositing the oxide metal precursor in a background of oxygen (ca 1 x 10-5 Torr). The thinness of these oxide samples facilitates investigation by an array of surface techniques, many of which are precluded when applied to the corresponding bulk oxide. Layered and mixed binary oxides have been prepared by sequential synthesis of dissimilar oxide layers or co-deposition of two different oxides. Recent work has shown that the underlying oxide substrate can markedly influence the electronic and chemical properties of the overlayer oxide. The structural, electronic, and chemical properties of these ultrathin oxide films have been probed using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (ELS), ion-scattering spectroscopy (ISS), high-resolution electron energy loss spectroscopy (HREELS), infrared reflectance absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS).

  8. Interfacial glass transition profiles in ultrathin, spin cast polymer films.

    PubMed

    Sills, Scott; Overney, René M; Chau, Wilson; Lee, Victor Y; Miller, Robert D; Frommer, Jane

    2004-03-15

    Interfacial glass transition temperature (T(g)) profiles in spin cast, ultrathin films of polystyrene and derivatives were investigated using shear-modulated scanning force microscopy. The transitions were measured as a function of film thickness (delta), molecular weight, and crosslinking density. The T(g)(delta) profiles were nonmonotonic and exhibited two regimes: (a) a sublayer extending about 10 nm from the substrate, with T(g) values lowered up to approximately 10 degrees C below the bulk value, and (b) an intermediate regime extending over 200 nm beyond the sublayer, with T(g) values exceeding the bulk value by up to 10 degrees C. Increasing the molecular weight was found to shift the T(g)(delta) profiles further from the substrate interface, on the order of 10 nm/kDa. Crosslinking the precast films elevated the absolute T(g) values, but had no effect on the spatial length scale of the T(g)(delta) profiles. These results are explained in the context of film preparation history and its influence on molecular mobility. Specifically, the observed rheological anisotropy is interpreted based on the combined effects of shear-induced structuring and thermally activated interdiffusion. PMID:15267406

  9. Biochemical applications of ultrathin films of enzymes, polyions and DNA

    PubMed Central

    Rusling, James F.; Hvastkovs, Eli G.; Hull, Dominic O.; Schenkman, John B.

    2012-01-01

    This feature article summarizes recent applications of ultrathin films of enzymes and DNA assembled layer-by-layer (LbL). Using examples mainly from our own research, we focus on systems developed for biocatalysis and biosensors for toxicity screening. Enzyme–poly(l-lysine) (PLL) films, especially when stabilized by crosslinking, can be used for biocatalysis at unprecedented high temperatures or in acidic or basic solutions on electrodes or sub-micron sized beads. Such films have bright prospects for chiral synthesis and biofuel cells. Excellent bioactivity and retention of enzyme structure in these films facilitates their use in detailed kinetic studies. Biosensors and arrays employing DNA–enzyme films show great promise in predicting genotoxicity of new drug and chemical product candidates. These devices combine metabolic biocatalysis, reactive metabolite–DNA reactions, and DNA damage detection. Catalytic voltammetry or electrochemiluminescence (ECL) can be used for high throughput arrays utilizing multiple LbL “spots” of DNA, enzyme and metallopolymer. DNA–enzyme films can also be used to produce nucleobase adduct toxicity biomarkers for detection by LC-MS. These approaches provide valuable high throughput tools for drug and chemical product development and toxicity prediction. PMID:18092072

  10. Photoelectron diffraction of magnetic ultrathin films: Fe/Cu(001)

    SciTech Connect

    Tobin, J.G. ); Wagner, M.K. . Dept. of Chemistry); Guo, X.Q.; Tong, S.Y. . Dept. of Physics)

    1991-01-03

    The preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p cross section measurements with multiple scattering calculations indicates that the Fe is in a fourfold hollow site with a spacing of 3.6{Angstrom} between it and the atom directly beneath it, in the third layer. This is consistent with an FCC structure. The possibility of utilizing spin-dependent photoelectron diffraction to investigate magnetic ultrathin films will be demonstrated, using our preliminary spectra of the multiplet-split Fe3s os near-monolayer Fe/Cu(001). 18 refs., 10 figs.

  11. Vibrational modes of ultrathin carbon nanomembrane mechanical resonators

    SciTech Connect

    Zhang, Xianghui E-mail: elke.scheer@uni-konstanz.de; Angelova, Polina; Gölzhäuser, Armin; Waitz, Reimar; Yang, Fan; Lutz, Carolin; Scheer, Elke E-mail: elke.scheer@uni-konstanz.de

    2015-02-09

    We report measurements of vibrational mode shapes of mechanical resonators made from ultrathin carbon nanomembranes (CNMs) with a thickness of approximately 1?nm. CNMs are prepared from electron irradiation induced cross-linking of aromatic self-assembled monolayers and the variation of membrane thickness and/or density can be achieved by varying the precursor molecule. Single- and triple-layer freestanding CNMs were made by transferring them onto Si substrates with square/rectangular orifices. The vibration of the membrane was actuated by applying a sinusoidal voltage to a piezoelectric disk on which the sample was glued. The vibrational mode shapes were visualized with an imaging Mirau interferometer using a stroboscopic light source. Several mode shapes of a square membrane can be readily identified and their dynamic behavior can be well described by linear response theory of a membrane with negligible bending rigidity. By applying Fourier transformations to the time-dependent surface profiles, the dispersion relation of the transverse membrane waves can be obtained and its linear behavior verifies the membrane model. By comparing the dispersion relation to an analytical model, the static stress of the membranes was determined and found to be caused by the fabrication process.

  12. Mechanical Characterization of Ultrathin DLC Suspended Membranes for CMUT Applications

    NASA Astrophysics Data System (ADS)

    Thibert, Sébastien; Ghis, Anne; Delaunay, Marc

    To increase the spatial resolution of CMUT based ultrasound imaging, the feasibility of devices made of arrays of vibrating areas in the square micrometer range is investigated. The manufacturing and characterization of ultrathin diamond like carbon suspended membranes that can act as the mobile electrode of capacitive micromachined ultrasonic transducers are described. To get significant displacements, the membrane thickness must be reduced to the nanometer range. Consequently, a 5 to 20 nm thick Ni/DLC/Ni stack is first deposited by electron cyclotron resonance. The three-layer stack is then transferred on test devices to form suspended membranes over 0.5 to 2 ?m wide trenches. The device characterization includes SEM imaging and AFM force measurements. The mechanical properties of the suspended sheets were extracted, which allows the determination of the bending rigidity (1 x 10-14 to 20 x10-14N.m) of the mobile part of the transducer. This parameter is required for device modelling as it integrates the properties of the final membrane (material, thickness, surface alteration, etc.).

  13. Transport properties of ultrathin black phosphorus on hexagonal boron nitride

    SciTech Connect

    Doganov, Rostislav A.; Özyilmaz, Barbaros; Koenig, Steven P.; Yeo, Yuting; Watanabe, Kenji; Taniguchi, Takashi

    2015-02-23

    Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO{sub 2} substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explain the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400?K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO{sub 2} substrates and reduces the hysteresis at room temperature.

  14. Lateral manipulation of atomic vacancies in ultrathin insulating films.

    PubMed

    Li, Zhe; Chen, Hsin-Yi Tiffany; Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Van Haesendonck, Chris; Pacchioni, Gianfranco; Lievens, Peter

    2015-05-26

    During the last 20 years, using scanning tunneling microscopy (STM) and atomic force microscopy, scientists have successfully achieved vertical and lateral repositioning of individual atoms on and in different types of surfaces. Such atom manipulation allows the bottom-up assembly of novel nanostructures that can otherwise not be fabricated. It is therefore surprising that controlled repositioning of virtual atoms, i.e., atomic vacancies, across atomic lattices has not yet been achieved experimentally. Here we use STM at liquid helium temperature (4.5 K) to create individual Cl vacancies and subsequently to laterally manipulate them across the surface of ultrathin sodium chloride films. This allows monitoring the interactions between two neighboring vacancies with different separations. Our findings are corroborated by density functional theory calculations and STM image simulations. The lateral manipulation of atomic vacancies opens up a new playground for the investigation of fundamental physical properties of vacancy nanostructures of any size and shape and their coupling with the supporting substrate, and of the interaction of various deposits with charged vacancies. PMID:25769024

  15. Dry etch fabrication of ultra-thin porous silicon membranes

    NASA Astrophysics Data System (ADS)

    Hajj-Hassan, Mohamad; Cheung, Maurice; Chodavarapu, Vamsy

    2010-06-01

    Porous silicon is a well-known material with interesting properties for a wide variety of applications in electronics, photonics, medicine, and informatics. We demonstrate fabrication of porous silicon using a dry etching technique. We demonstrate free standing porous silicon membranes that are only few microns thick. Free standing porous silicon membranes have the ability to behave as a size-selective permeable membrane by allowing specific sized molecules to pass through while retaining others. Here, we employ the XeF2 to develop few micrometers thick suspended porous silicon membranes. The flexibility of XeF2 etching process allows the production of mechanically stable membranes of different thicknesses. By choosing the appropriate etching parameters and conditions, pore size can be tuned to produce porous silicon with optically attractive features and desired optical behaviors. The pore size, porosity and thickness of the various developed ultra-thin free-standing porous silicon membranes were characterized with scanning electron microscopy and optical transmittance measurements. The fabricated free-standing porous membrane has a typical transmission spectrum of regular silicon modulated by Fabry-Perot fringes. Porous silicon thin membranes that combine the properties of a mechanically and chemically stable high surface area matrix with the function of an optical transducer may find many used in biomedical microdevices.

  16. Lift-off of large-scale ultrathin nanomembranes

    NASA Astrophysics Data System (ADS)

    Miller, Joshua J.; Carter, Robert N.; McNabb, Kelly B.; DesOrmeaux, Jon-Paul S.; Striemer, Christopher C.; Winans, Joshua D.; Gaborski, Thomas R.

    2015-01-01

    Ultrathin silicon-based nanomembranes hold significant promise for advancements in applications ranging from separations to tissue engineering. Widespread application of these membranes has been hindered by their small active area, which typically ranges from square micrometers to square millimeters. These membranes are typically supported on silicon chips as small windows as a result of a time-consuming through-wafer etch process. This approach results in a relatively low active area and can be challenging to integrate into devices because of the rigid silicon support. In this paper, a lift-off approach is demonstrated wherein the membrane is supported by a polymeric scaffold and separated from the wafer to enable fabrication of membrane sheets (>75?cm2) with >80% active area. The wafer-scale lift-off process is demonstrated with 50?nm thick microporous and nanoporous silicon nitride (SiN) membranes. Release of large-scale SiN membranes is accomplished with both wet and dry lift-off techniques. The dry approach uses XeF2 gas to etch a sacrificial silicon film, while the wet etch uses buffered oxide etchant to remove a silicon dioxide sacrificial layer. Finally, it is demonstrated that lift-off membranes have excellent optical properties and can be used to support cell culture on a conventional scale.

  17. Sub-amorphous thermal conductivity in ultrathin crystalline silicon nanotubes.

    PubMed

    Wingert, Matthew C; Kwon, Soonshin; Hu, Ming; Poulikakos, Dimos; Xiang, Jie; Chen, Renkun

    2015-04-01

    Thermal transport behavior in nanostructures has become increasingly important for understanding and designing next generation electronic and energy devices. This has fueled vibrant research targeting both the causes and ability to induce extraordinary reductions of thermal conductivity in crystalline materials, which has predominantly been achieved by understanding that the phonon mean free path (MFP) is limited by the characteristic size of crystalline nanostructures, known as the boundary scattering or Casimir limit. Herein, by using a highly sensitive measurement system, we show that crystalline Si (c-Si) nanotubes (NTs) with shell thickness as thin as ?5 nm exhibit a low thermal conductivity of ?1.1 W m(-1) K(-1). Importantly, this value is lower than the apparent boundary scattering limit and is even about 30% lower than the measured value for amorphous Si (a-Si) NTs with similar geometries. This finding diverges from the prevailing general notion that amorphous materials represent the lower limit of thermal transport but can be explained by the strong elastic softening effect observed in the c-Si NTs, measured as a 6-fold reduction in Young's modulus compared to bulk Si and nearly half that of the a-Si NTs. These results illustrate the potent prospect of employing the elastic softening effect to engineer lower than amorphous, or subamorphous, thermal conductivity in ultrathin crystalline nanostructures. PMID:25758163

  18. Three-dimensional ultrathin planar lenses by acoustic metamaterials.

    PubMed

    Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

    2014-01-01

    Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential. PMID:25354997

  19. Dielectric elastomer energy harvesting undergoing polarization saturation

    NASA Astrophysics Data System (ADS)

    Liu, Liwu; Luo, Xiaojian; Liu, Yanju; Leng, Jinsong

    2012-04-01

    Mechanical energy can be converted into electrical energy by using a dielectric elastomer generator. The elastomer is susceptible to various models of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretching. The models of failure define a cycle of maximal energy that can be converted. On the other hand, when subjected to voltage, the charge will be induced on a dielectric elastomer. When the voltage is small, the charge increases with the voltage. Along with the continuously increase of voltage, when the charge approaches a certain value, it would become saturated. This paper develops a thermodynamic model of dielectric elastomers undergoing polarization saturation. We studied the typical failure model with three variables of Gent Model silicone energy harvester and obtained an analytical solution of the constitutive equation of dielectric elastomer undergoing polarization saturation. These results can be used to facilitate the design and manufacture of dielectric elastomer energy harvesters.

  20. Ion implanted dielectric elastomer circuits

    NASA Astrophysics Data System (ADS)

    O'Brien, Benjamin M.; Rosset, Samuel; Anderson, Iain A.; Shea, Herbert R.

    2013-06-01

    Starfish and octopuses control their infinite degree-of-freedom arms with panache—capabilities typical of nature where the distribution of reflex-like intelligence throughout soft muscular networks greatly outperforms anything hard, heavy, and man-made. Dielectric elastomer actuators show great promise for soft artificial muscle networks. One way to make them smart is with piezo-resistive Dielectric Elastomer Switches (DES) that can be combined with artificial muscles to create arbitrary digital logic circuits. Unfortunately there are currently no reliable materials or fabrication process. Thus devices typically fail within a few thousand cycles. As a first step in the search for better materials we present a preliminary exploration of piezo-resistors made with filtered cathodic vacuum arc metal ion implantation. DES were formed on polydimethylsiloxane silicone membranes out of ion implanted gold nano-clusters. We propose that there are four distinct regimes (high dose, above percolation, on percolation, low dose) in which gold ion implanted piezo-resistors can operate and present experimental results on implanted piezo-resistors switching high voltages as well as a simple artificial muscle inverter. While gold ion implanted DES are limited by high hysteresis and low sensitivity, they already show promise for a range of applications including hysteretic oscillators and soft generators. With improvements to implanter process control the promise of artificial muscle circuitry for soft smart actuator networks could become a reality.

  1. Dielectric spectroscopy of plant protoplasts

    PubMed Central

    Asami, Koji; Yamaguchi, Tohru

    1992-01-01

    The relative permittivity and conductivity of the mesophyll protoplasts isolated from Brassica campestris leaves and Tulipa gesneriana petals were measured over a frequency range from 1kHz to 500 MHz.These protoplasts showed a broad dielectric dispersion, which was composed of three subdispersions, termed ?1-, ?2-, and ?3-dispersion in increasing order of frequency.The three subdispersions were assigned to the Maxwell-Wagner dispersion caused by charging processes at the interfaces of the surface and internal membranes; the plasma membrane, the tonoplast, and the membranes of cytoplasmic organelles (e.g., chloroplasts, granules, etc) primarily contribute to the ?1-, ?2-, and ?3-dispersion, respectively. The whole dielectric dispersion curve was satisfactorily interpreted in terms of a spherical cell model taking a large vacuole and cytoplasmic organelles into account. Using this model the capacitances of the plasma membranes and the tonoplasts were estimated to be 0.6-0.7 ?F/cm2 and 0.9-1.0 ?F/cm2, respectively. ImagesFIGURE 1 PMID:19431864

  2. Nanooptics of gradient dielectric films

    SciTech Connect

    Shvartsburg, Aleksandr B; Agranat, Mikhail B; Chefonov, O V

    2009-10-31

    The propagation of light through subwave photonic barriers formed by dielectric nanofilms with the refractive indices changing across the films according to the specified law n(z) is considered. Generalised Fresnel formulae depending on the gradient and profile curvature of the refractive index and describing reflection and transmission of such inhomogeneous films are found. For the specified material and thickness, the optical properties of such nanofilms can change from total transmission to total reflection by producing a technologically controlled profile n(z). The obtained results are based on exact analytic solutions of Maxwell's equations for new multiparametric models of inhomogeneous dielectric media. The possibility of producing new subwave dispersion elements, whose action is based on the dependence of the reflection and transmission spectra of gradient photonic barriers on their local dispersion determined by the shape and geometrical parameters of the profile n(z), is shown. The schemes are considered for producing such spectra in the visible and IR regions with the help of periodic nanostructures containing subwave photonic barriers with the normal and anomalous nonlocal dispersion. (nanostructures)

  3. Laser cutting of ultra-thin glasses based on a nonlinear laser interaction effect

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Wu, Zhouling

    2013-07-01

    Glass panel substrates have been widely used in consumer electronics such as in flat panel TVs, laptops, and cell phones. With the advancement in the industry, the glass substrates are becoming thinner and stronger for reduced weight and volume, which brings great challenges for traditional mechanical processes in terms of cut quality, yield, and throughput. Laser glass cutting provides a non-contact process with minimum impact and superior quality compared to the mechanical counterparts. In this paper, we presented recent progresses in advanced laser processing of ultra-thin glass substrates, especially laser-cutting of ultra-thin glasses by a high power laser through a nonlinear interaction effect. Our results indicate that this technique has great potential of application for mass production of ultra-thin glass substrates.

  4. Probing the effect of surface chemistry on the electrical properties of ultrathin gold nanowire sensors

    NASA Astrophysics Data System (ADS)

    Kisner, Alexandre; Heggen, Marc; Mayer, Dirk; Simon, Ulrich; Offenhäusser, Andreas; Mourzina, Yulia

    2014-04-01

    Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer.Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer. Electronic supplementary information (ESI) available: Current-voltage characteristics of Au NW devices modified with organothiols and measurements in salted solutions. See DOI: 10.1039/c3nr05927h

  5. Modification for Uniform Surface of Nafion Ultrathin Film Deposited by Inkjet Printing.

    PubMed

    Guo, Yanglu; Ono, Yutaro; Nagao, Yuki

    2015-09-22

    A lack of knowledge about the features of Nafion confined to ultrathin films at the interface has motivated additional examinations to promote the performance of polymer electrolyte membrane fuel cells (PEMFCs). In this work, we demonstrated the utilization of practical film-forming technique inkjet printing to fabricate a Nafion ultrathin film less than 10 nm thickness. However, the well-known "coffee-ring" effect caused poor quality of the printed pattern, which has restricted its application. This report describes a systematic investigation of necessary parameters such as ink concentration, substrate type, pitch, and offset for printing processes. Furthermore, post-treatment in an ethanol vapor atmosphere exhibited a significant effect on flattening and homogenizing the film surface morphology. Results show that the well-distributed Nafion ultrathin film modified by ethanol vapor annealing manifested much-improved proton conductivity. PMID:26327333

  6. Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

    SciTech Connect

    Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

    2014-12-01

    This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}? plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}? plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50?nm) tungsten film could be determined.

  7. Electric Field Effect on Magnetism in Metallic Ultra-thin Films

    NASA Astrophysics Data System (ADS)

    Chiba, Daichi

    2015-10-01

    Recent experimental developments on the electric field effect on magnetism in metallic magnetic materials are reviewed. The change in the electron density at the surface of metallic ultra-thin magnets by the application of an electric field results in modulations of the Curie temperature, magnetic moment, magnetic anisotropy, and domain wall velocity. The study focused on this paper is the electric field effect on the Curie temperature (magnetic phase transition) in Pt/Co ultra-thin film systems. Electric field modifications of the magnetic moment induced by ferromagnetic proximity effects in Pd, which is usually a nonmagnetic element, are also discussed.

  8. Templated 3D ultrathin CVD graphite networks with controllable geometry: synthesis and application as supercapacitor electrodes.

    PubMed

    Hsia, Ben; Kim, Mun Sek; Luna, Lunet E; Mair, Nisha R; Kim, Yongkwan; Carraro, Carlo; Maboudian, Roya

    2014-11-12

    Three-dimensional ultrathin graphitic foams are grown via chemical vapor deposition on templated Ni scaffolds, which are electrodeposited on a close-packed array of polystyrene microspheres. After removal of the Ni, free-standing foams composed of conjoined hollow ultrathin graphite spheres are obtained. Control over the pore size and foam thickness is demonstrated. The graphitic foam is tested as a supercapacitor electrode, exhibiting electrochemical double-layer capacitance values that compare well to those obtained with the state-of-the-art 3D graphene materials. PMID:25318008

  9. Growth behaviors of ultrathin ZnSe nanowires by Au-catalyzed molecular-beam epitaxy

    SciTech Connect

    Cai, Y.; Wong, T. L.; Chan, S. K.; Sou, I. K.; Wang, N.; Su, D. S.

    2008-12-08

    Ultrathin ZnSe nanowires grown by Au-catalyzed molecular-beam epitaxy show an interesting growth behavior of diameter dependence of growth rates. The smaller the nanowire diameter, the faster is its growth rate. This growth behavior is totally different from that of the nanowires with diameters greater than 60 nm and cannot be interpreted by the classical theories of the vapor-liquid-solid mechanism. For the Au-catalyzed nanowire growth at low temperatures, we found that the surface and interface incorporation and diffusion of the source atoms at the nanowire tips controlled the growth of ultrathin ZnSe nanowires.

  10. Spin-orbit torque opposing the Oersted torque in ultrathin Co/Pt bilayers

    SciTech Connect

    Skinner, T. D. Irvine, A. C.; Heiss, D.; Kurebayashi, H.; Ferguson, A. J.; Wang, M.; Hindmarch, A. T.; Rushforth, A. W.

    2014-02-10

    Current-induced torques in ultrathin Co/Pt bilayers were investigated using an electrically driven ferromagnetic resonance technique. The angle dependence of the resonances, detected by a rectification effect as a voltage, was analysed to determine the symmetries and relative magnitudes of the spin-orbit torques. Both anti-damping (Slonczewski) and field-like torques were observed. As the ferromagnet thickness was reduced from 3 to 1?nm, the sign of the sum of the field-like torque and Oersted torque reversed. This observation is consistent with the emergence of a Rashba spin orbit torque in ultra-thin bilayers.

  11. Copper-Based Ultrathin Nickel Nanocone Films with High-Efficiency Dropwise Condensation Heat Transfer Performance.

    PubMed

    Zhao, Ye; Luo, Yuting; Zhu, Jie; Li, Juan; Gao, Xuefeng

    2015-06-10

    We report a type of copper-based ultrathin nickel nanocone films with high-efficiency dropwise condensation heat transfer (DCHT) performance, which can be fabricated by facile electrodeposition and low-surface-energy chemistry modification. Compared with flat copper samples, our nanosamples show condensate microdrop self-propelling (CMDSP) function and over 89% enhancement in the DCHT coefficient. Such remarkable enhancement may be ascribed to the cooperation of surface nanostructure-induced CMDSP function as well as in situ integration and ultrathin nature of nanofilms. These findings are very significant to design and develop advanced DCHT materials and devices, which help improve the efficiency of thermal management and energy utilization. PMID:26011021

  12. Disclosed dielectric and electromechanical properties of hydrogenated nitrile-butadiene dielectric elastomer

    NASA Astrophysics Data System (ADS)

    Yang, Dan; Tian, Ming; Dong, Yingchao; Liu, Haoliang; Yu, Yingchun; Zhang, Liqun

    2012-03-01

    This paper presents a comprehensive study of the effects of acrylonitrile content, crosslink density and plasticization on the dielectric and electromechanical performances of hydrogenated nitrile-butadiene dielectric elastomer. It was found that by increasing the acrylonitrile content of hydrogenated nitrile-butadiene dielectric elastomer, the dielectric constant will be improved accompanied with a sharp decrease of electrical breakdown strength leading to a small actuated strain. At a fixed electric field, a high crosslink density increased the elastic modulus of dielectric elastomer, but it also enhanced the electrical breakdown strength leading to a high actuated strain. Adding a plasticizer into the dielectric elastomer decreased the dielectric constant and electrical breakdown strength slightly, but reduced the elastic modulus sharply, which was beneficial for obtaining a large strain at low electric field from the dielectric elastomer. The largest actuated strain of 22% at an electric field of 30 kV mm-1 without any prestrain was obtained. Moreover, the hydrogenated nitrile-butadiene dielectric actuator showed good history dependence. This proposed material has great potential to be an excellent dielectric elastomer.

  13. Aluminum nanoparticle/acrylate copolymer nanocomposites for dielectric elastomers with high dielectric constants

    NASA Astrophysics Data System (ADS)

    Hu, Wei; Zhang, Suki N.; Niu, Xiaofan; Liu, Chao; Pei, Qibing

    2014-03-01

    Dielectric elastomers are useful for large-strain actuation and energy harvesting. Their application has been limited by their low dielectric constants and consequently high driving voltage. Various fillers with high dielectric constants have been incorporated into different elastomer systems to improve the actuation strain, force output and energy density of the compliant actuators and generators. However, agglomeration may happen in these nanocomposites, resulting in a decrease of dielectric strength, an increase of leakage current, and in many instances the degree of enhancement of the dielectric constant. In this work, we investigated aluminum nanoparticles as nanofillers for acrylate copolymers. This metallic nanoparticle was chosen because the availability of free electrons could potentially provide an infinite value of dielectric constant as opposed to dielectric materials including ferroelectric nanocrystals. Moreover, aluminum nanoparticles have a self-passivated oxide shell effectively preventing the formation of conductive path. The surfaces of the aluminum nanoparticles were functionalized with methacrylate groups to assist the uniform dispersion in organic solutions and additionally enable copolymerization with acrylate copolymer matrix during bulk polymerization, and thus to suppress large range drifting of the nanoparticles. The resulting Al nanoparticle-acrylate copolymer nanocomposites were found to exhibit higher dielectric constant and increased stiffness. The leakage current under high electric fields were significantly lower than nanocomposites synthesized without proper nanoparticle surface modification. The dielectric strengths of the composites were comparable with the pristine polymers. In dielectric actuation evaluation, the actuation force output and energy specific work density were enhanced in the nanocomposites compared to the pristine copolymer.

  14. Challenges in Nanoelectronics - Gate Dielectrics and Device Modeling (invited)

    SciTech Connect

    Pantelides, Sokrates T

    2005-01-01

    Microelectronics has been tracking Moore's law for several decades with the same choices of materials: Silicon has been the semiconductor of choice; its native oxide, SiO{sub 2} has been used both as a gate dielectric (where a high dielectric constant is in principle desirable) and as an insulator for device isolation and interconnects (where low dielectric constant is in principle desirable); aluminum has been the metal of choice for interconnects. For device modeling, standard approximations to the Boltzmann equation, calculations of mobilities, and Fowler-Nordheim tunneling, have been very adequate. As feature dimensions are entering the 'nano' regime, however, revolutionary changes are becoming inevitable. Copper has already replaced aluminum as the metal of choice for interconnects. Silicon itself is facing changes, such as the adoption of strained layers for mobility enhancement, and is facing challenges from germanium as an alternative. The biggest change, however, is in the dominance of SiO{sub 2} as the gate dielectric. Despite decades of efforts, the Si-SiO{sub 2} system is the only one that works for a Metal-Oxide-Semiconductor field effect transistor. The key reason is that no other semiconductor has a stable native oxide that can serve as gate dielectric. Deposition of other insulators on semiconductors does not yield interfaces with low enough defect densities suitable for devices. Nevertheless, SiO{sub 2} has reached the end of its reign because scaling laws have pushed the gate-oxide thickness to about 1 nm, where tunneling currents become intolerable. Efforts to develop crystalline dielectrics deposited on Si have not been very promising. The main problem is the band offsets that one gets from materials that have a reasonable lattice match to Si. The most promising candidates are oxides that are 'piggy backed' on a very thin SiO{sub 2} layer. This talk covers new unpusblished results obtained by atomic-resolution Z-contrast microscopy on the Si-SiO{sub 2}-HfO{sub 2} system and first-principles theory. Z-contrast images show a very sharp Si-SiO{sub 2} interface, a very thin {approx}0.5 nm amorphous SiO{sub 2} layer, followed by HfO{sub 2}; they also show individual Hf atoms scattered in the SiO{sub 2} layer, but never getting closer than about 0.3 nm to the interface. First-principles calculations also find that approaching the interface closer than 0.3 nm is not energetically favored. The isolated Hf atoms have energy levels in the gap region and may contribute both to mobility degradation and to leakage currents. The new era of nanoelectronics also has raised new challenges in device modeling. Mobilities in MOSFETs fabricated with strained Si layers and in double-gated MOSFETs with ultrathin channels fabricated using SOI technology do not obey the 'universal mobility curve' that has served the industry very well for a long time. Attempts to model mobilities in these structures have run into difficulties because the standard approximations fail (effective approximation, infinite potential barrier at the Si-SiO{sub 2} interface, phenomenological interfaces roughness). This talk covers a new formulation for the calculation of mobilities using a first-principles approach. An atomic-scale model of an abrupt 'ideal' interface is used, the self-consistent Hamiltonian is calculated, and then the calculation is repeated for an interface containing elementary deviations from abruptness (Si-Si bonds on the oxide side, Si-O-Si protrusions in the Si side, single impurity, etc.). The difference represents a scattering potential that is used to calculate mobilities. The wave functions of Si electrons naturally penetrate into the oxide. Initial unpublished results are very illuminating and promising. Finally, modeling Fowler-Nordheim tunneling currents using the classical triangular potential barrier, even with modifications, is running into difficulties. Failure of the effective mass approximation is again the main culprit. This talk covers unpublished results of calculations of Fowler-Nordheim currents using atomic-s

  15. Microwave dielectric behavior of vegetation material

    NASA Technical Reports Server (NTRS)

    Elrayes, Mohamed A.; Ulaby, Fawwaz T.

    1987-01-01

    The microwave dielectric behavior of vegetation was examined through the development of theoretical models involving dielectric dispersion by both bound and free water and supported by extensive dielectric measurements conducted over a wide range of conditions. The experimental data were acquired using an open-ended coaxial probe that was developed for sensing the dielectric constant of thin layers of materials, such as leaves, from measurements of the complex reflection coefficient using a network analyzer. The probe system was successfully used to record the spectral variation of the dielectric constant over a wide frequency range extending from 0.5 to 20.4 GHz at numerous temperatures between -40 to +40 C. The vegetation samples were measured over a wide range of moisture conditions. To model the dielectric spectrum of the bound water component of the water included in vegetation, dielectric measurements were made for several sucrose-water solutions as analogs for the situation in vegetation. The results were used in conjunction with the experimental data for leaves to determine some of the constant coefficients in the theoretical models. Two models, both of which provide good fit to the data, are proposed.

  16. Autonomous dielectric elastomer generator using electret

    NASA Astrophysics Data System (ADS)

    Vu-Cong, T.; Jean-Mistral, C.; Sylvestre, A.

    2013-04-01

    Dielectric elastomers can work as a variable capacitor to convert mechanical energy such as human motion into electrical energy. Nevertheless, scavengers based on dielectric elastomers require a high voltage source to polarize them, which constitutes the major disadvantage of these transducers. We propose here to combine dielectric elastomer with an electret, providing a quasi-permanent potential, thus replacing the high voltage supply. Our new scavenger is fully autonomous, soft, lightweight and low cost. Our structure is made of a dielectric elastomer (Polypower from Danfoss) and an electret developing a potential of -1000V (Teflon from Dupont). The transducer is designed specifically to scavenge energy from human motion. Thus, it works on pure-shear mode with maximum strain of about 50% and it is textured in 3D form because electret is not deformable. The shape of the hybrid structure is critical to insure huge capacitance variation and thus higher scavenged energy. We present in this paper our process for the optimization of the 3D shape that leads us to the developpment and characterization of our first prototype. From an appropriate electromechanical analytical model, an energy density of about 1.48mJ.g-1 is expected on an optimal electrical load. Our new autonomous dielectric generator can produce about 0.55mJ.g-1 on a resistive load, and can further be improved by enhancing the performance of dielectric elastomer such as dielectric permittivity or by increasing the electret potential.

  17. Dielectric Heaters for Testing Spacecraft Nuclear Reactors

    NASA Technical Reports Server (NTRS)

    Sims, William Herbert; Bitteker, Leo; Godfroy, Thomas

    2006-01-01

    A document proposes the development of radio-frequency-(RF)-driven dielectric heaters for non-nuclear thermal testing of the cores of nuclear-fission reactors for spacecraft. Like the electrical-resistance heaters used heretofore for such testing, the dielectric heaters would be inserted in the reactors in place of nuclear fuel rods. A typical heater according to the proposal would consist of a rod of lossy dielectric material sized and shaped like a fuel rod and containing an electrically conductive rod along its center line. Exploiting the dielectric loss mechanism that is usually considered a nuisance in other applications, an RF signal, typically at a frequency .50 MHz and an amplitude between 2 and 5 kV, would be applied to the central conductor to heat the dielectric material. The main advantage of the proposal is that the wiring needed for the RF dielectric heating would be simpler and easier to fabricate than is the wiring needed for resistance heating. In some applications, it might be possible to eliminate all heater wiring and, instead, beam the RF heating power into the dielectric rods from external antennas.

  18. Dielectric investigation of some woven fabrics

    NASA Astrophysics Data System (ADS)

    Cerovic, Dragana D.; Dojcilovic, Jablan R.; Asanovic, Koviljka A.; Mihajlidi, Tatjana A.

    2009-10-01

    In this paper, we have investigated the temperature dependence of dielectric properties (relative dielectric permeabilities and dielectric tangents of losses) for woven fabrics of hemp, jute, flax, cotton, polyester (PES), cotton-PES mixture, and wool. The measurements have been carried out at a temperature range from -50 to 50 °C in the electric periodic field at a frequency 1 MHz in vacuum. For the same specimens, the values of the dielectric properties have also been measured at an air temperature of 21 °C and at relative humidities of 40%, 60%, and 80%. At different frequencies from 80 kHz to 5 MHz, the dielectric properties have been measured at a relative humidity of 40% and at a temperature of 21 °C. An investigation of the dielectric properties of woven fabrics can provide a better understanding of the relation between the dielectric properties of woven fabrics and the different raw material compositions, temperatures, relative air humidities, and frequencies for specimens. Hence, this investigation helps to improve textile material properties.

  19. Virtual gap dielectric wall accelerator

    DOEpatents

    Caporaso, George James; Chen, Yu-Jiuan; Nelson, Scott; Sullivan, Jim; Hawkins, Steven A

    2013-11-05

    A virtual, moving accelerating gap is formed along an insulating tube in a dielectric wall accelerator (DWA) by locally controlling the conductivity of the tube. Localized voltage concentration is thus achieved by sequential activation of a variable resistive tube or stalk down the axis of an inductive voltage adder, producing a "virtual" traveling wave along the tube. The tube conductivity can be controlled at a desired location, which can be moved at a desired rate, by light illumination, or by photoconductive switches, or by other means. As a result, an impressed voltage along the tube appears predominantly over a local region, the virtual gap. By making the length of the tube large in comparison to the virtual gap length, the effective gain of the accelerator can be made very large.

  20. Dielectric-constant gas thermometry

    NASA Astrophysics Data System (ADS)

    Gaiser, Christof; Zandt, Thorsten; Fellmuth, Bernd

    2015-10-01

    The principles, techniques and results from dielectric-constant gas thermometry (DCGT) are reviewed. Primary DCGT with helium has been used for measuring T-T90 below the triple point of water (TPW), where T is the thermodynamic temperature and T90 is the temperature on the international temperature scale of 1990 (ITS-90), and, in an inverse regime with T as input quantity, for determining the Boltzmann constant at the TPW. Furthermore, DCGT allows the determination of several important material properties including the polarizability of neon and argon as well as the virial coefficients of helium, neon, and argon. With interpolating DCGT (IDCGT), the ITS-90 has been approximated in the temperature range from 4?K to 25?K. An overview and uncertainty budget for each of these applications of DCGT is provided, accompanied by corroborating evidence from the literature or, for IDCGT, a CIPM key comparison.

  1. Standards for dielectric elastomer transducers

    NASA Astrophysics Data System (ADS)

    Carpi, Federico; Anderson, Iain; Bauer, Siegfried; Frediani, Gabriele; Gallone, Giuseppe; Gei, Massimiliano; Graaf, Christian; Jean-Mistral, Claire; Kaal, William; Kofod, Guggi; Kollosche, Matthias; Kornbluh, Roy; Lassen, Benny; Matysek, Marc; Michel, Silvain; Nowak, Stephan; O'Brien, Benjamin; Pei, Qibing; Pelrine, Ron; Rechenbach, Björn; Rosset, Samuel; Shea, Herbert

    2015-10-01

    Dielectric elastomer transducers consist of thin electrically insulating elastomeric membranes coated on both sides with compliant electrodes. They are a promising electromechanically active polymer technology that may be used for actuators, strain sensors, and electrical generators that harvest mechanical energy. The rapid development of this field calls for the first standards, collecting guidelines on how to assess and compare the performance of materials and devices. This paper addresses this need, presenting standardized methods for material characterisation, device testing and performance measurement. These proposed standards are intended to have a general scope and a broad applicability to different material types and device configurations. Nevertheless, they also intentionally exclude some aspects where knowledge and/or consensus in the literature were deemed to be insufficient. This is a sign of a young and vital field, whose research development is expected to benefit from this effort towards standardisation.

  2. A dual-stimuli-responsive fluorescent switch ultrathin film

    NASA Astrophysics Data System (ADS)

    Li, Zhixiong; Liang, Ruizheng; Liu, Wendi; Yan, Dongpeng; Wei, Min

    2015-10-01

    Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices.Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05376e

  3. Ultra-thin ZrO2/SrO/ZrO2 insulating stacks for future dynamic random access memory capacitor applications

    NASA Astrophysics Data System (ADS)

    Knebel, Steve; Peši?, Milan; Cho, Kyuho; Chang, Jaewan; Lim, Hanjin; Kolomiiets, Nadiia; Afanas'ev, Valeri V.; Muehle, Uwe; Schroeder, Uwe; Mikolajick, Thomas

    2015-06-01

    Aiming for improvement of the ZrO2-based insulator properties as compared to the state-of-the-art ZrO2/Al2O3/ZrO2 stacks beyond 20 nm dynamic random access memory (DRAM) technology applications, ultra-thin (5 nm) ZrO2/SrO/ZrO2 stacks with TiN electrodes deposited by physical vapor deposition are addressed. By replacing the Al2O3 interlayer with SrO, the effective dielectric permittivity of the stack can be increased as indicated by electrical analysis. At the same time, no degradation of the insulating properties of the SrO-containing stacks and minor changes in the reliability, compared to an Al2O3 interlayer, are found. These results are indicating the possibility of further reducing the effective oxide thickness of the ZrO2-based stacks to come close to 0.5 nm for future DRAM capacitors.

  4. A generalized "cut and projection" algorithm for the generation of quasiperiodic plasmonic concentrators for high efficiency ultra-thin film photovoltaics.

    PubMed

    Flanigan, Patrick W; Ostfeld, Aminy E; Serrino, Natalie G; Ye, Zhen; Pacifici, Domenico

    2013-02-11

    This report will present a generalized two-dimensional quasiperiodic (QP) tiling algorithm based on de Bruijn's "cut and projection" method for use in plasmonic concentrator (PC) / photovoltaic hybrid devices to produce wide-angle, polarization-insensitive, and broadband light absorption enhancement. This algorithm can be employed with any PC consisting of point-like scattering objects, and can be fine-tuned to achieve a high spatial density of points and high orders of local and long-range rotational symmetry. Simulations and experimental data demonstrate this enhancement in ultra-thin layers of organic photovoltaic materials resting on metallic films etched with arrays of shallow sub-wavelength nanoholes. These devices work by coupling the incident light to surface plasmon polariton (SPP) modes that propagate along the dielectric / metal interface. This effectively increases the scale of light-matter interaction, and can also result in constructive interference between propagating SPP waves. By comparing PCs made with random, periodic, and QP arrangements, it is clear that QP is superior in intensifying the local fields and enhancing absorption in the active layer. PMID:23481733

  5. Epoxy Foam Encapsulants: Processing and Dielectric Characterization

    SciTech Connect

    Linda Domeier; Marion Hunter

    1999-01-01

    The dielectric performance of epoxy foams was investigated to determine if such materials might provide advantages over more standard polyurethane foams in the encapsulation of electronic assemblies. Comparisons of the dielectric characteristics of epoxy and urethane encapsulant foams found no significant differences between the two resin types and no significant difference between as-molded and machined foams. This study specifically evaluated the formulation and processing of epoxy foams using simple methylhydrosiloxanes as the flowing agent and compared the dielectric performance of those to urethane foams of similar density.

  6. Dielectric constants of soils at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Geiger, F. E.; Williams, D.

    1972-01-01

    A knowledge of the complex dielectric constant of soils is essential in the interpretation of microwave airborne radiometer data of the earth's surface. Measurements were made at 37 GHz on various soils from the Phoenix, Ariz., area. Extensive data have been obtained for dry soil and soil with water content in the range from 0.6 to 35 percent by dry weight. Measurements were made in a two arm microwave bridge and results were corrected for reflections at the sample interfaces by solution of the parallel dielectric plate problem. The maximum dielectric constants are about a factor of 3 lower than those reported for similar soils at X-band frequencies.

  7. Dielectric Characterization of a Nonlinear Optical Material

    PubMed Central

    Lunkenheimer, P.; Krohns, S.; Gemander, F.; Schmahl, W. W.; Loidl, A.

    2014-01-01

    Batisite was reported to be a nonlinear optical material showing second harmonic generation. Using dielectric spectroscopy and polarization measurements, we provide a thorough investigation of the dielectric and charge-transport properties of this material. Batisite shows the typical characteristics of a linear lossy dielectric. No evidence for ferro- or antiferroelectric polarization is found. As the second-harmonic generation observed in batisite points to a non-centrosymmetric structure, this material is piezoelectric, but most likely not ferroelectric. In addition, we found evidence for hopping charge transport of localized charge carriers and a relaxational process at low temperatures. PMID:25109553

  8. Ultra-thin resistive switching oxide layers self-assembled by field-induced oxygen migration (FIOM) technique

    PubMed Central

    Lee, Sangik; Hwang, Inrok; Oh, Sungtaek; Hong, Sahwan; Kim, Yeonsoo; Nam, Yoonseung; Lee, Keundong; Yoon, Chansoo; Kim, Wondong; Park, Bae Ho

    2014-01-01

    High-performance ultra-thin oxide layers are required for various next-generation electronic and optical devices. In particular, ultra-thin resistive switching (RS) oxide layers are expected to become fundamental building blocks of three-dimensional high-density non-volatile memory devices. Until now, special deposition techniques have been introduced for realization of high-quality ultra-thin oxide layers. Here, we report that ultra-thin oxide layers with reliable RS behavior can be self-assembled by field-induced oxygen migration (FIOM) at the interface of an oxide-conductor/oxide-insulator or oxide-conductor/metal. The formation via FIOM of an ultra-thin oxide layer with a thickness of approximately 2–5?nm and 2.5% excess oxygen content is demonstrated using cross-sectional transmission electron microscopy and secondary ion mass spectroscopy depth profile. The observed RS behavior, such as the polarity dependent forming process, can be attributed to the formation of an ultra-thin oxide layer. In general, as oxygen ions are mobile in many oxide-conductors, FIOM can be used for the formation of ultra-thin oxide layers with desired properties at the interfaces or surfaces of oxide-conductors in high-performance oxide-based devices. PMID:25362933

  9. From optical magnetic resonance to dielectric nanophotonics (A review)

    NASA Astrophysics Data System (ADS)

    Savelev, R. S.; Makarov, S. V.; Krasnok, A. E.; Belov, P. A.

    2015-10-01

    The current state of research in the field of dielectric nanophotonics has been reviewed. "Dielectric nanophotonics" is considered to mean the field of science that studies the interaction of light with nanostructures composed of dielectric nanoparticles with a high value of the refractive index (high-index). These nanostructures allow to control not only the electric but also the magnetic component of light at the nanoscale. Optical properties of high-index dielectric nanoparticles are described; studies devoted to the development of dielectric nanophotonics devices, such as dielectric discrete waveguides, dielectric nanoantennas, and oligomers have been reviewed, and various methods of their preparation have been discussed.

  10. Structural and Electrical Properties of Zr x Y1-x O y Nanocomposites for Gate Dielectric Applications

    NASA Astrophysics Data System (ADS)

    Ebrahimzadeh, Masoud; Bahari, Ali

    2015-11-01

    The possibility of ultrathin Zr x Y1-x O y films was investigated as a good gate dielectric structure for metal-oxide-semiconductor field-effect transistors (MOSFETs). Zr-doped Y2O3 nanocrystallites were synthesized by the sol-gel method. The nanocrystallite size was determined using the Scherrer equation and x-ray powder method from the main peak of the sample phase observed in x-ray diffraction patterns. Moreover, qualitative elemental analysis was performed by energy-dispersive x-ray spectroscopy. The nanocrystallite properties were characterized by scanning electron microscopy. The nanocrystallite morphology was determined by atomic force microscopy, showing that the grain size of the nanoparticles observed at the surface depends on the type of metal dopant and the annealing temperature. The capacitance-voltage and current density-voltage characteristics of the Zr x Y1-x O y /Si structures were analyzed. The results indicate that the Zr0.1Y0.9O y nanocomposite can be used as a good gate dielectric for next-generation MOSFET devices. The conduction mechanism in electrical fields below 0.25 MV/cm and the temperature range of 333 K < T < 423 K was found to be ohmic emission. A thermal excitation model is proposed to explain the ohmic current conduction mechanism.

  11. Modification of low dielectric constant materials for ULSI multilevel interconnection by ion implantation

    NASA Astrophysics Data System (ADS)

    Roy, Alok Nandini Usha

    As integrated circuit (IC) dimensions continue to decrease, RC delay, cross-talk noise, and power dissipation of the interconnect structure become limiting factors for ultra-large-scale integration of integrated circuits. Low dielectric constant materials are being introduced and developed to replace silicon dioxide as inter level dielectrics into current interconnect technologies to meet RC delay goals and minimize cross-talk. These low kappa films generally have dielectric constants less than 3 (vs. 4 for silicon dioxide) and very poor mechanical strength. The elastic modulus (E) of the low kappa film is typically less than 10Gpa, compared with 70Gpa for SiO2. The poor mechanical strength of the low kappa dielectric films increases the risk of thermo-mechanical failures within the Cu/low kappa interconnect structure; e.g. thin film delamination and cracking. Maintaining the mechanical integrity of the low kappa films with the stresses of fab processing, packaging and reliability testing has proven challenging. Therefore, surface hardening is necessary to withstand processing (e.g. CMP). This research work will address the methods to enhance the mechanical strength of low dielectric films. Results of two classes of material (i.e. Xerogel (porous) and methyl silsesquioxane (MSQ (organic)) are discussed. Thin films of Ultra-Low kappa materials such as Xerogel (kappa = 1.76) and porous MSQ (kappa = 2.2) were implanted with argon, neon, nitrogen, carbon and helium with 2 x 1015 cm-2 and 1 x 1016 cm-2 dose at energies varying from 20 to 150 keV at room temperature. In this work we showed that the surface hardness of the porous films can be improved five times as compared to the as-deposited porous films by implanting Ar with 1 x 10 16 cm-2 doses at 50 keV, sacrificing only a slight increase (˜15%) in dielectric constant (e.g., from 1.76 to 2.0). The hardness persists after 450°C annealing. The ion implantation process suppressed the moisture uptake in the porous low kappa films. Surface chemical modification made the films hydrophobic. The results also reveal one possible route to attain the "zero thickness" requirement for interconnect systems. It is shown that ion implantation can prevent the penetration of chemical gases such as CVD precursors into the Ultra-Low kappa dielectrics during a CVD process. Surface modification of MSQ by converting its surface to a thin intrinsic barrier resembling SiO 2 dramatically reduced Cu ion penetration into the film. Surface modification by ion implantation is therefore a powerful strategy to realize the future requirement of ultra-thin barriers. Ion implantation improved the adhesion property of Cu/Low-kappa, interface.

  12. Thermoluminescence and dielectric response of gamma irradiated muscovite mica

    SciTech Connect

    Kaur, Sukhnandan Singh, Surinder Singh, Lakhwant; Lochab, S. P.

    2014-04-24

    The effect of gamma radiation dose on the thermoluminescence (TL) and dielectric properties of muscovite mica was studied. TL glow curves exhibited a single peak around 141 {sup 0}C and its activation energy was estimated to be about 0.89 eV. Different dielectric parameters like dielectric constant, dielectric loss and ac conductivity have been calculated in both pristine and gamma irradiated samples. These dielectric parameters have been studied as a function of irradiation dose.

  13. American Institute of Aeronautics and Astronautics Exploration of Ceramic Dielectrics for Microscale Dielectric

    E-print Network

    Roy, Subrata

    American Institute of Aeronautics and Astronautics 1 Exploration of Ceramic Dielectrics and Astronautics 2 I. Introduction YPICALLY consisting of two electrodes (one exposed and one insulated) separated

  14. Ultrathin willow-like CuO nanoflakes as an efficient catalyst for electro-oxidation of hydrazine

    NASA Astrophysics Data System (ADS)

    Ma, Yuanyuan; Li, Hao; Wang, Rongfang; Wang, Hui; Lv, Weizhong; Ji, Shan

    2015-09-01

    In this paper, preparation of ultrathin willow-like CuO nanoflakes via a one-step process was reported. X-ray diffraction pattern showed the formation of monoclinic CuO crystal, which was also confirmed by result of high resolution transmission electron microscopy. Scanning electron microscopy showed that ultrathin willow-like CuO nanoflakes were formed. Catalytic testing indicated that the ultrathin willow-like CuO nanoflakes exhibited high electrocatalytic activity and durability toward the electro-oxidation of hydrazine in alkaline medium. The results suggested that the as-prepared CuO nanoflakes were potential electrode materials for hydrazine fuel cell.

  15. Synthesized ultrathin MoS2 nanosheets perpendicular to graphene for catalysis of hydrogen evolution reaction.

    PubMed

    Deng, Z H; Li, L; Ding, W; Xiong, K; Wei, Z D

    2015-02-01

    We synthesize the ultrathin MoS2 nanosheets perpendicular to reduced graphene oxides (MoS2?RGO) as an electro-catalyst, which exhibits excellent catalytic activity and good stability for the hydrogen evolution reaction (HER) in acidic medium. PMID:25529835

  16. Thermal analysis of ultrathin, compliant sensors for characterization of the human skin

    E-print Network

    Rogers, John A.

    Thermal analysis of ultrathin, compliant sensors for characterization of the human skin Zuguang of the skin, with capabilities for spatial mapping, in forms that avoid irritation, thermal or mechanical screening, skin hydration sensing, and local skin heating and thermal therapy. A theoretical framework

  17. Evidence for magnetic ordering in ultrathin gadolinium Langmuir-Blodgett films

    SciTech Connect

    Tishin, A.M.; Koksharov, Y.A.; Bohr, J.; Khomutov, G.B.

    1997-05-01

    Magnetic ultrathin Langmuir-Blodgett films containing rare earths are investigated. Electron paramagnetic resonance measurements suggest the possible existence of a transition from a paramagnetic to a magnetically ordered state. In Langmuir-Blodgett films with one hundred layers of Gd, a transition takes place at T{sub 0}{approx}490K. {copyright} {ital 1997} {ital The American Physical Society}

  18. Investigations of ultra-thin single layer a-Si:H films

    SciTech Connect

    Koehler, S.A.

    1997-07-01

    Measurements are presented as direct evidence of tail states in ultra-thin a-Si:H single layer films. Including tail states in computer simulations completely removes the staircase structure in the differential optical spectra, previously associated with the quantum confinement of carriers.

  19. Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants.

    PubMed

    Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

    2015-01-01

    In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1?wt% ultrathin MoS2 nanosheets, at the temperature of 120?°C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry. PMID:26249536

  20. Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

    2015-08-01

    In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1?wt% ultrathin MoS2 nanosheets, at the temperature of 120?°C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

  1. Non-volatile resistive memory devices based on solution-processed ultrathin two-dimensional nanomaterials.

    PubMed

    Tan, Chaoliang; Liu, Zhengdong; Huang, Wei; Zhang, Hua

    2015-05-01

    Ultrathin two-dimensional (2D) nanomaterials, such as graphene and MoS2, hold great promise for electronics and optoelectronics due to their distinctive physical and electronic properties. Recent progress in high-yield, massive production of ultrathin 2D nanomaterials via various solution-based methods allows them to be easily integrated into electronic devices via solution processing techniques. Non-volatile resistive memory devices based on ultrathin 2D nanomaterials have been emerging as promising alternatives for the next-generation data storage devices due to their high flexibility, three-dimensional-stacking capability, simple structure, transparency, easy fabrication and low cost. In this tutorial review, we will summarize the recent progress in the utilization of solution-processed ultrathin 2D nanomaterials for fabrication of non-volatile resistive memory devices. Moreover, we demonstrate how to achieve excellent device performance by engineering the active layers, electrodes and/or device structure of resistive memory devices. On the basis of current status, the discussion is concluded with some personal insights into the challenges and opportunities in future research directions. PMID:25877687

  2. Anal. Chem. 1995, 67,3767-3774 Variable Index of Refraction Ultrathin Films

    E-print Network

    Anal. Chem. 1995, 67,3767-3774 Variable Index of Refraction Ultrathin Films Formedfrom Self[(p-phenylene)methylenelbis(phosphonate)(AZO). Byvaryingthe ratio of DBP toAZO monolayersin the ZP multilayer film,the indexof refraction canbe controlled of refraction of the ZP multilayerson transparent substrates. ZPfilmsconsistingof 100%DBP and 100% AZO

  3. Ultrathin Films and Surface Effects I Stefan Maat, Chairman Ultrahigh vacuum scanning tunneling microscopymagnetic force

    E-print Network

    Gomez, Romel D.

    microscopyÕmagnetic force microscopy study of ultrathin iron films grown on polycrystalline nickel oxide on nickel oxide is still a topic of considerable interest from both scientific and technological viewpoints. The base pressure inside the UHV chamber was better than 10 10 Torr. The nickel oxide substrates were

  4. Ultrathin film of nickel on the Cu (100) surface: Atomic structure and phonons

    SciTech Connect

    Borisova, Svetlana D. E-mail: rusina@ispms.tsc.ru Rusina, Galina G. E-mail: rusina@ispms.tsc.ru

    2014-11-14

    We investigated the structural and vibrational properties of the Cu (100) surface covered with ultrathin (1-5 ML) Ni films using interaction potential from the embedded atom method. The surface relaxation, dispersion relation and polarization of vibrational modes are discussed. Our calculated structural parameters are in good agreement with experimental results. The obtained vibrational frequencies compare well with the available experimental data.

  5. Numerical study of the thermoelectric power factor in ultra-thin Si nanowires

    E-print Network

    1 Numerical study of the thermoelectric power factor in ultra-thin Si nanowires Neophytos Neophytou thermoelectric (TE) performance because of a drastic reduction in their thermal conductivity, l. This has been observed for a variety of materials, even for traditionally poor thermoelectrics such as silicon. Other

  6. Rational Synthesis of Ultrathin n-Type Bi2Te3 Nanowires with Enhanced Thermoelectric Properties

    E-print Network

    Chen, Yong P.

    Rational Synthesis of Ultrathin n-Type Bi2Te3 Nanowires with Enhanced Thermoelectric Properties in high yield (up to 93%). Thermoelectric properties of bulk pellets fabricated by compressing-based thermoelectric power generation and solid-state cooling devices with superior performance in a reliable

  7. Wavelength Shifting in InP based Ultra-thin Quantum Well Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Sengupta, D. K.; Gunapala, S. D.; Bandara, S. V.; Pool, F.; Liu, J. K.; McKelvy, M.

    1998-01-01

    We have demonstrated red-shifting of the wavelength response of a bound-to-continuum p-type ultra-thin InGaAs/Inp quantum well infrared photodetector after growth via rapid thermal annealing. Compared to the as-grown detector, the peak spectral response of the annealed detector was shifted to longer wavelength without any major degradation in responsivity characteristics.

  8. Defect evolution in ultrathin films of polystyrene-block-polymethylmethacrylate diblock

    E-print Network

    Sibener, Steven

    Defect evolution in ultrathin films of polystyrene-block-polymethylmethacrylate diblock copolymers-forming polysty- rene-block-polymethylmethacrylate films with atomic force microscopy to elucidate the evolution of diblock domain topology during annealing. This evolution takes place through relinking, joining

  9. Dramatic depression of Curie temperature for magnetic Co/Cu(100) ultrathin films upon deposition

    E-print Network

    Lin, Minn-Tsong

    Dramatic depression of Curie temperature for magnetic Co/Cu(100) ultrathin films upon deposition a dramatic change in Curie temperature and coercivity of the films was observed. The drastic raising of Curie (TC ¼ 325 K). A simple theoretical estimation was proposed to evaluate the Curie temperature

  10. Interlaced semi-ellipsoid nanostructures for improving light trapping of ultrathin crystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Gao, Ge; Li, Juntao; Wang, Xuehua

    2015-10-01

    Ultrathin crystalline silicon (c-Si) solar cells, which are of several micrometers thick, have attracted much attention in recent years, since it can greatly save raw materials than the traditional ones. To enhance the absorption, as well as to improve the cell efficiency, of the ultrathin c-Si, light trapping nanostructures are used to increase the effective absorption length to close to the 4n2 of the materials thickness, which is determined by the Lambertian limit. Here, we propose a novel interlaced semi-ellipsoid nanostructures (ISENs) to improve the performance of ultrathin c-Si solar cells. In this structure, the large and small periods in x and y direction can improve the light trapping capability at long and short wavelengths respectively. Meanwhile, the graded refractive index of the surface can act as the antireflection coating. By optimizing the ISENs, the short circuit current density of 30.15mA/cm2 was achieved by simulations for a 2 ?m thick c-Si solar cell with rx = 500 nm, ry = 200 nm, rz= 550 nm and without antireflection coating and metal back reflector. The absorption is close to 87% of the Lambertian limit with equivalent thickness. We expect this structure can be fabricated by low cost nanosphere lithography technology and used to improve the efficiency of the ultrathin c-Si solar cells.

  11. Effect of Changes in Relative Humidity and Temperature on Ultrathin Chitosan Films

    E-print Network

    Dutcher, John

    of bound water and a chemical change similar to acetylation at elevated temperatures. Introduction own weight in water.9 In addition, the ability of chitosan hydrogels to absorb water depends on the pEffect of Changes in Relative Humidity and Temperature on Ultrathin Chitosan Films Christopher A

  12. Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

    PubMed Central

    Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

    2015-01-01

    In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1?wt% ultrathin MoS2 nanosheets, at the temperature of 120?°C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry. PMID:26249536

  13. PHYSICAL REVIEW B 89, 115313 (2014) Ultrathin GaN nanowires: Electronic, thermal, and thermoelectric properties

    E-print Network

    Knezevic, Irena

    2014-01-01

    PHYSICAL REVIEW B 89, 115313 (2014) Ultrathin GaN nanowires: Electronic, thermal with decreasing wire cross section, both boding well for TE applications of thin GaN NWs. However, at room-nm-thick NWs. The ZT of GaN NWs increases with increasing temperature beyond 1000 K, which further

  14. Facile fabrication of freestanding ultrathin reduced graphene oxide membranes for water purification.

    PubMed

    Liu, Huiyuan; Wang, Huanting; Zhang, Xiwang

    2015-01-14

    Freestanding ultrathin rGO membranes, with thicknesses down to 17 nm, are fabricated via a facile approach using hydroiodic acid vapor and water-assisted delamination. These unique membranes provide the potential for addressing the key challenge that limits the performance of current forward osmosis membranes. PMID:25406109

  15. Ultrathin Topological Insulator Bi2Se3 Nanoribbons Exfoliated by Atomic Force

    E-print Network

    Cui, Yi

    Ultrathin Topological Insulator Bi2Se3 Nanoribbons Exfoliated by Atomic Force Microscopy Seung Sae), the layered bismuth selenide (Bi2Se3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3

  16. Ultrathin CVD Cu Seed Layer Formation Using Copper Oxynitride Deposition and Room Temperature

    E-print Network

    Ultrathin CVD Cu Seed Layer Formation Using Copper Oxynitride Deposition and Room Temperature of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA Cu seed layers hydrogen plasma can make Cu layers that can serve as seed layers of future Cu interconnects. © 2008

  17. Impact of Metal Type on the Deformation and Conductivity of Ultrathin Nanowires

    E-print Network

    Impact of Metal Type on the Deformation and Conductivity of Ultrathin Nanowires Andrew P Santos1 Theory was used to calculate the zero-bias conductance of smaller elongated nanowires FCC Metals studied · Higher failure strength than bulk To identify structural motifs in metal nanowires under elongation

  18. Dielectric screening of excitons in monolayer graphene

    NASA Astrophysics Data System (ADS)

    Yadav, Premlata; Srivastava, Pawan Kumar; Ghosh, Subhasis

    2015-10-01

    Excitonic transitions in graphene monolayers embedded in different dielectric environments have been investigated using combined absorption and transmission spectroscopy techniques. To vary the dielectric environment, graphene monolayer has been exfoliated in liquid medium. It has been shown that exciton binding energy decreases with increase in the dielectric constant of exfoliating solvents due to the screening of electron-electron and electron-hole interactions in graphene. The typical line shape of the excitonic peak in the absorption spectra is explained by the Fano resonance between the excitonic state and band continuum. Further it has been shown that, there exists a scaling relationship between the dielectric constant of the liquid and the exciton binding energy.

  19. Impulse breakdown delay in liquid dielectrics

    E-print Network

    Jadidian, Jouya

    Theoretical images of streamers, revealing the mechanisms behind impulse breakdown in liquid dielectrics, are presented. Streamers lead to electrical breakdown by forming paths, capable of carrying large current amplitudes ...

  20. Performance of dissipative dielectric elastomer generators

    NASA Astrophysics Data System (ADS)

    Chiang Foo, Choon; Jin Adrian Koh, Soo; Keplinger, Christoph; Kaltseis, Rainer; Bauer, Siegfried; Suo, Zhigang

    2012-05-01

    Dielectric elastomer generators are high-energy-density electromechanical transducers. Their performance is affected by dissipative losses. This paper presents a theoretical analysis of a dielectric elastomer generator with two dissipative processes: viscoelasticity and current leakage. Conversion cycles are shown to attain steady-state after several cycles. Performance parameters such as electrical energy generated per cycle, average power, and mechanical to electrical energy conversion efficiency are introduced. Trade-offs between large electrical energy and power output and poor conversion efficiency are discussed. Excessive current leakage results in negative efficiency—the dielectric elastomer generator wastes energy instead of generating it. The general framework developed in this paper helps in the design and assessment of conversion cycles for dissipative dielectric elastomer generators.