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Sample records for ultrathin hfo2 dielectric

  1. Direct tunneling stress-induced leakage current in ultrathin HfO2/SiO2 gate dielectric stacks

    NASA Astrophysics Data System (ADS)

    Samanta, Piyas; Man, Tsz Yin; Zhang, Qingchun; Zhu, Chunxiang; Chan, Mansun

    2006-11-01

    The conduction mechanism(s) and behavior of direct tunneling stress-induced leakage current (SILC) through ultrathin hafnium oxide (HfO2)/silicon dioxide (SiO2) dual layer gate stack in metal-oxide-semiconductor (MOS) devices have been experimentally investigated in-depth. Both transient and steady-state SILCs have been studied after constant voltage stress (CVS) and constant current stress (CCS) in n-MOS capacitors with negative bias on the tantalum nitride (TaN) gate. The present report clearly indicates that the observed steady-state SILC is due to assisted tunneling via both monoenergetic trapped positive charges and neutral electron traps generated in the HfO2 layer during either CVS or CCS. SILC measured immediately after stress decays slowly due to tunnel detrapping of stress-induced trapped holes in the HfO2 layer. Furthermore, the mechanisms for stress-induced charge carrier generation/trapping and trap creation in the dielectric have been discussed. Our analysis also shows that CVS degrades the dielectric integrity more severely than CCS in the 4.2nm physically thick HfO2/SiO2 stack.

  2. Features of formation of high-k dielectric layer in w/ultrathin HfO2/Si (100) structures under annealing

    NASA Astrophysics Data System (ADS)

    Rudakov, Valery I.; Bogoyavlenskaya, Elena A.; Denisenko, Yury I.; Naumov, V. V.

    2013-01-01

    The initial structures of two types - HfO2(50 nm)/Si (100) and W(150 nm)/HfO2(5 nm)/Si (100) - were prepared by radio frequency magnetron sputtering (RF-MS) in Ar+-plasma and further were subjected to the annealing at 500-950 °C followed by forming an ohmic contact to Si-substrate. Investigation of the first type structures show that differences in various crystalline modifications and kind of I-V curves strongly depend on conditions of growth of the HfO2 films during RF-MS process where RF bias Ubias, applying to the substrate, is an effective parameter for quality and growth process control of the HfO2 films. For the second type structures, the ultrathin HfO2 films were grown at Ubias= -7 V, then an effect of RTA at 950 °C in a neutral atmosphere on both electrical characteristics and chemical state at interfaces was studied. In comparison with as-deposited structures, RTA leads to decrease in the both the maximum specific capacitance in accumulation of C-V characteristics (by 30 %) and the dielectric constant (from 27 to 23). The thermally activated processes of formation of WOx phase at the W/HfO2 interface and Hf-silicate phase (HfSixOy) at the HfO2/Si (100) interface were observed. The total thickness of formed oxide layer exceeded the thickness of as-deposited HfO2 film by 30 %.

  3. HfO2 gate dielectric on Ge (1 1 1) with ultrathin nitride interfacial layer formed by rapid thermal NH3 treatment

    NASA Astrophysics Data System (ADS)

    Agrawal, Khushabu S.; Patil, Vilas S.; Khairnar, Anil G.; Mahajan, Ashok M.

    2016-02-01

    Interfacial properties of the ALD deposited HfO2 over the surface nitrided germanium substrate have been studied. The formation of GeON (∼1.7 nm) was confirmed by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron spectroscopy (HRTEM) over the germanium surface. The effect of post deposition annealing temperature was investigated to study the interfacial and electrical properties of hafnium oxide/germanium oxynitride gate stacks. The high-k MOS devices with ultrathin GeON layer shows the good electrical characteristics including higher k value ∼18, smaller equivalent oxide thickness (EOT) around 1.5 nm and smaller hysteresis value less than 170 mV. The Qeff and Dit values are somewhat greater due to the (1 1 1) orientation of the germanium and may be due to the presence of nitrogen at the interface. The Fowler-Northeim (FN) tunneling of Ge MOS devices has been studied. The barrier height ΦB extracted from the plot is ∼1 eV.

  4. Reliability assessment of ultra-thin HfO2 films deposited on silicon wafer

    NASA Astrophysics Data System (ADS)

    Fu, Wei-En; Chang, Chia-Wei; Chang, Yong-Qing; Yao, Chih-Kai; Liao, Jiunn-Der

    2012-09-01

    Ultra-thin hafnium dioxide (HfO2) is used to replace silicon dioxide to meet the required transistor feature size in advanced semiconductor industry. The process integration compatibility and long-term reliability for the transistors depend on the mechanical performance of ultra-thin HfO2 films. The criteria of reliability including wear resistance, thermal fatigue, and stress-driven failure rely on film adhesion significantly. The adhesion and variations in mechanical properties induced by thermal annealing of the ultra-thin HfO2 films deposited on silicon wafers (HfO2/SiO2/Si) are not fully understood. In this work, the mechanical properties of an atomic layer deposited HfO2 (nominal thickness ≈10 nm) on a silicon wafer were characterized by the diamond-coated tip of an atomic force microscope and compared with those of annealed samples. The results indicate that the annealing process leads to the formation of crystallized HfO2 phases for the atomic layer deposited HfO2. The HfSixOy complex formed at the interface between HfO2 and SiO2/Si, where the thermal diffusion of Hf, Si, and O atoms occurred. The annealing process increases the surface hardness of crystallized HfO2 film and therefore the resistance to nano-scratches. In addition, the annealing process significantly decreases the harmonic contact stiffness (or thereafter eliminate the stress at the interface) and increases the nano-hardness, as measured by vertically sensitive nano-indentation. Quality assessments on as-deposited and annealed HfO2 films can be thereafter used to estimate the mechanical properties and adhesion of ultra-thin HfO2 films on SiO2/Si substrates.

  5. 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.

  6. 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.

  7. Interface and electrical properties of ultra-thin HfO2 film grown by radio frequency sputtering

    NASA Astrophysics Data System (ADS)

    Nath, Madhuchhanda; Roy, Asim

    2016-02-01

    Interfacial composition and electrical properties of ultra-thin hafnium oxide (HfO2) films on p-type <100> Si substrate are reported. Hafnium oxide (HfO2) thin films are prepared using radio-frequency sputtering method and subsequently annealed at different temperature. The effect of post-deposition annealing on the interfacial and chemical state of HfO2/Si gate stack has been characterised by means of X-ray reflectivity and X-ray photoelectron spectroscopy studies. Peaks of X-ray photoelectron spectroscopy spectra at 530.50 and 532.25 eV originate from Hf-O-Si bond illustrated the creation of Hf-silicate based interfacial layer at the high-k/Si interface. X-ray reflectivity fitting result also corroborated the formation of Hf silicate interfacial layer. Capacitance-voltage measurements revealed insignificant hysteresis in case of film annealed at 600 °C. Interface trap density has been extracted using Terman method and is found to be 3.18×10-11 cm-2 eV-1 at -1.0 V. Minimum equivalent oxide thickness (EOT) of 1.3 nm was obtained for the film annealed at 600° C. The gate leakage current density of the HfO2 film annealed at 600 °C is 1.5×10-5 A/cm2 at a bias voltage of -2 V.

  8. Chemical interface analysis of as grown HfO2 ultrathin films on SiO2

    NASA Astrophysics Data System (ADS)

    Maunoury, C.; Dabertrand, K.; Martinez, E.; Saadoune, M.; Lafond, D.; Pierre, F.; Renault, O.; Lhostis, S.; Bailey, P.; Noakes, T. C. Q.; Jalabert, D.

    2007-02-01

    The quality of the interface between a HfO2 high-k gate dielectric and the Si substrate directly influences its electrical properties. The chemical composition of the interfacial region of HfO2 deposited on a SiO2/Si(100) substrate by pulsed liquid injection metal organic chemical vapor deposition at 430 and 550°C was investigated by medium energy ion scattering, angular resolved x-ray photoemission spectroscopy analysis, and high resolution transmission electron microscopy. It is shown that the HfO2/SiO2 interface is abrupt with low roughness and no silicate. The interface roughness with SiO2 is found to be close to that generally measured in silicon technology (silicon oxide above silicon substrates) [E. A. Irene, Solid-State Electron., 45, 1207 (2001)]. The analysis of the experimental results indicates that the deposition technique does not lead to the formation of an extended silicate layer at the HfO2/SiO2 interface.

  9. Grain boundary-driven leakage path formation in HfO 2 dielectrics

    NASA Astrophysics Data System (ADS)

    Bersuker, G.; Yum, J.; Vandelli, L.; Padovani, A.; Larcher, L.; Iglesias, V.; Porti, M.; Nafría, M.; McKenna, K.; Shluger, A.; Kirsch, P.; Jammy, R.

    2011-11-01

    The evolution over time of the leakage current in HfO2-based MIM capacitors under continuous or periodic constant voltage stress (CVS) was studied for a range of stress voltages and temperatures. The data were analyzed based on the results of conductive atomic force microscopy (AFM) measurements demonstrating preferential current flow along grain boundaries (GBs) in the HfO2 dielectric and ab initio calculations, which show the formation of a conductive sub-band due to the precipitation of oxygen vacancies at the GBs. The simulations using the statistical multi-phonon trap-assisted tunneling (TAT) current description successfully reproduced the experimental leakage current stress time dependency by using the calculated energy characteristics of the O-vacancies. The proposed model suggests that the observed reversible increase in the stress current is caused by segregation of the oxygen vacancies at the GBs and their conversion to the TAT-active charge state caused by reversible electron trapping during CVS.

  10. 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 ΔVTH, 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 |ΔVTH| 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.

  11. Attenuated Total Reflection FTIR spectroscopy of Ultrathin Dielectrics Films

    NASA Astrophysics Data System (ADS)

    Liu, Ran

    2003-03-01

    Characterization of ultrathin dielectric films and surface layers becomes extremely crucial in the semiconductor industry. Although the standard transmission and reflection Fourier Transformed Infrared (FTIR) spectroscopy provides rich structural and chemical information, the lack of sensitivity in comparison with other surface techniques such as X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) calls for application of new IR sampling technique for ultrathin layer analysis. This paper will demonstrate the powerfulness of Attenuated Total Reflection (ATR) as a unique FTIR probing method that is capable of analyzing dielectric films with thickness down to 1 nm. Examples will be given in areas of characterization of regular (SiO_2, SiON), low-k (SiOF), and high-k (HfO_2, HfSiO_x, SrTiO_3) films on Si.

  12. Comparison of Multilayer Dielectric Thin Films for Future Metal-Insulator-Metal Capacitors: Al2O3/HfO2/Al2O3 versus SiO2/HfO2/SiO2

    NASA Astrophysics Data System (ADS)

    Park, Sang-Uk; Kwon, Hyuk-Min; Han, In-Shik; Jung, Yi-Jung; Kwak, Ho-Young; Choi, Woon-Il; Ha, Man-Lyun; Lee, Ju-Il; Kang, Chang-Yong; Lee, Byoung-Hun; Jammy, Raj; Lee, Hi-Deok

    2011-10-01

    In this paper, two kinds of multilayered metal-insulator-metal (MIM) capacitors using Al2O3/HfO2/Al2O3 (AHA) and SiO2/HfO2/SiO2 (SHS) were fabricated and characterized for radio frequency (RF) and analog mixed signal (AMS) applications. The experimental results indicate that the AHA MIM capacitor (8.0 fF/µm2) is able to provide a higher capacitance density than the SHS MIM capacitor (5.1 fF/µm2), while maintaining a low leakage current of about 50 nA/cm2 at 1 V. The quadratic voltage coefficient of capacitance, α gradually decreases as a function of stress time under constant voltage stress (CVS). The parameter variation of SHS MIM capacitors is smaller than that of AHA MIM capacitors. The effects of CVS on voltage linearity and time-dependent dielectric breakdown (TDDB) characteristics were also investigated.

  13. Electron energy-loss spectroscopy analysis of HfO2 dielectric films on strained and relaxed SiGe /Si substrates

    NASA Astrophysics Data System (ADS)

    Jang, Jiyoung; Park, Tae Joo; Kwon, Ji-Hwan; Jang, Jae Hyuck; Hwang, Cheol Seong; Kim, Miyoung

    2008-06-01

    In this investigation, HfO2 thin films were deposited on strained and strain-relaxed epitaxial-SiGe /Si substrates, and subsequently subjected to annealing. Electron energy-loss spectroscopy analysis was used to investigate the electronic structure and composition of the film as well as the interfacial layer (IL). While the energy-loss function of the dielectric films revealed predominant Si diffusion in the strained substrates, post deposition annealing (PDA) significantly influenced the diffusion and altered the local composition of the IL in strain-relaxed substrates. Analysis of electronic structures revealed the origin of significant loss of Ge atoms at the IL during PDA.

  14. Interfacial Transition Regions at Germanium/Hf Oxide Based Dielectric Interfaces: Qualitative Differences Between Non-Crystalline Hf Si Oxynitride and Nanocrystalline HfO2 Gate Stacks

    SciTech Connect

    Lucovsky, G.; Lee, S; Long, J; Seo, H; Luning, J

    2009-01-01

    The contribution from a relatively low-K SiON (K {approx} 6) interfacial transition region (ITR) between Si and transition metal high-K gate dielectrics such as nanocrystalline HfO2 (K {approx} 20), and non-crystalline Hf Si oxynitride (K {approx} 10-12) places a significant limitation on equivalent oxide thickness (EOT) scaling. This limitation is equally significant for metal-oxide-semiconductor capacitors and field effect transistors, MOSCAPs and MOSFETs, respectively, fabricated on Ge substrates. This article uses a novel remote plasma processing approach to remove native Ge ITRs and bond transition metal gate dielectrics directly onto crystalline Ge substrates. Proceeding in this way we identify (i) the source of significant electron trapping at interfaces between Ge and Ge native oxide, nitride and oxynitride ITRs, and (ii) a methodology for eliminating native oxide, or nitride IRTs on Ge, and achieving direct contact between nanocrystalline HfO2 and non-crystalline high Si3N4 content Hf Si oxynitride alloys, and crystalline Ge substrates. We then combine spectroscopic studies, theory and modeling with electrical measurements to demonstrate the relative performance of qualitatively different nanocrystalline and non-crystalline gate dielectrics for MOS Ge test devices.

  15. Influence of the oxygen concentration of atomic-layer-deposited HfO2 films on the dielectric property and interface trap density

    NASA Astrophysics Data System (ADS)

    Park, Jaehoo; Cho, Moonju; Kim, Seong Keun; Park, Tae Joo; Lee, Suk Woo; Hong, Sug Hun; Hwang, Cheol Seong

    2005-03-01

    The influence of the ozone concentration (160-370g/m3) during atomic layer deposition of HfO2-gate dielectrics on the dielectric performance of the films grown on Si was studied. Although ozone was effective in reducing the impurity concentration in the film compared to H2O, the higher concentration slightly deteriorated the dielectric performance. More importantly, the degradation in the interface trap property with increasing post-annealing temperature became more serious as the ozone concentration increased. Investigation of the interface states using x-ray photoelectron spectroscopy revealed that the excessive oxygen incorporated during the film growth made the interfacial sub-oxide species (SiO, Si2O3, and silicate) and SiO2 coordinate more with oxygen. This increased the interface trap density and degraded the interface properties.

  16. ZrO2 and HfO2 dielectrics on (001) n-InAs with atomic-layer-deposited in situ surface treatment

    NASA Astrophysics Data System (ADS)

    Babadi, Aein S.; Lind, Erik; Wernersson, Lars-Erik

    2016-03-01

    The electrical properties of ZrO2 and HfO2 gate dielectrics on n-InAs were evaluated. Particularly, an in situ surface treatment method including cyclic nitrogen plasma and trimethylaluminum pulses was used to improve the quality of the high-κ oxides. The quality of the InAs-oxide interface was evaluated with a full equivalent circuit model developed for narrow band gap metal-oxide-semiconductor (MOS) capacitors. Capacitance-voltage (C-V) measurements exhibit a total trap density profile with a minimum of 1 × 1012 cm-2 eV-1 and 4 × 1012 cm-2 eV-1 for ZrO2 and HfO2, respectively, both of which are comparable to the best values reported for high-κ/III-V devices. Our simulations showed that the measured capacitance is to a large extent affected by the border trap response suggesting a very low density of interface traps. Charge trapping in MOS structures was also investigated using the hysteresis in the C-V measurements. The experimental results demonstrated that the magnitude of the hysteresis increases with increase in accumulation voltage, indicating an increase in the charge trapping response.

  17. Competitive effects of oxygen vacancy formation and interfacial oxidation on an ultra-thin HfO2-based resistive switching memory: beyond filament and charge hopping models.

    PubMed

    Nakamura, Hisao; Asai, Yoshihiro

    2016-03-23

    We studied the quantum transport mechanism of an ultra-thin HfO2-based resistive random access memory (ReRAM) cell with TiN electrodes and proposed the design of a sub-10 nm scale device. It is believed that formation and rupture of the conduction path in the local filament causes the switching between high and low resistive states. However, the validity of this simple filament model is not obvious in the sub-10 nm scale device because the redox processes occur mainly in a few nm range at the interface. Furthermore, the intrinsic transport mechanism of the device, in particular, quantum coherence, depends on device materials and length-scale. The relationship between the redox states and the transport mechanism like ballistic or hopping is still under debate when the device length scale is less than 10 nm. In the present study, we performed first-principles calculations of the non-equilibrium Green's function including electron-phonon interactions. We examined several characteristic structures of the HfOx wire (nano-scale conduction path) and the interfaces between the resistive switching layer and electrodes. We found that the metal buffer layer induced a change in the oxygen-reduction site from the interface of HfOx/TiN to the buffer layer. Even when the inserted buffer layer is a few atomic layers, this effect plays an important role in the enhancement of the performance of ON/OFF resistive switching and in the reduction of the inelastic electric current by electron-phonon scattering. The latter suppresses the hopping mechanism, which makes the ballistic conduction the dominant mechanism. We evaluated the activation energy in the high temperature limit by using the first-principles results of inelastic current. Our theoretical model explains the observed crossover of the temperature dependence of ReRAM cells and gives a new insight into the principle of operation on a sub-10 nm scale ReRAM device. PMID:26975565

  18. Thickness Variation of HfO2 Films Under Post-Deposition Annealing Investigated By X-ray Reflectivity and X-ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Chang, Yong-Qing; Fu, Wei-En

    2011-11-01

    As transistor feature sizes scaling down, the ultra-thin HfO2 high-k dielectric has been used to replace SiO2 for the gate dielectric to meet a better EOT for good electric performances. X-ray Reflectivity (XRR) is an accurate instrument to analyze the ultra-thin HfO2 films based on an appropriate material structure model in the data analysis. However, the material structure model is not easily defined for the ultra-thin HfO2 films, especially when interfaces between layers are changed under thermal annealing. In this work, the interfaces between layers of the ultra-thin HfO2 films were investigated at the as-deposited condition (ASD) and post-deposition annealing (PDA) processes. X-ray Photoelectron Spectroscopy (XPS) was used to evaluate the layer structures, which were post-annealed up to 1000 °C using furnaces in the Ar ambiances. The experimental results and analysis showed that layer thicknesses, crystal phases and chemical structures of the ultra-thin HfO2 films were significantly dependent on annealing temperatures. Accordingly, the interface with increasing annealing temperatures was broadened due to the existence of HfSixOy. As a result, a four-layer material structure model of HfO2 (low-density)/HfO2/HfSixOy/SiO2/Si-substrate based on XPS analysis was constructed to significantly improve the XRR fitting process with genetic algorithm (GA). The structure analysis of the XRR spectra using the modified material structure model from the XPS analysis confirmed the interfacial broadening induced by the post-deposition annealing.

  19. Energy-band alignment of atomic layer deposited (HfO2)x(Al2O3)1 - x gate dielectrics on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Jia, Ren-Xu; Dong, Lin-Peng; Niu, Ying-Xi; Li, Cheng-Zhan; Song, Qing-Wen; Tang, Xiao-Yan; Yang, Fei; Zhang, Yu-Ming

    2015-03-01

    We study a series of (HfO2)x(Al2O3)1 - x /4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 eV and the conduction band offset of HfAlO is 1.11-1.72 eV. The conduction band offsets of (HfO2)x(Al2O3)1 - x are increased with the increase of the Al composition, and the (HfO2)x(Al2O3)1 - x offer acceptable barrier heights (> 1 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)x(Al2O3)1 - x/4H-SiC MOS capacitors result in a ˜ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ˜ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-SiC power MOS-based transistors. Project supported by the National Natural Science Foundation of China (Grant Nos. 51272202 and 61234006) and the Science Project of State Grid, China (Grant No. SGRI-WD-71-14-004).

  20. Investigation of HfO2 high-k dielectrics electronic structure on SiO2/Si substrate by x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Duan, T. L.; Yu, H. Y.; Wu, L.; Wang, Z. R.; Foo, Y. L.; Pan, J. S.

    2011-07-01

    In this Letter, x-ray photoelectron spectroscopy (XPS) was used to investigate electronic structures of HfO2 with various thicknesses on SiO2/Si substrate prepared by atomic layer deposition with post deposition annealing of 600 C, which is compatible with a gate last process in the fabrication of complementary metal oxide semiconductor. The hafnium silicate formed between HfO2 and SiO2 interface plays a key role in generating an internal electric field. This can be attributed to the presence of oxygen vacancies (Vo) at the interface. The XPS binding energy shifts of O 1s, Si 2p, and Hf 4f spectra with increasing HfO2 thicknesses can be explained by the presence of the internal field and differential charging effects. Electrical measurements of capacitor structures support the XPS result.

  1. Interfacial and electrical properties of HfO2 gate dielectrics grown on GaAs by atomic layer deposition using different oxidants

    NASA Astrophysics Data System (ADS)

    Byun, Young-Chul; Mahata, Chandreswar; An, Chee-Hong; Oh, Jungwoo; Choi, Rino; Kim, Hyoungsub

    2012-10-01

    In this paper, we examined the effects of two different oxidants (H2O and O3) used during the atomic layer deposition (ALD) of HfO2 films on GaAs, particularly focusing on its interfacial and electrical properties. In comparison with the H2O-based ALD process, the O3-based process produced a large amount of elemental As and Ga-O related bonds near the HfO2/GaAs interface due to its stronger oxidizing power. High interface state and border trap densities of the O3-based sample degraded the low-field electrical stability, which was confirmed by the capacitance and leakage current measurements under various voltage-stressing conditions. However, in terms of high-field stability, the O3-based sample showed a much stronger resistance to stress-induced trap generation than the H2O-based sample.

  2. Electrical and physicochemical properties of atomic-layer-deposited HfO2 film on Si substrate with interfacial layer grown by nitric acid oxidation

    NASA Astrophysics Data System (ADS)

    Kim, Seung Hyun; Seok, Tae Jun; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

    2016-03-01

    The ultrathin SiO2 interfacial layer (IL) was adopted at the interface between atomic-layer-deposited HfO2 gate dielectric film and a Si substrate, which was grown using nitric acid oxidation (NAO) and O3 oxidation (OZO) prior to HfO2 film deposition. X-ray photoelectron spectroscopy result revealed that Si diffusion from the substrate into the film was suppressed for the film with NAO compared to that with OZO, which was attributed to the higher physical density of IL. The electrical measurement using metal-insulator-semiconductor devices showed that the film with NAO exhibited higher effective permittivity and lower densities of fixed charge and slow state at the interface. Furthermore, the leakage current density at an equivalent electrical thickness was lower for the film with NAO than OZO.

  3. 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

  4. Crossbar Nanoscale HfO2-Based Electronic Synapses

    NASA Astrophysics Data System (ADS)

    Matveyev, Yury; Kirtaev, Roman; Fetisova, Alena; Zakharchenko, Sergey; Negrov, Dmitry; Zenkevich, Andrey

    2016-03-01

    Crossbar resistive switching devices down to 40 × 40 nm2 in size comprising 3-nm-thick HfO2 layers are forming-free and exhibit up to 105 switching cycles. Four-nanometer-thick devices display the ability of gradual switching in both directions, thus emulating long-term potentiation/depression properties akin to biological synapses. Both forming-free and gradual switching properties are modeled in terms of oxygen vacancy generation in an ultrathin HfO2 layer. By applying the voltage pulses to the opposite electrodes of nanodevices with the shape emulating spikes in biological neurons, spike-timing-dependent plasticity functionality is demonstrated. Thus, the fabricated memristors in crossbar geometry are promising candidates for hardware implementation of hybrid CMOS-neuron/memristor-synapse neural networks.

  5. Crossbar Nanoscale HfO2-Based Electronic Synapses.

    PubMed

    Matveyev, Yury; Kirtaev, Roman; Fetisova, Alena; Zakharchenko, Sergey; Negrov, Dmitry; Zenkevich, Andrey

    2016-12-01

    Crossbar resistive switching devices down to 40 × 40 nm(2) in size comprising 3-nm-thick HfO2 layers are forming-free and exhibit up to 10(5) switching cycles. Four-nanometer-thick devices display the ability of gradual switching in both directions, thus emulating long-term potentiation/depression properties akin to biological synapses. Both forming-free and gradual switching properties are modeled in terms of oxygen vacancy generation in an ultrathin HfO2 layer. By applying the voltage pulses to the opposite electrodes of nanodevices with the shape emulating spikes in biological neurons, spike-timing-dependent plasticity functionality is demonstrated. Thus, the fabricated memristors in crossbar geometry are promising candidates for hardware implementation of hybrid CMOS-neuron/memristor-synapse neural networks. PMID:26979725

  6. HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

    SciTech Connect

    Chen, P.T.; Sun, Y.; Kim, E.; McIntyre, P.C.; Tsai, W.; Garner, M.; Pianetta, P.; Nishi, Y.; Chui, C.O.; /UCLA

    2007-09-28

    The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopy cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.

  7. Interface Engineering for the Enhancement of Carrier Transport in Black Phosphorus Transistor with Ultra-Thin High-k Gate Dielectric.

    PubMed

    Ling, Zhi-Peng; Zhu, Jun-Tao; Liu, Xinke; Ang, Kah-Wee

    2016-01-01

    Black phosphorus (BP) is the most stable allotrope of phosphorus which exhibits strong in-plane anisotropic charge transport. Discovering its interface properties between BP and high-k gate dielectric is fundamentally important for enhancing the carrier mobility and electrostatics control. Here, we investigate the impact of interface engineering on the transport properties of BP transistors with an ultra-thin hafnium-dioxide (HfO2) gate dielectric of ~3.4 nm. A high hole mobility of ~536 cm(2)V(-1)s(-1) coupled with a near ideal subthreshold swing (SS) of ~66 mV/dec were simultaneously achieved at room temperature by improving the BP/HfO2 interface quality through thermal treatment. This is attributed to the passivation of phosphorus dangling bonds by hafnium (Hf) adatoms which produces a more chemically stable interface, as evidenced by the significant reduction in interface states density. Additionally, we found that an excessively high thermal treatment temperature (beyond 200 °C) could detrimentally modify the BP crystal structure, which results in channel resistance and mobility degradation due to charge-impurities scattering and lattice displacement. This study contributes to an insight for the development of high performance BP-based transistors through interface engineering. PMID:27222074

  8. Tailoring the Electrical Properties of HfO2 MOS-Devices by Aluminum Doping.

    PubMed

    Paskaleva, Albena; Rommel, Mathias; Hutzler, Andreas; Spassov, Dencho; Bauer, Anton J

    2015-08-12

    In this work dielectric and electrical properties of Al-doped HfO2 layers deposited by plasma-enhanced atomic layer deposition in dependence on the thickness and the added Al amount in the films have been investigated. Special attention is dedicated to C-V and I-V hysteresis analysis as a measure for trapping phenomena in the films. A detailed study of conduction mechanisms in dependence on the composition of the layers has also been performed. The densities and spatial and energy positions of traps have been examined. It is found that only a small amount of Al-doping decreases the trapping which is assigned to a reduction of oxygen vacancy-related traps in HfO2. On the contrary, higher amounts of Al introduced in HfO2 films increase the trapping ability of the stacks which is due to the introduction of deeper Al2O3-related traps. The results imply that by adding a proper amount of Al into HfO2 it is possible to tailor dielectric and electrical properties of high-k layers toward meeting the criteria for particular applications. PMID:26196163

  9. Direct tunneling through high-κ amorphous HfO2: Effects of chemical modification

    NASA Astrophysics Data System (ADS)

    Wang, Yin; Yu, Zhizhou; Zahid, Ferdows; Liu, Lei; Zhu, Yu; Wang, Jian; Guo, Hong

    2014-07-01

    We report first principles modeling of quantum tunneling through amorphous HfO2 dielectric layer of metal-oxide-semiconductor (MOS) nanostructures in the form of n-Si/HfO2/Al. In particular, we predict that chemically modifying the amorphous HfO2 barrier by doping N and Al atoms in the middle region—far from the two interfaces of the MOS structure—can reduce the gate-to-channel tunnel leakage by more than one order of magnitude. Several other types of modification are found to enhance tunneling or induce substantial band bending in the Si, both are not desired from leakage point of view. By analyzing transmission coefficients and projected density of states, the microscopic physics of electron traversing the tunnel barrier with or without impurity atoms in the high-κ dielectric is revealed.

  10. Epitaxial Thin Films of Y doped HfO2

    NASA Astrophysics Data System (ADS)

    Serrao, Claudy; Khan, Asif; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Hafnium oxide (HfO2) is one of a few metal oxides that is thermodynamically stable on silicon and silicon oxide. There has been renewed interest in HfO2 due to the recent discovery of ferroelectricity and antiferroelectricity in doped HfO2. Typical ferroelectrics - such as strontium bismuth tantalate (SBT) and lead zirconium titanate (PZT) - contain elements that easily react with silicon and silicon oxide at elevated temperatures; therefore, such ferroelectrics are not suited for device applications. Meanwhile, ferroelectric HfO2 offers promise regarding integration with silicon. The stable phase of HfO2 at room temperature is monoclinic, but HfO2 can be stabilized in the tetragonal, orthorhombic or even cubic phase by suitable doping. We stabilized Y-doped HfO2 thin films using pulsed laser deposition. The strain state can be controlled using various perovskite substrates and controlled growth conditions. We report on Y-doped HfO2 domain structures from piezo-response force microscopy (PFM) and structural parameters via X-ray reciprocal space maps (RSM). We hope this work spurs further interest in strain-tuned ferroelectricity in doped HfO2.

  11. Observation of Dielectrically Confined Excitons in Ultrathin GaN Nanowires up to Room Temperature.

    PubMed

    Zettler, Johannes K; Corfdir, Pierre; Hauswald, Christian; Luna, Esperanza; Jahn, Uwe; Flissikowski, Timur; Schmidt, Emanuel; Ronning, Carsten; Trampert, Achim; Geelhaar, Lutz; Grahn, Holger T; Brandt, Oliver; Fernndez-Garrido, Sergio

    2016-02-10

    The realization of semiconductor structures with stable excitons at room temperature is crucial for the development of excitonics and polaritonics. Quantum confinement has commonly been employed for enhancing excitonic effects in semiconductor heterostructures. Dielectric confinement, which gives rises to much stronger enhancement, has proven to be more difficult to achieve because of the rapid nonradiative surface/interface recombination in hybrid dielectric-semiconductor structures. Here, we demonstrate intense excitonic emission from bare GaN nanowires with diameters down to 6 nm. The large dielectric mismatch between the nanowires and vacuum greatly enhances the Coulomb interaction, with the thinnest nanowires showing the strongest dielectric confinement and the highest radiative efficiency at room temperature. In situ monitoring of the fabrication of these structures allows one to accurately control the degree of dielectric enhancement. These ultrathin nanowires may constitute the basis for the fabrication of advanced low-dimensional structures with an unprecedented degree of confinement. PMID:26675526

  12. Structural and Electrical Properties of EOT HfO2 (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability.

    PubMed

    Kang, Yu-Seon; Kang, Hang-Kyu; Kim, Dae-Kyoung; Jeong, Kwang-Sik; Baik, Min; An, Youngseo; Kim, Hyoungsub; Song, Jin-Dong; Cho, Mann-Ho

    2016-03-23

    We report on changes in the structural, interfacial, and electrical characteristics of sub-1 nm equivalent oxide thickness (EOT) HfO2 grown on InAs by atomic layer deposition. When the HfO2 film was deposited on an InAs substrate at a temperature of 300 °C, the HfO2 was in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and low preexisting interfacial defect states. During post deposition annealing (PDA) at 600 °C, the HfO2 was transformed from an amorphous to a single crystalline orthorhombic phase, which minimizes the interfacial lattice mismatch below 0.8%. Accordingly, the HfO2 dielectric after the PDA had a dielectric constant of ∼24 because of the permittivity of the well-ordered orthorhombic HfO2 structure. Moreover, border traps were reduced by half than the as-grown sample due to a reduction in bulk defects in HfO2 dielectric during the PDA. However, in terms of other electrical properties, the characteristics of the PDA-treated sample were degraded compared to the as-grown sample, with EOT values of 1.0 nm and larger interfacial defect states (Dit) above 1 × 10(14) cm(-2) eV(-1). X-ray photoelectron spectroscopy data indicated that the diffusion of In atoms from the InAs substrate into the HfO2 dielectric during the PDA at 600 °C resulted in the development of substantial midgap states. PMID:26928131

  13. Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Cherkaoui, K.; Monaghan, S.; Negara, M. A.; Modreanu, M.; Hurley, P. K.; O'Connell, D.; McDonnell, S.; Hughes, G.; Wright, S.; Barklie, R. C.; Bailey, P.; Noakes, T. C. Q.

    2008-09-01

    High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma (˜70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ˜6 Å. Very low leakage current density (<10-4 A/cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9±0.1 Å. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k ) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest (˜6 Å) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented.

  14. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors

    PubMed Central

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-01-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer. PMID:26861833

  15. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors

    NASA Astrophysics Data System (ADS)

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-02-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer.

  16. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors.

    PubMed

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-01-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer. PMID:26861833

  17. Time-resolved photoluminescence investigations on HfO2-capped InP nanowires.

    PubMed

    Münch, S; Reitzenstein, S; Borgström, M; Thelander, C; Samuelson, L; Worschech, L; Forchel, A

    2010-03-12

    We have employed time-resolved photoluminescence (PL) spectroscopy to study the impact of HfO(2) surface capping by atomic layer deposition (ALD) on the optical properties of InP nanowires (NWs). The deposition of high-kappa dielectrics acting as a gate oxide is of particular interest in view of possible applications of semiconductor NWs in future wrap-gated field effect transistors (FETs). A high number of charged states at the NW-dielectrics interface can strongly degrade the performance of the FET which explains the strong interest in high quality deposition of high-kappa dielectrics. In the present work we show that time-resolved spectroscopy is a valuable and direct tool to monitor the surface quality of HfO(2)-capped InP NWs. In particular, we have studied the impact of ALD process parameters as well as surface treatment prior to the oxide capping on the NW-dielectrics interface quality. The best results in terms of the surface recombination velocity (S(0) = 9.5 x 10(3) cm s(-1)) were obtained for InP/GaP core/shell NWs in combination with a low temperature (100 degrees C) ALD process. While the present report focuses on the InP material system, our method of addressing the surface treatment for semiconductors with high-kappa dielectrics will also be applicable to nanoelectronic devices based on other III/V material systems such as InAs. PMID:20157234

  18. Dielectric properties of cobalt ferrite nanoparticles in ultrathin nanocomposite films.

    PubMed

    Alcantara, Gustavo B; Paterno, Leonardo G; Fonseca, Fernando J; Pereira-da-Silva, Marcelo A; Morais, Paulo C; Soler, Maria A G

    2013-12-01

    Multilayered nanocomposite films (thickness 50-90 nm) of cobalt ferrite nanoparticles (np-CoFe2O4, 18 nm) were deposited on top of interdigitated microelectrodes by the layer-by-layer technique in order to study their dielectric properties. For that purpose, two different types of nanocomposite films were prepared by assembling np-CoFe2O4 either with poly(3,4-ethylenedioxy thiophene):poly(styrene sulfonic acid) or with polyaniline and sulfonated lignin. Despite the different film architectures, the morphology of both was dominated by densely-packed layers of nanoparticles surrounded by polyelectrolytes. The dominant effect of np-CoFe2O4 was also observed after impedance spectroscopy measurements, which revealed that dielectric behavior of the nanocomposites was largely influenced by the charge transport across nanoparticle-polyelectrolyte interfaces. For example, nanocomposites containing np-CoFe2O4 exhibited a single low-frequency relaxation process, with time constants exceeding 15 ms. At 1 kHz, the dielectric constant and the dissipation factor (tan δ) of these nanocomposites were 15 and 0.15, respectively. These values are substantially inferior to those reported for pressed pellets made exclusively of similar nanoparticles. Impedance data were further fitted with equivalent circuit models from which individual contributions of particle's bulk and interfaces to the charge transport within the nanocomposites could be evaluated. The present study evidences that such nanocomposites display a dielectric behavior dissimilar from that exhibited by their individual counterparts much likely due to enlarged nanoparticle-polyelectrolyte interfaces. PMID:24145704

  19. Optimal migration route of Cu in HfO2

    NASA Astrophysics Data System (ADS)

    Jinlong, Lu; Jing, Luo; Hongpeng, Zhao; Jin, Yang; Xianwei, Jiang; Qi, Liu; Xiaofeng, Li; Yuehua, Dai

    2014-01-01

    The movement of Cu in a HfO2-based resistive random access memory (RRAM) device is investigated in depth by first-principle calculations. Thermodynamics analysis shows that the dominant motion of Cu tends to be along the [001] orientation with a faster speed. The migration barriers along different routes are compared and reveal that the [001] orientation is the optimal migration route of Cu in HfO2, which is more favorable for Cu transportation. Furthermore, the preferable HfO2 growth orientation along [100], corresponding to Cu migration along [001], is also observed. Therefore, it is proposed that the HfO2 material should grow along [100] and the operating voltage should be applied along [001], which will contribute to the improvement of the response speed and the reduction of power consumption of RRAM.

  20. 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.

  1. Interaction of highly charged ions with ultrathin dielectric films

    NASA Astrophysics Data System (ADS)

    Lake, Russell E.

    The excitations occurring at a solid surface due to slow highly charged ion (HCI) impacts are interesting from the perspective of fundamental processes in atomic collisions and materials science. This thesis focuses on two questions: (1) How much HCI potential energy deposition is required to form permanent surface modifications?, (2) How does the presence of a thin dielectric surface film change the classical over-the-barrier picture for neutralization above a clean metal? I describe a measurement of craters in thin dielectric films formed by XeQ+ (26 ≤ Q ≤ 44) projectiles. Tunnel junction devices with ion-irradiated barriers were used to amplify the effect of charge-dependent cratering through the exponential dependence of tunneling conductance on barrier thickness. Electrical conductance of a crater sigmac(Q) increased by four orders of magnitude (7.9 x 10 -4 muS to 6.1 muS) as Q increased, corresponding to crater depths ranging from 2 A to 11 A. According to a heated spike model, the energy required to produce the craters spans from 8 keV to 25 keV over the investigated charge states. Considering energy from pre-equilibrium nuclear and electronic stopping as well as neutralization, we find that at least (27 +/- 2) % of available projectile neutralization energy is deposited into the thin film during impact. Additionally, an extension of the classical over-barrier model for HCI neutralization above dielectric covered metal surfaces is presented. The model is used to obtain the critical distance for the onset of neutralization above C60/Au(111), Al2O3/ Co, and LiF/Au(111) targets. The model predicts that for thin films with low electrical permittivity and positive electron affinity, the onset of neutralization can begin with the electrons in the metal, and at further ion-surface distances than for clean metals. The model describes three distinct over-the-barrier regimes of "vacuum limited" capture from the metal, "thin film" limited capture from the metal, and capture from the insulator. These regimes are detailed in terms of charge state, target material parameters and film thickness.

  2. 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.

  3. 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.

  4. Decoupled front/back dielectric textures for flat ultra-thin c-Si solar cells.

    PubMed

    Isabella, Olindo; Vismara, Robin; Ingenito, Andrea; Rezaei, Nasim; Zeman, M

    2016-03-21

    The optical analysis of optically-textured and electrically-flat ultra-thin crystalline silicon (c-Si) slabs is presented. These slabs were endowed with decoupled front titanium-dioxide (TiO2) / back silicon-dioxide (SiO2) dielectric textures and were studied as function of two types of back reflectors: standard silver (Ag) and dielectric modulated distributed Bragg reflector (MDBR). The optical performance of such systems was compared to that of state-of-the-art flat c-Si slabs endowed with so-called front Mie resonators and to those of similar optical systems still endowed with the same back reflectors and decoupled front/back texturing but based on textured c-Si and dielectric coatings (front TiO2 and back SiO2). Our optimized front dielectric textured design on 2-µm thick flat c-Si slab with MDBR resulted in more photo-generated current density in c-Si with respect to the same optical system but featuring state-of-the-art Mie resonators ( + 6.4%), mainly due to an improved light in-coupling between 400 and 700 nm and light scattering between 700 and 1050 nm. On the other hand, the adoption of textured dielectric layers resulted in less photo-generated current density in c-Si up to -20.6% with respect to textured c-Si, depending on the type of back reflector taken into account. PMID:27136888

  5. Dielectric inspired scaling of polarization conversion subwavelength resonances in open ultrathin chiral structures

    NASA Astrophysics Data System (ADS)

    Serebryannikov, Andriy E.; Mutlu, Mehmet; Ozbay, E.

    2015-11-01

    It is shown that the scaling of subwavelength resonances in open ultrathin chiral structures can be obtained by varying only the permittivity of dielectric spacers, while multiband one-way polarization conversion and related asymmetric transmission remain possible. These features are quite general and obtainable in a wide range of parameter variation. Surprisingly, the difference in the power of ɛ for the classical ɛ-1/2 scaling rule and the empirical rules obtained in the present letter does not exceed 22%, giving an important entry point for future theoretical studies and design strategies. Both spectral scaling and conservation of the polarization characteristics can be achieved by using either tunneling or real-index impedance matching. The scaled structures with strong polarization and directional selectivity may have thickness of λ/100 and smaller.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.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. Electronic supplementary information (ESI) available: Method, characterization results, calculation of photoresponsivity, and calculation of photoconductive gain. See DOI: 10.1039/c5nr06869j

  7. Optical properties of monoclinic HfO2 studied by first-principles local density approximation + U approach

    NASA Astrophysics Data System (ADS)

    Li, Jinping; Han, Jiecai; Meng, Songhe; Lu, Hantao; Tohyama, Takami

    2013-08-01

    The band structures and optical properties of monoclinic HfO2 are investigated by the local density approximation + U approach. With the on-site Coulomb interaction being introduced to 5d orbitals of Hf atom and 2p orbitals of O atom, the experimental band gap is reproduced. The imaginary part of the complex dielectric function shows a small shoulder at the edge of the band gap, coinciding with the experiments. This intrinsic property of crystallized monoclinic HfO2, which is absent in both the tetragonal phase and cubic phase, can be understood as a consequence of the reconstruction of the electronic states near the band edge following the adjustment of the crystal structure. The existence of a similar shoulder-like-structure in the monoclinic phase of ZrO2 is predicted.

  8. 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

    2016-01-01

    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

  9. Reliability study of high-κ La2O3/HfO2 and HfO2/La2O3 stacking layers on n-In0.53Ga0.47As metal-oxide-semiconductor capacitor

    NASA Astrophysics Data System (ADS)

    Chu, Chung-Ming; Lin, Yueh-Chin; Lee, Wei-I.; Dee, Chang Fu; Wong, Yuen-Yee; Yeop Majlis, Burhanuddin; Mat Salleh, Muhamad; Yap, Seong Ling; Chang, Edward Yi

    2016-02-01

    This study investigates the time-dependent dielectric breakdown (TDDB) characteristics of La2O3/HfO2 and HfO2/La2O3 stacking layers on an n-In0.53Ga0.47As metal-oxide-semiconductor capacitor. Both designs improved the reliability compared with a single layer of HfO2. The TDDB followed the thermochemical E model. The current transportation mechanism changed from thermionic emission to Frenkel-Poole emission because of the traps creation under voltage stress. Both designs resulted in similar lifespans and voltage accelerating factors. However, the La2O3/HfO2 design had a longer lifespan because of the lower interface trap density and insertion of the HfO2 diffusion barrier layer between La2O3 and n-In0.53Ga0.47As. The oxide stacks exhibited excellent reliability and achieved a lifespan of 28.4 years.

  10. Photoemission Studies of Pulsed-RF Plasma Nitrided Ultra-thin SiON Dielectric Layers

    SciTech Connect

    O'Connor,R.; McDonnell, S.; Hughes, G.; Smith, K.

    2006-01-01

    Results are presented of a photoemission study of the electronic structure of SiON layers formed by a pulsed-RF decoupled plasma nitration (DPN) of ultra-thin SiO{sub 2} grown base layers approximately 1.0 nm thick. The optical thickness of these device grade nitrided dielectric layers was in the range 1.4-1.6 nm. X-ray photoelectron spectroscopy (XPS) studies indicate that the nitrogen is incorporated in a single chemical environment at concentration levels in the range 15-17%. Angle resolved XPS measurements show that the nitrogen is distributed through the layer, with the binding energy of the N 1s peak at 398.3 eV which is indicative of a Si{sub 3}N{sub 4}-like chemical species in an oxide environment. High resolution core level photoemission studies of the spin orbit stripped Si 2p{sup 4+} peak revealed full width half maximum values in the range 1.4-1.55 eV, which are significantly larger than the 1.15 eV value reported for SiO{sub 2} layers. Synchrotron radiation photoemission studies of the valence band spectra enable the valence band off-set at the Si/SON interface to be evaluated as 2.3 eV and to infer a conduction band off-set of 2.1 eV.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  13. Multiple spectrum analysis and evaluation for optical constants of HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Liu, Dandan; Liu, Huasong; Jiang, Chenghui; Jiang, Yugang; Wang, Lishuan; Zhao, Zhihong; Ji, Yiqin

    2014-08-01

    HfO2 thin films were deposited on ZS1 silica by Ion Beam Sputtering (IBS) technique. Optical constants of HfO2 thin films were obtained by multiple spectrum analysis method, which combined the transmittance spectrum and ellipsometry spectrum of the film. The refractive index and extinction coiefficient of HfO2 thin films were evaluated by etching experiments of the film. The analysis spectral range was between 250nm and 850nm.

  14. Ab initio calculation of relative permittivity of La-doped HfO2

    NASA Astrophysics Data System (ADS)

    Ong, T. M.; Xu, S.

    2014-12-01

    First principles calculations of HfO2 and La-doped HfO2 structures were carried out to investigate the effect of La doping on the relative permittivity of HfO2 films. In this study 6.25% of La was incorporated into HfO2. Upon examination, we found out that La addition increased the value of the relative permittivity from 19 to 26 and this was because the La-induced distortion increased the range of frequencies that contribute to the IR-active modes.

  15. Electron beam induced local crystallization of HfO2 nanopores for biosensing applications

    PubMed Central

    Shim, Jiwook; Rivera, Jose; Bashir, Rashid

    2013-01-01

    We report the development of single, locally crystallized nanopores in HfO2 membranes for biosensing applications. HfO2 is chosen for its isoelectric point of 7.0, mechanical and chemical stability in solution, and for its potential as a high-k material for nanopore ionic field effect transistor applications. The HfO2 membrane is deposited on a graphene layer suspended over a 300 nm FIB hole, where graphene is used as the mechanical support. Exposure of the membrane to a focused electron beam causes crystallization in the vicinity of the nanopore during pore formation. We investigate the effects of crystallization on the electrical and surface properties of HfO2 films. Our surface analysis of HfO2 reveals improved hydrophilicity of crystallized HfO2, a notable advantage over the hydrophobicity of as-deposited HfO2. We also demonstrate detection of dsDNA translocation through HfO2 nanopores under various applied bias levels. In addition, our device architecture also presents a promising first step toward the realization of high-k HfO2 nanopore transistors. PMID:23945603

  16. Solid-state densification of spun-cast self-assembled monolayers for use in ultra-thin hybrid dielectrics

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

    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.

  17. 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

  18. TiO2 and HfO2 in electrolyte-oxide-silicon configuration for applications in bioelectronics

    NASA Astrophysics Data System (ADS)

    Wallrapp, Frank; Fromherz, Peter

    2006-06-01

    We study the electrical properties of thin TiO2 films made by atomic layer deposition (ALD) on p-doped silicon in an electrolyte-oxide-silicon (EOS) configuration. The electrolyte contact of the TiO2/Si heterostructure allows measurements of the differential capacitance for a wide range of bias voltages as they cannot be performed in a metal-oxide-silicon structure because of extensive leakage currents. In the accumulation region of p-silicon, we find a saturation of capacitance that decreases with oxide thickness, indicating an insulator with a dielectric constant of 34. In the inversion region of p-silicon, the capacitance increases in two steps far beyond the saturation capacitance. We assign this effect to the presence of electrons in TiO2 which is controlled by the bias voltage and by immobile positive charges at the TiO2/Si interface: When the Fermi energy in p-silicon is raised to the level of the low lying conduction band of TiO2, electrons accumulate in two layers near the TiO2/Si interface and at the electrolyte/TiO2 interface with a concomitantly enhanced differential capacitance. As a control, we study HfO2 films also made by ALD. We obtain a dielectric constant of 15 from the capacitance in the accumulation region of p-silicon. For HfO2 with a high lying conduction band, the capacitance decreases as expected in the inversion region for the high-frequency limit of silicon. The electrical characterization of TiO2 and HfO2 in EOS junctions opens future applications of high-κ materials in bioelectronics for efficient capacitive interaction of silicon chips and living cells.

  19. Modification of electronic properties of top-gated graphene devices by ultrathin yttrium-oxide dielectric layers.

    PubMed

    Wang, Lin; Chen, Xiaolong; Wang, Yang; Wu, Zefei; Li, Wei; Han, Yu; Zhang, Mingwei; He, Yuheng; Zhu, Chao; Fung, Kwok Kwong; Wang, Ning

    2013-02-01

    We report the structure characterization and electronic property modification of single layer graphene (SLG) field-effect transistor (FET) devices top-gated using ultrathin Y(2)O(3) as dielectric layers. Based on the Boltzmann transport theory within variant screening, Coulomb scattering is confirmed quantitatively to be dominant in Y(2)O(3)-covered SLG and a very few short-range impurities have been introduced by Y(2)O(3). Both DC transport and AC capacitance measurements carried out at cryogenic temperatures demonstrate that the broadening of Landau levels is mainly due to the additional charged impurities and inhomogeneity of carriers induced by Y(2)O(3) layers. PMID:23263255

  20. Study on void reduction in direct wafer bonding using Al2O3/HfO2 bonding interface for high-performance Si high-k MOS optical modulators

    NASA Astrophysics Data System (ADS)

    Han, Jae-Hoon; Takenaka, Mitsuru; Takagi, Shinichi

    2016-04-01

    We have investigated the direct wafer bonding (DWB) method with a thin bonding dielectric interface to fabricate Si high-k MOS optical modulators with a thin equivalent oxide thickness (EOT). To suppress void generation on the bonded wafer during high-temperature annealing, we examined the high-k dielectric bonding interfacial layers, such as Al2O3 and HfO2. We found that the Al2O3/HfO2 bilayer enables void-less wafer bonding in conjunction with pre-bonding annealing at 700 °C. By using the 0.5-nm Al2O3/2.0-nm HfO2 bonding interface, the density of voids is reduced by three orders of magnitude as compared with that in the case of using the Al2O3 bonding interface. We achieved a density of voids of approximately 2 × 10-3 cm-2 even when the bonded wafer is annealed at 700 °C. By thermal desorption spectroscopy (TDS), we found that degassing from the bonding interface is successfully suppressed by the introduction of the HfO2 layer and the pre-bonding annealing at 700 °C, which are considered to suppress void generation. Wafer bonding with thin Al2O3/HfO2 high-k bonding interface is promising for Si high-k MOS optical modulators.

  1. 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.

  2. Using dual plasma treatment to improve electrical characteristics and reduce flicker noise of high-κ 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-κ HfO2 gate dielectric, and aluminum metal gate. The dual plasma treatment involves a pre-deposition CF4 plasma treatment at a high-κ/poly-Si interface and post-deposition N2 plasma treatment at a high-κ HfO2 gate dielectric; this treatment enables reducing the interface-trap-state defects at the high-κ/poly-Si interface, grain boundary traps in the poly-Si channel film, and oxygen vacancy Vo in the high-κ 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.

  3. Spectroscopic analysis of Al and N diffusion in HfO2

    NASA Astrophysics Data System (ADS)

    Lysaght, P. S.; Woicik, J. C.; Sahiner, M. A.; Price, J.; Weiland, C.; Kirsch, P. D.

    2012-09-01

    X-ray photoelectron core level spectroscopy, secondary ion mass spectroscopy, spectroscopic ellipsometry, and extended x-ray absorption fine structure measurements have been employed to distinguish the effects of Al and N diffusion on the local bonding and microstructure of HfO2 and its interface with the Si substrate in (001)Si/SiOx/2 nm HfO2/1 nm AlOx film structures. The diffusion of Al from the thin AlOx cap layer deposited on both annealed and unannealed HfO2 has been observed following anneal in N2 and NH3 ambient. Both N2 and NH3 subsequent anneals were performed to decouple incorporated nitrogen from thermal reactions alone. Causal variations in the HfO2 microstructure combined with the dependence of Al and N diffusion on initial HfO2 conditions are presented with respect to anneal temperature and ambient.

  4. 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.

  5. Optimizing HiPIMS pressure for deposition of high-k (k = 18.3) amorphous HfO2

    NASA Astrophysics Data System (ADS)

    Ganesan, R.; Murdoch, B. J.; Partridge, J. G.; Bathgate, S.; Treverrow, B.; Dong, X.; Ross, A. E.; McCulloch, D. G.; McKenzie, D. R.; Bilek, M. M. M.

    2016-03-01

    Stoichiometric amorphous HfO2 films have been deposited by reactive High Power Impulse Magnetron Sputtering (HiPIMS) from a Hf target in a 1:1 Ar:O2 atmosphere at pressures 2-4.5 mTorr. An optimum pressure was found for depositing smooth, high refractive index and amorphous films. Stress and refractive index reached a maximum as deposition pressure was increased to 3.5 mTorr. At 3.5 mTorr, HfO2 films were deposited with a refractive index of 2.15 at 500 nm, low leakage currents, moderate fixed charge density and a high dielectric constant of ∼18.3. The intensification of energetic ion bombardment upon the film with increase in HiPIMS pressure plays a dominant role in film properties. Increase in pressure above the optimum relieved the stress in the films and degraded the optical and electrical properties. HiPIMS pressure enables to gain indirect control of ion flux and energy in the plasma and can be used to modify the properties of depositing films.

  6. Temperature dependent structural, optical and hydrophobic properties of sputtered deposited HfO2 films

    NASA Astrophysics Data System (ADS)

    Dave, V.; Dubey, P.; Gupta, H. O.; Chandra, R.

    2014-01-01

    Hafnium oxide being high-k dielectric has been successfully utilized in electronic and optical applications. Being thermodynamically stable and having good mechanical strength, it can be used as a protective coating for outdoor HV insulators which are suffering from surface flashover problem due to contamination. In this paper, we are investigating the effect of substrate temperature on structural, optical and hydrophobic properties of hafnium oxide coating deposited over glass insulators by DC magnetron sputtering. X-ray diffraction is applied to determine the crystalline phase and crystallite size of the film. The morphology of the samples is examined using atomic force microscopy. The optical properties are studied using UV-vis-NIR spectrophotometer. The wettability of the film is investigated using contact angle meter. The thickness is measured using surface profilometer and verified through optical data. The relationship between substrate temperature with grain size, roughness, refractive index, and hydrophobicity is manifested. The maximum contact angle for HfO2 film was found to be 106° at 400°C.

  7. Towards forming-free resistive switching in oxygen engineered HfO2-x

    NASA Astrophysics Data System (ADS)

    Sharath, S. U.; Bertaud, T.; Kurian, J.; Hildebrandt, E.; Walczyk, C.; Calka, P.; Zaumseil, P.; Sowinska, M.; Walczyk, D.; Gloskovskii, A.; Schroeder, T.; Alff, L.

    2014-02-01

    We have investigated the resistive switching behavior in stoichiometric HfO2 and oxygen-deficient HfO2-x thin films grown on TiN electrodes using reactive molecular beam epitaxy. Oxygen defect states were controlled by the flow of oxygen radicals during thin film growth. Hard X-ray photoelectron spectroscopy confirmed the presence of sub-stoichiometric hafnium oxide and defect states near the Fermi level. The oxygen deficient HfO2-x thin films show bipolar switching with an electroforming occurring at low voltages and low operating currents, paving the way for almost forming-free devices for low-power applications.

  8. Mechanical properties of low- and high-k dielectric thin films: A surface Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Zizka, J.; King, S.; Every, A. G.; Sooryakumar, R.

    2016-04-01

    Surface Brillouin light scattering measurements are used to determine the elastic constants of nano-porous low-k SiOC:H (165 nm) and high-k HfO2 (25 nm) as well as BN:H (100 nm) films grown on Si substrates. In addition, the study investigates the mechanical properties of ultra-thin (25 nm) blanket TiN cap layers often used as hard masks for patterning, and their effects on the underlying low-k dielectrics that support a high level of interconnected porosity. Depending on the relative material properties of individual component layers, the acoustic modes manifest as confined, propagating, or damped resonances in the light scattering spectra, thereby enabling the mechanical properties of the ultra-thin films to be determined.

  9. Interface and plasma damage analysis of PEALD TaCN deposited on HfO2 for advanced CMOS studied by angle resolved XPS and C-V

    NASA Astrophysics Data System (ADS)

    Piallat, Fabien; Beugin, Virginie; Gassilloud, Remy; Dussault, Laurent; Pelissier, Bernard; Leroux, Charles; Caubet, Pierre; Valle, Christophe

    2014-06-01

    Plasma enhanced atomic layer deposition (PEALD) TaCN deposited on HfO2 was studied by X-ray photoelectron spectroscopy (XPS) to understand the reactions taking place at the interface and connect them with C-V electrical characteristics of MOS devices. Moreover, angular resolved XPS (AR-XPS) was used for composition depth profiling of TaCN/HfO2/SiO2/Si stacks. Clear oxidation of the metal electrode through Tasbnd O bonding formation and migration of N in the dielectric with Hfsbnd N are shown. These modifications of chemical bonding give an insight on the electrical results. Low equivalent oxide thicknesses (EOT), as low as 0.89 nm and current leakage improvement by more than 5 decades, are observed for deposition with low plasma power and can be related to HfN content in HfO2 layer. The increase of plasma power used for TaCN deposition results in densification of the layer and promotes the creation of TaC in TaCN material. However H2 plasma has an impact on HfO2 with a reduction and scattering of the measured current leak gain. TaCN/HfO2 interface is also impacted with further creation of TaOx, leading to an increase of EOT when plasma power is increased. Based on these findings, reaction mechanisms with the corresponding Gibbs free energy are proposed.

  10. Properties of Ultrathin Al2O3-TiO2 Nanolaminate Films for Gate Dielectric Applications Deposited by Plasma-Assisted Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Garces, Nelson; Meyer, David; Nepal, Neeraj; Wheeler, Virginia; Eddy, Charles

    2012-02-01

    High permittivity dielectrics such as Al2O3, HfO2, Ta2O5, TiO2, etc., are an essential component of aggressively-scaled III-V and graphene field effect transistors (FETs) where insulators are necessary to reduce gate leakage current while maintaining high gate capacitance and charge control of the channel. Atomic layer deposition (ALD) has the capability to deposit hybrid films, or nanolaminates, of two or more dielectrics that have unique properties. Thin [Al2O3+TiO2] nanolaminates with varying TiO2 and Al2O3 content were deposited on n-Si substrates at ˜225-300 C using ALD. A nanolaminate is composed of bilayers, defined as the sum of (x)Al2O3 and (y)TiO2, where x, and y indicate the number of times a component monolayer is repeated. While the overall thickness of the dielectric was held at ˜ 17-20 nm, the relative ratio of Al2O3 to TiO2 in the bilayer stack was varied to evaluate changes in the material properties and electrical performance of the oxides. C-V and I-V measurements on various [(x)TiO2+(y)Al2O3] MOS capacitors were taken. The high-TiO2-content films show limited evidence of oxide charge trapping and relatively large dielectric constants (κ˜15), whereas the high-Al2O3-content films offer a larger optical bandgap and improved suppression of leakage current. We will discuss the properties of very thin nanolaminates and their possible use as gate oxides. Morphological, electrical, and XPS composition assessments will be presented.

  11. In-Line Compositional and Thickness Metrology Using XPS for Ultra-Thin Dielectric Films

    NASA Astrophysics Data System (ADS)

    Truman, J. Kelly; Gurer, Emir; Larson, C. Thomas; Reed, David

    2005-09-01

    65 nm and 45 nm silicon devices will utilize compositionally critical processes for gate dielectrics, capacitor dielectrics, gate and capacitor electrodes, and ultra shallow junction layers. For example, small changes in nitrogen composition have been correlated with unacceptable shifts in electrical properties of devices with SiOxNy gate dielectrics. Present optically-based metrology technologies for such applications are reaching limits for precise thickness measurements and do not provide direct and adequately precise compositional information. As a result, mature analytical techniques, such as x-ray photoelectron spectroscopy (XPS), are now being transitioned to in-line production metrology usage. We discuss the application of XPS optimized for 200/300 mm production to compositional and thickness metrology of SiOxNy and high k gate dielectrics, high k capacitor dielectrics, and new electrode materials. The development of optimized hardware, robust data analysis algorithms and high throughput, fully automated operation has led to production implementation of XPS in advanced logic applications. The precise correlation of plasma nitridation metrology data with electrical device parameters has proven valuable in detecting process drifts early in the process flow, without the need to prepare devices through the first metal layer for testing. High density maps of film thickness and composition have enabled optimization of oxidation, nitridation and post-nitridation anneal processes for SiOxNy film production for 90 nm, 65 nm and below. High precision compositional and thickness metrology data for high-k gate and capacitor dielectrics is also presented.

  12. Effect of postdeposition anneals on the Fermi level response of HfO2/In0.53Ga0.47As gate stacks

    NASA Astrophysics Data System (ADS)

    Hwang, Yoontae; Engel-Herbert, Roman; Rudawski, Nicholas G.; Stemmer, Susanne

    2010-08-01

    The electrical characteristics, in particular interface trap densities, oxide capacitance, and Fermi level movement, of metal oxide semiconductor capacitors with HfO2 gate dielectrics and In0.53Ga0.47As channels are investigated as a function of postdeposition annealing atmosphere. It is shown, using both conductance and Terman methods, that the Fermi level of nitrogen annealed stacks is effectively pinned at midgap. In contrast, samples annealed in forming gas show a large band bending in response to an applied gate voltage and a reduced midgap interface trap density compared to those annealed in nitrogen.

  13. 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

  14. 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.

  15. Self-assembled molecular monolayers as ultrathin gate dielectric in carbon nanotube transistors

    NASA Astrophysics Data System (ADS)

    Robert, Gaël; Derycke, Vincent; Goffman, Marcelo F.; Lenfant, Stéphane; Vuillaume, Dominique; Bourgoin, Jean-Philippe

    2008-10-01

    We demonstrate the use of a self-assembled monolayer of octadecanethiol on gold as thin gate dielectric for a single-walled carbon nanotube field-effect transistor. P-type transistors display very steep subthreshold slopes, greatly reduced hysteresis, and band-to-band tunneling. The suppression of the gate efficiency for n-type transistors emphasizes the key role of the electrical dipole of the molecular layer in controlling the switching. Combining the versatility of organic dielectrics with the exceptional electronic and mechanical properties of carbon nanotubes opens interesting ways toward the realization of fully organic nanoscale transistors.

  16. High performance p-type organic thin film transistors with an intrinsically photopatternable, ultrathin polymer dielectric layer☆

    PubMed Central

    Petritz, Andreas; Wolfberger, Archim; Fian, Alexander; Krenn, Joachim R.; Griesser, Thomas; Stadlober, Barbara

    2013-01-01

    A high-performing bottom-gate top-contact pentacene-based oTFT technology with an ultrathin (25–48 nm) and electrically dense photopatternable polymeric gate dielectric layer is reported. The photosensitive polymer poly((±)endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) is patterned directly by UV-exposure (λ = 254 nm) at a dose typical for conventionally used negative photoresists without the need for any additional photoinitiator. The polymer itself undergoes a photo-Fries rearrangement reaction under UV illumination, which is accompanied by a selective cross-linking of the macromolecules, leading to a change in solubility in organic solvents. This crosslinking reaction and the negative photoresist behavior are investigated by means of sol–gel analysis. The resulting transistors show a field-effect mobility up to 0.8 cm2 V−1 s−1 at an operation voltage as low as −4.5 V. The ultra-low subthreshold swing in the order of 0.1 V dec−1 as well as the completely hysteresis-free transistor characteristics are indicating a very low interface trap density. It can be shown that the device performance is completely stable upon UV-irradiation and development according to a very robust chemical rearrangement. The excellent interface properties, the high stability and the small thickness make the PNDPE gate dielectric a promising candidate for fast organic electronic circuits. PMID:24748853

  17. Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

    NASA Astrophysics Data System (ADS)

    Green, M. L.; Gusev, E. P.; Degraeve, R.; Garfunkel, E. L.

    2001-09-01

    The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal-oxide-semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si-O-N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices will be manufactured with SiO2 and Si-O-N for the foreseeable future, continued scaling of integrated circuit devices, essentially the continued adherence to Moore's law, will necessitate the introduction of an alternate gate dielectric once the SiO2 gate dielectric thickness approaches ˜1.2 nm. It is hoped that this article will prove useful to members of the silicon microelectronics community, newcomers to the gate dielectrics field, practitioners in allied fields, and graduate students. Parts of this article have been adapted from earlier articles by the authors [L. Feldman, E. P. Gusev, and E. Garfunkel, in Fundamental Aspects of Ultrathin Dielectrics on Si-based Devices, edited by E. Garfunkel, E. P. Gusev, and A. Y. Vul' (Kluwer, Dordrecht, 1998), p. 1 [Ref. 1]; E. P. Gusev, H. C. Lu, E. Garfunkel, T. Gustafsson, and M. Green, IBM J. Res. Dev. 43, 265 (1999) [Ref. 2]; R. Degraeve, B. Kaczer, and G. Groeseneken, Microelectron. Reliab. 39, 1445 (1999) [Ref. 3].

  18. 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

  19. Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric.

    PubMed

    Lee, Dongil; Yoon, Jinsu; Lee, Juhee; Lee, Byung-Hyun; Seol, Myeong-Lok; Bae, Hagyoul; Jeon, Seung-Bae; Seong, Hyejeong; Im, Sung Gap; Choi, Sung-Jin; Choi, Yang-Kyu

    2016-01-01

    Printing electronics has become increasingly prominent in the field of electronic engineering because this method is highly efficient at producing flexible, low-cost and large-scale thin-film transistors. However, TFTs are typically constructed with rigid insulating layers consisting of oxides and nitrides that are brittle and require high processing temperatures, which can cause a number of problems when used in printed flexible TFTs. In this study, we address these issues and demonstrate a method of producing inkjet-printed TFTs that include an ultra-thin polymeric dielectric layer produced by initiated chemical vapor deposition (iCVD) at room temperature and highly purified 99.9% semiconducting carbon nanotubes. Our integrated approach enables the production of flexible logic circuits consisting of CNT-TFTs on a polyethersulfone (PES) substrate that have a high mobility (up to 9.76 cm(2) V(-1) sec(-)1), a low operating voltage (less than 4 V), a high current on/off ratio (3 × 10(4)), and a total device yield of 90%. Thus, it should be emphasized that this study delineates a guideline for the feasibility of producing flexible CNT-TFT logic circuits with high performance based on a low-cost and simple fabrication process. PMID:27184121

  20. Memristor and selector devices fabricated from HfO2-xNx

    NASA Astrophysics Data System (ADS)

    Murdoch, B. J.; McCulloch, D. G.; Ganesan, R.; McKenzie, D. R.; Bilek, M. M. M.; Partridge, J. G.

    2016-04-01

    Monoclinic HfO2-xNx has been incorporated into two-terminal devices exhibiting either memristor or selector operation depending on the controlled inclusion/suppression of mobile oxygen vacancies. In HfO2 memristors containing oxygen vacancies, gradual conductance modulation, short-term plasticity, and long-term potentiation were observed using appropriate voltage-spike stimulation, suggesting suitability for artificial neural networks. Passivation of oxygen vacancies, confirmed by X-ray absorption spectroscopy, was achieved in HfO2-xNx films by the addition of nitrogen during growth. Selector devices formed on these films exhibited threshold switching and current controlled negative differential resistance consistent with thermally driven insulator to metal transitions.

  1. Quantum size effect on dielectric function of ultrathin metal film: a first-principles study of Al(1 1 1).

    PubMed

    Ming, Wenmei; Blair, Steve; Liu, Feng

    2014-12-17

    Using first-principles calculations, we show manifestations of the quantum size effect in the dielectric function ε(2) of free-standing Al(1 1 1) ultrathin films of 1 monolayer to 20 monolayers, taking into account size dependent contributions from both interband and intraband electronic transitions. Overall the in-plane components (interband transition) of ε(2) increase with film thickness at all frequencies, converging towards a constant value. However, the out-of-plane components of ε(2) show a more complex behavior, and, only at frequencies less than 0.75 eV, increase with film thickness without convergence. This suggests that ultrathin films can possibly be used for low-loss plasmonics devices in the visible and ultraviolet range. Our findings may shed light on searching for low-loss plasmonic materials via quantum size effect. PMID:25419653

  2. Characterization of ultrathin gate dielectrics using combined grazing x-ray reflectance and spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Boher, Pierre; Piel, Jean-Philippe; Evard, Patrick; Defranoux, Christophe; Stehle, Jean-Louis P.

    2001-04-01

    Precise characterization of high k gate dielectrics becomes a challenging task due to the very thin thicknesses (< 3 - 4 nm), which will be needed in the next generation integrated circuits. Conventional techniques such as spectroscopic ellipsometry in the visible range becomes difficult to use alone because of the great correlation between thickness and optical indices. To overcome this problem the following strategy is applied. First, grazing x- ray reflectance is used on all the samples to extract the different layer thickness using a simple model. Second, spectroscopic ellipsometry is applied and the results fitted with the structural models deduced from the x-ray results. In this conditions a precise structural model is built which can take into account the interface and surface behavior all factors that become critical for this range of thickness. This approach is applied to various types of oxide nitride gate dielectrics and ZrO2 films. In the fist case, the nitrogen content of the films can be precisely determined and also the inhomogeneity in depth of the layers in some cases. Interface problems can also be detected on ZrO2 films. Results are compared to x-ray photo-emission measurement in some cases.

  3. Single vacancy defect spectroscopy on HfO2 using random telegraph noise signals from scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Thamankar, R.; Raghavan, N.; Molina, J.; Puglisi, F. M.; O'Shea, S. J.; Shubhakar, K.; Larcher, L.; Pavan, P.; Padovani, A.; Pey, K. L.

    2016-02-01

    Random telegraph noise (RTN) measurements are typically carried out at the device level using standard probe station based electrical characterization setup, where the measured current represents a cumulative effect of the simultaneous response of electron capture/emission events at multiple oxygen vacancy defect (trap) sites. To better characterize the individual defects in the high-κ dielectric thin film, we propose and demonstrate here the measurement and analysis of RTN at the nanoscale using a room temperature scanning tunneling microscope setup, with an effective area of interaction of the probe tip that is as small as 10 nm in diameter. Two-level and multi-level RTN signals due to single and multiple defect locations (possibly dispersed in space and energy) are observed on 4 nm HfO2 thin films deposited on n-Si (100) substrate. The RTN signals are statistically analyzed using the Factorial Hidden Markov Model technique to decode the noise contribution of more than one defect (if any) and estimate the statistical parameters of each RTN signal (i.e., amplitude of fluctuation, capture and emission time constants). Observation of RTN at the nanoscale presents a new opportunity for studies on defect chemistry, single-defect kinetics and their stochastics in thin film dielectric materials. This method allows us to characterize the fast traps with time constants ranging in the millisecond to tens of seconds range.

  4. 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

  5. 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.

  6. 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

  7. 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).

  8. 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.

  9. 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.

  10. Growth of epitaxial orthorhombic YO1.5-substituted HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Funakubo, Hiroshi

    2015-07-01

    YO1.5-substituted HfO2 thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO1.5 amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO1.5 amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO2-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO1.5 amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO2-based film helps clarify the nature of ferroelectricity in HfO2-based films (186 words/200 words).

  11. 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 μm 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 μ-wires on flexible substrates.

  12. Effect of Electrode Roughness on Electroforming in HfO2 and Defect-Induced Moderation of Electric-Field Enhancement

    NASA Astrophysics Data System (ADS)

    Nandi, Sanjoy Kumar; Liu, Xinjun; Venkatachalam, Dinesh Kumar; Elliman, Robert Glen

    2015-12-01

    The roughness of Pt electrodes is shown to have a direct impact on the electroforming characteristics of Pt /Ti /HfO2/Pt device structures. Specifically, an increase in roughness leads to a reduction in the electroforming voltage of HfO2 , an increase in the failure rate of devices, and a corresponding reduction in resistive switching reliability. A finite-element model is used to investigate the significance of local electric-field enhancement on the breakdown process. This simulation shows that high-aspect-ratio asperities can produce field enhancements of more than an order of magnitude but that the generation and redistribution of defects moderate this effect prior to dielectric breakdown. As a consequence, the effect of field enhancement is less than anticipated from the initial electric-field distribution alone. Finally, it is argued that the increase in the device failure rate with increasing electrode roughness derives partly from an increase in the film defect density and effective device area and that these effects contribute to the reduction in breakdown voltage.

  13. 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 ΔG 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.

  14. 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.

  15. Silicon surface passivation using thin HfO2 films by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Gope, Jhuma; Vandana; Batra, Neha; Panigrahi, Jagannath; Singh, Rajbir; Maurya, K. K.; Srivastava, Ritu; Singh, P. K.

    2015-12-01

    Hafnium oxide (HfO2) is a potential material for equivalent oxide thickness (EOT) scaling in microelectronics; however, its surface passivation properties particularly on silicon are not well explored. This paper reports investigation on passivation properties of thermally deposited thin HfO2 films by atomic layer deposition system (ALD) on silicon surface. As-deposited pristine film (∼8 nm) shows better passivation with <100 cm/s surface recombination velocity (SRV) vis-à-vis thicker films. Further improvement in passivation quality is achieved with annealing at 400 °C for 10 min where the SRV reduces to ∼20 cm/s. Conductance measurements show that the interface defect density (Dit) increases with film thickness whereas its value decreases after annealing. XRR data corroborate with the observations made by FTIR and SRV data.

  16. 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 ν ˜ 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.

  17. Laser damage testing of SiO2 and HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Di Giulio, M.; Alvisi, Marco; Perrone, Maria R.; Protopapa, Maria L.; Valentini, Antonio; Vasanelli, Lorenzo

    1999-09-01

    SiO2 and HfO2 thin films have been deposited on polished fused silica substrates by the ion assisted electron beam evaporation technique in different deposition conditions. The role of the assisting ion beam parameters either on the otpical and structural film properties and the film damage threshold at 308 nm has been investigated. Laser damage thresholds have been determined by the photoacoustic mirage technique.

  18. 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

  19. Resistive switching behavior of HfO2 film with different Ti doping concentrations

    NASA Astrophysics Data System (ADS)

    Guo, Tingting; Tan, Tingting; Liu, Zhengtang

    2016-02-01

    The effect of Ti doping concentration on the resistive switching (RS) properties of Ti-doped HfO2 samples was investigated. An x-ray photoelectron spectroscope (XPS) was used to analyze the effects of defects caused by Ti doping on RS performance. The doping of Ti into the HfO2 film reduced the formation energy of oxygen vacancies. As the Ti doping concentration increased, the enlarged ON/OFF ratio and reduced switching voltages were observed for HfO2 samples with lower Ti doping concentrations of 2.1% and 4.8%, whereas the increased currents in the high resistance state (HRS) with scattered distribution were observed for the film with a high Ti doping concentration of 7.9% due to the excess oxygen vacancies. The dependence of switching voltages and resistances on the Ti doping concentration was investigated. The reliability properties in terms of endurance and retention time were also measured. The switching mechanisms for the prepared samples were illustrated based on the oxygen vacancy filament model. The results indicated that an appropriate concentration of oxygen vacancies was required for the optimization of the RS performance.

  20. Enhanced performance of supported HfO2 counter electrodes for redox couples used in dye-sensitized solar cells.

    PubMed

    Yun, Sining; Pu, Haihui; Chen, Junhong; Hagfeldt, Anders; Ma, Tingli

    2014-02-01

    Mesoporous-graphitic-carbon-supported HfO2 (HfO2 -MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2 -MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2 -MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application. PMID:24399514

  1. Band alignment of HfO2/AlN heterojunction investigated by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Ye, Gang; Wang, Hong; Ji, Rong

    2016-04-01

    The band alignment between AlN and Atomic-Layer-Deposited (ALD) HfO2 was determined by X-ray photoelectron spectroscopy (XPS). The shift of Al 2p core-levels to lower binding energies with the decrease of take-off angles θ indicated upward band bending occurred at the AlN surface. Based on the angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ΔEV of 0.4 ± 0.2 eV at HfO2/AlN interface was determined by taking AlN surface band bending into account. By taking the band gap of HfO2 and AlN as 5.8 eV and 6.2 eV, respectively, a type-II band line-up was found between HfO2 and AlN.

  2. 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.

  3. Surface and interfacial reaction study of half cycle atomic layer deposited HfO2 on chemically treated GaSb surfaces

    NASA Astrophysics Data System (ADS)

    Zhernokletov, D. M.; Dong, H.; Brennan, B.; Yakimov, M.; Tokranov, V.; Oktyabrsky, S.; Kim, J.; Wallace, R. M.

    2013-04-01

    An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO2 dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

  4. Effect of atomic layer deposition growth temperature on the interfacial characteristics of HfO2/p-GaAs metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Liu, C.; Zhang, Y. M.; Zhang, Y. M.; Lv, H. L.

    2014-12-01

    The effect of atomic layer deposition (ALD) growth temperature on the interfacial characteristics of p-GaAs MOS capacitors with ALD HfO2 high-k dielectric using tetrakis(ethylmethyl)amino halfnium precursor is investigated in this study. Using the combination of capacitance-voltage (C-V) and X-ray photoelectron spectroscopy (XPS) measurements, ALD growth temperature is found to play a large role in controlling the reaction between interfacial oxides and precursor and ultimately determining the interface properties. The reduction of surface oxides is observed to be insignificant for ALD at 200 °C, while markedly pronounced for growth at 300 °C. The corresponding C-V characteristics are also shown to be ALD temperature dependent and match well with the XPS results. Thus, proper ALD process is crucial in optimizing the interface quality.

  5. First-principles investigation of H2O on HfO2 (1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Li, Lu; Huang, Xin; Zhang, Yong-Fan; Guo, Xin; Chen, Wen-Kai

    2013-01-01

    As the water to be an important precursor mater in atomic layer deposition (ALD) of preparation of HfO2 thin film, water-gas shift (WGS) reaction and heterogeneous catalysis, surface hydroxyl groups played a vital role as the reactive species that remain on the surface. First-principle calculation based on density functional (DFT) approach and generalized gradient approximation (GGA) have been utilized to investigate the molecular and dissociative adsorption of water molecule on the stoichiometric cubic HfO2 (1 1 0) surface with different sites at different coverages. The calculation employed slab geometry and periodic boundary condition with partial relaxation of atom position. Adsorption geometries, Mulliken population charges and density of states for HfO2sbnd H2O, HfO2sbnd OH, HfO2sbnd O and HfO2sbnd H at the coverage of 0.5 ML were also calculated. It was found that the adsorption energies varied a little as coverages increased, and the most favorable configuration of H2O on HfO2 surface was corresponding to the coordination of H2O via its oxygen with the surface (surface Hf atom). It was also confirmed that the coordination interaction and hydrogen bonding were the main contributions in dissociative adsorption process. For both molecular and dissociative adsorption, it has been elucidated that the surface hafnium played a key role as the active site. For dissociation reaction H2O (ads) ? H (ads) + OH (ads), the barrier energy calculated to be 17.3 kJ/mol, whereas, the second step dehydrogenation reaction OH (ads) + H (ads) ? O (ads) + 2H (ads), hardly occurred on this surface because of the high barrier energy 208.3 kJ/mol.

  6. Hydrogen doping in HfO2 resistance change random access memory

    NASA Astrophysics Data System (ADS)

    Duncan, D.; Magyari-Köpe, B.; Nishi, Y.

    2016-01-01

    The structures and energies of hydrogen-doped monoclinic hafnium dioxide were calculated using density-functional theory. The electronic interactions are described within the LDA + U formalism, where on-site Coulomb corrections are applied to the 5d orbital electrons of Hf atoms and 2p orbital electrons of the O atoms. The effects of charge state, defect-defect interactions, and hydrogenation are investigated and compared with experiment. It is found that hydrogenation of HfO2 resistance-change random access memory devices energetically stabilizes the formation of oxygen vacancies and conductive vacancy filaments through multiple mechanisms, leading to improved switching characteristic and device yield.

  7. Reliability of HfO2 metal-insulator-metal capacitors under AC stress

    NASA Astrophysics Data System (ADS)

    Kassmi, M.; Jomni, F.; Gonon, P.; Khaldi, O.; Latu-Romain, L.; Mannequin, C.; Bsiesy, A.; Basrour, S.; Yangui, B.

    2016-04-01

    The electrical reliability of HfO2 based metal-insulator-metal capacitors is investigated under AC stress voltage. The capacitance-time (C-t) and conductance-time (G-t) responses are studied for different stress amplitudes and frequencies. Time-to-breakdown is observed to strongly depend on the electrode nature. Electrical degradation is discussed via a model based on oxygen vacancy/oxygen ions generation. Defect generation is controlled by the injecting nature of electrodes. Partial recovery, and so time-to-breakdown, are controlled by the ability of electrodes to store oxygen.

  8. 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

  9. Stress and environmental shift characteristics of HfO2/SiO2 multilayer coatings

    NASA Astrophysics Data System (ADS)

    Anzellotti, J. F.; Smith, Douglas J.; Sczupak, Robert J.; Chrzan, Z. Roman

    1997-05-01

    HfO2/SiO2 polarizer coatings for 1054 nm have been produced that have low stress at explicit environmental conditions without the employment of backside stress- compensation films. In this process hafnia is condensed from a metallic melt and silica from an oxide source, both via electron-beam evaporation. Specifically, this process has been adopted for multilayer designs with stringent requirements on spectral control and wavefront distortion. Efforts to meet these requirements have prompted various investigations of coating stress and spectral behavior, especially under changing environmental conditions. Results have shown that coating stress and optical thickness vary significantly with humidity. THese quantities have been measured under both ambient air and dry nitrogen atmospheres. The effects of coating parameters on stress and environmental stability have been examined for an experimental hafnia/silica polarizer coating. The aforementioned parameters are hafnia deposition rate, oxygen pressure during hafnia deposition, and oxygen pressure during silica deposition. Results indicate a strong correlation of coating stress to oxygen pressure during the silica evaporation. Data on the aging of stress in hafnia/silica coatings will also be presented. The HfO2/SiO2 process has ben utilized in high-laser-damage- threshold coatings for the OMEGA laser system and for National Ignition Facility development coatings at the Laboratory for Laser Energetics.

  10. Electron-Injection-Assisted Generation of Oxygen Vacancies in Monoclinic HfO2

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Understanding the mechanisms of generation of oxygen vacancies in monoclinic (m )-HfO2 is important for improving and controlling its performance as an oxide layer in transistor gate stacks and in resistive random-access memory (RRAM) devices. We use ab initio calculations to investigate the mechanism of formation of Frenkel pairs of oxygen vacancies and interstitial ions in m -HfO2 under electron-injection conditions. The results demonstrate that the formation of stable pairs of neutral oxygen vacancies and interstitial oxygen ions assisted by extra electrons is thermodynamically feasible and requires overcoming activation barriers of less than 1.3 eV at preexisting O vacancies. A preexisting oxygen vacancy can act as an electron trap and facilitate the formation of an O vacancy and O interstitial ion pair nearby. The resulting O divacancy is stabilized by weak attraction between neutral vacancies, further lowering the formation energy of the defect pair. The binding energy per vacancy in larger oxygen-vacancy aggregates increases as the aggregate grows, facilitating the formation of defect pairs next to larger vacancy aggregates. These results are useful for understanding the mechanisms of oxide degradation and electroforming in RRAM cells, which can proceed through creation of new O vacancies in the vicinity of preexisting vacancies complementing vacancy aggregation via diffusion processes.

  11. Low temperature atomic layer deposited HfO2 film for high performance charge trapping flash memory application

    NASA Astrophysics Data System (ADS)

    Chen, Guoxing; Huo, Zongliang; Jin, Lei; Zhang, Dong; Zhao, Shengjie; Han, Yulong; Liu, Su; Liu, Ming

    2014-04-01

    The impact of key process parameters on the electrical characteristics of atomic layer deposited HfO2 films has been systematically studied with MHOS devices via capacitance-voltage (C-V) measurement. C-V hysteresis curves revealed that charge storage capacity is significantly enhanced with decreasing substrate temperature from 350 down to 150 °C and/or increasing purge time of the inert gas. The developed HfO2 trapping layer was also demonstrated by a MAHOS memory device. Improved memory window, fast program speed and good retention characteristics have been obtained. The study provides a reference for memory performance improvement of HfO2-based charge trap flash memory.

  12. Characterization of high-k HfO2 films prepared using chemically modified alkoxy-derived solutions

    NASA Astrophysics Data System (ADS)

    Suzuki, Kazuyuki; Kato, Kazumi

    2009-03-01

    The HfO2 films were prepared using alkoxy-derived precursor solutions. The effects of the chemical composition of precursor solutions on the microstructure development and electrical properties were investigated. The flatness and refractive index of the HfO2 films were improved by using diethanolamine-added solution. This result is considered to be due to the difference in the progress of organic decomposition and the behavior of nucleation and grain growth. The difference in the chemical composition affected the electrical properties such as leakage current and capacitance-voltage characteristics, which are related to the defects in the film and interface state.

  13. The effect of high/low permittivity in bilayer HfO2/BN resistance random access memory

    NASA Astrophysics Data System (ADS)

    Huang, Jen-Wei; Zhang, Rui; Chang, Ting-Chang; Tsai, Tsung-Ming; Chang, Kuan-Chang; Lou, J. C.; Young, Tai-Fa; Chen, Jung-Hui; Chen, Hsin-Lu; Pan, Yin-Chih; Huang, Xuan; Zhang, Fengyan; Syu, Yong-En; Sze, Simon M.

    2013-05-01

    This letter investigated the electrical characteristics of resistance random access memory (RRAM) with HfO2/BN bilayer structures. By adopting the high/low permittivity structure, we obtained the excellent device characteristics such as uniform distribution of switching voltage and more stable resistance switching properties of RRAM. The current conduction mechanism of low resistance state in the HfO2/BN device was transferred to space-charge-limited current conduction from Ohmic conduction owing to space electric effect concentrated by the high/low permittivity bilayer structures. The electric field in the bilayer can be verified by comsol simulation software.

  14. RF Micro-Electro-Mechanical Systems Capacitive Switches Using Ultra Thin Hafnium Oxide Dielectric

    NASA Astrophysics Data System (ADS)

    Zhang, Yi; Onodera, Kazumasa; Maeda, Ryutaro

    2006-01-01

    A π-type RF capacitive switch using about 45-nm-thick HfO2 dielectric layer was fabricated. High isolation performance was obtained in wide-band range when the switch was down-state. The isolation was better than -40 dB at the frequency range of 4-35 GHz. Particularly, the isolation was better than -50 dB in the frequency range of 8-12 GHz, i.e., X band. HfO2 showed excellent process compatibility with conventional microfabrication procedure. The 45-nm-thick HfO2 film was prepared using sputtering at room temperature so that it was feasible to be integrated into RF switch and other microwave circuits. The results of constant bias stressing showed that the ultra thin HfO2 had excellent reliability. The electric breakdown of HfO2 was observed, which had no apparent negative effects on the reliability of the dielectric. HfO2 dielectrics were attractive in the application of RF micro-electro-mechanical systems (MEMS) switch for new generation of low-loss high-linearity microwave circuits.

  15. 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

  16. 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.

  17. First principle simulations on the effects of oxygen vacancy in HfO2-based RRAM

    NASA Astrophysics Data System (ADS)

    Dai, Yuehua; Zhao, Yuanyang; Wang, Jiayu; Xu, Jianbin; Yang, Fei

    2015-01-01

    HfO2-based resistive random access memory (RRAM) takes advantage of oxygen vacancy (V o) defects in its principle of operation. Since the change in resistivity of the material is controlled by the level of oxygen deficiency in the material, it is significantly important to study the performance of oxygen vacancies in formation of conductive filament. Excluding effects of the applied voltage, the Vienna ab initio simulation package (VASP) is used to investigate the orientation and concentration mechanism of the oxygen vacancies based on the first principle. The optimal value of crystal orientation [010] is identified by means of the calculated isosurface plots of partial charge density, formation energy, highest isosurface value, migration barrier, and energy band of oxygen vacancy in ten established orientation systems. It will effectively influence the SET voltage, forming voltage, and the ON/OFF ratio of the device. Based on the results of orientation dependence, different concentration models are established along crystal orientation [010]. The performance of proposed concentration models is evaluated and analyzed in this paper. The film is weakly conductive for the samples deposited in a mixture with less than 4.167at.% of V o contents, and the resistive switching (RS) phenomenon cannot be observed in this case. The RS behavior improves with an increase in the V o contents from 4.167at.% to 6.25at.%; nonetheless, it is found difficult to switch to a stable state. However, a higher V o concentration shows a more favorable uniformity and stability for HfO2-based RRAM.

  18. Investigation of thermal stability and reliability of HfO2 based resistive random access memory devices with cross-bar structure

    NASA Astrophysics Data System (ADS)

    Chand, Umesh; Huang, Kuan-Chang; Huang, Chun-Yang; Ho, Chia-Hua; Lin, Chen-Hsi; Tseng, Tseung-Yuen

    2015-05-01

    The effect of the annealing treatment of a HfO2 resistive switching layer and the memory performance of a HfO2-based resistive random access memory (cross-bar structure) device were investigated. Oxygen is released from HfO2 resistive switching layers during vacuum annealing, leading to unstable resistive switching properties. This oxygen release problem can be suppressed by inserting an Al2O3 thin film, which has a lower Gibbs free energy, between the HfO2 layer and top electrode to form a Ti/Al2O3/HfO2/TiN structure. This device structure exhibited good reliability after high temperature vacuum annealing and post metal annealing (PMA) treatments. Moreover, the endurance and retention properties of the device were also improved after the PMA treatment.

  19. Comparison of ultrathin CoTiO3 and NiTiO3 high-k gate dielectrics

    NASA Astrophysics Data System (ADS)

    Pan, Tung Ming; Lei, Tan Fu; Chao, Tien Sheng

    2001-03-01

    High-k cobalt-titanium oxide (CoTiO3) and nickel-titanium oxide (NiTiO3) were formed by directly oxidizing sputtered Co/Ti and Ni/Ti film. Al/CoTiO3/Si3N4/Si and Al/NiTiO3/Si3N4/Si capacitor structures were fabricated and measured. The effective dielectric constant (k value≅45) with buffer layer for CoTiO3 is larger than that of NiTiO3. In addition, CoTiO3 depicts excellent electrical properties at the same time. This metal oxide thus appears to be a very promising high-k gate dielectric for future ultralarge scale integrated devices.

  20. Evaluation of Chemical Bonding Features and Resistance Switching Behaviors of Ultrathin Si Oxide Dielectric Sandwiched Between Pt Electrodes

    NASA Astrophysics Data System (ADS)

    Ohta, Akio; Goto, Yuta; Nishigaki, Shingo; Murakami, Hideki; Higashi, Seiichiro; Miyazaki, Seiichi

    2012-06-01

    We investigated the chemical bonding features and resistance switching properties of ultrathin Si-rich oxides sandwiched between Pt electrodes to evaluate the feasibility of SiOx-based resistance random access memories (ReRAMs). In the early stages of SiOx deposition on Pt by radio-frequency (RF) sputtering in Ar + O2 gas mixture at 300 °C, the formation of a PtOx layer at the interface between SiOx and the Pt bottom electrode was observed. This interfacial PtOx layer decreased in thickness with increasing SiOx thickness. With decreasing as-deposited SiOx thickness down to 3.3 nm, the initial electrical state changed from the high resistance state (HRS) to the low resistance state (LRS), and resistance switching behavior was observed without the forming process. To gain a better understanding of the resistance switching mechanism, especially the role of oxygen deficiency in the SiOx network, we investigated the impact of O2 annealing after SiOx deposition on the switching behavior. The resistance switching behaviors were barely detectable for the samples at O2 annealing temperatures of over 500 °C. The results imply that the oxygen vacancies in the SiOx play an important role in resistance switching.

  1. Temperature dependent interfacial and electrical characteristics during atomic layer deposition and annealing of HfO2 films in p-GaAs metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Chen, Liu; Yuming, Zhang; Yimen, Zhang; Hongliang, Lü; Bin, Lu

    2015-12-01

    We have investigated the temperature dependent interfacial and electrical characteristics of p-GaAs metal-oxide-semiconductor capacitors during atomic layer deposition (ALD) and annealing of HfO2 using the tetrakis (ethylmethyl) amino hafnium precursor. The leakage current decreases with the increase of the ALD temperature and the lowest current is obtained at 300 °C as a result of the Frenkel-Poole conduction induced leakage current being greatly weakened by the reduction of interfacial oxides at the higher temperature. Post deposition annealing (PDA) at 500 °C after ALD at 300 °C leads to the lowest leakage current compared with other annealing temperatures. A pronounced reduction in As oxides during PDA at 500 °C has been observed using X-ray photoelectron spectroscopy at the interface resulting in a proportional increase in Ga2O3. The increment of Ga2O3 after PDA depends on the amount of residual As oxides after ALD. Thus, the ALD temperature plays an important role in determining the high-k/GaAs interface condition. Meanwhile, an optimum PDA temperature is essential for obtaining good dielectric properties. Project supported by the Advance Research Project of China (No. 5130803XXXX) and the National Natural Science Foundation of China (No. 61176070).

  2. Effects of nitrogen incorporation in HfO(2) grown on InP by atomic layer deposition: an evolution in structural, chemical, and electrical characteristics.

    PubMed

    Kang, Yu-Seon; Kim, Dae-Kyoung; Kang, Hang-Kyu; Jeong, Kwang-Sik; Cho, Mann-Ho; Ko, Dae-Hong; Kim, Hyoungsub; Seo, Jung-Hye; Kim, Dong-Chan

    2014-03-26

    We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO2 thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH3 vapor (PDN) at 600 °C, an InN layer formed at the HfO2/InP interface, and ionized NHx was incorporated in the HfO2 film. We demonstrate that structural changes resulting from nitridation of HfO2/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO2/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO2/InP interfaces). Consequently, the tetragonal structure of HfO2 transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO2 and InP. During postdeposition annealing (PDA) in HfO2/InP at 600 °C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO2/InP structures at 600 °C, nitrogen incorporation in the HfO2 film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (Dit) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO2/InP increased the electron-barrier height to ∼0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V. PMID:24467437

  3. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    PubMed

    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 (μRS) 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, μRS 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

  4. 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 (μRS) 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, μRS 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

  5. Interface engineered HfO2-based 3D vertical ReRAM

    NASA Astrophysics Data System (ADS)

    Hudec, Boris; Wang, I.-Ting; Lai, Wei-Li; Chang, Che-Chia; Jančovič, Peter; Fröhlich, Karol; Mičušík, Matej; Omastová, Mária; Hou, Tuo-Hung

    2016-06-01

    We demonstrate a double-layer 3D vertical resistive random access memory (ReRAM) stack implementing a Pt/HfO2/TiN memory cell. The HfO2 switching layer is grown by atomic layer deposition on the sidewall of a SiO2/TiN/SiO2/TiN/SiO2 multilayer pillar. A steep vertical profile was achieved using CMOS-compatible TiN dry etching. We employ in situ TiN bottom interface engineering by ozone, which results in (a) significant forming voltage reduction which allows for forming-free operation in AC pulsed mode, and (b) non-linearity tuning of low resistance state by current compliance during Set operation. The vertical ReRAM shows excellent read and write disturb immunity between vertically stacked cells, retention over 104 s and excellent switching stability at 400 K. Endurance of 107 write cycles was achieved using 100 ns wide AC pulses while fast switching speed using pulses of only 10 ns width is also demonstrated. The active switching region was evaluated to be located closer to the bottom interface which allows for the observed high endurance.

  6. Orientation control and domain structure analysis of {100}-oriented epitaxial ferroelectric orthorhombic HfO2-based thin films

    NASA Astrophysics Data System (ADS)

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Shogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-04-01

    Orientation control of {100}-oriented epitaxial orthorhombic 0.07YO1.5-0.93HfO2 films grown by pulsed laser deposition was investigated. To achieve in-plane lattice matching, indium tin oxide (ITO) and yttria-stabilized zirconia (YSZ) were selected as underlying layers. We obtained (100)- and (001)/(010)-oriented films on ITO and YSZ, respectively. Ferroelastic domain formation was confirmed for both films by X-ray diffraction using the superlattice diffraction that appeared only for the orthorhombic symmetry. The formation of ferroelastic domains is believed to be induced by the tetragonal-orthorhombic phase transition upon cooling the films after deposition. The present results demonstrate that the orientation of HfO2-based ferroelectric films can be controlled in the same manner as that of ferroelectric films composed of conventional perovskite-type material such as Pb(Zr, Ti)O3 and BiFeO3.

  7. 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

  8. Characterization and application of HfO2 - SiO2 mixtures produced by ion-beam sputtering technology

    NASA Astrophysics Data System (ADS)

    Kičas, S.; BatavičiÅ«tÄ--, GintarÄ--; Juškevičius, Kestutis; Tolenis, Tomas; Drazdys, Ramutis; Buzelis, Rytis; Melninkaitis, Andrius

    2013-11-01

    In the past years the usage of mixed oxides coatings lead to an important improvement of laser damage threshold and quality of optical elements. In this study influence of post treatment procedure - ex-situ annealing - is examined in terms of quality, optical constants and laser induced damage threshold (LIDT) of mixed HfO2 and SiO2 coatings. Monolayer thin films containing different fractions of HfO2 are deposited with ion beam sputtering technology (IBS.) All samples are post annealed at different temperatures and optimal regimes are defined. Refractive index and absorption coefficient dispersion is evaluated from transmission spectra measurements. Surface roughness of all samples is characterized before and after deposition and annealing, using atomic force microscopy (AFM). Microstructural changes are identified from changes in surface topography. Further, optical resistance was characterized by 5.7 ns duration pulses for 355 nm wavelength laser radiation, performing 1-on-1 sample exposure tests with high resolution micro-focusing approach for monolayer samples and S-on-1 tests for multilayer reflectors. Morphology of damaged sites was analyzed through optical microscopy. Finally, conclusions about annealing effect for mixed HfO2 and SiO2 monolayer and multilayer coatings are made.

  9. Feature Modeling of HfO2 Atomic Layer Deposition Using HfCl4/H2O

    NASA Astrophysics Data System (ADS)

    Stout, Phillip J.; Adams, Vance; Ventzek, Peter L. G.

    2003-03-01

    A Monte Carlo based feature scale model (Papaya) has been applied to atomic layer deposition (ALD) of HfO2 using HfCl_4/H_20. The model includes physical effects of transport to surface, specular and diffusive reflection within feature, adsorption, surface diffusion, deposition and etching. Discussed will be the 3D feature modeling of HfO2 deposition in assorted features (vias and trenches). The effect of feature aspect ratios, pulse times, cycle number, and temperature on film thickness, feature coverage, and film Cl fraction (surface/bulk) will be discussed. Differences between HfO2 ALD on blanket wafers and in features will be highlighted. For instance, the minimum pulse times sufficient for surface reaction saturation on blanket wafers needs to be increased when depositing on features. Also, HCl products created during the HfCl4 and H_20 pulses are more likely to react within a feature than at the field, reducing OH coverage within the feature (vs blanket wafer) thus limiting the maximum coverage attainable for a pulse over a feature.

  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. Efficient red-emission InGaN/GaN multilayered structure on Si with surface-nitrified HfO2 film as buffer layer

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Zhang, Xuehua; Wang, Yongjin; Hane, K.; Hu, Fangren

    2016-03-01

    A four-period InGaN/GaN (8 nm/48 nm) layered structure was deposited on a Si substrate with a surface-nitrified HfO2 film as a buffer layer (5 nm). A high In concentration of In0.36Ga0.64N was obtained in the InGaN layers. Red photoluminescence of 648 nm was observed from the layered structure. The internal quantum efficiency of the red emission from the InGaN layers on the surface-nitrified HfO2/Si was 52 %, which was more than 18 times larger than that on the Si substrate without HfO2. The surface-nitrified HfO2 provides another effective buffer layer to grow the InGaN/GaN layered structure on the Si substrate.

  12. Photoluminescence of rare earth3+ doped uniaxially aligned HfO2 nanotubes prepared by sputtering with electrospun polyvinylpyrolidone nanofibers as templates

    NASA Astrophysics Data System (ADS)

    Liu, L. X.; Ma, Z. W.; Xie, Y. Z.; Su, Y. R.; Zhao, H. T.; Zhou, M.; Zhou, J. Y.; Li, J.; Xie, E. Q.

    2010-01-01

    Rare earth (RE) ions (Eu3+,Tb3+) doped uniaxially aligned HfO2 nanotubes were prepared by radio frequency sputtering with electrospun polyvinylpyrolidone (PVP) nanofiber templates. The as-sputtered samples were annealed at different temperatures (500-1000 °C) in O2 ambient in order to remove their PVP cores and make the HfO2 shells well crystallized. Morphologies and crystal configuration of the samples were investigated by optical microscope, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. The nanotubes have uniform intact structure with an average diameter of 200 nm and a wall thickness of about 25 nm. Photoluminescence (PL) properties of the RE doped nanotubes have been studied in detail. The emission peaks of the aligned HfO2:Eu and HfO2:Tb nanotubes could correspond to the D50→F7J (J =0-2) transitions of Eu3+ and the D54→F7J (J =3-6) transitions of Tb3+, respectively. The PL intensities of the HfO2:RE3+ nanotubes were higher by several orders of magnitude than that of the films. This enhancement in the PL could be ascribed to the high density of surface states of HfO2:RE3+ nanotubes.

  13. Boron nitride as two dimensional dielectric: Reliability and dielectric breakdown

    NASA Astrophysics Data System (ADS)

    Ji, Yanfeng; Pan, Chengbin; Zhang, Meiyun; Long, Shibing; Lian, Xiaojuan; Miao, Feng; Hui, Fei; Shi, Yuanyuan; Larcher, Luca; Wu, Ernest; Lanza, Mario

    2016-01-01

    Boron Nitride (BN) is a two dimensional insulator with excellent chemical, thermal, mechanical, and optical properties, which make it especially attractive for logic device applications. Nevertheless, its insulating properties and reliability as a dielectric material have never been analyzed in-depth. Here, we present the first thorough characterization of BN as dielectric film using nanoscale and device level experiments complementing with theoretical study. Our results reveal that BN is extremely stable against voltage stress, and it does not show the reliability problems related to conventional dielectrics like HfO2, such as charge trapping and detrapping, stress induced leakage current, and untimely dielectric breakdown. Moreover, we observe a unique layer-by-layer dielectric breakdown, both at the nanoscale and device level. These findings may be of interest for many materials scientists and could open a new pathway towards two dimensional logic device applications.

  14. Synthesis and electrical characterization of a MOS memory containing Si nanoparticles embedded in high-k HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Ji, Mei; Zhu, Shiwei; Tu, Hailin; Du, Jun

    2009-03-01

    The size-controlled, non-agglomerated, 5nm Si nanoparticles were fabricated in the middle of HfO2 layers using a pulsed laser ablation (PLA) system at a relatively low pressure and formed trilayer structure (HfO2/Si-nps/HfO2) on n-type Si. These high density nanoparticles (>1x1011 cm-2) were imaged with SEM. The crystallinity of HfO2 and Si nanoparticles were characterized by HRTEM. The memory effect of a Si nanoparticles floating gate memory structure consisting of HfO2 tunneling and control oxides have been investigated by means of high-frequency (1 MHz) capacitance-voltage (C-V) measurements. HRTEM study revealed that the Si nanoparticles are single crystals with average size of about 5 nm in diameter and are well distributed within the amorphous HfO2 matrix. The memory effect was observed by the hysteresis loop in the C-V curves and a high storage charge density of about 5×1011cm-2 and a large flat-band voltage shift of 4.8V have been achieved due to charging and discharging to the nanoparticles.

  15. Deposition and characterization of titanium dioxide and hafnium dioxide thin films for high dielectric applications

    NASA Astrophysics Data System (ADS)

    Yoon, Meeyoung

    The industry's demand for higher integrated circuit density and performance has forced the gate dielectric layer thickness to decrease rapidly. The use of conventional SiO2 films as gate oxide is reaching its limit due to the rapid increase in tunneling current. Therefore, a need for a high dielectric material to produce large oxide capacitance and low leakage current has emerged. Metal-oxides such as titanium dioxide (TiO2) and hafnium dioxide (HfO2) are attractive candidates for gate dielectrics due to their electrical and physical properties suitable for high dielectric applications. MOCVD of TiO2 using titanium isopropoxide (TTIP) precursor on p-type Si(100) has been studied. Insertion of a TiO x buffer layer, formed by depositing metallic Ti followed by oxidation, at the TiO2/Si interface has reduced the carbon contamination in the TiO2 film. Elemental Ti films, analyzed by in-situ AES, were found to grow according to Stranski-Krastanov mode on Si(100). Carbon-free, stoichiometric TiO2 films were successfully produced on Si(100) without any parasitic SiO2 layers at the TiO 2/Si interface. Electron-beam deposition of HfO2 films on Si(100) has also been investigated in this work. HfO2 films are formed by depositing elemental Hf on Si(100) and then oxidizing it either in O2 or O 3. XPS results reveal that with oxidation Hf(4f) peak shifts +3.45eV with 02 and +3.65eV with O3 oxidation. LEED and AFM studies show that the initially ordered crystalline Hf becomes disordered after oxidation. The thermodynamic stability of HfO2 films on Si has been studied using a unique test-bed structure of Hf/O3/Si. Post-Oxidation of Layer Deposition (POLD) has been employed to produce HfO2 films with a desired thickness. XPS results indicate that stoichiometric HfO 2 films were successfully produced using the POLD process. The investigation of the growth and thin film properties of TiO 2 and HfO2 using oxygen and ozone has laid a foundation for the application of these metal-oxides into device structures. The novel process involving the TiOx buffer layer for TiO2 and the POLD process of HfO2 have been developed as new processing methods for high dielectric applications.

  16. Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO2) thin films grown using HfO2 ceramic target

    SciTech Connect

    Aguirre, B.; Vemuri, R. S.; Zubia, David; Engelhard, Mark H.; Shutthanandan, V.; Kamala Bharathi, K.; Ramana, Chintalapalle V.

    2011-01-01

    Hafnium oxide (HfO₂) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(100) substrates under varying growth temperature (Ts). HfO₂ ceramic target has been employed for sputtering while varying the Ts from room temperature to 500⁰C during deposition. The effect of Ts on the growth and microstructure of deposited HfO₂ films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive x-ray spectrometry (EDS). The results indicate that the effect of Ts is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO₂ films. Structural characterization indicates that the HfO₂ films grown at Ts<200 ⁰C are amorphous while films grown at Ts>200 ⁰C are nanocrystalline. An amorphous-to-crystalline transition occurs at Ts=200 ⁰C. Nanocrystalline HfO₂ films crystallized in a monoclinic structure with a (-111) orientation. XPS measurements indicated the high surface-chemical quality and stoichiometric nature of the grown HfO₂ films. An interface layer (IL) formation occurs due to reaction at the HfO₂-Si interface for HfO₂ films deposited at Ts>200 ⁰C. The thickness of IL increases with increasing Ts. XPS and EDS at the HfO₂-Si cross-section indicate the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing Ts.

  17. Low-Concentration NO2 Gas Sensor Based on HfO2 Thin Films Irradiated by Ultraviolet Light

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Barin, Özlem; Özer, Metin; Acar, Selim

    2016-04-01

    In this work, we investigate the gas-sensing properties of HfO2 thin films enhanced by ultraviolet (UV) light irradiation. The films were deposited on silicon substrate by atomic layer deposition (ALD) and annealed at 800°C. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used for characterization of the samples, which revealed that the degree of crystallinity and electrical properties of the HfO2 thin films were affected by the annealing temperature. Different film thicknesses (20 nm and 10 nm) were used for gas-sensing measurements. The gas-sensing properties of the films were affected by the UV irradiation time, with improvements in sensor properties observed for samples with more than 30 min of irradiation. The maximum response was found for the 10-nm sensor annealed at 800°C. Moreover, a linear dependence on NO2 concentration was observed for the response, suggesting that the sensing layer is highly suitable for detecting NO2 gas concentrations as low as 1 ppm.

  18. Photo-, cathodo- and thermoluminescent properties of dysprosium-doped HfO2 films deposited by ultrasonic spray pyrolysis.

    PubMed

    Manríquez, R Reynoso; Góngora, J A I Díaz; Guzmán-Mendoza, J; Montalvo, T Rivera; Olguín, J C Guzmán; Ramírez, P V Cerón; García-Hipólito, M; Falcony, C

    2014-09-01

    In this work, the photoluminescent (PL), cathodoluminescent (CL) and thermoluminescent (TL) properties of hafnium oxide films doped with trivalent dysprosium ions are reported. The films were deposited on glass substrates at temperatures ranging from 300 to 600°C, using chlorides as precursor reagents. The surface morphology of films showed a veins shaped microstructure at low deposition temperatures, while at higher temperatures the formation of spherical particles was observed on the surface. X-ray diffraction showed the presence of HfO2 monoclinic phase in the films deposited at temperatures greater than 400°C. The PL and CL spectra of the doped films showed the highest emission band centered at 575nm corresponding to the transitions (4)F9/2→(6)H13/2, which is a characteristic transition of Dy(3+) ion. The greatest emission intensities were observed in samples doped with 1 atomic percent (at%) of DyCl3 in the precursor solution. Regarding the TL behavior, the glow curve of HfO2:Dy(+3) films exhibited spectrum with one broad band centered at about 150°C. The highest intensity TL response was observed on the films deposited at 500°C. PMID:25016246

  19. Geometric conductive filament confinement by nanotips for resistive switching of HfO2-RRAM devices with high performance.

    PubMed

    Niu, Gang; Calka, Pauline; Auf der Maur, Matthias; Santoni, Francesco; Guha, Subhajit; Fraschke, Mirko; Hamoumou, Philippe; Gautier, Brice; Perez, Eduardo; Walczyk, Christian; Wenger, Christian; Di Carlo, Aldo; Alff, Lambert; Schroeder, Thomas

    2016-01-01

    Filament-type HfO2-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the "OFF" state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO2 films. We report highly stable endurance of TiN/Ti/HfO2/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability. PMID:27181525

  20. Temperature dependent electron effective mass and barrier height in HfO2 based metal/oxide/metal devices

    NASA Astrophysics Data System (ADS)

    El Kamel, F.

    2015-07-01

    Electrical measurements are realized on Cu/HfO2/Pt capacitors to extract the electron effective mass in HfO2 and the barrier height at the Cu/HfO2 interface. The dominant conduction mechanisms are found to be the Schottky emission at medium voltages and the Fowler-Nordheim tunneling at high voltages. Previous research has usually been carried out by assuming a constant value for either the electron effective mass in oxide or the interfacial potential barrier height to determine the other parameter. However, in contrast to that general practice, an iterative method was proposed in the present study to determine, at the same time, the electron effective mass in HfO2 and the barrier height at the Cu/HfO2 interface without making any prior assumption about their values. The temperature dependence of these two parameters was also studied in the 298-423 K range. It is found that they strongly vary with temperature. The effective mass decreases quadratically with temperature, while the barrier height increases linearly with temperature.

  1. Geometric conductive filament confinement by nanotips for resistive switching of HfO2-RRAM devices with high performance

    PubMed Central

    Niu, Gang; Calka, Pauline; Auf der Maur, Matthias; Santoni, Francesco; Guha, Subhajit; Fraschke, Mirko; Hamoumou, Philippe; Gautier, Brice; Perez, Eduardo; Walczyk, Christian; Wenger, Christian; Di Carlo, Aldo; Alff, Lambert; Schroeder, Thomas

    2016-01-01

    Filament-type HfO2-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the “OFF” state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO2 films. We report highly stable endurance of TiN/Ti/HfO2/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability. PMID:27181525

  2. An improvement of HfO2/Ge interface by in situ remote N2 plasma pretreatment for Ge MOS devices

    NASA Astrophysics Data System (ADS)

    Chi, Xiaowei; Lan, Xiaoling; Lu, Chao; Hong, Haiyang; Li, Cheng; Chen, Songyan; Lai, Hongkai; Huang, Wei; Xu, Jianfang

    2016-03-01

    In situ remote N2 plasma pretreatment of Ge substrate before deposition of HfO2 is proved effective to reduce GeOx interlayer at the HfO2/Ge interface, resulting in a smaller capacitance equivalent oxide thickness, lower interface trap density and leakage current density for the metal/HfO2/n-Ge capacitors. However, it has no obvious impact on the metal/HfO2/p-Ge capacitors, showing a much higher interface trap density than that on n-Ge. The high equivalent permittivity of the HfO2 gate stacks (∼24.2) confirmed the removal of GeOx interlayer by N2 plasma pretreatment. In situ remote N2 plasma pretreatment is demonstrated perspective to make metal/HfO2/n-Ge MOSFET with scaling capacitance equivalent oxide thickness.

  3. Forming-Free Reversible Bipolar Resistive Switching Behavior in Al-Doped HfO2 Metal-Insulator-Metal Devices

    NASA Astrophysics Data System (ADS)

    Mahapatra, R.; Horsfall, A. B.; Wright, N. G.

    2012-04-01

    Resistive switching (RS) characteristics are investigated in fabricated Al-doped HfO2 metal-insulator-metal devices. It is proposed that oxygen vacancies in Al-doped HfO2 devices play a key role as electron trap centers, leading to the forming-free reversible bipolar resistance switching behavior. The conduction mechanism can be explained by electron trapping and detrapping from such oxygen vacancy-related traps in the Al-doped HfO2 films and is dominated by a trap-controlled space-charge-limited current (SCLC) mechanism. A large RS ratio (~106) and excellent retention characteristics are also observed at room temperature as well as at 85°C. Such devices have potential for application in nonvolatile random-access memory.

  4. Analysis of thermal stresses in HfO2/SiO2 high reflective optical coatings for high power laser applications

    NASA Astrophysics Data System (ADS)

    Gao, Chunxue; Zhao, Zhiwei; Zhu, Zhuoya; Li, Shuang; Mi, Changwen

    2015-02-01

    HfO2/SiO2 high reflective optical coatings are widely used in high power laser applications because of their high laser damage resistance and appropriate spectral performance. The residual stresses strongly influence the performance and longevity of the optical coatings. Thermal stresses are the primary components of the residual stresses. In the present work, the distribution of thermal stresses in HfO2/SiO2 high reflective optical coatings was investigated using two different computational methods: finite element method (FEM) and an analytical method based on force and moment balances and classical beam bending theory. The results by these two methods were compared and found to be in agreement with each other, demonstrating that these two methods are effective and accurate ways to predict the thermal stresses in HfO2/SiO2 optical coatings. In addition, these two methods were also used to obtain the thermal stresses in HfO2/SiO2 optical coatings with different layer number to investigate the effect of the layer number on the thermal stresses of the HfO2/SiO2 optical coatings. The results show that with the increase of the layer number, the stresses in the substrate increase, while the stresses in the respective SiO2 and HfO2 layers decrease. Besides, it was also found that the radius of curvature of the coating system decreases as the layer number increases, leading to larger bending curvature in the system.

  5. Low-Frequency Noise Analysis in HfO2/SiON Gate Stack nMOSFETs with Different Interfacial Layer Thickness

    NASA Astrophysics Data System (ADS)

    Choi, Do-Young; Baek, Rock-Hyun; Jeong, Yoon-Ha

    2011-12-01

    Low-frequency noise of HfO2/SiON gate stack nMOSFETs with different interfacial layer (IL) thickness is investigated. All devices show a typical 1/fγ-like noise with frequency exponent (γ) equal to 1 and its dominant noise mechanism is found to be number fluctuations of channel carriers. The thicker-IL devices show lower noise characteristics and trap density than that of thinner-IL devices because SiON that has lower bulk trap density than that of HfO2 acts as a major noise source in the case of thicker-IL devices.

  6. 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.

  7. 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.

  8. Elucidation of Cu Diffusion Surface and Path in Monoclinic HfO2 Conducting-Bridge Memory

    NASA Astrophysics Data System (ADS)

    Yura, S.; Yamasaki, T.; Nakada, K.; Ishii, A.; Kishida, S.; Kinoshita, K.

    It is important to specify the Cu diffusion path in the oxide layer of a Cu/oxide/Pt-structured conducting-bridge random access memory (CB-RAM), in terms of both elucidation of resistive switching mechanism and optimization of memory performance. The first-principles calculation is effective in specifying the Cu diffusion path with atomic resolution. However, reported results of first-principles calculations are based on too simplified model to depict the actual system of CB-RAM. In this paper, a periodic slab model for first-principles calculation of Cu diffusion process in HfO2-CB-RAM was proposed based on experimental results. Both Cu diffusion surface and Cu diffusion path were suggested by the first-principles calculations based on the model.

  9. 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 μA. 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.

  10. 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.

  11. 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

  12. Consideration of the formation mechanism of an Al2O3-HfO2 eutectic film on a SiC substrate

    NASA Astrophysics Data System (ADS)

    Seya, Kyosuke; Ueno, Shunkichi; Nishimura, Toshiyuki; Jang, Byung-Koog

    2016-01-01

    An Al2O3-HfO2 eutectic EBC film was prepared on a SiC substrate by using the electric furnace heating and the optical zone melting methods. All of Al2O3 phase disappeared during the heating step at a temperature below the melting point, and all of the HfO2 phase reacted with the carbon and boron, which are included in SiC bulk as sintering agents, during the heating step at a temperature below the melting point. The thermal decomposition of the SiC phase, the reduction reaction of Al2O3 phase, the vaporization of the Al2O3 component, the reduction reaction of HfO2 and the formation of the HfC phase occurred at a temperature below the melting point. However, a highly dense HfC phase was formed on the SiC substrate. A rapid heating process becomes possible by using the optical zone melting method. A solidified film that was composed of a highly dense HfC layer as the intermediate layer and the Al2O3-HfO2 eutectic structure layer as the top coat was obtained by using the optical zone melting method.

  13. Band alignment of HfO2/multilayer MoS2 interface determined by x-ray photoelectron spectroscopy: Effect of CHF3 treatment

    NASA Astrophysics Data System (ADS)

    Liu, Xinke; He, Jiazhu; Liu, Qiang; Tang, Dan; Jia, Fang; Wen, Jiao; Lu, Youming; Yu, Wenjie; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun; Pan, Jisheng; He, Zhubing; Ang, Kah-Wee

    2015-09-01

    The energy band alignment between HfO2/multilayer (ML)-MoS2 was characterized using high-resolution x-ray photoelectron spectroscopy. The HfO2 was deposited using an atomic layer deposition tool, and ML-MoS2 was grown by chemical vapor deposition. A valence band offset (VBO) of 1.98 eV and a conduction band offset (CBO) of 2.72 eV were obtained for the HfO2/ML-MoS2 interface without any treatment. With CHF3 plasma treatment, a VBO and a CBO across the HfO2/ML-MoS2 interface were found to be 2.47 eV and 2.23 eV, respectively. The band alignment difference is believed to be dominated by the down-shift in the core level of Hf 4d and up-shift in the core level of Mo 3d, or the interface dipoles, which caused by the interfacial layer in rich of F.

  14. Fabrication of BaTiO3-Based Dielectrics for Ultrathin-Layer Multilayer Ceramic Capacitor Application by a Modified Coating Approach

    NASA Astrophysics Data System (ADS)

    Tian, Zhibin; Wang, Xiaohui; Zhang, Yichi; Song, Tae-Ho; Hur, Kang Heon; Li, Longtu

    2011-02-01

    The development of multilayer ceramic capacitor (MLCC) with base metal electrode (BME) requires precise controlling of the microstructure in a very thin dielectric layer (<1 µm). In this paper, a modified coating approach for high coverage of BaTiO3 powder for further MLCC application has been developed. The well dispersed and coated BaTiO3 powders are prepared and the relative mechanism has been discussed. Furthermore, the ultrafine grained X7R dielectric ceramics were produced by both conventional mixing and modified coating methods. Compared with the conventional mixing method, the ceramics prepared by the coating approach exhibited better TCC (the temperature coefficient of capacitance) performance, with dielectric constant over 2000 and grain size below 150 nm. In addition, it is found through the coating method the content of additives can be reduced to a relatively smaller amount than that required in conventional mixing method.

  15. Chemical states and electronic structure of a HfO(-2) / Ge(001) interface

    SciTech Connect

    Seo, Kang-ill; McIntyre, Paul C.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; Saraswat, Krishna C.; /Stanford U., Elect. Eng. Dept.

    2005-05-04

    We report the chemical bonding structure and valence band alignment at the HfO{sub 2}/Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO{sub 2} film using a dilute HF-solution. We found that a very non-stoichiometric GeO{sub x} layer exists at the HfO{sub 2}/Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO{sub x} was determined to be {Delta}E{sub v} (Ge-GeO{sub x}) = 2.2 {+-} 0.15 eV, and that between Ge and HfO{sub 2}, {Delta}E{sub v} (Ge-HfO{sub 2}) = 2.7 {+-} 0.15 eV.

  16. Interface trap and oxide charge generation under negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

    SciTech Connect

    Zhu Shiyang; Nakajima, Anri; Ohashi, Takuo; Miyake, Hideharu

    2005-12-01

    The interface trap generation ({delta}N{sub it}) and fixed oxide charge buildup ({delta}N{sub ot}) under negative bias temperature instability (NBTI) of p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for {delta}N{sub it} and {delta}N{sub ot}. At the earlier stress times, {delta}N{sub it} dominates the threshold voltage shift ({delta}V{sub th}) and {delta}N{sub ot} is negligible. With increasing stress time, the rate of increase of {delta}N{sub it} decreases continuously, showing a saturating trend for longer stress times, while {delta}N{sub ot} still has a power-law dependence on stress time so that the relative contribution of {delta}N{sub ot} increases. The thermal activation energy of {delta}N{sub it} and the NBTI lifetime of pMOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.

  17. Interface trap and oxide charge generation under negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

    NASA Astrophysics Data System (ADS)

    Zhu, Shiyang; Nakajima, Anri; Ohashi, Takuo; Miyake, Hideharu

    2005-12-01

    The interface trap generation (ΔNit) and fixed oxide charge buildup (ΔNot) under negative bias temperature instability (NBTI) of p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for ΔNit and ΔNot. At the earlier stress times, ΔNit dominates the threshold voltage shift (ΔVth) and ΔNot is negligible. With increasing stress time, the rate of increase of ΔNit decreases continuously, showing a saturating trend for longer stress times, while ΔNot still has a power-law dependence on stress time so that the relative contribution of ΔNot increases. The thermal activation energy of ΔNit and the NBTI lifetime of pMOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.

  18. A high-pressure high-temperature X ray study of phase relations and polymorphism of HfO2

    NASA Astrophysics Data System (ADS)

    Tang, J.; Kai, M.; Kobayashi, Y.; Endo, S.; Shimomura, O.; Kikegawa, T.; Ashida, T.

    X ray diffraction experiments have been carried out to study the two pressure-induced phase transitions in HfO2. Angle-dispersive experiments were performed at room temperature in a diamond anvil cell using synchrotron radiation and imaging plates. Experiments at high temperature were performed with a multianvil device using the energy dispersive technique and a rotating-anode generator with a solid state detector. It was found that the monoclinic-orthorhombic I (ortho I) transition occurred around 5 GPa with a volume reduction of 3.4% and the ortho I - ortho II transition occurred at 26 GPa with a volume reduction of 9.4%. The phase boundary between the ortho I and ortho II phases above 400°C is expressed approximately by a linear equation, T(°C)=4720-300P(GPa). The kinetic limit curves gradually towards the higher pressure side at lower temperatures because of the sluggishness of the transition. The ortho II phase was identified as the cotunnite-type structure for both at high pressure and quenched samples.

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

    NASA Astrophysics Data System (ADS)

    Winkowski, P.; Marszałek, 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.

  20. 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.

  1. IR study of fundamental chemical reactions in atomic layer deposition of HfO2 with tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor

    NASA Astrophysics Data System (ADS)

    Hirose, F.; Kinoshita, Y.; Kanomata, K.; Momiyama, K.; Kubota, S.; Hirahara, K.; Kimura, Y.; Niwano, M.

    2012-07-01

    The fundamental reactions in HfO2 atomic layer deposition (ALD) with the precursors tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor on Si (1 0 0) surfaces at room temperature (RT) were studied by infrared absorption spectroscopy (IRAS) with a multiple internal reflection geometry. The IRAS results indicated that TEMAH can be adsorbed at OH sites on Si surfaces at RT. Ozone irradiation on the TEMAH-adsorbed Si surface at RT effectively removes hydroaminocarbon adsorbates introduced in the course of TEMAH adsorption, although this treatment provides no OH-group adsorption sites for TEMAH on the Si surface at RT. For further adsorption, water-vapor treatment at around 160 °C is effective in restoring the adsorption sites. The IR study suggests that the cyclic process of TEMAH adsorption and ozone treatment at RT followed by OH restoration with water vapor at a temperature of 160 °C allows continuous HfO2 deposition.

  2. Band alignment and interfacial structure of ZnO/Si heterojunction with Al2O3 and HfO2 as interlayers

    NASA Astrophysics Data System (ADS)

    Lu, Hong-Liang; Yang, Ming; Xie, Zhang-Yi; Geng, Yang; Zhang, Yuan; Wang, Peng-Fei; Sun, Qing-Qing; Ding, Shi-Jin; Wei Zhang, David

    2014-04-01

    Energy band alignment of ZnO/Si heterojunction with thin interlayers Al2O3 and HfO2 grown by atomic layer deposition has been studied using x-ray photoelectron spectroscopy. The valence band offsets of ZnO/Al2O3 and ZnO/HfO2 heterojunctions have been determined to be 0.43 and 0.22 eV, respectively. Accordingly, the band alignment ZnO/Si heterojunction is then modified to be 0.34 and 0.50 eV through inserting a thin Al2O3 and HfO2 layer, respectively. The feasibility to tune the band structure of ZnO/Si heterojunction by selecting a proper interlayer shows great advantage in improving the performance of the ZnO-based optoelectronic devices.

  3. Differential Light Addressable Potentiometric Sensor with Poly(vinyl chloride) and HfO2 Membranes for pH Sensors

    NASA Astrophysics Data System (ADS)

    Lue, Cheng-En; Lai, Chao-Sung; Wang, Jer-Chyi; Wu, Ching-Mie; Yang, Chia-Ming

    2010-04-01

    In this paper, a differential measurement setup for the light addressable potentiometric sensor (LAPS) is proposed. The LAPS with a HfO2 layer as the sensing membrane was used, and different weight percentages of DNP/(PVC+DNP) [DNP: dinonylphtalate, PVC: poly(vinyl chloride)] membrane were cast on the surface of HfO2-LAPS. The pH sensitivity can be decreased from 58.6 to 24.5 mV/pH by using 60 wt % PVC cocktail. Then, the pH sensitivity measured through a differential circuit was 30.1 mV/pH, showing high potential for replacing the function of a conventional reference electrode as an ion-sensitive field-effect transistor (ISFET)/reference field-effect transistor (REFET) pair. In addition, to confirm the output signal of the two substrate electrodes, a specific measurement setup was used.

  4. Intermixing between HfO2 and GeO2 films deposited on Ge(001) and Si(001): Role of the substrate

    NASA Astrophysics Data System (ADS)

    Soares, G. V.; Krug, C.; Miotti, L.; Bastos, K. P.; Lucovsky, G.; Baumvol, I. J. R.; Radtke, C.

    2011-03-01

    Thermally driven atomic transport in HfO2/GeO2/substrate structures on Ge(001) and Si(001) was investigated in N2 ambient as function of annealing temperature and time. As-deposited stacks showed no detectable intermixing and no instabilities were observed on Si. On Ge, loss of O and Ge was detected in all annealed samples, presumably due to evolution of GeO from the GeO2/Ge interface. In addition, hafnium germanate is formed at 600 °C. Our data indicate that at 500 °C and above HfO2/GeO2 stacks are stable only if isolated from the Ge substrate.

  5. Dependence of Polarization and Dielectric response on Epitaxial Strain in (BaxSr1-x)TiO3 Ultrathin Films from First-Principles

    NASA Astrophysics Data System (ADS)

    Bin-Omran, Saad

    2012-02-01

    A first-principles-derived schemes is used to use a first-principles-derived technique to construct the temperature-versus-misfit strain phase diagrams for the whole BST composition rang (i.e., x=0.00,0.20,0.40,0.60,0.80,1.00). Moreover, we investigate the dependence of their dielectric and ferroelectric properties on the strain and the concentration. Our results reveal that the predicated phase diagrams show a topology similar to those calculated by Shirokov et. al. Phy. Rev. B. 79 144118 (2009) with quantitative discrepancies that will be revealed and explained. Our results also indicate that in-plane strain increases (respectively, decreases) the in-plane (respectively, out-of-plane) dielectric constants. Furthermore, the out-of-plane component of dielectric permittivity ɛ33 enhances with lowering x in (BaxSr1-x)TiO3 films. We hope that our results will be benefits to many scientists and will lead to new strategies for material design.

  6. Influence of Si/SiO 2 interface properties on electrical performance and breakdown characteristics of ultrathin stacked oxide/nitride dielectric films

    NASA Astrophysics Data System (ADS)

    Lee, Yi-Mu; Wu, Yider

    2008-05-01

    In this work, the influence of Si/SiO 2 interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO 2 interface evidenced by less negative Vt shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C- V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.

  7. Dielectric Engineering of a Boron Nitride/Hafnium Oxide Heterostructure for High-Performance 2D Field Effect Transistors.

    PubMed

    Zou, Xuming; Huang, Chun-Wei; Wang, Lifeng; Yin, Long-Jing; Li, Wenqing; Wang, Jingli; Wu, Bin; Liu, Yunqi; Yao, Qian; Jiang, Changzhong; Wu, Wen-Wei; He, Lin; Chen, Shanshan; Ho, Johnny C; Liao, Lei

    2016-03-01

    A unique design of a hexagonal boron nitride (h-BN)/HfO2 dielectric heterostructure stack is demonstrated, with few-layer h-BN to alleviate the surface optical phonon scattering, followed by high-κ HfO2 deposition to suppress Coulombic impurity scattering so that high-performance top-gated two-dimensional semiconductor transistors are achieved. Furthermore, this dielectric stack can also be extended to GaN-based transistors to enhance their performance. PMID:26762171

  8. Low temperature formation of higher-k cubic phase HfO2 by atomic layer deposition on GeOx/Ge structures fabricated by in-situ thermal oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, R.; Huang, P.-C.; Taoka, N.; Yokoyama, M.; Takenaka, M.; Takagi, S.

    2016-02-01

    We have demonstrated a low temperature formation (300 °C) of higher-k HfO2 using atomic layer deposition (ALD) on an in-situ thermal oxidation GeOx interfacial layer. It is found that the cubic phase is dominant in the HfO2 film with an epitaxial-like growth behavior. The maximum permittivity of 42 is obtained for an ALD HfO2 film on a 1-nm-thick GeOx form by the in-situ thermal oxidation. It is suggested from physical analyses that the crystallization of cubic phase HfO2 can be induced by the formation of six-fold crystalline GeOx structures in the underlying GeOx interfacial layer.

  9. Novel integration of ultrathin Al2O3 with low-k dielectric as bilayer liner for capacitance optimization and stress mitigation in Cu through-silicon-via

    NASA Astrophysics Data System (ADS)

    Zhang, Lin; Li, Hong Yu; Shang, Yang; Yoo, Woosik; Yu, Hao; Tan, Chuan Seng

    2016-04-01

    Through-silicon-via (TSV) used in three-dimensional (3D) stacked dies must present small electrical parasitic, such as capacitance, to allow for low latency signal transmission. Stable TSV capacitance is desired to overcome the spatial circuit performance variation caused by non-uniform hot-spot heating. In this work, a novel combination of low-k with ultrathin Al2O3 bilayer liner is successfully integrated in the TSV. The TSV capacitance is reduced by ˜26% as compared to plasma-enhanced tetrahydrothosilicate (PETEOS) oxide liner. Stable TSV capacitance within the operating voltage of interest (˜0-5 V) is achieved by operating the TSV in a stable accumulation capacitance region. The positive shift in the flat-band voltage (ΔV FB = +19 V) is achieved by utilizing Al2O3-induced negative fixed charge (|Q f| = 1.3 × 1012 cm-2) at the Si/low-k interface. Leakage current density of the bilayer liner is improved to a level comparable with the PETEOS oxide liner post annealing [forming gas (N2/H2) at 350 °C for 2 h or 400 °C for 0.5 h]. Low-k material with a smaller elastic modulus improves the thermo-mechanical stress exerted on the surrounding Si substrate compared with PETEOS oxide.

  10. Impacts of Ti on electrical properties of Ge metal-oxide-semiconductor capacitors with ultrathin high- k LaTiON gate dielectric

    NASA Astrophysics Data System (ADS)

    Xu, H. X.; Xu, J. P.; Li, C. X.; Chan, C. L.; Lai, P. T.

    2010-06-01

    Ge Metal-Oxide-Semiconductor (MOS) capacitors with LaON gate dielectric incorporating different Ti contents are fabricated and their electrical properties are measured and compared. It is found that Ti incorporation can increase the dielectric permittivity, and the higher the Ti content, the larger is the permittivity. However, the interfacial and gate-leakage properties become poorer as the Ti content increases. Therefore, optimization of Ti content is important in order to obtain a good trade-off among the electrical properties of the device. For the studied range of the Ti/La2O3 ratio, a suitable Ti/La2O3 ratio of 14.7% results in a high relative permittivity of 24.6, low interface-state density of 3.1×1011 eV-1 cm-2, and relatively low gate-leakage current density of 2.0×10-3 A cm-2 at a gate voltage of 1 V.

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

    NASA Astrophysics Data System (ADS)

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-12-01

    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.

  12. 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

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

    PubMed

    Xu, Toby; Tekes, Coskun; Degertekin, F

    2014-12-01

    Use of high-κ 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

  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-κ 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. Effect of O2 post-deposition anneals on the properties of ultra-thin SiOx/ZrO2 gate dielectric stacks

    NASA Astrophysics Data System (ADS)

    Houssa, M.; Naili, M.; Zhao, C.; Bender, H.; Heyns, M. M.; Stesmans, A.

    2001-01-01

    The effect of post-deposition anneal in O2 at different temperatures (500-700 °C) on the microstructure and electrical properties of SiOx/ZrO2 gate dielectric stacks is investigated. It is shown that the as-deposited ZrO2 layers are partly amorphous and crystallize after post-deposition anneal. From the analysis of high-frequency capacitance-voltage (C-V) characteristics, positive (negative) fixed charge is found in the as-deposited layer when Al (Au) electrodes are used. Furthermore, positive charge is generated in the gate stack and the density of interface states is increased during post-deposition anneal in O2. Both positive charge and interface state density can be greatly reduced by an additional post-metallization anneal in H2 at low temperature (400 °C). The dielectric constant of the gate stack presents a large increase after O2 post-deposition anneal at 700 °C, which may be attributed to the partial transformation of the silicon oxide interfacial layer into a Zr silicate. The leakage current through the gate stack is reduced by several orders of magnitude after O2 annealing, consistent with the increase in SiOx layer thickness, as well as the reduction in bulk trap density revealed by the reduced hysteresis effect observed in the C-V characteristics. The temperature dependence of the current density through the gate stack is also reduced after the post-deposition anneal in O2, which is attributed to the reduction in the trap-assisted tunnelling contribution to the leakage current.

  16. Characterization of Ultrathin Ta-oxide Films Formed on Ge(100) by ALD and Layer-by-Layer Methods

    NASA Astrophysics Data System (ADS)

    Mishima, K.; Murakami, H.; Ohta, A.; Sahari, S. K.; Fujioka, T.; Higashi, S.; Miyazaki, S.

    2013-03-01

    Atomic layer deposition (ALD) and Layer-by-Layer deposition of Ta-oxide films on Ge(100) with using tris (tert-butoxy) (tert-butylimido) tantalum have been studied systematically. From the analysis of the chemical bonding features of the interface between TaOx and Ge(100) using x-ray photoelectron spectroscopy (XPS), Ge atom diffusion into the Ta oxide layer and resultant TaGexOy formation during deposition at temperatures higher than 200°C were confirmed. Also, we have demonstrated that nanometer-thick deposition of Tantalum oxide as an interfacial layer effectively suppresses the formation of GeOx in the HfO2 ALD on Ge. By the combination of TaOx pre-deposition on Ge(100) and subsequent ALD of HfO2, a capacitance equivalent thickness (CET) of 1.35 nm and relative dielectric constant of 23 were achieved.

  17. Multi-layer high- κ interpoly dielectric for floating gate flash memory devices

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; He, Wei; Chan, Daniel S. H.; Cho, Byung Jin

    2008-04-01

    We present a systematic simulation and experimental study of tunneling leakage current of the interpoly dielectric (IPD) layer in a floating gate (FG) type flash memory. IPD layers with different structural and material combinations such as HfLaO and 4% Tb-doped HfO 2 were studied. It is shown that compared with a conventional Al 2O 3-HfO 2-Al 2O 3 high-low-high barrier structure, the HfO 2-Al 2O 3-HfO 2 multilayer IPD stack with a low-high-low barrier structure has a lower leakage current due to the longer effective electron tunneling distance. Results also show that multilayer IPD structure has advantage of better thermal stability compared to the single layer IPD. Further work with simulations and experiments results suggest that the presence of a thin interfacial layer between polysilicon FG and IPD can increase the magnitude of leakage current by two or three orders. Nitridation of polysilicon floating gate reduced the leakage current by around two orders of magnitude at a constant equivalent oxide thickness. This is due to the elimination of the interfacial layer between polysilicon and high- κ IPD.

  18. On the mechanisms of cation injection in conducting bridge memories: The case of HfO2 in contact with noble metal anodes (Au, Cu, Ag)

    NASA Astrophysics Data System (ADS)

    Saadi, M.; Gonon, P.; Vallée, C.; Mannequin, C.; Grampeix, H.; Jalaguier, E.; Jomni, F.; Bsiesy, A.

    2016-03-01

    Resistance switching is studied in HfO2 as a function of the anode metal (Au, Cu, and Ag) in view of its application to resistive memories (resistive random access memories, RRAM). Current-voltage (I-V) and current-time (I-t) characteristics are presented. For Au anodes, resistance transition is controlled by oxygen vacancies (oxygen-based resistive random access memory, OxRRAM). For Ag anodes, resistance switching is governed by cation injection (Conducting Bridge random access memory, CBRAM). Cu anodes lead to an intermediate case. I-t experiments are shown to be a valuable tool to distinguish between OxRRAM and CBRAM behaviors. A model is proposed to explain the high-to-low resistance transition in CBRAMs. The model is based on the theory of low-temperature oxidation of metals (Cabrera-Mott theory). Upon electron injection, oxygen vacancies and oxygen ions are generated in the oxide. Oxygen ions are drifted to the anode, and an interfacial oxide is formed at the HfO2/anode interface. If oxygen ion mobility is low in the interfacial oxide, a negative space charge builds-up at the HfO2/oxide interface. This negative space charge is the source of a strong electric field across the interfacial oxide thickness, which pulls out cations from the anode (CBRAM case). Inversely, if oxygen ions migration through the interfacial oxide is important (or if the anode does not oxidize such as Au), bulk oxygen vacancies govern resistance transition (OxRRAM case).

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

    NASA Astrophysics Data System (ADS)

    Marszałek, Konstanty; Winkowski, Paweł; 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.

  20. Low-cost bidirectional selector based on Ti/TiO2/HfO2/TiO2/Ti stack for bipolar RRAM arrays

    NASA Astrophysics Data System (ADS)

    Li, Yingtao; Li, Rongrong; Yuan, Peng; Gao, Xiaoping; Chen, Enzi

    2015-12-01

    In this paper, a low-cost Ti/TiO2/HfO2/TiO2/Ti stack structure is proposed as a selector for bipolar resistive random access memory (RRAM) cross-bar array applications. We demonstrate reproducible resistive switching characteristics with significant nonlinearity and good uniformity in the one selector and one resistor (1S1R) structure device that integrate the bidirectional selector with a bipolar Pt/Ti/HfO2/Pt RRAM device. These results provide a good point of reference for evaluating the potential low-cost applications in bipolar RRAM cross-bar array.

  1. 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 μm 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/μm, transconductance (Gm) of 0.84 mS/μm, 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/μm and 1.2 mS/μm, respectively.

  2. The dispersion in accumulation at InGaAs-based metal/oxide/semiconductor gate stacks with a bi-layered dielectric structure

    NASA Astrophysics Data System (ADS)

    Krylov, Igor; Ritter, Dan; Eizenberg, Moshe

    2015-08-01

    InGaAs gate stacks comprising the moderate dielectric constant (k) Al2O3 have a significantly lower dispersion in accumulation in comparison to stacks with the high-k HfO2 of the same physical thickness. As a result, a HfO2/Al2O3 bi-layer structure seems attractive in terms of both high effective dielectric constant and low dispersion in accumulation. The influence of Al2O3 thickness on the dispersion was investigated in metal/HfO2/Al2O3/InGaAs gate stacks with a fixed overall dielectric thickness. An effective suppression of the dispersion with the increase of the Al2O3 thickness was observed. However, the Al2O3 thickness required for passivation of the dispersion in accumulation was significantly higher in comparison to both the border traps related tunneling distance in Al2O3 and the minimal thickness required for the Al2O3/InGaAs band offset stabilization. The phenomenon can be explained by the lower dielectric constant of Al2O3 film (compared to the subsequently deposited HfO2 layer), where Al2O3 dielectric constant dependence on the film thickness enhances the dispersion intensity. As a result, the guidelines for the passivation layer engineering are: maximization of both majority carriers band offsets and of the dielectric constant of the passivation layer.

  3. 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

  4. Insights into thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks and their suppressed reaction with atomically thin AlOx interlayers

    NASA Astrophysics Data System (ADS)

    Ogawa, Shingo; Asahara, Ryohei; Minoura, Yuya; Sako, Hideki; Kawasaki, Naohiko; Yamada, Ichiko; Miyamoto, Takashi; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2015-12-01

    The thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that 18O-tracers composing the GeO2 underlayers diffuse within the HfO2 overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO2 also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO2 surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlOx interlayers between the HfO2 and GeO2 layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.

  5. 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.

  6. 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

    2015-05-01

    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.

  7. High-dose neutron irradiation performance of dielectric mirrors

    DOE PAGESBeta

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

    2015-05-01

    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 microscopymore » (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. Lastly, the ultimate goal of this work is the provide insight into the radiation-induced failure mechanisms of these mirrors.« less

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

    PubMed

    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 ~10(6) 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

  9. Lateral GaN nanowire prepared by using two-step TMAH wet etching and HfO2 sidewall spacer

    NASA Astrophysics Data System (ADS)

    Im, Ki-Sik; Won, Chul-Ho; Vodapally, Sindhuri; Son, Dong-Hyeok; Jo, Young-Woo; Park, YoHan; Lee, Jae-Hoon; Lee, Jung-Hee

    2016-05-01

    The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the <11 2 bar0> direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (11 2 bar0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4° when etched along the <1 1 bar00> direction, which is corresponding to the (1 1 bar01) plane. The GaN lateral nanowires with two different types of cross-sections, Ω-shape which is connected to underlying thick buffer layer through very narrow neck region and rectangle shape which is completely separated from underlying buffer layer, were realized with second lateral TMAH wet etching along the <11 2 bar0> direction and by using the atomic layer deposited (ALD) HfO2 layer as a sidewall spacer. The shape is dependent on both the height of the second dry-etched GaN sidewall below the HfO2 spacer and the second wet etching time in TMAH solution. It was found that the dangling bond density at the surface of the crystal plane is responsible for the strong lateral anisotropic etching property of the GaN layer in TMAH solution.

  10. 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

  11. In situ atomic layer deposition study of HfO2 growth on NH4OH and atomic hydrogen treated Al0.25Ga0.75N

    NASA Astrophysics Data System (ADS)

    Qin, Xiaoye; Brennan, Barry; Dong, Hong; Kim, Jiyoung; Hinkle, Christopher L.; Wallace, Robert M.

    2013-06-01

    The atomic layer deposition (ALD) of HfO2 on the native oxide, NH4OH, and atomic hydrogen treated Al0.25Ga0.75N surface was studied using in situ X-ray photoelectron spectroscopy (XPS), after each individual "half cycle" of the ALD process. During the deposition process, minimal change in the chemical states of Ga and Al is detected, with no evidence of interfacial oxide generation. The initial HfO2 growth rate on the native oxide Al0.25Ga0.75N surface is very low, however, exposure of the Al0.25Ga0.75N surface to atomic hydrogen decreases the concentration of carbon and oxygen and enhances the HfO2 growth rate.

  12. 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.

  13. A study on HfO2 RRAM in HRS based on I-V and RTN analysis

    NASA Astrophysics Data System (ADS)

    Puglisi, Francesco M.; Pavan, Paolo; Padovani, Andrea; Larcher, Luca

    2014-12-01

    This paper presents a statistical characterization of random telegraph noise (RTN) in hafnium-oxide-based resistive random access memories (RRAMs) in high resistive state (HRS). Complex RTN signals are analyzed exploiting a Factorial Hidden Markov Model (FHMM) approach, which allows to derive the statistical properties of the RTN signals, directly related to the physical properties of the traps responsible for the multi-level RTN measured in these devices. Noise characteristics in different reset conditions are explored through consecutive switching cycles. Noise spectral analysis is also performed to fully support the investigation. An RRAM compact model is also exploited to estimate the physical properties of the conductive filament and of the dielectric barrier from simple I-V data. These tools are combined together to prove the existence of a direct statistical relation between the reset conditions, the volume of the dielectric barrier created during the reset operation and the average number of active traps contributing to the RTN.

  14. 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.

  15. Ultrathin Dielectric Oxide Films On Silicon

    DOEpatents

    Klemperer, Walter G.; Lee, Jason; Mikalsen, Erik A.; Payne, David A.

    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.

  16. Synthesis, integration, and characterization of metal oxide films as alternative gate dielectric materials

    NASA Astrophysics Data System (ADS)

    Lin, You-Sheng

    ZrO2 and HfO2 were investigated in this study to replace SiO2 as the potential gate dielectric materials in metal-oxide-semiconductor field effect transistors. ZrO2 and HfO2 films were deposited on p-type Si (100) wafers by an atomic layer chemical vapor deposition (ALCVD) process using zirconium (IV) t-butoxide and hafnium (IV) t-butoxide as the metal precursors, respectively. Oxygen was used alternatively with these metal alkoxide precursors into the reactor with purging and evacuation in between. The as-deposited ZrO2 and HfO2 films were stoichiometric and uniform based on X-ray photoemission spectroscopy and ellipsometry measurements. X-ray diffraction analysis indicated that the deposited films were amorphous, however, the high-resolution transmission electron microscopy showed an interfacial layer formation on the silicon substrate. Time-of-flight secondary ion mass spectrometry and medium energy ion scattering analysis showed significant intermixing between metal oxides and Si, indicating the formation of metal silicates, which were confirmed by their chemical etching resistance in HF solutions. The thermal stability of ZrO2 and HfO2 thin films on silicon was examined by monitoring their decomposition temperatures in ultra-high vacuum, using in-situ synchrotron radiation ultra-violet photoemission spectroscopy. The as-deposited ZrO2 and HfO2 thin films were thermally stable up to 880°C and 950°C in vacuum, respectively. The highest achieveable dielectric constants of as-deposited ZrO 2 and HfO2 were 21 and 24, respectively, which were slightly lower than the reported dielectric constants of bulk ZrO2 and HfO 2. These slight reductions in dielectric constants were attributed to the formation of the interfacial metal silicate layers. Very small hysteresis and interface state density were observed for both metal oxide films. Their leakage currents were a few orders of magnitude lower than that of SiO 2 at the same equivalent oxide thickness. NMOSFETs were also fabricated with the as-deposited metal oxide films, and reasonable ID-V D and IG-VG results were obtained. The electron mobilities were high from devices built using a plasma etching process to pattern the metal oxide films. However, they can be degraded if an HF wet etching process was used due to the large contact resistences. Upon oxygen annealing, the formation of SiOx at the interface improved the thermal stability of the as-deposited metal oxide films, however, lower overall dielectric constant and higher leakage current were observed. Upon ammonia annealing, the formation of SiOxNy improved not only the thermal stability but also reduced the leakage current. However, the overall dielectric constant of the film was still reduced due to the formation of the additional interfacial layer.

  17. Improvement in the Cumulative Failure Distribution of High-k Dielectric Subjected to Nanoscale Stress by D2 Post-Deposition Annealing

    NASA Astrophysics Data System (ADS)

    Wu, You-Lin; Huang, Chiung-Yi; Liang, Cheng-Hsun

    2009-11-01

    By taking advantage of the small contact area of the conductive atomic force microscopy (CAFM) tip with the sample surface, and the powerful measurement capability of the semiconductor parameter analyzer, a nanoscale stress was applied to the atomic-layer-deposited (ALD) HfO2 high-k dielectrics prepared with N2, D2, and no post-deposition anneal (PDA), respectively. The statistical breakdown behavior of ALD HfO2 under nanoscale stresses was determined and is presented in this paper. It is evident that the cumulative failure distribution of breakdown voltage of high-k dielectrics under nanoscale CVS basically follows the Weibull statistics. We also found that the ALD HfO2 prepared with D2 PDA showed an obvious improvement in cumulative failure distribution when compared with those prepared with N2 PDA and no PDA. The result indicates that D2 PDA can substantially suppress the generation of defects during the application of nanoscale stress and improve the reliability of high-k dielectrics.

  18. High-k dielectrics on n-Al0.25Ga0.75N via atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Nepal, N.; Garces, N. Y.; Meyer, D.; Anderson, T. J.; Hite, J. K.; Mastro, M. A.; Eddy, C. R., Jr.

    2012-02-01

    AlGaN/GaN and AlInN/GaN high-electron-mobility transistors (HEMTs) are promising devices for high-temperature and high-power electronics applications. A key issue with these devices is the high gate leakage current, particularly for enhancement-mode HEMTs. There has been an increased interest in developing high quality gate insulators to reduce gate leakage current. Al2O3 and HfO2 layers (21nm thick)were deposited via atomic layer deposition on n-Al0.25Ga0.75N pretreated with one of two different surface preparations, H2O2:H2SO4 (1:5) (piranha) or HF:H2O (1:3). Dielectrics were characterized using spectroscopic ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy (AFM), and capacitance-voltage (C-V) measurements. AFM shows that Al2O3 and HfO2 layers are continuous and uniform in thickness on both HF and piranha pretreated surfaces. However, C-V measurement shows smaller (15%) hysteresis for HF pretreated samples. The estimated dielectric constants (ɛ) are 9 and 18 for Al2O3 and HfO2 on HF pretreated surfaces, respectively, in general agreement with theoretical values of 9 and 25. Al2O3 layers on Al0.25Ga0.75N exhibited a lower leakage (7x10-8 A/cm^2 at 5 V) current and higher forward breakdown voltage of 7.5 MV/cm compared to that of HfO2 layer. The higher breakdown voltage and lower leakage current for Al2O3 is due to larger conduction band offset with Al0.25Ga0.75N.

  19. Atomic layer deposition for fabrication of HfO2/Al2O3 thin films with high laser-induced damage thresholds.

    PubMed

    Wei, Yaowei; Pan, Feng; Zhang, Qinghua; Ma, Ping

    2015-01-01

    Previous research on the laser damage resistance of thin films deposited by atomic layer deposition (ALD) is rare. In this work, the ALD process for thin film generation was investigated using different process parameters such as various precursor types and pulse duration. The laser-induced damage threshold (LIDT) was measured as a key property for thin films used as laser system components. Reasons for film damaged were also investigated. The LIDTs for thin films deposited by improved process parameters reached a higher level than previously measured. Specifically, the LIDT of the Al2O3 thin film reached 40 J/cm(2). The LIDT of the HfO2/Al2O3 anti-reflector film reached 18 J/cm(2), the highest value reported for ALD single and anti-reflect films. In addition, it was shown that the LIDT could be improved by further altering the process parameters. All results show that ALD is an effective film deposition technique for fabrication of thin film components for high-power laser systems. PMID:25852341

  20. Near-ultraviolet absorption-annealing effects in HfO2 thin films subjected to continuous-wave laser irradiation at 355 nm

    NASA Astrophysics Data System (ADS)

    Papernov, S.; Kozlov, A. A.; Oliver, J. B.; Kessler, T. J.; Marozas, B.

    2013-11-01

    Hafnium oxide is the most frequently used high-index material in multilayer thin-film coatings for high-power laser applications ranging from near-infrared to near-ultraviolet. Absorption in this high-index material is also known to be responsible for nanosecond-pulse laser-damage initiation in multilayers. In this work, modification of the near-ultraviolet absorption of HfO2 monolayer films subjected to irradiation by continuous-wave (cw) 355-nm or 351-nm laser light focused to produce power densities of the order of ~100 kW/cm2 is studied. Up to a 70% reduction in absorption is found in the areas subjected to irradiation. Temporal behavior of absorption is characterized by a rapid initial drop on the few-tens-of-seconds time scale, followed by a longer-term decline to a steady-state level. Absorption maps generated by photothermal heterodyne imaging confirm the permanent character of the observed effect. Nanosecond-pulse, 351-nm and 600-fs, 1053-nm laser-damage tests performed on these cw laser-irradiated areas confirm reduction of absorption by measuring up to 25% higher damage thresholds. We discuss possible mechanisms responsible for near-ultraviolet absorption annealing and damage-threshold improvement resulting from irradiation by near-ultraviolet cw laser light.

  1. Annealing Effect of Al2O3 Tunnel Barriers in HfO2-Based ReRAM Devices on Nonlinear Resistive Switching Characteristics.

    PubMed

    Park, Sukhyung; Cho, Kyoungah; Jung, Jungwoo; Kim, Sangsig

    2015-10-01

    In this study, we demonstrate the enhancement of the nonlinear resistive switching characteristics of HfO2-based resistive random access memory (ReRAM) devices by carrying out thermal annealing of Al2O3 tunnel barriers. The nonlinearity of ReRAM device with an annealed Al2O3 tunnel barrier is determined to be 10.1, which is larger than that of the ReRAM device with an as-deposited Al2O3 tunnel barrier. From the electrical characteristics of the ReRAM devices with as-deposited and annealed Al2O3 tunnel barriers, it reveals that there is a trade-off relationship between nonlinearity in low-resistance state (LRS) current and the ratio of the high-resistance state (HRS) and the LRS. The enhancement of nonlinearity is attributed to a change in the conduction mechanism in the LRS of the ReRAM after the annealing. While the conduction mechanism before the annealing follows Ohmic conduction, the conduction of the ReRAM after the annealing is controlled by a trap-controlled space charge limited conduction mechanism. Additionally, the annealing of the Al2O3 tunnel barriers is also shown to improve the endurance and retention characteristics. PMID:26726373

  2. Stabilization of the high-k tetragonal phase in HfO2: The influence of dopants and temperature from ab initio simulations

    NASA Astrophysics Data System (ADS)

    Fischer, Dominik; Kersch, Alfred

    2008-10-01

    By means of ab initio simulations we investigate the influence of dopants (Si, C, Ge, Sn, Ti, and Ce) on the transition from the monoclinic to the tetragonal phase in HfO2. In this study we focus first on the internal energy only, an approach common to ab initio simulations. In the second step we go beyond this approach in considering the Helmholtz free energy by additionally taking into account the contribution of the phonon density of states. Finally we discuss the change in transition temperature in the regime of thin films based on an empirical model. We find that both the contributions of the internal energy and phonons can be understood in terms of a model relying on the ionic radius of the dopants. Among the investigated dopants silicon is identified to promote the tetragonal phase most efficiently. The effectiveness of the various dopants is compared on the basis of a qualitative phase diagram for doping concentrations up to ˜12%.

  3. The effect of a Ta oxygen scavenger layer on HfO2-based resistive switching behavior: thermodynamic stability, electronic structure, and low-bias transport.

    PubMed

    Zhong, Xiaoliang; Rungger, Ivan; Zapol, Peter; Nakamura, Hisao; Asai, Yoshihiro; Heinonen, Olle

    2016-03-14

    Reversible resistive switching between high-resistance and low-resistance states in metal-oxide-metal heterostructures makes them very interesting for applications in random access memories. While recent experimental work has shown that inserting a metallic "oxygen scavenger layer" between the positive electrode and oxide improves device performance, the fundamental understanding of how the scavenger layer modifies the heterostructure properties is lacking. We use density functional theory to calculate thermodynamic properties and conductance of TiN/HfO2/TiN heterostructures with and without a Ta scavenger layer. First, we show that Ta insertion lowers the formation energy of low-resistance states. Second, while the Ta scavenger layer reduces the Schottky barrier height in the high-resistance state by modifying the interface charge at the oxide-electrode interface, the heterostructure maintains a high resistance ratio between high- and low-resistance states. Finally, we show that the low-bias conductance of device on-states becomes much less sensitive to the spatial distribution of oxygen removed from the HfO2 in the presence of the Ta layer. By providing a fundamental understanding of the observed improvements with scavenger layers, we open a path to engineer interfaces with oxygen scavenger layers to control and enhance device performance. In turn, this may enable the realization of a non-volatile low-power memory technology with concomitant reduction in energy consumption by consumer electronics and offering significant benefits to society. PMID:26902598

  4. Field dependent electrical conduction in HfO2/SiO2 gate stack for before and after constant voltage stressing

    NASA Astrophysics Data System (ADS)

    Sahoo, S. K.; Misra, D.

    2011-10-01

    The electrical conduction mechanisms contributing to the leakage current at different field regions and different temperatures have been studied in this work. The current-voltage (I-V) measurement of TiN/HfO2/SiO2/P-Si nMOS capacitor in the temperature range from 25 °C to 125 °C, taken before stressing and in the temperature range of 25 °C to 65 °C after constant voltage stressing (CVS) at 3 V suggests that the Poole-Frenkel mechanism is the dominant conduction mechanism in the high field region. It was also observed that in the low electric field region Ohmic conduction is the dominant mechanism. Trap energy level (φt) of 0.36 eV, obtained from the Poole-Frenkel mechanism indicates that the defect is oxygen-related and is a good match with the reported value for V-/V-- in HfO2. Significant charge trapping at low level stress was observed whereas at high level and elevated temperature stressing suggests a variation of trap energy level indicating new defect formation. It is observed that the stress induced gate leakage current for the high temperature stressed devices is about three orders of magnitude more than that of room temperature stressed devices for the whole field range.

  5. 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.

  6. 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.

  7. On device design for steep-slope negative-capacitance field-effect-transistor operating at sub-0.2V supply voltage with ferroelectric HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Kobayashi, Masaharu; Hiramoto, Toshiro

    2016-02-01

    Internet-of-Things (IoT) technologies require a new energy-efficient transistor which operates at ultralow voltage and ultralow power for sensor node devices employing energy-harvesting techniques as power supply. In this paper, a practical device design guideline for low voltage operation of steep-slope negative-capacitance field-effect-transistors (NCFETs) operating at sub-0.2V supply voltage is investigated regarding operation speed, material requirement and energy efficiency in the case of ferroelectric HfO2 gate insulator, which is the material fully compatible to Complementary Metal-Oxide-Semiconductor (CMOS) process technologies. A physics-based numerical simulator was built to design NCFETs with the use of experimental HfO2 material parameters by modeling the ferroelectric gate insulator and FET channel simultaneously. The simulator revealed that NCFETs with ferroelectric HfO2 gate insulator enable hysteresis-free operation by setting appropriate operation point with a few nm thick gate insulator. It also revealed that, if the finite response time of spontaneous polarization of the ferroelectric gate insulator is 10-100psec, 1-10MHz operation speed can be achieved with negligible hysteresis. Finally, by optimizing material parameters and tuning negative capacitance, 2.5 times higher energy efficiency can be achieved by NCFET than by conventional MOSFETs. Thus, NCFET is expected to be a new CMOS technology platform for ultralow power IoT.

  8. Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides.

    PubMed

    Zeng, Qingfeng; Oganov, Artem R; Lyakhov, Andriy O; Xie, Congwei; Zhang, Xiaodong; Zhang, Jin; Zhu, Qiang; Wei, Bingqing; Grigorenko, Ilya; Zhang, Litong; Cheng, Laifei

    2014-02-01

    High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as a fitness function in conjunction with first-principles calculations and the global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some of which are new. The results allow us to propose characteristics (genes) common to high-fitness structures--these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue for discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery. PMID:24508952

  9. 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.

  10. 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.

  11. Reduced impurities and improved electrical properties of atomic-layer-deposited HfO2 film grown at a low temperature (100 °C) by Al2O3 incorporation

    NASA Astrophysics Data System (ADS)

    Park, Tae Joo; Byun, Youngchol; Wallace, Robert M.; Kim, Jiyoung

    2016-05-01

    The HfO2 films grown by atomic layer deposition (ALD) at a low temperature (100 °C) necessarily has a large amount of residual impurities due to lack of thermal energy for stable ALD reactions such as ligand removal and oxidation, which degrades various properties. However, Al2O3 incorporation into the film significantly decreased the residual impurities despite of a low growth temperature. The decrease in C impurity is attributed to the reduced oxygen vacancies by the incorporated Al2O3 phase or the high reactivity of Al precursor. Consequently, the electronic band structure of the film, and thereby the electrical properties were improved significantly.

  12. Evaluation of voltage vs. pulse width modulation and feedback during set/reset verify-programming to achieve 10 million cycles for 50 nm HfO2 ReRAM

    NASA Astrophysics Data System (ADS)

    Higuchi, Kazuhide; Takeuchi, Ken; Iwasaki, Tomoko Ogura

    2014-01-01

    50 nm HfO2 resistive memory cells were measured by 6 × 6 verification variations to determine the optimal method to achieve 107 endurance and yield. The combination of pulse width incrementation during reset and pulse height modulation during set provided the most stable and highest cycling capability. Based on these results, a new conceptual model is proposed which combines the physical conduction model with direct tunneling, and provides a calculation method to predict resistance and explain degradation and reset failure. Furthermore, intermediate storing of programming information on a page basis is proposed in order to improve overall endurance.

  13. Deviation from bulk behaviour in the cold crystallization kinetics of ultrathin films of poly(3-hydroxybutyrate)

    NASA Astrophysics Data System (ADS)

    Napolitano, S.; Wübbenhorst, M.

    2007-05-01

    The cold crystallization kinetics of ultrathin films of poly(3-hydroxybutyrate) (PHB) have been investigated by dielectric spectroscopy. Upon reduction of the film thickness, a lowering of the Avrami exponent accompanied by an increase of the crystallization time was observed. The experimental results are analysed in terms of reduction of the total number of nuclei involved in the crystallization process.

  14. Improved interface properties of atomic-layer-deposited HfO2 film on InP using interface sulfur passivation with H2S pre-deposition annealing

    NASA Astrophysics Data System (ADS)

    Jin, Hyun Soo; Cho, Young Jin; Seok, Tae Jun; Kim, Dae Hyun; Kim, Dae Woong; Lee, Sang-Moon; Park, Jong-Bong; Yun, Dong-Jin; Kim, Seong Keun; Hwang, Cheol Seong; Park, Tae Joo

    2015-12-01

    Surface sulfur (S) passivation on InP substrate was performed using a dry process - rapid thermal annealing under H2S atmosphere for III-V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process - (NH4)2S solution treatment. The H2S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH4)2S solution treatment, although S profiles at the interface of HfO2/InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H2S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H2S annealing.

  15. 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.

  16. Ultrathin metallized PBI paper

    NASA Technical Reports Server (NTRS)

    Chenevey, E. C.

    1978-01-01

    A study to determine the feasibility of preparing ultrathin papers with a target weight of 3.5 g/m squared from polybenzimidazole (PBI) fibrids was undertaken. Small hand sheets of target weight were fabricated. They were light brown, low density materials with sufficient strength to be readily handleable. Characterization of these sheets included strength, fold endurance, thermal gravimetric analysis in air and nitrogen and photomicrographs. Two different batches of PBI fibrids were studied and differences in fabrication performance were noted. In neither case could target weight papers be prepared using conventional paper making techniques.

  17. Low temperature fabrication of high performance ZnO thin film transistors with high-k dielectrics

    NASA Astrophysics Data System (ADS)

    Walker, Brandon; Pradhan, Aswini K.; Xiao, Bo

    2015-09-01

    We report on the study of the low-temperature fabrication of ZnO thin film transistors on high-k gate dielectrics: Al2O3, HfO2 and ZrO2. All gate dielectrics were grown by atomic layer deposition at 150 °C and the ZnO semiconductors were grown by rf magnetron sputtering at room temperature. The electrical characteristics and device performance have been investigated systematically, along with the thin film structural properties by X-ray diffraction and atomic force microscopy. Highly (0 0 0 2)-oriented ZnO thin films were observed and their surface morphology revealed similar microstructures regardless of the bottom gate oxides. The fabricated thin film transistors showed high on/off ratio larger than 105 and low subthreshold voltage swing. The discrepancy of the device performance in these combinations indicated a significant gate dielectrics and interface dependence.

  18. Characterization of Al2O3-HfO2-Al2O3 sandwiched MIM capacitor under DC and AC stresses

    NASA Astrophysics Data System (ADS)

    Kwak, Ho-Young; Kwon, Hyuk-Min; Jung, Yi-Jung; Kwon, Sung-Kyu; Jang, Jae-Hyung; Choi, Woon-Il; Ha, Man-Lyun; Lee, Ju-Il; Lee, Song-Jae; Lee, Hi-Deok

    2013-01-01

    In this paper, electrical properties and reliability of high capacitance density Metal-Insulator-Metal (MIM) capacitor with sandwiched hafnium-based dielectric is analyzed using three kinds of voltage stress; constant voltage stress (CVS), unipolar voltage and bipolar voltage stresses. The fabricated MIM capacitor shows not only high capacitance density but also low leakage current density of about ˜10 nA/cm2 at room temperature and 1 V. The relative variation of capacitance (ΔC/C0) increases and the variation of voltage linearity (α/α0) gradually decreases with stress-time due to the charge trapping effect in the high-k dielectric. The relative variations of capacitance and voltage linearity show the greater change by the bipolar voltage stress than CVS and unipolar voltage stresses.

  19. All-dielectric diffraction grating for multi-petawatt laser systems

    NASA Astrophysics Data System (ADS)

    Vyhlidka, Stepan; Kalinchenko, Galina; Kramer, Daniel; Lerer, Alexander; Rus, Bedrich

    2015-01-01

    All-dielectric grating with more than 98% efficiency over the reflective band of 40 nm with the central wavelength at 1053 nm is simulated for the angle of incidence 72 degrees. For the grating design we used the fact that chirped mirrors give wider reflective band than usual quarter-wavelength dielectric mirrors. Grating grooves and the very first layer under the grooves in our model is made of fused silica; underneath of the top layer we placed a chirped stack of 13 HfO2/SiO2 layers. Tolerances for groove depth and angle of incidence are estimated, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show excellent agreement.

  20. 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.

  1. All-dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    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.

  2. 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

  3. Ultrathin Hf0.5Zr0.5O2 Ferroelectric Films on Si.

    PubMed

    Chernikova, Anna; Kozodaev, Maksim; Markeev, Andrei; Negrov, Dmitrii; Spiridonov, Maksim; Zarubin, Sergei; Bak, Ohheum; Buragohain, Pratyush; Lu, Haidong; Suvorova, Elena; Gruverman, Alexei; Zenkevich, Andrei

    2016-03-23

    Because of their immense scalability and manufacturability potential, the HfO2-based ferroelectric films attract significant attention as strong candidates for application in ferroelectric memories and related electronic devices. Here, we report the ferroelectric behavior of ultrathin Hf0.5Zr0.5O2 films, with the thickness of just 2.5 nm, which makes them suitable for use in ferroelectric tunnel junctions, thereby further expanding the area of their practical application. Transmission electron microscopy and electron diffraction analysis of the films grown on highly doped Si substrates confirms formation of the fully crystalline non-centrosymmetric orthorhombic phase responsible for ferroelectricity in Hf0.5Zr0.5O2. Piezoresponse force microscopy and pulsed switching testing performed on the deposited top TiN electrodes provide further evidence of the ferroelectric behavior of the Hf0.5Zr0.5O2 films. The electronic band lineup at the top TiN/Hf0.5Zr0.5O2 interface and band bending at the adjacent n(+)-Si bottom layer attributed to the polarization charges in Hf0.5Zr0.5O2 have been determined using in situ X-ray photoelectron spectroscopy analysis. The obtained results represent a significant step toward the experimental implementation of Si-based ferroelectric tunnel junctions. PMID:26931409

  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 μm, 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. Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

    NASA Astrophysics Data System (ADS)

    Cortez-Valadez, M.; Fierro, C.; Farias-Mancilla, J. R.; Vargas-Ortiz, A.; Flores-Acosta, M.; Ramírez-Bon, R.; Enriquez-Carrejo, J. L.; Soubervielle-Montalvo, C.; Mani-Gonzalez, P. G.

    2016-06-01

    The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH- ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO-H was studied employing the B3LYP (Becke 3-parameter, Lee-Yang-Parr) hybrid functional and the PBE (Perdew-Burke-Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

  7. Effect of (HfO2) X (Al2O3)1- X /SiO2 double-layered blocking oxide on program and erase speed in charge trapping memory devices

    NASA Astrophysics Data System (ADS)

    Oh, Jinho; Ko, Eun Jung; Na, Heedo; Ko, Dae-Hong; Sohn, Hyunchul

    2016-03-01

    In this work, the effect of hole injection into the charge trap layers from channel prior to program operation is investigated in charge trapping (CT) memory with stacked blocking oxide (BO). For efficient hole injection, a (HfO2) X (Al2O3)1 - X /SiO2 stacked BO structure is used. The CT memory device with stacked BO shows faster programming and erasing speed compared with single-layered SiO2 BO. The enhanced programming speed is attributed to the enhanced electric field introduced by excess holes injected into SiN charge trap layer. In addition, efficient hole injection from channel produced the widened memory window in CT memory.

  8. Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Lee, Gwan-Hyoung; Yu, Young-Jun; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

    2011-12-01

    Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained; these values are comparable to those of SiO2.

  9. Analysis of the electroluminescence features of silicon metal-insulator-semiconductor structures as a tool for diagnostics of the injection properties of a dielectric layer

    NASA Astrophysics Data System (ADS)

    Illarionov, Yu. Yu.; Vexler, M. I.; Isakov, D.; Fedorov, V. V.; Sing, Yew Kwang

    2013-10-01

    A technique for diagnostics of the injection properties of thin dielectric layers based on analysis of the data on silicon electroluminescence in a metal-insulator-semiconductor structure is proposed. The possibility of applying this technique to control the electron injection energy (in particular, when the barrier parameters are poorly known) is demonstrated by the example of samples with CaF2 and HfO2/SiO2. The results obtained are important for application of the insulators under study in microelectronic devices.

  10. Investigation of metal oxide dielectrics for non-volatile floating gate and resistance switching memory applications

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Bhaswar

    Floating gate transistor based flash memories have seen more than a decade of continuous growth as the prominent non-volatile memory technology. However, the recent trends indicate that the scaling of flash memory is expected to saturate in the near future. Several alternative technologies are being considered for the replacement of flash in the near future. The basic motivation for this work is to investigate the material properties of metal oxide based high-k dielectrics for potential applications in floating gate and resistance switching memory applications. This dissertation can be divided into two main sections. In the first section, the tunneling characteristics of the SiO2/HfO 2 stacks were investigated. Previous theoretical studies for thin SiO 2/ thick high-k stacks predict an increase in tunneling current in the high-bias regime (better programming) and a decrease in the low-bias regime (better retention) in comparison to pure SiO2 of same equivalent oxide thickness (EOT). However, our studies indicated that the performance improvement in SiO2/HfO2 stacks with thick HfO2 layer is difficult due to significant amount of charge traps in thick HfO2 layers. Oxygen anneal on the stacks did not improve the programming current and retention. X-ray photoelectron spectroscopy (XPS) studies indicated that this was due to formation of an interfacial oxide layer. The second part of the dissertation deals with the investigation of resistive switching in metal oxides. Although promising, practical applications of resistive random access memories (RRAM) require addressing several issues including high forming voltage, large operating currents and reliability. We first investigated resistive switching in HfTiOx nanolaminate with conventional TiN electrodes. The forming-free switching observed in the structures could be described by the quantum point contact model. The modelling results indicated that the forming-free characteristics can be due to a higher number of filaments in comparison to a device that requires forming. Forming-free resistive switching with low current operation in graphene-insulator-graphene structures was also investigated. Electrical as well as Raman and XPS analysis indicated that low current operation is due to the migration and subsequent physisorption of oxygen ions on the graphene surface during the set operation. A statistical model was also developed for quantitative prediction of the effect of noise on RRAM characteristics.

  11. Formation of ultrathin silicon layers by PECVD and their modification for nanoelectronic and nanophotonic applications

    NASA Astrophysics Data System (ADS)

    Ber, Kamil; Beck, Romuald B.

    2013-07-01

    Nanoelectronic and nanophotonic applications have created a pressure on methods of fabrication double dielectric barriers stacks with ultrathin silicon layer located between dielectric layers. Among numerous possible methods, PECVD seems to be very promising. In order to increase possible number of applications, however, the ability to transform continuous silicon layer into nanocrystalline form in dielectric matrix is required. The work described below reports on experimental efforts to form such a structure by controlled high temperature recrystallization and oxidation of ultrathin PECVD silicon layer in the stack. The effects if high temperature annealing has been studied by spectroscopic ellipsometry. The applied model allowed for identification of composition and structural changes within the silicon PECVD layer due to different high temperature annealing processes applied. As a result of this study, it has been proved that it is feasible to fabricate complete two barrier stack consisting of ultrathin dielectric and silicon layers in one PECVD system without exposing samples to the ambient atmosphere. In order to reduce the PECVD silicon layer thickness to approximately 3 nm, we proposed using plasma oxidation in PECVD instead of PECVD oxide deposition. High temperature (especially in 1100°C) annealing in argon proved to allow formation of silicon nanocrystals in oxide matrix. Other effects resulting from high temperature annealing of fabricated stacks are also studied.

  12. Conformal surface plasmons propagating on ultrathin and flexible films

    PubMed Central

    Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J.

    2013-01-01

    Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

  13. InAs/GaAs quantum-dot intermixing: comparison of various dielectric encapsulants

    NASA Astrophysics Data System (ADS)

    Alhashim, Hala H.; Khan, Mohammed Zahed Mustafa; Majid, Mohammed A.; Ng, Tien K.; Ooi, Boon S.

    2015-10-01

    We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO2 and Si3N4 films, HfO2 and SrTiO3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO2 capped sample. Likewise, investigation of TiO2, Al2O3, and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ˜1060-1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green-yellow-orange coherent light generation, as well as addressing photonic integration via area-selective, and postgrowth bandgap engineering.

  14. 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.

  15. High-yield of memory elements from carbon nanotube field-effect transistors with atomic layer deposited gate dielectric

    NASA Astrophysics Data System (ADS)

    Rinkiö, Marcus; Johansson, Andreas; Zavodchikova, Marina Y.; Jussi Toppari, J.; Nasibulin, Albert G.; Kauppinen, Esko I.; Törmä, Päivi

    2008-10-01

    Carbon nanotube field-effect transistors (CNT FETs) have been proposed as possible building blocks for future nano-electronics. But a challenge with CNT FETs is that they appear to randomly display varying amounts of hysteresis in their transfer characteristics. The hysteresis is often attributed to charge trapping in the dielectric layer between the nanotube and the gate. We find that the memory effect can be controlled by carefully designing the gate dielectric in nm-thin layers. By using atomic layer depositions (ALD) of HfO2 and TiO2 in a triple-layer configuration, we achieve to our knowledge the first CNT FETs with consistent and narrowly distributed memory effects in their transfer characteristics. The study includes 94 CNT FET samples, providing a good basis for statistics on the hysteresis seen in five different CNT-gate configurations.

  16. Dielectric constants by multifrequency non-contact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kumar, Bharat; Bonvallet, Joseph C.; Crittenden, Scott R.

    2012-01-01

    We present a method to obtain capacitive forces and dielectric constants of ultra-thin films on metallic substrates using multifrequency non-contact atomic force microscopy with amplitude feedback in air. Capacitive forces are measured via cantilever oscillations induced at the second bending mode and dielectric constants are calculated by fitting an analytic expression for the capacitance (Casuso et al 2007 Appl. Phys. Lett. 91 063111) to the experimental data. Dielectric constants for self-assembled monolayers of thiol molecules on gold (2.0 ± 0.1) and sputtered SiO2 (3.6 ± 0.07) were obtained under dry conditions, in good agreement with previous measurements. The high Q-factor of the second bending mode of the cantilever increases the accuracy of the capacitive measurements while the low applied potentials minimize the likelihood of variation of the dielectric constants at high field strength and of damage from dielectric breakdown of air.

  17. High temperature calorimetric studies of heat of solution of NiO, CuO, La2O3, TiO2, HfO2 in sodium silicate liquids

    NASA Astrophysics Data System (ADS)

    Linard, Yannick; Wilding, Martin C.; Navrotsky, Alexandra

    2008-01-01

    The enthalpies of solution of La2O3, TiO2, HfO2, NiO and CuO were measured in sodium silicate melts at high temperature. When the heat of fusion was available, we derived the corresponding liquid-liquid enthalpies of mixing. These data, combined with previously published work, provide insight into the speciation reactions in sodium silicate melts. The heat of solution of La2O3 in these silicate solvents is strongly exothermic and varies little with La2O3 concentration. The variation of heat of solution with composition of the liquid reflects the ability of La(III) to perturb the transient silicate framework and compete with other cations for oxygen. The enthalpy of solution of TiO2 is temperature-dependent and indicates that the formation of Na-O-Si species is favored over Na-O-Ti at low temperature. The speciation reactions can be interpreted in terms of recent spectroscopic studies of titanium-bearing melts which identify a dual role of Ti4+ as both a network-former end network-modifier. The heats of solution of oxides of transition elements (Ni and Cu) are endothermic, concentration-dependent and reach a maximum with concentration. These indicate a charge balanced substitution which diminishes the network modifying role of Na+ by addition of Ni2+ or Cu2+. The transition metal is believed to be in tetrahedral coordination, charge balanced by the sodium cation in the melts.

  18. 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, Andr; 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.

  19. Elasticity theory of ultrathin nanofilms

    NASA Astrophysics Data System (ADS)

    Li, Jiangang; Narsu, B.; Yun, Guohong; Yao, Haiyan

    2015-07-01

    A self-consistent theoretical scheme for describing the elastic behavior of ultrathin nanofilms (UTNFs) was proposed. Taking into account the lower symmetry of an UTNF compared to its bulk counterpart, additional elastic and magnetoelastic parameters were introduced to model the elasticity rigorously. The applications of current theory to several elastic and magnetoelastic systems gave excellent agreement with experiments. More importantly, the surface elastic and magnetoelastic parameters used to fit the experimental results are physically reasonable and in close agreement with those obtained from experiment and simulation. This fact suggests that the additional elastic (magnetoelastic) constants due to symmetry breaking are of great importance in theoretical description of the mechanical properties of UTNFs. And we proved that the elasticity of UTNFs should be described by a three-dimensional model just including the intrinsic surface and bulk parameters, but not the effective surface parameters. It is believed that the theory reported here is a universal strategy for elasticity and magnetoelasticity of ultrathin films.

  20. Synthesis, characterization and biological study on Cr 3+, ZrO 2+, HfO 2+ and UO 22+ complexes of oxalohydrazide and bis(3-hydroxyimino)butan-2-ylidene)-oxalohydrazide

    NASA Astrophysics Data System (ADS)

    El-Asmy, A. A.; El-Gammal, O. A.; Radwan, H. A.

    2010-09-01

    Cr 3+, ZrO 2+, HfO 2+ and UO 22+ complexes of oxalohydrazide (H 2L 1) and oxalyl bis(diacetylmonoxime hydrazone) [its IUPAC name is oxalyl bis(3-hydroxyimino)butan-2-ylidene)oxalohydrazide] (H 4L 2) have been synthesized and characterized by partial elemental analysis, spectral (IR; electronic), thermal and magnetic measurements. [Cr(L 1)(H 2O) 3(Cl)]·H 2O, [ZrO(HL 1) 2]·C 2H 5OH, [UO 2(L 1)(H 2O) 2] [ZrO(H 3L 2)(Cl)] 2·2H 2O, [HfO(H 3L 2)(Cl)] 2·2H 2O and [UO 2(H 2L 2)]·2H 2O have been suggested. H 2L 1 behaves as a monobasic or dibasic bidentate ligand while H 4L 2 acts as a tetrabasic octadentate with the two metal centers. The molecular modeling of the two ligands have been drawn and their molecular parameters were calculated. Examination of the DNA degradation of H 2L 1 and H 4L 2 as well as their complexes revealed that direct contact of [ZrO(H 3L 2)(Cl)] 2·2H 2O or [HfO(H 3L 2)(Cl)] 2·2H 2O degrading the DNA of Eukaryotic subject. The ligands and their metal complexes were tested against Gram's positive Bacillus thuringiensis (BT) and Gram's negative ( Escherichia coli) bacteria. All compounds have small inhibitory effects.

  1. Plasma enhanced atomic layer deposition of ultrathin oxides on graphene

    NASA Astrophysics Data System (ADS)

    Trimble, Christie J.; Zaniewski, Anna M.; Kaur, Manpuneet; Nemanich, Robert J.

    2015-03-01

    Graphene, a single atomic layer of sp2 bonded carbon atoms, possesses extreme material properties that point toward a plethora of potential electronic applications. Many of these possibilities require the combination of graphene with dielectric materials such as metal oxides. Simultaneously, there is interest in new physical properties that emerge when traditionally three dimensional materials are constrained to ultrathin layers. For both of these objectives, we explore deposition of ultrathin oxide layers on graphene. In this project, we perform plasma enhanced atomic layer deposition (PEALD) of aluminum oxide on graphene that has been grown by chemical vapor deposition atop copper foil and achieve oxide layers that are <1.5 nm. Because exposure to oxygen plasma can cause the graphene to deteriorate, we explore techniques to mitigate this effect and optimize the PEALD process. Following deposition, the graphene and oxide films are transferred to arbitrary substrates for further analysis. We use x-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy to assess the quality of the resulting films. This work is supported by the National Science Foundation under Grant # DMR-1206935.

  2. 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

  3. 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.

  4. Surface cleaning effects on reliability for devices with ultrathin oxides or oxynitrides

    NASA Astrophysics Data System (ADS)

    Lai, Kafai; Hao, Ming-Yin; Chen, Wei-Ming; Lee, Jack C.

    1994-09-01

    A new wafer cleaning procedure has been developed for ultra-thin thermal oxidation process (Ultrathin thermal oxides (48 angstrom) and oxynitrides grown in N2O (42 angstrom) were prepared using this new cleaning and other commonly used cleaning methods to investigate the effects of surface preparation on dielectric integrity. It has been found that this two-dip method produces dielectrics with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxides. Furthermore, this new cleaning procedure improves both intrinsic and defect-related breakdown as well as the uniformity of the current- voltage characteristics across a 4-inch wafer. The methanol/HF dip time has also been optimized. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen, the reduced surface micro-roughness and the absence of native oxide.

  5. 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 μm lead to the formation of concave-shaped ultrathin PVA films, whereas uniform ultrathin PVA films are formed on 20 and 10 μm 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

  6. 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.

  7. Hybrid gate dielectric materials for unconventional electronic circuitry.

    PubMed

    Ha, Young-Geun; Everaerts, Ken; Hersam, Mark C; Marks, Tobin J

    2014-04-15

    Recent advances in semiconductor performance made possible by organic π-electron molecules, carbon-based nanomaterials, and metal oxides have been a central scientific and technological research focus over the past decade in the quest for flexible and transparent electronic products. However, advances in semiconductor materials require corresponding advances in compatible gate dielectric materials, which must exhibit excellent electrical properties such as large capacitance, high breakdown strength, low leakage current density, and mechanical flexibility on arbitrary substrates. Historically, conventional silicon dioxide (SiO2) has dominated electronics as the preferred gate dielectric material in complementary metal oxide semiconductor (CMOS) integrated transistor circuitry. However, it does not satisfy many of the performance requirements for the aforementioned semiconductors due to its relatively low dielectric constant and intransigent processability. High-k inorganics such as hafnium dioxide (HfO2) or zirconium dioxide (ZrO2) offer some increases in performance, but scientists have great difficulty depositing these materials as smooth films at temperatures compatible with flexible plastic substrates. While various organic polymers are accessible via chemical synthesis and readily form films from solution, they typically exhibit low capacitances, and the corresponding transistors operate at unacceptably high voltages. More recently, researchers have combined the favorable properties of high-k metal oxides and π-electron organics to form processable, structurally well-defined, and robust self-assembled multilayer nanodielectrics, which enable high-performance transistors with a wide variety of unconventional semiconductors. In this Account, we review recent advances in organic-inorganic hybrid gate dielectrics, fabricated by multilayer self-assembly, and their remarkable synergy with unconventional semiconductors. We first discuss the principals and functional importance of gate dielectric materials in thin-film transistor (TFT) operation. Next, we describe the design, fabrication, properties, and applications of solution-deposited multilayer organic-inorganic hybrid gate dielectrics, using self-assembly techniques, which provide bonding between the organic and inorganic layers. Finally, we discuss approaches for preparing analogous hybrid multilayers by vapor-phase growth and discuss the properties of these materials. PMID:24428627

  8. Silicon Nanowires with High-k Hafnium Oxide Dielectrics for Sensitive Detection of Small Nucleic Acid Oligomers

    PubMed Central

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

    2012-01-01

    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 (HfO2), 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 SiNWFET’s has been small oligonucleotides, more specifically microRNA (miRNA). MicroRNA’s are small RNA oligonucleotides which bind to messenger RNA’s, 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 HfO2 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 <100fM detection levels of miR-10b DNA analogue, with a theoretical limit of detection of 1fM. Moreover, the non-complementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

  9. Ultrathin, flexible organic-inorganic hybrid solar cells based on silicon nanowires and PEDOT:PSS.

    PubMed

    Sharma, Manisha; Pudasaini, Pushpa Raj; Ruiz-Zepeda, Francisco; Elam, David; Ayon, Arturo A

    2014-03-26

    Recently, free-standing, ultrathin, single-crystal silicon (c-Si) membranes have attracted considerable attention as a suitable material for low-cost, mechanically flexible electronics. In this paper, we report a promising ultrathin, flexible, hybrid solar cell based on silicon nanowire (SiNW) arrays and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The free-standing, ultrathin c-Si membranes of different thicknesses were produced by KOH etching of double-side-polished silicon wafers for various etching times. The processed free-standing silicon membranes were observed to be mechanically flexible, and in spite of their relatively small thickness, the samples tolerated the different steps of solar cell fabrication, including surface nanotexturization, spin-casting, dielectric film deposition, and metallization. However, in terms of the optical performance, ultrathin c-Si membranes suffer from noticeable transmission losses, especially in the long-wavelength region. We describe the experimental performance of a promising light-trapping scheme in the aforementioned ultrathin c-Si membranes of thicknesses as small as 5.7 μm employing front-surface random SiNW texturization in combination with a back-surface distribution of silver (Ag) nanoparticles (NPs). We report the enhancement of both the short-circuit current density (JSC) and the open-circuit voltage (VOC) that has been achieved in the described devices. Such enhancement is attributable to the plasmonic backscattering effect of the back-surface Ag NPs, which led to an overall 10% increase in the power conversion efficiency (PCE) of the devices compared to similar structures without Ag NPs. A PCE in excess of 6.62% has been achieved in the described devices having a c-Si membrane of thickness 8.6 μm. The described device technology could prove crucial in achieving an efficient, low-cost, mechanically flexible photovoltaic device in the near future. PMID:24568116

  10. Ultrathin BaTiO3 templates for multiferroic nanostructures

    NASA Astrophysics Data System (ADS)

    Chen, Xumin; Yang, Seolun; Kim, Ji-Hyun; Kim, Hyung-Do; Kim, Jae-Sung; Rojas, Geoffrey; Skomski, Ralph; Lu, Haidong; Bhattacharya, Anand; Santos, Tiffany; Guisinger, Nathan; Bode, Matthias; Gruverman, Alexei; Enders, Axel

    2011-08-01

    The structural, electronic and dielectric properties of high-quality ultrathin BaTiO3 films were investigated. The films, which were grown by ozone-assisted molecular beam epitaxy on Nb-doped SrTiO3(001) substrates and have thicknesses as low as 8 unit cells (u.c.) (3.2 nm), are unreconstructed and atomically smooth with large crystalline terraces. A strain-driven transition to three-dimensional (3D) island formation is observed for films of 13 u.c. thickness (5.2 nm). The high structural quality of the surfaces, together with dielectric properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, makes these films suitable templates for the synthesis of high-quality metal-oxide multiferroic heterostructures for the fundamental study and exploitation of magneto-electric effects, such as a recently proposed interface effect in Fe/BaTiO3 heterostructures based on Fe-Ti interface bonds.

  11. The O 1 s x-ray absorption spectra of transition-metal oxides: The TiO 2-ZrO 2-HfO 2 and V 2O 5-Nb 2O 5-Ta 2O 5 series

    NASA Astrophysics Data System (ADS)

    Soriano, L.; Abbate, M.; Fuggle, J. C.; Jiménez, M. A.; Sanz, J. M.; Mythen, C.; Padmore, H. A.

    1993-08-01

    We present the O 1 s x-ray absorption spectra of two series of transition-metal oxides including all the d0 oxides of the groups IVa and Va elements, namely TiO 2-ZrO 2-HfO 2 and V 2O 5-Nb 2O 5-Ta 2O 5. The spectra correspond to transitions to the conduction band and are related to the O p unoccupied density of states. The results provide direct information about crystal-field splitting, hybridization strengths and band dispersions.

  12. Low-Temperature Atomic-Layer-Deposited High-κ Dielectric for p-Channel In0.7Ga0.3As/GaAs0.35Sb0.65 Heterojunction Tunneling Field-Effect Transistor

    NASA Astrophysics Data System (ADS)

    Rajamohanan, Bijesh; Mohata, Dheeraj; Zhernokletov, Dmitry; Brennan, Barry; Wallace, Robert M.; Engel-Herbert, Roman; Datta, Suman

    2013-10-01

    The interface quality of a low temperature atomic-layer-deposited (ALD) HfO2/Al2O3 bilayer high-κ gate dielectric on a GaAs0.35Sb0.65 channel for heterojunction p-channel tunneling FETs is investigated. Lowering the ALD temperature from 250 to 110 °C results in improved capacitance-voltage characteristics and lower interface trap density in metal-oxide-semiconductor capacitor structures. Using the low-temperature ALD high-κ dielectric, a GaAs0.35Sb0.65/In0.7Ga0.3As heterojunction p-channel tunneling FET is demonstrated with an improved switching slope and higher on-off current ratio. X-ray photoelectron spectroscopy is performed to investigate the effect of the deposition temperature on the chemical composition of the high-κ/GaAs0.35Sb0.65 interface.

  13. 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.

  14. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, Harold K.; Babcock, Walter C.; Friensen, Dwayne T.; Smith, Kelly L.; Johnson, Bruce M.; Wamser, Carl C.

    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.

  15. Chemical control over the formation and reactivity of ultra-thin films and amino-terminated layers on silicon

    NASA Astrophysics Data System (ADS)

    Rodriguez-Reyes, Juan Carlos F.

    The physical-chemical properties of several interfacial systems of technological relevance are investigated, having as a common goal the elucidation of strategies towards their atomic- and molecular-level control. Such systems can be classified in three groups: (i) ultra-thin films deposited using metalorganic precursors, (ii) metalorganic monolayers on silicon, and (iii) amine-functionalized silicon surfaces. Experimental, theoretical and chemometric methods are conveniently combined to gain a solid understanding of these systems. The ultra-thin films under investigation are titanium carbonitride (TiNC) and hafnium oxide (HfO2). Since these films may serve as substrates for deposition of other materials in circuit components, their surface chemistry needs to be understood and controlled in order to facilitate further deposition steps. The surface of a TiCN film is transformed to titanium nitride (TiN) through nitridation with ammonia; this compositional change can be reversed by the partial decomposition of ethylene molecules on the surface. The surface reactivity is observed to depend on the film composition, and therefore the method described above serves to reversibly tune the reactivity of Ti-based films. As for HfO2 films, it is found that the deposition temperature affects the degree of crystallinity of the films, which in turn affects their surface chemistry. Thus, together with a control of the composition, it is found that the reactivity of a film can be controlled precisely by controlling the crystallinity. The investigation of metalorganic monolayers on silicon surfaces was motivated by the need for understanding the first steps of metalorganic-based deposition of films, which is usually characterized by a heavy presence of contaminants that degrade the film properties. Through a combination of vibrational (infrared) spectroscopy and theoretical methods, a feasible pathway for the adsorption and decomposition of Ti[N(CH3)2]4 is found. This pathway starts with the ligand-mediated attachment of the precursor (through a N atom), followed by dissociation of a metal-ligand bond. In addition, the C-H bond is broken, possibly forming Si-C bonds and causing carbon incorporation. This model is found to be rather robust and to adequately describe other types of metalorganic precursors. It allows establishing a generalized model able to explain the success or failure of a metalorganic precursor chemistry for film deposition. Finally, amine-functionalized silicon surfaces are considered as prototypical systems where the spatial distribution of adsorbates and the control over the reactivity of surface sites can be investigated. The spatial distribution of molecules is investigated at the atomic level by considering the saturation of a Si(100) surface with NH3. It is found that the distribution of (Si)NH2 species can be controlled thermally and, more importantly, that during thermal decomposition N inserts into the substrate in manners that minimize the arising strain. When the surface is covered with NH 3 or with organic amines, its chemical behavior is determined by the basicity of the molecule functionalizing the surface. The precise tuning of the reactivity (basicity) of surface sites opens the doors for highly controllable, selective reactions. Although these results are obtained from rather fundamental grounds, their interpretation is often translated into manners in which technological applications can be improved. Further directions worth exploring emanated from this work are outlined and discussed. Ultimately, this work intends to highlight the current importance of surface physical chemistry in the continuous development of modern society through the improvement of its technology.

  16. Anisotropic permittivity of ultra-thin crystalline Au films: Impacts on the plasmonic response of metasurfaces

    NASA Astrophysics Data System (ADS)

    Campbell, Sawyer D.; Ziolkowski, Richard W.; Cao, Jiangrong; Laref, Slimane; Muralidharan, Krishna; Deymier, Pierre

    2013-08-01

    It has been determined by density functional theory (DFT) simulations that the extracted permittivities of ultra-thin crystalline gold (Au) films exhibit large anisotropies which are not predicted by classical models or previous experimental determinations of the dielectric function. The optical scattering characteristics of a periodic array of Au discs are simulated with the DFT extracted permittivity and contrasted against those obtained with several commonly used Au permittivity models. It is demonstrated that the DFT-based transmittance spectra for these plasmonic metasurfaces lead to significantly redshifted results when compared to those predicted by standard Drude and Johnson-Christy permittivity models.

  17. 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.

  18. Dielectric metasurfaces

    NASA Astrophysics Data System (ADS)

    Valentine, Jason

    While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

  19. 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

  20. Design and fabrication of multilayer dielectric gratings for spectral beam combining

    NASA Astrophysics Data System (ADS)

    Cho, Hyun-Ju; Kim, Hyun-Tae; Lee, Yong-Soo

    2015-08-01

    Metal gratings are mostly used on low energy optics, but it has low laser damage threshold. Spectral beam combining is a method to make high power laser beam using diffraction gratings. Multilayer dielectric (MLD) high reflectance mirror is designed for high efficiency gratings using HfO2 and SiO2 for high laser damage threshold. On the top of the mirror, polarization dependent SiO2 grating structure is simulated by finite domain time division (FDTD) method at 1055nm for spectral beam combining. To estimate the far field diffraction characteristics, we first calculate near field electromagnetic wave properties at the substrate region and these are transformed to angular diffraction characteristics at about 1 meter apart from the grating. Multilayer dielectric mirror is deposited by electron beam evaporation method at the substrate temperature 250°C. Four types of high efficiency MLD gratings are selected and these are fabricated by lithography and reactive ion etching method. To fabricate the designed submicron structure, 4X stepper is used for pattern formation on the photo resistor. We use fused silica as a substrate and additional dummy silicon wafer substrates are used for grating structure confirmation using scanning electron microscope. The diffraction efficiencies are measured and these are compared with simulated results.

  1. 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 (Δnr) 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.

  2. Analytical drain current formulation for gate dielectric engineered dual material gate-gate all around-tunneling field effect transistor

    NASA Astrophysics Data System (ADS)

    Madan, Jaya; Gupta, R. S.; Chaujar, Rishu

    2015-09-01

    In this work, an analytical drain current model for gate dielectric engineered (hetero dielectric)-dual material gate-gate all around tunnel field effect transistor (HD-DMG-GAA-TFET) has been developed. Parabolic approximation has been used to solve the two-dimensional (2D) Poisson equation with appropriate boundary conditions and continuity equations to evaluate analytical expressions for surface potential, electric field, tunneling barrier width and drain current. Further, the analog performance of the device is studied for three high-k dielectrics (Si3N4, HfO2, and ZrO2), and it has been investigated that the problem of lower ION, can be overcome by using the hetero-gate architecture. Moreover, the impact of scaling the gate oxide thickness and bias variations has also been studied. The HD-DMG-GAA-TFET shows an enhanced ION of the order of 10-4 A. The effectiveness of the proposed model is validated by comparing it with ATLAS device simulations.

  3. 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.

  4. Lithography-Free Broadband Ultrathin-Film Absorbers with Gap-Plasmon Resonance for Organic Photovoltaics.

    PubMed

    Choi, Minjung; Kang, Gumin; Shin, Dongheok; Barange, Nilesh; Lee, Chang-Won; Ko, Doo-Hyun; Kim, Kyoungsik

    2016-05-25

    Strategies to confine electromagnetic field within ultrathin film emerge as essential technologies for applications from thin-film solar cells to imaging and sensing devices. We demonstrate a lithography-free, low-cost, large-scale method to realize broadband ultrathi-film metal-dielectric-metal (MDM) absorbers, by exploiting gap-plasmon resonances for strongly confined electromagnetic field. A two-steps method, first organizing Au nanoparticles via thermal dewetting and then transferring the nanoparticles to a spacer-reflector substrate, is used to achieve broader absorption bandwidth by manipulating geometric shapes of the top metallic layer into hemiellipsoids. A fast-deposited nominal Au film, instead of a conventional slow one, is employed in the Ostwald ripening process to attain hemiellipsoidal nanoparticles. A polymer supported transferring step allows a wider range of dewetting temperature to manipulate the nanoparticles' shape. By incorporating circularity with ImageJ software, the geometries of hemiellipsoidal nanoparticles are quantitatively characterized. Controlling the top geometry of MDM structure from hemisphere to hemiellipsoid increases the average absorption at 500-900 nm from 23.1% to 43.5% in the ultrathin film and full width at half-maximum of 132-324 nm, which is consistently explained by finite-difference time-domain simulation. The structural advantages of our scheme are easily applicable to thin-film photovoltaic devices because metal electrodes can act as metal reflectors and semiconductor layers as dielectric spacers. PMID:27160410

  5. 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.

  6. Atomic Structure of Ultrathin Gold Nanowires.

    PubMed

    Yu, Yi; Cui, Fan; Sun, Jianwei; Yang, Peidong

    2016-05-11

    Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1-2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications. PMID:27071038

  7. Characterization of ultrathin insulators in CMOS technology: Wearout and failure mechanisms due to processing and operation

    NASA Astrophysics Data System (ADS)

    Okandan, Murat

    In the CMOS technology the gate dielectric is the most critical layer, as its condition directly dictates the ultimate performance of the devices. In this thesis, the wear-out and failure mechanisms in ultra-thin (around 50A and lower) oxides are investigated. A new degradation phenomenon, quasi-breakdown (or soft-breakdown), and the annealing and stressing behavior of devices after quasi-breakdown are considered in detail. Devices that are in quasi-breakdown continue to operate as switches, but the gate leakage current is two orders of magnitude higher than the leakage in healthy devices and the stressing/annealing behavior of the devices are completely altered. This phenomenon is of utmost interest, since the reduction in SiO2 dielectric thickness has reached its physical limits, and the quasi-breakdown behavior is seen to dominate as a failure mode in this regime. The quasi-breakdown condition can be brought on by stresses during operation or processing. To further study this evolution through stresses and anneals, cyclic current-voltage (I-V) measurement has been further developed and utilized in this thesis. Cyclic IV is a simple and fast, two terminal measurement technique that looks at the transient current flowing in an MOS system during voltage sweeps from accumulation to inversion and back. During these sweeps, carrier trapping/detrapping, generation and recombination are observed. An experimental setup using a fast electrometer and analog to digital conversion (A/D) card and the software for control of the setup and data analysis were also developed to gain further insight into the detailed physics involved. Overall, the crucial aspects of wear-out and quasi-breakdown of ultrathin dielectrics, along with the methods for analyzing this evolution are presented in this thesis.

  8. Reflectance properties of one-dimensional metal-dielectric ternary photonic crystal

    NASA Astrophysics Data System (ADS)

    Pandey, G. N.; Kumar, Narendra; Thapa, Khem B.; Ojha, S. P.

    2016-05-01

    Metallic photonic crystal has a very important application in absorption enhancement in solar cells. It has been found that an ultra-thin metallic layer becomes transparent due to internal scattering of light through the each interface of the dielectric and metal surfaces. The metal has absorption due to their surface plasmon and the plasmon has important parameters for changing optical properties of the metal. We consider ternary metallic-dielectric photonic crystal (MDPC) for having large probabilities to change the optical properties of the MDPC and the photonic crystals may be changed by changing dimensionality, symmetry, lattice parameters, Filling fraction and effective refractive index refractive index contrast. In this present communication, we try to show that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged when air dielectric constant is considered. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metal.

  9. Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications.

    PubMed

    Guo, Lei; Qin, Xiangdong; Zaera, Francisco

    2016-03-01

    A protocol has been developed to selectively process low-k SiCOH dielectric substrates in order to activate or deactivate them toward the deposition of thin solid films by chemical (CVD or ALD) means. The original SiCOH surfaces are hydrophobic, an indication that they are alkyl- rather than silanol-terminated and that, consequently, they are fairly unreactive. However, the chemical-mechanical polishing (CMP) sometimes done during microelectronics fabrication renders them hydrophilic and reactive. It was shown here that silylation of the CMP-treated surfaces with any of a number of well-known silylation agents such as HMDS, ODTS, or OTS caps the reactive silanol surface groups and turns them back to being hydrophilic and unreactive. Further exposure of any of the passivated surfaces to a combination of ozone and UV radiation reinstates their hydrophilicity and chemical activity. Importantly, it was also demonstrated that all these changes could be induced without altering the original mechanical, optical, or electrical properties of the samples: atomic force microscopy (AFM) images show no increase in roughness, ellipsometry measurements yield the same values for the index of refraction and dielectric constant, and infrared absorption spectroscopy attests to the preservation of the organic fragments present in the original SiCOH samples. The chemical selectivity of the resulting surfaces was tested for the atomic layer deposition (ALD) of HfO2 films, which could be grown only on the UV/O3 treated substrates. PMID:26956428

  10. 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.

  11. Improved linearity and reliability in GaN metal-oxide-semiconductor high-electron-mobility transistors using nanolaminate La2O3/SiO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Hsu, Ching-Hsiang; Shih, Wang-Cheng; Lin, Yueh-Chin; Hsu, Heng-Tung; Hsu, Hisang-Hua; Huang, Yu-Xiang; Lin, Tai-Wei; Wu, Chia-Hsun; Wu, Wen-Hao; Maa, Jer-Shen; Iwai, Hiroshi; Kakushima, Kuniyuki; Chang, Edward Yi

    2016-04-01

    Improved device performance to enable high-linearity power applications has been discussed in this study. We have compared the La2O3/SiO2 AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with other La2O3-based (La2O3/HfO2, La2O3/CeO2 and single La2O3) MOS-HEMTs. It was found that forming lanthanum silicate films can not only improve the dielectric quality but also can improve the device characteristics. The improved gate insulation, reliability, and linearity of the 8 nm La2O3/SiO2 MOS-HEMT were demonstrated.

  12. Physical understanding of trends in current collapse with atomic layer deposited dielectrics in AlGaN/GaN MOS heterojunction FETs

    NASA Astrophysics Data System (ADS)

    Ramanan, Narayanan; Lee, Bongmook; Misra, Veena

    2016-03-01

    Many passivation dielectrics are pursued for suppressing current collapse due to trapping/detrapping of access-region surface traps in AlGaN/GaN based metal oxide semiconductor heterojuction field effect transistors (MOS-HFETs). The suppression of current collapse can potentially be achieved either by reducing the interaction of surface traps with the gate via surface leakage current reduction, or by eliminating surface traps that can interact with the gate. But, the latter is undesirable since a high density of surface donor traps is required to sustain a high 2D electron gas density at the AlGaN/GaN heterointerface and provide a low ON-resistance. This presents a practical trade-off wherein a passivation dielectric with the optimal surface trap characteristics and minimal surface leakage is to be chosen. In this work, we compare MOS-HFETs fabricated with popular ALD gate/passivation dielectrics like SiO2, Al2O3, HfO2 and HfAlO along with an additional thick plasma-enhanced chemical vapor deposition SiO2 passivation. It is found that after annealing in N2 at 700 °C, the stack containing ALD HfAlO provides a combination of low surface leakage and a high density of shallow donor traps. Physics-based TCAD simulations confirm that this combination of properties helps quick de-trapping and minimal current collapse along with a low ON resistance.

  13. Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates

    NASA Astrophysics Data System (ADS)

    Shahinur Rahman, Md.; Evangelou, E. K.; Konofaos, N.; Dimoulas, A.

    2012-11-01

    We report on the reliability characteristics and their analysis, of rare-earth oxides (REOs) dielectric degradation, when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-oxide-semiconductor (MOS) devices with these stacks, show dissimilar charge trapping phenomena under varying levels of constant-voltage-stress (CVS) conditions, influencing the measured densities of the interface (Nit) and border (NBT) traps. In the present study, we report on C-Vg hysteresis curves related to both Nit and NBT. We propose a new model based on the Maxwell-Wagner mechanism, and this model explains the current decay transient observed under CVS bias from low to higher fields of MOS gate stack devices grown on Ge substrates. The proposed model is unlike to those used for other MOS devices. Finally, CVS measurements for very long times at moderate fields reveal an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced leakage which eventually lead to hard breakdown.

  14. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  15. 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.

  16. Ultrasound-responsive ultrathin multiblock copolyamide vesicles

    NASA Astrophysics Data System (ADS)

    Huang, Lei; Yu, Chunyang; Huang, Tong; Xu, Shuting; Bai, Yongping; Zhou, Yongfeng

    2016-02-01

    This study reports the self-assembly of novel polymer vesicles from an amphiphilic multiblock copolyamide, and the vesicles show a special structure with an ultrathin wall thickness of about 4.5 nm and a combined bilayer and monolayer packing model. Most interestingly, the vesicles are ultrasound-responsive and can release the encapsulated model drugs in response to ultrasonic irradiation.This study reports the self-assembly of novel polymer vesicles from an amphiphilic multiblock copolyamide, and the vesicles show a special structure with an ultrathin wall thickness of about 4.5 nm and a combined bilayer and monolayer packing model. Most interestingly, the vesicles are ultrasound-responsive and can release the encapsulated model drugs in response to ultrasonic irradiation. Electronic supplementary information (ESI) available: Details of experiments and characterization, and FT-IR, TEM, DPD, FL and micro-DSC results. See DOI: 10.1039/c5nr08596a

  17. 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

    2015-10-21

    A route for fabricating structurally perfect cobalt ferrite magnetic nanostructures is demonstrated. Ultrathin islands of up to 100 μm(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

  18. Development of ultrathin SI solar cells

    NASA Astrophysics Data System (ADS)

    Matsuda, S.; Matsutani, T.; Saga, T.; Suzuki, A.

    The ultrathin BSFR (BSF + BSR) solar cells have been developed and qualified for space use using 55-micron thick silicon (Si) wafers. In order to recover the loss of electrical output caused by thinning substrates, the manufacturing process was improved. The diffusion from phosphine (PH3) gas source, fine gridline formation and double layer anti-reflective coating composed of titanium dioxide (TiO2) and aluminum oxide (Al2O3) have been applied. 2-cm x 2-cm ultrathin cells fabricated by the newly developed manufacturing process showed the electrical output of 72.5 mW (typical value). This value was 1.8 mW larger than that of 280-micron thick BSFR cells fabricated by the conventional manufacturing process and the demerit due to thinning substrates has been overcome. A pilot production run was carried out to check the ability of the new manufacturing process and 628 2-cm x 2-cm ultrathin cells were fabricated. The average electrical output was 71.5 mW and slightly lower than that of the technical trial run. The production yield was 55.1 percent and it is considered to be reasonable as the results of the first pilot production.

  19. 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.

  20. 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.

  1. Ultrathin-layer gel electrophoresis of biopolymers.

    PubMed

    Guttman, A; Rónai, Z

    2000-12-01

    Emerging need for large-scale, high-resolution analysis of biopolymers, such as DNA sequencing polymerase chain reaction, (PCR) product sizing, single nucleotide polymorphism (SNP) hunting and analysis of protein molecules necessitated the development of automated and high-throughput gel electrophoresis based methods enabling rapid, high-performance separations in a wide molecular weight range. Scaling down electric field mediated separation processes supports higher throughput due to the applicability of higher voltages, thus speeding up analysis time. Indeed, efforts in miniaturization resulted in faster, easier, less costly and more convenient analyses, fulfilling the needs of the emerging biotechnology industry for microscale and massively parallel assays. The two primary approaches in miniaturizing electrophoresis dimensions are the capillary and microslab formats. This latter one evolved towards ultrathin-layer gel electrophoresis which is, except from the thickness of the separation platform, slightly in the upper side of the scale, resulting in considerably easier handling. Ultrathin-layer gel electrophoresis combines the advantages of conventional slab-gel electrophoresis (multilane format) and capillary gel electrophoresis (rapid, high-efficiency separations). It is readily automated, automatic versions of it have been extensively used for large-scale DNA sequencing in the Human Genome Project and more recently became popular in high throughput DNA fragment analysis. Ultrathin-layer techniques are the first step towards the wider use of electrophoresis microchips in perfecting a user-friendly interface between the user and the microdevice. PMID:11192118

  2. Surface Control of Bottom Electrode in Ultra-Thin SiN Metal-Insulator-Metal Decoupling Capacitors for High Speed Processors

    NASA Astrophysics Data System (ADS)

    Inoue, Naoya; Kume, Ippei; Kawahara, Jun; Saito, Shinobu; Furutake, Naoya; Toda, Takeshi; Matsui, Koichiro; Iwaki, Takayuki; Furumiya, Masayuki; Shinmura, Toshiki; Ohto, Koichi; Hayashi, Yoshihiro

    2007-04-01

    Highly reliable metal-insulator-metal (MIM) capacitor with ultra-thin SiN dielectrics is developed on the surface-controlled bottom electrode in nanometer-scales. Coverage of the TiN bottom electrode with a Ta thin layer achieves smooth surface. In addition, this electrode structure exhibits excellent etching controllability even for the MIM with the ultra-thin SiN dielectrics. The smooth surface of the Ta/TiN stacked electrode improves the dielectric characteristics such as leakage, breakdown and time-dependent dielectric breakdown (TDDB) reliability in the MIM capacitors, integrated into Cu dual-damascene interconnects (DDIs). As a result, the SiN-MIM with the Ta/TiN bottom electrode achieves high capacitance of 7 fF/μm2 as well as high reliabilities, which are 20% higher breakdown field and 6000 times longer TDDB lifetime than that without Ta-insertion. These values guarantee the high performance operation for more than 10 years under the environment at 85 °C.

  3. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz.

    PubMed

    Zhang, Xuefeng; Li, Yixing; Liu, Rongge; Rao, Yi; Rong, Huawei; Qin, Gaowu

    2016-02-10

    Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match. PMID:26775668

  4. Microwave absorptions of ultrathin conductive films and designs of frequency-independent ultrathin absorbers

    SciTech Connect

    Li, Sucheng; Anwar, Shahzad; Lu, Weixin; Hang, Zhi Hong; Hou, Bo E-mail: phyhoubo@gmail.com; Shen, Mingrong; Wang, Chin-Hua

    2014-01-15

    We study the absorption properties of ultrathin conductive films in the microwave regime, and find a moderate absorption effect which gives rise to maximal absorbance 50% if the sheet (square) resistance of the film meets an impedance matching condition. The maximal absorption exhibits a frequency-independent feature and takes place on an extremely subwavelength scale, the film thickness. As a realistic instance, ∼5 nm thick Au film is predicted to achieve the optimal absorption. In addition, a methodology based on metallic mesh structure is proposed to design the frequency-independent ultrathin absorbers. We perform a design of such absorbers with 50% absorption, which is verified by numerical simulations.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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 μm/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.

  6. 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 μm/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

  7. 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 μm/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

  8. 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

  9. Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure

    PubMed Central

    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

  10. Terahertz Artificial Dielectric Lens

    PubMed Central

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  11. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  12. Terahertz Artificial Dielectric Lens.

    PubMed

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  13. Atomically thin mica flakes and their application as ultrathin insulating substrates for graphene.

    PubMed

    Castellanos-Gomez, Andres; Wojtaszek, Magdalena; Tombros, Nikolaos; Agrat, Nicols; van Wees, Bart J; Rubio-Bollinger, Gabino

    2011-09-01

    By mechanical exfoliation, it is possible to deposit atomically thin mica flakes down to single-monolayer thickness on SiO2/Si wafers. The optical contrast of these mica flakes on top of a SiO2/Si substrate depends on their thickness, the illumination wavelength, and the SiO2 substrate thickness, and can be quantitatively accounted for by a Fresnel-law-based model. The preparation of atomically thin insulating crystalline sheets will enable the fabrication of ultrathin, defect-free insulating substrates, dielectric barriers, or planar electron-tunneling junctions. Additionally, it is shown that few-layer graphene flakes can be deposited on top of a previously transferred mica flake. Our transfer method relies on viscoelastic stamps, as used for soft lithography. A Raman spectroscopy study shows that such an all-dry deposition technique yields cleaner and higher-quality flakes than conventional wet-transfer procedures based on lithographic resists. PMID:21805626

  14. 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.

  15. 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

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

    PubMed

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

    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

  17. 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 εr = 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 εr = 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

  18. Surface and interface characterization of high-k dielectric materials on III-antimony semiconductor substrates

    NASA Astrophysics Data System (ADS)

    Zhernokletov, Dmitry M.

    Interface formation between high-k dielectric oxide materials and semiconductor surfaces is of critical importance to the development of the next generation of metal-oxide-semiconductor field effect transistors (MOSFETs) and tunnel field effect transistors (TFETs). This work investigates the deposition and characterization of a range of candidate high-k materials on III-Sb (InSb and GaSb) semiconductor substrates, with the focus on interface formation. The characterization techniques used to study the interface were X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), ion scattering spectroscopy, while atomic force microscopy (AFM) was used in some experiments for surface roughness measurements. The first part of this study evaluates the in-situ evolution of aluminum oxide (Al2O3) on indium antimonide (InSb) and gallium antimonide (GaSb) surfaces discussing preparation methods prior to dielectric deposition aimed at removing the native oxides and passivating the surfaces while keeping surface roughness to a minimum. For InSb surface the optimization of the ammonium sulphide (NH4) 2S passivation treatment was investigated in terms of the effectiveness at native oxide removal and minimizing defect generation. The interactions between hafnium oxide (HfO2) on HCl acid etched and (NH4) 2S treated GaSb surfaces as well as Al2O3 evolution on oxide free GaSb substrate were examined in the second part. A crystalline oxide/InAs(100) interface, as a potential path to avoid interface defect formation, was also investigated in term of stability upon Al2O3 deposition and air exposure.

  19. 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.

  20. Multi-technique Approach for the Evaluation of the Crystalline Phase of Ultrathin High-k Gate Oxide Films

    NASA Astrophysics Data System (ADS)

    Bersch, E.; LaRose, J. D.; Wells, I.; Consiglio, S.; Clark, R. D.; Leusink, G. J.; Matyi, R. J.; Diebold, A. C.

    2011-11-01

    In order to continue scaling metal oxide semiconductor field effect transistors (MOSFETs) with HfO2 gate oxides, efforts are being made to further improve the deposited high-k film properties. Recently, a process whereby an HfO2 film is deposited through a series of depositions and anneals (so-called DADA process) has been shown to result in films that give rise to MOS capacitors (MOSCAPs) which are electrically scaled compared to MOSCAPs with HfO2 films that only received post deposition anneals (PDA) or no anneals. We have measured as-deposited, DADA and PDA HfO2 films using four measurement techniques, all of which are non-destructive and capable of being used for in-line processing, to evaluate their crystallinity and crystalline phases. Grazing incidence in-plane X-ray diffraction was used to determine the crystalline phases of the HfO2 films. We observed the crystalline phases of these films to be process dependent. Additionally, X-ray and UV photoelectron spectroscopy were used to show the presence of crystallinity in the films. As a fourth technique, spectroscopic ellipsometry was used to determine if the crystalline phases were monoclinic. The combination of techniques was useful in that XPS and UPS were able to confirm the amorphous nature of a 30 cycle DADA film, as measured by GIIXRD, and GIIXRD was able to help us interpret the SE data as being an indication of the monoclinic phase of HfO2.

  1. 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

  2. Ultra-thin plasmonic random lasers.

    PubMed

    Zhai, Tianrui; Xu, Zhiyang; Wu, Xiaofeng; Wang, Yimeng; Liu, Feifei; Zhang, Xinping

    2016-01-11

    An ultrathin plasmonic random laser is fabricated by a simple lift off process, which consists of a free-standing polymer membrane embedded with silver nanoparticles. Low threshold random lasing is observed when the 200-nm-thick membrane device is optically pumped, due to the strong plasmonic feedback and high-quality waveguide confinement provided by the silver nanoparticles and the polymer membrane, respectively. The free-standing polymer membrane is very flexible and transplantable, which can be attached to an optical fiber end face to achieve random lasing. This fabrication technique provides a promising way to realize plasmonic random lasing on surfaces with arbitrary shapes. PMID:26832274

  3. 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.

  4. 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.

  5. Arrays of ultrathin silicon solar microcells

    SciTech Connect

    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.

  6. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

    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.

  7. Effect of PVD process parameters on the quality and reliability of thin (10-30 nm) Al2O3 dielectrics

    NASA Astrophysics Data System (ADS)

    Dutta, Shibesh; Ramesh, Sivaramakrishnan; Shankar, Balakrishnan; Gopalan, Sundar

    2012-03-01

    Over the last decade, dielectric scaling in non-volatile memories (NVM) and CMOS logic applications has reached a point where better innovations will be required to meet the reliability and performance requirements of future products. For both these applications, high k materials are being explored as possible candidates to replace the traditional SiO2 and oxide/nitride/oxide-based films used today. While there are several attractive candidates to replace these materials, HfO2 and Al2O3 are considered as the most promising ones. Although there has been a lot of work on CVD-based Al2O3, there has not been much reported for PVD-based Al2O3 for NVM applications, especially in the thickness regime of 10-30 nm. This paper discusses the effects of process parameters such a plasma power and annealing conditions on the quality of Al2O3 dielectrics. It was observed that a post deposition anneal in O2 ambient at 700C for 15 s is essential to obtain a fully oxidized film with high density. While higher power (1,500 W) results in thicker films with better k values, they also lead to more substrate damage and poorer reliability. Annealing done at temperatures greater than 700C for 60 s or more results in failure of the film possibly due to diffusion of silicon into Al2O3 and its subsequent reaction.

  8. Dielectric spectroscopy in agrophysics

    NASA Astrophysics Data System (ADS)

    Skierucha, W.; Wilczek, A.; Szypłowska, 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.

  9. Aperture excited dielectric antennas

    NASA Technical Reports Server (NTRS)

    Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

    1974-01-01

    The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

  10. 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

  11. 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

  12. Ultrathin inorganic molecular nanowire based on polyoxometalates

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

  13. 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.

  14. 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

  15. Dielectric nonlinearity of ferroelectrics

    NASA Astrophysics Data System (ADS)

    Fujii, Ichiro

    The ac field dependence of the dielectric constant and first order reversal curves (FORC) distribution were employed to quantify the effect of dielectric thickness, grain size, oxygen vacancy concentration, and microstructural heterogeneity on the dielectric nonlinearity of PbZr0.52Ti0.48O 3 thin films and BaTiO3-based ceramics on a wide electric field range. With the FORC distribution, the dielectric properties were calculated using Preisach model. The FORC distribution of PbZr0.52Ti0.48O3 thin films was characterized as a function of film thickness. It was found that the thickness dependence of the small field dielectric constant is due primarily to differences in the domain wall contributions to the properties. The irreversible FORC distribution decreased and the switching fields increased as the thickness decreased. Prediction of the polarization-electric field curves and the ac field dependence of the dielectric constant were found to give a good fit to the experimental results. Some discrepancies remain in the high field dielectric constant, probably caused by its definition. The dielectric nonlinearity of BaTiO3 ceramics with grain sizes from 1.2 to 76 microm was investigated. Defect dipoles in samples with large grains led to pinching of minor polarization-electric field loops as well as a threshold field in the ac field dependence of the dielectric constant and loss. For samples with small grains, a sublinear ac field dependence was observed. The irreversible FORC distributions characterizing the responses showed two strong and narrow peaks for large-grained samples and a weak, broad peak centered near the origin for samples with small grains. As the grain size decreased, the reversible FORC distribution at zero-bias field increased. No grain size dependence of the reversible FORC distributions was observed at high dc electric fields. These results indicate that the grain size dependence of the small field dielectric constant is attributable to a domain wall contribution and long-range domain wall motion suppressed while short-range domain wall motion enhanced as the grain size decreased. The effect of the oxygen vacancies on the dielectric nonlinearity of formulated and undoped BaTiO3 ceramics was investigated by changing oxygen partial pressure during firing. For the formulated ceramics, the dielectric constant of both oxygen and air fired samples increased almost linearly with the amplitude of the ac driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sub-linear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sub-linearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move. FORC distributions as well as the ac field dependence of the dielectric constant were investigated for model BaTiO3-based multilayer ceramic capacitors with dielectric layer thicknesses from 2.2 microm to 8.6 microm and those in which the grain size of the dielectrics varied from 0.28 microm to 0.39 microm while the layer thickness was held constant. In both cases, core-shell microstructures were observed. It was found that as the dielectric thickness decreased, the small and high electric field dielectric constants decreased, as did the peaks near the origin in the irreversible and reversible parts of the FORC distribution. The reversible FORC distributions of all the parts did not converge at high bias. These results indicate that the thickness dependence is attributable to a low dielectric constant interfacial layer and/or Schottky depletion layer at dielectric-electrode interfaces. It was also found that the high field dielectric constant, the peak in the irreversible FORC distribution at the origin, and the reversible FORC distribution at zero bias decreased as grain size decreased, as was observed for the undoped ceramics. The reversible FORC distribution of all the parts converged at high biases, indicating the grain size dependence was influenced by domain wall contributions. Dielectric contributions from the core and shell were estimated based on the temperature dependence of the permittivity. Not unexpectedly, the relative response of the core decreased while that of the shell increased as the grain size decreased. A Preisach model using the measured FORC distribution gave a good fit to the experimental polarization-electric field loops as a function of grain size and dielectric layer thickness.

  16. An ultrathin but nearly perfect direct current electric cloak

    NASA Astrophysics Data System (ADS)

    Xiang Jiang, Wei; Yang Luo, Chen; Lei Mei, Zhong; Jun Cui, Tie

    2013-01-01

    We propose and experimentally demonstrate an ultrathin but nearly perfect dc electric invisibility cloak. In the dc limit, transformation optics reduces to transformation electrostatics. Based on a special coordinate transformation, we derive a nearly perfect dc electric cloak which is composed of homogeneous and anisotropic conducting material. Due to the homogeneity feature, the dc cloak is realized using an ultrathin dc metamaterial with only one-unit-cell thickness, which is the ultra limit for practical artificial materials. Although ultrathin, our experimental results show that the dc cloak has excellent performance with nearly perfect cloaking behaviour.

  17. Ultrathin planar hematite film for solar photoelectrochemical water splitting.

    PubMed

    Liu, Dong; Bierman, David M; Lenert, Andrej; Yu, Hai-Tong; Yang, Zhen; Wang, Evelyn N; Duan, Yuan-Yuan

    2015-11-30

    Hematite holds promise for photoelectrochemical (PEC) water splitting due to its stability, low-cost, abundance and appropriate bandgap. However, it suffers from a mismatch between the hole diffusion length and light penetration length. We have theoretically designed and characterized an ultrathin planar hematite/silver nanohole array/silver substrate photoanode. Due to the supported destructive interference and surface plasmon resonance, photons are efficiently absorbed in an ultrathin hematite film. Compared with ultrathin hematite photoanodes with nanophotonic structures, this photoanode has comparable photon absorption but with intrinsically lower recombination losses due to its planar structure and promises to exceed the state-of-the-art photocurrent of hematite photoanodes. PMID:26698797

  18. Characterization of ultrathin oxide-based multilayer SERS nanoprobes for intracellular sensing

    NASA Astrophysics Data System (ADS)

    Strobbia, Pietro; Cullum, Brian M.

    2014-05-01

    Photonic nanosensors (e.g. PEBBLES, quantum dots-based sensors, etc.) have begun to allow the study of these previously inaccessible environments. Unfortunately, many current techniques suffer from biocompatibility issues, limited ability to monitor multiple species simultaneously and/or complicated fabrication chemistries. Recently SERS immuno-nanoprobes have demonstrated the capability to overcome many of these limitations. Such intracellular SERS nanosensors require optimized substrate geometry to achieve the sensitivity necessary to detect the trace analyte concentrations present. To address this, we have developed a novel multilayered SERS substrate nanoarchitecture that is capable of enhancing SERS signals by over two orders of magnitude relative to comparable single layer substrates. These structures are fabricated using different deposition techniques (PVD, ALD, etc) in which multiple films of Ag (between 10-125 nm thick) are alternately deposited with ultrathin dielectric layers (tens of Å). This geometry allows surface plasmons from different metal layers to be generated. The resulting multilayer enhancement increases the sensitivity while also improving the robustness of the nanoprobes. In this paper, we investigate and characterize SERS immuno-nanoprobes fabricated using this multilayered geometry and discuss the effect of the dielectric spacer (Ag2O, TiO2, Ta2O5) work functions and conductive band offsets on the multilayer enhancement.

  19. 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.

  20. 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

    2015-11-21

    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 εr = 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

  1. 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

    2015-11-14

    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

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

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    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.

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

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    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.

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

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    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.

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

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    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.

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

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    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.

  7. PREFACE: Dielectrics 2011

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Lewin, Paul

    2011-08-01

    In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of 1968 at Gregynog Hall of the University of Wales. In the intervening 43 years, this series of meetings has addressed many topics, including dielectric relaxation, high field phenomena, biomaterials and even molecular electronics, and has been held at many different venues within the UK. However, in the early 1990s, a regular venue was established at the University of Kent at Canterbury and, it this respect, this year's conference can be considered as "Dielectrics coming home". The format for the 2011 meeting followed that established at Dielectrics 2009, in breaking away from the concept of a strongly themed event that held sway during the mid 2000s. Rather, we again adopted a general, inclusive approach that was based upon four broad technical areas: Theme 1: Insulation/HV Materials Theme 2: Dielectric Spectroscopy Theme 3: Modelling Dielectric Response Theme 4: Functional Materials The result was a highly successful conference that attracted more than 60 delegates from eight countries, giving the event a truly international flavour, and which included both regular and new attendees; it was particularly pleasing to see the number of early career researchers at the meeting. Consequently, the organizing committee would like to thank our colleagues at the IOP, the invited speakers, our sponsors and all the delegates for making the event such a success. Finally, we look forward to convening again in 2013, when we will be returning to The University of Reading. Prof Alun Vaughan and Prof Paul Lewin, Editors

  8. Nitric acid compensated aluminum oxide dielectrics with improved negative bias reliability and positive bias temperature response

    NASA Astrophysics Data System (ADS)

    Lin, Chien-Chih; Hwu, Jenn-Gwo

    2013-02-01

    The room-temperature nitric acid (HNO3) compensation method is introduced to effectively improve the dielectric quality of ultrathin aluminum oxide (Al2O3) gate dielectrics under low thermal budget consideration. The physical properties, electrical characteristics, and temperature response of Al2O3 metal-oxide-semiconductor (MOS) devices without and with HNO3 compensation are compared. The surface roughness and interface trap density are obviously decreased by utilizing HNO3 compensation. Under negative gate bias, the leakage current, hard breakdown characteristics, and temperature-dependent reliability of the Al2O3 MOS(p) capacitors are clearly improved by HNO3 compensation. Under positive gate bias, the highly temperature-dependent current is principally dominated by generation-recombination mechanism. However, the diodes without HNO3 compensation show irregular temperature response especially at temperature above 70 °C. From Frenkel-Poole emission analysis, the oxide traps in Al2O3 without HNO3 compensation are responsible to this abnormal temperature response. These results suggest that the quality of ultrathin Al2O3 gate dielectrics can be cost-effectively improved by HNO3 compensation.

  9. 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.

  10. Nanopyramid structure for ultrathin c-Si tandem solar cells.

    PubMed

    Li, Guijun; Li, He; Ho, Jacob Y L; Wong, Man; Kwok, Hoi Sing

    2014-05-14

    Recently, ultrathin crystalline silicon solar cells have gained tremendous interest because they are deemed to dramatically reduce material usage. However, the resulting conversion efficiency is still limited by the incomplete light absorption in such ultrathin devices. In this letter, we propose ultrathin a-Si/c-Si tandem solar cells with an efficient light trapping design, where a nanopyramid structure is introduced between the top and bottom cells. The superior light harvesting results in a 48% and 35% remarkable improvement of the short-circuit current density for the top and bottom cells, respectively. Meanwhile, the use of SiOx mixed-phase nanomaterial helps to provide the maximum light trapping without paying the price of reduced electrical performance, and conversion efficiencies of up to 13.3% have been achieved for the ultrathin tandem cell employing only 8 μm of silicon, which is 29% higher than the result obtained for the planar cell. PMID:24730470

  11. A luminescent ultrathin film with reversible sensing toward pressure.

    PubMed

    Li, Mingwan; Tian, Rui; Yan, Dongpeng; Liang, Ruizheng; Wei, Min; Evans, David G; Duan, Xue

    2016-03-17

    A flexible ultrathin film based on alternate assembly of a sodium polyacrylate (PAA) modified styrylbiphenyl derivative (BTBS) and layered double hydroxide nanosheets is fabricated, which exhibits pressure-responsive photoluminescence with a high sensitivity and good reversibility. PMID:26950695

  12. Coherent perfect absorption in an all-dielectric metasurface

    NASA Astrophysics Data System (ADS)

    Zhu, Weiren; Xiao, Fajun; Kang, Ming; Premaratne, Malin

    2016-03-01

    We design and analyze an ultra-thin metasurface consists of mono-layer all-dielectric fishnet structure. It is demonstrated that coherent perfect absorption (CPA) can be achieved in such a metasurface, and the coherent absorptivity is controllable from 0.38% to 99.85% by phase modulation. The angular selectivity of the metasurface shows the feasibility of CPA in oblique incidence circumstances, where the CPA frequency splits into two frequency bands for TE and TM polarizations. Further study reveals that while retaining CPA, the CPA frequency of the metasurface can be manipulated from 8.56 to 13.47 GHz by solely adjusting the thickness of the fishnet metasurface.

  13. Ultra-thin microporous/hybrid materials

    DOEpatents

    Jiang, Ying-Bing; Cecchi, Joseph L.; Brinker, C. Jeffrey

    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.

  14. 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.

  15. Self-organized ultrathin oxide nanocrystals.

    PubMed

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

    2009-03-01

    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. PMID:19206219

  16. 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.

  17. Ultrathin optical design for organic photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Man, J. X.; Luo, D. Y.; Yu, L. M.; Wang, D. K.; Liu, Z.; Lu, Z. H.

    2015-05-01

    A trilayer ultrathin-film model concept had been adapted to maximize optical absorption of organic photovoltaic cells (OPVs) with a structure of transparent-electrode/highly-absorbing active material/metal. As demonstrated, device with the structure of ITO/Lead phthalocyanine (SubPc):Buckerminster fullerene (C60) (1:4 wt%)/Al had been studied. It is found that more than 90% optical absorption can be obtained in the device with a broaden wavelength range of 480-620 nm. The calculated optical electric fields shows that the unusually high optical absorption is due to the enhanced optical interference inside the OPVs device. This work paved a new way to design the OPVs device.

  18. Improved Performance of Dye-Sensitized Solar Cells Fabricated from a Coumarin NKX-2700 Dye-Sensitized TiO2/MgO Core-Shell Photoanode with an HfO2 Blocking Layer and a Quasi-Solid-State Electrolyte

    NASA Astrophysics Data System (ADS)

    Maheswari, D.; Venkatachalam, P.

    2015-03-01

    Dye sensitized solar cells (DSSC) were fabricated from a coumarin NKX-2700 dye-sensitized core-shell photoanode and a quasi-solid-state electrolyte, sandwiched together, with a cobalt sulfide-coated counter electrode. The core-shell photoanode consisted of a composite mixture of 90% TiO2 nanoparticles and 10% TiO2 nanowires (TNPW) as core layer and MgO nanoparticles (MNP) as shell layer. Hafnium oxide (HfO2) was applied to the core-shell photoanode film as a blocking layer. TiO2 nanoparticles, TiO2 nanowires, and TNPW/MNP were characterized by x-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. It was apparent from the UV-visible spectrum of the sensitizing dye coumarin NKX-2700 that its absorption was maximum at 525 nm. Power conversion efficiency (PCE) was greater for DSSC-1, fabricated with a core-shell TNPW/MNP/HfO2 photoanode, than for the other DSSC; its photovoltaic properties were: short circuit photocurrent J sc = 19 mA/cm2, open circuit voltage ( V oc) = 720 mV, fill factor ( FF) = 66%, and PCE ( η) = 9.02%. The charge-transport and charge-recombination behavior of the DSSC were investigated by electrochemical impedance spectroscopy; the results showed that the composite core-shell film resulted in the lowest charge-transfer resistance ( R CE) and the longest electron lifetime ( τ eff). Hence, the improved performance of DSSC-1 could be ascribed to the core-shell photoanode with blocking layer, which increased electron transport and suppressed recombination of charge carriers at the photoanode/dye/electrolyte interface.

  19. Controlling birefringence in dielectrics

    NASA Astrophysics Data System (ADS)

    Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

    2011-06-01

    Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.

  20. Superdirective dielectric nanoantennas

    NASA Astrophysics Data System (ADS)

    Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

    2014-06-01

    We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

  1. 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)

  2. 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.

  3. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

    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.

  4. 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.

  5. 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.

  6. MoS2 functionalization for ultra-thin atomic layer deposited dielectrics

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated. It is found that a UV-O3 pre-treatment removes adsorbed carbon contamination from the MoS2 surface and also functionalizes the MoS2 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 MoS2 surface and provides nucleation sites for atomic layer deposition of Al2O3. The enhanced nucleation is found to be dependent on the thin film deposition temperature.

  7. 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

  8. 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.

  9. Dielectric elastomer memory

    NASA Astrophysics Data System (ADS)

    O'Brien, Benjamin M.; McKay, Thomas G.; Xie, Sheng Q.; Calius, Emilio P.; Anderson, Iain A.

    2011-04-01

    Life shows us that the distribution of intelligence throughout flexible muscular networks is a highly successful solution to a wide range of challenges, for example: human hearts, octopi, or even starfish. Recreating this success in engineered systems requires soft actuator technologies with embedded sensing and intelligence. Dielectric Elastomer Actuator(s) (DEA) are promising due to their large stresses and strains, as well as quiet flexible multimodal operation. Recently dielectric elastomer devices were presented with built in sensor, driver, and logic capability enabled by a new concept called the Dielectric Elastomer Switch(es) (DES). DES use electrode piezoresistivity to control the charge on DEA and enable the distribution of intelligence throughout a DEA device. In this paper we advance the capabilities of DES further to form volatile memory elements. A set reset flip-flop with inverted reset line was developed based on DES and DEA. With a 3200V supply the flip-flop behaved appropriately and demonstrated the creation of dielectric elastomer memory capable of changing state in response to 1 second long set and reset pulses. This memory opens up applications such as oscillator, de-bounce, timing, and sequential logic circuits; all of which could be distributed throughout biomimetic actuator arrays. Future work will include miniaturisation to improve response speed, implementation into more complex circuits, and investigation of longer lasting and more sensitive switching materials.

  10. 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.

  11. 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.

  12. Molds for cable dielectrics

    DOEpatents

    Roose, Lars D.

    1996-01-01

    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.

  13. Electrical and reliability characteristics of Mn-doped nano BaTiO3-based ceramics for ultrathin multilayer ceramic capacitor application

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Zhang, Shaopeng; Tian, Zhibin; Li, Longtu

    2012-12-01

    Nano BaTiO3-based dielectric ceramics were prepared by chemical coating approach, which are promising for ultrathin multilayer ceramic capacitor (MLCC) applications. The doping effects of Mn element on the microstructures and dielectric properties of the ceramics were investigated. The degradation test and impedance spectroscopy were employed to study the resistance degradation and the conduction mechanism of Mn-doped nano-BaTiO3 ceramic samples. It has been found that the reliability characteristics greatly depended on the Mn-doped content. Moreover, the BaTiO3 ceramic with grain size in nanoscale is more sensitive to the Mn-doped content than that in sub-micron scale. The addition of 0.3 mol. % Mn is beneficial for improving the reliability of the nano BaTiO3-based ceramics, which is an important parameter for MLCC applications. However, further increasing the addition amount will deteriorate the performance of the ceramic samples.

  14. 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.

  15. Model of dissipative dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Chiang Foo, Choon; Cai, Shengqiang; Jin Adrian Koh, Soo; Bauer, Siegfried; Suo, Zhigang

    2012-02-01

    The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric elastomers under cyclic voltage.

  16. Interfacial diffusion behavior in Ni-BaTiO 3 MLCCs with ultra-thin active layers

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Tian, Zhibin; Zhang, Hui; Li, Longtu

    2014-03-01

    The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from -55°C to 85°C, at a temperature capacitance coefficient within ±15%) with ultra-thin active layers ( T = 1-3 µm) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1-3 µm), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

  17. Cellulose as biodegradable high-k dielectric layer in organic complementary inverters

    NASA Astrophysics Data System (ADS)

    Petritz, A.; Wolfberger, A.; Fian, A.; Irimia-Vladu, M.; Haase, A.; Gold, H.; Rothländer, T.; Griesser, T.; Stadlober, B.

    2013-10-01

    We report on the natural source based and biodegradable material cellulose on Al2O3 as ultrathin hybrid high-k dielectric layer for applications in green electronics. Dielectric films of 16 nm cellulose (ɛ ≈ 8.4) and 8 nm Al2O3 (ɛ ≈ 9) exhibit low leakage currents up to electric fields of 1.5 MV/cm. Pentacene and C60 based organic thin film transistors show a well-balanced performance with operation voltages around 2 V. They are implemented in complementary inverters with excellent switching behavior, a small-signal gain up to 60 and with exceptionally high and balanced noise margin values of 82% at ultralow operation voltage (VDD = 2.5 V).

  18. Ultrathin CuO nanorods: controllable synthesis and superior catalytic properties in styrene epoxidation.

    PubMed

    Jia, Wei; Liu, Yuxi; Hu, Pengfei; Yu, Rong; Wang, Yu; Ma, Lei; Wang, Dingsheng; Li, Yadong

    2015-05-25

    Ultrathin copper oxide (CuO) nanorods with diameters of ∼3.6 nm were obtained in one step using oleylamine (OAm) as both the solvent and the surface controller. The oriented attachment is responsible for the formation of the ultrathin CuO nanorods. Furthermore, this ultrathin nanostructure catalyst exhibited excellent activity and high styrene oxide yields in styrene epoxidation. PMID:25920405

  19. 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.

  20. Versatile ultrathin nanoporous silicon nitride membranes

    PubMed Central

    Vlassiouk, Ivan; Apel, Pavel Y.; Dmitriev, Sergey N.; Healy, Ken; Siwy, Zuzanna S.

    2009-01-01

    Single- and multiple-nanopore membranes are both highly interesting for biosensing and separation processes, as well as their ability to mimic biological membranes. The density of pores, their shape, and their surface chemistry are the key factors that determine membrane transport and separation capabilities. Here, we report silicon nitride (SiN) membranes with fully controlled porosity, pore geometry, and pore surface chemistry. An ultrathin freestanding SiN platform is described with conical or double-conical nanopores of diameters as small as several nanometers, prepared by the track-etching technique. This technique allows the membrane porosity to be tuned from one to billions of pores per square centimeter. We demonstrate the separation capabilities of these membranes by discrimination of dye and protein molecules based on their charge and size. This separation process is based on an electrostatic mechanism and operates in physiological electrolyte conditions. As we have also shown, the separation capabilities can be tuned by chemically modifying the pore walls. Compared with typical membranes with cylindrical pores, the conical and double-conical pores reported here allow for higher fluxes, a critical advantage in separation applications. In addition, the conical pore shape results in a shorter effective length, which gives advantages for single biomolecule detection applications such as nanopore-based DNA analysis. PMID:19948951

  1. Crystallization Properties of Ultrathin Phase Change Films

    SciTech Connect

    Raoux,S.; Jordan-Sweet, J.; Kellock, A.

    2008-01-01

    The crystallization behavior of ultrathin phase change films was studied using time-resolved x-ray diffraction (XRD). Thin films of variable thickness between 1 and 50?nm of the phase change materials Ge2Sb2Te5 (GST), N-doped GST, Ge15Sb85, Sb2Te, and Ag- and In-doped Sb2Te were heated in a He atmosphere, and the intensity of the diffracted x-ray peaks was recorded. It was found for all materials that the crystallization temperature increases as the film thickness is reduced below 10?nm. The increase depends on the material and can be as high as 200? C for the thinnest films. The thinnest films that show XRD peaks are 2?nm for GST and N-GST, 1.5?nm for Sb2Te and AgIn-Sb2Te, and 1.3?nm for GeSb. This scaling behavior is very promising for the application of phase change materials to solid-state memory technology.

  2. Optimized actuators for ultrathin deformable primary mirrors.

    PubMed

    Laslandes, Marie; Patterson, Keith; Pellegrino, Sergio

    2015-05-20

    A novel design and selection scheme for surface-parallel actuators for ultrathin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented. PMID:26192533

  3. Inducing electric polarization in ultrathin insulating layers

    NASA Astrophysics Data System (ADS)

    Martinez-Castro, Jose; Piantek, Marten; Persson, Mats; Serrate, David; Hirjibehedin, Cyrus F.

    Studies of ultrathin polar oxide films have attracted the interest of researchers for a long time due to their different properties compared to bulk materials. However they present several challenges such as the difficulty in the stabilization of the polar surfaces and the limited success in tailoring their properties. Moreover, recently developed Van der Waals materials have shown that the stacking of 2D-layers trigger new collective states thanks to the interaction between layers. Similarly, interface phenomena emerge in polar oxides, like induced ferroelectricity. This represents a promising way for the creation of new materials with customized properties that differ from those of the isolated layers. Here we present a new approach for the fabrication and study of atomically thin insulating films. We show that the properties of insulating polar layers of sodium chloride (NaCl) can be engineered when they are placed on top of a charge modulated template of copper nitride (Cu2N). STM studies carried out in ultra-high vacuum and at low temperatures over NaCl/Cu2N/Cu(001) show that we are able to build up and stabilize interfaces of polar surface at the limit of one atomic layer showing new properties not present before at the atomic scale.

  4. Application of Infrared Nanooptics to Ultrathin Materials

    NASA Astrophysics Data System (ADS)

    Andreev, Gregory

    My thesis describes the study of nanoscale physics using infrared spectroscopy and nanoscopy methods. The first phase of my research was the development of new methods for tuning metamaterials, which possess custom tailored optical properties not easily found in nature. Working together with Tom Driscoll, I co-invented a simple yet effective method for tuning the magnetic permeability of a Split Ring Resonator based metamaterial. This is the topic of Chapter 1. My subsequent research dealt with near field optics, in particular the application of the infrared imaging method of scattering Scanning Nearfield Optical Microscopy to ultrathin materials such as single layer Graphene and 2nm thin SiO2 layers on Silicon. On both of these materials we demonstrated incredible sensitivity to ≤ 10x10x1nm3 volumes (Chapter 3). Thanks to the incredibly large momenta of the evanescent light utilized in sSNOM, we also discovered a rich array of previously unobserved physics in Graphene. In particular, we were able to observe the resonance enhancement of the SiO2 phonon by the presence of plasmon oscillations in Graphene (Chapter 2). Lastly, a large part of my thesis work also involved building the first cryogenic sSNOM with which we were able to directly image the metal to insulator transition in the correlated oxide: V2O3, shown in the last chapter.

  5. Temperature switchable polymer dielectrics.

    SciTech Connect

    Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

    2010-06-01

    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).

  6. 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).

  7. Principles of dielectrics

    SciTech Connect

    Scaife, B.K.P.

    1989-01-01

    This paper focuses on basic principles of the theory of dielectrics. Concentrates on fundamentals including relevant areas of electrostatics. Author takes a completely classical approach, avoiding quantum mechanics altogether. The electrostatic field in free space, multipole-moment fluctuations the generalized Kubo equation, the thermodynamics of electrostriction, and the incremental permittivity tensor are among the specific topics examined. Extensive appendices, specific journal references, and a general bibliography are included. Intended for advanced undergraduates in the physical sciences.

  8. Dielectric spectroscopy of polyaniline

    SciTech Connect

    Calleja, R.D.; Matveeva, E.M.

    1993-12-31

    Polyaniline films (PANI) are being considered as attractive new galvanic sources, electrochromic displays, chemical sensors, etc. So far much work has been done to study their optical, electrochemical and electrical properties. However, there are still doubts about the basic electric conductivity mechanisms of PANI. The aim of this paper is to study the influence of water molecules and acid anions on the properties of PANI films by dielectric spectroscopy.

  9. Resilience of ultra-thin oxynitride films to percolative wear-out and reliability implications for high-κ 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-κ-SiOx interfacial layer gate stacks, wherein the SiOx layer seems to be the weakest link for percolation event.

  10. A review of special gate coupling effects in long-channel SOI MOSFETs with lightly doped ultra-thin bodies and their compact analytical modeling

    NASA Astrophysics Data System (ADS)

    Rudenko, T.; Nazarov, A.; Kilchytska, V.; Flandre, D.

    2016-03-01

    The charge coupling between the front and back gates is a fundamental property of any fully-depleted silicon-on-insulator (SOI) MOSFET. It is traditionally described by the classical Lim and Fossum model (Lim and Fossum, 1983). However, in the case of lightly-doped ultra-thin-body (UTB) SOI MOSFETs with ultra-thin gate dielectrics, significant deviations from this model have been observed and analyzed over the years. In this paper, we present a thorough review of special features of gate coupling in such devices, combining a large set of results from one-dimensional numerical simulations in classical and quantum-mechanical modes, experimental data and analytical modeling. We show that UTB SOI MOSFETs with ultra-thin gate dielectrics feature stronger modulation of the threshold voltage at the conduction side with opposite gate bias and much wider range of gate voltages for interface coupling than predicted by the Lim and Fossum model. These differences originate from both electrostatic and quantization effects. A simple analytical model taking into account these effects is presented. The model enables an easy assessment of the quantization-induced threshold voltage increase in a long-channel SOI MOSFET versus opposite gate bias and the electric field in the silicon film associated with gate decoupling.

  11. 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.

  12. 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).

  13. 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

  14. Ultra-thin Graphitic Film: Synthesis and Physical Properties

    NASA Astrophysics Data System (ADS)

    Kaplas, Tommi; Kuzhir, Polina

    2016-02-01

    A scalable technique of chemical vapor deposition (CVD) growth of ultra-thin graphitic film is proposed. Ultra-thin graphitic films grown by a one-step CVD process on catalytic copper substrate have higher crystallinity than pyrolytic carbon grown on a non-catalytic surface and appear to be more robust than a graphene monolayer. The obtained graphitic material, not thicker than 8 nm, survives during the transfer process from a Cu substrate without a template polymer layer, typically used in the graphene transfer process to protect graphene. This makes the transfer process much more simple and cost-effective. Having electrical and optical properties compatible with what was observed for a few layers of CVD graphene, the proposed ultra-thin graphitic film offers new avenues for implementing 2D materials in real-world devices.

  15. Ultra-thin single crystal perovskite ferroelectric on Silicon

    NASA Astrophysics Data System (ADS)

    Bakaul, Saidur; Serrao, Claudy; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Single crystalline ultra-thin films (sub-10 nm) of ferroelectric complex oxides are important for tunnelling memory devices. Commercially viable realization of such devices requires their integration with the peripheral Si-based input-output electronics. Integration of single crystalline films of such oxides using direct synthesis remains challenging due to the fundamental crystal chemistry and mechanical incompatibility of dissimilar interfaces. In this work we report epitaxial transfer of ultra-thin single crystalline, oxide films (down to 1 unit cell) onto Si substrates, at room temperature. The thickness of the transferred films has been confirmed by atomic force microscopy. Piezoelectric force microscopy shows ferroelectric property is retained in the transferred film. Electrical transport studies on these transferred ultra-thin films are ongoing.

  16. 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

  17. Organic light-emitting diodes with nanostructured fullerene ultrathin layers

    NASA Astrophysics Data System (ADS)

    Lü, Zhaoyue; Deng, Zhenbo; Zheng, Jianjie; Yin, Yuehong; Chen, Yanli; Wang, Yongsheng

    2010-01-01

    Organic light-emitting diodes (OLEDs) with nanostructured fullerene (C 60) ultrathin layers were fabricated. The luminance and efficiency are decreased due to exciton quenching in the OLEDs with C 60 layers at the N,N‧-Di (naphth-2-yl)-N, N‧-diphenyl-benzidine (NPB)/8-hydroxyquinoline aluminum (Alq 3) interface. It is opposite to the results reported by Kato [K. Kato, K. Takahashi, K. Suzuki, T. Sato, K. Shinbo, F. Kaneko et al., Curr. Appl. Phys. 5, 2005, 321]. And C 60 ultrathin layers play a role of weak p-type delta-dopant in the NPB layer due to forming of a charge transfer complex C 60-:NPB +. The current density and luminance are enhanced in the OLEDs with 0.7 nm C 60 ultrathin layers inserted in NPB layer. A suggested explanation is p-type delta-doping effect in the NPB layer which increases the charge mobility of NPB films.

  18. Ultra-thin Graphitic Film: Synthesis and Physical Properties.

    PubMed

    Kaplas, Tommi; Kuzhir, Polina

    2016-12-01

    A scalable technique of chemical vapor deposition (CVD) growth of ultra-thin graphitic film is proposed. Ultra-thin graphitic films grown by a one-step CVD process on catalytic copper substrate have higher crystallinity than pyrolytic carbon grown on a non-catalytic surface and appear to be more robust than a graphene monolayer. The obtained graphitic material, not thicker than 8 nm, survives during the transfer process from a Cu substrate without a template polymer layer, typically used in the graphene transfer process to protect graphene. This makes the transfer process much more simple and cost-effective. Having electrical and optical properties compatible with what was observed for a few layers of CVD graphene, the proposed ultra-thin graphitic film offers new avenues for implementing 2D materials in real-world devices. PMID:26831692

  19. Tunable dielectric properties of ferrite-dielectric based metamaterial.

    PubMed

    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

  20. High dielectric hyperbranched polyaniline materials.

    PubMed

    Yan, X Z; Goodson, T

    2006-08-01

    New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency. PMID:16869570

  1. 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.

  2. Enhanced charge storage of ultrathin polythiophene films within porous nanostructures.

    PubMed

    Nejati, Siamak; Minford, Thomas E; Smolin, Yuriy Y; Lau, Kenneth K S

    2014-06-24

    In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance. PMID:24840296

  3. 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.

  4. Method for laser welding ultra-thin metal foils

    DOEpatents

    Pernicka, John C.; Benson, David K.; Tracy, C. Edwin

    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.

  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. 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 μm) 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.

  7. Gate Last Indium-Gallium-Arsenide MOSFETs with Regrown Source-Drain Regions and ALD Dielectrics

    NASA Astrophysics Data System (ADS)

    Carter, Andrew Daniel

    III-V-based MOSFETs have the potential to exceed the performance of silicon-based MOSFETs due to the semiconductor's small electron effective mass. Modern silicon-based MOSFETs with 22 nm gate lengths utilize high-k gate insulators and non-planar device geometries to optimize device performance. III-V HEMT technology has achieved similar gate lengths, but large source-drain access resistances and the lack of high-quality gate insulators prevent further device performance scaling. Sub-22 nm gate length III-V MOSFETs require metal-semiconductor contact resistivity to be less than 1 ohm-micron squared, gate insulators with less than 1 nm effective oxide thickness, and semiconductor-insulator interface trap densities less than 2E12 per square centimeter per electron volt. This dissertation presents InGaAs-based III-V MOSFET process flows and device results to assess their use in VLSI circuits. Previous III-V MOSFET results focused on long (>100 nm) gate lengths and ion implantation for source-drain region formation. Scaling III-V MOSFETs to shorter gate lengths requires source-drain regions that have low sheet resistance, high mobile charge densities, and low metal-semiconductor contact resistance. MBE- and MOCVD-based raised epitaxial source-drain regrowth meet these requirements. MBE InAs source-drain regrowth samples have shown 0.5 to 2 ohm-micron squared metal semiconductor contact resistivities. MOCVD InGaAs source-drain regrowth samples have shown < 100 ohm-micron single-sided access resistance to InGaAs MOSFETs. Gate insulators on III-V materials require large conduction band offsets to the channel, high dielectric permittivities, and low semiconductor-insulator interface trap densities. An in-situ hydrogen plasma / trimethylaluminum treatment has been developed to lower the gate semiconductor-insulator interface trap density. This treatment, done immediately before gate insulator deposition, has been shown to lower MOS capacitor interface trap densities by more than a factor of two. Devices using gate-first MBE regrowth, gate-last MBE regrowth, and gate-last MOCVD regrowth were fabricated and resulting devices characterized. 65 nm gate length gate-first MBE regrowth devices employing a 2.2 nm EOT Al 2O3 gate insulator show peak transconductances of 0.3 mS/micron at 1 V Vds. Gate-first FET performance scaling is limited by processed-induced damage and ungated access regions. 64 nm gate length gate-last MBE regrowth devices employing a 1.21 nm EOT Al2O 3 / HfO2 bi-layer gate insulator show peak transconductances of 1.4 mS/micron at 0.5 V Vds. Other gate-last MBE samples had long channel subthreshold swings as low as 117 mV/dec. 48 nm gate length gate-last MOCVD MOSFETs employing a 0.8 nm EOT HfO2 gate insulator and digital channel etching show peak transconductances of 2 mS/micron at 0.5 V Vds, with long channel devices having 97 mV/dec subthreshold swing.

  8. Utilizing self-assembled-monolayer-based gate dielectrics to fabricate molybdenum disulfide field-effect transistors

    NASA Astrophysics Data System (ADS)

    Kawanago, Takamasa; Oda, Shunri

    2016-01-01

    In this study, we apply self-assembled-monolayer (SAM)-based gate dielectrics to the fabrication of molybdenum disulfide (MoS2) field-effect transistors. A simple fabrication process involving the selective formation of a SAM on metal oxides in conjunction with the dry transfer of MoS2 flakes was established. A subthreshold slope (SS) of 69 mV/dec and no hysteresis were demonstrated with the ultrathin SAM-based gate dielectrics accompanied by a low gate leakage current. The small SS and no hysteresis indicate the superior interfacial properties of the MoS2/SAM structure. Cross-sectional transmission electron microscopy revealed a sharp and abrupt interface of the MoS2/SAM structure. The SAM-based gate dielectrics are found to be applicable to the fabrication of low-voltage MoS2 field-effect transistors and can also be extended to various layered semiconductor materials. This study opens up intriguing possibilities of SAM-based gate dielectrics in functional electronic devices.

  9. 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.

  10. Structure of Ultrathin MgO Films on Mo(001)

    SciTech Connect

    Gallagher, Marc C.; Fyfield, Margaret S.; Bumm, Lloyd A.; Cowin, James P.; Joyce , Stephen A.

    2003-11-24

    We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films.

  11. 4-fold photocurrent enhancement in ultrathin nanoplasmonic perovskite solar cells.

    PubMed

    Cai, Boyuan; Peng, Yong; Cheng, Yi-Bing; Gu, Min

    2015-11-30

    Although perovskite materials have been widely investigated for thin-film photovoltaic devices due to the potential for high efficiency, their high toxicity has pressed the development of a solar cell structure of an ultra-thin absorber layer. But insufficient light absorption could be a result of ultra-thin perovskite films. In this paper, we propose a new nanoplasmonic solar cell that integrates metal nanoparticles at its rear/front surfaces of the perovskite layer. Plasmon-enhanced light scattering and near-field enhancement effects from lumpy sliver nanoparticles result in the photocurrent enhancement for a 50 nm thick absorber, which is higher than that for a 300 nm thick flat perovskite solar cell. We also predict the 4-fold photocurrent enhancement in an ultrathin perovskite solar cell with the absorber thickness of 10 nm. Our results pave a new way for ultrathin high-efficiency solar cells with either a lead-based or a lead-free perovskite absorption layer. PMID:26698816

  12. 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.

  13. Microwave Propagation in Dielectric Fluids.

    ERIC Educational Resources Information Center

    Lonc, W. P.

    1980-01-01

    Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

  14. Low dielectric polyimide fibers

    NASA Technical Reports Server (NTRS)

    Dorogy, William E., Jr. (Inventor); St.clair, Anne K. (Inventor)

    1994-01-01

    A high temperature resistant polyimide fiber that has a dielectric constant of less than 3 is presented. The fiber was prepared by first reacting 2,2-bis (4-(4aminophenoxy)phenyl) hexafluoropropane with 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an aprotic solvent to form a polyamic acid resin solution. The polyamic acid resin solution is then extruded into a coagulation medium to form polyamic acid fibers. The fibers are thermally cured to their polyimide form. Alternatively, 2,2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane is reacted with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride to form a polyamic acid, and the polyamic acid is chemically converted to its polyimide form. The polyimide is then dissolved in a solvent to form a polyimide resin solution, and the polyimide resin is extruded into a coagulation medium to form a polyimide wet gel filament. In order to obtain polyimide fibers of increased tensile properties, the polyimide wet gel filaments are stretched at elevated temperatures. The tensile properties of the fibers were measured and found to be in the range of standard textile fibers. Polyimide fibers obtained by either method will have a dielectric constant similar to that of the corresponding polymer, viz., less than 3 at 10 GHz.

  15. Hexagonal boron nitride: Ubiquitous layered dielectric for two-dimensional electronics

    NASA Astrophysics Data System (ADS)

    Jain, Nikhil

    Hexagonal boron nitride (h-BN), a layer-structured dielectric with very similar crystalline lattice to that of graphene, has been studied as a ubiquitous dielectric for two-dimensional electronics. While 2D materials may lead to future platform for electronics, traditional thin-film dielectrics (e.g., various oxides) make highly invasive interface with graphene. Multiple key roles of h-BN in graphene electronics are explored in this thesis. 2D graphene/h-BN heterostructures are designed and implemented in diverse configurations in which h-BN is evaluated as a supporting substrate, a gate dielectric, a passivation layer, or an interposing barrier in "3D graphene" superlattice. First, CVD-grown graphene on h-BN substrate shows improved conductivity and resilience to thermally induced breakdown, as compared with graphene on SiO2, potentially useful for high-speed graphene devices and on-chip interconnects. h-BN is also explored as a gate dielectric for graphene field-effect transistor with 2D heterostructure design. The dielectric strength and tunneling behavior of h-BN are investigated, confirming its robust nature. Next, h-BN is studied as a passivation layer for graphene electronics. In addition to significant improvement in current density and breakdown threshold, fully encapsulated graphene exhibits minimal environmental sensitivity, a key benefit to 2D materials which have only surfaces. Lastly, reduction in interlayer carrier scattering is observed in a double-layered graphene setup with ultrathin h-BN multilayer as an interposing layer. The DFT simulation and Raman spectral analysis indicate reduction in interlayer scattering. The decoupling of the two graphene monolayers is further confirmed by electrical characterization, as compared with other referencing mono- and multilayer configurations. The heterostructure serves as the building element in "3D graphene", a versatile platform for future electronics.

  16. Self-assembly of large-scale and ultrathin silver nanoplate films with tunable plasmon resonance properties.

    PubMed

    Zhang, Xiao-Yang; Hu, Anming; Zhang, Tong; Lei, Wei; Xue, Xiao-Jun; Zhou, Yunhong; Duley, Walt W

    2011-11-22

    We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications. PMID:21955107

  17. Dielectric Actuation of Polymers

    NASA Astrophysics Data System (ADS)

    Niu, Xiaofan

    Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 °C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP in tactile display is investigated by the prototyping of a large scale refreshable Braille display device. Braille is a critical way for the vision impaired community to learn literacy and improve life quality. Current piezoelectrics-based refreshable Braille display technologies are limited to up to 1 line of Braille text, due to the bulky size of bimorph actuators. Based on the unique actuation feature of BSEP, refreshable Braille display devices up to smartphone-size have been demonstrated by polymer sheet laminates. Dots in the devices can be individually controlled via incorporated field-driven BSEP actuators and Joule heater units. A composite material consisting of silver nanowires (AgNW) embedded in a polymer substrate is brought up as a compliant electrode candidate for BSEP application. The AgNW composite is highly conductive (Rs: 10 Ω/sq) and remains conductive at strains as high as 140% (Rs: <10 3 Ω/sq). The baseline conductivity has only small changes up to 90% strain, which makes it low enough for both field driving and stretchable Joule heating. An out-of-plane bistable area strain up to 68% under Joule heating is achieved.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Multilayer optical dielectric coating

    DOEpatents

    Emmett, John L.

    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.

  3. Dielectric permittivity of suspensions

    SciTech Connect

    Sushko, M. Ya.

    2007-08-15

    A strict macroscopic analysis of the limiting long-wavelength permittivity of a model suspension is presented in which the suspension is considered as a finely dispersed system consisting of isotropic dielectric balls with piecewise-continuous radial permittivity profile. The analysis is performed within the framework of the notion of compact groups of inhomogeneities and the procedure of field averaging over volumes significantly exceeding the scale of these groups. The indicated value is described by the Lorentz-Lorenz formula. The effective polarizability of balls in the suspension is reconstructed from their parameters and the parameters of the medium by means of integration. The result is valid for any concentration of the balls at which the suspension remains macroscopically homogeneous and isotropic with respect to the field and for an arbitrary difference between the ball and medium permittivities.

  4. A formula for dielectric mixtures

    SciTech Connect

    Tuncer, Enis

    2005-01-01

    Dielectric properties of material mixtures are of importance in diagnostics, characterization and design of systems in various engineering fields. In this letter, we propose a new dielectric-mixture expression, which is based on the dielectric relaxation phenomena and the spectral density representation. The expression is tested on several composite systems. Results illustrate that the proposed expression can be used to obtain valuable structural informations in composites, even for highly filled, bi-percolating, systems. The proposed expression is an alternative to other existing homogenization formulas in the literature.

  5. Structural, Dielectric, and Interface Properties of Crystalline Barium Silicate Films on Si(100): A Robust High-κ Material

    NASA Astrophysics Data System (ADS)

    Islam, S.; Hofmann, K. R.; Feldhoff, A.; Pfnür, H.

    2016-05-01

    The quality and crystallinity of ultrathin dielectric layers depend crucially on the details of interface formation and chemical stability. Using a combination of photoelectron (XPS) and electron-energy-loss spectroscopy, low-energy electron-diffraction, and transmission electron microscopy (TEM), we show that crystalline epitaxial layers of Ba2 SiO4 can be grown on Si(100) substrates from evaporated Ba in oxygen background atmosphere at 650 °C . Since the silicate is chemically by far more stable than the oxides of Si and Ba, an atomically sharp interface with no interface oxide is formed, as confirmed by XPS and TEM. However, the interface is rough on the atomic scale. dc and frequency-dependent electrical measurements reveal a relative dielectric constant of 22.8, low hysteresis in C V measurements, and low leakage currents but still fairly high interface trap densities.

  6. 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.

  7. Ultrathin and lightweight organic solar cells with high flexibility

    NASA Astrophysics Data System (ADS)

    Kaltenbrunner, Martin; White, Matthew S.; Głowacki, 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 μm 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.

  8. Transport and electromagnetic properties of ultrathin pyrolytic carbon films

    NASA Astrophysics Data System (ADS)

    Kuzhir, Polina P.; Ksenevich, Vitaly K.; Paddubskaya, Alesia G.; Maksimenko, Sergey A.; Kaplas, Tommi; Svirko, Yuri

    2013-01-01

    We experimentally investigated the electrical and electromagnetic (EM) properties of pyrolytic carbon (PyC) ultrathin films synthesized on a quartz substrate by chemical vapor deposition at 1100°C using low pressure CH4∶H2 gas mixture as carbon source. PyC films consist of randomly oriented and intertwined graphene ribbons, which have a typical size of a few nanometers. We discovered that the manufactured PyC films of 35-nm thickness provided remarkably high attenuation caused by absorption of 37% to 24% of incident microwave power. The temperature dependence of PyC's direct-current (DC) conductivity represents typical behavior for disordered systems. Being semitransparent in visible and infrared spectral range and highly conductive at room temperature, PyC films emerge as a promising material for manufacturing ultrathin microwave (e.g., Ka band) coatings to be used in aerospace applications.

  9. Strain-induced water dissociation on supported ultrathin oxide films.

    PubMed

    Song, Zhenjun; Fan, Jing; Xu, Hu

    2016-01-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this work, 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. PMID:26953105

  10. Competing weak localization and weak antilocalization in ultrathin topological insulators.

    PubMed

    Lang, Murong; He, Liang; Kou, Xufeng; Upadhyaya, Pramey; Fan, Yabin; Chu, Hao; Jiang, Ying; Bardarson, Jens H; Jiang, Wanjun; Choi, Eun Sang; Wang, Yong; Yeh, Nai-Chang; Moore, Joel; Wang, Kang L

    2013-01-01

    We demonstrate evidence of a surface gap opening in topological insulator (TI) thin films of (Bi(0.57)Sb(0.43))(2)Te(3) below six quintuple layers through transport and scanning tunneling spectroscopy measurements. By effective tuning the Fermi level via gate-voltage control, we unveil a striking competition between weak localization and weak antilocalization at low magnetic fields in nonmagnetic ultrathin films, possibly owing to the change of the net Berry phase. Furthermore, when the Fermi level is swept into the surface gap of ultrathin samples, the overall unitary behaviors are revealed at higher magnetic fields, which are in contrast to the pure WAL signals obtained in thicker films. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications. PMID:23198980

  11. 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.

  12. Strain-induced water dissociation on supported ultrathin oxide films

    NASA Astrophysics Data System (ADS)

    Song, Zhenjun; Fan, Jing; Xu, Hu

    2016-03-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this work, 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.

  13. 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.

  14. Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Boulle, Olivier; Vogel, Jan; Yang, Hongxin; Pizzini, Stefania; de Souza Chaves, Dayane; Locatelli, Andrea; Menteş, Tevfik Onur; Sala, Alessandro; Buda-Prejbeanu, Liliana D.; Klein, Olivier; Belmeguenai, Mohamed; Roussigné, Yves; Stashkevich, Andrey; Chérif, Salim Mourad; Aballe, Lucia; Foerster, Michael; Chshiev, Mairbek; Auffret, Stéphane; Miron, Ioan Mihai; Gaudin, Gilles

    2016-05-01

    Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii–Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

  15. Ultrathin Free-Standing Ternary-Alloy Nanosheets.

    PubMed

    Hong, Jong Wook; Kim, Yena; Wi, Dae Han; Lee, Seunghoon; Lee, Su-Un; Lee, Young Wook; Choi, Sang-Il; Han, Sang Woo

    2016-02-01

    A synthesis strategy for the preparation of ultrathin free-standing ternary-alloy nanosheets is reported. Ultrathin Pd-Pt-Ag nanosheets with a thickness of approximately 3 nm were successfully prepared by co-reduction of the metal precursors in an appropriate molar ratio in the presence of CO. Both the presence of CO and the interplay between the constituent metals provide fine control over the anisotropic two-dimensional growth of the ternary-alloy nanostructure. The prepared Pd-Pt-Ag nanosheets were superior catalysts of ethanol electrooxidation owing to their specific structural and compositional characteristics. This approach will pave the way for the design of multicomponent 2D nanomaterials with unprecedented functions. PMID:26799639

  16. Ultra-thin 3D silicon sensors for neutron detection

    NASA Astrophysics Data System (ADS)

    Guardiola, C.; Fleta, C.; Pellegrini, G.; García, F.; Quirion, D.; Rodríguez, J.; Lozano, M.

    2012-03-01

    We present a novel neutron detector based on an ultra-thin 3D silicon sensor with a sensitive volume only 10 μm thick. This ultra-thin active volume allows a high gamma-ray rejection, a key requirement in order to discriminate the signal coming from the neutrons in a mixed neutron-gamma ray environment. The device upper-side is covered with a novel boron-based compound that detects neutrons by means of the 10B(n,α)7Li nuclear reaction. The performance of test devices has been investigated first with a gamma-ray source to evaluate the gamma-ray rejection factor, and then with an 241AmBe neutron source to assess the neutron-gamma ray discrimination properties.

  17. Strain-induced water dissociation on supported ultrathin oxide films

    PubMed Central

    Song, Zhenjun; Fan, Jing; Xu, Hu

    2016-01-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this work, 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. PMID:26953105

  18. Low temperature CVD growth of ultrathin carbon films

    NASA Astrophysics Data System (ADS)

    Yang, Chao; Wu, Peng; Gan, Wei; Habib, Muhammad; Xu, Weiyu; Fang, Qi; Song, Li

    2016-05-01

    We demonstrate the low temperature, large area growth of ultrathin carbon films by chemical vapor deposition under atmospheric pressure on various substrates. In particularly, uniform and continuous carbon films with the thickness of 2-5 nm were successfully grown at a temperature as low as 500 oC on copper foils, as well as glass substrates coated with a 100 nm thick copper layer. The characterizations revealed that the low-temperature-grown carbon films consist on few short, curved graphene layers and thin amorphous carbon films. Particularly, the low-temperature grown samples exhibited over 90% transmittance at a wavelength range of 400-750 nm and comparable sheet resistance in contrast with the 1000oC-grown one. This low-temperature growth method may offer a facile way to directly prepare visible ultrathin carbon films on various substrate surfaces that are compatible with temperatures (500-600oC) used in several device processing technologies.

  19. 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.

  20. Ultrathin and lightweight organic solar cells with high flexibility

    PubMed Central

    Kaltenbrunner, Martin; White, Matthew S.; Głowacki, 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 μm 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

  1. Ultrathin septuple layered PbBi2Se4 nanosheets.

    PubMed

    Chatterjee, Arindom; Guin, Satya N; Biswas, Kanishka

    2014-07-28

    Layered lead bismuth selenide, PbBi2Se4, an intergrowth compound of PbSe (rocksalt) and Bi2Se3 (hexagonal), is a topological insulator in the bulk phase. We present a simple solution based synthesis of two dimensional (2D) few seven atomic (septuple) layered PbBi2Se4 nanosheets (4-7 nm thick) for the first time. The excellent electrical transport in ultrathin PbBi2Se4 is attributed to the presence of dominant surface states that offer high electrical mobility (∼153 cm(2) V(-1) s(-1)) and scattering resistant carriers. Ultrathin 3-5 SLs PbBi2Se4 shows an n-type semiconducting behaviour with a band gap of ∼0.6 eV, which is confirmed by optical spectroscopy and thermopower measurements. PMID:24916418

  2. Ultrathin alternating copolymer nanotubes with readily tunable surface functionalities.

    PubMed

    Chen, Jianxin; Yu, Chunyang; Shi, Zengqian; Yu, Songrui; Lu, Zhongyuan; Jiang, Wengfeng; Zhang, Meng; He, Wei; Zhou, Yongfeng; Yan, Deyue

    2015-03-16

    Well-defined ultrathin nanotubes (30 nm in diameter and of micrometer-scale length) were generated through the self-assembly of a novel alternative copolymer synthesized using an epoxy-thiol click-chemistry reaction. The self-assembly mechanism was investigated both by experiments and using dissipative particle dynamics (DPD) simulations. The obtained nanotubes can be readily functionalized with carboxy groups, amino groups, peptides, or other groups by simple modular click copolymerization. PMID:25649301

  3. Spin Engineering in Ultrathin Cu/Co/Cu(110)

    NASA Astrophysics Data System (ADS)

    Hope, S.; Gu, E.; Choi, B.; Bland, J. A. C.

    1998-02-01

    We have studied the effect of depositing Cu overlayers onto CO gas dosed Co/Cu(110) ultrathin films \\(615 monolayers\\). This enables us to ``controllably engineer'' the direction of the easy axis at a constant Co thickness.

  4. 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

  5. Dielectric properties of marsh vegetation

    NASA Astrophysics Data System (ADS)

    Kochetkova, Tatiana D.; Suslyaev, Valentin I.; Shcheglova, Anna S.

    2015-10-01

    The present work is devoted to the measurement of the dielectric properties of mosses and lichens in the frequency range from 500 MHz to 18 GHz. Subjects of this research were three species of march vegetation - moss (Dicranum polysetum Michx), groundcedar (Diphasiastrum complanatum (L.) Holub) and lichen (Cladonia stellaris). Samples of vegetation were collected in Tomsk region, Western Siberia, Russia. Complex dielectric permittivity was measured in coaxial section by Agilent Technologies vector network analyzer E8363B. Green samples was measured for some moisture contents from 100% to 3-5 % during a natural drying. The measurements were performed at room temperature, which remained within 21 ÷ 23 ° C. The frequency dependence of the dielectric constant for the three species of marsh vegetation differ markedly. Different parts of the complex permittivity dependency on moisture were fitted by line for all frequency points. Two break point were observed corresponding to the transition of water in the vegetation in various phase states. The complex permittivity spectra of water in the vegetation allow determining the most likely corresponding dielectric model of water in the vegetation by the method of hypothesis testing. It is the Debye's model. Parameters of Debye's model were obtained by numerical methods for all of three states of water. This enables to calculate the dielectric constant of water at any frequency range from 500 MHz to 18 GHz and to find the parameters of the dielectric model of the vegetation.

  6. 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.

  7. Magnetism and surface structure of atomically controlled ultrathin metal films.

    SciTech Connect

    Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

    2007-01-01

    We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

  8. Features of transport in ultrathin gold nanowire structures.

    PubMed

    Pud, Sergii; Kisner, Alexandre; Heggen, Marc; Belaineh, Dagmawi; Temirov, Ruslan; Simon, Ulrich; Offenhäusser, Andreas; Mourzina, Yulia; Vitusevich, Svetlana

    2013-03-25

    The origin of the interface formation appearing due to the realization of contacts to ultrathin gold nanowire devices is revealed. Such interfaces play an important role in transport mechanisms in nanowire structures and can determine the electrical and operating parameters of a nanodevice. Based on experimental results, the specific electrical properties of bundles of ultrathin gold nanowires fabricated by wet chemical synthesis and subsequently assembled and contacted with gold electrodes are reported. It is demonstrated that these properties are strongly affected by the monolayers of organic molecules inevitably present on the surface of the nanowires due to synthetic conditions. In particular, such layers form a potential barrier to tunneling of the electrons from contacts to the nanowires. The electric transport behavior of the investigated nanowire structures in the temperature range from 500 mK to 300 K obeys the model of thermal fluctuation-induced tunneling conduction through the nanowire-metal electrode molecular junction. Application of this model allows calculation of the parameters of the molecular potential barrier. The formation of such a molecular barrier is verified by scanning tunneling microscope (STM) and transmission electron microscope (TEM) measurements performed using a supporting graphene layer. These findings are important for designing novel nanodevices for molecular electronics on the basis of ultrathin nanowires. PMID:23125023

  9. 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 μm, the thermal management of ultra-thin Si chips with thickness smaller than 20 μm 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 μm 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.

  10. 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).

  11. 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 μg 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.

  12. Extraordinary optical transmission in nanopatterned ultrathin metal films without holes.

    PubMed

    Peer, Akshit; Biswas, Rana

    2016-02-18

    We experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ∼750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller than the period, with an enhancement of ∼2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (∼5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ∼40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ∼30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing. PMID:26853881

  13. Microfluidic Fabrication of Functional Capsules with ultra-thin membranes

    NASA Astrophysics Data System (ADS)

    Kim, Shin-Hyun; Abbaspourrad, Alireza; Weitz, David

    2012-02-01

    We have developed a new emulsification technique to produce monodisperse double-emulsion drops with an ultra-thin middle layer through a one-step emulsification. A biphasic flow, consisting of sheath of one fluid flowing along the capillary wall and surrounding a second fluid flowing through center of the capillary, is created in a form of either a jet or drops, which is emulsified into double-emulsion drops with ultra-thin middle layer. The ultra-thin middle phases provide stability to the double-emulsion drops by putting the fluid in the middle phase in the lubrication regime. We have employed such stable double-emulsion drops to make functional microcapsules using evaporation-induced consolidation. Simplest form is microcapsules with homogenous membrane. Using biodegradable polymers such as PLA or PLGA as a membrane material, we can achieve a long-term release of various bioactives from the capsules as the membrane degrades by hydrolysis. Heterogeneous membrane can also be prepared by using polymer blends. For example, a polymer blend of PMMA and PLA with small interaction parameter makes heterogeneous structure at nanoscale, while a polymer blend of PS and PLA with large interaction parameter makes their phase separation at one micrometer scale.

  14. Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

    DOE PAGESBeta

    Peer, Akshit; Biswas, Rana

    2016-02-01

    In this study, we experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller thanmore » the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.« less

  15. Efficient time-domain model of the graphene dielectric function

    NASA Astrophysics Data System (ADS)

    Prokopeva, Ludmila J.; Kildishev, Alexander V.

    2013-09-01

    A honey-comb monolayer lattice of carbon atoms, graphene, is not only ultra-thin, ultra-light, flexible and strong, but also highly conductive when doped and exhibits strong interaction with electromagnetic radiation in the spectral range from microwaves to the ultraviolet. Moreover, this interaction can be effectively controlled electrically. High flexibility and conductivity makes graphene an attractive material for numerous photonic applications requiring transparent conducting electrodes: touchscreens, liquid crystal displays, organic photovoltaic cells, and organic light-emitting diodes. Meanwhile, its tunability makes it desirable for optical modulators, tunable filters and polarizers. This paper deals with the basics of the time-domain modeling of the graphene dielectric function under a random-phase approximation. We focus at applicability of Padé approximants to the interband dielectric function (IDF) of single layer graphene. Our study is centered on the development of a two-critical points approximation (2CPA) of the IDF within a single-electron framework with negligible carrier scattering and a realistic range of chemical potential at room temperature. This development is successfully validated by comparing reflection and transmission spectra computed by a numerical method in time-domain versus semi-analytical calculations in frequency domain. Finally, we sum up our results - (1) high-quality approximation, (2) tunability, and (3) second-order accurate numerical FDTD implementation of the 2CPA of IDF demonstrated across the desired range of the chemical potential to temperature ratios (4 - 23). Finally, we put forward future directions for time-domain modeling of optical response of graphene with wide range of tunable and fabrication-dependent parameters, including other broadening factors and variations of temperature and chemical potentials.

  16. 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.

  17. 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.

  18. Classical over-the-barrier model for neutralization of highly charged ions above thin dielectric films

    NASA Astrophysics Data System (ADS)

    Lake, R. E.; Sosolik, C. E.; Pomeroy, J. M.

    2013-06-01

    We apply the classical over-the-barrier (COB) model to charge transfer between highly charged ions (HCIs) and targets consisting of thin dielectric films on metals. Distances for the onset of classically allowed above-surface electron capture are obtained as a function of HCI charge state, film thickness, film permittivity, and film-metal electron binding energies. The model describes the crossover between the previously existing COB model for bulk metals and bulk dielectrics as the thickness of a dielectric film on a metal substrate increases through three distinct regimes. For ultrathin films with low permittivity and positive electron affinity, over-the-barrier charge transfer initiates from the metal electrons behind the film and critical distances are greater than those from bare metal targets. This result is consistent and compared with the recent observation of potential emission enhancement above thin C60 films on Au(111) with increasing film thickness [Bodewits, Hoekstra, Kowarik, Dobes, and Aumayr, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.042901 84, 042901 (2011)].

  19. Reliability of ultra-thin insulation coatings for long-term electrophysiological recordings

    NASA Astrophysics Data System (ADS)

    Hooker, S. A.

    2006-03-01

    Improved measurement of neural signals is needed for research into Alzheimer's, Parkinson's, epilepsy, strokes, and spinal cord injuries. At the heart of such instruments are microelectrodes that measure electrical signals in the body. Such electrodes must be small, stable, biocompatible, and robust. However, it is also important that they be easily implanted without causing substantial damage to surrounding tissue. Tissue damage can lead to the generation of immune responses that can interfere with the electrical measurement, preventing long-term recording. Recent advances in microfabrication and nanotechnology afford the opportunity to dramatically reduce the physical dimensions of recording electrodes, thereby minimizing insertion damage. However, one potential cause for concern is the reliability of the insulating coatings, applied to these ultra-fine-diameter wires to precisely control impedance. Such coatings are often polymeric and are applied everywhere but the sharpened tips of the wires, resulting in nominal impedances between 0.5 MOhms and 2.0 MOhms. However, during operation, the polymer degrades, changing the exposed area and the impedance. In this work, ultra-thin ceramic coatings were deposited as an alternative to polymer coatings. Processing conditions were varied to determine the effect of microstructure on measurement stability during two-electrode measurements in a standard buffer solution. Coatings were applied to seven different metals to determine any differences in performance due to the surface characteristics of the underlying wire. Sintering temperature and wire type had significant effects on coating degradation. Dielectric breakdown was also observed at relatively low voltages, indicating that test conditions must be carefully controlled to maximize reliability.

  20. Alternate capacitor dielectric film materials

    SciTech Connect

    Foster, J.C.

    1990-08-01

    New high-temperature, high-energy density, and high-radiation tolerant capacitor applications require the evaluation of alternate dielectric materials. Evaluation work was performed at GE Neutron Devices (GEND) and Sandia National Laboratories (SNL), Albuquerque. US Department of Energy (DOE) requirements for capacitor function and environments are unique, and the representations included in this report do not constitute an endorsement of any material or manufacturer. This report presents data on polymeric dielectric films evaluated to support the design of new high-energy density capacitors. Materials which were evaluated include polycarbonate (two sources), polyphenylene sulfide, polyvinylidene fluoride, polyetherimide (three sources), polyimide (four sources), polyethersulfone, and polyetherether ketone. A polyester was evaluated as the control material since many prior designs utilized this dielectric. The film evaluations were based on dielectric constant and dissipation factor variation as a function of temperature ({minus}55{degree}C to 300{degree}C) as well as dielectric breakdown strength. Additionally, film/foil capacitors in a dry wrap-and-fill configuration were fabricated and tested to determine insulation resistance, breakdown voltage, and radiation hardness. Results are given for all evaluations. 7 refs., 4 figs., 4 tabs.

  1. Agricultural applications of dielectric spectroscopy.

    PubMed

    Nelson, Stuart O

    2004-01-01

    A brief account of interest in dielectric properties of agricultural materials is presented, and some examples of dielectric spectroscopy applied to agricultural problems are discussed. Included are wide frequency range (250 Hz to 12 GHz) permittivity, or dielectric properties, measurements on adult rice weevils and hard red winter wheat, for the purpose of assessing selective dielectric heating of the insects, and broadband (200 MHz to 20 GHz) permittivity measurements on tissues of fresh fruits and vegetables. Similar measurements are shown for tree-ripened peaches, which were obtained to assess possibilities for a permittivity-based maturity index. Broadband (10 MHz to 1.8 GHz) permittivity measurements are shown for several fruits and vegetables as a function of temperature from 5 to 95 degrees C. Measurements over the same frequency range and similar temperature ranges are presented for two other food products, whey protein gel and apple juice. A few comments are offered on likely future dielectric spectroscopy applications in agriculture. PMID:15719907

  2. One-way absorption of terahertz waves in rod-type and multilayer structures containing polar dielectrics

    NASA Astrophysics Data System (ADS)

    Serebryannikov, Andriy E.; Nojima, Shunji; Ozbay, Ekmel

    2014-12-01

    One-way absorption can be obtained at terahertz frequencies in low-profile rod-type and multilayer dielectric structures with broken spatial inversion symmetry, which contain either a rod layer or an ultrathin homogeneous layer made of a polar dielectric. Perfect absorption for one of the two opposite incidence directions and perfect reflection for the other one are observed at the edge of the polaritonic gap in a wide range of the incident angle variation, when the thickness of the entire structure is of the order of the incident wavelength. Moreover, this regime appears in a wide frequency range, in which the forward-to-backward absorption contrast is strong. The exploited mechanism is connected with the parameter adjustment that enables the location of the polaritonic gap of the polar dielectric, of which the lossy part of the structure is made, inside the stop band arising due to the periodicity of the lossless part of the structure that is made of a nondispersive dielectric. It also exploits absorption enhancement in the lossy part by backing it with the highly reflecting lossless part, which has alternating stop and pass bands.

  3. Dielectric-based subwavelength metallic meanders for wide-angle band absorbers.

    PubMed

    Shen, Su; Qiao, Wen; Ye, Yan; Zhou, Yun; Chen, Linsen

    2015-01-26

    We propose nano-meanders that can achieve wide-angle band absorption in visible regime. The nano-meander consists of a subwavelength dielectric grating covered by continuous ultra-thin Aluminum film (less than one tenth of the incident wavelength). The excited photonic resonant modes, such as cavity mode, surface plasmonic mode and Rayleigh-Wood anomaly, are discussed in detail. Nearly total resonant absorption due to funneling mechanism in the air nano-groove is almost invariant with large incident angle in transverse magnetic polarization. From both the structural geometry and the nanofabrication point of view, the light absorber has a very simple geometrical structure and it is easy to be integrated into complex photonic devices. The highly efficient angle-robust light absorber can be potential candidate for a range of passive and active photonic applications, including solar-energy harvesting as well as producing artificial colors on a large scale substrate. PMID:25835855

  4. Supercritically exfoliated ultrathin vanadium pentoxide nanosheets with high rate capability for lithium batteries.

    PubMed

    An, Qinyou; Wei, Qiulong; Mai, Liqiang; Fei, Jiayang; Xu, Xu; Zhao, Yunlong; Yan, Mengyu; Zhang, Pengfei; Huang, Shizhe

    2013-10-21

    Ultrathin V2O5 nanosheets were successfully prepared through supercritical solvothermal reaction followed by annealing treatment. The formation of ultrathin nanosheets is owing to Ostwald ripening and the effect of supercritical fluids. As cathode material for lithium batteries, the ultrathin V2O5 nanosheets exhibit a capacity of 108 mA h g(-1) at a high rate of up to 10 C at 2.4-4 V and excellent cyclability with little capacity loss after 200 cycles. The enhanced rate performance is attributed to the shortened diffusion distance and the increased electrode-electrolyte contact area of the ultrathin nanosheet structure. It is also demonstrated that the supercritical solvothermal method is effective and facile to scalably synthesize ultrathin nanomaterials for lithium batteries. PMID:23963528

  5. Crystal and multiple melting behaviors of PCL lamellae in ultrathin films

    NASA Astrophysics Data System (ADS)

    Yu, Xiang; Wang, Na; Lv, Shanshan

    2016-03-01

    In this paper, isothermal crystallization at different temperatures and multiple melting of four molecular weights (MW) PCL ultrathin films were investigated by using Atomic Force Microscopy (AFM). The results showed that: two different crystal structures, Flat-on and Edge-on lamellae, were simultaneously formed in PCL ultrathin films when the Tc lower than 30 °C. During the heating process, Edge-on lamellae was melted firstly. This demonstrated that the multiple melting behavior of PCL in ultrathin films was caused by the two different lamellar structures. With the increase of MW, or with the decrease of Tc, PCL chains in ultrathin films changed from Flat-on to Edge-on, and the controlled factors of growth process in ultrathin films transformed from surface nucleation-limited (NL) to melt diffusion-limited (DL).

  6. Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

    PubMed Central

    Bell, David C.; Cohen-Karni, Tzahi; Rosenstein, Jacob K.; Wanunu, Meni

    2016-01-01

    We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) free-standing hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

  7. 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.

  8. 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...

  9. 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.

  10. 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.

  11. Dielectric spectroscopy in crystalline methocarbamol

    NASA Astrophysics Data System (ADS)

    Saini, Manoj K.

    2014-04-01

    We have used dielectric spectroscopy (20 Hz - 1 MHz) above liquid nitrogen temperature to study the room temperature crystalline phase of the methocarbamol (ML). The as received crystalline sample of ML shows a process (designated as β1) which is Arrhenius in nature in the dielectric measurements. It is also found to be non-Debye in nature. Annealing above 373 K for an hour the magnitude of this process came down by a factor of four indicating this to be due to water. Also found in crystalline phase another sub-Tg process (designated as β2) in temperature range 140K-170 K.

  12. Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

    NASA Astrophysics Data System (ADS)

    Peer, Akshit; Biswas, Rana

    2016-02-01

    We experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller than the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.We experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller than the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07903a

  13. Ultra-thin Materials from Atomic Layer Deposition for Microbolometers

    NASA Astrophysics Data System (ADS)

    Eigenfeld, Nathan Thomas

    This research focuses on the incorporation of atomic layer deposition (ALD) materials into microbolometer devices for infrared (IR) imaging. Microbolometers are suspended micro-electromechanical (MEMS) devices, which respond electrically to absorbed IR radiation. By minimizing the heat capacity (thermal mass) of these devices, their performance may be substantially improved. Thus, implementing ultra-thin freestanding ALD materials into microbolometer devices will offer a substantial reduction in the overall heat capacity of the device. A novel nanofabrication method is developed to produce robust ultra-thin suspended structures from ALD generated materials including W, Ru and Al2O 3. Unique aspects of ALD such as high conformality offer the ability to create 3-dimensional structures with mechanical reinforcement. Additionally, the ability to tune residual stresses via atomically precise thickness control enables the fabrication of flat suspended structures. Since microbolometer elements are electro-thermally active, the electro-thermal properties of ultra-thin ALD W, Ru and Al2O3 are investigated. Several distinct deviations from bulk electro-thermal properties of resistivity, temperature coefficient of resistance, thermal conductivity and specific heat capacity are identified and interpreted with traditional nanoscale transport modeling and theory. For example, for ALD W, the electrical resistivity is increased by up to 99%, thermal conductivity is reduced by up to 91% and specific heat capacity increased 70% from bulk. Finally, the developed ALD nano-fabrication process and measured ALD material properties are combined to fabricate an industrial level, state-of-the-art microbolometer pixel structure with 1.4X performance improvement. Further microbolomter performance enhancements based on the developed nanofabrication methods and electro-thermal measurements are discussed.

  14. 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 μm thick GaAs junction demonstrated an open circuit voltage of 0.9V.

  15. Suppression of superconductivity in epitaxial NbN ultrathin films

    SciTech Connect

    Kang, L.; Jin, B. B.; Liu, X. Y.; Jia, X. Q.; Chen, J.; Ji, Z. M.; Xu, W. W.; Wu, P. H.; Mi, S. B.; Pimenov, A.; Wu, Y. J.; Wang, B. G.

    2011-02-01

    This paper studies the suppression of superconducting transition temperature (T{sub c}) of ultrathin NbN film. We fabricated epitaxial NbN superconducting thin films of thicknesses ranging from 2.5 to 100 nm on single crystal MgO (100) substrates by dc magnetron sputtering. We performed structure analyses and measured their electric and far infrared properties. The experimental results were compared with several mechanisms of the suppression of superconductivity proposed in the literature, including the weak localization effect, the proximity effect, and quantum size effect (electron wave leakage model). We found that the electron wave leakage model matches best to the experimental data.

  16. Multicolor 4D Fluorescence Microscopy using Ultrathin Bessel Light Sheets.

    PubMed

    Zhao, Teng; Lau, Sze Cheung; Wang, Ying; Su, Yumian; Wang, Hao; Cheng, Aifang; Herrup, Karl; Ip, Nancy Y; Du, Shengwang; Loy, M M T

    2016-01-01

    We demonstrate a simple and efficient method for producing ultrathin Bessel ('non-diffracting') light sheets of any color using a line-shaped beam and an annulus filter. With this robust and cost-effective technology, we obtained two-color, 3D images of biological samples with lateral/axial resolution of 250 nm/400 nm, and high-speed, 4D volume imaging of 20 μm sized live sample at 1 Hz temporal resolution. PMID:27189786

  17. Environmentally benign synthesis of ultrathin metal telluride nanowires.

    PubMed

    Yang, Haoran; Finefrock, Scott W; Albarracin Caballero, Jonatan D; Wu, Yue

    2014-07-23

    Metal telluride nanowires are attractive materials for many applications, yet most synthesis recipes require hazardous reducing agents such as hydrazine or sodium borohydride. We describe a two-step synthesis of various metal tellurides with nanowire morphology using a nonhazardous reducing agent, ascorbic acid. In the first step, Te grows one-dimensionally to form ultrathin nanowires; in the second step, these nanowires are converted to metal telluride nanowires by adding metal precursors. Analysis of the reaction products versus time provides insights into the growth and conversion mechanisms as well as the reaction rates. PMID:25003347

  18. Chemical surface deposition of ultra-thin semiconductors

    DOEpatents

    McCandless, Brian E.; Shafarman, William N.

    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.

  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. Permeability of Ultra-Thin Amorphous Carbon Films

    NASA Astrophysics Data System (ADS)

    Bubenchikov, Mikhail A.; Bubenchikov, Aleksey M.; Usenko, Olesya V.; Ukolov, Anton V.

    2016-02-01

    The present paper deals with defining the energy of interaction between an ultra-thin hydrocarbon layer and helium molecules using a modification of the LJ-potential and the continual approach. The suggested approach allows determination of the statistically average motion of a test molecule through material layers under consideration. The obtained results made it possible to localize global sorption zones both inside the layer and at its external borders and to identify the parameters which are responsible for permeability of the layer.

  1. Helical Growth of Ultrathin Gold-Copper Nanowires.

    PubMed

    Mendoza-Cruz, Rubén; Bazán-Díaz, Lourdes; Velázquez-Salazar, J Jesús; Plascencia-Villa, Germán; Bahena-Uribe, Daniel; Reyes-Gasga, José; Romeu, David; Guisbiers, Grégory; Herrera-Becerra, Raúl; José-Yacamán, Miguel

    2016-03-01

    In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously. PMID:26849249

  2. 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.

  3. Metal Adatoms and Clusters on Ultrathin Zirconia Films

    PubMed Central

    2016-01-01

    Nucleation and growth of transition metals on zirconia has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Since STM requires electrical conductivity, ultrathin ZrO2 films grown by oxidation of Pt3Zr(0001) and Pd3Zr(0001) were used as model systems. DFT studies were performed for single metal adatoms on supported ZrO2 films as well as the (1̅11) surface of monoclinic ZrO2. STM shows decreasing cluster size, indicative of increasing metal–oxide interaction, in the sequence Ag < Pd ≈ Au < Ni ≈ Fe. Ag and Pd nucleate mostly at steps and domain boundaries of ZrO2/Pt3Zr(0001) and form three-dimensional clusters. Deposition of low coverages of Ni and Fe at room temperature leads to a high density of few-atom clusters on the oxide terraces. Weak bonding of Ag to the oxide is demonstrated by removing Ag clusters with the STM tip. DFT calculations for single adatoms show that the metal–oxide interaction strength increases in the sequence Ag < Au < Pd < Ni on monoclinic ZrO2, and Ag ≈ Au < Pd < Ni on the supported ultrathin ZrO2 film. With the exception of Au, metal nucleation and growth on ultrathin zirconia films follow the usual rules: More reactive (more electropositive) metals result in a higher cluster density and wet the surface more strongly than more noble metals. These bind mainly to the oxygen anions of the oxide. Au is an exception because it can bind strongly to the Zr cations. Au diffusion may be impeded by changing its charge state between −1 and +1. We discuss differences between the supported ultrathin zirconia films and the surfaces of bulk ZrO2, such as the possibility of charge transfer to the substrate of the films. Due to their large in-plane lattice constant and the variety of adsorption sites, ZrO2{111} surfaces are more reactive than many other oxygen-terminated oxide surfaces. PMID:27213024

  4. Cellulose Triacetate Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Jow, T. Richard

    1994-01-01

    Cellulose triacetate investigated for use as dielectric material in high-energy-density capacitors for pulsed-electrical-power systems. Films of cellulose triacetate metalized on one or both sides for use as substrates for electrodes and/or as dielectrics between electrodes in capacitors. Used without metalization as simple dielectric films. Advantages include high breakdown strength and self-healing capability.

  5. SOME AGRICULTURAL APPLICATIONS FOR DIELECTRIC SPECTROSCOPY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectric properties of agricultural products are of interest for several reasons. These include the sensing of moisture content through its correlation with the dielectric properties, or permittivities, of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of ...

  6. Dielectric properties of agricultural products and applications

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The use of dielectric properties of agricultural products for sensing moisture in grain and seed and their application in radio-frequency and microwave dielectric heating is discussed briefly. Values for the dielectric properties of a number of products, including grain and seed, fruits and vegetab...

  7. Applications for Dielectric Properties of Agricultural Products

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The use of dielectric properties of agricultural products for sensing moisture in grain and seed and their application in radio-frequency and microwave dielectric heating are discussed briefly. Values for the dielectric properties of a number of products, including grain, fruit, and poultry products...

  8. Soft Dielectrics: Heterogeneity and Instabilities

    NASA Astrophysics Data System (ADS)

    Rudykh, Stephan; Debotton, Gal; Bhattacharya, Kaushik

    2012-02-01

    Dielectric Elastomers are capable of large deformations in response to electrical stimuli. Heterogeneous soft dielectrics with proper microstructures demonstrate much stronger electromechanical coupling than their homogeneous constituents. In turn, the heterogeneity is an origin for instability developments leading to drastic change in the composite microstructure. In this talk, the electromechanical instabilities are considered. Stability of anisotropic soft dielectrics is analyzed. Ways to achieve giant deformations and manipulating extreme material properties are discussed. 1. S. Rudykh and G. deBotton, ``Instabilities of Hyperelastic Fiber Composites: Micromechanical Versus Numerical Analyses.'' Journal of Elasticity, 2011. http://dx.doi.org/2010.1007/s10659-011-9313-x 2. S. Rudykh, K. Bhattacharya and G. deBotton, ``Snap-through actuation of thick-wall electroactive balloons.'' International Journal of Non-Linear Mechanics, 2011. http://dx.doi.org/10.1016/j.ijnonlinmec.2011.05.006 3. S. Rudykh and G. deBotton, ``Stability of Anisotropic Electroactive Polymers with Application to Layered Media.'' Zeitschrift f"ur angewandte Mathematik und Physik, 2011. http://dx.doi.org/10.1007/s00033-011-0136-1 4. S. Rudykh, A. Lewinstein, G. Uner and G. deBotton, ``Giant Enhancement of the Electromechanical Coupling in Soft Heterogeneous Dielectrics.'' 2011 http://arxiv.org/abs/1105.4217v1

  9. 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.

  10. Scattering from Thin Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1984-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectric properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T is sufficiently large the disk will always be in one or the other of these regimes (T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  11. 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.

  12. The effect of electroactive interlayer on the ferroelectric properties in poly(vinylidene fluoride-trifluoroethylene) copolymer ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiuli; Hou, Ying; Zhang, Yuan; Lv, Zhaoyue; Xu, Guoqiang; Xu, Haisheng

    2012-10-01

    A series of ferroelectric polarization reversal measurements have been conducted on spin-coated ultrathin poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer films sandwiched with different electroactive materials between P(VDF-TrFE) and metal electrodes. Three types of electroactive interlayers, including highly polarizable material copper-phthalocyanine (CuPc), electron conductive polyethylene dioxythiophene/poly(styrene sulfonate acid), and ion (proton) conductive poly (vinyl phosphonic) acid, have been employed in our experiment. In addition, the ferroelectric film with CuPc exhibits larger remnant polarization and the enhancement of fatigue resistance although higher drive voltage and more switching time can be observed, which differs from the samples with electron and proton conductors as interlayers. The further analysis shows that this may be attributed to higher dielectric constant of CuPc than that of P(VDF-TrFE) layer. These results suggest that three types of interlayers can lead to a large improvement of ferroelectric switching, which is promising for potential applications.

  13. On the nature of the interfacial layer in ultra-thin TiN/LaLuO3 gate stacks

    NASA Astrophysics Data System (ADS)

    Mitrovic, I. Z.; Hall, S.; Sedghi, N.; Simutis, G.; Dhanak, V. R.; Bailey, P.; Noakes, T. C. Q.; Alexandrou, I.; Engstrom, O.; Lopes, J. M. J.; Schubert, J.

    2012-08-01

    We present a detailed investigation on the nature of the interfacial layer (IL) in ultra-thin TiN/LaLuO3 (LLO) gate stacks, which is of importance to facilitate CMOS scaling. The molecular beam deposited LaLuO3 films are found to be amorphous by high-resolution transmission electron microscopy. A ˜9 Å thick LaLuO3/interlayer transition observed by medium energy ion scattering correlates with the presence of a dual silicate/SiO2-like interfacial layer derived from the analysis of photoelectron line positions and electron energy loss spectra. A theoretical model is used for the dielectric transition in a bi-layer LaLuO3/IL structure, linking physical and electrical characterization data. The obtained leakage current of 10-3 A/cm2 at 1.5 V and equivalent oxide thickness of 0.75 nm for TiN/LaLuO3 gate stacks are adequate for scaling in the 14-12 nm node.

  14. Flexible metamaterial narrow-band-pass filter based on magnetic resonance coupling between ultra-thin bilayer frequency selective surfaces

    NASA Astrophysics Data System (ADS)

    Bai, Zhengyuan; Zhang, Qing; Ju, Yongfeng; Tao, Guiju; Jiang, Xiongwei; Kang, Ning; Liu, Chengpu; Zhang, Long

    2016-02-01

    A novel flexible metamaterial narrow-band-pass filter is designed and proved to be reliable by both numerical simulations and experimental measurements. The unit cell of the designed structure consists of circle ring resonators on top of a thin dielectric layer backed by a metallic mesh. The investigations on the distribution of the surface current and magnetic field as well as the analysis of the equivalent circuit model reveal that the magnetic resonance response between layers induced by the reverse surface current contributes to the high quality factor band-pass property. Importantly, it is a flexible design with a tunable resonance frequency by just changing the radius of the circle rings and can also be easily extended to have the multi-band-pass property. Moreover, this simplified structure with low duty cycle and ultra-thin thickness is also a symmetric design which is insensitive to the polarization and incident angles. Therefore, such a metamaterial narrow-band-pass filter is of great importance in the practical applications such as filtering and radar stealth, and especially for the conformal structure applications in the infrared and optical window area.

  15. TiO2/GeOxNy stacked gate dielectrics for Ge-MOSFETs

    NASA Astrophysics Data System (ADS)

    Bera, M. K.; Mahata, C.; Chakraborty, A. K.; Nandi, S. K.; Tiwari, Jitendra N.; Hung, Jui-Yi; Maiti, C. K.

    2007-12-01

    In this work, we present the results of physical and electrical characterization of Ti-based high-k gate dielectrics on Ge substrates. Titanium tetrakis iso- propoxide (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO2 films on p-Ge (1 0 0) at low temperature (<200 °C) by plasma enhanced chemical vapor deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of ~65 Pa. The presence of an ultra-thin lossy GeO2 interfacial layer between the deposited high-k film and the substrate, results in frequency-dependent capacitance-voltage (C-V) characteristics in strong accumulation and a high interface state density (~1013 cm-2 eV-1). To improve the electrical properties, nitrogen engineering has been employed to convert the lossy GeO2 interfacial layer to its oxynitride, thus forming TiO2/GeOxNy/Ge stacked-gate structure with improved interface/electrical properties. Different N sources, such as NO, NH3 and NO/NH3, have been used for nitrogen engineering. XPS and Raman spectroscopy analyses have been used for surface morphological study. Electrical properties, such as gate leakage current density, interface state density, charge trapping, flatband voltage shift, etc, have been studied in detail for TiO2/GeOxNy/Ge MIS capacitors using the current-voltage (I-V), capacitance-voltage (C-V), conductance-voltage (G-V) and stress (both constant voltage and current) measurements. Although a significant improvement in electrical characteristics has been observed after nitridation in general, the formation of the interfacial GeOxNy layer, obtained from NO-plasma nitridation, is found to provide the maximum improvement among all the nitridation techniques used in this study. It is shown that the insertion of an ultra-thin oxynitride (GeOxNy) interfacial layer is advantageous for producing gate-quality TiO2 high-k dielectric stacks on Ge substrates.

  16. 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.

  17. Anomalous dielectric behavior of nanoconfined electrolytic solutions.

    PubMed

    Zhu, H; Ghoufi, A; Szymczyk, A; Balannec, B; Morineau, D

    2012-09-01

    We report an anomalous dielectric effect of electrolytes under cylindrical nanoconfinement. In bulk phase, the decrease in the water dielectric constant (ε) with increasing salt concentration is well known, and is due to dielectric saturation. From molecular dynamic simulations of confined water and NaCl solutions, we show a dielectric anisotropy and an unexpected increase in ε(perpendicular) of NaCl solutions with respect to the confined pure liquid until a critical concentration is reached. We infer that this striking dielectric behavior results from the interplay between the effect of confinement and that of ions on the water hydrogen bonding network. PMID:23005328

  18. Broadband ultrathin low-profile metamaterial microwave absorber

    NASA Astrophysics Data System (ADS)

    Sood, Deepak; Tripathi, Chandra Charu

    2016-04-01

    In this paper, a single-layer broadband low-profile ultrathin metamaterial microwave absorber is proposed for wide angle of incidence. The proposed absorber provides triple-band absorption under normal incidence of electromagnetic wave with two peaks lying in X-band and one in Ku-band. The unit cell is designed by using parametric optimization in such a way that the three peaks merge together to give broadband absorption. The absorber exhibits full width at half maxima bandwidth (FWHM) of 7.75 GHz from 7.55 to 15.30 GHz for wide angle of incidence up to 60° for both TE and TM polarizations. The mechanism of absorption of the absorber has been analyzed by field and surface current distributions. The proposed absorber has been fabricated and experimentally tested for different angles of incidence and polarization of the incident wave. The absorber is low profile with unit cell dimension of the order of 0.168 λ 0, and it is ultrathin with a thickness of ~ λ 0/17 at the center frequency of 11.43 GHz corresponding to the FWHM absorption bandwidth. This proposed absorber can be used for many potential applications such as stealth technology, cloaking and in antenna systems.

  19. Transport in ultrathin gold films decorated with magnetic Gd atoms

    NASA Astrophysics Data System (ADS)

    Alemani, Micol; Helgren, Erik; Hugel, Addison; Hellman, Frances

    2008-03-01

    We have performed four-probe transport measurements of ultrathin Au films decorated with Gd ad-atoms. The samples were prepared by quench condensation, i.e., sequential evaporation on a cryogenically cooled substrate under UHV conditions while monitoring the film thickness and resistance. Electrically continuous Au films at thickness of about 2 mono-layers of material are grown on an amorphous Ge wetting layer. The quench condensation method provides a sensitive control on the sample growth process, allowing us to tune the morphological and electrical configuration of the system. The ultrathin gold films develop from an insulating to a metallic state as a function of film thickness. The temperature dependence of the Au conductivity for different thickness is studied. It evolves from hopping transport for the insulating films, to a ln T dependence for thicker films. For gold films in the insulating regime we found a decreasing resistance by adding Gd. This is in agreement with a decreasing tunneling barrier height between metallic atoms. The Gd magnetic moments are randomly oriented for isolated atoms. This magnetic disorder leads to scattering of the charge carriers and a reduced conductivity compared to nonmagnetic materials.

  20. Building blocks for ultrathin flexible organic electroluminescent devices

    NASA Astrophysics Data System (ADS)

    Guenther, Ewald; Kumar, Ramadas S.; Zhu, Furong; Low, Hong Y.; Ong, Kian S.; Auch, Mark D. J.; Zhang, Keran; Chua, Soo-Jin

    2002-02-01

    Displays based on organic electroluminescent (EL) materials have entered the marketplace already and demonstrated remarkable contrast, high brightness and crisp colors. However, one of the key advantages of this new technology has not been commercially exploited yet: Fabrication of a display that is still fully functional even when it is bent or flexed. This is possible since organic EL devices comprising only thin, amorphous solid state films and optical properties have no critical dependence on the film thickness. In this paper we address the important elements that are required to produce a flexible organic EL display. Most crucial is the selection of a flexible substrate. Here we present results obtained with ultra-thin inorganic glass materials as well as polymeric foils. For the glass substrates we determined the ultimate mechanical properties for different device configurations. In the case of polymeric substrates permeation of water and oxygen molecules through the substrate is the governing factor. We compare the performance of different barrier systems. In summary we demonstrate that OLED devices with certain flexibility can be reliably built on ultra-thin glass substrates. For polymeric substrates a lot of progress has been achieved in terms of the required barrier properties and other necessary ingredients and this might result later into a commercial organic EL product.

  1. Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures.

    PubMed

    Boulle, Olivier; Vogel, Jan; Yang, Hongxin; Pizzini, Stefania; de Souza Chaves, Dayane; Locatelli, Andrea; Menteş, Tevfik Onur; Sala, Alessandro; Buda-Prejbeanu, Liliana D; Klein, Olivier; Belmeguenai, Mohamed; Roussigné, Yves; Stashkevich, Andrey; Chérif, Salim Mourad; Aballe, Lucia; Foerster, Michael; Chshiev, Mairbek; Auffret, Stéphane; Miron, Ioan Mihai; Gaudin, Gilles

    2016-05-01

    Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii-Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions. PMID:26809057

  2. 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

  3. Stacked Ge nanocrystals with ultrathin SiO₂ separation layers.

    PubMed

    Zschintzsch, Manuel; von Borany, Johannes; Jeutter, Nicole M; Mücklich, Arndt

    2011-11-18

    The aim of this work is the tailored growth of Ge nanocrystals (NCs) in (GeO(x)/SiO(2)) multilayers (ML) for photovoltaic applications. For this purpose the fabrication of regularly stacked Ge NCs separated by ultrathin SiO(2) layers is essential to enable charge carrier transport by direct tunnelling. In this paper we report on the fabrication of (GeO(x)/SiO(2))(50) multilayer stacks via reactive dc magnetron sputtering and Ge NCs formation after subsequent annealing. It is shown that magnetron sputtering allows us to deposit very regular ML stacks with a total thickness of about 300 nm, characterized by ultrathin (down to 1 nm) and very smooth (roughness ∼ 0.6 nm) SiO(2) separation layers. A main challenge is to keep these properties for a thermal budget necessary to form Ge NCs. For this reason, the temperature dependence of phase separation. Ge crystallization and ML morphology was investigated by Rutherford backscattering, x-ray scattering, Raman spectroscopy and electron microscopy. The formation of size confined Ge NCs of about 5 nm after annealing of only 550 °C is confirmed. This low thermal budget ensures the suppression of GeO emanation and multilayer stability. Spectroscopic ellipsometry was applied to determine the optical Ge NC bandgap to (1.65 ± 0.5) eV. PMID:22032974

  4. 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.

  5. Optical properties of pentacene clusters and ultra-thin films (*)

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy G.; Pinczuk, Aron

    2005-03-01

    Photoluminescene spectra of pentacene clusters and films of few monolayer in thickness reveal two fundamental excitations that are assigned to the Davydov doublets of the lowest singlet exciton. While the energy splittings of the doublets have minor dependence on cluster thickness, their bandwidths become narrower as the pentacene clusters grow larger and into continuous ultra-thin films. The marked similarity of these Davydov doublets to those in optical absorption spectra of thicker pentacene films and crystals suggests a similarity in molecular arrangements. Luminescence of self-trapped excitons is quenched in the few monolayer clusters and ultra-thin films. Asymmetric 0-0 and 1-0 resonance Raman scattering excitation profiles are observed in these samples. (*) Supported primarily by the Nanoscale Science and Engineering Initiative of the NSF under NSF Award Number CHE- 0117752 and by the NYSTAR, and by a research grant of the W. M. Keck Foundation. We thank I. Dujovne and C. F. Hirjibehedin for their helpful discussions.

  6. Proton acceleration from short pulse lasers interacting with ultrathin foil

    NASA Astrophysics Data System (ADS)

    Petrov, George; McGuffey, Christopher; Thomas, Alec; Krushelnick, Karl; Beg, Farhat

    2015-11-01

    Two-dimensional particle-in-cell simulations using 50 nm Si3N4 and DLC foils are compared to published experimental data of proton acceleration from ultra-thin foils (<1 μm) irradiated by short pulse lasers (30-50 fs), and some underlying physics issues pertinent to proton acceleration have been addressed. 2D particle-in-cell simulations show that the maximum proton energy scales as I2/3, stronger than Target Normal Sheath Acceleration for thick foils (>1 μm), which is typically between I1/3 and I1/2. Published experimental data were found to depend primarily on the laser energy and scale as E2/3. The different scaling laws for thick (>1 μm) and ultra-thin (<1 μm) foils are explained qualitatively as transitioning from Target Normal Sheath Acceleration to more advanced acceleration schemes such as Radiation-Induced Transparency and Radiation Pressure Acceleration regimes. This work was performed with the support of the Air Force Office of Scientific Research under grant FA9550-14-1-0282.

  7. Exchange coupling in ultrathin epitaxial yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Popova, E.; Keller, N.; Jomard, F.; Thomas, L.; Brianso, M.-C.; Gendron, F.; Guyot, M.; Tessier, M.

    2003-01-01

    Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y3Fe5O12 or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y3Al5O12 or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied from 180 Å to 4600 Å. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis loops recorded for ultrathin YIG films have a ``bee-waist'' shape and show a coupling between two different magnetic phases. The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to be Y3Fe5-xAlxO12 due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures. This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling, the maximal interaction energy is estimated to be about 0.17 erg/cm2 at 5 K for (111) oriented sample.

  8. 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.

  9. 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.

  10. Microwave Dielectric Properties of Lossy Dielectric Composite Materials

    NASA Astrophysics Data System (ADS)

    An, Young Joon; Okino, Hirotake; Yamamoto, Takashi; Ueda, Shunkichi; Deguchi, Takeshi

    2006-09-01

    In recent years, because of the rapid progress in wireless technology, microwave absorbers or noise suppressors have become necessary for a safe-electromagnetic-wave-level environment. To design microwave absorbers or noise suppressors, it is necessary to have knowledge of complex permittivity and permeability. To this end, we used the coaxial waveguide method between 500 MHz-18 GHz and the free space method with a dielectric lens in the K-band (18-26.5 GHz). In this report, we show the complex permittivity, \\varepsilonr* and permeability, μr* of lossy dielectric composite materials such as barium titanate oxide (BaTiO3)/rubber and titanium oxide (TiO2)/rubber. The real part of the complex permittivity, \\varepsilon'r is available for changing the trimming weight ratio of rubber and replacing TiO2 or BaTiO3.

  11. 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.

  12. 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

  13. 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.

  14. Stripline dipole with dielectric covering

    NASA Astrophysics Data System (ADS)

    Wang, J.; Hansen, V.

    The use of stripline antennas has greatly increased during the last ten years. In connection with an employment of the antennas, it is often necessary to provide an additional dielectric covering layer to protect the antenna against atmospheric conditions. Water or ice layers can also be described as dielectric layers. The present investigation is concerned with the effect of such additional layers on the radiation characteristics of stripline dipoles. A description is presented of a procedure for the calculation of all important antenna characteristics, taking into account current distribution, input impedance, radiation characteristics, the excitation of surface waves, and aspects of coupling. With the aid of a number of examples it is shown that even a thin covering layer can have a pronounced effect. Such layers can, therefore, also be employed to modify the antenna radiation characteristics to improve their suitability for a given application.

  15. Perfect dielectric-metamaterial reflector

    NASA Astrophysics Data System (ADS)

    Slovick, Brian; Yu, Zhi Gang; Berding, Marcy; Krishnamurthy, Srini

    2013-10-01

    We exploit the Mie resonance in dielectric microparticles to design a single-negative metamaterial monolayer with near-unity reflectivity and negligible absorptivity. In contrast to Bragg reflectors and photonic band gap materials, which require multiple layers for high reflection, this metamaterial is both highly reflective and subwavelength in thickness. We identify the underlying physics necessary to design near-perfect all-dielectric reflectors at virtually any wavelength band of interest. Using full-wave, finite-element analysis and realistic optical constants for the constitutive materials, we develop a 0.45-μm-thick, silicon-based metamaterial monolayer with normal-incidence reflectivity over 99.999% and absorptivity less than 0.001% at a short-wave infrared wavelength of 1.5 μm.

  16. End moldings for cable dielectrics

    SciTech Connect

    Roose, L.D.

    1993-12-31

    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 are 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.

  17. Radiation Resistances of Dielectric Liquids

    NASA Technical Reports Server (NTRS)

    Bouquet, Frank L.; Somoano, Robert B.

    1987-01-01

    Report presents data on effects of ionizing radiation on dielectric liquids for high-energy-density, pulsed-power capacitors. Based on Jet Propulsion Laboratory test results, search of NASA and Department of Energy computer files, survey of open literature, and contacts with manufacturers and suppliers. Covers 22 organic liquids, although detailed data found for only one compound, polydimethyl siloxane. Generic data on effects of radiation on compounds with similar chemical structures provided where data on specific compounds lacking.

  18. Dielectric Relaxation of Hexadeutero Dimethylsulfoxide

    NASA Astrophysics Data System (ADS)

    Betting, H.; Stockhausen, M.

    1999-11-01

    The dielectric relaxation parameters of the title substance (DMSO-d6) in its pure liquid state are determined from meas-urements up to 72 GHz at 20°C in comparison to protonated DMSO. While the relaxation strengths do not differ, the relax-ation time of DMSO-d 6 is significantly longer (21.3 ps) than that of DMSO (19.5 ps).

  19. End moldings for cable dielectrics

    DOEpatents

    Roose, Lars D.

    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.

  20. 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.