Changes in the dielectric breakdown field of polyimide (PI) films have been studied from 25 to 400°C under dc ramps. Both the area (from 0.0707 to 19.635 mm 2 ) and thickness (from 1.4 to 6.7 ¿m) ...dependences of the dielectric breakdown field have been carried out using the Weibull distribution function. The 63%-breakdown field value (i.e. the ¿-scale parameter) of PI shows a decrease with increasing area, thickness and temperature but always remains above 2 MV/cm. The ß-scale parameter of the distribution shows a typical decrease with increasing area, however, it exhibits an increase with increasing thickness. This 'curious' behavior is discussed on the basis of the percolation theory. No temperature-dependence is clearly observed. Moreover, physical interpretations are carried out using the pre-breakdown current analysis.
The electrical conduction and dielectric breakdown of polyimide/boron nitride (PI/BN) are investigated in a large temperature range up to 350 °C. This work shows that BN nanofillers act as deep traps ...for mobile ions. Below 150 °C, the nanostructuration of PI slightly improves the DC conductivity and the breakdown field. On the contrary above 150 °C, while neat PI exhibits ionic space charge contribution on the charging currents, PI/BN nanocomposites show a return to normal polarization currents. In such combined high field and high temperature ranges, the nanostructuration of PI allows increasing the mean free path of ions by decreasing the ionic hopping distance. The consequence of the improvement of the total trap density is a huge decrease (5 orders of magnitude) in the steady state currents and an increase (factor 2) in the breakdown field of PI/BN. This study proves the possibility to extend both the electric field and temperature ranges of PI films thanks to an adequate nanostructuration.
Abstract
Recently, the topological insulators (TIs) antimony telluride (Sb
2
Te
3
) and bismuth telluride (Bi
2
Te
3
) are attracting high interest for applications based on spin-charge ...interconversion mechanisms. Aiming to make a step toward the technology transfer, it is of major importance to achieve and investigate epitaxial quality-TIs on large area Si-based substrates. In view of that, we report here magnetotransport and angle-resolved photoemission spectroscopy (ARPES) studies on Sb
2
Te
3
and Bi
2
Te
3
thin films grown by metal organic chemical vapor deposition (MOCVD) on top of 4″ Si(111) substrates. Clear weak antilocalization (WAL) effects are observed in both TIs, proving the existence of quantum transport mechanism, and the data are successfully interpreted in the framework of the Hikami–Larkin–Nagaoka model. Further, by dedicated magnetotransport experiments, it has been confirmed that the investigated WAL originates from two-dimensional (2D) topological states. ARPES has been performed ex-situ, and in both TIs the gapless Dirac cones have been observed and attributed to the topological surface states. Combining the proofs of the existence of quantum 2D transport as deduced from the analysis of the magnetoconductance curve with the direct observation of the Dirac-like band structure revealed by the ARPES spectra, it is possible to unambiguously confirm the topological nature of our Sb
2
Te
3
and Bi
2
Te
3
thin films. The results obtained on thin films grown by MOCVD on 4’’ Si(111) substrate mark an important step towards the technology transfer of the topological insulators studied in this work.
For Polyimides (PI) used as insulating inter-layers or passivation layers in microelectronics and power electronics, reliability and failure mechanisms are intimately linked to phenomena such as ...non-linear conduction, distortion of field distribution and electrical ageing that have all some relation to space charge processes. Knowledge about these space charge distributions is therefore of importance to optimize structures and designs involving PIs. However, in the thickness scale of interest for such applications, of the order of 10 μm, no results were reported for PI, and only scarce studies for other materials. Space charge measurements carried out on PI using the laser intensity modulation method (LIMM) are reported in this work. PI-containing metal-insulator-semiconductor structures were pre-stressed under DC fields up to 2 MV/cm. The impact of the doping type of the substrate (either n-type or, p-type silicon) has been evaluated to address the mechanisms of space charge formation. The nature of electrode substrate substantially impacts the measured charge amount and charge nature, pointing towards charge injection as the origin of space charge build-up. The interpretation is substantiated by results obtained using a SiO 2 layer as a barrier against electronic injection from the substrate into the PI layer.
Background
It is still unclear whether D2 lymphadenectomy improves the survival of patients with gastric cancer and should therefore be performed routinely or selectively. The aim of this multicentre ...randomized trial was to compare D2 and D1 lymphadenectomy in the treatment of gastric cancer.
Methods
Between June 1998 and December 2006, patients with gastric adenocarcinoma were assigned randomly to either D1 or D2 gastrectomy. Intraoperative randomization was implemented centrally by telephone. Primary outcome was overall survival; secondary endpoints were disease‐specific survival, morbidity and postoperative mortality.
Results
A total of 267 eligible patients were allocated to either D1 (133 patients) or D2 (134) resection. Morbidity (12·0 versus 17·9 per cent respectively; P = 0·183) and operative mortality (3·0 versus 2·2 per cent; P = 0·725) rates did not differ significantly between the groups. Median follow‐up was 8·8 (range 4·5–13·1) years for surviving patients and 2·4 (0·2–11·9) years for those who died, and was not different in the two treatment arms. There was no difference in the overall 5‐year survival rate (66·5 versus 64·2 per cent for D1 and D2 lymphadenectomy respectively; P = 0·695). Subgroup analyses showed a 5‐year disease‐specific survival benefit for patients with pathological tumour (pT) 1 disease in the D1 group (98 per cent versus 83 per cent for the D2 group; P = 0·015), and for patients with pT2–4 status and positive lymph nodes in the D2 group (59 per cent versus 38 per cent for the D1 group; P = 0·055).
Conclusion
No difference was found in overall 5‐year survival between D1 and D2 resection. Subgroup analyses suggest that D2 lymphadenectomy may be a better choice in patients with advanced disease and lymph node metastases. Registration number: ISRCTN11154654 (http://www.controlled‐trials.com).
No difference
About 40% of patients with diffuse large cell lymphoma (DLBCL) still have a poor prognosis. Additionally, DLBCL patients treated with doxorubicin are at risk of cardiac failure. Growing evidence ...suggests an antitumor and cardioprotective activity exerted by estrogen via its binding to estrogen receptor (ER) β. The aim of this study was to evaluate the anticancer activity of the phytoestrogen silibinin, an ERβ selective agonist, on DLBCL growth, and its potential cardioprotective effect.
DLBCL cell lines SUDHL-8, SUDHL-6, and RIVA were used. The anti-tumor activity of silibinin was also evaluated in vivo in NOD/SCID/IL2Rg-/- (NSG) xenografted mice. AC16 human ventricular cardiomyocytes were used to investigate the cardioprotective effects of silibinin.
In vitro silibinin induced apoptosis and autophagy, and blocked tumor cell proliferation, also protecting AC16 cardiomyocytes from doxorubicin-induced toxicity. In vivo silibinin induced cell death and autophagy, and reduced tumor volume.
Silibinin represents a promising therapeutic tool.
The dielectric properties of polyimide/boron nitride (PI/BN) nanocomposite films are investigated as a function of the BN nanofiller size from 20 to 350 °C and at low filler content (1-2 vol.%). The ...role of the BN nanofiller size on the large reduction of the electrode polarization relaxation phenomenon due to ionic movements is reported. For the two smallest BN nanoparticles (95 nm and 35 nm), the permittivity, dielectric losses and dc conductivity are strongly attenuated above 200 °C by a factor of 10 to 1000 compared to neat PI. Thus, the dc conductivity at 350 °C is reduced from 4 × 10−8 Ω−1 cm−1 for neat PI to 3 × 10−11 Ω−1 cm−1 for PI/BN (35 nm). Moreover, a further decrease is obtained by functionalizing the nanofiller surface with a silane coupling agent which improves the grafting of PI chains on those latter nanoparticles. These results highlight the trapping efficiency in the interphase region introduced by the small BN nanofillers (<100 nm) and provides evidence as to the huge nanodielectric effects on the charge carrier transport controlled by the nanoparticle diameter. This finding should be of great importance for advanced high temperature electrical insulation in the future.
The dielectric properties of poly(amide imide) (PAI) films are investigated in a large temperature range. A moisture-dependent relaxation (γ-relaxation between −100 °C and 20 °C) and a ...non-cooperative local dipole relaxation (β-relaxation between 40 °C and 200 °C) display an Arrhenius-type behaviour with an activation energy of 0.50 eV and 1.22 eV, respectively. In the near glass transition (Tg) region at 277 °C, a relaxation process (α-relaxation) occurs due to cooperative segmental motions of the chains and follows a non-linear Vogel-Fulcher-Tamman (VFT) temperature dependence with a strong fragility. Simultaneously in the same temperature range, both a conduction process (σ-conduction) and an electrode polarization phenomenon (ρ-relaxation) are also present. The σ-conduction also follows a VFT behaviour but it possesses a lower fragility in the above-Tg region. This discrepancy is assigned to a partial decoupling between ionic transport and segmental chain motions. The dielectric strength of PAI films exhibits a negative temperature dependence. The near-Tg region corresponds to a change from a thermal breakdown mechanism to an electromechanical breakdown due to the glass-liquid phase transition. Above Tg, the formation of a space-charge probably also involves an electro-thermal breakdown mechanism.
The dielectric properties of a novel high-glass transition polyamide-imide (hT g -PAI, T g =333°C) are investigated for its high temperature use as an insulating material in the range above 250°C in ...order to extend the limit of conventional PAI (c-PAI, T g =277°C). Four dielectric processes are identified between 50°C and 400°C. Among them, the electrical conduction (σ-conduction) is clearly reduced particularly in the range from 250°C to 320°C, i.e. T g (c-PAI)≤T≤ T g (hTg-PAI). The main reason explaining such an enhancement is the shift of ionic conduction contribution towards higher temperatures in hT g -PAI compared to c-PAI. In hT g -PAI, the higher-T g value allows better controlling the free volume expansion responsible of large ions motions in the bulk. In the range of potential applications (i.e. 250 to 320°C), the σ-conduction of hT g - PAI has an activation energy of 2.3 eV (~221.9 kJ mol-1).
This work deals with the isothermal aging mechanisms and their impact on the behaviour of polyimide thin films, usually used as dielectric material in high temperature electronic applications. The ...objectives were to achieve a better knowledge of the atmosphere and mechanical stress effects on the degradation mechanisms of deposited thin films during high temperature isothermal aging. Hence, BPDA/PDA aromatic polyimide (PI) thin films deposited on two different substrates (stainless steel and silicon) were aged slightly below their glass transition temperature (0.8 Tg) in air and in nitrogen atmospheres. During the aging, the dielectric strength, morphological characteristics (thickness, surface profile) and chemical variation were monitored for different initial film thicknesses (<10 μm). Results show that films aged under nitrogen and those deposited on silicon substrates aged in air do not show any remarkable degradation during the aging period. In contrast, the films deposited on stainless steel substrates present significant degradation during aging in air and the material lifetime is thickness dependent. In the latter conditions, the measured mean thickness losses for long aging periods are about 0.5 nm/h for all initial thicknesses, indicating that the degradation is not related to the bulk variation of the material but to a surface degradation mechanism. In addition, the breakdown field presents stabilization after an initial aging period, leading us to conclude that the bulk of the material is not affected by the aging. The coupled results indicate that the BPDA/PDA thermal degradation mechanism at temperature below its glass transition one is due to the attack on the outer film layer, related to the presence of oxygen in the atmosphere and strongly dependent on thermo-mechanical substrate properties. Hence, studying of the thermo-oxidative stability of freestanding polyimide films can lead to misestimated reliability.
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