The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions (birA) to complete dehydration, and the involved mechanisms were scrutinized. Density Functional Theory (DFT) simulations were employed to derive structural models for lamellar A0.33MnO2xH2O (A = Na+ or K+, x = 0 or 0.66), subsequently compared with the experimental results obtained for Na0.30MnO20.75H2O and K0.22MnO20.77H2O materials. Thermal analysis (TGA-DSC), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Near Ambient Pressure X-ray Photoemission Spectroscopy (NAP-XPS) measurements were conducted for both birnessites. Dehydration under vacuum, annealing, or controlled relative humidity were considered. Results indicated that complete birnessite dehydration was a two-stage process. In the first stage, water removal from the interlayer of fully hydrated birnessite (birA) down to a molar H2O/A ratio of similar to 2 (birB) led to the progressive shrinkage of the interlayer distance (3% for Na birnessite, 1% for K birnessite). In the second stage, water-free (birC) domains with a shorter interlayer distance (20% for Na birnessite, 10% for K birnessite) appeared and coexisted with birB domains. Then, birB was essentially transformed into birC when complete dehydration was achieved. The vibrational properties of birA were consistent with strong intermolecular interactions among water molecules, whereas partially dehydrated birnessite (birB) showed a distinct feature, with 3 (for Na-bir) and 2 (for K-bir) vibrations that were reproduced by DFT calculations for organized water into the interlayer (x = 0.66). The study also demonstrated that the electronic structure of Na birnessite depends on the interlayer water content. The external Na+ electronic level (Na 2p) was slightly destabilized (+0.3 eV binding energy) under near ambient conditions (birA) compared to drier conditions (birB and birC). The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions to complete dehydration, and the involved mechanisms were scrutinized.

This paper presents a study of the contact resistance between a metal M (M = Ni, Pt, and Au) and an array of n-type Bi2Te3−xSex thermoelectric nanowires deposited through the electrodeposition process in the alumina membrane. Contact resistances between different metals and thermoelectric nanowires have been tested and characterized after optimization of the mechanical thinning and polishing process of the top part of the membrane. A low areal contact resistance of 87 µΩ cm2 obtained with Au as the contact electrode is very encouraging for the development of thermoelectric modules based on nanowires in their membranes.

We investigate the structural and vibrational properties of Si:P thin films obtained by co-evaporation of Si and P in ultrahigh vacuum at room temperature followed by rapid thermal annealing. The thermal crystallization of the films was followed by Raman spectroscopy. Annealing at temperatures larger than 950 degrees C leads to the formation of crystalline phases. Density functional theory calculations of the vibrational modes allow us to identify orthorhombic SiP. Electron energy loss spectroscopy combined with energy-dispersive spectroscopy gives evidence of a plasmon signature of the SiP phase. The distribution of the crystalline phases in the film was imaged by energy-filtered transmission electron microscopy. Both Si and SiP areas having sizes of a few microns are found to coexist in the films. High-resolution scanning transmission imaging provides a clear evidence of the lamellar structure, while spatially resolved electron energy loss spectroscopy allows us to achieve chemical mapping for both Si and P atoms, which agrees quite well with the orthorhombic structure of SiP. Our results represent an important first step to obtain two-dimensional (2D) SiP, a promising new material for which a direct band gap has been predicted.

We investigate the structural, vibrational, and optical properties of phosphorus-rich SiO1.5 thin films annealed at 1100 degrees C. For phosphorus (P) contents larger than 3 atom %, high-resolution transmission electron microscopy characterizations reveal the presence of both spherical-shaped SiP2 nanoparticles crystallizing in an orthorhombic structure and bumps in epitaxy with the underlying Si substrate. Energy-dispersive spectroscopy measurements confirm the SiP2 stoichiometry. Moreover, electron energy loss spectroscopy characterizations allow us to determine the exact location of P and Si atoms. Apart from SiP2 nanoparticles, P atoms are found to be located in the bumps and in the Si substrate to a level of 1 atom %, which is explained by P diffusion during annealing. The vibrational properties determined by Raman spectroscopy are found to be in excellent agreement with density functional theory calculations of the vibration modes for the SiP2 alloy. Finally, the quenching of photoluminescence with an increasing P content is explained on the basis of structural data.

The effect of chemical vapor deposition (CVD) parameters on the surface morphology and the molecular structure of parylene-D (also called poly-dicloro-xylylene or PPX D) films were investigated. Relevant process parameters are defined by the sublimation temperature, pyrolysis temperatures, growth rate, and time of the deposition process. The sublimation temperatures strongly affects the layer growth rate which increases by a factor of about 4 as the temperature increases from 120 to 160 degrees C. The sublimation temperature at which the parylene-D cannot be deposit is estimated to be 105 degrees C. The present CVD experimental parameters have shown that appropriate sublimation temperatures can yield a controlled growth of the layer thickness ranging from tens of nanometers up to at least 8 gm with a good control of the amorphous and the crystalline amounts. Nearly amorphous parylene-D is obtained when sublimation temperatures are height. However, the crystallinity is increased considerably when the dimer T-sub is decreased. A decrease in the surface roughness is achieved by reducing the Tsub and the deposition rate. These experimental conditions giving rise to dense and transparent parylene-D films. The pyrolysis temperatures favorite growing of globules at the surface compared to the sublimation temperatures. The size of the globules increases from 1.3 mu m for T-pyr = 650 degrees C to 13.7 gm for T-pyr = 690 degrees C. It inferred also that the crystallinity content and the crystalline size decrease by increasing the pyrolysis temperatures. Electrical properties are very influenced by the CVD-processing parameters especially by modifying the pyrolysis temperature. Using these optimized conditions, state-of-the-art parylene-D films with promising properties are reproducibly processed. These results significantly expand the range of processing variables compatible with large applications domains. (C) 2016 Elsevier B.V. All rights reserved.

Thin and transparent Parylene D (-CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -) films have been prepared by chemical vapor deposition (CVD). The impact of the crystallinity transformations and the thermal stability were identified in Parylene D based on the dielectric spectroscopy (DS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Changes of (ac)-conductivity with temperature (from 240°C to 340°C) and frequency (from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> Hz to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Hz) are discussed. Good insulating properties of Parylene D were obtained until operating at high temperatures. Moreover, its dielectric properties were inserted between those of Parylene N and Parylene C making Parylene D interesting to replace the latter for specific applications. However, DSC measurements of these samples show after multiple melting-crystallization cycles the appearance of an instability endothermic peak when the crystallization of the sample is completed. This peak increases and shifts towards lower temperatures as the sample is further thermally treated. At this point, the thermal instability of Parylene D is associated to a crystallographic structure change and not due to a chemical degradation.

Parylene is a generic name indicating a family of polymers with the basic chemical structure of poly-p-xylylene. Parylene N and Parylene C are the most popular for applications. Curiously, Parylene D (poly( dichloro-p-xylylene), (C8H6Cl2)) was forgotten for applications. This report is the consequence of a later availability of a commercial dimer of Parylene D and also to the recent advent of fluorinated Parylenes allowing extending applications at higher temperatures. In our work, from a dielectric analysis, we present the potentialities of Parylene D for applications particularly interesting for integration in organic field-effect transistors. Dielectric and electrical properties, macromolecular structures, and dynamics interaction with electric field as a function of frequency and temperature are studied in 5.8 μm thick Parylene D grown by chemical vapor deposition. More exactly, the dielectric permittivity, the dissipation factor, the electrical conductivity, and the electric modulus of Parylene D were investigated in a wide temperature and frequency ranges from -140 to +350 °C and from 0.1 Hz to 1 MHz, respectively. According to the temperature dependence of the dielectric permittivity, Parylene D has two different dielectric responses. It is retained as a nonpolar material at very low temperature (like Parylene N) and as a polar material at high temperature (like parylene C). The dissipation factor shows the manifestation of two relaxations mechanisms: γ and β at very low and high temperatures, respectively. The γ relaxation is assigned to the local motions of the C-H end of the chains when the cryogenic temperature range is approached. A broad peak in tan δ is assigned to the β relaxation. It corresponds to rotational motion of some polar C-Cl groups. For temperature above 260 °C a mechanism of Maxwell-Wagner-Sillars polarization at the amorphous/crystalline interfaces was identified with two activation energies of Ea1 = 2.12 eV and Ea2 = 3.8 eV. Moreover, the conductivity and the dielectric permittivity relaxation processes have been discussed in terms of nearly constant loss (NCL) and universal dynamic regime (UDR). Finally, ionic conduction and electrode polarization effects are identified at very high temperatures and their physical origins are discussed.

58% semi-crystalline thin parylene-VT4 (-H2C-C6F4-CH2-)(n) films, have been investigated by dielectric spectroscopy for temperature and frequency ranges of [-120 to 380 degrees C] and [0.1-10(5) Hz] respectively. The study comprises a detailed investigation of the dielectric constant, dielectric loss and AC conductivity of this fluoropolymer. Dielectric behavior of parylene-VT4 is represented by a low dielectric constant with values in the range of 2.05-2.35 while the dielectric losses indicate the presence of two relaxation processes. Maxwell-Wagner-Sillars (MWS) polarization at the amorphous/crystalline interfaces with activation energy of 1.6 eV is due to the oligomer orientation. Electrical conductivity obeys to the well-known Jonscher law. The plateau in the low frequency part of this conductivity is temperature-dependent and follows an Arrhenius behavior with activation energy of 1.17 eV (deep traps) due to the fluorine diffusion. Due to its thermal stability with a high decomposition temperature (around 400 degrees C under air and 510 degrees C under nitrogen) and due to its good resistivity at low frequency (10(15)-10(17) Omega m(-1)), parylene-VT4 constitutes a very attractive polymer for microelectronic applications as low k dielectric. Moreover, when parylene-VT4 is subjected to an annealing, the dielectric properties can be still more improved. (C) 2013 Elsevier B.V. All rights reserved.

Research on poly(α,α difluoro‐p‐xylylene) thin films is described and summarized. The important physicochemical and dielectric properties are investigated. For this, characterization tools that can provide information on the nature of structural and physicochemical according substrate temperature are used. A summary of the main properties of poly(α,α difluoro‐p‐xylylene) is presented.

Plasma treatment of parylene-C surfaces not only causes structural modification of the surface during the plasma exposure, but also leaves active sites on the surfaces, which decreases the dielectric properties. In this work, the effects of oxygen, argon/hydrogen and fluorine plasma treatment on the surface and dielectric properties of parylene-C thin films were investigated using Fourier transform-IR spectroscopy, energy dispersive x-ray analysis and dielectric spectroscopy measurement. The results showed that the plasma treatment successfully introduced fluorine functional groups and decreased the oxygen content on the parylene-C surfaces. It appears that the replacement of oxygen and hydrogen by fluorine atoms led to a decrease in the local orientational polarizability of parylene-C. Consequently, it was found that the atmospheric fluorine plasma-treated parylene-C possessed lower dielectric characteristics, 16% lower than the untreated parylene-C at industrial frequencies (10-10(4) Hz). The Ar/H-2 plasma treatment is also an experimental means to reduce the dielectric properties and to decrease the oxygen content in parylene-C. In contrast, the oxygen plasma increases the dielectric constant and can cause deterioration of the leakage current associated with carbon depletion showing C-O and C=O formation. CF4 and Ar/H-2 plasma treatment does not significantly affect the long molecular motion (alpha-relaxation). Additional extrinsic oxygen content due to O-2 plasma treatment in the parylene-C structure reproduces the increase in the time constant of both the short (beta-relaxation) and long molecular motion.

Pentacene based organic field effect transistors (OFETs) were processed with poly(tetrafluoro-p-xylylene) as gate dielectric. This polymer (denoted VT4) was deposited by chemical vapor condensation-polymerization at room temperature. Hydrophobic character and surface energy of VT4 was determined by contact angle measurement and compared to usual gate dielectric polymers. The dielectric constant, obtained from impedance measurement on Metal-VT4-Metal diodes in dry nitrogen and relative humidity (RH = 56%) shows an extraordinary stability at epsilon(R) = 2.3. Transistors, processed in top gate configurations, have been characterized as a function of relative humidity to assess environmental stability of VT4/pentacene transistors.

Using dielectric spectroscopy analysis, three relaxation mechanisms have been identified in 60% semi-crystalline parylene AF4 ([–F2C–C6H4–CF2–]n) fluoropolymers. At high temperature, fluorine species located at the electrode/polymer interface involve a space-charge polarization. β-Process assigned to local molecular motions of the C–F dipoles and the γ-relaxation due to local fluctuations of the F2C–C6H4 groups are also evidenced at intermediate and cryogenic temperatures respectively. Space-charge fluorine F−, β and γ relaxations obey an Arrhenius law against temperature with activation energy Ea (F−)=1.26eV, Ea (β)=0.59eV and Ea (γ)=0.29eV.

We report the microfabrication and operation of a highly sensitive ac-calorimeter designed to characterize small mass magnetic systems operating at very low frequencies (from 0.1 to 5 Hz) in a temperature range from 20 to 300 K. The calorimetric cell is built in the center of a 500 nm thick polymeric membrane of parylene C held up by a Cu frame. On both sides of the membrane defining a three layer structure, electrical leads, heater, and thermometer are deposited as thin film layers of NbN(x), with different nitrogen contents, taking benefit of the poor thermal conductance of niobium nitride to thermally isolate the system. This suspended structure ensures very low heat capacity addenda with values in the microJ/K over the 1 mm(2) area of the measurement cell. The structuring of the membrane along with suspending of the sensing part only by the parylene bridges leads to a highly reduced thermal link. The calorimeter has been characterized as a function of frequency, temperature, and magnetic field. The thermal link measured is really small reaching values well below 10(-8) W/K at 50 K. With these characteristics the frequency of adiabaticity is typically around few hertz and energy exchanges as small as 1 pJ can be detected. Measurements have been performed on Co/Au thin films and on the GdAl(2) microcrystal where the ferromagnetic phase transition is clearly evidenced.

A sensor for thermal and thermodynamic measurements of small magnetic systems has been designed and built. It is based on a 5μm-thick suspended polymer membrane, which has a very low heat capacity (≈10-6J/K at nitrogen temperature), and on which a heater and a highly sensitive thermometer are deposited. The sensor properties have been characterized as a function of temperature and frequency. Energy exchanges as small as 1picojoule (10-12J) were detected in the 40–300K temperature range. Such values correspond to those required for measuring the thermal signatures occurring during magnetization reversal in very thin samples (typically 10nm thick), which would be deposited on the membrane. It is expected that this method will constitute a powerful tool in view of analyzing magnetization reversal processes in magnetic nanosystems, e.g. exhibiting the exchange–spring and exchange–bias phenomena.

We report on the stability of top gated pentacene field effect transistors processed on Kapton™ with Parylene-C as gate dielectric. The influence of bias stress and ambient atmosphere on device characteristics were investigated. Combined influence of moisture and gate bias stress led to an increase of depletion current and subthreshold slope as well as a drift of onset voltage and threshold voltage. We show that devices stressed in the off state exhibit a high stability.

Niobium nitride thin-film thermometry has been developed for the temperature range of 70 to 300 K. The deposition parameters have been optimized in order to get the best performances, i.e., the highest temperature coefficient of resistance (TCR), up to 300 K. The TCR is found to be largely higher than 1% as the temperature is lowered from 300 K, up to 6% at 77 K. These significant performances are compared to the one of regular platinum thermometer as well as to other resistive thermometer: semiconductor type or amorphous metal to insulator transition materials. It is discussed how the properties of the NbN thin films could be due to a high-temperature Mott transition.

We demonstrate the wafer-scale integration of single-electron memories based on carbon nanotube field-effect transistors (CNFETs) using a process based entirely on self assembly. First, a "dry" self-assembly step based on chemical vapor deposition (CVD) allows the growth and connection of CNFETs. Next, a "wet" self-assembly step is used to attach a single 30-nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead is used as the memory storage node while the CNFET operating in the subthreshold regime acts as an electrometer exhibiting exponential gain. Below 60 K, the transfer characteristics of gold-CNFETs show highly reproducible hysteretic steps. Evaluation of the capacitance confirms that these current steps originate from the controlled storage of single electrons with a retention time that exceeds 550 s at 4 K.

We present a full process based on chemical vapour deposition that allows fabrication and integration at the wafer scale of carbon-nanotube-based field effect transistors. We make a statistical analysis of the integration yield that allows assessment of the parameter fluctuations of the titanium-nanotube contact obtained by self-assembly. This procedure is applied to raw devices without post-process. Statistics at the wafer scale reveal the respective role of semiconducting and metallic connected nanotubes and show that connection yields up to 86% can be reached. For large scale device integration, our process has to implement both wafer-scale self-assembly of the nanotubes and high transistor performances. In order to address this last issue, a gate engineering process has been investigated. We present the improvements obtained using low and high. dielectrics for the gate oxide.