(1-x)Pb[Yb(1/2)Nb(1/2)]O(3)-xPbTiO(3) (PYbN-PT, x=0.5)(001) oriented thin films were deposited onto LaNiO3 (LNO)/Si(001) substrates by sol-gel processing. The crystallographic texture of the films was controlled by the annealing temperature and heating rate. Highly (001) oriented LNO thin films were prepared by a simple metal organic decomposition technique, and the samples were annealed at 700 °C and 750 °C using a rapid thermal annealing process and furnace, respectively. X-ray diffraction analysis revealed that the films of PYbN-PT were highly (001) oriented along LNO/Si substrates. The degree of PYbN-PT orientation is dependent on the heating rate and annealing temperature. Annealing heating rate of 10 °C/s and high annealing temperature near 750 °C produce the greatest degree of (001) orientation, which gives rise to improved dielectric properties.
The optical properties and electrical conductivity of highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) are reported as a function of the processing additive conditions. The addition of dimethyl sulfoxide (DMSO) increases the conductivity and modifies the dielectric response as observed from the ellipsometric studies. Also the surface roughness and morphology change with the composition of PEDOT:PSS:DMSO and film deposition conditions. The real part of the dielectric function becomes negative in highly conducting samples, indicating the presence of delocalized charge carriers. The real and imaginary parts of the refractive index were determined as a function of wavelength. The results are consistent with the increase in conductivity upon the addition of DMSO.
We present a titanium-silicon oxide film structure that permits polarization modulated infrared reflection absorption spectroscopy on silicon oxide surfaces. The structure consists of a ~6 nm sputtered silicon oxide film on a ~200 nm sputtered titanium film. Characterization using conventional and scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and X-ray reflectometry is presented. We demonstrate the use of this structure to investigate a selectively protein-resistant self-assembled monolayer (SAM) consisting of silane-anchored, biotin-terminated poly(ethylene glycol) (PEG). PEG-associated IR bands were observed. Measurements of protein-characteristic band intensities showed that this SAM adsorbed streptavidin whereas it repelled bovine serum albumin, as had been expected from its structure.
Titanium layers are used to promote adhesion between polymer substrates for flexible electronics and the Cu or Au conducting lines. Good adhesion of conducting lines in flexible circuits is critical in improving circuit performance and increasingcircuit lifetime. Nominally 50 nm thick Ti films on polyimide (PI) are investigated by fragmentation testing under uniaxial tensile load in the as-deposited state, at 350 °C, and after annealing. The cracking and buckling of the films show clear differences between the as-deposited and the thermally treated samples, cracks are much straighter and buckles are smaller following heat treatment. These changes are correlated to a drop in adhesion of the samples following heat treatment. Adhesion values are determined from the buckle dimensions using a total energy approach as described in the work of Cordill et al. (Acta Mater. 2010). Cross-sectional transmission electron microscopy of the Ti/PI interface found evidence of a ~ 5 nm thick interlayer between the largely columnar Ti and the amorphous PI. This interlayer is amorphous in the as-deposited state but nano-crystalline in those coatings tested at elevated temperature or annealed. It is put forward that this alteration of the interfacial structure causes the reduced adhesion.
The adsorption of tobacco mosaic virus (TMV) on self-assembled and Langmuir-Blodgett monolayers was investigated using total internal reflection fluorescence (TIRF) spectroscopy and scanning force microscopy (SFM). Substrates were chosen to probe electrostatic, hydrophobic and surface fluidity effects on TMV adsorption. Positively charged and hydrophobic surfaces demonstrated similar initial rates of TMV adsorption; however, their respective surface TMV coverages differed greatly. Likewise, positively charged surfaces which differed primarily in surface fluidity exhibited similar adsorption rates for TMV, but different TMV surface coverages. In contrast, virus adsorption to negatively charged and zwitterionic substrates was negligible. To elucidate these differences in adsorption behavior, SFM was used to image the distribution and the aggregation state of adsorbed TMV.
This paper presents experimental evidence that thin (< approximately 200 nm) boron coatings, deposited with a (vacuum) cathodic arc technique on pre-polished Co-Cr-Mo surfaces, could potentially extend the life of metal-on-polymer orthopedic devices using cast Co-Cr-Mo alloy for the metal component. The primary tribological test used a linear, reciprocating pin-on-disc arrangement, with pins made of ultra-high molecular weight polyethylene. The disks were cast Co-Cr-Mo samples that were metallographically polished and then coated with boron at a substrate bias of 500 V and at about 100 degrees C. The wear tests were carried out in a saline solution to simulate the biological environment. The improvements were manifested by the absence of a detectable wear track scar on the coated metal component, while significant polymer transfer film was detected on the uncoated (control) samples tested under the same conditions. The polymer transfer track was characterized with both profilometry and Rutherford Backscattering Spectroscopy. Mechanical characterization of the thin films included nano-indentation, as well as additional pin-on-disk tests with a steel ball to demonstrate adhesion, using ultra-high frequency acoustic microscopy to probe for any void occurrence at the coating-substrate interface.
In this work, we report low-loss single-mode integrated optical waveguides in the near ultra-violet and visible spectral regions with aluminum oxide (Al(2)O(3)) films using an atomic layer deposition (ALD) process. Alumina films were deposited on glass and fused silica substrates by the ALD process at substrate/chamber temperatures of 200 °C and 300 °C. Transmission spectra and waveguide measurements were performed in our alumina films with thicknesses in the range of 210 - 380 nm for the optical characterization. Those measurements allowed us to determine the optical constants (n(w) and k(w)), propagation loss, and thickness of the alumina films. The experimental results from the applied techniques show good agreement and demonstrate a low-loss optical waveguide. Our alumina thin-film waveguides is well transparent in the whole visible spectral region and also in an important region of the UV; the measured propagation loss is below 4 dB/cm down to a wavelength as short as 250 nm. The low propagation loss of these alumina guiding films, in particular in the near ultra-violet region which lacks materials with high optical performance, is extremely useful for several integrated optic applications.
Hydrogen silsesquioxane (HSQ) is a material with the potential for studying the effect of surface stiffness on stem cell differentiation. Here, the effects of electron beam dose on the topography and the mechanical properties of HSQ obtained with or without trimethylamine (TMA) development are characterised by atomic force microscopy imaging and indentation. A correlation between the surface stiffness (uniform across the sample) and electron beam exposure is observed. Surface roughness of HSQ samples developed in TMA decreases exponentially with increasing electron beam exposure. Surface coating with plasma polymerised allylamine (ppAAm) leads to an overall decrease in stiffness values. However, the increase in surface stiffness with increasing electron beam exposure is still evident. The ppAAm coating is shown to facilitate human mesenchymal stem cell adhesion.
Undoped and boron-doped nanocrystalline (NCD) diamond films were deposited on mirror polished Ti-6Al-4V substrates in a Microwave Plasma Assisted Chemical Vapor Deposition system. Sliding wear tests were conducted in ambient air with a nanotribometer. A systematic study of the tribological properties for both undoped and boron-doped NCD films were carried out. It was found for diamond/diamond sliding, coefficient of friction decreases with increasing normal loads. It was also found that the wear rate of boron-doped NCD films is about 10 times higher than that of undoped films. A wear rate of ~5.2×10(-9) mm(3)/Nm was found for undoped NCD films. This value is comparable to the best known value of that of polished polycrystalline diamond films. Although no surface deformation, film delamination or micro-cracking were observed for undoped films, boron-doped NCD film undergoes a critical failure at a normal stress of 2.2 GPa, above which surface deformation is evident. Combined with high hardness and modulus, tunable conductivity and improved open air thermal stability, boron-doped nanocrystalline diamond film has tremendous potentials for applications such as Atomic Force Microscope probes, Micro-Electro-Mechanical System devices and biomedical sensors.
A fully integrated, wireless neural interface device is being developed to free patients from the restriction and risk of infection associated with a transcutaneous wired connection. This device requires a hermetic, biocompatible encapsulation layer at the interface between the device and the neural tissue to maintain long-term recording/stimulating performance of the device. Hydrogenated amorphous silicon carbide (a-SiC(x):H) films deposited by a plasma enhanced chemical vapor deposition using SiH(4), CH(4), and H(2) precursors were investigated as the encapsulation layer for such device. Si-C bond density, measured by Fourier transform infrared absorption spectrometer, suggests that deposition conditions with increased hydrogen dilution, increased temperature, and low silane flow typically result in increase of Si-C bond density. From the variable angle spectroscopic ellipsometry measurement, no dissolution of a-SiC(x):H was observed during soaking tests in 90°C phosphate buffered saline. Conformal coating of the a-SiC(x):H in Utah electrode array was observed by scanning electron microscope. Electrical properties were studied by impedance spectroscopy to investigate the performance of a-SiC(x):H as an encapsulation layer, and the results showed long term stability of the material.
In this work the structure of ternary Ga
In1 - x P nanowires is investigated with respect to the chemical composition and homogeneity. The nanowires were grown by metal-organic vapor-phase epitaxy. For the investigation of ensemble fluctuations on several lateral length scales, X-ray diffraction reciprocal space maps have been analyzed. The data reveal a complicated varying materials composition across the sample and in the nanowires on the order of 20%. The use of modern synchrotron sources, where beam-sizes in the order of several 10 μm are available, enables us to investigate compositional gradients along the sample by recording diffraction patterns at different positions. In addition, compositional variations were found also within single nanowires in X-ray energy dispersive spectroscopy measurements.
Multinary Ti-Al-N thin films are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we study the effect of Zr addition on structure, mechanical and thermal properties of Ti(1-x)Al(x)N based coatings under the guidance of ab initio calculations. The preparation of Ti(1-x-z)Al(x)Zr(z)N by magnetron sputtering verifies the suggested cubic (NaCl-type) structure for x below 0.6-0.7 and z ≤ 0.4. Increasing the Zr content from z = 0 to 0.17, while keeping x at ~ 0.5, results in a hardness increase from ~ 33 to 37 GPa, and a lattice parameter increase from 4.18 to 4.29 Å. The latter are in excellent agreement with ab initio data. Alloying with Zr also promotes the formation of cubic domains but retards the formation of stable wurtzite AlN during thermal annealing. This leads to high hardness values of ~ 40 GPa over a broad temperature range of 700-1100 °C for Ti(0.40)Al(0.55)Zr(0.05)N. Furthermore, Zr assists the formation of a dense oxide scale. After 20 h exposure in air at 950 °C, where Ti(0.48)Al(0.52)N is already completely oxidized, only a ~ 1 μm thin oxide scale is formed on top of the otherwise still intact ~ 2.5 μm thin film Ti(0.40)Al(0.55)Zr(0.05)N.
Amorphous Ta-Si-N films of about 500 nm thickness were reactively sputter deposited on Si substrates using DC magnetron sputtering from TaSi<sub>0.1</sub>, TaSi<sub>0.4</sub> and TaSi<sub>0.6</sub> targets. The film properties were characterized by sheet resistance measurement and X-ray diffraction. With increasing amounts of nitrogen in the sputtering gas, the film resistivity increased. Surface erosion of the multiphase target material was analyzed by SEM. Particulate emission is minimized with increasing density and refined microstructure of the target material
The concept of treating interconnections as a device and designing
them while keeping both materials and structures in mind is presented.
An example using molybdenum and copper is demonstrated. Copper
introduces new problems such as diffusion in addition to the traditional
problems for interconnections such as adhesion. A new structure called a
sidewall barrier is presented and used as part of a copper
interconnection. This structure can be combined with a multilayer thin
film resulting in a completely encapsulated interconnection. The
technique is versatile enough that almost any material including
dielectrics can be used as the encapsulation material and the sidewall
barrier can be either on the outside of a feature or the inside of a
space. Several potential metals (Mo, TiN, W) for encapsulating copper
are examined and molybdenum is chosen and used. Electromigration
measurements of bilayered copper films reveal that there are problems
with TiN and tungsten barriers. Copper oxidation, stress,
electromigration, hillock growth, resistivity, diffusion and adhesion
are all studied
An experimental investigation is presented on the influence of the laser excitation on the photoluminescence (PL) linewidth in silicon-doped InAlAs layers grown lattice-matched to InP substrates by molecular beam epitaxy (MBE). It was observed that the linewidth decreases with increasing laser excitation power. A model describing an unbalanced migration of photo-generated charge carriers due to the presence of clusters is proposed to explain the effect of the linewidth reduction. Also, the trend of the linewidth decrease becomes more pronounced in InAlAs samples with higher silicon doping concentrations. These samples have broader linewidths which is the result of poorer alloy quality due to the presence of disorder. A similar trend of linewidth reduction was also observed at higher measurement temperatures of 15 and 30 K. Our results show that such measurement of linewidth vs. laser excitation power can be used as a supplementary method for InAlAs material characterization
Vertical p-MOS transistors with channel length of 130 nm have been fabricated using selective epitaxial growth (SEG) to define the channel region. The vertical layout offers the advantages of achieving short channel lengths and high integration densities while still using optical lithography to define lateral dimensions. Compared to other vertical concepts, this layout has reduced gate to source/drain overlap capacitances which is necessary for high speed applications. The use of SEG instead of blanket epitaxy avoids the deterioration of the Si-SiO2 interface due to reactive ion etching (RIE) and reduces punch-through due to facet growth. First nan-optimized p-channel MOSFETs With a 12-nm gate oxide show a transconductance of 90 mS/mm. The cut-off frequencies of this device turned out to be f(T) = 2.3 GHz and f(max) = 1.1 GHz.
The objects of this study were SnTe films grown by thermal evaporation in vacuum on KCl substrates. The dependences of the Seebeck coefficient S and the Hall coefficient R<sub>H</sub> on the SnTe film thickness (d = 5 - 700 nm) were obtained at room temperature. Distinct oscillations in the d-dependences of S and R<sub>H</sub> were observed and attributed to the size quantization in SnTe thin films. The discrepancy between the experimentally determined oscillation period Δd and the theoretical Δd estimated using the model of a quantum well with infinitely high walls is explained by an oversimplification of the model. The monotonic component of the d-dependences of S and R<sub>H</sub> changes with increasing thickness up to d∼100 nm, and then remains constant. It is suggested that this behavior can result from the dependence of the equilibrium concentration of non-stoichiometric cation vacancies on the SnTe film thickness.
DC and low-frequency-noise characteristics Of SiGe HBTs with a raised-emitter structure, fabricated by epitaxial growth of phosphorous-doped Si layers, were investigated. Experimental results indicate unexpected emitter-size dependencies of both base current and low-frequency noise, because mono-poly interfacial native oxides close to the intrinsic emitter-base junction are localized at the emitter periphery. The raised mono-Si emitter SiGe HBT with a scaled emitter exhibits low-frequency noise that is about ten times smaller than a conventional poly-Si emitter SiGe HBT (c) 2008 Elsevier B.V. All rights reserved.
A simple model of thermal dissociation of hydrogen from silicon
dangling bonds (P<sub>b</sub> centers) and their hydrogen passivation
with vacuum annealing is suggested. It takes into account the reactions
occurring for hydrogen with defect states at the interface of the Si/SiO
<sub>2</sub> structure as well as the diffusion process for atomic and
molecular hydrogen. The reaction kinetic coefficients were calculated in
diffusion approximation. Excellent agreement of calculations with
experimental data was obtained in the temperature range (480-700°C),
and oxide thickness of (200-1024 Å) for the (111) and (100)
For more than a decade, considerable effort has been put into the
development of light emitting devices based on evaporated layers of
organic semiconductors. To date, the properties of matrix displays
consisting of organic light emitting diodes (OLEDs) basically meet
automotive and consumer product requirements. OLED matrix displays offer
high contrast, wide viewing angle and a broad temperature range at low
power consumption. In contrast to polymer devices, OLEDs are processed
in ultrahigh vacuum systems. The organic source materials are sublimated
from effusion cells. Due to the sensitivity of organic thin films,
device structuring by conventional etching techniques is not feasible
and alternative structuring techniques were developed. Electrical
current in organic devices is limited by the low conductivity of organic
semiconductors and by energy barriers at the metal-organic semiconductor
interface. Photoelectric measurements facilitate the determination of
barrier height differences between various electrode set-ups. Further
insights into the energy band alignment at organic heterointerfaces are
gained by ultraviolet photoelectron spectroscopy (UPS). In addition to
widely employed electrical (I-V, C-V) and optical (PI) measurements,
thermally stimulated current (TSC) and luminescence (TSL) allow the
characterization and a more detailed understanding of carrier traps and
charge transport in organic devices. Energy transfer in a doped OLED
emitting layer can be investigated by time-resolved photoluminescence
The factors affecting adhesion are reviewed, and it is shown that the structure of the interfacial region is probably a controlling factor in film adhesion. Nucleation, film growth and surface effects control the structure of the interfacial region and may determine the adhesion obtained. The adhesion stability of a metallization system may be determined by processing and service requirements. Specific metallization systems in common use in the microelectronics industry are discussed together with their applications and limitations.
Ge on Si p-i-n photodetectors with areas which are compatible with commercially-available receivers have been fabricated and tested. A dark current density of 6 mA/cm(2) at -1 V bias has been measured at room temperature; when heated to 85 degrees C, the measured dark current increases by a factor of nine. A responsivity of 0.59 A/W at 850 nm has been measured from these Ge detectors, which matches or exceeds commercially available GaAs devices. We have measured bandwidths approaching 9 GHz at -2 V bias from 50 pm diameter Ge detectors.
We report here microstructural, magnetic and optical properties of high quality epitaxial thin films of diluted magnetic semiconductor Zn1 − xMnxO (0.01 ≤ × ≤ 0.25) grown on (0001) sapphire substrate (α-Al2O3) by pulsed laser deposition technique. Seven (01-10) planes of ZnMnO film are found to match with six (-12-10) planes of sapphire substrate through excellent domain matching epitaxy by 30° rotations of ZnMnO unit cell about c-axis with respect to the sapphire unit cell. From high resolution transmission electron micrograph image the misfit dislocations are observed at the interface of sapphire and ZnMnO film growth plane. The insulating Zn0.82 Mn0.18 O epitaxial thin film showed ferromagnetic behavior (hysteretic) with coercive field ∼ 6.2 mT, and a maximum saturation moment of 0.42 μB/Mn+2 ion at a field of 0.5 T at the lowest attainable temperature (T = 10 K). The strong concave behavior of magnetization as a function of the temperature curves in this strongly insulating ferromagnetic diluted magnetic semiconductor film has been best explained through non-mean-field polaron-percolation-theory. The increase of band gap from bulk ZnO with dopant concentration (x), observed from absorbance spectra, has been attributed to the sp-d spin — exchange interaction between the band electrons and localized d electrons of Mn+2 ions of Zn1 − xMnxO films in the presence of tetrahedral crystal field interaction.
Amorphous tantalum oxide thin films were deposited by reactive r.f. magnetron sputtering onto silicon substrates. Growth temperature, oxygen partial pressure and total gas pressure have been varied for optimizing thin film density. The as-deposited films were annealed in atmosphere at 700°C and transformed into a polycrystalline state. The thin films were analyzed by glancing-angle-of-incidence X-ray diffraction, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared (NIR) to vacuum-ultra-violet (VUV) spectral region for photon energies from 1 to 8.5 eV, and in the infrared (IR) region from 0.03 to 1 eV. We present the IR dielectric functions of amorphous and polycrystalline tantalum oxide, which were obtained by analyzing the experimental ellipsometric data with Lorentzian lineshapes for each phonon resonance absorption. We observe a shift of the characteristic phonon absorption in tantalum oxide to lower frequencies upon sample annealing. The optical properties in the NIR to VUV were analyzed by using a parametric model approach. The dielectric functions obtained thereby were further locally fitted by Lorentzian lineshapes in order to analyze critical point structures due to electronic band-to-band transitions.