Study of interfacial oxide layer of LaAlO3 gate dielectrics on Si for metal–insulator–semiconductor devices

Lanthanum aluminate (LAO) thin films were deposited on silicon by pulsed-laser deposition. It was found that oxygen partial pressure played an essential role in the formation of an interfacial layer. The films deposited in nitrogen at a pressure of 20 Pa had no interfacial layer. However, an interfacial layer was observed in the films deposited in 1×10^-2 Pa atmosphere. According to the thickness of the LAO film and interfacial layer and the measured capacitance, it could be deduced that the interfacial layer was not pure SiO₂. Auger electron spectroscopy, secondary ion mass spectroscopy and X-ray photoelectron spectroscopy depth analyses indicated that the interfacial layer was La–Al–silicate rather than pure silicon oxide and that the La and Al concentrations in the interfacial layer had gradients from the LAO layer to the substrate. PACS 79.61.Jv; 77.55.+f; 81.15.Gh     

Epitropic Liquid-Crystal Hexadecane Layer in the Rheological Model of a Heterophase Interlayer

The hydrodynamic model of a heterophase interlayer of a liquid, which includes an epitropic liquid-crystal (ELC) layer, is supplemented with its structural-rheological model. The application of these models and the technique developed for processing the results of viscosity measurements for n-hexadecane interlayers in the tribotriads has made it possible to conduct a detailed determination of the properties of its ELC layer and the overlapped layer, such as the equilibrium thickness and viscosity, their temperature variation, and the activations energy of the viscous flow.     

Note: Interfacial layer and phase inversion behavior in the blend of polyethersulfone and polycarbonate

A blend of polyethersulfone (PES) and polycarbonate (PC) with a ratio of 40/ 60 was studied by scanning electron microscopy (SEM), dynamic mechanical analysis, and transmission electron microscopy (TEM). It was found that the PES-PC blend is a partially miscible, two-phase system, and an interfacial layer exists between the phases of PES and PC. Specific interaction resulting from the n-complex between PES and PC provides the driving force for formation of the interfacial layer. In addition, phase inversion behavior was also observed for the 40/60 composition.     

Observation of the transient rotator phase of n-hexadecane in emulsified droplets with time-resolved two-dimensional small- and wide-angle X-ray scattering

Crystallization of n-hexadecane in emulsion droplets was studied using time-resolved two-dimensional small- and wide-angle x-ray scattering with differential scanning calorimetry (2D-SAXS-WAXS-in situ DSC) which provides information about both nano- and subnanoscale structural change. n-hexadecane in droplets reproducibly crystallized into the stable triclinic phase via a transient-rotator phase. This is in contrast with previous results that the rotator phase of n-hexadecane was observed only occasionally for bulk samples. Thus we confirmed the existence of rotator phase in n-hexadecane, which is important for the study of crystallization of soft materials. We suggest that the rotator phase at the interface of oil and water plays a precursor role for bulk crystallization. This study demonstrates that 2D-SAXS-WAXS-in situ DSC is a powerful tool for the study of a transient phase.     

Effect of fluorination on the partitioning of alcohols

ABSTRACT

In order to understand the role of fluorination on the interactions and partitioning of alcohols in aqueous and organic environments, isobaric-isothermal ensemble Monte Carlo simulations are used to determine environmental predictors, such as free energies of hydration and solvation in 1-octanol and n-hexadecane. Calculations are performed with the united-atom Transferable Potentials for Phase Equilibria (TraPPE) force field and compared against available experimental data. TraPPE was found to provide reliable qualitative predictions of trends with respect to the effect of fluorination on partitioning. Investigation of the local solvation environment around the hydroxyl group reveals that fluorination of carbons closest to the hydroxyl group has the greatest effect on solvation free energies for alcohols in water, 1-octanol and n-hexadecane.     

Barrier height enhancement and temperature dependence of the electrical characteristics of Al Schottky contacts on p-GaAs with organic Rhodamine B interfacial layer

In this work, two types of Schottky barrier diodes (SBDs) with and without Rhodamine B interfacial layer, were fabricated and measured at room temperature in order to investigate the effects of the Rhodamine B interfacial layer on the main electrical parameters. It was seen that the barrier height (BH) value of 0.78 eV calculated for the Al/Rhodamine B/p-GaAs device was higher than the value of 0.63 eV of the conventional Al/p-GaAs Schottky diodes. It has been observed that the Rhodamine B film increases the effective BH by influencing the space charge region of GaAs. The main diode parameters such as the ideality factor (n) and zero-bias BH of SBD with Rhodamine B interfacial layer were found to be strongly temperature dependent and while the BH decreases, the ideality factor increases with decreasing temperature. It has been concluded that the temperature dependent characteristic parameters for Al/Rhodamine B/p-GaAs SBDs can be successfully explained on the basis of thermionic emission (TE) mechanism with Gaussian distribution of the barrier heights.     

Photon irradiation-induced structural and interfacial phenomena in pure and alio-valently doped zirconia thin films

We report on the effect of ultra-violet (UV) irradiation on structural and interfacial phenomena in pure and doped zirconia thin film grown by physical vapour deposition. Interfacial layer formation by substrate oxidation and resultant densification of zirconia layer was found in yttria-doped zirconia (YDZ) films grown on Si, while no change was observed in identical films grown on Ge. A comparison of un-doped zirconia and YDZ films indicates yttria-doping significantly assists structural changes during UV irradiation. Interestingly, the effect of UV photons becomes minimal at ～300°C in films grown on Si, while the effect of UV becomes more pronounced in YDZ films grown on Ge. An interfacial layer was formed between the YDZ and Ge substrate at 300°C in the presence of UV irradiation, in contrast to the sharp interface maintained, even after annealing at 300°C, without UV. The results suggest that photon irradiation may be an elegant approach to tailor structural and interfacial properties at near-atomic length scales.     

Effect of the degree of crosslinking on the interfacial layer structure of poly(vinyl chloride) dispersed with crosslinked poly(n-butyl methacrylate) particles

The interfacial layer structure of a model incompatible polymer blend system was analyzed using ¹H pulse nuclear magnetic resonance (pulse NMR) spectroscopy. Non-crosslinked and crosslinked poly(n-butyl methacrylate) particles with a mean size of ca. 0.9 μm were prepared by seeded emulsion polymerization, and the degree of crosslinking was varied. The particles were powdered using a freeze-dry method and dispersed in poly(vinyl chloride) by melt blending. Dynamic mechanical analysis indicated that the non-crosslinked particles were completely compatible. In contrast, mutual diffusion of the polymer chains in the crosslinked particles was restricted within the particle/matrix interfacial layer. As a result, an incompatible phase structure in which the crosslinked particles were dispersed in the continuous phase was formed. Pulse NMR analysis indicated that the interfacial layer thickness was in the range of 17–98 nm. The thickness decreased with an increase in the degree of crosslinking in the particles. The interfacial layer thickness in the particles was approximately 10 times larger than that for the incompatible polymer pair. Tensile test results indicated that the elongation at break was dependent on the thickness of the interfacial layer. The yield stress was developed for the particles with high hardness that was independent of the interfacial thickness.     

LiCoO_2 Epitaxial Film Enabling Precise Analysis of Interfacial Degradations

Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO_2(LCO),the most widely studied and used cathode material in lithium ion batteries.To understand such processes requires precise and quantitative measurements.Herein,we use well-defined epitaxial LCO thin films to reveal the interfacial degradation mechanisms.Through our systematical investigations,we find that surface corrosion is significant after forming the surface phase transition layer,and the cathode electrolyte interphase(CEI) has a double layer structure,an inorganic inner layer containing CoO,LiF,LiOH/Li_2O and Li_xPF_yO_2,and an outmost layer containing Li_2CO_3 and organic carbonaceous components.Furthermore,surface cracks are found to be pronounced due to mechanical failures and chemical etching.This work demonstrates a model material to realize the precise measurements of LCO interfacial degradations,which deepens our understanding on the interfacial degradation mechanisms.     

The mica slit-pore as a tool to control the orientation and distortion of simple liquid monolayers

Grand canonical ensemble Monte Carlo computer simulations have been used to study mono-layer octamethylcyclotetrasiloxane (OMCTS) and cyclohexane films confined between mica-like surfaces to determine the effect of the mica surfaces on the orientation and distortion of the films at different surface alignments. The film molecules are packed as a highly ordered lattice. The orientation of the lattice is fixed relative to the mica surfaces and depends on the size of the film molecule. Registry shifts distort the film lattice by effectively stretching it along a particular direction that depends on the size of the film molecule. For a particular registry, OMCTS and cyclohexane monolayers are stretched in perpendicular directions. Coupling between the monolayers and the mica surfaces generates a nonzero shear stress when the surfaces are out of alignment, but the film does not become disordered or melt. It is possible that precisely controlled solid surfaces could be used to create packed arrays of film molecules with desired orientation and degree of distortion that may be useful in nanotechnological applications.     

Amorphous hydrogenated carbon films on semiconductors

The adhesion quality of amorphous hydrogenated carbon films (a-C:H) on semiconductor substrates depends to a large degree on the properties of the interface. The present work complements the photoemission results of the preceding paper with a detailed investigation of the atomic structure of the a-C:H/Si and a-C:H/GaAs interfaces. We show that the method of substrate cleaning and the deposition parameters affect the thickness of the interfacial layer and the interface roughness. The carbide compounds that form in the interfacial layer are found to be amorphous and we present evidence for the precipitation of metallic Ga at the a-C:H/GaAs interface. Finally, we have determined the extent of atomic intermixing in the interfacial region and compare our results with different mechanisms of adhesion.     

Structural comparison of gadolinium and lanthanum silicate films on Si(1 0 0) by HRTEM, EELS and SAED

High-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED) were used to study gadolinium and lanthanum silicate films deposited on Si(1 0 0) substrates using electron-beam evaporation from pressed-powder targets. As-deposited films consist of an amorphous silicate layer without an interfacial layer. After annealing at 900 °C in oxygen for 2 min, an interfacial SiO₂ layer is formed in the gadolinium silicate film, while this interfacial layer is a SiO₂-rich lanthanum silicate layer in the lanthanum silicate film. The formation of interfacial silicate layers is thermodynamically more favorable for the lanthanum films than for the gadolinium films. The gadolinium silicate films crystallize at a temperature between 1000 and 1050 °C, while the crystallization temperature for the lanthanum silicate films is between 900 and 950 °C.     

Enhanced laser induced damage threshold of dielectric antireflection coatings by the introduction of one interfacial layer

A new method for increasing laser induced damage threshold (LIDT) of dielectric antireflection (AR) coating is proposed. Compared with AR film stack of H2.5L (H:HfO2, L:SiO2) on BK7 substrate, SiO2 interfacial layer with four quarter wavelength optical thickness (QWOT) is deposited on the substrate before the preparation of H2.5L film. It is found that the introduction of SiO2 interfacial layer with a certain thickness is effective and flexible to increase the LIDT of dielectric AR coatings. The measured LIDT is enhanced by about 50%, while remaining the low reflectivity with less than 0.09% at the center wavelength of 1064 nm. Detailed mechanisms of the LIDT enhancement are discussed.     

The interfacial diffusion of chromium(III) fumarato coordination compound in the formation of aluminum-polyethylene composite film

The aqueous solution of chromium(III) fumarato coordination compound (Volan 82) is a coupling agent developed by DuPont in the early 1970's. The application of Volan 82 in the production of aluminum-polyethylene composite film greatly improves the water-resistance and durability of the composite film. Our previous studies demonstrated the chemical bonding between aluminum oxide and chromium(III) fumarato coordination compound. In this paper, AES is reported for the studies of the solvent-resistance of the interfacial polyethylene of the composite film. The AES sputter depth profile of the aluminum-polyethylene interfacial layer demonstrated that the chromium(III) fumarato coupling agent diffused into the interfacial polyethylene layer during the formation of aluminum-polyethylene composite film. This was confirmed by ESCA, when chromium was detected in the interfacial polyethylene layer. The interfacial diffusion of the coupling agent improves the adhesion between aluminum and polyethylene of the composite film.     

The electrical characterization of Zn(Phen)q/p-type Si/Al diode with interfacial layer by current–voltage characteristics

The current–voltage characteristics of Zinc (II) [(8-hydroxyquinoline)(1,10-phenanthroline)] complex (Zn(phen)q)/p-type Si/Al diode with interfacial layer have been investigated. The barrier height and ideality factor of the diode were found to be 0.71 eV and 2.05. Zn(phen)q/p-type Si/Al diode shows a metal–insulator–semiconductor structure resulted from presence of series resistance and an interfacial layer. The n and φ_B values obtained the presence of interfacial layer are 1.02 and 0.70 eV, respectively. The effect of series resistance was evaluated using a method developed by Cheung. The R_s and n values were determined from the d ln(I)/dV plot and were found to be 30.43 kΩ and 2.16, respectively. The barrier height and R_s values were calculated from the H(I)–I plot and were found to be 0.70 eV and 30.99 kΩ. The density of the interface states of the Zn(phen)q/p-type Si/Al diode was calculated and was found to be an order of 10¹³ eV⁻¹ cm⁻².     

Self-assembled octadecyltrichlorosilane monolayer formation on a highly hydrated silica film

A MVD silica layer that consists of a highly hydrated surface favorable for organosilane surface reaction is investigated. The MVD silica layer lacks free surface silanol groups while supporting a more extensive adsorbed water layer as compared to oxidized Si(1 0 0). Octadecyltrichlorosilane monolayers (OTS) deposited on the MVD silica layer are found to follow the same mechanisms of growth and exhibit properties comparable to those formed on oxidized Si(1 0 0) surfaces. The growth process of octadecylsiloxane films is investigated as a function of immersion time and temperature by utilizing ATR-FTIR, ellipsometry, contact angle analysis, and AFM. The MVD silica layer is shown to support an ordered interfacial water structure that is more tightly bound due to a higher degree of hydrogen bonding associated with the hydroxylated surface. The importance of interfacial water on the OTS film formation process is highlighted and the role of free OH groups on the adsorption mechanism is diminished. It is shown that OTS films can be formed on a highly hydrated surface comparable to those formed on oxidized Si(1 0 0) surfaces.     

铁电双层膜的反转动力学行为

基于Landau-Khalatnikov运动方程,本文研究了含有表面过渡层和铁电界面耦合的反转动力学行为(包括平均极化、反转时间、反转电流和矫顽场).研究结果表明:在铁电双层膜系统中存在一个竞争的机理,即表面过渡层与界面耦合的竞争作用.我们发现在双层膜反转过程中出现了反常行为,这些反常行为归因于表面过渡层与界面耦合之间的竞争.表面过渡层与界面耦合的共同行为对铁电双层膜的动力学特性起到了决定性的作用.     

Simulation studies of current transport in metal–insulator–semiconductor Schottky barrier diodes

The current–voltage characteristics of Schottky diodes with an interfacial insulator layer are analysed by numerical simulation. The current–voltage data of the metal–insulator–semiconductor Schottky diode are simulated using thermionic emission diffusion (TED) equation taking into account an interfacial layer parameter. The calculated current–voltage data are fitted into ideal TED equation to see the apparent effect of interfacial layer parameters on current transport. Results obtained from the simulation studies shows that with mere presence of an interfacial layer at the metal–semiconductor interface the Schottky contact behave as an ideal diode of apparently high barrier height (BH), but with same ideality factor and series resistance as considered for a pure Schottky contact without an interfacial layer. This apparent BH decreases linearly with decreasing temperature. The effects giving rise to high ideality factor in metal–insulator–semiconductor diode are analysed. Reasons for observed temperature dependence of ideality factor in experimentally fabricated metal–insulator–semiconductor diodes are analysed and possible mechanisms are discussed.     

A study of the effective magnetic anisotropy and the corresponding spin configurations in two dimensional ferromagnetic/antiferromagnetic system

The spin configurations of two dimensional ferromagnetic/antiferromagnetic system were investigated using model calculations and Monte-Carlo simulation methods. The lowest energy state was obtained under various coupling conditions to investigate the role of interfacial interaction on anisotropy. We found that the total ferromagnetic layer anisotropy is contributed not only from its own crystalline anisotropy but also from the antiferromagnetic layer spin flop effect. The overall ferromagnetic layer effective anisotropy is calculated as a function of the exchange energy of antiferromagnetic layer and the interfacial interaction energy. If the effective anisotropy from the spin flop effect is comparable with the crystalline anisotropy, the asymmetric spin configuration is generated. In this configuration, the magnetization direction of the ferromagnetic layer is neither perpendicular nor parallel to the antiferromagnetic spin direction. Temperature effect on the perpendicular-to-collinear coupling transition was also investigated using Monte-Carlo simulation, and the relationship between the effective anisotropy and the temperature was obtained.     

Model of hybrid interfacial domain wall in ferromagnetic/antiferromagnetic bilayers

A general model of a hybrid interfacial domain wall(HIDW) in ferromagnetic/antiferromagnetic exchange biased bilayers is proposed, where an interfacial domain wall is allowed to extend into either the ferromagnetic or antiferromagnetic layer or across both. The proposition is based on our theoretical investigation on thickness and field dependences of ferromagnetic domain wall(FMDW) and antiferromagnetic domain wall(AFDW), respectively. Good match of the simulation to the hysteresis loops of a series of Ni Fe/Fe Mn exchange-biased bilayers confirms the existence of the HIDW, where the AFDW part is found to preferentially occupy the entire antiferromagnetic layer while the FMDW shrinks with the increased magnetic field as expected. The observed asymmetry between the ascending and descending branches of the hysteresis loop is explained naturally as a consequence of different partition ratios between AFDW and FMDW.