Modulation Of Film Thickness Research Articles

Pressure-Induced Superconductivity in HgTe Single-Crystal Film.

HgTe film is widely used for quantum Hall well studies and devices, as it has unique properties, like band gap inversion, carrier‐type switch, and topological evolution depending on the film thickness modulation near the so‐called critical thickness (63.5 Å), while its counterpart bulk materials do not hold these nontrivial properties at ambient pressure. Here, much richer transport properties emerging in bulk HgTe crystal through pressure‐tuning are reported. Not only the above‐mentioned abnormal properties can be realized in a 400 nm thick bulk HgTe single crystal, but superconductivity is also discovered in a series of high‐pressure phases. Combining crystal structure, electrical transport, and Hall coefficient measurements, a p‐n carrier type switching is observed in the first high‐pressure cinnabar phase. Superconductivity emerges after the semiconductor‐to‐metal transition at 3.9 GPa and persists up to 54 GPa, crossing four high‐pressure phases with an increased upper critical field. Density functional theory calculations confirm that a surface‐dominated topologic band structure contributes these exotic properties under high pressure. This discovery presents broad and efficient tuning effects by pressure on the lattice structure and electronic modulations compared to the thickness‐dependent critical properties in 2D and 3D topologic insulators and semimetals.

Manganese vanadium sulfate-oxide cylindrical core-shell heterostructures by electro-spray deposition on graphite foil for Li+ ion intercalation

Heterostructure based on metal sulfides and oxides nanomaterials can be relevant to the charge storage devices. Here, we show that Mn(CH3COO)2·4H2O and VOSO4·xH2O can react in ethanol/water droplets generated by an electric field assisted spray system, so that MnSx-VSx/MnzV2O5 heterostructures in the shape of nanometric cylindrical particles can be deposited on a graphite foil substrate. The composite material phases were detected by several microscopies and microscopic probes spectroscopies, i.e., micro-Raman and scanning X-ray photoemission microscopy. The nanometric cylindrical particles were relatively homogenously distributed throughout the film covering the graphite foil. Film thickness modulation on surface was calculated between 100 and 300 nm range. We show that the segregation of MnV-O and MnV-S relative abundance in the internal and external volume of the cylindrical nanoparticles respectively, can be exploited during faradaic and non-faradaic processes in charge/discharge.

Nanoscale Block Copolymer Self‐Assembly and Microscale Polymer Film Dewetting: Progress in Understanding the Role of Interfacial Energies in the Formation of Hierarchical Nanostructures

AbstractBlock copolymer (BCP) self‐assembly (SA) can be exploited for next‐generation lithography for the advanced nanopatterning of surfaces with versatile nanoscale features. To render BCP‐SA suitable for the creation of tailored surface patterns, a fundamental understanding of interfacial interactions is crucial. This progress report gives an overview on the interplay of BCP microscale film thickness modulation and nanoscale microphase separation during BCP‐SA. Light is shed on the role of interfacial energies in both events. Microscale processes determining the topography of BCP films, i.e., hole/island formation and dewetting into droplets, are presented. Nanoscale microphase separation into energetically favorable pattern orientations in dependency on the polymer film thickness and influenced by surface polarities are discussed critically. Finally, examples are shown in which the combination of microscale dewetting and nanoscale microphase separation are exploited to create hierarchical nanostructures from BCPs. An outlook is given presenting successful applications of both mechanisms on prepatterned surfaces in order to control position and morphology of the hierarchical nanostructures. This approach is particularly promising for the creation of advanced surface architectures.

Understanding Film Thickness‐Dependent Block Copolymer Self‐Assembly by Controlled Polymer Dewetting on Prepatterned Surfaces

AbstractBlock copolymer (BCP) lithography is a versatile bottom‐up approach for the creation of regular nanoscale patterns on large surface areas. The pattern morphology evolving during the microphase separation of a BCP is strongly dependent on the polymer film thickness. Thus, surface wetting as well as interfacial energies between polymer and substrate determine the polymer behavior, however, the complex interplay of those effects is not yet fully understood. In this work, a model describing the film thickness dependence of BCP self‐assembly on prepatterned surfaces is proposed. Polymer dewetting on nanohole‐patterned surfaces is controlled using different prepattern dimensions, polymer amounts, and microphase‐separation temperatures. This is found to allow for a precise local film thickness modulation and thus allows to guide BCP self‐assembly into arrays of tailored hierarchical nanoarchitectures. Analytical calculations of the total surface free energies of the microphase‐separated polymer of different film thicknesses confined inside nanoholes confirm the model. The insights contribute to the understanding of fundamental processes in polymer dewetting and BCP self‐assembly and allow for the controlled creation of advanced hierarchical nanostructures on large areas for applications in optics, plasmonics, and biomedical devices.

Multi-modal surface grafting of [trans-bis(aminodiphenylphosphine) terpyridine-Ru(II)Cl]+Cl− complex onto glassy carbon electrode

The design of a ruthenium-terpyridine complex having 4-aminobenzyl-diphenylphosphine as remote ligands in a trans arrangement ([Ru(trans-PN)2(trpy)Cl]+Cl−, [trans-bis(aminodiphenylphosphine) terpyridine-Ru(II)Cl]+Cl−) is shown to be a highly versatile approach for the immobilization of the organometallics at a carbon surface. Three distinct strategies could be then successfully employed to achieve the grafting of the complex, namely i) the electroreduction of the corresponding in situ produced diazonium cation, ii) the electrooxidation of the aromatic amine moiety in the presence of a base and iii) an anodic electropolymerization in the absence of base. The modified surfaces were characterized by electrochemical or Scanning Electron Microscopy (SEM) studies. The reported approach allows a clean modulation of film thickness and anchoring modes, particularly useful for a given design of ruthenium containing films dedicated to a given application. In this context, the polymer films which contain the largest surface concentration of active ruthenium were employed as immobilized catalyst for oxidation of benzyl alcohol in water, allowing a test of the catalytic activity of the complexes as grafted materials.

Controlling wrinkles and assembly patterns in dried graphene oxide films using lyotropic graphene oxide liquid crystals

ABSTRACTWe fabricated graphene oxide (GO) films on glass substrates by blade coating a lyotropic GO liquid crystal dispersion. Substrate temperature and blading speed were precisely controlled to manipulate the surface morphologies of GO films. The temperature and blade speed influenced the drying rate of film and the amount GO dispersion supplied. By controlling these parameters, film-thickness modulation and three types of surface wrinkle patterns were selectively achieved. We also plotted the wrinkle patterns diagram as functions of the film fabrication conditions. The films exhibited different optical anisotropies depending on wrinkle patterns. GO films with controlled wrinkles can be used as electrodes for supercapacitor applications owing to the large surface areas.

Modulation of ZnO film thickness and formation of water-hyacinth nanostructure

The influence of precursor medium was investigated on the structural, morphological, optical and electrical properties of spray pyrolysis deposited nanostructured ZnO thin films. Three batches of ZnO thin films were deposited on glass substrates using three different solvents (water, water-ethanol [ratio of 1:1] and ethanol) based precursor solution of zinc nitrate hexahydrate. The substrate temperature was fixed at 523 K. The variation in film thickness from 150 to 875 nm was observed as the effect of changing solvent medium. X-ray diffraction (XRD) data confirmed the formation of polycrystalline ZnO thin films with hexagonal wurtzite crystallite structure and the estimated crystallite size was found to be ranging from 31 to 55 nm. Scanning electron micrographs revealed the formation of water-hyacinth shaped nanostructures when water-ethanol mixture was used as the solvent medium. Interestingly, UV-vis spectrophotometer revealed the formation of ZnO film with twin optical band gap of 3.15 eV and 3.56 eV when ethanol was used as the solvent medium. The modulation of film thickness and grain size by solvent medium has strongly influenced the electrical conductivity of ZnO thin films. The homogenous nano-spherical grains with uniform grain boundaries showed a good response towards 100 ppm of ammonia at room temperature.

Formation of surface relief grating in polymers with pendant azobenzene chromophores as studied by AFM/UFM

We studied peculiarities of the structural reconstruction within holographically recorded gratings on the surface of several different amorphous azobenzene-containing polymers. Under illumination with a light interference pattern, two processes take place in this type of polymer. The first process is the light-induced orientation of azobenzene units perpendicular to the polarization plane of the incident light. The second one is a transfer of macromolecules along the grating vector (i.e. perpendicular to the grating lines). These two processes result in the creation of a volume orientation grating (alternating regions of different direction or degree of molecular orientation) and a surface relief grating (SRG)—i.e. modulation of film thickness. One can assume that both orientation of molecules and their movement might change the local mechanical properties of the material. Therefore, formation of the SRG is expected to result also in modulation of the local stiffness of the polymer film. To reveal and investigate these stiffness changes within the grating, spin-coated polymer films were prepared and the gratings were recorded on them in two different ways: with an orthogonal circular or orthogonal linear polarization of two recording light beams. A combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) techniques was applied for SRG development monitoring. We demonstrate that formation of the phase gratings depends on the chemical structure of polymers being used, polymer film thickness, and recording parameters, with the height of grating structures (depth of modulation) increasing with both the exposure time and the film thickness. UFM images suggest that the slopes of the topographic peaks in the phase gratings exhibit an increased stiffness with respect to the grating depressions.

Modification of growth parameters of Ti anodic films by fluoride ion insertion

The potentiostatic growth of Ti anodic films formed in 0.1 M HClO4/x M HF (0.05 M ≤ x ≤ 0.50 M) media was studied by electrochemical impedance spectroscopy, EIS. The obtained EIS spectra were analyzed by using the surface charge approach model, which showed oxide growth parameters being modified as the HF concentration increased. While the electric field through the film decreased, oxide growth rate and atomic half jump distance increased, evidencing that fluoride ions are inserted into the oxide through oxygen vacancies, thereby modifying the lattice structure and electric properties of the oxide. Additionally, the experimental data obtained for the pseudocapacitance C 0, appearing at low-frequency domain, allowed the interpretation commonly given for this element (modulation of film thickness) to be discarded; instead, the F− ion diffusion coefficient was estimated, casting with variation of electric properties with HF concentration and E F.

Field Emission Enhancement in Semiconductor Nanofilms by Engineering the Layer Thickness: First-Principles Calculations

We investigated the field emission (FE) enhancement of semiconductor thin films on metal substrate by first-principles calculations. For the FE structure of GaN or AlN thin films on aluminum substrate, the calculated results show that by fine-tuning the film thickness, the FE current can be enhanced nearly 2 orders. It should be originated from reducing the surface work function. When the film thickness is less than ∼10 nm, the work function can be reduced as much as 0.5 eV by film thickness modulation of only several nanometers. The remarkable thickness effects on the work function for the semiconductor/metal structure result mainly from surface/interface charge transfer and interface states.

Soap Films Burst Like Flapping Flags

When punctured, a flat soap film bursts by opening a hole driven by liquid surface tension. The hole rim does not, however, remain smooth but soon develops indentations at the tip of which ligaments form, ultimately breaking and leaving the initially connex film into a mist of disjointed drops. We report on original observations showing that these indentations result from a flaglike instability between the film and the surrounding atmosphere inducing an oscillatory motion out of its plane. Just like a flag edge flaps in the wind, the film is successively accelerated on both sides perpendicularly to its plane, inducing film thickness modulations and centrifuging liquid ligaments that finally pinch off to form the observed spray. This effect exemplifies how the dynamics of fragile objects such as thin liquid films is sensitive to their embedding medium.

Film Thickness Modulations in Starved Elastohydrodynamically Lubricated Contacts Induced by Time-Varying Lubricant Supply

Many elastohydrodynamically lubricated contacts in practical applications, e.g., in bearings, operate in the starved lubrication regime. As a result their performance is sensitive to variations of the lubricant layers present on the surfaces, which form the supply to the contact. Their shape is often determined by previous overrollings of the track and also by replenishment mechanisms and various migration effects. Variations of the layers induced in the direction of rolling lead to a time-varying lubricant supply to the contact. In this paper, by means of numerical simulations using a starved lubrication model, the film thickness modulations in the center of the contact induced by a harmonically varying inlet supply have been investigated. First, for a given load condition and layer wavelength, the effect of the nominal layer thickness (degree of starvation) and the layer variation amplitude is illustrated. Subsequently, using results for different load conditions, wavelengths, and degrees of starvation, it is shown that the response of the contact to such variations is determined by a nondimensional parameter, which represents the ratio of the entrainment length of the contact to the wavelength of the induced variation, and by the degree of starvation. A simple formula is presented for use in engineering predicting the ratio of the amplitude of the film modulations in the center of the contact to the amplitude of the layer variations in the inlet.

Film thickness variations in elasto-hydrodynamically lubricated circular contacts induced by oscillatory entrainment speed conditions

In this paper, the effects of an oscillatory entrainment speed on the film thickness in an elasto-hydrodynamically lubricated circular contact operating in the piezo-viscous regime as predicted by a conventional elasto-hydrodynamic lubrication model are described in detail. The relative variation of the film thickness on the centreline of the contact mainly depends on two dimensionless parameters: relative entrainment velocity amplitude and dimensionless entrainment velocity frequency. For small to moderate values of dimensionless frequency, the results can be accurately predicted through a simplified ‘engineering approach’: propagation of inlet modulations along oscillatory characteristics. For values of the dimensionless frequency of O(1), film thickness modulations occur on a sub-contact scale. This work was initiated by the experimental results of Glovnea and Spikes obtained for two lubricants PAO and 5P4E, which have the same ambient viscosity but a different viscosity—pressure coefficient. During the experiments significant difference in behaviour was observed. In this paper, it is shown that a conventional model assuming Newtonian rheological behaviour predicts the same relative film thickness results for both the lubricants. This agrees well with the behaviour observed for PAO, which can be considered as a standard oil that is well characterized by its bulk viscosity, density, and their pressure dependence alone. Nevertheless, further experiments need to be carried out to validate the predictions for larger values of the dimensionless frequency. The behaviour observed in the experiments for 5P4E is significantly different. For accurate prediction of friction, the need to include non-Newtonian lubricant behaviour in models is well known. Film thickness predictions are often less sensitive to the specifics of the lubricant behaviour. However, the results presented here indicate that for film thickness calculations, under rapidly varying conditions in time, more advanced rheological models, including visco-elastic behaviour, may have to be considered as well.

Optical properties and instrumental performance of thin gold films near the surface plasmon resonance

The optical properties of very thin gold films have been evaluated by Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance (SPR) at the gold–water interface. The experimental SPR characteristic was evaluated in the angular interrogation mode. Film morphology was characterized by high resolution transmission electron microscopy. The magnitude of the resonance, i.e., the SPR signal, sensitively depends on, and is affected by film thickness and morphology. A sharply defined thickness of 55 ± 5 nm is required, to achieve optimum SPR excitation conditions, and instrumental sensitivity. With decreasing film thickness, below 40 nm, the resonance angle starts to shift to larger values. A substantial increase of the intrinsic resonance broadening parameter is observed below 70 nm, associated with an increasingly asymmetric SPR line shape. A similar effect occurs in the presence of a very thin chromium adhesion layer. Surface roughness and film thickness modulations determine the experimentally observed line broadening parameter. Instrumental noise levels largely depend on accuracy and quality at which the resonance angle can be determined. Substantial improvement and instrumental sub-pixel resolution is achievable by optimum fitting routines, accounting for drastic noise reduction and improved instrumental sensitivity, up to two orders of magnitude over the inherent geometric sensor pixel resolution.

Interactions between nano-spacing flying head sliders and ultra-thin liquid lubricant films with non-uniform distribution in hard disk drives

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of less than 10 nm spacing flying head sliders in hard disk drives. In particular, the effect of non-uniform lubricant film distributions on head/disk interface dynamics are studied. The disks with lubricant on one half of disk surface thicker than the other half were used in this study. The dynamics of sliders is monitored using acoustic emission (AE) and the interactions between the slider and disk are investigated experimentally. The disks were also examined with a scanning micro-ellipsometer before and after each test. Complicated slider responses were observed and clarified. In addition, it was found that the periodic lubricant film thickness modulations or non-uniformity caused by the slider-disk contact interactions could be observed. It is suggested that this lubricant film thickness non-uniformity will be one of the technical issues in order to achieve ultra-low head/disk contact interface of less than 10 nm.

HDI-24 Interactions between nano-spacing flying head sliders and ultra-thin liquid lubricant films with non-uniform distribution in hard disk drives

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of less than 10 nm spacing flying head sliders in hard disk drives. In particular, the effect of non-uniform lubricant film distributions on head/disk interface dynamics are studied. The dynamics of sliders is monitored using Acoustic Emission (AE) and the interactions between the slider and disk are investigated. The disks before and after test are also examined with a scanning micro-ellipsometer. Complicated slider responses were observed and clarified. In addition, it is found that the periodic lubricant film thickness modulations or re-distributions caused by the slider-disk contact interactions could be observed.

Effects of Structural Vibrations on the Film Thickness in an EHL Circular Contact

In elastohydrodynamic lubrication (EHL), one generally imposes force balance, i.e., the contact force resulting from the pressure in the contact is equal to the applied load. When studying the effect of structural vibrations, this force balance equation obviously does not hold and the more general equation of motion is required. In Wijnant and Venner (1996), an EHL contact model was introduced that incorporates both squeeze and entraining motion as well as the equation of motion. It was shown numerically that due to a small initial deviation or initial velocity, the rolling element starts an oscillatory motion around the equilibrium position. This motion is slightly damped because of the viscous losses in the lubricant. Moreover, it was shown that these oscillations cause film thickness modulations with a wavelength, directly related to the dimensionless frequency Ω. This paper compares results from experiments that were carried out on a ball and disk apparatus with results obtained with the EHL contact model. In this experiment, the applied load was rapidly increased by impacting a wedge between the base and the ball holder. This results in an increase of the contact area and, as a result of inertia forces of the ball, disk and supports, and oscillatory motion of the contacting bodies. Modulations in the film thickness which result from these oscillations, are clearly visible. The contact model was tailored to this experiment and a qualitatively close agreement has been found.

Characteristics of Bloch-Line Pair Propagation Using Film Thickness Modulation (FTM) Patterns for Bit Confinement

A new bit confinement method for Bloch-line (BL) memories which uses film thickness modulation (FTM) has been studied, as a means of making the BL pair propagation common to both sides of the stripe domain wall. Since it is necessary to make the modulation pattern edge smooth for propagation under low driving fields, we used tapered resist patterns for the ion milling mask and carried out the milling to produce a modulation of amplitude 100 nm in an O 2 atmosphere (10?6 Torr). BL pair propagation was tested using a sawtooth pulsed bias field with a 100 ns rise time and a 1000 ns fall time. It was found that the driving field margins did not depend on the propagation direction, because the bit confinement force acts symmetrically on both sides of the domain wall. Furthermore, it was confirmed that the temperature dependence of the driving field margin is larger than that when using the conventional magnetic pattern method.

膜厚変調ビット固定パターンによるブロッホライン対の磁界転送特性

A New bit cofinement method using film thickness modulation (FTM) has been studied on the Bloch-line (BL) memory to make the BL pair propagation cmmon to both sides of the stripe domain wall. Since it is necessary to make the modulation pattern edge smooth for low drive-field propagation, we used tapered resist patterns for the ion milling mask and carried out the milling to fabricate 100 nm thickness modulation in an O2 atmosphere (10-6 Torr). BL pair propagation was tested with applying the trianglar bias pulsed field with 100 ns rise time and 1000 ns fall time. It was found that the drive field margins did not depend on the propagation direction, because the bit confinement force acts symmetrically on both sides of the domain wall. Furthermore, it was confirmed that the temperature dependece of the drive field margin was larger than that in the conventonal magnetic pattern method.

Bloch line propagation with film thickness modulation bit patterns (abstract)

Bloch line (BL) propagation with a field-access scheme is necessary for the memory with low power consumption and high storage density. Previously we reported the field-access propagation using Co-Pt bit patterns.1 In these propagation patterns, (a) the drive field margins depend on the BL propagating direction to the magnetized direction of Co-Pt patterns and (b) the operating bias field margins are different at each corner of the stripe domain. The purpose of this paper is to solve these two problems. A new propagation method has been investigated using film thickness modulation patterns.2 The materials used here were magnetic bubble garnet films with composition of (YSmLuCa)3(FeGe)5O12. Fundamental characteristics of the samples are as follows: saturation induction 4πMs 200 G, anisotropy field Hk 1700 Oe, stripe width w and thickness h 5 μm. The thickness modulation patterns with an amplitude of about 1000 A were fabricated with the ion milling method. The stripe domains were stabilized around the 100% etched grooves, and aligned with 18 μm period. BL pair was propagated in the all part of the stripe domain walls at 500 kHz frequency, applying the triangular bias pulsed field with 50 ns rise time and 1000 ns fall time. As the result of the experiments, it has been found that the drive field margins are independent of BL propagation direction and the difference in the operating bias field margins at the each corner of the stripe domain becomes smaller. The BL propagation around the stripe domain was achieved with 5% bias field margin at the drive field of 8.5 Oe.