Ultrathin Bilayer Research Articles

In situ TEM observations on morphological instability of ultrathin Pb films

Abstract An ultrathin bilayer Pb–Al film was made by cold rolling and ion beam thinning techniques. Morphological instability of the Pb layer under electron beam irradiation was investigated by means of in situ transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Morphological instability of the Pb layer was characterized by spheroidization of Pb film and coalescence of Pb particles. Under electron beam irradiation, the ultrathin Pb layer with an incoherent Pb–Al interface was unstable and sphericized into Pb particles with an initial size about 3 nm. The Pb particles were mobile on the Al substrate and the coalescence of Pb particles took place. The Pb particles grew up only in the way of coalescence and the mobility of the particles decreased with the particle size increasing. The growth rates of Pb particles in different stages of coalescence were measured, respectively. The mechanism of spheroidization and coalescence was discussed. Driving forces for the spheroidization and the coalescence were attributed to minimizing the total energy. The intensive motion of the surface atoms for the Pb films and particles under irradiation activated the morphological instability of the system.

A method for monitoring thicknesses of nanodimensional bilayer film structures

We describe an atomic force microscopy technique for rapidly monitoring the nanodimensional thicknesses of ultrathin mono-and bilayer films sputter deposited at oblique incidence onto a porous glass substrate with smooth areas between pores. Bilayer films were obtained using the second target arranged at an angle 10°–15° greater than that of the first target relative to the substrate. The images of such films clearly display the interfaces between pore edge and film, as well as between upper and lower layers of the film. This allows the total film thickness and the separate layer thicknesses to be determined by measuring the heights of steps between pore edge and layer surfaces on the sample relief cross section.

Achieving Thermodynamic Control of Adsorption and Desorption at Layered Polymer Interfaces

We report on the achievement of differential control over adsorption and desorption kinetics of selected vapor phase molecules at ultrathin polymer bilayer interfaces. We synthesize and deposit maleimide−vinyl ether alternating copolymer layers, where each polymer layer contains different pendant side group functionalities and the order of layer deposition is controlled. The adsorption isotherm behavior of these interfacial structures, when exposed to methanol and hexane vapor, shows that the identity of the adsorbates and the order of polymer adlayer deposition both influence the interfacial adsorption characteristics. The absence of hysteresis in the isotherm data indicates that our measurements are made under equilibrium conditions, indicating the achievement of chemical and structural control over the thermodynamics of adsorption at these interfaces.

Prospects for photolithography at 121 nm

We have evaluated several subsystems that would be required for lithography at 121 nm: radiation sources, optics, ambient control, and resists. Dense plasma sources can generate significant power, >0.5 J of 121 nm radiation per pulse. An extensive survey of commercially available LiF, as well as specially grown LiF, shows that transmission losses are ∼20% per cm, a value which is at least 5× too high if LiF is to be used as lens material. At present it is not clear whether there is a fundamental limitation to LiF transparency at 121 nm, but the main source of absorption arises from lithium oxide or hydroxide in the crystal. Polymers, fluorinated or not, exhibit very high absorption at 121 nm, indicating that ultrathin resists or bilayer resists will have to be used at 121 nm. However, the photochemistry at 121 nm is probably not much different from that at longer wavelengths. The resists are sensitive, ∼1 mJ/cm2 required dose, and they have high contrast at 121 nm. Finally, we have also performed preliminary patterning experiments. Using contact printing with a phase shifting mask we have printed 45 nm features in an ultrathin photoresist.

In Situ TEM Observations on Morphological Instability of Ultrathin Pb Film

Journal Article In Situ TEM Observations on Morphological Instability of Ultrathin Pb Film Get access LH Zhang, LH Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China Search for other works by this author on: Oxford Academic Google Scholar ML Sui, ML Sui Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China Search for other works by this author on: Oxford Academic Google Scholar L Zhang, L Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China Search for other works by this author on: Oxford Academic Google Scholar DX Li DX Li Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 8, Issue S02, 1 August 2002, Pages 1410–1411, https://doi.org/10.1017/S1431927602103163 Published: 01 August 2002

( Zr,Ti ) O 2 interface structure in ZrO2–TiO2 nanolaminates with ultrathin periodicity

A mixed cation interfacial structure in ZrO2–TiO2 nanolaminate films with ultrathin bilayer periodicity grown by sputter deposition at 297 K was identified by x-ray diffraction and nonresonant Raman spectroscopy. This structure consists of an amorphous phase at a ZrO2-on-TiO2 bilayer interface, followed by an extensive crystalline monoclinic (Zr,Ti)O2 solid solution predicted by Vegard’s law. Monoclinic (Zr,Ti)O2 has previously been reported only once, in bulk powder of a single composition (ZrTiO4) at high pressure. Its stabilization in the nanolaminates is explained by the Gibbs–Thomson effect. This complex interfacial structure is shown to be a means of accommodating chemical mixing in the absence of a driving force for heteroepitaxy.

Nanoscale selective-area epitaxial growth of Si using an ultrathin SiO2/Si3Ni4 mask patterned by an atomic force microscope

We report selective epitaxial growth of Si using an ultrathin bilayer mask. The key feature of this process is direct writing of nanoscale patterns by means of local anodic oxidation of a Si3N4 layer using an atomic force microscope operated in air. Windows for selective growth are defined by wet etching of the locally oxidized regions. High growth selectivity upon chemical vapor deposition of Si is accomplished by employing the bilayer mask structure which is formed by oxidizing the Si3N4 surface and then selectively desorbing SiO2 in the windows. High-quality homoepitaxial growth is verified by transmission electron microscopy. We also report a simple plasma-treatment technique which solves the problem of retarded SiO2 desorption in the nanoscale windows.

Efficient photon harvesting at high optical intensities in ultrathin organic double-heterostructure photovoltaic diodes

We demonstrate a method for efficient photon harvesting in organic thin films, thereby increasing the efficiency of organic photovoltaic cells. By incorporating an exciton-blocking layer (EBL) inserted between the photoactive organic layers and the metal cathode, we achieved an external power conversion efficiency of 2.4%±0.3% in vacuum-deposited ultrathin organic bilayer photovoltaic (PV) cells employed in a simple light trapping geometry. Ultrathin (∼100 Å) cells incorporating the transparent, conductive EBL have an internal quantum efficiency as high as 33%±4% over a spectral region matched to the solar spectrum. The very thin organic layers have a low series resistance, allowing for efficient power conversion in organic PV cells under intense (>15 suns) AM1.5 illumination. This device structure demonstrates that control of exciton diffusion in solid-state organic devices leads to a significant increase in the photon-to-carrier conversion efficiency.

Involvement of C 60 fullerene monomers and aggregates in the photoconductivity of ultrathin bilayer lipid membranes

Due to its hydrophobic character, the hydrocarbon core of ultrathin phospholipid bilayer membranes lends itself to the insertion of fullerenes. When doped with C 60 these membranes are photoconducting, the photoconductivity being affected by the presence of quenchers of the excited triplet state such as oxygen. The photoconductivity involves trans-membrane electron transfer; its dependence on C 60 concentration and on the excitation wavelength suggests the participation of small aggregates in the membrane. As derived from time-resolved triplet absorption and fluorescence quenching measurements, the suggested mechanism makes more precise (i) the role of the aggregates which might act as a collecting antenna for the benefit of the monomers, and (ii) the role of the monomers which have a much higher yield of photoinduced triplet state formation than the aggregates.

Ultra-thin film superconductors of artificially synthesized Au/Ge layers

We have investigated the resistive transition of Au/Ge layered films. The ultra-thin bilayer of Au(10Ȧ)/Ge(13Ȧ) exhibits superconductivi ty below a temperature of 0.6 K. It has been found thatthe critical temperature TC is enhanced above TC0 by the application of low magnetic field parallel to the film surface. We have observed dimensional crossover in the temperature dependence of parallel critical field for the multilayers with Ge film ~25 Ȧ thick. Those with Ge film thicker than ~30 Ȧ show two-dimensional behavior and also the TC enhancement as observed in the bilayer.

Redox reactions in lipid bilayers and membrane bioenergetics

This paper begins with a consideration of electronic processes in ultrathin artificial bilayer lipid membranes (BLM) and biomembranes of chloroplasts and mitochondria. Methods and materials used in the study of BLMs are described next. The results of recent experiments, as obtained by voltammetric techniques, are summarized. The remaining sections of the paper deal with the application of basic electrochemistry to membrane research, in particular, the Eyring equation, the Butler-Volmer equation and the Tafel equation, and the origin of electronic processes in membranes in terms of electrostenolysis. The paper concludes with a discussion on the determination of standard potentials ( U o′) of redox protein components in the absence of the lipid bilayer, and finally a suggestion of the future experiments in relation to electron-transfer and bioredox reactions in bilayer lipid membranes.

Formation and stability of bilayer lipid membrane at a liquid-liquid interface

This paper presents an experimental study on the formation process of ultrathin (500-100 Å in thickness) bilayer liquid membranes at a liquid-liquid interface using oil-soluble chloroplast extract. With the aid of a microvideo system, the dynamics of membrane thinning, border suction, and equilibrium state were visually examined in detail, and the rate of spreading data for the black membrane is analyzed. The effect of salt concentration in aqueous solutions on the bifacial tension is measured over the concentration range of 0.01 to 0.05 N. Reproducibility of these bifacial tension measurements was typically ±21% of the mean value for a particular set of membranes. As an interfacial phenomenon, the formation of ultrathin lipid membranes is investigated in terms of membrane viscosity and bifacial tension. Based on experimental results, a semiquantitative two-step model is proposed for the rate of membrane formation.

215 - Light transduction by pigmented bilayer lipid membranes

Certain photoeffects observed in pigmented bilayer lipid membranes are explained in terms similar to those that take place at semi-conductor|electrolyte interfaces. There are two distinct steps in the light transduction: (I) photoexcitation of pigment molecules in and/or adjacent to the membrane to generate electrons and holes via exciton dissociation, and (2) electrons and holes effect redox reactions across the membrane. The existence of two redox solution interfaces connected by an ultrathin lipid bilayer make exciton—exciton possible, thereby providing a mechanism for generation of higher energetic species for water oxidation than are available in the exciting photon. The scheme has been applied to the thylakoid membrane of chloroplasts and the purple membrane of H. halobium.