Nanoscale Thin Films Research Articles

Effect of photon irradiation on conductivity of nanoscale yttria-doped zirconia thin films

The effect of photon irradiation on high temperature conductivity of nanoscale yttria-doped zirconia thin films is reported. Nanoscale films show substantial decrease in total conductivity (as high as ∼40%) during ultraviolet (UV) irradiation, while the conductivity of bulk single crystals shows negligible changes. The UV induced conductivity changes are rapid and reversible and activation energies for ion migration remain unaffected. The reduction in conductivity may arise from changes in effective oxygen vacancy concentration. Such UV-influenced alteration of electrical properties offers an elegant route to tailor surface catalytic activity of oxygen ion and mixed conductors used in various solid-state devices.

Quantitative analysis of molecularly stacked layer structures in supported organic thin films by synchrotron grazing-incidence X-ray scattering

In this study, we derive a grazing-incidence X-ray scattering (GIXS) formula to analyze quantitatively GIXS patterns for molecularly stacked layer structures in substrate-supported nanoscale thin films. We apply this formula in the quantitative analysis of GIXS patterns obtained for S-docosanylcysteine thin films on silicon substrates with native oxide layers. This analysis successfully provides information on the structural parameters and orientation of the molecular layer stack developed in S-docosanylcysteine thin films.

Fixtureless superlayer-driven delamination test for nanoscale thin-film interfaces

A fixtureless delamination test has been developed to measure the interfacial fracture toughness of patterned nanoscale thin films on a substrate. The driving energy for delamination propagation is supplied by a highly stressed superlayer deposited on top of the nanoscale thin film. The amount of energy available for delamination propagation is changed by depositing an etchable thin release layer with varying width between the nanoscale thin-film strip and the substrate. By designing a decreasing area of the release layer, it is possible to arrest the delamination at a given location, and the interfacial fracture toughness or critical energy release rate can be found at the location where the delamination ceases to propagate. For titanium film with a thickness of 90 nm, the results show that the interfacial fracture toughness of titanium/silicon ranges from 3.45 J/m 2 to 5.70 J/m 2 when the mode mixity increases from 6.8° to 38.4°. The methodology presented in this paper is generic in nature, and can be used to measure the process-dependent interfacial fracture toughness of various micro and nanoscale thin films on a substrate.

Transport and Optical Characteristics of Al-rich AlO Film and its Application to a Non-volatile Memory

ABSTRACTWe propose the new process for fabricating Al-rich Al2O3 thin film, which is used as a charge storage layer for non-volatile Al2O3 memory. Nanoscale Al-rich thin film is deposited using RF magnetron co-sputtering by setting an Al metal plate on an Al2O3 target. Al-rich Al2O3 shows a larger conduction current in I-V characteristics and larger optical absorption than stoichiometric Al2O3 due to the increased electron trap sites. The C-V characteristics of the Al-rich Al2O3 thin film show a large hysteresis window due to the charge trapping effect in the Al-rich structure.

A Combinatorial Approach Towards Functionalizing Copolymers with Effector Molecules that Attenuate Cyto-inflammatory Responses at the Biotic-abiotic Interface

AbstractFunctionalized copolymers offer the opportunity for tailored biology, where specific functionalities within these materials can be rapidly engineered on demand. Embedding effector molecules, for example, into these copolymers transforms an otherwise inactive component into a functional matrix for envisioned in vivo applications such as suppression of cellular inflammation/stress or immuno-regulatory implant coating, etc. Furthermore, our ability to utilize these copolymers in both a vesicular/planar configuration, coupled with their versatility in block composition empowers opportunities of utilizing vesicle-encapsulated effector molecules as dedicated drug delivery vehicles with targeting capabilities, or as modalities to replenish exhausted effector molecule stores within planar copolymer thin films. As such, these copolymeric membrane materials may potentially impact multiple medically-relevant fields in both scientific and technological contexts.An important element empowering this transition is the examination of the bio-inert properties of these materials. This includes the interrogation of the stress response of macrophages to the chemical/topographical stimuli presented by these materials. We have previously developed copolymers as neural implant coatings functionalized with a glucocorticoid anti-inflammatory Dexamethasone (Dex) using Langmuir-Blodgett deposition. This technology successfully suppressed, to a significant degree, RAW264.7 macrophage transcriptional machinery of several cytokines including TNFα, Il-6, and Il-12 analyzed using real time PCR (RT-PCR). These findings offered insight into both bio-abio material fabrication, as well as analysis of stress specific gene program activation which may be used to generate principles for optimizing neural implant biocompatibility and chronicity by attenuating innate immune responses.This study has broadened the range of applications of this material via its integration with a combination of intracellular signaling agonists (e.g. Liver X receptor-α/β (LXR α/β)) that function as non-steroidal anti-inflammatories to block transcriptional machinery associated with cell stress among other disorders. Here we demonstrate both planar encapsulation of an additional effector in the form of a robust, cell permeable LXRα/β agonist 3-((4-Methoxyphenyl)amino)-4-phenyl-1-(phenylmethyl)-1H-pyrrole-2, 5-dione using a crosslinked copolymer thin film. In addition, we investigated the underlying mechanisms of the attenuation of cellular inflammation via RT-PCR analysis of the resultant inhibition of lipopolysaccharide (LPS)-stimulated secretion of proinflammatory cytokine in murine macrophages. These advancements may potentially result in multi-functional nanoscale thin films that are chronically active, and can suppress cellular inflammation as implant coatings or bio-inert vesicular carriers of a non-steroidal pharmacological system.

Existence of weak solutions for a generalized thin film equation

In this paper, we consider an initial-boundary problem for a fourth-order nonlinear parabolic equations. The problem as a model shares the scaling properties of the thin film equation, or as a model arises in epitaxial growth of nanoscale thin films. Our approach lies in the combination of the energy techniques with some methods based on the framework of Campanato spaces. Based on the uniform estimates for the approximate solutions, we establish the existence of weak solutions.

Thermal and Electrical Properties of a Suspended Nanoscale Thin Film

This paper reports on measurements of in-plane thermal conductivities, electrical conductivities, and Lorentz number of two microfabricated, suspended, nanosized thin films with a thickness of 28 nm. The effect of the film thickness on the in-plane thermal conductivity is examined by measuring other nanofilm samples with a thickness of 40 nm. The experimental results show that the electrical conductivity, resistance–temperature coefficient, and in-plane thermal conductivity of the nanofilms are much smaller than the corresponding bulk values from 77 to 330 K. However, the Lorentz number of the nanofilms is about two times that of the bulk value at room temperature, and even up to three times that of the bulk value at 77 K. These results indicate that the relation between the thermal conductivity and electrical conductivity of the nanofilms does not follow the Wiedemann–Franz law for bulk metallic materials.

Electron Transfer Mediated Biosensor with Plasma-Polymerized Film Containing Redox Site

An electron transfer mediated amperometric enzyme biosensor based on a plasma-polymerized thin film of dimethylaminomethylferrocene (DMAMFc) is reported. A nanoscale thin polymer film containing a redox mediator was plasma-deposited directly onto an electrode with physisorbed glucose oxidase (GOD). Since the redox sites were introduced in the vicinity of the reaction centers of GOD, a highly efficient electron transfer system was formed in which almost all the reaction centers of GOD were connected to redox sites of the polymer matrix. The advantages of this strategy were: no need for prior or further chemical modification of the enzyme molecules, and simplicity of design compared with the use of a conventional polymer matrix. Moreover, the fact that the film deposition was performed using a microfabrication-compatible organic plasma promised great potential for high-throughput production of bioelectronic devices.

Fully flexible unit cell simulation with recursive thermostat chains

The recursive thermostat chained fully flexible cell molecular dynamic simulation (NsigmaT ensemble) is performed. The ensemble is based on the metric tensor, whose components are used as extended variables. These variables are combined with Nosé-Poincaré recursive thermostat chains. This extended Hamiltonian approach preserves Hamiltonian in structure, and the partition function satisfies the NsigmaT ensemble state in phase space. In the present study, the generalized leap frog method was employed for time integration. The resulting molecular dynamics simulation was performed for bulk and thin film solid materials in the face-centered-cubic crystal structure. Uniaxial tension test and simple shear test are performed to predict the behaviors of a solid material in the bulk state and nanoscale thin film state. The proposed flexible cell method should serve as a powerful tool for the prediction of mechanical and thermal properties of solid materials including nanoscale behavior.

Retrieval of the complex reflection coefficient from nano scale thin films by using polarized neutrons and magnetic substrates

A method is proposed for overcoming the famous ‘phase problem’ in neutron specular reflectometry. It is shown that the complex reflection coefficient of any unknown non magnetic layer, with real scattering length density, can be determined by using a magnetic transmitted media and by measuring the polarization of the reflected beam relative to the incident beam. The method follows directly from a recent one which is limited to a one-dimensional neutron polarization. Here, the theory is generalized for a neutron polarization of arbitrary direction. We show that some combinations between the polarization of the incident and reflected beam must be used to determine the reflection coefficient. Also, it is shown that instead of full polarization or reflectivity analysis, some combinations between polarization and reflectivity can be used in the analysis process. The method is supplemented with a schematic example to test the method and its stability in the presence of experimental uncertainties and roughness of the interfaces.

Rubbed Thin Films of Well-defined Brush Polyimides for Flat-Panel Liquid Crystal Displays: Surface Morphology, Molecular Orientation, and Liquid Crystal Alignability

A series of well-defined brush polyimide (PI) composed of two 4- n-alkyloxyphenyloxy bristles per repeat unit on a semi-rigid poly(4,4′-methylenyldiphenylene pyromellitimide), Cm-PMDA-MDA PIs, were synthesized and their nanoscale thin films prepared by conventional spin-coating of their soluble poly(amic acid) precursor solutions and subsequent drying and thermal imidization in a nitrogen atmosphere. All the PIs were determined to be a positively birefringent polymer. The surface morphology and molecular orientation of each PI in films before and after rubbing were investigated in detail by atomic force microscopy, optical retardation analysis, and linearly polarized infrared spectroscopy. The sequence of the rubbing-induced polymer segmental orientations was further investigated in detail. In addition, the liquid crystal alignment and pretilt ability of the rubbed PI films were examined, and their thermal stability investigated. The present study provides important information on the sequence of the polymer segmental orientations induced by rubbing and additionally the mechanisms of the alignment and pretilt of liquid crystal molecules in contact with the rubbed PI film surface.

An iterative regularization method for inverse phonon radiative transport problem in nanoscale thin films

AbstractAn inverse phonon radiative transport problem with an alternative form of adjoint equation is solved in this study by using conjugate gradient method (CGM) to estimate the unknown boundary temperature distributions, based on the phonon intensity measurements. The CGM in dealing with the present integro‐differential governing equations is not as straightforward as for the normal differential equations; special treatments are needed to overcome the difficulties. Results obtained in this inverse analysis will be justified based on the numerical experiments where two different unknown temperature (or phonon intensity) distributions are to be determined. Finally, it is shown that accurate boundary temperatures can always be obtained with CGM. Copyright © 2006 John Wiley & Sons, Ltd.

ALD: Emerging Materials, Processes, and Nanoscale Technology Applications

Nanoscale (zero-thickness) thin film growth processes such as atomic layer deposition are under extensive development for potential use in key nanoelectronics applications. The unique characteristics of these processes make them potentially enabling for a number of emerging nanotechnology-driven technologies. This paper discusses several of these potential applications and highlights specific fields where ALD is being researched.

Non-volatile Al2O3 Memory using Nanoscale Al-rich Al2O3 Thin Film as a Charge Storage Layer

This article describes the fabrication process and capacitance–voltage (C–V) characteristics of a new non-volatile Al2O3 memory with nanoscale thin film deposited by electron-cyclotron-resonance sputtering. Al-rich Al2O3 shows characteristics somewhere between Al and Al2O3 in the refractive index and wet etching rate. C–V characteristics of Al-rich Al2O3 memory show a large hysteresis window due to the Al-rich structure, while there is no hysteresis window in the case of stoichiometric Al2O3. This memory is expected to stay non-volatile for several years or more because the capacitance value after writing and erasing operation remained almost unchanged after 4 h at T=85 °C. Also, another new memory structure comprising SiO2/Al2O3 and the Al-rich Al2O3 structure is proposed, which features increased mobility due to the reduction of electron scattering at the Si/Al2O3 interface.

Nanoscale multilayer PbS thin films fabricated by liquid–liquid interface reaction technique for solar photovoltaic applications

In the present communication, the self-assembly of nanocrystalline PbS at the liquid–liquid interface is reported. The PbS nanocrystals were, subsequently, transformed in the form of thin films by dip coating. The resultant films were characterized by SEM-EDAX, TEM-SAED, XPS and UV–visible spectroscopy. Pyramidal features at the nanometer scale and a sharp excitonic peak at 656 nm are the salient aspects of this work. The band gap of the order of 1.8 eV (associated with the excitonic feature) is ideally suited for solar photovoltaic applications.

A hybrid mask–mould lithography scheme and its application in nanoscale organic thin filmtransistors

Nanoimprint lithography (NIL) has stimulated great interest in both academic research andindustrial development due to its high resolution, high throughput and low costadvantages. Though NIL has been demonstrated to be very successful in replicatingnanoscale features, it also has its limitations as a general lithography technique. Itsfundamental moulding characteristics (i.e. physically displacing polymer materials)frequently lead to pattern defects when replicating arbitrary patterns, especially patternswith broad size distribution. To solve this problem, we have developed a combinednanoimprint and photolithography technique that uses a hybrid mould to achieve goodpattern definitions. In this work, we applied this technique to fabricate finger-shapednanoelectrodes, and demonstrated nanoscale pentacene organic thin film transistors(OTFTs). Methods of the hybrid mask–mould (HMM) fabrication and resultson the device electrical characteristics are provided. With combined advantagesof both photolithography and NIL, and the applicability to general nanoscaledevice and system fabrication, this method can become a valuable choice for lowcost mass production of micro- and nanoscale structures, devices and systems.

Laser Deposited Ag3SbS3 and Tl3SbS3 Nanoscale Thin Films as Potential Electric Field Sensors

ABSTRACTPhase composition and electrical properties of Ag(Tl)SbS amorphous films obtained by pulse laser deposition technology are investigated. The films deposited on crystalline NaCl and Kcl substrates are amorphous with crystalline phase inclusions. Room-temperature current voltage characteristics showed a good electro-sensitivity of the films under applied bias up to 10 V and a space-charge-limited current was registered as a principal component of the charge carrier transport.

Design and modeling of a MEMS pico-Newton loading/sensing device

In this paper we present a novel MEMS force sensor that exploits the post-buckling phenomenon of slender silicon columns. The design philosophy and fabrication process is discussed and analytical expressions for the force-displacement characteristics are developed. The sensor can be used to perform quantitative and qualitative measurements in-situ in SEM, TEM or STM, where the small chamber size makes it challenging to integrate conventional force-displacement sensors. Potential applications for the sensor are characterization of carbon nanotube-polymer interfaces, nanoscale thin film testing and mechanical testing of single biological cells.

Nonvolatile memory using Al2O3 film with an embedded Al-rich layer

This letter describes the capacitance-voltage (C-V) characteristics of a new nonvolatile Al2O3 memory with nanoscale thin film deposited by electron-cyclotron-resonance sputtering. Al-rich Al2O3 was fabricated at a reduced oxygen gas flow rate and used as a charge storage layer of the Al2O3 memory, which is located between the tunnel insulator and blocking insulator. C-V characteristics show a large hysteresis window due to the Al-rich structure, but there is no hysteresis window in the case of stoichiometric Al2O3 structure. This memory will stay nonvolatile for several years or more. The number of electrons injected into the insulator in the case of nanoscale memory cell length is discussed. A discussion of the statistical Gaussian distribution indicates that about 50 localization sites are necessary in Al2O3 memory with 10nm cell length for realizing a 1.8V change of the threshold voltage, which corresponds to the control of ten electrons in the insulator. This structure is easily achieved by the proposed Al-rich Al2O3 memory.

Biomaterial Coatings by Stepwise Deposition of Silk Fibroin

A completely aqueous, stepwise deposition process with Bombyx mori silk fibroin for the assembly of nanoscale thin film coatings is reported the first time. The focus of this work was to develop an understanding of the control of this deposition process and to characterize the films formed from a physicochemical perspective. The deposition process was monitored by UV spectrophotometry and research quartz crystal microbalance. Both absorbance and film thickness correlated linearly with the number of silk fibroin layers deposited, analogous to multilayered materials fabricated from conventional polyelectrolytes. The polymer adsorption process was stable and reproducible, with control of a single layer thickness ranging from a few to tens of nanometers, determined by the concentrations of silk fibroin, salt concentration in the dipping solution, and method of rinsing. The driving force for the assembly of silk fibroin onto the substrate was primarily hydrophobic interactions, while some electrostatic interactions were also involved. The difference with this approach from traditional polyelectrolyte layer-by-layer techniques is that an intervening drying step is used to control the structure and stability of the self-assembled silk fibroin. The assembled films were stable under physiological conditions and supported human bone marrow stem cell adhesion, growth, and differentiation. This approach offers new options to engineer biomaterial coatings as well as bulk materials with control of both interfacial properties conducive to specific cellular or tissue responses and the potential to entrap and deliver labile molecules or other components due to the all-aqueous process described.