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The stability of polarization in ferroelectric BiFeO3 thin film stacked with a p-n junction of Cu2O/ZnO was studied in the Au/Cu2O/ZnO/BiFeO3/Pt heterostructure. It was observed that the downward ferroelectric polarization of BiFeO3 gradually relaxes once the external electric field is removed, which is driven by the depolarization effect induced by the reduction of compensating charges due to the charge redistribution within Cu2O/ZnO. This work contributes to an improved understanding on the polarization behavior in multilayer thin film structures comprising ferroelectrics and p-n junctions for guiding relevant device design and performance analysis.

Electroless Cu seed layer is essential for subsequent copper metallization by electroplating for sub-micron wafer technology. This layer is required to provide good step coverage and high uniformity. In the current work, electroless copper was deposited on a TiN surface activated by palladium. The effect of deposition time on the properties of electroless Cu films was reported. It shows that as the deposition time increases, the surface coverage of Cu film on activated TiN is improved and there is a significant reduction in sheet resistance and an increase in grain size of deposited copper film. Of particular interest is that there exists a preferred Cu (111) crystal orientation in the samples subjected to more than as short as 3 min of deposition. A surface roughness (Rrms) of ∼17 nm has been achieved. The results obtained in current study points out a promising process for laying down thin Cu seed layer. Accepted version

Scratches in the range of 1000 nm deep were produced on the surfaces of two polymers using diamond tip indenter to study the material deformation and wear debris generation characteristics. Our results show that the process of wear debris generation depends upon the manner in which scratches are produced on the surface. Single track scratches do not produce wear debris despite several passes of the indenter tip whereas intersecting scratches accelerate the wear debris generation process. The results indicate that the material near the four corners of intersecting scratches experience extremely high strain leading to extrusion and eventual breakage from the bulk of the polymer forming a debris particle.Copyright © 2003 by ASME

A rapid and accurate static and quasi-static method for determining the out-of-plane spring constraints of cantilevers and a micromachined vibratory sensor is presented. In the past, much of the effort in nanoindentation application was to investigate the thin-film mechanical properties. In this paper, we have utilized the nanoindentation method to measure directly some micromachined device (e.g. microgyroscope) spring constants. The cantilevers and devices tested were fabricated using the MUMPS process and an SOI process (patent pending). Spring constants are determined using a commercial nanoindentation apparatus UMIS-2000 configured with both Berkovich and spherical indenter tip that can be placed onto the device with high accuracy. Typical load resolution is 20micrometers N to 0.5N and a displacement resolution of 0.05nm. Information was deduced from the penetration depth versus load curves during both loading and unloading.

In this article, we investigate the effect of electric-field on the perpendicular magnetic anisotropy (PMA) and strain properties in nanoscaled CoFeB/MgO magnetic tunnel junction using tunnel magnetoresistance and piezoresponse force microscopy (PFM) measurements, respectively. We show that while the PMA change under electric-field is consistent with the previous reports, the PFM data show that the applied electric-field induces strain in a nanoscaled MgO. We demonstrate that the development of compressive and tensile strains corresponding to different polarities of applied electric-field. We discuss the interplay between the electric-field controlled PMA and strain properties. Our results may accelerate the development of magnetoelectrically controlled spintronic devices for low-power and high-density magnetic data storage applications.

An efficient bioartificial liver-assisted device can sustain the lives of patients with acute liver failure. Among different configurations of the bioreactor design, hepatocyte encapsulation has important features that satisfy most requirements of the device. We have encapsulated rat hepatocytes in a two-layer polymeric membrane by complex coacervation using a simple setup and demonstrated enhanced cellular functions up to three times higher than those of the monolayer control. These microcapsules of the functioning hepatocytes have a 2- to 3-microm outer layer of synthetic polymer with 25% 2-hydroxyethyl methacrylate, 25% methacrylic acid, and 50% methyl methacrylate and an inner layer of positively charged modified collagen as a suitable substrate for the enhanced cellular functions. Permeable only to small molecules up to albumin, the microcapsules should allow unimpeded exchange of nutrients, oxygen, growth factors, and metabolites but prevent attack by immunoglobulins of the immune system, and no "skin effect" of the collagen has been observed. Mechanical properties of the microcapsules measured with a nano-indentation method suggest that the microcapsules should be suitable for use in a bioartificial liver-assisted device.

We report the discovery of ferroelectricity in NH4TiOF3 by piezoresponse force microscopy (PFM) technique and first principles calculations. The first principles calculations show that the O has an in-plane site preference in the layered structure of this material and the energetics favor a ferroelectric ground state with a calculated polarization of approximately 8 μC/cm2. Lateral and vertical PFM results show stable ferroelectricity at ambient temperature. The ferroelectricity is first observed for mesocrystals. It also provides an explanation for observations of mesocrystal growth even in the absence of surfactants since electric dipolar interactions can guide self-assembly.

Seashells, the armor of one of the most ancient species, have demonstrated outstanding mechanical properties such as simultaneous strengthening and toughening. The seashells have also been proven to exhibit piezoelectric and ferroelectric properties, which may contribute to their mechanical behaviors and various functionalities. This work has elaborated in more details of the piezoelectric and ferroelectric behaviors of the nacre by using the DART (Dual-AC Resonance Tracking) and vector-PFM (Piezoresponse Force Microscope), as well as the SS-PFM (Switching Spectroscopy PFM) techniques. By using the vector-PFM technique, the local polarization directions of intracrystalline biopolymers are found to be very close to the direction perpendicular to the platelet surface, and it, therefore, shows strong piezoresponse along this direction. On the other hand, the interlamellar biopolymer shows strong piezoresponse in the direction parallel to the platelet surface. This intrinsic piezoelectric property of the biopolymer may be the basis for sensing and actuating during biomineralization process. Besides the piezoresponse, the locations of various biopolymers are also revealed in-situ by using the PFM technique. The ferroelectric behaviors of nacre have been observed by SS-PFM method. Based on the shapes of the ferroelectric hysteresis loops, it is found that the biopolymers in nacre exhibit the similar behaviors to that of the polyvinylidene fluoride (PVDF) based co- or ter-polymers for energy storage applications.

The capacitance dispersion in La and Mg co-substituted BiFeO3 thin film has been studied at different stages of polarization switching. A negative capacitance (NC) behavior is observed in the sample that is fatigued above 109 switching cycles. The origin of the NC is investigated through analyzing relaxation processes and charge transport kinetics by admittance spectroscopy. An activation energy of ∼0.6 eV and a zero field mobility μ0=5.33±0.02×10−13m2/Vs are thus obtained. A physical mechanism is proposed to explain this behavior. It involves a redistribution of oxygen vacancies, which are trapped at the film/electrode interface during the fatigue process.

This paper presents an in-situ study by combining contact dc-writing in biased scanning probe microscopy and non-contact Kelvin probe force microscopy to characterize the effect of bias-induced Li+ insertion/extraction on the changes of surface potential of TiO2 anode in an all-solid-state thin film Li-ion battery at nanoscale. With single layer TiO2 film as the reference, the factors affecting the changes of the surface potential, including the Fermi energy level shift and charge screening related to TiO2 semiconductor behavior, and bias-induced Li+ intercalation/ de-intercalation related to battery behavior are investigated. Surface potential hysteresis loop can be formed for TiO2 anode film, in which the potential value increases under the positive polarization and decreases under the negative polarization. In addition, TiO2 anode film after Li+ insertion/extraction cycles has a lower surface potential, indicating the decrease of charge sustaining capacity and the surface electrical degradation. In add...

We report highly efficient polymer solar cells (PSCs) with rhodamine 101, a conjugated zwitterion with positive and negative charges on the same molecule, as the electron-collection interlayer. Rhodamine 101 can be processed by solution processing techniques or thermal deposition. The rhodamine 101 interlayer simultaneously improves the short-circuit current, open-circuit voltage, fill factor so as to improve the photovoltaic efficiency of the PSCs with poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active materials in comparison with control PSCs with Al or Ca/Al as the cathode. The photovoltaic efficiency reaches 6.15% for the PSCs with rhodamine 101/Al as the cathode under AM1.5G illumination, whereas the efficiencies are only 3.81% and 4.57% for the control PSCs with Al and Ca/Al as the cathodes, respectively. On the other hand, the improvement on the photovoltaic performance by the rhodamine 101 interlayer is less remarkable for the PSCs with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or PC71BM as the active materials. The photovoltaic efficiency is 4.25% for the PSCs with rhodamine 101/Al as the cathode, almost the same as that (4.20%) of the control PSCs with Ca/Al as the cathode. The high efficiency of the PSCs with the rhodamine 101 interlayer is ascribed to the lowering of the work function of metals by rhodamine 101 that has a strong dipole moment. The different effects of the rhodamine 101 interlayer on the two PSCs with PCDTBT and P3HT as the donor materials are attributed to different reactivities of the two polymers with active metals like Ca and Al. PCDTBT consisting of both electron-donating and electron-withdrawing units is more reactive with the active metals. The reaction between PCDTBT and Ca leads to low photovoltaic efficiency of the PSCs with Ca/Al as the cathode.

The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3(BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a downward electric field above 80 oC. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO..) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutralization of VO...

The surface potential of undoped and copper-doped zinc oxide (ZnO:Cu) films has been studied using the Kelvin probe force microscopy at ambient condition. In contrast to the undoped ZnO with unipolar behavior, the ZnO:Cu film exhibits a bipolar surface potential behavior under a dc bias. The localized hole trapping phenomenon is attributed to the presence of Cu ions in ZnO films. With an appropriate amount of the Cu ions (∼8 at. %), the charge trapping is reasonably stable over a period of 20 h, which can be associated with the presence of oxygen vacancies. This coexistence of Cu ions and oxygen vacancies in ZnO gives rise to stable bipolar behavior, paving way to potential charge storage application.

We investigate the mechanical instabilities of hydrogel microlenses triggered by concentrated loadings. Depending on hydrogel microlenses, geometries, and loading conditions, a series of nontrivial instability pathways is observed, including transitions of localized polyhedral faceted shapes with multifold vertices created by bifurcation, snapping through curvature inversion and large load drop, and wrinkling driven by combined in-plane stretching and compression. These pathways reveal the richness of the mechanical behavior of hydrogel microlenses and provide potential strategies to control the design and shape of complex hydrogel microlenses.

Domain structures of [001]T and [011]T-cut Pb(Zn1/3Nb2/3)O3−(6%−7%)PbTiO3 (PZN-PT) single crystals are studied using scanning electron acoustic microscope (SEAM) technique. The observation of the orientation of domain walls agree reasonably well with the trigonometric projection of rhombohedral and orthorhombic dipoles on the (001) and (011) surfaces, respectively. After mechanical loading with microindentation, domain switching is also observed to form a hyperbolic butterfly shape and extend preferentially along four diagonal directions, i.e., ⟨110⟩ on (001) surface and ⟨111¯⟩ on (011) surface. The critical shear stress to cause domain switching for PZN-PT crystal is estimated to be approximately 49 MPa for both {110} and {111¯} planes based on theoretical analysis. Generally, the SEAM technique has been successfully demonstrated to be a valid technique for observation of domain structures in single crystal PZN-PTs.

This article presents studies on using a wedge indentation technique to determine interfacial adhesion properties of low-k dielectric films, namely, methyl-silsesquioxane (MSQ) and black diamond (BD™)films, both on a Si substrate. Interfacial crack initiation and propagation processes in the MSQ/Si system are studied by using focused-ion-beam sectioning of the indentation impressions created by wedge tips with 90° and 120° of inclusion angles, respectively. Furthermore, the indentation induced stress is found to be proportional to the ratio of the indentation volume and the interface delamination crack volume for both plane strain and nonplane strain cases. With this analysis, the interface toughness of the MSQ/Si and BD/Si system, in terms of the strain energy release rate, is determined. The interface toughness for the MSQ/Si system is found to be a value of 1.89±0.28J∕m2 for the 90° wedge tip indentation and 1.92±0.08J∕m2 for the 120° wedge tip indentation. In addition, using the 120° wedge tip, the in...

“Extracting the elastic and viscoelastic properties of a polymeric film using a sharp indentation relaxation test” [J. Mater. Res. 21, 2991 (2006)]

Porous interlayer dielectric films with interconnected pores pose a serious challenge for their integration into next-generation microchips. The opening of interconnected pores in the surface region needs to be sealed to prevent intrusion of atomic layer deposition precursors used to create metal diffusion barriers. In this paper, we report the formation of a thin, nonporous surface layer on a porous methyl-silsesquioxane-based dielectric film by NH 3 plasma treatment. Depth-profiled beam positronium annihilation lifetime spectroscopy was applied to conveniently examine the formation of the dense layer. A nonporous surface layer was readily identified by the curtailment of positronium escape into vacuum through the surface. Among plasma treatments at temperatures ranging from 25 to 300°C for duration of 3-600 s, the best result was achieved at 300°C for 10 s. A very thin skin layer, ∼ 10 nm, could be formed with little damage to the bulk of the low-κ film. This thin skin layer further proved to improve the performance of Ta barriers for Cu diffusion. Chemical analysis, infrared spectroscopy, and sputtering secondary ion mass spectroscopy were also performed to examine how the plasma treatment altered the dielectric film.

In this work, chemical vapor deposited low-k films using trimethylsilane (3MS) as the linear precursors and tetramethylcyclotetra siloxanes (TMCTS) as the cyclic precursors are studied. There are four processes studied: O 2 , O 2 + He process and CO 2 , CO 2 + O 2 process for 3MS and TMCTS precursors, respectively. Films deposited by the 3MS and TMCTS processes displayed similarities in the relationship between the Fourier transform infrared spectroscopy peak ratios, dielectric constants, refractive indexes, hardness, and modulus. The dielectric constant was found to have a linear relationship with hardness and modulus and inversely proportional with the Si-CH 3 /Si-O peak ratio for both precursors. It is believed that the introduction of a methyl group in the film has reduced the covalency of the Si-O bond thus reducing its dielectric constant in comparison with silica. In this work, the 3MS based low-k films appear to have slightly wider process windows compared to the TMCTS based low-k films. The linear precursors (3MS) in both O 2 + He and O 2 process and cyclic precursors (TMCTS) in both CO 2 + O 2 and CO 2 processes yielded similar hardness and modulus values for the same range of dielectric constants. In terms of the films electrical properties and stability, all films indicate mild stress where the 3MS system showed lower values of stress, good thermal stability, breakdown voltage, and leakage current values that are comparable to silica.

In this work, chemical vapor deposited carbon doped oxide films using trimethyl silane precursors with dielectric constant in the range of 2.75 to 3.62 were studied. Process parameters studied included low frequency RF (LFRF) and high frequency RF (HFRF) power, pressure, and helium flow rates as the oxidation influencing agents. Reliability and thermal stability of the films were studied and the dielectric constant (k), breakdown voltage, and leakage current were measured at 1 MHz. Numerous film properties (film stresses, hardness, modulus, refractive indices, and chemical bonding) were characterized. Results indicate that reduction of LFRF or HFRF power and the increase in pressure reduces the dielectric constant. Helium gases dissociate the Si–CH3 and C–H bond in the structure causing the dielectric constant to increase linearly as the helium flow rate increased while keeping the oxygen flow rate constant (O2+He process). It was observed that the O2 process window lowers the k value range and imparts sl...

The local domain structure and surface potential of Pb(Zn1/3Nb2/3)O3–9%PbTiO3 (PZN–9%PT) single crystals were investigated by Kelvin probe force microscopy (KPFM) and piezoresponse force microscopy (PFM), respectively. The results confirm the existence of the screening layer on the surface of the material. The relaxation of the surface potential and its relation to polarization switching within the poled regions in air and argon gas were analyzed. It is found that the surface potential increases with the poling voltage to a limited range. Comparing the relaxation behavior in ambient air with that in argon gas, we find that the relaxation time in argon is much shorter than that in air, and the relaxation in air is dominated by the space charge transport phenomena. In addition, the results show that the injected charges have significant effects on the pinning of the polarization in PZN–PT single crystals.

Indentation load–penetration curves from sharp indentations (Vickers indentation and nanoindentation) on several ceramic materials were analysed using newly developed three-dimensional finite-element (FEN numerical models, based on elastic and elastoplastic calculations. The results have led to a general methodology to analyse the penetration curves obtained from both Vickers indentations and nanoindentations on bulk materials. It is found that it is necessary to proceed with separate analyses for the loading and unloading curves, although the analyses are related. Through a detailed analysis of the load–depth curves, information related to various compressive mechanical properties is obtained from different portions of the load–penetration curves. From the loading curve, the hardness, yielding stress, strain hardening, surface displacement and plastic zone size are obtained, whereas the elastic modulus is obtained from the unloading curve. Experimentally reported indentation load–penetration cur...

This paper describes nanoindentation experiments on thin films of polycrystalline Al of known texture and different thicknesses, and of single crystal Al of different crystallographic orientations. Both single-crystalline and polycrystalline films, 400–1000 nm in thickness, are found to exhibit multiple bursts of indenter penetration displacement, h, at approximately constant indentation loads, P. Recent results from the nanoindentation studies of Suresh et al. (Suresh, S., Nieh T.-G. and Choi, B.W., Scripta mater., 1999, 41, 951) along with new microscopy observations of thin films of polycrystalline Cu on Si substrates are also examined in an attempt to extract some general trends on the discrete and continuous deformation processes. The onset of the first displacement burst, which is essentially independent of film thickness, appears to occur when the computed maximum shear stress at the indenter tip approaches the theoretical shear strength of the metal films for all the cases examined. It is reasoned that these displacement bursts are triggered by the nucleation of dislocations in the thin films. A simple model to estimate the size of the prismatic dislocation loops is presented along with observations of deformation using transmission electron microscopy and atomic force microscopy. It is demonstrated that the response of the nanoindented film is composed of purely elastic behavior with intermittent microplasticity. The overall plastic response of the metal films, as determined from nanoindentation, is shown to scale with film thickness, in qualitative agreement with the trends seen in wafer curvature or X-ray diffraction measurements.