Standalone Tensile Testing of Thin Film Materials for MEMS/NEMS Applications

The microelectronics industry has been consistently driven by the scaling roadmap, colloquially referred to as the Moore’s law. Consequently, during the past decades, integrated circuits have scaled down further. This shrinkage could have never been possible without the efficient integration and exploitation of thin film materials. Thin film materials, on the other hand, are the essential building blocks of the micro- and nano-electromechanical systems (MEMS and NEMS). Utilization of thin film materials provides a unique capability of further miniaturizing electromechanical devices in micro- and nano-scale. These devices are the main components of many sensors and actuators that perform electrical, mechanical, chemical, and biological functions. In addition to the wide application of thin film materials in micro- and nano-systems, this class of materials has been historically utilized in optical components, wear resistant coatings, protective and decorative coatings, as well as thermal barrier coatings on gas turbine blades. In some applications, thin film materials are used mainly as the load-bearing component of the device. Microelectromechanical systems (MEMS) are the example of these applications. Thin film materials carry mechanical loads in thermal actuators, switches and capacitors in RF MEMS, optical switches, micro-mirror hinges, micro-motors, and many other miniaturized devices. In these applications, one of the main criteria to choose a specific material is its ability to perform the mechanical requirements. Therefore, a clear understanding of the mechanical behavior of thin film materials is of great importance in these applications. This understanding helps better analyze the creep in thermal actuators (Tuck et al., 2005; Paryab et al., 2006), to investigate the fatigue of polysilicon (Mulhstein et al., 2001; Shrotriya et al., 2004) and metallic micro-structures (Eberl et al., 2006; Larsen et al., 2003), to scrutinize the relaxation and creep behavior of switches made of aluminum (Park et al., 2006; Modlinski et al., 2004) and gold films (Gall et al., 2004), to study the hinge memory effect (creep) in micro-mirrors (Sontheimer, 2002), and to address the wear issues in micro-motors. (van Spengen, 2003) In some other applications, the thin film material is not necessarily performing a mechanical function. However, during the fabrication process or over the normal life, the device experiences mechanical loads and hence may suffer from any of the mechanical failure issues. Examples of these cases are the thermal fatigue in IC interconnects (Gudmundson & Wikstrom, 2002), strain ratcheting in passivated films (Huang et al., 2002; He et al., 2000), the fracture and delamination of thin films on flexible substrates (Li & Suo, 2006), the fracture of porous low-k dielectrics (Tsui et al., 2005), electromigration (He et al., 2004), the chip-package-interaction (CPI) (Wang & Ho, 2005), and thin film buckling and delamination (Sridhar et al., 2001). In order to address the above-mentioned failure issues and to design a device that has mechanical integrity and material reliability, an in-depth knowledge of the mechanical behavior of thin film materials is required. This information will help engineers integrate materials and design devices that are mechanically reliable and can perform their specific functions during their life-time without any mechanical failure. In addition to the tremendous industrial and technological driving force that was mentioned earlier, there is a strong scientific motivation to study the mechanical behavior of thin film materials. The mechanical behavior of thin film structures have been known to drastically differ from their bulk counterparts. (Xiang, 2005) This discrepancy that has been referred to as the length-scale effect has been one of the main motivations in the scientific society to study the mechanical behavior of thin film materials. In order to provide fundamental mechanistic understanding of this class of materials, old problems and many of the known physical laws in materials science and mechanical engineering have to be revisited from a different and multidisciplinary prospective. These investigations will not be possible unless a concrete understanding of the mechanical behavior of thin film materials is achieved through rigorous experimental and theoretical research in this area.Natural Sciences and Engineering Research Council (NSERC) of Canad

An Experimental Technique for the Study of the Mechanical Behavior of Thin Film Materials at Micro- and Nano-Scale

An experimental technique has been presented to probe the mechanical behavior of thin film materials. The method is capable of tensile testing thin films on substrate and free-standing thin film specimens. A mechanical gripper was designed to address the current challenges in gripping thin film specimens. In order to measure the strain field across the gage section, the moire interferometry technique was used and the respective optical setup was designed. A versatile microfabrication process has been developed to fabricate free-standing dog-bone specimens. Aluminum was used as the model material; however, any other metallization material can be integrated in the process. Thin film specimens have been characterized using SEM, AFM, and TEM. A process has been developed to fabrication diffraction gratings on the specimen by FIB milling. Different grating geometries were fabricated and the diffraction efficiency of the gratings was characterized. The structural damage induced by the Ga+ ions during the FIB milling of the specimens was partially characterized using STEM and EDS. In order to extract the strain field information from the moire interferogram data, a numerical postprocessing technique was developed based on continuous wavelet transforms (CWT). The method was applied on simulated uniform and nonuniform strain fields and the wavelet parameters were tuned to achieve the best spatial localization and strain accuracy

Biomechanical regulation of epigenetics and chromatin organization in single living cells

Mechanical forces are known to play a key role in regulating various cellular functions that control human development, cancer, disease, and aging. It, however, remains elusive how mechanical cues regulate biochemical mechanisms in the nucleus that control cellular decision-making. These mechanisms include epigenetic modification, chromatin organization, and gene expression. It is, therefore, highly important to investigate force-induced regulation of these mechanisms to better understand human physiology and disease. In this research, we aim at answering two key questions: one, how mechanical forces regulate epigenetics in tumor repopulating cells (TRCs), and two, how these forces unfold chromatin and induce gene expression in single living cells. Our findings suggest that mechanical forces play critical roles in regulating nuclear structure and function. Biomechanical cues can propagate deep inside the nucleus and regulate epigenetics, chromatin organization, and gene expression

Modulation of astrocyte activity and improvement of oxidative stress through blockage of NO/NMDAR pathway improve posttraumatic stress disorder (PTSD)‐like behavior induced by social isolation stress

Abstract Background It has been well documented that social isolation stress (SIS) can induce posttraumatic stress disorder (PTSD)‐like behavior in rodents, however, the underlying mechanism is remained misunderstood. In the current study, we aimed to elucidate the role of NO/NMDAR pathway in PTSD‐like behavior through modulating of astrocyte activity and improvement of oxidative stress. Methods Male NMRI mice were used to evaluate the memory function by using Morris water maze (MWM) and fear memory extinction by using freezing response. We used MK‐801 (NMDAR‐antagonist), L‐NNA (NOS‐inhibitor), NMDA (NMDAR‐agonist), and L‐arginine (NO‐agent) to find a proper treatment. Also, immunohistochemistry, RT‐PCR, and oxidative stress assays were used to evaluate the levels of astrocytes and oxidative stress. We used five mice in each experimental task. Results Our results revealed that SIS could induce learning and memory dysfunction as well as impairment of fear memory extinction in MWM and freezing response tests, respectively. Also, we observed that combined treatment including blockage of NOS (by L‐NNA, 0.5 mg/kg) and NMDAR (by MK‐801, 0.001 mg/kg) at subeffective doses could result in improvement of both memory and fear memory. In addition, we observed that SIS significantly increases the GFAP expression and astrocyte activity, which results in significant imbalance in oxidative stress. Coadministration of MK‐801 and L‐NNA at subeffective doses not only decreases the expression of GFAP, but also regulates the oxidative stress imbalance Conclusion Based on these results, it could be hypothesized that blockage of NO/NMDAR pathway might be a novel treatment for PTSD‐like behavior in animals by inhibiting the astrocyte and regulating oxidative stress level

Enhanced Oil Recovery by In-Reservoir Hydrogenation of Carbon Dioxide Using Na-Fe₃O₄

In-situ conversion of carbon dioxide into value-added products is an essential process in terms of heavy oil upgrading and utilization of the main anthropogenic greenhouse gas. In this paper, we discuss a synthesis of sodium-coated magnetite (Fe3O4) particles for in-reservoir hydrogenation of CO2. The performance of the obtained catalyst was tested in upgrading of heavy oil in a High Pressure/High Temperature (HPHT) reactor imitating the reservoir conditions during steam injection techniques. The experiments were conducted for 48 h in a CO2 environment under the steam temperature and pressure of 250 °C and 90 bar, respectively. The results showed irreversible viscosity reduction of oil from 3931 mPa.s to 2432 mPa.s after the degassing of unreacted carbon dioxide. The content of resins in the composition of upgraded oil was significantly altered from 32.1 wt% to 19.01 wt%, while the content of aromatics rose from 32.5 wt% to 48.85 wt%. The GC-MS results show the presence of alkyl benzenes and phenanthrenes, which were initially concentrated in resins and asphaltenes, in the aromatics fraction of upgraded crude oil. Thus, Na-Fe3O4 exhibits promising results for in-situ heavy oil upgrading through the hydrogenation of carbon dioxide, which contributes not only to the reduction of greenhouse gas emissions, but also enhances heavy oil recovery

Inequality in Maternal Mortality in Iran: An Ecologic Study

Background : Maternal mortality (MM) is an avoidable death and there is national, international and political commitment to reduce it. The objective of this study is to examine the relation of MM to socioeconomic factors and its inequality in Iran′s provinces at an ecologic level. Methods : The overall MM from each province was considered for 3 years from 2004 to 2006. The five independent variables whose relations were studied included the literacy rate among men and women in each province, mean annual household income per capita, Gini coefficients in each province, and Human Development Index (HDI). The correlation of Maternal Mortality Ratio (MMR) to the above five variables was evaluated through Pearson′s correlation coefficient (simple and weighted for each province′s population) and linear regression-by considering MMR as the dependent variable and the Gini coefficient, HDI, and difference in literacy rate among men and women as the independent variables. Results: The mean MMR in the years 2004-2006 was 24.7 in 100,000 live births. The correlation coefficients between MMR and literacy rate among women, literacy rate among men, the mean annual household income per capita, Gini coefficient and HDI were 0.82, 0.90, −0.61, 0.52 and −0.77, respectively. Based on multivariate regression, MMR was significantly associated with HDI (standardized B=−0.93) and difference in literacy rate among men and women (standardized B=−0.47). However, MMR was not significantly associated with the Gini coefficient. Conclusion: This study shows the association between socioeconomic variables and their inequalities with MMR in Iran′s provinces at an ecologic level. In addition to the other direct interventions performed to reduce MM, it seems essential to especially focus on more distal factors influencing MMR

Distinct biophysical mechanisms of focal adhesion kinase mechanoactivation by different extracellular matrix proteins

Matrix mechanics controls cell fate by modulating the bonds between integrins and extracellular matrix (ECM) proteins. However, it remains unclear how fibronectin (FN), type 1 collagen, and their receptor integrin subtypes distinctly control force transmission to regulate focal adhesion kinase (FAK) activity, a crucial molecular signal governing cell adhesion/migration. Here we showed, using a genetically encoded FAK biosensor based on fluorescence resonance energy transfer, that FN-mediated FAK activation is dependent on the mechanical tension, which may expose its otherwise hidden FN synergy site to integrin α5. In sharp contrast, the ligation between the constitutively exposed binding motif of type 1 collagen and its receptor integrin α2 was surprisingly tension-independent to induce sufficient FAK activation. Although integrin α subunit determines mechanosensitivity, the ligation between α subunit and the ECM proteins converges at the integrin β1 activation to induce FAK activation. We further discovered that the interaction of the N-terminal protein 4.1/ezrin/redixin/moesin basic patch with phosphatidylinositol 4,5-biphosphate is crucial during cell adhesion to maintain the FAK activation from the inhibitory effect of nearby protein 4.1/ezrin/redixin/moesin acidic sites. Therefore, different ECM proteins either can transmit or can shield from mechanical forces to regulate cellular functions, with the accessibility of ECM binding motifs by their specific integrin α subunits determining the biophysical mechanisms of FAK activation during mechanotransduction

Changes in Heavy Oil Saturates and Aromatics in the Presence of Microwave Radiation and Iron-Based Nanoparticles

Our knowledge of electromagnetic heating’s effect on heavy oil upgrading is largely based on very limited data. The aim of the present research was thus to study in detail the effect of microwave exposure in the absence and presence of nanosized magnetite on the composition of heavy oil. The obtained data reveal that the use of nanosized magnetite improves not only microwave radiation application as a result of its absorption and release of thermal energy but also that these nanoparticles have a catalytic ability to break carbon–heteroatom bonds in the composition of resins and asphaltene molecules. In fact, the overall reduction in asphaltenes or resins does not always adequately describe very important changes in asphaltene composition. Even a small fraction of broken carbon–heteroatom bonds can lead to an increase in the mobility of asphaltenes. Moreover, this study has shed light on the important evidence for asphaltenes’ transformation, which was found to be the formation of light aromatic compounds, such as alkylbenzenes, naphthalenes and phenanthrenes. These compounds were fixed in the composition of the aromatic fraction. We believe that these compounds could be the fragments obtained from asphaltenes’ degradation. The evidence from this study points toward the idea that asphaltenes’ destruction is crucial for increasing oil mobility in the reservoir rock during its thermal stimulation