Critical Interfaces Research Articles

Safety factors comparison of landfill lining components using single & double interface shear strength results

The design of a competent basal lining system is crucial in ensuring a long-lasting and functional engineered municipal solid waste (MSW) landfill. However, due to the inclusion of numerous geosynthetics and geomaterials forming a multi-layered lining system, there rises an uncertainty on determining the critical or weakest interface. This is exacerbated by the different properties offered by these lining materials and their inter-crossing functions in landfills. According to ASTM D5321-20 standard, the interface shear strengths used in design of bases and side-slopes of lining systems are determined through a single interface testing configuration. However, minimal research has been done to evaluate the consequences of multi-interface testing configurations on the minimum factors of safety (FoSmin). The present study was thus conducted to further investigate this phenomena while establishing the appropriateness of double interface testing configuration using large direct shear equipment. It was found that, the difference in the FoSmin was insignificant for critical interfaces observed under single and double interface testing configurations.

Supporting the Analysis of Safety Critical User Interfaces

Use error due to user interface design defects is a major concern in many safety critical domains, for example avionics and health care. Early detection of latent user interface problems can be facilitated by user-centered design methods that integrate formal verification technologies. This article considers the role that formal verification technologies can play in the context of user-centered design by considering the following three existing tools: CIRCUS, PVSio-web, and IVY. These tools have been developed to support the model based analysis of critical user interfaces. They have their foundations in existing formal verification technologies, but each of them is focused towards particular issues relating to user interface design. The article explores the different phases of the user-centered design process and the extent to which each of these tools supports these phases. Criteria are developed for assessing their role at each stage of the design process. The results of the evaluation provide guidance to developers to help choose the most appropriate tool based on their analysis needs while at the same time setting challenges for future developments.

Low velocity impact behaviour of a hybrid carbon‐epoxy/cork laminate

AbstractThis work addresses low velocity impact behaviour of monolithic cross‐ply carbon‐epoxy and hybrid carbon‐epoxy/cork laminates. The [04, 904]s layup was selected due to its high mismatch bending between different oriented layers, which is a critical aspect concerning large delamination development at these critical interfaces. The effect of a cork layer inserted at the most critical interface on low velocity impact behaviour of the carbon‐epoxy laminate is discussed. Impact response and resulting damage profiles of monolithic and hybrid laminates are compared, and advantages of the hybrid solution are underlined. A numerical analysis including cohesive zone modelling was also performed to assess the damage profiles obtained for the two laminates analysed. The model revealed to be effective for a better comprehension of damage mechanism for both studied cases.

(Invited) Investigation of Critical Interfaces in Few-Layer MoS2 Field Effect Transistors with High-k Dielectrics

Transition metal dichalcogenides (TMDs) as 2D or few-layer semiconducting channel material are being widely studied to lower power consumption and obtain negligible short channel effects with continued transistor scaling [1-4]. Meanwhile, research needs to be conducted on top-gated, metal-oxide-semiconductor field effect transistors (MOSFETs) to correctly assess the possibility of TMDs supplanting silicon in the channel region. This is because top-gate device architectures face some key integration challenges that typical bottom-gate TMD FET structures do not experience. As an example, molybdenum disulfide (MoS2) is supposed to have no dangling interfacial bonds, making it difficult to form high-k dielectrics on them. Therefore, surface functionalization of TMDs has attracted attention [5-12]. However, detailed understanding on performance of transistors with metal/high-k/TMD top-gate stacks are still lacking. In addition, a major hurdle of incorporating these two-dimensional (2D) materials in device structures of any kind is the high contact resistance at the metal/TMD interface [13-15]. Recent results have shown that the backside dielectric can influence top-gate MOSFET performance [16]. In this work, few-layer MoS2 FET-based devices were fabricated using top and bottom high-k dielectrics (Al2O3 and/or HfO2). The C-V response of a top-gate, HfO2/MoS2 gate stack on a backside SiO2 layer demonstrated the existence of specific defects at the interface, which demonstrated frequency dependent “humps” in depletion – similar to conventional Si MOSFETs with unpassivated silicon dangling bonds in the dielectric/Si interfacial region. Also, a comparison of UHV and HV metal deposition on MoS2 as contacts for source and drain was done where results demonstrated that UHV deposited metals were superior to HV ones. In an additional experiment with Al2O3 as the bottom-gate dielectric layer, the intrinsic mobility and subthreshold slope were greatly improved compared to SiO2 or HfO2 as back gate dielectric FETs, indicating a positive influence on top-gate device performance even without any backside bias. Furthermore, a forming gas anneal is found to further enhance device performance due to a reduction in charge trap density at dielectric interfacial regions, and improved metal contact formation. Another significant finding in top-gate FET performance is the high-k dielectric screening effect of the backside Al2O3 layer. Results demonstrate that the extracted top-gate field effect mobility values are higher compared to SiO2 or HfO2 as a backside oxide – even though all FETs have the same top-side HfO2 dielectric oxide and no back bias. Acknowledgement – This work was supported in part by the US/Ireland R&D Partnership (UNITE) under the NSF award ECCS-1407765, Science Foundation Ireland under the US-Ireland R&D Partnership Programme Grant Number SFI/13/US/I2862, and the center for Low Energy Systems Technology (LEAST), one of six SRC STARnet Centers, sponsored by MARCO and DARPA.

(Invited) Investigation of Critical Interfaces in Few-Layer MoS2 Field Effect Transistors with High-k Dielectrics

In this work, few-layer MoS2 FET-based devices were fabricated using top and bottom high-k dielectrics (Al2O3 and/or HfO2). Frequency-dependent C-V data of top-gate FETs shows dispersion in both the depletion and accumulation regions for the MoS2 devices signifying electrically active interface and possible border traps. Also, metal contact deposition conditions and sulfur treatments on MoS2 for source and drain determined that ultra high vacuum deposited metals were superior to those deposited only under high vacuum, and the sulfur treatment coupled with a forming gas anneal provides the lowest contact resistance (~2 kΩ·µm). With Al2O3 as the bottom-gate dielectric layer, a positive influence on HfO2 top-gate FET performance was achieved – even without any backside bias – because the top-gate intrinsic mobility and subthreshold slope were improved compared to SiO2 or HfO2 as back gate dielectric. Furthermore, a forming gas anneal is found to enhance device performance due to a reduction in charge trap density at dielectric interfacial regions, and improved metal contact formation.

Critical interfaces and waste placement in landfill design

The purposes of this paper are to use the previous authors’ study to investigate the effect of geometrical dimensions on the changes of the failure interfaces and to develop a design procedure for waste placement operations. Four scenarios were selected to conduct analysis so as to find various failure interface changes of the waste depth and also changes of the front and back slopes. The critical liner interface with the minimum factor of safety can vary from one to another with such changes. The curves of FS = 1·0 developed for each case can also be used to evaluate whether the waste mass filled in these landfill cells will possibly fail at a certain waste depth. In addition, a waste-filling sequence was generated so as to maintain FS above a stipulated value during filling operations. It is important to ensure that the minimum FS at the critical interface is always equal to or greater than a targeted value during waste filling, which, in turn, corresponds to different geometric dimensions of the waste.

Multimodal and in-situ Chemical Imaging of Critical Surfaces and Interfaces in Advanced Batteries

Multimodal and in-situ Chemical Imaging of Critical Surfaces and Interfaces in Advanced Batteries

Multimodal and In-Situ Chemical Imaging of Critical Surfaces and Interfaces in Li Batteries

Multimodal and <i>In-Situ</i> Chemical Imaging of Critical Surfaces and Interfaces in Li Batteries

Critical interfaces in geosynthetic multilayer liner system of a landfill

This study is to identify the critical interface in a geosynthetic multilayer liner system by examining the effects of the interface shear strength of liner components, leachate level, leachate buildup cases, and peak and residual interface strengths. According to current landfill design procedures, conducting stability analysis along the same interface at both the back slope and base may result in a non-conservative result. The critical interfaces with the minimum factor of safety are generally found at different locations along the back slope and base. The critical interface for a multilayer liner system cannot simply be assumed during stability analysis. It can shift from one interface to another with changes in the leachate level and with different leachate buildup cases. The factor of safety for an interface with a high friction angle and low apparent cohesion generally drops much more quickly than it does under inverse conditions when the leachate level increases. The failure interface in a liner system under residual conditions is usually different from the failure interface under peak conditions.

ChemInform Abstract: The Role of Synchrotron Radiation in Elucidating the Biogeochemistry of Metal(loids) and Nutrients at Critical Zone Interfaces

AbstractReview: 123 refs.

Discussion of “Modification to Translational Failure Analysis of Landfills Incorporating Seismicity” by Xuede Qian and Robert M. Koerner

Discussion of “Modification to Translational Failure Analysis of Landfills Incorporating Seismicity” by Xuede Qian and Robert M. Koerner

Critical Interfaces in Organic Solar Cells and Their Influence on the Open-Circuit Voltage

Organic photovoltaics, which convert sunlight into electricity with thin films of organic semiconductors, have been the subject of active research over the past 20 years. The global energy challenge has greatly increased interest in this technology in recent years. Low-temperature processing of organic small molecules from the vapor phase or of polymers from solution can confer organic semiconductors with a critical advantage over inorganic photovoltaic materials since the high-temperature processing requirements of the latter limit the range of substrates on which they can be deposited. Unfortunately, despite significant advances, the power conversion efficiency of organic solar cells remains low, with maximum values in the range of 6%. A better understanding of the physical processes that determine the efficiency of organic photovoltaic cells is crucial to enhancing their competitiveness with other thin-film technologies. Maximum values for the photocurrent can be estimated from the light-harvesting capability of the individual molecules or polymers in the device. However, a better understanding of the materials-level processes, particularly those in layer-to-layer interfaces, that determine the open-circuit voltage (V(OC)) in organic solar cells is critical and remains the subject of active research. The conventional wisdom is to use organic semiconductors with smaller band gaps to harvest a larger portion of the solar spectrum. This method is not always an effective prescription for increasing efficiency: it ignores the fact that the value of V(OC) is generally decreased in devices employing materials with smaller band gaps, as is the case with inorganic semiconductors. In this Account, we discuss the influence of the different interfaces formed in organic multilayer photovoltaic devices on the value of V(OC); we use pentacene-C(60) solar cells as a model. In particular, we use top and bottom electrodes with different work function values, finding that V(OC) is nearly invariant. In contrast, studies on devices incorporating hole-transport layers with different ionization potentials confirm that the value of V(OC) depends largely on the relative energy levels of the donor and acceptor species that form the essential heterojunction. An analysis of the properties of solar cells using equivalent-circuit methods reveals that V(OC) is proportional to the logarithm of the ratio of the photocurrent density J(ph) divided by the reverse saturation current density J(0). Hence, an understanding of the physical origin of J(0) directly yields information on what limits V(OC). We assign the physical origin of J(0) to the thermal excitation of carriers from the donor to the acceptor materials that form the organic heterojunction. Finally, we show that the solution to achieving higher power conversion efficiency in organic solar cells will be to control simultaneously the energetics and the electronic coupling between the donor and acceptor materials, in both the ground and excited state.

Transportation and Emergency Services: Identifying Critical Interfaces, Obstacles, and Opportunities

Transportation and emergency services agencies have many shared and overlapping responsibilities in myriad situations, ranging from routine traffic incidents to large-scale events that threaten public health and safety. The importance of effective coordination among these groups is heightened by the need to improve highway operations, ensure homeland security, and enhance all-hazards emergency management. Research was done to identify and evaluate the underlying obstacles and opportunities for improving coordination among highway transportation and emergency services organizations. Institutional, operational, technological, and financial factors were considered. Most findings and conclusions are based on a survey administered to transportation and emergency services professionals in five states. On the basis of the survey results and subsequent focus group discussions, recommendations are offered for short-term improvement of emergency transportation operations and for additional research.

Evidence for dipole surface orientational order at critical interfaces

At the critical interface of dipolar systems theory predicts that the amplitude of the surface orientational order alpha(2)(z) approximately m(*4)d(2)v(z)/dz(2), where m(*) is a reduced dipole moment and v(z) is the local composition at position z within the interface. We find quantitative agreement with these predictions for two different critical binary liquid mixtures composed of a highly polar and a nonpolar component.

Interfacial Tension of Near-Critical Cyclohexane–Methanol Mixtures

We have measured the capillary length for the interface between the coexisting phases in the vicinity of the critical consolute temperature of mixtures of cyclohexane and methanol. The data on the capillary length a = 0.250 (Tc − T)0.44±0.02cm were combined with values of the difference in density Δρ between the coexisting phases calculated from the coexisting compositions to obtain the interfacial tension σ = a2Δρg / 2 = 100(1 − T / Tc)1.23 ± 0.05erg/cm2. Our measurements of σ for this system combine with the only existing measurements of the effective thickness of a critical interface in a new test of theories of critical interfaces. Data include 0.09 &amp;lt; Tc − T &amp;lt; 9°C.