Intrinsic and Atomic Layer Etching Enhanced Area-Selective Atomic Layer Deposition of Molybdenum Disulfide Thin Films

For continual scaling in microelectronics, new processes for precise high volume fabrication are required. Area-selective atomic layer deposition (ASALD) can provide an avenue for self-aligned material patterning and offers an approach to correct edge placement errors commonly found in top-down patterning processes. Two-dimensional transition metal dichalcogenides also offer great potential in scaled microelectronic devices due to their high mobilities and few-atom thickness. In this work, we report ASALD of MoS2 thin films by deposition with MoF6 and H2S precursor reactants. The inherent selectivity of the MoS2 atomic layer deposition (ALD) process is demonstrated by growth on common dielectric materials in contrast to thermal oxide/ nitride substrates. The selective deposition produced few layer MoS2 films on patterned growth regions as measured by Raman spectroscopy and time-of-flight secondary ion mass spectrometry. We additionally demonstrate that the selectivity can be enhanced by implementing atomic layer etching (ALE) steps at regular intervals during MoS2 growth. This area-selective ALD process provides an approach for integrating 2D films into next-generation devices by leveraging the inherent differences in surface chemistries and providing insight into the effectiveness of a supercycle ALD and ALE process

The Design and Development of a Stress Corrosion Cracking Sensor for Spent Nuclear Fuel Containers

Nuclear fuel is responsible for providing nearly 20% of the United States’ annual energy demands. An essential part of the nuclear fuel cycle, is the safe management and storage of radioactive waste. Some radioactive waste is stored within stainless steel canisters at the reactor site for up to 100 years as part of an engineered containment and storage system. To monitor the degradation of these canisters a novel sensor system has been developed. The design incorporates a humidity sensor, thermocouple, a set of stainless steel coupons and a modified circuit assembly to gather data remotely. Initial testing to verify the use of these stainless steel samples has been completed in custom designed test fixtures similar to those used in the sensor module. Testing has been carried out in an array of different solutions including hydrochloric acid and concentrated salt water. A final atmospheric testing plan has been initialized to demonstrate proof of concept. After demonstration, if successful, the sensor system will be mounted to dry storage containers to monitor real time conditions of the concrete-encased canisters and ensure long term safety

Comparison of Corrosion Properties of Bearing Steels

Bearing steels are a family of hardened steel alloys typically used for applications which require moving components. Given bearing steels’ prevalence in the aerospace industry, recent interest has arose regarding their corrosion properties. Corrosion resistance correlates with wear resistance and can provide a metric to assess and predict the relative wear lifetime of a bearing steel. Historically, an emphasis has been placed on designing bearing steels for high hardness values and a long fatigue life. However, low corrosion resistance can accelerate the wear rate of a bearing steel leading to unanticipated failure of the bearing component, increased maintenance cost, and possible catastrophic failure of an aircraft. This research aims to correlate the composition and microstructure of new candidate bearing steels with corrosion resistance. Generally, higher chromium content in the bearing steel gives higher corrosion resistance, but also greater cost and lower hardness. An optimized surface treatment is being sought. The corrosion properties of bearing steels with different surface treatments were determined using electrochemical impedance spectroscopy (EIS). The steel microstructure was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results indicated that the corrosion rate is dependent on composition, microstructure, and surface hardening method

Availability-Driven Design of Hairpin Fuels and Small Interfering Strands for Leakage Reduction in Autocatalytic Networks

DNA-based circuits and computational tools offer great potential for advanced biomedical and technological applications. However, leakage, which is the production of an output in the absence of an input, widely exists in DNA network. As a new approach to leakage reduction, this study utilizes availability to reduce leakage in an entropy-driven autocatalytic DNA reaction networks. Here, we report the performance improvements resulting from direct tailoring of fuel strand availability through two novel approaches: (1) the addition of interfering domains to fuel strands, and (2) the introduction of separate small interfering strands. The best performing fuel designs resulted in increased performance ratios of up to 22%. Employing small interfering strands (5–12 nucleotides (nt)) improved the performance ratios by up to 21%. Furthermore, the stability of the network using either leakage reduction method matched well with computed availability and experimental results showing Spearman correlation coefficients of −0.84 for modified fuel strands and −0.92 for small interfering strands

A Condition Monitor for Atmospheric Induced Stress Corrosion Cracking

A sacrificial sensor has been designed to detect the occurrence and rate of atmospheric corrosion and stress corrosion cracking. The sensor fixture was constructed using additive manufacturing and can be customized for use with small size wires or ribbons of any metallic material as a sensor electrode. Resistance change was used to monitor the degradation of arrays of small samples subjected to various stress and environmental conditions. Typical passive atmospheric corrosion sensors do not account for applied stress, or if they do, use statically loaded electrodes and stress relaxation during SCC precludes extended monitoring. However, this sensor allows for propagation of SCC to be monitored since the electrode experiences a dynamic applied stress. This low cost test system permits detection of degradation across multiple time and length scales and can be tailored for the intended application and environment. For proof of concept testing the sensor was used to detect corrosion and stress corrosion cracking of austenitic stainless steels exposed to liquid and high humidity corrosive environments

Toward Logic-Based Nucleic Acid Transducer Networks

Research in disease detection and diagnosis has established links between specific diseases and the presence of certain biomarkers found in bodily fluids. These biomarkers include micro-RNAs (miRNAs), which are small RNA molecules related to gene regulation and can be found in the blood stream. The presence of certain types of cancers alters the relative concentrations of certain miRNAs. Thus, detection and quantification of miRNA concentrations could enable a new type of blood test for a number of cancers. Here, we describe our efforts to implement logic-based DNA reaction networks for detection and quantification of miRNAs. Our system consists of a DNA transducer that implements Boolean logic for comparative detection of specific miRNA sequences. If the specific miRNAs are present, the transducer produces an output signal that initiates an amplification network, which produces a change in the solution color that can be detected by eye. Here, we present our system design and preliminary data

Developing a Novel Sensor to Detect Stress Corrosion Cracking of Spent Nuclear Fuel Storage Containers

A significant portion of the Unites States’ annual energy demand is provided by nuclear power. Safe storage of radioactive spent nuclear fuel is an essential part of the fuel life-cycle. Currently, spent fuel is stored at the reactor site in stainless-steel dry storage containers where the loaded containers are welded shut and backfilled with helium. Since the storage containers are passively cooled with air from the ambient environment, the canisters may become susceptible to atmospheric induced corrosion damage, particularly in the weld sensitized region. To ensure the integrity of the storage containers we are developing a sensor to determine the presence and extent of corrosion damage as well as provide a viable indicator for the future condition of these containers. We have developed a miniature stress corrosion cracking test fixture to provide an early warning signal at the initiation of corrosion damage. These fixtures use a three point bend test configuration to stress stainless steel samples while collecting resistance measurements over time. Sample failure is signaled by a sudden jump in resistance across the sample. The data these sensors provide can help predict the future health of the current storage containers and ensure long-term safe storage