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1. Side‐Group‐Mediated Mechanical Conductance Switching in Molecular Junctions

   https://doi.org/10.1002/anie.201709419  

   Ismael, Ali Khalid ; Wang, Kun ; Vezzoli, Andrea ; Al‐Khaykanee, Mohsin K. ; Gallagher, Harry E. ; Grace, Iain M. ; Lambert, Colin J. ; Xu, Bingqian ; Nichols, Richard J. ; Higgins, Simon J. ( November 2017 , Angewandte Chemie International Edition)

   A key target in molecular electronics has been molecules having switchable electrical properties. Switching between two electrical states has been demonstrated using such stimuli as light, electrochemical voltage, complexation and mechanical modulation. A classic example of the latter is the switching of 4,4′‐bipyridine, leading to conductance modulation of around 1 order of magnitude. Here, we describe the use of side‐group chemistry to control the properties of a single‐molecule electromechanical switch, which can be cycled between two conductance states by repeated compression and elongation. While bulky alkyl substituents inhibit the switching behavior, π‐conjugated side‐groups reinstate it. DFT calculations show that weak interactions between aryl moieties and the metallic electrodes are responsible for the observed phenomenon. This represents a significant expansion of the single‐molecule electronics “tool‐box” for the design of junctions with electromechanical properties.

    

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2. Charge transport in individual short base stacked single-stranded RNA molecules

   https://doi.org/10.1038/s41598-023-46263-0  

   Chandra, Subrata ; Williams, Ajoke ; Maksudov, Farkhad ; Kliuchnikov, Evgenii ; Pattiya Arachchillage, Keshani G. G. ; Piscitelli, Patrick ; Castillo, Aderlyn ; Marx, Kenneth A. ; Barsegov, Valeri ; Artes Vivancos, Juan M. ( November 2023 , Scientific Reports)

   Charge transport in biomolecules is crucial for many biological and technological applications, including biomolecular electronics devices and biosensors. RNA has become the focus of research because of its importance in biomedicine, but its charge transport properties are not well understood. Here, we use the Scanning Tunneling Microscopy-assisted molecular break junction method to measure the electrical conductance of particular 5-base and 10-base single-stranded (ss) RNA sequences capable of base stacking. These ssRNA sequences show single-molecule conductance values around$$10^{-3}G_0$$${10}^{-3}{G}_0$($$G_0= 2e^2/h$$$G_0=2e^2/h$), while equivalent-length ssDNAs result in featureless conductance histograms. Circular dichroism (CD) spectra and MD simulations reveal the existence of extended ssRNA conformations versus folded ssDNA conformations, consistent with their different electrical behaviors. Computational molecular modeling and Machine Learning-assisted interpretation of CD data helped us to disentangle the structural and electronic factors underlying CT, thus explaining the observed electrical behavior differences. RNA with a measurable conductance corresponds to sequences with overall extended base-stacking stabilized conformations characterized by lower HOMO energy levels delocalized over a base-stacking mediating CT pathway. In contrast, DNA and a control RNA sequence without significant base-stacking tend to form closed structures and thus are incapable of efficient CT.

    

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3. Highly Efficient Polarization‐Controlled Electrical Conductance Modulation in a van der Waals Ferroelectric/Semiconductor Heterostructure

   https://doi.org/10.1002/aelm.202200413  

   Parker, Jacob ; Gu, Yi ( September 2022 , Advanced Electronic Materials)

   Utilizing the unique in‐plane/out‐of‐plane polarization coupling in ferroelectric van der Waals α‐In₂Se₃, ferroelectric‐polarization‐controlled electrical conductance modulation in two‐dimensional (2D) MoS₂with a large dynamic range of over 5 orders of magnitude and excellent non‐volatility is demonstrated. This highly efficient control of the electrical conductance is facilitated by enhanced capacitive coupling through atomic‐layer‐deposition‐grown Al₂O₃as the dielectric medium. By varying the in‐plane poling bias to the ferroelectric α‐In₂Se₃, the electrical conductance of vertically stacked 2D MoS₂can be tuned continuously. This approach enables simplified device design and provides great flexibility in device integrations, and it can be applied in principle to manipulate the electronic states in any 2D semiconductors for various applications such as transistors, tunneling devices, and reconfigurable electronics. The results also provide insight into the ferroelectric polarization screening by ambient chemical species, highlighting the need for surface passivation, and/or device encapsulations.

    

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4. GaN-based Mach-Zehnder Modulators for Highly Efficient Optical Modulation and Switching Applications

   Su, Patrick ; Carlson, John ; and Dallesasse, John ( September 2018 , SRC TECHCON)

   The recent development of 8-in Gallium Nitride on Silicon (GaN-on-Si) wafers has facilitated cost effective, large-scale manufacturability of GaN-based electronics. Leveraging its wide band gap, capability to support a two dimensional electron gas (2DEG) layer, and strong built-in polarization effects, GaN-based electronic devices have become a viable cost-effective successor to silicon-based devices for high-performance applications where the large bandgap and high breakdown field are required. The advantageous properties of GaN-on-Si material, however, have yet to be utilized for photonic integrated circuit applications. Therefore, the exploration of GaN for efficient on-chip optical modulation and switching applications is examined. In order to effectively characterize GaN’s capabilities for optical modulation and switching, GaN-based Mach-Zehnder modulators are designed and fabricated. Through simulating the propagating optical modes supported in a GaN-based Mach-Zehnder structure, the geometry of the device is designed to optimize optical modal overlap with the 2DEG layer while maintaining single-mode performance. Through electrical and optical characterization, the effective electro-optic coefficient and Vπ length are measured. These measurements provide a method of benchmarking GaN-based photonic devices for their optical modulation and switching efficiency. 

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5. GaN-based Mach-Zehnder Modulators for Highly Efficient Optical Modulation and Switching Applications

   Su, Patrick ; Carlson, John ; Dallesasse, John ( September 2018 , SRC TECHCON)

   The recent development of 8-in Gallium Nitride on Silicon (GaN-on-Si) wafers has facilitated cost effective, large-scale manufacturability of GaN-based electronics. Leveraging its wide band gap, capability to support a two dimensional electron gas (2DEG) layer, and strong built-in polarization effects, GaN-based electronic devices have become a viable cost-effective successor to silicon-based devices for high-performance applications where the large bandgap and high breakdown field are required. The advantageous properties of GaN-on-Si material, however, have yet to be utilized for photonic integrated circuit applications. Therefore, the exploration of GaN for efficient on-chip optical modulation and switching applications is examined. In order to effectively characterize GaN’s capabilities for optical modulation and switching, GaN based Mach-Zehnder modulators are designed and fabricated. Through simulating the propagating optical modes supported in a GaN-based Mach-Zehnder structure, the geometry of the device is designed to optimize optical modal overlap with the 2DEG layer while maintaining single-mode performance. Through electrical and optical characterization, the effective electro-optic coefficient and Vπ length are measured. These measurements provide a method of benchmarking GaN-based photonic devices for their optical modulation and switching efficiency. 

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