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1. Ultra-thin inorganic oxide and nitride films as an alternative blocking layer for electrochemical sensors

   https://doi.org/10.1016/j.tsf.2025.140712  

   McHenry, Adam; Jolly, Grant; Young, Thomas; Brothers, Michael; Coyle, Victoria; Kim, Steve; Heikenfeld, Jason (August 2025, Thin Solid Films)

   The desire to translate biosensors for real time molecular monitoring has intensified due to the commercial success of 2-week continuous glucose monitors. However, a common limitation for emerging biosensors is that their lifetimes are often too short for commercially expected benchmarks of at least 3-day and ideally 2-week operation. Electrochemical sensors remain the preferred format of biochemical sensing thanks to their low cost, size, weight, and power requirements for mobile deployment. When exposed to biological fluid, all electrochemical sensors require a blocking layer to protect the electrode surface from fouling and redox interferents. Traditional blocking layer approaches rely on self-assembled monolayers which are often fragile to biological interferents like proteins and require specific electrode materials to improve their stability. Presented here is an evaluation of ultra-thin inorganic oxide and nitride films as an alternative to self-assembled monolayer blocking layers. Specifically, silicon oxide, silicon nitride, and aluminum oxide films were deposited by electron beam evaporation or atomic layer deposition at thicknesses of several nanometers to mimic the electrical capacitance of a conventional monolayer blocking layer. These oxide films were characterized over 7-days and demonstrated to provide poor protection against interfering redox currents from dissolved ferricyanide (150 - 300 µA/cm2) and oxygen reduction interference (30 - 60 µA/cm2). The oxide films were then used as a blocking layer in an electrochemical aptamer sensor using the previously published aptamer for phenylalanine. The phenylalanine sensor showed a binding affinity stronger than found in literature, but a reduced signal gain (∼ 20 % change in methylene blue redox current compared to the expected 50 % previously published on gold). It is speculated and supported by literature that these oxide and nitride films gradually dissolve over periods of days in an aqueous environment. Results further show that if lower quality oxide or nitride films are used, they may be more stable, but at the cost of initially higher in currents. While oxide and nitride films fail to improve upon the performance of thiol-blocking layers on gold electrodes, they may provide utility in some applications by allowing for alternate electrode materials and surfaces to be used instead of traditional self-assembled monolayers on gold electrodes. 

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2. Stability of organic permeable base transistors

   https://doi.org/10.1063/1.5125233  

   Subedi, Kashi; Al-Shadeedi, Akram; Lussem, Bjorn (November 2019, Applied physics letters)

   Organic Permeable Base Transistors (OPBTs) reach a very high transit frequency and large on-state currents. However, for a later commercial application of this technology, a high operational stability is essential as well. Here, the stability of OPBTs during continuous cycling and during base bias stress is discussed. It is observed that the threshold voltage of these transistors shifts toward more positive base voltages if stressed by applying a constant potential to the base electrode for prolonged times. With the help of a 2D device simulation, it is proposed that the observed instabilities are due to charges that are trapped on top of an oxide layer formed around the base electrode. These charges are thermally released after removing the stress, and the device reaches its initial performance after around 24–48 h. 

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3. Impact of a prestrained graded InGaN/GaN interlayer towards enhanced optical characteristics of a multi-quantum well LED based on silicon substrate

   https://doi.org/10.1364/AO.470083  

   Das, Samadrita; Lenka, Trupti_Ranjan; Talukdar, Fazal_Ahmed; Sadaf, Sharif_Md; Velpula, Ravi_Teja; Nguyen, Hieu_Pham_Trung (October 2022, Applied Optics)

   This paper presents alternate pairs of InGaN/GaN prestrained layers with varying indium compositions, which are inserted between the GaN/InGaN MQW active region and the n-GaN layer in a light-emitting diode (LED) nanostructure in order to obtain enhanced optical characteristics. The device is mounted on a silicon substrate followed by a GaN buffer layer that promotes charge injection by minimizing the energy barrier between the electrode and active layers. The designed device attains more than 2.897% enhancement in efficiency when compared with the conventional LED, which is attributed to the reduction of a polarization field within the MQW region. The proposed device with 15% indium composition in the prestrained layer attains a maximum efficiency of 85.21% and a minimized efficiency droop of 3.848% at an injection current of 40 mA, with high luminous power in the output spectral range. The device also shows a minimum blueshift in the spectral range, indicating a decrease in the piezoelectric polarization. 

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4. 3D Printed MXene Aerogels with Truly 3D Macrostructure and Highly Engineered Microstructure for Enhanced Electrical and Electrochemical Performance

   https://doi.org/10.1002/adma.202104980  

   Tetik, Halil; Orangi, Jafar; Yang, Guang; Zhao, Keren; Mujib, Shakir_Bin; Singh, Gurpreet; Beidaghi, Majid; Lin, Dong (November 2021, Advanced Materials)

   Abstract Assembling 2D materials such as MXenes into functional 3D aerogels using 3D printing technologies gains attention due to simplicity of fabrication, customized geometry and physical properties, and improved performance. Also, the establishment of straightforward electrode fabrication methods with the aim to hinder the restack and/or aggregation of electrode materials, which limits the performance of the electrode, is of great significant. In this study, unidirectional freeze casting and inkjet‐based 3D printing are combined to fabricate macroscopic porous aerogels with vertically aligned Ti₃C₂T_xsheets. The fabrication method is developed to easily control the aerogel microstructure and alignment of the MXene sheets. The aerogels show excellent electromechanical performance so that they can withstand almost 50% compression before recovering to the original shape and maintain their electrical conductivities during continuous compression cycles. To enhance the electrochemical performance, an inkjet‐printed MXene current collector layer is added with horizontally aligned MXene sheets. This combines the superior electrical conductivity of the current collector layer with the improved ionic diffusion provided by the porous electrode. The cells fabricated with horizontal MXene sheets alignment as current collector with subsequent vertical MXene sheets alignment layers show the best electrochemical performance with thickness‐independent capacitive behavior. 

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5. Design and novel turn-off mechanism in transistor lasers

   Wu, B; Dallesasse, J; Leburton, J-P (July 2021, JPhys photonics)

   null (Ed.)

   We provide a quantitative analysis of the spontaneous recombination time in the quantum well (QW) of a transistor laser (TL) that shows that owing to the heavy doping in the base of the transistor, Auger recombination is responsible for the short carrier lifetime and low quantum efficiency of the device. By taking advantage of the QW location close to the collector in the TL three-terminal configuration, we devise a new turn-off mechanism that results in quick electron tunneling through the QW barrier by applying a high base-collector reverse bias to deplete the QW and suppress further recombination. For practical base-collector reverse bias, tunneling time from the QW is on the order of 10th of picosecond, which with a lighter base doping density would simultaneously achieve a fast TL turn-off response, while reducing Auger recombination. 

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