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1. Introducing gallium in silicon and thin film polysilicon using self assembled monolayer doping

   https://doi.org/https://doi.org/10.1016/j.matlet.2022.132839  

   Carolyn Spaulding; Alex Taylor; Scott Williams; Glenn Packard; Gabriel Curvacho; Santosh Kurinec (October 2022, Materials letters)

   Aldo R. Boccaccini (Ed.)

   Monolayer Doping (MLD) is a technique involving the fmmation of a self-assembled dopant-containing layer on the substrate. The dopant is subsequently incorporated into the substrate by annealing, fmming a diffused region. Following MLD, samples were capped with silicon dioxide and rapid the1mal annealed (RTA). In this work, gallium doping using MLD has been demonstrated. Gallium containing compound Tris (2,4 pentanedionato) gallium(III) was synthesized, and shown to be suitable for monolayer doping silicon subsa-ates and deposited thin film polysi!icon. Seconda1y ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements were performed to determine the dopant profiles and dopant elecu-ical activation. TI1ese results showed that a dose of l.6*1015 atoms/cm2 was received, and the gallium dopant produced a 0.2 µm junction in 11-type silicon. For polysilicon, tlle entire 0.4 µm film was evenly doped, witll a concenu-ation greater than 1019 atoms/cm3 tllroughout. 

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2. First Measurements of a Microwave Frequency Comb with a Semiconductor Sample in a Scanning Tunneling Microscope

   https://doi.org/10.1109/WMED.2016.7458278  

   Rhoades, Chad; Rasmussen, Joel; Bowles, Patrick H.; Hagmann, Mark J.; Yarotski, Dmitry A. (April 2016, First Measurements of a Microwave Frequency Comb with a Semiconductor Sample in a Scanning Tunneling Microscope)

   The first two harmonics of a microwave frequency comb (MFC) were measured at a probe which must be within 1 mm of the tunneling junction at the surface of a semiconductor as the sample electrode in a scanning tunneling microscope. The MFC was generated using a passively mode-locked Ti:Sapphire laser with GaN, but lasers with lower photon energy would be required with silicon. The attenuation of the MFC is primarily caused by the spreading resistance in a sub-nm spot at the tunneling junction. Thus, the measured attenuation could be used to determine the carrier density at this spot as an extension of scanning spreading resistance microscopy (SSRM). We anticipate that this effect will enable new nondestructive methods for sub-nm carrier profiling of semiconductors. 

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3. Model supports asymmetric regulation across the intercellular junction for collective cell polarization

   https://doi.org/10.1371/journal.pcbi.1012216  

   Levandosky, Katherine; Copos, Calina (December 2024, PLOS Computational Biology)

   Vavylonis, Dimitrios (Ed.)

   Symmetry breaking, which is ubiquitous in biological cells, functionally enables directed cell movement and organized embryogenesis. Prior to movement, cells break symmetry to form a well-defined cell front and rear in a process called polarization. In developing and regenerating tissues, collective cell movement requires the coordination of the polarity of the migration machineries of neighboring cells. Though several works shed light on the molecular basis of polarity, fewer studies have focused on the regulation across the cell-cell junction required for collective polarization, thus limiting our ability to connect tissue-level dynamics to subcellular interactions. Here, we investigated how polarity signals are communicated from one cell to its neighbor to ensure coordinated front-to-rear symmetry breaking with the same orientation across the group. In a theoretical setting, we systematically searched a variety of intercellular interactions and identified that co-alignment arrangement of the polarity axes in groups of two and four cells can only be achieved with strong asymmetric regulation of Rho GTPases or enhanced assembly of complementary F-actin structures across the junction. Our results held if we further assumed the presence of an external stimulus, intrinsic cell-to-cell variability, or larger groups. The results underline the potential of using quantitative models to probe the molecular interactions required for macroscopic biological phenomena. Lastly, we posit that asymmetric regulation is achieved through junction proteins and predict that in the absence of cytoplasmic tails of such linker proteins, the likeliness of doublet co-polarity is greatly diminished. 

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4. Zinc Oxide/Molybdenum Disulfide as Nanocomposite for Multifunctional Sensor Prototype

   https://doi.org/10.3390/mi16040358  

   Palomera, Netzahualcóyotl; Feng, Peter (April 2025, Micromachines)

   Different materials are studied for environmental gas sensors as well as photodetection prototypes. A ZnO/MoS2 p-n junction was synthetized to act as a multifunctional sensor prototype. After the ZnO was prepared on a silicon substrate by using DC sputtering at room temperature, molybdenum disulfide layers were spin-coated on a nanostructured zinc oxide flake-shaped surface to form an active layer. The heterostructure’s composite surface was examined using scanning electron microscopy, energy-dispersed X-ray, and Raman spectroscopy. Responses to light frequencies, light intensities, and gas chemical tracing were characterized, revealing an enhanced multifunctional performance of the prototype. Characterizations of light-induced photocurrents indicted that the obtained response strength (photocurrent/illumination light power) was up to 0.01 A/W, and the response time was less than 5 ms. In contrast, the gas-sensing measurements showed that its response strength (variation in resistance/original resistance) was up to 3.7% and the response time was down to 150 s when the prototype was exposed to ammonia gas, with the concentration down to 168 ppm. The fabricated prototype appears to have high stability and reproducibility, quick response and recovery times, as well as a high signal-to-noise ratio. 

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5. Investigating charge transport in a p -Si/ n -poly(benzimidazobenzophenanthroline)-BBL thin film heterojunction diode

   https://doi.org/10.1088/1361-648X/adcdb0  

   Cruz-Arzon, Alejandro J; Pinto, Nicholas J (April 2025, Journal of Physics: Condensed Matter)

   Abstract The physics of charge transport across the interface in an inorganic Si/organic conducting polymer junction diode has received little attention compared to the inorganicp–nsilicon diode. One reason is the amorphous nature of the organic polymer and the polymer chain orientation which introduces disorder and barriers to charge flow. Herein we first present an easy technique to fabricate an inorganic/organic,p-Si/n-poly(benzimidazobenzophenanthroline-BBL) junction diode. The physics of charge transport across the heterojunction, and in the BBL film is then analyzed from the device current-voltage characteristics as a function of temperature in the range 150 K <T< 370 K. The temperature dependence of the diode ideality parameter and of the saturation current density demonstrate that tunneling enhanced charge recombination via exponential trap distributions in the depletion region was responsible for charge transport across the junction. Furthermore, the temperature dependence of the diode conductance revealed that thermal activation and hopping both contributed to charge transport in the BBL film away from the junction. BBL is a ladder polymer with a discrete layered crystal structure that is oriented perpendicular to the substrate. Such polymer chain orientation, combined with a distribution of bond lengths and numerous conjugation paths available for charge delocalization result in the multiple charge transport mechanisms as observed in the diode. 

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