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1. Lattice and electronic structure of ScN observed by angle-resolved photoemission spectroscopy measurements

   https://doi.org/10.1063/5.0119628  

   Al-Atabi, Hayder A. ; Zhang, Xiaotian ; He, Shanmei ; chen, Cheng ; Chen, Yulin ; Rotenberg, Eli ; Edgar, James H. ( November 2022 , Applied Physics Letters)

   Scandium nitride (ScN) has recently attracted much attention for its potential applications in thermoelectric energy conversion, as a semiconductor in epitaxial metal/semiconductor superlattices, as a substrate for GaN growth, and alloying it with AlN for 5G technology. This study was undertaken to better understand its stoichiometry and electronic structure. ScN (100) single crystals 2 mm thick were grown on a single crystal tungsten (100) substrate by a physical vapor transport method over a temperature range of 1900–2000 °C and a pressure of 20 Torr. The core level spectra of Sc 2p3/2,1/2 and N 1s were obtained by x-ray photoelectron spectroscopy (XPS). The XPS core levels were shifted by 1.1 eV toward higher values as the [Sc]:[N] ratio varied from 1.4 at 1900 °C to ∼1.0 at 2000 °C due to the higher binding energies in stoichiometric ScN. Angle-resolved photoemission spectroscopy measurements confirmed that ScN has an indirect bandgap of ∼1.2 eV.

    

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2. Isotropic plasma-thermal atomic layer etching of aluminum nitride using SF6 plasma and Al(CH3)3

   https://doi.org/10.1116/6.0002476  

   Wang, Haozhe ; Hossain, Azmain ; Catherall, David ; Minnich, Austin J. ( May 2023 , Journal of Vacuum Science & Technology A)

   We report the isotropic plasma atomic layer etching (ALE) of aluminum nitride using sequential exposures of SF6 plasma and trimethylaluminum [Al(CH3)3]. ALE was observed at temperatures greater than 200 °C, with a maximum etch rate of 1.9 Å/cycle observed at 300 °C as measured using ex situ ellipsometry. After ALE, the etched surface was found to contain a lower concentration of oxygen compared to the original surface and exhibited a ∼35% decrease in surface roughness. These findings have relevance for applications of AlN in nonlinear photonics and wide bandgap semiconductor devices. 

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3. Oxygen Incorporation in the Molecular Beam Epitaxy Growth of Sc x Ga 1−x N and Sc x Al 1−x N

   https://doi.org/10.1002/pssb.201900612  

   Casamento, Joseph ; Xing, Huili Grace ; Jena, Debdeep ( January 2020 , physica status solidi (b))

   Secondary‐ion mass spectrometry (SIMS) is used to determine impurity concentrations of carbon and oxygen in two scandium‐containing nitride semiconductor multilayer heterostructures: Sc_xGa_1−xN/GaN and Sc_xAl_1−xN/AlN grown by molecular beam epitaxy (MBE). In the Sc_xGa_1−xN/GaN heterostructure grown in metal‐rich conditions on GaN–SiC template substrates with Sc contents up to 28 at%, the oxygen concentration is found to be below 1 × 10¹⁹ cm⁻³, with an increase directly correlated with the scandium content. In the Sc_xAl_1−xN–AlN heterostructure grown in nitrogen‐rich conditions on AlN–Al₂O₃template substrates with Sc contents up to 26 at%, the oxygen concentration is found to be between 10¹⁹and 10²¹ cm⁻³, again directly correlated with the Sc content. The increase in oxygen and carbon takes place during the deposition of scandium‐alloyed layers.

    

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4. Intrinsically Switchable Dual‐Band Scandium‐Aluminum Nitride Lamb‐Wave Filter

   https://doi.org/10.1002/pssr.202200135  

   Mo, Dicheng ; Rassay, Sushant ; Li, Chao ; Tabrizian, Roozbeh ( August 2022 , physica status solidi (RRL) – Rapid Research Letters)

   A dual‐band scandium‐aluminum nitride (Sc_0.28Al_0.72N) Lamb‐wave bandpass filter is implemented with intrinsically configurable center frequencies at 628 MHz and 1.07 GHz. The filter is created from electrical coupling of dual‐mode resonators with complementary‐switchable operation states defined by spatial polarization tuning in ferroelectric Sc_0.28Al_0.72N film. The resonators are created with patterning interdigitated transducers (IDT) on the top surface and exploit the floating bottom electrode for application of low‐frequency polarization switching pulses. Switching polarization direction under consecutive electrode fingers in unified and alternating directions results in excitation of Lamb modes with different wavelengths equal and twice the IDT pitch size, with a frequency ratio of ≈1.70. The intrinsically configurable dual‐band filter shows bandwidths of 11.9 MHz and 10.8 MHz, insertion losses of 2.6 and 2.8 dB, and on‐off switching isolations of 12 and 9 dB, when operating at 628 MHz and 1.07 GHz, respectively. The intrinsic configuration of center frequency, enabled by ferroelectric polarization switching, highlights the potential of dual‐band scandium‐aluminum nitride Lamb‐wave filters for creation of compact multifrequency spectral processors.

    

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5. An osteogenic magnesium alloy with improved corrosion resistance, antibacterial, and mechanical properties for orthopedic applications

   https://doi.org/10.1002/jbm.a.37476  

   Aboutalebianaraki, Nadia ; Zeblisky, Peter ; Sarker, M. D. ; Jeyaranjan, Aadithya ; Sakthivel, Tamil S. ; Fu, Yifei ; Lucchi, John ; Baudelet, Matthieu ; Seal, Sudipta ; Kean, Thomas J. ; et al ( December 2022 , Journal of Biomedical Materials Research Part A)

   The aim of this study was to develop a novel biodegradable magnesium (Mg) alloy for bone implant applications. We used scandium (Sc; 2 wt %) and strontium (Sr; 2 wt %) as alloying elements due to their high biocompatibility, antibacterial efficacy, osteogenesis, and protective effects against corrosion. In the present work, we also examined the effect of a heat treatment process on the properties of the Mg‐Sc‐Sr alloy. Alloys were manufactured using a metal casting process followed by heat treatment. The microstructure, corrosion, mechanical properties, antibacterial activity, and osteogenic activity of the alloy were assessed in vitro. The results showed that the incorporation of Sc and Sr elements controlled the corrosion, reduced the hydrogen generation, and enhanced mechanical properties. Furthermore, alloying with Sc and Sr demonstrated a significantly enhanced antibacterial activity and decreased biofilm formation compared to control Mg. Also, culturing Mg‐Sc‐Sr alloy with human bone marrow‐derived mesenchymal stromal cells showed a high degree of biocompatibility (>90% live cells) and a significant increase in osteoblastic differentiation in vitro shown by Alizarin red staining and alkaline phosphatase activity. Based on these results, the Mg‐Sc‐Sr alloy heat‐treated at 400°C displayed optimal mechanical properties, corrosion rate, antibacterial efficacy, and osteoinductivity. These characteristics make the Mg‐Sc‐Sr alloy a promising candidate for biodegradable orthopedic implants in the fixation of bone fractures such as bone plate‐screws or intramedullary nails.

    

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