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1. Epitaxial Growth of Large‐Scale 2D CrTe ₂ Films on Amorphous Silicon Wafers With Low Thermal Budget

   https://doi.org/10.1002/adma.202311591  

   Zhang, Xiaoqian; Li, Yue; Lu, Qiangsheng; Xiang, Xueqiang; Sun, Xiaozhen; Tang, Chunli; Mahdi, Muntasir; Conner, Clayton; Cook, Jacob; Xiong, Yuzan; et al (March 2024, Advanced Materials)

   Abstract 2D van der Waals (vdW) magnets open landmark horizons in the development of innovative spintronic device architectures. However, their fabrication with large scale poses challenges due to high synthesis temperatures (>500 °C) and difficulties in integrating them with standard complementary metal‐oxide semiconductor (CMOS) technology on amorphous substrates such as silicon oxide (SiO₂) and silicon nitride (SiN_x). Here, a seeded growth technique for crystallizing CrTe₂films on amorphous SiN_x/Si and SiO₂/Si substrates with a low thermal budget is presented. This fabrication process optimizes large‐scale, granular atomic layers on amorphous substrates, yielding a substantial coercivity of 11.5 kilo‐oersted, attributed to weak intergranular exchange coupling. Field‐driven Néel‐type stripe domain dynamics explain the amplified coercivity. Moreover, the granular CrTe₂devices on Si wafers display significantly enhanced magnetoresistance, more than doubling that of single‐crystalline counterparts. Current‐assisted magnetization switching, enabled by a substantial spin–orbit torque with a large spin Hall angle (85) and spin Hall conductivity (1.02 ×  10⁷ℏ/2e  Ω⁻¹  m⁻¹), is also demonstrated. These observations underscore the proficiency in manipulating crystallinity within integrated 2D magnetic films on Si wafers, paving the way for large‐scale batch manufacturing of practical magnetoelectronic and spintronic devices, heralding a new era of technological innovation. 

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2. Hydrogen gas sensing using aluminum doped ZnO metasurfaces

   https://doi.org/10.1039/d0na00289e  

   Chatterjee, Sharmistha; Shkondin, Evgeniy; Takayama, Osamu; Fisher, Adam; Fraiwan, Arwa; Gurkan, Umut A.; Lavrinenko, Andrei V.; Strangi, Giuseppe (January 2020, Nanoscale Advances)

   Hydrogen (H 2 ) sensing is crucial in a wide variety of areas, such as industrial, environmental, energy and biomedical applications. However, engineering a practical, reliable, fast, sensitive and cost-effective hydrogen sensor is a persistent challenge. Here we demonstrate hydrogen sensing using aluminum-doped zinc oxide (AZO) metasurfaces based on optical read-out. The proposed sensing system consists of highly ordered AZO nanotubes (hollow pillars) standing on a SiO 2 layer deposited on a Si wafer. Upon exposure to hydrogen gas, the AZO nanotube system shows a wavelength shift in the minimum reflectance by ∼13 nm within 10 minutes for a hydrogen concentration of 4%. These AZO nanotubes can also sense the presence of a low concentration (0.7%) of hydrogen gas within 10 minutes. Their rapid response time even for a low concentration, the possibility of large sensing area fabrication with good precision, and high sensitivity at room temperature make these highly ordered nanotube structures a promising miniaturized H 2 gas sensor. 

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3. Research Toward a Heterogeneously Integrated InGaN Laser on Silicon

   https://doi.org/10.1002/pssa.201900770  

   Kamei, Toshihiro; Kamikawa, Takeshi; Araki, Masahiro; DenBaars, Steven P.; Nakamura, Shuji; Bowers, John E. (December 2019, physica status solidi (a))

   A heterogeneously integrated InGaN laser diode (LD) on Si is proposed as a path toward visible wavelength photonic integrated circuits (PICs) on Si. Herein, InGaN films are vertically stacked on a TiO₂waveguide (WG) fabricated on a Si wafer by bonding. In the light propagation direction, it is composed of a hybrid InGaN/TiO₂section, a TiO₂WG, an adiabatic taper, and mirrors that can form a cavity. As the refractive index of GaN is well matched with that of TiO₂, the optical transverse mode extends to both the GaN and TiO₂in a hybrid mode. Modes between a hybrid InGaN/TiO₂and a pure TiO₂WG can transfer with an adiabatic taper structure. The coupling loss is calculated to be less than 0.5 dB with fairly short taper length of 78 μm and tip width of 200 nm. GaN substrate removal and bonding are critical fabrication steps of this LD and PIC. The substrate removal is successfully done by photoelectrochemical etching. Although direct bonding of GaN wafers with thermal oxide on Si is successful, GaN epitaxial wafers are more difficult. An implication and remedy of this is discussed in terms of surface roughness of GaN epitaxial film. 

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4. Wafer-Scale Synthesis of WS ₂ Films with In Situ Controllable p-Type Doping by Atomic Layer Deposition

   https://doi.org/10.34133/2021/9862483  

   Yang, Hanjie; Wang, Yang; Zou, Xingli; Bai, Rongxu; Wu, Zecheng; Han, Sheng; Chen, Tao; Hu, Shen; Zhu, Hao; Chen, Lin; et al (January 2021, Research)

   Wafer-scale synthesis of p-type TMD films is critical for its commercialization in next-generation electro/optoelectronics. In this work, wafer-scale intrinsic n-type WS₂films and in situ Nb-doped p-type WS₂films were synthesized through atomic layer deposition (ALD) on 8-inchα-Al₂O₃/Si wafers, 2-inch sapphire, and 1 cm²GaN substrate pieces. The Nb doping concentration was precisely controlled by altering cycle number of Nb precursor and activated by postannealing. WS₂n-FETs and Nb-doped p-FETs with different Nb concentrations have been fabricated using CMOS-compatible processes. X-ray photoelectron spectroscopy, Raman spectroscopy, and Hall measurements confirmed the effective substitutional doping with Nb. The on/off ratio and electron mobility of WS₂n-FET are as high as 10⁵and 6.85 cm² V^-1 s^-1, respectively. In WS₂p-FET with 15-cycle Nb doping, the on/off ratio and hole mobility are 10 and 0.016 cm² V^-1 s^-1, respectively. The p-n structure based on n- and p- type WS₂films was proved with a 10⁴rectifying ratio. The realization of controllablein situNb-doped WS₂films paved a way for fabricating wafer-scale complementary WS₂FETs. 

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5. PO and PN in the Envelope of VY Canis Majoris: Elucidating the Chemistry and Origin of Phosphorus

   https://doi.org/10.3847/2041-8213/ad6660  

   Ravi, R.; Singh, A_P; Richards, A_M_S; Humphreys, R_M; Decin, L.; Ziurys, L_M (August 2024, The Astrophysical Journal Letters)

   Abstract TheJ= 5.5 → 4.5 andJ= 5 → 4 transitions of PO and PN, respectively, have been imaged in the envelope of hypergiant star VY Canis Majoris (VY CMa) using the Atacama Large Millimeter/submillimeter Array with angular resolutions of 0.″2 and 1.″5 and data from the Submillimeter Telescope of the Arizona Radio Observatory. These maps are the first high-fidelity images of PO and PN in a circumstellar envelope. Both molecules are primarily present in a spherical, star-centered region with a radius ∼60R_*(0.″5), indicating formation by LTE chemistry and then condensation into grains. PN, however, shows additional, fan-shaped emission 2″ southwest of the star, coincident with dust features resolved by Hubble Space Telescope (HST), as well as four newly identified distinct structures 1″–2″ toward the north, east, and west (Cloudlets I–IV), not visible in HST images. The “SW Fan” and the cloudlets are also prominent in theJ= 5.5 → 4.5 transition of NS. The correlation of PN with NS, SiO, and dust knots in the SW Fan suggests a formation in shocked gas enhanced with nitrogen. Excess nitrogen is predicted to favor PN synthesis over PO. Abundances for PN and PO in the spherical source aref∼ 4.4 × 10⁻⁸and 1.4 × 10⁻⁷, respectively, relative to H₂. Given a cosmic abundance of phosphorus, an unusually high fraction (∼35%) is contained in PO and PN. Alternatively, the stellar winds may be enriched in P (and N) by dredge-up from the interior of VY CMa. 

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