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1. Preferentially oriented growth of diamond films on silicon with nickel interlayer

   https://doi.org/10.1007/s42452-022-05092-y  

   K.C., Anupam ; Siddique, Anwar ; Anderson, Jonathan ; Saha, Rony ; Gautam, Chhabindra ; Ayala, Anival ; Engdahl, Chris ; Holtz, Mark W. ; Piner, Edwin L. ( July 2022 , SN Applied Sciences)

   A multistep deposition technique is developed to produce highly oriented diamond films by hot filament chemical vapor deposition (HFCVD) on Si (111) substrates. The orientation is produced by use of a thin, 5–20 nm, Ni interlayer. Annealing studies demonstrate diffusion of Ni into Si to form nickel silicides with crystal structure depending on temperature. The HFCVD diamond film with Ni interlayer results in reduced non-diamond carbon, low surface roughness, high diamond crystal quality, and increased texturing relative to growth on bare silicon wafers. X-ray diffraction results show that the diamond film grown with 10 nm Ni interlayer yielded 92.5% of the diamond grains oriented along the (110) crystal planes with ~ 2.5 µm thickness and large average grain size ~ 1.45 µm based on scanning electron microscopy. Texture is also observed to develop for ~ 300 nm thick diamond films with ~ 89.0% of the grains oriented along the (110) crystal plane direction. These results are significantly better than diamond grown on Si (111) without Ni layer with the same HFCVD conditions. The oriented growth of diamond film on Ni interlayers is explained by a proposed model wherein the nano-diamond seeds becoming oriented relative to the β₁-Ni₃Si that forms during the diamond nucleation period. The model also explains the silicidation and diamond growthmore »processes.

   High quality diamond film with minimum surface roughness and ~93% oriented grains along (110) crystallographic direction is grown on Si substrate using a thin 5 to 20 nm nickel layer.

   A detailed report on the formation of different phases of nickel silicide, its stability with different temperature, and its role for diamond film texturing at HFCVD growth condition is presented.

   A diamond growth model on Si substrate with Ni interlayer to grow high quality-oriented diamond film is established.

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2. Near-ideal electromechanical coupling in textured piezoelectric ceramics

   https://doi.org/10.1038/s41467-022-31165-y  

   Yan, Yongke ; Geng, Liwei D. ; Liu, Hairui ; Leng, Haoyang ; Li, Xiaotian ; Wang, Yu U. ; Priya, Shashank ( June 2022 , Nature Communications)

   Electromechanical coupling factor,k, of piezoelectric materials determines the conversion efficiency of mechanical to electrical energy or electrical to mechanical energy. Here, we provide an fundamental approach to design piezoelectric materials that provide near-ideal magnitude ofk, via exploiting the electrocrystalline anisotropy through fabrication of grain-oriented or textured ceramics. Coupled phase field simulation and experimental investigation on <001> textured Pb(Mg_1/3Nb_2/3)O₃-Pb(Zr,Ti)O₃ceramics illustrate thatkcan reach same magnitude as that for a single crystal, far beyond the average value of traditional ceramics. To provide atomistic-scale understanding of our approach, we employ a theoretical model to determine the physical origin ofkin perovskite ferroelectrics and find that strong covalent bonding between B-site cation and oxygen viad-phybridization contributes most towards the magnitude ofk. This demonstration of near-idealkvalue in textured ceramics will have tremendous impact on design of ultra-wide bandwidth, high efficiency, high power density, and high stability piezoelectric devices.
3. Beyond Substrates: Strain Engineering of Ferroelectric Membranes

   https://doi.org/10.1002/adma.202003780  

   Pesquera, David ; Parsonnet, Eric ; Qualls, Alexander ; Xu, Ruijuan ; Gubser, Andrew J. ; Kim, Jieun ; Jiang, Yizhe ; Velarde, Gabriel ; Huang, Yen‐Lin ; Hwang, Harold Y. ; et al ( September 2020 , Advanced Materials)

   Strain engineering in perovskite oxides provides for dramatic control over material structure, phase, and properties, but is restricted by the discrete strain states produced by available high‐quality substrates. Here, using the ferroelectric BaTiO₃, production of precisely strain‐engineered, substrate‐released nanoscale membranes is demonstrated via an epitaxial lift‐off process that allows the high crystalline quality of films grown on substrates to be replicated. In turn, fine structural tuning is achieved using interlayer stress in symmetric trilayer oxide‐metal/ferroelectric/oxide‐metal structures fabricated from the released membranes. In devices integrated on silicon, the interlayer stress provides deterministic control of ordering temperature (from 75 to 425 °C) and releasing the substrate clamping is shown to dramatically impact ferroelectric switching and domain dynamics (including reducing coercive fields to <10 kV cm⁻¹and improving switching times to <5 ns for a 20 µm diameter capacitor in a 100‐nm‐thick film). In devices integrated on flexible polymers, enhanced room‐temperature dielectric permittivity with large mechanical tunability (a 90% change upon ±0.1% strain application) is demonstrated. This approach paves the way toward the fabrication of ultrafast CMOS‐compatible ferroelectric memories and ultrasensitive flexible nanosensor devices, and it may also be leveraged for the stabilization of novel phases and functionalities not achievable via direct epitaxial growth.
4. Silicon-doped β -Ga ₂ O ₃ films grown at 1 µ m/h by suboxide molecular-beam epitaxy

   https://doi.org/10.1063/5.0139622  

   Azizie, Kathy ; Hensling, Felix V. ; Gorsak, Cameron A. ; Kim, Yunjo ; Pieczulewski, Naomi A. ; Dryden, Daniel M. ; Senevirathna, M. K. ; Coye, Selena ; Shang, Shun-Li ; Steele, Jacob ; et al ( April 2023 , APL Materials)

   We report the use of suboxide molecular-beam epitaxy ( S-MBE) to grow β-Ga 2 O 3 at a growth rate of ∼1 µm/h with control of the silicon doping concentration from 5 × 10 16 to 10 19  cm −3 . In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98% Ga 2 O, i.e., gallium suboxide, is supplied. Directly supplying Ga 2 O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of β-Ga 2 O 3 by conventional MBE. As a result, a growth rate of ∼1 µm/h is readily achieved at a relatively low growth temperature ( T sub ≈ 525 °C), resulting in films with high structural perfection and smooth surfaces (rms roughness of <2 nm on ∼1 µm thick films). Silicon-containing oxide sources (SiO and SiO 2 ) producing an SiO suboxide molecular beam are used to dope the β-Ga 2 O 3 layers. Temperature-dependent Hall effect measurements on a 1 µm thick film with a mobile carrier concentration of 2.7 × 10 17  cm −3 reveal a room-temperature mobility of 124 cm 2  V −1  s −1 that increases to 627 cm 2  V −1more » s −1 at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working metal–semiconductor field-effect transistors made from these silicon-doped β-Ga 2 O 3 films grown by S-MBE at growth rates of ∼1 µm/h.« less
5. Molybdenum-Suboxide Thin Films as Anode Layers in Planar Lithium Microbatteries

   https://doi.org/10.3390/electrochem1020012  

   Lakshmi-Narayana, Ambadi ; Hussain, Obili M. ; Ramana, Chintalapalle V. ; Camacho-Lopez, Marco ; Abdel-Ghany, Ashraf ; Hashem, Ahmed ; Mauger, Alain ; Julien, Christian M. ( June 2020 , Electrochem)

   In this paper, we investigate the effects of operational conditions on structural, electronic and electrochemical properties on molybdenum suboxides (MoO3-δ) thin films. The films are prepared using pulsed-laser deposition by varying the deposition temperature (Ts), laser fluence (Φ), the partial oxygen pressure (PO2) and annealing temperature (Ta). We find that three classes of samples are obtained with different degrees of stoichiometric deviation without post-treatment: (i) amorphous MoO3-δ (δ < 0.05) (ii) nearly-stoichiometric samples (δ ≈ 0) and (iii) suboxides MoO3-δ (δ > 0.05). The suboxide films 0.05 ≤ δ ≤ 0.25 deposited on Au/Ti/SiO2/flexible-Si substrates with appropriate processing conditions show high electrochemical performance as an anode layer for lithium planar microbatteries. In the realm of simple synthesis, the MoO3-δ film deposited at 450 °C under oxygen pressure of 13 Pa is a mixture of α-MoO3 and Mo8O23 phases (15:85). The electrochemical test of the 0.15MoO3-0.85Mo8O23 film shows a specific capacity of 484 µAh cm−2 µm−1 after 100 cycles of charge-discharge at a constant current of 0.5 A cm−2 in the potential range 3.0-0.05 V.