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1. Remote surface optical phonon scattering in ferroelectric Ba _0.6 Sr _0.4 TiO ₃ gated graphene

   https://doi.org/10.1063/5.0106939  

   Chen, Hanying; Li, Tianlin; Hao, Yifei; Rajapitamahuni, Anil; Xiao, Zhiyong; Schoeche, Stefan; Schubert, Mathias; Hong, Xia (October 2022, Journal of Applied Physics)

   We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba 0.6 Sr 0.4 TiO 3 films, with field effect mobility up to 23 000 cm 2  V −1  s −1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba 0.6 Sr 0.4 TiO 3 , from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for by considering the scattering from the intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter dominated by the mode at 35.8 meV. Our study reveals the room temperature mobility limit of ferroelectric-gated graphene transistors imposed by RSO phonon scattering. 

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2. Significant ballistic thermal transport across graphene layers: Effect of nanoholes and lithium intercalation

   https://doi.org/10.1063/5.0275738  

   Crosby, John; Cui, Haoran; Wang, Yan (August 2025, Applied Physics Letters)

   Porous graphene and graphite are increasingly utilized in electrochemical energy storage and solar-thermal applications due to their unique structural and thermal properties. In this study, we conduct a comprehensive analysis of the lattice thermal transport and spectral phonon characteristics of holey graphite and multilayer graphene. Our results reveal that phonon modes propagating obliquely with respect to the graphene basal planes are the primary contributors to cross-plane thermal transport. These modes exhibit a predominantly ballistic nature, resulting in an almost linear increase in cross-plane thermal conductivity with the number of layers. The presence of nanoholes in graphene induces a broadband suppression of cross-plane phonon transport, whereas lithium-ion intercalation shows potential to enhance it. These findings provide critical insights into the mechanisms governing cross-plane heat conduction in key graphene-based structures, offering valuable guidance for thermal management and engineering of van der Waals materials. 

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3. A Surface Modification Strategy Towards Reversible Na-ion Intercalation on Graphitic Carbon Using Fluorinated Few-Layer Graphene

   https://doi.org/10.1149/1945-7111/ac9c33  

   Sarbapalli, Dipobrato; Lin, Yu-Hsiu; Stafford, Sean; Son, Jangyup; Mishra, Abhiroop; Hui, Jingshu; Nijamudheen, A; Romo, Adolfo I.; Gossage, Zachary T.; van der Zande, Arend M.; et al (October 2022, Journal of The Electrochemical Society)

   Na-ion batteries (NIBs) are proposed as a promising candidate for beyond Li-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na + intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na + intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC 14–18 . These stoichiometries are higher than the previously reported values of NaC 186 in graphite. Our experiments revealed that reversible Na + ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs. 

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4. Distinct spin–lattice and spin–phonon interactions in monolayer magnetic CrI ₃

   https://doi.org/10.1039/c8cp03599g  

   Webster, Lucas; Liang, Liangbo; Yan, Jia-An (January 2018, Physical Chemistry Chemical Physics)

   We apply the density-functional theory to study various phases (including non-magnetic (NM), anti-ferromagnetic (AFM), and ferromagnetic (FM)) in monolayer magnetic chromium triiodide (CrI 3 ), a recently fabricated 2D magnetic material. It is found that: (1) the introduction of magnetism in monolayer CrI 3 gives rise to metal-to-semiconductor transition; (2) the electronic band topologies as well as the nature of direct and indirect band gaps in either AFM or FM phases exhibit delicate dependence on the magnetic ordering and spin–orbit coupling; and (3) the phonon modes involving Cr atoms are particularly sensitive to the magnetic ordering, highlighting distinct spin–lattice and spin–phonon coupling in this magnet. First-principles simulations of the Raman spectra demonstrate that both frequencies and intensities of the Raman peaks strongly depend on the magnetic ordering. The polarization dependent A 1g modes at 77 cm −1 and 130 cm −1 along with the E g mode at about 50 cm −1 in the FM phase may offer a useful fingerprint to characterize this material. Our results not only provide a detailed guiding map for experimental characterization of CrI 3 , but also reveal how the evolution of magnetism can be tracked by its lattice dynamics and Raman response. 

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5. Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor

   Yiping Wang, Jesse Balgley (November 2020, Nano letters)

   null (Ed.)

   Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with ab initio calculations establish the large work function and narrow bands of α-RuCl3 enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe2, and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride. Short-ranged lateral doping (≤65 nm) and high homogeneity are achieved in proximate materials with a single layer of α-RuCl3. This leads to the best-reported monolayer graphene mobilities (4900 cm2 /(V s)) at these high hole densities (3 × 1013 cm−2 ) and yields larger charge transfer to bilayer graphene (6 × 1013 cm−2). 

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