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1. Interaction of in-plane Drude carrier with c-axis phonon in PdCoO2

   https://doi.org/10.1038/s41535-023-00607-1  

   Seo, Dongmin ; Ahn, Gihyeon ; Rimal, Gaurab ; Khim, Seunghyun ; Chung, Suk Bum ; Mackenzie, A. P. ; Oh, Seongshik ; Moon, S. J. ; Choi, Eunjip ( December 2023 , npj Quantum Materials)

   We performed polarized reflection and transmission measurements on the layered conducting oxide PdCoO₂thin films. For theab-plane, an optical peak near Ω ≈ 750 cm⁻¹drives the scattering rate 1/τ(ω) and effective massm^*(ω) of the Drude carrier to increase and decrease respectively forω ≧ Ω. For thec-axis, a longitudinal optical phonon (LO) is present at Ω as evidenced by a peak in the loss function Im[−1/ε_c(ω)]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at Ω results from an electron-phonon coupling of theab-plane carrier with thec-LO phonon, which leads to the frequency-dependent 1/τ(ω) andm^*(ω). This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared (IR) band and ac-LO. On the contrary, it is the Drude carrier that couples in PdCoO₂. The coupling between theab-plane Drude carrier andc-LO suggests that thec-LO phonon may play a significant role in the characteristicab-plane electronic properties of PdCoO₂, including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.

    

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2. A Nonheme Mononuclear {FeNO} 7 Complex that Produces N 2 O in the Absence of an Exogenous Reductant

   https://doi.org/10.1002/ange.202109062  

   Dey, Aniruddha ; Gordon, Jesse B. ; Albert, Therese ; Sabuncu, Sinan ; Siegler, Maxime A. ; MacMillan, Samantha N. ; Lancaster, Kyle M. ; Moënne‐Loccoz, Pierre ; Goldberg, David P. ( August 2021 , Angewandte Chemie)

   A new nonheme iron(II) complex, Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1), is reported. Reaction of1with NO_(g)gives a stable mononitrosyl complex Fe(NO)(Me₃TACN)((OSi^Ph2)₂O) (2), which was characterized by Mössbauer (δ=0.52 mm s⁻¹, |ΔE_Q|=0.80 mm s⁻¹), EPR (S=3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2is an {FeNO}⁷complex with anS=3/2 spin ground state. The RR spectrum (λ_exc=458 nm) of2combined with isotopic labeling (¹⁵N,¹⁸O) reveals ν(N‐O)=1680 cm⁻¹, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm⁻¹). Complex2reacts rapidly with H₂O in THF to produce the N‐N coupled product N₂O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N₂O in the absence of an exogenous reductant.

    

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3. A Nonheme Mononuclear {FeNO} 7 Complex that Produces N 2 O in the Absence of an Exogenous Reductant

   https://doi.org/10.1002/anie.202109062  

   Dey, Aniruddha ; Gordon, Jesse B. ; Albert, Therese ; Sabuncu, Sinan ; Siegler, Maxime A. ; MacMillan, Samantha N. ; Lancaster, Kyle M. ; Moënne‐Loccoz, Pierre ; Goldberg, David P. ( August 2021 , Angewandte Chemie International Edition)

   A new nonheme iron(II) complex, Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1), is reported. Reaction of1with NO_(g)gives a stable mononitrosyl complex Fe(NO)(Me₃TACN)((OSi^Ph2)₂O) (2), which was characterized by Mössbauer (δ=0.52 mm s⁻¹, |ΔE_Q|=0.80 mm s⁻¹), EPR (S=3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2is an {FeNO}⁷complex with anS=3/2 spin ground state. The RR spectrum (λ_exc=458 nm) of2combined with isotopic labeling (¹⁵N,¹⁸O) reveals ν(N‐O)=1680 cm⁻¹, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm⁻¹). Complex2reacts rapidly with H₂O in THF to produce the N‐N coupled product N₂O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N₂O in the absence of an exogenous reductant.

    

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4. Distinguishing Optical and Acoustic Phonon Temperatures and Their Energy Coupling Factor under Photon Excitation in nm 2D Materials

   https://doi.org/10.1002/advs.202000097  

   Wang, Ridong ; Zobeiri, Hamidreza ; Xie, Yangsu ; Wang, Xinwei ; Zhang, Xing ; Yue, Yanan ( May 2020 , Advanced Science)

   Under photon excitation, 2D materials experience cascading energy transfer from electrons to optical phonons (OPs) and acoustic phonons (APs). Despite few modeling works, it remains a long‐history open problem to distinguish the OP and AP temperatures, not to mention characterizing their energy coupling factor (G). Here, the temperatures of longitudinal/transverse optical (LO/TO) phonons, flexural optical (ZO) phonons, and APs are distinguished by constructing steady and nanosecond (ns) interphonon branch energy transport states and simultaneously probing them using nanosecond energy transport state‐resolved Raman spectroscopy. ΔT_{OP −AP}is measured to take more than 30% of the Raman‐probed temperature rise. A breakthrough is made on measuring the intrinsic in‐plane thermal conductivity of suspended nm MoS₂and MoSe₂by completely excluding the interphonon cascading energy transfer effect, rewriting the Raman‐based thermal conductivity measurement of 2D materials.G_OP↔APfor MoS₂, MoSe₂, and graphene paper (GP) are characterized. For MoS₂and MoSe₂,G_OP↔APis in the order of 10¹⁵and 10¹⁴W m⁻³K⁻¹andG_ZO↔APis much smaller thanG_LO/TO↔AP. Under ns laser excitation,G_OP↔APis significantly increased, probably due to the reduced phonon scattering time by the significantly increased hot carrier population. For GP,G_LO/TO↔APis 0.549 × 10¹⁶W m⁻³K⁻¹, agreeing well with the value of 0.41 × 10¹⁶W m⁻³K⁻¹by first‐principles modeling.

    

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5. Interface Thermal Resistance between Monolayer WSe 2 and SiO 2 : Raman Probing with Consideration of Optical–Acoustic Phonon Nonequilibrium

   https://doi.org/10.1002/admi.202102059  

   Hunter, Nicholas ; Azam, Nurul ; Zobeiri, Hamidreza ; Van Velson, Nathan ; Mahjouri‐Samani, Masoud ; Wang, Xinwei ( January 2022 , Advanced Materials Interfaces)

   This work explores the 2D interfacial energy transport between monolayer WSe₂and SiO₂while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (ΔT_OA) in various nanostructures upon laser irradiation. Generally, characterizations of interfacial thermal resistance (R′′_tc) at the nanoscale are difficult and depend on Raman‐probed temperature measurements, which only reveal optical phonon temperature information. Here it is shown that ΔT_OAfor supported monolayer WSe₂can be as high as 48% of the total temperature rise revealed by optothermal Raman methods—a significant proportion that can introduce sizeable error toR′′_tcmeasurements if not properly considered. A frequency energy transport state‐resolved Raman technique (FET‐Raman) along with a 3D finite volume modeling of 2D material laser heating is used to extract the true interfacial thermal resistanceR′′_tc(determined by acoustic phonon transport). Additionally, a novel ET‐Raman technique is developed to determine the energy coupling factorGbetween optical and acoustic phonons (on the order of 10¹⁵W m⁻³K⁻¹). This work demonstrates the need for special consideration of thermal nonequilibriums during laser–matter interactions at the nanoscale.

    

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