Flexible Large-Area Graphene Films of 50-600 nm Thickness with High Carrier Mobility

Bulk graphene nanofilms feature fast electronic and phonon transport in combination with strong light-matter interaction and thus have great potential for versatile applications,spanning from photonic,electronic,and optoelectronic devices to charge-stripping and electromagnetic shielding,etc.However,large-area flexible close-stacked graphene nanofilms with a wide thickness range have yet to be reported.Here,we report a polyacrylonitrile-assisted’substrate replacement’strategy to fabricate large-area free-standing graphene oxide/polyacrylonitrile nanofilms(lateral size~20 cm).Linear polyacrylonitrile chains-derived nanochannels promote the escape of gases and enable macro-assembled graphene nanofilms(nMAGs)of 50-600 nm thickness following heat treatment at 3,000℃.The uniform nMAGs exhibit 802-1,540 cm^(2)V-1s-1carrier mobility,4.3-4.7 ps carrier lifetime,and>1,581 W m^(-1)K^(-1)thermal conductivity(n MAG-assembled 10μm-thick films,mMAGs).nMAGs are highly flexible and show no structure damage even after 1.0×10^(5)cycles of folding-unfolding.Furthermore,n MAGs broaden the detection region of graphene/silicon heterojunction from near-infrared to mid-infrared and demonstrate higher absolute electromagnetic interference(EMI)shielding effectiveness than state-of-the-art EMI materials of the same thickness.These results are expected to lead to the broad applications of such bulk nanofilms,especially as micro/nanoelectronic and optoelectronic platforms.

Macroscopic assembled graphene nanofilms based room temperature ultrafast mid-infrared photodetectors

Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields,especially in the mid-infrared range.Here,we report a macroscopic assembled graphene(nMAG)nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection.The assembled Schottky diode works in 1.5-4.0μm at room temperature with fast response(20-30 ns,rising time,4 mm2 window)and high detectivity(1.61011 to 1.9109 Jones from 1.5 to 4.0μm)under the pulsed laser,outperforming single-layer-graphene/silicon photodetectors by 2-8 orders.These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption(~40%),long carrier relaxation time(~20 ps),low work function(4.52 eV),and suppressed carrier number fluctuation.The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials,leading to broadband and ultrafast MIR active imaging devices at room temperature.

Intralayer Phonons in Multilayer Graphene Moiré Superlattices

Moirépattern in twisted multilayers(tMLs)induces many emergent phenomena by subtle variation of atomic registry to modulate quasiparticles and their interactions,such as superconductivity,moiréexcitons,and moiréphonons.The periodic superlattice potential introduced by moirépattern also underlies patterned interlayer coupling at the interface of tMLs.Although this arising patterned interfacial coupling is much weaker than in-plane atomic interactions,it is crucial in moirésystems,as captured by the renormalized interlayer phonons in twisted bilayer transitional metal dichalcogenides.Here,we determine the quantitative relationship between the lattice dynamics of intralayer out-of-plane optical(ZO)phonons and patterned interfacial coupling in multilayer graphene moirésuperlattices(MLG-MS)by the proposed perturbation model,which is previously challenging for MLGs due to their out-of-phase displacements of adjacent atoms in one atomic plane.We unveil that patterned interfacial coupling introduces profound modulations on Davydov components of nonfolded ZO phonon that are localized within the AB-stacked constituents,while the coupling results in layer-extended vibrations with symmetry of moirépattern for moiréZO phonons.Our work brings further degrees of freedom to engineer moiréphysics according to the modulations imprinted on the phonon frequency and wavefunction.