Erratum to:Tribological behaviour of Ti_(3)C_(2)T_(x)nano-sheets:Substrate-dependent tribo-chemical reactions

Erratum to Alberto Rota,Nicolas Bellina,Bo Wang&Andreas Rosenkranz.Tribological behaviour of Ti_(3)C_(2)T_(x)nano-sheets:Substratedependent tribo-chemical reactions.Friction 11(8):1522–1533(2023).

Tribological behaviour of Ti_(3)C_(2)T_(x) nano-sheets: Substrate-dependent tribo-chemical reactions

MXenes,a newly emerging class of layered two dimensional(2D)materials,are promising solid lubricants due to their 2D structure consisting of weakly-bonded layers with a low shear strength and ability to form beneficial tribo-layers.This work aims at evaluating for the first time MXenes lubrication performance and tribofilm formation ability on different metallic substrates(mirror-lapped Fe and Cu discs).After depositing MXenes via ethanol(1 wt%)on the substrates,pronounced differences in the resulting substrate-dependent frictional evolution are observed.While MXenes are capable to reduce friction for both substrates after the full evaporation of ethanol,MXenes lubricating effect on Cu is long-lasting,with a 35-fold increased lifetime compared to Fe.Raman spectra acquired in the wear-tracks of the substrates and counter-bodies reveal notable differences in the friction-induced chemical changes depending on the substrate material.In case of Fe,the progressive failure of MXenes lubrication generates different Fe oxides on both the substrate and the ball,resulting in continuously increasing friction and a poor lubrication effect.For Cu,sliding induces the formation of a Ti_(3)C_(2)-based tribofilm on both rubbing surfaces,enabling a long-lasting lubricating effect.This work boosts further experimental and theoretical work on MXenes involved tribo-chemical processes.

Frequency-tunable continuous-wave random lasers at terahertz frequencies

Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence.However,for many applications ranging from sensing and spectroscopy to speckle-free imaging,it is essential to have high-radiance sources operating in continuous-wave(CW).In this paper,we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional(2D)random distribution of air holes is patterned into the top metal waveguide.We obtain a highly collimated vertical emission at ~3 THz,with a 430 GHz bandwidth,device operation up to 110 K,peak(pulsed)power of 21 mW,and CW emission of 1.7 mW.Furthermore,we show that an external cavity formed with a movable mirror can be used to tune a random laser,obtaining continuous frequency tuning over 11 GHz.

Unveiling the detection dynamics of semiconductor nanowire photodetectors by terahertz near-field nanoscopy

Semiconductor nanowire field-effect transistors represent a promising platform for the development of roomtemperature(RT)terahertz(THz)frequency light detectors due to the strong nonlinearity of their transfer characteristics and their remarkable combination of low noise-equivalent powers(<1 nW Hz^(−1/2))and high responsivities(>100 V/W).Nano-engineering an NW photodetector combining high sensitivity with high speed(subns)in the THz regime at RT is highly desirable for many frontier applications in quantum optics and nanophotonics,but this requires a clear understanding of the origin of the photo-response.Conventional electrical and optical measurements,however,cannot unambiguously determine the dominant detection mechanism due to inherent device asymmetry that allows different processes to be simultaneously activated.Here,we innovatively capture snapshots of the photo-response of individual InAs nanowires via high spatial resolution(35 nm)THz photocurrent nanoscopy.By coupling a THz quantum cascade laser to scattering-type scanning near-field optical microscopy(s-SNOM)and monitoring both electrical and optical readouts,we simultaneously measure transport and scattering properties.The spatially resolved electric response provides unambiguous signatures of photo-thermoelectric and bolometric currents whose interplay is discussed as a function of photon density and material doping,therefore providing a route to engineer photo-responses by design.

Continuous-wave laser operation of a dipole antenna terahertz microresonator

Resonators and the way they couple to external radiation rely on very different concepts if one considers devices belonging to the photonic and electronic worlds.The terahertz frequency range,however,provides intriguing possibilities for the development of hybrid technologies that merge ideas from both fields in novel functional designs.In this paper,we show that high-quality,subwavelength,whispering-gallery lasers can be combined to form a linear dipole antenna,which creates a very efficient,lowthreshold laser emission in a collimated beam pattern.For this purpose,we employ a terahertz quantum-cascade active region patterned into two 19-μm-radius microdisks coupled by a suspended metallic bridge,which simultaneously acts as an inductive antenna and produces the dipole symmetry of the lasing mode.Continuous-wave vertical emission is demonstrated at approximately 3.5 THz in a very regular,low-divergence(±10°)beam,with a high slope efficiency of at least 160 mWA^(−1) and a mere 6 mA of threshold current,which is ensured by the ultra-small resonator size(VRES/λ^(3)≈10^(−2)).The extremely low power consumption and the superior beam brightness make this concept very promising for the development of miniaturized and portable THz sources to be used in the field for imaging and sensing applications as well as for exploring novel optomechanical intracavity effects.

Modulation of the magnetic properties of gold-spinel ferrite heterostructured nanocrystals

The rational design of complex nanostructures is of paramount importance to gain control over their chemical and physical properties.Recently,magnetic-plasmonic heterostructured nanocrystals have been recognized as key players in nanomedicine as multifunctional therapeutic-diagnostic tools and in catalysis.Here we show how the properties of gold-iron oxide heterostructured nanocrystals can be tuned by chemical doping of the magnetic subunit.The divalent cations in the iron oxide were substituted with cobalt and manganese to obtain a general formula Au-MFe2O4(M=Fe,Co,Mn).Magnetic properties of the heterostructures could be tuned,while maintaining well-defined plasmon resonance signatures,confirming the dual magnetic-plasmonic functional capability of these nanostructures.

Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns

Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation.Once implemented on the top surface of a semiconductor laser,a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature.Therefore,this methodology offers the possibility to achieve efficient emission,combined with tailored spectra and controlled beam divergence.Here,we apply this concept to a onedimensional quantum cascade wire laser.By lithographically patterning a series of air slits with different widths,following the Octonacci sequence,on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies,we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth,achieving a maximum peak optical power of 240mW(190 mW)in multimode(single-frequency-mode)lasers,with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η≈1%.