Phase modulated scanning near field optical luminescence imaging as a probe of exciton dark lifetime and diffusivity in persistently luminescent micro- and nanocrystals

Wong, Victor; Yeung, Edith; Cole-André, M.G.; Fanchini, Giovanni

doi:10.1039/d2tc02645g

Cited by 1 publication

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References 67 publications

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“…Near-field thermoreflectance [30,31] is a class of pumpprobe techniques based on super-resolution, aperture-type, scanning near-field optical microscopes (SNOMs) -optical instruments capable of lateral resolution beyond the diffraction limit through the use of evanescent light waves. [32,33] Aperture-type SNOMs make use of atomic-force cantilevers in which nanosized apertures are drilled via focussed ion-beams and, therefore, the acquisition of an atomic force micrograph (AFM) of the sample surface is possible in conjunction with nano-optical imaging. [34][35][36][37][38] In pump-probe near-field thermoreflectance experiments, samples are periodically heated by a pump laser beam from an inverted optical microscope, while periodic changes in the sample's local reflectivity caused by the resulting heat waves are measured, in phase and amplitude, through an upright aperture-type SNOM operating in reflection mode from a low-intensity direct-current (DC) laser ("probe") of wavelength different from the pump.…”

Section: Introductionmentioning

confidence: 99%

Contactless Scanning Near‐Field Optical Dilatometry Imaging at the Nanoscale

Wong,

Ezugwu,

Fanchini

2024

Adv Materials Inter

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To date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring quantitative maps of the thermal expansivity of 2D materials and nanostructured thin films with nanoscale lateral resolution in spite of huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable because probes in contact with the sample significantly perturb any thermal measurements. Here, ω‐2ω near‐field thermoreflectance imaging is presented as a novel, all‐optical, and contactless technique to map the TEC at the nanoscale with precision. Testing of this technique is performed on nanogranular films of gold and multilayer graphene (ML‐G) platelets. With ω‐2ω near‐field thermoreflectance, it is demonstrated that the TEC of Au is higher at the metal‐insulator interface, with an average of (17.12 ± 2.30) ×10−6 K−1 in agreement with macroscopic techniques. For ML‐G, the average TEC is (−5.77 ± 3.79) x10−6 K−1 and is assigned to in‐plane vibrational bending modes. A vibrational‐thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. The nanoscale method here reported demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.

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