Nanoscale Disorder Generates Subdiffusive Heat Transport in Self-Assembled Nanocrystal Films

Utterback, James K.; Sood, Aditya; Coropceanu, Igor; Güzeltürk, Burak; Talapin, Dmitri V.; Lindenberg, Aaron M.; Ginsberg, Naomi S.

doi:10.1021/acs.nanolett.1c00413

Cited by 8 publications

(13 citation statements)

References 51 publications

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“…These measurements directly track the motion of excitons in real space with picosecond resolution and few-nanometer precision. Contrast in stroboSCAT is generated by pump-induced changes to material polarizability, ,, and is thus sensitive to species such as momentum-dark excitons because their presence modifies the polarizability of optically allowed transitions, even if there is no direct population exchange between dark and bright excitons. In contrast, photoluminescence (PL), a powerful contrast mechanism often used for spatiotemporal imaging of exciton transport in TMDs, − requires population transfer from dark to bright states followed by recombination through momentum-allowed channels, or alternative brightening mechanisms, to be sensitive to momentum-dark excitons at room temperature.…”

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confidence: 99%

Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors

Cheng

et al. 2022

Nano Lett.

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The optoelectronic and transport properties of two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are highly susceptible to external perturbation, enabling precise tailoring of material function through post-synthetic modifications. Here we show that nanoscale inhomogeneities known as nanobubbles can be used for both strain and, less invasively, dielectric tuning of exciton transport in bilayer tungsten disulfide (WSe2). We use ultrasensitive spatiotemporally resolved optical scattering microscopy to directly image exciton transport, revealing that dielectric nanobubbles are surprisingly efficient at funneling and trapping excitons at room temperature, even though the energies of the bright excitons are negligibly affected. Our observations suggest that exciton funneling in dielectric inhomogeneities is driven by momentum-indirect (dark) excitons whose energies are more sensitive to dielectric perturbations than bright excitons. These results reveal a new pathway to control exciton transport in 2D semiconductors with exceptional spatial and energetic precision using dielectric engineering of dark state energetic landscapes. Main text:Two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are van der Waals materials that hold great promise for nanoscale optoelectronics thanks to their strong light-matter interactions even at the atomically-thin limit. The optoelectronic properties of 2D TMDs are in large part governed by their Coulomb-bound electron-hole pairs (excitons), with relatively large binding energies of up to hundreds of milli-electronvolts (meV) due to weak out-of-plane dielectric screening. [1][2][3][4][5][6] Unlike free charges, excitons are charge neutral and are therefore difficult to manipulate with external electric fields in electronic devices. [7][8][9] Therefore, the transport properties of excitons are largely dictated by random, diffusive motion with no long-range directionality, limiting their use as information and energy carriers. Finding new ways to manipulate exciton transport in 2D TMDs without radically altering other material properties would result in excitonic devices that combine strong light-matter interactions and precise control over energy and information flow in atomically thin materials.An attractive route to controlling the properties of 2D TMDs is to leverage their extreme sensitivity to extrinsic factors such as strain, 10-21 and dielectric screening by the environment (Figure 1a), 5,[22][23][24][25][26] enabling post-synthetic tuning of their optoelectronic and transport properties. For example, tensile strain reduces the optical transition energy of 2D TMDs; 16,18,27,28 localized strain regions thus create energy gradients that can funnel and trap excitons in nanoscale low-energy sites, a process that was leveraged to create long-lived quantum emitters. 14,[29][30][31][32][33] Strain engineering, however, is difficult to control over macroscopic scales and can introduce undesired disorder.A less invasive and in principle more contr...

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Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors

Cheng

et al. 2022

Nano Lett.

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“…6,7,5 Non-diffusive heat transport can lead to a substantial reduction of the phonon thermal conductivity of the material, resulting in erroneous absolute temperature and heat transport predictions when employing bulk thermal parameters. 8 Although non-diffusive thermal transport has been observed in nanoparticles, 9,10 nanoparticle disordered lms, 11 and nanowire arrays, 12 studying thermal dynamics and discriminating between heat propagation regimes remains a big challenge, especially for nano uids. Current techniques including time-domain thermore ectance, 13 scanning thermal microscopy, 14 transient thermal grating, 15 and other microscale imaging techniques 16 are relatively complex and limited only to surface probing.…”

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confidence: 99%

“…Luminescent thermometers with spatially-delayed temperature sensing were synthesized by hot-injection thermal decomposition which facilitates layer-by-layer growth of the UCNPs and allows to place Ln 3+ dopants at the designated positions, henceforth thermometric layers (Supplementary Section I, Figs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Er 3+ ,Yb 3+ and Tm 3+ ,Yb 3+ co-dopants were rationally introduced in the NaGdF 4 host (Fig.…”

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confidence: 99%

Untangling heat transport dynamics using luminescence nanothermometry

Brites

Skripka

Benayas

et al. 2022

Preprint

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Temperature touches all aspects of our daily life, including climate, production plants, food storage, transportation, metrology, microelectronics, and medicine, and is a major factor dictating performance of nanotechnologies.1-4 However, while the heat transfer is well understood in bulk, neither experimental nor theoretical models provide a complete picture of the thermal dynamics at the nanoscale.5-7 Here, in situ luminescence thermometry is used to probe the heat propagation taking place within lanthanide (Ln3+)-doped upconverting nanoparticles (UCNPs). We have designed UCNPs with Er3+ and Tm3+ thermometric layers positioned at different locations relative to their surface, varying the distance a heat wave travels before encountering the layers. Despite being separated only by a few tens of nanometers, the thermometric layer closer to the surface of UCNPs detects temperature increase much earlier than the one located at the center – yielding the heat propagation speed in UCNPs ~1.3 nm/s. The UCNPs featuring the two thermometric layers in a single nanostructure confirmed the above result and allowed us to uncover diffusive and non-diffusive (ballistic) heat transport regimes, as well as their interplay and complex heat exchange dynamics taking place in colloidal nanoparticles (nanofluids) at a room temperature.

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“…Atomic defects are ubiquitous in two-dimensional (2D) materials with van der Waals bonds and have the potential to significantly modulate properties and bring about useful functionalities. , Together with interactions due to charge, orbital, spin, and lattice degrees of freedom, inhomogeneity due to nanoscale defects leaves a significant imprint on electronic and thermal transport properties. , …”

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confidence: 99%

“…1,2 Together with interactions due to charge, orbital, spin, and lattice degrees of freedom, inhomogeneity due to nanoscale defects leaves a significant imprint on electronic and thermal transport properties. 3,4 The Boltzmann equation has been widely used in the past century to explain transport properties in solids. 5−9 A cornerstone of the Boltzmann transport model is Matthiessen's rule, which treats all scattering processes as independent and additive.…”

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Mooij Law Violation from Nanoscale Disorder

Wang

Naamneh

et al. 2022

Nano Lett.

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Nanoscale inhomogeneity can profoundly impact properties of two-dimensional van der Waals materials. Here, we reveal how sulfur substitution on the selenium atomic sites in Fe1–y Se1–x S x (0 ≤ x ≤ 1, y ≤ 0.1) causes Fe–Ch (Ch = Se, S) bond length differences and strong disorder for 0.4 ≤ x ≤ 0.8. There, the superconducting transition temperature T c is suppressed and disorder-related scattering is enhanced. The high-temperature metallic resistivity in the presence of strong disorder exceeds the Mott limit and provides an example of the violation of Matthiessen’s rule and the Mooij law, a dominant effect when adding moderate disorder past the Drude/Matthiessen’s regime in all materials. The scattering mechanism responsible for the resistivity above the Mott limit is unrelated to phonons and arises for strong Se/S atom disorder in the tetrahedral surrounding of Fe. Our findings shed light on the intricate connection between the nanostructural details and the unconventional scattering mechanism, which is possibly related to charge-nematic or magnetic spin fluctuations.

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Nanoscale Disorder Generates Subdiffusive Heat Transport in Self-Assembled Nanocrystal Films

Cited by 8 publications

References 51 publications

Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors

Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors

Untangling heat transport dynamics using luminescence nanothermometry

Mooij Law Violation from Nanoscale Disorder

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