Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

Niemelä, Janne-Petteri; Karppinen, Maarit

doi:10.1039/c4dt02550d

Cited by 33 publications

(44 citation statements)

References 36 publications

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“…1(b). The film thickness dictates the small fringes corresponding to the interference minima and maxima of the reflected beam film-air and filmsubstrate interfaces, respectively [33]. The XRR also includes interference maxima with higher intensities that represent constructive interference from the periodic introduction of the organic layers.…”

Section: Methodsmentioning

confidence: 99%

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

et al. 2016

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Nanomaterial interfaces and concomitant thermal resistances are generally considered as atomic-scale planes that scatter the fundamental energy carriers. Given that the nanoscale structural and chemical properties of solid interfaces can strongly influence this thermal boundary conductance, the ballistic and diffusive nature of phonon transport along with the corresponding phonon wavelengths can affect how energy is scattered and transmitted across an interfacial region between two materials. In hybrid composites composed of atomic layer building blocks of inorganic and organic constituents, the varying interaction between the phononic spectrum in the inorganic crystals and vibronic modes in the molecular films can provide a new avenue to manipulate the energy exchange between the fundamental vibrational energy carriers across interfaces. Here, we systematically study the heat transfer mechanisms in hybrid superlattices of atomic-and molecular-layer-grown zinc oxide and hydroquinone with varying thicknesses of the inorganic and organic layers in the superlattices. We demonstrate ballistic energy transfer of phonons in the zinc oxide that is limited by scattering at the zinc oxide/hydroquinone interface for superlattices with a single monolayer of hydroquinone separating the thicker inorganic layers. The concomitant thermal boundary conductance across the zinc oxide interfacial region approaches the maximal thermal boundary conductance of a zinc oxide phonon flux, indicative of the contribution of long wavelength vibrations across the aromatic molecular monolayers in transmitting energy across the interface. This transmission of energy across the molecular interface decreases considerably as the thickness of the organic layers are increased.

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Section: Methodsmentioning

confidence: 99%

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

et al. 2016

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“…19 In brief, the fabrication route consisted of alternate chemisorption of the precursor vapors of TiCl4 (0. 2 s) , H2O ( 0.1 s) and hydroquinone (HQ) (15 s) onto the substrate surface; N2 was used as the carrier gas to transport the precursor vapors into the ALD reactor (Picosun R100), and as a purging gas, that removes any unreacted precursor molecules after each precursor pulse.…”

Section: Methodsmentioning

confidence: 99%

“…16 Besides simple homogeneous hybrid thin-film materials, such a combinatorial approach enables one to fabricate inorganicorganic superlattices with atomic/molecular monolayer precision via self-limiting surface reactions. [17][18][19] The selflimited film growth moreover allows for conformal coating of nanostructures, the key requirement for many future applications. [20][21] Recently, notably low thermal conductivity values were realized for ZnO-based ALD/MLD-fabricated hybrid structures obtained via incorporation of molecular organic layers; this observation has arisen great interest in thermal properties of ALD/MLD hybrid thin films -in particular for low-temperature thermal-barrier and thermoelectric applications.…”

Section: Introductionmentioning

confidence: 99%

Ultra-low thermal conductivity in TiO₂:C superlattices

et al. 2015

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TiO2:C superlattices are fabricated from atomic/molecular layer deposited (ALD/MLD) inorganic-organic [(TiO2)m(Ti-O-C6H4-O-)k=1]n thin films via a post-deposition annealing treatment that converts the as-deposited monomolecular organic layers into sub-nanometerthick graphitic interface layers confined within the TiO2 matrix. The internal graphitic layers act as effective phonon-scattering boundaries that bring about a ten-fold reduction in thermal conductivity of the films with decreasing superlattice period down to an ultra-low value of 0.66±0.04 Wm -1 K -1 -a finding that makes inorganic-C superlattices fabricated with the present method as promising structures for e.g. high-temperature thermal barriers and thermoelectrics. IntroductionMaterials with ultra-low thermal conductivity are needed, e.g., for thermal-barrier and thermoelectric applications; the latter application calls for novel heavily-doped semiconductors able to combine thermal insulation with high electronic conductivity and thermopower. General pathways to suppress thermal transport in fully-dense solid materials exploit the introduction of structural disorder in the form of, e.g., point defects, alloying components, amorphous phases, grain boundaries or material interfaces. Both experiments and theory have shown that the introduction of material interfaces is particularly well harnessed in various superlattice and multilayer thin-film materials where the interfaces between alternating layers of dissimilar materials act as phonon-scattering boundaries: not only may thermal conductivity be suppressed by an order of magnitude across the film plane 1-2 but a significant drop may also be seen in the inplane direction. [3][4] Furthermore, careful balancing between order and disorder in multilayers may enable achieving ultralow thermal conductivities comparable to or even lower than those of amorphous or porous materials, as evidenced by the results for, e.g., W/Al2O3 nanolaminates (~0.6 Wm -1 K -1 ) and layered WSe2 crystals (~0.05 Wm -1 K -1 ). [5][6][7] For small-period superlattices the dominance of the phononboundary scattering at the internal interfaces over the scattering by the bulk of the constituent materials enables the control of thermal conductivity through careful adjustment of the superlattice period; 8 efficient suppression is achieved for incoherent phonons by decreasing the period, until potentially, phonon coherence may yield an upturn for periods similar to (and smaller than) phonon mean free path. 9-10 However, control over thermal conductivity in layered materials is not limited to simple size effects, as in particular for inorganic-organic materials, the drastic mismatch of the vibrational properties and the control over the bond strength over the internal interfaces may allow for further suppression of phonon transport. [11][12] Regarding inorganic-organic materials, use of organic layers of proper thicknesses could also allow for exploitation of phonon filtering realized due to interference effects within the organic layer. 13...

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“…12 Preliminary studies have also demonstrated interesting optical phenomena for ALD/MLD hybrid thin films, such as sensitization of nanoscale TiO 2 layers to absorption of visible light. 13 This could be beneficial in applications such as photocatalysis and solar cells, particularly since the ALD/MLD technique (like conventional ALD) would inherently allow conformal coating of nanostructured electrodes.…”

Section: Introductionmentioning

confidence: 99%

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

2015

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Ab initio calculationsWe investigate crystalline ZnO:hydroquinone (HQ) superlattices grown layer-by-layer by the combined atomic/molecular layer deposition (ALD/MLD) technique; such ALD/MLD layerengineered inorganic-organic thin films form a fundamentally new category of functional coherent hybrid materials that cannot be prepared by any other existing technique. Using quantum chemical methods, we derive atomic-level structural models for the ZnO:HQ superlattices and investigate their structural, spectroscopic, and electronic properties. By comparing the theoretical results with our experimental data we provide a detailed interpretation of experimentally measured infrared spectra, proving the presence of organic interfaces within the crystalline ZnO:HQ superlattices. We moreover show how the band structure of the hybrid material can be tailored by simple and experimentally feasible modifications of the organic constituent. The guidelines for the bandstructure engineering of ZnO:HQ superlattices should be valuable for the systematic enhancement and exploitation of the functional properties of ALD/MLD-grown inorganic-organic superlattices and nanolaminates in general.

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Tunable optical properties of hybrid inorganic–organic [(TiO₂)_m(Ti–O–C₆H₄–O–)_k]_n superlattice thin films

Cited by 33 publications

References 36 publications

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

Ultra-low thermal conductivity in TiO₂:C superlattices

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

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Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

Cited by 33 publications

References 36 publications

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

Ultra-low thermal conductivity in TiO2:C superlattices

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

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Tunable optical properties of hybrid inorganic–organic [(TiO₂)_m(Ti–O–C₆H₄–O–)_k]_n superlattice thin films

Ultra-low thermal conductivity in TiO₂:C superlattices