Thermoelectric characteristics of (Zn,Al)O/hydroquinone superlattices

Abstract

Thin ZnO layers doped with aluminum and interspersed with regularly repeating single layers of organic molecules are deposited by a combined atomic layer deposition (ALD) and molecular layer deposition (MLD) method at 220 C using diethyl zinc, trimethyl aluminum, water and hydroquinone (HQ) as precursors. Hydroquinone is found to form distinct layers within the (Zn,Al)O framework such that clear inorganic-organic superlattice structures are realized. Aluminum doping efficiently offsets the decrease in carrier concentration caused by the organic layers, and enables enhanced electrical conductivities for the co-doped (Al plus HQ) thin films. Since superlattice structures in general are known to be highly beneficial in blocking the phonon transport in different materials, our ALD/MLD grown (Zn,Al)O:HQ thin films possess a lot of promise for new types of thermoelectrics.

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

“…12,13 Most interestingly, use of metal precursors together with organic precursors enables hybrid inorganic-organic thin films to be fabricated with combined ALD/MLD processes, 14,15 where the organic precursors can be, e.g., organic alcohols 14,16 or carboxylic acids. 17,18 Such combined ALD/MLD processes also allow for fabrication of hybrid inorganic-organic materials in the form of nanolaminates [19][20][21] and superlattices [22][23][24] in an elegant manner.…”

Efficiently suppressed thermal conductivity in ZnO thin films via periodic introduction of organic layers

“…However, care should be taken when drawing conclusions on this point, because while the TDTR technique measures the cross-plane thermal conductivity of the thin films, our existing power factor measurements were made in-plane. 14 Thus, the values may not be comparable, especially in a highly anisotropic structure such as the current layered (Zn,Al)O:HQ thin films. Nonetheless, the observed thermal conductivity values represent a significant reduction and should prove effective in improving the thermoelectric performance of ZnO thin films.…”

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

“…As an example of a novel class of * phopkins@virginia.edu nanocomposites of recent interest, hybrid organic/inorganic nanomaterials grown by a combined alternation of atomic layer deposition (ALD) and molecular layer deposition (MLD) have exhibited enhanced electrical, optical, magnetic, and mechanical functionalities compared to conventional organic or inorganic materials [10][11][12][13]. For example, using this ALD/MLD technique, inorganic/organic superlattices (SLs) have shown promise as potential thermoelectric materials [14,15]. However, paramount in advancing ALD/MLD hybrid structures for use in thermoelectric, or other applications, is an understanding of the phonon transport and scattering processes in these materials; referring to ALD/MLD SLs, this requires understanding phonon scattering at the ALD/MLD boundary, and its correlation with phonon transmission and resulting boundary conductance across the molecular interface.…”