3D Islands Research Articles

Sn-mediated transformations on Si(111) surface: Reconstructions, Electromigration, Homoepitaxy

We have studied Si mass transport and morphological transformations on the Si(111) surface during (√3 × √3)-Sn reconstruction formation and following Si homoepitaxy in 600–825°C interval by in situ ultrahigh vacuum reflection electron microscopy (UHV REM) and ex situ atomic force microscopy (AFM). We have shown that the formation of a metallic α-(√3 × √3)-Sn phase during Sn deposition at T < 650 °С leads to Si 2D island nucleation on > 1 μm terraces, while the formation of a mosaic γ-(√3 × √3)-Sn phase at T > 650 °С is followed by monatomic step shift in the step-up direction and provides Sn/Si(111) interface with wide atomically flat terraces. The step shift value has been measured as functions of substrate temperature and Sn deposition rate to determine emitted by the steps Si coverage participating in γ-phase formation. The electromigration-induced drift of disordered “1 × 1”-Sn domains has been shown to entail enhanced noncompensated Si mass transport followed by the Si(111)-(√3 × √3)-Sn surface roughening. The kinetics of 2D island nucleation and growth near monatomic steps and on wide (up to 10 μm) terraces on the Si(111)-γ-(√3 × √3)-Sn surface during Si deposition at 700°C is limited by surface diffusion only, and critical nucleus i consists of ∼ 20–100 Si atoms.

A mechanism for thickness-controllable single crystalline 2D materials growth

Recent efforts in growing two-dimensional (2D) multilayers have enabled the synthesis of single crystalline 2D multilayers in a wafer scale through the seamless stitching of multiple epitaxial 2D islands. Unlike previously observed wedding-cake or inverted-wedding-cake structures, these multilayer islands have the same size and shape in each layer with aligned edges. In this study, we investigated the underlying growth mechanisms of synchronic 2D multilayers growth and have showed that a heterogenous layer on a crystalline substrate is critical for maintaining the synchronic growth of 2D multilayers. During growth, the heterogenous layer passivates the edges of multilayer 2D island and thus prevents the coalescence of these active edges, while the high interfacial energy between the heterogenous surface layer and the substrate stabilizes the synchronic structure. Based on this model, we have successfully explained the previously observed synchronic growth of graphene and hexagonal boron nitride multilayers (Nat Nanotech 2020, 15: 861; Nature 2022, 606: 88). The deep understanding on the mechanism paves a way towards the synthesis of wafer-scale single-crystal 2D multilayers with a uniform thickness.

Controlled Synthesis and Accurate Doping of Wafer-Scale Two-Dimensional Semiconducting Transition Metal Dichalcogenides.

Two-dimensional (2D) semiconducting transition metal dichalcogenide (TMDCs) possess atomically thin thickness, dangling-bond free surface, flexible band structure, and silicon-compatible feature, making them one of the most promising channels for constructing state-of-the-art field-effect transistors in the post-Moore's era. However, the existing 2D semiconducting TMDCs fall short of meeting the industry criteria for practical applications in electronics due to their small domain size and the lack of effective approach to modulate intrinsic physical properties. Therefore, it is crucial to prepare and doping of 2D semiconducting TMDCs single crystals with wafer size. In this review, wesystematically summary the up-to-date progresses regarding the wafer-scale growth of 2D semiconducting TMDCs polycrystalline and single-crystal films. The domain orientation control of 2D TMDCs and the seamless stitching of unidirectionally aligned 2D islands by means of substrate design are proposed. In addition, the accurate and uniform doping of 2D semiconducting TMDCs and the effect on electronic device performances are also discussed. Finally, the dominating challenges pertaining to enhance electronic device performances of TMDCs are emphasized, and the further development directions are put forward. This review provides a systematically and in-depth summary for high-performance device applications of 2D semiconducting TMDCs. This article is protected by copyright. All rights reserved.

Incorporation of tungsten or cobalt into TaN barrier layers controls morphology of deposited copper

Progress in semiconductor devices, which has enabled the information and communications technology explosion of the 21st century, has been driven by Moore’s Law and the accompanying aggressive scaling of transistors. However, it is now acknowledged that the currently used copper interconnects are becoming a bottleneck in sub-nm scaling. Semiconductor devices require a diffusion barrier and a seed layer in the volume available to the interconnect metal. This then limits the minimum size of the interconnect and copper suffers from a preference to form 3D islands which are non-conducting rather than conducting films. Therefore there is a pressing need to either replace copper, which has its own difficulties, or to reduce the volume taken up by the diffusion barrier and liner; ideally finding a single material displaying both properties is needed. We have previously shown that incorporation of Ru into the surface layer of TaN is a strong alternative to the usual TaN/Ta or TaN/Ru stacks. In this work we study other possible metals that can be incorporated into TaN, namely Co and W, which are less expensive and critical than Ru and can potentially outperform it. Our first principles density functional theory results from static relaxations and ab initio molecular dynamics show that there are several compositions of both Co- and W-doped TaN which should promote growth of 2D copper interconnects without compromising the barrier properties of TaN. With this selection of materials it should be possible to design new experimental processes that promote downscaled copper interconnects for the next generation of electronic devices. Additionally, our work presents an improved method towards prediction of thin film morphology on a given substrate, which can be of use for a variety of materials science applications.

Molecular beam epitaxy and crystal structure of majority a-plane-oriented and substrate-strained Mn3Sn thin films grown directly on sapphire (0001)

The Kagome antiferromagnet Mn3Sn has garnered much attention due to the presence of exciting properties such as anomalous Hall and Nernst effects. This paper discusses the synthesis of crystalline Mn3Sn thin films, prepared on Al2O3 (0001) substrates at 453±5°C using molecular beam epitaxy. The growth is monitored in situ using reflection high energy electron diffraction and measured ex situ using x-ray diffraction, Rutherford back-scattering, and cross-sectional scanning transmission electron microscopy. Our analysis shows the in-plane lattice constants of a1,M=4.117±0.027 Å and a2,M=4.943±0.033 Å, which is a very unexpected result when compared to the bulk a-plane Mn3Sn. This indicates a strain in the film and makes it challenging to provide a straightforward explanation. In an effort to explain our results, we discuss two possible orientation relationships between the Mn3Sn films and the sapphire substrates. Samples prepared under these conditions appear to have smooth surfaces locally, but overall the film has a 3D island morphology. First-principles calculations provide atomic models of the Mn3Sn (112¯0) lattice on Al2O3 (0001) high symmetry sites, indicating that the L3-R90° is the most stable configuration. A detailed discussion of the experimental data and theoretical results, as well as strain effects, is provided.

Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Seismic performance of advanced three-dimensional base-isolated nuclear structures in complex-layered sites

The application of three-dimensional (3D) base isolation for nuclear structures is advantageous. In this study, an advanced 3D base isolation technique was developed and the nonlinear seismic response of 3D base-isolated nuclear structures in complex layered sites was investigated using a global method. The study first designed a novel 3D isolation system, including horizontal and vertical isolation, based on the disc spring theory, which can flexibly adjust the structural stiffness and vertical bearing capacity. To verify the applicability of 3D base isolation, the dynamic behaviour of a 3D base-isolated nuclear island building in complex-layered sites subjected to beyond-design basis ground motion was investigated using a proposed high-precision simulation program of soil-structure interaction (SSI) based on the global method. The findings demonstrate that in complex-layered sites, the SSI increases the horizontal floor response spectra (FRS) but decreases the vertical FRS of 3D base-isolated nuclear power plants, and both the horizontal and vertical isolation rates remarkably decrease. The influence of the SSI becomes more evident as the intensity of the ground motion increases. The proposed 3D base isolation system exhibits excellent isolation effects. When the vertical stiffness is reduced, the vertical isolation effect becomes more significant. However, the adverse rocking motion of the island building should be effectively controlled. The research results support the practical application of 3D base isolation technology for nuclear structures located in complex-layered sites with high seismic intensities.

InGaN surface morphology evolution investigated by atomic force microscope with power spectral density analysis

The morphology of thin InGaN layers grown at varying temperature by metalorganic chemical vapor deposition (MOCVD) has been studied by atomic force microscope (AFM). The surface morphology undergoes a transition process from three-dimensional (3D) island growth mode to two-dimensional (2D) nucleated mound and hillock growth mode and finally to layer-by-layer step-meandering and step flow growth mode. The changes in morphology were analyzed from a thermodynamic (mostly based on the BCF theory of crystal growth by Burton, Cabrera and Frank) and kinetic (mostly the ESB theory based on the Ehrlich-Schwöbel barrier) perspective. Power spectral density (PSD) analysis of AFM surface images is used to determine the dominant smoothing mechanisms that contribute to the feature of surface morphology of InGaN, and validate our analysis based on BCF and ESB theories.

What lies beneath? Investigations of atomic force microscopy-based nano-machining to reveal sub-surface ferroelectric domain configurations in ultrathin films

Multiferroic materials, encompassing simultaneous ferroelectric and ferromagnetic polarization states, are enticing multi-state materials for memory scaling beyond existing technologies. Aurivillius phase B6TFMO (Bi6TixFeyMnzO18) is a unique room temperature multiferroic material that could ideally be suited to future production of revolutionary memory devices. As miniaturization of electronic devices continues, it is crucial to characterize ferroelectric domain configurations at very small (sub-10 nm) thickness. Direct liquid injection chemical vapor deposition allows for frontier development of ultrathin films at fundamental (close to unit cell) dimensions. However, layer-by-layer growth of ultrathin complex oxides is subject to the formation of surface contaminants and 2D islands and pits, which can obscure visualization of domain patterns using piezoresponse force microscopy (PFM). Herein, we apply force from a sufficiently stiff diamond cantilever while scanning over ultrathin films to perform atomic force microscopy (AFM)-based nano-machining of the surface layers. Subsequent lateral PFM imaging of sub-surface layers uncovers 45° orientated striped twin domains, entirely distinct from the randomly configured piezoresponse observed for the pristine film surface. Furthermore, our investigations indicate that these sub-surface domain structures persist along the in-plane directions throughout the film depth down to thicknesses of less than half of an Aurivillius phase unit cell (˂ 2.5 nm). Thus, AFM-based nano-machining in conjunction with PFM allows demonstration of stable in-plane ferroelectric domains at thicknesses lower than previously determined for multiferroic B6TFMO. These findings demonstrate the technological potential of Aurivillius phase B6TFMO for future miniaturized memory storage devices. Next-generation devices based on ultrathin multiferroic tunnel junctions are projected.

Transition from monolayer-thick 2D to 3D nano-clusters on α-Al2O3(0001).

This paper reports on the long-standing puzzle of the atomic structure of the Ag/α-Al2O3(0001) interface by combining X-ray absorption spectroscopy, to determine Ag local environment [i.e. average Ag-Ag (dAg-Ag) and Ag-O (dAg-O) interatomic distances and Ag coordination numbers (CN)], and numerical simulations on nanometric-sized particles. The experimental key was the capability of a structural study of clusters involving only a few atoms. The concomitant decrease of dAg-Ag and CN with decreasing cluster size provides unambiguous fingerprints for the dimensionality of the Ag clusters in the subnanometric regime leading to a series of unexpected results regarding the size-dependent interface structures. At low coverage, Ag atoms sit on surface Al sites to form buckled monolayer-thick islands associated with a Ag-Ag distance (2.75 Å) which fits the alumina lattice. Upon increasing Ag coverage, as 3D clusters appear, the Ag interface atoms tend to leave Al sites to sit atop O atoms as dAg-Ag increases. The then highlighted size-dependent evolution, is built on structural models which seemed so far contradictory in a static vision of the interface. Theory generalizes the case as it predicts the existence of alumina-supported 2D clusters of Pd and Pt at small coverage and a similar 2D-3D transition upon increasing the size. The structural transformation from 2D Ag clusters to macroscopic 3D islands is accompanied by a noticeable reduction of adhesion energy at the Ag/α-Al2O3(0001) interface.

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

The formation of the radial electric field, in the scrape-off layer (SOL) has been experimentally studied for attached divertor conditions in stellarator W7-X. The main objective of this study is to test the validity in a complex three-dimensional (3D) island divertor of simple models, typically developed in tokamaks, relating in the SOL to the sheath potential drop gradient at the target. Additionally, we investigate the effect of the edge shear on the reduction of density fluctuation amplitude, a well-established phenomenon according to the existing bibliography. The main diagnostic for measurements in the SOL is a V-band Doppler reflectometer that can provide the measurement of the and density fluctuations with good spatial resolution. 3D measurements of divertor parameters have been carried out using infrared cameras, with the exponential decay length of the divertor heat flux () resulting in a suitable proxy for the model-relevant , the exponential decay length of the temperature at the divertor. In the investigated attached regimes, it is shown for the first time that the formation of the in the SOL depends on parameters at the divertor, following a qualitatively similar to that found in a tokamak. Then, from the analyzed plasmas, the observed shear at the edge is linked to a moderate local reduction of the amplitude of density fluctuations.

Effects of Al-doping concentration on the structure and electromagnetic shielding properties of transparent Ag thin films

The ultra-thin Ag films with fascinating optical properties and shielding performance have broad applications in the fields of solar cells, transparent electrodes, optical spectrum filters, low-emissivity coatings, transparent electromagnetic shielding windows, etc. In this work, by introducing Al dopant, ultra-thin Ag transparent films were successfully prepared on quartz glass substrates using magnetron co-sputtering method. Effects of the Al-doping concentration on the structure, transmittance and electromagnetic shielding properties of Ag thin films were investigated in detail. It was found that a certain amount of Al can suppress the 3D island growth of Ag granules, and thus promote nucleation and continuous in plane growth. At the Al doped concentration of 5 mol%, the prepared 9 nm Al doped Ag thin films exhibited continuous, uniform and smooth surface morphology with the RMS roughness of only 0.89 nm. Meanwhile, it has good optical property with the highest transmittance value of 80.2% in the visible range and 76.8% at 550 nm. As the increase of Al concentration, the shielding effectiveness of the films goes up and then down, and the optimum concentration for maximum shielding effectiveness (SE) is about 5 mol% at which the maximum SE can reach up to 34.5 dB. These features make the Al-doped Ag thin films very useful and practical for transparent electromagnetic shielding window.

A multilevel block preconditioner for the HDG trace system applied to incompressible resistive MHD

We present a scalable block preconditioning strategy for the trace system arising from the high-order hybridized discontinuous Galerkin (HDG) discretization of incompressible resistive magnetohydrodynamics (MHD). We construct the block preconditioner with a least squares commutator (BFBT) approximation for the inverse of the Schur complement that segregates out the pressure unknowns of the trace system. The remaining velocity, magnetic field, and Lagrange multiplier unknowns form a coupled nodal unknown block for which a system algebraic multigrid (AMG) is used to approximate the inverse. The complexity of the MHD equations together with the algebraic nature of the statically condensed HDG trace system makes the choice of smoother in the system AMG part critical for the convergence and performance of the block preconditioner. Our numerical experiments show GMRES preconditioned by ILU(0) of overlap zero as a smoother inside system AMG performs best in terms of robustness, time per nonlinear iteration and memory requirements. With several transient test cases in 2D and 3D including the island coalescence problem at high Lundquist number we demonstrate the robustness and parallel scalability of the block preconditioner. Additionally for the upper block a preliminary study of an alternate nodal block system solver based on a multilevel approximate nested dissection is presented. On a 2D island coalescence problem the multilevel approximate nested dissection preconditioner shows better scalability with respect to mesh refinement than the system AMG, but is relatively less robust with respect to Lundquist number scaling. In the Appendix B, we rigorously show: (1) the uniqueness of the solution of the nonlinear MHD system for small time, (2) the convergence of the Picard iterations for each backward Euler step, and (3) the convergence of the entire time stepping procedure.

Cluster-mediated stop-and-go crystallization‬

Impurities control the formation of bio-crystals and can fully paralyze crystal growth at low levels of supersaturation. Traditional impurity models predict that an escape from this so-called “dead zone” requires an increase in the driving force (i.e. supersaturation). In this work, using protein crystals as a model system, we uncover an alternative escape route from the dead zone that does not involve an increase in supersaturation. We demonstrate that the merger of a protein cluster with the crystal surface triggers the formation of an ordered multi-layered island. The newly created surface on top of the resulting 3D island is initially devoid of impurities and therefore characterized by near-pure step growth kinetics. The accelerated step advancement on this relatively uncontaminated surface limits the available time for impurities to adsorb on the emerging terraces and by extension their resulting surface density. Cluster-mediated crystal growth occurring in heterogeneous media can therefore lead to stop-and-go dynamics, which offers a new model to explain crystallization taking place under biological control (e.g. biomineralization).

Interfacial effect and strain on the electrical and magnetic properties of SrRuO3/NdNiO3 bilayers with 3D island surface layer

Interfacial effect and strain on the electrical and magnetic properties of SrRuO3/NdNiO3 bilayers with 3D island surface layer

Parasitic behavior of different V/III ratios on the properties of InGaN/GaN heterostructures by MOCVD technique

In this study, InGaN/GaN heterostructures were grown on a c-plane flat sapphire substrate (FSS) by using the metalorganic chemical vapor deposition (MOCVD) technique. The flow rates of the ammonia gas varied from 9 SLM to 24 SLM for the growth of InGaN thin film, which was equivalent to the V/III ratio of 6211–16562. Results indicated that a higher V/III ratio promotes parasitic behavior by hydrogen dissociated from ammonia. The parasitic behavior from hydrogen species etches the InN away from the growing surface and transforms the growth morphology from 3D islands to 2D growth mode. A slight reduction in indium composition was observed when increasing the V/III ratio. Next, more stable bandgap energy was observed for the InGaN thin films grown at higher V/III ratios. Improvements in electrical properties in terms of electron mobility and sheet resistance were observed at a higher V/III ratio which is associated with the improvement of crystalline quality and less defect density at a higher V/III ratio. The correlation of strain and carrier density of the thin films was further discussed. It was concluded that the growth of high crystalline quality and thick InGaN thin film was possible for solar cell applications at higher V/III ratio growth conditions.

Role of nitrogen source flow on the growth of 2D GaN crystals

As a class of non-layered compounds, ultrathin III-V semiconductors possess excellent physical and chemical properties, are promising candidates for optoelectronic and thermoelectric applications. Due to the strong chemical bonds both in plane and out of plane, the controllable growth of two-dimensional (2D) III-V semiconductors is quite challenging. In this study, we report the successful synthesis of 2D GaN crystals by chemical vapor deposition (CVD) on liquid Ga. The nitrogen source flow is found to be a key factor that governs the transformation of GaN growth from 2D layered mode to three-dimensional (3D) island mode. This study provides further understanding on the growth of non-layered 2D III-nitride materials.

The shapes of synthesized two‐dimensional materials

AbstractThe shapes of as‐grown/as‐etched two‐dimensional (2D) islands are the most recognizable features of the chemical vapor deposition (CVD) process which reveal a lot of information about the chemical environment of growth/etching, the effect of the substrate and the growth/etching kinetics. Here, we summarize experimentally observed shapes of CVD‐grown 2D materials from previous reports, theoretical understanding on the corresponding mechanisms and the simulations of the corresponding growth/etching processes. Each part of the review article is organized by combining the fundamental principles that govern the shapes of crystals during growth/etching and the related experimental observations to facilitate the readers to read and understand the content. The content of the review includes attachment‐limited 2D materials growth, diffusion‐limited 2D materials growth (both with and without influence of the substrate), etching and merging of 2D materials with and without considering the effect of the substrate. We also discuss growth and etching of multilayered 2D islands during CVD—a topic still under development. We wish this review will also guide the audience to understand the kinetics of 2D materials growth and to improve controllable synthesis of various 2D materials.

Dual-Phase MoS2/Mxene/CNT Ternary Nanohybrids for Efficient Electrocatalytic Hydrogen Evolution

Hydrogen (H2) shows great potential in reducing greenhouse gas emissions and improving energy efficiency due to its environmentally friendly nature and high gravimetric energy density [1]. It can be generated via electrochemical water splitting based on the hydrogen evolution reaction (HER). It is well known that Pt-group metals (PGMs) are excellent catalysts for HER, but their broad adoption is limited by high cost and scarcity. Recently, two-dimensional (2D) molybdenum disulfide (MoS2) is regarded as a promising alternative to PGMs due to its large surface area, rich active sites, and ideal hydrogen adsorption energy [2]. However, its practical application is hindered by the intrinsically low electrical conductivity arising from the semiconducting nature of2H phase MoS2[3]. On the other hand, 2D Ti3C2 MXene with high electrical conductivity, excellent hydrophilicity, and large interlayer distance has been intensively investigated in energy storage devices lately[4]. Compared with charge-neutral graphene, MXene exhibits a negatively charged surface due to the existence of numerous surface functional groups (-OH, -O, -F, etc.), which not only enhances the dispersion of MoS2 precursors but also promotes MoS2 nucleation, making it a superior template for MoS2 synthesis. Nevertheless, undesired oxidation of MXene occurs in aqueous solutions [5], reducing the overall catalyst stability.To address the above issues, we employed a one-step solvothermal method using DI water/DMF as bisolvent and constructed metallic 1T phase-enriched MoS2/MXene composite as HER catalyst. The advantages of using bisolvent lie in twofold: (i) suppress undesired oxidation and thus preserve high conductivity of MXene framework, and (ii) improve MoS2 electrical conductivity by inducing 2H to 1T phase transition. The introduction of metallic 1T phase MoS2 is triggered by ion intercalation. Specifically, during the synthesis, both ammonium molybdate (Mo precursor) and DMF can act as abundant sources of NH4+ which can intercalate into MoS2 layers. This process stimulated charge imbalance between Mo3+ and Mo4+ and led to the S plane sliding [6]. As a result, crystal structure distortion and therefore phase transformation of MoS2 occur along with interlayer distance expansion. To further improve the catalyst conductivity, carbon nanotubes (CNTs)were introduced into the binary composite as crosslinks to bridge the 2D islands. As a result, a low overpotential (169 mV) and Tafel slope (51 mV/dec) along with the highest turnover frequency (7 s-1 at -0.23V vs. RHE) and an ultralong lifetime (72 hours) was successfully achieved. The origin of the outstanding HER performance of the ternary composite can be ascribed to: (i) the prevention of 2D layer restacking as well as the enlarged surface area due to the 2D/2D MoS2/MXene integration and ion intercalation. This will promote the contact between electrolyte and catalyst, resulting in an increased hydrogen ion adsorption; (ii)the vertical growth of MoS2 flakes on MXene template which increases the exposure of MoS2 edge planes, maximizing the total number of active sites; (iii) the synergistically enhanced conductivity because of the formation of hybrid 1D/2D conductive network via the integration of 1T-phase metallic MoS2, conductive MXene backbone with suppressed oxidation along with the CNT crosslinks, minimizing the charge transfer resistance at the electrode/electrolyte interface. This work demonstrated an effective strategy for low-dimensional material structure-property engineering with the aim of optimizing the HER performance which will shed light on the development of the next-generation PGM-free HER electrocatalysts.

The effect of Bi doping on the thermal conductivity of ZnO and ZnO:Al thin films

The dissipation of heat generation has been one of the largest obstacles in the design of semiconductor devices and reducing the thermal conductivity is vital for improving thermoelectric efficiency. This work focuses on the Bi doping effect on ZnO, and ZnO:Al thin films produced by magnetron sputtering with thickness varying between 500 and 900 nm. The approach introduces Bi ions, a higher mass element, into the ZnO metal-oxide matrix, to hinder phonon-mediated heat conduction and, consequently, reduce thermal conductivity. Atom probe tomography (APT) was employed to survey Bi doping distribution in ZnO:Al:Bi and ZnO:Bi thin films and to study the morphology of the grain boundaries. The thermal properties of the thin films were measured by frequency-domain thermoreflectance. Based on thermal conductivity results, it is concluded that the doping of ZnO films with Al has a significant effect on thermal conductivity, being reduced from 6.0 W m−1 K−1 in its undoped state to 3.3 W m−1 K−1 for ZnO with ∼3 at.% of Al, mainly due to alloy scattering of phonons in the wurtzite cell. Further doping with Bi contributes to a slight reduction in the thermal conductivity of ZnO:Al.Bi films (2.9 W m−1 K−1), due to grain boundary scattering by Bi/Bi2O3 phases. This result is understood as the confluence of two counteracting effects. On the one hand, the thermal conductivity of the film decreases because Bi, unlike Al, is segregated to grain boundaries and does not substitute Zn in the wurtzite crystal lattice, which is unequivocally demonstrated by APT results. On the other hand, the simultaneous presence of Al and Bi triggers a morphological change with the film's microstructure becoming more columnar. This change in microstructure from 3D island growth in ZnO:Al and ZnO:Bi to a more regular columnar structure in ZnO:Al,Bi limits further reduction in the thermal conductivity.