Pre-nucleation and particle attachment of bismuth tri-iodide onto graphene substrates

Journal Pre-proofs Pre-nucleation and particle attachment of bismuth tri-iodide onto graphene substrates L. Fornaro, D. Ferreira, H. Bentos Pereira, A. Olivera PII: DOI: Reference:

S0022-0248(19)30669-4 https://doi.org/10.1016/j.jcrysgro.2019.125454 CRYS 125454

To appear in:

Journal of Crystal Growth

Received Date: Revised Date: Accepted Date:

13 October 2019 16 December 2019 19 December 2019

Please cite this article as: L. Fornaro, D. Ferreira, H. Bentos Pereira, A. Olivera, Pre-nucleation and particle attachment of bismuth tri-iodide onto graphene substrates, Journal of Crystal Growth (2019), doi: https://doi.org/ 10.1016/j.jcrysgro.2019.125454

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier B.V.

Pre-nucleation and particle attachment of bismuth tri-iodide onto graphene substrates L. Fornaro*, D. Ferreira, H. Bentos Pereira, A. Olivera Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, CURE, Universidad de la República, Rocha, URUGUAY

Abstract BiI3 nucleation was performed by physical vapor transport (PVT) onto graphene covered TEM grids and graphene covered SiO2 substrates. Depositions were characterized by High Resolution Transmission Electron Microscopy (HR-TEM) and by Scanning Electron Microscopy with Field Emission Gun (SEMFEG). Amorphous entities 2-3 nm in size were observed. They continue to be present even under the TEM beam and suffer rapid transformations between ordered and disordered structures. Given their size and amorphous character, we conclude that they are pre-nucleation entities, similar to the ones observed in solution and chemical vapor deposition (CVD) systems in the reports of non-classical nucleation research. The oriented attachment and amorphous addition of entities about 2-3 nm in size, giving larger ones of about 10-20 nm was observed. Nanoparticles interact among them by these non-classical mechanisms giving stable and oriented crystalline structures, in agreement with the different pathways reported in nonclassical nucleation investigations. Platelets up to about 100-200 nm in size were also obtained, similar when imaged by TEM and by SEM. They give TEM clear Moirè diagrams, similar to the ones obtained for other van der Waals superstructures. Non-classical nucleation here reported is similar to the one obtained for bismuth tri-iodide onto amorphous substrates, although the post growth - dictated by the crystalline substrate- is different, and gives van der Waals heterostructures.

Results may be a valuable contribution to the development of a general theory for non-classical nucleation mechanisms in all kind of systems, and, as well, of 2D van der Waals materials and their applications.

Highlights Highlight 1: Bismuth tri-iodide non-classical nucleation via amorphous pre-nucleation entities onto graphene Transmission Electron Microscopy (TEM) grids as substrates is reported Highlight 2: Further growth of pre-nucleation entities follows crystallization by oriented attachment and by amorphous addition mechanisms Highlight 3: Results agree with similar ones obtained for other solution-solid and vapor-solid systems, are discussed in the framework of non-classical nucleation investigations and compared with similar ones obtained for the same substance onto amorphous substrates Keywords A1. Nucleation, A3. Physical vapor deposition processes, B1. Bismuth compounds * Corresponding author Laura Fornaro, Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, CURE, Universidad de la República, Route 9 and route 15, Rocha, 27000, URUGUAY, Phone: 598 4472 7001, E-mail: [email protected] Introduction In recent times, more and more results are showing that various crystal growth systems do not obey the Classical Nucleation Theory (CNT). Although most of research refers to liquid-solid systems [1-8], there are contributions about vapor-solid systems as well [9, 10]. This has led to a new research field on non-classical nucleation, where several mechanisms were proposed for explaining the pre-nucleation stages [1, 8, 9, 11, 12]. Nowadays, a comprehensive and fully

developed theory about non-classical nucleation, applicable in all types of systems is still pending (if it actually exists). More or less coinciding in time with the development of non-classical nucleation approaches, 2D van der Waals materials is emerging as an impressive research field. By far, transition metal dichalcogenides (TMDs) (MX2, M: Mo, W and X: S, Se) are the most studied 2D materials, because of their outstanding properties which may give applications in optoelectronics and quantum technologies, among others [13, 14]. The growth of monolayer and few-layers of TMDs has been mainly reported by Physical Vapor Transport (PVT) [15], and by Metalorganic Chemical Vapor Deposition (MOCVD) [16-19] onto several kinds of substrates, amorphous as SiO2 and crystalline as graphene, hexagonal boron nitride (hBN) and (0 0 1) sapphire. Most of the reported growth of 2D van der Waals mono or few crystalline layers by PVT and by MOCVD do not look deeply into nucleation of the studied material, but mainly search further epitaxial stages useful for characterization and applications, although there are exceptions [20]. Without ignoring the relevance of TMDs 2D mono and few-layers, the map of possible 2D van der Waals materials is wide and rich in other interesting combination of compounds which are – in a less extent than TMDs- also being studied or may be considered. In particular, some halides are crystallographically compatible with graphene and hBN structures, and their heterostructures onto them are potential interesting 2D van der Waals materials. Crystalline layers of metal halides of the type MXn (M a heavy metal atom Hg, Pb, Bi and X a halogen atom I, Br), were investigated mainly for radiation detectors [21-23]. Among these heavy metal halides, bismuth tri-iodide, because of being less toxic than lead and mercury compounds, has been studied first for application in radiation detectors [24-27], but lately, it has motivated growing attention to be used for photovoltaic applications [28-33] (band gap 1,67 eV for bulk [34]).

Bismuth tri-iodide is a layered compound, whose crystal lattice is built from three layer packages (I-Bi-I) with weak van der Waals bonding between adjacent planes of iodine atoms and perpendicular to the c axis [35-37]. Two structures were calculated and measured for BiI3: rhombohedral R-3 and hexagonal P-31m [38]. As layered, BiI3 is an anisotropic compound, its heterogeneous nucleation depends on the adhesion energy of each plane, and different orientations of nuclei are possible. When growing thick crystalline layers of this material, different orientations were reported [21, 25]. During the last years, BiI3 has begun to be studied as a component for van der Waals materials, theoretically (onto graphene [39]) and experimentally (onto WSe2 [40] and onto graphene [41]), with promising results. As for TMDs van der Waals layers, BiI3 van der Waals heterostructures have been also simulated and grown thinking on their characterization and use, but not paying attention to nucleation. Lately, we have reported the nucleation of bismuth tri-iodide onto amorphous substrates by PVT, showing that it follows, at least, a non-classical pathway [42]. Now, we report here the nucleation of bismuth tri-iodide onto graphene, compare the results with the ones obtained for amorphous substrates and evaluate them in the framework of recent research in non-classical nucleation. Experimental BiI3 was synthesized from Bi2O3CO2.H2O and KI and then treated with HI in order to avoid hydrolysis, which leads to BiOI. After that, bismuth tri-iodide was purified by zone refining, followed by three sublimations for restoring stoichiometry. Zone refining was performed in quartz ampoules 1 cm in diameter sealed with an initial pressure of 5x104 Pa of high purity grade Ar, in a vertical zone refining furnace (Z24 Zone melting, Crystal Research) at 420 ºC and at about 3 cm/hr down the length of the ingot, 100 passes. Sublimation experiments were

performed in quartz ampoules 5 cm in diameter charged with bismuth tri-iodide powder, sealed with an initial pressure of 5x104 Pa of high purity grade Ar. The hot extreme of the ampoule, with the purified bismuth tri-iodide, was heated at 370 ºC (Carbolite furnace), maintaining the cold extreme of the ampoule at room temperature. After purification and stoichiometry restoration, BiI3 was deposited by Physical Vapor Transport (PVT) onto graphene Transmission Electron Microscopy (TEM) grids (PELCO® Single Layer Graphene on Holey Silicon Nitride, 2.5µm Holes, 0.5 x 0.5mm Window),

which act as

substrates, and onto graphene covered substrates (PELCO® 3-5 Layer Graphene on Ultra-flat Thermal SiO2 Substrate, 5 x 5mm). Deposition was performed in a chamber specially designed and constructed for such purpose, which permits amenable control of nucleation parameters such as BiI3 mass, distance sourcesubstrate, nucleation time, source and substrate temperatures, initial and final pressure and atmosphere. Several experiments were run varying these parameters in order to study the first stages of nucleation of BiI3 onto graphene. We have selected two sets for reporting here, which give similar, although differentiated results from each other. For all experiments, source and substrate temperatures were 260 °C and 42 °C respectively, and initial and final pressure were 5 x 10-3 and 60 Pa respectively. In this way, at initial time, supersaturation was the same for all the experiments. BiI3 source-substrate distance and sublimation time were established as variable parameters. Two experimental sets were stablished. For Set 1, BiI3 was vapor transported at 30 mm of the substrate during 2 s, whereas for Set 2, BiI3 was vapor transported at 15 mm of the substrate during 10 s. A BiI3 amount of about 75-160 mg was deposited onto each grid or substrate.

Depositions onto grids were characterized by High Resolution Transmission Electron Microscopy (HR-TEM) (JEOL 2100, 200 kV), obtaining the respective Fast Fourier Transform (FFT) diagrams when convenient. Some HR-TEM images were filtered with HRTEM Filter for Digital Micrograph. Depositions onto substrates were characterized by Scanning Electron Microscopy with Field Emission Gun (SEM-FEG) (Sigma Gemini I, Zeiss).

Results and discussion Figure 1 exhibits HR-TEM images of nucleation for Set 1 conditions. For the lowest deposition time and the highest source-substrate distance of these experiments, most of the obtained entities are less than 5 nm in size and not crystalline. Figure 1.b is representative of the coverage of the grid with these entities. Considering the lower vapor pressure under the boiling point of BiI3, it would be expected that, under the TEM beam, unstable particles would sublimate. However, the observed entities continue to be present even under the TEM beam, with fast transformations between ordered and disordered structures. However, a few amount of entities are larger and crystalline structures, about 10 nm in size, as can be seen in Figure 2. Even more, sequences of particle growth by oriented attachment, improving crystallinity, can be observed in the samples, as can be seen in Figure 3.

a

b

Figure 1. HR-TEM images of BiI3 vapor transported at 30 mm of the substrate during 2 s

a

b

Figure 2. Crystalline structure formed by oriented attachment of several previous particles

a

b

c

d

Figure 3. A representative sequence of particle growth by oriented attachment. a and b: HR-TEM image of the same region of interest of the sample captured with a time interval of 84 s, c and d: FFT diagrams of a and b respectively

Figure 4 exhibits HR-TEM and SEM-FEG images of samples belonging to Set 2, which means a longer deposition time and a shorter source-substrate distance. Platelets of about 100-200 nm in length were obtained, similar when imaged by TEM and by SEM, with the well defined hexagonal morphology of BiI3 in the SEM images. In addition to these structures, smaller particles (5-10 nm) can be observed, and they transform from amorphous to crystalline state, as can be seen in Figure 5. Furthermore, in some cases, a reversible transformation crystallineamorphous-crystalline could be registered; a representative example of these sequences is shown in Figure 6. Another interesting mechanism observed in these samples is amorphous addition, as is shown in Figure 7.

a Figure 4.

b

a: HR-TEM Image (Grid) b: SEM-FEG Image (substrate) of BiI3 vapor

transported at 15 mm of the substrate during 10 s

a

b

c

d

Figure 5. A representative sequence of amorphous-crystalline transformation. a and b: HR-TEM video snapshots (filtered) of the same region of interest of the sample with a time interval of 23 s, c and d: FFT diagrams of a and b respectively

a

b

c

d

e

f

Figure 6. A representative sequence of a crystalline-amorphous-crystalline transformation. a-c: HR-TEM video snapshots (filtered), of the same region of interest of the sample at times 6, 19 and 27 s, d-f: FFT diagrams of a-c respectively

Figure 7. HR-TEM video snapshots of a representative sequence of amorphous addition during a total elapsed time of 5s

The results already exposed lead us to highlight interesting issues related to BiI3 nucleation onto graphene substrates. A longer distance source-substrate and a shorter nucleation time determine a deposition with mainly amorphous entities as first stages of nucleation, which, under the TEM beam, transform orderer-disordered and continue to be present in such a metastable state, even under such beam. Assuming that when ordered, they have BiI3 usual crystalline structure, and considering a=b=7.5 Å and c=20.7 Å as BiI3 crystalline lattice parameters [38], the entities may contain about 1.5 - 4 unit cells depending their phase and orientation, which means about 24 - 72 atoms. Because of their size and nature, these entities turn out to be very similar to the pre-nucleation clusters reported in solution systems [4-8, 12, 43, 44] and in CVD systems [9], in the framework of nonclassical nucleation research. Certainly, and as it happens for all those reported results, we only know that the entities were consequence of the deposition by PVD at the initial instant of observation, then they are under the effect of the TEM beam, as all the experiments observed by this technique. It is important to highlight that these pre-nucleation entities are in solid phase (ex-situ TEM). We have not made experiments to determine if some kind of cluster might exist in the fluid phase (vapor phase in PVT), as was reported for liquid-solid systems [7, 8, 12], and vapor-solid systems (vapor-phase nucleation of charged nanoparticles) [9, 10]. If such fluid entities exist in the vapor phase, the available equipment and experimental set-up do not permit us to determine their presence. For this reason, we cannot assure if we are observing pre-nucleation clusters or amorphous nanoparticles, formed by the aggregation of pre-nucleation clusters. However, we can say that the entities are an intermediate metastable phase, amorphous and not crystalline, as should be the first stable nuclei according to CNT, and therefore, that such amorphous phase is

not the same of the bulk crystal, as CNT predicts as well [44, 45]. These conclusions are the same as those reached by other authors for pre-nucleation [4-9, 12, 43, 44]. For these reasons, we conclude that BiI3 nucleation onto crystalline graphene by PVT follows a non-classical pathway, with a pre-nucleation phase with amorphous/crystalline entities. At a longer deposition time (going from 2 to 10 s) and a shorter source-substrate distance (going from 30 to 15 mm), only a few of the 2-3 nm entities can be found, but the conditions permit that most of the metastable entities grow up to about 10 nm and be crystalline (about 4 to 12 BiI3 unit cells), following non-classical pathways as well. A representative crystalline structure can be seen in Figure 8. The Fast Fourier Transform (FFT) analysis of the Region of Interest (ROI) indicates that we are observing BiI3 in its rhombohedral phase, and not other species such as oxides (BiOI, Bi2O4 and Bi2O3 were analyzed and discarded from the FFT data).

Figure 8. Nuclei about 10 nm in size, crystalline (HR-TEM image, filtered region of interest and FFT analysis) Whatever the conditions, nanoparticles about less than 5 nm in size

grow by oriented

attachment, giving larger and stable crystalline structures. Moreover, they grow by amorphous

addition, as is shown in Figure 7. These last two results agree with recent non-classical nucleation reports, which indicate several pathways for nucleation, for instance, that clusters grow by the oriented attachment of primary amorphous or crystalline nanoparticles (crystallization by particle attachment) as well as amorphous addition and other mechanisms, and not by addition of monomeric species, as CNT predicts [2, 5, 6, 9, 11, 43, 44, 46]. Our results, as well as the others reported, may be consequence of the deposition in the cases we observed at the initial time (entities are already attached). Also, these processes may be due to the energy of the TEM beam, when we observe sequences of attachment or addition, as should occur for other reported results. Consequently, it is important to remark that our results, in a similar way as other reported ones which arise from TEM techniques, may be directly due to the deposits (registered at the initial time) but due to the action of the TEM beam as well. Figures 1 and 4 indicate that nanoparticles less than 5 nm in size are separated distances about 10-20 nm, but in both cases they coexist with larger structures. In the case of Set 1, these larger structures are separated distances about 200-400 nm, but in the case of Set 2, they tend to cover the grid. The existence of such larger structures, some of them with the hexagonal morphology of bismuth tri-iodide, may be indicating that, simultaneously with the exposed pathways of prenucleation followed by amorphous attachment and/or amorphous addition mechanisms, other via, perhaps following classical mechanisms, gives rise larger and separated structures for Set 1, or more continuous coverage for Set 2, thanks to a different kinetic than the one which dominates the non-classical processes previously discussed. It is very interesting to compare nucleation and further growth of bismuth tri-iodide by PVT performed onto amorphous (C-TEM grid [42]) or crystalline graphene substrates (this work). The primary stages, which mean pre-nucleation and amorphous attachment, result to follow very

similar processes for both kind of substrates. However, for the conditions selected for Set 2, individual rods and plates grow onto amorphous substrates, whereas when depositing onto graphene, crystalline entities thrive over individual rods and plates and tend to give a monolayer, as can be observed in Figures 8 and 9. As heteroepitaxy concepts allowed to foresee, graphene substrate determines an improved post-grow, and, even more, generates evidence of hexagonal Moirè interference as is shown in Figure 9. From these results it is possible to conclude that a

crystalline substrate as graphene, with hexagonal planar structures, determines the growth of hexagonal BiI3 structures onto it (and therefore van der Waals heterostructures), remedying the lattice mismatch, as was theoretically predicted [39]. This agrees with reports for other van der Waals structures whose Moirè patterns have been widely reported [48, 49]. Therefore, results show that the crystalline substrate does not influence the first stages of pre-nucleation and the pathways of attachment and addition, which seem to be independent of the amorphous or crystalline nature of the substrate.

Figure 9. a: HR-TEM image of the BiI3-graphene van der Waals superstructure layer and b: FFT showing the Moirè diagram of the superstructure

Although results are very interesting, there are almost more pending than resolved issues about the BiI3-graphene nucleation and post-growth. For instance, results exposed here were obtained ex-situ, in-plane, and under the TEM beam. Therefore, it will be appropriate to study possible pre-nucleation in the vapor phase and the existence of vapor-phase charged nanoparticles, as well as to perform cryotransmission electron microscopy (cryo-TEM) in order to diminish the TEM beam heating of the samples. As two phases of BiI3 exist, the elucidation of which phase occurs in each case (pre-nucleation, attachment, post growth and even changes under the TEM beam) is an interesting challenge, as well as –due to its anisotropy- to determine BiI3 orientation obtained under the different conditions. On the other hand, to assign Moirè diagram spots to graphene, BiI3 and their superstructure as well as to determine the rotated angle between both structures will be another work. Finally, theoretically studies and modeling of all the observed processes, as well as the correlation with experimental results, will surely enlight the knowledge of the processes, as is occurring with liquid-solid systems [12, 50]. . Conclusions We can conclude that BiI3 nucleation onto graphene by PVT follows a non-classical pathway giving a first amorphous metastable phase (ordered/disordered) before forming crystalline nanoparticles, which follow at least two pathways to give further larger structures: oriented attachment and amorphous addition. These results agree with reported ones about non-classical nucleation for various compounds in solution-solid and vapor-solid systems. Therefore, they may be included in the comprehensive development of a general theory about these phenomena. Likewise, results can be of relevance in the field of 2D van der Waals materials and their applications, contributing to obtain improved epitaxial layers.

Funding: This work was supported by Comisión Sectorial de Investigación CIentífica (CSIC), Universidad de la República, and by the Agencia Nacional de Investigación e Innovación (ANII), fellowship associated to Project grant number FCE_1_2014_1_104904 References [1] J.J. De Yoreo, A holistic view of nucleation and self-assembly, MRS Bulletin, 42(07) (2017) 525– 536, https://doi.org/10.1557mrs.2017.143 [2] H. Zhang, J.J. De Yoreo, and J.F. Banfield, A Unified Description of Attachment-Based Crystal Growth. ACS Nano, 8(7) (2014) 6526–6530. https://doi.org/10.1021/nn503145w [3] J.P. Andreassen and A.E.Lewis, Classical and Nonclassical Theories of Crystal Growth, in: A. van Driessche, M. Kellermeier, L. Benning and D. Gebauer, New perspectives in mineral nucleation and growth – From solution precursors to solid materials, Chapter 7, Springer, 2017 [4] J.J. DeYoreo, More than one pathway, Nature Materials, Vol 12 (2013) 284-285 [5] J.J. de Yoreo and N.A.J.M. Sommerdijk, Investigating materials formation with liquid-phase and cryogenic TEM, Nature Reviews Materials, Article number 16035, https://doi.org/10.1038/natrevmats. 2016.35, 2016 [6] J. Baumgartner, A. Dey, P.H.H. Bomans, C. Le Coadou, P. Fratzl, N.A.J.M. Sommerdijk and D. Faivre, Nucleation and growth of magnetite from solution, Nature Materials, Vol 12 (2013) 310-314 [7] D. Gebauer, A. Völkel and H. Cölfen, Science 322 (2008) 1819-1822 [8] D. Gebauer and H. Cölfen, Prenucleation clusters and non-classical nucleation, Nano Today 6 (2011) 564-584 [9] J. Jung and N. Hwang, Non-Classical Crystallization of Thin Films and Nanostructures in CVD Process, Chapter 2 in Chemical Vapor Deposition - Recent Advances and Applications in Optical, Solar Cells and Solid State Devices, Intech, Edited by S Neralla, 2016, https://doi.org/10.5772/63926

[10] N. Hwang and D. Lee, Charged nanoparticles in thin film and nanostructure growth by chemical vapour deposition, J. Phys. D: Appl. Phys. 43 (2010) 483001 (38pp) https://doi.org/10.1088/00223727/43/48/483001 [11] J.J. de Yoreo, P.U. Gilbert, N.A. Sommerdijk, R. Lee Penn, S. Whitelam, D. Joester, H. Zhang, J. Rimer, A. Navrotsky, J. Banfield, A. Wallace, F. Michel, F. Meldrum, H. Cölfen, and P. Dove, Crystallization by particle attachment in synthetic, biogenic, and geologic environments, Science, 349 (2015) (6247), https://doi.org/10.1126&science.aaa6760 [12] D. Gebauer, P. Raiteri, J.D. Gale and H. Cölfen, On classical and non-classical views on nucleation, American Journal of Science, 318(9) (2018), 969–988, https://doi.org/10.2475/09.2018.05 [13] K. S. Novoselov, A. Mishchenko, A. Carvalho and A. H. Castro Neto, 2D materials and van der Waals heterostructures, Science Vol. 353, Issue 6298 (2016) https://doi.org/10.1126/science.aac9439, 2016 [14] A.T. Hanbicki, M. Currie, G. Kioseoglou, A.L. Friedman and B.T. Jonker, Measurement of high exciton binding energy in monolayer transition-metal dichalcogenides WS2 and WSe2, Solid State Commun. Vol 203 (2015) 16-20 [15] F. Zhang, K. Momeni, M. A. AlSaud, A. Azizi, M. F. Hainey Jr, J. M. Redwing, L.Q. Chen and N. Alem, Controlled synthesis of 2D transition metal dichalcogenides: from vertical to planar MoS2, 2D Materials, Vol 4, N 2 (2017) 025029 [16] V. K. Kumar, S. Dhar, T. H. Choudhury, S. A. Shivashankar and S. Raghavan, A predictive approach to CVD of crystalline layers of TMDs: the case of MoS2, Nanoscale 7 (2015) 7802 [17] M. Marx, S. Nordmann, J. Knoch, C. Franzen, C. Stampfer, D. Andrzejewski, T. Kümmell, G. Bacher, M. Heuken, H. Kalisch and A. Vescan, Large-area MoS2 deposition via MOVPE, J. Cryst. Growth 464 (2017) 100-104, https://doi.org/10.1016/j.jcrysgro.2016.11.020 [18] S. M. Eichfeld, L. Hossain, Y. Lin, A. F. Piasecki, B. Kupp, A. G. Birdwell, R. A. Burke, N. Lu, X. Peng, J. Li, A. Azcatl, S. McDonnell, R. M. Wallace, M. J. Kim, T. S. Mayer, J. M. Redwing and J. A.

Robinson, Highly Scalable, Atomically Thin WSe2 Grown via Metal–Organic Chemical Vapor Deposition, ACS Nano 9 (2015) 20180, 2015, https://doi.org/10.1021/nn5073286 [19] X. Zhang, Z. Y. Al Balushi, F. Zhang, T. H. Choudhury, S. M. Eichfeld, N. Alem, T. N. Jackson, J. A. Robinson and J. M. Redwing, Influence of Carbon in Metalorganic Chemical Vapor Deposition of Few-Layer WSe2 Thin Films, J. Electron Mater. 45, 12 (2016) 6273-6279, doi: doi. 10.1007/s1166 [20] R. Yue, Y. Nie, L.A. Walsh, R. Addou, C. Liang, N. Lu, C.L. Hinkle, Nucleation and growth of WSe2:

enabling

large

grain

transition

metal

dichalcogenides,

2D

Materials,

4(4)

(2017)

045019, https://doi.org/10.1088/2053-1583/aa8ab5 [21] L. Fornaro, State of the art of the heavy metal iodides as photoconductors for digital imaging, Journal of Crystal Growth, Volume 371 (2013) 155–162 [22] L. Fornaro, A. Cuña, A. Noguera, I. Aguiar, M. Pérez, L. Mussio, A. Gancharov, Low dark current (0 0 l) Mercuric Iodide thick film for X- Ray direct and digital imagers, IEEE Transactions on Nuclear Science, vol. 52/6 (2005) 3107-3110. [23] P. R Bennett, K. S. Shah, Y. Dmitriyev, M. Klugerman, T. Gupta, M Squillante, Polycrystalline lead iodide films for digital X-Ray sensors, Nucl. Instr. and Meth., vol A505 (2003) 269-272 [24] L. Fornaro, E. Saucedo, L. Mussio, A. Gancharov, A. Cuña, Bismuth tri-iodide polycrystalline films for digital X-ray radiography applications, IEEE Tran. Nucl. Sci., Vol. 51/1 (2004) 96-100 [25] A.Cuña, I. Aguiar, A. Gancharov, M. Pérez, L. Fornaro, Correlation between growth orientation and growth temperature for bismuth tri-iodide films, Crystal Research and Technology, 39, 10 (2004) 899905 [26] I. Aguiar, S. Kröger, L. Fornaro, Bismuth Tri-Iodide Polycrystalline Films For X-ray Direct And Digital Imagers, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 610 (2009) 332-334 [27] A. Garg, M. Tomar, V. Gupta, Synthesis and Characterisation of Thin Films of Bismuth Triiodide for Semiconductor Radiation Detectors, In Conference Papers in Science; Hindawi: Dehradun, India, 2014; Vol. 2014, p 370436.

[28] R. E. Brandt, R. C. Kurchin, R. L. Z. Hoye, J. R. Poindexter, M. W. Brennan Wilson, S. Sulekar, F. Lenahan, P. X.T. Yen, V. Stevanovic, J. C. Nino, M. G. Bawendi, and T. Buonassisi, Investigation of Bismuth Triiodide (BiI3) for Photovoltaic Application, J. Phys. Chem. Lett., 6 (21) (2015) 4297–4302 [29] A. J. Lehner, H. Wang, D.H. Fabini, Ch. D. Liman, C-A. Hebert, E.E. Perry, M. Wang, G. C. Bazan, M. L. Chabinyc and R. Seshadri, Electronic structure and photovoltaic application of BiI3, Appl. Phys. Lett. 107 (2015) 131109 [30] D. Tiwari, D. Alibhai and D. J Fermin, Above 600 mV Open-Circuit Voltage BiI3 Solar Cells, ACS Energy Lett., 3 (2018) 1882−1886 [31] N. F. Coutinho, R. B. Merlo, N. F. V. Borrero and F. C. Marques, “Thermal Evaporated Bismuth Triiodide

(BiI3)

Thin

Films

for

Photovoltaic

Applications”,

MRS

Advances,

2018,

https://doi.org/10.1557/adv.2018.405 [32] W-B. Zhang, L-J. Xiang adn H-B. Li, Theoretical perspective of energy harvesting properties of atomically thin BiI3, Journal of Materials Chemistry A (2016) https://doi.org/ 10.1039/C6TA06806E [33] U. H. Hamdeh, R. D. Nelson, B. J. Ryan, U. Bhattacharjee, J. W. Petrich, and M. G. Panthani, Solution-Processed BiI3 Thin Films for Photovoltaic Applications: Improved Carrier Collection via Solvent Annealing, Chem. Mater., 28 (18) (2016) 6567–6574 [34] N.J. Podraza, W. Qiu, B.B. Hinojosa, H. Xu, M.A. Motyka, S.R. Phillpot, J.E. Baciak, S. TrolierMcKinstry and J.C. Nino, Band Gap and Structure of Single Crystal BiI3: Resolving Discrepancies in Literature, J. Appl. Phys. 114,(2013) 033110 [35] D. Nason, L. Keller, The growth and crystallography of bismuth tri-iodide crystals grown by vapor transport, J. Crystal Growth, 156 (1995) 221-226 [36] Y. Dmitriev, P. Bennett, L. Cirignano, M. Klugerman, K. Shah, Bismuth iodide crystals as a detector material: Some optical and electrical properties, Proc. SPIE, 3766 (1999) 521-529 [37] M.A. George, K-T. Chen, W.E. Collins, A. Burger, D. Nason, L. Boatner, Layered heavy metal iodides examined by atomic force microscopy, J. Vac. Sci. Technol., B 14(2), (1996) 1096-1104

[38] X. Sun, Y. Li, G. Zhong, H. Lu and Z. Zeng, The structural, elastic and electronic properties of BiI3: First-principles calculations, Physica B 407 (2012) 735-739 [39] F. Ma, M. Zhou, Y. Jiao, G. Gao, Y. Gu, A. Bilic, Z. Chen and A. Du, Single Layer Bismuth Iodide: Computational Exploration of Structural, Electrical, Mechanical and Optical Properties, Nature Scientific Reports Article Number 5:17558 (2015) https://doi.org/10.1038/srep17558 [40] J. Li, X. Guan, Ch. Wang, H-Ch. Cheng, R. Ai, K. Yao, P. Chen, Z. Zhang, X. Duan and X. Duan, Synthesis of 2D layered BiI3 nanoplates, BiI3/WSe2 van der Waals heterostructures and their electronic, optoelectronic properties, Small (2017) https://doi.org/10.1002/smll.201701034 [41] P-H. Chang, Ch-S. Li, F-Y. Fu, K-Y. Huang, A-S. Chou, and Ch-I. Wu, Ultrasensitive Photoresponsive Devices based on graphene/BiI3 van der Waals epitaxial heterostructures, Adv. Funct. Mater. 1800179 (2018) [42] L. Fornaro, D. Ferreira, H. Bentos Pereira, A. Olivera, Nucleation and pre-nucleation precursor phase of bismuth tri-iodide onto amorphous substrates, sent to publish to Journal of Crystal Growth, 2019 [43] Lee, J. Yang, S. G. Kwon and T. Hyeon, Nonclassical nucleation and growth of inorganic nanoparticles, Nature Reviews (2016) https://doi.org/10.1038/natrevmats.2016.34 [44] J.J. de Yoreo, In-situ liquid phase TEM observations of nucleation and growth processes, Progress in Crystal Growth and Characterization of Materials 62 (2016) 69-88 [45] D. Gebauer, Prenucleation Clusters, Encyclopedia of Nanotechnology, https://doi.org/10.1007/97894-007-6178-0_380-2, 2015 [46] M. Niederberger and H. Cölfen, Oriented attachment and mesocrystals: Non-classical crystallization mechanisms based on nanoparticle assembly, Phys. Chem. Chem. Phys. 8 (2006) 3271-3287 [47] J.J. De Yoreo, N.A.J.M. Sommerdijk and P.M. Dove, Nucleation Pathways in Electrolyte Solutions, in: A. van Driessche, M. Kellermeier, L. Benning and D. Gebauer, New perspectives in mineral nucleation and growth – From solution precursors to solid materials, Chapter 1, Springer, 2017

[48] Y. Liao, W. Cao, J. W. Connell, Z. Chen and Y. Lin, Evolution of Moiré Profiles from van der Waals Superstructures of Boron Nitride Nanosheets, Nature Scientific Reports

6:26084 (2016)

https://doi.org/ 10.1038/srep26084 [49] M. Adrian, A. Senftleben, S. Morgenstern and T. Baumert, Complete analysis of a transmission electron diffraction pattern of a MoS2–graphite heterostructure, Ultramicroscopy166 (2016) 9–15 [50] B.A. Legg, and J.J.De Yoreo, The energetics of prenucleation clusters in lattice solutions, The Journal of Chemical Physics, 145(21) (2016) 211921, https://doi.org/10.1063/1.4964489

Highlights Highlight 1: BiI3 nucleation via amorphous pre-nucleation entities onto graphene is reported Highlight 2: Pre-nucleation further growth follows oriented attachment and amorphous addition Highlight 3: Results agree with others obtained for solution-solid and vapor-solid systems Highlight 4: Results are discussed in the framework of non-classical nucleation investigations Highlight 5: Results are compared with similar ones for BiI3 onto amorphous substrates

Declaration of interests

☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.