An efficient method for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films

Simbrunner, J.; Schrode, Benedikt; Domke, Jari; Fritz, Torsten; Salzmann, Ingo; Resel, Roland

doi:10.1107/s2053273320001266

Cited by 8 publications

(35 citation statements)

References 34 publications

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“…Our procedure for indexing an unknown crystalline system has been described in detail in a previous paper. 40 In the following, we summarize the relevant steps.…”

Section: Methodsmentioning

confidence: 99%

“…Considering experimental inaccuracies, the unit cell parameters can be optimized using various methods. 40 …”

Section: Methodsmentioning

confidence: 99%

“… 38 , 39 In our previous work, we have shown the theoretical concept of the assignment of diffraction peaks to individually oriented crystallites. 40 In this paper, we will apply this methodology to a number of examples with known and unknown bulk polymorphs. By indexing the complete diffraction patterns, we can identify the known phases that are present within the films.…”

Section: Introductionmentioning

confidence: 99%

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Searching for New Polymorphs by Epitaxial Growth

et al. 2020

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The formation of unknown polymorphs due to the crystallization at a substrate surface is frequently observed. This phenomenon is much less studied for epitaxially grown molecular crystals since the unambiguous proof of a new polymorph is a challenging task. The existence of multiple epitaxial alignments of the crystallites together with the simultaneous presence of different polymorphs does not allow simple phase identification. We present grazing incidence X-ray diffraction studies on conjugated molecules like perylenetetracarboxylic dianhydride (PTCDA), pentacene, dibenzopentacene (trans-DBPen), and dicyanovinylquater-thiophene (DCV4T-Et2) grown by physical vapor deposition on single crystalline surfaces like Ag(111), Cu(111), and graphene. A new method for indexing the observed Bragg peaks allows the determination of the crystallographic unit cells so that the type of crystallographic phase can be clearly identified. This approach even works when several polymorphs are simultaneously present within a single sample as shown for DCV4T-Et2 on Ag(111). Additionally, epitaxial relationships between the epitaxially grown crystallites and the single crystalline surfaces are determined. In a subsequent step, the experimental data are used for the crystal structure solution of an unknown polymorph, as shown for the example trans-DBPen grown on Cu(111).

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“…Our procedure for indexing an unknown crystalline system has been described in detail in a previous paper. 40 In the following, we summarize the relevant steps.…”

Section: Methodsmentioning

confidence: 99%

“…Considering experimental inaccuracies, the unit cell parameters can be optimized using various methods. 40 …”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Searching for New Polymorphs by Epitaxial Growth

et al. 2020

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“…In both implemented algorithms, that using the specular diffraction peak and that not using the specular diffraction peak, the final solutions for the lattice constants are optimized by performing first-order corrections (Simbrunner et al, 2020). Furthermore, it is checked whether the final unit cells correspond to the reduced cells (Buerger, 1957).…”

Section: Common Final Stepsmentioning

confidence: 99%

“…Consequently, additional unknown parameters must be determined by the algorithm. A comprehensive formalism that addresses exactly this problem is proposed in recent work (Simbrunner et al, 2018(Simbrunner et al, , 2019(Simbrunner et al, , 2020. The general (triclinic) case as well as systems of higher symmetry have been dealt with.…”

Section: Introductionmentioning

confidence: 99%

GIDInd: an automated indexing software for grazing-incidence X-ray diffraction data

Kainz¹,

Legenstein²,

Holzer³

et al. 2021

J Appl Cryst

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Grazing-incidence X-ray diffraction (GIXD) is a widely used technique for the crystallographic characterization of thin films. The identification of a specific phase or the discovery of an unknown polymorph always requires indexing of the associated diffraction pattern. However, despite the importance of this procedure, only a few approaches have been developed so far. Recently, an advanced mathematical framework for indexing of these specific diffraction patterns has been developed. Here, the successful implementation of this framework in the form of an automated indexing software, named GIDInd, is introduced. GIDInd is based on the assumption of a triclinic unit cell with six lattice constants and a distinct contact plane parallel to the substrate surface. Two approaches are chosen: (i) using only diffraction peaks of the GIXD pattern and (ii) combining the GIXD pattern with a specular diffraction peak. In the first approach the six unknown lattice parameters have to be determined by a single fitting procedure, while in the second approach two successive fitting procedures are used with three unknown parameters each. The output unit cells are reduced cells according to approved crystallographic conventions. Unit-cell solutions are additionally numerically optimized. The computational toolkit is compiled in the form of a MATLAB executable and presented within a user-friendly graphical user interface. The program is demonstrated by application on two independent examples of thin organic films.

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A New Approach to Polymorphism in Molecular Crystals: Substrate‐Mediated Structures Revealed by Lattice Phonon Dynamics

Salzillo

Brillante

2022

Adv Materials Inter

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The experimental search for polymorph screening is often assisted by computational studies on crystal structure predictions. [8] Lastly, a subtle perspective of Bernstein cleared up a final revision of the terminology and of the nomenclature of multiple crystal forms. [9] In more recent years a new approach to polymorphism has taken momentum in the search of new crystal structures of organic materials, the so-called thin film structures or substrate-induced polymorphs (SIP), meaning a phase grown in the vicinity of a substrate with a distinct structure from those of the bulk. [10] An earlier discussion on the subject was held in a dedicated workshop about fifteen years ago. [11] At that time the discussion was mostly focused on organic semiconductors such as pentacene and perylene diimide derivatives. Since the majority of the thin film structures showed crystal parameters not very dissimilar from those of the corresponding parent bulk forms, these structures were indicated as "distortedbulk," where the term "distorted" was ascribed to the perturbation of the substrate on the molecular layers. Approximately ten years later, [12] a new grammar on substrate-induced structures was established. The growth at the interface of a variety of different substrates led to the definition of the general class of surface-mediated structures, portraying more detailed definitions such as "surface-induced" and "surface-selected" polymorphs, with the former indicating a bulk-distorted form and the latter being a new genuine structure with no association to any crystal phase of the bulk. This is the nomenclature that we shall initially follow in the present survey, with some new hints on additional cases that will be encountered, such as substratestabilized polymorphs, as detailed further on.Certainly, the starting point of surface-mediated polymorphs cannot be separated by the exhaustive review on SIP as discussed in Jones et al. [10] In that paper, examples of sixteen molecules were given, for which thin film polymorphs had been observed on solid substrates, showing new structures with respect to the previously known single crystals polymorphs. The impact of polymorphism on the material properties was mostly addressed on organic electronics, because every structure has its own mobility with relevant consequences on the efficiency of the device. Besides, it is wellThe issue of polymorphism in molecular crystals is discussed, taking into account the substrate-mediated structures, that is, structures grown at the interface of different substrates. Bulk and thin films of a compound both share the potentiality to display different crystal forms. However, unlike bulk polymorphs, whose structures are determined by their different molecular packing, thin film structures depend very much on the molecular organization of the organic layers on the substrate, which may, or may not, lead to an ordered structure, depending on the nature of the interface and on the growth conditions. Based on large part in some of the authors' recent works, the...

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An efficient method for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films

Cited by 8 publications

References 34 publications

Searching for New Polymorphs by Epitaxial Growth

Searching for New Polymorphs by Epitaxial Growth

GIDInd: an automated indexing software for grazing-incidence X-ray diffraction data

A New Approach to Polymorphism in Molecular Crystals: Substrate‐Mediated Structures Revealed by Lattice Phonon Dynamics

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