Stacking Arrangements Research Articles

Electronic Properties and Interlayer Interactions in Antimony Oxide Homo‐ and Heterobilayers

Antimony shows promise as a 2D mono‐elemental crystal, referred to as antimonene. When exposed to ambient conditions, antimonene layers react with oxygen, forming new crystal structures, leading to significant changes in electronic properties. These changes are influenced by the degree of oxidation. Utilizing density‐functional theory calculations, stable configurations of bilayer antimony oxide and their corresponding electronic properties are studied. Additionally, different stacking arrangements and their effects on the physical properties of the materials are investigated. Furthermore, the analysis encompasses strain‐free heterobilayers containing both pristine and oxidized antimonene layers, aiming to understand the interplay between these materials and their collective impact on the bilayer properties. In the results, insight is provided into how the properties of antimony‐based bilayer structures can be modified by adjusting stoichiometry and stacking configurations.

Performance and Thermal Stress Evaluation of Full-Scale SOEC Stack Using Multi-Physics Modeling Method

A three-dimensional computational fluid dynamics (CFD) method coupled with multi-physics phenomena is developed and applied for a 10-cell full-scale SOEC stack in this study. Effects of gas flow patterns, operating temperature, and manifold configurations are simulated and analyzed for stack performance and thermal stress. It is demonstrated the hydrogen production and thermal stress obtained in cross-flow mode stack are about 8% and 36 MPa higher compared to that in other flow cases. Furthermore, it is found the temperature gradient is the predominant factor affecting the thermal stress distribution and failure probability. Lastly, a stack arrangement with 2-inlet and 1-outlet is proposed and analyzed to enhance gas distribution uniformity within the cell channels. The findings of this study hold significance as a reference for investigating the impact on the SOEC stack performance and thermal stress distribution.

Stacked LSTM-GRU Long-Term Forecasting Model for Indonesian Islamic Banks

The development of the Islamic banking industry in Indonesia has become a significant concern in recent years, with rapid growth in the number of banks operating based on Sharia principles. To face emerging challenges and opportunities, a deep understanding of the long-term financial behavior of Islamic banks is becoming increasingly important. This study aims to predict the share price of PT Bank Syariah Indonesia Tbk, over 28 days using the LSTM-GRU stack. The observation stage includes importing the dataset, data separation, model variations, the training process, output, and evaluation. Observations were conducted using 10 model variations from 4 stacks of LSTM and GRU. Each model performs the training process in four epochs (200, 500, 750, and 1000). The results of observations in this study show that long-term predictions (28 days ahead) using four stacks of LSTM-GRU and daily training accumulation techniques produce better accuracy than the general method (using multiple outputs). From the observations we have made for predictions for the next 28 days, the model with the LGLG stack arrangement (LSTM-GRU-LSTM-GRU) produces the best accuracy at epoch 750 with an MSE LSTM-GRU 63.43762863. This study will undoubtedly continue in order to achieve even better precision, either by utilizing a new design or by further improving the technology we are now employing.

Real-world study of the leakage of two types of infusion bags in multicenter pharmacy intravenous admixture service (PIVAS).

Background: This study sought to analyze the leakage rate, economic loss caused by leakage, leakage reasons, and usage of upright polypropylene infusion bags and non-polyvinyl chloride (PVC) infusion bags, two types of closed intravenous infusion containers used in pharmacy intravenous admixture service (PIVAS), to improve the product quality of drug infusion packaging materials, reduce drug and clinical economic losses, and reduce the safety hazards of medication. Method: A real-world study was used to collect statistics for these infusion containers. The study was conducted in 21 hospitals in China from September to December 2022. Upright polypropylene infusion bags or non-PVC infusion bags in PIVAS of these 21 hospitals were chosen as the research material. Results: In total, 2,349,899 upright polypropylene infusion bags and 3,301,722 non-PVC infusion bags were collected. Eleven cases of upright polypropylene infusion bag leakage occurred (with a the leakage rate of 0.05‱), and 394 cases of non-PVC infusion bag leakage occurred (with a leakage rate of 1.19‱). The leakage rate of non-PVC infusion bags was significantly higher than that of upright polypropylene infusion bags (p < 0.01). The main reason for leakage in upright polypropylene infusion bags was sharp objects such as glass fragments or aluminum caps piercing the bag. The main reason for leakage in non-PVC infusion bags was squeezing, stacking, and uneven arrangement that causes folding of edges. For non-PVC bags, additional reasons for leakage included leakage at the nozzle joint, excessive manual or machine throwing force, and excessive dosage. The economic loss of upright polypropylene infusion bags was 1,116.56 CNY. The economic loss of non-PVC infusion bags was 32,210.86 CNY. Conclusion: Based on real-world study data on the leakage of upright polypropylene infusion bags and non-PVC infusion bags in multicenter PIVAS, it can be concluded that the leakage rates of upright polypropylene infusion bags are significantly lower than those of non-PVC infusion bags in PIVAS, and the economic losses due to upright polypropylene infusion bags are lower than those due to non-PVC infusion bags in PIVAS. Therefore, we can infer that upright polypropylene infusion bags are superior to non-PVC infusion bags.

Supramolecular Polymer Polymorphism: Spontaneous Helix-Helicoid Transition through Dislocation of Hydrogen-Bonded π-Rosettes.

Polymorphism, a phenomenon whereby disparate self-assembled products can be formed from identical molecules, has incited interest in the field of supramolecular polymers. Conventionally, the monomers that constitute supramolecular polymers are engineered to facilitate one-dimensional aggregation and, consequently, their polymorphism surfaces primarily when the states of assembly differ significantly. This engenders polymorphs of divergent dimensionalities such as one- and two-dimensional aggregates. Notwithstanding, realizing supramolecular polymer polymorphism, wherein polymorphs maintain one-dimensional aggregation, persists as a daunting challenge. In this work, we expound upon the manifestation of two supramolecular polymer polymorphs formed from a large discotic supramolecular monomer (rosette), which consists of six hydrogen-bonded molecules with an extended π-conjugated core. These polymorphs are generated in mixtures of chloroform and methylcyclohexane, attributable to distinctly different disc stacking arrangements. The face-to-face (minimal displacement) and offset (large displacement) stacking arrangements can be predicated on their distinctive photophysical properties. The face-to-face stacking results in a twisted helix structure. Conversely, the offset stacking induces inherent curvature in the supramolecular fiber, thereby culminating in a hollow helical coil (helicoid). While both polymorphs exhibit bistability in nonpolar solvent compositions, the face-to-face stacking attains stability purely in a kinetic sense within a polar solvent composition and undergoes conversion into offset stacking through a dislocation of stacked rosettes. This occurs without the dissociation and nucleation of monomers, leading to unprecedented helicoidal folding of supramolecular polymers. Our findings augment our understanding of supramolecular polymer polymorphism, but they also highlight a distinctive method for achieving helicoidal folding in supramolecular polymers.

Numerical Reconstruction of Proton Exchange Membrane Fuel Cell Gas Diffusion Layers

Stochastic reconstruction is widely employed for effective and flexible imitation of Gas Diffusion Layers (GDLs), e.g., to facilitate the study of their properties. However, the reconstruction often overlooks crucial factors such as fiber curvature, fiber stack arrangement, and fiber anisotropy. Consequently, the impact of these structural characteristics remains poorly understood. In this study, an in-house reconstruction procedure is developed based on the periodic surface model. This procedure enables the generation of GDLs with either straight or curved fibers, layer-by-layer or random arrangement, and different probabilities of through-plane fiber orientation angles. The porosity, domain size, and fiber diameter are extracted from an experimental image-based GDL and utilized as input data for the reconstruction. Furthermore, the different GDLs are compared in terms of pore size distribution and through-plane porosity distribution. It is concluded that introducing proper selections of these fiber features gives the reconstruction more realistic properties.

Pressure-Induced Neutral to Ionic Phase Transition in TTF-Fluoranil, DimethylTTF-Fluoranil and DimethylTTF-Chloranil: A Comparative THz Raman Study

The Neutral to Ionic phase Transition (NIT) that occurs in few mixed stack charge transfer cocrystals at high pressure or low temperature is a charge instability combined with a structural instability. The lattice contraction, which increases the 3D Coulomb interactions, favors a higher degree of charge transfer. Due to Peierls instability, this leads to the dimerization of the stack, breaking its inversion symmetry. The 3D interactions also determine the arrangement of the adjacent dimerized polar stacks, making the ionic phase ferroelectric or antiferroelectric. The role of these parameters that modulate the NIT has been widely studied in Tetrathiafulvalene-haloquinone cocrystals. Here, we compare the high-pressure behavior of three of them: the newly synthesized TTF-FA and DMTTF-FA with the known DMTTF-CA and isostructural DMTTF-FA. We followed the evolution of the lattice phonons via THz Raman spectroscopy, assessing the pressure-dependent structural changes. While the FA-based crystals undergo strong first-order NIT, DMTTF-CA shows a continuous transition. The high-pressure behavior of each crystal is also compared with the low-temperature behavior.

In-situ monitoring of thiazine molecular aggregation in various solvents via a free-standing acoustic levitator

In this work, we explored the in-situ reaction modeling of the molecular self-aggregation of methylene blue (MB), which is a cationic thiazine dye, in different solvents via a container-less acoustic levitator by floating of a single droplet. Our in-situ spectroscopic study revealed that the dimer essentially has a sandwich structural geometry with a deviation from parallel stacking and horizontal arrangements in the molecular planes. The real time conversion of the monomer in MB into a dimer and their dynamics in water and ethanol media were monitored using a free-standing acoustic levitator droplet system. The absorption spectra revealed changes in the two resolved peaks (monomer and dimer) and orderliness when water and ethanol were used as the media. Interestingly, the enhancement in the dimerization of MB could be attributed to droplet evaporation, which is difficult to observe in typical reactor containers. Moreover, acidic protonation resulted in a change in the aggregation orientation direction of the MB molecules, forming an unusual J-aggregation. Theoretical DFT calculations revealed that MB underwent typical H-aggregation and J-aggregation in the different solvent environments, and their orientations well matched the spectroscopic data.

π-Stacking among the Anthracenyl Groups of a Copper Complex Resulted in Doubling of Unit Cell Volume To Provide New Polymorphs.

Two polymorphs of the 9-N-(3-imidazolylpropylamino)methylanthracene (Hanthraimmida) containing hydrated copper(II)-2,6-pyridinedicarboxylate complex are reported. The two polymorphs have either lamellar or Herringbone arrangements of π-stacks among the anthracenyl groups of organocation. The difference between the two polymorphs originated from having face-to-face stacking arrangements between the two anthracenyl groups of the symmetry independent cations within the unit cell in one of the polymorphs. The π-stacked anthracenyl groups in consecutive layers of the polymorphs are oriented in one direction in the polymorph designated as P1, whereas the polymorph designated as P2 has such orientations in opposite directions. The unit cell volume of the polymorph P2 (Z = 4) has approximately twice the volume of the polymorph P1 (Z = 2); it happend due to coalescence of two unit cells of P1 in the ab-crystallographic plane. A mixed methanol/water solvate of the copper complex is also reported. It has a channel-like arrangement of the cations; has the anions and the solvents within the cation embraced channel-like enclosures. This complex is unstable, once taken out from the methanol solvent, it transforms in real time to P2 by replacements of the methanol molecules by water molecules.

Emergent layer stacking arrangements in c-axis confined MoTe2

The layer stacking order in 2D materials strongly affects functional properties and holds promise for next-generation electronic devices. In bulk, octahedral MoTe2 possesses two stacking arrangements, the ferroelectric Weyl semimetal Td phase and the higher-order topological insulator 1T′ phase. However, in thin flakes of MoTe2, it is unclear if the layer stacking follows the Td, 1T′, or an alternative stacking sequence. Here, we use atomic-resolution scanning transmission electron microscopy to directly visualize the MoTe2 layer stacking. In thin flakes, we observe highly disordered stacking, with nanoscale 1T′ and Td domains, as well as alternative stacking arrangements not found in the bulk. We attribute these findings to intrinsic confinement effects on the MoTe2 stacking-dependent free energy. Our results are important for the understanding of exotic physics displayed in MoTe2 flakes. More broadly, this work suggests c-axis confinement as a method to influence layer stacking in other 2D materials.

Four Slip-Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid-State Fluorescence of 3,6-Diaryl Substituted Furo[3,4-c]furanone Polymorphs and Regioisomers.

Six symmetrical 3,6-diaryl (aryl=phenyl, 2-, 3- and 4-tolyl, 2,4- and 3,5-xylyl) substituted furo[3,4-c]furanones (DFF) were synthesized. The computational analysis, based on density functional theory, found eight possible centrosymmetrical slipped π-stack arrangements, formed according to electron repulsion minimization principle, as for previously reported for π-isoelectronic diketopyrrolopyrroles (DPP). One of these slipped stack arrangements was found to form infinite columns in the crystals of a new polymorph of parent phenyl derivative (with centre-to-centre distance CC=6.975 Å), other three types of stacks were found for 3-tolyl (CC=6.153 Å), 4-tolyl (CC=3.849 Å) and 2,4-xylyl (CC=4.856 Å) derivatives by single crystal X-ray diffractometry. All six derivatives show intense solution fluorescence in blue/green region, with a maximum driven entirely by a number and position of methyl substituents on phenyl rings. On the other hand, the solid-state fluorescence from yellow over orange to red is observed only for four derivatives and its presence/absence, spectral position and vibronic structure is driven exclusively by the slips in π-stacks (with interplanar distance always less than 3.5 Å) of almost planar DFF molecules, resulting in J-type emission, H-type excimer-like emission and H-type quenching.

The Zintl Concept Applied to Intergrowth Structures: Electron‐Hole Matching, Stacking Preferences, and Chemical Pressures in Pd5InAs

AbstractEnumerating the potential stacking sequences of layers is a fundamental way to account for the structure diversity of solid state compounds. In many cases, these stacking variations represent polymorphs with only small energetic differences. Here, we examine a compound for which the preferred stacking pattern instead reveals key aspects about its chemical bonding: Pd5InAs. Its structure is based on the intergrowth of slabs of the AuCu3 and PtHg2 (or alternatively, fluorite) structure types. Two basic stacking arrangements are available to this compound, represented by the Pd5TlAs and HoCoGa5 structure types. DFT total energy calculations reveal that the former outcompetes the latter by a staggering 0.65 eV/formula unit. Through a combination of DFT‐reversed approximation Molecular Orbital (DFT‐raMO) and DFT‐Chemical Pressure (DFT‐CP) analysis we trace this preference to two factors. First, with DFT‐raMO analysis, we derive a Zintl‐like bonding scheme of Pd5InAs. This scheme, along with the inspection of selected crystal orbitals, is then connected to preferred stacking through the coordination environments of the Pd atoms at the interface between the Pd−In and Pd−As layers. In the hypothetical HoCoGa5‐type and observed Pd5InAs‐type structures, different Pd coordination environments arise at the interfaces. The hypothetical structure features square planar PdIn2As2 units, in each of which the same 4d‐orbital serves in the Pd sublattice's role as both Lewis acid (for interactions with the As) and Lewis base (for interactions with the In). In the observed structure, tetrahedral PdIn2As2 units occur instead, so that these contradictory roles are distributed to separate 4d‐orbitals, leading to more effective bonding. DFT‐CP analysis illustrates that this driving force for the Pd5TlAs‐type arrangement is supplemented by a favorable alignment of the packing tensions in the parent structures. Altogether, the resulting picture demonstrates how the reaction of simple intermetallic structures to form intergrowths can be guided by recognizable chemical interactions.

Optimisation of stacked, bulk high temperature superconductors for trapped-field magnet applications

It is necessary to fabricate (RE)BCO bulk high temperature superconductors in the form of individual single grains in order to maximise the length scale over which current flows, and hence the trapped magnetic field. However, inherent difficulties in the grain growth process place limitations on the diameter and height of the single grain that may be achieved by existing melt processes. A practical approach to increase the height of the sample and the trapped field at its surface is by assembling individual single grains in a stack formation with their ab planes aligned parallel, primarily to avoid the expensive process of fabricating large, individual monoliths. The trapped fields observed at the top and bottom surfaces of a single grain sample are frequently different since both the superconducting and physical properties of single grain (RE)BCO samples are generally non-uniform. This leads to challenges in determining how to spatially arrange stacks of single grain samples to generate the largest and most uniform trapped field overall. In this study, we report the optimisation of two-stack configurations involving a total of 8 individual GdBCO/Ag single grains. The samples were arranged in four pairs and configured with different surfaces in contact in the assembly of the stack. The primary superconducting properties for trapped field and total flux distributions were measured at 77 K and compared for each stack arrangement. The initial results indicate that surfaces with inferior flux trapping properties (measured in terms of the overall trapped field value) of a two-sample stack should be positioned at the middle of the assembly to achieve the best overall trapped field and higher total flux at the external, and therefore, usable surface of the stack sample. A numerical modelling method that incorporates different Jc-B characteristics for the top and bottom layers of a single grain to take account of the variability in physical properties and spatial non-uniformity confirmed the optimised experimental arrangement of the stacked bulk samples. Furthermore, the optimisation of single grains of ring geometry to achieve a longer and wider uniform magnetic field zone inside the bore was also performed.

Energetics and electronic structure of bilayer Janus WSSe

Employing density functional theory along with the effective screening medium method, we investigated the energetics and electronic structure of bilayer Janus WSSe in terms of their interlayer stacking arrangement. Through the orbital hybridization between chalcogen atoms at interfaces, the energetics are sensitive to the interlayer stacking orientation and interface atomic arrangements. This interface atomic arrangement creates the unique electronic structure of bilayer Janus WSSe determined by the dipole moment arrangement of the constituent WSSe layers. The net polarity of thin films of Janus transition-metal dichalcogenides is a simple superposition of the dipole moments of the constituent layers.

Topological phases in coupled polyyne chains

We study the electronic properties of coupled parallel polyyne chains in a couple of symmetric stacking arrangements, namely the AA stacking and the AB stacking, with the single and triple carbon bonds of one chain aligned (AA) and anti-aligned (AB) with those of the other chain. Both these arrangements described by tight-binding Hamiltonians, whose parameters are calibrated by matching low energy dispersion provided by first principle calculations, fall in the BDI class of topological classification scheme. We calculate the topological invariants for all three topological phases of the system: one for the AA stacking and 2 for the AB one. In AA stacking, both the insulating and the metallic phase belongs to the same topological phase. Whereas, the model exhibits two different values of the topological invariant in the two different insulating phases (structurally differentiated by transverse strain). In this later stacking though the transition between two distinct topological phases with the closure of the gap is practically unachievable due to the requirement of the high transverse strain. We also show the existence of four non-zero energy edge modes in the AA stacking and that of two zero energy edge modes in one of the topological phases for the AB stacking.

Structure of crystalline water ice formed through neon matrix sublimation under cryogenic and vacuum conditions.

Ice I has three forms depending on the stacking arrangements of its layers: hexagonal ice Ih, cubic ice Ic, and stacking disordered ice Isd. Below ∼60K, amorphous water becomes metastable, and the formation of any form of ice I is often implicitly precluded. Using a newly developed low-temperature reflection high-energy electron diffraction (RHEED) technique, we show that crystalline ice with cubic stacking sequences (i.e., ice Ic) formed through Ne sublimation from a solid H2O/Ne (1:1000 ratio) matrix at 13K. The extent of stacking disorder (disordered cubic and hexagonal stacking sequences) in the ice formed by Ne matrix sublimation is smaller than that in vapor-deposited ice Isd prepared at 143K and below the limit of detection of low-temperature RHEED. Dependence of the resulting ice structures on the thickness of the H2O/Ne matrix shows that amorphous water first forms in the early stages of Ne sublimation, and the cubic stacking sequence subsequently takes place. As the cubic ice Ic formed here at a much lower temperature (13K) than previously observed (typically above 78K), Ne matrix sublimation represents a novel route to the formation of cubic ice Ic under low-temperature and low-pressure conditions.

Custom-tailored cross-cylinder tribotest to emulate wear mechanism in drilling of CFRP-Ti stacks

While drilling of CFRP-Ti stacks, tool experiences complex tribomechanical interaction due to dissimilar workpiece constituents. For emulating tool wear behavior, the typical tribotest configuration such as reciprocating and pin-on-disc test are not representative for imitating contact scenario underwent during the drilling operation. Cross-cylinder tribotest is an effective test configuration to emulate contact in different manufacturing processes by providing fresh contact surface during sliding. In this work, for the first-time, tool wear of WC-Co cylinders was analyzed in cross-cylinder configuration against multi-material stack arrangement. Moreover, cross-cylinder testing against multi-material [CFRP-Ti]n workpiece showed cyclic variation in coefficient of friction against different workpiece constituents and wear mechanism is a combination of adhesive and abrasive wear on WC-Co tool, comparable to actual drilling operation.

Structural arrangement and improved thermoelectric figure of merit in hexagonal SiX (X = N, P, As, Sb, Bi) monolayers: understanding from first-principles calculations

Materials with thermoelectric (TE) efficiencies comparable to Carnot efficiency are desirable for applications in devices that use TE effects to produce electricity from heat. The figure of merit of a TE material is a measure of its efficiency. This quantity is determined by the intricate interplay of electronic and thermal transport parameters. Layered materials at low dimensions, such as 2D monolayers, have been in focus with regard to the quest for new TE materials. Group III–VI semiconductors in their 2D monolayers have exhibited fascinating TE properties. Naturally, it is expected that isoelectronic IV–V semiconductors will possess similar novelty. In this work, we have investigated the electronic, dynamical and TE properties of IV–V monolayer SiN, SiP, SiAs, SiSb and SiBi using first-principles electronic structure methods in conjunction with the semiclassical Boltzmann transport theory. Unlike previous studies, here the focus was to compute and analyse the effects of structural arrangements on TE properties. We found that upon consideration of an alternative stacking arrangement in the systems, significant changes occur in the transport phenomena, leading to a large figure of merit and thus TE efficiency. A comprehensive comparative analysis is presented to interpret the results. This work bears significance in the fact that it demonstrates a very important structure–property relationship aspect for these compounds that has been overlooked so far, and this approach may lead to the discovery of new TE materials with desirable efficiencies.

Temperature-induced transformation between layered herringbone polymorphs in molecular bilayer organic semiconductors

Herein we investigated the temperature-induced transformation between distinct layered herringbone (LHB) polymorphs in model organic semiconductors (OSCs) of a series of $2\text{\ensuremath{-}}\mathrm{mono}\text{\ensuremath{-}}\mathrm{alkylated}\text{\ensuremath{-}}\mathrm{benzothieno}[3,2\text{\ensuremath{-}}b][1]\mathrm{benzothiophenes} (mono\text{\ensuremath{-}}{\mathrm{C}}_{n}\text{\ensuremath{-}}\mathrm{BTBTs})$. The component molecules are composed of a one-sided linkage between the BTBT core and alkyl chains of various lengths. We propose that the polymorphism originates from a unique feature of LHB structures in which two types of $T$-shaped contacts are possible for BTBT cores that exhibit relatively low symmetry. Based on polarized UV-visible absorption spectra and powder x-ray diffraction analyses, we show that four long-alkylated $mono\text{\ensuremath{-}}{\mathrm{C}}_{n}\text{\ensuremath{-}}\mathrm{BTBTs}$ ($n=8$, 9, 10, and 11) undergo mostly irreversible structural phase transformations into short-chain-type polymorphs at elevated temperatures of approximately $85\ensuremath{-}100{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. These transformations allowed the investigation of the stability of each polymorph in terms of thermal analysis. Based on the chain-length dependent transition entropies, we demonstrate that the polymorphic transformations are triggered by the partial entropy gain of alkyl chains, followed by the total entropy gain at solid--liquid transitions observed at higher temperatures of approximately $110{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. We also analyzed the structure and intermolecular interactions of the four compounds. The results confirm that each molecular packing consists of a balance between the core--core and chain--chain interactions and also that the unique odd--even parity alkyl-chain-length effect of the transitions emerges as a result of the variation in interlayer stacking arrangements. We highlight the critical role of alkyl chains in terms of their large structural degrees of freedom in solution-processable and highly layered crystalline OSCs. These findings lead to a better understanding of molecular packing toward a more rational design of OSCs for efficient carrier transport.

Structure of Dunaliella photosystem II reveals conformational flexibility of stacked and unstacked supercomplexes.

Photosystem II (PSII) generates an oxidant whose redox potential is high enough to enable water oxidation , a substrate so abundant that it assures a practically unlimited electron source for life on earth . Our knowledge on the mechanism of water photooxidation was greatly advanced by high-resolution structures of prokaryotic PSII . Here, we show high-resolution cryogenic electron microscopy (cryo-EM) structures of eukaryotic PSII from the green alga Dunaliella salina at two distinct conformations. The conformers are also present in stacked PSII, exhibiting flexibility that may be relevant to the grana formation in chloroplasts of the green lineage. CP29, one of PSII associated light-harvesting antennae, plays a major role in distinguishing the two conformations of the supercomplex. We also show that the stacked PSII dimer, a form suggested to support the organisation of thylakoid membranes , can appear in many different orientations providing a flexible stacking mechanism for the arrangement of grana stacks in thylakoids. Our findings provide a structural basis for the heterogenous nature of the eukaryotic PSII on multiple levels.