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| 2. |
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| 3. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 4. |
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| 5. |
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| 6. |
- Marçal, L. A.B., et al.
(författare)
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Structural and chemical properties of anion exchanged CsPb(Br(1−x)Cl x )3 heterostructured perovskite nanowires imaged by nanofocused x-rays
- 2024
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Ingår i: Nanotechnology. - 0957-4484. ; 35:26
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Tidskriftsartikel (refereegranskat)abstract
- Over the last years metal halide perovskites have demonstrated remarkable potential for integration in light emitting devices. Heterostructures allow for tunable bandgap depending on the local anion composition, crucial for optoelectronic devices, but local structural effects of anion exchange in single crystals is not fully understood. Here, we investigate how the anion exchange of CsPbBr3 nanowires fully and locally exposed to HCl vapor affects the local crystal structure, using nanofocused x-rays. We study the nanoscale composition and crystal structure as function of HCl exposure time and demonstrate the correlation of anion exchange with changes in the lattice parameter. The local composition was measured by x-ray fluorescence and x-ray diffraction, with general agreement of both methods but with much less variation using latter. The heterostructured nanowires exhibit unintentional gradients in composition, both axially and radially. Ferroelastic domains are observed for all HCl exposure times, and the magnitude of the lattice tilt at the domain walls scales with the Cl concentration.
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| 7. |
- A. B. Marçal, L., et al.
(författare)
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Spatially resolved structural and chemical properties of the white layer in machined Inconel 718 super alloy
- 2024
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Ingår i: Materials and Design. - 0264-1275. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Inconel 718 is one type of nickel-based alloy used for a large range of applications, including gas turbines and aeroengines components. Although mechanical and thermodynamic properties of this material have been deeply studied in the past years, a method able to investigate local properties of the thin white layer formed on the alloy surface after machining remains challenging. Here, a 90 nm X-ray beam is used to probe the local strain, crystal orientation, and chemical composition of grains in the white layer. Data reveals mosaicity induced by the tool during machining. The high spatial resolution, combined with crystal lattice sensitivity, shows that the average grain size is around 30 nm throughout the white layer, while the strain is anisotropic nearest to the surface. Results provide new insights on the basic properties of the white layer in super alloys, revealing important information about the impact of finish machining which might help to explain fatigue and cracking formation on these materials during their usage phase.
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| 8. |
- Dzhigaev, D, et al.
(författare)
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Three-dimensional coherent x-ray diffraction imaging of ferroelastic domains in single CsPbBr3 perovskite nanoparticles
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites attract significant interest due to their remarkable performance in optoelectronic devices. However, the gap in understanding the relationship between their nanoscale structure and properties limits their application towards novel devices. In this work, twinned ferroelastic domains in single 500 nm CsPbBr3 particles are studied with 3D Bragg coherent x-ray diffraction imaging. A preferential double-domain structure is revealed in four identical particles, with one domain oriented along the [110] and the other along the [002] direction. The particles exhibit similar scattering volume ratios of 0.12 0.026 between twin phases, suggesting the possibility of a deterministic formation process. The domains exhibit a difference in lattice tilt of 0.59 degrees, in excellent agreement with calculations of the lattice mismatch at the (112) twin boundary. These results provide important insights both for the fundamental understanding of ferroelastic nanoscale materials and for the performance improvement of perovskite-based devices. Moreover, this work paves the way towards real-time imaging of the domain dynamics in ferroic systems.
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| 9. |
- Antoniazzi, Igor, et al.
(författare)
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Oxygen intercalated graphene on SiC(0001) : Multiphase SiOx layer formation and its influence on graphene electronic properties
- 2020
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 167, s. 746-759
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Tidskriftsartikel (refereegranskat)abstract
- Low-dimensionality materials are highly susceptible to interfaces. Indeed, intercalation of different chemical species in between epitaxial graphene and silicon carbide (SiC), for instance, may decouple the graphene with respect to the substrate due to the conversion of the buffer layer into a graphene layer. O-intercalation is known to release the strain of such 2D material and to lead to the formation of high structural quality AB-stacked bilayer graphene. Nonetheless, this interface transformation concomitantly degrades graphene electronic transport properties. In this work we employed different techniques in order to better understand the structure of the graphene/SiC interface generated by O-intercalation and to elucidate the origin of the poor electronic properties of graphene. Experimental results revealed the formation of a SiO2 rich layer with a defective transition layer in between it and the SiC, which is characterized by the existence of silicon oxycarbide structures. Scanning tunneling spectroscopy measurements revealed an extensive presence of electronic states just around the Fermi level all over the sample surface, which may suppress the charge carriers mobility around this region. According to theoretical calculations, such states are mainly due to the formation of silicon oxicarbides within the interfacial layer.
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| 10. |
- Bernardes, Yuri, et al.
(författare)
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Direct observation of large-area strain propagation on free-standing nanomembranes
- 2023
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Ingår i: Physical Review Materials. - 2475-9953. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- Investigations on epitaxial nanostructures with size of tens of nanometers have been a challenging issue for techniques that present high strain sensitivity but restricted spatial resolution. This is the case of recently developed x-ray nanoprobe techniques. Despite its inherent nondestructive character, submicron x-ray spots have only been successfully applied to the study of individual nanostructures which are either strain free or present extremely mild spatial lattice parameter gradients. Such limitation, with an uttermost barrier given by the diffraction limit, leads to voxel or pixel sizes between 5 and 10 nm obtained in coherent diffraction imaging or ptychographic reconstructions of real-space objects. Whenever the strain field of a nanostructure is successfully reconstructed from reciprocal space measurements, it cannot vary considerably in short distances since this would induce diffraction peak broadening and cause abrupt phase variations, leading to convergence issues on reconstruction algorithms. Here we show how epitaxial systems with large lattice mismatch and appreciable interfacial strain can be identified and directly analyzed throughout their strain field propagation in nanometer-thin crystalline membrane platforms, using the InGaAs/GaAs Stranski-Krastanov system as a model. The strain-induced footprint becomes observable along a few microns if the membrane thickness is comparable to the nanostructure size. It is possible to retrieve both interfacial strain and nanostructure size by probing individual objects.
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| 11. |
- Björling, Alexander, et al.
(författare)
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Chemical Limits on X-ray Nanobeam Studies in Water
- 2023
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Ingår i: Journal of Physical Chemistry C. - 1932-7447. ; 127:28, s. 13877-13885
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Tidskriftsartikel (refereegranskat)abstract
- Operando X-ray studies of chemical reactions have gained increasing interest lately, fueled by the emergence of a new generation of powerful focused X-ray sources. Although it is well known that ionizing radiation causes damage to samples via radical chemistry, this effect is often overlooked in studies of working devices or catalysts where intense focused beams are used as nanoscale probes. Here, we show how an X-ray nanobeam directly causes a phase transition in shape-controlled Pd nanoparticles and that a large oxidative potential must be applied to counteract the effect. In addition, we present a chemical reaction-diffusion model that offers a plausible qualitative explanation of the observations, and which also suggests that prohibitive concentrations of reactive species will arise under any focused X-ray probe, calling into question the validity of these methods as applied to aqueous chemical and catalytic systems.
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| 12. |
- Björling, Alexander, et al.
(författare)
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Three-Dimensional Coherent Bragg Imaging of Rotating Nanoparticles
- 2020
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 125:24
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Tidskriftsartikel (refereegranskat)abstract
- Bragg coherent diffraction imaging is a powerful strain imaging tool, often limited by beam-induced sample instability for small particles and high power densities. Here, we devise and validate an adapted diffraction volume assembly algorithm, capable of recovering three-dimensional datasets from particles undergoing uncontrolled and unknown rotations. We apply the method to gold nanoparticles which rotate under the influence of a focused coherent x-ray beam, retrieving their three-dimensional shapes and strain fields. The results show that the sample instability problem can be overcome, enabling the use of fourth generation synchrotron sources for Bragg coherent diffraction imaging to their full potential.
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| 13. |
- Castellano-Gonzalez, G., et al.
(författare)
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Epigallocatechin-3-gallate induces oxidative phosphorylation by activating cytochrome c oxidase in human cultured neurons and astrocytes
- 2016
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Ingår i: Oncotarget. - 1949-2553. ; 7:7, s. 7426-7440
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial dysfunction and resulting energy impairment have been identified as features of many neurodegenerative diseases. Whether this energy impairment is the cause of the disease or the consequence of preceding impairment(s) is still under discussion, however a recovery of cellular bioenergetics would plausibly prevent or improve the pathology. In this study, we screened different natural molecules for their ability to increase intracellular adenine triphosphate purine (ATP). Among them, epigallocatechin-3-gallate (EGCG), a polyphenol from green tea, presented the most striking results. We found that it increases ATP production in both human cultured astrocytes and neurons with different kinetic parameters and without toxicity. Specifically, we showed that oxidative phosphorylation in human cultured astrocytes and neurons increased at the level of the routine respiration on the cells pre-treated with the natural molecule. Furthermore, EGCG-induced ATP production was only blocked by sodium azide (NaN3) and oligomycin, inhibitors of cytochrome c oxidase (CcO; complex IV) and ATP synthase (complex V) respectively. These findings suggest that the EGCG modulates CcO activity, as confirmed by its enzymatic activity. CcO is known to be regulated differently in neurons and astrocytes. Accordingly, EGCG treatment is acting differently on the kinetic parameters of the two cell types. To our knowledge, this is the first study showing that EGCG promotes CcO activity in human cultured neurons and astrocytes. Considering that CcO dysfunction has been reported in patients having neurodegenerative diseases such as Alzheimer's disease (AD), we therefore suggest that EGCG could restore mitochondrial function and prevent subsequent loss of synaptic function.
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| 14. |
- Dagli-Hernandez, C, et al.
(författare)
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Genetic Variant ABCC1 rs45511401 Is Associated with Increased Response to Statins in Patients with Familial Hypercholesterolemia
- 2022
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Ingår i: Pharmaceutics. - : MDPI AG. - 1999-4923. ; 14:5
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Tidskriftsartikel (refereegranskat)abstract
- Statins are the first-line treatment for familial hypercholesterolemia (FH), but response is highly variable due to genetic and nongenetic factors. Here, we explored the association between response and genetic variability in 114 Brazilian adult FH patients. Specifically, a panel of 84 genes was analyzed by exon-targeted gene sequencing (ETGS), and the functional impact of variants in pharmacokinetic (PK) genes was assessed using an array of functionality prediction methods. Low-density lipoprotein cholesterol (LDL-c) response to statins (reduction ≥ 50%) and statin-related adverse event (SRAE) risk were assessed in carriers of deleterious variants in PK-related genes using multivariate linear regression analyses. Fifty-eight (50.8%) FH patients responded to statins, and 24 (21.0%) had SRAE. Results of the multivariate regression analysis revealed that ABCC1 rs45511401 significantly increased LDL-c reduction after statin treatment (p < 0.05). In silico analysis of the amino-acid change using molecular docking showed that ABCC1 rs45511401 possibly impairs statin efflux. Deleterious variants in PK genes were not associated with an increased risk of SRAE. In conclusion, the deleterious variant ABCC1 rs45511401 enhanced LDL-c response in Brazilian FH patients. As such, this variant might be a promising candidate for the individualization of statin therapy.
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| 15. |
- Hammarberg, Susanna, et al.
(författare)
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Fast nanoscale imaging of strain in a multi-segment heterostructured nanowire with 2D Bragg ptychography
- 2024
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Ingår i: Journal of Applied Crystallography. - 0021-8898. ; 57, s. 60-70
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Tidskriftsartikel (refereegranskat)abstract
- Developing semiconductor devices requires a fast and reliable source of strain information with high spatial resolution and strain sensitivity. This work investigates the strain in an axially heterostructured 180 nm-diameter GaInP nanowire with InP segments of varying lengths down to 9 nm, simultaneously probing both materials. Scanning X-ray diffraction (XRD) is compared with Bragg projection ptychography (BPP), a fast single-projection method. BPP offers a sufficient spatial resolution to reveal fine details within the largest segments, unlike scanning XRD. The spatial resolution affects the quantitative accuracy of the strain maps, where BPP shows much-improved agreement with an elastic 3D finite element model compared with scanning XRD. The sensitivity of BPP to small deviations from the Bragg condition is systematically investigated. The experimental confirmation of the model suggests that the large lattice mismatch of 1.52% is accommodated without defects.
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| 16. |
- Luo, Xiyu, et al.
(författare)
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Effects of local compositional heterogeneity in mixed halide perovskites on blue electroluminescence
- 2024
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Ingår i: Matter. - 2590-2393. ; 7:3, s. 1054-1070
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Tidskriftsartikel (refereegranskat)abstract
- Compositional heterogeneity is commonly observed in mixed bromide/iodide perovskite photoabsorbers, typically with minimal effects on charge carrier recombination and photovoltaic performance. Consistently, it has so far received very limited attention in bromide/chloride-mixed perovskites, which hold particular significance for blue light-emitting diodes. Here, we uncover that even a minor degree of localized halide heterogeneity leads to severe non-radiative losses in mixed bromide/chloride blue perovskite emitters, presenting a stark contrast to general observations in photovoltaics. We not only provide a visualization of the heterogeneity landscape spanning from micro-to sub-microscale but also identify that this issue mainly arises from the initially formed chloride-rich clusters during perovskite nucleation. Our work sheds light on a long-term neglected factor impeding the advancement of blue light-emitting diodes using mixed halide perovskites and provides a practical strategy to mitigate this issue.
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| 17. |
- Marçal, Lucas A.B., et al.
(författare)
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In Situ Imaging of Ferroelastic Domain Dynamics in CsPbBr3Perovskite Nanowires by Nanofocused Scanning X-ray Diffraction
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:11, s. 15973-15982
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Tidskriftsartikel (refereegranskat)abstract
- The interest in metal halide perovskites has grown as impressive results have been shown in solar cells, light emitting devices, and scintillators, but this class of materials have a complex crystal structure that is only partially understood. In particular, the dynamics of the nanoscale ferroelastic domains in metal halide perovskites remains difficult to study. An ideal in situ imaging method for ferroelastic domains requires a challenging combination of high spatial resolution and long penetration depth. Here, we demonstrate in situ temperature-dependent imaging of ferroelastic domains in a single nanowire of metal halide perovskite, CsPbBr3. Scanning X-ray diffraction with a 60 nm beam was used to retrieve local structural properties for temperatures up to 140 °C. We observed a single Bragg peak at room temperature, but at 80 °C, four new Bragg peaks appeared, originating in different real-space domains. The domains were arranged in periodic stripes in the center and with a hatched pattern close to the edges. Reciprocal space mapping at 80 °C was used to quantify the local strain and lattice tilts, revealing the ferroelastic nature of the domains. The domains display a partial stability to further temperature changes. Our results show the dynamics of nanoscale ferroelastic domain formation within a single-crystal perovskite nanostructure, which is important both for the fundamental understanding of these materials and for the development of perovskite-based devices.
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| 18. |
- Marçal, Lucas A.B., et al.
(författare)
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In situ imaging of temperature-dependent fast and reversible nanoscale domain switching in a single-crystal perovskite
- 2022
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Ingår i: Physical Review Materials. - 2475-9953. ; 6:5
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites exhibit a rich crystal structure, with multiple phases as well as ferroelastic domains, which is crucial for the optical and electrical properties. The average crystal phase-transition temperatures can be shifted by size, strain, or defects, but it is not clear whether such differences can also appear locally within a single crystal. The experimental study of domain dynamics within nanocrystals is challenging and requires a method capable of probing crystal lattice variations with both high spatial and temporal resolution. Here, we show that in situ full-field diffraction x-ray microscopy can be used to image domains in a single crystal CsPbBr3 nanoplatelet as the temperature traverses the orthorhombic to tetragonal phase transition, at 150 nm spatial resolution and 6 s time resolution. The images reveal sudden domain pattern changes faster than the temporal resolution. Surprisingly, we observe substantial local variations during heating, with domain changes occurring at different temperatures within the single crystal. The nanoplatelet exhibits a high-temperature domain pattern completely different from the low-temperature one, but both patterns are reproducible, and we reversibly switch between them in multiple cycles. These results demonstrate that single CsPbBr3 crystals can exhibit substantial local variation of their basic crystal properties.
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| 19. |
- Marçal, Lucas A.B., et al.
(författare)
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Inducing ferroelastic domains in single-crystal CsPbBr3 perovskite nanowires using atomic force microscopy
- 2021
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Ingår i: Physical Review Materials. - 2475-9953. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric and ferroelastic domains have been predicted to enhance metal halide perovskite (MHP) solar cell performance. While the formation of such domains can be modified by temperature, pressure, or strain, established methods lack spatial control at the level of single domains. Here, we induce the formation of ferroelastic domains in CsPbBr3 nanowires at room temperature using an atomic force microscope (AFM) tip and visualize the domains using nanofocused x-ray diffraction with a 60 nm beam. Regions scanned with a low AFM tip force show orthorhombic 004 reflections along the nanowire axis, while regions exposed to higher forces exhibit 220 reflections. The applied stress locally changes the crystal structure, leading to lattice tilts that define ferroelastic domains, which spread spatially and terminate at {112}-type domain walls. The ability to induce individual ferroelastic domains within MHPs using AFM gives new possibilities for device design and fundamental experimental studies.
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| 20. |
- Rodrigues-Junior, Gilberto, et al.
(författare)
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Direct observation of large strain through van der Waals gaps on epitaxial B i2 T e3 /graphite : Pseudomorphic relaxation and the role of B i2 layers on the B ix T ey topological insulator series
- 2020
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Ingår i: Physical Review Materials. - 2475-9953. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Layered materials can usually grow without strain on top of distinct substrates if the only interaction between them is due to van der Waals forces. In such a scenario it would be expected that the heterointerface made up of weak bounds would not affect the overlayed material significantly for several large lattice-mismatched systems. Here we have studied the first stages of the heteroepitaxial growth of layered bismuth telluride topological insulator on top of highly oriented pyrolitic graphite (HOPG) by molecular beam epitaxy. Samples were investigated by atomic force microscopy (AFM), synchrotron x-ray diffraction (XRD), and micro-Raman spectroscopy. AFM images show hexagonal/triangular flat islands with exposed HOPG areas for the low coverage regime, and the lattice parameter of these Bi2Te3 structures were measured by XRD. The existence of pseudomorphic strain at the initial Bi2Te3 layers was retrieved by both XRD and Raman spectroscopy. We have found evidence that Bi2Te3 layers near the interface are subject to an in-plane compressive strain, leading to a pseudomorphic out-of-plane lattice expansion. Furthermore, the presence of Bi2Te3 islands locally distorts the topmost layer of HOPG, resulting in tensile strain which was measured by Raman spectroscopy. The observed relaxation of 0.1-0.2% for each van der Waals gap is used to calculate elastic constants of Bi2 bilayers, which are crucial building blocks for the formation of other BixTey topological insulator compounds. Finally, the impact of such a strain in Bi2Te3 electronic structure was investigated by density functional theory calculations. The results show that the band structure of this strained material remains unchanged at the center of the Brillouin zone, confirming the robustness of surface states, but it is consistently affected at the M and K zone edges.
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