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1. Combined electronic excitation and knock-on damage in monolayer MoS2

Author

Speckmann, Carsten, Lang, Julia, Madsen, Jacob, Monazam, Mohammad Reza Ahmadpour, Zagler, Georg, Leuthner, Gregor T., McEvoy, Niall, Mangler, Clemens, Susi, Toma, and Kotakoski, Jani

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Electron irradiation-induced damage is often the limiting factor in imaging materials prone to ionization or electronic excitations due to inelastic electron scattering. Quantifying the related processes at the atomic scale has only become possible with the advent of aberration-corrected (scanning) transmission electron microscopes and two-dimensional materials that allow imaging each lattice atom. While it has been shown for graphene that pure knock-on damage arising from elastic scattering is sufficient to describe the observed damage, the situation is more complicated with two-dimensional semiconducting materials such as MoS2. Here, we measure the displacement cross section for sulfur atoms in MoS2 with primary beam energies between 55 and 90 keV, and correlate the results with existing measurements and theoretical models. Our experimental data suggests that the displacement process can occur from the ground state, or with single or multiple excitations, all caused by the same impinging electron. The results bring light to reports in the recent literature, and add necessary experimental data for a comprehensive description of electron irradiation damage in a two-dimensional semiconducting material. Specifically, the results agree with a combined inelastic and elastic damage mechanism at intermediate energies, in addition to a pure elastic mechanism that dominates above 80 keV. When the inelastic contribution is assumed to arise through impact ionization, the associated excitation lifetime is on the order of picoseconds, on par with expected excitation lifetimes in MoS2, whereas it drops to some tens of femtoseconds when direct valence excitation is considered., Comment: 19 pages, 4 figures, 1 table

Published
2023
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2. Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Author

Åhlgren, E. Harriet, Markevich, Alexander, Scharinger, Sophie, Fickl, Bernhard, Zagler, Georg, Herterich, Felix, McEvoy, Niall, Mangler, Clemens, and Kotakoski, Jani

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Some of the materials are more affected by oxidation than others. To elucidate the oxidation-induced degradation mechanisms in transition metal chalcogenides, the chemical effects in single layer MoS$_2$ and MoTe$_2$ were studied in situ in an electron microscope under controlled low-pressure oxygen environments at room temperature.Oxidation is the main cause of degradation of many two-dimensional materials, including transition metal dichalcogenides, under ambient conditions. MoTe$_2$ is found to be reactive to oxygen, leading to significant degradation above a pressure of 1$\times 10^{-7}$ torr. Curiously, the common hydrocarbon contamination found on practically all surfaces accelerates the damage rate significantly, by up to a factor of forty. In contrast to MoTe$_2$, MoS$_2$ is found to be inert under oxygen environment, with all observed structural changes being caused by electron irradiation only, leading to well-defined pores with high proportion of molybdenum nanowire-terminated edges. Using density functional theory calculations, a further atomic-scale mechanism leading to the observed oxygen-related degradation in MoTe$_2$ is proposed and the role of the carbon in the etching is explored. Together, the results provide an important insight into the oxygen-related deterioration of two-dimensional materials under ambient conditions relevant in many fields., Comment: 17 pages, 9 figures and 3 tables

Published
2022
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3. Interface effects on titanium growth on graphene

Author

Zagler, Georg, Trentino, Alberto, Mustonen, Kimmo, Mangler, Clemens, and Kotakoski, Jani

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Poor quality interfaces between metal and graphene cause non-linearity and impair the carrier mobility in graphene devices. Here, we use aberration corrected scanning transmission electron microscopy to observe hexagonally close-packed Ti nano-islands grown on atomically clean graphene, and establish a 30{\deg} epitaxial relationship between the lattices. Due to the strong binding of Ti on graphene, at the limit of a monolayer, the Ti lattice constant is mediated by the graphene epitaxy, and compared to bulk Ti, is strained by ca. 3.7% to a value of 0.306(3) nm. The resulting interfacial strain is slightly greater than what has been predicted by density functional theory calculations. Our early growth stage investigations also reveal that, in contrast to widespread assumptions, Ti does not fully wet graphene but grows initially in clusters with a thickness of 1-2 layers. Raman spectroscopy implies charge transfer between the Ti islands and graphene substrate., Comment: 11 pages, 5 figures

Published
2022
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5. Beam-driven dynamics of aluminium dopants in graphene

Author

Zagler, Georg, Stecher, Maximilian, Trentino, Alberto, Kraft, Fabian, Su, Cong, Postl, Andreas, Längle, Manuel, Pesenhofer, Christian, Mangler, Clemens, Åhlgren, E Harriet, Markevich, Alexander, Zettl, Alex, Kotakoski, Jani, Susi, Toma, and Mustonen, Kimmo

Subjects
Physical Sciences, Condensed Matter Physics, scanning transmission electron microscopy, atomic dynamics, heteroatom doping, Ferrari, Aston Martin, Macromolecular and Materials Chemistry, Materials Engineering, Nanotechnology, Materials engineering, Condensed matter physics
Abstract

Substituting heteroatoms into graphene can tune its properties for applications ranging from catalysis to spintronics. The further recent discovery that covalent impurities in graphene can be manipulated at atomic precision using a focused electron beam may open avenues towards sub-nanometer device architectures. However, the preparation of clean samples with a high density of dopants is still very challenging. Here, we report vacancy-mediated substitution of aluminium into laser-cleaned graphene, and without removal from our ultra-high vacuum apparatus, study their dynamics under 60 keV electron irradiation using aberration-corrected scanning transmission electron microscopy and spectroscopy. Three- and four-coordinated Al sites are identified, showing excellent agreement with ab initio predictions including binding energies and electron energy-loss spectrum simulations. We show that the direct exchange of carbon and aluminium atoms predicted earlier occurs under electron irradiation, although unexpectedly it is less probable than the same process for silicon. We also observe a previously unknown nitrogen-aluminium exchange that occurs at Al─N double-dopant sites at graphene divacancies created by our plasma treatment.

Published
2022

6. CuAu, a hexagonal two-dimensional metal

Author

Zagler, Georg, Reticcioli, Michele, Mangler, Clemens, Scheinecker, Daniel, Franchini, Cesare, and Kotakoski, Jani

Subjects
Condensed Matter - Materials Science
Abstract

Growth of two-dimensional metals has eluded materials scientists since the discovery of the atomically thin graphene and other covalently bound 2D materials. Here, we report a two-atom-thick hexagonal copper-gold alloy, grown through thermal evaporation on freestanding graphene and hexagonal boron nitride. The structures are imaged at atomic resolution with scanning transmission electron microscopy and further characterized with spectroscopic techniques. Electron irradiation in the microscope provides sufficient energy for a phase transformation of the 2D structure--atoms are released from their lattice sites with the gold atoms eventually forming face-centered cubic nanoclusters on top of 2D regions during observation. The presence of copper in the alloy enhances sticking of gold to the substrate, which has clear implications for creating atomically thin electrodes for applications utilizing 2D materials. Its practically infinite surface-to-bulk ratio also makes the 2D CuAu particularly interesting for catalysis applications., Comment: 24 pages, including 4 figures in main text and 6 in the supplementary information

Published
2019
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10. Two-step implantation of gold into graphene

Author

Trentino, Alberto, primary, Mizohata, Kenichiro, additional, Zagler, Georg, additional, Längle, Manuel, additional, Mustonen, Kimmo, additional, Susi, Toma, additional, Kotakoski, Jani, additional, and Åhlgren, E Harriet, additional

Published
2022
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11. Speleothems in the dry cave parts of the Gamslöcher- Kolowrat Cave, Untersberg near Salzburg (Austria)

Author

Bieniok Anna, Zagler Georg, Brendel Uwe, and Neubauer Franz

Subjects
calcite powder, mirabilite, thenardite, gypsum, sulfur isotope analysis, Untersberg, Salzburg, Austria, Biology (General), QH301-705.5, Geology, QE1-996.5
Abstract

New, remarkably dry parts of the Gamslöcher-Kolowrat Cave at 728 to 853 m depth have been explored in the Untersberg nearSalzburg in Austria. This region is called the Desert, its greatest cavity is called the White Hall. The new cave part is characterizedby various white speleothems. The predominant ones are snow-like calcite powder with an extremely low density, and finegypsum needles. Gypsum also occurs in the form of balls stuck to vertical walls. In addition, fluorescent hydromagnesite crusts,Mg5(CO3)4(OH)2·4H2O, as well as the sodium sulfate mineral mirabilite were identified in this part of the cave. Mirabilite and gypsumneedles differ from the gypsum balls in their isotopic sulfur signature (δ34S of -16.9‰ and -18.4‰ vs. +2.9‰). The unusually lowsulfur isotopic compositional values are tentatively explained by a source of bacteriogenetic sulfur from sulfides.

Published
2011

12. Atomic‐Scale Oxygen‐Mediated Etching of 2D MoS2 and MoTe2.

Author

Åhlgren, E. Harriet, Markevich, Alexander, Scharinger, Sophie, Fickl, Bernhard, Zagler, Georg, Herterich, Felix, McEvoy, Niall, Mangler, Clemens, and Kotakoski, Jani

Subjects
NANOWIRES, REACTIVE oxygen species, DENSITY functional theory, ETCHING, MOLYBDENUM, DETERIORATION of materials, ELECTRON microscopes
Abstract

Oxidation is the main cause of degradation of many 2D materials, including transition metal dichalcogenides (TMDs), under ambient conditions. Some of the materials are more affected by oxidation than others. To elucidate the oxidation‐induced degradation mechanisms in TMDs, the chemical effects in single layer MoS2 and MoTe2 are studied in situ in an electron microscope under controlled low‐pressure oxygen environments at room temperature. MoTe2 is found to be reactive to oxygen, leading to significant degradation above a pressure of 1 × 10−7 torr. Curiously, the common hydrocarbon contamination found on practically all surfaces accelerates the damage rate significantly, by up to a factor of forty. In contrast to MoTe2, MoS2 is found to be inert under oxygen environment, with all observed structural changes being caused by electron irradiation only, leading to well‐defined pores with high proportion of molybdenum nanowire‐terminated edges. Using density functional theory calculations, a further atomic‐scale mechanism leading to the observed oxygen‐related degradation in MoTe2 is proposed, and the role of the carbon in the etching is explored. Together, the results provide an important insight into the oxygen‐related deterioration of 2D materials under ambient conditions relevant in many fields. [ABSTRACT FROM AUTHOR]

Published
2022
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17. Process Pathway Controlled Evolution of Phase and Van‐der‐Waals Epitaxy in In/In2O3 on Graphene Heterostructures.

Author

Elibol, Kenan, Mangler, Clemens, Gupta, Tushar, Zagler, Georg, Eder, Dominik, Meyer, Jannik C., Kotakoski, Jani, and Bayer, Bernhard C.

Subjects
SCANNING transmission electron microscopy, PHYSICAL vapor deposition, HETEROSTRUCTURES, GRAPHENE, METALLIC oxides
Abstract

Many applications of 2D materials require deposition of non‐2D metals and metal‐oxides onto the 2D materials. Little is however known about the mechanisms of such non‐2D/2D interfacing, particularly at the atomic scale. Here, atomically resolved scanning transmission electron microscopy (STEM) is used to follow the entire physical vapor deposition (PVD) cycle of application‐relevant non‐2D In/In2O3 nanostructures on graphene. First, a "quasi‐in‐situ" approach with indium being in situ evaporated onto graphene in oxygen‐/water‐free ultra‐high‐vacuum (UHV) is employed, followed by STEM imaging without vacuum break and then repeated controlled ambient air exposures and reloading into STEM. This allows stepwise monitoring of the oxidation of specific In particles toward In2O3 on graphene. This is then compared with conventional, scalable ex situ In PVD onto graphene in high vacuum (HV) with significant residual oxygen/water traces. The data shows that the process pathway difference of oxygen/water feeding between UHV/ambient and HV fabrication drastically impacts not only non‐2D In/In2O3 phase evolution but also In2O3/graphene out‐of‐plane texture and in‐plane rotational van‐der‐Waals epitaxy. Since non‐2D/2D heterostructures' properties are intimately linked to their structure and since influences like oxygen/water traces are often hard to control in scalable fabrication, this is a key finding for non‐2D/2D integration process design. [ABSTRACT FROM AUTHOR]

Published
2020
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18. Ferdowsiite:a new mineral from the Barika ore deposit, Iran

Author

Makovicky, Emil, Topa, Dan, Tajeddin, Husein, Putz, Hubert, Zagler, Georg, Makovicky, Emil, Topa, Dan, Tajeddin, Husein, Putz, Hubert, and Zagler, Georg

Abstract

Ferdowsiite is a member of a mineral association subsidiary to the principal metamorphic minerals of the Barika ore deposit in NW Iran. The empirical formula of ferdowsiite (based on 32 apfu, 16Me + 16S) is Ag7.97Pb0.08 Sb4.75As3.15Bi0.01S16.04. The crystal-structure formula is Ag8(Sb5.49As2.51)∑8S16; the simplified formula is Ag8(Sb5As3)∑8S16. The slightly plumbian variety of ferdowsiite has the idealized formula Pb2xAg4−xSb3−xAsS8 with x =~0.2. Ferdowsiite is monoclinic, space group P21/n, a 8.677(2) Å, b 5.799(1) Å, c 13.839(3) Å, β 96.175(4)°, V 692.28(10) Å3, Z = 1 for the formula Ag8(Sb5As3)∑8S16. Calculated powder X-ray data are listed; main diffraction lines are [dcalc (Irel) (hkl)]: 3.225 (96)(113); 3.205 (100)(2̅12); 2.8995 (78)(020); 2.7559 (90)(301); 2.7073 (79)(1̅05); 1.9401 (22)(206); 1.9226 (22)(4̅04). Plumbian ferdowsiite has the same space group, P21/n. It has a 8.746(7) Å, b 5.805(4) Å, c 13.929(10) Å, β 96.236(11)°, unit cell volume 703.05 Å3. The mineral is greyish black, opaque, with dark grey streak and metallic luster. It is brittle with irregular fracture; no cleavage or parting was observed. Calculated density is 5.3 g/cm3. In reflected light ferdowsiite is greyish white. Internal reflections are not observable. Pleochroism is distinct, white to grey. Bireflectance is distinct; reflectance values are [λ(nm), Rmin,Rmax]: 470, 34.9, 37.3; 546, 33.4, 35.9; 589, 32.4, 35.1; 650, 30.7, 33.5. Anisotropism is distinct and rotation tints vary between dark brown and bluish grey. Ferdowsiite is associated with large corroded crystals of arsenquatrandorite and is partly replaced by guettardite. It also corrodes smithite. Ferdowsiite is often associated with tetrahedrite/tennantite and forms worm-like symplectites with it. This symplectite is partly replaced on the surface by guettardite. Ferdowsiite is one more member of the group of ABX2-type sulfosalts of silver, combining antimony and arsenic, with a crystal structure different from other members of

Published
2013

19. Jasrouxite, a new Pb-Ag-As-Sb member of the lillianite homologous series from Jas Roux, Hautes Alpes, France

Author

Topa, Dan, Makovicky, Emil, Favreau, Georges, Bourgoin, Vincent, Boulliard, Jean-Claude, Zagler, Georg, Putz, Hubert, Topa, Dan, Makovicky, Emil, Favreau, Georges, Bourgoin, Vincent, Boulliard, Jean-Claude, Zagler, Georg, and Putz, Hubert

Abstract

The thallium-rich sulfosalt deposit of Jas Roux, situated in the Pelvoux Massif (Hautes-Alpes de´partement, France), occurs in a Triassic sedimentary series. Jasrouxite belongs to the early lead-containing stages of the Tl–As–Sb period of mineralization. It occurs in a silicified gangue, along with smithite and late realgar. Jarouxite forms dark gray anhedral grains with metallic luster, up to several millimeters in size, as well as aggregates of grains which range to more than 10 mm in diameter. From their surface, grains of jasrouxite are embayed by a three-phase myrmekite aggregate composed of stibnite, boscardinite and smithite. The mineral is brittle, with irregular fracture; no cleavage or parting was observed. In reflected light, color is off-white. Bireflectance is weak, in off-white tones; anisotropy is distinct. Rare straight twin lamellae occur in otherwise untwinned crystals. The empirical formula, on the basis of 132 apfu derived from the crystal-structure determination, is Cu0.79Ag14.64Pb4.10Tl0.05As15.37Sb24.87S72.18. Calculated density is 4.87 g.cm3. The simplified formula is Ag16Pb4(Sb25As15)40S72; the only notable variation is the partial substitution As$Sb. Jasrouxite is triclinic, space group P-1. Lattice parameters are a 8.2917(5) A ° , b 19.101(1) A ° , c 19.487(1) A ° , a 89.731(1), b 83.446(1), g 89.944(1), V 3066.1(3) A ° 3, Z ¼ 1 for Ag16Pb4(Sb24As16)40S72. Jasrouxite is a member of the lillianite homologous series, its order number is 4 and degree of Ag þ (Sb, As)$2 Pb substitution is 36.5 % above the theoretical 100 % substitution expressed as PbAg(Sb,As)3S6. The most important features of the crystal structure are: substantial replacement of lead in selected trigonal prismatic sites by Sb, formation of a string of large volumes for accommodation of lone electrons of Sb and As in the central portions of galena-like slabs, and high contents of Ag and (Sb,As).

Published
2013

21. Litochlebite, Ag2PbBi4Se8, a new selenide mineral species from Zalesi, Czech Republic: description and crystal structure

Author

Makovicky, Emil, Topa, Dan, Sejkora, Jiri, Putz, Hubert, Zagler, Georg, Plasil, Jakub, Makovicky, Emil, Topa, Dan, Sejkora, Jiri, Putz, Hubert, Zagler, Georg, and Plasil, Jakub

Abstract

Moravia, Czech Republic. It occurs as irregular grains up to 200 mm, which form aggregates up to 1–2 mm in size in a quartz gangue. These aggregates are replaced along the margins and fractures by a heterogeneous supergene Bi–Se–O phase. Other associated minerals included uraninite, hematite, and uranophane. Litochlebite is opaque, dark grey to black, has a dark grey streak and a metallic luster. No cleavage was observed; the mineral is brittle with an irregular fracture. The VHN10g microhardness 230 (227–234) kg/mm2 corresponds to a Mohs hardness of about 3; the calculated density is 7.90 g/cm3. In reflected light, litochlebite is white, with weak bireflectance (only in oil) and pleochroism from white with a very faint yellowish tint to white with a very faint bluish tint. Between crossed polars, the anisotropy is moderate both in air and in oil, with dark grey to brown polarization-colors. Reflectance values in air (Rmin, Rmax in %, l nm) are: 44.5–49.9 (470), 45.1–50.5 (546), 45.6–51.3 (589), 45.4–51.8 (650). Litochlebite is monoclinic, space group P21/m, with a 13.182(2), b 4.1840(8), c 15.299(2) Å, b 109.11(1)°, V 797.3(2) Å3, and a:b:c 3.1506:1:3.6565. The main lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 3.684(53)(301), 3.201(76)(104), 3.028(100)(311), 2.980(88)(312) and 2.892(95)(005). Its average composition (electron-microprobe data) is Cu 0.10, Ag 10.27, Cd 0.05, Pb 11.73, Bi 43.27, Se 32.93, S 0.01, total 98.36 wt.%. The resulting empirical formula, written on the basis 15 apfu, is (Ag1.84Cu0.03)S1.87 (Pb1.09Cd0.01)S1.10Bi3.99Se8.04. The ideal formula, Ag2PbBi4Se8, requires Ag 11.41, Pb 10.96, Bi 44.22, Se 33.41, total 100.00 wt.%. The crystal structure of litochlebite has been solved by direct methods and refined to R1 = 3.89% on the basis of 938 unique reflections [Fo > 4s(Fo)] collected on a Bruker AXS diffractometer with a CCD detector and MoKa radiation. The crystal structure contains one lead site, four independent Bi site

Published
2011

23. Jasrouxite, a new Pb-Ag-As-Sb member of the lillianite homologous series from Jas Roux, Hautes-Alpes, France

Author

Topa, Dan, Makovicky, Emil, Favreau, Georges, Bourgoin, Vincent, Boulliard, Jean-Claude, Zagler, Georg, and Putz, Hubert

Abstract

The thallium-rich sulfosalt deposit of Jas Roux, situated in the Pelvoux Massif (Hautes-Alpes département, France), occurs in a Triassic sedimentary series. Jasrouxite belongs to the early lead-containing stages of the Tl-As-Sb period of mineralization. It occurs in a silicified gangue, along with smithite and late realgar. Jarouxite forms dark gray anhedral grains with metallic luster, up to several millimeters in size, as well as aggregates of grains which range to more than 10 mm in diameter. From their surface, grains of jasrouxite are embayed by a three-phase myrmekite aggregate composed of stibnite, boscardinite and smithite. The mineral is brittle, with irregular fracture; no cleavage or parting was observed. In reflected light, color is off-white. Bireflectance is weak, in off-white tones; anisotropy is distinct. Rare straight twin lamellae occur in otherwise untwinned crystals. The empirical formula, on the basis of 132 apfuderived from the crystal-structure determination, is Cu0.79Ag14.64Pb4.10Tl0.05As15.37Sb24.87S72.18. Calculated density is 4.87 g. cm-3. The simplified formula is Ag16Pb4(Sb25As15)S40S72; the only notable variation is the partial substitution As?Sb. Jasrouxite is triclinic, space group P-1. Lattice parameters are a8.2917(5) Å, b19.101(1) Å, c19.487(1) Å, a 89.731(1)°, ß 83.446(1)°, ? 89.944(1)°, V3066.1(3) Å3, Z= 1 for Ag16Pb4(Sb24As16)S40S72. Jasrouxite is a member of the lillianite homologous series, its order number is 4 and degree of Ag + (Sb, As) ? 2 Pb substitution is 36.5 % above the theoretical 100 % substitution expressed as PbAg(Sb, As)3S6. The most important features of the crystal structure are: substantial replacement of lead in selected trigonal prismatic sites by Sb, formation of a string of large volumes for accommodation of lone electrons of Sb and As in the central portions of galena-like slabs, and high contents of Ag and (Sb, As).

Published
2014
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