Martin Tømterud

• Tømterud, Martin; Eder, Sabrina Daniela; Hellner, Simen Kaasa; Büchner, Christin; Heyde, Markus & Freund, Hans-Joachim [Show all 11 contributors for this article] (2025). Helium atom scattering investigation of the boson peak presence in amorphous and crystalline two-dimensional materials. Physical review B (PRB). ISSN 2469-9950. 111(20). doi: 10.1103/PhysRevB.111.205423. Full text in Research Archive Show summary

  The boson peak was recently detected experimentally for the first time in a 2D material (bilayer silica). The experiment was performed using helium atom scattering. Here we apply helium atom scattering in further experimental investigations of the presence of the boson peak in 2D materials. We investigate two crystalline 2D materials (graphene and AB-bilayer graphene) as well as one amorphous 2D material: a 2D silica sample containing nanoscale holes, thus displaying a different mass density from the 2D silica investigated in the previously published experiment. The crystalline materials graphene and bilayer graphene show no indication of the presence of a boson peak. The boson peak in the bilayer silica containing a random distribution of holes is identified at 7±1 meV, which is within the error bars of the value for the first bilayer silica sample previously investigated.

• Tømterud, Martin; Hellner, Simen Kaasa; Eder, Sabrina Daniela; Forti, Stiven; Convertino, Domenica & Manson, Joseph R. [Show all 9 contributors for this article] (2025). Observation of increasing bending rigidity of graphene with temperature. Carbon. ISSN 0008-6223. 238. doi: 10.1016/j.carbon.2025.120150. Full text in Research Archive Show summary

  The mechanical properties of two-dimensional materials are important for a wide range of applications including composite and van der Waals-materials, flexible electronics and superconductivity. Several aspects are highly debated in the literature: For example, the theoretically predicted bending rigidity 𝜅 at 0 K for quasi free-standing graphene varies from 0.8 to 1.6 eV, and there are predictions that it could either increase or decrease with temperature. Here we present an experimental study of the temperature-dependent bending rigidity 𝜅(𝑇 ) of graphene. From the phonon dispersion relation measured with helium atom scattering for the out-of-plane acoustic (ZA) mode, we find 𝜅(𝑇 ) to increase with sample temperature. We compare our experimental results with novel molecular dynamics (MD) simulations performed as part of this study as well as available literature data. The calculations reproduce the temperature trend of our experiments, but with a slightly weaker slope. A probable cause for the observed differences is the slight strain associated with experimental substrate supported graphene that is not present in the calculations.

• Tømterud, Martin; Eder, Sabrina Daniela; Büchner, Christin; Wondraczek, Lothar; Simonsen, Ingve & Schirmacher, Walter [Show all 8 contributors for this article] (2023). Observation of the boson peak in a two-dimensional material. Nature Physics. ISSN 1745-2473. 19, p. 1910–1915. doi: 10.1038/s41567-023-02177-2. Full text in Research Archive Show summary

  The boson peak is an excess in the phonon vibrational density of states relative to the Debye model. It has been observed in a wide range of amorphous materials, from inorganic glasses to polymers. Two-dimensional random matrix models and molecular dynamics simulations predict that the boson peak should also be present in amorphous two-dimensional materials, a notion that is of practical importance because it leads to an excess of heat capacity and influences transport properties. However, up until now, experimental observations in actual materials have not been possible due to the limited surface sensitivity of the methods usually applied to measure the boson peak. Here we present the experimental evidence of a boson peak in two-dimensional silica, through phonon spectra measured by means of inelastic helium-atom scattering. We identify the boson peak as a wavenumber-independent spectral maximum at a frequency similar to what has been observed in and predicted for bulk vitreous silica. Furthermore, we present a heterogeneous-elastic theory calculation in two dimensions, which shows how the vibrational coupling of the transversal and flexural shear vertical phonon modes produces the boson peak in two-dimensional materials at a frequency similar to that of the bulk, in agreement with our measurements.

• Fiedler, Johannes; Berland, Kristian; Borchert, James; Corkery, Robert; Eisfeld, Alexander & Gelbwaser-Klimovsky, David [Show all 20 contributors for this article] (2022). Perspectives on weak interactions in complex materials at different length scales. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 25, p. 2671–2705. doi: 10.1039/d2cp03349f. Full text in Research Archive Show summary

  Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties.

• Tømterud, Martin; Eder, Sabrina Daniela; Büchner, Christin; Heyde, Markus; Freund, Hans Joachim & Manson, Joseph R. [Show all 7 contributors for this article] (2022). Variation of bending rigidity with material density: bilayer silica with nanoscale holes. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 24(30), p. 17941–17945. doi: 10.1039/d2cp01960d. Full text in Research Archive Show summary

  Two dimensional (2D) materials are a young class of materials that is foreseen to play an important role as building blocks in a range of applications, e.g. flexible electronics. For such applications, mechanical properties such as the bending rigidity κ are important. Only a few published measurements of the bending rigidity are available for 2D materials. Nearly unexplored is the question of how the 2D material density influences the bending rigidity. Here, we present helium atom scattering measurements on a “holey” bilayer silica with a density of 1.4 mg m−2, corresponding to 1.7 monolayers coverage. We find a bending rigidity of 6.6 ± 0.3 meV, which is lower than previously published measurements for a complete 2D film, where a value of 8.8 ± 0.5 meV was obtained. The decrease of bending rigidity with lower density is in agreement with theoretical predictions.

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• Tømterud, Martin; Eder, Sabrina Daniela; Bücher, Christin; Wondraczek, Lothar; Simonsen, Ingve & Schirmacher, Walter [Show all 8 contributors for this article] (2022). Observation of the Boson Peak in a 2D Material. Full text in Research Archive
• Tømterud, Martin; Eder, Sabrina Daniela; Bücher, Christin; Wondraczek, Lothar; Simonsen, Ingve & Schirmacher, Walter [Show all 8 contributors for this article] (2022). Observation of the Boson Peak in a 2D Material. Full text in Research Archive
• Tømterud, Martin; Eder, Sabrina Daniela; Bücher, Christin; Wondraczek, Lothar; Simonsen, Ingve & Schirmacher, Walter [Show all 8 contributors for this article] (2022). Observation of the Boson Peak in a 2D Material. Full text in Research Archive
• Tømterud, Martin (2022). The nature of superconductivity in 2D materials revealed by helium atom scattering? Full text in Research Archive

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