arXiv subjects

Helmut H. Telle

Publications and source records attributed to Helmut H. Telle.

4 recordsLinked to original sources

arXiv2026

Following the Long-Term Evolution of sp$^3$-type Defects in Tritiated Graphene using Raman Spectroscopy

We report on the evolution of tritium-induced sp$^3$-defects in monolayer graphene on a Si/SiO$_2$ substrate, by comparing large-area Raman maps of the same two samples, acquired just after fabrication and twice thereafter, about 9-12 months apart. Inbetween measurements the samples were kept under standard laboratory conditions. Using a conservative classification of sp$^3$-type spectra, based on the D/D' peak intensity ratio, we observed almost complete depletion of sp$^3$-type defects over the investigation period of about two years. This by far exceeds the ~5.5% annual reduction expected from tritium decay alone (~3x larger). This change in the defect composition is accompanied by a recovery of the 2D-band of graphene and an overall decrease in defect-density, as determined via the D/G intensity ratio. Hydogenated graphene is reported to be reasonably stable over several months, when kept under vacuum, but suffers substantial hydrogen loss under laboratory air conditions. While the results shown here for tritiated graphene exhibit similarities with hydrogenated graphene, however, some distinct differences are observed.

cond-mat.mtrl-sci↗

arXiv2024

Demonstration of tritium adsorption on graphene

In this work, we report on studies of graphene exposed to tritium gas in a controlled environment. The single layer graphene on a $\textrm{SiO}_2$/Si substrate was exposed to 400 mbar of $\textrm{T}_2$ for a total time of $\approx$ 55 h. The resistivity of the graphene sample was measured $\textit{in situ}$ during tritium exposure using the Van der Pauw method. We found that the sheet resistance increases by three orders of magnitude during the exposure, suggesting significant chemisorption of tritium. After exposure, the samples were characterised $\textit{ex situ}$ via spatio-chemical mapping with a confocal Raman microscope, to study the effect of tritium on the graphene structure (tritiation yielding T-graphene), as well as the homogeneity of modifications across the whole area of the graphene film. The Raman spectra after tritium exposure were comparable to previously observed results in hydrogen-loading experiments, carried out by other groups. By thermal annealing we also could demonstrate, using Raman spectral analysis, that the structural changes were largely reversible. Considering all observations, we conclude that the graphene film was at least partially tritiated during the tritium exposure, and that the graphene film by and large withstands the bombardment by electrons from the $β$-decay of tritium, as well as by energetic primary and secondary ions.

cond-mat.mes-hall↗

arXiv2023

The Generation and Analysis of Tritium-substituted Methane

An unavoidable category of molecular species in large-scale tritium applications, such as nuclear fusion, are tritium-substituted hydrocarbons; these form by radiochemical reactions in the presence of (circulating) tritium and carbon (mainly from the steel of vessels and tubing). Tritiumsubstituted methane species, CQ$_4$ (with Q = H , D , T), are often the precursor for higher-order reaction chains, and thus are of particular interest. Here we describe the controlled production of CQ$_4$ carried out in the CAPER facility of the Tritium Laboratory Karlsruhe (TLK), exploiting catalytic reactions and species-enrichment via the CAPER-integral permeator. CQ4 was generated in substantial quantity (>1000 cm$^3$ at ~850 mbar, with CQ$_4$ - content of up to ~20 %). These samples were analyzed using laser Raman and mass spectrometry, to determine the relative isotopologue composition and to trace the generation of tritiated chain-hydrocarbons.

physics.chem-ph↗

arXiv2012

Monitoring of tritium purity during long-term circulation in the KATRIN test experiment LOOPINO using laser Raman spectroscopy

The gas circulation loop LOOPINO has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK) to perform Raman measurements of circulating tritium mixtures under conditions similar to the inner loop system of the neutrino-mass experiment KATRIN, which is currently under construction. A custom-made interface is used to connect the tritium containing measurement cell, located inside a glove box, with the Raman setup standing on the outside. A tritium sample (purity > 95%, 20 kPa total pressure) was circulated in LOOPINO for more than three weeks with a total throughput of 770 g of tritium. Compositional changes in the sample and the formation of tritiated and deuterated methanes CT_(4-n)X_n (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium β decay. A precision of 0.1% was achieved for the monitoring of the T_2 Q_1-branch, which fulfills the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box.

physics.ins-det↗