Current Status and Future Challenges for Teacher Training for ESD

STEM micrographs of 99% ¹³C graphene imaged with electrons accelerated by a voltage of 100 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed

12C graphene, 85 kV

STEM micrographs of 99% ¹²C graphene imaged with electrons accelerated by a voltage of 85 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed.<br

12C graphene, 95 kV

STEM micrographs of 99% ¹²C graphene imaged with electrons accelerated by a voltage of 95 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed.<br

Atomic Structure of Intrinsic and Electron-Irradiation-Induced Defects in MoTe₂

Studying the atomic structure of intrinsic defects in two-dimensional transition-metal dichalcogenides is difficult since they damage quickly under the intense electron irradiation in transmission electron microscopy (TEM). However, this can also lead to insights into the creation of defects and their atom-scale dynamics. We first show that MoTe₂ monolayers without protection indeed quickly degrade during scanning TEM (STEM) imaging, and discuss the observed atomic-level dynamics, including a transformation from the 1H phase into 1T′, 3-fold rotationally symmetric defects, and the migration of line defects between two 1H grains with a 60° misorientation. We then analyze the atomic structure of MoTe₂ encapsulated between two graphene sheets to mitigate damage, finding the as-prepared material to contain an unexpectedly large concentration of defects. These include similar point defects (or quantum dots, QDs) as those created in the nonencapsulated material and two different types of line defects (or quantum wires, QWs) that can be transformed from one to the other under electron irradiation. Our density functional theory simulations indicate that the QDs and QWs embedded in MoTe₂ introduce new midgap states into the semiconducting material and may thus be used to control its electronic and optical properties. Finally, the edge of the encapsulated material appears amorphous, possibly due to the pressure caused by the encapsulation

12C graphene, 100 kV

STEM micrographs of 99% ¹²C graphene imaged with electrons accelerated by a voltage of 100 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed.<br

13C graphene, 90 kV

STEM micrographs of 99% ¹³C graphene imaged with electrons accelerated by a voltage of 90 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed

12C graphene, 90 kV

STEM micrographs of 99% ¹²C graphene imaged with electrons accelerated by a voltage of 90 kV. Each item in the fileset is a ZIP archive containing a single time series of consecutive frames recorded with a medium angle annular dark field detector until an ejection was observed.<br

Atomic Structure of Intrinsic and Electron-Irradiation-Induced Defects in MoTe₂

Studying the atomic structure of intrinsic defects in two-dimensional transition-metal dichalcogenides is difficult since they damage quickly under the intense electron irradiation in transmission electron microscopy (TEM). However, this can also lead to insights into the creation of defects and their atom-scale dynamics. We first show that MoTe₂ monolayers without protection indeed quickly degrade during scanning TEM (STEM) imaging, and discuss the observed atomic-level dynamics, including a transformation from the 1H phase into 1T′, 3-fold rotationally symmetric defects, and the migration of line defects between two 1H grains with a 60° misorientation. We then analyze the atomic structure of MoTe₂ encapsulated between two graphene sheets to mitigate damage, finding the as-prepared material to contain an unexpectedly large concentration of defects. These include similar point defects (or quantum dots, QDs) as those created in the nonencapsulated material and two different types of line defects (or quantum wires, QWs) that can be transformed from one to the other under electron irradiation. Our density functional theory simulations indicate that the QDs and QWs embedded in MoTe₂ introduce new midgap states into the semiconducting material and may thus be used to control its electronic and optical properties. Finally, the edge of the encapsulated material appears amorphous, possibly due to the pressure caused by the encapsulation

Size and Purity Control of HPHT Nanodiamonds down to 1 nm

High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterized. Moreover we provide experimental evidence of diamond stability down to 1 nm. Controlled annealing at 450 °C in air leads to efficient purification from the nondiamond carbon (shells and dots), as evidenced by X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and scanning transmission electron microscopy. Annealing at 500 °C promotes, besides of purification, also size reduction of nanodiamonds down to ∼1 nm. Comparably short (1 h) centrifugation of the nanodiamonds aqueous colloidal solution ensures separation of the sub-10 nm fraction. Calculations show that an asymmetry of Raman diamond peak of sub-10 nm HPHT nanodiamonds can be well explained by modified phonon confinement model when the actual particle size distribution is taken into account. In contrast, larger Raman peak asymmetry commonly observed in Raman spectra of detonation nanodiamonds is mainly attributed to defects rather than to the phonon confinement. Thus, the obtained characteristics reflect high material quality including nanoscale effects in sub-10 nm HPHT nanodiamonds prepared by the presented method