Abstract:Effects of thickness on the electronic structure of e-beam evaporated thin titanium films were studied using near-edge X-ray absorption fine structure (NEXAFS) technique at titanium L 2,3 edge in total electron yield (TEY) mode and transmission yield mode. Thickness dependence of L 2,3 branching ratio (BR) of titanium was investigated and it was found that BR below 3•5 nm shows a strong dependence on film thickness. Mean electron escape depth (λ) in titanium, an important parameter for surface applications, wa… Show more
“…Previous studies showed that increase of 3d electrons spatial localization causes growth of the BR as the screening of the 2p -3d interaction becomes weaker. [63][64][65][66] This phenomenon was observed for a wide set of 3d TMs in thin layers with different thickness 63,65,66 and clusters of different size. 64 In both systems, increase of the layer thickness or cluster radius leads to gradual decrease in the BR.…”
“…Previous studies showed that increase of 3d electrons spatial localization causes growth of the BR as the screening of the 2p -3d interaction becomes weaker. [63][64][65][66] This phenomenon was observed for a wide set of 3d TMs in thin layers with different thickness 63,65,66 and clusters of different size. 64 In both systems, increase of the layer thickness or cluster radius leads to gradual decrease in the BR.…”
“…An additional 100 nm thick Al layer is prepared on top of Au and Ti. Although the Ti layer is relatively thinner than the other metal layers, its electrons state should be comparable to that of the thicker, e.g., 10 nm, Ti film 19 so that its covalent bonding ability with the WSe 2 layer is guaranteed.Figure 2( a–c ) Optical images of WSe 2 flakes prepared on an Al 2 O 3 substrate. ( d – f ) Time-domain thermoreflectance mapping results for Al/WSe 2 /Al 2 O 3 , Al/Au/WSe 2 /Al 2 O 3 , and Al/Ti/WSe 2 /Al 2 O 3 .…”
Section: Distinct Thermal Properties Of the Mono- And Bi-layered Wse2mentioning
In nano-device applications using two-dimensional (2D) van der Waals materials, a heat dissipation through nano-scale interfaces can be a critical issue for optimizing device performances. By using a time-domain thermoreflectance measurement technique, we examine a cross-plane thermal transport through mono-layered (
n
= 1) and bi-layered (
n
= 2) WSe
2
flakes which are sandwiched by top metal layers of Al, Au, and Ti and the bottom Al
2
O
3
substrate. In these nanoscale structures with hetero- and homo-junctions, we observe that the thermal boundary resistance (TBR) is significantly enhanced as the number of WSe
2
layers increases. In particular, as the metal is changed from Al, to Au, and to Ti, we find an interesting trend of TBR depending on the WSe
2
thickness; when referenced to TBR for a system without WSe
2
, TBR for
n
= 1 decreases, but that for
n
= 2 increases. This result clearly demonstrates that the stronger bonding for Ti leads to a better thermal conduction between the metal and the WSe
2
layer, but in return gives rise to a large mismatch in the phonon density of states between the first and second WSe
2
layers so that the WSe
2
-WSe
2
interface becomes a major thermal resistance for
n
= 2. By using photoemission spectroscopy and optical second harmonic generation technique, we confirm that the metallization induces a change in the valence state of W-ions, and also recovers a non-centrosymmetry for the bi-layered WSe
2
.
We report on the soft x-ray absorption spectroscopy investigation of thin film capacitors using a modified total electron yield detection mode. This mode utilizes two ammeters instead of one as commonly employed in the classical total electron yield scheme to measure photocurrents of devices under soft x-ray irradiation. The advantage of this configuration over the surface sensitive classical total electron yield mode is that it can provide information from buried layers and interfaces up to a thickness equal to the penetration depth of soft x-rays. The method can be easily adapted to existing synchrotron end stations. We investigate dielectric capacitors with dissimilar electrodes to assess the feasibility of the modified total electron yield method. Furthermore, in operando soft x-ray absorption spectroscopy measurements are performed on ferroelectric capacitors under bias and using two ammeters. The experimental results are discussed in terms of the external and internal photoemission processes and their distribution in thin film capacitors under an external bias condition. The proposed detection method opens the way to perform electronic and chemical state analyses of the buried interfaces and layers in various devices like multiferroic tunnel junctions, memristive devices, etc., during operation under an applied bias.
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