Abstract:X-ray excited photoelectron spectroscopy is used to analyse the near-surface properties of CuInTez single crystals grown by the vertical Bridgman method. It is found that keeping the crystals at room temperature in air for relatively short times is sufficient for the formation of an oxide layer which consists mainly of TeOz. No detectable amounts of copper or indium oxides could be observed.
“…Instead, the Te chalcogen signal of PdTe 2 comprises three observed features: a conspicuous Te 3d 5/2 peak at 575.9 eV that corresponds to Te(IV) species; a broad shoulder Te 3d 5/2 peak at 577.6 eV that stems from Te(VI) species; and a modest Te 3d 5/2 peak at 573.1 eV that arises from the Te(0) state. PtTe 2 demonstrates a pair of distinct doublet Te signals (3d 5/2 and 3d 3/2 ) at binding energies of 572.8 and 583.2 eV, and 575.2 and 585.6 eV, which are respectively indexed to Te(0) and Te(IV) states. ,, …”
Section: Results
and Discussionmentioning
confidence: 99%
“…PtTe 2 demonstrates a pair of distinct doublet Te signals (3d 5/2 and 3d 3/2 ) at binding energies of 572.8 and 583.2 eV, and 575.2 and 585.6 eV, which are respectively indexed to Te(0) and Te(IV) states. 12,29,30 The discrepancy in the oxidation states of metal and chalcogen from the ideal states is rationalized by the electronic band structure of PdTe 2 and PtTe 2 . Both noble metal tellurides display strong orbital mixing in p and d bands, anomalous to the energetically separated bands reported for layered TMDs belonging to earlier groups.…”
Section: ■ Results and Discussionmentioning
confidence: 99%
“…Focusing on 3d 5/2 binding energies, the pair of peaks of the reduced PdTe 2 occurring at 575.5 and 572.3 eV ascribes to Te(IV) and combined Te(0) and Te(−II) states in sequence. Substantial amounts of Te(0) and Te(−II) assigned at 3d 5/2 binding energies of 572.8 and 572.0 eV merge into a peak at 572.3 eV 12,24,29. Similarly, electrochemical treatment of PtTe 2 also engendered marked shifts in the Te 3d signals.…”
Owing to the anisotropic nature, layered transition metal dichalcogenides (TMDs) have captured tremendous attention for their promising uses in a plethora of applications. Currently, bulk of the research is centered on Group 6 TMDs. Layered noble metal dichalcogenides, in particular the noble metal tellurides, belong to a subset of Group 10 TMDs, wherein the transition metal is a noble metal of either palladium or platinum. We address here a lack of contemporary knowledge on these compounds by providing a comprehensive study on the electrochemistry of layered noble metal tellurides, PdTe and PtTe, and their efficiency as electrocatalysts toward the hydrogen evolution reaction (HER). Observed parallels in the electrochemical peaks of the noble metal tellurides are traced to the tellurium electrochemistry. PdTe and PtTe can be discriminated by their distinct reduction peaks in the first cathodic scans. Considering the influence of the metal component, PtTe outperforms PdTe in aspects of charge transfer and electrocatalysis. The heterogeneous electron transfer (HET) rate of PtTe is an order of magnitude faster than PdTe, and a lower HER overpotential of 0.54 V versus reversible hydrogen electrode (RHE) at a current density of -10 mA cm is evident in PtTe. On PdTe and PtTe surfaces, adsorption via the Volmer process has been identified as the limiting step for HER. A general phenomenon for the noble metal tellurides is that faster HET rates are observed upon electrochemical reductive pretreatment, whereas slower HET rates occur when the noble metal tellurides are oxidized during pretreatment. PtTe becomes successfully activated for HER when subject to oxidative treatment, whereas oxidized or reduced PdTe shows a deactivated HER performance. These findings provide fundamental insights that are pivotal to advancing the field of the underemphasized TMDs. Furthermore, electrochemical tuning as a means to tailor specific properties of the TMDs is advantageous for the development of their future applications.
“…Instead, the Te chalcogen signal of PdTe 2 comprises three observed features: a conspicuous Te 3d 5/2 peak at 575.9 eV that corresponds to Te(IV) species; a broad shoulder Te 3d 5/2 peak at 577.6 eV that stems from Te(VI) species; and a modest Te 3d 5/2 peak at 573.1 eV that arises from the Te(0) state. PtTe 2 demonstrates a pair of distinct doublet Te signals (3d 5/2 and 3d 3/2 ) at binding energies of 572.8 and 583.2 eV, and 575.2 and 585.6 eV, which are respectively indexed to Te(0) and Te(IV) states. ,, …”
Section: Results
and Discussionmentioning
confidence: 99%
“…PtTe 2 demonstrates a pair of distinct doublet Te signals (3d 5/2 and 3d 3/2 ) at binding energies of 572.8 and 583.2 eV, and 575.2 and 585.6 eV, which are respectively indexed to Te(0) and Te(IV) states. 12,29,30 The discrepancy in the oxidation states of metal and chalcogen from the ideal states is rationalized by the electronic band structure of PdTe 2 and PtTe 2 . Both noble metal tellurides display strong orbital mixing in p and d bands, anomalous to the energetically separated bands reported for layered TMDs belonging to earlier groups.…”
Section: ■ Results and Discussionmentioning
confidence: 99%
“…Focusing on 3d 5/2 binding energies, the pair of peaks of the reduced PdTe 2 occurring at 575.5 and 572.3 eV ascribes to Te(IV) and combined Te(0) and Te(−II) states in sequence. Substantial amounts of Te(0) and Te(−II) assigned at 3d 5/2 binding energies of 572.8 and 572.0 eV merge into a peak at 572.3 eV 12,24,29. Similarly, electrochemical treatment of PtTe 2 also engendered marked shifts in the Te 3d signals.…”
Owing to the anisotropic nature, layered transition metal dichalcogenides (TMDs) have captured tremendous attention for their promising uses in a plethora of applications. Currently, bulk of the research is centered on Group 6 TMDs. Layered noble metal dichalcogenides, in particular the noble metal tellurides, belong to a subset of Group 10 TMDs, wherein the transition metal is a noble metal of either palladium or platinum. We address here a lack of contemporary knowledge on these compounds by providing a comprehensive study on the electrochemistry of layered noble metal tellurides, PdTe and PtTe, and their efficiency as electrocatalysts toward the hydrogen evolution reaction (HER). Observed parallels in the electrochemical peaks of the noble metal tellurides are traced to the tellurium electrochemistry. PdTe and PtTe can be discriminated by their distinct reduction peaks in the first cathodic scans. Considering the influence of the metal component, PtTe outperforms PdTe in aspects of charge transfer and electrocatalysis. The heterogeneous electron transfer (HET) rate of PtTe is an order of magnitude faster than PdTe, and a lower HER overpotential of 0.54 V versus reversible hydrogen electrode (RHE) at a current density of -10 mA cm is evident in PtTe. On PdTe and PtTe surfaces, adsorption via the Volmer process has been identified as the limiting step for HER. A general phenomenon for the noble metal tellurides is that faster HET rates are observed upon electrochemical reductive pretreatment, whereas slower HET rates occur when the noble metal tellurides are oxidized during pretreatment. PtTe becomes successfully activated for HER when subject to oxidative treatment, whereas oxidized or reduced PdTe shows a deactivated HER performance. These findings provide fundamental insights that are pivotal to advancing the field of the underemphasized TMDs. Furthermore, electrochemical tuning as a means to tailor specific properties of the TMDs is advantageous for the development of their future applications.
“…The spectra have therefore been fitted with three components. The major component at 582.9 eV is related with the TiTe alloy using simple electronegativity arguments, the second component at 583.6 eV is characteristic of elemental semiconductor Te and the HBE component at 584.9 eV is related to the oxide (TeO x ) 32,33 .Figure 3( a ) Te 3 d 3/2 and ( b ) Al 1 s core level peaks obtained by HAXPES at 6.9 keV on as-grown, formed and the reset sample of the TaN/TiTe/Al 2 O 3 /Ta stack.…”
We report the chemical phenomena involved in the reverse forming (negative bias on top electrode) and reset of a TaN/TiTe/Al2O3/Ta memory stack. Hard X-ray photoelectron spectroscopy was used to conduct a non-destructive investigation of the critical interfaces between the electrolyte (Al2O3) and the TiTe top and Ta bottom electrodes. During reverse forming, Te accumulates at the TiTe/Al2O3 interface, the TiOx layer between the electrolyte and the electrode is reduced and the TaOx at the interface with Al2O3 is oxidized. These interfacial redox processes are related to an oxygen drift toward the bottom electrode under applied bias, which may favour Te transport into the electrolyte. Thus, the forming processes is related to both Te release and also to the probable migration of oxygen vacancies inside the alumina layer. The opposite phenomena are observed during the reset. TiOx is oxidized near Al2O3 and TaOx is reduced at the Al2O3/Ta interface, following the O2− drift towards the top electrode under positive bias while Te is driven back into the TiTe electrode.
International audienceWe investigated origins of the resistivity change during the forming of ZrTe/Al$_2$O$_3$ based conductive-bridge resistive random access memories. Non-destructive hard X-ray photoelectron spectroscopy was used to investigate redox processes with sufficient depth sensitivity. Results highlighted the reduction of alumina correlated to the oxidation of zirconium at the interface between the solid electrolyte and the active electrode. In addition the resistance switching caused a decrease of Zr-Te bonds and an increase of elemental Te showing an enrichment of tellurium at the ZrTe/Al$_2$O$_3$ interface. XPS depth profiling using argon clusters ion beam confirmed the oxygen diffusion towards the top electrode. A four-layer capacitor model showed an increase of both the ZrO$_2$ and AlO$_x$ interfacial layers, confirming the redox process located at the ZrTe/Al$_2$O$_3$ interface. Oxygen vacancies created in the alumina help the filament formation by acting as preferential conductive paths. This study provides a first direct evidence of the physico-chemical phenomena involved in resistive switching of such devices
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