Two-dimensional layered materials have attracted a lot of attention as building block in memristive devices owing to their high downscaling potential, easy stacking due to van der Waals forces and mechanical flexibility. In this study, memristive switching is explored in vertical device structures based on layered Sb ₂ Te ₃ . For this, epitaxial 2D-like Sb ₂ Te ₃ thin films with thicknesses of ∼20 nm were directly grown on conductive p-type Si (111) substrates by pulsed laser deposition. Analog programmability mimicking neuromorphic operation, stable multilevel retention and endurance performance with a memory window larger than one order of magnitude are achieved by utilizing Ag as electrode metal. However, Cu top electrodes lead to a memristive switching with generally smaller memory window and volatility of programmed states. Devices with both electrode metals offer forming-free operation and self-compliance. Structural and chemical characterization reveal a diffusion of Ag and Cu into the Sb ₂ Te ₃ . It is suggested that charge trapping is involved in the memristive switching mechanism. Overall, this work shows the high potential of thin layered Sb ₂ Te ₃ for neuromorphic computing and offers a scalable method for integration into the existing Si platform.

Ge-Sb-Te-based phase change memory alloys have recently attracted a lot of attention due to their promising applications in the fields of photonics, non-volatile data storage, and neuromorphic computing. Of particular interest is the understanding of the structural changes and underlying mechanisms induced by short optical pulses. This work reports on structural changes induced by single nanosecond UV laser pulses in amorphous and epitaxial Ge₂Sb₂Te₅ (GST) thin films. The phase changes within the thin films are studied by a combined approach using X-ray diffraction and transmission electron microscopy. The results reveal different phase transitions such as crystalline-to-amorphous phase changes, interface assisted crystallization of the cubic GST phase and structural transformations within crystalline phases. In particular, it is found that crystalline interfaces serve as crystallization templates for epitaxial formation of metastable cubic GST phase upon phase transitions. By varying the laser fluence, GST thin films consisting of multiple phases and different amorphous to crystalline volume ratios can be achieved in this approach, offering a possibility of multilevel data storage and realization of memory devices with very low resistance drift. In addition, this work demonstrates amorphization and crystallization of GST thin films by using only one UV laser with one single pulse duration and one wavelength. Overall, the presented results offer new perspectives on switching pathways in Ge-Sb-Te-based materials and show the potential of epitaxial Ge-Sb-Te thin films for applications in advanced phase change memory concepts.

Electrochemical metallization memories have received much attention as candidates for next generation non-volatile memory applications, due to their fast switching speed, simple structure, high scalability and low energy consumption. Chalcogenide compounds like Ge–Sb–Te-based materials are extensively studied solid electrolytes for such devices and considered within the most promising candidates. In this work, the influence of different electrode materials on bipolar resistive switching characteristics of amorphous Ge–Sb–Te thin films with close composition to 2:2:5, prepared by pulsed laser deposition, is studied. Detailed investigations by current-voltage measurements, secondary ion mass spectrometry and cross-sectional transmission electron microscopy in conjunction with energy-dispersive x-ray spectroscopy are presented. Depending on the utilized electrode material, analog switching (Cu, Ag, Ti), digital switching (Co, Cr, Ta, Al) or no switching (Pt, Au and Cr-CrO _x ) occurs. This work shows that the switching behavior of Ge–Sb–Te strongly depends on the solubility and reactivity of the electrode material.

We propose a new design for electrocatalysts consisting of two electrocatalysts (platinum and iron oxide) that are deposited on the surfaces of an oxidized graphene substrate. This design is based on a simple structure where the catalysts were deposited separately on both sides of oxidized graphene substrate; while the iron oxide precipitated out of the etching solution on the bottom-side, the surface of the oxidized graphene substrate was decorated with platinum using the atomic layer deposition technique. The Fe₂O₃-decorated CVD-graphene composite exhibited better hydrogen electrooxidation performance (area-normalized electrode resistance (ANR) of ~600 Ω·cm⁻²) and superior stability in comparison with bare-graphene samples (ANR of ~5800 Ω·cm⁻²). Electrochemical impedance measurements in humidified hydrogen at 240 °C for (Fe₂O₃|Graphene|Platinum) electrodes show ANR of ~0.06 Ω·cm⁻² for a platinum loading of ~60 µg_Pt·cm⁻² and Fe₂O₃ loading of ~2.4 µg_Fe·cm⁻², resulting in an outstanding mass normalized activity of almost 280 S·mg_Pt⁻¹, exceeding even state-of-the-art electrodes. This ANR value is ~30% lower than the charge transfer resistance of the same electrode composition in the absence of Fe₂O₃ nanoparticles. Detailed study of the Fe₂O₃ electrocatalytic properties reveals a significant improvement in the electrode’s activity and performance stability with the addition of iron ions to the platinum-decorated oxidized graphene cathodes, indicating that these hybrid (Fe₂O₃|Graphene|Platinum) materials may serve as highly efficient catalysts for solid acid fuel cells and beyond.