The structural properties of optically thin (15 nm) silver (Ag) films deposited on SiO2/Si(100) substrates with a germanium (Ge) nucleation layer were studied. The morphological and crystallographical characteristics of Ag thin films with different Ge nucleation layer thicknesses were assessed by cross-sectional transmission electron microscopy (XTEM), reflection high-energy electron diffraction (RHEED), X-ray diffractometry (XRD), grazing incidence X-ray diffractometry (GIXRD), X-ray reflection (XRR), and Fourier transform infrared spectroscopy (FTIR). The surface roughness of Ag thin films was found to decrease significantly by inserting a Ge nucleation layer with a thickness in the range of 1 to 2 nm (i.e., smoothing mode). However, as the Ge nucleation layer thickness increased beyond 2 nm, the surface roughness increased concomitantly (i.e., roughing mode). For the smoothing mode, the role of the Ge nucleation layer in the Ag film deposition is discussed by invoking the surface energy of Ge, the bond dissociation energy of Ag-Ge, and the deposition mechanisms of Ag thin films on a given characteristic Ge nucleation layer. Additionally, Ge island formation, the precipitation of Ge from Ag-Ge alloys, and the penetration of Ge into SiO2 are suggested for the roughing mode. This demonstration of ultrasmooth Ag thin films would offer an advantageous material platform with scalability for applications such as optics, plasmonics, and photonics.

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Pt/TiO 2 /Pt vertical resistive random-access memory switching devices were fabricated in a vertical three-dimensional structure by combining conventional photolithography, electron-beam evaporation for electrodes and atomic layer deposition for dielectric layers. The active switching cross-sectional area was ∼0.02 µm 2 , which is comparable to nanosized devices that require more elaborative fabrication processes. Structural integrity and electrical characteristics of the vertical memory device were analysed by cross-sectional scanning, transmission electron microscopy and current-voltage characteristics.1. Introduction: Leon Chua's theoretical discovery of the memristor circuit element in 1971 [1, 2] began the search for a practical material system that displays memristive electrical characteristics. It has the potential to revolutionise computing with application for non-volatile random access memory, dynamic random access memory and flash memory [3][4][5]. Memristor implementation in data routing networks and neuromorphic brain-mimicking networks has also been discussed [6,7]. Resistive memory characteristics were demonstrated by Chen et al.[8] from Spansion LLC using cuprous oxide switching material in a metal-insulator-metal (MIM) structure. Williams and co-workers [9] from HP Labs also realised a non-volatile switching material system in 2006 using a two-terminal Pt/TiO 2 /Pt stack. Since this recent revival of Chua's pursuit of a memristor circuit element, memristive switching, often called resistive random-access memory (RRAM) behaviour, has been identified in a variety of other material systems [10,11]. Chua's recent review of memristors [12] highlights the evolution of memristive systems beginning with pre-historic jellyfish ion channels found from fossil records, then Chua's theoretical discovery in 1971, finalised by HP Labs' successful nanoscale memristor fabrication and then synthesis of a single-molecule memristor at Karlsruhe Technical University.The vacancy drift mechanism understood in HP Labs' MIM material system [13,14] has driven a significant amount of novel studies in fabrication, characterisation and application of metal oxide-based memory material systems. Transition metal oxides have attracted interest in memory devices because of their structural simplicity, high-density integration, fast switching and low power consumption. RRAM devices based on TiO 2 , which shows superior non-volatile switching behaviour [15], have been fabricated using a variety of methods including solution-based processing on flexible substrates [16], electrohydrodynamic inkjet printing [17] and nanoimprint lithography (NIL) [18]. Ella Gale's recent review of TiO 2 devices presents the most current comparison of switching mechanisms, modelling and the overlapping TiO 2 -based research in the memristor and RRAM fields [19]. However, the quest for smaller devices continues, as the vacancy drift mechanism has been accurately modelled and experimentally proven to occur in a device with an active switching area much sm...