Rare-earth oxide superlattices on Si(111)
- TEM images of a 12 x (2 ML Lu2O3, 2 ML La2O3) + 2 ML Lu2O3 layer on Si(111) grown at a substrate temperature of 500 °C. The low resolution image on the right shows the periodic superlattice.
Digital epitaxial rare-earth oxide layers are grown on Si(111) substrates from oxide source material by molecular beam epitaxy at substrate temperatures as low as 200 °C. X-ray diffraction and transmission electron microscopy confirm the formation of digital layers with an abrupt interface to the substrate. The large lattice mismatch of 9% between La2O3 and Lu2O3 symmetric to Si allows for an intentional variation of both the internal strain of the superlattice and its average lattice mismatch with the substrate over a wide range. Theoretical investigations employing density functional theory indicate that the physical properties of the layer such as its dielectric constant vary with internal strain, thereby offering new ways for the design of gate dielectrics for future CMOS devices.
In situ x-ray diffraction MBE system with TUBO sources for oxide growth by CreaTec.
Frank Grosse, Sergiy Bokoch, Steffen Behnke, Andre Proessdorf, Michael Niehle, Achim Trampert, Wolfgang Braun, Henning Riechert, Rare-earth oxide superlattices on Si(111), J. Cryst. Growth 323 (2011) 95.
Drift of LT-STM
Long-term drift (lateral image stability) of the CreaTec Besocke Type STM with Au(111) measured at 5K (base temperature).
Data courtesy of Dr. Daniel Wegner (CeNTech, Münster).
2011-06-28
Multistable switching in adatom chains on a III-V semiconductor surface
- Three-dimensional rendering of an STM image showing a sequence of eight In adatoms positioned by vertical manipulation on an InAs(111)A surface to form a linear chain. Pairs of adjacent adatoms can be reversibly switched by the STM tip to form a defect imaged as a large uniform protrusion. The prominent features in the image show two such defects.
Scanning tunneling microscopy (STM) at 5 K reveals that native In atoms in the surface layer of a InAs(111)A crystal become bistable in vertical height when a nanostructure is assembled nearby. The binary (reversible) switching of surface atoms, driven by the STM tip, changes their charge state. Coupling between these switching units via Coulomb interaction is facilitated by assembling adatom chains, allowing us to explore the emergence of complex multiple switching at the atomic scale.
LT-STM by CreaTec.
Jianshu Yang, Steven C. Erwin, Kiyoshi Kanisawa, Christophe Nacci, Stefan Fölsch, Emergent multistability in assembled nanostructures, Nano Letters 11 (2011) 2486.
Low temperature synthesis of quantum wires
- Analytical transmission electron micrograph of a cross-section of an Al/Si bilayer during annealing. Si migrates along the Al grain boundaries at temperatures as low as 120 °C (© MPI for Intelligent Systems, Stuttgart).
Semiconductor nanowires are key materials for advanced technologies, such as highly efficient solar cells, high energy density batteries and nanoscale electronic devices. Their large scale production, however, is hampered by the high process temperatures (600-900 °C) and the use of expensive catalysts, such as gold.
A new process has been developed which allows the synthesis of Si nanowires at strikingly low temperatures of 150 °C, while using cheap Al as a catalyst. The high-purity Si film deposited on top of the Al layer migrates along the Al grain-boundary network upon annealing, thereby forming a dense array of crystalline nanowires. This new process does not require a solubility of the semiconductor in the catalyst material. The low-temperature nature of the process thus allows the direct integration of nanostructured semiconductor devices on heat sensitive polymers.
Si grown from TUBO Si source by CreaTec.
Zumin Wang, Lin Gu, Fritz Phillipp, Jiang Y. Wang, Lars P.H. Jeurgens, Eric J. Mittemeijer, Metal-catalyzed growth of semiconductor nanostructures without solubility and diffusivity constraints, Advanced Materials 23 (2011) 854-859.