The identification of defects and their controlled generation in titanate nanostructures is a key to their successful application in photoelectronic devices. We comprehensively explored the effect of vacuum annealing on morphology and composition of Na(2)Ti(3)O(7) nanowires and protonated H(2)Ti(3)O(7) nanoscrolls using a combination of scanning electron microscopy, Auger and Fourier-transform infrared (FT-IR) spectroscopy, as well as ab initio density functional theory (DFT) calculations. The observation that H(2)Ti(3)O(7) nanoscrolls are more susceptible to electronic reduction and annealing-induced n-type doping than Na(2)Ti(3)O(7) nanowires is attributed to the position of the conduction band minimum. It is close to the vacuum level and, thus, favors the Fermi level-induced compensation of donor states by cation vacancies. In agreement with theoretical predictions that suggest similar formation energies for oxygen and sodium vacancies, we experimentally observed the annealing induced depletion of sodium from the surface of the nanowires.

Graphical Abstract Beam me up: A novel two-step process allows iron nanostructures to be generated locally on SiOx/Si at 300 K. The surface is first locally activated by an electron beam. Then the activated structures are exposed to [Fe(CO)5], which decomposes and grows autocatalytically to give pure Fe nanocrystals.

Elektronen als “Geheimtinte”: Eine SiOx-Oberfläche kann durch einen fokussierten Elektronenstrahl lokal aktiviert werden (1). Zudosiertes [Fe(CO)5] zersetzt sich dann an den vorherbestimmten Stellen (2), sodass in einem autokatalytischen Prozess reine Fe-Nanokristalle wachsen (3). In ihrer Zuschrift auf S. 4774 ff. beschreiben H. Marbach et al. diesen Zweistufenprozess als möglichen Ausgangspunkt für die Herstellung von Nanostrukturen am Beispiel einer Eisenlinie (siehe 3D-Darstellung von SEM-Daten im Bildhintergrund).

Electrons as Invisible Ink A SiOx surface can be locally activated with a focused electron beam (1) such that subsequently dosed [Fe(CO)5] decomposes (2) and autocatalytically grows to pure Fe nanocrystals (3) at predefined positions until the precursor supply is stopped. In their Communication on page 4669 ff., H. Marbach et al. describe how the two-step process might be the starting point of a novel way to generate nanostructures (see the 3D representation of the SEM data in the background).

Ein neuer zweistufiger Prozess ermöglicht die gezielte Herstellung von Fe- Nanostrukturen auf SiOx/Si bei 300 K. Zunächst wird die Oberfläche lokal mit einem Elektronenstrahl aktiviert. Dann wird auf die aktivierten Strukturen [Fe(CO)5] dosiert, das sich zu Fe zersetzt und autokatalytisch zu Fe-Nanokristalliten weiterwächst.

We explore the electron-beam-induced deposition (EBID) of iron pentacarbonyl, Fe(CO)5, in ultrahigh vacuum (UHV) on clean and modified Rh(110) surfaces by scanning electron microscopy (SEM), scanning Auger microscopy (SAM), and local Auger electron spectroscopy (AES). In EBID a highly focused electron beam is used to locally decompose the iron pentacarbonyl precursor molecules with the goal to generate pure iron nanostructures. It is demonstrated that the selectivity of the process strongly depends on the surface properties. On a perfect, clean Rh(110) surface almost no selectivity is observed; i.e., deposition of Fe is found on irradiated and nonirradiated surface regions due to catalytic decomposition of the Fe(CO)5. However, on a structurally nonperfect Rh(110) surface and on a Ti-precovered Rh(110) surface high selectivity is found; i.e., Fe deposits are primarily formed in irradiated regions. The role of catalytic and autocatalytic growth of iron on clean Rh respective iron deposits is discussed. The purity of the Fe deposits was always very high (>88%). It is demonstrated that the deposited Fe structures can be selectively oxidized to iron oxide by exposure to oxygen. Furthermore, attempts to write Fe line deposits were also successful, and line diameters smaller than 25 nm could be achieved.

The appearance of tetraphenylporphyrins in scanning tunneling micrographs depends strongly on the applied bias voltage. Here, we report the observation and identification of certain features in scanning tunneling microscopy (STM) images of intermixed layers of tetraphenylporphyrin (2HTPP) and cobalt-tetraphenylporphyrin (CoTPP) on Ag(111). A significant fraction of an ordered monolayer of commercially available CoTPP appears as "pits" at negative bias voltages around -1 V. The obvious possibility that these pits are missing molecules within the ordered layer could be ruled out by imaging the molecules at reduced bias voltages, at which the contrast of the pits fades, and at positive bias voltages around +1 V, at which the image contrast is inverted. With the investigation of the electronic structure, in particular the density of states (DOS) close to the Fermi level, of CoTPP and 2HTPP layers by means of ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS), the contrast mechanism was clarified. The correlation of the bias dependent contrast with the UPS data enabled us to interpret the "pits" as individual 2HTPP molecules. Additional evidence could be provided by imaging layers of different mixtures of 2HTPP and CoTPP and by high-resolution STM imaging of the features in CoTPP.

The generation of nanostructures with arbitrary shapes and well-defined chemical composition is still a challenge and targets the core of the fast-growing field of nanotechnology. One approach is the maskless nanofabrication technique of electron-beam-induced deposition (EBID). Up to now, the purity of these EBID structures has been rather poor. Here we demonstrate that by performing the EBID process solely under ultrahigh vacuum conditions, the lithographic generation of iron nanostructures on Si(100) with an unprecedented purity of higher than 95% is possible. One particular new aspect is the formation of EBID deposits with reduced size in a strain-induced diffusive process, resulting in deposits significantly smaller than 10 nm.

The interaction of cobalt(II) tetraphenylporphyrin (CoTPP) and cobalt(II) tetrakis-(3,5-di-tert-butylphenyl)porphyrin (CoTTBPP) with a Ag(111) surface has been investigated with photoelectron spectroscopy (XPS/ UPS). It is demonstrated that these adsorbed metal complexes are excellent model systems for studying the electronic interaction between a coordinated metal ion and a metal surface. The photoelectron spectra and work function data provide evidence that the electronic interaction between the cobalt ion and the silver surface results in a transfer of electron density from the surface to the ion. The presence of an additional electronic state located similar to 1 eV above the singly occupied molecular orbital (SOMO) of the metalloporphyrins is consistent with a molecular orbital (MO) model of the Co-Ag interaction as is the fact that the energetic position of this state depends on the distance between the Co ion and the Ag surface. The adsorbate-induced work function changes for the saturated monolayers amount to -0.72 eV for CoTPP and -0.91 eV for CoTTBPP. For comparison, we also present data of monolayer films of tetraphenylporphyrin and zinc(II) tetraphenylporphyrin.