Armin Brechling

STM lithography in an organic self-assembled monolayer

We describe the suitability of ultra-high vacuum scanning tunneling microscopy (UHV-STM) based nanolithography by using highly ordered monomolecular organic films, called self-assembled monolayers (SAMs), as ultrathin resists. Organothiol-type SAMs such as hexadecanethiol (SH-(CH2)(15)-CH3) and N-biphenylthiol (SH-(C6H6)(2)-NO2) monolayers have been prepared by immersion on gold films and Au(111) single crystals. Organosilane-type SAMs such as octadecyltrichlorosilane (SiCl3-(CH2)(17)-CH3) monolayers have been prepared on hydroxylated Si(100) surfaces as well as hydroxylated chromium film surfaces Dense line patterns have been written by UHV-STM in constant current mode for various tunneling parameters (gap voltage, tunneling current, scan speed, and orientation) and transferred into the underlying substrate by wet etch techniques The etched structures have been analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). Best resolution has been achieved without etch transfer for a 20 nm x 20 nm square written in hexadecanethiol/Au(111) with an edge definition of about 5 nm. Etch transfer of the STM nanopatterns in Au films resulted in 55 nm dense lint: patterns (15 nm deep) mainly broadened by the isotropic etch characteristic. while 35 nm wide and 30 nm deep dense line patterns written in octadecyl trichlorosilane/Si(100) and anisotropically etched into Si(100) could be achieved.

Characterization of DMPC bilayers and multilamellar islands on hydrophobic self-assembled monolayers of ODS/Si(100) and mixed ODS-DDS/Si(100)

Abstract We have examined the lamellar structure of l -α-dimyristoylphosphatidylcholine (DMPC) bilayers and multilamellar islands grown on monocomponent and bicomponent Self-Assembled Monolayers (SAM) of octadecylsiloxane (ODS), and mixed octadecylsiloxane/dodecylsiloxane (ODS/DDS), respectively. Electron density profiles revealed by hard X-ray reflectometry measurements show significant structural differences of the DMPC films on both surfaces. While DMPC grown on uniform ODS results in the formation of unilamellar and multilamellar islands of DMPC bilayers, DMPC growth on a mixed ODS/DDS-SAM results in the formation of a (almost) closed DMPC bilayer adsorbed onto the mixed SAM. The results are explained in terms of an increased van der Waals interaction of the DMPC alkyl chains with the SAM alkyl chains of the mixed ODS/DDS SAM. Swelling in water at increasing temperatures in between 50 °C and 95 °C, results in a reduced DMPC island height due to thermal unbinding of DMPC bilayers, in case of the DMPC/ODS system. Further, characterization by nc-AFM displays the lateral shape and size of the islands as well as the discrete height distribution of the islands, which is in good agreement with the X-ray reflectometry measurements.

Spin resolved photoelectron spectroscopy of [Mn6IIICrIII]3 + single-molecule magnets and of manganese compounds as reference layers

Properties of the manganese-based single-molecule magnet [Mn(6)(III)Cr(III)](3+) are studied. It contains six Mn(III) ions arranged in two bowl-shaped trinuclear triplesalen building blocks linked by a hexacyanochromate and exhibits a large spin ground state of S(t) = 21/2. The dominant structures in the electron emission spectra of [Mn(6)(III)Cr(III)](3+) resonantly excited at the L(3)-edge are the L(3)M(2, 3)M(2, 3), L(3)M(2, 3)V and L(3)VV Auger emission groups following the decay of the primary p(3/2) core hole state. Significant differences of the Auger spectra from intact and degraded [Mn(6)(III)Cr(III)](3+) show up. First measurements of the electron spin polarization in the L(3)M(2, 3)V and L(3)VV Auger emission peaks from the manganese constituents in [Mn(6)(III)Cr(III)](3+) resonantly excited at the L(3)-edge near 640 eV by circularly polarized synchrotron radiation are reported. In addition spin resolved Auger electron spectra of the reference substances MnO, Mn(2)O(3) and Mn(II)(acetate)(2)·4H(2)O are given. The applicability of spin resolved electron spectroscopy for characterizing magnetic states of constituent atoms compared to magnetic circular dichroism (MCD) is verified: the spin polarization obtained from Mn(II)(acetate)(2)·4H(2)O at room temperature in the paramagnetic state compares to the MCD asymmetry revealed for a star-shaped molecule with a Mn(4)(II)O(6) core at 5 K in an external magnetic field of 5 T.

Actinic extreme ultraviolet lithography mask blank defect inspection by photoemission electron microscopy

A new method for the actinic inspection of defects inside and on top of extreme ultraviolet (EUV) lithography multilayer-coated mask blanks is presented. The experimental technique is based on photoemission electron microscopy supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5nm. Experimental results on programed defect samples based on electron beam lithographic structures or silica balls overcoated with an EUV multilayer show that buried defects with a lateral size down to 50nm are detectable. Furthermore, phase structures as shallow as 6nm in height on a programed phase grating sample have been detected by this technique. The contrast of the phase defect structures has shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface, and thus can be optimized by tuning the inspection wavelength.

Preparation of monolayers of [MnIII6CrIII]3+ single-molecule magnets on HOPG, mica and silicon surfaces and characterization by means of non-contact AFM

We report on the characterization of various salts of [MnIII6CrIII]3+ complexes prepared on substrates such as highly oriented pyrolytic graphite (HOPG), mica, SiO2, and Si3N4. [MnIII6CrIII]3+ is a single-molecule magnet, i.e., a superparamagnetic molecule, with a blocking temperature around 2 K. The three positive charges of [MnIII6CrIII]3+ were electrically neutralized by use of various anions such as tetraphenylborate (BPh4-), lactate (C3H5O3-), or perchlorate (ClO4-). The molecule was prepared on the substrates out of solution using the droplet technique. The main subject of investigation was how the anions and substrates influence the emerging surface topology during and after the preparation. Regarding HOPG and SiO2, flat island-like and hemispheric-shaped structures were created. We observed a strong correlation between the electronic properties of the substrate and the analyzed structures, especially in the case of mica where we observed a gradient in the analyzed structures across the surface.

Bufferlayer and caplayer engineering of Mo/Si EUVL multilayer mirrors

Bufferlayer and caplayer engineering strategies are getting progressively important for improving crucial properties of EUVL multilayer optics and EUV reflection masks. While bufferlayers modifying the contact between the reflecting interference multilayer and the superpolished substrate aim for a partial smoothing of the residual substrate roughness or for a mitigation of local substrate defects as well as for multilayer film stress relaxation, surface caplayers are capable to enhance the multilayer reflectivity of EUV mirrors and masks. We present experimental results on various bufferlayer systems (singlelayer and multilayer) applied to different substrate materials (ULE, Zerodur, silicon). The bufferlayers have been deposited by e-beam evaporation and ion-polishing techniques at UHV conditions and substrates with and without bufferlayer have been coated with standard Mo/Si multilayers (50 doublelayers, d-spacing 6.8 nm) in the same deposition run. The samples have been analyzed exsitu by means of AFM, TEM, X-ray scattering and reflection and normal-incidence EUV reflectance measurements. We have found significant improvement (+ 0.7 %) of the Mo/Si multilayer EUV reflectivity for some bufferlayer systems applied to substrates with 0.2 - 0.3 nm r.m.s. high spatial frequency roughness (HSFR), while no effect was found on superpolished substrates exhibiting 0.1 nm r.m.s HSFR. The effect of caplayer modification applied to Mo/Si multilayers has been examined regarding EUV reflectivity. The native siliconoxide layer on top of the Mo/Si multilayer coatings has been replaced by an ultrathin (2 nm) chemically inert caplayer. We have found a 1 % - 1.5 % improvement in EUV peak reflectance for one cap material applied to several Mo/Si multilayer in comparison to a native siliconoxide cap.

Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

Monolayers and submonolayers of [MnIII6CrIII]3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

The structure of [MnIII6 CrIII]3+ single-molecule magnets deposited in submono-layers and monolayers on surfaces studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin Probe Force Microscopy in UHV

Single molecule magnets (SMM) deposited in submonolayers and monolayers have been analyzed with respect to their structures by means of non-contact AFM (topographic as well as damping mode) and Kelvin Probe Force Microscopy with molecular resolution.

The local magnetic properties of [MnIII6 CrIII]3+ and [FeIII6 CrIII]3+ single-molecule magnets deposited on surfaces studied by spin-polarized photoemission and XMCD with circularly polarized synchrotron radiation

It is demonstrated that local magnetic moments of single molecule magnets (SMM) normally studied by XMCD at very low temperatures and high magnetic fields can be measured by means of spin-resolved electron emission in the paramagnetic phase at room temperature by use of circularly polarized radiation.

The adsorption, stability and properties of Mn6Cr Single-Molecule-Magnets studied by means of nc-AFM, STM, XAS and Spin-resolved Photoelectron Spectroscopy

The ionic single-molecule-magnet [MnIII6CrIII]3 with corresponding three counterions has been deposited on different surfaces and studied with respect to its structure and its electronic and magnetic properties. This is the first time that spin polarization of photoelectrons ejected by means of circularly polarized synchrotron radiation has been measured in a single-molecule-magnet.