SESSION E - ADVANCED METHODS OF PREPARATION AND CHARACTERIZATION OF NANOMATERIALS

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) allow to image surfaces with atomic resolution, to perform local spectroscopy of current versus voltage, forces and dissipation. The qPlus force sensor [1] is a sensitive eye and hand to the nanoworld by combining STM and AFM capability, enabling highly precise imaging and spectroscopy functions and measuring the forces that act during atomic manipulation [2]. While STM had better spatial resolution than AFM in the past, the situation is reversed now with modern AFM [3]. Angular dependencies of chemical bonding forces have been observed before for Si tips interacting with Si surfaces [4], W tips interacting with graphite [5] and similarities exist between metal tips interacting with CO molecules on Cu and Si adatoms [6]. In the latter two cases, light atoms such as carbon or oxygen interacted with much heavier and much larger metal atoms. Recently, Gross et al. found that CO is an excellent probe for organic molecules. For example, pentacene can be imaged at excellent resolution with CO terminated tips [7], although the softness of CO on tips can lead to image distortions [8,9]. Tips made of permanent magnets such as CoSm allow to resolve the spin order in the antiferromagnetic insulator nickel oxide [10]. The stiff cantilever/small amplitude technique used here also allows true atomic resolution in ambient conditions [11], and small iron clusters on Cu (111) (a trimer and a dimer on the figure above) are resolved by force microscopy [12].
REFERENCES:
[1] F. J. Giessibl, Appl. Phys. Lett. 73, 3956 (1998).
[2] M. Ternes et al., Science 319, 1066 (2008).
[3] J. Welker, F. J. Giessibl, Science 336, 444 (2012).
[4] F. J. Giessibl, S. Hembacher, H. Bielefeldt, J. Mannhart, Science 289, 422 (2000).
[5] S. Hembacher, F. J. Giessibl, J. Mannhart, Science 305, 380, (2004).
[6] J. Welker, J. Weymouth, F. J. Giessibl, ACS Nano, DOI: 10.1021/nn403106v (2013).
[7] L. Gross et al. Science 325, 1110 (2009).
[8] A. J. Weymouth, Th. Hofmann, F. J. Giessibl, Science 343, 1120 (2014).
[9] M. Neu et al., Phys. Rev. B 89, 205407 (2014).
[10] F. Pielmeier, F. J. Giessibl, Phys. Rev. Lett. 110, 266101 (2013).
[11] D. Wastl, J. Weymouth, F. J. Giessibl, Phys. Rev. B 87, 245415 (2013).
[12] M. Emmrich et al., Science 348 308 (2015).

Metal-organic interactions have been the focus of intense multidisciplinary research such as catalytic chemistry, materials science, and molecular electronics.1 Surface-enhanced Raman scattering (SERS) has been widely recognized as a powerful spectroscopic tool for studying molecular adsorbates on a metal surface due to its high surface sensitivity and accessibility to low wave-number region, which gives direct information on metal-molecule interactions, even in IR-opaque media such as aqueous solutions.2 The intensive research of metal-organic interactions by SERS detection has been focused on two different types: (1) molecular modification on substrates, including physical adsorption and chemical adsorption3 and (2) molecular aggregation through self-assembly on substrates4. On the other hand, metalloporphyrin are compounds formed by a combination of porphyrin and metal ions, playing an important roles in catalysis, fluorescence, sensing, optical imaging, electronics, photochemistry, and biological applications.5 Recently, many research groups reported that diverse metalloporphyrin-containing nano-/micro-scale particles can be synthesized through a bottom-up self-assembly process assisted by surfactants, such as Pluronic F127, SDS, CTAB, and others.6 However, less work was dictated to the identification of metalloporphyrin-containing CPPs in the solution. In this work, we chose a metalloporphyrin, zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H, 23H-porphyrin (abbreviated to ZnTPyP), to investigate the identification of metalloporphyrin-containing CPPs in aqueous solution by SERS methods.

In the contribution we present an overview of development of a large area Scanning Thermal Microscope combined with infrared radiometry sensor. Large area Scanning Probe Microscopy (SPM) is a technique bridging the gap between high resolution surface properties mapping 3D state-of-the-art techniques available at limited spatial range in various commercial SPM systems and conventional methods acting on much larger spatial scales like profilometry or confocal microscopy. Development of 3D tools capable of acquiring high resolution data on large areas is very important not only for metrological support in semiconductor or optical industry, but it is also crucial for traceability of the SPM techniques itself. Presented combined large area Scanning Thermal Microscopy (SThM) and Infrared Radiometry system was developed for analysis of local temperature and local thermal conductivity variations with very high spatial resolution. Main purpose of this device is to form a traceability route from conventional thermal conductivity and temperature measurement methods (which have poor spatial resolution, but excellent temperature/conductivity resolution) towards Scanning Thermal Microscopy, which has high spatial 3D resolution, but is still understood more like qualitative rather than quantitative technique. Measurement examples using unique device prototype are shown on both passive and active experimental setups.

The development of nanotechnology needs novel methods for characterization and quantification of nanoparticles (NPs). It has been recently demonstrated that the surface plasmon microscopy (SPM) [1] provides a possibility for visualization the binding of individual NP to the surface of a gold sensor. This offers a powerful tool to study particle properties and processes of particle-surface interactions. In the present work, an analytical model of particle transfer to the sensor surface is validated by SPM.
The SPM sensor consists of a gold layer deposited on a glass prism. The gold layer is illuminated by a laser light in order to excite surface plasmons. Due to interactions of NPs with surface plasmons the light is radiated. This radiation is detected by a CCD or CMOS camera. Any nano-particle binding event emerges as a bright spot with surrounding fringes on processed images. Assuming that a particle sticks irreversibly to the sensor surface, the model allows estimation of the particle concentration without calibration. The measured dependency of the binding rate on the flow velocity is in a good agreement with the theory. If the binding rate is smaller than predicted by theory this indicates that the sticking coefficient is less than 100 %. This fact can be used for the characterization of particle-surface interactions under various conditions.
REFERENCES:
[1] A.Zybin et al. Real-time Detection of Single Immobilized Nanoparticles by Surface Plasmon Resonance Imaging. Plasmonics (2010), V.5, pp.31-35

Imaging of soft objects, like living cells, bacteria and other bio-material with atomic force microscopy is challenging. Very precise force control and advanced scanning routines are needed to obtain realistic data from the surface. Force measurement can show a lot of new informations, but force curve measurement can be time consuming and complex. Combining techniques, like AFM and fluorescent imaging is highly demanded. New developments from Bruker in techniques and instrumentation will help a lot to minimise difficulties and obtain relevant data for scientist in the life-science field.

Our recent attempts to apply standard molecular simulation techniques to the process of electrospinning are reviewed. We employ a molecular dynamics simulation to study phenomena involved in electrospining, with particular attention to the formation of the Taylor cone and the development of the jet. Unlike the continuum methods, a molecular-based approach allows us to reveal the role of solution components – solvent, ions, and polymer – by analyzing the molecular structure and dynamics.

Binary metallic nanoparticles (often referred to as nanoalloys) present a wide variety of structures and properties, which make them
suitable for many applications in catalysis, optics, magnetism and biomedicine. When the two components are weakly miscible, phase-separated arrangements, such as core-shell and Janus arrangements, are the expected to be the most favourable.
Here we consider a series of binary nanoparticles (Ag–Cu, Ag–Co, Ag–Ni, Au–Co, Cu-Ni) and computationally determine their most stable structures for different sizes and compositions. We single out transitions between core-shell and (quasi)-Janus arrangements, showing that they can be rationalized by a unifying concept, that is symmetry breaking caused by the accumulation of strain at the
atomic level and its subsequent release. The computational results are compared to the experimental data with good agreement.

Nanostructured titanium oxide films are widely used for various applications, for instance solar energy conversion, where an increment in the surface-to-volume ratio and band-gap tuning may drastically improve the film performance. In our work to date, we have investigated the anodic process of porous-alumina-assisted formation of titanium oxide nanocolumn arrays from pure and doped titanium layers. We observe a substantial increase of chemical stability in the case of a doped titanium, which is caused by suppressing the field crystallization of titanium oxide and its mixing with alumina during the anodic process.
Experimental samples were thin aluminium layers superimposed on either a pure Ti or a doped Ti layer sputtered onto SiO2/Si substrates. Pieces of both samples were anodized in an organic-acid-based electrolyte at 40 V and reanodized to potentials up to 150 V in order to grow titania nanocolumns in the alumina pores. The alumina matrix was then removed by selective etching in a CrO3/H3PO4-based solution.
SEM and XPS analyses revealed that TiO2 nanocolumns grown on the pure Ti underlayer at higher potentials were unstable in the etching solution and soon dissolved away from the sample surface. In the case of the doped titanium, the anodizing/reanodizing process resulted in the formation of titanium oxide nanocolumns that were chemically stable during the substantially prolonged time spans in the etching solution.
These results enable preparation of long-aspect-ratio titanium-oxide nanocolumns slightly doped with different impurities, which may exhibit improved functional properties compared with the pure titanium oxide nanostructures.
ACKNOWLEDGEMENTS:
Research leading to these results was supported by GAČR grant no.15-23005Y.

Anodic alumina in both of its forms – a barrier type and a porous type – has received numerous studies and practical applications. Its potential could be further increased with the recent development of aluminium thin film sputter-deposition technologies. Most of the research has been performed towards Al foil anodizing; however in case of Al thin films the important knowledge is missing. In this study we have investigated the influence of the Al film structure and morphology on the electrochemical response during aluminium anodizing. Various Al thin films were prepared via an ion beam assisted deposition, a magnetron sputter-deposition and a thermal evaporation. The films were then anodized in a barrier-type-giving electrolyte to various final potentials. The as prepared and anodized films were characterized by scanning electron microscopy and stylus profilometry to reveal the effect of the surface morphology on the anodizing behavior and dielectric breakdown in the anodic films. The breakdown potential was found to be typical for all the films tested, although being greatly dependent upon the initial film surface morphology. A model for explanation of the phenomena observed has been developed and justified experimentally.
ACKNOWLEGEMENTS:
Research leading to these results was supported by a grant from the Czech Science Foundation (GAČR) no. 14-29531S.

We have developed the method for calculation of size-dependent phase diagrams, applicable to nanoalloys with variable size of the particles. We have employed combination of CALPHAD method for the modelling of bulk phase diagrams with ab initio calculations of the surface stresses of the constituting elements and relevant intermetallic phases existing in the phase diagram. In this way we have taken into account the surface energy contribution of spherical nanoparticles to the overall Gibbs free energy. In several cases, we studied the variance of surface stress with different crystallographic orientation of the surface. The results have been used for the calculation of phase diagrams of nanoalloys containing Sn, Sb, Ni and Bi, important for the lead free soldering.

Gold nanoparticles are currently experiencing an exposion of researches of their properties and their application potentials. The development to the next generation of nanotechnologies reqiures products of gold nanoparticles having preciesly controlled size, shape, purity, and large production fecility.
Up to now it has not been yet possible to produce gold nanoparticles in large scale for industrial productuion. Such the present investigation aims an efficient and convienient production routes to generate spherical and purified gold nanoparticles. The main tagets are to generate uniform gold nanoparticles in aquous solutions via chemical reduction methods, and to modify the production routes for their industrial production which could generate final products in good quality and large quantity.
Here we present the citrate reduction process and the NaBH4 reduction process in aqueous solutions, and both of these processes were scaled up. Different experimental parameters have been studied to optimize the process. Dialysis and diafiltration are applied as the post treatment for gold nanoparticles in aqueous solutions to achieve high drgree purity, together with the study of the stability of gold nanoparticles.
Nanotrac Wave analyzer, TEM and ICP analysis methods are used in the study to measure the particle size distribution, and the purification degree of the gold nanoparticles.

Nowadays the study of diamond films is of significant practical interest due to their potential application in bioelectronics, life science and antibacterial field. However, one of the main concerns about the use of diamond films is the lack of information about their surface and bulk quality, resistance to harsh conditions as strong acids, irradiation or ion bombardment, etc. This fact enlarges the scope of investigation methods, since selected applications of diamond require specific properties to be measured. In this study we investigate in situ chemical structure of H- and O-terminated nano- and polycrystalline diamond (NCD and PCD) films before and after Ar+ cluster ion beam sputtering. A slight amount of implanted Ar+ atoms (max. 0.7 %) after 66 min etching time was detected by XPS. SEM scans confirmed etching of all diamond surfaces at the rate about 0.5±0.2 nm/min. Raman and XPS measurements reveal transformation of sp3 carbon phase to sp2 (i.e. graphitization). XPS did not detect O atoms after 2 min of etching (in the depth of 1.5 nm) on H-terminated PCD film, whereas H-NCD films still exhibited 0.2 at. % of oxygen even after 66 min of sputtering. These observations will be discussed and correlated to the film structure and deposition conditions (e.g. gas mixture). Finally, valence band spectra of diamond films with different surface terminations were measured by XPS. The potential of the method for the band diagram mapping is discussed.
ACKNOWLEDGEMENTS:
This work was supported by projects GA15-016879 and SVV-267305-2013.

This work is a contribution to our previous research in which we dealt with the influence of different preparation methods on fundamental properties of ZnO nanoparticles, such as the nanoparticle size, value of band-gap energy, photoluminescence properties, specific surface area and photocatalytic activity. Especially, the band-gap energy, photoluminescence properties and photocatalytic activity were found to depend on the presence of oxygen vacancies which dominated in the ZnO nanoparticles prepared by precipitation under UV irradiation. Our current research was focused on molecular modelling of the oxygen vacancies and on finding appropriate mechanisms of their formation.
The models of ZnO vacant structures were built in the Materials Studio Environment. It was found that the ZnO structures with oxygen vacancies located together were preferred to the structures with oxygen vacancies equally distributed in the whole crystal volume. We assume that the presence of such large defects can cause tension inside the ZnO nanoparticles and thus, lead to disintegration into the small ZnO nanoparticles as observed by transmission electron microscopy.
Measuring of the concentrations of dissolved oxygen in the ZnO aqueous nanodispersions during their synthesis with and without UV irradiation were performed. The formation of hydroxyl radicals by UV irradiation is likely the key reason for the formation of oxygen vacancies in the ZnO nanoparticles.