Hierarchical assembly of nano-scale building blocks

Resume : We search for the rules which connect the functionality of the self-assembled nanostructures and the design building blocks of which it is composed. We study subtle parameters of the molecular design, i.e. stiffness, amphiphilic balance and geometrical packing. We find that the tendency for self-assembly of ligand molecules can be transferred to other species, i.e. nanoparticles. The proper design of capping ligands or addition of judiciously chosen molecules result in control over 2D self-assembly of nanoparticles. The advances in manipulation of nanoparticles allowed us to prepare novel surface enhance Raman spectroscopy (SERS) platform according to true “bottom-up” approach. Three consecutive steps were utilized. First, gold nanoparticles were deposited on a solid substrates. Afterwards such substrates were used for the chemical vapor deposition process of gallium nitride nanowires growth. On such scaffolding a third step of material fabrication was performed, i.e. deposition of gold microflowers. The final morphology was controlled at each step to tailor the properties for the desired purposes. The recorded SERS enhancement factor was around 107 for p mercaptobeznoic acid. SERS spectra were reproducible both across a single sample and between different platforms. The material proved to be very mechanically stable. Our platforms were suitable for biological and biomedical applications. We demonstrated the label free detection of DNA.

Resume : With designed bulk nanostructures, one could potentially combine properties that are mutually exclusive in a single bulk material, and, as a result, dramatically improve the desired performance. However, a major research challenge and roadblock is how to produce 3D nanostructured materials consistently with the required phases arranged in designated spatial order that are at the same time fully dense without porosity and detrimental phases. Known state-of-the-art techniques for producing bulk nanostructures cannot simultaneously meet all these requirements. As a result, the inherent properties of such bulk monolithic nanostructured materials are greatly unknown and unexplored. We developed an Enhanced High Pressure Sintering (EHPS) approach to consolidate oxide, metal, and semiconductor nanoparticles into 3-dimensional nanostructured materials. EHPS incorporates stringent environmental control and utilizes high pressures to break agglomerates while simultaneously exploiting the increased pristine surface potential of nanoparticles for surface-energy-driven densification without microstructural changes. Using this approach, monolithic nanocrystalline transparent ceramics with grain size bellow 30 nm are demonstrated. Such ceramics exhibit a 30% increase in hardness over a corresponding order of magnitude reduction in grain size and suggest that Hall-Petch type (strengthening via grain size reduction) relations exist in ceramics at least down to 30nm.

Resume : During the last decades the synthesis, modification and functionalization of nanoparticles has been intensively studied. In order to fully exploit their properties, it is essential to control the nanoparticles position, allowing to connect the nanoobjects to the macro-world. For a sufficient statistics it is desirable to contact many nanoparticles in parallel. To this end we have developed a template-assisted self-assembly technique which allows us to create inside microfluidic channels millimeter long rows of nanogap electrodes attached to macroscopic contacts. Dielectrophoresis is used to trap particles in the inhomogeneous electric field formed between the electrodes. For single particle trapping the electrodes gap size needs to be tuned to the particle dimensions. For this polystyrene-spheres from colloidal suspensions are arranged in a linear chain in trenches on Si-surfaces by means of convective self-assembly. The spheres act as shadow masks in a subsequent metal deposition step. Opposing pairs of sharp metallic nanotips remain after sphere removal, with tip distances adjustable from several hundred nm to less than 30 nm. We demonstrate that an applied voltage leads to strong field enhancements at the tips. The field gradients between tips are exploited to arrange fluorescent core-shell SiO2 nanoparticles in the channel. Fluorescence microscopy and scanning electron microscopy are used to study the dielectrophoretic arrangement.

Resume : Cooperation of few functionally different spices in one heterostructure in general is not prohibited. However, the conditions for its merging should be find out in any case. Magnetic nanoparticles, carbon nanostructure and/or biologically active particles is possible to link by bond activation between immobilized proteins and surface of the nanostructures [1]. Not only magnetic or noble metals nanoparticles are key players used in nanotechnology but also carbon structures in nanosize (nanodiamonds, fullerenes, nanotubes) have shown widespread interest due to their unique specification. Each of these structures shows extraordinary magnetic, electrical, mechanical and optical properties. Therefore by linking more than two different items combination of the characteristic features can be obtained. Similarly to magnetic nanoparticles surface of the carbon structures should be chemically modified by attachment of various (needed) functional groups. This opens possibility for creation of hierarchical structures – such as composites or hybrid nanostructures. Fabrication of heterostructures causes that carbon nanomaterials brings to medicine possibility of electronic science [2]. In this study, nanocomposites from different kind of nanoparticles were fabricated, and compared. In the first step, various magnetic nanoparticles were synthesized and both with carbon nanostructures were functionalized at the surface to amine or carboxyl groups. Finally either particles were used as a building blocks for composites fabrication and with vitamin-biotin immobilization. The resulting nanocomposites were tested by infra-red spectroscopy, Transmission Electron Microscope, X-ray diffraction, Mössbauer spectroscopy. [1] K.Woo, J.Hong, J.P.Ahn., Journal of Magnetism and Magnetic Materials 293 (2005) 177-181 [2] Z.Markovic, V.Trajkovic, Biomaterials 29 (2008) 3561-3573

Resume : Emulsion polymerization is a well developed technology which allows producing polymer colloids or nanoparticle with highly controlled size and polydispersity, in a variety of different chemical composition and with well controlled morphology. Typically, after the polymerization reactors latexes are coagulated into powders again using consolidated processes. Recent results in the theory of colloidal systems indicated the possibility to exploit these aggregation and breakage events under controlled conditions to produce macrostructures which are other ways not realizable. For example one can mix dispersions of different composition and realize composites with a well controlled dispersion of one phase into the other. By controlling the gelation process one can create inside such composites percolating phases which allow transporting at the macroscopic scale properties exhibited by colloids only at the nanoscale. Examples of different structured materials of interest in various application fields are discussed. These include the production of controlled porous materials in the form of micro-particles or monoliths, which can be used as adsorbents for large (bio) molecules or as thermal insulators. Other areas of interest include drug delivery and enhanced oil recovery.

Resume : In the last decade the field of thermoelectrics had seen many advances, originating largely from the engineering of suitable nanostructured materials. So far the dominating strategies for producing bulk thermoelectric nanomaterials are grinding and precipitation of secondary phases in metastable solid solutions. Both approaches have limited control over the distribution of phases at the nanoscale and/or lack compositional versatility. Another powerful strategy can be devised from the bottom-up assembly and consolidation of colloidal nanoparticles (NPs) into bulk-like materials. Such approach is virtually unlimited in terms of compositional variety and dimensionality of constitutents. Efficient and predictable electronic doping remains a key challenge for maximizing carrier density (deliberately for holes or electrons). At nanoscale, conventional substitutional atomic doping can be supplemented with the “mesoscale doping” - carrier donation between individual NPs. Here we demonstrate that through the engineering of nanocomposites by simple co-assembly of various NP building blocks the charge carrier concentration can be enhanced via mutual doping, while preserving low thermal conductivities and high Seebeck coefficients, thereby increasing the overall thermoelectric figure of merit.

Resume : The design and engineering of nanomaterials by the bottom-up assembly of solution-processed nanocrystal building blocks opens up countless opportunities to produce metamaterials with controlled functional properties. Furthermore, solution-based thin film deposition methods are particularly interesting as they promise lower manufacturing costs, and open the door to new routes for the design of flexible solid-state thermoelectric devices [1] that can play a big role on remote power or personal devices, i.e. wearables. In this work, we detail the preparation of bulk thermoelectric nanocomposites from the bottom-up assembly of solution-processed nanocrystals. Taking advantage of the versatility [2,3] of this technique, we engineer nanocomposites by simple assembly of precisely designed nanocrystal building blocks. We will prove that this methodology provides the necessary level of compositional and morphological control to produce high performance thermoelectric materials. In addition, we have step forward into the preparation of a flexible thermoelectric device based on the solution-processed material developed. References: [1] Z. Lu, M. Layani, X. Zhao, L. P. Tan, T. Sun, S. Fan, Q. Yan, S. Magdassi, H. H. Hng, Fabrication of flexible thermoelectric thin film devices by inkjet printing, Small, 10 (17), 3551-3554 (2014). [2] D. Cadavid, M. Ibáñez, S. Gorsse, A. M. López, J. R. Morante, A. Cabot, Bottom-up processing of thermoelectric nanocomposites from colloidal nanocrystal building blocks: the case of Ag2Te-PbTe, J. Nanopart. Res., 14, 1328 (2012). [3] M. Ibáñez, R. Zamani, S. Gorsse, J. Fan, S. Ortega, D. Cadavid, J. R. Morante, J. Arbiol, and A. Cabot, Core-Shell Nanoparticles As Building Blocks for the Bottom-Up Production of Functional Nanocomposites: PbTe_PbS Thermoelectric properties, ACS Nano, 7 (3), 2573-2586 (2013).

Resume : we investigate the structural, electronic and magnetic properties of the diluted magnetic semiconductors (DMSs) CdCoTe and CdMnTe in the zinc blende phase with 25% of Co and Mn. The calculations are performed by the recent ab initio full potential augmented plane waves (FP_L/APW) method within the spin polarized density-functional theory (DFT) and the generalized gradient approximation GGA. Structural properties are determined from the total energy calculations and we found that these compounds are stable in the ferromagnetic phase. We discuss the electronic structures, total and partial densities of states and total magnetic moments. The calculated densities of states presented in this study identify the half-metallic of CdCoTe and CdMnTe.

Resume : Nanosphere lithography is an established technique for the formation of ordered nanoparticles on large areas at low cost. Hexagonally self-arranged mono- or bilayers of colloidal nanospheres act as a shadow mask for subsequent site-controlled surface modifications such as material deposition, leaving a periodic array of nanoparticles. The hexagonal order as well as defects of the sphere mask are directly transferred to the nanoparticle pattern. We use the doctor blade technique based on a convective self-assembly process to form hexagonal monolayers of polystyrene beads from an aqueous suspension on silicon surfaces. The particles arrange themselves at the triple-phase boundary between suspension, solid substrate and surrounding gas phase. This process depends on several experimental parameters such as the relative humidity, substrate temperature, particle concentration, particle size distribution and blade velocity. We investigate the influence of these parameters on the formation of typical defects in the monolayer such as voids, quadratic arrangements, grain boundaries and other inhomogeneities. Optical and scanning electron microscope images are analyzed by a new algorithm based on Delaunay triangulation and defect densities are calculated. We show, that the densities of different defect types correlate directly with the experimental parameters. This allows to minimize selected defect densities by adjusting experimental conditions during the self-assembly process.

Resume : With as main prospective the localized eradication of malignant cells, the radiosensitization of gold nanoparticles is most effective in close proximity to the cellular DNA. However, the preservation of colloidal stability and the implementation of specific cell targeting requires a supplementary organic coating grafted on the gold nanoparticle surface. The latter consisting of functionalizing polymers and antibodies, necessary for the internalization to the nucleus, attenuates the irradiation dose enhancement caused by the GNPs. The influence of the nanoparticle capping layer thickness, build up with PEG polymers of MW 1 to 20 kDa, on the radiosensitizing effect of GNPs is demonstrated by evaluation of the relaxation pattern of supercoiled DNA. Image analysis of gel electrophoresis and subsequent quantification conclude that on average 58% of the radiosensitizing efficiency is lost when the radial dimensions of the functionalizing layer are increased from 4.1 to 15.3 nm. An experimental supplement is thereby provided for biophysical simulations and demonstrates the influence of an important parameter in the development of nanomaterials for targeted therapies in cancer radiotherapy. Alongside the PEG functionalization, supplementary antibodies are then introduced to create cell specific interactions. Maximal affinity and stability of the nanocomplex is created and proposed for further experimental research on the radiosensitization performances of gold nanoparticles.

Resume : Today, preparation of 0D well-defined nanoparticles which represents inert structure divided on core and shell have obtained extensive interest among scientist. The reason of such popularity of low dimensional structures is that the core-shell nanoparticles have many interesting optical, magnetic, electrical, and mechanical properties which can be combined in one species [1] in contrast to single element particles. In presented paper, core-shell ferrite nanoparticles, with various composition of the core were prepared. Presented nanoparticles, has a core obtained from a mixture of Fe3+, Fe2+ and Men+ ions (where Me = Co2+, Co3+, Mn2+, Mn3+ or Ni2+), in such way, to preserve crystalline structure of magnetite. Then the magnetite shell layer was added, to obtain core-shell structure. Seeds of nanoparticles were fabricated from the proper metal acetylacetonate salts in diphenyl ether, oleic acid and oleyl amine environment. Characterization of the nanoparticles was done by Transmission Electron Microscopy, X-ray diffraction, Infrared spectroscopy, and Mössbauer spectroscopy. [1] Y. Zhu, H. Da, X. Yang, Y. Hu, Colloids and Surfaces A: Physicochem. Eng. Aspects 231 (2003) 123-129

Resume : Silicon carbide SiC has many advantageous properties including the high thermal, mechanical, and chemical stabilities, relatively low density, and semiconducting properties. In this regard, the high thermal conductivity makes this material a valuable catalyst support for exothermic reactions, for instance, in reacting carbon monoxide and hydrogen towards methane. Herein, presented is a study on the effect of temperature of the first aerosol-assisted stage on silicon carbide crystallization during the second stage temperature treatment of the bulk raw powder. Nanocrystalline SiC was prepared from aerosolized hexamethyldisiloxane at 1200 and 1400 C followed by a second stage pyrolysis under argon at 1650 C. Additionally, the sample obtained in the first aerosol-assisted stage at 1400 C was thermally treated in bulk at the same temperature for 1 hour under argon. The as-prepared products were characterized by powder XRD, SEM, solid state 29Si MAS NMR, and FT-IR spectroscopy. The data clearly confirmed the impact of the temperature treatment on the kind of polytype(s) and average crystallite size of the resulting nano-SiC. Acknowledgment. This work was supported by AGH University of Science and Technology Grant No. 11.11.210.213.

Resume : For most practical applications, metal nanoparticles (NPs) need to be supported on a substrate that can act as a deposition template for the growth of regular arrays and is relevant in preventing sintering at high temperatures, a process that would deactivate the catalytic devices. The Moire’ pattern due to the small lattice mismatch between graphene and Ir(111) could be an efficient template for an ordered array of metal NPs. With the help of ab-initio calculations we compare the behaviour of different metals, with the aim of finding those more suitabile for an ordered growth. The role of a possible seed is also discussed.

Resume : Colloidal metallic and semiconductor nanocrystals (NCs), functionalized with inorganic capping ligands such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials for applications in photovoltaics, photodetectors, thermoelectrics, and field-effect transistors. As-prepared MCC-capped NCs are highly charged and dispersible only in polar solvents, and lack the ability to spontaneously form long-range ordered NC superlattices. Here we present a simple and general methodology, based on host-guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport in films of NCs, as demonstrated here for the photoconductive properties of PbS NCs. In particular, high infrared photon detectivities of 3.3·10e11 Jones with a fast response (3 dB cut-off at 3 kHz) at 1200 nm were obtained for a photoconductor based on PbS/K3AsS4/decyl-18-crown-6 films. At the same time, films of crown-free PbS/K3AsS4 NCs are too conductive to observe efficient photocurrent generation, while initial oleate-capped PbS NCs are fully insulating.

Resume : Nanoscopic objects stabilized with charged organics exhibit properties fundamentally different from either molecular or macromoleculer ions, and can combine ionic-like properties with electronic and ionic conductivity and/or photoexcitability. By careful control of electrostatic interactions, ”nanoions” of various shapes and material compositions can be assembled into functional nanomaterials including 3D supracrystals, ”layered” crystals, or extended films. Depending on the properties of the charged organics, these nanomaterials can act as chemical amplifiers, photoconductors, diodes, transistors, or even full-fledged electronic circuits containing no semiconductors. This last set of constructs can integrate on the nanoparticles electronic function with chemical sensing.

Resume : Self-assembly of nanoparticles has led to a fascinating variety of accessible well-defined super structures. Of particular interest is the assembly of binary nanoparticle arrays with complementary or synergistic properties. The electrostatic assembly of oppositely charged nanoparticles offers the possibility of a high degree of control and increased variety of accessible superstructures such as diamond-like Au-Ag supercrystals compared to van-der-Waals driven processes [Kalsin et al. Science 2006, 312, 420]. There is number of strategies to achieve sufficient charging of nanoparticles, from atomic to polymeric ligands, from aqueous synthesis to ligand exchange. A critical point in the assembly process is the colloidal stability of the charged particles. Different strategies for charging nanoparticles and their implications on colloidal stability and for the later assembly will be discussed with an emphasis on post-synthetic ligand exchange and binary semiconductor-metal systems.

Resume : SiO2 encapsulation of alloyed CdSeZnS nanocrystals (NCs) shows differences in terms of optical properties and luminescence quantum yield, depending on the surface composition, size, and ligand content. In this work, emphasis has been placed on the fine control required to obtain luminescent SiO2 encapsulated NCs by studying the role of oleic acid (OA), stearic acid (SA), and dodecanethiol (DDT) ligands on the alloyed NCs. While the use of anchored DDT molecules is essential to preserve the optical properties, intercalated OA and SA play a critical role for SiO2 nucleation, as stated by 1H NMR (including DOSY and NOESY) spectroscopy. (1). Furthermore, optical trapping (2,3) of these encapsulated NCs allows for their individual manipulation and acquisition of their optical properties and evolution in solution. Surface effects generated by the laser beams composing the optical tweezer and the surrounding medium will be discussed. These results emphasize the importance of surface chemistry in semiconducting NCs.

Resume : The employment of nanoparticles in optical applications is an ideal strategy for minimizing the light scattering associated with the discrete form of the material. The control over structure and emission maxima is crucial in order to tailor materials for the final application. Hafnium dioxide is a wide band-gap semiconductor with outstanding thermal stability, remarkable chemical inertness, high density, and UV-visible transparency. We report a strategy for the production of nearly spherical HfO2 nano-dots obtained by nonaqueous sol-gel where the multifunctional role of rare earth doping is evidenced. On one hand, rare earth dopant ions activate the visible luminescence of the nanocrystals. On the other hand the incorporation of trivalent ions is shown to be suitable for the room temperature stabilization of the cubic polymorph of HfO2, with potentially great benefits in the realization of new polycrystalline optical ceramics for scintillator applications with reduced birefringence. We incorporated the colloids into trasparent hosts such as polymers and oxides, obtaining luminescent composites where the processability of the host and the outstanding photostability of inorganic nano-phosphors are merged together. These systems might be suitable for new low-cost/solution-processed radiation detectors and scintillators, and for luminescent solar concentrators expressly designed for the photoconversion in harsh conditions of high energy radiation, from the UV to the X-rays rang