The oriented and patterned growth of fluorescent metal–organic frameworks onto functionalized surfaces

A metal–organic framework (MOF) material, [Zn2(adc)2(dabco)] (adc = anthracene-9,10-dicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]­octane), the fluorescence of which depends on the loading of its nanopores, was synthesized in two forms: as free-flowing nanocrystals with different shapes and as surface-attached MOFs (SURMOFs). For the latter, we used self-assembled monolayers (SAMs) bearing functional groups, such as carboxylate and pyridyl groups, capable of coordinating to the constituents of the MOF. It could be demonstrated that this directed coordination also orients the nanocrystals deposited at the surface. Using two different patterning methods, i.e., microcontact printing and electron-beam lithography, the lateral distribution of the functional groups could be determined in such a way that the highly localized deposition of the SURMOF films became possible

Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst

In this work the applicability of neopentasilane (Si(SiH3)4) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of “liquid bright gold”, a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires

Triptycene-terminated thiolate and selenolate monolayers on Au(111)

To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs), triptycyl thiolates and selenolates with and without methylene spacers on Au(111) surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se–Au binding energy in the investigated SAMs was found to be higher than the S–Au binding energy

Lateral dipole moments induced by all-cis-pentafluorocyclohexyl groups cause unanticipated effects in self-assembled monolayers

C. F. and A. T. thank the Fonds der Chemischen Industrie (FCI) for providing a PhD stipend. S. D., Y. B. L. and M. Z. thank the Helmholtz Zentrum Berlin for the allocation of synchrotron radiation beamtime at BESSY II and financial support. Y. L. thanks the China Scholarship Council (CSC) for financial support.All-cis-hexafluoro- and all-cis-pentafluoro-cyclohexane (PFCH) derivatives are new kinds of materials, the structures and properties of which are dominated by the highly dipolar Janus-face motif. Here, we report on the effects of integrating the PFCH groups into self-assembled monolayers (SAMs) of alkanethiolates on Au(111). Monolayers with an odd (eleven) and even (twelve) number of methylene groups were characterized in detail by several complementary experimental tools, supported by theoretical calculations. Surprisingly, all the data show a high similarity of both kinds of monolayers, nearly lacking the typically observed odd-even effects. These new monolayers have a packing density about 1/3 lower than that of non-substituted alkanethiolate monolayers, caused by the bulkiness of the PFCH moieties. The orientations of the PFCH groups and the alkyl chains could be determined independently, suggesting a conformation similar to the one found in the solid state structure of an analogous compound. Although in the SAMs the PFCH groups are slightly tilted away from the surface normal with the axial fluorine atoms pointing downwards, most of the dipole moments of the group remain oriented parallel to the surface, which is a unique feature for a SAM system. The consequences are much lower water contact angles compared to other partly fluorinated SAMs as well as rather moderate work function values. The interaction between the terminal PFCH moieties results in an enhanced stability of the PFCH-decorated SAMs toward exchange reaction with potential molecular substituents in spite of the lower packing density of these films.Publisher PDFPeer reviewe

Mobility of charge carriers in self-assembled monolayers

We present a new approach to study charge transport within 2D layers of organic semi-conductors (OSCs) using atomic force microscopy (AFM)-based lithography applied to self-assembled monolayers (SAMs), fabricated from appropriate organothiols. The extent of lateral charge transport was investigated by insulating pre-defined patches within OSC-based SAMs with regions of insulating SAM made from large band gap alkanethiolates. The new method is demonstrated using a phenyl-linked anthracenethiolate (PAT), 4-(anthracene-2-ylethynyl)benzyl thiolate. I-V characteristics of differently shaped PAT-islands were measured using the AFM tip as a top electrode. We were able to determine a relationship between island size and electrical conductivity, and from this dependence, we could obtain information on the lateral charge transport and charge carrier mobility within the thin OSC layers. Our study demonstrates that AFM nanografting of appropriately functionalized OSC molecules provides a suitable method to determine intrinsic mobilities of charge carriers in OSC thin films. In particular, this method is rather insensitive with regard to influence of grain boundaries and other defects, which hamper the application of conventional methods for the determination of mobilities in macroscopic samples. © 2019 Fu et al

Inkjet- and flextrail-printing of silicon polymer-based inks for local passivating contacts

In this work innovative additive printing methods for formation of polycrystalline silicon (poly-Si) and polycrystalline silicon carbide (poly-SiC) layers of local tunnel oxide passivating contacts (TOPCon) is evaluated. Replacement of conventional vacuum processes and vapor-phase deposition by additive printing of Si in fabrication process of high efficiency solar cells reduces processing complexity, and, hence manufacturing costs. Reliable inkjet- and FlexTrail-printing processes are developed for liquid-phase polysilane and organic polysilazane inks that are precursors of Si and SiC, respectively. FlexTrail is introduced as a potential technology to print uniform closed thin films of polysilane free of ruptures. Moreover, from inkjet-printing of the developed polysilane ink, homogenous, closed and crack free thin films of poly-Si are obtained after high temperature annealing. The polysilane ink is formulated considering evaluation of several solvents and photoinduced polymerization conditions. Inkjet-printing process development and optimization according to high frequency rheological characterization of organic polysilazane (OPSZ) is presented. Printed thin films are characterized after high temperature annealing (T = 950 °C, t = 60 min) to be uniform and free of micro cracks

Reusable plasmonic substrates fabricated by interference lithography: a platform for systematic sensing studies

Surface-enhanced Raman scattering (SERS) has become increasingly popular in the scientific and industrial communities because of its analytical capabilities and potential to study fundamentals in plasmonics. Although under certain conditions extremely high sensitivity is possible, the practical use of SERS is frequently limited by instability and poor reproducibility of the enhancement factor. For analytical applications or for comparative measurements to enable the distinction between electromagnetic and chemical enhancement, the development of standardized and recyclable SERS substrates, having uniform and persistent performance, is proposed. To this end, we have fabricated periodic nanoslit arrays using extreme ultraviolet lithography that provide average large (2*106) and homogeneous SERS enhancement factors with a spot-to-spot variability of less than 3%. In addition, they are reusable without any degradation or loss of enhancement. The fabrication of such arrays consists of two steps only, lithographic patterning followed by metal evaporation. Both processes may be performed over areas of several square mm on any planar substrate. The sensor capabilities were demonstrated by substrates with monomolecular films of several different thiols. The concept of reusable SERS substrates may open a powerful platform within an analytical tool and in particular for systematic SERS studies for the investigation of fundamental parameters such as chemical enhancement, surface selection rules, and molecular alignmen

Cell Death and Ultrastructural Morphology of Femtosecond Laser-Assisted Anterior Capsulotomy

PURPOSE. To evaluate cell death and ultrastructural effects on capsulotomy specimens derived from femtosecond laser-assisted cataract surgery. METHODS. In 26 eyes, an anterior capsulotomy was performed using a femtosecond laser. In 10 eyes (group 1), the laser-pulse energy was set to 15 lJ using a rigid curved interface and in another 10 eyes (group 2) to 5 lJ using a curved interface combined with a soft contact lens. The control group (6 eyes, group 3) underwent manual anterior capsulorhexis using forceps. All extracted capsule specimens underwent cell death analysis using the TUNEL kit, ultrastructural analyses using atomic force microscopy (AFM), and scanning electron microscopy (SEM). Counterstaining was performed with 4 0 ,6-diamidino-2-phenylindol (DAPI) and hematoxylin-eosin (HE). RESULTS. Cell death was found in all capsule specimens along the cutting edge but was significantly more pronounced in group 1. DAPI and HE staining showed regular epithelial cell distribution with a demarcation line along the cutting edge of both laser groups, which was more pronounced in group 1. In AFM analysis, laser spot size in the femtosecond laser groups were in accordance with the preoperative planned size (P < 0.01). Cutting edges in SEM observations were smoother and more roundly shaped using 5 lJ (group 2). CONCLUSIONS. Cutting edges of femtosecond laser-performed capsulotomies are precise and laser spot lesions are within planned size. Cell death reaction depends on the laser pulse energy settings and can be reduced to the level observed in a manual capsulorhexis. Keywords: femtosecond laser, capsulotomy, capsulorhexis, laser energy, cell death, apoptosis, atomic force microscopy, scanning electron microscopy A precise and well-performed capsulorhexis is crucial to perform an uncomplicated cataract extraction, intraocular lens implantation, and centration. 1-3 This main step in cataract surgery and refractive lens exchange surgery is commonly performed manually. Femtosecond lasers are now changing how lens surgery is performed by becoming involved in the main steps of the surgical process: corneal incisions, capsulotomy, and lens fragmentation. Dick et al. 2 recently suggested a new terminology for opening the anterior lens capsule with a femtosecond laser: capsulotomy instead of capsulorhexis, as the femtosecond laser operates as a cutting knife by using focal photodisruption. Recent studies have already demonstrated that femtosecond laser-performed capsulotomies allow repeatable and precise sizing and centration; furthermore, they improve the safety of hydrodissection, nuclear fragmentation, and cortical cleanup. 10 During capsulotomy, the anterior capsule is being injured and epithelial cell death is induced. This effect might be stronger with the assistance of femtosecond lasers. Therefore, the purpose of this study was to investigate cell death reaction after anterior capsulotomy either performed by a femtosecond laser using different energy levels or manually by using forceps. Furthermore, laser spot lesions and cutting edge of all capsulotomy specimens were investigated on the ultrastructural level. METHODS The experimental study was approved by the ethics committee of the Goethe-University, Frankfurt am Main, Germany, and was performed in accordance with the Declaration of Helsinki at the Department of Ophthalmology, Goethe-University. In 26 eyes of 26 patients diagnosed with corticonuclear cataract formation anterior femtosecond laser-assisted capsulotomy (n ¼ 20) or manual capsulorhexis (n ¼ 6) using forceps was performed. In 10 eyes (group 1) that underwent femtosecond laser capsulotomy, the laser pulse energy was set to 15 lJ and applanation to the ocular surface was performed using a rigid curved interface. For another 10 eye