"Dip-Pen" nanolithography on semiconductor surfaces

Dip-Pen Nanolithography (DPN) uses an AFM tip to deposit organic molecules through a meniscus onto an underlying substrate under ambient conditions. Thus far, the methodology has been developed exclusively for gold using alkyl or aryl thiols as inks. This study describes the first application of DPN to write organic patterns with sub-100 nm dimensions directly onto two different semiconductor surfaces: silicon and gallium arsenide. Using hexamethyldisilazane (HMDS) as the ink in the DPN procedure, we were able to utilize lateral force microscopy (LFM) images to differentiate between oxidized semiconductor surfaces and patterned areas with deposited monolayers of HMDS. The choice of the silazane ink is a critical component of the process since adsorbates such as trichlorosilanes are incompatible with the water meniscus and polymerize during ink deposition. This work provides insight into additional factors, such as temperature and adsorbate reactivity, that control the rate of the DPN process and paves the way for researchers to interface organic and biological structures generated via DPN with electronically important semiconductor substrates.     

Superamphiphilic Silicon Wafer Surfaces and Applications for Uniform Polymer Film Fabrication

Silicon wafers have been widely used in the semiconductor industry for many decades. Over the past decades, with the development of organic optoelectronic materials, silicon-based organic–inorganic hybrid devices have received more and more interest in fundamental and applied research. To obtain uniform organic films for hybrid devices, superamphiphilic surfaces, on which both water and oil can spread completely, show great advantages. Herein, we prepared superamphiphilic silicon wafer surfaces with contact angles (CAs) near 0° for both water and typical organic liquids. Interestingly, lateral force mode (LFM) atomic force microscopy (AFM) images indicate that the superamphiphilicity is induced by alternating hydrophilic and hydrophobic nanodomains. By making use of these superamphiphilic silicon wafer surfaces, uniform polypyrrole (PPy) films were generated in both water and cyclopentanone, providing a versatile and effective way for the integration of organic optoelectronic materials with inorganic microelectronic devices.     

Fabrication and Visualization of Metal‐Ion Patterns on Glass by Dip‐Pen Nanolithography

Fluorescent self‐assembled monolayers (SAMs) are used as dip‐pen nanolithography (DPN) substrates for the fabrication of patterns of Ca²⁺ and Cu²⁺ ions. The driving force for the transfer of these ions from an atomic force microscopy (AFM) tip to the surface is their complexation to organic ligands on the monolayer. By means of fluorescent surfaces, the patterns can be visualized under a fluorescence microscope. We use a custom‐built atomic force fluorescence microscope (AFFM), a combination of atomic force and confocal fluorescence microscopes, to deposit the metal ions onto the sensing SAMs by DPN and to subsequently visualize modulations of fluorescence intensity in a sequential write–read mode.     

Cleaning and hydrophilization of atomic force microscopy silicon probes

The silicon surface of commercial atomic force microscopy (AFM) probes loses its hydrophilicity by adsorption of airborne and package-released hydrophobic organic contaminants. Cleaning of the probes by acid piranha solution or discharge plasma removes the contaminants and renders very hydrophilic probe surfaces. Time-of-flight secondary-ion mass spectroscopy and X-ray photoelectron spectroscopy investigations showed that the native silicon oxide films on the AFM probe surfaces are completely covered by organic contaminants for the as-received AFM probes, while the cleaning methods effectively remove much of the hydrocarbons and silicon oils to reveal the underlying oxidized silicon of the probes. Cleaning procedures drastically affect the results of adhesive force measurements in water and air. Thus, cleaning of silicon surfaces of the AFM probe and sample cancelled the adhesive force in deionized water. The significant adhesive force values observed before cleaning can be attributed to formation of a bridge of hydrophobic material at the AFM tip-sample contact in water. On the other hand, cleaning of the AFM tip and sample surfaces results in a significant increase of the adhesive force in air. The presence of water soluble contaminants at the tip-sample contact lowers the capillary pressure in the water bridge formed by capillary condensation at the AFM tip-sample contact, and this consequently lowers the adhesive force.     

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by dip pen nanolithography

We report on DNA arrays produced by dip pen nanolithography (DPN) on a novel Au-Ag micropatterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting multi-instrument and multitechnique local detection and analysis. Moreover the smooth surface of the Au squares ( approximately 5-10 A roughness) allows AFM/STM to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label-free detection methods for DNA nanoarrays based on the use of scanning probes.     

Dip-pen刻蚀技术直接构建聚-L-赖氨酸纳米结构

Dip-pen纳米刻蚀技术(简称DPN技术)为在目标基底上沉积一个有序或连续的图案提供了一条简单而有效的途径,DPN技术是一种直接书写的扫描探针刻蚀技术,它使用原子力显微镜探针针尖,在一定的驱动力下,直接将化学试剂“墨水”转移到目标基底上．近年来,利用DPN技术已经成功地实现了多种“墨水一基底”组合。     

Stability of monomolecular films of archaebacterial tetraether lipids on silicon wafers: a comparison of physisorbed and chemisorbed monolayers

The monomolecular organisation of symmetric, chemically modified tetraether lipids caldarchaeol-PO(4) was studied using Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Solid silicon wafer substrates were modified to hydrophobic, hydrophilic, and amino-silanised surfaces; and Langmuir-Blodgett (LB)-films were transferred onto each. LB-caldarchaeol-PO(4) films were subjected to further rinsing with organic solvent and additional physical treatments, to compare their resistance and stability on chemisorbed (amino-silanised) and physisorbed (hydrophobic and hydrophilic) surfaces. The resistance and stability of these monolayer films was characterized by ellipsometry and AFM, and film thickness was determined using ellipsometry. AFM was also employed to observe surface morphology. Monolayer films on hydrophobic surfaces were found to be more resistant to rinsing with organic solvent and additional physical treatments than monolayer films on either amino-silanised or hydrophilic surfaces. The hydrophobic effect with hydrophobic surfaces appears to support the formation of stronger caldarchaeol-PO(4) films on silicon wafer substrates, with increased resistance and stability.     

Horseradish Peroxidase Catalyzed Polymerization of Tyrosine Derivatives for Nanoscale Surface Patterning

Abstract

Tyrosine and its derivatives can be polymerized by enzymatic catalysis with horseradish peroxidase (HRP). In the present study, tyrosine ethyl ester hydrochloride was nanopatterned on mercaptohexadecanoic acid (MHA) modified gold surfaces using dip‐pen nanolithography (DPN). Enzymatic polymerization was carried out on the well‐organized nanofeatures and confirmed by atomic force microscopy (AFM) phase images and electrostatic force microscopy (EFM) phase‐lag images. The results extend DPN to amino acid derivatives as biocompatible conducting circuitry with nanoscale features.     

Molecular transfer of surfactant bilayers: widening the range of substrates

Handling nanometer-thick films and nano-objects remains a challenge. Applying self-assembly properties of surfactants to nanomaterials manipulation may be the key to the fast, easy, cost-effective growth of 2D and 3D nanostructures. Newton black films (NBFs) are self-assembled bilayers of surfactant, well-organized, but fragile objects. To render such films amenable to practical applications, it is necessary to find ways to transfer them onto solid substrates. A method developed recently to transfer NBFs onto a solid substrate while preserving their molecular organization (Benattar, J.-J.; Nedyalkov, M.; Lee, F. K.; Tsui, O. K. C. Angew. Chem., Int. Ed. 2006, 45, 4186) is broadened here to different surfaces. The method requires hydrophobic, planar, atomically smooth surfaces. This study presents the adhesion of a fluorinated NBF surfactant onto hydrophobically treated silica and silicon surfaces (with etching or silanization). The structures of the free-standing film, bare substrates, and transferred films are investigated using X-ray reflectivity. The homogeneity of the surfaces before and after bilayer deposition is examined by atomic force microscopy (AFM). Multiple transfers are tested and described for the future development of more complex architectures involving many surfactant layers and inserted nanosized objects.     

Layer-by-layer assembly and spontaneous flocculation of oppositely charged oxide and hydroxide nanosheets into inorganic sandwich layered materials

Exfoliated oxide nanosheets such as Ti0.91O2 and Ca2Nb3O10 and layered double hydroxide (LDH) nanosheets of Mg2/3Al1/3(OH)2 were restacked into inorganic sandwich layered materials. Sequential adsorption of these oppositely charged nanosheets from their colloidal suspensions yielded multilayer ultrathin films while their simple mixing produced lamellar flocculates. Eliminating carbonate ions from the reaction system was found to be essential for successfully achieving the sandwich structures. The flocculated materials as well as the films were characterized by atomic force microscopy (AFM), UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis, which all supported the formation of the ordered sandwich structures. AFM observations revealed alternate dense tiling of LDH nanosheets and oxide nanosheets onto a substrate surface. UV-visible absorption spectra exhibited progressive enhancement of optical density due to oxide nanosheets as a function of deposition cycles, providing strong evidence for regular growth of multilayer films. The combinations of Mg2/3Al1/3(OH)2/Ti0.91O2 and Mg2/3Al1/3(OH)2/Ca2Nb3O10 produced XRD Bragg peaks having multilayer spacings of 1.2 and 2.0 nm, respectively. These basal spacing values are compatible with the sum of thickness of LDH nanosheets and corresponding oxide nanosheets. TEM images of flocculated samples displayed lamellar features with two different constituent layers appearing alternately.     

Dip-pen nanolithography in tapping mode

Dip-pen nanolithography (DPN) is becoming a popular nano-patterning technique for depositing materials onto a substrate using the probe of an atomic force microscope (AFM). Here, we demonstrate the deposition of a short synthetic peptide by DPN using the Tapping Mode of AFM rather than the commonly used contact mode. DPN in Tapping Mode requires drive amplitude modifications for deposition, yet allows for gentle imaging of the deposited material and enables deposition on soft surfaces.     

Coordination-based gold nanoparticle layers

Gold nanoparticle (NP) mono- and multilayers were constructed on gold surfaces using coordination chemistry. Hydrophilic Au NPs (6.4 nm average core diameter), capped with a monolayer of 6-mercaptohexanol, were modified by partial substitution of bishydroxamic acid disulfide ligand molecules into their capping layer. A monolayer of the ligand-modified Au NPs was assembled via coordination with Zr4+ ions onto a semitransparent Au substrate (15 nm Au, evaporated on silanized glass and annealed) precoated with a self-assembled monolayer of the bishydroxamate disulfide ligand. Layer-by-layer construction of NP multilayers was achieved by alternate binding of Zr4+ ions and ligand-modified NPs onto the first NP layer. Characterization by atomic force microscopy (AFM), ellipsometry, wettability, transmission UV-vis spectroscopy, and cross-sectional transmission electron microscopy showed regular growth of NP layers, with a similar NP density in successive layers and gradually increased roughness. The use of coordination chemistry enables convenient step-by-step assembly of different ligand-possessing components to obtain elaborate structures. This is demonstrated by introducing nanometer-scale vertical spacing between a NP layer and the gold surface, using a coordination-based organic multilayer. Electrical characterization of the NP films was carried out using conductive AFM, emphasizing the barrier properties of the organic spacer multilayer. The results exhibit the potential of coordination self-assembly in achieving highly controlled composite nanostructures comprising molecules, NPs, and other ligand-derivatized components.     

Immobilization of histidine-tagged proteins on nickel by electrochemical dip pen nanolithography

Dip-pen nanolithography (DPN) is becoming a popular technique to "write" molecules on a surface by using the tip of an atomic force microscope (AFM) coated with the desired molecular "ink". In this work, we demonstrate that poly-histidine-tagged peptides and proteins, and free-base porphyrins coated on AFM probes, can be chelated to ionized regions on a metallic nickel surface by applying an electric potential to the AFM tip in the DPN process. DPN has been accomplished in the Tapping Mode of AFM, which creates many possible applications of positioning and subsequently imaging biomolecules, especially on soft surfaces.     

Morphology-controlled fabrication of polygonal ZnO nanobowls templated from spherical polymeric nanowell arrays

We report a facile and effective strategy for synthesizing morphology-controlled patterned ZnO nanostructures. Polymeric nanowell arrays were employed as scaffold templates, followed by solution dipping and calcination process, polygonal ZnO nanobowl structures were fabricated on silicon substrate. The ordered polymeric nanowell arrays not only provided confined areas for depositing desired materials, but also induced shape transition of ZnO nanobowls from circular to polygonal. The morphology of the patterned ZnO nanostructures can be easily controlled by tuning parameters of polymeric nanowell arrays and other treatment conditions. The patterned structures were characterized by field emission scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA).     

Photochemically driven shape changes of crystalline organic nanorods

Nanorods composed of 9-tert-butylanthroate (9-TBAE) are synthesized using an Al2O3 template and solvent annealing. The rods consist of micron-scale crystalline domains, and UV light induces a [4 + 4] photodimerization that results in a uniform 15% expansion along the rod axis. This is in contrast to random 9-TBAE crystals, which disintegrate under the same conditions. Transmission electron microscopy, atomic force microscopy, and comparison of the X-ray crystal structures of the monomer and photodimer all provide evidence for a mechanism based on a crystal-to-crystal photoreaction leading to an increase in molecular volume. It is likely that the high surface-to-volume ratio in the nanorods provides a strain relief pathway that is absent in larger crystals. Preliminary attempts to reverse the reaction using shorter wavelength light to photodissociate the dimers were only partly successful. These results suggest that crystalline organic nanostructures may provide an efficient way to transform photochemical energy into mechanical motion on the nanometer scale.     

Assessing the Functional Properties of TiZr Nanotubular Structures for Biomedical Applications,through Nano-Scratch Tests and Adhesion Force Maps

In this work we present the results of a functional properties assessment via Atomic Force Microscopy (AFM)-based surface morphology, surface roughness, nano-scratch tests and adhesion force maps of TiZr-based nanotubular structures. The nanostructures have been electrochemically prepared in a glycerin + 15 vol.% H₂O + 0.2 M NH4F electrolyte. The AFM topography images confirmed the successful preparation of the nanotubular coatings. The Root Mean Square (RMS) and average (Ra) roughness parameters increased after anodizing, while the mean adhesion force value decreased. The prepared nanocoatings exhibited a smaller mean scratch hardness value compared to the un-coated TiZr. However, the mean hardness (H) values of the coatings highlight their potential in having reliable mechanical resistances, which along with the significant increase of the surface roughness parameters, which could help in improving the osseointegration, and also with the important decrease of the mean adhesion force, which could lead to a reduction in bacterial adhesion, are providing the nanostructures with a great potential to be used as a better alternative for Ti implants in dentistry.     

Alternative method for fabricating chemically functionalized AFM tips: silane modification of HF-treated Si3N4 probes

An alternative method for fabricating functionalized, atomic force microscopy (AFM) tips is presented. This technique is simple and requires only minimal preparation and tip modification to generate chemically sensitive probes that have a robust organic monolayer of flexible terminal chemistry attached to the surface. Specifically, commercially microfabricated Si3N4 AFM tips were modified with self-assembled monolayers (SAMs) of octadecyltrichlorosilane and (11-bromoundecyl)trichlorosilane after removing the native silicon oxide surface layer with concentrated hydrofluoric acid. The structure of these SAM films on solid silicon nitride surfaces was studied using contact angle goniometry and Fourier transform infrared spectroscopy. Pull-off force measurements on various bare (mica, graphite, and silicon) and SAM-functionalized substrates confirm that mechanically robust, long-chain organic silane SAMs can be formed on HF-treated Si3N4 tips without the presence of an intervening oxide layer. Adhesion experiments show that the integrity of the organic film on the chemically modified tips is maintained over repeated measurements and that the functionalized tips can be used for chemical sensing experiments since strong discrimination between different surface chemistries is possible.     

Self-assembly of nanosize coordination cages on si(100) surfaces

Bottom-up fabrication of 3D organic nanostructures on Si(100) surfaces has been achieved by a two-step procedure. Tetradentate cavitand 1 was grafted on the Si surface together with 1-octene (Oct) as a spatial spectator by photochemical hydrosilylation. Ligand exchange between grafted cavitand 1 and self-assembled homocage 2, derived from cavitand 5 bearing a fluorescence marker, led to the formation of coordination cages on Si(100). Formation, quantification, and distribution of the nanoscale molecular containers on a silicon surface was assessed by using three complementary analytical techniques (AFM, XPS, and fluorescence) and validated by control experiments on cavitand-free silicon surfaces. Interestingly, the fluorescence of pyrene at approximately 4 nm above the Si(100) surface can be clearly observed.     

Docking of Antibodies into the Cavities of DNA Origami Structures

Immobilized antibodies are extensively employed for medical diagnostics, such as in enzyme‐linked immunosorbent assays. Despite their widespread use, the ability to control the orientation of immobilized antibodies on surfaces is very limited. Herein, we report a method for the covalent and orientation‐selective immobilization of antibodies in designed cavities in 2D and 3D DNA origami structures. Two tris(NTA)‐modified strands are inserted into the cavity to form NTA–metal complexes with histidine clusters on the Fc domain. Subsequent covalent linkage to the antibody was achieved by coupling to lysine residues. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) confirmed the efficient immobilization of the antibodies in the origami structures. This increased control over the orientation of antibodies in nanostructures and on surfaces has the potential to direct the interactions between antibodies and targets and to provide more regular surface assemblies of antibodies.