Formation Of Nanopattern Research Articles

Local (111)-like reconstruction on highly-compressed Cu(001) regions

Nitrogen adsorption on a Cu(001) surface leads to formation of the grid-like nanopattern where square c(2 × 2) N-adsorbed islands of the size, 5nm×5nm, are aligned along [100] and [010] directions. The grid pattern leaves bare Cu(001) regions (“patches”) at grid intersections. Using scanning tunneling microscopy, we find that short bright lines running in [110] directions appear on patch edges only when the grid pattern approaches completion. We propose the structural model for the bright line that a Cu row moves by half period to form local (111)-like close-packed structure. The local structure can relieve effectively compressive stress imposed by expanding N-adsorbed islands. The model can be smoothly connected with our missing-Cu-row model proposed for a narrow boundary (“monoatomic line”) between N-adsorbed islands [M. Yamada et al., Surf. Sci. 604 (2010) 1961]. Unlike heavy 5d metals such as Au, a Cu(001) surface keeps its bulk-truncated structure. However, it is shown that large compressive stress can induce local (111)-like reconstruction on Cu(001).

Nanosecond pulsed laser-induced formation of nanopattern on Fe-based metallic glass surface

Fe-based metallic glasses (MGs) have attracted much attention because of their cheap raw materials, outstanding soft magnetic properties and superior catalytic activity. Meanwhile, the fabrication of micro/nano-structures on its surface could further improve its functional properties. In this study, it was attempted to fabricate micro/nano-structures on a Fe-based MG (Fe52Cr13Mo12C15B6Er2, in at. %) surface by nanosecond pulsed laser irradiation technology. The surface characteristics and microstructural evolution of Fe-based MG were investigated. The experimental results showed that under different laser fluences, the laser-irradiated areas exhibited distinguished microstructures, i.e., nanoparticles, the network nanostructures or a combination of these two microstructures. Furthermore, oxygen and erbium were enriched inside the network nanostructures. By analyzing the microstructural evolution, formation mechanisms of the nanoparticles and the network nanostructures were discussed. The nanoparticles were actually caused by laser-induced element enrichment (i.e. amorphous erbium oxide) and the mismatch of its wettability with the substrate; the formation of the network nanostructures was attributed to the diffusion and connection of nanoparticles under the combined influence of recoil pressure and surface topography.

Formation and Characterization of Hole Nanopattern on Photoresist Layer by Scanning Near-Field Optical Microscope.

Patterning of lines of holes on a layer of positive photoresist SX AR-P 3500/6 (Allresist GmbH, Strausberg, Germany) spin-coated on a quartz substrate is carried out by using scanning near-field optical lithography. A green 532 nm-wavelength laser, focused on a backside of a nanoprobe of 90 nm diameter, is used as a light source. As a result, after optimization of parameters like laser power, exposure time, or sleep time, it is confirmed that it is possible to obtain a uniform nanopattern structure in the photoresist layer. In addition, the lines of holes are characterized by a uniform depth (71–87 nm) and relatively high aspect ratio ranging from 0.22 to 0.26. Numerical modelling performed with a rigorous method shows that such a structure can be potentially used as a phase zone plate.

Nanofiltration membranes of poly(styrene-co-chloro-methylstyrene)-grafted-DGEBA reinforced with gold and polystyrene nanoparticles for water purification

The matrix material for nanofiltration membranes was prepared through chemical grafting of poly(styrene-co-chloromethylstyrene) (PSCMS) to DGEBA using hexamethylenediamine as linker. The phase inversion technique was used to form PSCMS-g-DGEBA membranes. This effort also involves the designing of gold nanoparticles and its composite nanoparticles with polystyrene microspheres as matrix reinforcement. The nanoporous morphology was observed at lower filler content and there was formation of nanopattern at increased nanofiller content. The tensile strength was improved from 32.5 to 35.2 MPa with the increase in AuNPs-PSNPs loading from 0.1 to 1 wt%. The glass transition temperature was also enhanced from 132 to 159 °C. The membrane properties were measured via nanofiltration set-up. Higher pure water permeation flux, recovery, and salt rejection were measured for novel membranes. PSCMS-g-DGEBA/AuNPs-PSNPs membrane with 1 wt% loading showed flux of 2.01 mL cm−2 min−1 and salt rejection ratio of 70.4 %. Efficiency of the gold/polystyrene nanoparticles reinforced membranes for the removal of Hg2+ and Pb2 was found to be 99 %. Novel hybrid membranes possess fine characteristics to be utilized in industrial water treatment units.

Anisotropic magnetization of epitaxial Ni nanogroove-arrays prepared by reduction of self-organized oxides

A straight and periodic nanogroove-array pattern was formed on the surface of epitaxial Ni (111) thin films via a unique process, which included self-organization and reduction of oxides. In the formation of the Ni nanopattern, the epitaxial NiO (111) thin film grown on an α-Al2O3 (0001) substrate by laser molecular-beam epitaxy (LaserMBE) was used as a starting material. The NiO (111) films were subsequently subjected to thermal treatment at 700°C in air for the formation of self-organized nanopatterns, and then at 500°C in a hydrogen atmosphere for reducing NiO to Ni. The epitaxy and morphology of the Ni (111) nanogroove array were proved by exsitu X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Anisotropic magnetization behavior of the Ni (111) nanogroove-array pattern was examined by a M–H measurement using a superconducting quantum interference device (SQUID) magnetometer. The M–H squareness ratios for the directions parallel and perpendicular to the nanogrooves were about 0.83 and 0.52, respectively. The coercivity along the parallel line was ∼0.5kOe, which was approximately 200% of the value for the other direction. From the magnetization results, the parallel direction was considered as the magnetic easy axis in the in-plane orientation, probably due to the shape effect.

Formation of TiO2 Nano Pattern on GaN-Based Light-Emitting Diodes for Light Extraction Efficiency

A TiO2 nano-structure was formed on the indium-tin-oxide electrode of a GaN-based light-emitting diode (LED) in order to enhance the light extraction efficiency. The UV bi-layer imprinting and lift-off processes were used to form the TiO2 nano-structure without any plasma etching process, which can lead to degradation of the electrical properties of the device. As a result, the light output power of the LED on the patterned sapphire substrate (PSS) with the TiO2 nano-structure was enhanced up to 12% compared to identical LED formed on the PSS without TiO2 nano-structure. No electrical degradation was observed for the patterned LED device.

The formation of sub-10 nm nanohole array on block copolymer thin films on gold surface using surface neutralization based on O 2 plasma treatment and self-assembled monolayer

Blockcopolymer (BCP) lithography is an emerging nanolithography technique for fabrications of various nanoscale devices and materials. In this study, self-assembled BCP thin films having cylindrical nanoholes were prepared on gold by surface neutralization using self-assembled monolayer (SAM). Oxygen plasma treatment was investigated as a way to enhance the functionality of Au surface toward SAM formation. After surface neutralization, well-ordered nanoholes with 9 to 20 nm diameters were formed inside BCP thin films on Au surfaces through microphase separation. The effects of oxygen plasma treatment on the formation of BCP nanopattern were investigated using surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Au nanodot arrays were fabricated on gold film by utilizing the BCP nanotemplate and investigated by atomic force microscopy (AFM).

Scanning Tunneling Microscopy Investigation of Self-Assembled CuPc/F16CuPc Binary Superstructures on Graphite

The self-assembly of the binary molecular system comprising copper(II) phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F(16)CuPc) on graphite has been investigated by in situ low-temperature scanning tunneling microscopy (LT-STM). The adsorption of this binary molecular system on graphite results in the formation of a well-ordered chessboardlike nanopattern. The in-plane molecular orientation of the guest CuPc molecules can be tuned by varying the coverage. At low coverage, the sparse CuPc molecules are randomly embedded in the host F(16)CuPc monolayer, possessing two different in-plane orientations; as the CuPc coverage increases, the in-plane molecular orientations of CuPc and F(16)CuPc become unidirectional and a highly ordered chessboardlike pattern forms. Molecular dynamic (MD) simulation results suggest that the selective and directional intermolecular hydrogen bonding determines the in-plane molecular orientation as well as the supramolecular packing arrangement.

Electrochemical Cross-Linking and Patterning of Nanostructured Polyelectrolyte−Carbazole Precursor Ultrathin Films

Nanostructured ultrathin films of pendant carbazole-modified polyelectrolytes were fabricated using the layer-by-layer deposition technique in order to correlate the importance of highly ordered structures and well-defined layer composition in electrochemical cross-linking and nanopatterning. Both UV−vis and surface plasmon resonance (SPR) spectroscopy studies indicated differences in the film structure and bilayer formation based on the degree of electrostatic interaction and carbazole content. Cyclic voltammetry (CV) and SPR studies confirmed the relationship between film structure and the amount of carbazole units per layer affecting the degree of electrochemical cross-linking. CV in particular was used to determine the mechanism of electron transport and electrochemical cross-linking phenomena. Nanopatterning was demonstrated using current sensing AFM (CS-AFM) in which different applied voltages, writing speeds, and composition of polyelectrolytes were studied together with the formation of a complex nanopattern.

Reversible Nanopatterning on Self-Assembled Monolayers on Gold

The reversible fabrication of positive and negative nanopatterns on 1-hexadecanethiol (HDT) self-assembled monolayers (SAMs) on Au(111) was realized by bias-assisted atomic force microscopy (AFM) nanolithography using an ethanol-ink tip. The formation of positive and negative nanopatterns via the bias-assisted nanolithography depends solely on the polarity of the applied bias, and their writing speeds can reach 800 μm/s and go beyond 1000 μm/s, respectively. The composition of the positive nanopatterns is gold oxide and the nanometer-scale gold oxide can be reduced by ethanol to gold, as proved by X-ray photoelectron spectroscopy (XPS) analysis, forming the negative nanopatterns which can be refilled with HDT to recover the SAMs. The inked material of ethanol acts as a reductant which is transferred to the substrate for the local chemical reactions like that in dip-pen nanolithography (DPN). The negative nanopatterns can be used as templates, for example, for the immobilization of magnetic nanoparticles. Interestingly, we found that the nanometer-scale gold oxide was very stable on hydrophobic HDT/Au(111) in air, whereas on hydrophilic SAMs it decomposed soon and resulted in the formation of the negative nanopattern. In addition, the effect of bias on the nanolithography was investigated.

Adsorbate induced self-ordering of germanium nanoislands on Si(113)

The impact of Ga preadsorption on the spatial correlation of nanoscale three-dimensional (3D) Ge-islands has been investigated by low-energy electron microscopy and low-energy electron diffraction. Submonolayer Ga adsorption leads to the formation of a 2D chemical nanopattern, since the Ga-terminated (2×2) domains exclusively decorate the step edges of the Si(113) substrate. Subsequent Ge growth on such a partially Ga-covered surface results in Ge 3D islands with an increased density as compared to Ge growth on clean Si(113). However, no pronounced alignment of the Ge islands is observed. Completely different results are obtained for Ga saturation coverage, which results in the formation of (112) and (115) facets regularly arranged with a periodicity of about 40 nm. Upon Ge deposition, Ge islands are formed at a high density of about 1.3×1010 cm−2. These islands are well ordered as they align at the substrate facets. Moreover, the facet array induces a reversal of the Ge islands' shape anisotropy as compared to growth on planar Si(113) substrates.

Electrochemically Nanopatterned Conducting Coronas of a Conjugated Polymer Precursor: SPM Parameters and Polymer Composition

Here we describe the formation of precisely controlled corona-type nanopatterns on electroactive polymer precursor films using scanning probe microscopy (SPM) methods. The binary composition of electroactive groups in the polymer triggers the formation of corona-type nanopatterns at particular voltages and tip writing speeds through the electrooxidation of the polymer precursor film. Various parameters such as tip speed and applied bias were explored in the nanopatterning process, and the formation of a conductive nanopattern was investigated using conducting atomic force microscopy (C-AFM). The formation of the nanopattern was attributed to the flow of electrons from the AFM tip to the polymer film in a controlled electric field distribution. We also report a new method to distinguish the polymer composition and distribution of a polymer blend film by characterizing biasing differences in the patterning of a polymer film.

Self-organized 2D nanopatterns after low-coverage Ga adsorption on Si (1 1 1)

The evolution of the Si(1 1 1) surface after submonolayer deposition of Ga has been observed in situ by low-energy electron microscopy and scanning tunnelling microscopy. A phase separation of Ga-terminated -R 30° reconstructed areas and bare Si(1 1 1)-7 × 7 regions leads to the formation of a two-dimensional nanopattern. The shape of this pattern can be controlled by the choice of the surface miscut direction, which is explained in terms of the anisotropy of the domain boundary line energy and a high kink-formation energy. A general scheme for the nanopattern formation, based on intrinsic properties of the Si(1 1 1) surface, is presented. Experiments performed with In instead of Ga support this scheme.

Ion-beam nano-patterning by using porous anodic alumina as a mask

Anodized aluminium oxide (AAO) with self-organized and ordered nano-hole arrays may bea good candidate for an irradiation mask to modify the properties of a nano-scaleregion. In order to use AAO as a mask for ion beam patterning, the ion beamtransmittance of AAO should first be tested. In an AAO with a high aspect ratio (about100), anodized from Al bulk foil, the ion beam transmittance was extremely low.However, when AAO with low aspect ratio (about 5), fabricated with thin film Al onSiO2, was irradiated with 80 keV Co ions, the Co ion transmittance was enormouslyimproved. After selective etching of the unirradiated region, ion beam patterned 80 nmSiO2 dot arrays have been fabricated. This shows a potential of AAO with a low aspect ratio foran ion beam patterning nano-mask. In order to demonstrate the ion beam nano-patterning,magnetic nano-patterning was performed. A Co/Pt multilayer film with a perpendicularmagnetic anisotropy was ion irradiated through an AAO mask with a low aspect ratio,460 nm height and 50 nm diameter, and the magnetic properties were investigatedby MOKE. The formation of a magnetic nano-pattern was confirmed by MFM.

Arrays of magnetic nanodots on nitrogen-modified Cu(001) surfaces

A self-organized nanometre-scale pattern on a nitrogen-adsorbed Cu(001)-c(2 × 2)surface is used as a template for the fabrication of a magnetic nanodot array. Byadjusting the coverage of nitrogen on this surface, 5 nm × 5 nm square patches ofthe c(2 × 2)–N surface can be arranged squarely and separated by 2 nm wide stripsof clean Cu surface. Magnetic transition metals grow selectively on the clean Cusurface, and two-monolayers thick dots are dominantly formed at the intersectionsof the 2 nm wide Cu strips. Consequently, magnetic dots of a few nanometres indiameter are squarely organized with 7 nm intervals. Both the formation of thenitrogen-adsorbed nanopattern and the growth of the magnetic nanodotshave been studied in detail by using scanning tunnelling microscopy andelectron diffraction. Strain relief of the partly nitrogen-covered surface is thedriving force producing the square arrangement of the nitrogen-adsorbedpatches. The organization of the magnetic dots is ascribed both to selectivenucleation of the magnetic metal dots on the clean Cu surface and to thelarge growth rate at the intersections. The magneto-optical Kerr effectis employed to examine the magnetic properties of the Co dot array. Along-range order among double-layer dots is established before their percolationoccurs with increasing size. The origin of the novel magnetism is discussed.

Order−Disorder Transition in Surface-Induced Nanopattern of Diblock Copolymer Films

Formation of surface-induced nanopattern (SINPAT) in ultrathin diblock copolymer films is studied by scanning force microscopy and Monte Carlo simulation. The pattern is caused by strong adsorption of one of the two blocks forming a quasi-two-dimensional coil while the other block dewets this adsorption layer. Scanning force microscopy allowed to observe an order−disorder transition for a SINPAT film of polystyrene-block-poly(2-vinylpyridine) on mica when the length of the dewetting polystyrene block was varied. The experimental data are compared with the Monte Carlo simulations which demonstrate how the pattern formation depends on the degree of polymerization of the dewetting block and the unfavorable interaction potential between the different components.