Oligo(ethylene glycol)-terminated monolayers on silicon surfaces and their nanopatterning with a conductive atomic force microscope

Functionalization of silicon substrate surfaces with a stable monolayer for resisting non-specific adsorption of proteins has attracted great interest,since it is directly relevant to the development of miniature,silicon-based biosensors and implantable microdevices,such as silicon-neuron interfaces.This brief review summarizes our contribution to the development of robust monolayers grown by surface hydrosilylation on atomically flat,hydrogen-terminated silicon surfaces.The review also outlines our strateg...     

Spontaneous evolution of nanotips on silicon surface below the laser ablation threshold

A low power density single-pulse laser irradiation of the Si surface has been used for the study of formation and self-organization of silicon nanotips. A two dimensional regular array of hillock-like nanotips has been created in the central region, a disturbed array comprising crossed lines of hillocks in the near-central region, and the “V”-shaped array in the peripheral region. Therefore, the long-range organization of hillocks changes from the center toward the periphery, following the Gaussian-like laser power profile. The evolution of hillocks due to the flow instability of molten silicon is equivalent to the instability of a liquid layer falling down a vertical plate. The novel result is that the hillock-like soliton structures can be identified with the lump solitons resulting from the nonlinear hydrodynamic instability evolution.     

5 nm Ordered Structures Self-Assembled by C2-Symmetric Hybrids with Polyhedral Oligomeric Silsesquioxane and Hexa-peri-Hexabenzocoronene.

Hybrids consisting of polyhedral oligomeric silsesquioxane (POSS) and hexa-peri-hexabenzocoronene (HBC) with a dumbbell topology and C₂ symmetry were designed and synthesized. They self-assemble into 5 nm ordered structures. In particular, the increased steric effect with increasing POSS units stabilizes a square columnar phase (Col_squ) which is important in nanotemplating. These hybrids containing discotic liquid crystal HBC and POSS units have an excellent etching contrast and present an approach to obtain 5 nm nanopatterns.     

Nanopatterning of mesoporous inorganic oxide films for efficient light harvesting of dye-sensitized solar cells

Nanopatterning provides facile process to well-arrayed mesoporous inorganic oxide films at low cost by using readily available pastes and elastomeric nanostamps. The fabricated nanopattern boosted the light-harvesting efficiency of dye-sensitized solar cells (DSSCs) by a light-trapping technique. The iodine-free solid-state DSSCs showed a 40 % increase in the current density and high efficiency (7.03 %).     

Bessel and annular beams for materials processing

Non‐Gaussian beam profiles such as Bessel or annular beams enable novel approaches to modifying materials through laser‐based processing. In this review paper, properties, generation methods and emerging applications for non‐conventional beam shapes are discussed, including Bessel, annular, and vortex beams. These intensity profiles have important implications in a number of technologically relevant areas including deep‐hole drilling, photopolymerization and nanopatterning, and introduce a new dimension for materials optimization and fundamental studies of laser‐matter interactions.     

Manipulating Ge quantum dots on ultrathin SixGe1−x oxide films using scanning tunneling microscope tips

Germanium quantum dots (QDs) were extracted from ultrathin Si_xGe_1−x oxide films using scanning tunneling microscope (STM) tips. The extraction was most efficiently performed at a positive sample bias voltage of +5.0 V. The tunneling current dependence of the extraction efficiency was explained by the electric field evaporation transfer mechanism for positive Ge ions from QDs to STM tips. Ge QDs (∼7 nm) were formed and isolated spatially by extracting the surrounding Ge QDs with an ultrahigh density of >10¹² cm⁻². Scanning tunneling spectroscopy of the spatially-isolated QDs revealed that QDs with an ultrahigh density are electrically-isolated from the adjacent dots.     

A novel integrated method realizing iteratively optimized modeling for proximity field patterning nanolithography

Processing methods used in photonics and nanotechnology have many limitations hindering the ability to realize devices and restricting the actual number of applications. An ideal processing method should require low-cost equipment, be able to produce very fine details, and be scalable to process large area specimens in an acceptable amount of time. Proximity field nanopatterning (PnP) is a lithography method possessing these features. By using interference patterns produced by a two-dimensional phase mask, the technique is able to generate a submicron detailed exposure on a millimeter-size slab of light sensitive photopolymer, which is then developed like a photographic plate to reveal three-dimensional interference patterns from the phase mask. While it is possible to use computer aided simulations to obtain the interference patterns produced by a mask with a certain pattern, the inverse problem of producing a mask for a desired interference pattern cannot be solved in the same way due to the intricacies of light interactions involved in producing the final interference pattern. An alternative method is to iteratively optimize the phase mask so that the interference patterns obtained converge to the desired pattern. The method is elaborated in this article.     

Nanopatterning in a compact setup using table top extreme ultraviolet lasers

The recent development of table top extreme ultraviolet (EUV) lasers have enabled new applications that so far were restricted to the use of large facilities. These compact sources bring now to the laboratory environment the capabilities that will allow a broader application of techniques related to nanotechnology and nanofabrication. In this paper we review the advances in the utilization of EUV lasers in nanopatterning. In particular we show results of the nanopatterning using a table-top capillary discharge laser producing 0.12-mJ laser pulses with 1.2-ns time duration at a wavelength λ = 46.9 nm. The nanopatterning was realized by interferometric lithography using a Lloyd’s mirror interferometer. Two standard photoresists were used in this work, polymethyl methacrylate (PMMA) and hydrogen silsesquioxane (HSQ). Pillars with a full width half maximum (FWHM) diameter of 60 nm and holes with FWHM diameter of 130 nm were obtained over areas in excess of 500×500 μm².     

The link between nanoscale feature development in a negative resist and the Hansen solubility sphere

By systematically studying development of a high resolution, negative electron beam resist, hexa‐methyl acetoxy calix(6)arene, we have elicited a more general understanding of the underlying development mechanisms for negative resists. Using the three dimensional Hansen solubility parameters for more than 40 solvents, we have constructed a Hansen solubility sphere (HSS). From this sphere, we have estimated the Flory Huggins interaction parameter for solvents with hexa‐methyl acetoxy calix(6)arene and found a correlation between resist development contrast, nanoscale patterned feature quality, and the polymer‐solvent solubility. Conducting Atomic Force Microscopy (AFM) in a liquid cell, we have measured swelling for hexa‐methyl acetoxy calix(6)arene in four solvents. The swelling measurements indicate that the HSS gives an indication of the Flory‐Huggins interaction parameter. These measurements provide new insights into the development behavior of nanoscale features – necessary for obtaining the ultimate lithographic resolution. In addition, it demonstrates a methodology for choosing appropriate polymer‐solvent combinations for nanoscience applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2091–2105, 2009