Nanoscale patterning on insulating substrates by critical energy electron beam lithography

This Letter describes a method to generate nanometer scale patterns on insulating substrates and wide band gap materials using critical energy electron beam lithography. By operating at the critical energy (E2) where a charge balance between incoming and outgoing electrons leaves the surface neutral, charge-induced pattern distortions typically seen in e-beam lithography on insulators were practically eliminated. This removes the need for conductive dissipation layers or differentially pumped e-beam columns with sophisticated gas delivery systems to control charging effects. Using a "scan square" method to find the critical energy, sub-100 nm features in 65 nm thick poly(methyl methacrylate) on glass were achieved at area doses as low as 10 microC/cm2 at E2 = 1.3 keV. This method has potential applications in high-density biochips, flexible electronics, and optoelectronics and may improve the fidelity of low voltage e-beam lithography for parallel microcolumn arrays.     

Photo-deprotection patterning of self-assembled monolayers

Photo-deprotectable self-assembled monolayers (SAMs) provide a versatile platform for creating functional patterned surfaces. In this study, we present nanoscale photo-patterning, multi-component patterning, and a method for producing molecular gradients using photo-deprotectable SAMs. Nanoscale patterning of photo-deprotectable SAMs was achieved by coupling a UV laser (365 nm) through a scanning near field probe to produce nanoscale lines of ～40 nm, i.e. λ/9. Multi-component patterning was achieved by a two-stage method combining both microcontact printing and soft-UV photo-patterning. The example demonstrated in this study produced a three-component patterned surface with regions of CF₃, CH₃ and COOH/CF₃ functionality. The versatility of these photocleavable SAMs is further demonstrated by creating linear molecular gradients of two functionalities along a distance of ～25 mm. The use of ‘soft’ UV gives several advantages including the ability to pattern SAMs with micron-scale features over large areas quickly, with greater control over the photochemical reactions, and compatibility with existing lithographic facilities thus offering an effective alternative to other patterning methods such microcontact-printing or deep UV patterning.     

Nano-pillars using electron beam lithography and electroplating

##正##Mechanical testing of submicrometer-sized metal pillars has shown significant strengthening on decreasing the pillar dimensions. Analysis of such experiments is complicated, however, because the traditional focused ion beammethod for making the     

Polystyrene as a zwitter resist in electron beam lithography based electroless patterning of gold

The resist action of polystyrene (M _w, 2,600,000) towards electroless deposition of gold on Si(100) surface following cross-linking by exposing to a 10 kV electron beam, has been investigated employing a scanning electron microscope equipped with electron beam lithography tool. With a low dose of electrons (21 μC/cm²), the exposed regions inhibited the metal deposition from the plating solution due to cross-linking—typical of the negative resist behaviour of polystyrene, with metal depositing only on the developed Si surface. Upon increased electron dosage (160 μC/cm²), however, Au deposition took place even in the exposed regions of the resist, thus turning it into a positive resist. Raman measurement revealed amorphous carbon present in the exposed region that promotes metal deposition. Further increase in dosage led successively to negative (220 μC/cm²) and positive (13,500 μC/cm²) resist states. The zwitter action of polystyrene resist has been exploited to create line gratings with pitch as low as 200 nm and gap electrodes down to 80 nm.     

Nanoscale programmable sequence-specific patterning of DNA scaffolds using RecA protein

Molecular self-assembly inherent to many biological molecules, in conjunction with suitable molecular scaffolds to facilitate programmable positioning of nanoscale objects, offers a promising approach for the integration of functional nanoscale complexes into macroscopic host devices. Here, we report the use of the protein RecA as a means of highly efficient programmable patterning of double-stranded (ds)DNA molecules with molecular-scale precision at specific locations along the DNA strand. RecA proteins form nucleoprotein filaments with single-stranded (ss)DNA molecules, which are chosen to be of sequence homologous to the desired binding region on the dsDNA scaffold. We show that the patterning yield can be in excess of 85% and we demonstrate that concurrent patterning of multiple locations on the same dsDNA scaffold can be achieved with separation between the assembled nucleoprotein filaments of less than 4?nm. This is an important prerequisite for this programmable and flexible DNA scaffold patterning technique to be employed in molecular-?and nanoscale assembly applications.     

Ice-assisted electron beam lithography of graphene

We demonstrate that a low energy focused electron beam can locally pattern graphene coated with a thin ice layer. The irradiated ice plays a crucial role in the process by providing activated species that locally remove graphene from a silicon dioxide substrate. After patterning the graphene, the ice resist is easily removed by sublimation to leave behind a clean surface with no further processing. More generally, our findings demonstrate that ice-assisted e-beam lithography can be used to pattern very thin materials deposited on substrate surfaces. The procedure is performed in situ in a modified scanning electron microscope. Desirable structures such as nanoribbons are created using the method. Defects in graphene from electrons backscattered from the bulk substrate are identified. They extend several microns from the e-beam writing location. We demonstrate that these defects can be greatly reduced and localized by using thinner substrates and/or gentle thermal annealing.     

Fabrication of molecular nanotemplates in self-assembled monolayers by extreme-ultraviolet-induced chemical lithography

Extreme-UV interference lithography (EUV-IL) is applied to create chemical nanopatterns in self-assembled monolayers (SAMs) of 4'-nitro-1,1'-biphenyl-4-thiol (NBPT) on gold. X-ray photoelectron spectroscopy shows that EUV irradiation induces both the conversion of the terminal nitro groups of NBPT into amino groups and the lateral crosslinking of the underlying aromatic cores. Large-area ( approximately 2 mm(2)) nitro/amino chemical patterns with periods ranging from 2000 nm to 60 nm can be generated. Regions of pristine NBPT on the exposed samples are exchanged with protein-resistant thiol SAMs of polyethyleneglycol, resulting in the formation of molecular nanotemplates, which can serve as the basis of complex biomimetic surfaces.     

Focused ion beam lithography and anodization combined nanopore patterning

In this study, focused ion beam lithography and anodization are combined to create different nanopore patterns. Uniform-, alternating-, and gradient-sized shallow nanopore arrays are first made on high purity aluminum by focused ion beam lithography. These shallow pore arrays are then used as pore initiation sites during anodization by different electrolytes. Depending on the nature of the anodization electrolyte, the nanopore patterns by focused ion beam lithography play different roles in further pore development during anodization. The pore-to-pore distance by focused ion beam lithography should match with that by anodization for guided pore development to be effective. Ordered and heterogeneous nanopore arrays are obtained by the focused ion beam lithography and anodization combined approach.     

电子束曝光机的偏转系统

电子束曝光机的偏转系统控制电子束偏转扫描。像差低、偏转灵敏度高、扫描速度快是它的基本要求。对各种偏转器、偏转方式进行分析、比较,从偏转器空间场的数值计算方法、偏转系统的优化、像差校正、偏转器制作工艺、电气参数等方面阐述设计过程和工程实现上一些值得注意的问题。综合考虑偏转器和偏放电路的设计可以得到最优性能的系统。     

Fabrication of uniform and high resolution copper nanowire using intermediate self-assembled monolayers through direct AFM lithography

Electrochemical AFM lithography was used to directly fabricate copper nanowires. The copper ions were strongly reduced by a negative sample bias at the point where the AFM tip was localized, and copper metal wires were successfully fabricated following the direction of the electrical field of the bias. A TDA?HCl self-assembled monolayer (SAM) was found to play an important role as an intermediate layer for enhancing the capability of high resolution and complete development after the AFM lithographic process. The physical and electrical properties of the wires were analyzed by AFM, EFM, SEM, TEM and I-V measurement. The fabricated copper has promising potential for applications such as masks and interconnectors for nanoelectronic devices.     

A novel method for patterning of poly(3,4-ethylenedioxythiophene) films using UV exposure-activated self-assembled monolayers

We have investigated a novel method for patterning of (3, 4-ethylenedioxythiophene) PEDOT, which has involved a selective polymerization of PEDOT on an UV-activated Self-Assembled-Monolayer surface. OTS coated surface has been activated by UV exposure, and the UV-exposed area served as adsorption sites for FeCl3 oxidants, providing a selective deposition of PEDOT films on FeCl3 adsorbed area, and thus leading to the selective patterning of PEDOT films. UV irradiation time and mask pattern dimension are main contributors to patternability: UV irradiation through Cr-mask (3 microm design) lead to approximately 3-5 microm patterns of PEDOT films, depending on the UV exposure time. In addition, a scotch tape peel test revealed excellent adhesion property of PEDOT to SiO2. Consequently, this simple method can be applied to define deep submicron dimensions due to its ability of providing a direct transfer of mask patterns to the substrate.     

Production of nanopatterns by a combination of electron beam lithography and a self-assembled monolayer for an antibody nanoarray

We report on a flexible method of producing antibody (IgG) nanopatterns by combining electron beam (EB) lithography and a perfluorodecyltriethoxysilane (FDTES) self-assembled monolayer (SAM). Using EB lithography of the FDTES SAM, we easily fabricated IgG patterns with feature sizes on the order of 100 nm. The patterned IgG retained its ability to interact specifically with an anti-LgG. The influence of different concentrations of the IgG and anti-IgG on the resulting fluorescent IgG arrays was investigated. These IgG nanopatterns appeared to be remarkably well controlled and showed almost no detectable nonspecific binding of proteins on a hydrophobic SAM under a suitable incubation condition, characterized by atomic force microscopy, and epi-fluorescence microscopy. The technique enables the realization of high-throughput protein nanoscale arrays with high specificity.     

Sub-10 nm patterning using EUV interference lithography

Extreme ultraviolet (EUV) lithography is currently considered as the leading technology for high-volume manufacturing below sub-20 nm feature sizes. In parallel, EUV interference lithography based on interference transmission gratings has emerged as a powerful tool for industrial and academic research. In this paper, we demonstrate nanopatterning with sub-10 nm resolution using this technique. Highly efficient and optimized molybdenum gratings result in resolved line/space patterns down to 8 nm half-pitch and show modulation down to 6 nm half-pitch. These results show the performance of optical nanopatterning in the sub-10 nm range and currently mark the record for photon-based lithography. Moreover, an efficient phase mask completely suppressing the zeroth-order diffraction and providing 50 nm line/space patterns over large areas is evaluated. Such efficient phase masks pave the way towards table-top EUV interference lithography systems.     

Stability of Ag nanoparticles fabricated by electron beam lithography

The stability of silver nanoparticles on indium tin oxide coated glass substrates under atmospheric condition was investigated. These nanoparticles were fabricated using electron beam lithography. Energy dispersive spectroscopy analysis revealed a high concentration of sulfur in the silver nanoparticles exposed to laboratory air for 12 weeks at room temperature. Morphological changes in the silver nanoparticles were also observed for nanoparticles stored under the same conditions. In contrast, silver nanoparticles kept in vacuum did not show chemical or morphological changes after 12 weeks. The present work clearly shows the need to consider ambient exposure when using Ag nanoparticles for sensors.     

High-resolution electron beam lithography and DNA nano-patterning for molecular QCA

Electron beam lithography (EBL) patterning of poly(methylmethacrylate) (PMMA) is a versatile tool for defining molecular structures on the sub-10-nm scale. We demonstrate lithographic resolution to about 5 nm using a cold-development technique. Liftoff of sub-10-nm Au nanoparticles and metal lines proves that cold development completely clears the PMMA residue on the exposed areas. Molecular liftoff is performed to pattern DNA rafts with high fidelity at linewidths of about 100 nm. High-resolution EBL and molecular liftoff can be applied to pattern Creutz-Taube molecules on the scale of a few nanometers for quantum-dot cellular automata.     

Controlling liquid crystal alignment using photocleavable cyanobiphenyl self-assembled monolayers

We report on the development of novel cyano-biphenyl-based thiolate self-assembled monolayers designed to promote homeotropic alignment of calamitic liquid crystals. The molecules developed contain an ortho-nitrobenzyl protected carboxylic acid group that on irradiation by soft UV (365 nm) is cleaved to yield carboxylic acid groups exposed at the surface that promote planar alignment. Using a combination of wetting, X-ray photoelectron spectroscopy, Fourier transform-infrared reflection absorption spectroscopy, and ellipsometry we show that high photolysis yields (>90%) can be achieved and that the patterned SAMs are suitable for the controlled alignment of calamitic liquid crystals. This study further shows that such photo-patterned SAMs can be used to control the formation of focal conic domains (FCDs) in the smectic-A phase in terms of positioning and size confinement on surfaces.     

Nanowire conductive polymer gas sensor patterned using self-assembled block copolymer lithography

Nanostructured conjugated organic thin films are essential building blocks for highly integrated organic devices. We demonstrate the large-area fabrication of an array of well-ordered 15 nm wide conducting polymer nanowires by using an etch mask consisting of self-assembled patterns of cylinder-forming poly(styrene-b-dimethylsiloxane) diblock copolymer confined in topographic templates. The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) nanowires operated as an ethanol vapor sensor, suggesting that the electronic properties of the organic film were preserved during the patterning processes. The higher sensitivity to ethanol vapor, compared to an unpatterned film with the same thickness, was attributed to the enhanced surface-to-volume ratio of the nanowire array.     

Osteoprogenitor response to low-adhesion nanotopographies originally fabricated by electron beam lithography

It is considered that cells can use filopodia, or microspikes, to locate sites suitable for adhesion. This has been investigated using a number of mature cell types, but, to our knowledge, not progenitor cells. Chemical and topographical cues on the underlying substrate are a useful tool for producing defined features for cells to respond to. In this study, arrays of nanopits with different symmetries (square or hexagonal arrays with 120 nm diameters, 300 nm center–centre spacings) and osteoprogenitor cells were considered. The pits were fabricated by ultra-high precision electron-beam lithography and then reproduced in polycarbonate by injection moulding with a nickel stamp. Using scanning electron and fluorescence microscopies, the initial interactions of the cells via filopodia have been observed, as have subsequent adhesion and cytoskeletal formation. The results showed increased filopodia interaction with the surrounding nanoarchitecture leading to a decrease in cell spreading, focal adhesion formation and cytoskeletal organisation.     

Controlling charge injection in organic field-effect transistors using self-assembled monolayers

We have studied charge injection across the metal/organic semiconductor interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect transistors, with Au source and drain electrodes modified by self-assembled monolayers (SAMs) prior to active polymer deposition. By using the SAM to engineer the effective Au work function, we markedly affect the charge injection process. We systematically examine the contact resistivity and intrinsic channel mobility and show that chemically increasing the injecting electrode work function significantly improves hole injection relative to untreated Au electrodes.