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In this manuscript, we demonstrate the potential of replacing the standard bottom anti-reflective coating (BARC) with a polymethylglutarimide (PMGI) layer for wafer-scale nanofabrication by means of deep-UV displacement talbot lithography (DTL). PMGI is functioning as a developable non-UV sensitive bottom anti-reflective coating (DBARC). After introducing the fabrication process using a standard BARC-based coating and the novel PMGI-based one, the DTL nanopatterning capabilities for both coatings are compared by means of the fabrication of etched nanoholes in a dielectric layer and metal nanodots made by lift-off. Improvement of DTL capabilities are attributed to a reduction of process complexity by avoiding the use of O2 plasma etching of the BARC layer. We show the capacity of this approach to produce nanoholes or nanodots with diameters ranging from 95 to 200 nm at a wafer-scale using only one mask and a proper exposing dose. The minimum diameter of the nanoholes is reduced from 118 to 95 nm when using the PMGI-based coating instead of the BARC-based one. The possibilities opened by the PMGI-based coating are illustrated by the successful fabrication of an array of nanoholes with sub-100 nm diameter for GaAs nanowire growth on a 2″ GaAs wafer, a 2″ nanoimprint lithography (NIL) master stamp, and an array of Au nanodots made by lift-off on a 4″ silica wafer. Therefore, DTL possess the potential for wafer-scale manufacturing of nano-engineered materials.

We report on electrical and optical properties of p+-i-n+ photodetectors/solar cells based on square millimeter arrays of InP nanowires (NWs) grown on InP substrates. The study includes a sample series where the p+-segment length was varied between 0 and 250 nm, as well as solar cells with 9.3% efficiency with similar design. The electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+-segment length. Without a p+-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p+-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the NWs, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the zinc blende and wurtzite InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, transmission electron microscopy (TEM), as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations.

Gate-defined quantum point contacts (QPCs) were fabricated with Al0.25Ga0.75N/GaN heterostructures grown by metal-organic chemical vapor deposition (MOCVD). In the transport study of the Zeeman effect, greatly enhanced effective g factors (g*) were obtained. The in-plane g* is found to be 5.5 ± 0.6, 4.8 ± 0.4, and 4.2 ± 0.4 for the first to the third subband, respectively. Similarly, the out-of-plane g* is 8.3 ± 0.6, 6.7 ± 0.7, and 5.1 ± 0.7. Increasing g* with the population of odd-numbered spin-splitted subbands are obtained at 14 T. This portion of increase is assumed to arise from the exchange interaction in one-dimensional systems. A careful analysis shows that not only the exchange interaction but the spin-orbit interaction (SOI) in the strongly confined QPC contributes to the enhancement and anisotropy of g* in different subbands. An approach to distinguish the respective contributions from the SOI and exchange interaction is therefore proposed.

This paper describes the fabrication and initial characterization of an ultra-thin silicon PIN detector using a new technique in silicon nanotechnology. In collaboration with the Nuclear Physics Division and the Lund Nano Lab at Lund University, we have developed and manufactured ultra thin ΔE-detectors for spectroscopic applications. The fabrication process has been carried out using a double-polished silicon substrate n-type wafer and locally thinning by means of a 10:1 solution of 25% tetramethyl ammonium hydroxide (TMAH) with Isopropyl alcohol. More than 100 detectors of different thicknesses, down to 5 μm with active areas ranging from 0.71 to 0.172 mm2, have been fabricated. The main design considerations of our thin detectors were a very low leakage current below 12 nA and a low full depletion voltage at a reverse bias less than 1.5 V. Finally, most of our thin detectors offer an energy resolution (FWHM) as low as 31 keV for 5.487 MeV alpha particles from a 241Am source.

Devices based on molecular motor-driven cytoskeletal filaments, e.g., actin filaments, have been developed both for biosensing and biocomputational applications. Commonly, these devices require nanoscaled tracks for guidance of the actin filaments which has limited the patterning technique to electron beam lithography. Thus, large scale systems become intractable to fabricate at a high throughput within a reasonable time-frame. We have studied the possibility to fabricate molecular motor-based devices using the high throughput, high resolution technique of nanoimprint lithography. Molecular motor-based devices require wide open regions (loading zones) to allow filaments to land for later propulsion into the nanoscale tracks. Such open zones are challenging to fabricate using nanoimprint lithography due to the large amount of material displaced in the process. We found that this challenge can be overcome by introducing nanoscaled pillars inside the loading zones, into which material can be displaced during imprint. By optimising the resist thickness, we were able to decrease the amount of material displaced without suffering from insufficient filling of the stamp. Furthermore, simulations suggest that the shape and positioning of the pillars can be used to tailor the overall cytoskeletal filament transportation direction and behaviour. This is a potentially promising design feature for future applications that however, requires further optimisations before experimental realisation.

Position controlled nanowire growth is important for nanowire-based optoelectronic components which rely on light emission or light absorption. For solar energy harvesting applications, dense arrays of nanowires are needed; however, a major obstacle to obtaining dense nanowire arrays is seed particle displacement and coalescing during the annealing stage prior to nanowire growth. Here, we explore three different strategies to improve pattern preservation of large-area catalyst particle arrays defined by nanoimprint lithography for nanowire growth. First, we see that heat treating the growth substrate prior to nanoimprint lithography improves pattern preservation. Second, we explore the possibility of improving pattern preservation by fixing the seed particles in place prior to annealing by modifying the growth procedure. And third, we show that a SiNx growth mask can fully prevent seed particle displacement. We show how these strategies allow us to greatly improve the pattern fidelity of grown InP nanowire arrays with dimensions suitable for solar cell applications, ultimately achieving 100% pattern preservation over the sampled area. The generic nature of these strategies is supported through the synthesis of GaAs and GaP nanowires. [Figure not available: see fulltext.] (Less)

We report on the realization of a novel interdigitated cantilever array with electrostatic control of the shape of the interdigitated array. It consists of an array of SiO2/metal double-finger cantilevers in a grating configuration together with an electrical connection part. The complete grating structure is fabricated with nanoimprint lithography, UV lithography and reactive ion etching. The patterns of the cantilever arrays are defined by nanoimprint lithography. The electrical contact pads are defined and aligned with the imprinted grating pattern by UV lithography. The two steps of reactive ion etching are optimized to get vertical sidewalls of the SiO2 cantilevers and finally to release them from the Si substrate. By applying a bias, the shape of the cantilever array can be altered due to the electrostatic force. The dimensions of the cantilevers and the spacing between them are optimized to achieve the desired functional operating characteristics of the structures. Since the fabrication scheme is based on nanoimprint lithography, such electrostatically controlled periodic structures may be relatively easily and non-expensively realized in various configurations, allowing them to function as optical switching elements, electrical filters, mass sensors, etc.

A new experimental technique to measure stopping forces for swift heavy ions was tested and has been found effective. A commercial PIN photodiode was coated with a patterned stopping medium of gold. This allowed the simultaneous detection of stopped- and reference-ions of C-14 and N-14 in the energy range E = 6.4-10.4 MeV. The stopping forces of these ions in gold have been measured with excellent accuracy. They are up to 10% larger than expected from present tabulations. It would be straightforward to use the same modified PIN diode in other experiments providing direct comparisons for an identical stopping medium.

We report a novel a lift-off method for nanoimprint lithography. This is a bi-layer method, using a polymethyl methacrylate (PMMA) on lift-off layer (LOL) resist scheme. For the imprint step, direct evidence for good pattern transfer down to 20 nm is shown. Oxygen plasma ashing is required to remove residual PMMA. A liquid solvent, MF 319, is used to transfer the pattern down to the silicon. The LOL is dissolved isotropically while the PMMA is unaffected. Ashing time can kept to a minimum through the wet etch method. This reduces the line widening effect. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface electrostatically. At first warm acetone breakes apart the metal layer and dissolves the PMMA, then warm Remover S-1165 removes the LOL and remaining metal. Structures of lines down to 50 mn and dots with a diameter of sub 20 nm are presented.

We present processing technology based on nanoimprint lithography (NIL) and wet etching for fabrication of GaInAs/InP three-terminal ballistic junction (TBJ) devices. To transfer sub-100 nm features into a high-mobility InP-based 2DEG material, we used SiO2/Si stamps made with electron beam lithography and reactive ion etching. After the NIL, the resist residues are removed in oxygen plasma followed by wet etching of GaInAs/InP to define the TBJ-structures. Fabricated TBJ-devices are characterized using scanning electron microscopy and electron transport measurements. Highly non-linear electrical characteristics of the TBJ structures are demonstrated and compared with E-beam defined devices.

The smaller the features on the stamp the more important are the interactions between stamp and polymer layer. A stamp rich in small structures will effectively show a surface area enlargement, which generally leads to adhesion of the polymer to the stamp. This makes a subsequent imprint impossible without troublesome and time-consuming cleaning. The anti-adhesion properties of Si- or SiO2-based stamps can be improved by binding fluorinated silanes covalently to the surface. In this paper, we demonstrate that the deposition procedure as well as the environment during deposition are important with respect to the quality and performance of the molecular layer. (C) 2002 Published by Elsevier Science B.V.

Semiconductor nanowires are great candidates for building novel electronic devices. Considering the cost of fabricating such devices, substrate reuse and gold consumption are the main concerns. Here we report on implementation of high throughput gold electrodeposition for selective deposition of metal seed particles in arrays defined by lithography for nanowire synthesis. By use of this method, a reduction in gold consumption by a factor of at least 300 was achieved, as compared to conventional thermal evaporation for the same pattern. Because this method also facilitates substrate reuse, a significantly reduced cost of the final device is expected. We investigate the morphology, crystallography, and optical properties of InP and GaAs nanowires grown from electrodeposited gold seed particles and compare them with the properties of nanowires grown from seed particles defined by thermal evaporation of gold. We find that nanowire synthesis, as well as the material properties of the grown nanowires are comparable and quite independent of the gold deposition technique. On the basis of these results, electrodeposition is proposed as a key technology for large-scale fabrication of nanowire-based devices.

Si 3 N 4 / Si (1 0 0), SiO 2 / Si (1 0 0) and SiO 2 / Si (1 1 1) wafers were implanted by keV Co ions under technical conditions to form thin silicide surface films. A metal vapour vacuum arc (MEVVA) source was employed to produce a high fluence of Co ions that was just sufficient to remove the oxide/nitride overlayer by sputter erosion. This high-fluence implantation under technical vacuum introduces foreign atoms into the implanted layer. The behaviour of these impurities following ∼900°C heat treatment in a N2 atmosphere has been studied. Elemental redistributions, crystal recovery, phase formation and electric properties were analysed. The results show that the annealing leads to an increase in crystal ordering within the implanted layer and stable phase formation, as indicated by a reduction in the channeling signal and a decrease in electrical resistivity. In the case of nitride-coated samples, the heat treatment leads to a reduction in the residual carbon and nitrogen in the samples, while the oxygen content is largely unchanged. In contrast, a remarkable increase in the carbon and especially the oxygen contents is observed in the case of the samples with oxide overlayers, and the Co shows a tendency to spread to greater depths.

In order to fabricate and characterise nanometer structures, silicon wafers were implanted with masks ranging from several μm down to 200 nm in lateral dimensions. The masks were produced by an electron beam lithography, metal deposition and metal lift-off sequence. 10 keV 75 As + -ions were implanted to a fluence of 2.5×10 14 cm −2 to create nanometer-sized doped and undoped volumes. Characterisation of the ion-implanted patterns was carried out by etching away the metal masks and subsequently using atomic force microscopy (AFM) and scanning capacitance microscopy (SCM) images of the patterns. The simultaneous AFM and SCM measurements gave sharp contrasts between implanted and unimplanted regions, showing highly resistive swelled structures. The swelling also showed structure with a concave shape for implanted regions and a convex shape for unimplanted regions, which is most probably a result of damage evolution from the implantation.

A complete nanobiosensor structure consisting of a 200 @mm x 200 @mm area containing 100 nm sized interdigitated nanoelectrodes with varied interelectrode distances has been fabricated using nanoimprint lithography (NIL) in combination with UV-lithography. The complete structure has been characterized with admittance spectroscopy. In the paper are discussed the needs and key issues for nanosensors and the capability offered by using NIL for fabrication of such sensors.

The partial sputtering yields of different species from silicon dioxide/Si and silicon nitride/Si during high-fluence keV Co Metal Vapour Vacuum Arc (MEVVA) irradiation are of importance for both silicide formation and interpretation of sputter profiling. Three sets of samples, nitride/Si(1 0 0), oxide/Si(1 0 0) and oxide/Si(1 1 1), have been bombarded to different normal fluences, Θ, from 1 × 1016 to 2.6 × 1018 ions cm−2. The partial sputtering yields for N and Si in the thick nitride films are ∼1.0 and ∼0.65, respectively, which indicates that the relative sputtering ratio of N/Si is ∼1.5. The partial sputtering yields for O and Si of oxide/Si(1 0 0) samples are determined as ∼1.0 and ∼0.3, respectively. Although the O and Si sputtering yields from oxide/Si(1 1 1) samples are ∼15% higher, the average sputtering ratio of O/Si is ∼3.4, the same for both sets of oxide/Si samples. As expected, the partial sputtering yield of Co, YCo(Θ), is small for low fluence implantation and increases with increasing Co fluence. At a normal fluence of ∼5 × 1017 ions cm−2, YCo(Θ) reaches the high fluence quasi-equilibrium limit, the value is very close to unity. The sputtering yield of Co reduces slightly at even higher fluences, which is associated with erosion of the sample surface.

The unit of y axis in Fig. 2 in the original version of this article was unfortunately wrongly written on page 2856, instead of m−2. (Figure Presented.).

Essentially all approaches to artificial molecular motors rely on diffusional stepping, i.e. the free energy input that powers the motor is used to rectify thermal motion. However, many models for biological motors, e.g. myosins or kinesins, include directed motion due to a “power stroke”. In this project we are employing a bottom-up approach to developing a relatively simple experimental model system, the “Inchworm”, with the intention to create the first artificial motor with a power stroke. Specifically, the Inchworm consists of a stretch of DNA confined inside a nanochannel, with ligand-gated repressor proteins immobilized on the nanochannel walls. By cyclically stretching and contracting the Inchworm DNA, via changes in buffer ionic strength, and simultaneously externally controlling the DNA repressor proteins’ binding and unbinding states, the motor is designed to achieve processive and unidirectional motion along the nanochannel. Here we report the status of this project: we have constructed the Inchworm DNA, expressed the ligand-gated repressor proteins and tested their specificity. In addition, we have developed a protocol for immobilization of the repressor proteins to the nanochannel walls and produced nanochannels (100-200 nm) in quartz, which can be interfaced with preexisting micro-fluidic systems.Acknowledgment: This work was supported by MONAD, HFSP, the Swedish Research Council and nmC@LU.

This paper describes the fabrication of efficient ultra-thin silicon transmission detectors for use as pre-cell detectors in single-ion experiments on living cells at the Lund Ion Beam Analysis Facility. More than 40 detectors of different thicknesses down to 5 μm have been fabricated and packaged. The main design considerations were very low leakage current (below 9 nA) and low full depletion voltage at biases less than 0.5 V at room temperature. In addition, we have shown that cooling the device can reduce the leakage current to 3 nA. The experimental testing of the pre-cell detection system is based on counting the passage of ions through the transmission (ΔE) detector before hitting the stopping (E) detector placed behind it, to ensure the accurate delivery of specific doses of radiation to the sample. Optimal detection of the fabricated detectors for the passage of an external beam of 2.2 MeV protons was obtained by cooling the device to below 2°C. Cooling the ΔE detectors provides up to 20% better energy resolution and up to 98% detection efficiency for 2.2 MeV protons. The development of this kind of efficient pre-cell detector enables a range of new experiments to be conducted on thick biological samples.

Nanoimprint lithography over 2 inch wafers with a patterned area of 40,000 micrometer squared consisting of interdigitated lines of 100 nm width with varying distance between the lines has been performed. By performing metal lift-off and subsequent UV-lithography for definition of contact regions and pads, complete metal arrays have been fabricated. The structure is electrically characterized by admittance spectroscopy. In this paper we describe the design and realization of a compact nanoimprint lithography system. Furthermore, various aspects of nanoimprint lithography are discussed, and nanoimprint lithography is compared with other nanostructuring technologies.

In this study, nickel pattern electrodes were electrochemically investigated in a three-electrode setup, operating both with H-2/H2O and CO/CO2 atmospheres. Heating introduced structural differences in the nickel layer among the pattern electrodes, which appear to affect the electrode performance. Both dense and porous nickel pattern electrodes were formed by heating. Holes appeared in the nickel layer of the porous pattern electrodes, where the open cavity triple phase boundaries exhibited different limiting processes than open triple phase boundary electrodes of the dense electrode. As the temperature was raised in the experiment, the electrodes stabilized, with a degraded behavior that seemed to be strongly coupled to the structural changes in the electrode. It was possible to compare literature results with high temperature impedance measurements in H-2/H2O presented here, while new results at lower temperatures in H-2/H2O are also presented. Impedance spectroscopy measurements were performed, and the gas dependence of the polarization resistance was observed as the mixture ratios and temperatures were varied in both atmospheres. A positive relation between the polarization resistance and the partial pressure of CO was determined for the dense nickel pattern electrode, which agrees with previous results using nickel point electrodes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3484091] All rights reserved. (Less)

In this study we will report on the development of a process to establish antisticking layers on nickel-based stamps, which are used in several industrial applications of nanoimprint lithography or related methods. The fluorinated alkyl silane films have been deposited onto different Ni-based stamp surfaces in order to minimize the adhesion tendency at the stamp/polymer interface. Film thickness, chemical composition, purity, and binding mechanisms of the silane groups to different stamp surface materials have been determined by photoelectron spectroscopy (XPS). In the case of electroplated nickel stamps—where low imprint qualities are observed—multilayer thick films cover the stamp surfaces, consisting of polymerized, cross-linked alkyl silanes, which are poorly bound to the surface. In order to overcome these restrictions a 100 A thick polycrystalline titanium layer has been established in a sandwich position between the nickel substrate and the silane film. Here, silane film thicknesses in the monomolecular region together with evidences for strong covalent linkage between the silane groups and the oxidized Ti surface can be concluded from the XPS results, leading to film properties and imprint qualities, which are comparable to those formerly observed for silicon stamps.

We demonstrate fabrication technology and characterization results of GaInAs/InP electron waveguides with lengths between 0.2 and 6 /spl mu/m. The waveguides, 50 to 100 nm wide, are produced by deep wet etching of high mobility 2DEG MOVPE-grown G/sub 0.25/In/sub 0.75/As/InP structures. The waveguide structures are defined by electron beam lithography and a nonselective etching in either HCl:CH/sub 3/COOH:H/sub 2/O/sub 2/ or HBr-based solutions. A 250 nm-thick ZEP520 electron beam resist is used as an etch mask after a post-development baking at 120/spl deg/C to enhance its adhesion to the substrate. After etching, the structures were regrown by nominally undoped InP layer in a low-pressure MOVPE process or by Fe-doped InP in an atmospheric pressure hydride vapor phase epitaxy (HVPE). The Fermi energy is controlled by applying voltage to resist-insulated top gate or side gates. A well defined quantized conductance at 0.3 K of heterostructurally-defined electron waveguides with length of up to 3 /spl mu/m is demonstrated.

The authors report on the fabrication of subsurfaced 100–600 nm wide nanochannels in fused silica with top slit openings in the size range of 5–10 nm. Such nanochannels can be used in combination with a nanofluidics system to guide molecular motors and quickly switch the chemical environment inside the nanochannels through diffusion via the top slits. To realize nanochannel top slits in this size range, the authors here demonstrate the use of a self-closing effect based on the volume expansion of a thin Si layer during oxidation. A high contrast electron beam lithography exposure step in conjunction with dry etching of SiO2 by reactive ion etching (RIE) and Si by inductively coupled plasma-RIE followed by wet etching of a fused silica substrate is used to create the initial slit before oxidation. The details of nanochannel fabrication steps are described and discussed.