J. Alexander Liddle

Soft X-ray microscopy at a spatial resolution better than 15 nm

Analytical tools that have spatial resolution at the nanometre scale are indispensable for the life and physical sciences. It is desirable that these tools also permit elemental and chemical identification on a scale of 10 nm or less, with large penetration depths. A variety of techniques in X-ray imaging are currently being developed that may provide these combined capabilities. Here we report the achievement of sub-15-nm spatial resolution with a soft X-ray microscope—and a clear path to below 10 nm—using an overlay technique for zone plate fabrication. The microscope covers a spectral range from a photon energy of 250 eV (∼5 nm wavelength) to 1.8 keV (∼0.7 nm), so that primary K and L atomic resonances of elements such as C, N, O, Al, Ti, Fe, Co and Ni can be probed. This X-ray microscopy technique is therefore suitable for a wide range of studies: biological imaging in the water window; studies of wet environmental samples; studies of magnetic nanostructures with both elemental and spin-orbit sensitivity; studies that require viewing through thin windows, coatings or substrates (such as buried electronic devices in a silicon chip); and three-dimensional imaging of cryogenically fixed biological cells.

Lithographically directed self-assembly of nanostructures

The combination of lithography and self-assembly provides apowerful means of organizing solution-synthesized nanostructures for awide variety of applications. We have developed a fluidic assembly methodthat relies on the local pinning of a moving liquid contact line bylithographically produced topographic features to concentratenanoparticles at those features. The final stages of the assembly processare controlled first by long-range immersion capillary forces and then bythe short-range electrostatic and Van der Waals interactions. We havesuccessfully assembled nanoparticles from 50 nm to 2 nm in size usingthis technique and have also demonstrated the controlled positioning ofmore complex nanotetrapod structures. We have used this process toassemble Au nanoparticles into pre-patterned electrode structures andhave performed preliminary electrical characterization of the devices soformed. The fluidic assembly method is capable of very high yield, interms of positioning nanostructures at each lithographically-definedlocation, and of excellent specificity, with essentially no particledeposition between features.

Soft X-ray microscopy of nanomagnetism

Magnetic materials with dimensions of a few tens of nanometers are important for the development of ultrahigh-density magnetic storage and sensor devices. Magnetic microstructure largely determines functionality, and imaging of magnetic domains and magnetization reversal behavior is an outstanding challenge. Magnetic X-ray microscopy makes it possible to investigate magnetization phenomena with elemental specificity and high spatial and temporal resolution.

Implementation of an imprint damascene process for interconnect fabrication

Advanced integrated circuits require eight or more levels of wiring to transmit electrical signal and power among devices and to external circuitry. Each wiring level connects to the levels above and below it through via layers. The dual damascene approach to fabricating these interconnected structures creates a wiring level and a via level simultaneously, thereby reducing the total number of processing steps. However, the dual damascene strategy (of which there are several variations) still requires around 20 process steps per wiring layer. In this work, an approach to damascene processing that is based on step-and-flash imprint lithography (SFIL) is discussed. This imprint damascene process requires fewer than half as many steps as the standard photolithographic dual damascene approach. Through use of a template with two tiers of patterning, a single imprint lithography step can replace two photolithography steps. Further improvements in efficiency are possible if the imprint material is itself a functi...

Quantum-Dot Fluorescence Lifetime Engineering with DNA Origami Constructs†

The ability to organize nanostructures of disparate types and materials—such as metal nanoparticles and semiconductor quantum dots—is challenging but essential for the creation of novel materials and devices. Metal nanoparticles (NPs) have interesting individual plasmonic properties and can be organized to exhibit useful collective responses. Quantum dots (Qdots) provide a powerful means to optically access the nanoscale. Bringing the two together in a well-controlled manner can create structures with interesting properties such as fluorescence enhancement/quenching and high efficiency Fçrster resonance energy transfer. It also has been an area of intense study, both theoretical and experimental, for a wide range of applications including photodetectors, optical modulators and nanoscale lasers. In particular, changing the fluorescence intensity and lifetime of Qdots, when proximate to metal NPs can be used in sensing applications because of the strong distance dependence of the interaction between the Qdots and the ability to engineer the properties (e.g. size, absorbance/emission spectrum) of the individual components over wide ranges. Numerous strategies have been used to connect and control the distance between Qdots and NPs with nanometer precision. 3,7–9] The structures used previously, however, exhibit a limited persistence length (about 50 nm), making the construction of complex geometries required for eventual use in real devices challenging. DNA origami offers a platform with significant advantages: a more rigid scaffold to organize various moieties, increased geometrical complexity, no need to control the stoichiometry of the spacer per NP, and more control over distances. We have therefore chosen to exploit DNA origami for this purpose. We have developed a novel, flexible approach to fluorescence lifetime engineering of CdSe/ZnS (core/shell) Qdots by controlling their coupling to adjacent gold nanoparticles (AuNPs) at geometrically different locations on the DNA origami. To examine these templates in their native state in solution, we use a three-dimensional (3D), real-time, single-particle tracking system. We determine the influence of AuNPs on the Qdot fluorescence lifetime by systematically varying the location, number, and size of AuNPs as well as the interparticle distance and spectral overlap between AuNPs and Qdots. The DNA origami template serves as a programmable nano-pegboard for heterogeneous integration of Qdots and AuNPs wherein complex geometries are created by using modified staple strands on the DNA origami to capture specific nanoparticles (Figure 1). Herein, we manipulate and control the average photon count rate and lifetime of Qdots by varying the geometrical configuration of Qdot–AuNP conjugates on DNA origami and observe good agreement between theory and measurement. Solution-based measurements are important, because they provide insight into how the templates will behave in a biological environment. The single-particle tracking system enables us to follow the 3D motion of individual diffusing

20-nm-resolution Soft x-ray microscopy demonstrated by use of multilayer test structures

A spatial resolution of 20 nm is demonstrated at 2.07-nm wavelength by use of a soft x-ray microscope based on Fresnel zone plate lenses and partially coherent illumination. Nanostructural test patterns, formed by sputtered multilayer coatings and transmission electron microscopy thinning techniques, provide clear experimental results.

Kilohertz Rotation of Nanorods Propelled by Ultrasound, Traced by Microvortex Advection of Nanoparticles

We measure the microvortical flows around gold nanorods propelled by ultrasound in water using polystyrene nanoparticles as optical tracers. We infer the rotational frequencies of such nanomotors assuming a hydrodynamic model of this interaction. In this way, we find that nanomotors rotate around their longitudinal axes at frequencies of up to ≈ 2.5 kHz, or ≈ 150 000 rpm, in the planar pressure node of a half-wavelength layered acoustic resonator driven at ≈ 3 MHz with an acoustic energy density of <10 J·m(-3). The corresponding tangential speeds of up to ≈ 2.5 mm·s(-1) at a nanomotor radius of ≈ 160 nm are 2 orders of magnitude faster than the translational speeds of up to ≈ 20 μm·s(-1). We also find that rotation and translation are independent modes of motion within experimental uncertainty. Our study is an important step toward understanding the behavior and fulfilling the potential of this dynamic nanotechnology for hydrodynamically interacting with biological media, as well as other applications involving nanoscale transport, mixing, drilling, assembly, and rheology. Our results also establish the fastest reported rotation of a nanomotor in aqueous solution.

3D Particle Trajectories Observed by Orthogonal Tracking Microscopy

We demonstrate high-resolution, high-speed 3D nanoparticle tracking using angled micromirrors. When angled micromirrors are introduced into the field of view of an optical microscope, reflected side-on views of a diffusing nanoparticle are projected alongside the usual direct image. The experimental design allows us to find the 3D particle trajectory using fast, centroid-based image processing, with no nonlinear computing operations. We have tracked polystyrene particles of 190 nm diameter with position measurement precision <20 nm in 3D with 3 ms frame duration (i.e., at an imaging rate >330 frames per second). Because the image processing requires only approximately 1 ms per frame, this technique could enable real-time feedback-controlled nanoparticle assembly applications with nanometer precision.

Nanomanufacturing: A Perspective

Nanomanufacturing, the commercially scalable and economically sustainable mass production of nanoscale materials and devices, represents the tangible outcome of the nanotechnology revolution. In contrast to those used in nanofabrication for research purposes, nanomanufacturing processes must satisfy the additional constraints of cost, throughput, and time to market. Taking silicon integrated circuit manufacturing as a baseline, we consider the factors involved in matching processes with products, examining the characteristics and potential of top-down and bottom-up processes, and their combination. We also discuss how a careful assessment of the way in which function can be made to follow form can enable high-volume manufacturing of nanoscale structures with the desired useful, and exciting, properties.

At-wavelength alignment and testing of the 0.3 NA MET optic

Extreme ultraviolet (EUV) interferometry has been successfully performed for the first time at 0.3 numerical aperture (NA). Extensive EUV “at-wavelength” testing including alignment, was performed on a newly created Micro Exposure Tool (MET) optic designed for sub-50-nm EUV lithographic imaging experiments. The two-mirror, 0.3 NA MET is among the highest resolution light-projection lithography tools ever made. Using both lateral shearing and phase-shifting point-diffraction interferometry, the wavefront was measured across the field of view, and the alignment was optimized in preparation for imaging. The wavefront quality reached 0.55nm RMS (λEUV∕24.5) in a 37-term annular Zernike polynomial series, dominated by higher-order spherical aberration. Measurements included calibrations of the interferometer accuracy, assessment of repeatability, and cross-comparisons of visible and EUV interferometric measurements.