M. G. Capeluto

Patterning of nano-scale arrays by table-top extreme ultraviolet laser interferometric lithography

Arrays of nanodots were directly patterned by interferometric lithography using a bright table-top 46.9 nm laser. Multiple exposures with a Lloyds mirror interferometer allowed to print arrays of 60 nm FWHM features. This laser-based extreme ultraviolet interferometric technique makes possible to print different nanoscale patterns using a compact table-top set up.

Nanopatterning with interferometric lithography using a compact /spl lambda/=46.9-nm laser

We report the imprinting of nanometer-scale gratings by interferometric lithography at /spl lambda/=46.9 nm using an Ne-like Ar capillary discharge laser. Gratings with periods as small as 55 nm were imprinted on poly-methyl methacrylate using a Lloyds mirror interferometer. This first demonstration of nanopatterning using an extreme ultraviolet (EUV) laser illustrates the potential of compact EUV lasers in nanotechnology applications.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures

Nanowire arrays heated by laser pulses of relativistic intensity open a path to extreme energy densities and pressures. Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 108 J cm−3 and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world’s largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 × 1019 W cm−2, we demonstrate energy penetration depths of several micrometers, leading to UHED plasmas of that size. Relativistic three-dimensional particle-in-cell simulations, validated by these measurements, predict that irradiation of nanostructures at intensities of >1 × 1022 W cm−2 will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 × 1010 J cm−3, equivalent to a pressure of 0.35 Tbar.

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.

New opportunities in interferometric lithography using extreme ultraviolet tabletop lasers

The development of tabletop extreme ultraviolet EUV lasers opens now the possibility to realize interferometric lithography systems at EUV wavelengths that easily fit on the top of an optical table. The high degree of spatial and temporal coherence and high brightness of the compact EUV laser sources make them a good option for interferometric applications. The combination of these novel sources with interferometric lithography setups brings to the laboratory environment capabilities that so far had been restricted exclusively to large synchrotron facilities.

Interferometric lithography at 46.9 nm

We present the first results of nano-patterning in poly-methyl methacrylate (PMMA) photo-resist using a 46.9 nm tabletop extreme ultraviolet (EUV) laser. As a proof of principle, we recorded a Fresnel diffraction pattern of a copper mesh with 19 μm square holes. Results of ongoing interference experiments will also be presented.

Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime

The efficient conversion of optical laser light into bright ultrafast x-ray pulses in laser created plasmas is of high interest for dense plasma physics studies, material science, and other fields. However, the rapid hydrodynamic expansion that cools hot plasmas has limited the x-ray conversion efficiency (CE) to 1% or less. Here we demonstrate more than one order of magnitude increase in picosecond x-ray CE by tailoring near solid density plasmas to achieve a large radiative to hydrodynamic energy loss rate ratio, leading into a radiation loss dominated plasma regime. A record 20% CE into hν>1  keV photons was measured in arrays of large aspect ratio Au nanowires heated to keV temperatures with ultrahigh contrast femtosecond laser pulses of relativistic intensity. The potential of these bright ultrafast x-ray point sources for table-top imaging is illustrated with single shot flash radiographs obtained using low laser pulse energy. These results will enable the deployment of brighter laser driven x-ray sources at both compact and large laser facilities.

Design of a phase-shifting interferometer in the extreme ultraviolet for high-precision metrology

The design of a phase-shift interferometer in the extreme ultraviolet (EUV) is described. The interferometer is expected to achieve a significantly higher precision as compared with similar instruments that utilize lasers in the visible range. The interferometers design is specifically adapted for its utilization with a table top pulsed capillary discharge EUV laser. The numerical model evaluates the errors in the interferograms and in the retrieved wavefront induced by the shot-to-shot fluctuations and pointing instabilities of the laser.

Nanopillars and arrays of nanoholes fabricated by extreme ultraviolet interferometric laser lithography

Arrays of holes and pillars were fabricated by multiple exposure interferometric lithography using a table top lambda = 46.9 nm wavelength laser. Size and the feature characteristic is controlled changing the applied exposure dose.

Arrays of sub-100 nm features fabricated with table top extreme ultraviolet interferometric laser lithography

Arrays of nano-dots were demonstrated by multiple exposure interferometric lithography using a table top lambda=46.9 nm wavelength laser. Patterns of different geometries with features ~60 nm FWHM were printed controlling the exposure dose.