A. Wrulich

Fabrication of all-metal field emitter arrays with controlled apex sizes by molding

The authors proposed a method to fabricate field emitter arrays with uniform apex diameters in tens of nanometer scale based on the molding technique and apply it to fabricate molybdenum field emitter arrays. Apex diameter equal to 23±5nm was observed in a 6×6 tip array by high-resolution scanning electron microscope. They also studied the field-emission characteristics in devices with gate electrodes fabricated on top of the arrays by a self-aligned process. In single-gate devices, emission current of up to 20μA per tip with negligible gate leak current was observed. The gate-fabrication process was extended to fabricate double-gated emitters. Further optimization of the fabrication process for higher emission current, together with metallurgical and lithographic methods, is discussed.

Commissioning of the Swiss Light Source

The Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI) consists of a turn key 100 MeV linac, a novel type of booster synchrotron and a 12-TBA storage ring providing 5 nm-rad natural emittance at 2.4 GeV, The SLS project was approved by Swiss Government in Sept. 1997. By June 1999 the building was finished. Linac and booster commissioning concluded by April, resp. Sept. 2000. First beam in the ring was stored Dec. 15, 2000. By June 2001 storage ring commissioning entered the final phase: The design current of 400 mA was reached, an excellent agreement of lattice functions with design calculations was achieved and first undulator spectra were measured. Commissioning of booster and storage ring included commissioning of the innovative subsystems like the digital BPM system, the digital power supplies, the high stability injection system and the CORBA based beam dynamics software.

Static and optical field enhancement in metallic nanotips studied by two-photon photoemission microscopy and spectroscopy excited by picosecond laser pulses

The authors studied the photoemission from molybdenum nanotip arrays with controlled apex curvatures by photoelectron microscopy and spectroscopy excited by 10 ps visible laser pulses under dc electric field. While two-photon photoemission microscopy demonstrates the enhancement of photoabsorption at the sharp tip apex, spatially resolved analysis of the photoelectron energy revealed anomalous energy distribution that is ascribed to the dc field enhancement and resultant barrier reduction at the tip apex. The results show the applicability of photoelectron microscopy and spectroscopy to study the distribution of dc and optical electric field enhancement in field-emitter arrays.

Nanoseconds field emitted current pulses from ZrC needles and field emitter arrays

The properties of the electron source define the ultimate limit of the beam quality in linear accelerators such as free electron lasers (FELs). The goal is to develop an electron gun delivering beam emittance lower than the current state of the art. Such a gun should reduce the cost and size of an x-ray FEL (XFEL). In this article we present two concepts of field emitter cathodes which could potentially produce low emittance beam. The first challenging parameter for such cathode is to emit peak current as high as 5 A. This is the minimum current requirement for the XFEL concept from Paul Scherrer Institut (http://leg.web.psi.ch). Maximum currents of 0.12 and 0.58 A have been reached, respectively, with field emitter arrays and single needle cathodes. Laser assisted field emission gave encouraging results to reach even higher peak current and to prebunch the beam.

Pulsed field emitted current from different commercial samples in the purpose of a free electron laser application

The development of an electron gun with the lowest possible emittance would help reduce the total length and cost of a free electron laser. Recent progress in vacuum microelectronics makes field emitter tips an attractive technology to explore for high brightness electron sources. In order to be a good candidate for a low emittance gun, field emission cathodes must provide at least the peak current, stability, and homogeneity of current state of the art electron sources. In this article, we report on current voltage measurements of commercially available field emitter samples in both continuous and pulsed mode. Pulsed electron emission is of particular interest for a free electron laser application. As mentioned by other authors [F. Charbonnier, Appl. Surf. Sci. 94/95, 26 (1996); P. R. Schwoebol et al., J. Vac. Sci. Technol B 19, 980 (2001)], higher peak current and more stable emission can be achieved when using short square voltage pulses at low frequency. We present maximum peak currents achieved with ...

Field emitter arrays for a free electron laser application

In this paper, the results on current performance of some field emitter materials showed high and stable current pulses at low frequency can be emitted with less contamination problems. For a free electron laser application, peak current values are still too small but by using shorter pulses and small internal field emitter array resistance, a required current was expected to be reached.

Characterization of metallic field emitter array devices fabricated by molding for x-ray free electron laser applications

A low-emittance and high-brightness electron source is a prerequisite for the successful development of sub-nm wavelength x-ray free electron lasers (XFEL). For that application, a field emitter array (FEA) device equipped with a focusing gate is potentially advantageous over the state-of-the-art photocathode. In the low-emittance gun design of the PSI-XFEL project at the Paul Scherrer Institut, the cathode is assumed to emit above 0.2 nC within 10-40 ps, or -10 A, from an array of total area below 1 mm in diameter. So far, the current of the commercially available FEA device is limited to -0.1 A/mm2. To reach higher currents, we explore the field-emission properties of pyramidal-shaped molybdenum FEAs based on the molding-technique. For high-current applications, the pyramidal tip with low-aspect ratio is advantageous over a conical/cylindrical one because of the higher thermal conductance and thermal spread. Here we present fabrication and characterization of pyramidal-shaped molybdenum FEAs with relatively small numbers of tips (1) to measure the maximum current Imax per tip for single-gate devices, and (2) to explore the spatially- and energy-resolved photoemission in FEAs without gate electrodes.

Development of All-metal Field Emitter Arrays for high Current Applications

We are developing high-current field emitter arrays for the PSI-FEL project. By sputtering into molds and electroplating, we produce metal tips on a metal substrate. The single tip current is ~ 0.1 - 1.0 muA.

Development of a low emittance electron gun based on field emission cathodes

Field emitters are investigated for use as a low emittance electron gun. Two available field emitter technologies are currently explored; the field emitter arrays (FEAs) with individual focusing and single tip cathode with robust and fairly blunt apex. The challenge is to achieve several amperes of peak current without tip destructions. Very good cathode and environmental conditioning procedures with extremely short emission duration (ns) at low repetition rate (10 Hz) gave encouraging results to reach high peak current emission. For a free electron laser application, very short emission durations are preferred. Such operation regime should prevent the tip from overheating so that higher current densities could be reached. Another possible low emittance electron sources are single needle tips made from etched wires and which can be coated and formed in order to carry high current emission. One way to achieve short emission duration is to use pulsed laser light illuminating the tip while high electric field is applied.

A high-brightness accelerator-based EUV source for metrology applications

One of the challenges of actinic metrology tools for EUV lithography is the availability of light sources with high brightness, stability, and availability. In particular, actinic patterned mask inspection on EUV reticles is considered an essential tool for the EUV lithography ecosystem and it requires an EUV source of high brightness. We present the design of a compact and accelerator-based light source producing EUV radiation with high-brightness for actinic metrology applications in the semiconductor industry. Our design is based on the well-established components and design principles. The specifications required for actinic mask inspection is achieved using a short period undulator and 430 MeV electron energy. The concentric design of storage and booster rings enables stable operation with a relatively small footprint. This study shows the commercial viability of a compact and high-brightness EUV source with high stability and reliability and demonstrates its feasibility for actinic metrology applications.