L P. Ratliff

Non-kinetic Damage on Insulating Materials by Highly Charged Ion Bombardment

Abstract We have measured the damage caused by the impact of low velocity, highly charged ions on insulating surfaces. Atomic force microscopy allows us to observe directly the surface topography with nanometer resolution. Using constant velocity (100 keV) Xe q + ions (25 ⩽ q ⩽ 50) impinging on mica, we observe damage caused by single ion impacts. Impact sites typically are circular hillocks. Within the range and accuracy of the data, the height and volume of the damaged regions are well approximated by a linear function of ion potential energy.

Masked Ion Beam Lithography with Highly Charged Ions

Masked ion beam lithography using highly charged ions is demonstrated for the first time by producing an array of hundreds of ordered micrometer wide dots using Xe44+ on poly(methylmethacrylate) resist. At low dose, exposure of the resist is incomplete and isolated single-ion impact sites can be seen within the exposed areas. Atomic force microscope images of the single-ion impact sites show craters with a width of 24 nm. At high dose, the exposure is complete and the dot morphology is consistent with limitations from the mask. Scanning electron microscope images indicate that the sidewall slope is steeper than four.

Exposure of self-assembled monolayers to highly charged ions and metastable atoms

The doses of neutral metastable argon atoms (Ar*) and highly charged xenon ions (HCIs) required to damage self-assembled monolayers (SAMs) of alkanethiolates on gold are compared in a set of experiments carried out concurrently. The extent of damage to the SAM is determined by developing the samples in a gold etching solution, then measuring the decrease in reflectivity of the gold; ≈105 Ar* are required to cause the same amount of damage as 1 HCI, as measured by this assay. We have also demonstrated HCI micropatterning of a surface using a physical mask, suggesting the application of this system in lithography.

Continuous highly charged ion beams from the National Institute of Standards and Technology electron-beam ion trap

We describe our newly modified beam line and present its performance in conjunction with the National Institute of Standards and Technology electron-beam ion trap. We find that, contrary to previously reported results from similar ion sources, the highest intensity time-averaged ion fluxes are achieved by letting the ions boil out of the trap in a continuous stream rather than periodically dumping the trap to produce a pulsed beam. We produced continuous beams of 3.0(6)×106 Xe44+ ions per second and lower flux beams of charge states up to Xe49+. Also, in pulsed mode, we created beams with very high peak flux, over 1010 Xe44+ ions per second.

A beam line for highly charged ions

The design and operation of a beam line for transporting and charge‐to‐mass selecting highly charged ions extracted from the National Institute of Standards and Technology electron beam ion trap (EBIT) are described. This beam line greatly extends the range of experiments possible at this facility. Using the transport system, pure beams of low‐energy, highly charged ions up to Xe44+ have been produced with substantially higher fluxes than previously reported from an EBIT source. Design choices and computer modeling for the various components of the beam line are explained in detail.

Astrophysics and spectroscopy with microcalorimeters on an electron beam ion trap

Electron beam ion traps combined with X-ray microcalorimeters provide an indispensable tool for laboratory astrophysics supporting recent and future X-ray missions. The program at the National Institute of Standards and Technology uses spectroscopic methods to study highly ionized plasmas and atomic physics related to astrophysics problems.

Cascade transition X-rays from electron capture into highly charged ions in collisions with neutral gas targets

Abstract X-rays originating from a series of the cascades after electron capture into highly excited Rydberg states have been observed from low energy, highly charged Kr q + ions ( q =27–36) colliding with neutral Ar atoms. The intensity ratio between L ( n =3→2) X-rays and the sum of M X-rays ( n =4→3, n =5→3, n =6→3, etc.) is drastically changed from Kr 27+ to Kr 28+ and constant for higher ion charge states ( q =29–36). This feature can be understood to be due to the metastable states formed during cascades after electron capture into Kr 27+ ions. This is also supported by time-dependent population calculations.

X-ray, visible and electron spectroscopy with the NIST EBIT

An overview is given of recent activities at the NIST electron beam ion trap (EBIT) facility. The machine has been operational for almost three years. Important characteristics and demonstrated capabilities of our EBIT are presented. Selected results include experiments with trapped highly charged ions (X-ray and visible spectroscopy), and with extracted ions (ion-surface collision studies).

Highly Charged Ion Bombardment of Silicon Surfaces

Visible photoluminescence from Si(100) surfaces irradiated by highly charged ions has recently been reported [1]. In an attempt to reproduce these results, highly charged ion‐irradiated silicon samples were prepared at the Electron Beam Ion Trap at the National Institute of Standards and Technology. Two highly sensitive fluorescence detection schemes were employed, both using ultraviolet light from an argon‐ion laser for excitation. In the first detection scheme, the Xe44+‐Si(100) samples were excited by the ultraviolet light while a spectrograph equipped with a liquid nitrogen‐cooled charge‐coupled device camera detected the fluorescence. The second detection scheme was a high throughput laser‐scanning confocal microscope equipped with a photon‐counting photomultiplier tube. We characterized the sensitivities in each detection scheme, allowing the assessment of the photoluminescence efficiency of Xe44+‐Si(100). No photoluminescence was detected in either setup.

X-ray Emission for 3-137 keV Ar17+ Impacting SiO2

Abstract We report X-ray spectra from Ar17+ impacting a SiO2 surface at 30° from normal incidence, for projectile energies ranging from 3 to 137 keV. At the highest energy we see only X-rays from the filling of the argon K shell. As the projectile energy is reduced, these argon X-rays are gradually reduced to zero while a silicon Kα peak appears. We interpret these data to be the result of the onset of a direct transfer of a silicon K-shell electron to the K-shell vacancy in the argon projectile. We suggest that this transfer occurs through an argon-silicon Auger process which takes place during a close collision in the solid. The velocity dependence of this process is not yet fully understood.