AVS2014 Session HI+2D+AS+BI+MC-ThM: Fundamental Aspects and Imaging with the Ion Microscope
Thursday, November 13, 2014 8:00 AM in Room 316
HI+2D+AS+BI+MC-ThM-1 He+ and Ne+ Ion Beam Microscopy and Microanalysis
David C. Joy (University of Tennessee, Oak Ridge National Laboratory)
After one hundred years of use the electron microscope is now being overtaken by ion beam systems because of their many advantages. A wide variety of different ions are available, each of which has its own particular strengths, but the two most commonly used at present are Helium (He+) and Neon (Ne+). Changing from one to the other takes only a couple of minutes to complete. for operation at beam energies between 20 and 50kV both He+ and Ne+ generate ‘ion induced secondary electrons’ (iSE) which yield images which are comparable with those from a conventional SEM but offer image resolutions of 0.4nm or less even on bulk samples, a much greater depth of field, and an enhanced signal to noise ratio. At typical imaging currents between 10-12 to 10-14Amps damage to most samples is very limited for He+ although more severe for Ne+ but at higher beam currents both He+ and Ne+ can pattern, deposit, or remove, a wide range of materials. In such applications He+ provides the best resolution, but Ne+ is much faster.
The production of X-rays depends on the speed of the incident particle, not on its energy. At typical operating energies the He+ or Ne+ ions are traveling too slowly to generate X-rays so another approach is required for chemical microanalysis. The most promising option is “Time of Flight-Secondary Ion Mass Spectrometry” (TOF-SIMS). Here the incoming ion “splashes” material from the top few layers of the specimen surface. These fragments are then characterized by determining their mass to charge ratios. The chemical data this generates is much more detailed than the bare list of elements that is produced by X-ray microanalysis.
HI+2D+AS+BI+MC-ThM-3 Gas Field Ion Sources
Jason Pitters, Radovan Urban (National Institute for Nanotechnology, Canada); Robert Wolkow (University of Alberta and The National Institute for Nanotechnology, Canada)
Single atom tips (SATs) prepared by the spatially controlled field assisted etching method are proving to have utility as ion sources, electron sources and in scan probe applications.
As Gas Field Ion Sources (GFISs), there is potential for operation in scanning ion microscopes (SIMs) and our efforts to prepare and characterize SAT ion emission will be discussed. It will be shown that etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom. SATs can be prepared reproducibly with emission along a fixed direction for all tip rebuilds. It will also be shown that the emission properties of the SAT can be altered by shaping of the tip shank during the etching procedure. In this manner, the operating voltage can be controlled and a lensing effect of the tip base is demonstrated. During formation, the tip shape can be evaluated by using both helium and neon imaging gases. The stability of helium and neon ion beams generated by SATs will also be demonstrated and compared to other tip orientations. The remarkable robustness of these tips to atmosphere exposure will also be shown and the ability to prepare SATs from material other than tungsten will be demonstrated.
SATs also have utility in electron emission. By shaping the tip appropriately, electron emission characteristics can also be tailored and the coherence properties of an SAT will be presented as deduced from holographic measurements in a low-energy electron point source microscope. Initial utility in scan probe experiments including atomic force microscopy and scanning tunneling microscopy will also be discussed.
HI+2D+AS+BI+MC-ThM-5 Ion Beam Profiles Generated by W(111) Single Atom Tips
Radovan Urban, Robert Wolkow (University of Alberta and The National Institute for Nanotechnology, Canada); Jason Pitters (National Institute for Nanotechnology, Canada)
Single atom tips (SATs) gained significant attention over the past decade because they serve as high brightness, field emission electron sources and gas field ion sources (GFISs). Small virtual source size makes these attractive candidates for advanced scanning imaging applications such as SEM, TEM, and scanning ion microscopy (SIM) as well as for non-staining ion beam writing applications.
The ion beam diameter σ, together with total ion current I generated by a single surface atom of W(111) nanotip, are crucial parameters which determine angular current density and brightness of gas field ion sources. It is, therefore, essential to understand underlying mechanisms that govern beam width. Furthermore, mapping both σ and I to a large parameter space of tip temperature, imaging gas pressure, and extraction voltage is necessary to optimize gas field ion source operation. In this contributions we will explore both σ and I as a function of temperature and extraction voltage at different imaging gas pressures using a field ion microscope (FIM) to monitor beam shape and total current. The qualitative model of our results will be also discussed. Finding “the best imaging voltage” for a SAT will be briefly discussed.
HI+2D+AS+BI+MC-ThM-6 Defect Observation by using Scanning Helium Ion Microscopy
Hongxuan Guo, Ling Zhang, Daisuke Fujita (National Institute for Materials Science (NIMS), Japan)
Scanning helium ion microscopy (HIM) is an innovative method to characterize surface of various materials. With a secondary electron detector (SED) and a micro plate detector (CPD), Orion Plus system can obtain surface information including morphology , composition, and crystal orientation. [1, 2] Improve the abilities of characterization of materials with HIM will benefit the develop of new materials, such as structure materials including metals, ceramics and others.
In this presentation, we will show the investigation of the crystal structure of metal with HIM. We prepared an sample stage with a reflector that can be used to obtain the transmission helium ions intensities in the samples. With this sample stage, we observed the Ni-Co base super alloy and aerogel composed with hollow nanosphere. The Rutherford backscattered image (RBI) of metal surface show different orientation of poly crystal. The nano-twins and other defects in Ni-Co base superalloy were investigated by HIM in scanning and transmission mode. The nano-twins also be observed by other techniques, such as transmission electron microscopy and electron backscatter diffraction. The scattering of helium ions with different energy was analyzed. This work provide some new methods to improve the research on defects and structure of crystal.
. H. X. Guo, D. Fujita, Scanning helium ion microscopy, Characterization of Materials, 2rd Edition(Wiley, New York, 2012)
. H. X. Guo. J. H. Gao, M. S. Xu, D. Fujita, Applied Physics Letters, 104, 031607 , 2014
|10:00 AM||BREAK - Complimentary Coffee in Exhibit Hall|
HI+2D+AS+BI+MC-ThM-10 Helium Ion Microscopy (HIM) for the Imaging of Biological Samples at Sub-nanometer Resolution
James Fitzpatrick (Salk Institute for Biological Studies)
Scanning Electron Microscopy (SEM) has long been the standard in imaging the sub-micrometer surface ultrastructure of both hard and soft materials. In the case of biological samples, it has provided great insights into their physical architecture. However, three of the fundamental challenges in the SEM imaging of soft materials are that of limited imaging resolution at high magnification, charging caused by the insulating properties of most biological samples and the loss of subtle surface features by heavy metal coating. These challenges have recently been overcome with the development of the Helium Ion Microscope (HIM), which boasts advances in charge reduction, minimized sample damage, high surface contrast without the need for metal coating, increased depth of field, and 5 angstrom imaging resolution. We demonstrate the advantages of HIM for imaging biological surfaces as well as compare and contrast the effects of sample preparation techniques and their consequences on sub-nanometer ultrastructure.
HI+2D+AS+BI+MC-ThM-12 Helium Ion Microscopy of Biological Cells
Natalie Frese, André Beyer, Matthias Schürmann, Barbara Kaltschmidt, Christian Kaltschmidt, Armin Gölzhäuser (University of Bielefeld, Germany)
In this presentation HIM images of biological cells are presented. The presented study focuses on neuronal differentiated human inferior turbinate stem cells, mouse neurons and mouse fibroblasts. The cells were prepared by critical point drying or freeze drying and a flood gun was used to compensate charging, so no conductive coating was necessary.
Therewith, extremely small features at native cell surfaces were imaged with an estimated edge resolution of 1.5 nm. Due to the size of the structures and the preparation methods of the cells the observed features could be an indicator for lipid rafts. This hypothesis will be discussed.
HI+2D+AS+BI+MC-ThM-13 Helium Ion Microscopy Analysis of Ag Nanoparticle Implanted Biological Samples for MILDI-MS (Matrix Implanted Laser Desorption/Ionization) Imaging
Samir Shubeita (Rutgers University); Ludovic Muller (NIDA-IRP); HangDong Lee, Can Xu (Rutgers University); Damon Barbacci (Ionwerks Inc.); Katrin Baldwin (NIDA-IRP); J.Albert Schultz (Ionwerks Inc.); Leszek Wielunski, Torgny Gustafsson, LeonardC. Feldman (Rutgers University); AminaS. Woods (NIDA-IRP)
MILDI mass spectrometry is an emerging tool for detecting changes in brain tissue. An ~20 nm thick region of rat brain tissue implanted with 1013/cm2 Au(400)4+ nanoparticle (NP) ions at 40 keV, produces analytically useful signals of lipids, peptides and proteins using a pulsed nitrogen laser . When a dose of 1012/cm2 500 eV AgNP (approximately 6 nm diameter) is implanted as a matrix, only lipids are detected . To understand this it is essential to measure the spatial distribution of the nanoparticles. We have used Rutherford Backscattering and Helium Ion Microscopy imaging to determine the Ag NP distributions and areal densities in an implanted coronal rat brain section. We then correlate the ion beam analysis and imaging with individual lipid intensities from several hundred MILDI mass distributions. The results show a high degree of uniformity of the Ag atomic and particulate distribution on a sub-micron scale among different regions of the tissue. Helium Ion Microscopy provides verification of NP matrix uniformity, validating the use of MILDI for quantitative mass analysis.
This work is partially supported by NSF (DMR 1126468), NIH (R44DA030853-03) and IAMDN.
 A. Novikov et al, Analytical Chemistry 76 (2004) 7288.  S. N. Jackson et al, Analyt. and Bioanal. Chem. (e-pubed Dec 2013).