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High‐resolution time‐of‐flight mass spectrometer

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Abstract

To perform experiments with clusters, a time‐of‐flight mass spectrometer with a mass resolution of 35 000 (m/Δm, 50% definition) has been constructed. The main design features of the instrument are presented.

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... e.g. [198][199][200][201] ). The mass-selected ions are detected on e.g. a microchannel plate detector, amplified and analyzed by an oscilloscope and specialized software. ...
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Combined IR and UV laser spectroscopic techniques in molecular beams merged with theoretical approaches have proven to be an ideal tool to elucidate intrinsic structural properties on a molecular level. It offers the possibility to analyze structural changes, in a controlled molecular environment, when successively adding aggregation partners. By this, it further makes these techniques a valuable starting point for a bottom-up approach in understanding the forces shaping larger molecular systems. This bottom-up approach was successfully applied to neutral amino acids starting around the 1990s. Ever since, experimental and theoretical methods developed further, and investigations could be extended to larger peptide systems. Against this background, the review gives an introduction to secondary structures and experimental methods as well as a summary on theoretical approaches. Vibrational frequencies being characteristic probes of molecular structure and interactions are especially addressed. Archetypal biologically relevant secondary structures investigated by molecular beam spectroscopy are described, and the influences of specific peptide residues on conformational preferences as well as the competition between secondary structures are discussed. Important influences like microsolvation or aggregation behavior are presented. Beyond the linear α-peptides, the main results of structural analysis on cyclic systems as well as on β- and γ-peptides are summarized. Overall, this contribution addresses current aspects of molecular beam spectroscopy on peptides and related species and provides molecular level insights into manifold issues of chemical and biochemical relevance.
... On the other hand, the large, specialized ToF MS systems employed for MPI applications may deliver up to 30 000 m/Δm resolution performance. 8 Note that an orthogonal acceleration ToF MS configuration, 9 which affords higher resolution, 10 is typically not directly compatible with the pulsed ionization scheme due to mass discrimination. ...
... The reflection type TOFMS has also been developed by several groups. [15][16][17][18] Compared to the Wiley-McLaren type spectrometer, this requires more fields and more grids with well controlled planarity, resulting in lower transmission efficiency of the spectrometer. In 1995, Nagesha et al. 19 had developed a TOFMS to study the absolute DEA cross section of different molecules. ...
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A new time of flight mass spectrometer (TOFMS) has been developed to study the absolute dissociative electron attachment (DEA) cross section using a relative flow technique of a wide variety of molecules in gas phase, ranging from simple diatomic to complex biomolecules. Unlike the Wiley-McLaren type TOFMS, here the total ion collection condition has been achieved without compromising the mass resolution by introducing a field free drift region after the lensing arrangement. The field free interaction region is provided for low energy electron molecule collision studies. The spectrometer can be used to study a wide range of masses (H− ion to few hundreds atomic mass unit). The mass resolution capability of the spectrometer has been checked experimentally by measuring the mass spectra of fragment anions arising from DEA to methanol. Overall performance of the spectrometer has been tested by measuring the absolute DEA cross section of the ground state SO2 molecule, and the results are satisfactory.
... This type of ion source was first proposed by O'Halloran [6]. However, really effective time-offlight mass spectrometers were built with such ion sources only later [5,[7][8][9][10][11][12]. In this article we present an orthogonal ion source originally designed for analysis of cometary gases and ions. ...
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... There are a variety of sources available including arc cluster ion source [42], laser vaporization cluster source [43,44], gas aggregation source [45,46], seeded supersonic nozzle source [47], ion sputtering source [48,49], and liquid metal ion source [50,51]. Based on these we developed low energy cluster beam deposition method. ...
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... In the recent past there have been a few reports on high-resolution reflectron time-of-flight mass spectrometers. Using a grid reflectron and a sophisticated orthogonal extraction source a mass resolution of 35 000 was achieved with a 3.5 m overall length instrument [2]. Using a grid free reflectron and a 4 m overall length instrument mass resolutions between 10 000 and 20 000 were obtained [3]. ...
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... This is especially important for the spectroscopy of reacted clusters like TinH;;, clusters (see below). Because of the need of extremely high anion intensities the mass resolution of the discussed setup is limited to rn/!:3.rn 400, although in principle with such types of mass spectrometers a resolution of > 35000 can be achieved [51]. ...
Chapter
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Chapter
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Chapter
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Chapter
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Chapter
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Chapter
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Article
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Chapter
Traditionally, structural analysis by mass spectrometry has been limited to small organic molecules that are volatile and thermally stable, since the initial step involves heating the sample in a vacuum. During the past several years, new ionization methods have been developed that can produce gas-phase molecular and fragment ions from nonvolatile samples; these are presented to the mass spectrometer as liquids (solutions) or solids. As a consequence of these developments, mass spectrometry has come to play an increasing role in the biological sciences.
Chapter
This chapter discusses that the purpose of the mass spectrometer is to separate ions according to their mass-to-charge ratio and the methods and technology involved have improved rapidly. It focuses on the practical aspects of those mass analyzers in current use and helps in selecting the device most suited. Without exception, mass analyzers must be immersed in a high-vacuum environment. The performance of all mass analyzers degrades with increasing pressure as ion-neutral collisions scatter ions and, in some cases, changes their identity through ion-molecule reaction. Resolution and ion transmission increase with decreasing collision frequency and the instruments with long ion path lengths are particularly sensitive to the vacuum environment. An important parameter, characterizing any mass analyzer, is the mass resolution that defines its ability to separate ions of different mass. The chapter also reviews that increased resolution is achieved only with a sacrifice in sensitivity. For applications in which the mass analyzer is used simply as a mass-sensitive detector, the resolution is reduced to maximize transmission within the confines of the experimental objectives. A parameter sometimes used to describe the resolution of magnetic sector instruments is the mass dispersion produced by the magnetic field that is directly proportional to the radius of the ion path through the magnet. Although the constant of proportionality is dependent on the geometry of the instrument, increased size translates into increased resolution, and most sector instruments are physically large.
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In this paper the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed. Recent results obtained for free clusters are summarized with special attention to new observed structures. As for the specific structures and properties of cluster-assembled materials, two main aspects are specially emphasized: the memory effect of the free cluster properties leading to the formation of new phases and the effect of the specific nanostructure of the cluster-assembled materials related to the random cluster stacking mechanism characteristic of the LECBD. These effects and the corresponding potential applications are illustrated using some selected examples: new diamond-like carbon films produced by fullerene depositions (memory effect) and grain effect on the magnetic properties of cluster-assembled transition metal films.
This paper describes a new method to achieve high-resolution mass spectra in a linear time-of-flight mass spectrometer. Both direct and matrix assisted laser desorption/ionization of large molecules are performed on this instrument. Using post-source pulse-focusing a mass resolution of 4600 (FWHM) has been achieved. This technique can correct high initial ion translational energies as well as long periods of ion formation. Therefore it is predestinated to laser desorption/ionization applications. Experimental results will be shown demonstrating the capability of this new instrument to produce high-resolution ion signals. In addition, a simple way to calibrate masses is discussed.
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Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22000 atoms. For small clusters (Nan, n⩽ 1500) the anomalies appear to be due to the filling of electronic shells. The mass spectra of larger clusters are well explained by the completion of icosahedral or cuboctahedral shells of atoms.
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The current paper presents a state-of-the-art review in the field of interaction of atomic and molecular clusters with solids. We do not attempt to overview the entire broad field, but rather concentrate on the impact phenomena: how the physics of the cluster–surface interaction depends on the kinetic energy and what effects are induced under different energetic regimes. The review starts with an introduction to the field and a short history of cluster beam development. Then fundamental physical aspects of cluster formation and the most common methods for the production of cluster beams are overviewed. For cluster–surface interactions, one of the important scenarios is the low-energy regime where the kinetic energy per atom of the accelerated cluster stays well below the binding (cohesive) energy of the cluster constituents. This case is often called soft landing: the deposition typically does not induce cluster fragmentation, i.e. the clusters tend to preserve their composition but not necessarily their shape. Specific characteristic phenomena for soft landing of clusters are summarized. They pave the way for the use of cluster beams in the formation of nanoparticle arrays with required properties for utilization in optics and electronics, as magnetic media and catalysts, in nanobiology and nanomedicine. We pay considerable attention to phenomena occurring on impact of clusters with increased kinetic energies. In particular, we discuss the physics of the intermediate regime between deposition and implantation, i.e. slight cluster embedding into the surface—otherwise known as cluster pinning. At higher impact energies, cluster structure is lost and the impact results in local damage of the surface and often in crater and hillock formation. We consider both experimental data and theoretical simulations and discuss mechanisms of these phenomena. Some analogies to the impact of macroscopic objects, e.g. meteorites are shown. This part of the paper also overviews the research on surface sputtering under high-fluence cluster beam treatment and the existing models explaining how this phenomenon can be used for efficient smoothing of surfaces on the macroscopic scale. Several examples of successful applications of the cluster beam technique for polishing of surfaces are given. We also discuss how the physical sputtering can be combined with reactive accelerated cluster erosion. The latter can be an efficient tool for dry etching of surfaces on the nanoscale. Specificity of cluster (multicomponent projectile) stopping in matter and formation of radiation damage under keV-to-MeV energy implantations are analyzed. The part about fundamental aspects of cluster implantation is followed by several examples of practical applications of keV-energy cluster ion beams. This includes ultra-shallow doping of semiconductors and formation of ultrathin insulating layers. A few examples of MeV-energy cluster implantation, leading to the formation of nanosize hillocks or pillars on the surface as well as to local phase transitions (for instance, graphite-to-diamond) are also discussed. The review is finalized by an outlook on the future development of cluster beam research.
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A resonance ionization time-of-flight mass spectrometer is presented and mass spectra are shown which demonstrate its analytical capability, i.e. the possibility of soft and hard ionization, the wavelength selectivity and the mass resolution of 6500 (50% valley) at mass 96, which is expected to increase much more at higher masses.
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UV laser-induced surface ionization with prism internal reflection is demonstrated to be a useful ion source for the Time-of-Flight mass spectrometer (TOF-MS). Spraying aniline (93 amu) on the prism surface and using 2 ns UV laser pulses, mass resolutions of 3,900 and 11,000 have been achieved in a linear TOF-MS and in a reflectron TOF-MS, respectively. Theoretical calculations indicate that mass resolution of over one million is possible, if a picosecond laser and appropriate electronics are employed.
An electrostatic mirror has been built to achieve time focusing and high mass resolution with a new 252Cf time-of-flight mass spectrometer. The first results show that M/ΔM50% values are around 2 500 for organic molecules. The apparatus is described and results are presented. Future applications for metastable ion studies are briefly discussed.
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Details of the novel method of laser desorption with a low powered IR-laser and resonance-enhanced multiphoton ionization (REMPI) combined with a high-resolution Reflectron-Time-of-Flight (RETOF) mass spectrometer are explained. Different features of the method are discussed. Some results of mass spectrometric investigations of biomolecules are shown.
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It is shown that time-of-flight mass analyzers are capable of reaching high mass resolving powers as compared to sector field instruments. By combining a new electron-impact ion source with an optimized grid-free ion mirror, mass resolving powers m/Δm of about 20000 are reached.
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In many secondary ion mass spectrometry (SIMS) investigations, the total number of generated secondary ions is limited by the amount of sample material available. This is the case in surface reaction studies as well as in organic and inorganic trace analysis or imaging SIMS. In such cases a time‐of‐flight mass spectrometer has some considerable advantages: quasisimultaneous detection of all masses, unlimited mass range, and very high transmission. We have developed a high‐resolution reflectron based time‐of‐flight secondary ion mass spectrometer with a new electrodynamic mass separation and beam chopping technique based on a pulsed 90° deflection of the primary ion beam. A primary ion pulse width of less than 1.5 ns has been obtained. Second‐order energy focusing in the flight path of the secondary ions is achieved by a two‐stage reflectron. A mass resolution m/Δm=13 000 and a dynamic range of five orders of magnitude have been obtained with this instrument.