Vacuum Electrospray Research Articles

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches.

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e.g. cut-outs of a textile. A bi-functional cross-shaped monomer was designed, synthesized and was in-detail characterized by means of 1H-NMR and chiro-optical spectroscopy. In addition, x-ray structure crystallography was used to assess the absolute configuration. The monomer was used in an in-solution oligomerization to assemble the molecular patches via imine condensation, which revealed the formation of predominately dimeric patches. The imine-oligomer mixtures were further analyzed by reduction and cleaved to investigate the conditions required post mono-layer assembly. All reaction stages were followed by FT-IR and 1H-NMR analysis. Finally, we address the adsorption of the cross-shaped monomer onto a Au(111) surface, via high vacuum electrospray deposition. The subsequent annealing of the interface induced the on-surface imine condensation reaction, leading to unidimensional oligomers co-adsorbed with clusters of cyclic-dimers. Nc-AFM analysis revealed the tridimensional molecular structures, and together with electrospray deposition technique showed to be a promising pathway to investigate potential monomer candidates.

Amorphous Poly(3-hexylthiophene) (P3HT) Thin Films by Vacuum Electrospray Deposition

Amorphous Poly(3-hexylthiophene) (P3HT) Thin Films by Vacuum Electrospray Deposition

Molecular-Scale Imaging Enables Direct Visualization of Molecular Defects and Chain Structure of Conjugated Polymers.

Conjugated polymers have become materials of choice for applications ranging from flexible optoelectronics to neuromorphic computing, but their polydispersity and tendency to aggregate pose severe challenges to their precise characterization. Here, the combination of vacuum electrospray deposition (ESD) with scanning tunneling microscopy (STM) is used to acquire, within the same experiment, assembly patterns, full mass distributions, exact sequencing, and quantification of polymerization defects. In a first step, the ESD-STM results are successfully benchmarked against NMR for low molecular mass polymers, where this technique is still applicable. Then, it is shown that ESD-STM is capable of reaching beyond its limits by characterizing, with the same accuracy, samples that are inaccessible to NMR. Finally, a recalibration procedure is proposed for size exclusion chromatography (SEC) mass distributions, using ESD-STM results as a reference. The distinctiveness of the molecular-scale information obtained by ESD-STM highlights its role as a crucial technique for the characterization of conjugated polymers.

Mass-selected ion beam generation using two rotating electric-field mass separation technique

This paper describes the origin, principles, practical applications, and future perspectives of mass-selected ion beams generated using two rotating electric-field mass (REF-MS) filters. Our team has been investigating the underlying principles of REF-MS separation and assessing the feasibility of developing suitable systems to realize mass separation and ion beam convergence using rotating electric fields as well as the practicability of this method. This paper focuses on the mechanism underlying the observed cycloid trajectories followed by REF-MS-selected ions. A focused ion beam column with Ga and AuGe liquid metal ion sources (LMISs) was connected to REF-MS optics to assess the mass-selection performance of the filter. The mass-separation ability of this system was demonstrated by the ion projection images of Ga-LMIS (69Ga+ and 71Ga+) and AuGe-LMIS (97Au2+, Au2Ge+, and Au2Ge2+). The column was then replaced with a vacuum electrospray ionization (ESI) source. The size-selected water-cluster ion beams [(H2O)nH]+ were separated based on cluster size, and a microscale crater was created. Co-containing molecular ion beams were revealed using different concentrations of ESI sources, and a mass-separated [Co(DEGBE)4]+ ion beam was constructed.

Sputtering produced by vacuum electrospray droplet ions with different sizes and charges

We have been developing a vacuum electrospray droplet ion (V-EDI) beam technique that uses water droplet ions generated by electrospraying aqueous solutions under vacuum. The V-EDI beam is one of the massive cluster ion beams that have the potential to significantly improve the performance of surface analysis. In order to utilize the V-EDI beams effectively as ionization and sputtering probes in secondary ion mass spectrometry and x-ray photoelectron spectroscopy, it is necessary to optimize the sizes and charge states of the droplet ions included in the V-EDI beams. However, the droplet ions themselves in the V-EDI beams are not well understood. In this study, the V-EDI beams generated from the capillaries with different inner diameters were irradiated on polystyrene film samples under constant electrospray and accelerating voltage conditions, and then their surfaces were analyzed with atomic force microscopy and spectroscopic ellipsometer. The impact trace distributions produced by the droplet ions and the sputtered volumes produced by each droplet ion impact were investigated.

Effects of the temperature of a protic ionic liquid on ion beam production by vacuum electrospray

Ionic liquid ion sources generate ion beams from ionic liquids by vacuum electrospray. Electrospray characteristics generally depend on the physical properties of the liquids used. A key factor affecting physical properties is temperature. In this study, ion beam production was investigated using a protic ionic liquid, propylammonium nitrate (PAN), at temperatures ranging from 22 to 60 °C. An ion beam was produced using a needle emitter equipped with a cartridge heater, thermocouple, and sharpened glass rod externally wetted with PAN. The experimental results showed that the heating of the emitter increased the ion beam current. This will be due to an increase in the conductivity and a decrease in the viscosity of PAN with increasing temperature. Furthermore, the abundance of larger cluster ions increased, whereas that of smaller cluster ions decreased with increasing temperature. It turned out, however, that higher heating of the emitter stopped ion beam production. Two hypotheses for the beam stop are proposed and discussed.

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) applied to the analysis of explosives

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) was applied to the analyses of explosives including HMTD (hexamethylenetriperoxidediamine), RDX (cyclotrimethylene trinitroamine), HMX (cyclotetramethylenetetranitroamine), PETN (pentaerythritol tetranitrate), and TNT (2,4,6-trinitrotoluene) in positive- and negative-mode of operation. A mixture of H2O/CH3OH (9/1) containing 0.01 M trifluoroacetic acid (TFA) was used as a solvent for vacuum electrospray. For all explosives described above, intact molecules were detected by EDI/SIMS. HMX which is the least volatile compound tested could be readily detected in both positive- and negative-mode of operations. Nitramines of RDX and HMX were detected as proton- and Na+-bound cluster ions with H2O and CH3OH ligands. TNT and the nitrate ester PETN were not detected in positive mode. In negative mode, RDX, HMX and PETN were detected as adduct ions with NO2−, NO3−, and CF3COO−. TNT gave TNT−• and fragment ions similar to those detected in atmospheric-pressure chemical ionization. The characteristic difference in reactivity between the nitramine compounds (RDX and HMX) and the nitrate ester compound (PETN) is likely to be due to the more diffused negative charge in nitrate ester groups than in nitro groups.

Development of Mass-controlled Ion Beam through a Vacuum Electrospray Method

Development of Mass-controlled Ion Beam through a Vacuum Electrospray Method

High-Throughput Screening Using a Synchronized Pulsed Self-aspiration Vacuum Electrospray Ionization Miniature Mass Spectrometer.

With the advantages of rapid analysis, high sensitivity, and multicomponent identification, mass spectrometry (MS) is recognized as an appealing choice for high-throughput screening (HTS) analysis. Aiming at the small size, simple operation, and adequate performance, the development of miniature mass spectrometers has made great progress over the last 2 decades. Besides the essential analytical performance, simple operation and HTS capability are two other crucial features desired in miniature MS instruments. In this paper, an induced self-aspiration vacuum electrospray ionization source (ISA-VESI) was developed and coupled to a miniature ion trap mass spectrometer. A special timing sequence was designed to synchronize all the operation steps in each measurement, including dual-pulse sample injection, multipulse gas injection, MS analysis, and the movement of the homemade HTS platform used as the sampler. Then, the automatic high-throughput analysis of multiple samples can be accomplished with close coordination among the sample delivery, the sample introduction and ionization, and the ion trap operation. The measurement time of each ISA-VESI-MS analysis was about 7 s, with a sample consumption of less than 100 nL.

Depositing Molecular Graphene Nanoribbons on Ag(111) by Electrospray Controlled Ion Beam Deposition: Self-Assembly and On-Surface Transformations.

The chemical processing of low‐dimensional carbon nanostructures is crucial for their integration in future devices. Here we apply a new methodology in atomically precise engineering by combining multistep solution synthesis of N‐doped molecular graphene nanoribbons (GNRs) with mass‐selected ultra‐high vacuum electrospray controlled ion beam deposition on surfaces and real‐space visualisation by scanning tunnelling microscopy. We demonstrate how this method yields solely a controllable amount of single, otherwise unsublimable, GNRs of 2.9 nm length on a planar Ag(111) surface. This methodology allows for further processing by employing on‐surface synthesis protocols and exploiting the reactivity of the substrate. Following multiple chemical transformations, the GNRs provide reactive building blocks to form extended, metal–organic coordination polymers.

Depositing Molecular Graphene Nanoribbons on Ag(111) by Electrospray Controlled Ion Beam Deposition: Self‐Assembly and On‐Surface Transformations

AbstractThe chemical processing of low‐dimensional carbon nanostructures is crucial for their integration in future devices. Here we apply a new methodology in atomically precise engineering by combining multistep solution synthesis of N‐doped molecular graphene nanoribbons (GNRs) with mass‐selected ultra‐high vacuum electrospray controlled ion beam deposition on surfaces and real‐space visualisation by scanning tunnelling microscopy. We demonstrate how this method yields solely a controllable amount of single, otherwise unsublimable, GNRs of 2.9 nm length on a planar Ag(111) surface. This methodology allows for further processing by employing on‐surface synthesis protocols and exploiting the reactivity of the substrate. Following multiple chemical transformations, the GNRs provide reactive building blocks to form extended, metal–organic coordination polymers.

Fundamental Aspects of Droplet Ions Investigated by Vacuum Electrospray Droplet Ion Induced Sputtering

Fundamental Aspects of Droplet Ions Investigated by Vacuum Electrospray Droplet Ion Induced Sputtering

Current Status of a Vacuum Electrospray Droplet Ion Beam and towards TOF-SIMS Applications

真空下で水溶液をエレクトロスプレーすることによって発生させた真空エレクトロスプレー液滴イオン（V-EDI）ビームを表面分析装置におけるイオン化やエッチングに利用するための研究開発を行っている．V-EDIビームは有機分子を極めて高い効率でソフトにイオン化できるため，飛行時間型二次イオン質量分析（TOF-SIMS）に応用できれば，その分析性能は大幅に向上することが期待できる．しかしながら一般的なTOF-SIMS装置では一次イオンビームを短パルス化することが必須であるため，短パルス化できないV-EDIビームはこれまでTOF-SIMS装置において実用的に利用できていない．本稿ではTOF-SIMS応用に向けたV-EDIビームの現状と課題およびビームの短パルス化に向けた試みについて紹介する．

STUDY OF THE FORMATION OF TAYLOR CONE IN HIGH-VACUUM ELECTROSPRAY IONIZATION PROCESS

In this work, the formation of the Taylor cone in high-vacuum electrospray ionization using a static magnetic mass-spectrometer was studied. A simple vacuum electrospray ionization source was designed and combined with a mass-spectrometer. The effect of the solution composition, flow rate, high voltage and temperature on the formation of charged liquid droplets was determined at highvacuum conditions.

Development of a Vacuum Electrospray Droplet Ion Gun for Secondary Ion Mass Spectrometry.

Atmospheric pressure electrospray had been used in previous studies to generate massive water droplet ion beams, and the beams successfully achieved efficient desorption/ionization of biomolecules, low damage etching of polymers and nonselective etching of metal oxides. However, this droplet ion beam was not practical as a primary ion beam for surface analysis instruments because it required differential pumping and lacked adequate beam current and density. To improve the beam performance, we have proposed to use vacuum electrospray of aqueous solutions as a beam source, and developed a technique for producing a stable electrospray of aqueous solution in vacuum. We also designed a prototype of a vacuum electrospray droplet ion gun, and measured the beam properties. Finally, the applicability of this ion gun in secondary ion mass spectrometry is discussed.

水溶液の真空エレクトロスプレーにより発生する帯電液滴の質量および価数

水溶液の真空エレクトロスプレーにより発生する帯電液滴の質量および価数

Developing a Vacuum Electrospray Source To Implement Efficient Atmospheric Sampling for Miniature Ion Trap Mass Spectrometer.

The performance of a miniature mass spectrometer in atmospheric analysis is closely related to the design of its sampling system. In this study, a simplified vacuum electrospray ionization (VESI) source was developed based on a combination of several techniques, including the discontinuous atmospheric pressure interface, direct capillary sampling, and pneumatic-assisted electrospray. Pulsed air was used as a vital factor to facilitate the operation of electrospray ionization in the vacuum chamber. This VESI device can be used as an efficient atmospheric sampling interface when coupled with a miniature rectilinear ion trap (RIT) mass spectrometer. The developed VESI-RIT instrument enables regular ESI analysis of liquid, and its qualitative and quantitative capabilities have been characterized by using various solution samples. A limit of detection of 8 ppb could be attained for arginine in a methanol solution. In addition, extractive electrospray ionization of organic compounds can be implemented by using the same VESI device, as long as the gas analytes are injected with the pulsed auxiliary air. This methodology can extend the use of the proposed VESI technique to rapid and online analysis of gaseous and volatile samples.

Time-of-flight secondary ion mass spectrometry using a new primary ion beam generated by vacuum electrospray of a protic ionic liquid, propylammonium nitrate.

Protic ionic liquids have the potential to be useful materials for primary ion beams in terms of protonation, since they have active protons. Selecting protic ionic liquids suitable for primary ion beams is of great importance to increase molecular secondary ion yields. Propylammonium nitrate ([C3 H7 NH3 ][NO3 ]) seems promising in view of its proton affinity. It is likely that [C3 H7 NH3 ]+ cations can act as proton donors, and [NO3 ]- anions can work as proton acceptors. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments have been performed to verify the usefulness of [C3 H7 NH3 ][NO3 ]. A primary propylammonium nitrate cluster ion beam was generated by vacuum electrospray, and then used to analyze amino acids (arginine, glutamic acid, aspartic acid), angiotensin II and polyethylene glycol. Positive and negative secondary ion mass spectra were obtained to study both protonation and deprotonation. The propylammonium nitrate cluster ion beam successfully generated protonated molecules [M+H]+ of all the analytes in positive ion mode. The primary ion beam also generated deprotonated molecules [M-H]- of glutamic acid, aspartic acid and angiotensin II in negative ion mode. Additionally, adduct ions related to [C3 H7 NH3 ][NO3 ] were detected in the case of arginine and polyethylene glycol. The TOF-SIMS experiments confirmed that the propylammonium nitrate cluster ion beam was useful in generating molecular secondary ions, demonstrating that it is well suited for a primary ion beam in TOF-SIMS.

Electronic Structures of Nucleosides as Promising Functional Materials for Electronic Devices

The energy level alignments of nucleosides fabricated between conventional Al and indium tin oxide (ITO) electrodes by means of a vacuum electrospray deposition technique were investigated using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. The electronic structures of four nucleosides—deoxyguanosine, deoxyadenosine, deoxycytidine, and deoxythymidine—were determined, and their interactions with Al and ITO were analyzed. When in contact with ITO, each nucleoside showed an interface dipole that reduced the work function. On the other hand, when Al was deposited on the nucleoside layers, strong chemical interactions were observed due to electron transfer from Al to the nucleosides. Compared to their nucleobase counterparts, nucleosides commonly had lower ionization energies (IEs) and electron affinities (EAs). The origin of this difference in electronic structure was analyzed with density functional theory calculations. The sugar moieties in the nucleosides were found to induce electron-donating effects on the base moiety and led to reductions in IE and EA.

On the suitability of high vacuum electrospray deposition for the fabrication of molecular electronic devices

We present a series of three studies investigating the potential application of high vacuum electrospray deposition to construct molecular electronic devices. Through the use of time of flight secondary ion mass spectrometry we explore the use of this novel deposition technique to fabricating multilayer structures using materials that are compatible with the same solvents and films containing a mixture of molecules from orthogonal solvents. Using X-ray photoelectron spectroscopy we study the deposition of a polymer blend using electrospray and find evidence of preferential deposition of one of the components.