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Polyvinyl polymers bearing pendant hole transport functionalities have been extensively explored for solution-processed hole transport layer (HTL) technologies, yet there are only rare examples of high anisotropic packing of the HT moieties of these polymers into substrate-parallel orientations within HTL films. For small molecules, substrate-parallel alignment of HT moieties is a well-established approach to improve overall device performance. To address the longstanding challenge of extension from vapor-deposited small molecules to solution-processable polymer systems, a fundamental chemistry tactic is reported here, involving the positioning of HT side chains within macromolecular frameworks by the construction of HT polymers having bottlebrush topologies. Applying state-of-the-art polymer synthetic techniques, various functional subunits, including triphenylamine (TPA) for hole transport and adhesion to the substrate, and perfluoro alkyl-substituted benzyloxy styrene for migration to the air interface, were organized with exquisite control over the composition and placement throughout the bottlebrush topology. Upon assembling the HT bottlebrush (HTB) polymers into monolayered HTL films on various substrates through spin-casting and thermal annealing, the backbones of HTBs were vertically aligned while the grafts with pendant TPAs were extended parallel to the substrate. The overall design realized high TPA π-stacking along the out-of-plane direction of the substrate in the HTLs, which doubled the efficiency of organic light-emitting diodes compared with linear poly(vinyl triphenylamine)s.

Nanoscale molecular characterization plays a crucial role in enhancing our insights into fundamental and materials processes occurring at the nanoscale. However, for many traditional techniques, measurements on different ensembles are mixed and the analytical result reflects the average surface composition or arrangement. Advances in nanometrologies that allow for measurements to be differentiated based on the chemical environment examined are critical for accurate analysis. Here, we present a variant of secondary ion mass spectrometry, SIMS, termed nanoprojectile SIMS, NP-SIMS, capable of nanoscale molecular analysis. The technique examines the sample with a suite, 10

Extracellular vesicles (EVs) are lipid bilayer particles secreted from various cells. EVs carry molecular information of parent cells and hold considerable promise for early disease diagnostics. This paper describes a general strategy for multiplexed immunosensing of EV surface proteins, focusing on surface markers CD63, CD81, nephrin, and podocin to prove the concept. This sensing strategy entailed functionalizing gold nanoparticles (AuNPs) with two types of antibodies and then tagging with metal ions, either Pb2+ or Cu2+. The metal ions served as redox reporters, generating unique redox peaks at -0.23 and 0.28 V (vs Ag/AgCl) during electrochemical oxidation of Pb2+ and Cu2+, respectively. Capture of EVs on the working electrode, followed by labeling with immunoprobes and square wave voltammetry, produced redox currents proportional to concentrations of EVs and levels of expression of EV surface markers. Importantly, metal-ion tagging of immunoprobes enabled detection of two EV surface markers simultaneously from the same electrode. We demonstrated dual detection of either CD63/CD81 or podocin/nephrin surface markers from urinary EVs. The NP-enabled immunoassay had a sensitivity of 2.46 × 105 particles/mL (or 40.3 pg/mL) for CD63- and 5.80 × 105 particles/mL (or 47.7 pg/mL) for CD81-expressing EVs and a linear range of four orders of magnitude. The limit of detection for podocin and nephrin was 3.1 and 3.8 pg/mL, respectively. In the future, the capacity for multiplexing may be increased by extending the repertoire of metal ions used for redox tagging of AuNPs.

We describe a technique based on secondary ion mass spectrometry with nanoprojectiles (NP-SIMS) for determining the protein content of extracellular vesicles, EVs, via tagged antibodies. The technique uses individual gold nanoprojectiles (e.g., Au4004+ and Au28008+), separated in time and space, to bombard a surface. For each projectile impact (10-20 nm in diameter), the co-emitted molecules are mass analyzed and recorded as an individual mass spectrum. Examining these individual mass spectra for co-localized species allows for nanoscale mass spectrometry to be performed. The high lateral resolution of this technique is well suited for analyzing nano-objects. SIMS is generally limited to analyzing small molecules (below ∼1500 Da); therefore, we evaluated three molecules (eosin, erythrosine, and BHHTEGST) as prospective mass spectrometry tags. We tested these on a model surface comprising a mixture of all three tags conjugated to antibodies and found that NP-SIMS could detect all three tags from a single projectile impact. Applying the method, we tagged two surface proteins common in urinary EVs, CD63 and CD81, with anti-CD63-erythrosine and anti-CD81-BHHTEGST. We found that NP-SIMS could determine the relative abundance of the two proteins and required only a few hundred or thousand EVs in the analysis region to detect the presence of the tagged antibodies.

One of the challenges of surface characterization at the nano-scale is that analytical tools which are capable of topological nano-scale analysis have limited capabilities for molecular characterization. Here we present a study on molecular characterization of positive tone photo-resist films with varying exposure dose. The technique is based on secondary ion mass spectrometry, SIMS, with gold nanoparticles (e.g. Au4+400). In the methodology a sequence of individual gold nanoparticles is used to stochastically bombard the photoresist films, where each impact results in the emission of ions from a region 10-20 nm in diameter. The technique has several unique features which enable molecular characterization at the nano-scale. Firstly, the use of individual massive clusters impacts which sample nano-volumes, and from these nano-volumes multiple molecular ions can be ejected simultaneously. Secondly, the acquisition of the mass spectra from each projectile impact allows co-ejected ions to be collected in the same mass spectrum. These two features allow for tests on the nano-scale homogeneity of molecules. This is of particular interest for photoresist films, where nano-scale inhomogeneity may result in poor quality films. In this study we examined bulk photoresist films with varying dose post development, in order to probe physical aggregation and chemical transformation on the partially exposed resist pattern side wall and surface. We found that the cation and anion of the photoacid generator were not removed equally during development, and we found that the quencher is not completely removed by the developer.

International audience; Andromede is a new instrument for mass spectrometry analysis of nanodomains and nano-objects present on a surface. The molecular sample information (mass and structure) is obtained from time-of-flight spectra of secondary ions emitted under the impact of nanoparticles (NPs), as A u n q + with n/q up to 200 accelerated by a 4 MV single stage electrostatic Pelletron® accelerator. Such projectiles, providing huge emission rates per impact, permit the topographic analysis of complex samples. The energy deposition of these massive gold NPs induces surprisingly large holes of about 100 nm diameter in very thin graphene foils and average sputtered volume per impact of about 106 nm3 in a thick polymer material. The use of such massive clusters associated with multianode detectors, allowing the simultaneous detection of several ions of a given mass, permits correlation studies between the emitted ions within a single impact, shedding additional light on the chemical composition and structure of the analysed sample as illustrated here for various samples from metallic surfaces to biologic molecules deposits.

We report on the ion emission from impacts of hypervelocity massive gold clusters for use in secondary ion mass spectrometry. Two massive gold clusters are considered, 520 keV Au4004+ and 1040 keV Au28008+. The emission of fragment ions and molecular ions is evaluated for a series of neat samples, glycine, phenylalanine, arginine, and gramicidin S. A 2 to 4-fold increase of molecular ion emission is observed from impacts of 1040 keV Au28008+ versus 520 keV Au4004+. Compared to impacts of 20 keV Ar2000+ and 20 keV (H2O)7000+ in static conditions, impacts of 1040 keV Au28008+ display a 6 to 9-fold increase in the number of detected molecular ions per projectile impact. To explain the increased emission of molecular species, we examine the size of the impact craters and calculate the ratio of molecular ions to fragment ions. The characterization of Au28008+ and the operating conditions of the gold liquid metal ion source are presented.

In this study, we report on the mechanical cleavage of conductive metal-based aluminum diboride (AlB2) flakes. The cleavage resulted in a highly single crystalline 2D material and had an atomically flat and smooth surface as shown by atomic force microscopy (AFM) and secondary ion mass spectrometry. Nanoindentation and AFM imaging of freshly cleaved specimens revealed sub-nm roughness and 30% improvement in the nanomechanical properties as compared to the as-grown AlB2 flakes. Once exposed to ambient air, the cleaved AlB2 flakes formed a superficial oxidation layer of less than 1 nm thickness within 5 min. Owing to the smooth surface, ultra-thin and stable oxide layer, and the excellent mechanical and electrical characteristics of AlB2, the cleaved flakes present an ideal 2D material for emerging applications in microfabrication such as the growth of epitaxial thin films. To prove the sub-nm surface characteristics of cleaved AlB2, a 10-nm thick TiO2 film was deposited on a freshly cleaved AlB2 using atomic layer deposition. Surface roughness and compositional consistency of this film were compared with a control sample deposited on Si. The TiO2 film on AlB2 showed a distinct thin interface layer with fewer defects than TiO2 on Si and superior flatness.

We investigate the formation of surface phases on nickel (Ni) during cathodic charging in 1 M H2SO4 solution. Using complementary characterization techniques, we show that these phases are aggregated into filamentary structures with a thickness of ∼150 nm and ∼30 % sample surface coverage. The phases are rich in Ni, O, H, and S, but free of C. Their surface potential is cathodic with respect to the surrounding Ni by ∼70 mV. We propose that these phases may be products of a reaction between the aqueous electrolyte and a metastable nickel surface hydride, assumed to form during cathodic charging. These findings stand to advance understanding of the catalytic activity of Ni cathodes, H uptake and embrittlement in Ni, and the onset of localized corrosion during cathodic charging.

This paper describes a label free technique for determining ligand loading on metal nanoparticles using a variant of secondary ion mass spectrometry. Au(400)(4+) clusters bombard DNA-functionalized anisotropic gold nanostars and isotropic nanospheres with similar surface areas to determine ligand density. For each projectile impact, co-localized molecules within the emission area of a single impact (diameter of 10–15 nm) were examined for each particle. Individual nanoparticle analysis allows for determination of the relationship between particle geometry and DNA loading. We found that branched particles exhibited increased ligand density versus nanospheres and determined that positive and neutral curvature could facilitate additional loading. This methodology can be applied to optimize loading for any ligand–core interaction independent of nanoparticle core, ligand, or attachment chemistry.

Here we describe a methodology for molecular analysis at the nano-scale and present its capabilities. The analysis method is based on secondary ion mass spectrometry, SIMS, with gold nanoparticles (e.g. Au4004+). The methodology presented here has unique features which enable molecular analysis at the nanoscale, namely the method of acquiring the mass spectrum and the nature of the impacting projectile. In the method a sequence of individual gold nanoparticles (Au4004+) are used to bombard the sample, each impact results in ion emission from an area 10-20 nm in diameter. For each of impact of Au4004+, the emitted ions are mass analyzed by time of flight mass spectrometry, detected and stored together in one mass spectrum prior to the arrival of the subsequent projectile. Each mass spectrum contains elementals, and molecules which were co-localized within 10-20 nm of one another. Examining the co-emitted ions allows to test the molecular homogeneity, and chemical composition at the nanoscale. We applied this method to a chemically amplified resist before and after exposure and development. After development the method was used to chemically characterize defect sites, which were not removed by the developing solution.

As the semiconductor industry continuously pursues smaller and more advanced device nodes, improving the lithographic performance of photoresists becomes more critical and challenging. The homogeneity of the photoresist formulation components within the thin film, such as the distribution of photoacid generator (PAG) molecules, are critical factors influencing resolving capability and the sidewall roughness after development. However, there is still lack of fundamental experimental approaches to probe the distribution of these components at the nanoscale throughout the photoresist film. Herein, we present the use of a new methodology, namely, massive cluster secondary ion mass spectrometry (MC-SIMS), to determine PAG homogeneity on a 10-15 nm scale within a photoresist film. In comparison to conventional SIMS, of which the detection spatial resolution is limited to large domains and the data is aggregated prior to analysis, MC-SIMS bombards the sample with a sequence of massive Au400 +4 nanoprojectiles, each separated in time and space, collecting and mass analyzing the co-emitted secondary ions from each projectile impact. Each sample is analyzed with a large quantity (106-107) of individual projectile impacts within an analysis area 125 μm in diameter. Analysis of co-emission of these independent 106-107 mass spectra allows for identification of co-localized molecules within nanodomains ~10-15 nm diameter and ~10 nm in depth (the emission area of a single impact) from the film surface. This unique method therefore reveals spatial distributions of molecules at the nanoscale. Using MC-SIMS methodology, we directly measured key factors influencing the PAG homogeneity at the nanoscale including (1) PAG concentration, (2) the nature of the polymer matrix, (3) the nature of the PAG, and (4) additives. We discovered that 85-95% of PAG salts aggregate at the nanoscale. The majority of the PAG aggregates are less than 10 nm in size and are highly homogeneously distributed within the polymer matrix in the film. Furthermore, the size of the PAG aggregates can be manipulated by additives through an ion-exchange mechanism.

This work is concerned with investigating the effect of substrate hydrophobicity and zeta potential on the dynamics and kinetics of the initial stages of bacterial adhesion. For this purpose, bacterial pathogens Staphylococcus aureus and Escherichia coli O157:H7 were inoculated on the substrates coated with thin thiol layers (i.e., 1-octanethiol, 1-decanethiol, 1-octadecanethiol, 16-mercaptohexadecanoic acid, and 2-aminoethanethiol hydrochloride) with varying hydrophobicity and surface potential. The time-resolved adhesion data revealed a transformation from an exponential dependence to a square root dependence on time upon changing the substrate from hydrophobic or hydrophilic with a negative zeta potential value to hydrophilic with a negative zeta potential for both pathogens. The dewetting of extracellular polymeric substances (EPS) produced by E. coli O157:H7 was more noticeable on hydrophobic substrates, compared to that of S. aureus, which is attributed to the more amphiphilic nature of staphylococcal EPS. The interplay between the timescale of EPS dewetting and the inverse of the adhesion rate constant modulated the distribution of E. coli O157:H7 within microcolonies and the resultant microcolonial morphology on hydrophobic substrates. Observed trends in the formation of bacterial monolayers rather than multilayers and microcolonies rather than isolated and evenly spaced bacterial cells could be explained by a colloidal model considering van der Waals and electrostatic double-layer interactions only after introducing the contribution of elastic energy due to adhesion-induced deformations at intercellular and substrate-cell interfaces. The gained knowledge is significant in the context of identifying surfaces with greater risk of bacterial contamination and guiding the development of novel surfaces and coatings with superior bacterial antifouling characteristics.

We present the data on ejection of molecules and emission of molecular ions caused by single impacts of 50 keV C602+ on a molecular layer of deuterated phenylalanine (D8Phe) deposited on free standing, 2-layer graphene. The projectile impacts on the graphene side stimulate the abundant ejection of intact molecules and the emission of molecular ions in the transmission direction. To gain insight into the mechanism of ejection, Molecular Dynamic simulations were performed. It was found that the projectile penetrates the thin layer of graphene, partially depositing the projectile's kinetic energy, and molecules are ejected from the hot area around the hole that is made by the projectile. The yield, Y, of negative ions of deprotonated phenylalanine, (D8Phe-H)-, emitted in the transmission direction is 0.1 ions per projectile impact. To characterize the ejection and ionization of molecules, we have performed the experiments on emission of (D8Phe-H)- from the surface of bulk D8Phe (Y = 0.13) and from the single molecular layer of D8Phe deposited on bulk pyrolytic graphite (Y = 0.15). We show that, despite the similar yields of molecular ions, the scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. The projectile impact on the graphene-D8Phe sample stimulates the collective radial movement of analyte atoms, which compresses the D8Phe layer radially from the hole. At the same time, this compression bends and stretches the graphene membrane around the hole thus accumulating potential energy. The accumulated potential energy is transformed into the kinetic energy of correlated movement upward for membrane atoms, thus the membrane acts as a trampoline for the molecules. The ejected molecules are effectively ionized; the ionization probability is ∼30× higher compared to that obtained for the bulk D8Phe target. The proposed mechanism of ionization involves tunneling of electrons from the vibrationally excited area around the hole to the molecules. Another proposed mechanism is a direct proton transfer exchange, which is suitable for a bulk target: ions of molecular fragments (i.e., CN-) generated in the impact area interact with intact molecules from the rim of this area. There is a direct proton exchange process for the system D8Phe molecule + CN-.

We present the application of cluster-SIMS for the analysis of the nanoscopic surface of diblock brush terpolymers (DBTs). This novel SIMS technique differs from conventional SIMS. It uses Au4004+ projectiles at 520 keV and an event-by-event bombardment/detection regime for the analysis of co-localized molecular species. The performance of this SIMS method was tested on ‘bottle brush’ block molecules featuring a vertical aligned backbone structure. We were able to assess the extent of secondary ion emissions from the surface and analyze the degree of ordered alignment for DBTs by the fluorocarbon surface coverage. We demonstrate the feasibility of characterizing the homogeneity of macromolecular films at the nanoscale. Copyright © 2015 John Wiley & Sons, Ltd.

We present the first data on emission of C60− stimulated by single impacts of 50 keV C602+ on the self-assembled molecular layer of C60 deposited on free standing 2 layer graphene. The yield, Y, of C60− emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules, we have measured the emission of C60− from the surface of bulk C60 (Y = 3.7%) and from a single layer of C60 deposited on bulk pyrolytic graphite (Y = 3.3%). To gain insight into the mechanism(s) of ejection, molecular dynamic simulations were performed. The scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+ impacts on graphene plus C60, the C atoms of the projectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energy of the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impact site. The...

Molecular dynamics computer simulations have been employed to investigate the effect of substrate thickness on the ejection mechanism of phenylalanine molecules deposited on free-standing graphene. The system is bombarded from the graphene side by 10 keV C60 projectiles at normal incidence and the ejected particles are collected both in transmission and reflection directions. It has been found that the ejection mechanism depends on the substrate thickness. At thin substrates mostly organic fragments are ejected by direct collisions between projectile atoms and adsorbed molecules. At thicker substrates interaction between deforming topmost graphene sheet and adsorbed molecules becomes more important. As this process is gentle and directionally correlated, it leads predominantly to ejection of intact molecules. The implications of the results to a novel analytical approach in Secondary Ion Mass Spectrometry based on ultrathin free-standing graphene substrates and a transmission geometry are discussed.

International audience; We present here the study of the individual hypervelocity massive projectiles (440-540 keV, 33-36 km/s Au-400(4+) cluster) impact on 1-layer free-standing graphene. The secondary ions were detected and recorded separately from each individual impact in the transmission direction using a time-of-flight mass spectrometer. We observed C-1-10(+/-) ions emitted from graphene, the projectiles which penetrated the graphene, and the Au-1-3(+/-) fragment ions in mass spectra. During the projectile-graphene interaction, the projectile loses similar to 15% of its initial kinetic energy (similar to 0.18 keV/atom, 72 keV/projectile). The Au projectiles are neutralized when approaching the graphene and then partially ionized again via electron tunneling from the hot rims of the holes on graphene, obtaining positive and negative charges. The projectile reaches an internal energy of similar to 450-500 eV (similar to 4400-4900 K) after the impact and then undergoes a similar to 90-100 step fragmentation with the ejection of Au-1 atoms in the experimental time range of similar to 0.1 mu s.

Secondary ion mass spectrometry (SIMS) with 520 keV A u 400 4 + projectiles operating in event-by-event bombardment/detection mode was applied to investigate pyrolized mixtures of catalyst (vitamin B12) and carbon supports (carbon black). The specimens are alternative cathode materials to platinum for fuel cells. The goal was to understand the effect of temperature on the chemical environment of the catalytically active sites formed on the carbon supports during pyrolysis. The A u 400 4 + projectiles probed the samples one-at-a-time in a stochastic manner and the resulting secondary ions from the individual impacts were recorded separately. The coincidental methodology allows one to compile mass spectra comprising selectively the secondary ions from the impacts on the active sites, extracting the local molecular information of the active sites within a nanodomain (∼10 3 nm 3 ). The detection of CoN 4 C x − suggests Co-N 4 be the moiety retained from the pyrolized vitamin B12 in the presence of the carbon black. Variations in the local chemical environment of the active sites as a function of pyrolysis temperature were also observed. Additionally, we could quantify the dispersion of the active sites among the carbon supports, a measure providing a direction for future device optimization.

Guorong Sun, Sangho Cho, Fan Yang, Xun He, Adriana Pav ia-Sanders, Corrie Clark, Jeffery E. Raymond, Stanislav V. Verkhoturov, Emile A. Schweikert, James W. Thackeray, Peter Trefonas, Karen L. Wooley Department of Chemistry, Texas A&M University, College Station, Texas 77842 Department of Chemical Engineering, Texas A&M University, College Station, Texas 77842 Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77842 Laboratory for Synthetic-Biologic Interactions, Texas A&M University, College Station, Texas 77842 Dow Electronic Materials, Marlborough, Massachusetts 01752 Correspondence to: J. W. Thackeray (E-mail: jthackeray@dow.com) or P. Trefonas (E-mail: ptrefonas@dow.com) or K. L. Wooley (E-mail: wooley@chem.tamu.edu)

Background: The homogeneity of photoacid generator (PAG) is a critical factor influencing the resolving capability and the sidewall roughness of a photoresist, yet fundamental understanding of the PAG homogeneity lacks at the nanoscale. Aim: We present a methodology, massive cluster secondary ion mass spectrometry (MC-SIMS), to determine PAG homogeneity on a 10- to 15-nm scale at the photoresist film surface. Approach: MC-SIMS bombards the sample with a sequence of massive Au400 + 4 nanoprojectiles, each separated in time and space, collecting and mass analyzing the coemitted secondary ions from each impact. Each sample is analyzed with one million individual projectile impacts. Analysis of coemission of these independent more than one million mass spectra allows for identification of colocalized molecules within nanodomains ∼10- to 15-nm diameter and ∼10 nm in depth from the film surface, therefore revealing spatial molecular distributions at the nanoscale. Results: About 85% to 95% of the measurements showed PAG–PAG coemission and over 90% showed polymer–PAG coemission. Ion-exchanging additive increases polymer–PAG coemission. Conclusions: The majority of PAG molecules exist as small aggregates that are

We describe a methodology for nanoscale molecular analysis and present its capabilities. The analysis method is based on secondary-ion mass spectrometry with gold nanoparticles (e.g., Au4004+). The methodology presented has unique features that enable nanoscale molecular analysis, namely the method of acquiring the mass spectrum and the nature of the impacting projectile. In the method, a sequence of individual gold nanoparticles (Au4004+) is used to bombard the sample; each impact results in ion emission from an area ∼10–20 nm in diameter. For each of impact of Au4004+, the emitted ions are mass analyzed by time-of-flight mass spectrometry, detected and stored together in one mass spectrum prior to the arrival of the subsequent projectile. Each mass spectrum contains elements and molecules, which are colocalized within ∼10 to 20 nm of one another. Examination of the coemitted ions allows us to test the molecular homogeneity and chemical composition at the nanoscale. We applied this method to a chemically amplified resist before and after exposure and development. After development the method was used to chemically characterize defect sites that were not removed by the developing solution.

We present results from experiments and molecular dynamics (MD) simulations obtained with C60 and Au400 impacting on free-standing graphene, graphene oxide (GO), and graphene-supported molecular layers. The experiments were run on custom-built ToF reflectron mass spectrometers with C60 and Au-LMIS sources with acceleration potentials generating 50 keV C602+ and 440–540 keV Au4004+. Bombardment-detection was in the same mode as MD simulation, i.e., a sequence of individual projectile impacts with separate collection/identification of the ejecta from each impact in either the forward (transmission) or backward (reflection) direction. For C60 impacts on single layer graphene, the secondary ion (SI) yields for C2 and C4 emitted in transmission are ∼0.1 (10%). Similar yields were observed for analyte-specific ions from submonolayer deposits of phenylalanine. MD simulations show that graphene acts as a trampoline, i.e., they can be ejected without destruction. Another topic investigated dealt with the chemical composition of free-standing GO. The elemental composition was found to be approximately COH2. We have also studied the impact of Au400 clusters on graphene. Again SI yields were high (e.g., 1.25 C−/impact). 90–100 Au atoms evaporate off the exiting projectile which experiences an energy loss of ∼72 keV. The latter is a summation of energy spent on rupturing the graphene, ejecting carbon atoms and clusters and a dipole projectile/hole interaction. The charge distribution of the exiting projectiles is ∼50% neutrals and ∼25% either negatively or positively charged. We infer that free-standing graphene enables detection of attomole to zeptomole deposits of analyte via cluster-SI mass spectrometry.We present results from experiments and molecular dynamics (MD) simulations obtained with C60 and Au400 impacting on free-standing graphene, graphene oxide (GO), and graphene-supported molecular layers. The experiments were run on custom-built ToF reflectron mass spectrometers with C60 and Au-LMIS sources with acceleration potentials generating 50 keV C602+ and 440–540 keV Au4004+. Bombardment-detection was in the same mode as MD simulation, i.e., a sequence of individual projectile impacts with separate collection/identification of the ejecta from each impact in either the forward (transmission) or backward (reflection) direction. For C60 impacts on single layer graphene, the secondary ion (SI) yields for C2 and C4 emitted in transmission are ∼0.1 (10%). Similar yields were observed for analyte-specific ions from submonolayer deposits of phenylalanine. MD simulations show that graphene acts as a trampoline, i.e., they can be ejected without destruction. Another topic investigated dealt with the chemical ...

Thermal stability is important for many thin film organic semiconductor devices but is challenging due to their weakly Van der Waals-bonded nature. Here, we show that diluting common small molecule hole transport materials through co-evaporation with the amorphous fluoropolymer Teflon AF leads to a dramatic improvement in their thermal and morphological stability without sacrificing electrical performance. Blend films with 25 vol. % Teflon decrease the drive voltage of single layer hole-only devices by more than 30% and dramatically increase their operating temperature limit to over 250 °C. The stability improvement appears to result from a nanoscale network of Teflon chains that repolymerize throughout the blend film following evaporation and inhibit gross movement of the organic semiconductor molecules. These results open up a pathway to stabilize the morphology of small molecule organic semiconductors and point to a more general opportunity to exploit semiconductor dilution to systematically vary thermal, optical, and other material properties without compromising electrical transport.

The feasibility of metal-assisted secondary ion mass spectrometry (MetA-SIMS) for increasing secondary ion yields from massive gold projectile impacts is investigated using polymeric and plastic additive test molecules. Poly(methyl methacrylate) (PMMA) and Irganox 1010 surfaces were deposited with various amounts of gold and silver and then analyzed using both Bi+ and Au400 4+. The Bi+ primary ion displays a fivefold ion yield increase for some species while the massive gold cluster exhibits significant suppression due to the metal overlayer, with more than a tenfold decrease in ion yields for most species. Consequently, MetA-SIMS does not lead to enhanced secondary ion yields when using the Au400 4+ projectile. Overall, the Au400 4+ projectile leads to secondary ion yields that are ∼2 orders of magnitude larger than for Bi+, even when MetA-SIMS is employed. © 2013 Elsevier B.V. All rights reserved.

This study reports on the secondary ion (SI) emission from individual Au nanoparticles (AuNPs) with secondary ion mass spectrometry (SIMS) operating in event-by-event bombardment/detection mode. This methodology allows one to obtain quantitatively the effective yields of SI emission from individual nano-objects. The analyses of gold cluster emission from a series of AuNPs of different sizes (2, 5, 10, 15, 20, 50 nm in diameter) were conducted with two massive projectiles, 50 keV C602+ and 520 keV Au4004+. The results indicate that the emission of Au2− and Au3− varies as a function of particle size. Due to different mechanisms of energy transfer and energy densities deposited into the NPs, the optimum sizes for maximum Au2− and Au3− emission are: 20 nm for 520 keV Au4004+ and 10 nm for 50 keV C602+. Moreover, the abundance of Au2− and Au3− is also affected by the nature of the projectile. In the case of Au400 impacts, the enhanced SI emission of larger clusters is observed not only from 15 and 20 nm but also from 10 nm AuNPs. The observation of the size- and projectile-dependent SI emission points out the necessity of accurate data interpretation when dealing with nanoscale objects.

This study deals with assessing the homogeneity of a mixture of ultrasmall nanoparticles differing only by their respective functionalization. While measuring the relative abundance of nanoparticles with specific functionalization is feasible with mass spectrometry, the determination of mixed or segregated moieties is beyond current capabilities. Our approach is based on SIMS with massive projectiles, specifically Au400+4. A distinct feature of bombardment with Au400+4 is abundant emission of multiple secondary ions from one projectile impact. Their analysis allows for examination of coemitted and thus colocalized molecules within the emission area of a single impact (∼10–15 nm in diameter). It is possible to collect the mass spectrum from each projectile impact, which probes individual nanodomains, allowing for examination of molecular homogeneity at the nanoscale.

Secondary ion mass spectrometry (SIMS) applied in the event-by-event bombardment/detection mode is uniquely suited for the characterization of individual nano-objects. In this approach, nano-objects are examined one-by-one, allowing for the detection of variations in composition. The validity of the analysis depends upon the ability to physically isolate the nano-objects on a chemically inert support. This requirement can be realized by deposition of the nano-objects on a Nano-Assisted Laser Desorption/Ionization (NALDI™) plate. The featured nanostructured surface provides a support where nano-objects can be isolated if the deposition is performed at a proper concentration. We demonstrate the characterization of individual nano-objects on a NALDI™ plate for two different types of nanometric bacteriophages: Qβ and M13. Scanning electron microscope (SEM) images verified that the integrity of the phages is preserved on the NALDI™ substrate. Mass spectrometric data show secondary ions from the phages are identified and resolved from those from the underlying substrate.

The current limitation for SIMS analyses is insufficient secondary ion yields, due in part to the inefficiency of traditional primary ions. Massive gold clusters are shown to be a route to significant gains in secondary ion yields relative to other commonly used projectiles. At an impact energy of 520 keV, [Formula: see text] is capable of generating an average of greater than ten secondary ions per projectile, with some impact events generating >100 secondary ions. The capability of this projectile for signal enhancement is further displayed through the observation of up to seven deprotonated molecular ions from a single impact on a neat target of the model pentapeptide leu-enkephalin. Positive and negative spectra of leu-enkephalin reveal two distinct emission regimes responsible for the emission of either intact molecular ions with low internal energies or small fragment species. The internal energy distribution for this projectile is measured using a series of benzylpyridinium salts and compared with the small polyatomic projectile [Formula: see text] at 110 keV as well as distributions previously reported for electrospray ionization and fast atom bombardment. These results show that [Formula: see text] offers high secondary ion yields not only for small fragment ions, e.g. CN(-), typically observed in SIMS analyses, but also for characteristic molecular ions. For the leu-enkephalin example, the yields for each of these species are greater than unity.

This paper describes the application of nanoparticle bombardment with time-of-flight secondary ion mass spectrometry (NP-ToF-SIMS) for the analysis of native biological surfaces for the case of sagittal sections of mammalian brain tissue. The use of high energy, single nanoparticle impacts (e.g. 520 keV Au400) permits desorption of intact lipid molecular ions, with enhanced molecular ion yield and reduced fragmentation. When coupled with complementary molecular ion fragmentation and exact mass measurement analysis, high energy nanoparticle probes (e.g. 520 keV Au400 NP) provide a powerful tool for the analysis of the lipid components from native brain sections without the need for surface preparation and with ultimate spatial resolution limited to the desorption volume per impact (~103 nm3).

This letter presents the first application of high energy, single nanoparticle probes (e.g., 520 keV Au(400) 2nm NP) in the characterization of surfaces containing fluorescent proteins (e.g., GFP variants) by their co-emitted photon, electron and secondary ion signals. NP induced protein luminescence increases with the NP incident energy, is originated by the NP impact and is transferred to the protein fluorophor via electronic energy transfer. Multi-electron emission is observed per single NP impacts and their distributions are specific to the target morphology and composition. Fragment ions of protein sub-units consisting of 2-7 amino acid peptides are observed under individual NP impacts that can be correlated to the random protein orientation relative to the impact site (e.g., outer layer or "skin" of the protein).

Cluster C 60 ToF-SIMS (time-of-flight secondary ion mass spectrometry) operated in the event-by-event bombardment-detection method has been applied to: (a) quantify the binding density of Au nanoparticles (AuNPs)–antiCD4 conjugates on the cell surface and (b) identify the binding sites between AuNPs and antibody. Briefly, our method consists of recording the secondary ions, SIs, individually emitted from a single C 60 1,2+ impact. From the cumulative mass spectral data we selected events where a specific SI was detected. The selected records revealed the SIs co-ejected from the nanovolume impacted by an individual C 60 with an emission area of ∼10 nm in diameter as an emission depth of 5–10 nm. The fractional coverage is obtained as the ratio of the effective number of projectile impacts on a specified sampling area ( N e ) to the total number of impacts ( N o ). In the negative ion mass spectrum, the palmitate (C 16 H 31 O 2 − ) and oletate (C 18 H 33 O 2 − ) fatty acid ions present signals from lipid membrane of the cells. The signals at m / z 197 (Au − ) and 223 (AuCN − ) originate from the AuNPs labeled antibodies (antiCD4) bound to the cell surface antigens. The characteristic amino acid ions validate the presence of antiCD4. A coincidence mass spectrum extracted with ion at m / z 223 (AuCN − ) reveals the presence of cysteine at m / z 120, documenting the closeness of cysteine and the AuNP. Their proximity suggests that the binding site for AuNP on the antibody is the sulfur-terminal cysteine. The fractional coverage of membrane lipid was determined to be ∼23% of the cell surfaces while the AuNPs was found to be ∼21%. The novel method can be implemented on smaller size NPs, it should thus be applicable for studies on size dependent binding of NP–antibody conjugates.

Secondary ion mass spectrometry (SIMS) performed in the event-by-event bombardment detection mode when coupled to an electron emission microscope allows one to investigate individual nano-objects. Two groups of Au and Al oxide nano-objects were compared with their bulk counterparts based on their secondary ion and electron emission from individual C60 impacts at 15 and 30 keV total impact energy. Our results show that electron yields depend on the size and surroundings of the nano-object, and at higher impact energies, these differences in electron emission are more pronounced. A second key observation for systems of similar chemical makeup but different surface topography and size is that the emission of secondary ions and electrons is independent of each other.

International audience; The objective of this project is the development of the SIMS associated to a new probe of the solid: massive clusters consisting of 100–1000 bismuth or gold atoms. The systematic study of the ionic emission intensities as a function of the mass and energy of these projectiles showed that 100–200 qkeV is sufficient energy for the new probe. It is possible to obtain a time of flight (ToF) spectrum with a single impact. These spectra permit to characterize light molecules (MW∼ a few hundreds) with their fragments and intact molecular ion peaks. To analyze the surface, we propose to obtain cluster beams of 100–150 qkeV with a diameter of 10–100 µm, and to associate measurements of time of flight mass spectrometry with the detection of electron emission in order to locate the impact on the surface. We describe the simulation and the installation, on a 130 kV platform, of our column including a LMIS (Liquid Metal ion Source), lenses and Wien Filter, and of a focusing beam line made of an accelerating gap with its shield and a 130 kV insulator. We shall give the experimental beam specifications obtained with the massive cluster ion source Pegase for bismuth and gold.

We report on nanoprojectile-nanoparticle (NP) interaction when the two collision partners are in the same size range. The experiments involved C 60 + accelerated to 26 keV impacting isolated NPs of Ag and Au, both ~5 nm in diameter, deposited as single layers on an organic substrate. A direct 'bulls-eye' impact of one C 60 + onto one NP can result in two processes: fragmentation of the NP and emission of metallic ions, or fragmentation of the NP with fragmentation of substrate molecule followed by recombination and emission of ions. The NPs were covered with self assembled monolayers (SAMs), grazing impacts were readily observed via emission of fragments of SAMs. A mix of Ag and Au NPs showed that emission can be affected by surrounding NPs. Mass spectrometric data from vanishingly small objects reflect size-dependant processes and effects.

We report on the secondary ion emission under massive cluster (from 100 to 1600 atoms) impacts from different organic samples. The study has been preformed at the Orsay Tandem Accelerator equipped with a Liquid Metal Ion Source (LMIS) using a time of flight (ToF) mass spectrometer (MS) with a multianode localization detector. The influence of the projectile mass and energy is studied in order to investigate the new hydrodynamic regime of the solid-particle interaction related to the use of these massive clusters. We shall present this study, the energy range of which extends from 10 qkeV up to 4 qMeV. The results show that the ionic emission intensities increase with the energy and the mass of the projectiles (from n/q = 25 to n/q = 400) which allows the simultaneous emission of a few tens ions of the same mass per impact, what had never before been observed in SIMS. The study of the positive ionic emission is surprising. There is an important emission (also a few tens ions) of H + , H 2 + , H 3 + and C + . The setup permits to determine the angular velocity distributions of the ejected ions. We present the results which permit to distinguish four classes of ionic emission. The molecular ions and molecular clusters are preferentially pushed from the surface by a pressure wave which rises perpendicularly to the beam trajectory.

We assembled hardware and software for the synchronized detection of electrons and ions emitted under the impacts of the individual C 60 + and C 60 2+ ions. A projectile impact is localized via the ejected electron(s) with an emission electron microscope (EEM). The (x,y) coordinates of each impact combined with the corresponding record of detected secondary ions (Sis), allow the construction of mass-selected surface maps. The setup comprises a custom-built ToF-SIMS with a C 60 1,2+ source, an EEM with an electron imaging detector consisting of dual microchannel plates (MCPs), phosphor screen and a 1.3 megapixel CMOS camera. The electron pulse on the aluminized phosphor screen triggers the camera resulting in a frame with the electron image. It also triggers the ToF electronics resulting in a suite of SI time records corresponding to each individual impact event. The data processing and management are handled by custom software including combination of the positional and the mass spectrometric information from each impact. The present study demonstrates the feasibility of mapping a surface by localizing the SI emission from single C 60 2+ impacts. A spatial resolution of 1.3 μm has been obtained. Interestingly, maps of coemitted SIs from a given localization display chemically resolved information from an emission area of ~10 2 nm 2 .

We have recently reported a nanoprobe technique based on time-of-flight secondary ion mass spectrometry (ToF-SIMS) capable of obtaining molecular information from individual nanoobjects. The technique is based on event-by-event bombardment/detection, where information from individual objects is obtained via coincidental secondary ion emission from single projectile impacts. Here, we demonstrate that the event-by-event mode is sensitive to the chemical and/or physical separation of molecular species. As a test case, two nanoobject samples with the same chemical composition were prepared with different morphologies. Both consisted of polystyrene spheres deposited onto nanoalumina whiskers, but their structures differed. One sample contained 30 nm spheres intact, and the other produced nanoflake structures. Bombardment with Au 400 4+ at 136 keV total impact energy demonstrates that conventional mass spectra do not reflect differences between the morphologies, whereas the coincidental mass spectra show significant differences in coemission of aluminum-based and carbon-based secondary ions.

Micropatterning is used widely in biosensor development, tissue engineering and basic biology. Creation of biological micropatterns typically involves multiple sequential steps which may lead to cross-contamination and contribute to suboptimal performance of the surface. Therefore, there is a need to develop novel strategies for characterizing location-specific chemical composition of biological micropatterns. In this paper, C 60 + time-of-flight secondary ion mass spectrometry (ToF-SIMS) operating in the event-by-event bombardment/detection mode was used for spatially resolved chemical analysis of micropatterned indium tin oxide (ITO) surfaces. Fabrication of the micropatterns involved multiple steps including self-assembly of poly(ethylene glycol)-silane (PEG-silane), patterning of photoresist, treatment with oxygen plasma and adsorption of collagen (I). The ITO surfaces were analyzed with 26-keV C 60 + SIMS run in the event-by-event bombardment/detection mode at different steps of the modification process. We were able to evaluate the extent of cross-contamination between different steps and quantify coverage of the immobilized species. The methodology described here provides a novel means for characterizing the composition of biological micropatterns in a quantitative and spatially resolved manner.

This paper describes a novel surface engineering approach that combines oxygen plasma treatment and electrochemical activation to create micropatterned cocultures on indium tin oxide (ITO) substrates. In this approach, photoresist was patterned onto an ITO substrate modified with poly(ethylene) glycol (PEG) silane. The photoresist served as a stencil during exposure of the surface to oxygen plasma. Upon incubation with collagen (I) solution and removal of the photoresist, the ITO substrate contained collagen regions surrounded by nonfouling PEG silane. Chemical analysis carried out with time-of-flight secondary ion mass spectrometry (ToF-SIMS) at different stages in micropatterned construction verified removal of PEG-silane during oxygen plasma and presence of collagen and PEG molecules on the same surface. Imaging ellipsometry and atomic force microscopy (AFM) were employed to further investigate micropatterned ITO surfaces. Biological application of this micropatterning strategy was demonstrated through selective attachment of mammalian cells on the ITO substrate. Importantly, after seeding the first cell type, the ITO surfaces could be activated by applying negative voltage (-1.4 V vs Ag/AgCl). This resulted in removal of nonfouling PEG layer and allowed to attach another cell type onto the same surface and to create micropatterned cocultures. Micropatterned cocultures of primary hepatocytes and fibroblasts created by this strategy remained functional after 9 days as verified by analysis of hepatic albumin. The novel surface engineering strategy described here may be used to pattern multiple cell types on an optically transparent and conductive substrate and is envisioned to have applications in tissue engineering and biosensing.

Silver nanoparticles (NPs) of approximately 5 nm diameter deposited in a single layer on glycine were examined with cluster secondary ion mass spectrometry (SIMS) in the event-by-event bombardment-detection mode. The projectiles used were Au(3)(+), C(60)(+), and Au(400)(4+) with impact energies of 34, 26, and 136 keV, respectively. The highest secondary ion yields were obtained with Au(400)(4+). The method presented can test single or multilayer organization and determine surface coverage. NPs are identified one-by-one for chemical composition. Chemical and physical information in a nonimaging mode was resolved at approximately 10 nm. Grazing vs direct impacts on NPs were identified and quantified. NP fragmentation from direct impacts with Au(400)(4+) and C(60)(+) was observed for the first time.

We present secondary ion mass spectrometry (SIMS) data obtained from the bombardment of a novel nanomaterial with a suite of projectiles: Au1+, Au3+, Au9+, and Au400(4+). These are the first experiments where free-standing nano-objects were bombarded with kiloelectronvolt projectiles of atomic to nanoparticle size (Au400(4+)). The objects are aluminum monohydrate nanowhiskers, identified as crystalline boehmite (AlOOH) using X-ray diffraction. The nanoalumina is bonded to a microglass fiber that serves as a scaffold. The largest projectile, Au400(4+), has a diameter of approximately 2 nm, comparable to the nominal diameter of the nanowhiskers. There are notable differences in secondary ion (SI) response from sample volumes too small for full projectile energy deposition. The whisker spectra are dominated by small clusters--the most abundant species being AlO- and AlO2-. Bulk samples have larger yields for AlO2- than AlO-, whereas this trend is reversed in the whisker samples. Bulk samples give similar abundances of large SI cluster families [(Al2O3)(n)AlO2]- and [(Al2O3)(n)OH]-, whereas the whisker samples give an order of magnitude lower yield of these SIs. Given the nature of our experiments, i.e., the event-by-event bombardment/detection mode, we are uniquely able to obtain information from SIs emitted from single-projectile impacts. As such, effective yields were calculated in order to determine quantitative differences between the nano-objects and bulk samples.

This paper describes a novel approach of controlling cell-surface interactions through an electrochemical “switching” of biointerfacial properties of optically transparent microelectrodes. The indium tin oxide (ITO) microelectrodes, fabricated on glass substrates, were modified with poly(ethylene glycol) (PEG) silane to make glass and ITO regions resistant to protein and cell adhesion. Cyclic voltammetry, with potassium ferricyanide serving as a redox reporter molecule, was used to monitor electron transfer across the electrolyte–ITO interface. PEG silane modification of ITO correlated with diminished electron transfer, judged by the disappearance of ferricyanide redox activity. Importantly, application of reductive potential (−1.4 V vs Ag/AgCl reference) corresponded with reappearance of typical ferricyanide redox peaks, thus pointing to desorption of an insulating PEG silane layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization of the silanized ITO surfaces after electrical stimulation indicated complete removal of the silane layer. Significantly, electrical stimulation allowed to “switch” chosen electrodes from nonfouling to protein-adhesive while leaving other ITO and glass regions protected by a nonfouling PEG silane layer. The spatial and temporal control of biointerfacial properties afforded by our approach was utilized to micropattern proteins and cells and to construct micropatterned co-cultures. In the future, control of the biointerfacial properties afforded by this novel approach may allow the organization of multiple cell types into precise geometric configurations in order to create better in vitro mimics of cellular complexity of the native tissues.

Alternating nanometric thin layer films made from poly(diallyldimethylammonium chloride), poly(styrene sulfonate) and montmorillonite clay were analyzed with 26 keV C 60 + (433 eV/atom) and 136 keV Au 400 4+ (340 eV/atom). Secondary ion (SI) emission depth from such thin films was determined to be ∼6–9 nm with C 60 + bombardment. Similar depth of emission was also reported with Au 400 4+ projectile impacts [Z. Li, S.V. Verkhoturov, E.A. Schweikert, Anal. Chem. 78 (2006) 7410]. The SI spectra contain recoiled C 60 projectile constituents ( m / z = 12, 13, 36). They track the compositional variation of the assembled thin layers except for C − and CH − whose abundances appear to correlate with the presence of metal atoms in the topmost layer.