Surface modification using a commercial triple quadrupole mass spectrometer

We report instrumental modifications to a commercial mass spectrometer that allow surface modification experiments to be performed using low-energy (electronvolt range) mass-selected ion beams. The design of the detector housing allows placement of the surface on the ion optical axis and some distance beyond the off-axis detector. Manipulation of the potentials applied to the final lens, detector housing, conversion dynode, and electron multiplier allow the ions to pass through the detector housing and impinge upon the surface without loss of the normal mode of detector operation. Ex situ analysis of the modified surface is performed using a home-built multisector mass spectrometer. The ability to modify organic thin films is demonstrated by a number of soft landing and surface modification experiments including (i) soft landing of (CH3)2SiNCS+ ions formed from trimethylsilyl isothiocyanate upon a fluorinated self-assembled monolayer (F-SAM) surface, (ii) soft landing and dissociative soft landing of the pseudomolecular cation of triphenylpyrylium tetrafluoroborate, viz. the triphenylpyrylium cation, upon an F-SAM surface, (iii) dissociative soft landing of 35ClCH2(CH3)2SiOSi(CH3)2+ formed from 1,3-bis(chloromethyl)disiloxane upon an F-SAM surface, (iv) surface passivation by reaction of the trimethylsilyl cation, Si(CH3)3+, with a hydroxyl-terminated self-assembled monolayer (OH-SAM), and (v) transhalogenation by reaction of CCl3+ (m/z 119) with an F-SAM surface.     

Preparation and in situ characterization of surfaces using soft landing in a Fourier transform ion cyclotron resonance mass spectrometer

Mass-selected peptide ions produced by electrospray ionization were deposited onto fluorinated self-assembled monolayer surfaces (FSAM) surfaces by soft landing using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially designed for studying interactions of large ions with surfaces. Analysis of the modified surface was performed in situ by combining 2-keV Cs+ secondary ion mass spectrometry with FT-ICR detection of the sputtered ions (FT-ICR-SIMS). Regardless of the initial charge state of the precursor ion, the SIMS mass spectra included singly protonated peptide ion, peptide fragment ions, and peaks characteristic of the surface in all cases. In some experiments, multiply protonated peptide ions and [M + Au]+ ions were also observed upon SIMS analysis of modified surfaces. For comparison with the in situ analysis of the modified surfaces, ex situ analysis of some of the modified surfaces was performed by 25-keV Ga+ time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The ex situ analysis demonstrated that a significant number of soft-landed peptide ions remain charged on the surface even when exposed to air for several hours after deposition. Charge retention of soft-landed ions dramatically increases the ion yields obtained during SIMS analysis and enables very sensitive detection of deposited material at less than 1% of monolayer coverage. Accumulation of charged species on the surface undergoes saturation due to coulomb repulsion between charges at close to 30% coverage. We estimated that close to 1 ng of peptide could be deposited on the spot area of 4 mm2 of the FSAM surface without reaching saturation.     

Improved temperature stability of Mo/Si multilayers by carbide based diffusion barriers through implantation of low energy CHx ions

To improve the thermal stability of Mo/Si multilayers, a novel method to form carbide based diffusion barriers, produced by the implantation of Si with CH_x⁺ ions, has been developed. The multilayers were grown by e-beam evaporation, while CH_x⁺ ions were implanted at the Mo/Si interfaces, using a Kaufman ion source with a Ne / CH₄ gas mixture. Energies were varied from 300 to 1000 eV. The growth as well as the implantation procedure were monitored by in situ X-ray reflectometry. Auger Electron Spectroscopy was used to characterize the surface composition before and after CH_x⁺ ion implantation. The shift of the Si LVV Auger peak revealed the formation of SiC. Ex situ X-ray reflectometry showed a thermal stability of both the reflectivity and the multilayer period up to 430 K.     

Ti/n型6H-SiC(0001)接触界面的研究

用同步辐射光电子能谱(SRPES)和X射线光电子能谱(XPS)的方法研究了Ti/n型6H-SiC(0001)的接触界面。Ti/n型6H-SiC(0001)样品采用磁控溅射的方法获得,然后将表面的Ti用氩离子刻蚀的方法慢慢刻蚀掉,Ti2p3/2用XPS测得,结合能从刻蚀时间为245 min的457.86 eV逐渐移动到刻蚀时间为255 min时的457.57 eV,移动约为0.3 eV。Si2p用同步辐射光测得,结合能从刻蚀245 min时的101.12 eV移动到干净的100.67 eV,峰形状未发生变化,表明Ti与衬底之间没有发生化学反应,SiC的价带发生弯曲,形成的势垒高度为0.89 eV。向SiC上蒸Si 2.5 min,退火30 min,观察LEED花样,发现当发射电流为30mA,能量37 eV时,SiC表面有√3*√3重构,发射电流为40 mA时,有6√3*6√3的重构。     

Design and performance of an instrument for soft landing of biomolecular ions on surfaces

A new ion deposition apparatus was designed and constructed in our laboratory. Our research objectives were to investigate interactions of biomolecules with hydrophilic and hydrophobic surfaces and to carry out exploratory experiments aimed at highly selective deposition of spatially defined and uniquely selected biological molecules on surfaces. The apparatus includes a high-transmission electrospray ion source, a quadrupole mass filter, a bending quadrupole that deflects the ion beam and prevents neutral molecules originating in the ion source from impacting the surface, an ultrahigh vacuum (UHV) chamber for ion deposition by soft landing, and a vacuum lock system for introducing surfaces into the UHV chamber without breaking vacuum. Ex situ analysis of surfaces following soft landing of mass-selected peptide ions was performed using 15 keV Ga+ time-of-flight secondary ion mass spectrometry and grazing incidence infrared reflection-absorption spectroscopy. It is shown that these two techniques are highly complementary methods for characterization of surfaces prepared with a range of doses of mass-selected biomolecular ions. We also demonstrated that soft landing of peptide ions on surfaces can be utilized for controlled preparation of peptide films of known coverage for fundamental studies of matrix effects in SIMS.     

强碱弱酸盐溶液对单晶硅太阳能电池表面织构化的影响

对晶向为（100）的p型单晶硅片进行表面刻蚀,制作减反射绒面。本实验是在传统氢氧化钠-异丙醇混合液中分别加入不同浓度的醋酸钠溶液、硅酸钠溶液和碳酸钠溶液对单晶硅片进行刻蚀。实验发现：分别加入醋酸钠溶液、碳酸钠溶液并没有在降低表面反射率方面起到很大作用,而只有加入硅酸钠溶液降低了表面反射率,有利于形成较好的腐蚀绒面。因此...     

Analysis of VX on soil particles using ion trap secondary ion mass spectrometry.

The direct detection of the nerve agent VX (methylphosphonothioic acid, S-[2-[bis(1-methylethyl)amino]ethyl] O-ethyl ester) on milligram quantities of soil particles has been achieved using ion trap secondary ion mass spectrometry (IT-SIMS). VX is highly adsorptive toward a wide variety of surfaces; this attribute makes detection using gas-phase approaches difficult but renders the compound very amenable to surface detection. An ion trap mass spectrometer, modified to perform SIMS, was employed in the present study. A primary ion beam (ReO4-) was fired on axis through the ion trap, where it impacted the soil particle samples. [VX + H]+, [VX + H]+ fragment ions, and ions from the chemical background were sputtered into the gas-phase environment of the ion trap, where they were either scanned out or isolated and fragmented (MS2). At a surface concentration of 0.4 monolayer, intact [VX + H]+, and its fragment ions, were readily observable above background. However, at lower concentrations, the secondary ion signal from VX became obscured by ions derived from the chemical background on the surface of the soil particles. MS2 analysis using the ion trap was employed to improve detection of lower concentrations of VX: detection of the 34S isotopic ion of [VX + H]+, present at a surface concentration of approximately 0.002 monolayer, was accomplished. The study afforded the opportunity to investigate the fragmentation chemistry of VX. Semiempirical calculations suggest strongly that the molecule is protonated at the N atom. Deuterium labeling showed that formation of the base peak ion (C2H4)N(i-C3H7)2+ involves transfer of the amino proton to the phosphonothioate moiety prior to, or concurrent with, C-S bond cleavage. To manage the risk associated with working with the compound, the vacuum unit of the IT-SIMS was located in a hood, connected by cables to the externally located electronics and computer.     

Low-energy ion--surface reactions of pyrazine with two classes of self-assembled monolayers: influence of alkyl chain orientation

Collisions of pyrazine with two classes of self-assembled monolayer (SAM) films are employed to determine whether surface confinement and the resulting alkyl chain orientation, influences low-energy ion-surface reactions. SAM films formed from n-alkanethiols (CH3(CH2)n-S-Au, n = 14-17) and 4-(4-alkoxyphenylbenzenethiols (4-(4-CH3(CH2)mOC6H4)-C6H4-S-Au, m = 14-17) chemisorbed onto Au (111) substrates are known to exhibit a chain-length-dependent odd-even effect that places the terminal C-C bond into different orientations. Ion-surface collisions (20 eV) of pyrazine molecular ion (M = m/z 80) with these surfaces yield reaction product ions corresponding to the addition of hydrogen atoms ([M + H]+ = m/z 81) and methyl groups ([M + CH3]+ = m/z 95) from the surface to the probe ion. Differences in the relative abundance of the reaction product ions are measured as a function of chain length for both classes of SAM film. SAM films with odd chain lengths (n, m = 14 and 16) have a consistently higher abundance of H addition product ions than SAM films with even chain lengths (n, m = 15 and 17). Alternating reactivity is also observed for the addition of CH3, with methyl addition occurring more readily on even-chain-length films. The variations are consistent with the well-characterized orientation differences known to exist for films of this type. Specifically, odd-chain-length films are oriented such that the last C-C bond is more parallel to the plane of the surface than it is for even-chain-length films. The critical element of the parallel orientation is that it leaves, on average, one hydrogen atom on the terminal methyl and both hydrogen atoms on the first underlying methylene in more reactive positions compared to even chain lengths. Conversely, the trend in the relative abundance of CH3 addition indicates that the orientation produced by an even-chain-length film, with the last C-C bond more perpendicular to the surface, allows the probe ion better access to the methyl carbon. Reflection absorption IR spectroscopy (RAIRS) data independently confirm the orientational disposition of the films. The RAIRS data show that the odd-even effect is less dramatic for the n-alkanethiols when compared to 4-(4-alkoxyphenyl)benzenethiols. A smaller difference in ion-surface reactivity is measured for n-alkanethiols, demonstrating that ion-surface reactions can distinguish subtle differences in average orientation. In short, we report that the extent of ion-surface reactions of pyrazine ion with two classes of SAM films is directed by the spatial orientation of the surface-confined species that participate in the reaction.     

Swift heavy ion irradiation induced modification of structure and surface morphology of BiFeO3 thin film

BiFeO₃ (BFO) thin films of thickness about 800 nm deposited on Si (100) substrates by sol–gel spin coating method were irradiated by 200 MeV Ag ions. Modification of structure and surface morphology of the films under irradiation was studied using glancing incidence X-ray diffraction (GIXRD) and atomic force microscope (AFM). Fluence dependence of GIXRD peak intensity indicated formation of 10 nm diameter cylindrical amorphous columns in crystalline BFO due to 200 MeV Ag ion irradiation. AFM analysis indicated that the pristine film consists of agglomerated grains with diffuse grain boundary. Irradiation led to reduced agglomeration of the grains with the formation of sharper grain boundaries. The rms roughness (σ _rms) estimated from AFM analysis increased from 6·2 in pristine film to 12·7 nm when the film irradiated at a fluence of 1 × 10¹¹ ions cm ^???2 . Further irradiation led to decrease of σ _rms which finally saturated at a value of 7–8 nm at high ion fluences. The power spectral density analysis indicated that the evolution of surface morphology of the pristine film is governed by the combined effect of evaporation condensation and volume diffusion processes. Swift heavy ion irradiation seems to increase the dominance of volume diffusion in controlling surface morphology of the film at high ion fluences.     

Synthesis of nanoscale copper nitride thin film and modification of the surface under high electronic excitation

Nanoscale (approximately 90 nm) Copper nitride (Cu3N) films are deposited on borosilicate glass and Si substrates by RF sputtering technique in the reactive environment of nitrogen gas. These films are irradiated with 200 MeV Au15+ ions from Pelletron accelerator in order to modify the surface by high electronic energy deposition of heavy ions. Due to irradiation (i) at incident ion fluence of 1 x 10(12) ions/cm2 enhancement of grains, (ii) at 5 x 10912) ions/cm2 mass transport on the films surface, (iii) at 2 x 10(13) ions/cm2 line-like features on Cu3N/glass and nanometallic structures on Cu3N/Si surface are observed. The surface morphology is examined by atomic force microscope (AFM). All results are explained on the basis of a thermal spike model of ion-solid interaction.     

Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers

The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH═CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH═CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon nitride-coated microdevices, and in particular of microfabricated filtration membranes.     

Surface plasmon resonance analysis of Alzheimer's beta-amyloid aggregation on a solid surface: from monomers to fully-grown fibrils

We analyzed the aggregation of Alzheimer's beta-amyloid (1-42) (Abeta42) peptides from fresh monomers to fully grown fibrils by using in situ surface plasmon resonance (SPR) spectrometry and ex situ atomic force microscopy (AFM). To immobilize Abeta42 peptide on an SPR chip surface, different carboxy-terminated surfaces were investigated: (1) self-assembled monolayer of 11-mercaptoundecanoic acid and (2) carboxylated dextran-modified surface. It was found that the carboxylated dextran surface was more appropriate due to a much lower degree of nonspecific binding. By using the carboxylated dextran surface, we further investigated effects of key environmental factors, such as the density of surface-bound Abeta42, the concentration of Abeta42 in solution phase, and the presence of Fe3+ ions on Abeta42 fibrillation. The increase in either the surface density of Abeta42 or its concentration in incubation solution highly accelerated the formation of amyloid fibrils on the chip surface. The presence of Fe3+ ions in the incubation solution induced significantly denser aggregates, resulting in a nearly 6-fold increase of SPR angle shift. This work shows that SPR analysis coupled with AFM can be effectively used for analyzing amyloid aggregation and deposition on a solid surface from the very beginning to fully grown fibrils.     

Photoelectron spectroscopy study of Mn/n-Si interfacial structure

The Mn/n-Si interfacial structure is susceptible to intermixing even at room temperature. To investigate the chemistry as a result of the intermixing, valence band and core level photoelectron spectroscopy of Mn/Si has been carried out using synchrotron radiation of 134 eV energy and Al K_α X-ray (λ = 1,486.6 Å) source. The fabricated structures have also been irradiated from swift heavy ions (Fe⁷⁺ of ~100 MeV) to investigate the ion beam mixing in such structures. Valence band photoelectron spectroscopy with 134 eV photons shows the evolution of Mn3d, Mn3p and Si2p levels with a shifting towards lower binding energy side compared to their elemental values of the binding energy. This binding energy shift shows the formation of chemical compound of Si and Mn. Evolution of Si2p core level prior to and after the swift heavy ion irradiation shows strong chemical reactivity of manganese thin film with silicon. Deconvolution of Mn3d valence band has shown the formation of silicide phase due to the hybridization of Mn3d and Si3sp states. Mn2p core level study shows that the oxide and silicide formation takes place during the growth and for successive etching, oxide part is decreasing whereas silicide part is increasing.     

Various nanostructures on macroscopically large areas prepared by tunable ion-swelling

Various nanostructures were fabricated by ion irradiation on large area (100) Si surfaces covered by colloidal Langmuir-Blodgett films as nanolithographic masks. The ordered structure of the Langmuir-Blodgett monolayer composed from spherical St?ber silica particles of 200 nm and 450 nm diameter offer the possibility to form local surface swelling patterns during the ion bombardment step. Utilizing the dependence of the surface morphology on the irradiation parameters the tunability of nanostructuring was studied for 40 keV Ar+ and 500 keV Xe2+ ions. We show that the periodicity of the resulted surface pattern is determined by the size of the masking particles, while the height of nanostructures can be tuned by the ion fluence. The quality of projection of the nanomask contours to the substrate-the contrast of masking-can be set by choosing appropriate ion energy, thereby determining the curvature of the surface pattern. Moreover, deformation of the nanomask due to ion-nanoparticle interactions should be taken into account since these effects can be also utilized for tailoring various structures. The silica masking layers before and after ion irradiation and the resulting Si surface patterns were investigated by field emission scanning electron microscopy and atomic force microscopy analysis.     

SIMS of organic anions adsorbed onto an aminoethanethiol self-assembled monolayer: an approach for enhanced secondary ion emission

Secondary ion mass spectrometry (SIMS) was used to monitor the uptake of organic anions from solution by aminoethanethiol (AET) monolayers on Au substrates, as a test of the applicability of this monolayer as a substrate for organic SIMS analysis. Event-by-event bombardment and detection mode coupled with coincidence counting allowed the atomic and polyatomic projectile impacts on a particular sample surface to be compared simultaneously and under the same experimental conditions. The mass spectra produced from the monolayer surface and those from Au and Si blanks demonstrate that the AET monolayer is important to the uptake of the organic anion. The exchanged monolayer surfaces were used to measure secondary ion yields, defined as the number of secondary ions detected per incident primary ion, produced from ultrathin films by (CsI)nCs+ (n = 0-2) projectiles at the limit of single-ion impacts. The yield of a tetradecyl sulfate (IDS) anion was improved by a factor of 200 using the AET substrate instead of the thick salt target. The intact ion and fragment ion yield trends produced from the AET surface were measured as a function of number of atoms in the primary projectile and energy. We observed a yield increase for both the intact ion and the fragment ion with the projectile complexity and energy. The increase in yield per projectile atom was linear for the emission of intact TDS and intact dodecyl sulfate from the AET surfaces. A supralinear yield enhancement, however, was observed for the fragment ion SO3- when the three-atom (CsI)Cs+ cluster was used. The experiments demonstrate that the various organosulfate and suffonates are weakly bound to the AET surface and their adsorption to the AET monolayer is reversible. The utility of the AET monolayer on Au was also tested as a general substrate for the characterization of derivatized organic molecules with biological and industrial importance by TOF-SIMS.     

Interaction of TEMAHf precursor with OH-terminated Si (001) surface: a first principles study

We performed a first principles study to investigate the interaction of tetrakis-ethylmethylaminohafnium (4[(C2H5)(CH3)N]Hf, TEMAHf) precursors with an OH-terminated Si (001) surface that is the initial stage of atomic layer deposition (ALD). When TEMAHf reacted on the OH-terminated Si surface, there were two reaction mechanisms. One was the reaction with one -OH, and the other was the reaction with two -OH's. When TEMAHf reacted with an -OH on the Si (001) surface, an ethylmethylamine ((C2H5)(CH3)NH, EMA) was produced as a by-product and the trikis-ethylmethylaminohafnium group (3[(C2H5)(CH3)N]Hf) was attached to the O atom of the -OH. There were five reaction sites for TEMAHf to react with two -OH's to form the dikis-ethylmethylaminohafnium group (2[(C2H5)(CH3)N]Hf): Inter-dimer, intra-dimer, inter-row, cross-dimer, and cross-row. The reaction with two -OH's on the inter-dimer, intra-dimer, and inter-row sites were more favorable than the reaction with one -OH. Since the inter-dimer reaction was the most favorable, the energy barrier on the inter-dimer site for the reaction of the trikis-ethylmethylaminohafnium group with -OH to form the dikis-ethylmethylaminohafnium group was calculated, and the result was 0.19 eV. An extra energy of 0.25 eV was needed to remove EMA from the surface. Four TEMAHf's reacted with the surface and these reactions were exothermic by -7.77 eV, and the calculated Hf coverage of the first-half ALD cycle was 1.67 x 10(14)/cm2.     

Secondary ion emission from solutions: time dependence and surface phenomena.

The temporal behavior of FAB mass spectra from glycerol solutions of tetradecyltrimethylammonium bromide (C14H29-N(CH3)3Br, TTAB) and tetraethylammonium iodide (TEAI) was investigated. FAB spectra of the TTAB solution displayed a continuous decrease in TTA+ with time. Spectra obtained from the TEAI solution were initially invariant for several minutes and then displayed a gradual increase in the relative abundance of TEA+ to a maximum, followed by a precipitous drop in ion intensity. Secondary ion images of droplets of TTAB solution showed that emission of both TTA+ and glycerol secondary ions was homogeneous across the sample. Secondary ion images of droplets of TEAI solution showed heterogeneous and segregated emission of both TEA+ and protonated glycerol. Results from the FAB spectra and the secondary ion images were correlated and rationalized on the basis of surface tension-induced mass transport and matrix evaporation.     

Selective gas-phase cleavage at the peptide bond C-terminal to aspartic acid in fixed-charge derivatives of Asp-containing peptides

This study focuses on the molecular level interpretation of the selective gas-phase cleavage at aspartic acid residues (Asp) in protonated peptides. A phi3P+CH2C(=O)group (phi = 2,4,6-trimethoxyphenyl) is attached to the N-terminal nitrogen of the selected peptides LDIFSDF and LDIFSDFR, via solid-phase synthesis, to "mimic" the tightly held charge of a protonated arginine (Arg) residue. Collision-induced dissociation in a quadrupole ion trap instrument and surface-induced dissociation in a dual quadrupole instrument were performed for electrospray-generated ions of the fixed-charge peptide derivatives. Selective cleavages at Asp-Xxx are observed for those ions with charge provided only by the fixed charge or for those with a fixed charge and one Arg plus one added proton. This supports a previously proposed mechanism which suggests that the cleavages at Asp-Xxx, initiated by the acidic hydrogen of the Asp residue, become significant when ionizing protons are strongly bound by Arg in the protonated peptides. It is clear that the fixed charge is indeed serving as a "mimic" of protonated Arg and that a protonated Arg side chain is not required to interact with the Asp to induce cleavage at Asp-Xxx. When the number of protons exceeds the number of Arg in a peptide containing Arg and Asp, nonselective cleavages occur. The fragmentation efficiency of the peptides is consistent with the idea that these nonselective cleavages are promoted by a mobile proton. The peptide with a fixed charge and one added proton, [phi3P+CH2C(=O)-LDIFSDF + H]2+, fragments much more efficiently than the corresponding peptide with a fixed charge, an Arg and one added proton, [phi3P+CH2C(=O)-LDIFSDFR + H]2+; both of these fragment more efficiently than the peptide with a fixed charge and no added proton, phi3P+CH2C(=O)-LDIFSDF. MS/MS/MS (i.e., MS3) experimental results for bn ions formed at Asp-Xxx from phi3P+CH2C(=O)-LDIFSDF and its H/D exchange derivative, phi3P+CH2C(=O)-LDIFSDF-d11, are consistent with the bn ions formed at Asp-Xxx having a succinic anhydride cyclic structure. MS/MS experiments were also carried out for phi3P+CH2C(=O)-AAAA, a peptide derivative containing active hydrogens only at amide nitrogens plus the C-terminus, and its active H/D exchange product, phi3P+CH2C(=O)-AAAA-d5. The results show that a hydrogen originally located at an amide nitrogen is transferred away in the formation of a cyclic charge remote b ion.     

低能Ar+离子束辅助沉积择优取向Pt(111)膜

采用低能Ar+离子束辅助沉积方法,在Mo/Si(100)基底上沉积Pt膜,离子/原子到达比分别为0.1、0.2、0.3.若Ar+离子的入射角为0°,XRD谱分析表明,沉积的Pt膜均呈(111)和(200)混合晶向;当Ar+离子的入射角为45°,沉积的Pt膜均呈很强的(111)择优取向.因此若合理控制Ar+离子束的入射角,可在Mo/Si(100)衬底上制备出具有显著择优取向的Pt(111)薄膜.本文采用Monte Carlo方法模拟低能Ar+离子注入 Pt单晶所引起的原子级联碰撞过程,得出Ar+离子入射单晶铂(200)晶面时,Ar+离子的溅射率与入射角的关系,对Pt膜择优取向的机理作了初步的探讨和分析.     

Resolving oligomers from fully grown polymers with IMS-MS

Ion mobility and mass spectrometry techniques, combined with electrospray ionization, have been used to examine distributions of poly(ethylene glycols) (PEG) with average molecular masses of 6550 and 17900 Da. The analysis provides information about the polymer size distributions as well as smaller oligomers existing over a wide range of charge states and sizes (i.e., [HO(CH2CH2O)xH + nCs]n+, where x ranges from 21 to 151 and n = 2 to 11 for the 6550 Da sample; and, x ranges from 21 to 362 and n = 2 to 23 for the 17 900 Da sample). The present data show that oligomer distributions also fall into families, corresponding to much narrower size distributions for individual charge states; this dramatically simplifies data analysis. For example, we show evidence for baseline resolution of the +10 charge state of polymers. Unlike the charge-state trends reported previously for peptide ion families, which show generally increasing mobilities with increasing charge state (for a given m/z value), the mobilities of [HO(CH2CH2O)xH + nCs]n+ families generally decrease with increasing charge state. This requires that the addition of charges leads to substantial changes in the average structures of the ions. Comparisons of cross section calculations from molecular modeling results for multiply cesiated PEG ions with experimental cross sections indicate that these ions adopt highly extended (in many cases nearly linear) conformations, except for the high degree of coordination of the charged sites.