Ion crystal size and structure in Paul traps.

Ions stored in an electrodynamic ion trap can be forced from the center of the ion trap to regions of higher radio frequency (RF) electric fields by exposing them to a dipolar DC (DDC) potential applied across opposing electrodes. Such ions absorb power from the trapping RF field, resulting in increased ripple motion at the frequency of the trapping RF. When a bath gas is present, ions undergo energetic collisions that result in "RF-heating" sufficient to induce fragmentation. DDC is therefore a broad-band (i.e., mass-to-charge-independent) means for collisional activation in ion traps with added bath gas. Under appropriate conditions, the internal energy distribution of an ion population undergoing dissociation can be approximated with an effective temperature, Teff. In such cases, it is possible to determine thermal activation parameters, such as Arrhenius activation energies and A-factors, by measuring dissociation kinetics. In this work, the well-studied thermometer ion, protonated leucine enkephalin, was subjected to DDC activation under rapid energy exchange conditions and in two separate bath gases, N2 and Ar, to measure Teff as a function of the ratio of DDC and RF voltages. As a result, an empirically derived calibration was generated to link experimental conditions to Teff. It was also possible to quantitatively evaluate a model described by Tolmachev et al. that can be used to predict Teff. It was found that the model, which was derived under the assumption of an atomic bath gas, accurately predicts Teff when Ar was used as the bath gas but overestimates Teff when N2 was the bath gas. Adjustment of the Tolmachev et al. model for a diatomic gas resulted in an underestimate of Teff. Thus, use of an atomic gas can provide accurate activation parameters, while an empirical correction factor should be used to generate activation parameters using N2.

Collisional activation of ions in RF ion traps and ion guides: The effective ion temperature treatment

Summary This work addresses the development of some alternative hybrid and mixed variational formulations for the geometrically-exact three-dimensional first-order-shear shell boundary value problem [1,2]. In the framework of the complementaryenergy-based formulations, a Legendre transformation is used to introduce the complementary energy density in the variational statements as a function of the cross-sectional resultants only. The corresponding variational principles are shown to feature stationarity within the framework of the boundary-value-problem. The main features of the principles are highlighted, giving special attention to their relationships from both theoretical and numerical point of view. Variational principles constitute the core of the development of numerical methods in Solid Mechanics. The utility of such principles is two-fold: first, they provide a very convenient method for the derivation of the governing equations and natural boundary conditions of the boundary value problem and, second, they provide the mathematical foundation required to produce consistent numerical approximations. In this second role, the variational methods have been most useful in Computational Solid Mechanics [3]. Many different variational principles can be constructed depending on the equations enforced in the weak form. Perhaps the most remarkable variational principle is the Principle of Stationary Total Potential Energy, which states that, among all kinematically admissible displacement fields, those that satisfy the equilibrium conditions in the domain and at the boundary, lead to a stationary value of the total potential energy functional. In this paper, after the presentation of many mixed variational principles for the nonlinear analysis of shells, we derive a hybrid form of the Two-field Principle of Total Complementary Potential Energy, which is used on a totally consistent derivation of equilibrated co-rotational finite elements [4].

Novel radio-frequency quadrupole ion trap with spherical geometry

We have developed a trapped ion system for producing two-dimensional (2D) ion crystals for applications in scalable quantum computing, quantum simulations, and 2D crystal phase transition and defect studies. The trap is a modification of a Paul trap with its ring electrode flattened and split into eight identical sectors and its two endcap electrodes shaped as truncated hollow cones for laser and imaging optics access. All ten trap electrodes can be independently DC-biased to create various aspect ratio trap geometries. We trap and Doppler cool 2D crystals of up to 30 Ba+ ions and demonstrate the tunability of the trapping potential both in the plane of the crystal and in the transverse direction.

Valence stability of aliovalent ions is mostly correlated with lattice site potential in ionic crystals. Madelung electrostatic potential is obtained by adding all the lattice site potentials for all the ions present in a crystal structure. Therefore, valence stability and the stability of a crystal structure can be better understood with consideration of both the lattice site potential and Madelung electrostatic potential. This was first demonstrated more than four decades ago by one of the present authors. We revisit this situation by using re-calculated lattice site potential and Madelung electrostatic potential for perovskite structure type ABO3 compounds using a new computer program VESTA. We show that the formation of a perovskite structure type compound with the general formula ABO3 (where A and B are cations and O is an oxide ion) becomes energetically favorable when it has a higher Madelung electrostatic potential than the combined Madelung electrostatic potential of parent binary compounds AO and B2O3 or BO2. It is further shown that strong lattice site potential results in stability of high valence or high valence ions can be stabilized in a lattice site with strong lattice-site potential. It further follows that certain ions experience maximum lattice site potential at the B ion lattice site of the perovskite structure when compared to other structures such as fluorite BO2, rutile BO2 and corundum B2O3. Therefore, (i) the stability of an ion with a high (and uncommon) valence state at the B site being higher than that at the A site, (ii) occurrence of point defects at A or O sites with weak lattice site potentials, respectively and (iii) instability of perovskite A4+B2+O3, and A5+B1+O3 compounds, respectively can be rationalized by lattice site potential and Madelung electrostatic potential analysis.

<p>In this work, we study, by sol-gel method, CCO doped with Fe and Cr dopants, the implications for the aspects, crystal structure, crystal size, thermal conductivity, and electrical conductivity. Nevertheless, CCO has low thermoelectric efficiency and thus still longs for optimization in response to the performance, stability, and ecological environment requirement, which needs improvement. Dope would enhance the concentration of charge carriers without modifying the material structure itself. X-ray diffraction (XRD) to characterize the crystal structure and the Williamson–Hall (WH) method to calculate the crystal size were performed. SEM-EDS analyses provide surface morphology, particle size distribution, and elemental composition. The results show that the dopants change, among others, crystal size, microstrain, crystallinity index, and thermal and electrical conductivity, but no change in the crystal structure itself for any of these dopants. Fe doping increased the crystal size of CCO to 144.816 nm (versus 143.382 nm for pure CCO). Compared to Cr doping, the crystal's size was reduced to 65.232 nm. Where the estimated thermal conductivity increased for both dopants, attaining a value of 1.985967 W/mK for CCO-Fe and 1.952233 W/mK for CCO-Cr, concerning the value of 1.740633 W/mK of undoped CCO. Electrical conductivity also expanded (14.50 S/cm for CCO; 14.67 S/cm for CCO-Fe; 14.83 S/cm for CCO-Cr). These improvements highlight the potency of Fe and Cr dopants to fine-tune the CCO for thermoelectric usage.</p>

Surface-induced dissociation of molecular ions in a quadrupole ion trap mass spectrometer

Classification and role of modulators on crystal engineering of metal organic frameworks (MOFs)

Feldspars are ubiquitous natural dosimeters widely used in luminescence dating. Despite decades of research, the lattice defects as well as the mechanisms involved in luminescence production in feldspars remain poorly understood. The recently developed method of infrared photoluminescence (IRPL) excitation-emission spectroscopy has revealed the presence of two electron trapping centres emitting IRPL at 1.3 eV and 1.41 eV (IRPL1.3 and IRPL1.41 centres), and it enables detailed investigations into the ground and excited state energies of these centres. Here we make measurements of a range of single crystal alkali feldspars to understand the effects of feldspar chemical composition, crystal structure and framework disorder on the physical characteristics of IRPL1.3 and IRPL1.41 electron trapping centres. Measurements of our sample suite reveals IRPL and IR-radioluminescence (RL) emissions at 1.41 eV, 1.3 eV and, for the first time, at 1.2 eV. Our results show that whilst the IRPL1.3 trapping centre is unaffected by the M site cation occupancy, the presence of IRPL1.41 trapping centres seems to be linked to the presence of K+ ions on M sites. However, no clear trends in IRPL and IR-RL emission energies and signal intensities with chemical composition of the samples were found. Exploring the effect of framework disorder on IRPL1.3 and IRPL1.41 emissions revealed no significant changes to IRPL and IR-RL emission energies or ground state energies of the trapping centres, suggesting that the corresponding defects are not located on bridging O ions. Variations in ground state energies across the whole sample suite range from 2.04 eV to 2.20 eV for the IRPL1.3 centre and from 2.16 eV to 2.46 eV for the IRPL1.41 centre. Variations in trap depth seem to be driven by other factors than sample chemistry, degree of Al3+ disorder and number of phases present in a single crystal feldspar. Interestingly, the IR resonance peak is invariant between samples. Regarding the use of IRPL in luminescence dating, we show that optical resetting differs for the three different emissions, with the emission at ∼1.41 eV not being reset in some samples even after 18 h of solar bleaching.

We derive expressions for classical isothermal and adiabatic elastic constants for periodic systems with the boundary contributions included explicitly. The potential-dependent part of these expressions is written in terms of potential energies of atomic groups that make up the total potential energy. It is shown that in the thermodynamic limit, the Born term, which depends on the second derivatives of potential energy, can be expressed exactly in terms of equilibrium averages that involve two types of atomic-group virials. As a result, the new form of the Born term involves only first derivatives of either atomic-group or total potential energies. The derived elastic constant expressions involving the two forms of the Born terms are tested and compared using molecular-dynamics simulations of crystalline argon and silicon. For both materials, the elastic constants obtained using the two forms of the Born term are in good agreement. In particular, the new form of the Born term converges to the same value as the original Born term but at a slower rate. The results for silicon also agree well with the results from the previous molecular-dynamics studies.

In this work, we have studied the effect of mass variation of graphene oxide (GO) on the lattice parameter, crystal structure, crystal size, surface morphology, and optical properties of Fe3O4/GO nanocomposite materials. The Fe3O4 was synthesized from the iron sand obtained from Glagah beach located in Kulon Progo, Yogyakarta, Indonesia by using the coprecipitation method. The resulted Fe3O4 was then doped with GO to become Fe3O4/GO nanocomposites by means of ultrasonication method. The composition of the nanocomposites was 5 mg Fe3O4 and 4 mass variations of GO, namely 4 mg, 8 mg, 12 mg, and 16 mg. Each composition was then dispersed in distilled water with a ratio of 1:3 for Fe3O4/GO to distilled water and ultrasonicated for 70 minutes at 35C. Based on XRD data, the mass variation of GO in Fe3O4/GO nanocomposites did not affect the lattice parameters and crystal structure, but did affect the crystal size. The lattice parameter value obtained in Fe3O4/GO is a=b=c=8,3967 A with a cubic crystal structure that has a crystal size of 167,9 nm, 169,1 nm, 158,3 nm, and 62,3 nm corresponding to the GO addition of 4 mg, 8 mg, 12 mg, and 16 mg, respectively. The typical SEM image of the Fe3O4/GO nanocomposite showed the surface morphology of GO in the form of sheets with a length of 6070,52 nm and a width of 2135,8 nm; and Fe3O4 in the form of grain with a grain size of 720 nm. Furthermore, the EDS characterization showed that the chemical composition of the main ingredients of sample 1 was 42,35% C, 39,9% O, and 6,06% Fe with 11,69% impurities, which indicates the success of the production of Fe3O4/GO nanocomposite. In addition, the UV-Vis spectra of the samples showed the change of the band gap of the nanocomposites with the change of GO composition, i.e. 1,94 eV and 2,9 eV for GO composition of 4 mg, 8 mg, respectively. Based on these XRD, SEM-EDS, and UV-Vis characterizations, the Fe3O4/GO nanocomposites have been successfully fabricated with the properties of crystal size and band gap are significantly affected by the addition of GO composition.

New nonbonded parameters of a “6-exp-1” all-atom force field are presented for amines, imidazoles, amides, and carboxylic acids. These results are part of our work to derive a general force field for the prediction of crystal and protein structures (the nonbonded parameters for aliphatic and aromatic hydrocarbons and alcohols were published recently, J. Phys. Chem. B 2003, 107, 7143). The parameters were derived by using our global-optimization-based method (J. Phys. Chem. B 2003, 107, 712) which provides the best possible set of parameters for crystal structure prediction for a given form of the potential. The method consists of two steps. First, an initial set of parameters is derived from ab initio quantum mechanical interaction energies of dimers; then, the initial set is refined to satisfy the following criteria: the parameters should reproduce the observed crystal structures and sublimation enthalpies, and the experimental crystal structure should correspond to the global minimum of the potential. The refinement procedure uses information about the potential energy surface of the crystal obtained by global energy minimization. Vector Monte Carlo (J. Phys. Chem. B 2003, 107, 712) and force-minimization methods are used in the refinement step. The parameters presented in this paper reproduce experimental crystal structures with high accuracy. The experimental structures of all molecules tested were found as the global or one of the lowest-energy minima of the potential.

Ion/molecule reactions of dimethylamine with protonated analytes facilitate the identification of tertiary N-oxide functionalities in a linear quadrupole ion trap mass spectrometer

New ionic plastic crystals of NR4BEt3Me (R = Me and Et) and NRxR′4−xBEt3Me (R = Et, R′ = Me and Pr, x = 1–3) were formed in a new region of plastic crystal. In this area, globular cations and anions are assembled by weak interactions. On the basis of our results of 1H and 13C NMR spectra and electrical conductivity measurements, we could conclude that isotropic reorientation and self-diffusion of globular cations and anions were detected in the crystal. X-ray diffraction (XRD) lines observed in RxR′4−xBEt3Me (R = Et, R′ = Me, x = 0–4) revealed a CsCl-type cubic crystal structure. Additionally, DSC spectra revealed that this new class of plastic crystals displays low phase-transition temperatures in the plastic phase and have high melting points. The former tendency is frequently detected in molecular plastic crystals while the latter is often found in ionic plastic crystals.