Development of Ultrafast Broadband Electronic Sum Frequency Generation for Charge Dynamics at Surfaces and Interfaces

Understandings of population and relaxation of charges at surfaces and interfaces are essential to improve charge collection efficiency for energy conversion, catalysis, and photosynthesis. Existing time-resolved surface and interface tools are limited to either under ultrahigh vacuum or in a narrow wavelength region with the loss of spectral information. There lacks an efficient time-resolved surface/interface-specific electronic spectroscopy under ambient conditions for the ultra fast surface/interface dynamics. Here we developed a novel technique for surface/interface-specific broadband electronic sum frequency generation (ESFG). The broadband ESFG was based on a stable two-stage BiB3O6 crystal-based optical parametric amplifier, which generates a strong broadband short-wave infrared (SWIR) from 1200 nm to 2400 nm. A resultant surface spectrum covers almost all visible light from 480 nm to 760 nm, combined a broadband electronic second harmonic generation (ESHG) with the ESFG from the SWIR laser source. We further developed the steady-state and transient broadband ESFG and ESHG techniques to investigate the structure and dynamics of charges at oxidized p-type GaAs (100) semiconductor surfaces, as an example. Both the steady-state and transient experiments have shown that two surface states exist inside the bandgap of the GaAs. The kinetic processes at the GaAs surface include both the population and recombination of the surface states after photoexcitation, in addition to the build-up of the space photo-voltage (SPV). The build-up SPV occurs with a rate of 0.56 ± 0.07 ps−1, while the population rate of the surface states exhibits a two-body behavior with a rate constant of (0.012 ± 0.002) × 1012 s−1 cm2. The photo-generated electron-hole pairs near the surface recombine with a rate of 0.002 ± 0.0002 ps−1 for the oxidized p-type GaAs (100). All the methodologies developed here are readily applied to any optically accessible interfaces and surfaces, in particular buried interfaces under ambient conditions

Systematic study of proton radioactivity of spherical proton emitters within various versions of proximity potential formalisms

In this work we present a systematic study of the proton radioactivity half-lives of spherical proton emitters within the Coulomb and proximity potential model. We investigate 28 different versions of the proximity potential formalisms developed for the description of proton radioactivity, $\mathcal{\alpha}$ decay and heavy particle radioactivity. It is found that 21 of them are not suitable to deal with the proton radioactivity, because the classical turning points $r_{\text{in}}$ cannot be obtained due to the fact that the depth of the total interaction potential between the emitted proton and the daughter nucleus is above the proton radioactivity energy. Among the other 7 versions of the proximity potential formalisms, it is Guo2013 which gives the lowest rms deviation in the description of the experimental half-lives of the known spherical proton emitters. We use this proximity potential formalism to predict the proton radioactivity half-lives of 13 spherical proton emitters, whose proton radioactivity is energetically allowed or observed but not yet quantified, within a factor of 3.71.Comment: 10 pages, 5 figures. This paper has been accepted by The European Physical Journal A (in press 2019

Systematic study of α\boldsymbol{\mathcal{\alpha}} decay of nuclei around Z=82\boldsymbol{Z=82}, N=126\boldsymbol{N=126} shell closure within the cluster-formation model and proximity potential 1977 formalism

In the present work, we systematically study the $\mathcal{\alpha}$ decay preformation factors $P_{\alpha}$ within the cluster-formation model and $\mathcal{\alpha}$ decay half-lives by the proximity potential 1977 formalism for nuclei around $Z=82$, $N=126$ closed shells. The calculations show that the realistic $P_{\alpha}$ is linearly dependent on the product of valance protons (holes) and valance neutrons (holes) $N_pN_n$. It is consistent with our previous works [X.-D. Sun \textit{et al.}, \href{https://journals.aps.org/prc/abstract/10.1103/PhysRevC.94.024338}{ Phys. Rev. C 94, 024338 (2016)}, J.-G. Deng \textit{et al.}, \href{https://journals.aps.org/prc/abstract/10.1103/PhysRevC.96.024318}{Phys. Rev. C 96, 024318 (2017)}], which $P_{\alpha}$ are model-dependent and extracted from the ratios of calculated $\mathcal{\alpha}$ half-lives to experimental data. Combining with our previous works, we confirm that the valance proton-neutron interaction plays a key role in the $\mathcal{\alpha}$ preformation for nuclei around $Z=82$, $N=126$ shell closures whether the $P_{\alpha}$ is model-dependent or microcosmic. In addition, our calculated $\mathcal{\alpha}$ decay half-lives by using the proximity potential 1977 formalism taking $P_{\alpha}$ evaluated by the cluster-formation model can well reproduce the experimental data and significantly reduce the errors.Comment: 4 figures, 7 tables; Accepted by Physical Review

Differentiation between tuberculosis and leukemia in abdominal and pelvic lymph nodes: evaluation with contrast-enhanced multidetector computed tomography

PURPOSE: To compare the characteristics of tubercular vs. leukemic involvement of abdominopelvic lymph nodes using multidetector computed tomography (CT). MATERIALS AND METHODS: We retrospectively reviewed multidetector computed tomography features including lymph node size, shape, enhancement patterns, and anatomical distribution, in 106 consecutive patients with newly diagnosed, untreated tuberculosis (55 patients; 52%) or leukemia (51 patients; 48%). In patients with leukemia, 32 (62.7%) had chronic lymphocytic leukemia, and 19 (37.3%) had acute leukemias; of these, 10 (19.6%) had acute myeloid leukemia, and 9 (17.6%) had acute lymphocytic leukemia. RESULTS: The lower para-aortic (30.9% for tuberculosis, 63.2% for acute leukemias and 87.5% for chronic lymphocytic leukemia) and inguinal (9.1% for tuberculosis, 57.9% for acute leukemias and 53.1% for chronic lymphocytic leukemia) lymph nodes were involved more frequently in the three types of leukemia than in tuberculosis (both with

Molecular Rotation in 3 Dimensions at an Air/Water Interface Using Femtosecond Time Resolved Sum Frequency Generation

This paper presents the first study of the rotations of rigid molecules in 3 dimensions at the air/water interface, using the femtosecond time resolved sum frequency generation (SFG) technique. For the purpose of this research, the aromatic dye molecule C153 was chosen as an example of a molecule having two functional groups that are SFG active, one being the hydrophilic −−C==O group and the other the hydrophobic −−CF3 group. From polarized SFG measurements, the orientations of the two chromophores with respect to the surface normal were obtained. On combining these results with the known relative orientation of the two chromophores in the molecule yields the absolute orientation of C153 at the air/water interface. It was found that the −−CF3 axis projected towards the bulk air at an angle of 59○ with respect to the interface normal and the −−C==O group projected towards the bulk water at an angle of 144○ . In order to observe the rotational motions of C153 at the air/water interface, the approach was used to perturb the ground electronic state equilibrium orientational distribution using a polarized resonant pump pulse, which preferentially excites ground state molecules that have their electronic S0 → S1 transition moment aligned closely to the electric field of the incident pump pulse. As a consequence of the photoselection perturbation, the orientational distribution of the remaining ground state molecules was not the equilibrium distribution. Similarly, the orientational distribution of the excited state molecules that were created by the polarized pump pulse was not in their final equilibrium orientational distribution. The rotational motions of the interfacial molecules towards equilibrium were obtained from time dependent measurements of the intensities of the SFG signal generated by the simultaneous incidence at the air/water interface of a visible probe pulse plus an IR probe pulse. In this way, the recovery times to achieve the orientational equilibrium of the two chromophores including the orientation of the normal of the C153 plane with respect to the interface were obtained. The photo-selection process shifts the average orientation angle of the hydrophilic −−C==O group by an increase of 4○ ± 0.6○ with a rotational recovery time constant of 130 ± 20 ps, which is the time to return to an orientational equilibrium distribution. The hydrophobic –CF3 group undergoes a shift that increases its angle by 8○ ± 1.5○ with a rotational recovery time constant of 210 ± 38 ps. We find that the orientational change of the molecular normal is 4○ ± 0.5○ and has a rotational recovery time constant of 125 ± 26 ps. The interface-specific time-dependent polarized measurements allowed us to monitor the orientational motions of molecules at interfaces, both in 3 dimensions and in real time