Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy

This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques

The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S(2-) (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S(2-) species, but significantly increases the concentration of larger S clusters [polysulfides (Sn(2-), n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples.

The electronic and magnetic properties of strained La0.85Zr0.15MnO3films

The electronic and magnetic properties of strained tetravalent-ion-doped La0.85Zr0.15MnO3 (LZMO) thin films that were epitaxially grown on SrTiO3 (STO) and MgO substrates were studied using temperature-dependent x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) at the Mn L3,2- and K-edge. XRD studies reveal that the LZMO thin films have compressive and tensile strains on the STO and MgO substrates, respectively. As temperature is reduced from room temperature to below magnetic transition temperature, the preferentially occupied Mn majority-spin eg orbital changes from the in-plane dx2-y2 to the out-of-plane d3z2-r2 orbital for LZMO/STO, and vice versa for LZMO/MgO. Experimental results suggest that the new hopping path that is mediated by the Mn2+ ions triggers a stronger d3z2-r2 orbital ordering of Mn3+ ions and enhances the ferromagnetic coupling between the Mn spin moments of t2g electrons in LZMO/STO, whereas the tensile strain stabilizes the dx2-y2 orbital by inducing lattice distortions of the MnO6 octahedra in LZMO/MgO.

First-principles method of propagation of tightly bound excitons: verifying the exciton band structure of LiF with inelastic x-ray scattering

We propose a simple first-principles method to describe the propagation of tightly bound excitons. By viewing the exciton as a composite object (an effective Frenkel exciton in Wannier orbitals), we define an exciton kinetic kernel to encapsulate the exciton propagation and decay for all binding energies. Applied to prototypical LiF, our approach produces three exciton bands, which we verified quantitatively via inelastic x-ray scattering. The proposed real-space picture is computationally inexpensive and thus enables study of the full exciton dynamics, even in the presence of surfaces and impurity scattering. It also provides an intuitive understanding to facilitate practical exciton engineering in semiconductors, strongly correlated oxides, and their nanostructures.

The study on core conflictual relationship of short-term counseling

This study utilizes the Core Conflictual Relationship Theme Method (CCRT; Luborsky and Crits-Christoph, 1997) on process study of short-term counseling. The purpose was to evaluate the formation and variation of interpersonal conflicts presented by nine clients, so as to enhance the understanding of the core conflicts of each client and how these clients were influenced by short-term counseling. CCRT was conducted by two raters to analyze the content of core conflictual relationship themes. The raters started with taking a twenty-minute vignette from four tapes of the counseling sessions which were the 1st, 2nd, 11th and the 12th. A transcript was taken for each session and the raters searched for relationship episodes (REs) in it. Further, other main persons were identified in REs. Three components, including wish(W), response from others(RO), and response of self(RS) were investigated and analyzed. The raters calculated the appearance frequency of each component and transferred them into formulation of relationship theme in written language. The findings are as follows. (1) The interrater reliabilities between the two raters over W, RO, RS are significant (Kappa = .21-.82, P < .01) (2) The most frequently described other main persons in 201 REs were 'clleague' (N = 87, 43. 3%), the second 'self' (N = 42, 32.8%) and the third 'family members' (N = 41, 20. 4%). The first three described wishes were 'to assert self and be independent' (N = 66, 32.8%), 'to be close and accepted' (N = 48, 23.9%), and 'to be loved and understood' (N = 35, 17.4%) (3) The change of pervasiveness scores of each component in terms of positive and negative responses evaluated by t-test were found to decrease significantly in NRO (r = -2.73, p < .05). The score was most significantly decreased in 'rejecting and opposing' item (t = -3.83, p < .01). Conclusions and suggestions regarding application of the Core Conflictual Relationship Theme analytical and categorization methods in the Chinese context are presented.

The inducible lactose operator-repressor system is functional in the whole animal

Mouse liver cell lines that bear a stably integrated lactose operon repressor (lacI) gene and a Ha-ras gene linked to a lactose operator-containing SV40 early promoter were generated. When grown in medium containing more than 0.1 mM isopropyl beta-D-thiogalactoside (IPTG), the Ha-ras gene was induced up to 20-fold. Maximum induction of Ha-ras gene expression occurred after 12 h of exposure. The tumorigenicity of these cell lines in syngeneic mice was enhanced when the mice were maintained on drinking water containing 12.5 mM IPTG. Ha-ras gene expression in tumors was strongly induced in the presence of IPTG in vivo. Induction of Ha-ras gene expression in mice was consistently observed after 48 hr of exposure to drinking water containing IPTG. This system provides an approach for studying the function of oncogene in vivo as well as other genes of interest.

Expression pattern of nuclear p53 is unique in COS-1 cells

As p53 is transcriptionally inactive in COS-1 cells, we felt it would be interesting to study the relative time course of expression of nuclear p53 and the onset of S phase. Our results indicated that the expression of nuclear p53 lagged behind the onset of S phase in COS-1 cells. In addition, rapid nuclear expression of p53, probably resulting from nuclear translocation, occurred immediately after the addition of serum into COS1 cells. No such phenomena were found in B104-1 and BHK cells.