New soft X-ray facility SINS for surface and nanoscale science at SSLS

Yu, Xiaojiang; Wilhelmi, O.; Moser, H. O.; Vidyaraj, S V; Gao, Xingyu; Wee, Andrew Thye Shen; Nyunt, Tun; Huang, Qian; Zheng, Hongwei

doi:10.1016/j.elspec.2005.01.256

Cited by 117 publications

(91 citation statements)

References 8 publications

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“…NEXAFS spectra were acquired on the SINS beamline [33] of the Singapore Synchrotron Light Source using linearly-polarized X-rays (polarization purity, P ≥ 0.97) monochromatized by a 57.4 m radius spherical grating with 600 line mm -1 . Background pressure was less than 5 × 10 -10 mbar (1 bar = 100 000 Pa).…”

Section: Experimental General Procedures and Nexafsmentioning

confidence: 99%

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Chua

Dipankar

et al. 2007

Advanced Materials

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The orientation and packing of semiconducting polymer chains at film interfaces crucially affects charge injection and transport at those interfaces. Although X-ray diffraction techniques have been used extensively as a structural probe, they are not particularly sensitive to these interfaces. Near-edge X-ray absorption fine-structure spectroscopy (NEXAFS), on the other hand, is sensitive to surface orientation and has been applied to investigate polymer structures, for example, in polyimide, [1] polyfluorene, [2] and polythiophene.[3] Here we show that NEXAFS band shapes and intensities are in fact also sensitive to the intermolecular p-interaction in regioregular poly(3-hexylthiophene) (rreg-P3HT) films. NEXAFS spectra of the same material deposited from different solvents and processing conditions are substantially different. This indicates a far more extensive breakdown of the "building-block" picture than previously reported, [4,5] allowing p-interactions to be studied. The surface sensitivity has recently been established to be ca. 2.5 nm for the total electron yield in rreg-P3HT, [6] which is highly relevant to interfacial charge transport and surface-induced self-organization. Rreg-P3HT thin films were deposited from a wide range of solvent qualities, and both the air and substrate interfaces were studied. Delamination was used to expose the substrate interface. We found that: i) the thiophene (Th)-ring orientation at both these interfaces was disordered and showed only a weak preference for the out-of-plane (oop) stacking favorable for field-effect mobility (l FET ); ii) the hexyl side chains were also disordered; and iii) the interchain p-interaction was strongly dependent on the deposition solvent quality, and varied in opposite directions between the air and substrate interfaces, being generally better at the substrate than the air interface. Direct imaging by friction-mode atomic force microscopy (AFM) revealed the expected presence of a mosaic surface morphology with a finer length scale than surface topography. Transistor l FET measurements suggested that the high l FET of rreg-P3HT is still limited by heterogeneity, which we attribute to the distribution of interface domains of varying orientation and/or packing. This ability to directly measure chain segmental orientation and interaction at the interfaces will open the way to their systematic optimization for even higher device performance.The self-organization behavior of polymers at interfaces is of significant scientific and technological interest. Much of the structural knowledge of conjugated polymers such as rreg-P3HT, a prototype high-l FET polymer, has come from wideangle [7,8] and grazing-angle X-ray diffraction (GIXRD) [9,10] studies. For polythiophenes, the chains p-stack to give short interchain distances (3.8 Å in rreg-P3HT) in the lamellae plane, but long distances (17 Å in rreg-P3HT) between lamellae separated by the alkyl side chains. [7][8][9][10] These p stacks further show a preference for either oop stacking in which the plane...

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Section: Experimental General Procedures and Nexafsmentioning

confidence: 99%

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Chua

Dipankar

et al. 2007

Advanced Materials

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“…All the measurements were performed at room temperature in an ultrahigh vacuum chamber with a base pressure of 1 Â 10 À 10 mbar (ref. 53). The photon energy was calibrated using the Au 4f 7/2 core level peak at 84.0 eV of a sputter-cleaned gold foil in electrical contact with the sample.…”

Section: Methodsmentioning

confidence: 99%

Controlling the direction of rectification in a molecular diode

et al. 2015

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A challenge in molecular electronics is to control the strength of the molecule-electrode coupling to optimize device performance. Here we show that non-covalent contacts between the active molecular component (in this case, ferrocenyl of a ferrocenyl-alkanethiol self-assembled monolayer (SAM)) and the electrodes allow for robust coupling with minimal energy broadening of the molecular level, precisely what is required to maximize the rectification ratio of a molecular diode. In contrast, strong chemisorbed contacts through the ferrocenyl result in large energy broadening, leakage currents and poor device performance. By gradually shifting the ferrocenyl from the top to the bottom of the SAM, we map the shape of the electrostatic potential profile across the molecules and we are able to control the direction of rectification by tuning the ferrocenyl-electrode coupling parameters. Our demonstrated control of the molecule-electrode coupling is important for rational design of materials that rely on charge transport across organic-inorganic interfaces.

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“…In the first method, the XAS data were taken with two opposite circular polarizations relative to a fixed sample magnetization direction (this was achieved by turning on a 0.2 T field for a short duration). The absorption coefficients, m + and m − , which are directly proportional to XAS, have a photon helicity (spin) direction parallel (m + ) and anti-parallel (m − ) to the sample magnetization and magnetic field (M , H ) direction, respectively [27,28]. Therefore, the SXMCD is equal to (m − − m + ).…”

Section: (B) Magnetic Propertiesmentioning

confidence: 99%

“…Although the SQUID data clearly show the presence of room temperature FM in the Ti 1−x Ta x O 2 (x ∼ 0.05) films (prepared at 600 • C), they do not provide microscopic insight into the origin of the ferromagnetic ordering. Thus, SXMCD measurements were performed in total yield mode as a function of photon energy, using elliptically polarized light with a degree of circular polarization p = 90 and an energy resolution of 0.25 eV at the SINS beam line of the Singapore Synchrotron Light Source [27] because this technique is not only element-specific but also capable of estimating both the spin and orbital magnetic moments and their anisotropies [28][29][30]. To measure the in-plane magnetic moments, the light was incident at a grazing angle of 20 • from the sample surface, with its propagation direction along the sample in-plane magnetization direction.…”

Section: (B) Magnetic Propertiesmentioning

confidence: 99%

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti _{1−
x} Ta _x O ₂ ( x ∼0.05) thin films

Rusydi

Dhar

Barman

et al. 2012

Phil. Trans. R. Soc. A.

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We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti 1−x Ta x O 2 (x ∼ 0.05) thin films grown by pulsed laser deposition on LaAlO 3 substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, protoninduced X-ray emission, X-ray absorption spectroscopy (XAS) and time-of-flight secondary-ion mass spectrometry indicated negligible magnetic contaminants in the films. The presence of FM with concomitant large carrier densities was determined by a combination of superconducting quantum interference device magnetometry, * Authors for correspondence (phyandri@nus.edu.sg; eleds@nus.edu.sg; venky@nus.edu.sg). † These authors contributed equally to this work. electrical transport measurements, soft X-ray magnetic circular dichroism (SXMCD), XAS and optical magnetic circular dichroism, and was supported by first-principles calculations. SXMCD and XAS measurements revealed a 90 per cent contribution to FM from the Ti ions, and a 10 per cent contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites, though carrier activation was only 50 per cent at 5 per cent Ta concentration, implying compensation by cationic defects. The role of the Ti vacancy (V Ti ) and Ti 3+ was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the V Ti signal was strong while the Ti 3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, V Ti sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to FM in wide-band-gap semiconducting oxides without any magnetic elements.

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New soft X-ray facility SINS for surface and nanoscale science at SSLS

Cited by 117 publications

References 8 publications

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Controlling the direction of rectification in a molecular diode

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti _{1−
x} Ta _x O ₂ ( x ∼0.05) thin films

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New soft X-ray facility SINS for surface and nanoscale science at SSLS

Cited by 117 publications

References 8 publications

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Solvent Effects on Chain Orientation and Interchain π‐Interaction in Conjugated Polymer Thin Films: Direct Measurements of the Air and Substrate Interfaces by Near‐Edge X‐ray Absorption Spectroscopy

Controlling the direction of rectification in a molecular diode

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti 1− x Ta x O 2 ( x ∼0.05) thin films

Contact Info

Product

Resources

About

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti _{1−
x} Ta _x O ₂ ( x ∼0.05) thin films