Shabbir M. Mian

Large Work Function Shift of Gold Induced by a Novel Perfluorinated Azobenzene-Based Self-Assembled Monolayer

Tune it with light! Self-assembled monolayers on gold based on a chemisorbed novel azobenzene derivative with a perfluorinated terminal phenyl ring are prepared. The modified substrate shows a significant work function increase compared to the bare metal. The photo-conversion between trans and cis isomers chemisorbed on the surface shows great perspectives for being an accessible route to tune the gold properties by means of light.

Experimental and theoretical investigation of thermal lensing effects in mode-locked femtosecond Z-scan experiments

We show that the closed aperture refractive Z-scan signatures using high-repetition rate ultrafast laser systems are strongly influenced by thermal lensing. We demonstrate that a stationary thermal lens develops even in the case of very low linear absorption. In addition, we have developed a stationary thermal lens model using the Gaussian decomposition method and applied it for the first time to Z-scan experiments and find good agreement between theory and experiment.

Experimental and modelling study of pulsed optically stimulated luminescence in quartz, marble and beta irradiated salt

Optical stimulation luminescence (OSL) signals can be obtained using continuous-wave optical stimulation (CW-OSL), the linear modulation optical stimulation method (LM-OSL) and the time-resolved optical stimulation (TR-OSL) method. During TR-OSL measurements, the stimulation and emission of luminescence are experimentally separated in time by using short light pulses. This paper presents new TR-OSL data for annealed high purity synthetic quartz, for marble and for commercially available iodized salt. A new type of behaviour for TR-OSL signals for quartz and iodized salt is presented, in which the OSL signal exhibits a nonmonotonic behaviour during optical stimulation; this type of behaviour has not been reported previously in the literature for quartz. Furthermore, a luminescence component with very long luminescence lifetime is reported for some quartz aliquots, which may be due to the presence of a delayed-OSL (DOSL) mechanism in quartz. A new kinetic model for TR-OSL in quartz is presented, which is based on a main electron trap and on several luminescence centres. The model is used to quantitatively fit several sets of experimental data of pulsed optically stimulated luminescence from quartz.

Increased efficiency of light-emitting diodes incorporating anodes functionalized with fluorinated azobenzene monolayers and a green-emitting polyfluorene derivative

We investigate the functionalization of gold anodes with azobenzene-based self-assembled monolayers (AZO-SAM) and the influence of such functionalization on the external quantum efficiency (EQE) of polyfluorene-based light-emitting diodes (LEDs). Photoluminescence and electroluminescence measurements show that the AZO-SAMs do not modify the shape of the emission spectrum of the active layer. Instead, AZO-SAMs enhance the EQE of LEDs by an order of magnitude (from 0.018% to 0.18%) and decrease the turn-on voltage from 7.9 V to 6.2 V by reducing the injection barrier at the anode, thus promoting a better balance between hole and electron populations in the active layer.

Using Nonprinciple Rays to Form Images in Geometrical Optics.

Constructing ray diagrams to locate the image of an object formed by thin lenses and mirrors is a staple of many introductory physics courses at the high school and college levels, and has been the subject of some pedagogy-related articles. Our review of textbooks distributed in the United States suggests that the singular approach involves drawing principle rays to locate an objects image. We were pleasantly surprised to read an article in this journal by Suppapittayaporn et al. in which they use an alternative method to construct rays for thin lenses based on a “tilted principle axis” (TPA). In particular, we were struck by the generality of the approach (a single rule for tracing rays as compared to the typical two or three rules), and how it could help students more easily tackle challenging situations, such as multi-lens systems and occluded lenses, where image construction using principle rays may be impractical. In this paper, we provide simple “proofs” for this alternative approach for the case of thin lenses and single refracting surfaces.

Hybrid-organic photonic structures for light emission modification

We report the modification of the photoluminescence (PL) and decay rates of two different green-emitting conjugated polymers incorporated into photonic crystals with the stop-bands spectrally tuned on their emission. We observe both suppression (in the stop-band) and enhancement (at the high-energy band-edge) of the photoluminescence. Time-resolved measurements also reveal a concomitant modification of the emission lifetime that is enhanced at the band-edge and suppressed within the stop-band, thus confirming a variation of the radiative decay rate of the excitations in such photonic nanostructures. We propose two examples of fluorescent photonic composite systems. The first consists of a hybrid Si-organic system, obtained by infiltration of the polymer inside a rugate filter (a 1D photonic crystal). The second example is a fully organic system obtained by self-assembling of solvent-compatible microspheres-polymer system for obtaining a synthetic opal (a 3D photonic crystal) with a uniform distribution of the emitting material across the photonic structure.

Attitudes of Undergraduate General Science Students Toward Learning Science and the Nature of Science

We investigated general science students’ attitudes regarding the acquisition of scientific knowledge and the nature of science by administering a 32‐item attitudinal survey. To assemble a representative array of epistemological attitudes at our institution and to determine the impact of instruction, we administered this survey to over 250 students from 19 sections of three general science courses. We characterized the instructional styles for each course using three broad categories: Traditional, Transitional, and Learning‐centered. This paper focuses on the impact those different instructional styles had on students’ epistemological beliefs.

Enhanced optical coupling into periodically segmented KTiOPO/sub 4/ waveguides using interference effects

Summary form only given.This work demonstrates the use of interference effects in enhancing the coupling of an input laser beam into the tight cross-section of a periodically segmented KTiOPO/sub 4/ waveguide yielding a three fold increase in its SHG output. In combination with the differential heating technique reported earlier, the use of this technique can result in compact blue laser sources meeting the minimum power requirements for several applications.