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Ram Chandra Subedi

Other affiliations: University of Georgia
Bio: Ram Chandra Subedi is an academic researcher from King Abdullah University of Science and Technology. The author has contributed to research in topics: Nanowire & Molecular beam epitaxy. The author has an hindex of 15, co-authored 31 publications receiving 592 citations. Previous affiliations of Ram Chandra Subedi include University of Georgia.

Papers
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Journal ArticleDOI
TL;DR: A review of major advances in organic spin valve research can be found in this paper, where the underlying physics in spin injection and transport, high temperature operations, and functionality are discussed.
Abstract: Organic spintronics is an emerging and potential platform for future electronic devices. Significant progress has been made in understanding the spin injection, manipulation, and detection in organic spin valves in the past decade plus since its discovery. Studies have also been advanced to a range of materials combination of organic semiconductors and ferromagnetic electrodes for improving their performance especially at high temperatures. In addition, there are several remarkable studies on development of the spin valves as a multifunctional device. However, the research in this field is still in its infancy and there is a need to resolve many issues which keep this field far away from applications. In this report, we review major advances in organic spin valves such as understanding the underlying physics in spin injection and transport, high temperature operations, and functionality. We also highlight some of the outstanding challenges in this promising research field. Finally, we suggest an outlook on the future of organic spintronics.

102 citations

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TL;DR: In this article, a comprehensive review on the recent achievements made in the field of III-nitride nanowires is presented, along with their respective applications, including light-emitting diodes, lasers, photodetectors, and photoelectrodes.

69 citations

Journal ArticleDOI
TL;DR: This work investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules and found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures.
Abstract: We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Julliere equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

53 citations

Journal ArticleDOI
TL;DR: In this article, a novel nanowire structure adopting a graded-index separate confinement heterostructure (GRINSCH) in which the active region is sandwiched between two compositionally graded AlGaN layers, namely, a GRINSCH diode, is proposed.
Abstract: High-density dislocations in materials and poor electrical conductivity of p-type AlGaN layers constrain the performance of the ultraviolet light emitting diodes and lasers at shorter wavelengths. To address those technical challenges, we design, grow, and fabricate a novel nanowire structure adopting a graded-index separate confinement heterostructure (GRINSCH) in which the active region is sandwiched between two compositionally graded AlGaN layers, namely, a GRINSCH diode. Calculated electronic band diagram and carrier concentrations show an automatic formation of a p–n junction with electron and hole concentrations of ∼1018 /cm3 in the graded AlGaN layers without intentional doping. The transmission electron microscopy experiment confirms the composition variation in the axial direction of the graded AlGaN nanowires. Significantly lower turn-on voltage of 6.5 V (reduced by 2.5 V) and smaller series resistance of 16.7 Ω (reduced by nearly four times) are achieved in the GRINSCH diode, compared with the ...

48 citations


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01 Mar 2004
TL;DR: In this paper, a self-aligned regioregular poly(3-hexylthiophene) (P3HT) has been used to control the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (NH2, NH2, OH, and CH3).
Abstract: With the aim of enhancing the field-effect mobility by promoting surface-mediated two-dimensional molecular ordering in self-aligned regioregular poly(3-hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (–NH2, –OH, and –CH3). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field-effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm2 V–1 s–1. This surprising increase in field-effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the π–H interactions between the thienyl-backbone bearing π-systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.

391 citations

Journal ArticleDOI
07 Jun 2017
TL;DR: In this article, the authors highlight recent research in which small-molecule chirality has had an enabling impact in technological applications, including the detection and emission of chiral light, help to control molecular motion, or provide a means to control electron spin and bulk charge transport.
Abstract: Chirality is a fundamental symmetry property; chiral objects, such as chiral small molecules, exist as a pair of non-superimposable mirror images. Although small-molecule chirality is routinely considered in biologically focused application areas (such as drug discovery and chemical biology), other areas of scientific development have not considered small-molecule chirality to be central to their approach. In this Review, we highlight recent research in which chirality has enabled advancement in technological applications. We showcase examples in which the presence of small-molecule chirality is exploited in ways beyond the simple interaction of two different chiral molecules; this can enable the detection and emission of chiral light, help to control molecular motion, or provide a means to control electron spin and bulk charge transport. Thus, we demonstrate that small-molecule chirality is a highly promising avenue for a wide range of technologically oriented scientific endeavours. Although it is a fundamental property of many small molecules, chirality is not widely exploited in materials applications as its benefits are not widely recognized — indeed, the need for stereoselective synthesis may be seen as a disadvantage. In this Review, we highlight recent research in which chirality has had an enabling impact in technological applications.

377 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide guidelines on successfully choosing spacers and incorporating them into crystalline materials and optoelectronic devices and provide a summary of various synthetic methods to act as a tutorial for groups interested in pursuing synthesis of novel 2D halide perovskites.
Abstract: Two-dimensional (2D) halide perovskites have emerged as outstanding semiconducting materials thanks to their superior stability and structural diversity. However, the ever-growing field of optoelectronic device research using 2D perovskites requires systematic understanding of the effects of the spacer on the structure, properties, and device performance. So far, many studies are based on trial-and-error tests of random spacers with limited ability to predict the resulting structure of these synthetic experiments, hindering the discovery of novel 2D materials to be incorporated into high-performance devices. In this review, we provide guidelines on successfully choosing spacers and incorporating them into crystalline materials and optoelectronic devices. We first provide a summary of various synthetic methods to act as a tutorial for groups interested in pursuing synthesis of novel 2D perovskites. Second, we provide our insights on what kind of spacer cations can stabilize 2D perovskites followed by an extensive review of the spacer cations, which have been shown to stabilize 2D perovskites with an emphasis on the effects of the spacer on the structure and optical properties. Next, we provide a similar explanation for the methods used to fabricate films and their desired properties. Like the synthesis section, we will then focus on various spacers that have been used in devices and how they influence the film structure and device performance. With a comprehensive understanding of these effects, a rational selection of novel spacers can be made, accelerating this already exciting field.

343 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the most striking recent advances in the field of ultrafast spectroscopy of semiconductors and their nanostructures and present a monograph written by an outstanding expert.
Abstract: This monograph, written by an outstanding expert in time resolved spectroscopy of semiconductors, presents the most striking recent advances in the field of ultrafast spectroscopy of semiconductors and their nanostructures. The book contains 8 chapters with in total 1160 references and 186 figures, preface and subject index. It begins with an introductory chapter on basic concepts of semiconductor physics and ultrafast spectroscopic techniques. The following five chapters are arranged in the order of occurrence of events in a homogeneous semiconductor following photoexcitation by an ultrashort pulse. These events comprise four temporally-overlapping regimes:

342 citations