Himadri Majumdar | VTT Techn. Res. centre of Finland (original) (raw)
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Papers by Himadri Majumdar
Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene ... more Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene thin film for
spintronics applications. The use of organic material for spintronics is motivated by the advantages such as long spin
diffusion length due to low spin-orbit and hyperfine coupling, chemical tuning of electronic functionality, easy
structural modifications, ability of self-assembly and mechanical flexibility etc. However, a major drawback of OS is its low mobility compared to inorganic semiconductors. The PLD growth of rubrene aims on fabricating OS films under
more controlled environment to achieve higher crystalline order to improve its mobility and spin coherence length.
Among organic materials, rubrene reveals the highest hole mobility - up to 40 cm2/(V∙s) and can be exploited in organic
light-emitting diodes (OLEDs) or field-effect transistors (OFETs) 4. In this work the rubrene thin films are produced
from hardened pellets in vacuum using Nd:YAG pulsed laser operated at 1064 nm, 2 Hz and energy fluence around 0.2
J/cm2. For the reference rubrene samples on SiO2 glass the AFM data reveal continuous 5-7 nm thick films. The
amorphous structures are confirmed by XRD measurements and also Raman spectra which show signatures of both
tetracene and phenyl bands and a broadband at 1373 cm-1. The obtained results indicate that continuous, defect-free
rubrene films can be prepared by means of PLD for investigation of the spin polarization properties of organic-inorganic hybrids. Further studies are on the way to improve crystalline qualities of the rubrene films for less grain boundary
related defects and improved mobility and spin diffusion length.
The purpose of this work is to fabricate large-scale solution processable graphene-based films fr... more The purpose of this work is to fabricate large-scale solution processable graphene-based films from graphene oxide (GO) solution and to characterize the transport properties of these films. The graphene like film is produced by annealing of the GO film to form reduced graphene oxide (rGO) thin films. The conductive rGO thin films are useable as spacer layers in spin valves and as organic electrodes. Atomic Force Microscope (AFM) characterizations on the film thickness and morphology have been carried out and simple electrical transport studies performed on spin coated rGO thin films. We have fabricated rGO thin films ranging from few to tens of nanometers in thickness with conductivities in the order of 1-100 S/m. We also show that the morphology of the films play an important role in facilitating higher conductivities for rGO thin films.
Applied Physics Letters, 2006
The authors report on fabrication and characterization of a polymeric spin valve with the conjuga... more The authors report on fabrication and characterization of a polymeric spin valve with the conjugated polymer regioregular (poly 3-hexylthiophene) (RRP3HT) as the spacer layer. The device structure is La0.67Sr0.33MnO3 (LSMO)/polymer/Co, with half-metallic, spin-polarized LSMO acting as the spin-injecting electrode. The spin valve shows behavior similar to a magnetic tunnel junction though the nonmagnetic spacer layer (∼100 nm) is much thicker than the tunneling limit. They attribute this behavior to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by RRP3HT, chemically attaching to LSMO as observed by x-ray photoelectron spectroscopy measurement. This gives rise to ∼80% magnetoresistance (MR) at 5 K and ∼1.5% MR at room temperature. They found that by introducing monolayer of different organic insulators between LSMO and RRP3HT the spin-selective interface is destroyed and the spin injection is reduced. Their results show that organic materials are promising candidates for spintronic applications.
Journal of Alloys and Compounds, 2006
Organic Electronics, 2005
![Research paper thumbnail of Organic memory using [6,6]-phenyl-C61 butyric acid methyl ester: morphology, thickness and concentration dependence studies](https://attachments.academia-assets.com/50237876/thumbnails/1.jpg)
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Applied Physics Letters, 2008
... Sayani Majumdar (Abo Akademi University and University of Turku). ... to the formation of a t... more ... Sayani Majumdar (Abo Akademi University and University of Turku). ... to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by the chemical bonding between RRP3HT and LSMO as observed by x-ray photoelectron spectroscopy ...
Journal of Materials Chemistry, 2006
Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene ... more Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene thin film for
spintronics applications. The use of organic material for spintronics is motivated by the advantages such as long spin
diffusion length due to low spin-orbit and hyperfine coupling, chemical tuning of electronic functionality, easy
structural modifications, ability of self-assembly and mechanical flexibility etc. However, a major drawback of OS is its low mobility compared to inorganic semiconductors. The PLD growth of rubrene aims on fabricating OS films under
more controlled environment to achieve higher crystalline order to improve its mobility and spin coherence length.
Among organic materials, rubrene reveals the highest hole mobility - up to 40 cm2/(V∙s) and can be exploited in organic
light-emitting diodes (OLEDs) or field-effect transistors (OFETs) 4. In this work the rubrene thin films are produced
from hardened pellets in vacuum using Nd:YAG pulsed laser operated at 1064 nm, 2 Hz and energy fluence around 0.2
J/cm2. For the reference rubrene samples on SiO2 glass the AFM data reveal continuous 5-7 nm thick films. The
amorphous structures are confirmed by XRD measurements and also Raman spectra which show signatures of both
tetracene and phenyl bands and a broadband at 1373 cm-1. The obtained results indicate that continuous, defect-free
rubrene films can be prepared by means of PLD for investigation of the spin polarization properties of organic-inorganic hybrids. Further studies are on the way to improve crystalline qualities of the rubrene films for less grain boundary
related defects and improved mobility and spin diffusion length.
The purpose of this work is to fabricate large-scale solution processable graphene-based films fr... more The purpose of this work is to fabricate large-scale solution processable graphene-based films from graphene oxide (GO) solution and to characterize the transport properties of these films. The graphene like film is produced by annealing of the GO film to form reduced graphene oxide (rGO) thin films. The conductive rGO thin films are useable as spacer layers in spin valves and as organic electrodes. Atomic Force Microscope (AFM) characterizations on the film thickness and morphology have been carried out and simple electrical transport studies performed on spin coated rGO thin films. We have fabricated rGO thin films ranging from few to tens of nanometers in thickness with conductivities in the order of 1-100 S/m. We also show that the morphology of the films play an important role in facilitating higher conductivities for rGO thin films.
Applied Physics Letters, 2006
The authors report on fabrication and characterization of a polymeric spin valve with the conjuga... more The authors report on fabrication and characterization of a polymeric spin valve with the conjugated polymer regioregular (poly 3-hexylthiophene) (RRP3HT) as the spacer layer. The device structure is La0.67Sr0.33MnO3 (LSMO)/polymer/Co, with half-metallic, spin-polarized LSMO acting as the spin-injecting electrode. The spin valve shows behavior similar to a magnetic tunnel junction though the nonmagnetic spacer layer (∼100 nm) is much thicker than the tunneling limit. They attribute this behavior to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by RRP3HT, chemically attaching to LSMO as observed by x-ray photoelectron spectroscopy measurement. This gives rise to ∼80% magnetoresistance (MR) at 5 K and ∼1.5% MR at room temperature. They found that by introducing monolayer of different organic insulators between LSMO and RRP3HT the spin-selective interface is destroyed and the spin injection is reduced. Their results show that organic materials are promising candidates for spintronic applications.
Journal of Alloys and Compounds, 2006
Organic Electronics, 2005
Applied Physics Letters, 2008
... Sayani Majumdar (Abo Akademi University and University of Turku). ... to the formation of a t... more ... Sayani Majumdar (Abo Akademi University and University of Turku). ... to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by the chemical bonding between RRP3HT and LSMO as observed by x-ray photoelectron spectroscopy ...
Journal of Materials Chemistry, 2006