M. K. Dalai
National Physical Laboratory
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Featured researches published by M. K. Dalai.
Applied Physics Letters | 2012
D. Haranath; Savvi Mishra; Sumit Yadav; R. K. Sharma; L. M. Kandpal; N. Vijayan; M. K. Dalai; G. Sehgal; Virendra Shanker
Manganese-doped sodium zinc phosphate (NaZnPO4:Mn) phosphor with exceptional features having ultra-violet (UV) to visible absorption (300–470 nm), yellow-green (∼543 nm) broad-band photoluminescence (PL), and appreciable color co-ordinates (x = 0.39, y = 0.58) is reported. It has a crystal structure consisting of discrete PO4 tetrahedra linked by ZnO4 and NaO4 distorted tetrahedral such that three tetrahedra, one of each kind, share one corner. The presence of UV sensitive Zn-O-Zn bonds and their efficient energy transfer to Mn2+ ions resulted in brightest PL and external quantum yield of 63% at 418 nm. Our experiment demonstrated the possibility of producing inexpensive white-light emitting devices for future.
ACS Applied Materials & Interfaces | 2013
Neeraj Dwivedi; Sushil Kumar; J. David Carey; R. K. Tripathi; Hitendra K. Malik; M. K. Dalai
A simple approach is proposed for obtaining low threshold field electron emission from large area diamond-like carbon (DLC) thin films by sandwiching either Ag dots or a thin Ag layer between DLC and nitrogen-containing DLC films. The introduction of silver and nitrogen is found to reduce the threshold field for emission to under 6 V/μm representing a near 46% reduction when compared with unmodified films. The reduction in the threshold field is correlated with the morphology, microstructure, interface, and bonding environment of the films. We find modifications to the structure of the DLC films through promotion of metal-induced sp2 bonding and the introduction of surface asperities, which significantly reduce the value of the threshold field. This can lead to the next-generation, large-area simple and inexpensive field emission devices.
ACS Applied Materials & Interfaces | 2012
Neeraj Dwivedi; Sushil Kumar; R. K. Tripathi; J. D. Carey; Hitendra K. Malik; M. K. Dalai
The origin of low threshold field-emission (threshold field 1.25 V/μm) in nanocrystalline diamond-like carbon (nc-DLC) thin films is examined. The introduction of nitrogen and thermal annealing are both observed to change the threshold field and these changes are correlated with changes to the film microstructure. A range of different techniques including micro-Raman and infrared spectroscopy, X-ray diffraction, electron microscopy, energy-dispersive X-ray analysis and time-of-flight-secondary ion mass spectroscopy are used to examine the properties of the films. A comparison of the field emission properties of nc-DLC films with atomically smooth amorphous DLC (a-DLC) films reveals that nc-DLC films have lower threshold fields. Our results show that nc-DLC can be a good candidate for large area field emission display panels and cold cathode emission devices.
AIP Advances | 2013
S. S. Kushvaha; M. Senthil Kumar; K. K. Maurya; M. K. Dalai; Nita Dilawar Sharma
Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for t...
Physical Review B | 2006
M. K. Dalai; P. Pal; B. R. Sekhar; N. L. Saini; R. K. Singhal; K.B. Garg; B. P. Doyle; Stefano Nannarone; C. Martin; F. Studer
We have investigated the temperature-dependent changes in the near-
Physical Review B | 2007
P. Pal; M. K. Dalai; R. Kundu; M. Chakraborty; B.R. Sekhar; C. Martin
{E}_{F}
Journal of Materials Chemistry C | 2013
Savvi Mishra; R. Rajeswari; N. Vijayan; Virendra Shanker; M. K. Dalai; C.K. Jayasankar; S. Surendra Babu; D. Haranath
occupied and unoccupied states of
Optics Letters | 2013
Priyanka Tyagi; Arunandan Kumar; Lalat Indu Giri; M. K. Dalai; Suneet Tuli; M. N. Kamalasanan; Ritu Srivastava
{\mathrm{Pr}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}
RSC Advances | 2013
Priyanka Tyagi; M. K. Dalai; C. K. Suman; Suneet Tuli; Ritu Srivastava
which shows the presence of ferromagnetic and antiferromagnetic phases. The temperature-dependent changes in the charge and orbital degrees of freedom and associated changes in the
Physical Review B | 2008
P. Pal; M. K. Dalai; R. Kundu; B.R. Sekhar; C. Martin
\mathrm{Mn}\phantom{\rule{0.3em}{0ex}}3d\char21{}\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p