Research Interest

Role of Oxide ( SnO₂ quantum dots, & YSZ, CuO, ZnO, VO₂ V₂O₅ , V₂O₅ ) nanostructures for gas sensing at low temperatures

13. Wavelength dependence of photothermal deflection in Au/Si bimaterial microcantilevers. M. Raghu Ramaiah, K. Prabakar, S. T. Sundari, S. Dhara Sensors and Actuators A 315 (2020) 112233; doi : 10.1016/j.sna.2020.112233

12. Geometrically controlled Au decorated ZnO heterojunction nanostructures for NO₂ detection. D. V. Ponnuvelu, J. Dhakshinamoorthy, A. K. Prasad, S. Dhara, M. Kamruddin, P. Biji ACS Appl. Nano Mater. 3 (2020) 5898-5909; doi: 10.1021/acsanm.0c01053

11. Near room temperature CH₄ sensing and role of oxidation states for phase pure Wadsley V_nO_2n+1 nanostructures. R. Basu, Reshma P. R., A. K. Prasad, and S. Dhara Mater. Chem. Phys. 248 (2020) 122901; doi: 10.1016/j.matchemphys.2020.122901

10. Nano-molar to milli-molar level Ag (I) determination using absorption of light by ZnS QDs without organic ligand R. N. Juine, S. Amirthapandian, S. Dhara, A.Das Sensors and Actuators B 273 (2018) 1687-1693; doi: 10.1016/j.snb.2018.07.080

9. Native defect assisted enhanced response to CH₄ near room temperature by Al_0.07Ga_0.93N nanowires. S. Parida, A. Das, A. K. Prasad, J. Ghatak, S. Dhara Phys. Chem. Chem. Phys. 20 (2018) 18391; doi: 10.1039/C8CP02879F

8. Highly sensitive, atmospheric pressure operatable sensors based on Au nanoclusters decorated TiO₂@Au heterojunction nanorods for trace level NO₂ gas detection. P. V. Dinesh, P. Biji, A. K Prasad, S. Dhara, M. Kamruddin A. K. Tyagi, Baldev Raj J. Mater. Sci.: Mater. Electron. 28 (2017) 9738-9748; doi 10.1007/s10854-017-6725-9 [IF=2.478]

7. Localized Charge Transfer Process and Surface Band Bending in Methane Sensing by GaN Nanowires. A. Patsha, P. Sahoo, S. Amirthapandian, A. K. Prasad, A. Das, A. K. Tyagi, M. A. Cotta, S. Dhara J. Phys. Chem. C (2015) DOI: 10.1021/acs.jpcc.5b06971

6. Rapid synthesis and characterization of novel hybrid ZnO@Au core-shell nanorods for high performance, low temperature NO2 gas sensor applications. V.P.Dinesh, P.Biji, A. K. Prasad, A. Ashok, S. K. Dhara, M. Kamruddin, A.K.Tyagi, and B. Raj Appl. Surf. Sci. 355 (2015) 726–735 DOI:10.1016/j.apsusc.2015.07.143

5. Influence of in-plane and bridging oxygen vacancies of SnO₂ nanostructures on CH₄ sensing at low operating temperatures. B. Venkataramana, A. Das, N. G. Krishna, A. K Prasad, S. Dhara, A. K.Tyagi, Appl. Phys. Lett. 105 (2014) 243102 DOI: 10.1063/1.4904457

4. Novel single phase vanadium dioxide nano-rod film based gas sensor for methane sensing at very low temperature. A. K. Prasad, S. Amirthapandian, S. K. Nori, S. Dhara, S. Dash, N. Murali, A.K. Tyagi Sensors and Actuators B: Chemical 191 (2014) 252– 256. [IF=3.535]

3. Role of SnO₂ quantum dots for sensing methane at low temperature. A. Das, Bonu Venkatramana, A.K. Prasad, D. Panda, S. Dhara, and A K Tyagi, J. Mater. Chem. C 2 (2014) 164-171. [IF=6.101]

2. Facile synthesis of nanostructured CuO for low temperature NO₂ sensing A. Das, B. Venkataramana, D. Partheephan, A.K. Prasad, S. Dhara, A.K. Tyagi, Physica E 54 (2013) 40-44 [IF= 2.313]

1. Selective Capacitive Sensor for Ammonia Hydroxide at Room Temperature, A. Das, M. Gupta, S. Rajagopalan, and A. K. Tyagi IEEE Sensors J. 7 (2013) 2757

Focused ion beam induced nanowelding and defect doping as building block for nanoscale electronics in GaN nanowires

Typical configurations and features of a) dispersion of nanowires with a close view in the inset (in-situ FESEM image of FIB), metallization of b) a single nanowire (in-situ FESEM image of FIB) and c) two nanowires with welded nanojunction (ex-situ image with JEOL FESEM) and d) defect doping in one of the nanowire as indicated. Isolation of unwanted nanowires is typically shown in both c) and d).

Nanoelectronics

Two GaN nanowires are formed as nanojunction using focused ion beam (FIB) assisted implantation of Ga⁺ self-ion. FIB induced metallization and electrical isolation by cutting the nanowires are also used for the completion of contact formation. Defect doping, employing the formation energies of vacancies and interstitials, in the energetic non-equilibrium ion beam processing is successfully attempted for the formation of p-type GaN nanowire. Detailed transport measurements of welded nanojunctions and rectification in the form of p-n junctions for two nanowires are reported in this process of in-situ nanoengineering. The rectification is also reported for the p-n junction formed in a single nanowire. This is a unique technique demonstrating an all FIB nanoelectronic fabrication for future miniaturization of devices.

2. Nonpolar p-GaN/n-Si heterojunction diode characteristics: A comparison between ensemble and single nanowire devices A.Patsha, R. Pandian, S. Dhara and A. K. Tyagi J. Phys. D: Appl. Phys.(In press) (2015)

1. S. Dhara, C. Y. Lu, C. T. Wu, C. W. Hsu, W. S. Tu, K. H. Chen, Y. L. Wang, and L. C. Chen J. Phys. Chem C 114 (2010) 15260. (Abstract)

Phase Formation and Defect Study in Nanostructured Materials

Enhanced Dynamic Annealing in Ga⁺ Ions Implanted GaN Nanowires

Bright field HRTEM image of samples irradiated at fluences of (a) 3.16x10¹⁵ (b) 5x10¹⁵ (c) 1x10¹⁶ and (d) 2x10¹⁶ ions.cm^-2. Inset [top right corner (d)] shows the amorphous electron diffraction pattern for the sample. Insets show the observed nanowires at low magnifications for the respective samples.

Ga⁺ ion implantation of chemical-vapor-deposited GaN nanowires (NWs) is studied using 50 keV Ga⁺ focused ion beam. Role of dynamic annealing (defect-annihilation) is discussed with an emphasis on the fluence-dependent defect structure. Unlike heavy-ion-irradiated epitaxial GaN film, large-scale amorphization is suppressed until a very high fluence of 2x10¹⁶ ions·cm^-2. In contrast to extended-defects as reported for heavy-ion-irradiated epitaxial GaN film, point-defect clusters are identified as major component in irradiated NWs. Enhanced dynamic annealing induced by high diffusivity of mobile point-defects in the confined geometry of NWs is identified as the probable reason for observed differences.

Hexagonal-to-Cubic Phase Transformation in GaN Nanowires by Ga⁺-Implantation

Hexagonal to cubic phase transformation is studied in focused ion beam assisted Ga⁺-implanted GaN nanowires. Optical

photoluminescence and cathodoluminescence studies along with high-resolution transmission electron microscopic structural studies are

performed to confirm the phase transformation. In one possibility, sufficient accumulation of Ga from the implanted source might have

reduced the surface energy and simultaneously stabilized the cubic phase. Other potential reason may be that the

fluctuations in the short-range order induced by enhanced dynamic annealing (defect annihilation) with the irradiation process stabilize the

cubic phase and cause the phase transformation.

1. Dhara, S.; Datta, A.; Wu, C. T.; Lan, Z. H.; Chen, K. H.; Wang, Y. L.; Chen, L. C.; Hsu, C. W.; Lin, H. M.; Chen, C. C.

2. Appl. Phys. Lett. 2003, 82, 451-453. (Abstract)

3. Dhara, S.; Datta, A.; Wu, C. T.; Lan, Z. H.; Chen, K. H.; Wang, Y. L.; Chen, L. C.; Hsu, C. W.; Lin, H. M.; Chen, C. C.

4. Appl. Phys. Lett. 2004, 84, 3486-3488.(Abstract)

5. Dhara, S.; Datta, A.; Hsu, C. W.; Wu, C. T.; Shen, C. H.; Lan, Z. H.; Chen, K. H.; Chen, L. C.; Wang, Y. L.; Chen, C. C.

6. Appl. Phys. Lett. 2004, 84, 5473-5475.(Abstract)

7. Dhara, S.; Datta, A.; Wu, C. T.; Chen, K. H.; Wang, Y. L.; Muto, S.; Tanabe, T.; Hsu, C. W.; Shen, C. H.; Chen, L. C.; Maruyama, T.

8. Appl. Phys. Lett. 2005, 86, 203119-1-3.(Abstract)

Nanoindentation

Direct observation of amophization in load rate dependent

nanoindentation studies of crystalline Si

Indentation at very low load rate showed region of constant volume with releasing load in crystalline (c-)Si, indicating a direct

observation of liquidlike amorphous phase which is incompressible under pressure. Signature of amorphization is also confirmed from

load dependent indentation study where increased amount of amorphized phase is made responsible for the increasing elastic recovery

of the sample with increasing load. Ex situ Raman study confirmed the presence of amorphous phase at the centre of indentation. The

molecular dynamic simulation has been employed to demonstrate that the effect of indentation velocities has a direct influence on c-Si

during nanoindentation processes.

1. C. R. Das, S. Dhara, B. Raj, A. K. Bhaduri, S. K. Albert, Y.-R. Jeng and P.-C. Tsai Appl. Phys. Lett. 96 (2010) 253113.(Abstract)

2. C. R. Das, H. C. Hsu, S. Dhara, A. K. Bhaduri, B. Raj, L. C. Chen, K. H. Chen, S. K. Albert, A. Ray and Y. Tzeng

J. Raman Spectroscopy 41 (2010) 334.(Abstract)

The mechanism of recrystallization process in epitaxial GaN under dynamic stress field : Atomistic origin of planar defect formation

a) Variation of hardness with indentation strain rate. Typical (b) log-log plot of hardness vs strain rate, and (c) log (indentation strain rate) vs hardness plot for the peak load of 100mN

a) Micro-Raman spectra for epi-GaN outside and different regions inside the indentation spot. Inset shows corresponding optical image of the indentation spot. Area mappings of outside and inside of the indentation spot, using different spectral regions indicated in the picture, are shown at the outset. Scale bar is 1 mm. b) Different Raman scattering configuration for WZ crystal in the backward (top) and right angled (botttom) direction corresponding to E2, and TO modes of E1 and A1 symmetries for usual incident and scattering notations. (Drawn after Figure 6 of Phys. Rev. 1969; 181: 1351 permission taken from American Physical Society)

The mechanism of recrystallization in epitaxial (0001) GaN film, introduced by indentation technique, is probed by lattice dynamic studies using Raman spectroscopy. The recrystallized region is identified by Micro-Raman area mapping. ‘Pop-in’ bursts in loading lines indicate nucleation of dislocations and climb of dislocations. These processes set in plastic motion of lattice atoms under stress field at the center of indentation for the initiation of recrystallization process. A planar defect migration mechanism is evolved. A pivotal role of vacancy migration is pointed out, for the first time, as the rate limiting factor for the dislocation dynamics initiating the recrystallization process in GaN.

1. S. Kataria, T. W. Liu, C. L. Hsiao, S. Dhara, L, C, Chen, K. H. Chen, S. Dash and A. K. Tyagi J. Nanosci. Nanotechnol. 10 (2010) 5170. (Abstract)

2.C. R. Das, S. Dhara, H. C. Hsu, L. C. Chen, Y. R. Jeng, A. K. Bhaduri, Baldev Raj, K. H. Chen, S. K. Albert,

J. Raman Spectroscopy 40 (2009) 1881.(Abstract)

3. S. Dhara, C. R. Das, H. C. Hsu, Baldev Raj, A. K. Bhaduri, S. K. Albert, L. C. Chen, K. H. Chen and Ayan Ray Appl. Phys. Lett. 92 (2008) 143114 (Abstract).http://research.ncku.edu.tw/re/reck/e/20081107/home.html

Plasmonics: Plasmon Study in Metal Nanoclusters

Surface plasmon polariton assisted optical switching

Plasmonic Switching in Au Functionalized GaN Nanowires in the Realm of Surface Plasmon Polatriton Propagation

: A Single Nanowire Switching Device

Surface plasmon polariton assisted optical switching in noble bimetallic nanoparticle system

1. S. Dhara, C.-Y. Lu, P. Magudapathy, Y.-F. Huang, W.-S. Tu, K.-H. Chen Appl. Phys. Lett. 106 (2014) 023101.

2. S. Dhara, C.-Y. Lu, K.-H. Chen Plasmonics (2014) DOI: 10.1007/s11468-014-9815-z

3. S. Dhara, Sharat Chandra, P. Magudapathy, S. Kalavathi, B. K. Panigrahi, K.G.M. Nair, V.S. Sastry, C. W. Hsu, C.T. Wu, K.H. Chen, L.C. Chen J. Chem. Phys. 121 (2004) 12595 (Virtual J. of Nanoscale Science & Technology, Vol. 10, Issue 26, 2004) (Abstract)

4. S. Dhara, B. Sundaravel, T. R. Ravindran, K. G. M. Nair, C. David, B. K. Panigrahi, P. Magudapathy, and K. H. Chen Chem. Phys. Lett. 399 (2004) 354.(Abstract)