Research

Research

My research interest is the fundamental study of the photonic interaction of the system in a low-dimensional regime. My main focus is to design appropriate nanocavities that artfully confine photons over a large cross-sectional area. The atomically thin two-dimensional (2D) materials, 1000 times thinner than our human hair, are suitably used to fabricate different nanostructures to regulate the sensitivity of the electromagnetic interaction. My approach is to design different architectures inspired by nature like wrinkle/wavy, paper scrolls, pyramids, and tubular structures in a nanoscale regime to stimulate resonant cavity modes inherently and to improve the functionality of the device. The geometry of these nanostructures is comparable to the wavelength of the incident light to manipulate the optical response of the system. To amplify the photonic interaction, I conjugated nanomaterials of different dimensions (eg. 2D, 0D) to explore the hybrid exciton generation mechanism at heterointerfaces. Prior study of band structure, strain tunability, and photoabsorption quality are the key factors for me to decide on the candidate materials. Depending upon the above observations, I fabricated different nanoscale devices to study their optoelectronic and photoelectrochemical performances for future green energy applications.

Research work:

Optoelectronic device fabrication:

I am interested to study the interaction of light with controlled precision in a nano-dimensional system. Basically, light is utilized as a tool to investigate the photophysics of the semiconductor materials and to explore their exciton generation mechanism. I particularly studied the photonic interaction of different 2D materials (eg. Graphene, TMDs) and their combined system with photoactive materials (Perovskite QDs, TMD QDs, Semiconductor core-shell QDs). I have used photolithography, and self-assembly techniques to design nanostructures on both flexible (Polymer-based) and solid substrates. The as-fabricated devices can be studied under ambient conditions and depending upon the band-alignment (Type-I, II, or III) of the constituent materials the charge carrier dynamic varies under proper bias voltages. The varied functionality of these devices makes them compatible with the next generation of optoelectronic device designs.

(i) Photosensors:

Particularly my focus is to design photodetectors, phototransistors, and LEDs with the high performance out of different 2D materials and their complex heterostructures. My main purpose is to fabricate photonic devices at room temperature and pressure conditions with vivid functionality (i.e. omnidirectional sensing, emission and detection, chirality sensing, and chemical sensing). For the graphene-based tubular photodetector, I have achieved a wide-angular (± 180°) photosensing capability (Manuscript submitted). In the case of quasi 1D nanoscroll structure, 3000-fold improved photosensitivity has been observed in comparison to their flat counterpart [1],[2]. Another important aspect of my research is to fabricate flexible and stretchable devices with impressive bendability which suit the criteria of modern wearable device design. I have demonstrated a hybrid graphene/ReS2/QD based photosensor that can be stretched by 100% and can be bent by 14% for 120 bending cycles with much responsivity decline [3].

(ii) Random Lasing:

Room-temperature lasing strongly depends on the nanocavity structure and depending upon the dimension of the cavity the mode of emission strongly varies. The spontaneous to stimulated transition threshold largely depends on the gain medium and the multiple internal reflections at the cavity walls. This motivated me to design intriguing nanostructures like scrolls, and wrinkles having dimensions comparable to the wavelength of the incident photon. For the WS2/QD nanoscroll structure, an exceptionally low lasing threshold (8 W cm-2) has been achieved [2]. Linearly polarized lasing is also demonstrated in this nanoscroll structure. In wrinkle Graphene/ Carbon QD based structures a cavity-free white lasing is achieved with a low threshold value (40 W cm-2) [4]. Proper designing of the cavity helps to achieve directional lasing (Fabry-Perot, WGM) which I am working on in my future projects.

(iii) Photoelectrochemical system:

Semiconductor TMD materials are nowadays emerging as a promising catalyst because of their inexpensivity, good stability, and intriguing photoresponsive behavior. Strain-induced heterogeneous TMD material act as an efficient photoelectrochemical catalyst in H2 and O2 generation process. I have particularly synthesized the WS2/MoS2 heterojunction scroll structure as an efficient catalyst material. Specially designed microelectrochemical cells have been utilized to get precise in-depth information about the catalytically active edge sites. Using the lithography technique patterned electrodes are fabricated to get fundamental information about the Tafel slope, active site density, and onset potential related to the catalysis process. A low Tafel value of 39 mV dec-1 with an excellent current density of 1.44 × 10-4 A cm-2 is achieved in this strain mediated phototrapping structure [5]. This technique can be utilized to analyze the reaction kinetics for other 2D material-based electrochemical systems.

(iv) Stretchable Electronics:

Another important aspect of our research is to fabricate flexible and stretchable devices with impressive bendability. Stretchable electronics are nowadays playing a major role in the modern optoelectronics field. Polymer-based substrates are majorly used for this purpose which can be stretched or bent 100% of their original length. We have achieved a responsivity of 10-7 A W-1 by using a polymer substrate with graphene as conducting channel and ReS2/Perovskite quantum dot as an active material. This device can be stretched from 0 to 100% longitudinally by 100 times and can be bent by almost 14% for 120 times without much responsivity decline [3]. This proves that the as-fabricated device has the capability to withstand paramount stretching which suits the criteria of modern wearable devices. This also indicates that intricate device design is a crucial part to determine devices' functionality.


You can also visit my google scholar and ORCID for the list of publications.

References:

  1. R. Ghosh, H.-I. Lin, Y.-S. Chen, M. Hofmann, Y.-P. Hsieh, Y.-F. Chen. J. Mater. Res. 37, 660–669 (2022).

  2. R. Ghosh, H.-I. Lin, Y.-S. Chen, M. Singh, Z.-L. Yen, S. Chiu, H.-Y. Lin, K. P. Bera, Y.-M. Liao, M. Hofmann, Y.-P. Hsieh, Y.-F. Chen. Small 16, 2003944 (2020).

  3. R. Ghosh, K. Yadav, M. Kataria, H.-I. Lin, C. R. Paul Inbaraj, Y.-M. Liao, Y. Nguyen, C.-H. Lu, M. Hofmann, R. Sankar, W.-H. Shih, Y.-P. Hsieh, Y.-F. Chen. ACS Appl. Mater. Interfaces 11, 26518 (2019).

  4. G.-Z. Lu, Y.-J. Li, C.-F. Hou, R. Ghosh, J.-L. Shen, M.-J. Wu, T.-Y. Lin, Y.-F. Chen,. Opt. Express 30, 20213 (2022).

  5. R. Ghosh, M. Singh, L. W. Chang, H.-I. Lin, Y. S. Chen, J. Muthu, B. Papnai, Y. S. Kang, Y.-M. Liao, K. P. Bera, G.-Y. Guo, Y.-P. Hsieh, M. Hofmann, Y.-F. Chen. ACS Nano 16, 4, 5743–5751 (2022).