@article {42586, title = {Electrical bistability in a xanthene class molecule: conduction mechanisms}, journal = {Applied Physics Letters}, volume = {89}, year = {2006}, month = {OCT}, pages = {Article No: 142110}, abstract = {

The author study conduction mechanism in two conducting states of a bistable device at range. They find that in the electrical bistable devices, electrical switching is associated with a change in the conduction mechanism. Device current in the low-conducting state follows an injection-limited mechanism. The current in the high-conducting state conforms a bulk-dominated mechanism, namely, space-charge limited conduction with an exponential distribution of traps. The bistability has an associated memory phenomenon. The devices exhibit read-only and random-access memory applications for several hours.

}, doi = {10.1063/1.2358946}, author = {Rath, Arup Kumar and Sahu, Satyajit and Pal, Amlan J.} } @article {47385, title = {Crack-free conjugated PbS quantum dot-hole transport layers for solar cells}, journal = {ACS Applied Nano Materials}, volume = {4}, year = {2021}, month = {APR}, pages = {4016-4025}, type = {Article}, abstract = {

Colloidal quantum dots (QDs) benefit from solution-phase processing and band-gap tuning for their application in solar cell development. Today{\textquoteright}s QD solar cells rely on solid-state ligand exchange (SLE) to replace bulky oleic acid (OA) ligands with small 1,2-ethanedithiol (EDT) ligands to develop a conducting hole transport layer (HTL). High volume contraction in EDT conjugated QD films, however, leads to crack and porosity in the HTL, which is a major cause of concern for the device reproducibility and large-area solar cell development. We show that partial removal of the OA ligands in the solution phase reduces the volume contraction in solid films, thereby allowing the growth of crack-free QD films in the SLE process. The cleaning of QDs by repeated precipitation and redispersion using a protic methanol (MeOH) solvent helps with partial removal of the OA ligands, but it is detrimental to the electronic properties of QDs. We develop a one-step solution-phase partial ligand-exchange process using ammonium salts, which enable partial replacement of the OA ligands and passivation of the QD surface. Introduction of the facile partial ligand-exchange process eliminates the need for tedious and wasteful multiple cleaning steps with MeOH, while improving the photophysical properties of QDs. The advancement in QD processing helps to build crack-free, smooth, and conjugated QD films for their deployment as HTLs in solar cell development. Partial ligand exchange with NH4SCN leads to a 1.5 times increase in p doping and mobility over multiple MeOH-cleaned PbS QD films. HTLs developed using NH4SCN QDs show an improved photovoltaic performance to attain a 10.5\% power conversion efficiency. Improvement in the depletion width and hole collection efficiency leads to a superior photovoltaic performance, as confirmed from experimental studies and one-dimensional solar cell capacitance simulation.

}, keywords = {Efficiency, ligand, polydispersity, quantum dot, solar cells, thin film}, issn = {2574-0970}, doi = {10.1021/acsanm.1c00373}, author = {Sharma, Ashish and Dambhare, V. Neha and Bera, Jayanta and Sahu, Satyajit and Rath, Arup K.} } @article {48206, title = {CdSe quantum dot-based nanocomposites for ultralow-power memristors}, journal = {ACS Applied Nano Materials}, volume = {5}, year = {2022}, month = {JUN}, pages = {8502-8510}, type = {Article}, abstract = {

The explosion in digital communication with the huge amount of data and the internet of things (IoT) led to the increasing demand for data storage technology with faster operation speed, high-density stacking, nonvolatility, and low power consumption for saving energy. Metal chalcogenide-based quantum dots (QDs) show excellent nonvolatile resistive memory behavior owing to their tunable electronic states and control in trap states by passivating the surface with different ligands. Here, we synthesized high-quality colloidal monodispersed CdSe QDs by the hot injection method. The CdSe QDs were blended with an organic polymer, poly(4-vinylpyridine) (PVP), to fabricate an Al\textbackslashCdSe-PVP\textbackslashAl device. Our device shows excellent bipolar nonvolatile resistive random access memory (RRAM) switching behavior with a high current ON/OFF ratio (I-ON/OFF) of 6.1 x 10(4), and it consumes ultralow power. The charge trapping and detrapping in the potential well formed by the CdSe QD and PVP combination result in resistive switching. This CdSe-PVP-based resistive random access memory (RRAM) device with a high I-ON/OFF, ultrafast switching speed, high endurance, low operating voltage, and long retention period can be used as a high-performance and ultralow-power memristive device.

}, keywords = {memory switching, memristor, metal chalcogenides, nonvolatile, quantum dots}, doi = {10.1021/acsanm.2c01894}, author = {Bera, Jayanta and Betal, Atanu and Sharma, Ashish and Shankar, Uday and Rath, Arup Kumar and Sahu, Satyajit} } @article {48166, title = {Colloidal MoS2 quantum dots for high-performance low power resistive memory devices with excellent temperature stability}, journal = {Applied Physics Letters}, volume = {120}, year = {2022}, month = {JUN}, pages = {253502}, type = {Article}, abstract = {

Conventional memory technologies are facing enormous problems with downscaling, and are hence unable to fulfill the requirement of big data storage generated by a huge explosion of digital information. A resistive random access memory device (RRAM) is one of the most emerging technologies for next-generation computing data storage owing to its high-density stacking, ultrafast switching speed, high non-volatility, multilevel data storage, low power consumption, and simple device structure. In this work, colloidal MoS2 quantum dots (QDs) embedded in an insulating matrix of poly-(4vinylpyridine) (PVP) were used as an active layer to fabricate a RRAM device. The MoS2 QDs-PVP based RRAM device reveals an excellent nonvolatile resistive switching (RS) behavior with a maximum current on-off ratio (I-ON/I-OFF) of 10(5). High endurance, long retention time, and successive {\textquoteleft}{\textquoteleft}write-read-erase-read{\textquoteright}{\textquoteright} cycles indicate high-performance RRAM characteristics. The ultimate power consumption by this RRAM device is considerably low for energy saving. In addition, the MoS2 QDs-PVP based device shows RS behavior even at 130 degrees C. High I-ON/I-OFF, low operating power, high endurance, long retention time, and excellent stability with temperatures reveal that the MoS2 QDs-PVP based device can be a promising candidate for high-performance low power RRAM devices that can be operated at relatively higher temperatures. Published under an exclusive license by AIP Publishing.

}, issn = {0003-6951}, doi = {10.1063/5.0094892}, author = {Bera, Jayanta and Betal, Atanu and Sharma, Ashish and Rath, Arup Kumar and Sahu, Satyajit} } @article {48115, title = {Composition and surface morphology invariant high on-off ratio from an organic memristor}, journal = {ACS Applied Electronic Materials}, volume = {4}, year = {2022}, month = {MAR }, pages = {1109-1116}, type = {Article}, abstract = {

Material composition plays a crucial role in the device performance; thus, nonvolatile memory devices from a small molecule named 5-mercapto-1-methyl tetrazole (MMT) in an insulating polymer matrix of poly(4-vinyl pyridine) (PVP) were fabricated. The composition of the active material in the device was varied to observe its influence on the device{\textquoteright}s electronic properties. The device with a more or less weight ratio of MMT has a much smoother surface morphology, whereas when the contributions of MMT and PVP were equal, the average surface roughness increased. However, the maximum on-off current ratio for all the devices is 10(5), suggesting that the MMT molecule does not show any change in its characteristic properties when surrounded by an insulating material. When the device was fabricated without the polymer matrix, the surface morphology of the device completely changed as it was filled with large holes. These holes provide short-circuited pathways for the current by forming the direct metal contact between the top and bottom electrodes. The carrier transport through these devices follows various conduction mechanisms. Some of the dominating conduction mechanisms are direct tunneling and trap-free and trap-assisted space-charge-limited conduction.

}, keywords = {Nonvolatile memory, Polymer, small molecule, space-charge, tunneling}, doi = {10.1021/acsaelm.1c01234}, author = {Betal, Atanu and Bera, Jayanta and Sharma, Ashish and Rath, Arup K. and Sahu, Satyajit} } @article {48321, title = {Charge trapped CdS quantum dot embedded polymer matrix for a high speed and low power memristor}, journal = {Physical Chemistry Chemical Physics}, volume = {25}, year = {2023}, month = {FEB }, pages = {3737-3744}, type = {Article}, abstract = {

The data storage requirement in the digital world is increasing day by day with the advancement of the internet of things. In this respect, nonvolatile resistive random-access memory is an option that provides high density and low power data storage capabilities. In this work, zero-dimensional colloidal CdS quantum dots and a polymer composite at an appropriate ratio were used to fabricate a memristive device. Comparison with a pristine CdS quantum dot-based device reveals that a surrounding matrix around the quantum dots is needed for observing memristive behavior. The quantum dots embedded in the polymer matrix device showed extremely stable electrical switching behavior that can be operated for more than 300 cycles and 60 000 seconds. Moreover, the device needs extremely low power to operate at a very high speed. The smooth surface morphology dictates a charge trapping mechanism for the switching phenomenon; however, an interplay between different charge transport mechanisms leads to the fast switching and high on-off ratio of the device.

}, issn = {1463-9076}, doi = {10.1039/d2cp05014e}, author = {Betal, Atanu and Bera, Jayanta and Sharma, Ashish and Rath, Arup K. K. and Sahu, Satyajit} } @article {48785, title = {Photogating induced high sensitivity and speed from heterostructure of few-layer MoS2 and reduced graphene oxide-based photodetector}, journal = {Physical Chemistry Chemical Physics}, volume = {25}, year = {2023}, month = {NOV}, pages = {30419-30427}, type = {Article}, abstract = {

Over the past few years, two-dimensional transition metal dichalcogenides (2D-TMDC) have attracted huge attention due to their high mobility, high absorbance, and high performance in generating excitons (electron and hole pairs). Especially, 2D molybdenum disulfide (MoS2) has been extensively used in optoelectronic and photovoltaic applications. Due to the low photo-to-dark current ratio (I-photo/dark) and low speed, pristine MoS2-based devices are unsuitable for these applications. So, they need some improvements, i.e., by adding layers or decorating with materials of complementary majority charges. In this work, we decorated pristine MoS2 with reduced graphene oxide (rGO) and got improved dark current, I-photo/dark, and response time. When we compared the performance of pristine MoS2 based device and rGO decorated MoS2 based device, the rGO/MoS2-based device showed an improved performance of responsivity of 3.36 A W-1, along with an I-photo/dark of about 154. The heterojunction device exhibited a detectivity of 4.75 x 10(12) Jones, along with a very low response time of 0.184 ms. The stability is also outstanding having the same device performance even after six months.

}, issn = {1463-9076}, doi = {10.1039/d3cp03518b}, author = {Das, Chayan and Kumar, Ashok and Kumar, Suresh and Dambhare, Neha V. and Kumar, Mahesh and Rath, Arup K. and Sahu, Satyajit} } @article {49639, title = {High-performance photodetector from p-n junction of vertically aligned SnS2 and reduced graphene oxide}, journal = {ACS Applied Electronic Materials}, volume = {6}, year = {2024}, month = {SEP}, pages = {6965-6973}, type = {Article}, abstract = {

Semiconducting 2D transition metal dichalcogenides (TMDC) became very popular in photodetection due to their high mobility and high rate of generating electron and hole pairs. Over the past decade, MoS2 and WS2 became the most popular TMDC for several applications. On the other hand, due to the complex synthesis process compared to MoS2 and WS2, SnS2 became a less popular 2D material for photodetection. We synthesized vertically aligned SnS2 flakes by a chemical vapor deposition (CVD) process with three temperature zones with controlled argon (Ar) gas flow. Pristine SnS2-based devices are not very suitable for photodetection applications because of their low photo-to-dark current ratio (I ph /I (dark) ), high response time, and low stability. So, they need to be decorated with oppositely doped materials. We decorated pristine SnS2-based devices with rGO nanoparticles, which significantly increased the device{\textquoteright}s performance. We found a high responsivity (R) of 1.33 A/W, detectivity (D) of 6.95 x 10(11) Jones, I ph /I dark of 102, and a rise time of 0.241 ms (fall time of 1.318 ms) with the rGO decorated SnS2-based device.

}, keywords = {2D-SnS2, CVD, p-njunction, photodetector, rGO}, doi = {10.1021/acsaelm.4c01311}, author = {Das, Chayan and Kumar, Suresh and Dambhare, Neha V. and Kumar, Mahesh and Rath, Arup K. and Sahu, Satyajit} } @article {49077, title = {Scanning tunneling microscopy investigation of synaptic behavior in AgInS2 quantum dots: effect of ion transport in neuromorphic applications}, journal = {ACS Applied Nano Materials }, volume = {7}, year = {2024}, month = {MAR}, pages = {7226-7236}, type = {Article}, abstract = {

Scanning tunneling microscopy (STM) is a powerful technique for investigating the nanoscale properties of functional materials. Additionally, scanning tunneling spectroscopy (STS) facilitates the determination of the local density of states (LDOS) within the material. In this study, we present an exploration of the resistive switching (RS) properties and neuromorphic computing capabilities of individual AgInS2 quantum dots, utilizing STM and STS techniques. By examining the material{\textquoteright}s bandgap and its temperature dependence, we uncover a nonlinear variation below the Debye temperature and a linear trend at higher temperatures. Moreover, STS measurements demonstrate changes in the conducting states induced by localized pulses, further confirming the unique characteristics of the quantum dots. The experimental devices constructed by using these quantum dots effectively replicate the RS properties observed at the nanoscale. To assess the neuromorphic application of the devices, pulse transient measurements simulating the learning and forgetting processes were conducted. The gradual set and reset processes successfully mimic the information retention and erasure capabilities essential for neuromorphic computing. Notably, the resistive switching mechanism in these devices is attributed to localized ionic transport, which highlights the significant involvement of ionic species in the observed RS behavior. The outcomes of this study contribute to the fundamental understanding of RS properties in single AgInS2 quantum dots and offer valuable insights into their potential applications in neuromorphic computing.

}, keywords = {corona poling, Ion transport, neuromorphic computing, quantum dots, resistive switching, Scanning tunneling microscopy, STS}, doi = {10.1021/acsanm.3c06272}, author = {Betal, Atanu and Chetia, Anupam and Bera, Jayanta and Saikia, Dibyajyoti and Sharma, Ashish and Rath, Arup K. and Sahu, Satyajit} } @article {49582, title = {Air-stable double halide perovskite Cs2CuBiBr6: synthesis and memristor application}, journal = {Physical Chemistry Chemical Physics}, volume = {27}, year = {2025}, month = {FEB}, pages = {3150-3159}, type = {Article}, abstract = {

The excellent optical and electronic properties of halide perovskite materials have attracted researchers to investigate this particular field. However, the instability in ambient conditions and toxicity of materials like lead have given some setbacks to commercial use. To overcome these issues, perovskite-inspired materials with less toxic and excellent air-stable materials are being studied. Double perovskite materials are one of the perovskite materials. In this study, we have synthesized air-stable double perovskite Cs2CuBiBr6 using a solution process approach. The characterization of the material revealed that it has excellent crystallinity and high stability. The material shows excellent optical and electronic properties. It can be used in resistive memory devices. It shows stable current-voltage characteristics and analog switching. The ion migration through the active layer and accumulation of charge near the electrode region are the reasons behind the resistive switching.

}, issn = {1463-9076}, doi = {10.1039/d4cp04639k}, author = {Betal, Atanu and Chetia, Anupam and Saikia, Dibyajyoti and Karmakar, Krishnendu and Bera, Ganesh and Dambhare, Neha V. and Rath, Arup K. and Sahu, Satyajit} } @article {49906, title = {WS2 nanoparticle-decorated, vertically aligned SnS2-based high-performance heterostructures for ambient-stable ultrafast photodetection}, journal = {ACS Applied Nano Materials}, volume = {8}, year = {2025}, month = {OCT }, pages = {21047-21056}, type = {Article}, abstract = {

The development of visible-light photodetectors with high responsivity, rapid response, and long-term ambient stability remains a critical challenge in optoelectronics. Here, we report a high-performance photodetector based on a vertically aligned SnS2 film interfaced with WS2 nanoparticles, forming a p-n heterojunction. This device is fabricated using a scalable two-step method-chemical vapor deposition (CVD) for SnS2 growth and solution-based drop-casting for WS2 deposition-enabling precise control over the heterointerface, but trap states are inevitable due to the use of thermal CVD and the drop-casting method. The resulting photodetector exhibits remarkable optoelectronic characteristics, including a responsivity of 0.76 A/W, a detectivity of 7.56 x 10(11) Jones, a photo-to-dark current ratio of 119, and a fast rise time of 0.297 ms under visible illumination. These performance metrics are directly attributed to the optimized heterointerface, where the built-in electric field at the nanoscale WS2/SnS2 junctions promotes efficient charge separation and minimizes recombination losses. Notably, the device retains over 95\% of its initial performance even after 1 week of ambient exposure, highlighting its superior environmental robustness. This work introduces an interface-engineering strategy that leverages the unique electronic properties of earth-abundant, nontoxic two-dimensional materials, offering a viable pathway for scalable, high-speed, and stable photodetectors suitable for next-generation optoelectronic systems.

}, keywords = {2D, CVD, heterojunction, photodetector, SnS2, WS2}, doi = {10.1021/acsanm.5c04078}, author = {Das, Chayan and Kumar, Suresh and Sharma, Anjali and Kumar, Mahesh and Rath, Arup K. and Sahu, Satyajit} }