Fabrication, functionalization and electrical conductance modulation of nanoparticle based molecular electronic Nano-devices

Over the years many techniques have been proposed for the purpose of the formation of electrically conducting metal-molecule-metal junctions. One such technique utilizes gold-nanoparticles (AuNPs) that could assist in contacting small molecules between large gaps. The Ideal device structure then comprises of one nanoparticle and two molecules that are aligned as electrode1-molecule-AuNP-molecule-electrode2. In present work these AuNP-molecule hybrids were fabricated inside sub 20 nm sized nanogaps between nanoelectrodes. The nanogaps were fabricated by milling of thin gold wires using focused ion beam. The tuning of the ion dosage resulted in the tuning of the gap size and the smallest nanogap of 2.3 nm was achieved. The nano molecular electronic device (nanoMoED) platform comprised of the AuNPs that were assembled inside the nanogaps via dielectrophoresis. Two types of the AuNPs were used that were different from each other due to their functionalization chemistry. The low bias resistance 'RLB' of the nanoMoED platform was (i) reduced as compared to the nanogaps (ii) remained stable in toluene and air, and (iii) was reduced when exposed to the electron beam. The nanoMoED platform was functionalized with various molecules using the molecular place exchange method. The successful functionalization resulted in the reduction of the 'RLB'. The smallest value of the 'RLB' of the nanoMoED devices was achieved when the inserted molecule was not only highly conducting but also its length was same as the initial spacing between the AuNPs. The nitrogen dioxide (NO2) molecules reduced the 'RLB' of the nanoMoED devices that were made with 4,4'-biphenyl dithiol. The theoretical simulations showed that this reduction was due to the induced states at Fermi energy of the junction. The nanoMoED devices made with 1,8-octanedithiol showed conductance switching between two levels because of different geometries of the Au-S contact. This switching vanished when these devices were exposed to NO2 and a strong enhancement of signal to noise ratio was observed. On the basis of these results this thesis suggests possible routes for the fabrication of highly conducting nanoMoED devices as well as elucidates the possibility of using the nanoMoED devices for gas sensing applications

Fabrication, functionalization and electrical conductance modulation of nanoparticle based molecular electronic Nano-devices

Over the years many techniques have been proposed for the purpose of the formation of electrically conducting metal-molecule-metal junctions. One such technique utilizes gold-nanoparticles (AuNPs) that could assist in contacting small molecules between large gaps. The Ideal device structure then comprises of one nanoparticle and two molecules that are aligned as electrode1-molecule-AuNP-molecule-electrode2. In present work these AuNP-molecule hybrids were fabricated inside sub 20 nm sized nanogaps between nanoelectrodes. The nanogaps were fabricated by milling of thin gold wires using focused ion beam. The tuning of the ion dosage resulted in the tuning of the gap size and the smallest nanogap of 2.3 nm was achieved. The nano molecular electronic device (nanoMoED) platform comprised of the AuNPs that were assembled inside the nanogaps via dielectrophoresis. Two types of the AuNPs were used that were different from each other due to their functionalization chemistry. The low bias resistance 'RLB' of the nanoMoED platform was (i) reduced as compared to the nanogaps (ii) remained stable in toluene and air, and (iii) was reduced when exposed to the electron beam. The nanoMoED platform was functionalized with various molecules using the molecular place exchange method. The successful functionalization resulted in the reduction of the 'RLB'. The smallest value of the 'RLB' of the nanoMoED devices was achieved when the inserted molecule was not only highly conducting but also its length was same as the initial spacing between the AuNPs. The nitrogen dioxide (NO2) molecules reduced the 'RLB' of the nanoMoED devices that were made with 4,4'-biphenyl dithiol. The theoretical simulations showed that this reduction was due to the induced states at Fermi energy of the junction. The nanoMoED devices made with 1,8-octanedithiol showed conductance switching between two levels because of different geometries of the Au-S contact. This switching vanished when these devices were exposed to NO2 and a strong enhancement of signal to noise ratio was observed. On the basis of these results this thesis suggests possible routes for the fabrication of highly conducting nanoMoED devices as well as elucidates the possibility of using the nanoMoED devices for gas sensing applications

Fabrication, functionalization and electrical conductance modulation of nanoparticle based molecular electronic Nano-devices

Over the years many techniques have been proposed for the purpose of the formation of electrically conducting metal-molecule-metal junctions. One such technique utilizes gold-nanoparticles (AuNPs) that could assist in contacting small molecules between large gaps. The Ideal device structure then comprises of one nanoparticle and two molecules that are aligned as electrode1-molecule-AuNP-molecule-electrode2. In present work these AuNP-molecule hybrids were fabricated inside sub 20 nm sized nanogaps between nanoelectrodes. The nanogaps were fabricated by milling of thin gold wires using focused ion beam. The tuning of the ion dosage resulted in the tuning of the gap size and the smallest nanogap of 2.3 nm was achieved. The nano molecular electronic device (nanoMoED) platform comprised of the AuNPs that were assembled inside the nanogaps via dielectrophoresis. Two types of the AuNPs were used that were different from each other due to their functionalization chemistry. The low bias resistance 'RLB' of the nanoMoED platform was (i) reduced as compared to the nanogaps (ii) remained stable in toluene and air, and (iii) was reduced when exposed to the electron beam. The nanoMoED platform was functionalized with various molecules using the molecular place exchange method. The successful functionalization resulted in the reduction of the 'RLB'. The smallest value of the 'RLB' of the nanoMoED devices was achieved when the inserted molecule was not only highly conducting but also its length was same as the initial spacing between the AuNPs. The nitrogen dioxide (NO2) molecules reduced the 'RLB' of the nanoMoED devices that were made with 4,4'-biphenyl dithiol. The theoretical simulations showed that this reduction was due to the induced states at Fermi energy of the junction. The nanoMoED devices made with 1,8-octanedithiol showed conductance switching between two levels because of different geometries of the Au-S contact. This switching vanished when these devices were exposed to NO2 and a strong enhancement of signal to noise ratio was observed. On the basis of these results this thesis suggests possible routes for the fabrication of highly conducting nanoMoED devices as well as elucidates the possibility of using the nanoMoED devices for gas sensing applications

Fabrication of reproducible sub-5 nm nanogaps by a focused ion beam and observation of Fowler-Nordheim tunneling

Creating a stable high resistance sub-5 nm nanogap in between conductive electrodes is one of the major challenges in the device fabrication of nano-objects. Gap-sizes of 20 nm and above can be fabricated reproducibly by the precise focusing of the ion beam and careful milling of the metallic lines. Here, by tuning ion dosages starting from 4.6 x 10(10) ions/cm and above, reproducible nanogaps with sub-5 nm sizes are milled with focused ion beam. The resistance as a function of gap dimension shows an exponential behavior, and Fowler-Nordheim tunneling effect was observed in nanoelectrodes with sub-5 nm nanogaps. The application of Simmon's model to the milled nanogaps and the electrical analysis indicates that the minimum nanogap size approaches to 2.3 nm

Enhanced gas sensing performance of graphene/ZnS-CdS hetero-nanowires gas sensor synthesized by Langmuir-Blodgett self-assembly method

Graphene is a promising material in the field of solid-state gas sensors due to the unique two-dimensional structure. Here, we have shown by fabricating graphene/ZnS-CdS hetero-nanowire structure, the gas sensor sensitivity has a two-fold increase to 20% under 15 ppm gaseous concentration compared to a 10% response in pristine graphene. Spectroscopy and microscopy analysis indicate that the semi-conducting ZnS-CdS hetero-nanowires are 2 nm wide and densely packed on top of graphene. By combining UV illumination, the device approaches a fast response/recovery and high gas sensitivity, thus has a potential to be used in a detection of wide range of gases.

Designing sterically demanding thiolate coated gold nanoparticles for electrical characterization of biphenyl dithiol in a nanoparticle-​molecule-​nanoelectrode platform

International audienceMolecular electronics with single or few molecules requires a stable metal-molecule nanojunction platform. Herein, we report the design and synthesis of gold nanoparticles coated with sterically demanding thiol ligands that are essential to fabricate a versatile and stable nanoelectrode-molecule- nanoparticle platform suitable for electrical characterization of small organic molecules. By combining ω-tetraphenylmethane ether functionalized alkyl thioacetate and alkyl thiols, we prepare highly stable gold nanoparticles in a one-phase reaction providing simple and efficient purification. This robust preparation gives highly pure nanoparticles in very high yields (up to 90%) with long-time shelf stability. The synthesis in this work has superior reproducibility compared to the previous synthesis processes that are currently being used for such molecular electronics platforms. Electron microscopy confirms the formation of uniform and small nanoparticles in the range of 5 to 7 nm. These nanoparticles with different ligand surface coverages are placed in a 20 nm nanoelectrodes setup using dielectrophoretic forces. This setup was utilized to characterize the conductivity of the molecular wire 4,4’-biphenyldithiol introduced via ligand place-exchange under ambient conditions

A sub 20 nm metal-conjugated molecule junction acting as a nitrogen dioxide sensor

The interaction of a gas molecule with a sensing material causes the highest change in the electronic structure of the latter, when this material consists of only a few atoms. If the sensing material consists of a short, conductive molecule, the sensing action can be furthermore probed by connecting such molecules to nanoelectrodes. Here, we report that NO2 molecules that adhere to 4,4'-biphenyldithiol (BPDT) bound to Au surfaces lead to a change of the electrical transmission of the BPDT. The related device shows reproducible, stable measurements and is so far the smallest (<20 nm) gas sensor. It demonstrates modulation of charge transport through molecules upon exposure to nitrogen dioxide down to concentrations of 55 ppb. We have evaluated several devices and exposure conditions and obtained a close to linear dependence of the sensor response on the gas concentration

Physicochemical characterization, phytochemical analysis, and pharmacological evaluation of Sambucus wightiana

Sambucus wightiana (SW) is a 4–5-foot herbaceous stem with 5–9 leaflets and pinnatifid leaves (15–30 cm). It is used to treat stomach disorders, as an emetic for expelling poisonous substances, and as a laxative for controlling skin diseases. Phytochemical research based on ethnopharmacological knowledge is frequently regarded as an appropriate approach for discovering new agents from higher-altitude plants. Therefore, the present study focussed on identifying, collecting, and authenticating the S. wightiana and, isolating and characterizing the phytoconstituents using the DPPH method, reducing power, total flavonoid, phenolic content, anti-hyperglycemic and antioxidant capacity. Furthermore, the evaluation of antidiabetic studies of extracts/fraction and pure phytoconstituents of S. wightiana in alloxan-induced diabetic model and OGTT methods were carried out. The observed results revealed that the methanolic extract of Sambucus wightiana has significant anti-hyperglycemic and anti-oxidant activity. The methanolic extracts of S. wightiana, a dose of alloxan/SW-400 mg/Kg (111.55 ± 6.9 mg/dl) also decreased significantly the serum ALP level (p < 0.05). The methanol extracts of S. wightiana showed highly significant anti-hyperglycemic activity (p < 0.05). From the methanolic extracts, alloxan/SW-400 mg/Kg (89.55 ± 2.5 mg/dl) showed highly significant decrease in serum LDL level (p < 0.05) in extract-treated groups, not changing the body weight substantially and methanolic extract of S. wightiana at a dose of 400 mg/Kg exhibited substantial lipid, and blood glucose levels and liver enzymes lowering capacity compared to the diabetic control group. Consequently, the prevention of hyperglycaemia by various other drugs, S. wightiana could contribute to a new formulation with significant pharmacological effects