Highly Tunable Aptasensing Microarrays with Graphene Oxide Multilayers

A highly tunable layer-by-layer (LbL)-assembled graphene oxide (GO) array has been devised for high-throughput multiplex protein sensing. In this array, the fluorescence of different target-bound aptamers labeled with dye is efficiently quenched by GO through fluorescence resonance energy transfer (FRET), and simultaneous multiplex target detection is performed by recovering the quenched fluorescence caused by specific binding between an aptamer and a protein. Thin GO films consisting of 10 bilayers displayed a high quenching ability, yielding over 85% fluorescence quenching with the addition of a 2 mu M dye-labeled aptamer. The limit for human thrombin detection in the 6- and 10-bilayered GO array is estimated to be 0.1 and 0.001 nM, respectively, indicating highly tunable nature of LbL assembled GO multilayers in controlling the sensitivity of graphene-based FRET aptasensor. Furthermore, the GO chip could be reused up to four times simply by cleaning it with distilled water.open4

FIB synthesis of Bi2Se3 1D nanowires demonstrating the co-existence of Shubnikov-de Haas oscillations and linear magnetoresistance

Since the discovery of topological insulators (TIs), there are considerable interests in demonstrating metallic surface states (SS), their shielded robust nature to the backscattering and study their properties at nanoscale dimensions by fabricating nanodevices. Here we address an important scientific issue related to TI whether one can clearly demonstrate the robustness of topological surface states (TSS) to the presence of disorder that does not break any fundamental symmetry. The simple straightforward method of FIB milling was used to synthesize nanowires of Bi2Se3 which we believe is an interesting route to test robustness of TSS and the obtained results are new compared to many of the earlier papers on quantum transport in TI demonstrating the robustness of metallic SS to gallium (Ga) doping. In the presence of perpendicular magnetic field, we have observed the co-existence of Shubnikov-de Haas oscillations and linear magnetoresistance (LMR), which was systematically investigated for different channel lengths, indicating the Dirac dispersive surface states. The transport properties and estimated physical parameters shown here demonstrate the robustness of SS to the fabrication tools triggering flexibility to explore new exotic quantum phenomena at nanodevice level

Fast switching response of Na-doped CZTS photodetector from visible to NIR range

It is important to study the photoconductivity to understand the optoelectronic properties of semiconductor thin films. Here, we report the effect of Na doping on the photoconductivity properties of CZTS (Cu2ZnSnS4) in the visible and NIR region. CZTS thin films were deposited on quartz and silicon dioxide substrates using stacked layer reactive sputtering and annealing. The photoconductivity of undoped CZTS and Na-doped CZTS in visible region (excitation wavelength - 532 nm) and in the NIR region (excitation wavelength - 1064 nm) were studied. At a bias voltage of 150 mV, response rise time for undoped CZTS in the visible region was 1.02 s which decreased to 391 ms for Na-doped CZTS. The rise time in NIR region decreased from 245 ms (for undoped CZTS) to 1.06 ms (for Na-doped CZTS). The decay time for undoped sample (in the visible region) was 1.20 s, which decreased to 221 ms (for Na-doped CZTS). In the NIR region, the decay time decreased from 342 ms (undoped CZTS) to 29.80 ms (Na-doped CZTS). A large increase in the photocurrent response (from 6.5 to 2320 times in the visible region and from 12.6 to 3384 times in the NIR region) in the CZTS upon Na doping was observed. Thus, switching in the NIR region is improved drastically upon Na doping in CZTS. Therefore, it can be concluded that Na-doped CZTS can be utilized as NIR photodetector

FIB synthesis of Bi2Se3 1D nanowires demonstrating the co-existence of Shubnikov-de Haas oscillations and linear magnetoresistance

Since the discovery of topological insulators (TIs), there are considerable interests in demonstrating metallic surface states (SS), their shielded robust nature to the backscattering and study their properties at nanoscale dimensions by fabricating nanodevices. Here we address an important scientific issue related to TI whether one can clearly demonstrate the robustness of topological surface states (TSS) to the presence of disorder that does not break any fundamental symmetry. The simple straightforward method of FIB milling was used to synthesize nanowires of Bi2Se3 which we believe is an interesting route to test robustness of TSS and the obtained results are new compared to many of the earlier papers on quantum transport in TI demonstrating the robustness of metallic SS to gallium (Ga) doping. In the presence of perpendicular magnetic field, we have observed the co-existence of Shubnikov-de Haas oscillations and linear magnetoresistance (LMR), which was systematically investigated for different channel lengths, indicating the Dirac dispersive surface states. The transport properties and estimated physical parameters shown here demonstrate the robustness of SS to the fabrication tools triggering flexibility to explore new exotic quantum phenomena at nanodevice level

Proximity-induced supercurrent through topological insulator based nanowires for quantum computation studies

Proximity-induced superconducting energy gap in the surface states of topological insulators has been predicted to host the much wanted Majorana fermions for fault-tolerant quantum computation. Recent theoretically proposed architectures for topological quantum computation via Majoranas are based on large networks of Kitaev's one-dimensional quantum wires, which pose a huge experimental challenge in terms of scalability of the current single nanowire based devices. Here, we address this problem by realizing robust superconductivity in junctions of fabricated topological insulator (Bi2Se3) nanowires proximity-coupled to conventional s-wave superconducting (W) electrodes. Milling technique possesses great potential in fabrication of any desired shapes and structures at nanoscale level, and therefore can be effectively utilized to scale-up the existing single nanowire based design into nanowire based network architectures. We demonstrate the dominant role of ballistic topological surface states in propagating the long-range proximity induced superconducting order with high IcRN product in long Bi2Se3 junctions. Large upper critical magnetic fields exceeding the ChandrasekharClogston limit suggests the existence of robust superconducting order with spin-triplet cooper pairing. An unconventional inverse dependence of IcRN product on the width of the nanowire junction was also observed

Observation of quantum oscillations in FIB fabricated nanowires of topological insulator (Bi2Se3)

In the last few years, research based on topological insulators (TIs) has been of great interest due to their intrinsic exotic fundamental properties and potential applications such as quantum computers or spintronics. The fabrication of TI nanodevices and the study of their transport properties has mostly focused on high quality crystalline nanowires or nanoribbons. Here, we report a robust approach to Bi2Se3 nanowire formation from deposited flakes using an ion beam milling method. Fabricated Bi2Se3 nanowire devices were employed to investigate the robustness of the topological surface state (TSS) to gallium ion doping and any deformation in the material due to the fabrication tools. We report on the quantum oscillations in magnetoresistance (MR) curves under the parallel magnetic field. The resistance versus magnetic field curves are studied and compared with Aharonov- Bohm (AB) interference effects, which further demonstrate transport through the TSS. The fabrication route and observed electronic transport properties indicate clear quantum oscillations, and these can be exploited further in studying the exotic electronic properties associated with TI- based nanodevices

Nanostructured Cu2ZnSnS4 (CZTS) thin film for self-powered broadband photodetection

Nanostructured materials exhibit broad spectral photodetection, strong light matter interaction and exotic optoelectronic properties compared to their bulk counterpart. To overcome the limitations of silicon based photodetectors, various nanomaterials have been investigated. Here we have used industrially viable stacked layer reactive sputtering method to grow rice-like nanostructured (rln) Cu2ZnSnS4 (CZTS) thin films. The rln-CZTS film showed optical absorption coefficient one order of magnitude greater than the plain thin films of CZTS. Further, even under zero bias condition, broad spectral response (in visible and near infrared range) was observed. The rise and decay time constants for visible (532 nm) and near infrared (NIR) (1064 nm) light incident were 208 ms, 175 ms and 681 ms, 778 ms, respectively (for 1 mV bias). The improvement in photocurrent has been attributed to enhanced light harvesting due to the presence of nanostructures in thin film. Detectivity of 4.48 x 10(8) Jones over a large area was observed indicating that rln-CZTS would be a potential material for other technical applications. Deposition of nanostructured CZTS using industrially viable reactive sputtering with short anneal and fabrication of self-powered broadband photodetection device with low rise and decay time constants are the novelties of this work

Enhanced photoresponse of Cu2ZnSn(S, Se)(4) based photodetector in visible range

Fast switching response of photodetectors is needed for many applications. Therefore, it is necessary to study the photoconductivity properties of earth abundant and cost effective materials. Till now, there are only two reports based on photoconductivity study of Cu2ZnSnS4 (CZTS) based materials. In this study, CZTSSe thin film on soda-lime glass substrate was deposited using one-step reactive sputtering from CZTSe target in presence of H2S followed by annealing. Optical, structural, morphological and elemental compositional analyses were carried out to characterize the CZTSSe thin film. The value of optical band gap estimated using Tauc's plot was 1.45 eV. The presence of very intense peak corresponding to (112) plane in the XRD pattern suggested growth to be oriented. Similar was the case with Raman studies. Photoconductivity study of CZTSSe thin film in visible region (excitation wavelength 532 nm) is carried out. At a bias voltage of 5 V, response rise time and decay time in visible range for CLIsSe were 330 ms and 0.986 ms, respectively. The values of responsivity, detectivity, sensitivity (I-light/I-dark) and external quantum efficiency were 14.6 mA/W, 3.5 x 10(9) Jones, 6.9363 and 3.5%, respectively. The shortest reported response decay time by CZTSSe based photodetector is the novelty of this work. This work shows the possibility of utilizing CZTSSe thin film as photodetector for various applications