Nikolai Kouklin

Carbon nanotube probes for single-cell experimentation and assays

Integrating nanotechnology with experimental biology is paramount to advancing fundamental biological science and technology, and, therefore, of high current interest and importance. In this article, we report on a new possibility of utilizing carbon nanotube probes assembled by a modified dielectrophoretic based technique for single-cell experimentation and delivery. The modified approach permits highly reproducible construction of water-stable, highly-aligned, and electrically-conductive probes several hundred microns in length, which hold a great promise for enhancing previously developed molecular-scale intracellular experimental techniques. The results of this work, in particular, indicate that the minimally invasive nanotube probes could be advantageous for studies involving permeabilization and subsequent desorption of molecules into a cell’s interior, thereby obviating permeabilization and diffusion across membranes.

Photothermovoltaic effect in carbon nanotubes: En route toward junctionless infrared photocells and light sensors

Optically induced voltage was studied in carbon nanotube films configured as two-terminal resistive elements and operating as junctionless photocells in the infrared. The photovoltage is found to appear only for asymmetric/off-contact illuminations and the effect is explained based on photogenerated heat flow model. The engineered cell prototypes were found to yield electrical powers of ∼30 pW while demonstrating improved conversion efficiency under high-flux illumination. The cell is also shown to act as uncooled infrared sensor with its dark-to-photocurrent ratio improving as temperature increases. The concept might enable nanotube’s use in applications ranging from heat recycling to self-powered infrared sensors.

Negative photoconduction of planar heterogeneous random network of ZnO-carbon nanotubes

In this letter, the authors report on the effect of negative photoconduction observed in heterogeneous two-dimensional random networks comprising single-walled nanotubes and ZnO particles, and investigated by room temperature dc-photoconduction measurements. For this, two-terminal thin film devices engineered by solution coating of the nanotubes with ZnO microparticles consistently exhibited increase in the resistance versus decrease in the nanotubes alone with ultraviolet illumination, which is explained within the model of interface-mediated charging/discharging effects. The study suggests the possibility of engineering reduced-cost and multirange nanotube light sensors based on extrinsic carrier modulation via external gating at the interface.

Spectral investigation of carrier recombination processes in ZnO nanorods at high temperatures

The mechanism of near-band-edge (NBE) emission from crystalline ZnO (c‐ZnO) nanorods grown on c‐Si by a catalyst-assisted vapor-liquid-solid method has been investigated by performing temperature-, power-, and time-dependent photoluminescence (PL) measurements at a temperature (T) range of 143–503K. In contrast to previous reports, we find that the NBE PL is primarily associated with free exciton emission, whereas the contribution of band-to-band and free-to-bound radiative recombinations remains negligible up to the highest T studied. A spectral evolution of the NBE band with T was further analyzed within the framework of a three-parameter model, proposed recently, with the results presented and discussed. Finally, the ratio of excitonic-to-defect luminescence intensity has been observed to change nonmonotonically with T, which is explained based on the difference in the quenching mechanisms of exciton and defect PL.

Temperature-dependent studies of defect-assisted light emission and excitation processes in crystalline ZnO nanowire phosphors

A series of photoluminescence and photoluminescence-excitation spectroscopies have been performed to probe the processes regulating defect-assisted light emission from one-dimensional ZnO nanowire phosphors in a wide temperature range of 123–463 K. The observed nonmonotonic change of the integral defect-photoluminescence intensity as well as its peak position with temperature are explained based on the interplay of competing effects of thermal quenching and carrier redistribution over radiative channels. A temperature-induced broadening of the defect photoluminescence band is observed and attributed to the appearance of ∼2.1 eV band, the intensity of which is also found to quench quickly with the onset of higher temperature. The results of photoluminescence-excitation measurements show that band-to-band excitations remain a primary excitation channel of defects especially at low and moderate temperature range, whereas the role of direct, one-photon absorption channel is found to progress as temperature ap...

Self-assembled network of carbon nanotubes synthesized by chemical vapor deposition in alumina porous template

Relying on self-assembly principles and mechanisms to engineer new and previously unachievable devices and systems on nano- and microscales is a highly promising field of research today. In this work, a self-assembly of partially exposed and free-standing carbon nanotubes (CNTs) grown in the pores of alumina matrix into a quasiperiodic two-dimensional static network is reported. The network pattern is analyzed with a fast Fourier transformation and reveals a short-range order, which does not replicate that of underlying alumina template. The network formation is likely to be driven by short-range interactions involving hydrophobic-hydrophobic interactions and van der Waals forces balanced by mechanical deformation forces. The work might help realize new possibilities for self-guided, bottom-up, and large scale assembly of multifunctional and electrically conductive CNTs grown in alumina matrix for applications in electronic circuits, sensor networks and interconnects.

Concrete Embedded Dye-Synthesized Photovoltaic Solar Cell

This work presents the concept of a monolithic concrete-integrated dye-synthesized photovoltaic solar cell for optical-to-electrical energy conversion and on-site power generation. The transport measurements carried out in the dark revealed the presence of VOC of ~190 mV and ISC of ~9 μA, induced by the electrochemical conversion of concrete-supplied ionic impurities at the electrodes. The current-voltage measurements performed under illumination at incident optical powers of ~46 mW confirmed the generation of electrical power of ~0.64 μW with almost half generated via battery effect. This work presents a first step towards realizing the additional pathways to low-cost electrical power production in urban environments based on a combined use of organic dyes, nanotitania and concrete technology.

Self-driven formation and structure of single crystal platelets of Zn3As2

In this work the authors introduce and provide details on the stoichiometrically controlled self-driven formation of freestanding single crystal platelets in Zn3As2 by a direct self-catalytic vapor-solid growth mechanism. The platelets feature dimensions of up to ∼1cm and mirrorlike microscopically flat top surfaces. A coherent formation of pyramids and wires has been further observed on some of the platelet top surfaces, the growth mechanism of which is discussed. This study might open pathways for facile engineering of high-performance semiconductor via a direct vapor-solid conversion of polycrystalline semiconductor powders into single crystal substrates on a large scale and with low cost.

Towards controlled manipulation and assembly of ZnO nanowires for nanoscale imaging applications

In this letter the authors develop a technique enabling both facile alignment and placement of ZnO nanorods onto the support electrodes in a highly controlled manner and with high yield. The approach takes advantage of the surface tension effect and the formation of nonvanishing electrical dipoles at the metal-semiconductor and semiconductor/semiconductor interfaces in highly nonpolar solvents. Experimental tests confirmed excellent mechanical resilience of single crystal ZnO nanorods and overall stability of the engineered assemblies. Finally, use of ZnO nanorods as tips for high-resolution atomic force microscope nanoscale imaging is demonstrated.

Transition Metal-Doped ZnO Nanowires: En Route Towards Multi-colour Light Sensing and Emission Applications

Opto-electronics is one of the largest and fastest evolving market segments, with revenues expected to surpass