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Ivanov, Ilia N

Publications and source records attributed to Ivanov, Ilia N.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Deciphering Halogen Competition in Organometallic Halide Perovskite Growth

Organometallic halide perovskites (OHPs) hold great promise for next-generation, low-cost optoelectronic devices. During the chemical synthesis and crystallization of OHP thin films a major unresolved question is the competition between multiple halide species (e.g. I-, Cl-, Br-) in the formation of the mixed halide perovskite crystals. Whether Cl- ions are successfully incorporated into the perovskite crystal structure or alternatively, where they are located, is not yet fully understood. Here, in situ X-ray diffraction measurements of crystallization dynamics are combined with ex situ TOF-SIMS chemical analysis to reveal that Br- or Cl- ions can promote crystal growth, yet reactive I- ions prevent them from incorporating into the lattice of the final perovskite crystal structure. The Cl- ions are located in the grain boundaries of the perovskite films. These findings significantly advance our understanding of the role of halogens during synthesis of hybrid perovskites, and provide an insightful guidance to the engineering of high-quality perovskite films, essential for exploring superior-performance and cost-effective optoelectronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Spatially resolved resistance of NiO nanostructures under humid environment

The spatially resolved electrical response of polycrystalline NiO films composed of 40 nm crystallites was investigated under different relative humidity levels (RH). The topological and electrical properties (surface potential and resistance) were characterized with sub 25nm resolution using Kelvin probe force microscopy (KPFM) and conductive scanning probe microscopy under argon atmosphere at 0%, 50%, and 80% relative humidity. The dimensionality of surface features obtained through autocorrelation analysis of topological maps increased linearly with increased relative humidity, as water was adsorbed onto the film surface. Surface potential decreased from about 280mV to about 100 mV and resistance decreased from about 5 G to about 3 G , in a nonlinear fashion when relative humidity was increased from 0% to 80%. Spatially resolved surface potential and resistance of the NiO films was found to be heterogeneous throughout the film, with distinct domains that grew in size from about 60 nm to 175 nm at 0% and 80% RH levels, respectively. The heterogeneous character of the topological, surface potential, and resistance properties of the polycrystalline NiO film observed under dry conditions decreased with increased relative humidity, yielding nearly homogeneous surface properties at 80% RH, suggesting that the nanoscale potential and resistance properties converge with the mesoscale properties as water is adsorbed onto the NiO film.

conductive AFM↗
DOE OSTI2016

Low-cost scalable quartz crystal microbalance array for environmental sensing

Proliferation of environmental sensors for internet of things (IoT) applications has increased the need for low-cost platforms capable of accommodating multiple sensors. Quartz crystal microbalance (QCM) crystals coated with nanometer-thin sensor films are suitable for use in high-resolution (~1 ng) selective gas sensor applications. We demonstrate a scalable array for measuring frequency response of six QCM sensors controlled by low-cost Arduino microcontrollers and a USB multiplexer. Gas pulses and data acquisition were controlled by a LabVIEW user interface. We test the sensor array by measuring the frequency shift of crystals coated with different compositions of polymer composites based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) while films are exposed to water vapor and oxygen inside a controlled environmental chamber. Our sensor array exhibits comparable performance to that of a commercial QCM system, while enabling high-throughput 6 QCM testing for under $1,000. We use deep neural network structures to process sensor response and demonstrate that the QCM array is suitable for gas sensing, environmental monitoring, and electronic-nose applications.

Anazagasty, Cristain↗
DOE OSTI2016

Effect of film morphology on oxygen and water interaction with copper phthalocyanine

Copper phthalocyanine (CuPc) films of thickness 25 nm and 100 nm were grown by thermal sublimation at 25 C, 150 C, and 250 C in order to vary morphology. Using a source-measure unit and a quartz crystal microbalance (QCM), we measured changes in electrical resistance and film mass in situ during exposure to controlled pulses of O2 and H2O vapor. Mass loading by O2 was enhanced by a factor of 5 in films deposited at 250 C, possibly due to the ~200 C CuPc transition which allows higher O2 mobility between stacked molecules. While gas/vapor sorption occurred over timescales of < 10 minutes, resistance change occurred over timescales > 1 hour, suggesting that mass change occurs by rapid adsorption at active surface sites, whereas resistive response is dominated by slow diffusion of adsorbates into the film bulk. Resistive response generally increases with film deposition temperature due to increased porosity associated with larger crystalline domains. The 25 nm thick films exhibit higher resistive response than 100 nm thick films after an hour of O2/H2O exposure due to the smaller analyte diffusion length required for reaching the film/electrode interface. We found evidence of decoupling of CuPc from the gold-coated QCM crystal due to preferential adsorption of O2/H2O molecules on gold, which is consistent with findings of other studies.

Miller, Nicholas↗
DOE OSTI2015

Correlating highpower conversion efficiency of PTB7:PC 71 BM inverted organic solar cells with nanoscale structures [Unraveling the correlation between the structural aspects and power conversion efficiency in PTB7:PC 71 BM inverted organic solar cells]

Advances in materials design and device engineering led to inverted organic solar cells (i-OSCs) with superior power conversion efficiencies (PCEs) to their conventional counterparts, in addition to the well-known better ambient stability. Despite the significant progress, however, it has so far been unclear how the morphologies of the photoactive layer and its interface with the cathode modifying layer impact device performance. Here, we report an in-depth morphology study of the i-OSC active and cathode modifying layers, employing a model system with the well-established bulk-heterojunction, PTB7:PC 71 BM as the active layer and poly-[(9,9-bis(3 -( N,N -dimethylamino)propyl)-2,7-fluorene)- alt -2,7-(9,9-dioctylfluorene)] (PFN) as the cathode surface modifying layer. We have also identified the role of a processing additive, 1,8-diiodooctane (DIO), used in the spin-casting of the active layer to increase PCE. Using a variety of characterization techniques, we demonstrate that the high PCEs of i-OSCs are due to the smearing (diffusion) of electron-accepting PC 71 BM into the PFN layer, resulting in improved electron transport. The PC 71 BM diffusion occurs after spin-casting the active layer onto the PFN layer, when residual solvent molecules act as a plasticizer. Furthermore, the DIO additive, with a higher boiling point than the host solvent, has a longer residence time in the spin-cast active layer, resulting in more PC 71 BM smearing and therefore more efficient electron transport. This work provides important insight and guidance to further enhancement of i-OSC performance by materials and interface engineering.

14 SOLAR ENERGY↗
DOE OSTI2015

High-Performance Flexible Perovskite Solar Cells by Using a Combination of Ultrasonic Spray-Coating and Low Thermal Budget Photonic Curing

Realizing the commercialization of high-performance and robust perovskite solar cells urgently requires the development of economically scalable processing techniques. Here we report a high-throughput ultrasonic spray-coating (USC) process capable of fabricating perovskite film-based solar cells on glass substrates with power conversion efficiency (PCE) as high as 13.04%. Perovskite films with high uniformity, crystallinity, and surface coverage are obtained in a single step. Moreover, we report USC processing on TiOx/ITO-coated polyethylene terephthalate (PET) substrates to realize flexible perovskite solar cells with PCE as high as 8.02% that are robust under mechanical stress. In this case, an optical curing technique was used to achieve a highly-conductive TiOx layer on flexible PET substrates for the first time. The high device performance and reliability obtained by this combination of USC processing with optical curing appears very promising for roll-to-roll manufacturing of high-efficiency, flexible perovskite solar cells.

Sanjib, Das↗
DOE OSTI2014

Array of titanium dioxide nanostructures for solar energy utilization

An array of titanium dioxide nanostructures for solar energy utilization includes a plurality of nanotubes, each nanotube including an outer layer coaxial with an inner layer, where the inner layer comprises p-type titanium dioxide and the outer layer comprises n-type titanium dioxide. An interface between the inner layer and the outer layer defines a p-n junction.

14 SOLAR ENERGY↗
DOE OSTI2014

Superhydrophobic coated apparatus for liquid purification by evaporative condensation

Disclosed are examples of apparatuses for evaporative purification of a contaminated liquid. In each example, there is a first vessel for storing the contaminated fluid. The first vessel includes a surface coated with a layer of superhydrophobic material and the surface is at least partially in contact with the contaminated liquid. The contaminants do not adhere to the surface as the purified liquid evaporates, thus simplifying maintenance of the apparatus.

42 ENGINEERING↗
DOE OSTI2014

Pulsed Laser Deposition of Photoresponsive Two-Dimensional GaSe Nanosheet Networks

Here we explore pulsed laser deposition (PLD), a well known and versatile synthesis method principally used for epitaxial oxide thin film growth, for the synthesis of functional metal chalcogenide (GaSe) nanosheet networks by stoichiometric transfer of laser vaporized material from bulk GaSe targets in Ar background gas. Uniform coverage of interconnected, crystalline, few-layer, photoresponsive GaSe nanosheets in both in-plane and out-of-plane orientations were achieved under different ablation plume conditions over ~1.5 cm2 areas. Plume propagation was characterized by in situ ICCD-imaging. High (1 Torr) Ar background gas pressures were found to be crucial for the stoichiometric growth of GaSe nanosheet networks. Individual 1-3 layer GaSe triangular nanosheets of ~ 200 nm domain size were formed within 30 laser pulses, coalescing to form nanosheet networks in as few as 100 laser pulses. The thickness of the deposited networks increased linearly with pulse number, adding layers in a two-dimensional (2D) growth mode while maintaining a surface roughness of 2 GaSe layers for increasing overall thickness. Field effect transistors using these interconnected crystalline GaSe networks showed p-type semiconducting characteristics with mobilities reaching as high as 0.1 cm2V-1s-1. Spectrally-resolved photoresponsivities and external quantum efficiencies ranged from 0.4 AW-1 and 100% at 700 nm, to 1.4 AW-1 and 600 % at 240 nm, respectively. Pulsed laser deposition under these conditions appears to provide a versatile and rapid approach to stoichiometrically transfer and deposit photoresponsive networks of 2D nanosheets with digital thickness control and substrate-scale uniformity for a variety of applications.

GaSe↗
DOE OSTI2014

Anomalous Photodeposition of Ag on Ferroelectric Surfaces with Below Bandgap Excitation

Ferroelectric lithography, a recent method of fabricating functional interfaces, traditionally involves photoreduction on polarized ferroelectric surfaces at optical energies above the bandgap of the ferroelectric. In this work, we report for the first time, photochemical deposition of elemental Ag nanoparticles on a specifically poled lithium niobate substrate, with broad white light spectrum light transmitted through the crystal. The transmitted light has energies only below the bandgap, leading to the conclusion that the Ag reduction proceeds through non-linear effects, specifically, second harmonic generation.

Seal, Katyayani↗
DOE OSTI2014

Scalable production of microbially-mediated ZnS nanoparticles and application to functional thin films

A series of semiconducting zinc sulfide (ZnS) nanoparticles were scalably, reproducibly, controllably, and economically synthesized with anaerobic metal-reducing Thermoanaerobacter species. They reduced partially oxidized sulfur sources to sulfides that extracellularly and thermodynamically incorporated with zinc ions to produce sparingly soluble ZnS nanoparticles with ~5 nm crystallites at yields of ~5 g l 1 month 1. A predominant sphalerite formation was facilitated by rapid precipitation kinetics, low cation/anion ratio, higher zinc concentration, water stabilization, or some combination of the four. The sphalerite ZnS nanoparticles exhibited narrow size distribution, high emission intensity, and few native defects. Scale-up and emission tunability using copper-doping were confirmed spectroscopically. Surface characterization was determined using Fourier transform infrared and X-ray photoelectron spectroscopies, which confirmed amine and carboxylic acid not only maintaining a nano-dimensional average crystallite size, but also increasing aggregation. Application of ZnS nanoparticle ink to a functional thin film was successfully tested for potential future applications.

Moon, Ji Won↗
DOE OSTI2014

Synthesis and properties of SiN coatings as stable fluorescent markers on vertically aligned carbon nanofibers

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains mostly Si and N. In fluorescent microscopy experiments, imaging VACNF interfacing to live cell cultures it turned out that this material is broadly fluorescent, which made VACNFs useful as spatial markers, or created nuisance when DNA-labeling got masked. In this paper we provide insight into nature of this silicon/nitrogen in situ coatings. Here we have proposed a potential mechanism for deposition of SiNx coating on the sidewalls of VACNFs during PECVD synthesis in addition to exploring the origin of the coatings fluorescence. It seems most likely that the substrate reacts with the process gases through both processes similar to reactive sputtering and CVD to form silane and other silicon bearing compounds before being deposited isotropically as a SiNx coating onto the VACNFs. The case for the presence of Si-NCs is made strong through a combination of the strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies.

Pearce, Ryan↗
DOE OSTI2014

Untangling the isotopic effects of deuteration on the optoelectronic properties of conducting polymers

The attractive optoelectronic properties of conducting polymers depend sensitively upon intra- and inter-polymer chain interactions, and therefore new methods to manipulate these interactions are continually being pursued. Here, we report a study of the isotopic effects of deuterium substitution on the structure, morphology, and optoelectronic properties of regioregular poly(3-hexylthiophene)s (P3HT) with an approach that combines the synthesis of deuterated materials, optoelectronic properties measurements, theoretical simulation, and neutron scattering. Selective substitutions of deuterium on the backbone or side-chains of P3HT result in distinct optoelectronic responses in P3HT/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) photovoltaics. Specifically, the weak non-covalent intermolecular interactions induced by the main-chain deuteration are shown to change the film crystallinity and morphology of P3HT/PCBM blends, and consequently reduce the short circuit current. However, decreased electronic coupling, the formation of a charge transfer state, and increased electron-phonon coupling resulting from side chain deuteration are shown to induce a remarkable reduction in open circuit voltage.

Shao, Ming↗
DOE OSTI2014

Cooperative Island Growth of Large Area Single-Crystal Graphene by Chemical Vapor Deposition on Cu

We describe a two-step approach for suppressing nucleation of graphene on Cu using chemical vapor deposition. In the first step, as received Cu foils are oxidized in air at temperatures up to 500 C to remove surface impurities and to induce the regrowth of Cu grains during subsequent annealing in H2 flow at 1040 C prior to graphene growth. In the second step, transient reactant cooling is performed by using a brief Ar pulse at the onset of growth to induce collisional deactivation of the carbon growth species. The combination of these two steps results in a three orders of magnitude reduction in the graphene nucleation density, enabling the growth of millimeter-size single crystal graphene grains. A kinetic model shows that suppressing nucleation promotes a cooperative island growth mode that favors the formation of large area single crystal graphene, and it is accompanied by a roughly 3 orders of magnitude increase in the reactive sticking probability of methane compared to that in random nucleation growth.

chemical vapor deposition↗
DOE OSTI2013

Carbon nanotube temperature and pressure sensors

The present invention, in one embodiment, provides a method of measuring pressure or temperature using a sensor including a sensor element composed of a plurality of carbon nanotubes. In one example, the resistance of the plurality of carbon nanotubes is measured in response to the application of temperature or pressure. The changes in resistance are then recorded and correlated to temperature or pressure. In one embodiment, the present invention provides for independent measurement of pressure or temperature using the sensors disclosed herein.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Transparent conductive nano-composites

The present invention, in one embodiment, provides a method of forming an organic electric device that includes providing a plurality of carbon nanostructures; and dispersing the plurality of carbon nanostructures in a polymeric matrix to provide a polymeric composite, wherein when the plurality of carbon nanostructures are present at a first concentration an interface of the plurality of carbon nanostructures and the polymeric matrix is characterized by charge transport when an external energy is applied, and when the plurality of carbon nanostructures are present at a second concentration the interface of the plurality of carbon nanostructures and the polymeric matrix are characterized by exciton dissociation when an external energy is applied, wherein the first concentration is less than the second concentration.

36 MATERIALS SCIENCE↗