George Biskos

Bio: George Biskos is an academic researcher from The Cyprus Institute. The author has contributed to research in topics: Aerosol & Particle. The author has an hindex of 29, co-authored 104 publications receiving 3156 citations. Previous affiliations of George Biskos include Delft University of Technology & Harvard University.

Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles

Abstract: The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of parti...

Description and Theoretical Analysis of a Differential Mobility Spectrometer

Abstract: Electrical mobility analysis is the most efficient technique for measuring aerosol particle size distributions in the submicron size range. Recent advances in aerosol science underline the need of fast measurements of particle size spectra in this range, and therefore a great amount of effort has been focused towards this direction. This paper provides the description and a theoretical framework for the analysis of a fast-response differerntial mobility spectrometer (DMS). In common with other instruments of its category, it consists of a particle charger, a classification column, and a series of detectors. Passing the sample flow first through a corona-wire diffusion charger that sets a charge on the particles, the aerosol is introduced around the central rod of an inside-out cylindrical classifier equipped with a series of isolated electrode rings connected to sensitive electrometers. Current readings produced by deposition of the charged particles on the electrometer rings are then translated to partic...

Generation and Sizing of Particles for Aerosol-Based Nanotechnology

Abstract: Traditionally, the generation of nanoparticles for technological applications has been mostly performed by classical wet chemistry or lithographic methods, and their size has been commonly determined in situ by electron microscopy techniques. Advances in aerosol technology over the past 30 years have provided methods that enable the generation and measurement of nanosize building blocks, and have opened up new oppor tunities in the assembly of nanostructured materials and nanodevices. This article provides a brief review on state-of-the-art techniques for generating nanoparticles of well-defined size and chemical composition in view of applications in nanotechnology. Covering atomization techniques from the liquid phase and nanoparticle synthesis from the gas phase, we discuss the advantages and limitations of each method. Considering the advantages of on-line methods that aerosols instruments of fer, we describe the most ef ficient techniques for measuring the size distributions of airborne nanosize particles. Finally, we provide a brief discussion on existing and emerging applications of aerosol-based nanotechnology.

Enhancement of the Photoelectrochemical Performance of CuWO4 Thin Films for Solar Water Splitting by Plasmonic Nanoparticle Functionalization

Abstract: The effect of plasmonic nanoparticles (NPs) on the photoelectrochemical water splitting performance of CuWO4 is studied here for the first time. CuWO4 thin films were functionalized with well-defined Au NPs in two composite configurations: with the NPs (I) at the CuWO4–electrolyte interface and (II) at the CuWO4 back contact. In both cases, the incident photon to current conversion efficiency of the film was increased (∼6-fold and ∼1.2-fold for configurations I and II (at λ = 390 nm), respectively). Two important advantages of placing the NPs on the CuWO4–electrolyte interface are identified: (1) Au NPs, coated with a 2 nm TiO2 layer, are found to significantly enhance the surface catalysis of the film, decreasing the surface charge recombination from ∼60% to ∼10%, and (2) the NP’s near-field can promote additional charge carriers within the space charge layer region, where they undergo field-assisted transport, essentially avoiding recombination. Our study shows that Au NPs, coated with a 2 nm TiO2 layer...

Toward industrial scale synthesis of ultrapure singlet nanoparticles with controllable sizes in a continuous gas-phase process

Abstract: Continuous gas-phase synthesis of nanoparticles is associated with rapid agglomeration, which can be a limiting factor for numerous applications. In this report, we challenge this paradigm by providing experimental evidence to support that gas-phase methods can be used to produce ultrapure non-agglomerated “singlet” nanoparticles having tunable sizes at room temperature. By controlling the temperature in the particle growth zone to guarantee complete coalescence of colliding entities, the size of singlets in principle can be regulated from that of single atoms to any desired value. We assess our results in the context of a simple analytical model to explore the dependence of singlet size on the operating conditions. Agreement of the model with experimental measurements shows that these methods can be effectively used for producing singlets that can be processed further by many alternative approaches. Combined with the capabilities of up-scaling and unlimited mixing that spark ablation enables, this study provides an easy-to-use concept for producing the key building blocks for low-cost industrial-scale nanofabrication of advanced materials.

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Abstract: Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Introduction to the Finite Element Method

Abstract: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer

Abstract: The application of mass spectrometric techniques to the realtime measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between similar to 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li(+) ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described. (c) 2007 Wiley Periodicals, Inc.