Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity.This work was supported by the Office of Basic Energy Sciences (BES) of the U.S. Department of Energy (DOE) under contract DE-AC02-05CH11231 through the Structure and Dynamics of Materials Interfaces Program (FWP KC31SM) and the Molecular Foundry. M.L. acknowledges funds from Comunidad de Madrid (P2018/EMT-4308), a Fulbright grant PRX16/00564, and the MCIU-AEI-FEDERUE (RTI2018-096937-B-C22 and MAT2014-59772-C2-1-P). J.C. acknowledges financial support from Ministerio de Ciencia e Innovación (MICINN) and the European Union through the project PID2019-104272RB-C52. Also, Y.H. acknowledges financial support from MCIU through MAT2014-59772-C2-2- P and L.M. from EC through ERC-2013-SYG-610256. V.A.P.O. and M.B. acknowledge the financial support from EC through ERC CoG HyMAP 648319, MINECO PID2019- 106315RB-I00 and ENE2017-89170-R, ″Comunidad de Madrid″ and European Structural Funds (FotoArt-CM project S2018/NMT-4367) and Fundación Ramón Areces (Art-Leaf project). M.B. also thanks the Juan de la Cierva Incorporación contract (IJC2019042430-I). X.Z. was supported by the NSF-BSF 359 grant number 1906014. The authors thank Prof. Eran Edri, María Ujué González Sagardoy, and Judit Meseguer- Oliver for fruitful discussions and Asylum customer support for help with modifications of the AFM

Experimental Study on Reverse Osmosis System with Carbon Nano Tubes from Candle Soot

Conventionally, water Purification system contains two important purification stages, namely Carbon Filtration and Reverse Osmosis (RO). There has been significant research work reported in the literature on enhancing the RO water purification efficiency. Moreover, for obtaining desired quality of water as well as the production rates, the importance of system engineering is evident. We present two fold contributions in this field, (1) prepared and used candle flame soot as Nano carbon tubes as the dsorbents. An adsorption purification stage with carbon Nano tubes has been used before the RO stage in the water purification system. Experimental study of the purification system with and without Nano tube filtration stage has been presented. (2) Experimental study of transient analysis of RO system has been presented to understand the dynamics of the two stage process. The effect of feed pressure, water feed rate, and ratio of rejected and retentate flow rate have been investigated on the water quality.by N V Ravi Teja Chintala and Nitin Padhiyarby N V Ravi Teja Chintala, and Nitin Padhiya

A simple scheme of molecular electronic devices with multiwalled carbon nanotubes as the top electrodes

A simple fabrication scheme for molecular electronic junctions is presented with multiwalled carbon nanotubes (MWCNTs) as the top electrodes. Results indicate that our approach retains the molecular character of the chosen molecules [a self-assembled monolayer of octadecanethiol on gold bottom electrodes] and opens the door for studying a wide variety of organothiol candidates for molecular electronics. The fabrication scheme is designed in a way that it can be modified into all-carbon devices in the future by using graphitic carbon bottom electrodes functionalized with nitrozoabenzene, for example, and MWCNTs or graphene as the top electrodes. Alternatively, the scheme is applicable for all-gold devices with gold bottom electrodes and gold nanowire top electrodes

Surface characterization of InP trenches embedded in oxide using scanning probe microscopy

© 2015 AIP Publishing LLC. Metrology for structural and electrical analyses at device level has been identified as one of the major challenges to be resolved for the sub-14 nm technology nodes. In these advanced nodes, new high mobility semiconductors, such as III-V compounds, are grown in narrow trenches on a Si substrate. Probing the nature of the defects, the defect density, and the role of processing steps on the surface of such structures are prime metrology requirements. In order to enable defect analysis on a (III-V) surface, a proper sample preparation for oxide removal is of primary importance. In this work, the effectiveness of different chemical cleanings and thermal annealing procedures is investigated on both blanket InP and oxide embedded InP trenches by means of scanning probe microscopy techniques. It is found that the most effective approach is a combination of an HCl-based chemical cleaning combined with a low-temperature thermal annealing leading to an oxide free surface with atomically flat areas. Scanning tunneling microscopy (STM) has been the preferred method for such investigations on blanket films due to its intrinsic sub-nm spatial resolution. However, its application on oxide embedded structures is non-trivial. To perform STM on the trenches of interest (generally <20 nm wide), we propose a combination of non-contact atomic force microscopy and STM using the same conductive atomic force microscopy tip Our results prove that with these procedures, it is possible to perform STM in narrow InP trenches showing stacking faults and surface reconstruction. Significant differences in terms of roughness and terrace formation are also observed between the blanket and the oxide embedded InP.status: publishe

Modeling of precipitation of ultra-fine particles by pressure reduction over CO2-expanded liquids

A mathematical model has been developed to describe the process of precipitation of ultrafine particles by pressure reduction over gas (CO2)-expanded liquids. A rapid pressure reduction over a CO2-expanded organic solution, from 30–70 to 1 bar at 303 K decreases the solution temperature by 30–80 K in a very short span of time (0.5–1.5 min), which generates a rapid, high, and uniform supersaturation of the dissolved solute in the solution and facilitates precipitation of ultrafine particles. The model developed in this work estimates the supersaturation attained, nucleation and growth rates obtained during the pressure reduction over CO2-expanded organic solutions, and the particle size distribution of the precipitated particles. Cholesterol has been chosen as a model solute to be precipitated, and acetone has been chosen as a solvent. A new method has been developed for prediction of equilibrium solubility of solute which is affected by a decrease in CO2 mole fraction as well as a simultaneous decrease in solution temperature during pressure reduction. This method combines the semi-empirical approach of using the partial molar volume fraction of solvent in a CO2-solvent binary mixture and solid–liquid equilibrium data for a solute–solvent system. Size distributions of the precipitated particles have been calculated assuming primary nucleation (homogeneous as well as heterogeneous nucleation) and diffusion-limited growth kinetics. The predicted mean average particle sizes are then compared with the size of cholesterol particles precipitated by pressure reduction of a CO2-expanded acetone solution of cholesterol. The particle sizes predicted assuming heterogeneous nucleation are found to be closer to the experimentally observed particle sizes, indicating that the heterogeneous nucleation could be the main mechanism of nucleation, which could occur at the gas–liquid interface of the CO2 bubbling out of CO2-expanded solution during pressure reduction.by Rajarshi Chattaraj, Umesh Dhumal and Sameer V. Dalv

Nanoscale 3D characterisation of soft organic material using conductive scanning probe tomography

The 3D nanostructure of organic materials plays a key role in their performance in a broad range of fields, from life sciences to electronics. However, characterising the functionality of their morphologies presents a critical challenge requiring nanometre resolution in 3 dimensions and methods that do not excessively distort the soft matter during measurement. Here we present scanning probe tomography using a commercial Pt-Ir coated tip and controlling the tip loading force to sequentially characterise and remove layers from the surface of a sample. We demonstrate this process on a sample exhibiting a polymer nanowire morphology, which is typically used for organic electronic applications, and present a tomographic reconstruction of the nanoscale charge transport network of the semi-crystalline polymer. Good electrical connectivity in 3D is demonstrated by directly probing the electrical properties of the inter-nanowire charge conduction

Sacrificial Self-Assembled Monolayers for the Passivation of GaAs (100) Surfaces and Interfaces

© 2016 American Chemical Society. The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga-S and As-S bonds at the GaAs-thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al-S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending.status: publishe

Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2.

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity