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1.
Nano Lett ; 23(15): 6920-6926, 2023 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-37499227

RESUMO

We demonstrate the epitaxial coating of GaN NWs with an epitaxial ZnO shell by atomic layer deposition at 300 °C. Scanning transmission electron microscopy proves a sharp and defect-free coherent interface. The strain in the core-shell structure due to the lattice mismatch and different thermal expansion coefficients of GaN and ZnO was analyzed using 4D-STEM strain mapping and Raman spectroscopy and compared to theoretical calculations. The results highlight the outstanding advantages of epitaxial shell growth using atomic layer deposition, e.g., conformal coating and precise thickness control.

2.
Nanotechnology ; 34(41)2023 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-37402361

RESUMO

Glyphosate (N-(phosphonomethyl)glycine) is well known nonselective and broad-spectrum herbicide that has been extensively used in agricultural areas around the world to increase agricultural productivity. However, the utilization of glyphosate can cause environmental contamination and health problems. Therefore, the detection of glyphosate with a fast, low-cost, and portable sensor is still important. In this work, the electrochemical sensor has been developed by modifying of working surface on the screen-printed silver electrode (SPAgE) with a mixtures solution between zinc oxide nanoparticles (ZnO-NPs) and poly(diallyldimethylammonium chloride) (PDDA) by the drop-casting process. The ZnO-NPs have been prepared based on a sparking method by using pure zinc wires. The ZnO-NPs/PDDA/SPAgE sensor shows a wide range of glyphosate detection (0µM-5 mM). The limit of detection of ZnO-NPs/PDDA/SPAgE is 2.84µM. The ZnO-NPs/PDDA/SPAgE sensor exhibits high selective towards glyphosate with minimal interference from other commonly used herbicides including paraquat, butachlor-propanil and glufosinate-ammonium. Furthermore, the ZnO-NPs/PDDA/SPAgE sensor demonstrates a good estimation of glyphosate concentration in real samples such as green tea, corn juice and mango juice.

3.
Microsc Microanal ; 25(3): 592-600, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30829197

RESUMO

In situ transmission electron microscope (TEM) characterization techniques provide valuable information on structure-property correlations to understand the behavior of materials at the nanoscale. However, understanding nanoscale structures and their interaction with the electron beam is pivotal for the reliable interpretation of in situ/ex situ TEM studies. Here, we report that oxides commonly used in nanoelectronic applications, such as transistor gate oxides or memristive devices, are prone to electron beam induced damage that causes small structural changes even under very low dose conditions, eventually changing their electrical properties as examined via in situ measurements. In this work, silicon, titanium, and niobium oxide thin films are used for in situ TEM electrical characterization studies. The electron beam induced reduction of the oxides turns these insulators into conductors. The conductivity change is reversible by exposure to air, supporting the idea of electron beam reduction of oxides as primary damage mechanism. Through these measurements we propose a limit for the critical dose to be considered for in situ scanning electron microscopy and TEM characterization studies.

4.
Nanotechnology ; 28(24): 245503, 2017 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-28452329

RESUMO

Novel tin oxide field-effect-transistors (SnO2 NW-FET) for pH and protein detection applicable in the healthcare sector are reported. With a SnO2 NW-FET the proof-of-concept of a bio-sensing device is demonstrated using the carrier transport control of the FET channel by a (bio-) liquid modulated gate. Ultra-thin Al2O3 fabricated by a low temperature atomic layer deposition (ALD) process represents a sensitive layer to H+ ions safeguarding the nanowire at the same time. Successful pH sensitivity is demonstrated for pH ranging from 3 to 10. For protein detection, the SnO2 NW-FET is functionalized with a receptor molecule which specifically interacts with the protein of interest to be detected. The feasibility of this approach is demonstrated via the detection of a biotinylated protein using a NW-FET functionalized with streptavidin. An immediate label-free electronic read-out of the signal is shown. The well-established Enzyme-Linked Immunosorbent Assay (ELISA) method is used to determine the optimal experimental procedure which would enable molecular binding events to occur while being compatible with a final label-free electronic read-out on a NW-FET. Integration of the bottom-up fabricated SnO2 NW-FET pH- and biosensor into a microfluidic system (lab-on-a-chip) allows the automated analysis of small volumes in the 400 µl range as would be desired in portable on-site point-of-care (POC) devices for medical diagnosis.


Assuntos
Técnicas Biossensoriais , Dispositivos Lab-On-A-Chip , Nanofios/química , Proteínas Repressoras/análise , Compostos de Estanho/química , Transistores Eletrônicos , Óxido de Alumínio/química , Biotina/química , Ensaio de Imunoadsorção Enzimática , Humanos , Concentração de Íons de Hidrogênio , Limite de Detecção , Sistemas Automatizados de Assistência Junto ao Leito , Estreptavidina/química
5.
Nano Lett ; 16(3): 1583-9, 2016 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-26898670

RESUMO

Comparison of the measured absolute absorption cross section on a per Si atom basis of plasma-synthesized Si nanocrystals (NCs) with the absorption of bulk crystalline Si shows that while near the band edge the NC absorption is weaker than the bulk, yet above ∼ 2.2 eV the NC absorbs up to 5 times more than the bulk. Using atomistic screened pseudopotential calculations we show that this enhancement arises from interface-induced scattering that enhances the quasi-direct, zero-phonon transitions by mixing direct Γ-like wave function character into the indirect X-like conduction band states, as well as from space confinement that broadens the distribution of wave functions in k-space. The absorption enhancement factor increases exponentially with decreasing NC size and is correlated with the exponentially increasing direct Γ-like wave function character mixed into the NC conduction states. This observation and its theoretical understanding could lead to engineering of Si and other indirect band gap NC materials for optical and optoelectronic applications.

6.
Nanotechnology ; 26(1): 014001, 2015 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-25489994

RESUMO

A unique composite nanonet of metal oxide@carbon interconnected sheets is obtained by atomic layer deposition (ALD)-assisted fabrication. In this nanonet structure, mesoporous metal oxide nanosheets are covered by a layer of amorphous carbon nanoflakes. Specifically, quasi-vertical aligned and mesoporous Ni(x)Co(1-x)O nanosheets are first fabricated directly on nickel foam substrates by a hydrothermal method. Then, an ALD-enabled carbon coating method is applied for the growth of carbon nanoflakes on the surface of the nanosheets. The thus formed 3D hierarchical structure of Ni(x)Co(1-x)O@carbon composite flakes have a higher surface area, better electrical conductivity and structure stability than the bare Ni(x)Co(1-x)O. The application of such composite nanomaterials is demonstrated as electrodes for a supercapacitor and a lithium-ion battery. In both tests, the composite electrode shows enhancement in capacity and cycling stability. This effective composite nanostructure design of metal oxides@carbon flakes could provide a promising method to construct high-performance materials for energy and environment applications.

7.
Nanotechnology ; 26(12): 125707, 2015 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-25743098

RESUMO

In this article a microfabricated thermoelectric nanowire characterization platform to investigate the thermoelectric and structural properties of single nanowires is presented. By means of dielectrophoresis (DEP), a method to manipulate and orient nanowires in a controlled way to assemble them onto our measurement platform is introduced. The thermoelectric platform fabricated with optimally designed DEP electrodes results in a yield of nanowire assembly of approximately 90% under an applied peak-to-peak ac signal Vpp = 10 V and frequency f = 20 MHz within a series of 200 experiments. Ohmic contacts between the aligned single nanowire and the electrodes on the platform are established by electron beam-induced deposition. The Seebeck coefficient and electrical conductivity of electrochemically synthesized Bi2Te3 nanowires are measured to be -51 µV K(-1) and (943 ± 160)/(Ω(-1) cm(-1)), respectively. Chemical composition and crystallographic structure are obtained using transmission electron microscopy. The selected nanowire is observed to be single crystalline over its entire length and no grain boundaries are detected. At the surface of the nanowire, 66.1 ± 1.1 at.% Te and 34.9 ± 1.1 at.% Bi are observed. In contrast, chemical composition of 64.2 at.% Te and 35.8 at.% Bi is detected in the thick center of the nanowire.

8.
ACS Appl Mater Interfaces ; 15(23): 28387-28397, 2023 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-37269318

RESUMO

Tin oxide (SnO2)/zinc oxide (ZnO) core/shell nanowires as anode materials in lithium-ion batteries (LIBs) were investigated using a combination of classical electrochemical analysis and high-resolution electron microscopy to correlate structural changes and battery performance. The combination of the conversion materials SnO2 and ZnO is known to have higher storage capacities than the individual materials. We report the expected electrochemical signals of SnO2 and ZnO for SnO2/ZnO core/shell nanowires as well as unexpected structural changes in the heterostructure after cycling. Electrochemical measurements based on charge/discharge, rate capability, and electrochemical impedance spectroscopy showed electrochemical signals for SnO2 and ZnO and partial reversibility of lithiation and delithiation. We find an initially 30% higher capacity for the SnO2/ZnO core/shell NW heterostructure compared to the ZnO-coated substrate without the SnO2 NWs. However, electron microscopy characterization revealed pronounced structural changes upon cycling, including redistribution of Sn and Zn, formation of ∼30 nm particles composed of metallic Sn, and a loss of mechanical integrity. We discuss these changes in terms of the different reversibilities of the charge reactions of both SnO2 and ZnO. The results show stability limitations of SnO2/ZnO heterostructure LIB anodes and offer guidelines on material design for advanced next-generation anode materials for LIBs.

9.
Small ; 8(21): 3307-14, 2012 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-22826095

RESUMO

A new technique is reported for the transformation of smooth nonpolar ZnO nanowire surfaces to zigzagged high-index polar surfaces using polycrystalline ZnO thin films deposited by atomic layer deposition (ALD). The c-axis-oriented ZnO nanowires with smooth nonpolar surfaces are fabricated using vapor deposition method and subsequently coated by ALD with a ZnO particulate thin film. The synthesized ZnO-ZnO core-shell nanostructures are annealed at 800 °C to transform the smooth ZnO nanowires to zigzagged nanowires with high-index polar surfaces. Ozone sensing response is compared for all three types of fabricated nanowire morphologies, namely nanowires with smooth surfaces, ZnO-ZnO core-shell nanowires, and zigzagged ZnO nanowires to determine the role of crystallographic surface planes on gas response. While the smooth and core-shell nanowires are largely non-responsive to varying O(3) concentrations in the experiments, zigzagged nanowires show a significantly higher sensitivity (ppb level) owing to inherent defect-rich high-index polar surfaces.

10.
Nanotechnology ; 23(23): 235607, 2012 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-22609898

RESUMO

In this work, the controlled fabrication of highly ordered ZnO nanowire (NW) arrays on silicon substrates is reported. Si NWs fabricated by a combination of phase shift lithography and etching are used as a template and are subsequently substituted by ZnO NWs with a dry-etching technique and atomic layer deposition. This fabrication technique allows the vertical ZnO NWs to be fabricated on 4 in Si wafers. Room temperature photoluminescence and micro-photoluminescence are used to observe the optical properties of the atomic layer deposition (ALD) based ZnO NWs. The sharp UV luminescence observed from the ALD ZnO NWs is unexpected for the polycrystalline nanostructure. Surprisingly, the defect related luminescence is much decreased compared to an ALD ZnO film deposited at the same time ona plane substrate. Electrical characterization was carried out by using nanomanipulators. With the p-type Si substrate and the n-type ZnO NWs the nanodevices represent p­n NW diodes.The nanowire diodes show a very high breakthrough potential which implies that the ALD ZnO NWs can be used for future electronic applications.


Assuntos
Nanoestruturas/química , Nanoestruturas/ultraestrutura , Semicondutores , Silício/química , Óxido de Zinco/química , Condutividade Elétrica , Galvanoplastia , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
11.
Nano Lett ; 11(9): 3513-8, 2011 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-21077688

RESUMO

Semiconductor nanowire devices have several properties which match future requirements of scaling down the size of electronics. In typical microelectronics production, a number of microstructures are aligned precisely on top of each other during the fabrication process. In the case of nanowires, this mandatory condition is still hard to achieve. A technological breakthrough is needed to accurately place nanowires at any specific position and then form devices in mass production. In this article, an upscalable process combining conventional micromachining with phase shift lithography will be demonstrated as a suitable tool for nanowire device technology. Vertical Si and ZnO nanowires are demonstrated on very large (several cm(2)) areas. We demonstrate how the nanowire positions can be controlled, and the resulting nanowires are used for device fabrication. As an example Si/ZnO heterojunction diode arrays are fabricated. The electrical characterization of the produced devices has also been performed to confirm the functionality of the fabricated diodes.

12.
Sci Rep ; 12(1): 2641, 2022 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-35173193

RESUMO

The effect of an externally applied electric field on exciton splitting and carrier transport was studied on 3.5 nm Si nanocrystals embedded in SiO2 superlattices with barrier oxide thicknesses varied between 2 and 4 nm. Through a series of photoluminescence measurements performed at both room temperature and with liquid N2 cooling, it was shown that the application of an electric field resulted in a reduction of luminescence intensity due to exciton splitting and charging of nanocrystals within the superlattices. This effect was found to be enhanced when surface defects at the Si/SiO2 interface were not passivated by H2 treatment and severely reduced for inter layer barrier oxide thicknesses above 3 nm. The findings point to the surface defects assisting in carrier transport, lowering the energy required for exciton splitting. Said enhancement was found to be diminished at low temperatures due to the freezing-in of phonons. We propose potential device design parameters for photon detection and tandem solar cell applications utilizing the quantum confinement effect based on the findings of the present study.

13.
Small ; 6(16): 1705-22, 2010 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-20712030

RESUMO

Nanowires are important potential candidates for the realization of the next generation of sensors. They offer many advantages such as high surface-to-volume ratios, Debye lengths comparable to the target molecule, minimum power consumption, and they can be relatively easily incorporated into microelectronic devices. Accordingly, there has been an intensified search for novel nanowire materials and corresponding platforms for realizing single-molecule detection with superior sensing performance. In this work, progress made towards the use of nanowires for achieving better sensing performance is critically reviewed. In particular, various nanowires types (metallic, semiconducting, and insulating) and their employment either as a sensor material or as a template material are discussed. Major obstacles and future steps towards the ultimate nanosensors based on nanowires are addressed.


Assuntos
Técnicas Biossensoriais , Nanofios/química , Técnicas Biossensoriais/instrumentação , Eletroquímica , Nanotecnologia/métodos , Semicondutores , Silício/química , Ressonância de Plasmônio de Superfície
14.
Beilstein J Nanotechnol ; 11: 843-853, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32551209

RESUMO

In this study, we used simulations as a guide for experiments in order to switch freestanding nanowire growth to a laterally aligned growth mode. By means of finite element simulations, we determined that a higher volumetric flow and a reduced process pressure will result in a preferred laterally aligned nanowire growth. Furthermore, increasing the volumetric flow leads to a higher species dilution. Based on our numerical results, we were able to successfully grow laterally aligned SnO2 nanowires out of gold film edges and gold nanoparticles on a-plane sapphire substrates. In our experiments a horizontal 2-zone tube furnace was used. The generation of Sn gas was achieved by a carbothermal reduction of SnO2 powder. However, we observed no elongation of the nanowire length with an increase of the process time. Nevertheless, an alternating gas exchange between an inert gas (Ar) and an oxygen-containing process atmosphere yielded an elongation of the laterally aligned nanowires, indicating that the nanowire growth takes place in a transient period of the gas exchange.

15.
Polymers (Basel) ; 11(4)2019 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-30959918

RESUMO

The brittleness of acrylic photopolymers, frequently used in 3D Inkjet printing, limits their utilization in structural applications. In this study, a process was developed for the production and characterization of an alumina-enhanced nanocomposite with improved mechanical properties for Inkjet printing. Ceramic nanoparticles with an average primary particle size (APPS) of 16 nm and 31 nm, which was assessed via high-resolution scanning electron microscopy (HRSEM), were functionalized with 3.43 and 5.59 mg/m² 3-(trimethoxysilyl)propyl methacrylate (MPS), respectively, while being ground in a ball mill. The suspensions of the modified fillers in a newly formulated acrylic mixture showed viscosities of 14 and 7 mPa∙s at the printing temperature of 60 °C. Ink-jetting tests were conducted successfully without clogging the printing nozzles. Tensile tests of casted specimens showed an improvement of the tensile strength and elongation at break in composites filled with 31 nm by 10.7% and 74.9%, respectively, relative to the unfilled polymer.

16.
Beilstein J Nanotechnol ; 9: 1501-1511, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29977683

RESUMO

Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be fabricated by plasma-enhanced chemical vapour deposition (PECVD). Conventionally, SiH4 and N2O are used as precursor gasses, which inevitably leads to the incorporation of ≈10 atom % nitrogen, rendering the matrix a silicon oxynitride. Alternatively, SiH4 and O2 can be used, which allows for completely N-free silicon oxide. In this work, we investigate the properties of B- and P-incorporating Si NCs embedded in pure silicon oxide compared to silicon oxynitride by atom probe tomography (APT), low-temperature photoluminescence (PL), transient transmission (TT), and current-voltage (I-V) measurements. The results clearly show that no free carriers, neither from P- nor from B-doping, exist in the Si NCs, although in some configurations charge carriers can be generated by electric field ionization. The absence of free carriers in Si NCs ≤5 nm in diameter despite the presence of P- or B-atoms has severe implications for future applications of conventional impurity doping of Si in sub-10 nm technology nodes.

17.
Small ; 3(10): 1660-71, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17890644

RESUMO

The Kirkendall effect is a consequence of the different diffusivities of atoms in a diffusion couple causing a supersaturation of lattice vacancies. This supersaturation may lead to a condensation of extra vacancies in the form of so-called "Kirkendall voids" close to the interface. On the macroscopic and micrometer scale these Kirkendall voids are generally considered as a nuisance because they deteriorate the properties of the interface. In contrast, in the nanoworld the Kirkendall effect has been positively used as a new fabrication route to designed hollow nano-objects. In this Review we summarize and discuss the demonstrated examples of hollow nanoparticles and nanotubes induced by the Kirkendall effect. Merits of this route are compared with other general methods for nanotube fabrication. Theories of the kinetics and thermodynamics are also reviewed and evaluated in terms of their relevance to experiments. Moreover, nanotube fabrication by solid-state reactions and non-Kirkendall type diffusion processes are covered.


Assuntos
Nanopartículas/química , Nanotubos/química , Difusão , Microscopia Eletrônica de Transmissão
18.
Beilstein J Nanotechnol ; 8: 2315-2323, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29181288

RESUMO

The absorption cross section (ACS) of silicon nanocrystals (Si NCs) in single-layer and multilayer structures with variable thickness of oxide barriers is determined via a photoluminescence (PL) modulation technique that is based on the analysis of excitation intensity-dependent PL kinetics under modulated pumping. We clearly demonstrate that roughly doubling the barrier thickness (from ca. 1 to 2.2 nm) induces a decrease of the ACS by a factor of 1.5. An optimum separation barrier thickness of ca. 1.6 nm is calculated to maximize the PL intensity yield. This large variation of ACS values with barrier thickness is attributed to a modulation of either defect population states or of the efficiency of energy transfer between confined NC layers. An exponential decrease of the ACS with decreasing temperature down to 120 K can be explained by smaller occupation number of phonons and expansion of the band gap of Si NCs at low temperatures. This study clearly shows that the ACS of Si NCs cannot be considered as independent on experimental conditions and sample parameters.

19.
Sci Rep ; 7: 46703, 2017 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-28425460

RESUMO

All electronic, optoelectronic or photovoltaic applications of silicon depend on controlling majority charge carriers via doping with impurity atoms. Nanoscale silicon is omnipresent in fundamental research (quantum dots, nanowires) but also approached in future technology nodes of the microelectronics industry. In general, silicon nanovolumes, irrespective of their intended purpose, suffer from effects that impede conventional doping due to fundamental physical principles such as out-diffusion, statistics of small numbers, quantum- or dielectric confinement. In analogy to the concept of modulation doping, originally invented for III-V semiconductors, we demonstrate a heterostructure modulation doping method for silicon. Our approach utilizes a specific acceptor state of aluminium atoms in silicon dioxide to generate holes as majority carriers in adjacent silicon. By relocating the dopants from silicon to silicon dioxide, Si nanoscale doping problems are circumvented. In addition, the concept of aluminium-induced acceptor states for passivating hole selective tunnelling contacts as required for high-efficiency photovoltaics is presented and corroborated by first carrier lifetime and tunnelling current measurements.

20.
Sci Rep ; 7(1): 863, 2017 04 13.
Artigo em Inglês | MEDLINE | ID: mdl-28408757

RESUMO

Phosphorus doping of silicon nanostructures is a non-trivial task due to problems with confinement, self-purification and statistics of small numbers. Although P-atoms incorporated in Si nanostructures influence their optical and electrical properties, the existence of free majority carriers, as required to control electronic properties, is controversial. Here, we correlate structural, optical and electrical results of size-controlled, P-incorporating Si nanocrystals with simulation data to address the role of interstitial and substitutional P-atoms. Whereas atom probe tomography proves that P-incorporation scales with nanocrystal size, luminescence spectra indicate that even nanocrystals with several P-atoms still emit light. Current-voltage measurements demonstrate that majority carriers must be generated by field emission to overcome the P-ionization energies of 110-260 meV. In absence of electrical fields at room temperature, no significant free carrier densities are present, which disproves the concept of luminescence quenching via Auger recombination. Instead, we propose non-radiative recombination via interstitial-P induced states as quenching mechanism. Since only substitutional-P provides occupied states near the Si conduction band, we use the electrically measured carrier density to derive formation energies of ~400 meV for P-atoms on Si nanocrystal lattice sites. Based on these results we conclude that ultrasmall Si nanovolumes cannot be efficiently P-doped.

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