Solid Bridging during Pattern Collapse (Stiction) Studied on Silicon Nanoparticles

2011 ◽  
Vol 1299 ◽  
Author(s):  
Daniel Peter ◽  
Michael Dalmer ◽  
Andriy Lotnyk ◽  
Lorenz Kienle ◽  
Alfred Lechner ◽  
...  
Keyword(s):  
Silicon Nanoparticles ◽  
High Surface ◽  
Volume Ratio ◽  
Model System ◽  
Core Shell ◽  
Surface Phenomena ◽  
Drying Process ◽  
Sio2 Shell ◽  
Local View ◽  
Shell Particles

ABSTRACTThe high surface to volume ratio of nanoparticles allows a detailed experimental study of the surface phenomena associated with solid bridging. Besides bulk analyses, the local view on the structure and composition via HRTEM is particularly essential. 50 nm core shell particles consisting of a silicon (Si) core and a SiO2 shell were used as model system to understand surface phenomena appearing for Si-based nanostructures. Evaporative drying from de-ionized water shows the most significant bridging effect based on SiO2. There is only a localized deposition of oxides between the particles during the drying process and no overall oxidation. For the deposition material, silicates are the most likely candidates.

Atomistic Study of Creation of Bimetallic Clusters by Coalescence

2008 ◽  
Vol 1087 ◽  
Author(s):  
S. Mizuno ◽  
K. Shintani
Keyword(s):  
Surface Energy ◽  
Morphological Evolution ◽  
High Surface ◽  
Chemical Properties ◽  
Volume Ratio ◽  
Dynamics Simulation ◽  
Bimetallic Clusters ◽  
Core Shell ◽  
Metallic Clusters ◽  
Growth Modes

AbstractMetallic clusters show excellent performance as catalysts because of their high surface-to-volume ratio. An inert-gas aggregation source is an experimental method by which clusters are produced. In such a method, cluster coalescence is one of growth modes of clusters. Bimetallic clusters also attract much attention of researchers because of their novel physical and chemical properties. At coalescence of two metallic clusters of different species, alloying or core-shell structuring tends to occur spontaneously. Resulting alloyed clusters or core-shell clusters will behave as unique catalysts. In this paper, morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics simulation. All pair combinations of the elements Au, Ag, Pt, and Pd are considered. The interactions between such metallic atoms are calculated by using generic embedded-atom method (GEAM) potential. Two clusters of icosahedral structure are equilibrated at specified temperature beforehand. The two clusters are put close to each other, where the nearest two atoms belonging to the two clusters, respectively, start to interact with each other. After coalescence the original surfaces of the two clusters decrease, and the surface energy is transformed into the kinetic energy. Consequently, the temperature of the united cluster rises. If this temperature is higher than the melting temperature, melting and local alloying at the interface occur. If alloying spreads into the united cluster, an alloyed bimetallic cluster is synthesized. If melting occurs only in one of the two clusters, and the atoms in liquid phase gradually cover the surface of the other cluster, a core-shell cluster appears. The morphological evolutions in the two modes of coalescence are followed, and under what conditions each mode of coalescence occurs is discussed.The results show that the surface energy and atom size of two clusters determine which mode is selected at coalescence.

scholarly journals Distinguishing cap and core contributions to the photoconductive terahertz response of single GaAs based core–shell–cap nanowire detectors

2018 ◽  
Vol 58 (1) ◽  
Author(s):  
Kun Peng ◽  
Patrick Parkinson ◽  
Lan Fu ◽  
Qiang Gao ◽  
Jessica Boland ◽  
...  
Keyword(s):  
High Surface ◽  
Surface Recombination ◽  
Volume Ratio ◽  
Low Noise ◽  
Relative Volume ◽  
Surface Recombination Velocity ◽  
Core Shell ◽  
Carrier Lifetimes ◽  
Response Characteristics ◽  
Cap Layer

GaAs nanowires are promising candidates for advanced optoelectronic devices, despite their high surface recombination velocity and large surface-area-to-volume ratio, which renders them problematic for applications that require efficient charge collection and long charge-carrier lifetimes. Overcoating a bare GaAs nanowire core with an optimized larger-bandgap AlGaAs shell, followed by a capping layer of GaAs to prevent oxidation, has proven an effective way to passivate the nanowire surface and thereby improve electrical properties for enhanced device performance. However, it is difficult to quantify and distinguish the contributions between the nanowire core and cap layer when measuring the optoelectronic properties of a nanowire device. Here, we investigated the photoconductive terahertz (THz) response characteristics of single GaAs/AlGaAs/GaAs core–shell–cap nanowire detectors designed for THz time-domain spectroscopy. We present a detailed study of the contributions of the GaAs cap layer and GaAs core on the ultrafast optoelectronic performance of the detector. We show that both the GaAs cap and core contribute to the photoconductive signal in proportion to their relative volume in the nanowire. By increasing the cap volume ratio to above 90% of the total GaAs volume, a quasi-direct-sampling type photoconductive nanowire detector can be achieved that is highly desirable for low-noise and fast data acquisition detection.

scholarly journals SnO2 -SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

2021 ◽  
Author(s):  
Muhammad Hamid Raza ◽  
Navpreet Kaur ◽  
Elisabetta Comini ◽  
Nicola Pinna
Keyword(s):  
Shell Thickness ◽  
High Surface ◽  
Depletion Layer ◽  
Masking Effect ◽  
Electronic Coupling ◽  
Core Shell ◽  
Dramatic Improvement ◽  
Shell Layer ◽  
Sio2 Shell ◽  
Shell Nanowires

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,<br>electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.<br>

scholarly journals A comprehensive study of synthesis and applications of core/shell nanoparticles

2021 ◽  
Vol 13 (1) ◽  
pp. 153-157
Author(s):  
Anju Tiwari ◽  
Ankit Kumar Tripathi ◽  
Prateek Khare
Keyword(s):  
Volume Ratio ◽  
Functional Materials ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
The Core ◽  
Crust Layer ◽  
Metal Metal ◽  
Shell Particles ◽  
Core Shell Nanoparticles ◽  
Distinct Features

When we consider matter at nanoscale, one of the most important aspects to be considered is that due to the small size of the particles, these have increased surface area to volume ratio. The large value of this ratio increases the dominance of the surface atoms of the nanoparticles in relation to those in its interior. A special category of materials at nanoscale level has gained popularity in the recent times due to their interesting properties and applications. When classified on the basis of structure, the types of core/shell particles can have a large variety. Each of this structural classification has its own importance, method of synthesis and application. The core/shell  nanoparticles have some distinct features that is responsible for their importance. The properties of Core/shell nanoparticles are highly modified from that of their simple pure nanomaterials, thus they usually called highly functional materials. The introduction of a different crust layer over the core particle has many reasons, such as it helps in implementing surface modification, increases functionality, stability and dispersibility, control on the release of the core, lowering the consumption of precious materials, and so on. These nanostructures can have a number of combinations in close interaction, depending upon the selection of material used, which highly influences the end application. This paper has an overview of the present methods involved in synthesis and tunable factors responsible for their end  applications. The development of metal/metal oxide core-shell nanoparticles has become popular nowadays due to their widespread use in catalysis and other environmental remedial applications.

scholarly journals SnO2 -SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

2021 ◽  
Author(s):  
Muhammad Hamid Raza ◽  
Navpreet Kaur ◽  
Elisabetta Comini ◽  
Nicola Pinna
Keyword(s):  
Shell Thickness ◽  
High Surface ◽  
Depletion Layer ◽  
Masking Effect ◽  
Electronic Coupling ◽  
Core Shell ◽  
Dramatic Improvement ◽  
Shell Layer ◽  
Sio2 Shell ◽  
Shell Nanowires

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,<br>electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.<br>

Magnetic Properties of Fe3O4/CoFe2O4 Composite Nanoparticles with Core/Shell Architecture

2020 ◽  
Vol 65 (10) ◽  
pp. 904
Author(s):  
V. O. Zamorskyi ◽  
Ya. M. Lytvynenko ◽  
A. M. Pogorily ◽  
A. I. Tovstolytkin ◽  
S. O. Solopan ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Spinel Ferrite ◽  
Composite Nanoparticles ◽  
Core Shell ◽  
Cofe2o4 Nanoparticles ◽  
Core Diameter ◽  
The Core ◽  
Shell Particles ◽  
Interface Parameters ◽  
Shell Composite

Magnetic properties of the sets of Fe3O4(core)/CoFe2O4(shell) composite nanoparticles with a core diameter of about 6.3 nm and various shell thicknesses (0, 1.0, and 2.5 nm), as well as the mixtures of Fe3O4 and CoFe2O4 nanoparticles taken in the ratios corresponding to the core/shell material contents in the former case, have been studied. The results of magnetic research showed that the coating of magnetic nanoparticles with a shell gives rise to the appearance of two simultaneous effects: the modification of the core/shell interface parameters and the parameter change in both the nanoparticle’s core and shell themselves. As a result, the core/shell particles acquire new characteristics that are inherent neither to Fe3O4 nor to CoFe2O4. The obtained results open the way to the optimization and adaptation of the parameters of the core/shell spinel-ferrite-based nanoparticles for their application in various technological and biomedical domains.

scholarly journals Iron Based Core-Shell Structures as Versatile Materials: Magnetic Support and Solid Catalyst

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 72
Author(s):  
Christian Zambrzycki ◽  
Runbang Shao ◽  
Archismita Misra ◽  
Carsten Streb ◽  
Ulrich Herr ◽  
...  
Keyword(s):  
Water Purification ◽  
Functional Materials ◽  
Core Material ◽  
Solid Catalyst ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
The Core ◽  
Shell Nanostructures ◽  
Sio2 Shell ◽  
Iron Based

Core-shell materials are promising functional materials for fundamental research and industrial application, as their properties can be adapted for specific applications. In particular, particles featuring iron or iron oxide as core material are relevant since they combine magnetic and catalytic properties. The addition of an SiO2 shell around the core particles introduces additional design aspects, such as a pore structure and surface functionalization. Herein, we describe the synthesis and application of iron-based core-shell nanoparticles for two different fields of research that is heterogeneous catalysis and water purification. The iron-based core shell materials were characterized by transmission electron microscopy, as well as N2-physisorption, X-ray diffraction, and vibrating-sample magnetometer measurements in order to correlate their properties with the performance in the target applications. Investigations of these materials in CO2 hydrogenation and water purification show their versatility and applicability in different fields of research and application, after suitable individual functionalization of the core-shell precursor. For design and application of magnetically separable particles, the SiO2 shell is surface-functionalized with an ionic liquid in order to bind water pollutants selectively. The core requires no functionalization, as it provides suitable magnetic properties in the as-made state. For catalytic application in synthesis gas reactions, the SiO2-stabilized core nanoparticles are reductively functionalized to provide the catalytically active metallic iron sites. Therefore, Fe@SiO2 core-shell nanostructures are shown to provide platform materials for various fields of application, after a specific functionalization.

scholarly journals Ultra-Narrow Metallic Nano-Trenches Realized by Wet Etching and Critical Point Drying

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 783
Author(s):  
Jeeyoon Jeong ◽  
Hyosim Yang ◽  
Seondo Park ◽  
Yun Daniel Park ◽  
Dai-Sik Kim
Keyword(s):  
Critical Point ◽  
Terahertz Spectroscopy ◽  
High Surface ◽  
Wet Etching ◽  
Drying Process ◽  
Metal Structures ◽  
Critical Point Drying ◽  
Metal Insulator Metal ◽  
Gap Width ◽  
Optical Structure

A metallic nano-trench is a unique optical structure capable of ultrasensitive detection of molecules, active modulation as well as potential electrochemical applications. Recently, wet-etching the dielectrics of metal–insulator–metal structures has emerged as a reliable method of creating optically active metallic nano-trenches with a gap width of 10 nm or less, opening a new venue for studying the dynamics of nanoconfined molecules. Yet, the high surface tension of water in the process of drying leaves the nano-trenches vulnerable to collapsing, limiting the achievable width to no less than 5 nm. In this work, we overcome the technical limit and realize metallic nano-trenches with widths as small as 1.5 nm. The critical point drying technique significantly alleviates the stress applied to the gap in the drying process, keeping the ultra-narrow gap from collapsing. Terahertz spectroscopy of the trenches clearly reveals the signature of successful wet etching of the dielectrics without apparent damage to the gap. We expect that our work will enable various optical and electrochemical studies at a few-molecules-thick level.

scholarly journals Electrospun Nanofibers for Sensing and Biosensing Applications—A Review

2021 ◽  
Vol 22 (12) ◽  
pp. 6357
Author(s):  
Kinga Halicka ◽  
Joanna Cabaj
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Toxic Metal ◽  
Volume Ratio ◽  
Electrospun Nanofibers ◽  
Clinical Diagnostics ◽  
Loading Capacity ◽  
Electrospun Nanofiber ◽  
Sensing Platforms ◽  
Different Types

Sensors and biosensors have found applications in many areas, e.g., in medicine and clinical diagnostics, or in environmental monitoring. To expand this field, nanotechnology has been employed in the construction of sensing platforms. Because of their properties, such as high surface area to volume ratio, nanofibers (NFs) have been studied and used to develop sensors with higher loading capacity, better sensitivity, and faster response time. They also allow to miniaturize designed platforms. One of the most commonly used techniques of the fabrication of NFs is electrospinning. Electrospun NFs can be used in different types of sensors and biosensors. This review presents recent studies concerning electrospun nanofiber-based electrochemical and optical sensing platforms for the detection of various medically and environmentally relevant compounds, including glucose, drugs, microorganisms, and toxic metal ions.

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