scholarly journals Fabrication of Antireflective Nanostructures on a Transmission Grating Surface Using a One-Step Self-Masking Method

Nanomaterials ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 180 ◽  
Author(s):  
Ting Shao ◽  
Feng Tang ◽  
Laixi Sun ◽  
Xin Ye ◽  
Junhui He ◽  
...  
Keyword(s):  
Effective Medium Theory ◽  
Low Cost ◽  
Fused Silica ◽  
Subwavelength Structures ◽  
Simple Method ◽  
Medium Theory ◽  
Transmission Grating ◽  
Wide Range ◽  
Nanostructure Surface ◽  
One Step

Suppression of Fresnel reflection from diffraction grating surfaces is very important for many optical configurations. In this work, we propose a simple method to fabricate subwavelength structures on fused-silica transmission grating for optical antireflection. The fabrication is a one-step self-masking reaction ion etching (RIE) process without using any masks. According to effective medium theory, random cone-shaped nanopillars which are integrated on the grating surface can act as an antireflective layer. Effects of the nanostructures on the reflection and transmission properties of the grating were investigated through experiments and simulations. The nanostructure surface exhibited excellent antireflection performance, where the reflection of the grating surface was suppressed to zero over a wide range of incident angles. Results also revealed that the etching process can change the duty cycle of the grating, and thus the diffraction orders if there are oblique lateral walls. The simulation results were in good agreement with the experimental ones, which verified our physical comprehension and the corresponding numerical model. The proposed method would offer a low-cost and convenient way to improve the antireflective performance of transmission-diffractive elements.

Characterizing Anisotropic Fracture Toughness of Shale Using Nanoindentation

2021 ◽  
pp. 1-13
Author(s):  
Erica Esatyana ◽  
Mehdi Alipour ◽  
A. Sakhaee-Pour
Keyword(s):  
Fracture Toughness ◽  
Conceptual Model ◽  
Effective Medium Theory ◽  
Fused Silica ◽  
Small Samples ◽  
Medium Theory ◽  
Anisotropic Fracture ◽  
Cube Corner ◽  
Induced Fractures ◽  
Anisotropic Fracture Toughness

Summary Shale, which has pores as small as 10 nm, is economically viable for hydrocarbon recovery when it is fractured. Although the fracture toughness dictates the required energy for the improvement, the existing techniques are not suitable for characterization at scales smaller than 1 cm. Developing practical methods for characterization is crucial because fractures can contribute to an accessible pore volume at different scales. This study proposes a conceptual model to characterize the anisotropic fracture toughness of shale using nanoindentations on a sub-1-cm scale. The conceptual model reveals the complexities of characterizing shales and explains why induced fractures differ from those observed in more-homogeneous media, such as fused silica. Samples from the Wolfcamp Formation were tested using Berkovich and cube-corner tips, and the interpreted fracture toughness values are promising. The conceptual model is the first application of the effective-medium theory for fracture toughness characterization using nanoindentation. In addition, it can quantify fracture toughness variations when using small samples, such as drill cuttings.

Effect of Particle Size and Aggregation on Thermal Conductivity of Metal-Polymer Nanocomposite

2016 ◽  
Author(s):  
Xiangyu Li ◽  
Wonjun Park ◽  
Yong P. Chen ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Effective Medium Theory ◽  
Low Cost ◽  
Polymer Nanocomposite ◽  
Theoretical Models ◽  
Effective Medium ◽  
Metal Nanoparticle ◽  
Local Concentration ◽  
Medium Theory ◽  
Aggregation Effect

Metal nanoparticle has been a promising option for fillers in thermal interface materials due to its low cost and ease of fabrication. However, nanoparticle aggregation effect is not well understood because of its complexity. Theoretical models, like effective medium approximation model, barely cover aggregation effect. In this work, we have fabricated nickel-epoxy nanocomposites and observed higher thermal conductivity than effective medium theory predicts. Smaller particles are also found to show higher thermal conductivity, contrary to classical models indicate. A two-level EMA model is developed to account for aggregation effect and to explain the size-dependent enhancement of thermal conductivity by introducing local concentration in aggregation structures.

Fabrication of an Atomic Resolution Low Cost STM-SNOM Hybrid Probe

2006 ◽  
Vol 6 (1) ◽  
pp. 72-76
Author(s):  
Ruggero Micheletto ◽  
Masatoshi Yokokawa ◽  
Satoshi Okazakaki ◽  
Yoichi Kawakami
Keyword(s):  
Optical Fiber ◽  
Optical Fibers ◽  
Chemical Etching ◽  
Low Cost ◽  
Resolving Power ◽  
Atomic Resolution ◽  
Hybrid Fiber ◽  
Horizontal Scale ◽  
Simple Method ◽  
One Step

We derived a simple method to fabricate STM-SNOM hybrid probes obtained from commercial cheap communication optical fibers. The tips are fabricated by a methodology that combines two well-known techniques: the selective attack by a buffered solution and the protected layer chemical etching, in a single new one-step technique. The tailored probes are then sputtered by metal and mounted on a STM setup. The usual difficulties of integrating the optical fiber in the STM head are solved originally with a particular home made mount described in details. We will show that the resulting probes reach atomic resolution on both vertical and horizontal scale, and that the optical imaging is free of artifacts and satisfactory with a lateral resolution in the order of λ/20, as far as we know the finest resolution obtained with a system based on a hybrid fiber probe. We believe that our methodology is very interesting for its simplicity of realization and for the good resolving power in both SNOM and STM modes.

A physical based model to describe effective hydraulic conductivity of the soil mixtures

2020 ◽  
Author(s):  
Deep Chandra Joshi ◽  
Mahyar Naseri ◽  
Wolfgang Durner
Keyword(s):  
Hydraulic Conductivity ◽  
Effective Conductivity ◽  
Effective Medium Theory ◽  
Mixture Component ◽  
Conductivity Data ◽  
Medium Theory ◽  
Effective Hydraulic Conductivity ◽  
Wide Range ◽  
Simple Physical Model ◽  
Soil Mixtures

<p>There is a long-lasting interest in obtaining the effective hydraulic conductivity functions of soil mixtures. The few available models to obtain hydraulic conductivity of mixtures are mostly empirical and applicable for saturated conditions. We propose a simple physical model based on the effective medium theory to calculate the effective hydraulic conductivity of soil mixtures with two or more components. The model incorporates the volumetric content of each mixture component and their hydraulic conductivity to calculate the effective conductivity of the mixture. The results of the model were compared with the measured hydraulic conductivity data obtained from the simplified evaporation method using the Hyprop device. Samples were prepared by packing homogeneous mixtures of different soil textures in cylinders with a volume of 250 cm<sup>3</sup>. Packed soil mixtures were saturated and exposed to evaporation in a climate controlled laboratory with constant air temperature and humidity. The results show an acceptable match between the measured and modeled hydraulic conductivity of the tested soil mixtures. The model can be used as a physical way to describe the effective hydraulic conductivity of mixtures in a wide range of moisture.</p>

Ultrasonic velocity‐porosity relationships for sandstone analogs made from fused glass beads

Geophysics ◽  
1995 ◽  
Vol 60 (1) ◽  
pp. 108-119 ◽  
Author(s):  
Patricia A. Berge ◽  
Brian P. Bonner ◽  
James G. Berryman
Keyword(s):  
Upper Bound ◽  
Effective Medium Theory ◽  
Effective Medium ◽  
Glass Beads ◽  
Composite Medium ◽  
Host Material ◽  
Consistent Theory ◽  
Medium Theory ◽  
Wide Range ◽  
Self Consistent

Using fused glass beads, we have constructed a suite of clean sandstone analogs, with porosities ranging from about 1 to 43 percent, to test the applicability of various composite medium theories that model elastic properties. We measured P‐ and S‐wave velocities in dry and saturated cases for our synthetic sandstones and compared the observations to theoretical predictions of the Hashin‐Shtrikman bounds, a differential effective medium approach, and a self‐consistent theory known as the coherent potential approximation. The self‐consistent theory fits the observed velocities in these sandstone analogs because it allows both grains and pores to remain connected over a wide range of porosities. This behavior occurs because this theory treats grains and pores symmetrically without requiring a single background (host) material, and it also allows the composite medium to become disconnected at a finite porosity. In contrast, the differential effective medium theory and the Hashin‐Shtrikman upper bound overestimate the observed velocities of the sandstone analogs because these theories assume the microgeometry is represented by isolated pores embedded in a host material that remains continuous even for high porosities. We also demonstrate that the differential effective medium theory and the Hashin‐Shtrikman upper bound correctly estimate bulk moduli of porous glass foams, again because the microstructure of the samples is consistent with the implicit assumptions of these two theoretical approaches.

One-step synthesis and deposition of few-layer graphene via facile, dry ball-free milling

MRS Advances ◽  
2017 ◽  
Vol 2 (15) ◽  
pp. 847-856 ◽  
Author(s):  
Abdul Hai Alami ◽  
Kamilia Aokal ◽  
Mhd Adel Assad ◽  
Di Zhang ◽  
Hussain Alawadhi ◽  
...  
Keyword(s):  
Low Cost ◽  
High Vacuum ◽  
Chemical Vapor ◽  
Hydrophobic Surface ◽  
Graphite Powder ◽  
High Energy ◽  
Layer Graphene ◽  
Wide Range ◽  
One Step ◽  
Few Layer Graphene

ABSTRACTGraphene is a 2-D carbon material showing considerable prominence in a wide range of optoelectronics, energy storage, thermal and mechanical applications. However, due to its unique features which are typically associated with difficulty in handling (ultra-thin thickness and hydrophobic surface, to name a few), synthesis and subsequent deposition processes are thus critical to the material properties of the prepared graphene films. While existing synthesis approaches such as chemical vapor deposition and epitaxial growth can grow graphene with high degree of order, the costly high temperature and/or high vacuum process prohibit the widespread usage, and the subsequent graphene transfer from the growth substrates for deposition proves to be challenging. Herein, a low-cost one-step synthesis and deposition approach for preparing few-layer graphene (FLG) on flexible copper substrates based on dry ball-free milling of graphite powder is proposed. Different from previous reports, copper substrates are inserted into the milling crucible, thus accomplishing simultaneous synthesis and deposition of FLG and eliminating further deposition step. Furthermore, while all previously reported high energy milling processes involve using balls of various sizes, we adopt a ball-free milling process relying only on centrifugal forces, which significantly reduces the surface damage of the deposition substrates. Sample characterization indicates that the process yields FLG deposited uniformly across all tested specimens. Consequently, this work takes graphene synthesis and deposition a step closer to full automation with simple and low-cost process.

High-Throughput Screening of Aperiodic Superlattice for Minimum Thermal Conductivity Based on Atomistic Simulation-Informed Effective Medium Theory and Genetic Algorithm

2021 ◽  
Author(s):  
Shangchao Lin ◽  
Yixuan Liu ◽  
Zhuangli Cai
Keyword(s):  
Thermal Conductivity ◽  
Genetic Algorithm ◽  
High Throughput ◽  
High Throughput Screening ◽  
Effective Medium Theory ◽  
Effective Medium ◽  
Correction Function ◽  
Stable Range ◽  
Medium Theory ◽  
Wide Range

Abstract Superlattices with suppressed thermal conductivity are of great significance in the field of thermoelectricity and can improve the thermoelectric conversion efficiency of materials. Due to Anderson localization of coherent phonons, aperiodic superlattices have lower thermal conductivity than their periodic counterparts. At present, the thermal conductivity of superlattices is mostly predicted through ab initio or molecular dynamics simulations, which is computationally expensive and limits the size of the system. Meanwhile, there are many layered structural combinations for aperiodic superlattices, making it difficult to efficiently screen through all the combinations to search structures with the minimum thermal conductivity. In this work, based on a modified series thermal resistance model (STRM), a new effective medium theory (EMT) is established to predict the thermal conductivity of periodic and aperiodic superlattices. An adjacency factor near the maximum-resistance layers and a correction function, respectively, are introduced to account for the phonon coherence effect and the degree of randomization in the layer thickness. Combined with the genetic algorithm, EMT enables high-throughput screening of millions of aperiodic superlattice structures. This work demonstrates that the thermal conductivities of aperiodic superlattices at a wide range of system size can be constantly reduced to 1.4∼1.8 W/(m·K), which occurs at averaged periodic thicknesses in a stable range of 2.0∼2.5 nm.

scholarly journals A REVIEW ON LIQUID CRYSTALLINE NANOPARTICLES (CUBOSOMES): EMERGING NANOPARTICULATE DRUG CARRIER

2020 ◽  
pp. 5-9 ◽  
Author(s):  
S. NAVEENTAJ ◽  
Y. INDIRA MUZIB
Keyword(s):  
Drug Delivery ◽  
Liquid Crystalline ◽  
Low Cost ◽  
Drug Carrier ◽  
Water System ◽  
Cubic Phase ◽  
Simple Method ◽  
Wide Range ◽  
Spherical Structures

Cubosomes are novel biocompatible drug delivery system and have honeycombed (cavernous) structures whose diameter size range from 10–500 nm. They appear like dots, which are likely to be spherical structures. Each dot corresponds to the presence of a pore containing aqueous cubic phase in the lipid water system. Cubosomes posse’s great significance in the field of cosmeceuticals and Pharmaceuticals due to its unique features and become an attractive choice of vehicle for in vivo drug delivery due to their low cost, safety, efficacy and versatility for controlled release application and functionalization. Cubosomes have a very simple method of preparation; biodegradability of selected lipids has the capability to encapsulate hydrophobic and hydrophilic substances. Cubosomes are considered to be versatile systems, and prepared cubosomes can be administrated by different ways such as oral, percutaneous and parenteral routes. On the whole, cubosomes offer high consequence in nano-based drug preparations for melanoma (skin cancer) treatment, targeted drug delivery systems and comprise a wide range of applications in many areas and are characterized by various parameters. Consequently, cubosomes are in progress forward of awareness in the Pharmaceutical division. This review article mainly focuses on the methods of preparation, advantages, and applications of cubosomes.

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