Microand Nanostructures Research Articles

Review—On Atomic Layer Deposition: Current Progress and Future Challenges

Atomic layer deposition (ALD) relies on self-limiting reaction within a cyclic process and is being considered as a potential technique for synthesizing nanomaterials with precisely controlled internal structure. Therefore, the design and synthesis of advanced ultrafine nanomaterials becomes feasible through a rigorous control over the morphology, micro-and nano-structure, composition, thickness and particle size. Currently, ALD is mostly adopted for semiconductor applications; however, several other areas (i.e. catalysis and energy storage) can hugely benefit from ALD capabilities if the process is finely tuned. In this review paper, significant previous works on ALD of nanomaterials have been discussed via focusing on the deposition of noble metals, metal oxides, two-dimensional materials and metal-organic frameworks on various substrates. Major contributing parameters (e.g. deposition temperature, ALD cycles, and type of the precursor) affecting the deposition process have also been covered. The review concludes with a summary of opportunities for future research to enable large-scale implementation of ALD as a reliable and robust technique for synthesizing nanomaterials.

Laser radiation impact on a solid surface and formation of micro- and nanostructures

The work is devoted to the problem of microand nanostructuring of the surface of solids as a result of exposure to laser radiation. The method of forming periodic surface structures by means of femtosecond laser processing is presented using the example of solving the problem of titanium structuring.

Superhydrophobic Plant Leaves with Micro-line Structures: An Optimal Biomimetic Objective in Bionic Engineering

It has been well demonstrated that there are two kinds of surface morphologies, including binary structures (namely micro-and nanostructures) and less common unitary structures (such as micro-line structures), which play crucial roles in endowing the plant leaves with superhydrophobic properties. In this work, five superhydrophobic plant leaves in nature are introduced, by means of the combination of surface morphology and wettability with the aid of Scanning Electron Microscopy (SEM) and contact angle measurement. The results indicate that either the binary structures or the unitary structures enable the construction of a superhydrophobic surface, and the latter shows likely better mechanics compared with the former according to the corresponding theory. This research aims at introducing two different types of corresponding morphologies of superhydrophobic plant leaves.

Non-Invasive Temperature-Feedback SERS with all-Dielectric Resonant Nanostructures

All-dielectric resonant micro-and nanostructures emerge as a promising platform, which can complement the metal-based counterparts in routine biosensing measurements based on surface-enhanced Raman scattering (SERS). However, lack of in-situ temperature control limits performance of nanostructures for precise SERS-based applications. Here, we present an approach for SERS measurement with simultaneous temperature control and employ Raman spectroscopy to mapping of temperature-dependent Raman signal distribution. We attest a chemically inert black silicon (b-Si) substrate for a non-invasive (chemically non-perturbing) SERS identification of the molecular fingerprints at low concentrations. Additional studies of the slow daylight-driven para-aminothiophenol (PATP)-to-4,4'-dimercaptoazobenzene (DMAB) catalytic conversion in the aqueous methanol solution loaded with colloidal silver nanoparticles confirm the non-invasive SERS performance of the all-dielectric crystalline b-Si substrate. Proposed SERS substrates can be fabricated using easy-to-implement scalable technology of plasma etching making such inexpensive all-dielectric substrates promising for routine SERS applications, where the temperature-feedback and the noninvasiveness are of mandatory importance.

Superhydrophobic surface prepared by micro-milling and WEDM on aluminum alloy

To simulate the hydrophobic microstructure of rice leaf surface, high-speed precision micro-milling machine was used to fabricate micro groove array structure on the surface of aluminum alloy. The micro-and nanostructure was constructed on the surface of the grooved convex platform by Wire Cut Electrical Discharge Machining (WEDM). The surface morphology and hydrophobic properties of the aluminum alloy microstructures fabricated by two processing methods were observed respectively, and the hydrophobic mechanism was analyzed. The results show that the contact angle was effectively improved from 49° up to 158.4° in the vertical direction, and 146.7° in the parallel direction. The change of surface wettability from hydrophilic to hydrophobic was realized. By comparison, the micro-and nanostructure fabricated by WEDM had improved the hydrophobic stability of the aluminum alloy surface while enlarging the contact Angle, and the micro-milling groove structure further amplified the contact angle and greatly reduced the contact area of the water droplet, it was also observed that the drop took longer to completely spread on the sample after WEDM.

Shape controlled synthesis of Cu3BiS3 nano- and microstructures by PEG assisted solvothermal method and functional properties

One-dimensional Cu3BiS3 nano-and microstructures were synthesized by solvothermal route using structural directing agent polyethylene glycol (PEG) as soft template. The effects of thiourea concentration on the morphological, structural and optical properties of Cu3BiS3 nano- and microstructures were investigated. X-ray diffraction study revealed that the synthesized Cu3BiS3 belongs to orthorhombic structure. Raman spectrum of the Cu3BiS3 exhibited its functional groups. The chemical bonding of the ions was examined by X-ray photoelectron spectroscopy. Field emission scanning electron microscope and transmission electron microscope analyses evidently showed that thiourea concentration acts as a crucial factor in tuning the morphology of Cu3BiS3 nano- and microstructures. The presence of Cu3BiS3 was confirmed by Energy Dispersive X-ray Analysis and elemental mapping. The growth mechanism of Cu3BiS3 nanostructures has been discussed. Conductivity of Cu3BiS3 measured by I-V characteristics of the nano- and microstructured film of ~ 2.5 µm thickness deposited on FTO substrate using electron beam evaporation method showed linear curve. The Hall measurements of the Cu3BiS3 films deposited on glass substrate were determined.

Dopamine self-polymerized along with hydroxyapatite onto the preactivated titanium percutaneous implants surface to promote human gingival fibroblast behavior and antimicrobial activity for biological sealing.

The clinical success of dental implants requires not only the optimum osseointegration but also the integration of implant surface with soft tissues to form biological sealing. In this study, alkali-heat treatment was applied to modify the pure titanium surface constructing a unique micro-and nano-structure. Then, poly(dopamine), along and with the additional incorporation of hydroxyapatite and carboxymethyl chitosan have been successfully infiltrated into the preactivated Ti surface during dopamine self-polymerization proceeding. Here, the effects of poly(dopamine)-modified surface coating on the biological behaviors of human gingival fibroblasts (HGFs) and oral pathogens have been systematically studied, which was critical for the early peri-implant soft tissue integration. The results showed that the poly(dopamine)-modified alkali-heat-titanium surface was a superior substrate for human gingival fibroblast adhesion, spread and proliferation. Moreover, further enhancements on cytoskeleton organization, collagen secretion and fibronectin adsorption were generally observed through the additional incorporation of hydroxyapatite. The addition of carboxymethyl chitosan exerted a positive modulation effect on antibacterial activity. Overall, our study demonstrated that combined superior soft tissue integration and antibacterial activity can be achieved by using poly(dopamine)-modified titanium implant, which has great potential in the optimal design of dental implant.

A method to improve the quality of 2.5 dimensional micro-and nano-structures produced by focused ion beam machining

The present work deals with a new technique to produce complex micro- and nano-scale patterns with high accuracy by FIB micro machining. The proposed method is related to the production of stream file, which is optimized through a software interface. A unique sampling approach is used to optimize the conversion from a 3D meshed CAD object to the focused ion beam (FIB) digital to analogue converter (DAC). The method uses a novel scan strategy, sensitive to the pattern local geometry and size, to define the optimal ion beam path, dwell time and the scanning pitch. This not only allows to minimize the redeposition but also to obtain accurate and scalable milling routines. In order to show the applicability of the method, a hemisphere and a pyramid shape are milled and compared to the shapes obtained using the conventional techniques. Results show that the method is very effective in producing complex shapes while overcoming the detrimental effect of conventional raster/serpentine FIB strategies, such as redeposition. Lastly, a fish-net structure with a pitch of ∼200nm as well as a series of truncated cones with sub-micrometrical details are realized to show the potential impact of this new method. Results show that a spatial resolution of less than 100nm is achievable with the help of this method.

Facile synthesis of morphology and size-controlled α-Fe2O3 and Fe3O4 nano-and microstructures by hydrothermal/solvothermal process: The roles of reaction medium and urea dose

This paper reports a systematic study of the influences on the synthesis of α-Fe2O3 and Fe3O4 via a hydro/solvothermal process at 200°C. Both the reaction medium and urea dose have been investigated. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). Results showed that the reaction mediums, such as water and ethylene glycol, played important roles in forming different types of iron oxides. Pure crystalline α-Fe2O3 was formed via the hydrothermal process, and Fe3O4 was obtained through a solvothermal route with ethylene glycol as reaction medium. Increasing urea dose tuned the particle sizes of α-Fe2O3 and Fe3O4 from a few hundreds to several tens of nanometers. With addition of urea, the morphology of α-Fe2O3 evolved from olive-like to rhomb-like, and Fe3O4 evolved from hollow sphere, to pinecone-like, and finally into cracked nanostructures. The variations of the surface area of products were mainly dependent on the microstructure and intrinsic features of the iron oxide particles. Results of the mechanistic studies indicated that the generation of CO2 and NH3 via in situ thermal decomposition of urea was crucial for the formation of α-Fe2O3 and Fe3O4 nano-and microstructures. The as-synthesized α-Fe2O3 and Fe3O4 were used as catalysts for methylene blue degradation in the presence of H2O2, and α-Fe2O3 showed a higher degradation efficiency. Our findings demonstrated a promising strategy for the developments of rationally designed iron oxides.

Wetting behavior and drag reduction of superhydrophobic layered double hydroxides films on aluminum

We present a novel method to fabricate Zn–Al LDH (layered double hydroxides) film with 3D flower-like micro-and nanostructure on the aluminum foil. The wettability of the Zn–Al LDH film can be easily changed from superhydrophilic to superhydrophobic with a simple chemical modification. The as-prepared superhydrophobic surfaces have water CAs (contact angles) of 165±2°. In order to estimate the drag reduction property of the surface with different adhesion properties, the experimental setup of the liquid/solid friction drag is proposed. The drag reduction ratio for the as-prepared superhydrophobic sample is 20–30% at low velocity. Bearing this in mind, we construct superhydrophobic surfaces that have numerous technical applications in drag reduction field.

Backscattered electron imaging of microand nanostructures: 4. Structures with a trapezoidal profile and large side-wall inclination angles

The results of investigation into the imaging of grooves in silicon with a trapezoidal profile and small side-wall inclination angles, which are obtained using a scanning electron microscope operating in the backscattered electron recording mode, are presented. It is shown that there exist four imaging mechanisms. The first of them is caused by primary electrons of the probe. The next two are related to the multiple scattering of primary and secondary (ionizing) electrons. The fourth mechanism is associated with the interaction between electrons released into free space and the sample relief. The first three mechanisms provide direct image contrast, and the fourth is characterized by opposite contrast.

Simulation of the Bosch process for micro- and nanostructures

This paper describes the capabilities of the Bosch process simulation for microand nanostructures with the aid of NEMO ETCHING software. The heart of this program is an original hybrid algorithm, which is based on the Monte–Carlo method and on the cell-graph approximation of the string model. It is shown that this algorithm considerably improves the performance of the model without loss of accuracy. The etching model is calibrated according to the real Bosch experiment process. The comparison between the simulation and experimental results shows this model is highly accurate.

Advances in Modeling of Solidification Microstructures

In different manufacturing processes, such as casting, welding, and additive manufacturing, metallic materials go through solidification to produce parts with different sizes and shapes. Microstructures that develop during solidification control the property and performance of the manufactured parts, thereby predicting the solidification microstructures as functions of alloying composition and processing parameters is essential to control the quality of products. The multiscale nature of solidification microstructures, which depend on temperature distribution, solute concentration, capillary forces, and kinetic length, make the understanding and prediction of these microstructures exceptionally difficult. In recent years, and because of emergence of new and powerful supercomputers, it has become more feasible to computationally simulate the materials nanoand microstructures in large scales and with finest details. The computational models for solidification of metallic materials need to be developed based on the actual multiphysics of solidification, while considering the need for efficient numerical algorithms to solve the governing equations of the models. To quantitatively predict solidification microstructures, computational models at mesoscale need information from theory, experiments, lower scale models (e.g., density functional theory calculations, molecular dynamics simulations, etc.), and phase diagram calculations. The current computational models for simulating dendritic growth at the microscopic scale are based on different methods such as phase field (diffusive interface), level set, direct interface tracking, and cellular automaton methods. Each of these methods has its advantages and disadvantages: some can simulate the finest details of solidification microstructures with high accuracy, while others can simulate dendritic growth in large-scale domains with high computational efficiency. In this Journal of Metals topic, we present recent contributions in modeling of solidification microstructures. Damien Tourret et al. present a three-dimensional (3D) version of the dendritic needle network (DNN) model for directional solidification. They apply the DNN model to predict the stable range of primary dendritic spacings for an Al-9.8 wt%Si alloy over a range of growth velocities. They compare their predictions to spacings measured from in situ x-ray imaging of directional solidification experiments. Mohsen Eshraghi et al. present a parallel 3D lattice Boltzmann-cellular automaton model to simulate dendritic growth during solidification of metallic binary alloys. Their large-scale simulations show a great scale-up performance up to 40,000 computing cores and an excellent speed-up performance on up to 1000 computing cores. Yasushi Shibuta and co-workers performed simulations of solidification from atomic to microstructural levels using a graphics processing unit (GPU) architecture. They use million-atom molecular dynamics simulations to study nucleation of solid phase in undercooled melt and to capture evolution of anisotropy for solid seeds. Using a quantitative phasefield model, they simulate dendrite growth in directional solidification at millimeter scale in two– dimensional (2D) and 3D by multi-GPU computation on a supercomputer. These two articles present promising techniques to predict solidification microstructures in large macro-scale domains with good computational efficiency. Alexander Monas et al. present 3D phase-field simulations of solidification microstructures of MgAl alloy. They use the Calphad method to obtain the phase diagram and necessary parameters for their simulations. Michael Rappaz and Guven Kurtuldu discuss a new nucleation mechanism in liquid metallic alloys based on thermodynamics arguments. They explain that the two-step nucleation mechanism starts with Mohsen Asle Zaeem is the guest editor for the Solidification Committee of the TMS Materials Processing & Manufacturing Division, and coordinator of the topic Advances in Modeling of Solidification Microstructures in this issue. JOM, Vol. 67, No. 8, 2015

A Method of Industrial Image Processing Based on Enhancement of Object Boundaries

In this work, the necessity of automatic processing of images of micro-and nanostructures is shown. A method for preliminary processing of such images for reliable separation of inseparable structures in them is developed. The method is based on a more accurate calculation of the brightness gradient and enhancement of image boundaries. The results of processing a photograph of a nanostructure are presented.

Plasma chemical etching of high-aspect-ratio silicon micro- and nanostructures

High-aspect-ratio (HAR) silicon etching of micro-and nanostructures in a time-multiplexed deep etching process (Bosch process) is reviewed, including applications, different technological methods, critical challenges, and main principles of the technologies. HAR silicon etching is an application associated primarily with micro- and nanostructures. This potentially large-scale application requires HAR etching with a high throughput and controllable profile and surface properties. The most significant effects like RIE lag, bowing, stop effect, and profile shape dependence are discussed.

Large-scale micro- and nanopatterns of Cu(In,Ga)Se2 thin film solar cells by mold-assisted chemical-etching process.

A reactive mold-assisted chemical etching (MACE) process through an easy-to-make agarose stamp soaked in bromine methanol etchant to rapidly imprint larger area micro- and nanoarrays on CIGS substrates was demonstrated. Interestingly, by using the agarose stamp during the MACE process with and without additive containing oil and triton, CIGS microdome and microhole arrays can be formed on the CIGS substrate. Detailed formation mechanisms of microstructures and the chemical composition variation after the etching process were investigated. In addition, various microand nanostructures were also demonstrated by this universal approach. The microstructure arrays integrated into standard CIGS solar cells with thinner thickness can still achieve an efficiency of 11.22%, yielding an enhanced efficiency of ∼18% compared with that of their planar counterpart due to an excellent absorption behavior confirmed by the simulation results, which opens up a promising way for the realization of high-efficiency micro- or nanostructured thin-film solar cells. Finally, the complete dissolution of agarose stamp into hot water demonstrates an environmentally friendly method by the mold-assisted chemical etching process through an easy-to-make agarose stamp.

Where micro- and nano-worlds meet: multiscale polymer composites

data has been published on the preparation and characterization of polymer nanocomposites. Despite the very intense research efforts, the mechanical properties reported so far for nanocomposites are quite disappointing, particularly when compared to that of structural composites reinforced with highperformance continuous fibers (DOI: 10.1126/science.1151434). Among the main causes invoked to explain the obtained results one could mention i) poor dispersion and alignment of nanofillers, ii) difficulties in achieving an elevated volume fraction of nanofillers and iii) scarce bond and load transfer ability at the nanofiller/matrix interface. Intensive research is currently ongoing to tackle and possibly solve the above mentioned problems. Recently, new strategies emerged for the preparation of structural materials in which both microand nano-reinforcements coexist in multiscale composites (DOI: 10.1177/0731684412456612). Nanoscale reinforcements have been included within fiber reinforced composites in several ways, such as i) grafting or electrophoretic deposition (mostly of carbon nanomaterials) onto the fiber surface (DOI: 10.1016/j.compscitech.2014.06.019), ii) localization in sizing/coatings for fiber treatment (DOI: 10.1016/j.compositesa.2012.08.027) iii) homogeneous dispersion in the whole polymer matrix (DOI: 10.1177/0731684414542668). The presence of nanoreinforcements in traditional microcomposites has been proven to play beneficial effects on several properties, including delamination resistance, fiber/ matrix shear strength (DOI: 10.1016/j.compscitech. 2012.12.016), electrical and thermal conductivities. The possibility to improve the electrical conductivity of typically insulating materials such as glass/ epoxy laminates, is opening new possibilities for the monitoring of deformation and damage in composite structures under service. For example, it has been proven that an integrated system of carbon nanotubes and piezoelectric sensors can be used to detect both microcracks and localized damage/ delamination in composite structures (DOI: 10.1016/ j.carbon.2012.04.008). Therefore, nanomodified matrices can be used for a continuous monitoring of deformational levels and damage of structural composites under various loading conditions such as fatigue, impact and creep (DOI: 10.1016/j.compositesa.2012.03.019). Can we dream of polymer composites in which microand nano-structures synergistically operate to provide both structural and functional features, including self-repairing and adaptive responses?

Modeling of abiotic ATP synthesis in the context of problems of early biosphere evolution

The pathway of adenosine triphosphate (ATP) synthesis in living organisms consists of two autonomous stages; this must be taken into account during the design and analysis of chemical models of the abiogenesis of this key participant of metabolic processes. The first stage is construction of an adenine heterocycle linked to a ribose-5-phosphate molecule to yield AMP, while the following stage is the attachment of phosphoryl residues to the nucleotide molecule by macroergic phosphoanhydride bonds. Involvement of the same set of precursor molecules in both de novo biosynthesis of AMP and abiogenesis of this nucleotide is a very important issue for the analysis of metabolic pathways. Photochemical matrix systems that convert light energy into macroergic bond energy are functional prototypes of photosynthetic phosphorylation; they are of special interest for the construction of abiotic phosphorylation models. Interaction of substrates with a purely mineral matrix (montmorillonite particles) under UV irradiation resulted in the formation of ATP from ADP and orthophosphate. Micro-and nanostructures that formed upon the interaction of the mineral component (sodium polysilicate) with an abiogenic organic pigment (a flavin conjugate with a random amino acid polymer) exhibited phosphorylating activity as well when irradiated with visible light. The properties of AMP and ATP abiosynthesis models investigated are in good accordance with the current views on the environmental conditions of the ancient Earth; evident structural differences exist between these models and the biosynthetic systems in modern organisms.

Cell Therapy for Dermal Reconstruction

Skin is the largest organ of human which plays a critical role in different functions of the human body, such as homeostasis, sensory detection, protecting against external insults, and healing. Skin is consisted of thin epidermis and relatively acellular dermis of collagenrich extracellular matrix (ECM) (1). One of the major applications of tissue-engineered skin substitutes in wound healing is to promote cutaneous wound healing. The skin wounds can be caused by mechanical trauma, surgical procedures, reduced blood circulations, burns, or aging procedures. Most of the skin wounds can heal naturally, but additional surgery requires immediate coverage, using skin substitutes, to facilitate skin repair and regeneration, in cases with extensive or irreversible skin damages (2). However, the available skin substitutes often cause a range of problems including wound contraction, scar formation, and poor integration to the underlying host. Engineering the skin substitutes through tissue engineering approaches has relied upon the creation of three-dimensional scaffolds to guide cell adhesion, growth, and differentiation to form functional and structural tissues (3). The scaffolds not only cover the wounds and provide a physical barrier against external infection, but also provide support both for dermal fibroblasts and the overlying keratinocytes. A good tissue scaffold should exhibit appropriate physical and mechanical characteristics and should have appropriate surface chemical and nanoand microstructures to facilitate cellular attachment, proliferation, and differentiation (4). The composition of fibroblastkeratinocyte is formed based on the membrane with the promoted three dimensions, which can produce skin equivalent, and promising in vitro results suggested the potential application of these for the treatment of burns and chronic wounds. Significant improvements have been made to identify and to locate the stem cells in the skin. Several studies have proved that stem cells can be used for skin reconstitution in healing the skin wounds. The limited regenerative capacity of epidermal keratinocytes could be overcome by self-renewing keratinocyte stem cells. Locating hair follicle stem cells can bring possible hope to form hair follicle in future bioengineered skin products (5). However, there are still many challenges that are collectively faced by bioengineers, cell biologists and clinicians; further development in this area needs ongoing interactions and collaborations. New technologies are being developed to provide hope for future regenerative skin technologies. Stem cell technology is making new milestones in the efficiency of cell culturing.

Drag Reduction Technology with Nanomaterial ShUNP2-10 in Oilfield

Drag reduction with the nanomaterial is a new technique for EOR aiming at the problem of high injection pressure but shortage of injection rate in oilfield. The ShUNP2-10 is a nanomaterial which was prepared for this drag reduction technology. The structure and properties of nanomaterial ShUNP2-10 were characterized by transmission electron microscope (TEM), laser particle analyzer (LPA) and other methods. The microstructure and the wettability of the core surface before and after adsorbed by ShUNP2-10 were investigated. Drag reduction effects of the nanomaterial ShUNP2-10 in microchannels was studied by core displacement experiments (CDE) and field tests. The results show that the ShUNP2-10 is a spherical particle with 10~20nm in diameter, and particle surface have many hydrophilic groups and many hydrophobic groups, but the nanomaterial exhibits high hydrophobic. It was observed that many nanoparticles adsorbed firmly on core surface and formed nanoparticle layers with micro-and nanostructure. The nanolayers changed the core surface wettability from strong hydrophilicity to high hydrophobicity. The water phase permeability (WPP) of these cores displaced with the nanomaterial increased averagely more than 130.6% by CDE and a maximum injection pressure reduction of 12.5 MPa was achieved in-situ test. All these results indicate this nanomaterial ShUNP2-10 has significant drag reduction property and important practical value in Oilfield.