Research

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11 pages, 2440 KiB

Open AccessArticle

Laser Irradiation-Induced Nanoscale Surface Transformations in Strontium Titanate

by Ashish Kumar Gupta, Siddharth Gupta, Soumya Mandal and Ritesh Sachan

Crystals 2022, 12(5), 624; https://doi.org/10.3390/cryst12050624 - 27 Apr 2022

Cited by 5 | Viewed by 1858

We studied the structural transformations and atomic rearrangements in strontium titanate (SrTiO₃) via nanosecond pulsed laser irradiation-induced melting and ultrafast quenching. Using scanning transmission electron microscopy, we determine that the laser-irradiated surface in single-crystalline SrTiO₃ transforms into an amorphous phase [...] Read more.

We studied the structural transformations and atomic rearrangements in strontium titanate (SrTiO₃) via nanosecond pulsed laser irradiation-induced melting and ultrafast quenching. Using scanning transmission electron microscopy, we determine that the laser-irradiated surface in single-crystalline SrTiO₃ transforms into an amorphous phase with an interposing disordered crystalline region between amorphous and ordered phases. The formation of disordered phase is attributed to the rapid recrystallization of SrTiO₃ from the melt phase constrained by an epitaxial relation with the pristine region, which eases up on the surface, leading to amorphous phase formation. With electron energy-loss spectroscopic analysis, we confirm the transformation of Ti⁺⁴ to Ti⁺³ due to oxygen vacancy formation as a result of laser irradiation. In the disordered region, the maximum transformation of Ti⁺⁴ is observed to be 16.2 ± 0.2%, whereas it is observed to be 20.2 ± 0.2% in the amorphous region. Finally, we deduce that the degree of the disorder increases from atomically disordered to amorphous transition in SrTiO₃ under laser-irradiation. The signatures of short-range ordering remain similar, leading to a comparable fingerprint of electronic structure. With these results, this study addresses the gap in understanding the atomic and electronic structure modified by pulsed laser irradiation and functionalizing pristine SrTiO₃ for electronic, magnetic, and optical applications. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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16 pages, 28947 KiB

Open AccessArticle

Fabrication of Q-Carbon Nanostructures, Diamond and Their Composites with Wafer-Scale Integration

by Nayna Khosla and Jagdish Narayan

Crystals 2022, 12(5), 615; https://doi.org/10.3390/cryst12050615 - 26 Apr 2022

Cited by 10 | Viewed by 3493

Abstract

We report the formation of Q-carbon nanolayers, Q-carbon nanoballs, nanodiamonds, microdiamonds, and their composites by controlling laser and substrate variables. The choice of these parameters is guided by the SLIM (simulation of laser interactions with materials) computer modeling. For a constant film thickness [...] Read more.

We report the formation of Q-carbon nanolayers, Q-carbon nanoballs, nanodiamonds, microdiamonds, and their composites by controlling laser and substrate variables. The choice of these parameters is guided by the SLIM (simulation of laser interactions with materials) computer modeling. For a constant film thickness and initial sp³ content, we obtain different microstructures with increasing pulse energy density as a result of different quenching rate and undercooling. This is related to decreasing undercooling with increasing pulse energy density. The structure of thin film Q-carbon evolves into Q-carbon nanoballs with the increase in laser annealing energy density. These Q-carbon nanoballs interestingly self-organize in the form of rings with embedded nanodiamonds to form Q-carbon nanoballs/diamond composites. We form high quality, epitaxial nano, and micro diamond films at a higher energy density and discuss a model showing undercooling and quenching rate generating a pressure pulse, which may play a critical role in a direct conversion of amorphous carbon into Q-carbon or diamond or their composites. This ability to selectively tune between diamond or Q-carbon or their composites on a single substrate is highly desirable for a variety of applications ranging from protective coatings to nanosensing and field emission to targeted drug delivery. Furthermore, Q-carbon nanoballs and nanodiamonds are utilized as seeds to grow microdiamond films by HFCVD. It is observed that the Q-carbon nanoballs contain diamond nuclei of critical size, which provide available nucleation sites for diamond growth, leading to stress-free, adherent, and denser films, which are needed for a variety of coating applications. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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8 pages, 2494 KiB

Open AccessEditor’s ChoiceArticle

The Growth of Hexagonal Boron Nitride Quantum Dots on Polycrystalline Nickel Films by Plasma-Assisted Molecular Beam Epitaxy

by Nurzal Nurzal, Wei-Cyuan Huang, Cheng-Yu Liu, Su-Hua Chen and Ing-Song Yu

Crystals 2022, 12(3), 347; https://doi.org/10.3390/cryst12030347 - 03 Mar 2022

Cited by 3 | Viewed by 2095

Abstract

In this report, quantum dots of hexagonal boron nitride (h-BN) were fabricated on the surface of polycrystalline Ni film at low growth temperatures (700, 750, and 800 °C) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction could trace the surface condition during [...] Read more.

In this report, quantum dots of hexagonal boron nitride (h-BN) were fabricated on the surface of polycrystalline Ni film at low growth temperatures (700, 750, and 800 °C) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction could trace the surface condition during the growth and perform the formation of BN. The observation of surface morphology by scanning electron microscopy and atomic force microscopy showed the nanodots of BN on Ni films. The existence of crystal h-BN quantum dots was determined by the analysis of Raman spectra and Kevin probe force microscopy. The cathodoluminescence of h-BN quantum dots performed at the wavelength of 546 and 610 nm, attributed to the trapping centers involving impurities and vacancies. Moreover, the influence of temperatures for the substrate and boron source cell was also investigated in the report. When the k-cell temperature of boron and growth temperature of substrate increased, the emission intensity of cathodoluminescence spectra increased, indicating the better growth parameters for h-BN quantum dots. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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16 pages, 3458 KiB

Open AccessArticle

Electromagnetically Modified Wettability and Interfacial Tension of Hybrid ZnO/SiO₂ Nanofluids

by Yarima Mudassir Hassan, Beh Hoe Guan, Lee Kean Chuan, Mayeen Uddin Khandaker, Surajudeen Sikiru, Ahmed Halilu, Abdullahi Abbas Adam, Bashir Abubakar Abdulkadir and Fahad Usman

Crystals 2022, 12(2), 169; https://doi.org/10.3390/cryst12020169 - 25 Jan 2022

Cited by 14 | Viewed by 2343

Abstract

Worldwide, reservoirs are having serious challenges on crude oil removal due to various factors affecting its mobility; hence, the approach of oil production needs to be rectified. Recently, various nanoparticles (NPs) were discovered to have aided in oil displacement to improve oil production [...] Read more.

Worldwide, reservoirs are having serious challenges on crude oil removal due to various factors affecting its mobility; hence, the approach of oil production needs to be rectified. Recently, various nanoparticles (NPs) were discovered to have aided in oil displacement to improve oil production by modifying some reservoir conditions thereby reducing interfacial tension (IFT) and rock surface wettability. However, the injected NPs in the reservoir are trapped within the rock pores and become worthless due to high temperature and pressure. Hence, introducing energy to the nanofluids via electromagnetic (EM) waves can improve nanoparticle (NPs) mobility in the reservoir for the attainment of oil displacements. In this work, hybrid ZnO/SiO₂ NPs were selected by considering that the combination of two dielectric NPs may produce a single nanofluid that is expected to make the fluids more electrified under EM waves. The result showed that ZnO/SiO₂ NPs reduced the IFT (mN/m) from 17.39 to 2.91, and wettability (°) from 141 to 61. Moreover, by introducing the EM waves to the fluids, the IFT was further reduced to 0.02 mN/m from 16.70 mN/m, and solid surface wettability was also reduced from 132° to 58°. The advancement observed during exposure to EM waves was attributed to the energy propagated to the fluids that polarize the free charges of the NPs and consequently activate the fluids by creating disturbances at the fluid/oil interface, which resulted in reduced IFT and wettability. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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10 pages, 3939 KiB

Open AccessArticle

Atomic-Scale Insights on Large-Misfit Heterointerfaces in LSMO/MgO/c-Al₂O₃

by Soumya Mandal, Ashish Kumar Gupta, Braxton Hays Beavers, Vidit Singh, Jagdish Narayan and Ritesh Sachan

Crystals 2021, 11(12), 1493; https://doi.org/10.3390/cryst11121493 - 01 Dec 2021

Cited by 7 | Viewed by 2359

Abstract

Understanding the interfaces in heterostructures at an atomic scale is crucial in enabling the possibility to manipulate underlying functional properties in correlated materials. This work presents a detailed study on the atomic structures of heterogeneous interfaces in La_0.7Sr_0.3MnO₃ [...] Read more.

Understanding the interfaces in heterostructures at an atomic scale is crucial in enabling the possibility to manipulate underlying functional properties in correlated materials. This work presents a detailed study on the atomic structures of heterogeneous interfaces in La_0.7Sr_0.3MnO₃ (LSMO) film grown epitaxially on c-Al₂O₃ (0001) with a buffer layer of MgO. Using aberration-corrected scanning transmission electron microscopy, we detected nucleation of periodic misfit dislocations at the interfaces of the large misfit systems of LSMO/MgO and MgO/c-Al₂O₃ following the domain matching epitaxy paradigm. It was experimentally observed that the dislocations terminate with 4/5 lattice planes at the LSMO/MgO interface and with 12/13 lattice planes at the MgO/c-Al₂O₃ interface. This is consistent with theoretical predictions. Using the atomic-resolution image data analysis approach to generate atomic bond length maps, we investigated the atomic displacement in the LSMO/MgO and MgO/c-Al₂O₃ systems. Minimal presence of residual strain was shown at the respective interface due to strain relaxation following misfit dislocation formation. Further, based on electron energy-loss spectroscopy analysis, we confirmed an interfacial interdiffusion within two monolayers at both LSMO/MgO and MgO/c-Al₂O₃ interfaces. In essence, misfit dislocation configurations of the LSMO/MgO/c-Al₂O₃ system have been thoroughly investigated to understand atomic-scale insights on atomic structure and interfacial chemistry in these large misfit systems. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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17 pages, 21843 KiB

Open AccessArticle

One-Step Formation of Reduced Graphene Oxide from Insulating Polymers Induced by Laser Writing Method

by Parand R. Riley, Pratik Joshi, Hristo Penchev, Jagdish Narayan and Roger J. Narayan

Crystals 2021, 11(11), 1308; https://doi.org/10.3390/cryst11111308 - 27 Oct 2021

Cited by 11 | Viewed by 4130

Abstract

Finding a low-cost and effective method at low temperatures for producing reduced graphene oxide (rGO) has been the focus of many efforts in the research community for almost two decades. Overall, rGO is a promising candidate for use in supercapacitors, batteries, biosensors, photovoltaic [...] Read more.

Finding a low-cost and effective method at low temperatures for producing reduced graphene oxide (rGO) has been the focus of many efforts in the research community for almost two decades. Overall, rGO is a promising candidate for use in supercapacitors, batteries, biosensors, photovoltaic devices, corrosion inhibitors, and optical devices. Herein, we report the formation of rGO from two electrically insulating polymers, polytetrafluoroethylene (PTFE) and meta-polybenzimidazole fiber (m-PBI), using an excimer pulsed laser annealing (PLA) method. The results from X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy confirm the successful generation of rGO with the formation of a multilayered structure. We investigated the mechanisms for the transformation of PTFE and PBI into rGO. The PTFE transition occurs by both a photochemical mechanism and a photothermal mechanism. The transition of PBI is dominated by a photo-oxidation mechanism and stepwise thermal degradation. After degradation and degassing procedures, both the polymers leave behind free molten carbon with some oxygen and hydrogen content. The free molten carbon undergoes an undercooling process with a regrowth velocity (<4 m·s⁻¹) that is necessary for the formation of rGO structures. This approach has the potential for use in creating future selective polymer-written electronics. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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11 pages, 10382 KiB

Open AccessArticle

Controlled Synthesis of Au Nanoparticles by Modified Polyol Methods: Determination of Their Size, Shape, and Crystal Structure

by Nguyen Thi Nhat Hang, Yong Yang, Nguyen Quang Thanh Nam, Masayuki Nogami, Le Hong Phuc, Nguyen Huu Tri, Ho Van Cuu and Nguyen Viet Long

Crystals 2021, 11(11), 1297; https://doi.org/10.3390/cryst11111297 - 26 Oct 2021

Cited by 5 | Viewed by 2941

Abstract

We successfully prepared Au nanoparticles using the modified polyol methods and design of experiments. The desirable crystal structure and particle size of Au nanoparticles with various kinds of polyhedral and spherical shapes as well as various kinds of their morphologies or complete and [...] Read more.

We successfully prepared Au nanoparticles using the modified polyol methods and design of experiments. The desirable crystal structure and particle size of Au nanoparticles with various kinds of polyhedral and spherical shapes as well as various kinds of their morphologies or complete and rough spherical crystal surfaces were experimentally predicted in TEM and XRD measurements according to the theoretical calculation and data. The fine crystal formation of Au nanostructures by modified polyol methods with EG, PVP, and NaBH₄ is of great importance to their practical applications. Our research shows that the critical nucleation, growth, and formation of sizes, shapes, and morphologies of Au nanoparticles were experimentally discussed in modified polyol methods and design of experiments. In this context, our particle size calculation can hold the greatest attraction for researchers in the field of nanoparticles. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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8 pages, 1915 KiB

Open AccessArticle

Controlled Morphology and Its Effects on the Thermoelectric Properties of SnSe₂ Thin Films

by Muhammad Siyar, Maroosha Farid, Haad Khan, Malik Adeel Umar, Waqas Hassan Tanveer and Amna Safdar

Crystals 2021, 11(8), 942; https://doi.org/10.3390/cryst11080942 - 13 Aug 2021

Cited by 3 | Viewed by 3485

Abstract

In the last few years, the thermoelectric properties of tin selenide (SnSe) have been explored in much detail due to its high efficiency and green nature, being free of Te and Pb. In the same chalcogenide family, SnSe₂ is also a layered [...] Read more.

In the last few years, the thermoelectric properties of tin selenide (SnSe) have been explored in much detail due to its high efficiency and green nature, being free of Te and Pb. In the same chalcogenide family, SnSe₂ is also a layered structured material, but its thermoelectric potential has not been widely explored experimentally. Since SnSe₂ has the layered structure, its electrical transport properties may strongly be affected by its microstructure and morphology. Here, we report the effect of reaction time on the structure, phase, and morphology of the SnSe₂ during solvothermal synthesis process. We have studied four SnSe₂ samples with different reaction times. The sample obtained after 16 h of reaction time was named as M1, for 20 h M2, similarly for 24 h was M3 and for 48 hours’ time, the sample was named as M4. We investigated its thermoelectric properties and found that phase purity and morphology can affect the thermoelectric performance of the synthesized samples. The peak power factor (PF) value along the ab plane was (0.69 μWcm⁻¹K⁻²) for the M4 sample at 575 K, which was the highest among all the measured samples. The comparatively larger PF value of sample M4 can be related to the increase in its electrical conductivity due to increase in phase purity and band gap reduction. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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Review

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14 pages, 3307 KiB

Open AccessReview

Cellulose Nanomaterials as a Future, Sustainable and Renewable Material

by Hoang Thi Phuong, Nguyen Kim Thoa, Phung Thi Anh Tuyet, Quyen Nguyen Van and Yen Dao Hai

Crystals 2022, 12(1), 106; https://doi.org/10.3390/cryst12010106 - 14 Jan 2022

Cited by 11 | Viewed by 3409

Abstract

Cellulose nanomaterials (CNs) are renewable, bio-derived materials that can address not only technological challenges but also social impacts. This ability results from their unique properties, for example, high mechanical strength, high degree of crystallinity, biodegradable, tunable shape, size, and functional surface chemistry. This [...] Read more.

Cellulose nanomaterials (CNs) are renewable, bio-derived materials that can address not only technological challenges but also social impacts. This ability results from their unique properties, for example, high mechanical strength, high degree of crystallinity, biodegradable, tunable shape, size, and functional surface chemistry. This minireview provides chemical and physical features of cellulose nanomaterials and recent developments as an adsorbent and an antimicrobial material generated from bio-renewable sources. Full article

(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)

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