Comment on “A Mechanistic Understanding of Nonclassical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires”

Sodium yttrium fluoride (NaYF4) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF4 nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb3+ point defects within NaYF4 are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF4.

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A Mechanistic Understanding of Non-Classical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

10.26434/chemrxiv.10029599 ◽

2020 ◽

Author(s):

Alex Bard ◽

Xuezhe Zhou ◽

Xiaojing Xia ◽

Guomin Zhu ◽

Matthew Lim ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Crystal Growth ◽

Materials Science ◽

Atom Probe ◽

Oriented Attachment ◽

Yttrium Fluoride ◽

X Ray ◽

Transmission Electron ◽

Classical Crystal

Sodium yttrium fluoride (NaYF4) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF4 nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb3+ point defects within NaYF4 are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF4.

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Montmorillonite Dendrites

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052286 ◽

1974 ◽

Vol 32 ◽

pp. 454-455

Author(s):

Necip Güven ◽

Rodney W. Pease

Keyword(s):

Crystal Growth ◽

Growth Mechanism ◽

Growth Front ◽

Morphological Features ◽

Dendritic Crystal ◽

Crystal Growth Mechanism

Morphological features of montmorillonite aggregates in a large number of samples suggest that they may be formed by a dendritic crystal growth mechanism (i.e., tree-like growth by branching of a growth front).

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TEM and cathodoluminescence of precipitates in II-VI semiconductors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104509 ◽

1988 ◽

Vol 46 ◽

pp. 488-489

Author(s):

Joanna L. Batstone

Keyword(s):

Crystal Growth ◽

Band Gap ◽

Local Strain ◽

Wide Band ◽

Optoelectronic Device ◽

Wide Band Gap ◽

Bulk Crystal Growth ◽

Transmission Electron ◽

Device Applications ◽

Stoichiometry Control

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-x Te are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.

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STM studies of crystal growth

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086179 ◽

1991 ◽

Vol 49 ◽

pp. 374-375

Author(s):

M. G. Lagally

Keyword(s):

Crystal Growth ◽

Molecular Beam ◽

Chemical Vapor ◽

Sputter Deposition ◽

Field Of View ◽

Scanning Tunneling ◽

Wide Field ◽

Tunneling Microscopy ◽

Wide Field Of View ◽

The One

It has been recognized since the earliest days of crystal growth that kinetic processes of all Kinds control the nature of the growth. As the technology of crystal growth has become ever more refined, with the advent of such atomistic processes as molecular beam epitaxy, chemical vapor deposition, sputter deposition, and plasma enhanced techniques for the creation of “crystals” as little as one or a few atomic layers thick, multilayer structures, and novel materials combinations, the need to understand the mechanisms controlling the growth process is becoming more critical. Unfortunately, available techniques have not lent themselves well to obtaining a truly microscopic picture of such processes. Because of its atomic resolution on the one hand, and the achievable wide field of view on the other (of the order of micrometers) scanning tunneling microscopy (STM) gives us this opportunity. In this talk, we briefly review the types of growth kinetics measurements that can be made using STM. The use of STM for studies of kinetics is one of the more recent applications of what is itself still a very young field.

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Cristal-growth dynamics of n-doped gaAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100132352 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1544-1545

Author(s):

Pham V. Huong ◽

Stéphanie Bouchet ◽

Jean-Claude Launay

Keyword(s):

Crystal Growth ◽

Spatial Resolution ◽

Epitaxial Layer ◽

Outer Surface ◽

Gaas Substrate ◽

Structural Modification ◽

Growth Dynamics ◽

Argon Laser ◽

High Anisotropy ◽

Crystal Gaas

Microstructure of epitaxial layers of doped GaAs and its crystal growth dynamics on single crystal GaAs substrate were studied by Raman microspectroscopy with a Dilor OMARS instrument equipped with a 1024 photodiode multichannel detector and a ion-argon laser Spectra-Physics emitting at 514.5 nm.The spatial resolution of this technique, less than 1 μm2, allows the recording of Raman spectra at several spots in function of thickness, from the substrate to the outer deposit, including areas around the interface (Fig.l).The high anisotropy of the LO and TO Raman bands is indicative of the orientation of the epitaxial layer as well as of the structural modification in the deposit and in the substrate at the interface.With Sn doped, the epitaxial layer also presents plasmon in Raman scattering. This fact is already very well known, but we additionally observed that its frequency increases with the thickness of the deposit. For a sample with electron density 1020 cm-3, the plasmon L+ appears at 930 and 790 cm-1 near the outer surface.

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