In this review we will focus on how magnetic fields can be used to manipulate the motion of various micro- and nanostructures in solution. We will distinguish between ferromagnetic, paramagnetic and diamagnetic materials. Furthermore, the use of various kinds of magnetic fields, such as homogeneous, inhomogeneous and rotating magnetic fields, is discussed. To date most research has focused on the use of ferro- and paramagnetic materials, but here we also describe the possibilities of magnetic manipulation of diamagnetic materials. Since the vast majority of soft matter is diamagnetic, this paves the way for many new applications to manipulate the motion of micro- and nanostructures.

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Manipulation of micro- and nanostructure motion with magnetic fields

We review recent advances in quantum dot (QD)- enhanced liquid crystal displays (LCDs), including material formulation, device configuration, and system integration. For the LCD system, we first compare the color gamut difference between the commonly used Gaussian fitting method and that using real emission spectra. Next, we investigate the Helmholtz–Kohlrausch effect. Our simulation results indicate that QD-enhanced LCD appears 1.26X more efficient than organic light-emitting diode (OLED) display due to its wider color gamut. Finally, two new trends for QD-LCDs are discussed: 1) replacing conventional color filters with a QD array, and 2) emerging quantum rod (QR)-enhanced backlight. Their inherent advantages, technical challenges, and potential solutions are presented. We believe the prime time for QD-enhanced LCDs is around the corner.

Recent Advances on Quantum-Dot-Enhanced Liquid-Crystal Displays

Using liquid–liquid interfacial assembly, we control the deposition of CdSe nanoplatelets into face-down or edge-up configurations. Controlled assembly, combined with back focal plane imaging, enabled unambiguous determination of the transition dipole orientation. The transition dipole moment of the emissive band-edge exciton in CdSe nanoplatelets was found to be isotropically oriented within the plane of the nanoplatelet with no measurable out-of-plane component and no preference for the long- or short-axis of the nanoplatelet. Importantly, CdSe nanoplatelet films in the face-down configuration exhibited unity dipole orientation within the plane of the film, which could improve the external efficiency of nanoplatelet LEDs, lasers, photodetectors, and photovoltaic cells beyond that which is possible with isotropic emitters. We also show that the two self-assembled configurations have different Forster energy transfer rates, as a result of different dipole orientation and internanoplatelet distance.

CdSe Nanoplatelet Films with Controlled Orientation of their Transition Dipole Moment

Herein, emerging applications of luminescent semiconductor nanocrystals are addressed, such as quantum dots and quantum rods as down-conversion materials used in liquid crystal displays (LCD). Their precisely tunable emission wavelengths and narrow emission bandwidths offer high color purity resulting in a wide color gamut with vivid colors for LCDs. Anisotropic materials, such as quantum rods, have the additional advantage of polarized emission, which can bring a significant improvement to the efficiency of LCD displays. The basic optical properties of these nanomaterials are considered, with a focus on quantum rods, and the challenges and progress in their assembly are discussed. Different techniques for quantum rod alignment are introduced such as shear-oriented, electric field and magnetic field assisted assembly, mechanical rubbing, stretching, and electrospinning. The photoalignment approach allows for an easy arrangement of quantum rods in-plane, and the implications of this method to patterning are considered. Different configurations of LCDs utilizing semiconductor quantum dots and quantum rods as down-conversion layers are also presented, and the potential applications that are enabled by the wide range of emerging materials are highlighted.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201901345

Luminescent Down-Conversion Semiconductor Quantum Dots and Aligned Quantum Rods for Liquid Crystal Displays.

One-dimensional semiconductor nanorods are a very promising class of materials for applications in modern optoelectronic devices, such as light-emitting diodes, solar cells, displays, and lasers. Their ability to emit linearly polarized light is considered to simplify device structures and improve the overall efficiencies. To ensure macroscopic polarization in such devices, the biggest challenge is the long-range alignment of nanorods by controllable means. We propose a technique that combines photoinduced alignment with nanorod’s self-assembly. With this approach, we are able to actively control the alignment directions of highly emissive semiconductor nanorods in both microscopic and macroscopic scale with the order parameter as high as 0.87. As a result, polarized emission has been achieved with the degree of polarization of 0.62. Furthermore, patterned alignment of nanorods with spatially varying local orientations has been realized to demonstrate the great flexibility of this approach. Besides opport...

Combination of Photoinduced Alignment and Self-Assembly to Realize Polarized Emission from Ordered Semiconductor Nanorods

Birefringence measurements at high magnetic field strength of up to 33 T were used to detect magnetically induced alignment of bicelles composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), cholesterol, and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-diethylenetriaminepentaacetate (DMPE-DTPA) with complexed lanthanide ions. These birefringence measurements together with a small-angle neutron scattering (SANS) analysis in a magnetic field showed parallel alignment of the bicelles if the lanthanide was thulium (Tm3+), and perpendicular alignment with dysprosium (Dy3+). With the birefringence measurements, the order parameter S can be determined as a function of the magnetic field strength, if the magnetic alignment reaches saturation. Additional structural information can be obtained if the maximum induced birefringence is considered. The degree of alignment of the studied bicelles increased with decreasing temperature from 40 to 5 °C and showed a new bicellar structure comprising a transient...

Alignment of bicelles studied with high-field magnetic birefringence and small-angle neutron scattering measurements.

We studied spontaneously self-assembled aggregates in a suspension of CdSe/CdS core/shell nanorods (NRs). The influence of the length and concentration of the NRs and the suspension temperature on the size of the aggregates was investigated using in situ small-angle X-ray scattering (SAXS) and linear dichroism (LD) measurements under high magnetic fields (up to 30 T). The SAXS patterns reveal the existence of crystalline 2-dimensional sheets of ordered NRs with an unusually large distance between the rods. The LD measurements show that the size of the sheets depends on the free-energy driving force for NR self-assembly. More precisely, the sheets are larger if the attraction between NRs is stronger, if the temperature is lower, or if the NR concentration is higher. We show that the formation of large NR sheets is a slow process that can take days. Our in situ results of the structures that spontaneously form in the bulk suspension could further our understanding of NR self-assembly into mono- or multilaye...

Self-assembled cdse/cds nanorod sheets studied in the bulk suspension by magnetic alignment

Tuning the plasmonic response with an external magnetic field is extremely promising to achieve active magnetoplasmonic devices, such as next generation refractometric sensors or tunable optical components. Noble metal nanostructures represent an ideal platform for studying and modeling magnetoplasmonic effects through the interaction of free electrons with external magnetic fields, even though their response is relatively low at the magnetic field intensities commonly applied in standard magneto-optical spectroscopies. Here we demonstrate a large magnetoplasmonic response of silver nanoparticles by performing magnetic circular dichroism spectroscopy at high magnetic fields, revealing a linear response to the magnetic field up to 30 T. The exploitation of such high fields allowed us to probe directly the field-induced splitting of circular plasmonic modes by performing absorption spectra with static circular polarizations, giving direct experimental evidence that the magneto-optical activity of plasmonic nanoparticles arises from the energy shift of field-split circular magnetoplasmonic modes. 

https://flore.unifi.it/bitstream/2158/1258676/1/Gabbani_01-2022.pdf

High Magnetic Field Magneto-optics on Plasmonic Silica-Embedded Silver Nanoparticles

Computational metrology has been proposed as the way forward to resolve the need for increased metrology density, resulting from extending correction capabilities, without adding actual metrology budget. By exploiting TWINSCAN based metrology information, dense overlay fingerprints for every wafer can be computed. This extended metrology dataset enables new use cases, such as monitoring and control based on fingerprints for every wafer of the lot. This paper gives a detailed description, discusses the accuracy of the fingerprints computed, and will show results obtained in a DRAM HVM manufacturing environment. Also an outlook for improvements and extensions will be shared.

Computational metrology: enabling full-lot high-density fingerprint information without adding wafer metrology budget, and driving improved monitoring and process control

Peter G. van Rhee

Papers

Alignment of bicelles studied with high-field magnetic birefringence and small-angle neutron scattering measurements.

Self-assembled cdse/cds nanorod sheets studied in the bulk suspension by magnetic alignment

High Magnetic Field Magneto-optics on Plasmonic Silica-Embedded Silver Nanoparticles

Computational metrology: enabling full-lot high-density fingerprint information without adding wafer metrology budget, and driving improved monitoring and process control