Practical implications for the quality assurance of modulated radiation therapy techniques using point detector arrays.

PURPOSE: Linac parameters potentially influencing the delivery quality of IMRT and VMAT plans are investigated with respect to threshold ranges, consequently to be considered in a linac based quality assurance procedure. Three commercially available 2D arrays are used to further investigate the influence of the measurement device. METHODS: Using three commercially available 2D arrays (Mx: MatriXXevolution , Oc: Octavius1500 , Mc: MapCHECK2), simple static measurements, measurements for MLC characterization and dynamic interplay of gantry movement, MLC movement and variable dose rate were performed. The results were evaluated with respect to each single array as well as among each other. RESULTS: Simple static measurements showed different array responses to dose, dose rate and profile homogeneity and revealed instabilities in dose delivery and profile shape during linac ramp up. Using the sweeping gap test, all arrays were able to detect small leaf misalignments down to ±0.1 mm, but this test also demonstrated up to 15% dose deviation due to profile instabilities and fast accelerating leaves during linac ramp up. Tests including gantry rotation showed different stability of gantry mounts for each array. Including gantry movement and dose rate variability, differences compared to static delivery were smaller compared to dose differences when simultaneously controling interplay of gantry movement, leaf movement and dose rate variability. CONCLUSION: Linac based QA is feasible with the tested commercially available 2D arrays. Limitations of each array and the linac ramp up characteristics should be carefully considered during individual plan generation and regularly checked in linac QA. Especially the dose and dose profile during linac ramp up should be checked regularly, as well as MLC positioning accuracy using a sweeping gap test. Additionally, dynamic interplay tests including various gantry rotation speeds and angles, various leaf speeds and various dose rates should be included.

A Method for Promoting Assembly of Metallic and Nonmetallic Nanoparticles into Interfacial Monolayer Films.

Two-dimensional metal nanoparticle arrays are normally constructed at liquid-oil interfaces by modifying the surfaces of the constituent nanoparticles so that they self-assemble. Here we present a general and facile new approach for promoting such interfacial assembly without any surface modification. The method use salts that have hydrophobic ions of opposite charge to the nanoparticles, which sit in the oil layer and thus reduce the Coulombic repulsion between the particles in the organic phase, allowing the particles to sit in close proximity to each other at the interface. The advantage of this method is that because it does not require the surface of the particles to be modified it allows nonmetallic particles including TiO2 and SiO2 to be assembled into dense interfacial layers using the same procedure as is used for metallic particles. This opens up a route to a new family of nanostructured functional materials.

Reconfigurable Two-Dimensional DNA Molecular Arrays.

In biology, molecular cascade signaling is an essential tool to mediate various pathways and downstream behaviors. Mimicking these molecular cascades plays an important role in synthetic biology. The use of DNA self-assembly represents an elegant way to build sophisticated molecular cascades. For instance, a DNA molecular array connected by a number of dynamic anti-junction units was able to realize prescribed, multistep, long-range cascaded transformation. The dynamic DNA molecular array is able to execute transformations with programmable initiation, propagation, and regulation. The transformation of the array can be initiated at selected units and then propagated, without addition of extra triggers, to neighboring units and eventually the entire array.

Monolithic 45 Degree Deflecting Mirror as a Key Element for Realization of 2D Arrays of Laser Diodes Based on AlInGaN Semiconductors.

In this study, we propose a solution for realization of surface emitting, 2D array of visible light laser diodes based on AlInGaN semiconductors. The presented system consists of a horizontal cavity lasing section adjoined with beam deflecting section in the form of 45° inclined planes. They are placed in the close vicinity of etched vertical cavity mirrors that are fabricated by Reactive Ion Beam Etching. The principle of operation of this device is confirmed experimentally; however, we observed an unexpected angular distribution of reflected rays for the angles lower than 45°, which we associate with the light diffraction and interference between the vertical and deflecting mirrors. The presented solution offers the maturity of edge-emitting laser technology combined with versatility of surface-emitting lasers, including on-wafer testing of emitters and addressability of single light sources.

Organic Semiconductor Crystal Engineering for High-Resolution Layer-Controlled 2D Crystal Arrays.

2D organic semiconductor crystals (2DOSCs) have extraordinary charge transport capability, adjustable photoelectric properties, and superior flexibility, and have stimulated continuous research interest for next-generation electronic and optoelectronic applications. The prerequisite for achieving large-area and high-throughput optoelectronic device integration is to fabricate high-resolution 2DOSC arrays. Patterned substrate- and template-assisted self-assembly is an effective strategy to fabricate OSC arrays. However, the film thickness is difficult to control due to the complicated crystallization process during solvent evaporation. Therefore, the manufacturing of 2DOSC arrays with high-resolution and controllable molecular-layer numbers through solution-based patterning methods remains a challenge. Herein, a two-step strategy to produce high-resolution layer-controlled 2DOSC arrays is reported. First, large-scale 2DOSCs with well-defined layer numbers are obtained by a solution-processed organic semiconductor crystal engineering method. Next, the high-resolution layer-controlled 2DOSC arrays are fabricated by a polydimethylsiloxane mold-assisted selective contact evaporation printing technique. The organic field-effect transistors (OFETs) based on 2DOSC arrays have high electrical performance and excellent uniformity. The 2,6-bis(4-hexylphenyl)anthracene 2DOSC arrays-based OFETs have a small variation of 12.5% in mobility. This strategy can be applied to various organic semiconductors and pattern arrays. These demonstrations will offer more opportunities for 2DOSCs for integrated optoelectronic devices.

Self-Assembly of Polymer End-Tethered Gold Nanorods into Two-Dimensional Arrays with Tunable Tilt Structures.

We demonstrated a facile yet effective strategy for self-assembly of polymer end-tethered gold nanorods (GNRs) into tunable two-dimensional (2D) arrays with the assistance of supramolecules of hydrogen bonded poly(4-vinyl pyridine) (P4VP) and 3-n-pentadecylphenol (PDP). Well-ordered 2D arrays with micrometer size were obtained by rupturing the assembled supramolecular matrix with a selective solvent. The formation of long-range ordered 2D arrays during a drying process was observed via small-angle X-ray scattering. Interestingly, the packing structure of the ordered arrays strongly depends on the molecular weight (Mw) of the polymer ligands and the size of the GNRs. By increasing Mw of the polymer ligands, tilted arrays can be obtained. The average angle between GNRs and the surface normal direction of the layered 2D arrays changes from 0 to 37° with the increase in Mw of the polymer ligands. A mechanism for assembly behavior of dumbbell shapes with a soft shell structure has been proposed. The resulting GNR arrays with different orientations showed anisotropic surface-enhanced Raman scattering (SERS) performance. We showed that the vertically ordered GNR arrays exhibited ∼3 times higher SERS signals than the tilt ordered arrays. The results prove that the polymer end-tethered GNRs can be used as a building block for preparing the tilted 2D arrays with tunable physicochemical properties, which could have a wide range of potential applications in photonics, electronics, plasmonics, etc.

Bottom-Up Fabrication of Large-Scale Gold Nanorod Arrays by Surface Diffusion-Mediated DNA Origami Assembly.

Self-assembly of anisotropic metal nanoparticles serves as an effective bottom-up route for the nanofabrication of novel artifacts. However, there still are many challenges to rationally manipulate anisotropic particles due to the size and geometric restrictions. To avoid the aggregation and mishybridization from DNA sticky-end-guided assembly in buffer solution, in this work, we utilized a cation-controlled surface diffusion strategy to the spatial arrangement of gold nanorods (AuNRs) into 1D and 2D arrays by using DNA origami tiles as binding frames on the solid-liquid interface through π-π stacking interactions. To facilitate the further manipulation of those patterns, a novel pattern transfer method was introduced to transfer the arrays of AuNRs from a liquid to a dry ambient environment with high yield and minor structural damage. The results demonstrated a successful strategy of DNA origami-assisted, large-scale assembly of AuNRs for constructing complex superstructures with potential applications in the nanofabrication of plasmonic and electronic devices.

Wideband 2-D sparse array optimization combined with multiline reception for real-time 3-D medical ultrasound.

Three-dimensional (3-D) ultrasound medical imaging provides advantages over a traditional 2-D visualization method. However, the use of a 2-D array to acquire 3-D images may result in a transducer composed of thousands of elements and a large amount of data in the front-end, making it impractical to implement high volume rate imaging and individually control all elements with the scanner. This paper proposes an original approach, valid for wideband operations centered on the design center frequency, to maintain a limited number of active elements and firing events, while preserving high resolution and volume rate. A 7 MHz 2-D array is composed of two circular concentric subparts. In the inner footprint the elements are distributed following a regular grid, while in the outer subpart a sparse non-grid solution is adopted. The inner circular dense array is composed of 256 elements with a pitch of 0.5λ. The overall footprint, delimited by the outer subpart, is equivalent to a 256-element array with a pitch of 1.5λ. All the elements of the inner subpart are activated in transmission. Following an optimization procedure, both subparts, including a subset of the elements placed in the inner footprint (i.e., sparse on-the-grid array) and the elements spread over the outer subpart (i.e., sparse off-the-grid array) are used to receive. A total number of 256 elements, defined by the sum of elements distributed in the inner and outer subparts, is fixed in reception. The proposed approach implies a multiline reception strategy, where for each transmission 3 × 3 firing events occur in reception. The sparse receive array is optimized by using a simulated annealing optimization. An original cost function is designed specifically to achieve successful results in wideband conditions. The receive array is optimized in order to obtain consistent results for different signal bandwidths of the excitation pulse. For all the desired bandwidths, the optimized array will provide the recovery of the lower lateral resolution of the transmission phase and, at the same time, a significant reduction of the undesired side lobe raised in the 3-D two-way beam pattern. The 3-D two-way beam pattern analysis reveals that the proposed solution is able to guarantee a lateral resolution of 1.35 mm at a focus depth of 25 mm for the three fractional signal bandwidths of interest (i.e., 30%, 50% and 70%) considered in the optimization process. The undesired side lobes are successfully suppressed especially when, as a consequence of the multiline strategy, non-coincident steering angles are used in transmission and reception. Moreover, thanks to the firing scheme adopted, a high-volume rate of 63 volumes per second may be achieved at the focus depth. The volume rate decreases to 32 volumes per second at twice the focal depth. Phantom image simulations show that the proposed method maintains a satisfactory and almost uniform image quality in terms of resolution and contrast for all the signal bandwidths of interest.

Chemical Solution Deposition of Ordered 2D Arrays of Room-Temperature Ferrimagnetic Cobalt Ferrite Nanodots.

Over the past decades, the development of nano-scale electronic devices and high-density memory storage media has raised the demand for low-cost fabrication methods of two-dimensional (2D) arrays of magnetic nanostructures. Here, we present a chemical solution deposition methodology to produce 2D arrays of cobalt ferrite (CFO) nanodots on Si substrates. Using thin films of four different self-assembled block copolymers as templates, ordered arrays of nanodots with four different characteristic dimensions were fabricated. The dot sizes and their long-range arrangement were studied with scanning electron microscopy (SEM) and grazing incident small-angle X-ray scattering (GISAXS). The structural evolution during UV/ozone treatment and the following thermal annealing was investigated through monitoring the atomic arrangement with X-ray absorption fine structure spectroscopy (EXAFS) and checking the morphology at each preparation step. The preparation method presented here obtains array types that exhibit thicknesses less than 10 nm and blocking temperatures above room temperature (e.g., 312 K for 20 nm diameter dots). Control over the average dot size allows observing an increase of the blocking temperature with increasing dot diameter. The nanodots present promising properties for room temperature data storage, especially if a better control over their size distribution will be achieved in the future.

A Self-Assembling Two-Dimensional Protein Array is a Versatile Platform for the Assembly of Multicomponent Nanostructures.

Rationally designed two-dimensional (2D) arrays that support the assembly of nanoscale components are of interest for catalysis, sensing, and biomedical applications. The computational redesign of a protein called TTM that undergoes calcium-induced self-assembly into nanostructured lattices capable of growing to dozens of micrometers are previously reported. The work demonstrates here that the N- and C-termini of the constituent monomers are solvent-accessible and that they can be modified with a hexahistidine extension, a gold-binding peptide, or a biotinylation tag to decorate nickel-nitriloacetic acid beads with self-assembled protein islands, conjugate gold nanoparticles to planar arrays, or control the immobilization density of avidin molecules onto 2D lattices through co-polymerization of biotinylated and wild type TTM monomers. These results showcase the potential of TTM as a versatile 2D scaffold for the fabrication of hierarchical structures comprising a broad range of nanoscale elements.

Capture of 2D Microparticle Arrays via a UV-Triggered Thiol-yne "Click" Reaction.

Immobilization of colloidal assemblies onto solid supports via a fast UV-triggered click-reaction is achieved. Transient assemblies of microparticles and colloidal materials can be captured and transferred to solid supports. The technique does not require complex reaction conditions, and is compatible with a variety of particle assembly methods.

Assembly of designed protein scaffolds into monolayers for nanoparticle patterning.

The controlled assembly of building blocks to achieve new nanostructured materials with defined properties at different length scales through rational design is the basis and future of bottom-up nanofabrication. This work describes the assembly of the idealized protein building block, the consensus tetratricopeptide repeat (CTPR), into monolayers by oriented immobilization of the blocks. The selectivity of thiol-gold interaction for an oriented immobilization has been verified by comparing a non-thiolated protein building block. The physical properties of the CTPR protein thin biomolecular films including topography, thickness, and viscoelasticity, are characterized. Finally, the ability of these scaffolds to act as templates for inorganic nanostructures has been demonstrated by the formation of well-packed gold nanoparticles (GNPs) monolayer patterned by the CTPR monolayer.