New technique simplifies creation of nanoparticle ‘magic-sized clusters’

One of the cool things about nanoparticles is also what makes them so difficult to work with: the fact that their properties are dependent on their size.

A critical challenge in translating nanomaterials from the laboratory into commercial applications, such as lighting or optical memory storage, is making a batch of nanoparticles all the same size. Two Cornell research groups have joined forces to lay out a solution for this issue.

Researchers in the labs of Richard Robinson and Tobias Hanrath – using X-ray analysis at the Cornell High Energy Synchrotron Source (CHESS) – have developed a new nanosynthetic pathway to achieve ultra-pure and highly stable groups of same-sized particles – known as “magic-sized clusters.”

Their paper, “Mesophase Formation Stabilizes High-Purity Magic-Sized Clusters,” published online Jan. 27 in the Journal of the American Chemical Society, and will be on a cover of the March 14 print edition. Lead authors are Curtis Williamson, doctoral student in both the Robinson and Hanrath groups, and Douglas Nevers, doctoral student in the Hanrath Group. Lena Kourkoutis, assistant professor of applied and engineering physics, also contributed.

>Read more on the Cornell Hight Energy Synchrotron Source (CHESS) website

Image: Schematic of the magic-sized clusters hexagonal mesophase. The mesophase (left) is an assembly of nanofibers (center), which are composed of magic-sized clusters (right).
Credit: Richard Robinson

A comparison of the etch mechanisms of germanium and silicon

Time multiplexed, deep reactive ion etching (DRIE) is a standard silicon microfabrication technique for fabricating MEMS sensors, actuators, and more recently in CMOS development for 2.5D and 3D memory devices.

At CHESS, we have adopted this microfabrication technique to develop novel x-ray optics called,Collimating Channel Arrays  (CCAs) [1], for confocal x-ray fluorescence microscopy (CXRF). Because the first CCA optics were fabricated from silicon substrates, the range of x-ray fluorescence energies for which they could be used, and hence the elements they could be used to study, was limited. Unwanted x-rays above about 11 keV could penetrate through the silicon, showing up as background and interfering with the measurement.

To solve the background problem, germanium substrates were used to fabricate the CCA optics. Germanium, which is much denser and therefore x-ray opaque than silicon, is also etch compatible with the fluorine etch chemistry for silicon DRIE. However, small differences in etch behavior between germanium and silicon can cause big differences in the outcome. Here, Genova et al JVST B [2] report a systematic comparison of  the etch mechanisms of silicon and germanium, performed with the Plasma Therm Versaline deep silicon etcher at the Cornell NanoScale Science & Technology Facility (CNF). The etch rates of silicon and germanium were compared by varying critical parameters in the DRIE process, especially the applied power and voltage used for each of 3 steps in the etch process,  on custom-designed wafers with a variety of features with systematically varying dimensions.

>Read more on the CHESS website

Image: (extract, full image here) SEM of high aspect ratio (>13:1) etched features in Si at 3.7 μm/min (a) and Ge at 3.4 μm/min (b)

X-ray detector for studying characteristics of materials

Sol M. Gruner’s group, Physics, has been a leader in the development of x-ray detectors for scientific synchrotron applications, and the team’s technology is used around the world. Their detectors utilize pixelated integrated circuit silicon layers to absorb x-rays to produce electrical signals. The wide dynamic range, high sensitivity, and rapid image frame rate of the detectors enable many time-resolved x-ray experiments that have been difficult to perform until now.

The detectors are limited by the silicon layer. Low atomic number materials such as silicon become increasingly transparent to x-rays as the energy of the x-rays rises. Gruner’s group is now developing a variant of their detector that will use semiconductors comprised of high atomic weight elements to absorb the x-rays and produce the resultant electrical signals. The Detector Group, led by Antonio Miceli, at the United States Department of Energy’s Advanced Photon Source (APS) will simultaneously develop the ancillary electronics and interfacing required to produce fully functional prototypes suitable for high x-ray energy experiments at the APS and CHESS.

>Read more on the CHESS website

Image: Sol M. Gruner, Physics, College of Arts and Sciences
Credit: Jesse Winter

 

Notes from the NSF INCLUDES Summit

Broadening the participation of underrepresented populations

For the past 20+ years, the National Science Foundation has been funding initiatives aimed at broadening the participation of underrepresented populations though the Broader Impact efforts supported by the various research divisions.

Millions of dollars and countless hours of work have done little to “move the needle” towards the desired outcome of achieving the full participation of diverse individuals in all facets of STEM. According to Dr. Alicia Knoedler who serves on NSF’s Committee on Equal Opportunities in Science and Engineering (CEOSE), states that the “cumulative, overall impact on underrepresented groups is minimal.”  To address this shortcoming, CEOSE released a list of recommendations to the NSF in their 2011-2012 report to implement a bold new initiative to fund broadening participation through institutional transformation and systems change using clear benchmarks of success, longitudinal data, and significant financial support. NSF Inclusion across the Nation of Communities of Learners of Underrepresented Discoverers in Engineering and Science (INCLUDES) is what emerged from this report, along with adoption of a framework to ensure shared accountability to promote participation and excellence.

>Read more on the CHESS website

Image caption: Visual display depicting one brain-storming session held by NSF INCLUDES participants during the Summit held January 8-10th, 2018.

CHESS-U accelerator work update

Production of CESR accelerator components for CHESS-U is well underway

The fabrication of magnets, vacuum systems, power conversion components, instrumentation, and other systems has been ramping up over the last 6 months. The first few components of each type were fabricated in house, but most are contracted to upstate NY businesses. The following is an illustrated series of snapshots of activities.

The single most massive (and expensive!) system is the array of precision magnets needed to bend and focus the stored electrons. Machining precision for some low-carbon iron surfaces is ±0.0005 inches. The coils must satisfy rigid mechanical and radiation resistance properties.

>Read more on the CHESS website

Image caption: Tested quadrupole coils ready for assembly.

SXRF shows anthers have a craving for copper

Research links micronutrient copper with pollen fertility and seed/grain yield

The global demand for high-yield crops is increasing with growing population and decreasing farmland resources. These trends force the utilization of marginal lands for agricultural purposes. The bioavailability of essential mineral nutrients such as copper in these soils is often low, causing the reduced crop growth and fertility, and consequently low grain yield or even total crop failure. Although copper is recognized as an essential micronutrient for plant fertility, scientists still do not completely know which reproductive structures of plants require copper, how copper is delivered there and how copper transport processes are regulated. These questions are currently being addressed in the Vatamaniuk lab using model plants Arabidopsis thaliana and Brachypodium distachyon as well as a crop species, wheat, Triticum aestivum.

In studies using A. thaliana, the Vatamaniuk research group identified a new protein, CITF1, whose transcript accumulates in A. thaliana flowers during periods of copper deficiency. CITF1 acts as a transcription regulator: it regulates copper uptake into the roots and its delivery to flowers, working in tandem with SPL7 that is the central regulator of copper homeostasis in this plant species. When SPL7 and CITF1 do not function, as in the citf1 spl7 double mutant, its seedlings die and its pollen becomes infertile. Working with CHESS scientist, Rong Huang, at F3 beamline, a member of the Vatamaniuk research group, Ju-Chen Chia has shown that the sites of pollen production, anthers of flowers, accumulate the majority of the absorbed copper in A. thaliana. Huang and Chia also showed that copper accumulation was somewhat lower in anthers and carpels of the citf1 mutant and was further reduced in anthers and carpels of the spl7 mutant compared to wild-type plants (Fig. 1). They also showed that the majority of anthers of the citf1 spl7 double mutant lacked copper and that this deficiency resulted in pollen infertility.

>Read more on the CHESS website

Serial microcrystallography at CHESS

What if large crystals are not available?

The standard X-ray protein crystallography experiment requires a single protein crystal specimen that is large enough to collect a “complete” data set, that is, to collect all the available diffraction peaks to a given resolution.

But what if large crystals are not available? A team of scientists at MacCHESS and the University of Toronto is pushing what is possible for small protein crystals at storage ring sources.

While structural biologists have expanded their purview to increasingly large and complex biological systems, the necessity for reliable, atomic resolution structural data for those systems has not changed. However, it is simply not possible to grow sufficiently large crystals for many systems. The necessity of large crystals in protein crystallography stems primarily from two factors. First, all other things being equal, microcrystals diffract more weakly than large ones, because the crystal volume, and thus number of protein molecules diffracting the X-rays, is lessened. Second, and more insidiously, protein microcrystals succumb more quickly to radiation damage – a loss of diffraction intensity resulting from X-ray induced, stochastic ionization and bond cleavage. These factors result in apparently contradictory solutions: increase the beam intensity to induce more diffraction, but at the expense of crystal lifetime; or lower the beam intensity, but collect weak data.

>Read more on the CHESS website

Image caption: The sample chip loaded and placed on the piezo stage.

Ruling out Weyl points in MoTe2

Sometimes the hunt for new kinds of fundamental particles takes place in the low-energy degrees of freedom of exotic quantum materials

Over the past decade, such strange entities as magnetic monopoles, Majorana fermions, and even Higgs modes have been predicted and identified inside materials at low temperatures.  The goal of learning to manipulate these new quanta for technological purposes is a grand challenge for science, predicted to spark a “second quantum revolution”.  Among the intriguing zoo of new particles which exploit the topological properties of electronic wavefunctions, the Weyl fermions (which are charged, massless, and chiral) were originally postulated in the 1920s but have never been observed in high-energy physics experiments.  However, compelling evidence for Weyl physics inside certain classes of semi-metals has accumulated over the past three years.  The material TaAs, for example, has been shown to host special electronic band crossings (“nodes”) where the quasiparticles act like Weyl fermions.  Subsequently, a second type of Weyl semimetal (called “type-II”) was theoretically predicted to exist in the material MoTe2.  Weyl semi-metals are predicted to host Fermi surface lines with non-trivial topological properties at the material surface. Initial support for the type-II Weyl picture of MoTe2 has been published in the form of ARPES experiments, but the full, bulk electronic structure was until recently unknown.

>Read more on the CHESS website

Synchrotron “X-ray Micromechanics” course now online

An online course for novice X-ray users with backgrounds in engineering

As part of the mission of InSitμ@CHESS, the ONR-funded center focused on developing new High Energy X-ray Diffraction (HEXD) users and methods, the staff has developed and made available an online course for novice X-ray users with backgrounds in engineering.

>Read more on the CHESS website

CHESS-U is taking shape

Over six days this past September, two new hutches were installed in the L0 experimental hall of Wilson Lab

CHESS unveils fresh new website

Parallel to the CHESS-U project performing necessary equipment upgrades here at Wilson Lab, the CHESS website was also in the shop for a makeover.

Although the desire to streamline was paramount along with a responsive display that works across multiple devices, we wanted to visually highlight our users and scientists in action at the lab and sprinkle their news articles across the site. We chose a CMS platform, Drupal 8, which in addition to those and many other engaging digital experience features, allows for accessible content entry. The results of the project were revealed last month.

>Read more on the CHESS website

Watching nanocrystals in action

The assembly of colloidal nanocrystal building blocks into ordered superlattices presents many scientifically interesting and technologically important research challenges to create programmable matter from “crystals-of-crystals”.

The formation of superlattices is a fascinating mesoscale phenomenon governed by the interplay of a range of thermodynamic and kinetic factors. Long-time collaborators Detlef Smilgies, CHESS, and Tobias Hanrath, Chemical and Biomolecular Engineering, have recently summarized the role of time-resolved X-ray scattering techniques in combination with in-situ sample environments to gain unique insights into the relevant processes. Their EPL Focus Article was recently published in a special issue on superlattice formation, edited by Marie-Paule Pileni [1].

A variety of factors influence the assembly. First of all there are the nanoparticles themselves: their size variation, their shape, and their ligand coverage influence which superlattice symmetries are formed. A spectacular example has been the self-assembly of lead sulfide and lead selenide nanocrystals: These spheroidal nanocrystals have well defined facets formed by (100) and (111) crystallographic planes of the inorganic cores which form cuboctrahedra. Initially these nanocrystals form the expected FCC superlattice, but as solvent further evaporates and particles move closer together, the lattice symmetry changes to body-centered tetragonal and finally to BCC [2,3]. This transition is accompanied by increasing orientational ordering of particles relative to each other. The reason for this peculiar behavior seems to lie in the ligand-ligand and solvent-ligand interactions as superlattices dry. Due to the facetting of the particles the ligand density around the particle is inhomogeneous; in particular at edges and corners there is sterically not enough space to anchor ligands at the same density as on the facets.  As particles move closer to each other this anisotropy becomes more pronounced and leads to orientational ordering and superlattice symmetry change.

>Read more on the CHESS website

Image Caption: The “periodic table” of nanocrystal superlattices. Nanocrystals can be made from most elements in the periodic table. In addition, their size, shape and dimensionality is controlled by the synthesis. Finally superlattices with different symmetries can be made by exploiting shape and dimensionality as well as processing parameters. 
Credit:Tobias Hanrath, Cornell

Lt. Gov. Hochul announces $15M from state for CHESS upgrade

The funding announcement was held before a gathering of approximately 75 media members, CHESS scientists and Cornell staff at Wilson Synchrotron Laboratory.

Also making brief remarks were President Martha E. Pollack, State Sen. Thomas O’Mara, R-58th District, Assemblywoman Barbara Lifton, D-125th, and Alex Deyhim M.S. ’93, MBA ’98, CEO of Advanced Design Consulting in Lansing, New York, who detailed some of the benefits his company has reaped as a result of the CHESS funding.

CHESS, which annually attracts more than 1,200 users from around the world to take advantage of its world-class X-ray beams, is using the funding for its “CHESS-U” upgrade initiative. The grant will provide CHESS with enhanced capabilities, making it a leading synchrotron source in the U.S. for high-energy, high-flux studies.

Located 40 feet below the Cornell campus, the nearly half-mile-long accelerator and storage ring is being upgraded to enhance X-ray capabilities generated by rotating positrons.

 

>Read more on the CHESS website

Image: Lt. Gov. Kathy Hochul speaks to a gathering of about 75 media and Cornell staff, announcing a $15 million grant to the Cornell High Energy Synchrotron Source (CHESS), through the Upstate Revitalization Initiative, Nov. 15 at Wilson Laboratory.

 

A gem of an activity

“Who wants to see if they are a Zombie?” asks Professor Carl Franck, causing all twelve Girl Scouts in the room to look up from their work and stare in bewilderment.  “Let’s go outside and see if you are really alive by using a TV satellite dish to measure your body heat!”  Still doubtful, a handful of girls get out of their seats and walk excitedly towards the door, following Professor Franck outside. The dish, which picks up microwave frequencies around 12GHz, will be used to measure the amount of thermal radiation being emitted from a girl standing in front of it against the cold sky. This amounts to a microwave thermometer test that allow the girls to see if their bodies radiate heat in the way that a Zombie’s cannot.  Happily, all the scouts who try pass this test and the program moves along without fear except that they now know that at least some of them are a source of microwave radiation.

>Read more on the CHESS website

Image: Betul Pamuk oversees two girl scouts soldering the taps to their coil.

 

Associate Director Matthew Miller promoted

He is promoted to the rank of fellow in the American Society of Mechanical Engineers (ASME)

CHESS congratulates Professor Matthew Miller, the associate director of CHESS and the director of InSitµ@CHESS, for a recent promotion to the rank of fellow in the American Society of Mechanical Engineers (ASME).

The rank of fellow is bestowed on members who “have been responsible for significant engineering achievements” and have been active members for at least ten years. Professor Miller’s work developing new X-ray techniques, primarily at CHESS, and his development of the In-Sitµ center were mentioned prominently in his award citation, highlighting their importance to the mechanical engineering community. “Professor Matthew P. Miller is an international leader in the development and engineering application of high energy x-rays to probe the micro-structure of materials under live loads. Prof. Miller founded and directs InSitµ@CHESS (Integrated Simulation and x-ray Interrogation Tools and Training for µmechanics at CHESS).