Manufacturing Bits: Jan. 27

Calibration systems go portable
The National Institute of Standards and Technology (NIST) is selling a new portable, vacuum-based calibration unit for use in instruments and other systems.

The system, dubbed the Portable Vacuum Standard (PVS), is a compact unit that enables precise calibrations and measurements at a customer’s facility. Housed in the white “igloo” enclosure, the system eliminates the need for the expensive and time-consuming process of transporting instruments to NIST for calibration. It can replace the traditional mercury manometer for these applications. The PVS package does not contain mercury, which is a safety issue.

The PVS is housed within the white “igloo” enclosure at left. At right is an auxiliary vacuum system used for pressure calibrations. (Source: NIST)

The PVS is calibrated against NIST’s existing standards. The latest version of the standard, which has been under development for more than a decade, enables pressure measurements from 1 Pa to 130,000 Pa. (Air pressure at sea level is about 101,325 Pa.) It is possible to extend the instrument’s range to 370,000 Pa, according to NIST.

The PVS combines two different kinds of low-pressure sensors, which are enclosed in an insulated container. The first is a resonance silicon gauge (RSG). This monitors two capacitance diaphragm gauges (CDGs).

RSGs are MEMS-based devices that measure the effect of pressure-induced strain on the resonant frequency of a silicon oscillator. CDGs measure pressure-induced changes in the position of an alloy diaphragm that serves as one plate of a capacitor. They are workhorse sensors for most high-precision vacuum operations.

On its Web site, NIST project scientist Jay Hendricks said: “CDGs have extremely fine resolution at low pressure. RSGs have outstanding long-term drift stability—in the range of 0.01%, which is a factor of 10 better than the CDGs. So to get the best of both, we use an RSG to calibrate the CDGs.”

Measuring molecules
Using scanning tunneling microscopy (STM), Aalto University and the University of Zurich have imaged how electrons interact within a single molecule.

Researchers demonstrated the ability to measure and image cobalt phthalocyanine (CoPC), an organic molecule. CoPC is a molecule used in organic optoelectronic devices. This could include organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and solar cells.

The experiments were performed on cobalt phthalocyanine (CoPC) molecules deposited on a one-atom thick layer of hexagonal boron nitride on an iridium surface. (Source: Aalto University)

To conduct the experiment, researchers used an STM. The STM makes use of a tiny current between a sharp probe tip and a conducting sample. It measures the properties of the sample surface at atomic resolutions.

Researchers used the STM to measure the current passing through a single molecule on a surface. They also injected or removed electrons at different energies. “We saw several additional features in the recorded current where there should have been none according to the usual interpretation of these so-called tunneling spectra,” said Fabian Schulz, a post-graduate researcher, on Aalto University’s Web site.

“Here, we show that the simple single-particle picture fails qualitatively to account for the resonances in the tunneling spectra of different charge states of cobalt phthalocyanine molecules,” according to a paper from researchers. “Instead, these resonances can be understood as a series of many-body excitations of the different ground states of the molecule. Our theoretical approach opens an accessible route beyond the single-particle picture in quantifying many-body states in molecules.”

Mapping atoms
Also using STM technology, the University of Basel and the Paul Scherrer Institute have mapped the condensation of individual atoms. This could lead to clues in the nature of atomic bonding.

Condensation processes play a key role in chemistry and physics. In the lab, researchers monitored how xenon atoms condensate in microscopic measuring beakers, or quantum wells.

Using this process, researchers were able to study xenons in an atom-by-atom process with the STM. This, in turn, provided a clue how the atoms formed in atomically-defined quantum boxes.

In one case, “some units consisting of four atoms are only formed when there are at least seven atoms in the quantum well. And if there are twelve atoms in the quantum well, this results in the creation of three highly stable four-atom units,” according to researchers.

“But this system is not restricted exclusively to noble gases,” said researcher Sylwia Nowakowska, on the University of Basel’s Web site. “We can also use it to research other atoms and the way that they bond.”