Facilities & Laboratories
Non-Oxide Materials Synthesis Laboratory (NOMSL)
The Non-Oxide Materials Synthesis Laboratory (NOMSL) at the Pacific Northwest National Laboratory (PNNL) is located in the Applied Processing Engineering Laboratory (APEL) building. The NOMSL is designed to prepare and process various types of non-oxide materials. NOMSL assists projects such as Radiation Detection, and uses state-of-the-art equipment which include the following:
- LAB Master 130 M-Braun nitrogen glovebox (< 0.1 ppm of O2 and H2O) equipped with a Deltech®; high temperature furnace (T < 1200ºC)
- Oxygen-propane glass-blowing station for making custom shaped and sized quartz ampoules used as reaction vessels
- Quartz-lined Thermolyne F79400 tube furnace (T < 1200ºC) for annealing and baking out quartz ampoules
- VARIAN, Inc., vacuum system (V301 turbo pump and scroll pump) with ConFlat® flanges and copper gaskets to evacuate ampoules to high vacuum (P < 1.3×10-6 Pa); system is equipped to purge ampoules prior to sealing with ultra high purity (6N) Matheson ULSI semiconductor-grade argon with 2.6% H2 as an oxygen scavenger
- Deltech furnace on a custom-built rocking platform to facilitate agitation of non-oxide materials in sealed reaction vessels and Inconel® secondary containment vessel for holding ampoules during heat-treatment; the secondary containment vessel is designed to safely relieve pressure inside the hot zone of the furnace in the event of an ampoule rupture during heating
- Top-loading Deltech furnace for multi-scale materials processing applications (winner of 2008 R&D100 Award, Multi-Scale Processing)
Figure 1. (left) Multi-Scale Processing poster. (right) Arsenic sulfide microstructure variation by temperature.
- EDG12-Sunfire Mellen crystal growth gradient furnace
- Chalcogel processing capabilities which include Parr bombs and supercritical drying
- JEOL, Ltd 5900 scanning electron microscope
- Bruker D8 Advance X-Ray diffractometer
Materials made or prepared in the NOMSL since 2002 include:
- As-S, As-Se, As-Te, As-S-Se, As-Se-Te, As-S-AgI, Ge-S, Ge-S-l, and As-Se-l chalcogenide glasses for various applications, e.g., chemical sensing, iodine waste forms, semiconductor radiation detection.[1-11]
Figure 2. As-S-Se ternary plot showing the compositional location of chalcogenide glasses made at PNNL as of 2005.
Figure 3. Ge4S10 glass with 5 mol% iodine.
- CdGexAs2 amorphous and polycrystalline chalcopyrite materials, Cu(In0.7Ga0.3)0.95Se2 (or CIGS) polycrystalline chalcopyrite materials, and Cd3Ge2As4 in polycrystalline state.[12-13]
Figure 4. Rod of melted/casted CIGS material.
- CdCr2Se4 and CoCr2S4 polycrystalline materials (i.e., spinel).
- Pt-Ge-S and Mo-Ni,Co-S chalcogen-based aerogels, termed chalcogels.[14-15]
Figure 5. Gelation process of Ge-Pt-S chalcogel materials.
- Single crystal Ge and CdxZn1-xTe.[16]
Figure 6. Other related works outside of NOMSL but still in the Radiological Materials & Technology Development group include the investigation of heavy metal oxide (HMO) glasses for various uses.[17]
Radiation detection
In 2005–2008, staff in the Glass and Materials Science team worked on a project studying the radiation detection properties of amorphous semiconductors. In particular we looked at the chalcopyrite cadmium germanium arsenide (CdGexAs2, where x = 0.45, 0.65, 0.85, and 1) and the chalcogenide arsenic selenide telluride (As40Se48Te12). Both of these chemistries are non-oxide materials and therefore required special preparations to eliminate the presence of oxygen during heating. A process was developed in which they were vacuum sealed in fused quartz tubes and agitated during heating using a special rocking furnace.
Staff encountered difficulties when attempting to make bulk quantities of amorphous CdGexAs2 compounds at a high x value, so alternate processing methods were explored. Commonly, polycrystalline CdGeAs2 was observed throughout the bulk of the ingot where grain boundaries could be distinguished optically using cross-polarized light (see Figure 2-A and -B). Here, staff observed small crystallites along the perimeter, where the cooling rate was fastest, and larger sized crystallites towards the center of the ingot, where the cooling rate was the slowest. Once such alternate processing method involved use of a secondary ampoule that contained the inner ampoule as well as a high thermal conductivity powder (e.g., Cu, Ag, SiC) filling the void between the ampoules (see Figure 7). This method was referred to as a double containment (DC) ampoule method.
The DC method, when implemented to CdGexAs2 chemistries with x < 1, produced bulk amorphous, 4-cm long cylindrical ingots with 1 cm diameter. However, when the DC method was applied to CdGeAs2, something new was observed. Staff discovered a 3-phase solid that contained an amorphous phase, polycrystalline CdGeAs2, and a new, previously unseen phase (see Figure 8-C and -D). The new phase could not be identified by X-ray diffraction (XRD) comparison of the crystallography databases suggesting that no one had observed this phase before. Upon further analysis with scanning (SEM) and transmission electron microscopy (TEM) along with energy dispersive spectroscopy (EDS), the composition of the new phase was determined to be Cd3Ge2As4.
The staff involved with the development of the DC method and creation of this new phase are currently writing a paper to summarize the work. Most of the properties of this compound remain unknown though work is currently underway to determine the crystal structure of the compound. Future work with the DC method could potentially result in the discovery of additional new crystalline phases made with elemental substitutions in the crystal structure, e.g., Cd3Si2As4, Zn3Ge2As4.
Figure 7. Schematic of the DC method process. (A) Stoichiometric quantities of constituents batched into a 10 × 12 mm (ID × OD) fused quartz ampoule, evacuated, and sealed. (B) Inner ampoule is loaded into a larger, 19 × 22 mm, ampoule and copper powder is added to the void between the two ampoules, the outer ampoule is evacuated and sealed (prior to heat treatment). (C) After heat treatment. (D) Inner ampoule with sintered copper jacket removed from outer ampoule. (E) Ingot removed from inner ampoule.
Figure 8. Microstructure observed in CdGeAs2 samples. (A) and (B) were processed using a single ampoule containment method. (C) and (D) were processed using the DC ampoule method. (A) and (C) are low magnification micrographs showing the full diameter (1 cm) of the ingot and (B) and (D) are higher magnification micrographs showing the microstructures. The geometric multi-colored crystallites are polycrystalline CdGeAs2, the solid-colored regions are amorphous materials, and the rod-shaped objects in (B) and (D) are the Cd3Ge2As4 phase. False color is created using a polarizing optical microscope.