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Molybdenum Mo Notes


Molybdenum (Mo) General Information

Molybdenum is categorized as a transition metal on the Periodic Table. It is metallic grey in appearance with a melting point of 2,617°C, a density of 10.2 g/cc, and a vapor pressure of 10-4 Torr at 2,117°C. Due to its strength and high melting point, molybdenum is primarily alloyed with other metals to make corrosion resistant materials and can be found in tools, aircraft parts, and electrical contacts. Molybdenum is evaporated under vacuum to make advanced displays, semiconductors, and sensors.

Molybdenum Mo Specifications

Material TypeMolybdenum
SymbolMo
Atomic Weight95.96
Atomic Number42
Color/AppearanceGrey, Metallic
Thermal Conductivity139 W/m.K
Melting Point (°C)2,617
Coefficient of Thermal Expansion4.8 x 10-6/K
Theoretical Density (g/cc)10.2
SputterDC
Max Power Density
(Watts/Square Inch)
150*
Type of BondIndium, Elastomer
Z Ratio0.257
E-BeamExcellent
E-Beam Crucible Liner MaterialFABMATE®, Graphite
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  1,592
10-6:  1,822
10-4:  2,117
CommentsFilms smooth, hard. Careful degas required.

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

Z-Factors

Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

  • Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
  • Place a new substrate adjacent to the used quartz sensor.
  • Set QCM Density to the calibrated value; Tooling to 100%
  • Zero thickness
  • Deposit approximately 1000 to 5000 A of material on the substrate.
  • Use a profilometer or interferometer to measure the actual substrate film thickness.
  • Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.