4 ms·

The Superpowers of Super-Thin Materials

54 points by prostoalex 6y ago

kurthr 6y ago
Not directly relevant to the article, but it's worth mentioning that these 2D (and crystalline) effects don't necessarily even require monoatomic layers. In the early days of MEMS (when it was called micromachining) one of the first big development efforts was the TI Micromirrors (DLP) for large projectors, which used fairly standard semiconductor materials to actuate torsional mirrors to steer light. By applying electrostatic forces to a large array of mirror pixels with reasonable voltages to reflect a beam +/-20 deg at high frequency TI was able to do PWM of their light source over the array (and color with a wheel). However, they chose Aluminum as their structural material. Any mechanical engineer is now having a heart attack, because modulating an Al hinge through % strain at MHz frequencies is a recipe for cracking and failure... BUT IT DIDN'T! The EEs who originally chose the process and structures got lucky... very lucky. Some of this comes down to decent design and selection of materials, but fundamentally at table top size such a design would fail in 100s or 1000s of cycles. Why didn't it fail? Eventually (after production and sales) it was determined that due to the very thin and narrow supporting flexures (to keep forces and costs low) the crystal grain size was typically significantly larger than the hinge. As a result there were not defect sites for dislocations to create cracks or hardening... effectively they were single crystal Al hinges in the area of high cyclic strain... most of the time except for the odd occasional pixel... but proper etching and annealing improved even that through process control. Why change what isn't broken?
- tape_measure 6y ago
  The New Science of Strong Materials, or Why You Don't Fall Through the Floor by J.E. Gordon is a great casual introduction to material science that touches on this relation between size and fatigue life. However, it was written in 1968 before these semiconductors were developed. Do you have any recommendations for further reading on the design or history of MEMS?
  - NortySpock 6y ago
    Structures: Or Why Things Don't Fall Down, also by J.E. Gordon, is the macroscopic plain-English version. Highly recommend it. I once described it as "Civil Engineering for Dummies", and the chemical engineer across the table from me said "Isn't that a redundant statement?" (she's married to a civil engineer, so perhaps that colored her experience.)
    - tape_measure 6y ago
      Structures is great. I picked it up after receiving The New Science... as a gift. It's propping up my monitor at my WFH desk now, so it literally is why things don't fall down.
- agumonkey 6y ago
  Did they find any new properties of Al or other alloys after the DLP production ?
  - kurthr 6y ago
    To my knowledge, no... but I didn’t work at TI, only with the grad student who did the analysis. The effect isn’t unexplained, just mostly accidental and likely due to other constraints. It’s possible that after the effect was known that particular process changes were made to ensure/enhance it, but again I have no knowledge of it.
    - agumonkey 6y ago
      aight, no worries, and thanks for the anecdote
ashton314 6y ago
I'm not very familiar with this field - sounds really exciting! I do have to wonder: what are some of the potential effects on humans in this ever-thickening "soup" of radio waves?
- chorsestudios 6y ago
  Non-ionizing electromagnetic waves don't have enough energy to remove electrons from molecules or DNA. So as long as the "soup" consists of waves with longer wavelength than visible light we should be fine.
  - ben_w 6y ago
    Although the first sentence is true, the second doesn’t follow perfectly from it. Microwave ovens are much longer wavelengths than visible light, and some biological processes are sensitive to a few degrees of temperature change. I have close to zero reason to believe that current environmental EM exposure is even close to strong enough to be relevant (Mythbusters or a similar show tried to use a hundred cellphones at the same time to cook food, and demonstrated that no it doesn’t), but this sort of thing could reasonably prevent microwave beamed power from seeing widespread use.
typeformer 6y ago
Wait till we see the alien stuff...

54 points by prostoalex 6y ago

Not directly relevant to the article, but it's worth mentioning that these 2D (and crystalline) effects don't necessarily even require monoatomic layers. In the early days of MEMS (when it was called micromachining) one of the first big development efforts was the TI Micromirrors (DLP) for large projectors, which used fairly standard semiconductor materials to actuate torsional mirrors to steer light. By applying electrostatic forces to a large array of mirror pixels with reasonable voltages to reflect a beam +/-20 deg at high frequency TI was able to do PWM of their light source over the array (and color with a wheel). However, they chose Aluminum as their structural material. Any mechanical engineer is now having a heart attack, because modulating an Al hinge through % strain at MHz frequencies is a recipe for cracking and failure... BUT IT DIDN'T! The EEs who originally chose the process and structures got lucky... very lucky. Some of this comes down to decent design and selection of materials, but fundamentally at table top size such a design would fail in 100s or 1000s of cycles. Why didn't it fail? Eventually (after production and sales) it was determined that due to the very thin and narrow supporting flexures (to keep forces and costs low) the crystal grain size was typically significantly larger than the hinge. As a result there were not defect sites for dislocations to create cracks or hardening... effectively they were single crystal Al hinges in the area of high cyclic strain... most of the time except for the odd occasional pixel... but proper etching and annealing improved even that through process control. Why change what isn't broken?

tape_measure 6y ago
The New Science of Strong Materials, or Why You Don't Fall Through the Floor by J.E. Gordon is a great casual introduction to material science that touches on this relation between size and fatigue life. However, it was written in 1968 before these semiconductors were developed. Do you have any recommendations for further reading on the design or history of MEMS?
- NortySpock 6y ago
  Structures: Or Why Things Don't Fall Down, also by J.E. Gordon, is the macroscopic plain-English version. Highly recommend it. I once described it as "Civil Engineering for Dummies", and the chemical engineer across the table from me said "Isn't that a redundant statement?" (she's married to a civil engineer, so perhaps that colored her experience.)
  - tape_measure 6y ago
    Structures is great. I picked it up after receiving The New Science... as a gift. It's propping up my monitor at my WFH desk now, so it literally is why things don't fall down.
agumonkey 6y ago
Did they find any new properties of Al or other alloys after the DLP production ?
- kurthr 6y ago
  To my knowledge, no... but I didn’t work at TI, only with the grad student who did the analysis. The effect isn’t unexplained, just mostly accidental and likely due to other constraints. It’s possible that after the effect was known that particular process changes were made to ensure/enhance it, but again I have no knowledge of it.
  - agumonkey 6y ago
    aight, no worries, and thanks for the anecdote

ashton314 6y ago

I'm not very familiar with this field - sounds really exciting! I do have to wonder: what are some of the potential effects on humans in this ever-thickening "soup" of radio waves?

chorsestudios 6y ago
Non-ionizing electromagnetic waves don't have enough energy to remove electrons from molecules or DNA. So as long as the "soup" consists of waves with longer wavelength than visible light we should be fine.
- ben_w 6y ago
  Although the first sentence is true, the second doesn’t follow perfectly from it. Microwave ovens are much longer wavelengths than visible light, and some biological processes are sensitive to a few degrees of temperature change. I have close to zero reason to believe that current environmental EM exposure is even close to strong enough to be relevant (Mythbusters or a similar show tried to use a hundred cellphones at the same time to cook food, and demonstrated that no it doesn’t), but this sort of thing could reasonably prevent microwave beamed power from seeing widespread use.

typeformer 6y ago

Wait till we see the alien stuff...