Expertise

Letian Wang

Machine Learning and Deep Learning

ML and DL for heat transfer design

Data source: FEM simulation
Model: logistic regression, Convolutional Neural Networks
Tool: Python, TensorFlow, Google Compute Engine
Results:
- High classification rate with both models
- Pattern recognition is best with CNN in terms of the reproducing best
- clustering effect in the rank plotting

Video+CNN for additive manufacturing

Data source: video data of nozzle during printing process, defects in the
Model: pre-trained CNN (ResNet-50) , supervised learning, classification
Tool: Python, TensorFlow, Google Compute Engine;
Implemented data augmentation accounting for the random vibration to improve the robustness of the predictor(98%)
Details upon request- for publication concern.

Machine learning for additive manufacturing

Data source: real-time temperature data+ laser coordinations
Model: SVM, Logistic regression
Tool: Python, TensorFlow, Google Compute Engine;
Results: Non-complete report

ml_for_slm_incomplete.pdf
File Size:	822 kb
File Type:	pdf

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Optics, Nanophotonics and Nanofabrication

Transient Reflective Probing

Nano fabrication

Laser sources: CW, nanosecond lasers
Optics: PBS, 1/4 wave, 1/2 wave, notch filter
Oscilloscope, photodetector, color camera
Motion control, NC programming.

Home-built Microscope

Microscale transmission and reflection probing with different light sources.

* Nanofabrication for Non-MOS wafer scale photonics metasurfaces and electrical test circuits:
-250nm node layout design (L-edit, Tanner)
-Photolithography(ASML 5500/300)
-RIE(Lam Research, STS)
-Deposition(Ebeam Evaporation, ALD, LPCVD, PECVD)
-Metrology(AFM, Ellipsometry, SEM, Nanospec, FIB)
-Epitaxial growth of Ge on Si (Applied Materials, Centura)
-CD reduction: double deposition and over-etch

*Tool development:
Upgrade the Laser-assisted chemical vapor deposition (LACVD) tool with
-additional high power nanosecond pulsed laser. Carried out damage threshold, beam alignment and focusing tests.
-additional vacuum chamber

*Research and Process Development:
-Laser-assisted atomic layer etching of amorphous silicon film and silicon wafers with Cl2 gases.