Thermal analysis of the operation of microscale inorganic light emitting diodes

An analytical model is developed to study the thermal properties of microscale inorganic light emitting diodes (μ-ILEDs) with ultra-thin geometries and layouts. The predicted surface and μ-ILED temperatures agree well with experiments and finite element simulations. A simple scaling law is obtained for the normalized μ-ILED temperature versus the normalized μ-ILED size. This study provides theory to guide the design of layouts that minimize adverse thermal effects not only on the performance of μ-ILEDs for solid state lighting, but also for applications integrating μ-ILED devices on complex/soft substrate as are currently of interest in optogenetics and other emerging areas in biology

Thermo-mechanical modeling of scanning Joule expansion microscopy imaging of single-walled carbon nanotube devices

An analytical model, validated by experiments and finite element simulations, is developed to study the thermal -imaging of single-walled carbon nanotube (SWNT) devices by scanning Joule expansion microscopy (SJEM). A simple scaling law for thermal expansion at low frequencies, which only depends on two nondimensional -geometric parameters, is established. Such a scaling law provides a simple way to determine the surface temperature distribution and power dissipation per unit length in SWNT from the measured thermal expansion in experiments. The results suggest the spatial resolution of SJEM measurement is as good as ~50 nm

A cohesive law for interfaces in graphene/hexagonal boron nitride heterostructure

Graphene/hexagonal boron nitride (h-BN) heterostructure has showed great potential to improve the performance of graphene device. We have established the cohesive law for interfaces between graphene and monolayer or multi-layer h-BN based on the van der Waals force. The cohesive energy and cohesive strength are given in terms of area density of atoms on corresponding layers, number of layers, and parameters in the van der Waals force. It is found that the cohesive law in the graphene/multi-layer h-BN is dominated by the three h-BN layers which are closest to the graphene. The approximate solution is also obtained to simplify the expression of cohesive law. These results are very useful to study the deformation of graphene/h-BN heterostructure, which may have significant impacts on the performance and reliability of the graphene devices especially in the areas of emerging applications such as stretchable electronics

Mechanics of Boron Nitride Nanotubes: A Continuum Theory Based on the Interatomic Potential

64 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.A hybrid atomistic/continuum model based on the interatomic potential for boron nitride is also developed to study the Stone-Wales transformation (90° rotation of an atomic bond) in boron nitride nanotubes under tension. It is found that the critical strains for Stone-Wales transformation for BNNTs agree well with the atomistic simulations.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Mechanics of Boron Nitride Nanotubes: A Continuum Theory Based on the Interatomic Potential

64 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.A hybrid atomistic/continuum model based on the interatomic potential for boron nitride is also developed to study the Stone-Wales transformation (90° rotation of an atomic bond) in boron nitride nanotubes under tension. It is found that the critical strains for Stone-Wales transformation for BNNTs agree well with the atomistic simulations.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Buckling of thin gel strip under swelling

The buckling of thin gel film has attracted much attention due to its applications in the design of three-dimensional structure from two-dimensional template. We have established an analytical model to study the swelling-induced buckling of a thin gel strip with one edge clamped and the others free. The closed-form solutions for the amplitude and wavelength of the buckled shape are obtained by energy minimization of the total potential energy. The analytical results agree well with finite element analysis based on the inhomogeneous gel theory without any parameter fitting. The model provides a route to study complex postbuckling behaviors of thin gel films and guidelines to design the buckled configuration quantitatively by controlling the swelling ratio