A Novel Graphene Quantum Dot-Based mRNA Delivery Platform

During the last decades, there has been growing interest in using therapeutic messager RNA (mRNA) together with drug delivery systems. Naked, unformulated mRNA is, however, unable to cross the cell membrane and is susceptible to degradation. Here we use graphene quantum dots (GQDs) functionalized with polyethyleneimine (PEI) as a novel mRNA delivery system. Our results show that these modified GQDs can be used to deliver intact and functional mRNA to Huh-7 hepatocarcinoma cells at low doses and, that the GQDs are not toxic, although cellular toxicity is a problem for these first-generation modified particles. Functionalized GQDs represent a potentially interesting delivery system that is easy to manufacture, stable and effective

Multiple growth of graphene from a pre-dissolved carbon source

Mono- to few-layer graphene materials are successfully synthesized multiple times using Cu-Ni alloy as a catalyst after a single-chemical vapor deposition (CVD) process. The multiple synthesis is realized by extracting carbon source pre-dissolved in the catalyst substrate. Firstly, graphene is grown by the CVD method on Cu-Ni catalyst substrates. Secondly, the same Cu-Nicatalyst foils are annealed, in absence of any external carbon precursor, to grow graphene using the carbon atoms pre-dissolved in the catalyst during the CVD process. This annealing process is repeated to synthesize graphene successfully until carbon is exhausted in the Cu-Ni foils. After the CVD growth and each annealing growth process, the as-grown graphene is removed using a bubbling transfer method. A wide range of characterizations are performed to examine the quality of the obtained graphene material and to monitor the carbon concentration in the catalyst substrates. Results show that graphene from each annealing growth process possesses a similar quality, which confirmed the good reproducibility of the method. This technique brings great freedom to graphene growth and applications, and it could be also used for other 2D material synthesis

High porosity and light weight graphene foam heat sink and phase change material container for thermal management

During the last decade, graphene foam emerged as a promising high porosity 3-dimensional (3D) structure for various applications. More specifically, it has attracted significant interest as a solution for thermal management in electronics. In this study, we investigate the possibility to use such porous materials as a heat sink and a container for a phase change material (PCM). Graphene foam (GF) was produced using chemical vapor deposition (CVD) process and attached to a thermal test chip using sintered silver nanoparticles (Ag NPs). The thermal conductivity of the graphene foam reached 1.3 W m(-1)K(-1), while the addition of Ag as a graphene foam silver composite (GF/Ag) enhanced further its effective thermal conductivity by 54%. Comparatively to nickel foam, GF and GF/Ag showed lower junction temperatures thanks to higher effective thermal conductivity and a better contact. A finite element model was developed to simulate the fluid flow through the foam structure model and showed a positive and a non-negligible contributions of the secondary microchannel within the graphene foam. A ratio of 15 times was found between the convective heat flux within the primary and secondary microchannel. Our paper successfully demonstrates the possibility of using such 3D porous material as a PCM container and heat sink and highlight the advantage of using the carbon-based high porosity material to take advantage of its additional secondary porosity

An Electron Microscopy Study on Materials in Electronic Packaging

This thesis is concerned with an investigation of the microstructure on materials in electronic packaging. The materials include Ag-filled conductive adhesives, Sn-Ag-based lead free solders and metal-oxide semiconductors. In order to characterize the microstructure, several transmission electron microscopy techniques were applied: imaging, selected area electron diffraction, energy dispersive x-ray spectroscopy, convergent beam electron diffraction and high-resolution electron microscopy. Some other techniques were also utilized to assist the analysis, scanning electron microscopy, secondary ion mass spectrometry and x-ray diffraction. The direct observation of the distribution of micro-sized, nano-sized, micro/nano-sized mixed Ag-particles and Ag flakes in epoxy resin was carried out by TEM. The perfect continuous linkage of particles is hard to find and the chance of contact and subsequent contact area becomes less with increasing amount of nano-sized particles. So the conductivity in micro-sized particle fillers is dominated by the constriction resistance, while with increasing content of nano-sized fillers, the conductivity is controlled by thermionic emission. The microstructure of Ag3Sn and Sn becomes finer and more uniform in Sn-3.5Ag-0.5Cu-0.5B solder. It is suggested that the dispersed boron particles provide heterogeneous nucleation sites on the Ag3Sn particle and Sn matrix during solidification. The Cu6Sn5 phase keeps its high-temperature crystal structure after soldering. Two types of modulation structures were observed by electron diffraction patterns after the samples were heat treated at 100oC for 1000h. Both of the modulation structures are caused by the ordering of extra Cu atoms in trigonal bipyramidal sites in a NiAs-type hexagonal structure. Two crystal structure models were constructed for the three-time modulation structure, and according to the arrangement of extra Cu atoms, the composition for this modulation structure is Cu7Sn6. Besides the modulation structure in Cu7Sn6, satellites and diffuse scattering co-exist in the diffraction patterns. They correspond to short-range order of Cu atoms. The thermal cycling tests on solder joints show that the lead-free solder has lower microstructural coarsening effect compared with tin-lead solders. However, the dissolution of Pb from component leads decreased the melting temperature and caused obvious grain growth in Pb-containing phases. Two phases, (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5, were found at the interface between Sn-3.5Ag-0.5Cu and Au/Ni/Cu metallized substrates. The content of Cu in the (Ni,Cu)3Sn4 phase is as high as 21 at.%, but the crystal structure is still the same as that of Ni3Sn4. A P-rich area was found in the Ni layer due to the electroless plating, and two metastable phases were formed after heat treatment. The Si/SiO2/PolySi1-xGex interface was characterized by high-resolution electron microscopy, and the strain fields at the SiO2/Si interface were revealed by large angle convergent beam electron diffraction and two-dimensional reciprocal space mapping

Mechanical characterization ofnanoparticleenhancedSn-3.0Ag-0.5Cu solder

Solder plays an important role as interconnect in the electronics assembly, which provide the necessary electrical, mechanical and thermal continuity. In recent years, miniaturization of the portable products demands better solder-joint performance and conventional solder technology can not guarantee device reliability. The particle reinforced solder alloy is considered as the potentially available method to enhance the solder joints. The particle size should be small enough to hinder the grain boundary sliding and suppress the growth of intermetallic compound. Nanocomposite solders are regarded as one of the most promising interconnect materials for the high density electronic packaging due to their high mechanical strength and fine microstructure. However, the developments of nanocomposite solders have been limited by the inadequate compatibility between nanoparticles and solder matrix with respect to density, hardness, coefficient of thermal expansion, and surface activity. In order to solve this problem, carbon nanotube (CNT) was selected as reinforcement materials in Sn-3.0Ag-0.5Cu solder in this work. The effect of the nanoparticle on void content of solder bump was studied. The microstructure and shear strength of nanosocomposite solders were also investigated