How pluralistic is the research field on adult education? Dominating bibliometrical trends, 2005-2012

What the field of adult education research is and how it can be described has been a debated issue over the decades. Several scholars argue that the field today is heterogeneous, borrowing theories and methods from a range of disciplines. In this article, we take such statements as a starting point for empirical analysis. In what ways could it be argued that the field is pluralistic rather than monolithic; heterogeneous rather than homogenous? Drawing on bibliographic data of the top cited articles in three main adult education journals between 2005 and 2012, we illustrate how the citation patterns have tendencies of homogeneity when it comes to the geographical country of authorship, since the USA, UK, Australia and Canada dominate, as well as the research methods adopted, since qualitative approaches have near total dominance. Furthermore, there is a tendency to adopt similar theoretical approaches, since sociocultural perspectives, critical pedagogy and post-structuralism represent more than half of the articles in our sample. At the same time, the results of our analysis indicate signs of scholarly pluralism, for instance, in terms of authorship, since both early career researchers and established researchers are represented among the top cited publications. We conclude the article by arguing that empirical analysis of publication and citation patterns is important to further the development of reflexivity within the field, not least for early career researchers, who might benefit from knowledge about what has been recognized among peers as worth citing in recent times. (DIPF/Orig.

Fundamental Characterization of Low Dimensional Carbon Nanomaterials for 3D Electronics Packaging

Transistor miniaturization has over the last half century paved the way for higher value electronics every year along an exponential pace known as \u27Moore\u27s law\u27. Now, as the industry is reaching transistor features that no longer makes economic sense, this way of developing integrated circuits (ICs) is coming to its definitive end. As a solution to this problem, the industry is moving toward higher hanging fruits that can enable larger sets of functionalities and ensuring a sustained performance increase to continue delivering more cost-effective ICs every product cycle. These design strategies beyond Moore\u27s law put emphasis on 3D stacking and heterogeneous integration, which if implemented correctly, will deliver a continued development of ICs for a foreseeable future. However, this way of building semiconductor systems does bring new issues to the table as this generation of devices will place additional demands on materials to be successful. The international roadmap of devices and systems (IRDS) highlights the need for improved materials to remove bottlenecks in contemporary as well as future systems in terms of thermal dissipation and interconnect performance. For this very purpose, low dimensional carbon nanomaterials such as graphene and carbon nanotubes (CNTs) are suggested as potential candidates due to their superior thermal, electrical and mechanical properties. Therefore, a successful implementation of these materials will ensure a continued performance to cost development of IC devices.This thesis presents a research study on some fundamental materials growth and reliability aspects of low dimensional carbon based thermal interface materials (TIMs) and interconnects for electronics packaging applications. Novel TIMs and interconnects based on CNT arrays and graphene are fabricated and investigated for their thermal resistance contributions as well electrical performance. The materials are studied and optimized with the support of chemical and structural characterization. Furthermore, a reliability study was performed which found delamination issues in CNT array TIMs due to high strains from thermal expansion mismatches. This study concludes that CNT length is an important factor when designing CNT based systems and the results show that by further interface engineering, reliability can be substantially improved with maintained thermal dissipation and electrical performance. Additionally, a heat treatment study was made that enables improvement of the bulk crystallinity of the materials which will enable even better performance in future applications

Fabrication and Characterisation of Carbon Nanotube Array Thermal Interface Materials

The performance of electronic devices has long been limited by thermal dissipation which will result in device failure if not handled properly. The next generation of integrated circuit (IC) devices will feature new packaging technologies like heterogeneous integration as well as 3D stacking which entails additional emphasis on the thermal management solutions employed. Therefore, new materials are in demand to meet the increased thermal dissipation requirements to allow continued scaling in terms of cost per performance and increased device reliability.The largest bottleneck in thermal dissipation originates from thermal interfaces between different surfaces. For this purpose thermal interface materials (TIMs) are used to conform and bridge the interface and thereby alleviate the thermal dissipation restrictions in the interface. However, commercially available TIMs are either of metallic or polymeric nature which implies a compromise between thermal performance and reliability. Carbon nanotube (CNT) arrays have been suggested as a future potential material in order to achieve a TIM with superior thermal and mechanical properties that would ensure simultaneous high thermal performance and reliability. However, proper bonding solutions are still to be developed in order to apply CNT array TIMs in thermal dissipation applications and to ensure a successful market realisation.\ua0This thesis first outlines the field by presenting a thorough literature review of organic functionalization methods for CNT array TIMs. Three different approaches are identified: polymer embedding, polymer bonding and self-assembly based functionalization. The thesis then presents two experimental studies on CNT array TIMs. The first focuses on the development and characterisation of a CNT array TIM using a novel self-assembly based bonding method by employing epoxy chemistry for covalent anchoring. The second part focuses on a reliability study of a CNT array TIM assembled using a polymer bonding method, which is an aspect that previously has been overlooked. The results from the reliability study gave indications that themechanical bonding between the CNT array and the growth substrate was susceptible for rapid degradation and further research is required in this field to address this challenge

Degradation of Carbon Nanotube Array Thermal Interface Materials through Thermal Aging: Effects of Bonding, Array Height, and Catalyst Oxidation

Carbon nanotube (CNT) array thermal interface materials (TIMs) are promising candidates for high-performance applications in terms of thermal performance. However, in order to be useful in commercial applications, the reliability of the interfaces is an equally important parameter, which so far has not been thoroughly investigated. In this study, the reliability of CNT array TIMs is investigated through accelerated aging. The roles of CNT array height and substrate configuration are studied for their relative impact on thermal resistance degradation. After aging, the CNT catalyst is analyzed using X-ray photoelectron spectroscopy to evaluate chemical changes. The CNT-catalyst bond appears to degrade during aging but not to the extent that the TIM performance is compromised. On the other hand, coefficient of thermal expansion mismatch between surfaces creates strain that needs to be absorbed, which requires CNT arrays with sufficient height. Transfer and bonding of both CNT roots and tips also create more reliable interfaces. Crucially, we find that the CNT array height of most previously reported CNT array TIMs is not enough to prevent significant reliability problems

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

Characterization of process-related interfacial dielectric loss in aluminum-on-silicon by resonator microwave measurements, materials analysis, and imaging

We systematically investigate the influence of the fabrication process on dielectric loss in aluminum-on-silicon superconducting coplanar waveguide resonators with internal quality factors ($Q_i$) of about one million at the single-photon level. These devices are essential components in superconducting quantum processors; they also serve as proxies for understanding the energy loss of superconducting qubits. By systematically varying several fabrication steps, we identify the relative importance of reducing loss at the substrate-metal and the substrate-air interfaces. We find that it is essential to clean the silicon substrate in hydrogen fluoride (HF) prior to aluminum deposition. A post-fabrication removal of the oxides on the surface of the silicon substrate and the aluminum film by immersion in HF further improves the $Q_i$. We observe a small, but noticeable, adverse effect on the loss by omitting either standard cleaning (SC1), pre-deposition heating of the substrate to 300$\deg$C, or in-situ post-deposition oxidation of the film's top surface. We find no improvement due to excessive pumping meant to reach a background pressure below $6{\times} 10^{-8}$ mbar. We correlate the measured loss with microscopic properties of the substrate-metal interface through characterization with X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM).Comment: 22 pages, 11 figure

Signal crosstalk in a flip-chip quantum processor

Quantum processors require a signal-delivery architecture with high addressability (low crosstalk) to ensure high performance already at the scale of dozens of qubits. Signal crosstalk causes inadvertent driving of quantum gates, which will adversely affect quantum-gate fidelities in scaled-up devices. Here, we demonstrate packaged flip-chip superconducting quantum processors with signal-crosstalk performance competitive with those reported in other platforms. For capacitively coupled qubit-drive lines, we find on-resonant crosstalk better than -27 dB (average -37 dB). For inductively coupled magnetic-flux-drive lines, we find less than 0.13 % direct-current flux crosstalk (average 0.05 %). These observed crosstalk levels are adequately small and indicate a decreasing trend with increasing distance, which is promising for further scaling up to larger numbers of qubits. We discuss the implication of our results for the design of a low-crosstalk, on-chip signal delivery architecture, including the influence of a shielding tunnel structure, potential sources of crosstalk, and estimation of crosstalk-induced qubit-gate error in scaled-up quantum processors.Comment: 16 pages, 12 figures, includes appendice

Reliability investigation of a carbon nanotube array thermal interface material

As feature density increases within microelectronics, so does the dissipated power density, which puts an increased demand on thermal management. Thermal interface materials (TIMs) are used at the interface between contacting surfaces to reduce the thermal resistance, and is a critical component within many electronics systems. Arrays of carbon nanotubes (CNTs) have gained significant interest for application as TIMs, due to the high thermal conductivity, no internal thermal contact resistances and an excellent conformability. While studies show excellent thermal performance, there has to date been no investigation into the reliability of CNT array TIMs. In this study, CNT array TIMs bonded with polymer to close a Si-Cu interface were subjected to thermal cycling. Thermal interface resistance measurements showed a large degradation of the thermal performance of the interface within the first 100 cycles. More detailed thermal investigation of the interface components showed that the connection between CNTs and catalyst substrate degrades during thermal cycling even in the absence of thermal expansion mismatch, and the nature of this degradation was further analyzed using X-ray photoelectron spectroscopy. This study indicates that the reliability will be an important consideration for further development and commercialization of CNT array TIMs