Nanoscale & Nanoscale Advances Blog

Recently, the 50th anniversary of Moore’s law has been celebrated by the semiconductor industry. Although the current ITRS (International Technology Roadmap for Semiconductors) continues to propose “traditional” transistor materials such as Si and GaAs, attractive, two-dimensional alternatives have become visible on the horizon.

Schwierz et al. have recently published a Feature article in Nanoscale compiling the current knowledge on 2D materials. Their article focuses on the application of these as the channel material in field effect transistors.

According to the authors, two large trends can currently be observed: More Moore and More than Moore. The former utilizes well known semiconductors and improves performance by sophisticated manufacturing and scaling techniques. In contrast, the latter one employs compound semiconductors and novel alloys as 2D materials with a wide range of new properties.

Two-dimensional materials and their prospects in transistor electronics

The main material classes researched to date are explained further, covering X-anes, Fluoro-X-enes, TMDs (transition metal–chalcogen combinations), SMCs (semimetal–chalcogen combinations), MX-enes and (currently theoretical) group IV-IV and III-V 2D materials.

To assess the viability of the materials for applications within electronic circuits, Schwierz et al. also describe a wish list of ideal properties of next generation channel materials: bandgap, carrier mobility, heat conductivity, contact resistance and scale length. Based on experiences from established semiconductors, they also derive practical values needed for high performance FET.

The final part of the review examines the current status of the material classes. Notable performance records of well researched materials (e.g. 100 GHz graphene FET) as well as first demonstrators (e.g. first X-ane based FET) are given here. Finally, some arguments for a revival of silicon as a promising material for future applications are also given.

Two-dimensional materials and their prospects in transistor electronics
F. Schwierz, J. Pezoldt and R. Granzner
Nanoscale, 2015, 7, 8261-8283. DOI: 10.1039/C5NR01052G

Sebastian Axmann is a guest web-writer for the Nanoscale blog. His interests comprise manufacturing and metrology of nanostructures as well as their usage in current semiconductor devices. He also posts links to interesting research articles on Twitter: @SebastianAxmann.

As cancer treatments evolve, focus has shifted to techniques and tools, which provide tumor-targeting capabilities and are uncoupled from common detrimental side effects.  The efficient delivery of new therapeutics has been a common area of interest, with studies focused on nanoparticle delivery systems being an eminent research area.

(a) TEM image of PS/Fe3O4 microspheres showing the amorphous coating entrapping multiple Fe3O4 nuclei. (b) TEM image of PAA/Fe3O4 and (c) cumulant size distribution of PAA/Fe3O4.

In this review article, Shi and co-workers draw attention to the properties of magnetite nanoparticles (Fe₃O₄), which can be utilised as customized therapeutics.  This review provides an overview of the synthesis of magnetite nanoparticles with an in-depth discussion related to their synthesis, functionalization and applications in a biological environment.

A highlight of this review includes an exploration into the recently discovered photo-luminescence properties of magnetite nanoparticles through studies of the electronic band structures to explain the emission mechanisms occurring.  The implications of thermal and magnetic induced hypothermia treatments utilizing these nanoparticles are also discussed relative to the patients being treated by such techniques.

From this review it can be determined that a new theragnostic platform has emerged with multi-functional capabilities both in terms of imaging and drug delivery.

Photo-fluorescent and magnetic properties of iron oxide nanoparticles for biomedical applications
Donglu Shi, M. E. Sadat, Andrew W. Dunn and David B. Mast
Nanoscale, 2015, 7, 8209-8232. DOI: 10.1039/C5NR01538C

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.

Precision printing and optical modeling of ultrathin SWCNT/C60 heterojunction solar cells

Inexpensive photovoltaics (PV) are an attractive avenue of research in the field of solar cells. In particular, semi-conducting single-walled carbon nanotubes  (s-SWCNTs) are a promising photo-absorbing material due to their strong near-infrared (near-IR) absorption and high carrier mobility. However, most current production methods for SWCNT PVs suffer from high surface roughness and lack nanometer-scale deposition precision, thereby hampering the reproducibility of ultrathin PV devices.

To this end, the authors have utilized ultrasonic spraying in order to tune the thickness of s-SWCNT layers with nanometer-scale precision. The researchers have used a combination of atomic force microscopy (AFM) and optical profilometry to show that their ultrasonic spraying method produces smooth, uniform films with an average roughness of about 5 nm.  The advantage of this low roughness enables fabrication of s-SWCT/C₆₀ bilayer devices with significantly thinner C₆₀ layers than previously reported.

The results reported by the authors help to advance the production of low-cost PV devices by improving the performance and scalability of ultra-thin SWCNT-based solar cells. Ultra-thin SWCNTs reported here could find potential use in other emerging technologies such as vertical field effect transistors and light-emitting diodes incorporating s-SWCNT injection layers.

Precision printing and optical modeling of ultrathin SWCNT/C₆₀ heterojunction solar cells
Sarah L. Guillot, Kevin S. Mistry, Azure D. Avery, Jonah Richard, Anne-Marie Dowgiallo, Paul F. Ndione, Jao van de Lagemaat, Matthew O. Reese and Jeffrey L. Blackburn
Nanoscale, 2015, 7, 6556-6566. DOI: 10.1039/C5NR00205B

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS). Follow him on Twitter: @L_Bargie.

TEM images and size distribution (inset) of various Au25 (1 wt%)/support samples before and after 300 °C calcination.

The use of nanogold (Au NP) catalysts has been widely established for various applications including pharmaceuticals and perfumes.  However, their usage has been limited due to the conventional protocols employed for Au NP synthesis producing polydisperse size ranges, which have proven problematic for identifying catalytic active sites. Recently, this issue has been circumvented through instead using Au nanoclusters (Au NCs), which produce defined cluster sizes with well-defined physiochemical properties. As a direct consequence of being able to exert such control, there have been a number of applications established using such catalysts for processes including CO oxidation, and the oxidation of styrene and cyclohexane. However, whilst the role of the solid support is well established for Au NP catalysis, there currently exists a lack of knowledge on what effect/role the support plays in Au NCs catalysis.

In this study, Fang and co-workers report a systematic assessment of thiolated Au NCs on five different solid supports through examination of the size and electronic structure evolution of the Au NCs during heat treatment, and their catalytic performance when applied to the hydrogenation of nitrobenzene and oxidation of styrene.  The solid supports investigated include hydroxy-apatite (HAP), TiO₂ (P25), activated carbon (AC), pyrolyzed grapheme oxide (PGO) and fumed SiO₂.

The key findings of these studies establish that AuNCs on HAP and P25 supports presented enhanced activities over the other considered supports. This was found to be due to a number of factors, including reduced NC growth during calcination (heat treatment) following the removal of the thiolated ligands from the nanocluster surface. Further to this, the catalytic activity established during the hydrogenation of nitrobenzene and oxidation of styrene overwhelmingly showed that AuNC-HAP had a greater activity than any of the other supported catalysts. This was found to be due to both the reduced NC growth following heat treatment, and a change in the electronic structure of bound Au, resulting in strengthened metal support interactions.

Although this study has shown HAP to be a superior support in comparison to the others investigated, it should be noted that during heat treatment, an increase in the size of the nanoclusters was still observed.  As a consequence of this, the authors have objectively established improvements which should be made for future studies, including pursuing different support methods and improving the conditions under which the thiolated ligands can be removed from the Au NCs.

The support effect on the size and catalytic activity of thiolated Au₂₅ nanoclusters as precatalysts
Jun Fang, Jingguo Li, Bin Zhang, Xun Yuan, Hiroyuki Asakura, Tsunehiro Tanaka, Kentaro Teramura, Jianping Xie and Ning Yan
Nanoscale, 2015, 7, 6325-6333. DOI: 10.1039/C5NR00549C

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.

Radiolabelling of core–shell and dumbbell-like nanoparticles

Bi-modal imaging agents are becoming more popular as they can be used to overcome limitations of single imaging modalities. In this work, radiolabelling of gold containing magnetic nanoparticles (Fe₃O_4-Au) with a nuclear isomer of technetium (^99mTc), a commonly used radionuclide for clinical photon emission computed tomography (SPECT), was assessed using two different methods.  In the first approach, Fe₃O_4-Au core-shell nanoparticles were coated with ligands containing thiol groups to bind to gold and chelator groups for [^99mTc(CO)₃]⁺. In the second approach, ^99mTc containing ligands were first synthesised, then attached to gold on Fe₃O_4-Au dumbbell-like nanoparticles. Both synthetic routes were successful in providing a sufficient radiochemical yield on the surface of magnetic nanoparticles, and are ideal candidates as dual magnetic resonance imaging MRI/SPECT imaging agents. In future studies, the authors plan to use the radiolabelled magnetic particles for bimodal imaging of tumours, through attachment of cancer-specific targeting vectors.

^99mTc radiolabelling of Fe₃O₄–Au core–shell and Au–Fe₃O₄ dumbbell-like nanoparticles
M. Felber and R. Alberto
Nanoscale, 2015, 7, 6653-6660. DOI: 10.1039/C5NR00269A

Dr Mike Barrow is a guest web writer for the Nanoscale blog. He currently works as a Postdoctoral Researcher at the University of Liverpool.

Visual image after EBL treatment, corresponding Raman spectroscopy map of a graphene flake and Raman spectra recorded at different spots on the sample.

Research articles on graphene have been numerously been presented throughout the last decade, indicating the promising future of this material. However, bridging the gap between laboratory research and industrial application remains difficult due to missing specialized large-scale production equipment.

A new article recently published by A. Caglinani et al. introduces an electron beam-based patterning technique using solely widely available clean-room equipment. Based on the findings of the paper, graphene structuring could become a more widespread processing technique.

The researchers developed a patterning process utilizing an industry-standard electron beam lithography system and a standard oven to achieve a resolution of 40 nm.

In the first step, a graphene layer is irradiated by the electron beam which locally generates defects within the crystal lattice. The damage was found by the researchers to be spatially confined to the exposed areas, thus allowing for arbitrary patterns.

The second step comprised etching the irradiated areas by means of hot air at atmospheric pressure. The high defect density (e.g. dangling bonds) induced by the electron beam lead to a large difference in the etch rate compared to the unmodified areas. By exposing the samples for 16 min at 435°C to air, the previously irradiated areas were selectively etched.

In conclusion, the presented process can be used to easily structure graphene layers for future application without the need for specialized equipment. According to the authors, future improvements could reduce the minimum feature size further.

Sebastian Axmann is a guest web-writer for the Nanoscale blog. His interests comprise manufacturing and metrology of nanostructures as well as their usage in current semiconductor devices. He also posts links to interesting research articles on Twitter: @SebastianAxmann.

Viruses are highly complex biological nanostructures.  This complexity has renewed an interest in viruses from the perspective of fundamental physics at the nanoscale. An understanding of the mechanical properties of virus particles at the molecular level can reveal information regarding stiffness, intrinsic elasticity, structural strength and resistance to mechanical fatigue.  This information can provide a basis for researchers to engineer virus-based nanoparticles as nanodevices/ nanocontainers for different biotechnological applications.

The MVM virion.

Castellanos and co-workers have endeavoured to understand the conformational stability and dynamics of the minute virus of mice (MVM), a small ~ 25 nm virus particle, which serves as a model system to understand some of the mechanical properties of viruses. To this end, the researchers have investigated the linkage between the DNA-mediated increase in mechanical stiffness and heat-induced structural changes, and a quantitative relationship between mechanical elasticity and conformational dynamics in MVM nanoparticles.

The researchers used a combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM) for determining the thermal inactivation behaviour and the mechanical stiffness of the viruses, respectively.  By utilizing these techniques, the researchers have deduced that infectious MVM particles may have evolved architectural functions that increase their survival in thermally stressed environments.

This proof-of-principle study has demonstrated that nanoscale features of virus nanoparticles can be probed analytically using AFM and the elucidation of these features have future impact in the field of protein engineering.

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS). Follow him on twitter @L_Bargie.