A new precision measurement of the {\alpha}-decay half-life of 190Pt

A laboratory measurement of the $\alpha$-decay half-life of $^{190}$Pt has been performed using a low background Frisch grid ionisation chamber. A total amount of 216.60(17) mg of natural platinum has been measured for 75.9 days. The resulting half-life is $(4.97\pm0.16)\times 10^{11}$ years, with a total uncertainty of 3.2%. This number is in good agreement with the half-life obtained using the geological comparison method

Correlation of lithographic performance of the electron beam resists SML and ZEP with their chemical structure

Study of topographical and structural changes occurring in a positive resist known as SML after electron beam lithography are presented in this article. The authors also defined its chemical structure, which is very important for understanding the lithographic performance of the resist. The structural and lithographic properties of SML have been compared to the traditional ZEP resist. First, the change in the surface roughness with respect to the electron dose of SML and ZEP resists was measured. It was found that both resists start off with similar initial roughness values. However, ZEP was observed to have a higher roughness at the apex electron dose, thereafter a reduction in roughness was observed. The roughness variation in the two resists reflected on the resolution of the gratings that were patterned in both the resists. Gratings in SML showed smoother line edge roughness, and the patterns transferred using SML resist showed more even features than the ones transferred with ZEP. Subsequently, to understand the chemical composition of the new resist, Fourier transform infrared spectroscopy (FTIR) measurements were performed on both the resists as well as on poly(methyl methacrylate) (PMMA) and their spectra were compared. The FTIR spectra revealed that SML had a chemical structure similar to ZEP and PMMA polymers. The high sensitivity of ZEP is attributed to the Cl group in the compound, which is not present in SML and PMMA and can therefore explain their lower sensitivity to electron exposure in comparison to ZEP. Unlike PMMA but comparable to ZEP, SML shows an IR peak at a wavenumber close to 850 cm−1, suggesting the presence of α-methylstyrene group within its chemical structure, which accounts for the resist's high etch durability, similar to ZEP. Additional FTIR measurements of pre- and postexposed resists together with their attributions to the resolution of the SML and ZEP resists is also demonstrated in this article. The data presented in the study highlights the chemical properties of SML and ZEP resists polymers and correlates them to their lithographic performance

New generation electron beam resists: a review

The semiconductor industry has already entered the sub-10 nm region, which has led to the development of cutting-edge fabrication tools. However, there are other factors that hinder the best outcome of these tools, such as the substrate and resist materials, pre- and postfabrication processes, etc. Among the lithography techniques, electron beam lithography (EBL) is the prime choice when a job requires dimensions lower than 10–20 nm, since it can easily achieve such critical dimensions in reasonable time and effort. When obtaining pattern features in single nanometer regime, the resist material properties play an important role in determining the size. With this agenda in mind, many resists have been developed over the years suitable for attaining required resolution in lesser EBL writing time. This review article addresses the recent advancements made in EBL resists technology. It first describes the different lithography processes briefly and then progresses on to the parameters affecting the EBL fabrications processes. EBL resists are then bifurcated into their “family types” depending on their chemical composition. Each family describes one or two examples of the new resists, and their chemical formulation, contrast-sensitivity values, and highest resolution are described. The review finally gives an account of various alternate next-generation lithography techniques, promising dimensions in the nanometer range

Нанохайку и нанохайга, или как нанотехнологиите се срещат с изкуството

The present work combines science and arts in an innovative and intriguing way. Using Electron Beam Lithography (EBL) and Directed Self-Assembly (DSA) of Block Co-Polymers (BCP) in conjunction with the shortest poetic form, haiku, the paper attractively demonstrate the capabilities of these nanofabrication techniques and explores the interaction between the top-down EBL process and the bottom-up DSA approach. Silicon (Si) substrates and EBL with the hydrogen silsesquioxane (HSQ) negative tone resist were used for capturing examples of the tiniest haiku poems written and translated into six languages having four different character styles. Subsequently, the haiku nanostructures (“nanohaiku”) were used as guiding features between which the poly(styrene)-blockpoly(ethylene oxide) (PS-b-PEO) diblock copolymer is spin coated to create self-organised nanopatterns. The annealing was done in toluene solvent vapours at 50°C for 1.5 hours and then the samples were immersed in ethanol for 15 hours at 40°C to dissolve the PEO copolymer. In areas within and in-between the individual characters and syllables of the poems, unusual patterns were observed. We interpret them as self-assembled “nanohaiga” directed by the morphology and the linguistic geometry of the nanohaiku. Moreover, we demonstrate how the BCP pattern changes when interacting with the same verse translated into different languages. Thus we add to the haiku poem's own nanostructure and meaning a new visual identity, nanohaiga, combining for the first time poetry, visual art and advanced nanofabrication technologies

Porous to non-porous transition in the morphology of metal assisted etched silicon nanowires

A single step metal assisted etching (MAE) process, utilizing metal ion-containing HF solutions in the absence of an external oxidant, has been developed to generate heterostructured Si nanowires with controllable porous (isotropically etched) and non-porous (anisotropically etched) segments. Detailed characterisation of both the porous and non-porous sections of the Si nanowires was provided by transmission electron microscopy studies, enabling the mechanism of nanowire roughening to be ascertained. The versatility of the MAE method for producing heterostructured Si nanowires with varied and controllable textures is discussed in detail

Solvent vapor annealing of block copolymers in confined topographies: commensurability considerations for nanolithography

The directed self-assembly of block copolymer (BCP) materials in topographically patterned substrates (i.e., graphoepitaxy) is a potential methodology for the continued scaling of nanoelectronic device technologies. In this Communication, an unusual feature size variation in BCP nanodomains under confi nement with graphoepitaxially aligned cylinder-forming poly(styrene)- block -poly(4-vinylpyridine) (PS- b -P4VP) BCP is reported. Graphoepitaxy of PS- b -P4VP BCP line patterns (C II ) is accomplished via topography in hydrogen silsequioxane (HSQ) modified substrates and solvent vapor annealing (SVA). Interestingly, reduced domain sizes in features close to the HSQ guiding features are observed. The feature size reduction is evident after inclusion of alumina into the P4VP domains followed by pattern transfer to the silicon substrate. It is suggested that this nanodomain size perturbation is due to solvent swelling effects during SVA. It is proposed that using a commensurability value close to the solvent vapor annealed periodicity will alleviate this issue leading to uniform nanofins

Detection of ultra-low protein concentrations with the simplest possible field effect transistor

Silicon nanowire (Si NW) sensors have attracted great attention due to their ability to provide fast, low-cost, label-free, real-time detection of chemical and biological species. Usually configured as field effect transistors (FETs), they have already demonstrated remarkable sensitivity with high selectivity (through appropriate functionalisation) towards a large number of analytes in both liquid and gas phases. Despite these excellent results, Si NW FET sensors have not yet been successfully employed to detect single molecules of either a chemical or biological target species. Here we show that sensors based on silicon junctionless nanowire transistors (JNTs), the simplest possible transistors, are capable of detecting the protein streptavidin at a concentration as low as 580 zM closely approaching the single molecule level. This ultrahigh detection sensitivity is due to the intrinsic advantages of junctionless devices over conventional FETs. Apart from their superior functionality, JNTs are much easier to fabricate by standard microelectronic processes than transistors containing p–n junctions. The ability of JNT sensors to detect ultra-low concentrations (in the zeptomolar range) of target species, and their potential for low-cost mass production, will permit their deployment in numerous environments, including life sciences, biotechnology, medicine, pharmacology, product safety, environmental monitoring and security

Electrical characterization of high performance, liquid gated vertically stacked SiNW-based 3D FET for biosensing applications

A 3D vertically stacked silicon nanowire (SiNW) field effect transistor featuring a high density array of fully depleted channels gated by a backgate and one or two symmetrical platinum side-gates through a liquid has been electrically characterized for their implementation into a robust biosensing system. The structures have also been characterized electrically under vacuum when completely surrounded by a thick oxide layer. When fully suspended, the SiNWs may be surrounded by a conformal high-κ gate dielectric (HfO2) or silicon dioxide. The high density array of nanowires (up to 7 or 8 × 20 SiNWs in the vertical and horizontal direction, respectively) provides for high drive currents (1.3 mA/μm, normalized to an average NW diameter of 30 nm at VSG = 3 V, and Vd = 50 mV, for a standard structure with 7 × 10 NWs stacked) and high chances of biomolecule interaction and detection. The use of silicon on insulator substrates with a low doped device layer significantly reduces leakage currents for excellent Ion/Ioff ratios >106 of particular importance for low power applications. When the nanowires are submerged in a liquid, they feature a gate all around architecture with improved electrostatics that provides steep subthreshold slopes (SS 10 μS) while allowing for the entire surface area of the nanowire to be available for biomolecule sensing. The fabricated devices have small SiNW diameters (down to dNW ∼ 15–30 nm) in order to be fully depleted and provide also high surface to volume ratios for high sensitivities

Characterisation of a novel electron beam lithography resist, SML and its comparison to PMMA and ZEP resists

As transistor dimensions continue to diminish, techniques for fabrication need to be adapted. In particular, crystal recovery post ion implantation is required due to destructive ion bombardment inducing crystal damage including amorphization. Here, we report a study on the post-implant recrystallization in germanium (Ge) nanowires (NWs) following gallium (Ga) ion doping. In this work a variation of NW diameters and orientations were irradiated and annealed in situ to investigate the mechanism of recrystallization. An added complication of misorientation of crystal grains increases the complexity of crystal recovery for suspended NWs. We show that when the misorientation is prevented, by leaving a crystal link between two seeds and providing a rigid support, recrystallization occurs primarily via solid phase epitaxial growth (SPEG). Finally, we demonstrate that top-down fabricated Ge NWs on insulator can be recovered with no extended defects. This work highlights both experimentally and through molecular dynamic simulations the importance of engineering crystal recovery in Ge NWs which may have potential for next-generation complementary metal-oxide semiconductor (CMOS) devices

A miniaturised autonomous sensor based on nanowire materials platform: the SiNAPS mote

A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing, on a chip area of 0.25mm2. Direct charging of the target battery (e.g., NiMH microbattery) is achieved with end-to-end efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, Voc, of 450-500mV. To match the battery’s voltage the miniaturised solar cells (~1mm2 area) are connected in series via wire bonding. The chemical sensor platform (mm2 area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both temperature and H2 concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are less than 350nW and 2.1 μW respectively. Low-power miniaturised chemical sensors of liquid analytes through microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire materials platform