In the last 30 days

• Open/close Non-volatile domain nucleation and growth in multiferroic BiFeO₃ films

  Yi-Chun Chen et al 2011 Nanotechnology 22 254030 Tag this article

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  We have presented a systematical study of the domain nucleation and growth behaviors in multiferroic BiFeO ₃ (BFO) films. Both the ferroelectric and the ferroelastic switching dynamics were investigated. Several environmental parameters, including the polarization orientations, the monodomain-like matrix, and the ordered domain walls as local boundaries, were well controlled by thin-film strain engineering through changing the vicinal angles of the substrates. The tip-based domain dynamics was studied by subsequent piezoresponse force microscope (PFM) imaging of the domain evolution under external voltage pulses. For the nanodomains written in the monodomain-like environment, the domain wall performed the thermal activated motion. The as-grown 71° domain walls can act as pinning centers for the ferroelectric domain growth driven by low fields; moreover, ferroelastic nucleation near a 71° domain wall will cause the deformation of the domain wall. The ferroelastic domain growth possessed relatively small activation fields, and therefore usually performed non-activated motion. This study revealed the effects of local environments on the dynamics forming nanoscale domains, and opened a pathway for applications in novel non-volatile functional devices.

• Open/close A novel technique for synthesizing dense alumina nanostructures

  A Pancholi et al 2007 Nanotechnology 18 215607 Tag this article

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  The formation of highly ordered nanoporous alumina membranes by anodizing high-purity aluminium under optimum conditions (i.e., anodization time, electrolyte temperature, and cell voltage) in various electrolyte solutions is a well established process. In this paper we report on the formation of a wide range of alumina nanostructures, including nanotubes/nanochannels, nanoplates, and nanofibres, by using a technique that involves anodization and etching processing steps similar to the ones that yield nanopores, under slightly modified experimental conditions. The effects of the anodization voltage, time, and temperature, as well as the effects of the etching time, on the formation and the properties of the alumina nanostructures are analysed. We propose a simple analytical model to describe the formation of different types of alumina nanostructures, as a result of irreversible breakage of the pore walls for long etching times. The geometry of the nanostructures and their dimensions, ranging between 10 and 100 nm, were found to be dependent on the pore dimensions and on the location of the cleavage/breakage of the pore walls.

• Open/close Ballistic resistance capacity of carbon nanotubes

  Kausala Mylvaganam and L C Zhang 2007 Nanotechnology 18 475701 Tag this article

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  Carbon nanotubes have high strength, light weight and excellent energy absorption capacity and therefore have great potential applications in making antiballistic materials. By examining the ballistic impact and bouncing-back processes on carbon nanotubes, this investigation shows that nanotubes with large radii withstand higher bullet speeds and the ballistic resistance is the highest when the bullet hits the centre of the CNT; the ballistic resistance of CNTs will remain the same on subsequent bullet strikes if the impact is after a small time interval.

• Open/close Facile fabrication of gold nanoparticle arrays for efficient surface-enhanced Raman scattering

  Yuling Wang et al 2008 Nanotechnology 19 105604 Tag this article

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  An effective and facile method for the fabrication of a surface-enhanced Raman scattering (SERS)-active film with closely packed gold nanoparticle (AuNP) arrays is proposed by self-assembly of different sizes (16, 25, 40 and 70 nm) of AuNPs at a toluene/water interface with ethanol as the inducer. The as-prepared AuNP arrays exhibit efficient Raman scattering enhancement, and the enhancement factors estimated using p-aminothiophenol as a probe molecule range from 10 ⁵ to 10 ⁷. This is attributed to the coupling electromagnetic SERS enhancement mechanism with additional localization field within closely packed AuNPs, which have greater SERS activity and reproducibility than that on aggregates and on self-assembled monolayers of isolated AuNPs on glass.

• Open/close Self-assembly of CdTe nanocrystals at the water/oil interface by amphiphilic hyperbranched polymers

  Yunfeng Shi et al 2008 Nanotechnology 19 445609 Tag this article

  Article References Full text PDF (531 KB)

  A general strategy for realizing the self-assembly of aqueous CdTe nanocrystals (NCs) at the water/oil interface by means of an amphiphilic core-shell hyperbranched polymer has been proposed. Aqueous CdTe NCs were firstly transferred into the chloroform phase in the presence of palmityl chloride functionalized hyperbranched poly(amidoamine) (HPAMAM-PC), and then self-assembled at the water/chloroform interface by decreasing the pH value of the aqueous phase or introducing α-CDs to the aqueous phase. The resulting CdTe/HPAMAM-PC self-assembly film was characterized by fluorescence microscopy, UV–vis, PL, TEM, EDS, FT-IR, DSC and TGA.

• Open/close Nanostructured materials for water desalination

  T Humplik et al 2011 Nanotechnology 22 292001 Tag this article

  Article References Full text PDF (2.50 MB)

  Desalination of seawater and brackish water is becoming an increasingly important means to address the scarcity of fresh water resources in the world. Decreasing the energy requirements and infrastructure costs of existing desalination technologies remains a challenge. By enabling the manipulation of matter and control of transport at nanometer length scales, the emergence of nanotechnology offers new opportunities to advance water desalination technologies. This review focuses on nanostructured materials that are directly involved in the separation of water from salt as opposed to mitigating issues such as fouling. We discuss separation mechanisms and novel transport phenomena in materials including zeolites, carbon nanotubes, and graphene with potential applications to reverse osmosis, capacitive deionization, and multi-stage flash, among others. Such nanostructured materials can potentially enable the development of next-generation desalination systems with increased efficiency and capacity.

• Open/close Nanofilamentary resistive switching in binary oxide system; a review on the present status and outlook

  Kyung Min Kim et al 2011 Nanotechnology 22 254002 Tag this article

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  This review article summarized the recent understanding of resistance switching (RS) behavior in several binary oxide thin film systems. Among the various RS materials and mechanisms, TiO ₂ and NiO thin films in unipolar thermo-chemical switching mode are primarily dealt with. To facilitate the discussions, the RS was divided into three parts; electroforming, set and reset steps. After short discussions on the electrochemistry of 'electrolytic' oxide materials, the general and peculiar aspects of these RS systems and mechanism are elaborated. Although the RS behaviors and characteristics of these materials are primarily dependent on the repeated formation and rupture of the conducting filaments (CFs) at the nanoscale at a localized position, this mechanism appears to offer a basis for the understanding of other RS mechanisms which were originally considered to be irrelevant to the localized events. The electroforming and set switching phenomena were understood as the process of CF formation and rejuvenation, respectively, which are mainly driven by the thermally assisted electromigration and percolation (or even local phase transition) of defects, while the reset process was understood as the process of CF rupture where the thermal energy plays a more crucial role. This review also contains several remarks on the outlook of these resistance change devices as a semiconductor memory.

• Open/close Diameter of titanium nanotubes influences anti-bacterial efficacy

  Batur Ercan et al 2011 Nanotechnology 22 295102 Tag this article

  Article References Full text PDF (2.58 MB)

  Bacterial infection of in-dwelling medical devices is a growing problem that cannot be treated by traditional antibiotics due to the increasing prevalence of antimicrobial resistance and biofilm formation. Here, due to changes in surface parameters, it is proposed that bacterial adhesion can be prevented through nanosurface modifications of the medical device alone. Toward this goal, titanium was created to possess nanotubular surface topographies of highly controlled diameters of 20, 40, 60, or 80 nm, sometimes followed by heat treatment to control chemistry and crystallinity, through a novel anodization process. For the first time it was found that through the control of Ti surface parameters including chemistry, crystallinity, nanotube size, and hydrophilicity, significantly changed responses of both Staphylococcus epidermidis and Staphylococcus aureus (pathogens relevant for orthopaedic and other medical device related infections) were measured. Specifically, heat treatment of 80 nm diameter titanium tubes produced the most robust antimicrobial effect of all surface treatment parameters tested. This study provides the first step toward understanding the surface properties of nano-structured titanium that improve tissue growth (as has been previously observed with nanotubular titanium), while simultaneously reducing infection without the use of pharmaceutical drugs.

• Open/close Big challenges and nanosolutions

  Anna Demming 2011 Nanotechnology 22 290201 Tag this article

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  Population increases have triggered a number of concerns over the impact of human activity on the global environment. In addition these anxieties are exacerbated by the trend towards high levels of energy consumption and waste generation in developed nations. Pollutants that figure highly in environmental debate include greenhouse gases from fuel combustion and waste decomposition [1] and nitrogen from fertilisers [2]. In fact, human activity is transforming the nitrogen cycle at a record pace [3], and the pressure on available natural resources is mounting. As a collaboration of researchers in Saudi Arabia and the US explain in this issue, 26 countries across the world do not have sufficient water resources to sustain agriculture and economic development, and approximately one billion people lack access to safe drinking water [4]. They also point out a number of ways the potential of nanoscience and technology can be harnessed to tackle the problem.

  The key to managing pollutants is their detection. The biodegradation of waste in land fill sites can generate a build up of a number of green house and other gases. Olfactometry using the human expertise of a trained test panel is not a viable option for continuous monitoring of potentially odourless gases on industrial scales with any valid objectivity. Researchers in Italy have fabricated forest-like structures of carbon nanotubes loaded with metal nanoparticles and unmodified nanotubes on low-cost iron-coated alumina substrates [1]. The structure was able to detect NO ₂ in a multicomponent gas mixture of CO ₂, CH ₄, H ₂, NH ₃, CO and NO ₂ with sensitivity better than one part per million.

  Nanostructures exhibit a number of properties that lend themselves to sensing applications. They often have unique electrical properties that are readily affected by their environment. Such features were exploited by researchers in China who created nanoporous structures in ZnO sheets that can detect formaldehyde and ammonia, the dominant indoor gas contaminants that are generated by building and decorative materials [5]. The sensors have high gas-sensing responses, short response and recovery times, and significant long-term stability.

  Fluorescent nanoparticles can provide another form of sensor as the fluorescence is enhanced or quenched by surrounding materials. Researchers in China have demonstrated that cysteine-capped CdTe quantum dots provide an effective sensor for the presence of trinitrotoluene, an industrial contaminant found in soil and ground water that can cause anemia, hepatic damage and cancer [6].

  The photocatalytic properties of nanostructures such as BiVO ₄ can be used to remove unwanted and potentially harmful contaminants from wastewater, including dyes, which may be resistant to microbial and chemical degradation and can be converted to toxic or carcinogenic compounds [7]. These properties are often dependent on the morphology, which can be controlled through the synthesis conditions. In China, researchers have demonstrated that hierarchically structured SiO ₂@γ–AlOOH spheres can be an efficient way of adsorbing harmful Cr(VI) ions from model waste water [8].

  As 98% of the world's water supply is sea or brackish water, desalination is becoming an increasingly important water treatment for keeping pace with the demands of the multiplying global population. In this issue, researchers in the US and Saudi Arabia provide an in-depth overview of the use of nanomaterials in desalination treatments [4]. The review discusses separation mechanisms and novel transport phenomena in a range of materials including zeolites, carbon nanotubes, and graphene. It highlights possible processes such as reverse osmosis, capacitive deionization, and multi-stage flash, among others that may contribute to the development of next-generation desalination systems with increased efficiency and capacity.

  Back in 1968 Garrett Hardin suggested that 'the population problem has no technical solution' [9]. How population dynamics will evolve throughout future generations attracts considerable debate and a range of strong opinions. But in the meantime, as this issue's review highlights, there is a great deal of scope in exploiting nanotechnology to find potential technological solutions to the challenges increasing populations pose at present. And that's not to mention the intriguing insights into nanoscale physics that may be discovered along the way.

  References

  [1] Penza M, Rossi R, Alvisi M and Serra E 2010 Nanotechnology 21 105501

  [2] Gu B, Zhu Y, Chang J, Peng C, Liu D, Min Y, Luo W, Howarth R W and Ge Y 2011 Environ. Res. Lett. 6 014011

  [3] Galloway J N, Townsend A R, Erisman J W, Bekunda M, Cai Z, Freney J R, Martinelli L A, Seitzinger S P and Sutton M A 2008 Science 320 889–92

  [4] Humplik T et al 2011 Nanotechnology 22 292001

  [5] Guo Z, Meng F, Luo T, Li M and Liu J 2009 Nanotechnology 20 125501

  [6] Chen Y, Chen Z, He Y, Lin H, Sheng P, Liu C, Luo S and Cai Q 2010 Nanotechnology 20 105102

  [7] Ren L, Ma L, Jin L, Wang J-B, Qiu M and Yu Y 2009 Nanotechnology 20 405602

  [8] Wang Y, Wang G, Wang H, Cai W, Liang C and Zhang L 2009 Nanotechnology 20 156604

  [9] Hardin G 1968 Science 162 1243–8

• Open/close Direct growth of tellurium nanorod arrays on Pt/FTO/glass through a surfactant-assisted chemical reduction

  Hongmei Liu et al 2011 Nanotechnology 22 305608 Tag this article

  Article References Full text PDF (3.53 MB)

  Uniform tellurium nanorod arrays (TNA) have been successfully deposited directly on Pt/FTO (F-doped SnO ₂)/glass substrate through a facile surfactant-assisted approach, which involved chemical reduction of TeO ₃ ^{2 −} ions by hydrazine hydrate. The whole synthesis process is highly repeatable and performed simply by immersing the Pt/FTO/glass in the solution for a certain time. During the growth of TNA, Pt catalyzed the reduction of TeO ₃ ^{2 −} ions by hydrazine hydrate and Te nanoparticles were deposited firmly on the substrate at first. Then, under the regulation of the surfactant (cetyltrimethylammonium bromide, CTAB), the deposited Te grew into nanorod arrays and adhered firmly to the substrate. Similar Te nanorod arrays could also grow on a Pd substrate which has the same catalytic performance as that of Pt. The as-synthesized TNA could be used as a good template to synthesize platinum-and gold-coated nanorods through convenient galvanic replacement. As a demonstration of potential application, the gold/tellurium nanorods showed uniform surface-enhanced Raman scattering (SERS) using rhodamine 6G (Rh6G) as the analyte. This approach provides a simple route for the growth of standing Te nanorods on a substrate, which may be used for the synthesis of other standing one-dimensional materials through a similar mechanism.