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Peter Eklund grew up in Southern California and attended the University of California at Berkeley, majoring in physics. After working for one year at the Lockheed Missile and Space Company in Sunnyvale, California, he left to pursue graduate studies at Purdue University. There he carried out PhD research in strongly correlated electron and phonon systems under the supervision of J M Honig and L L van Zandt.

Peter joined the group of Millie and Gene Dresselhaus at MIT in 1974 as a Postdoctoral Fellow after one year as an instructor at the University of Kentucky. At MIT, he continued work on strongly correlated systems in collaboration with Professor David Adler (who had an adjoining office), but for the most part he got excited about sp² carbon systems and graphite intercalation compounds, a new research direction which the Dresselhaus group had started one year before Peter's arrival at MIT. Over the next 35 years Peter, Millie and Gene co-authored over 50 research articles, several review articles, and a big nine-hundred-and-fifty page book. In 1974, they saw graphite intercalation compounds as a long-neglected research direction of great promise. They studied these new materials together over the next 16 years, focusing on their optical spectroscopy. Their pioneering vibrational spectroscopy studies provided a means to characterize the fundamental properties of carbon materials. Optical spectroscopy became a centerpiece in the research portfolios of all three, both when they were together at MIT and after Peter left for the University of Kentucky in 1977 to start his independent career as an Assistant Professor of Physics.

Peter became a full Professor at Kentucky in 1986. He continued to work with Millie and Gene and also acquired an ever-expanding network of students, postdocs and collaborators. As each new carbon nanostructure emerged—graphite intercalation compounds, fullerenes, carbon nanotubes, and most recently graphene—Peter was at the cutting edge, leading the charge forward. His work on fullerenes, starting around 1988, culminated in a book co-authored with Millie and Gene in 1996, The Science of Fullerenes and Carbon Nanotubes [1]. Through careful sample handling and analysis, his group at Kentucky discovered the mechanism of photo-polymerization in fullerenes. In 2000, Peter co-edited the research monograph Fullerene Polymers and Fullerene Polymer Composites with A M Rao, a former student [2]. His group at Kentucky also performed the first definitive Raman study of the phonons responsible for superconductivity in alkali-doped fullerene compounds. Peter was awarded the prestigious University of Kentucky Research Professorship for his contributions to graduate education and research discoveries in carbon materials.

In the summer of 1991, Peter held early discussions with his two long-time collaborators on the possibility of carbon nanotubes. These discussions inspired a talk by Millie at a fullerene workshop the next day concerning the possible existence of single-walled carbon nanotubes [3]. The first papers by Iijima on the synthesis of multiwalled nanotubes appeared soon thereafter [4]. In 1994, Peter measured an early Raman spectrum on a sample containing just 1% of single-walled tubes. On the basis of this early work, he convinced Rick Smalley to provide him with a proper sample of single-walled carbon nanotubes in 1996; this is the sample on which the highly cited single-walled carbon nanotube Raman spectrum was taken [5]. Carbon nanotubes then became a central focus of the Eklund group. Peter, Millie and Gene worked together on many aspects of carbon nanotubes, including the study of infrared-active modes, Raman active modes, Raman spectra for single-walled nanotubes, and the differences in the Raman spectra of semiconducting and metallic tubes. In 2009 they combined efforts to investigate phonons in graphene.

Peter was also an entrepreneur. He started a company, CarboLex, to make and sell nanotubes in large quantities, thereby giving industrial support to advancing fundamental science. He co-founded two additional companies: PhotoStealth produced computer-generated camouflage patterns printed on textiles and ICMR pursued laser-driven synthesis of nanoparticles and coatings. ICMR moved from Lexington to Silicon Valley and evolved into Nanogram, later reorganized as NeoPhotonics. Both CarboLex and NeoPhotonics are still actively engaged in the research and development of nano-materials.

Peter joined the Physics Department at Penn State University in 1999, becoming a Distinguished Professor in 2008. In 2002, he also joined the faculty of the Department of Materials Science and Engineering. In addition to further seminal work on carbon materials, Peter initiated a research effort in semiconducting nanowires, obtaining the first clear evidence of phonon confinement in 1D nanostructures. After the Novoselov-Geim work on monolayer graphene appeared, once again Peter Eklund was there to publish very early Raman spectra on monolayer, bilayer and few-layer graphene. Thus, the work of Peter Eklund unfolds the leading wave of discoveries in carbon nanostructures starting in 1974 and continuing over a thirty-five year period to August 2009.

Peter mentored more than 40 graduate students and postdoctoral fellows. He co-authored over 300 research articles and more than 20 chapters in monographs. His scientific oeuvre has been cited more than 16 000 times. Peter acquired three US patents with five more pending. He was recognized with the Japan Carbon Award (2008), the American Carbon Society Graffin Award (2005), American Physical Society Fellowship (1990), and visiting/honorary professorships in Nankai University, Yokohama City University, Shinshu University, Tokyo Science University, and (as a visiting scientist) in the Solid State Division of Oak Ridge National Laboratory. From 2003 to 2006 he was a member of the Solid State Sciences Committee of the US National Academy of Sciences.

Peter enjoyed challenges. He was in his glory while interpreting the stories told by experimental data in partnership with his colleagues and research team of dedicated postdocs and students. Peter was admired all over the world for his creativity, his kindness, his engaging personality, his breadth of interests, his sensitive character and his quick wit.

Several friends have shared their memories:

Kumble Subbaswamy(University of Kentucky, USA): 'Peter, along with Karen, were the gentlest and most generous souls I have ever met. He picked up stray dogs and stray graduate students alike, nurturing them through sickness and health. I will never forget the hospice-like care he provided to one international student who worked in his lab, but succumbed to cancer.

In his early days at Kentucky, when funds to support his research were very scarce, he made frequent visits to the military surplus store nearby and behaved like a kid in a candy store, bringing back all sorts of electrical and mechanical parts for his experiments. It is in no small measure due to this ability that he built such a successful career.

Peter was without peer when it came to instrument design and fabrication. I mentioned to him, during my job interview at the University of Kentucky (where he arrived one year before me), my interest in studying the Raman spectra of molten alkali halides. Several months later when I arrived on campus, I was surprised to find he had constructed a beautifully crafted Raman chamber supporting a contactless molten sample! He had anticipated and addressed every possible complication.'

Qihua Xiong(Nanyang Technical University, Singapore): 'Peter was a great mentor; he knew how to stimulate students to explore their full potential. Students could knock on his door with questions or with new data any time. He was always patient. He explained physics with his fountain pen on a notepad or with a marker on a white board until students understood.

When students made mistakes, he never blamed the student, because he believed it is part of training to allow students to make mistakes. I once designed a mask adapter to connect our existing three-inch photomasks to Srinivas's four-inch mask aligner. The design looked beautiful and the machine shop did a perfect job to machine and polish the piece. Unfortunately, I made a stupid mistake. The central opening was slightly larger than the square vacuum groves behind the mask holder and as a result, it leaked! I was very disappointed in myself, as I not only wasted grant money but also delayed our experiment. Peter patted my shoulder, picked up a sharpie and wrote on the mask adapter, 'even great people make mistakes, but they learn.' So we machined another one, and it worked well. This failure piece still stands on my bookshelf. I keep it as a motto: it warns me not to make any mistakes like that, but more importantly it encourages me to be a supervisor like Peter.'

Joe Brill(University of Kentucky, USA): 'Peter's occasional impetuousness and his love of physics are illustrated by the following anecdote. In December, 1979, I had just joined the faculty at the University of Kentucky, excited about the prospect of collaborating with Peter, who had arrived two years before. I was, therefore, dumbfounded when Peter abruptly announced his resignation to join IBM to do research on printer ink. After less than two days at IBM, however, he sheepishly asked to come back to the UK, explaining that he couldn't enjoy doing research that didn't involve 'h-bar'. His UK colleagues, who had not even had the chance to raid his lab, of course agreed with great amusement and relief. His joy and enthusiasm for physics remained contagious and unforgettable.'

Milton Cole(Penn State University, USA): 'Somehow my very last conversation with Peter, two days before his death, typified the hundreds of conversations we had about science, or even philosophy. His first words after greeting me consisted of a hypothetical explanation of the physical mechanism of a new intravenous tube he was obliged to use. He conveyed on that occasion the very same excitement that he displayed years earlier when he volunteered to present a demonstration of electrical circuitry to a group of third-grade students. Those eight-year olds became as enthusiastic as Peter. It is no wonder that Peter was so admired and loved.'

Jackie Bortiatynski(Penn State University, USA): 'I loved working with Peter on summer science camps for kids. He was creative, funny, brilliant, and an inspiration. I just don't know where he got all his energy. I will truly miss him as a colleague.'

Toshiaki Enoki(Tokyo Institute of Technology, Japan): 'Peter was very serious in his research work, but he also had an amiable personality with a very good sense of humour. I remember the occasion of a small international workshop, which was chaired by me in Ise, Japan in 1985. We had serious and intensive discussions in the scientific session, then in the evening we enjoyed an excursion and banquet in Ise, a small old town with a famous shrine named Ise Jingu. Peter romped out with joy wearing yukata (Japanese traditional night clothes) after taking a hot spring.'

Robert Haddon(University of California, Riverside, USA): 'Peter was the driving force in creating a position for me at the University of Kentucky in 1997. After I joined Kentucky, we immediately focused on the large-scale synthesis of single-walled carbon nanotubes and we became one of a handful of research groups that could produce single-walled nanotubes in quantity. Soon after, we founded CarboLex and the university was awarded an NSF MRSEC on Advanced Carbon Materials. For most of the time that I spent at Kentucky, our research groups met as a unit and our collaboration greatly assisted me in making the transition to academia. Above all, Peter was a physicist in very much the same tradition as the great colleagues that I had been privileged to work with at the Bell Labs. Peter and Karen made me welcome in their home from the time I arrived in Lexington and I have fond memories of the time we spent together.'

Keith Williams(University of Virginia, USA): 'In 1993, Peter introduced me, in the dark, to his postdoc Apparao Rao, who was then doing Raman on C₆₀ at Kentucky. I thought it was pretty interesting and that was how I began working for Peter. I was an exile from high-energy physics: the SSC had just been canceled and I had drifted in and out of biophysics and AMO and finally settled on Peter's brand of experimental nanomaterials physics. I immediately enjoyed Peter's ingenuity and his wonderful sense of humour. One aspect of Peter's character not widely appreciated by his students was his thrift: if something could be made, borrowed (with or without consent), or used after-hours then he always advocated that strongly. More than once, we got demo equipment, ran an all-nighter on it to collect data and then sent it back a day later. Almost nothing was bought off the shelf! Peter attributed these tendencies to his ancestry, and that was an unending joke between us. Of course, the strategy of making every penny count benefited me greatly in the long run, and last year I told him I had outdone him in my lab: almost everything was built from scratch, and everything else was on loan. He smiled a proud smile. On the personal side, however, Peter was always very generous; I fondly recall the dinners with him and Karen and the other students, their beloved dogs, with the Beach Boys inevitably playing in the background. Peter and Karen were wonderful to me and so many other students, and it didn't surprise me at all to learn that Peter's last scientific concern was that a proposal had been funded and that his students were going to be okay.'

Kenichi Kojima(Yokohama City University, Japan): 'In 1997, Peter came to Yokohama as a Guest Professor at Yokohama City University to give his lectures to our graduate students. Peter was an excellent lecturer, of course. But when I played tennis with him for the first time, I found that he was an amazing tennis player as well. He hit the ball really hard, and his serves were amazingly fast. During his stay, Peter liked stopping over at a typical traditional Japanese-style pub for dinner by himself. One day he wanted to have a beer before dinner. However, he was not sure how to order draft beer in Japanese, and the manager of the pub did not understand English. He carefully listened to what the customers around him said when they ordered beer. He then said in a loud voice, 'Please give me a glass of mama beer.' In Japan, female servers in pubs are often called 'mama' by customers, and we call draft beer 'nama beer' because 'nama' means 'living' in Japanese. Probably 'nama' sounded like 'mama' to Peter. Later he proudly told me, with a happy smile, how he got a delicious draft Kirin beer. Peter loved not only science but also traditional Japanese culture. He was a polished person. I would like to show you the words written in his own hand in my visitor's book when he came to my home after playing tennis in 1997. May his soul rest in peace!'

Millie Dresselhaus(Massachusetts Institute of Technology, USA): 'At the time of Peter's entry into the study of sp² carbons in 1974, the field was an eclectic area of science that only interested a small group of aficionados. Through his many contributions during the next 35 years as well as those of others, the field has grown dramatically, and now it is a major area of interest in condensed matter and materials physics worldwide. Working on joint projects together with Peter Eklund was both educational and enjoyable. In our joint efforts, I was responsible for the big picture, Peter was the master of experimental details and Gene Dresselhaus was the man responsible for getting things done well and on time.

During the last 35 years of his life, starting from his postdoctoral period, we enjoyed a close working relation, especially for the first 25 of these years, overlapping with his stay at the University of Kentucky. As his career developed, our relationship changed from a postdoctoral advisor, to a collaborator, friend, and confidant. After his mother passed away I assumed the role of his 'second mother' as he called me. We remained very close personally, even though far away in location and despite his many other professional collaborators. Looking to the future, life without Peter will never be the same.'

References

[1] Dresselhaus M S, Dresselhaus G, and Eklund P C 1996 Science of Fullerenes and Carbon Nanotubes (New York: Academic Press)

[2] Eklund P C and Rao A M 1999 Fullerene Polymers and Fullerene-Polymer Composites (Springer Series in Materials Science vol 38) (Berlin: Springer)

[3] Dresselhaus M S 1991 Recent advances in electronic materials Proc. of the 38th Sagamore Army Mater. Res. Conf. (Watertown, MA, Materials Technology Laboratory) ed Thomas V Hynes p 45

[4] Iijima S 1991 Helical microtubules of graphitic carbon Nature354 56–8

[5] Rao A M, Richter E, Bandow S, Chase B, Eklund P C, Williams K W, Fang S, Subbaswamy K R, Menon M, Thess A, Smalley R E, Dresselhaus G and Dresselhaus M S 1997 Diameter-selective Raman scattering from vibrational modes in carbon nanotubes Science275 187–91

This review addresses the field of nanoscience as viewed through the lens of the scientific career of Peter Eklund, thus with a special focus on nanocarbons and nanowires. Peter brought to his research an intense focus, imagination, tenacity, breadth and ingenuity rarely seen in modern science. His goal was to capture the essential physics of natural phenomena. This attitude also guides our writing: we focus on basic principles, without sacrificing accuracy, while hoping to convey an enthusiasm for the science commensurate with Peter's. The term 'colloquial review' is intended to capture this style of presentation.

The diverse phenomena of condensed matter physics involve electrons, phonons and the structures within which excitations reside. The 'nano' regime presents particularly interesting and challenging science. Finite size effects play a key role, exemplified by the discrete electronic and phonon spectra of C₆₀ and other fullerenes. The beauty of such molecules (as well as nanotubes and graphene) is reflected by the theoretical principles that govern their behavior. As to the challenge, 'nano' requires special care in materials preparation and treatment, since the surface-to-volume ratio is so high; they also often present difficulties of acquiring an experimental signal, since the samples can be quite small. All of the atoms participate in the various phenomena, without any genuinely 'bulk' properties. Peter was a master of overcoming such challenges.

The primary activity of Eklund's research was to measure and understand the vibrations of atoms in carbon materials. Raman spectroscopy was very dear to Peter. He published several papers on the theory of phonons (Eklund et al 1995a Carbon33 959–72, Eklund et al 1995b Thin Solid Films257 211–32, Eklund et al 1992 J. Phys. Chem. Solids53 1391–413, Dresselhaus and Eklund 2000 Adv. Phys.49 705–814) and many more papers on measuring phonons (Pimenta et al 1998b Phys. Rev. B 58 16016–9, Rao et al 1997a Nature338 257–9, Rao et al 1997b Phys. Rev. B 55 4766–73, Rao et al 1997c Science275 187–91, Rao et al 1998 Thin Solid Films331 141–7). His careful sample treatment and detailed Raman analysis contributed greatly to the elucidation of photochemical polymerization of solid C₆₀ (Rao et al 1993b Science259 955–7). He developed Raman spectroscopy as a standard tool for gauging the diameter of a single-walled carbon nanotube (Bandow et al 1998 Phys. Rev. Lett.80 3779–82), distinguishing metallic versus semiconducting single-walled carbon nanotubes, (Pimenta et al 1998a J. Mater. Res.13 2396–404) and measuring the number of graphene layers in a peeled flake of graphite (Gupta et al 2006 Nano Lett.6 2667–73). For these and other ground breaking contributions to carbon science he received the Graffin Lecture award from the American Carbon Society in 2005, and the Japan Carbon Prize in 2008.

As a material, graphite has come full circle. The 1970s renaissance in the science of graphite intercalation compounds paved the way for a later explosion in nanocarbon research by illuminating many beautiful fundamental phenomena, subsequently rediscovered in other forms of nanocarbon. In 1985, Smalley, Kroto, Curl, Heath and O'Brien discovered carbon cage molecules called fullerenes in the soot ablated from a rotating graphite target (Kroto et al 1985 Nature318 162–3). At that time, Peter's research was focused mainly on the oxide-based high-temperature superconductors. He switched to fullerene research soon after the discovery that an electric arc can prepare fullerenes in bulk quantities (Haufler et al 1990 J. Phys. Chem.94 8634–6). Later fullerene research spawned nanotubes, and nanotubes spawned a newly exploding research effort on single-layer graphene. Graphene has hence evolved from an oversimplified model of graphite (Wallace 1947 Phys. Rev.71 622–34) to a new member of the nanocarbon family exhibiting extraordinary electronic properties. Eklund's career spans this 35-year odyssey.

The Raman spectrum of monolayer graphene deposited on the top of a silicon oxide/silicon substrate was investigated as a function of temperature up to 515 K. An anomalous temperature dependence of the Raman features was observed, including an important frequency upshift for the Raman G band at room temperature, after the heating process. On the other hand, the frequency of the Raman G^' band is only slightly affected by the thermal treatment. We discuss our experimental results in terms of doping and strain effects associated with the interaction of graphene with the substrate and with the presence of water in the sample. We conclude that the doping effect gives the most important contribution to the spectral changes observed after the thermal cycle.

Raman spectra of graphene nanoribbons with zigzag and armchair edges are calculated within non-resonant Raman theory. Depending on the edge structure and polarization direction of the incident and scattered photon beam relative to the edge direction, a symmetry selection rule for the phonon type appears. These Raman selection rules will be useful for the identification of the edge structure of graphene nanoribbons.

Raman scattering is used to study the effect of low energy (90 eV) Ar ⁺ ion bombardment in graphene samples as a function of the number of layers N. The evolution of the intensity ratio between the G band (1585  cm ^{− 1}) and the disorder-induced D band (1345 cm ^{− 1}) with ion fluence is determined for mono-, bi-, tri- and ∼ 50-layer graphene samples, providing a spectroscopy-based method to study the penetration of these low energy Ar ⁺ ions in AB Bernal stacked graphite, and how they affect the graphene sheets. The results clearly depend on the number of layers. We also analyze the evolution of the overall integrated Raman intensity and the integrated intensity for disorder-induced versus Raman-allowed peaks.

Micro-Raman scattering from folds in single-layer graphene sheets finds a D-band at the fold for both incommensurate and commensurate folding, while the parent single-layer graphene lacks a D-band. A coupled elastic-continuum/tight-binding calculation suggests that this D-band arises from the spatially inhomogeneous curvature around a fold in a graphene sheet. The polarization dependence of the fold-induced D-band further reveals that the inhomogeneous curvature acts as a very smooth, ideal one-dimensional defect along the folding direction.

Three problems involving quasi-one-dimensional (1D) ideal gases are discussed. The simplest problem involves quantum particles localized within the 'groove', a quasi-1D region created by two adjacent, identical and parallel nanotubes. At low temperature (T), the transverse motion of the adsorbed gas, in the plane perpendicular to the axes of the tubes, is frozen out. Then, the low T heat capacity C(T) of N particles is that of a 1D classical gas: . The dimensionless heat capacity C^* increases when T ≥ 0.1T_{x, y} (transverse excitation temperatures), asymptoting at C^* = 2.5. The second problem involves a gas localized between two nearly parallel, co-planar nanotubes, with small divergence half-angle γ. In this case, too, the transverse motion does not contribute to C(T) at low T, leaving a problem of a gas of particles in a 1D harmonic potential (along the z axis, midway between the tubes). Setting ω_z as the angular frequency of this motion, for , the behavior approaches that of a 2D classical gas, C^* = 1; one might have expected instead C^* = 1/2, as in the groove problem, since the limit is 1D. For , the thermal behavior is exponentially activated, C^* ∼ (τ_z/T)²e ^{− τ_z/T}. At higher T (), motion is excited in the y direction, perpendicular to the plane of nanotubes, resulting in thermal behavior (C^* = 7/4) corresponding to a gas in 7/2 dimensions, while at very high T (), the behavior becomes that of a D = 11/2 system. The third problem is that of a gas of particles, e.g. ⁴He, confined in the interstitial region between four square parallel pores. The low T behavior found in this case is again surprising—that of a 5D gas.

The quantum sieving effect of D₂ over H₂ is examined at 40 and 77 K by means of experiments and GCMC simulations, for two types of single-wall carbon nanotubes that are distinguishable by their unique entangled structures; (1) a well-bundled SWCNT and (2) loosely-assembled SWCNT produced by the super growth method (SG-SWCNT). Oxidized SWCNT samples of which the so-called internal sites are accessible for H₂ and D₂, are also studied. Experimental H₂ and D₂ adsorption properties on the well-bundled SWCNTs are compared with the simulated ones, revealing that pore-blocking and restricted diffusion of the molecules suppress the high selectivity of D₂ over H₂. The non-oxidized SG-SWCNT assembly shows the highest selectivity among the SWCNT samples, both at 40 and 77 K. The high selectivity of the SG-SWCNT assembly, which is pronounced even at 77 K, is ascribed to their unique assembly structure.

The adsorption/desorption processes of oxygen are investigated in nanoporous carbon (activated carbon fiber (ACF)) consisting of a disordered network of nanographene sheets. The heat-induced desorption at 200 °C shows the decomposition of oxygen-including functional groups weakly bonded to nanographene edges. The removal of these oxygen-including negatively charged functional groups brings about a change in the type of majority carriers, from holes to electrons, through charge transfer from the functional groups to the interior of nanographene sheets. The oxygen adsorption brings ACF back to the electronic state with holes being majority carriers. In this process, a large concentration of negatively charged O₂^{δ −} molecules with δ ∼ 0.1 are created through charge transfer from nanographene sheets to the adsorbed oxygen molecules. The changes in the thermoelectric power and the electrical resistance in the oxygen desorption process is steeper than that in the oxygen adsorption process. This suggests the irreversibility between the two processes.

Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powder at 1000 °C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet, while the sample prepared in 100% of Ar does not show such magnetism. The observed magnetism was unchanged over months in the ambient. The structure of this nanomaterial resembles the foam of a laundry detergent and transmission electron microscopy indicates a clear corrugated line contrast. On the other hand, a sample without strong magnetism does not give such an image contrast. The x-ray diffraction pattern coincides with that of graphite and no other peak is detected. Thermogravimetry indicates that all samples completely burn out up to approx.  820 °C and no material remains after combustion, indicating that the sample does not contain impurity metals. Magnetization is easily saturated by ∼ 10 000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon is explained by introducing a crystalline anisotropy which restricts the motion of the magnetic moment and stabilizes the remnant magnetization at zero magnetic field. Magnitudes of the saturation magnetization are in the range of 1–5  emu G g ^{− 1} at 4.2 K, which correspond to 0.002–0.01 Bohr magneton per carbon atom. This concentration may be increased by ten times or more, because only about 4–10% of particles have a magnetic domain in the present samples.

The recent discovery of magnetism in a variety of diverse non-magnetic materials containing defects has challenged conventional thinking about the microscopic origin of magnetism in general. Especially intriguing is the complete absence of d electrons that are traditionally associated with magnetism. By a systematic microscopic investigation of two completely dissimilar materials (namely, ZnO and rhombohedral-C₆₀ polymers) exhibiting ferromagnetism in the presence of defects, we show that this new phenomenon has a common origin and the mechanism responsible can be used as a powerful tool for inducing and tailoring magnetic features in systems which are not magnetic otherwise. Based on our findings, we propose a general recipe for developing ferromagnetism in new materials of great technological interest. The recipe is quite general, although its realization is system specific. In each case, the required basic step is to find two synergistic codopants, one for providing the unpaired electrons and the other for facilitating the ferromagnetic coupling.

We have investigated the structural and magnetic properties of two classes of spin S = 1/2 antiferromagnetic quasi-triangular lattice materials: Cu_{2(1 − x)}Zn_2x(OH)₃NO₃ (0 ≤ x ≤ 0.65) and its long chain organic derivatives Cu_{2(1 − x)}Zn_2x(OH)₃(C₇H₁₅COO)·mH₂O (0 ≤ x ≤ 0.29). The series of layered structure compounds constitute a substitutional magnetic system, in which spin S = 1/2Cu^{2 +} ions and nonmagnetic Zn^{2 +} ions are arranged on a two-dimensional quasi-triangular lattice. For the nitrate compounds we found that the substitution of Zn^{2 +} ions can continuously decrease the Néel temperature, T_N, but never completely remove the magnetic order. In addition, the frustration effect in these materials is suppressed by a three-dimensional interlayer interaction. On the other hand, the corresponding long chain alkyl carboxylic acid group of intercalated materials, Cu_{2(1 − x)}Zn_2x(OH)₃(C₇H₁₅COO)·mH₂O, show spin-glass-like behavior, which is caused by the interplay of geometric frustration and mixed sign interactions. A tentative explanation for these findings is proposed in terms of a cluster-glass picture.

We have studied the effect of low energy (30 keV) electron beam exposure on carbon nanotube field-effect transistors, using an electron beam lithography system to provide spatially controlled dosage. We show that reversible tuning of the transport behavior is possible when a backgate potential is applied during exposure. n-type behavior can be obtained by electron beam exposure of a device with positive gate bias, while ambipolar behavior can be obtained via negative gate bias. The observed transport behavior is relatively stable in time. We propose possible mechanisms for the observed phenomena and suggest directions for further research.

Here we report a new approach for producing clean and homogeneous boron-doped single-walled carbon nanotubes. This approach combines the homogeneous dispersion of B_nO_m ⁺ ionic molecules over the nanotube surfaces in a liquid solution, with a high temperature chemical reaction that incorporates the boron atoms into the sp² carbon network of the nanotube wall. A comparative study of sheet resistance versus optical transmission in nanotube network films with and without boron-doping is also presented. Although electron energy loss spectroscopy revealed very low B-doping levels (<1 at.%), the dc conductivity of doped samples was raised by a factor of 3.4. Changes in the free carrier contribution to the optical conductivity of single-walled carbon nanotube (SWCNT) films induced by boron-doping was also studied via optical transmission in the far-infrared (IR) (50–7000 cm ^{− 1}). A Drude model was fitted to the changes in the far-IR conductivity to quantify the additional free carrier concentration induced by the B-doping.

We have studied the intrinsic doping level and gate hysteresis of graphene-based field effect transistors (FETs) fabricated over Si/SiO₂ substrates. It was found that the high p-doping level of graphene in some as-prepared devices can be reversed by vacuum degassing at room temperature or above depending on the degree of hydrophobicity and/or hydration of the underlying SiO₂ substrate. Charge neutrality point (CNP) hysteresis, consisting of the shift of the charge neutrality point (or Dirac peak) upon reversal of the gate voltage sweep direction, was also greatly reduced upon vacuum degassing. However, another type of hysteresis, consisting of the change in the transconductance upon reversal of the gate voltage sweep direction, persists even after long-term vacuum annealing at 200 °C, when SiO₂ surface-bound water is expected to be desorbed. We propose a mechanism for this transconductance hysteresis that involves water-related defects, formed during the hydration of the near-surface silanol groups in the bulk SiO₂, that can act as electron traps.

We find that the electrical and thermal connectivity in multiwalled carbon nanotube buckypaper can be tuned using a spark plasma sintering (SPS) technique. Elevated SPS temperatures promote the formation of inter-tube connections and consequently impact the electrical resistivity, thermoelectric power and thermal conductivity of the buckypaper. In particular, the electrical resistivity as a function of SPS temperature exhibits a percolation-type behavior while the low temperature lattice thermal conductivity shows a crossover behavior in the sample dimensionality. The results are discussed in terms of the quasi-one-dimensional metallic nature of multiwalled carbon nanotubes, the packing density and the electron–phonon coupling.

We report the thermal conductivities of graphite nanoplatelet–epoxy composites prepared by exfoliation of natural graphite flakes of varying lateral sizes. We found that utilization of natural graphite flakes of the optimum lateral dimensions (∼200–400 µm) as a starting material for exfoliation significantly enhanced the thermal conductivity of the composite. In order to understand this enhancement we developed a procedure for evaluation of the particle size distribution of graphite nanoplatelets and correlated the measured distributions with the resulting thermal conductivities. In order to expand the scope of our study we applied our statistical and thermal analysis to commercially available graphite nanoplatelet materials.

We present results of a fluorescent quantum efficiency (Φ_F) study on the encapsulation of the near-infrared dye indocyanine green (ICG) in bioresorbable calcium phosphate nanoparticles (CPNPs). The Φ_F (described as the ratio of photons emitted to photons absorbed) provides a quantitative means of describing the fluorescence of an arbitrary molecule. However, standard quantum efficiency measurement techniques provide only the Φ_F of the smallest fluorescing unit—in the case of a nanoparticle suspension, the nanoparticle itself. This presents a problem in accurately describing the Φ_F of fluorophores embedded in an inorganic nanoparticle. Combining the incidence of scattering with an evaluation of the differences in local electric field and photochemical environment, we have developed a method to determine the Φ_F of the constituent fluorescent molecules embedded in such a nanoparticle, which provides a more meaningful comparison with the unencapsulated fluorophore. While applicable to generic systems, we present results obtained by our method for the ICG–CPNP in a phosphate buffered 0.15 M saline solution (PBS, pH 7.4)—specifically, Φ_{F, free dye} = 0.027 ± 0.001, Φ_{F, particle} = 0.053 ± 0.003, and for the individual encapsulated molecules, Φ_{F, molecule} = 0.066 ± 0.004. The method developed also provides insight into the influences of encapsulation and key parameters to engineer resonant enhancement effects from the emission of the encapsulated fluorophores corresponding to an eigenmode of the embedding particle for tailored optical properties.

Subwavelength optical imaging can be accomplished by scanning a nanoscale aperture or a nanoprobe containing a locally defined nanoscale optical source. Currently, most such methods, including various implementations of near-field scanning optical microscopy (NSOM), form near-field images by measuring the intensity of optical signals generated by optical transmission, scattering or fluorescence. Here we report the development of a nanoprobe that can extend NSOM functionalities by focusing on the dynamical aspects of light emission (such as fluorescence lifetime measurement) and nonlinear optical processes (such as second harmonic generation). Our nanoprobes consist of a silica fiber taper, a single nanowire or a nanotube, and appropriate functional nano-optical structures. The fabrication, characterization and potential applications of such nanoprobes are discussed.

Nitrogen-containing multiwalled nanotubes (N-MWCNTs), formed by CVD from a nitrogen-containing feedstock have a 'bamboo' structure in which the axes of the graphene planes are not parallel to the axis of the nanotube and the core is periodically bridged. We find that thermal and chemical treatment of these materials can produce nanotubes that have been cut longitudinally in either a linear or in a spiral manner. In addition, these longitudinally cut nanotubes can be partially or fully unrolled by sonication in an aqueous surfactant, producing graphite platelets as well as narrow structures that could be thin graphite ribbons or very narrow, intact N-MWCNTs. These different morphologies of graphite, available from one source, suggest that there are multiple structures of N-MWCNTs present, few as simple as stacked cups or nested scrolls.

We use ab initio density functional calculations to study the stability, elastic properties and electronic structure of sp² carbon minimal surfaces with negative Gaussian curvature, called schwarzites. We focus on two systems with cubic unit cells containing 152 and 200 carbon atoms, which are metallic and very rigid. The porous schwarzite structure allows for efficient and reversible doping by electron donors and acceptors, making it a promising candidate for the next generation of alkali ion batteries. We identify schwarzite structures that act as arrays of interconnected spin quantum dots or become magnetic when doped. We introduce two interpenetrating schwarzite structures that may find their use as the ultimate super-capacitor.

The effects of processing conditions and apparent nanotube length on properties are investigated for carbon nanotube yarns obtained by solid-state drawing of an aerogel from a forest of multi-walled carbon nanotubes. Investigation of twist, false twist, liquid densification and combination methods for converting the drawn aerogel into dense yarn show that permanent twist is not needed for obtaining useful mechanical properties when nanotube lengths are long compared with nanotube diameters. Average mechanical strengths of 800 MPa were obtained for polymer-free twist-spun multi-walled carbon nanotube (MWNT) yarns and average mechanical strengths of 1040 MPa were obtained for MWNT yarns infiltrated with 10 wt% polystyrene solution. Strategies for increasing the mechanical properties are suggested based on analysis of intra-wall, intra-bundle and inter-bundle stress transfer.

Surface composition plays an important role in carbon nanotube dispersibility in different environments. Indeed, it determines the choice of dispersion medium. In this paper the effect of oxidation on the dispersion of HiPCO single-walled carbon nanotubes (SWNTs) in N-methyl-pyrrolidinone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), N-dodecyl-pyrrolidinone (N12P) and cyclohexyl-pyrrolidinone (CHP) was systematically studied. During the oxidation process, similar amounts of carboxylic acid and phenolic groups were introduced to mostly already existing defects. For each solvent the dispersion limits and the absorption coefficients were estimated by optical absorption analysis over a range of SWNT concentrations. The presence of acid oxygenated groups increased SWNT dispersibility in NMP, DMF and DMA, but decreased in N12P and CHP. The absorption coefficients, however, decreased for all solvents after oxidation, reflecting the weakening of the effective transition dipole of the π–π transition with even limited extension functionalization and solvent interaction. The analysis of the results in terms of Hansen and Flory–Huggins solubility parameters evidenced the influence of dipolar interactions and hydrogen bonding on the dispersibility of oxidized SWNTs.

The adsorption of oxygen and hydrogen (deuterium) on small neutral palladium clusters was investigated in a cluster beam experiment. The beam passes through two low-pressure reaction cells, and the clusters, with and without adsorbed molecules, are detected using laser ionization and mass spectrometry. Both H₂ and O₂ adsorb efficiently on the palladium clusters with only moderate variations with cluster size in the investigated range, i.e. between 8 and 28 atoms. The co-adsorption of H₂ and O₂ results in the formation of H₂O, detected as a decrease in the number of adsorbed oxygen atoms with an increasing number of collisions with H₂ molecules. A comparison is done with an earlier similar study of clusters of Pt. Furthermore a comparison is done with what is known for sticking and reactivity of surfaces.

We have studied how the hysteretic voltage-induced torsional strain, associated with charge-density-wave (CDW) depinning, in orthorhombic tantalum trisulfide depends on square-wave and triangle-wave voltages of different frequencies and amplitudes. The strains are measured by placing the sample, with a wire glued to the center as a transducer, in a radio frequency cavity and measuring the modulated response of the cavity. From the triangle waves, we map out the time dependence of the hysteresis loops, and find that the hysteresis loops broaden for waves with periods less than 30 s. The square-wave response shows that the dynamic responses to positive and negative voltages can be quite different. The overall frequency dependence is relaxational, but with multiple relaxation times which typically decrease with increasing voltage. The detailed dynamic response is very sample dependent, suggesting that it depends in detail on interactions of the CDW with sample defects.