@article{narayan_bhaumik_gupta_joshi_riley_narayan_2021, title={Formation of self-organized nano- and micro-diamond rings}, volume={9}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2021.1907627}, abstractNote={We report formation of self-organized nanodiamond ring structures due to dynamical heterogeneity in super undercooled carbon, created by nanosecond laser melting of amorphous carbon layers. We envisage that diamond tetrahedra self-organize and lead to formation of string and ring structures on which nanodiamonds nucleate and grow. Denser ring structures are formed in Q-carbon due to higher undercooling and enhanced diamond nucleation. The average size is larger under heterogeneous nucleation compared to homogeneous nucleation due to lower critical size and free energy, allowing more time for growth. With nanosecond laser melting, growth velocities range 5–10 ms−1 and even higher for Q-carbon. GRAPHICAL ABSTRACT IMPACT STATEMENT Significant advancement in the creation of self-organized nanodiamond ring and string structures by laser processing at ambient pressure and temperature}, number={7}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, J. and Bhaumik, A. and Gupta, S. and Joshi, P. and Riley, P. and Narayan, R. J.}, year={2021}, month={Mar}, pages={300–307} }
 @article{narayan_bhaumik_gupta_joshi_riley_narayan_2021, title={Role of Q-carbon in nucleation and formation of continuous diamond film}, volume={176}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2021.02.049}, abstractNote={Formation of continuous and adherent diamond films on practical substrates presents a formidable challenge due to lack of diamond nucleation sites needed for diamond growth. This problem has been solved through the formation of interfacial Q-carbon layers by nanosecond laser melting of carbon layers in a highly undercooled state and subsequent quenching. The Q-carbon layer provides ready nucleation sites for epitaxial films on planar matching substrates such as sapphire, and polycrystalline films on amorphous substrates such as glass. Each laser pulse converts about a one-cm-square area, which can be repeated with a 100–200 Hz laser to produce potentially 100–200 cm2s-1 of diamond films. This is essentially a low-temperature processing, where substrate stays close to ambient temperature, because the total heat input is quite small. The Q-carbon layer is also responsible for improved adhesion of diamond films on sapphire and glass substrates. It is also argued that the formation of Q-carbon layer is also responsible for efficient diamond nucleation during negatively biased MPCVD diamond depositions.}, journal={CARBON}, author={Narayan, J. and Bhaumik, A. and Gupta, S. and Joshi, P. and Riley, P. and Narayan, R. J.}, year={2021}, month={May}, pages={558–568} }
 @article{sachan_bhaumik_pant_prater_narayan_2019, title={Diamond film growth by HFCVD on Q-carbon seeded substrate}, volume={141}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2018.09.058}, abstractNote={While hot-filament assisted chemical vapor deposition (HFCVD) is a well-established technique to synthesize diamond thin films using microdiamond seeds, the quality of grown diamond thin films is often compromised due to the presence of contaminants, i.e. graphitic entities and the eroded tungsten filament remnants, at the film-substrate interface. Here, we present a novel approach to form high-quality, contamination-free diamond thin films with HFCVD using Q-carbon precursor. The Q-carbon is a metastable phase which is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the superundercooled state and consists of ∼75% sp3 and rest sp2 hybridized carbon. Using Q-carbon seeds in HFCVD, we demonstrate the growth of polycrystalline diamond film with a clean interface without any tungsten filament impurities. With large-area vibrational Raman mode analysis, we also observe a significant reduction in the presence of overall graphitic entities in the diamond film. With the realization of such a high-quality interface, we present a pathway to fabricate significantly improved diamond coatings and solid-state devices.}, journal={CARBON}, author={Sachan, Ritesh and Bhaumik, Anagh and Pant, Punam and Prater, John and Narayan, Jagdish}, year={2019}, month={Jan}, pages={182–189} }
 @article{bhaumik_narayan_2019, title={Direct conversion of carbon nanofibers into diamond nanofibers using nanosecond pulsed laser annealing}, volume={21}, ISSN={["1463-9084"]}, DOI={10.1039/c9cp00063a}, abstractNote={Here, we show the direct conversion of carbon nanofibers (CNFs) into diamond nanofibers (DNFs) by irradiating CNFs with an ArF nanosecond laser at room temperature and atmospheric pressure. The nanosecond laser pulses melt the tips of CNFs into a highly undercooled state, and their subsequent quenching results in the formation of DNFs. This formation of DNFs is dependent on the degree of undercooling which is controlled by nanosecond laser energy density and one-dimensional heat flow characteristics in CNFs. The conversion process starts at the top and extends with the number of pulses. Therefore, our highly non-equilibrium nanosecond laser processing opens a new avenue for the synthesis of exciting pure and doped diamond structures at ambient temperatures and pressures for a variety of applications.}, number={13}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, month={Apr}, pages={7208–7219} }
 @article{bhaumik_narayan_2019, title={Formation and characterization of nano- and microstructures of twinned cubic boron nitride}, volume={21}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/C8CP04592E}, DOI={10.1039/c8cp04592e}, abstractNote={Nano- and microstructures of phase-pure cubic boron nitride (c-BN) are synthesized by employing nanosecond pulsed-laser annealing techniques at room temperature and atmospheric pressure. In a highly non-equilibrium synthesis process, nanocrystalline h-BN is directly converted into phase-pure twinned c-BN from a highly undercooled melt state of BN. By changing nucleation and growth rates, we have synthesized a wide range of sizes (90 nm to 25 μm) of c-BN. The electron diffraction patterns show the formation of twinned c-BN with [11[combining macron]1] as the twin axis. The twinning density in c-BN can be controlled by the degree of undercooling and quenching rates. The formation of twins predominantly occurs prior to the formation of amorphous quenched BN (Q-BN). Therefore, the defect density in nano c-BN formed under higher undercooling conditions is considerably larger than that in micro c-BN, which is formed under lower undercooling conditions. The temperature-dependent Raman studies show a considerable blue-shift of ∼6 cm-1 with a decrease in temperature from 300 to 78 K in nano c-BN as compared to micro c-BN. The size-effects of c-BN crystals in Raman spectra are modeled using spatial correlation theory, which can be used to calculate the correlation length and twin density in c-BN. It has also been found that the Raman blue-shift in nano c-BN is caused by anharmonic effects, and the decrease in Raman linewidth with decreasing temperature (300 to 78 K) is caused by three- and four-phonon decay processes. The bonding characteristics and crystalline nature of the synthesized c-BN are also demonstrated by using electron energy-loss spectroscopy and electron backscatter diffraction, respectively. We envisage that the controlled growth of phase-pure nano and microstructures of twinned c-BN and their temperature-dependent Raman-active vibrational mode studies will have a tremendous impact on low-temperature solid-state electrical and mechanical devices.}, number={4}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, pages={1700–1710} }
 @article{bhaumik_narayan_2019, title={Nano-to-micro diamond formation by nanosecond pulsed laser annealing}, volume={126}, ISSN={["1089-7550"]}, DOI={10.1063/1.5118890}, abstractNote={Here, we report the synthesis and characterization of nano-, micro-, twinned, and lonsdaleite diamonds, which are formed after melting and quenching of amorphous carbon or Q-carbon essentially at room temperature and atmospheric pressure. These conversions depend on the degree of undercooling, which is controlled by the laser parameters and thermal conductivities of the amorphous carbon and the substrate. The laser melting and undercooling provide liquid-phase packing of atoms similar to high-pressure, which facilitate the conversion of amorphous carbon into diamond or Q-carbon without using any catalyst. By changing the nucleation and growth rates, we have synthesized a wide range of sizes (4 nm to 3 μm) of diamond crystals. The formation of twinned and lonsdaleite diamonds is controlled by the quenching rate. Therefore, we have created a “factory of diamonds” at ambient conditions by nanosecond laser annealing, which will pave the pathway to design high-speed mechanical and electrical devices.Here, we report the synthesis and characterization of nano-, micro-, twinned, and lonsdaleite diamonds, which are formed after melting and quenching of amorphous carbon or Q-carbon essentially at room temperature and atmospheric pressure. These conversions depend on the degree of undercooling, which is controlled by the laser parameters and thermal conductivities of the amorphous carbon and the substrate. The laser melting and undercooling provide liquid-phase packing of atoms similar to high-pressure, which facilitate the conversion of amorphous carbon into diamond or Q-carbon without using any catalyst. By changing the nucleation and growth rates, we have synthesized a wide range of sizes (4 nm to 3 μm) of diamond crystals. The formation of twinned and lonsdaleite diamonds is controlled by the quenching rate. Therefore, we have created a “factory of diamonds” at ambient conditions by nanosecond laser annealing, which will pave the pathway to design high-speed mechanical and electrical devices.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, month={Sep} }
 @article{narayan_bhaumik_hague_2019, title={Pseudo-topotactic growth of diamond nanofibers}, volume={178}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2019.08.008}, abstractNote={We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure <110> nanodiamonds along the growth directions. Subsequent laser pluses melt regions below <110> nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of <110> nanodiamond fibers can be increased, as each pulse results in ∼50 nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of <110> nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C–C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp3 bonding (σ∗), and absence of 284 eV peak for sp2 (π∗) graphitic bonding. The characteristic diamond Raman peak at 1332 cm−1 is found to downshift to 1321 cm−1 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.}, journal={ACTA MATERIALIA}, author={Narayan, J. and Bhaumik, A. and Hague, A.}, year={2019}, month={Oct}, pages={179–185} }
 @article{narayan_sachan_bhaumik_2019, title={Search for near room-temperature superconductivity in B-doped Q-carbon}, volume={7}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2019.1569566}, abstractNote={ABSTRACT We present 1D, 2D and 3D structures of boron-doped Q-carbon with a higher superconducting transition temperature than the current value of 55 K in 25 at% B-doped amorphous Q-carbon. The higher transition temperature is predicted for 1D and 2D crystalline structures with increasing density of states near the Fermi level through dopant trapping in substitutional sites. We have synthesized 50at% B-doped Q-carbon where diamond tetrahedra are arranged randomly and packed with over 80% efficiency to generate an amorphous structure. Detailed EELS measurements show higher density of states near the Fermi level above 90 K and preliminary transport data show signature of Tc above 100 K. GRAPHICAL ABSTRACT IMPACT STATEMENT Novel 1D, 2D and 3D structures of boron-doped Q-carbon with higher Tc than current BCS record of 55K by increasing B-concentration and the density of states near the Fermi level.}, number={4}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, J. and Sachan, R. and Bhaumik, A.}, year={2019}, pages={164–172} }
 @article{bhaumik_narayan_2019, title={Structure–property correlations in phase-pure B-doped Q-carbon high-temperature superconductor with a record Tc = 55 K}, volume={11}, ISSN={2040-3364 2040-3372}, url={http://dx.doi.org/10.1039/C9NR00562E}, DOI={10.1039/c9nr00562e}, abstractNote={Here, we report the detailed structure-property correlations in phase-pure B-doped Q-carbon high-temperature superconductor having a superconducting transition temperature (Tc) of 55 K. This superconducting phase is a result of nanosecond laser melting and subsequent quenching of a highly super undercooled state of molten B-doped C. The temperature-dependent resistivity in different magnetic fields and magnetic susceptibility measurements indicate a type-II Bardeen-Cooper-Schrieffer superconductivity in B-doped Q-carbon thin films. The magnetic measurements indicate that the upper and lower critical fields follow Hc2(0)[1 - (T/Tc)1.77] and Hc1(0)[1 - (T/Tc)1.19] temperature dependence, respectively. The structure-property characterization of B-doped Q-carbon indicates a high density of electronic states near the Fermi-level and large electron-phonon coupling. These factors are responsible for s-wave bulk type superconductivity with enhanced Tc in B-doped Q-carbon. The time-dependent magnetic moment measurements indicate that B-doped Q-carbon thin films follow the Anderson-Kim logarithmic decay model having high values of pinning potential at low temperatures. The crossover from the two-dimensional to the three-dimensional nature of Cooper pair transport at T/Tc = 1.02 also indicates a high value of electron-phonon coupling which is also calculated using the McMillan formula. The superconducting region in B-doped Q-carbon is enclosed by Tc = 55.0 K, Jc = 5.0 × 108 A cm-2, and Hc2 = 9.75 T superconducting parameters. The high values of critical current density and pinning potential also indicate that B-doped Q-carbon can be used for persistent mode of operation in MRI and NMR applications. The Cooper pairs which are responsible for the high-temperature superconductivity are formed when B exists in the sp3 sites of C. The electron energy loss spectroscopy and Raman spectroscopy indicate a 75% sp3 bonded C and 70% sp3 bonded B in the superconducting phase of B-doped Q-carbon which has 27 at% B and rest C. The dimensional fluctuation and magnetic relaxation measurements in B-doped Q-carbon indicate its practical applications in frictionless motors and high-speed electronics. This discovery of high-temperature superconductivity in strongly-bonded and light-weight materials using non-equilibrium synthesis will provide the pathway to achieve room-temperature superconductivity.}, number={18}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, pages={9141–9154} }
 @article{bhaumik_sachan_narayan_2019, title={Tunable charge states of nitrogen-vacancy centers in diamond for ultrafast quantum devices}, volume={142}, ISSN={0008-6223}, url={http://dx.doi.org/10.1016/J.CARBON.2018.10.084}, DOI={10.1016/j.carbon.2018.10.084}, abstractNote={A prerequisite condition for next-generation quantum sensing, communication, and computing is the precise modulation of the charge states of nitrogen-vacancy (NV) centers in diamond. We have achieved tuning of these centers in highly concentrated NV-diamonds using photons, phonons, and electrons. These NV-diamonds are synthesized employing a unique nanosecond laser processing technique which results in ultrafast melting and subsequent quenching of nitrogen-doped molten carbon films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can exceed thermodynamic solubility limits through solute trapping. This ultrafast synthesis technique generates fewer surface traps thereby forming ∼75% NV− centers at room-temperature, which are optically and magnetically distinct as compared to NV0 centers. We dramatically increase the NV− concentration in NV-diamonds by ∼53% with decreasing temperature from 300 to 80 K. With negative electrical biasing, the Fermi level in NV-diamond rises and crosses the NV0/- level, thereby promoting an exponential conversion of NV0 to NV− centers. We have also photonically enhanced the photoluminescence signal from NV− centers, thereby ascertaining the conversion of NV0 into NV− via absorption of electrons (excited by 532 nm photons) from the valence band in NV-diamond. These NV-centers in diamonds also reveal large excitation lifetime, which ultimately leads to ∼65% quantum efficiency at room-temperature. With these results, we believe that the precise tuning of charge states in these uniquely prepared highly concentrated NV-diamonds will lead to superior quantum devices.}, journal={Carbon}, publisher={Elsevier BV}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2019}, month={Feb}, pages={662–672} }
 @article{bhaumik_narayan_2018, title={Electrochromic effect in Q-carbon}, volume={112}, number={22}, journal={Applied Physics Letters}, author={Bhaumik, A. and Narayan, J.}, year={2018} }
 @article{gupta_sachan_bhaumik_narayan_2018, title={Enhanced mechanical properties of Q-carbon nanocomposites by nanosecond pulsed laser annealing}, volume={29}, ISSN={["1361-6528"]}, url={https://doi.org/10.1088/1361-6528/aadd75}, DOI={10.1088/1361-6528/aadd75}, abstractNote={Q-carbon is a metastable phase of carbon formed by melting and subsequently quenching amorphous carbon films by a nanosecond laser in a super undercooled state. As Q-carbon is a material harder than diamond, it makes an excellent reinforcing component inside the softer matrix of a composite coating. In this report, we present a single-step strategy to fabricate adherent coatings of hard and lubricating Q-carbon nanocomposites. These nanocomposites consist of densely-packed sp3-rich Q-carbon (82% sp3), and sp2-rich α-carbon (40% sp3) amorphous phases. The nanoindentation tests show that the Q-carbon nanocomposites exhibit a hardness of 67 GPa (Young’s modulus ∼ 840 GPa) in contrast to the soft α-carbon (hardness ∼ 18 GPa). The high hardness of Q-carbon nanocomposites results in 0.16 energy dispersion coefficient, in comparison with 0.74 for α-carbon. The soft α-carbon phase provides lubrication, resulting in low friction and wear coefficients of 0.09 and 1 × 10−6, respectively, against the diamond tip. The nanoscale dispersion of hard Q-carbon and soft α-carbon phases in the Q-carbon nanocomposites enhances the toughness of the coatings. We present detailed structure-property correlations to understand enhancement in the mechanical properties of Q-carbon nanocomposites. This work provides insights into the characteristics of Q-carbon nanocomposites and advances carbon-based superhard materials for longer lasting protective coatings and related applications.}, number={45}, journal={NANOTECHNOLOGY}, publisher={IOP Publishing}, author={Gupta, Siddharth and Sachan, Ritesh and Bhaumik, Anagh and Narayan, Jagdish}, year={2018}, month={Nov} }
 @article{narayan_bhaumik_sachan_2018, title={High temperature superconductivity in distinct phases of amorphous B-doped Q-carbon}, volume={123}, number={13}, journal={Journal of Applied Physics}, author={Narayan, J. and Bhaumik, A. and Sachan, R.}, year={2018} }
 @article{bhaumik_sachan_narayan_2018, title={Magnetic relaxation and three-dimensional critical fluctuations in B-doped Q-carbon - a high-temperature superconductor}, volume={10}, ISSN={["2040-3372"]}, DOI={10.1039/c8nr03406k}, abstractNote={Three-dimensional critical fluctuations and Anderson–Kim logarithmic magnetic relaxations in B-doped Q-carbon high-temperature superconductor will lead to multifunctional high-speed electronic devices.}, number={26}, journal={NANOSCALE}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2018}, month={Jul}, pages={12665–12673} }
 @article{narayan_bhaumik_gupta_haque_sachan_2018, title={Progress in Q-carbon and related materials with extraordinary properties}, volume={6}, ISSN={["2166-3831"]}, url={https://doi.org/10.1080/21663831.2018.1458753}, DOI={10.1080/21663831.2018.1458753}, abstractNote={ABSTRACT This paper summarizes our research related to Q-carbon and Q-BN and direct conversion of carbon into diamond and h-BN into c-BN. Synthesis and processing of these materials are accomplished by nanosecond laser melting and subsequent quenching of amorphous carbon and nanocrystalline h-BN. Depending upon the degree of undercooling, molten carbon (or h-BN) can be converted into Q-carbon (or Q-BN) or diamond (or c-BN). The primary focus here is on the outstanding properties of these materials, including hardness greater than diamond, ferromagnetism, p- and n-type doping, NV nanodiamonds, high-temperature superconductivity in B-doped Q-carbon, enhanced field emission, superhard composite coatings, and future applications. IMPACT STATEMENT This research represents a fundamental breakthrough in the direct conversion of carbon into diamond at ambient temperatures and pressures in the air and their extraordinary properties. GRAPHICAL ABSTRACT}, number={7}, journal={MATERIALS RESEARCH LETTERS}, publisher={Taylor & Francis}, author={Narayan, Jagdish and Bhaumik, Anagh and Gupta, Siddharth and Haque, Ariful and Sachan, Ritesh}, year={2018}, pages={353–364} }
 @article{narayan_gupta_bhaumik_sachan_cellini_riedo_2018, title={Q-carbon harder than diamond}, volume={8}, ISSN={["2159-6867"]}, url={https://doi.org/10.1557/mrc.2018.35}, DOI={10.1557/mrc.2018.35}, abstractNote={A new phase of carbon named Q-carbon is found to be over 40% harder than diamond. This phase is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the super-undercooled state. Closely packed atoms in molten metallic carbon are quenched into Q-carbon with 80-85% sp ^3 and the rest sp ^2. The number density of atoms in Q-carbon can vary from 40% to 60% higher than diamond cubic lattice, as the tetrahedra packing efficiency increases from 70% to 80%. Using this semiempirical approach, the corresponding increase in Q-carbon hardness is estimated to vary from 48% to 70% compared to diamond.}, number={2}, journal={MRS COMMUNICATIONS}, publisher={Cambridge University Press (CUP)}, author={Narayan, Jagdish and Gupta, Siddharth and Bhaumik, Anagh and Sachan, Ritesh and Cellini, Filippo and Riedo, Elisa}, year={2018}, month={Jun}, pages={428–436} }
 @article{gupta_sachan_bhaumik_pant_narayan_2018, title={Undercooling driven growth of Q-carbon, diamond, and graphite}, volume={8}, ISSN={["2159-6867"]}, url={https://doi.org/10.1557/mrc.2018.76}, DOI={10.1557/mrc.2018.76}, abstractNote={We provide insights pertaining the dependence of undercooling in the formation of graphite, nanodiamonds, and Q-carbon nanocomposites by nanosecond laser melting of diamond-like carbon (DLC). The DLC films are melted rapidly in a super-undercooled state and subsequently quenched to room temperature. Substrates exhibiting different thermal properties-silicon and sapphire, are used to demonstrate that substrates with lower thermal conductivity trap heat flow, inducing larger undercooling, both experimentally and theoretically via finite element simulations. The increased undercooling facilitates the formation of Q-carbon. The Q-carbon is used as nucleation seeds for diamond growth via laser remelting and hot-filament chemical vapor deposition.}, number={2}, journal={MRS COMMUNICATIONS}, publisher={Cambridge University Press (CUP)}, author={Gupta, Siddharth and Sachan, Ritesh and Bhaumik, Anagh and Pant, Punam and Narayan, Jagdish}, year={2018}, month={Jun}, pages={533–540} }
 @article{bhaumik_sachan_narayan_2017, title={A novel high-temperature carbon-based superconductor: B-doped Q-carbon}, volume={122}, number={4}, journal={Journal of Applied Physics}, author={Bhaumik, A. and Sachan, R. and Narayan, J.}, year={2017} }
 @article{bhaumik_narayan_2017, title={Conversion of p to n-type reduced graphene oxide by laser annealing at room temperature and pressure}, volume={121}, number={12}, journal={Journal of Applied Physics}, author={Bhaumik, A. and Narayan, J.}, year={2017} }
 @article{bhaumik_sachan_gupta_narayan_2017, title={Discovery of High-Temperature Superconductivity (T-c=55 K) in B-Doped Q-Carbon}, volume={11}, ISSN={["1936-086X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85040089020&partnerID=MN8TOARS}, DOI={10.1021/acsnano.7b06888}, abstractNote={We have achieved a superconducting transition temperature (Tc) of 55 K in 27 at% B-doped Q-carbon. This value represents a significant improvement over previously reported Tc of 36 K in B-doped Q-carbon and is the highest Tc for conventional BCS (Bardeen-Cooper-Schrieffer) superconductivity in bulk carbon-based materials. The B-doped Q-carbon exhibits type-II superconducting characteristics with Hc2(0) ∼ 10.4 T, consistent with the BCS formalism. The B-doped Q-carbon is formed by nanosecond laser melting of B/C multilayered films in a super undercooled state and subsequent quenching. It is determined that ∼67% of the total boron exists with carbon in a sp3 hybridized state, which is responsible for the substantially enhanced Tc. Through the study of the vibrational modes, we deduce that higher density of states near the Fermi level and moderate to strong electron-phonon coupling lead to a high Tc of 55 K. With these results, we establish that heavy B doping in Q-carbon is the pathway for achieving high-temperature superconductivity.}, number={12}, journal={ACS NANO}, author={Bhaumik, Anagh and Sachan, Ritesh and Gupta, Siddharth and Narayan, Jagdish}, year={2017}, month={Dec}, pages={11915–11922} }
 @article{narayan_bhaumik_2017, title={Fundamental Discovery of Q-Phases and Direct Conversion of Carbon into Diamond and h-BN into c-BN}, ISBN={["978-3-319-51096-5"]}, ISSN={["2367-1181"]}, DOI={10.1007/978-3-319-51097-2_17}, abstractNote={This article reviews the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and addresses critical issues related to direct conversion of carbon into diamond and h-BN into c-BN at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon and Q-BN are formed as a result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon, and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled (4000 K) carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles and thin films are formed. The large-area epitaxial diamond and c-BN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid state. Scale-up processing of diamond, c-BN and diamond/c-BN heterostructures and related nanostructures such as nanodots, microdots, nanoneedles, microneedles and large-area single-crystal thin films will have tremendous impact on applications ranging from abrasive and tool coatings to high-power devices and myriad of biomedical applications.}, journal={MECHANICAL AND CREEP BEHAVIOR OF ADVANCED MATERIALS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2017}, pages={219–228} }
 @article{bhaumik_sachan_narayan_2017, title={High-Temperature Superconductivity in Boron-Doped Q-Carbon}, volume={11}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.7b01294}, abstractNote={We report high-temperature superconductivity in B-doped amorphous quenched carbon (Q-carbon). This phase is formed after nanosecond laser melting of B-doped amorphous carbon films in a super-undercooled state and followed by rapid quenching. Magnetic susceptibility measurements show the characteristics of type-II Bardeen-Cooper-Schrieffer superconductivity with a superconducting transition temperature (Tc) of 36.0 ± 0.5 K for 17.0 ± 1.0 atom % boron concentration. This value is significantly higher than the best experimentally reported Tc of 11 K for crystalline B-doped diamond. We argue that the quenching from metallic carbon liquid leads to a stronger electron-phonon coupling due to close packing of carbon atoms with higher density of states at the Fermi level. With these results, we propose that the non-equilibrium undercooling-assisted synthesis method can be used to fabricate highly doped materials that provide greatly enhanced superconducting properties.}, number={6}, journal={ACS NANO}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2017}, month={Jun}, pages={5351–5357} }
 @article{narayan_bhaumik_2017, title={Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures}, volume={5}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2016.1249805}, abstractNote={ABSTRACT We report a novel method for synthesis and processing of pure and nitrogen-vacancy (NV)-doped nanodiamonds with sharp NV0 and NV− transitions at ambient temperatures and pressures in air. Carbon films are melted by nanosecond lasers in super undercooled state and quenched rapidly. We can form single-crystal nanodiamonds, microdiamonds, nanoneedles and microneedles, and large-area films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can far exceed thermodynamic solubility limits through solute trapping. These nanodiamonds can be placed deterministically and the transitions between NV− and NV0 can be controlled electrically and optically by laser illumination. GRAPHICAL ABSTRACT IMPACT STATEMENT This research represents a fundamental breakthrough in controlled synthesis of nanodiamonds and doping of diamond with NV centers in nanostructures needed for quantum devices operating at room temperature.}, number={4}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2017}, pages={242–250} }
 @article{narayan_bhaumik_xu_2016, title={Direct conversion of h-BN into c-BN and formation of epitaxial c-BN/diamond heterostructures}, volume={119}, number={18}, journal={Journal of Applied Physics}, author={Narayan, J. and Bhaumik, A. and Xu, W. Z.}, year={2016} }
 @article{narayan_bhaumik_2016, title={Discovery of Q-BN and Direct Conversion of h-BN into c-BN and Formation of Epitaxial cBN/Diamond Heterostructures}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.472}, abstractNote={We review the discovery of a new phase BN (named Q-BN) which has been created by nanosecond laser melting in the super undercooled state and quenching rapidly with rates exceeding several billion degrees per second. This phase, sequel to our earlier discovery of Q-Carbon, has amorphous structure from which phase-pure c-BN is formed in the form of nanodots, microcrystals, nanoneedles, and microneedles. Large-area single c-BN are formed by providing a template for epitaxial growth during quenching of super undercooled liquid BN. Since there is a rapid crystal growth from liquid, both n- and p-type dopants can be incorporated into electrically active substitutional sites with concentrations exceeding solubility limits through the phenomenon of solute trapping. We have grown diamond on c-BN by pulsed laser deposition of carbon at 500°C without the presence of hydrogen, and created c-BN and diamond epitaxial composites. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon. This discovery on direct conversion of h-BN into phase-pure c-BN at ambient temperatures and pressures in air, represents a seminal contribution to the field of boron nitride, which is quite complementary to our discovery of graphite to diamond conversion. We have bypassed thermodynamics with the help of kinetics and time control. This research represents a major breakthrough for c-BN and diamond based high-power electronic and photonic devices, and host of other applications related to high-speed machining, deep-sea drilling, field-emission displays and biomedical applications.}, number={37}, journal={MRS ADVANCES}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, pages={2573–2584} }
 @article{narayan_bhaumik_narayan_2016, title={Discovery of Q-phases and direct conversion of carbon into diamond and h-BN into c-BN}, volume={174}, number={3}, journal={Advanced Materials & Processes}, author={Narayan, J. and Bhaumik, A. and Narayan, R.}, year={2016}, pages={24–28} }
 @article{narayan_bhaumik_2016, title={Fundamental discovery of new phases and direct conversion of carbon into diamond and hBN into cBN and properties (retraction of vol 47, pg 1481, 2016)}, volume={47A}, number={8}, journal={Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, author={Narayan, J. and Bhaumik, A.}, year={2016}, pages={4351–4351} }
 @article{narayan_bhaumik_2016, title={Q-carbon discovery and formation of single-crystal diamond nano- and microneedles and thin films}, volume={4}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2015.1126865}, abstractNote={We report the formation of single-crystal diamond nanoneedles, microneedles and thin films on sapphire (0001). By using nanosecond excimer laser pulses, we convert amorphous carbon into a new state of Q-carbon by rapid melting and quenching. The Q-carbon consists of amorphous mostly sp3 bonded carbon and rest 10–15% sp2, from which diamonds are nucleated. These nanodiamond nuclei in Q-carbon provide a seed for growth of diamond. These nanoneedles and microneedles are found to be single crystals often oriented along ⟨110⟩ directions. The (111) single-crystal diamond film are formed, when sapphire (0001) provides a seed for diamond growth from super undercooled liquid. GRAPHICAL ABSTRACT}, number={2}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, pages={118–126} }
 @article{narayan_bhaumik_2016, title={Research update: Direct conversion of h-BN into pure c-BN at ambient temperatures and pressures in air}, volume={4}, number={2}, journal={APL Materials}, author={Narayan, J. and Bhaumik, A.}, year={2016} }
 @article{bhaumik_narayan_2016, title={Wafer scale integration of reduced graphene oxide by novel laser processing at room temperature in air}, volume={120}, number={10}, journal={Journal of Applied Physics}, author={Bhaumik, A. and Narayan, J.}, year={2016} }
 @article{narayan_bhaumik_2015, title={Novel phase of carbon, ferromagnetism, and conversion into diamond}, volume={118}, number={21}, journal={Journal of Applied Physics}, author={Narayan, J. and Bhaumik, A.}, year={2015} }
 @article{narayan_bhaumik_2015, title={Research update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air}, volume={3}, number={10}, journal={APL Materials}, author={Narayan, J. and Bhaumik, A.}, year={2015} }
 @article{narayan_bhaumik, title={Fundamental discovery of new phases and direct conversion of carbon into diamond and hBN into cBN and properties}, volume={47A}, number={4}, journal={Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, author={Narayan, J. and Bhaumik, A.}, pages={1481–1498} }