Dynamic friction behavior of ultrananocrystalline diamond films: A depth-resolved chemical phase analysis

Panda, Kalpataru,Rani, Revati,Kumar, Niranjan,Sankaran, Kamatchi Jothiramalingam,Park, Jeong Young,Ganesan, K.,Lin, I-Nan Elsevier 2019 Ceramics international Vol.45 No.17

<P><B>Abstract</B></P> <P>Investigation of dynamic changes in friction behavior of ultrananocrystalline diamond (UNCD) films is a complex mainly because of the rapid change in chemical composition at the sliding interfaces. To address this issue, for the first time, we report chemical phase analysis of transferfilm using the depth-resolved X-ray photoelectron spectroscopy (XPS) technique. The friction coefficient of the UNCD films was high during the initial run-in regime, but it gradually decreased to an ultralow value after longer sliding cycles at the ambient atmospheric tribo-condition. Depth-resolved XPS analysis showed a higher sp<SUP>3</SUP>/sp<SUP>2</SUP> carbon ratio during the initial run-in regime. This ratio decreased with increasing sliding cycles and consequently the friction coefficient decreased. However, a higher value of the friction coefficient throughout the run-in regime persisted at the high-vacuum tribo-condition. In this case, the sp<SUP>3</SUP>/sp<SUP>2</SUP> carbon ratio inside the transferfilm was quite high and no considerable changes were observed in the depth-resolved XPS analysis. This investigation confirmed that the dynamic friction behavior in UNCD films was manipulated by the sp<SUP>3</SUP>/sp<SUP>2</SUP> carbon ratio inside the transferfilm which showed tribo-atmospheric dependence.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced tribo-chemical properties of oxygen functionalized mechanically exfoliated hexagonal boron nitride nanolubricant additives

Sahu, Jayakrushna,Panda, Kalpataru,Gupta, Bhavana,Kumar, Niranjan,Manojkumar, P.A.,Kamruddin, M. Elsevier 2018 Materials chemistry and physics Vol.207 No.-

<P><B>Abstract</B></P> <P>Two dimensional (2D) materials with layered lattice structure as nanofluid additives are useful to improve the tribological properties of metallic sliding interfaces. To enhance the tribological efficiency, the bulk crystalline hexagonal boron nitride (h-BN) powder sample was mechanically exfoliated by ball milling, and further processed through ultrasonication for de-aggregation. High resolution X-ray diffraction (HR XRD) and high resolution transmission electron microscopy (HR TEM) results clearly indicate the exfoliation of bulk h-BN into thinner two-dimensional (2D) crystalline sheets without creating noticeable structural defects. The topography of exfoliated nanosheets is well confirmed by atomic force microscopy (AFM). Oxygen functionalization into the h-BN nanosheets after the mechanical exfoliation was investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Oxygen functionalization of h-BN improved the cohesive compatibility between h-BN and commercial 10W30 lubricant oil for stable dispersion. Friction coefficient and wear of sliding metallic interfaces were reduced significantly in the presence of few layered exfoliated h-BN nanofluid as compared to neat lubricated oil. Micro- XPS and energy-disperse X-ray spectroscopy (EDX) analysis demonstrated the presence of adsorbed h-BN tribofilm in the metallic wear track. Thin 2D sheets of h-BN nanofluid was effective as an additive for low shear resistance under the tribo stressed condition which is the main reason for significant reduction in friction coefficient. Moreover, the enhanced wear resistance of exfoliated h-BN additives was explained by low shear resistance and high compressive/tensile strength of planer sheets which restricted the mechanical damage and protected the metallic interfaces against deformation and wear.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mechanical exfoliation of bulk 3D into 2D hexagonal boron nitride. </LI> <LI> Chemical functionalization of 2D hexagonal boron nitride during ball milling. </LI> <LI> Chemical compatibility of 2D hexagonal boron nitride with 10W30 commercial oil. </LI> <LI> High tribo-mechanical efficiency of 2D hexagonal boron nitride. </LI> <LI> High efficient 2D hexagonal boron nitride as nanolubricant modifiers in 10W30 commercial oil. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Triboenvironment Dependent Chemical Modification of Sliding Interfaces in Ultrananocrystalline Diamond Nanowall Film: Correlation with Friction and Wear

Rani, Revati,Panda, Kalpataru,Kumar, Niranjan,Sankaran, Kamatchi Jothiramalingam,Pandian, Ramanathaswamy,Ficek, Mateusz,Bogdanowicz, Robert,Haenen, Ken,Lin, I-Nan American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.1

<P>Tribological properties of ultrananocrystalline diamond nanowall (UNCD NW) films were investigated quantitatively in three different and controlled triboenvironmental conditions, proposing the passivation and graphitization mechanisms. However, these mechanisms are rather complicated and possibly can be understood in well-controlled tribological conditions. It was shown that the friction and wear of these films were high in high-vacuum and room temperature (HV–RT) tribo conditions where the passivation of carbon dangling bonds were restricted and frictional shear-induced transformation of sp<SUP>3</SUP> carbon into amorphous carbon (a-C) and tetrahedral amorphous carbon (t-aC) were noticed. However, the friction coefficients were reduced to the ultralow value in ambient atmospheric and room temperature (AA–RT) tribo conditions. Here, both passivation of dangling bonds through atmospheric water vapor and graphitization of the contact interfaces were energetically favorable mechanisms. Furthermore, the conversion of diamond sp<SUP>3</SUP> into hydrogenated–graphitized phase was the dominating mechanism for the observed superlow friction coefficient and ultrahigh wear resistance of films in high-vacuum and high temperature (HV–HT) tribo conditions. These mechanisms were comprehensively investigated by micro-Raman and X-ray photoelectron spectroscopy analyses of the sliding interfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-1/acs.jpcc.7b10992/production/images/medium/jp-2017-10992p_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b10992'>ACS Electronic Supporting Info</A></P>

Tribological Properties of Ultrananocrystalline Diamond Films in Inert and Reactive Tribo-Atmospheres: XPS Depth-Resolved Chemical Analysis

Rani, Revati,Panda, Kalpataru,Kumar, Niranjan,Sankaran, Kamatchi Jothiramalingam,Ganesan, K.,Lin, I-Nan American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.15

<P>Tribological properties of diamond films are sensitive to the chemically reactive and inert tribo-atmospheric media, and therefore, it is difficult to understand the underlying tribological mechanisms. In the present work, tribological properties of surface-modified ultrananocrystalline diamond (UNCD) thin films were investigated in four distinct tribo-environmental conditions of ambient humid-atmosphere, nitrogen (N<SUB>2</SUB>), argon (Ar), and methane (CH<SUB>4</SUB>) gases. The in situ depth-resolved X-ray photoelectron spectroscopy (XPS) showed the desorption of oxygen and oxy-functional additives and sputtering of weakly bonded amorphous carbon species from the UNCD film surface after the Ar<SUP>+</SUP>-ion sputtering process. After desorption of these chemical entities, friction and wear were decreased and run-in regime cycles became shorter in UNCD films. Friction in the ambient humid-atmosphere was higher compared to other tribo-environmental conditions, and it was explained by the oxidation mechanism of the sliding interfaces and the formation of the oxidized carbon transferfilm. However, low friction and wear in the N<SUB>2</SUB> atmosphere was associated with the adsorption of N<SUB>2</SUB> species, forming nitrogen-terminated carbon bonds at the sliding interfaces. This was directly investigated by XPS and energy dispersive X-ray spectroscopy techniques. Furthermore, low friction in the Ar atmosphere was explained by the physical adsorption of Ar gaseous species, which tend to avoid the covalent carbon bond formation across the sliding interfaces. Moreover, ultralow friction in the CH<SUB>4</SUB> atmosphere was governed by the passivation of dangling carbon bonds by dissociative CH<SUB>4</SUB> complexes, which creates hydrogen-terminated repulsive sliding interfaces. More importantly, a shorter run-in regime with low friction and wear in Ar<SUP>+</SUP>-ion-sputtered UNCD films were explained by desorption of the oxygen and oxy-functional groups, which are inherently present in the UNCD films.</P> [FIG OMISSION]</BR>

Nanofluid lubrication and high pressure Raman studies of oxygen functionalized graphene nanosheets

Karuna Kara Mishra,Kalpataru Panda,Niranjan Kumar,Deepika Malpani,T.R. Ravindran,Om P. Khatri 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.61 No.-

Ultralow friction coefficient in reduced graphene oxide (rGO) nanofluid was observed at high pressure lubrication conditions. High pressure Raman spectroscopic studies of graphene oxide (GO) and rGO in a hydrostatic pressure medium in diamond anvil cell (DAC) showed an increase in G-band linewidth in GO but this value was decreased in rGO at same pressure range due to the defect relaxation in sp2 networks. Moreover, loss of recovery of G band linewidth in decompression cycles was clearly noticed in both the samples but it was significantly higher in GO due to the irreversible sp3 into sp2 planar phase.

Nanoscale investigation of improved triboelectric properties of UV-irradiated ultrananocrystalline diamond films

Kim, Jae-Eun,Panda, Kalpataru,Choi, Joong Il Jake,Park, Jeong Young The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.13

<P>We report improved the triboelectric properties of ultraviolet (UV)-irradiated ultrananocrystalline diamond (UNCD) films that were measured using atomic force microscopy (AFM). Fabricated using the chemical vapor deposition (CVD) method, UNCD is an artificial diamond film with mechanical properties similar to single-crystal diamond. Surface modification by means of UV irradiation is a simple method to modify the surface properties of carbon-based and oxide materials. While the physical properties (<I>e.g.</I>, roughness, adhesion, and friction) of these UNCD films did not exhibit any significant change following the UV treatment, we found that the UV-irradiated UNCD surface was oxidized and became graphitic, as confirmed using X-ray photoelectron spectroscopy, work function measurements using Kelvin probe force microscopy, and ultraviolet photoelectron spectroscopy. The work function of the samples increased with increasing UV exposure time, which is associated with the reduction of carbon atoms on the surface and oxygen-rich surfaces. Tribocharges were generated by scratching the surface of the UNCD films with a diamond-coated AFM tip. The duration of the tribocharges increased because of reactive radicals and the insulating property resulting from the UV/ozone treatment. The radicals were responsible for trapping charges; the UV-irradiated UNCD films preserved the charges for more than 5 h, which is five times longer than that on bare UNCD. This study demonstrated that UNCD is a promising material for generating triboelectricity and that UNCD can be used as a charge-trapping layer in charge-trap flash memory devices.</P>

Self-organized multi-layered graphene-boron-doped diamond hybrid nanowalls for high-performance electron emission devices

Sankaran, Kamatchi Jothiramalingam,Ficek, Mateusz,Kunuku, Srinivasu,Panda, Kalpataru,Yeh, Chien-Jui,Park, Jeong Young,Sawczak, Miroslaw,Michałowski, Paweł Piotr,Leou, Keh-Chyang,Bogdanowicz, Robert,Li The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.3

<P>Carbon nanomaterials such as nanotubes, nanoflakes/nanowalls, and graphene have been used as electron sources due to their superior field electron emission (FEE) characteristics. However, these materials show poor stability and short lifetimes, which prevent their use in practical device applications. The aim of this study was to find an innovative nanomaterial possessing both high robustness and reliable FEE behavior. Herein, a hybrid structure of self-organized multi-layered graphene (MLG)-boron doped diamond (BDD) nanowall materials with superior FEE characteristics was successfully synthesized using a microwave plasma enhanced chemical vapor deposition process. Transmission electron microscopy reveals that the as-prepared carbon clusters have a uniform, dense, and sharp nanowall morphology with sp<SUP>3</SUP> diamond cores encased by an sp<SUP>2</SUP> MLG shell. Detailed nanoscale investigations conducted using peak force-controlled tunneling atomic force microscopy show that each of the core-shell structured carbon cluster fields emits electrons equally well. The MLG-BDD nanowall materials show a low turn-on field of 2.4 V μm<SUP>−1</SUP>, a high emission current density of 4.2 mA cm<SUP>−2</SUP> at an applied field of 4.0 V μm<SUP>−1</SUP>, a large field enhancement factor of 4500, and prominently high lifetime stability (lasting for 700 min), which demonstrate the superiority of these materials over other hybrid nanostructured materials. The potential of these MLG-BDD hybrid nanowall materials in practical device applications was further illustrated by the plasma illumination behavior of a microplasma device with these materials as the cathode, where a low threshold voltage of 330 V (low threshold field of 330 V mm<SUP>−1</SUP>) and long plasma stability of 358 min were demonstrated. The fabrication of these hybrid nanowalls is straight forward and thereby opens up a pathway for the advancement of next-generation cathode materials for high brightness electron emission and microplasma-based display devices.</P>

Tribochemistry of contact interfaces of nanocrystalline molybdenum carbide films

Kumar, D. Dinesh,Kumar, N.,Panda, Kalpataru,Kamalan Kirubaharan, A.M.,Kuppusami, P. Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.447 No.-

<P><B>Abstract</B></P> <P>Transition metal carbides (TMC) are known for their improved tribological properties and are sensitive to the tribo-atmospheric environment. Nanocrystalline molybdenum carbide (MoC) thin films were deposited by DC magnetron sputtering technique using reactive CH<SUB>4</SUB> gas. The friction and wear resistance properties of MoC thin films were significantly improved in humid-atmospheric condition as compared to high-vacuum tribo-condition. A comprehensive chemical analysis of deformed contact interfaces was carried out by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. XPS and Raman spectroscopy showed the formation of stable molybdenum-oxide (MoO), molybdenum carbide (MoC) and amorphous carbon (a-C) tribo-phases. Moreover, during the sliding in humid-atmospheric condition, these phases were extensively deposited on the sliding steel ball counter body which significantly protected against undesirable friction and wear.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reactive DC magnetron sputtered cubic phase of nanocrystalline MoC thin films. </LI> <LI> Chemical bonding analysis of MoC films using X-ray photoelectron spectroscopy. </LI> <LI> Tribological properties of MoC films in ambient and high-vacuum tribo-atmospheres. </LI> <LI> Comprehensive tribochemical analysis of contact interfaces. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Friction and wear behavior of nanocrystalline MoC films under atmospheric and high-vacuum conditions.</P> <P>[DISPLAY OMISSION]</P>

Microwave cavity perturbation of nitrogen doped nano-crystalline diamond films

Cuenca, Jerome A.,Sankaran, Kamatchi Jothiramalingam,Pobedinskas, Paulius,Panda, Kalpataru,Lin, I-Nan,Porch, Adrian,Haenen, Ken,Williams, Oliver A. Elsevier 2019 Carbon Vol.145 No.-

<P><B>Abstract</B></P> <P>Non-contact and non-destructive electrical conductivity measurements of nitrogen doped nano-crystalline diamond films have been demonstrated using a microwave cavity perturbation system. The conductivity of the films was controlled by simply varying the CH<SUB>4</SUB> gas concentration during microwave plasma assisted chemical vapour deposition, thereby promoting the formation of sp<SUP>2</SUP> carbon at the grain boundaries. The presence of sp<SUP>2</SUP> carbon is verified through Raman spectroscopy, x-ray photoelectron spectroscopy and electron energy loss spectroscopy, while scanning electron microscopy confirms an increasing surface area for sp<SUP>2</SUP> to form. The microwave cavity perturbation results show that the measured cavity quality factor varies with CH<SUB>4</SUB> concentration. The extraction of conductivity is achieved through a depolarisation model, which must be considered when the sample is smaller than the cavity and through both electric and magnetic field perturbations. The microwave measurements are comparable to contacting and damaging measurements when the film conductivity is greater than the substrate, thus demonstrating an invaluable method for determining conductivity without the need for depositing any electrodes on the film.</P>