Surface smoothing of thin HTc YBa2Cu3O7-superconducting films by high-energy iodine ions

A. Markwitz,V. J. Kennedy,A. Bubendorfer,N. Long 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4

A variety of techniques were applied to probe for surface modications and structural changes in thin highTcYBa2Cu3O7. d(YBCO) superconducting lms prepared onto MgO substrates after time of ight heavy ion elastic recoil detection analysis(HERDA).Films have been prepared by ex-situ processing of a spin-coated organic solgel precursor.Evidence is provided for the smoothening of the surface of the films accompanied with an amorphisation of the YBCO lms in the HERDA spot region.Thevirgin surface roughness of 30-50 nm could be reduced to 1-2 nm after bombarding the lm for a short time with pA current.However, large scale surface roughness on the 200 nm scale remained unchanged.Importantly, the integrity of the superconductorlms did not change signicantly during HERDA allowing simultaneous measurements of high resolution Y, Cu, Mg and C depth proles.Further research will utilise the HERDA depth proling capability for carbon and copper since the copper stoichiometry and fraction of carbon as an impurity are crucial for an understanding of the performance of the YBCO films.

Optimised process for fabricating functional silicon nanowhisker arrays

A. Markwitz,M. Rudolphi,B. Barry,H. Baumann 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4

Silicon nanostructures, called silicon nanowhiskers, are grown by electron beam annealing of wafer silicon. It is desirable to be able tocontrol sizes and locations of arrays of silicon nanowhiskers for eld emission applications. Nitrogen, oxygen and silicon ions wereimplanted at 1524 keV with uences ranging from 1012 to 1015 ions cm. 2 whisker growth in specied regions and to search for the minimum level of implanted ions necessary to suppress silicon nanowhiskergrowth. Particularly interesting results were obtained for the nitrogen ion implantation series where total suppression is achieved byimplanting 5 · 1014 N+ cm. 2. However, implanting 1· 1014 N+ cm. 2 results in an increase in nanowhisker density of a factor of threecoupled with a decrease in nanowhisker height by a factor of two. Silicon was also found to suppress silicon nanowhisker growth suc-cessfully; however oxygen implantations resulted in a decrease of nanowhisker growth with increasing uence but suppression of nano-whisker growth at 1· 1015 O+ cm. 2 nanowhisker growth area by low-energy nitrogen and silicon ion implantation.

Carbon depth profiling of superconducting YBCO thin films on nanometer scale

V. J. Kennedy,A. Markwitz,A. Bubendorfer,N. Long,N. Dytlewski 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4

Ion beam analysis techniques have been used to probe for carbon contamination in high temperature superconductor thin lms.These techniques provide a powerful tool to detect C with limit of detection close to 0.01 at.% and to measure carbon depth proleson the nanometer scale with a depth resolution of 10 nm at the surface. In the present study, a series of YBa2Cu3O7. d (YBCO) lmshave been formed on MgO substrates by a solgel method. Dierent lm thicknesses and heat treatments were studied. Typicalformation temperatures were 770850.C resulting in thicknesses from 50 to 600 nm. It was found that, depending on the samplepreparation conditions, carbon was incorporated in the lms at a concentration of 0.54.6 at.%. Carbon was homogeneously distributed throughout the films.

Plasma immersion nitrogen implantation into silicon and rapid thermal electron beam annealing for surface structuring

A. Markwitz,V. J. Kennedy,K. Short,M. Rudolphi,H. Baumann 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4

(100) and (111) silicon substrates were implanted with 10 keV Nþ2 ions using plasma immersion ion implantation (PI3). Series ofspecimens were implanted in the uence range from 0.5 to 1.6· 1016 cm. 2 and subsequently annealed at 1000.C (radiation tem-perature) for 60 s with a raster scanned electron beam (EB-RTA) to investigate surface structuring after EB-RTA. Atomic forcemicroscopy (AFM) revealed that the combination of PI3 and EB-RTA resulted in a roughening of the surface on the lower 100 nmscale depending on the nitrogen uence used in the experiments. Similar ion implantation and annealing protocols using an ac-celerator based system in conjunction with EB-RTA showed, however, smooth surfaces on the 3 nm scale. Selected results arepresented providing evidence for the possibility of controlling the surface structuring of implanted surfaces via PI3 process para-meters.

Formation of large SiC nanocrystals on Si(1 0 0) by 12C implantation and electron beam annealing

A. Markwitz,S. Johnson,J. Kennedy,M. Rudolphi,H. Baumann 한국물리학회 2006 Current Applied Physics Vol.6 No.3

Scanning electron microscopy and nuclear reaction analysis have been used to study annealing eects of 10 keV12C implanted andelectron beam annealed silicon (10) substrates that cause the formation of large SiC nanocrystals named nanoboulderson silicon.Wafer silicon was implanted with varying uences from 0.38 to 1.14· 1017 atoms cm. 2 and subsequently annealed at 1000.C for15 s. The deuterium induced12C(d,p)13C reaction was used to measure the12C dose quantitatively. It was found that the implanted car-bon remained in the specimen after annealing. This result, coupled with geometrical analyses of the resulting nanostructures suggest thatfollowing nucleation, the SiC nanocrystals grow as a result of C and Si diusion across the substrate surface, that became oxide freeduring annealing under vacuum conditions.

Self-assembled germanium nanostructures formed using electron-beam annealing

D.A. Carder,A. Markwitz,H. Baumann,J. Kennedy 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4

Germanium nanostructures have been fabricated on silicon substrates using ion-beam sputtering growth followed by an exsitu annealing step. The substrates are not heated during growth, resulting in a post-growth deposited layer ~225 nm thick with a surface which has no evidence of nanostructure formation. Following annealing at temperatures of 400–700℃ dramatic nanostructuring isobserved at the surface. For temperatures below 600℃ atomic force microscopy analysis reveals dense arrays of nanostructures withheights typically around 5-30 nm. Increased feature size and surface roughening is observed for samples annealed above 600℃, witha broadened size distribution centred at 450 nm. This is assigned to intermixing at the Si/Ge interface, which reduces the stress in thelayer, allowing larger features to form.

Modification of electrical conductivity in RF magnetron sputtered ZnO films by low-energy hydrogen ion implantation

J. Kennedy,A. Markwitz,Z. Li, W. Gao,C. Kendrick,S.M. Durbin,R. Reeves 한국물리학회 2006 Current Applied Physics Vol.6 No.3

The electrical conductivity of ZnO lms deposited on Si by the RF sputtering technique were modied by low-energy hydrogen· 1016 to 1.0· 1017 ions cm. 2.High resolution quantitative hydrogen depth proles of the un-doped and doped samples were measured non-destructively with elasticrecoil detection analysis using a nely focussed 2.5 MeV4He+ ion beam impinging onto the samples at 20.surements were carried out on the lms by SEM, XRD and Hall probe measurements to explore the eects of hydrogen implantation. Itwas observed that the electrical conductivity is decreased by as much as an order of magnitude after hydrogen implantation. The lmsremained polycrystalline after implantation. The results suggest that reducing the n-type conductivity using low-energy hydrogen implan-tation without annealing may provide a pathway for passivating the donors for a possible subsequent formation of p-type acceptors byion implantation.

Raman scattering investigation of hydrogen and nitrogen ion implanted ZnO thin films

J. Kennedy,B. Sundrakannan,R.S. Katiyar,A. Markwitz,Z. Li,W. Gao 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4

Acceptor nitrogen and a donor–acceptor combination of hydrogen and nitrogen ions at 23 keV with fluences in the range from 1 × 1015 to 5 × 1016 ions cm-² have been implanted into ZnO films grown on Si substrate. DYNAMIC-TRIM calculations have been performed to obtain theoretical quantitative implantation profiles for various fluences. Ion beam analysis measurements confirmed the presence of implanted ions and were in agreement with the predicted concentrations. Raman spectroscopy was used to measure the characteristic vibrations of the various implanted ZnO/Si thin films. A correlation was found between the vibrational modes and the ion fluences. Silent B1 modes are observed due to disorder-activated Raman scattering in the as-grown films, indicating that structural disorder is present. The enhanced features seen in the co-implanted sample indicate that the disordered phase is increased. Acceptor nitrogen and a donor–acceptor combination of hydrogen and nitrogen ions at 23 keV with fluences in the range from 1 × 1015 to 5 × 1016 ions cm-² have been implanted into ZnO films grown on Si substrate. DYNAMIC-TRIM calculations have been performed to obtain theoretical quantitative implantation profiles for various fluences. Ion beam analysis measurements confirmed the presence of implanted ions and were in agreement with the predicted concentrations. Raman spectroscopy was used to measure the characteristic vibrations of the various implanted ZnO/Si thin films. A correlation was found between the vibrational modes and the ion fluences. Silent B1 modes are observed due to disorder-activated Raman scattering in the as-grown films, indicating that structural disorder is present. The enhanced features seen in the co-implanted sample indicate that the disordered phase is increased.

Analysis of heteroepitaxial germanium on gallium arsenide grown by pulsed laser deposition

S. M. Durbin,J. P. Zheng,A. Markwitz,V. J. Kennedy,A. Pun 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4

Interest in the pulsed laser deposition (PLD) technique now extends far beyond growth of multiple component oxides, the area inwhich it rst proved itself. In particular, it shows promise as a viable technique for high-quality crystalline thin lms on substrates with low thermal tolerance. In this paper, we report the PLD growth of single-crystal Ge on (10) GaAs substrates in the tem-perature range of 150550.C. In situ reection high-energy electron diraction shows the formation of a reconstructed surface afteras few as two laser pulses, corresponding to approximately 4% monolayer coverage. Transmission electron microscopy conrms heteroepitaxial growth with good quality interfaces and smooth surfaces, despite the presence of oxygen and carbon impurities.

Characterisation of polycrystalline gallium nitride grown by plasma-assisted evaporation

S. M. Durbin,V. J. Kennedy,S. I. Liem,R. J. Reeves,A. Markwitz,V. A. Christie 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4

The remarkable success of GaN-based devices despite comparatively large defect densities has prompted many groups to explorepolycrystalline and amorphous GaN thin lms for various device applications. In this paper we present the results of a series of lmgrowths performed using an RF plasma assisted molecular beam epitaxy system. GaN lms were grown on quartz substrates in thetemperature range of 150650.C, and in all cases were found to be polycrystalline and largelyc-axis oriented. Rutherford back-scattering spectroscopy indicates lms have gallium-rich stoichiometry, except for those grown below 200.C. Bandedge photo-luminescence was observed at room temperature even for the lms grown at 150.C, and many lms exhibited a measurable changein resistivity under exposure to ultraviolet radiation.